How can I make low sodium (140mg or less per serving) pancakes / waffles?

Question: I work with heart failure patients who have to limit their sodium intake, but still would like to enjoy some of their favorite foods. How can I reduce the sodium (to 140mg or less) in pancakes and waffles?
Comment: salt is for flavor in these recipes so you can leave it out altogether. They're not going to taste the same but that's a different question.
Answer: Reduce or leave out the salt.  It is not essential to the chemistry of the recipe.  I will not speculate on salt substitutes, as that is a health and medical issue, off topic for this site.
The pancakes will then not taste as good, but that is unavoidable.  Perhaps you can serve them with a highly flavorful accompaniment, like a reduced peach chutney or similar, to make the entire dish more interesting.
Not sure what kind of advice you expected.
Edit:  Based on the discussion of baking soda (sodium bicarbonate) usually used in pancakes:   as Kate Gregory points out, there may be alternate chemical leaveners.
Another possibility is to use mechanical leavening, by beating the eggs, fat, and any sugar well until they reach the ribbon stage (probably more than necessary, per Harold McGee, but still a clear indication); at this point they will have the maximum amount of air incorporated.   This batter cannot be held, but it should rise reasonably well, even without baking powder.
There are also recipes that use whipped egg whites to leaven pancakes, but they produce a different, fluffier product that may be called Fluffy Pancakes or Swedish Pancakes depending on the recipe.
Comment: What about the baking soda--sodium bicarbonate--used to make the products fluffy?
Comment: There are also recipes for yeast raised pancakes (sourdough are especially delicious!) which would be another way to leave out the baking soda.
Answer: I agree with SAJ14SAJ. You can leave out the salt or use a small amount of it, without a problem. What you can add to minimize the loss of flavour, is a pinch of vanilla (for neutral-tasting pancakes) or a different aroma, for instance almond extract (for a variation).
Answer: A random web site I have no reason to trust claims that half a teaspoon of baking soda contains 616 mg of sodium. This more reputable site says 150 for 1/8 tsp, which pretty much agrees, and also says 100-200 in 1/4 tsp of baking powder. Let's take those as correct for now. My favourite pancake recipe uses 2 tsp of baking powder to make about 12 pancakes, so that's 800-1600 mg, meaning a person could have one (or possibly two if the sodium content is more to the low end) of those pancakes and meet your requirements, assuming you didn't add any salt.
If you would like to serve them 2 or 3 pancakes (which I think is a more reasonable serving size) then you probably want to look into low-sodium and sodium free baking powder and baking soda. Discuss with the pancake-eater's dietician whether the substitute is actually ok or not, (sometimes low-sodium also means low-bunch-of-other-stuff) but that same Low Sodium FAQ lists several brands of baking soda and baking powder with no sodium at all. Using those brands would let you serve all the pancakes you want!
Comment: If you can't get low-sodium baking powder, you may want to consider alternate leavening methods, such as an eggwhite foam or sourdough.
Comment: This is a good point. I have no problem with the taste of pancakes made without salt (I have generally observed that the idea of "add a pinch of salt to everything or it will taste bland" depends a lot on the usual amount a person likes in their food, which is a trainable taste). But sodium bicarbonate (baking soda) is an obvious source of sodium. A good alternative may be ammonium-based chemical leavener (hirschhornsalz), if the eaters are OK with the taste it introduces.
Answer: My husband has had a low sodium diet due to kidney and heart disease since 2008 and I've faced this challenge already.  Baking soda is the culprit - not added table salt.  There are several low or no sodium recipes online for pancakes but be sure to select using a no sodium baking powder.  One of my favorite websites is lowsodiumcooking.com.  There is a no sodium / gluten free baking powder online called Featherweight Baking Powder by Hain Foods.  I purchase mine on Amazon as I cannot locate it in the Boise area.  In the past I've tried to use a product found at Walmart - Rumford Reduced Sodium Baking Power but the content is still quite high for our needs at 35 mg per 1/8 teaspoon.  Most pancake recipes call for a minimum of 2 t of powder which equates to 280 mg per serving size.  With syrup is added to the equation it just adds up too quickly for us.  If kidney disease is also an issue, do not use a salt substitute as the potassium levels are increased.
Answer: Assuming you are making savoury crepes/pancakes/waffles then missing salt could a big compromize on the flavour/taste. There's no substitue for salt but low-sodium table salt(that contains Potassium chloride). (So I still prefer sea salt). Lemon juice activates the same taste receptors as sodium, so adding a spritz of lemon to your food in place of salt makes biological sense. Anyway it's not a substitute. However for savoury bits, if you can use very little portions (puree) of herbs (e.g. tamerind) that could save the palate...with that sour-saltyness. I use this herb and some others with absolutely less salt to even marinade fish/meat, make pickles.
Low Sodium Salts:
<code>* Morton Lite Salt, 50% less sodium than table salt
* Diamond Crystal Salt Sense, 33% less sodium
</code>
But hey! For Sweet pancakes, salt is not a must. Infact never used. As everyone else pointing out you may leave it out for sweeties.
Comment: To expand on the lemon juice idea -- other tart or tangy flavors would help to offset the blandness from lack of salt.  Sourdough, buttermilk or sour cream pancakes might be good alternatives.
Answer: You can buy no sodium baking powder and baking soda as far as salt goes I just leave it out but I do whip my yolks and whites separately.


Should siding be replaced or can it be repaired?

Question: we are considering purchasing a 32 year old home that has regular wood siding on much of the second story. It has been patched in places but from the eye looks nice. It was painted most recently 8 - 10 years ago. During our engineers inspection he found some rot and they are willing to patch again but we feel like it should all be replaced. How long should siding last on a home? (generally) We would consider Hardy Plank but would also consider good quality wood as well. We can't get a price quote on either as we don't own the home but would consider a monetary compensation from the seller so we could do the work after we closed on the house. If the patch job is done, can we assume that we'd be good to go for a while or should we really insist that some sort of new siding be put up there...........
Answer: First off, never assume anything. You should take some pictures and know the basic dimensions of the house. You could talk with some local contractors, armed with pics and dimensions and get some ballpark prices.  New siding on an existing building can go $250 to $400 a square (10ft X 10ft), removal and replace.
Just because your inspector found some rot, don't expect the sellers to discount for an entire siding job. You can try for what ever you think you can get, but I bet your offer to buy contingencies won't cover that. Unless the inspector committed and said the siding was unserviceable, you will need to negotiate.
Wood siding can last 100 years if well maintained, but I have seen 20 year old siding that was junk.  The type of wood, whether the wood was back primed when installed, and how often it was stained or painted will make a huge difference.
Although this is not in a pure sense a home improvement question, I could not stand to not answer this one. I am a home inspector and these questions come up all the time with my customers.


What holidays would be on a European-centric calendar from the 11th - 13th Centuries?

Question: I've often come across readings that mentioned there were numerous holidays in calendars in use within the Christian Churches or Church controlled lands, with work stopping on worship days, feast days and so on.  While this opens a wide geographical area I am curious if there are any sources that note holidays within a typical year for a European-centric area (say current day France-Germany-Italy) between the 11th-13th Centuries.  What holidays were there and were these religious (feast or sanctified days) or were there celebrations for any other purpose (such as we have for memorial days within many current calendars).
Answer: Saints Days, in particular, the local saint's day
Shrove Tuesday
Lent
Easter
Christmas was less important.
In any area of importance four quarterly Saint's days would be identified with local days when legal actions occurred and markets occurred in the local large city.  As such courts were either rotating, or held on feudal bases, it is usual for surrounding regions to have different days.
Memorial days as we currently understand them are a modern thing.  All holidays, as saints days, were in memory of X.  The most important being in memory of the suffering of our Lord.

Any calendar of relevant saints days will be local in effect, because locality defined the importance of particular saint's days.
Comment: Nice overview, thanks.  I figured Saints would be local, I got into some of that from being a fan of the Cadfael series, but didn't think of legal days.
Answer: If we're talking about strictly catholic holidays, a good example that became popular across medieval Europe is the Feast of Corpus Christi, which started in Germany in the middle of 13th century. Soon it has spread both in Western and Eastern Europe, after pope Urban IV decision to make it official for all Latin Rite countries.
In different areas of Europe, local saints were often connected with previous, pagan beliefs and folk traditions. Catholic church adopted a lot of such beliefs and transformed them its own way. Good example for that can be St. John's Eve, which took advantage of St. John being connected with water, to take over traditional midsummer events from pagan era.
Another one would be All Souls' Day, started at the very end of 10th century, by Odilo, abott of Cluny, which was also a day connected with pagan traditions across all Europe.
It's worth to mention that with saints days, religious importance of particular saint wasn't the only priority. It also relied on which saints were patrons to local churches and monasteries, especially to those most important for local community, which was changing with time and was sometimes determined by random happenings.


master to multi-slave replication

Question: I am looking at replication of the master database (PostgreSQL) and this is the configuration I have to setup
<code>master -- hot-standby (hs)
|
|
 --- read only slave (r1)
|
|
 --- read only slave (r2)
</code>
My requirement is that the either of master or standby should be available all the time and r1-r2 should be available most of the time.
I have setup streaming replication with recovery on hs and without recovery on r1,r2. All these 3 get the WAL logs from master.
My question is, when the master goes down and we trigger the failover on standby, what should I do to r1 and r2 ? re-parenting them to standby would mean a full base-backup and when eventually master comes up, i may need to re-parent again.
This is my first attempt at replication-setup. So if there is anything obvious I am missing or doing wrong, please let me know. If there are tools/solutions which cater to this sort of a thing, I would be very glad to know and learn.
Answer: There are some tricks to make r1/r2 follow new parent, but generally I see them as tricks, which means I wouldn't really depend on them in production environment.
You might want to check this blogpost: http://www.pateldenish.com/2010/11/possibility-of-graceful-switchover.html

master to multi-slave replication


How is the photography printing on newpaper is possible in the WW2 era?

Question: How is the photography printing on newpaper is possible in the WW2 era?
For example, how is the photo on the newpaper at the below link is possible especially on HD quality?
http://www.grahamcounty.net/vetweb/newspaper/np13.htm
Comment: The link is a high quality scan of a low quality image. I think you have a good question here though.
Answer: Printing of images in newspapers use halftones to create the various shades of grey in the photos.  The resolution of halftones is given in lines per inch (LPI).  For standard newsprint, which is rather porous, the maximum LPI is 85 -- any higher than that, the dots bleed and run together.
This photograph linked to was published in Current Events, the "national school newspaper".  It is possible that this paper used higher quality paper than newsprint.  This would allow a much higher LPI, thus providing for higher-quality images.  LIFE Magazine, a photojournalism magazine of that era, used 150 LPI.  A very high quality magazine, like National Geographic, uses 300 LPI (essentially, a "retina" display on paper).
I remember reading something like this called "My Weekly Reader" while in grade school in the early 1950's.  I don't think it was printed on newsprint, as the pages were more like regular typing paper (but not glossy magazine paper) as I recall.
Answer: Apart from the half-tone process, the other component was the process that allowed the photographer to scan their photo on location, and then send it back to the home office by way of telegraph or telephone.
The first of these technologies was the Telediagraph that demanded special telegraph connections. By WWII, the process was refined enough to use ordinary telephone connections, even over intercontinental lines, and inexpensive enough where even remote branch offices of major news services and large daily papers had one on-site. Some offices had equipment could scan and send photos by short-wave radio.


Forcing the combat in Warhammer: Invasion

Question: I've been playing several games of Warhammer: Invasion Core Set with my friend and a couple of times we've encountered a situation where he had pretty good attack force set up in his battlefield and I has good one as well. But I already had one district burning and he had bunch of damage tokens on two of his districts.
So what I wanted to do in this situation is to attack his forces so his chances for gathering enough strength to finish me off would be smaller. I've attacked his battlefield and what he usually did is he didn't set any defenders and allowed the whole damage to be dealt to his district (even if it meant burning it down). Then in his turn he launch his full force agains one of my other districts and burn it down thus winning the game.
I was wondering are there any cards or rules in this game or it's expansions that would force him to fight me instead of letting all the damage to be dealt to his capital? This would allow for more tactical approach in my opinion because right now his best tactics is to ignore all my attacks and hope to get stronger force to destroy a district in one round then me.
Answer: You are not defending you quest and kingdom zones enough.  There is no reason for him to attack your battlefield if your defenses are weak in the other two zones.  It's better for him to attack those and win than fight your battlefield.


Axial skeletal system

Question: I was curious about a fact given in my biology textbook as to why the Japanese have  3 pairs o floating ribs unlike the rest who have just two?
Answer: Because your textbook is probably worded poorly.
It appears that the Japanese (and several other ethnic groups) apparently have a higher proclivity for the 10th rib to be a true floating rib, but every ethnic group has the chance of having a floating 10th rib.
With that said, the one McGraw-Hill book cited in the Wiki article is the only source I've seen for this higher morphology rate. I, personally, wouldn't trust just one source, and (if true) the rate may not be much higher.

Axial skeletal system


"Shelach Lecha": What is "Lecha"?

Question: In the 2nd verse in Shelach, it says שלח לך (Shelach Lecha), which Rashi explains as "
לדעתך, אני איני מצוה לך". Why don't we give the same explanation the other places in the Torah it says לך. E.g. in Parshas Lech Lecha, or by the Ketores (קח לך)?
Comment: Actually the Kli Yakar says the reason it says LCha because Hashem wanted to send Women as spies as they would have never spoken Negatively of Ertez Yisroel so what he was saying Lcha because you only want to send MEN!!
Answer: It has to do with the fact that in this case, the same incident recorded later in the Torah, seems to tell us that it was Moshe's own decision (and the populace's initiative) to send the mission. We do not have such exceptional circumstances in the other cases you mentioned.

Edit: Actually, this only answers why Rash"i does comment here. The truth about why he doesn't comment elsewhere is probably just because a verb with a purposeful prepositional pronoun is a standard way to express a certain type of imperative in Tana"ch. See this interesting hirhurim post on the "polite imperative" as a description of this form.
Answer: The Maskil Ledavid says that Rashi actually learns that it was Moshe's choice from the word "Shlach", not "Lecha".
He says Rashi had a question. Shlach would normally be a command, and if so, what was the purpose of the command? Also, how could G-d command Moshe to do something that would end badly (since G-d new what the spies would do)?
To answer this, Rashi says that Shlach here means if you want to, it is not a commandment, as it would normally be.
Also, the Maskil LeDavid says that Rashi learned out from "Lecha" why this story is said right after the story of Miriam. G-d was basically saying that the spies should learn from what happened to you (i.e. Miriam got punished for saying Lashon Harah about you), and they should realize that saying Lashon Harah about the land would be a bad idea.
If Rashi already uses the word "Lecha" to learn something else, he must learn that it was optional from the word "Shlach".
See there for more details.
Answer: Its likely an ambiguous phrase that can be darshened in different ways. So by lech l'cha, chazal say it means "go for yourself", for your benefit. Over here, they expalin it slightly differently, "go according to yourself", your own choice.
Answer: I second Ariel K's answer, that it is an ambiguous phrase, which is darshened according to context and purpose. Midrash is really not that systematic.
But to take the answer in the opposite direction, Shadal actually takes the derasha of לטובתך, from Lech Lecha, and applies it here. See my presentation and translation of Shadal here.
But this is something that many meforshei Rashi would address. For example, Gur Aryeh says that letovatcha == ledaatcha. If you are up for it, you can run through the various meforshei Rashi in my source roundup on Shelach and see what they all have to say on this topic.
Answer: Just another great answer I saw that I must Share.The Ohr Hachaim Hakodosh on the question of why such Great people as the Meraglim that the torah says when they left where Tzaddikim became so evil so fast (excluding the Teretz that they wanted Moshe to live Longer And they where afraid of not being able to live on a close level to Hashem when  not living off Mon meaning afraid of becoming "Kochi Votzum Yodi")So  he answers that "Shliach Shel Adom Kimoso"
and granted they where Tzaddikim but once you are doing the Shlichus for Klal Yisroel You are going to get there Bad Habits too and The Chasam Sofer builds on this Yesoid and says thats why it say Shlach Li'cha because if not they will get the traits of Klal Yisroel instead of getting the Shlichus of Moshe and getting his Tzidkus and we see what the outcome was.
Answer: There is rather a long and interesting Ohr aHaim on the word "lecha". I will make it very simple and short.
1."lecha" means permission and not command.
2."lecha" refers to "anashim", i.e. when they are close to you, Moshe, - they are tzadikim but when they are away from you - they are reshaim.
3."lecha" gives a hint that God wanted that the whole meraglim mission should seem to be initiated by Moshe and not by God!
4."lecha" means that the goal of the mission should be like you think of it and not like people think.
5."lecha" means that Moshe will get extra 40 years of his life, so this is 'lahanatecha" like in Lech lecha.
I guess this is it. Id someone is interested in details my advice is to read Ohr aHaim aKadosh!

"Shelach Lecha": What is "Lecha"?


Can I lay pavers over a concrete patio?

Question: I have a concrete patio in my backyard that's in pretty good condition.  We don't like how it looks, so we'd like to cover it up with brick or pavers.  Looking online, it appears that most people install pavers over gravel, so I was wondering if it was a good idea to lay the pavers straight on the concrete patio.  Would drainage be an issue?  What kind of cement would I use to secure the pavers on the concrete?
Comment: What part of the country are you in?  Does it freeze in the winter?
Comment: Maryland.  Yes, it does freeze in the winter.
Comment: Some manufacturers make special thin pavers just for this kind of installation.
Answer: If you have a drainage issue, or you're likely to have freezing conditions, I'd personally want to lay a small coating of gravel across the concrete first - allow that pent-up water to get out of the way.
If you're building this in, say, Phoenix, though, that may not really matter and laying them directly atop the concrete shouldn't be a problem.
To the 'cement' part of your question: why not go with dry-laid? As long as there is some form of rim to the patio, or you're not driving over them, dry-laying would make both maintenance and modification easier.
Comment: Why gravel and not sand?
Comment: @MatthewPK - gravel is less likely to wash away than sand, in my experience
Answer: If you are not in a freezing condition, then the only other problem I see is that the pavers will shift on top of the concrete pad. Gravel would make that worse. You are going to have to brace the pavers to keep them from shifting.
Answer: I would not put pavers on top of concrete. I was going to do that (I live in Illinois) but my contractor said NO. He ripped out the old concrete patio and installed pavers (Unilock) and it looks fantastic! I believe in the long run, the cost of replacement is well worth it as opposed to putting pavers on top of a concrete slab. Your concrete slab might look decent now, but over the years it will will eventually crack all over and become uneven due to the constant freeze/thaw cycles over the years, so you can imagine what will happen to those pavers if they are on top of that patio. Like another poster said, if you live in a temperate climate, it probably would not hurt to put pavers over a slab.

Can I lay pavers over a concrete patio?


How safe is steak tartare?

Question: How safe is steak tartare?
What can I do when preparing it make sure it is safe to eat?
Comment: @Stefano Borini: People always repeat that argument. It's silly. The ones who died aren't here to comment. :P
Comment: @hobodave : good point :) but it's unlikely you die. You just get sick eventually.
Comment: ate it a lot of times (with horse meat). I'm still alive :)
Comment: not exactly dupes, but the following questions also provide good enough: http://cooking.stackexchange.com/questions/2923/is-it-safe-to-eat-raw-fish http://cooking.stackexchange.com/questions/2957/is-it-safe-to-eat-raw-eggs
Answer: Butchered meat is generally sterile except on its exterior.  (That doesn't mean parasite- or botulism-free, but it's a start.)
Get the best quality you can from a source you trust.  Keep it at as low a temperature as possible, and don't expose it to warm air for more than the few minutes it takes to prepare.
Cut with a clean knife on a clean surface. Put it right back into the fridge at a very low temp.
Salt and acid, if you use them in your sauce, will provide some anti-bacterial benefits, but this is not foolproof.
People all over the world eat raw meat, but it's best to start with small amounts and see how your system handles it.  If you're a child/pregnant/old/sick, it's much less of a good idea.
Comment: Surely you should qualify this as "Butchered **red** meat ..."? Then again I'm not much of a cook.
Answer: It's as safe as any other raw meat consumption. It all comes down to quality beef and best practices when handling.
Two rules of thumb:

Don't use steak from a supermarket. Use a butcher, preferably one you know and trust.
Tell your butcher you intend to eat it raw.
Comment: Three: eat it soon!
Comment: +1. Finding a trusted butcher is the most important part of a steack tartare recipe.
Answer: If you are really nervous, a trick I have heard of is to start with a really thick piece of beef.  Then sear it on both sides in a hot pan.  At this point the outside would be deemed safe and the interior is typically safe so you cut away the cooked parts.  Then proceed to make the steak tartare with the still raw inside part. As a bonus those nice browned parts from the outside are a treat for the chef.
Answer: Use fresh beef that has been properly stored and handled. The natural state of beef is generally sterile, external pathogens are introduced in processing and multiply quickly on the beef. A good butcher who maintains a clean environment significantly decreases the chances of contamination. Keeping the beef cold until eaten slows the reproduction of any bacteria that happen to have made a home on your meat.
There is always a small risk of contamination, so people with compromised immune systems shouldn't eat raw meat. Most others are able to fight off bacterial infections, although it won't be pleasant.
Answer: I have eaten raw beef (including store bought ground beef) all my life. In fact, my mother told me our butcher fed me a small ball of raw, ground beef when I was a baby. She said it was my first solid food. I am now 80 years old & have never had any type of food borne illness, Probably have eaten at least a thousand pounds of raw beef of almost all cuts, gallons of raw oysters including some in southern Mexico, & still tell the waiter in the resturants "just knock off their horns, wipe their ----, & throw it on the plate" My step dad always said the way I ate a steak was "put a bandaid on it & it will get well", but he is now deceased, may he RIP.
Comment: I'm glad things have worked out for you, but it's definitely not always that way - entities like the FDA recommend cooking meat for a reason. The other answers here are a lot more realistic, telling people what they need to know to be confident they will be safe, even if they're not as lucky as you.

How safe is steak tartare?


Dry hopping in the keg.

Question: I have been bottling my beer for years now and am just getting in to kegging. I would love to start to dry hop directly in the keg but am worried about sediment in my beer. Is dry hopping in the keg even an option or should I stick to dry hopping in the carboy?
Comment: Anyone ever dry hop with fresh hops?
Comment: @J Times: It's called wet hopping.
Answer: I will sanitize a mesh bag, put the whole hops in the bag, roll it up and shove it up near the top of the keg, between the dip tube and the keg wall.  When you drink about a gallon of your beer, the hops will be suspended above the beer preventing over-exposure.  I've done this at least a dozen times with great results.
Comment: That's different then my method.  In my method I pressurize the beer, and serve it at the same time as I am dry hopping.  I push the hops toward the top of the keg to reduce hop/beer contact time.  Once a gallon or so is drank the hops are no longer in contact with the beer.  I remove the hops after the keg is finished and empty.
Comment: Sometimes the hops will float. Sanitize a metal washer or something else non-reactive and heavy and put it in the mesh bag.  I leave the drawstring of the mesh bag poking out of the lid. You can't pressurize the keg this way.
Answer: There is a thing called a SureScreen that can slip over the dip tube of the keg so you can dry hop in the keg.  Here's the description from Northern Brewer:
"The SureScreen is a welded stainless steel screen that slips onto your racking cane or keg dip tube and filters out fruit or dry hops from the fermenter or whole hops and trub from the kettle. Also allows dry hopping to be done directly in the keg. Stainless steel construction makes it easy to sanitize (do not use bleach!). Not recommended for use with plastic racking tubes or plastic fermenters. Pellet hops have a tendency to clog the SureScreen - it works far better with whole hops"
Answer: For those using pellet hops, the stainless steel mesh balls usually used for steeping tea are an option. I've used ones I bought from Northern Brewer on several batches and each one can hold up to about an ounce, though I try to go lighter to make sure liquid can flow through and around the hops. I typically just toss the SS balls in there and leave them until the keg blows. I've had some batches where the hop aroma just kept getting more and more intense as the keg stayed on tap.
Something to consider: Although they are billed as all stainless, the pin that connects the closure will eventually corrode away in beer. When that happens I just tie them shut with dental floss and hope I haven't ingested any carcinogens.
Answer: After my latest experiment with it, I'll be sticking with dry hopping in a carboy/secondary fermentor from now on.   It was mostly a process fault, but even so, the keg will be harder to clean with all the little vegetative bits left in it.
Basically, I made a "bag" out of some cheesecloth and put my 2oz of cascade pellets in it, tossed it into the keg, and racked the beer onto it.   Unfortunately, I didn't get the bag tied very well, so now (2 weeks after I fished the bag out), every time I move the keg at all, either the plumbing gets clogged with hop bits, or my first 2 or 3 pints are muddy with hop solids.

Dry hopping in the keg.


What theories allow for "Tractor Beams"?

Question: NASA recently announced $100k grant to study the possibility of using laser tractor beams. What tractor beam concepts have been published but not been dis-proven?
Answer: Most of these effects are simply thermal gradients in air (or some other atmopshere).
Heat an area to the left of a molecule with a laser and the gas expands moving the sample right, a bit of careful control and you can move a dust particle into a sensor. Pulling it toward you is tricky, but you could have a very dispersed beam which comes to focus on the other side of the particle and blows it toward you.
It's not really star-wars tractor beams but Nasa's particular expertise these days is getting media attention.


How does $E=mc^2$ put an upper limit to velocity of a body?

Question: How does $E=mc^2$ put a upper limit to velocity of a body? I have read some articles on speed of light and they just tell me that it is the maximum velocity that can be acquired by any particle. How is it so? What is violated if $v>c$ ?
Comment: The equation $E=mc^2$ does not put an upper limit to the velocity of an object. The limit in the velocity of an object comes from the fact that the speed of light in the vacuum is the same for all the observers, this is an experimental fact. Plus, in the development of special theory of relativity one can see that $v$ must be less than $c$. And if this condition is violated then the "causality" of events is violated. This means that your mother could born after you born, in some reference system if $v>c$.
Comment: @Anuar that should probably be an answer :-)
Answer: $E_0 = m_0 c^2$ is only the equation for the "rest energy" of a particle/object.
The full equation for the kinetic energy of a moving particle is actually:
$$E-E_0 = \gamma m_0c^2 - m_0c^2,$$ where $\gamma$ is defined as $\gamma = \frac{1}{\sqrt{1 - (v/c)^2}}, $
where $v$ is the relative velocity of the particle.
An "intuitive" answer to the question can be seen by noticing that the particle's energy approaches $\infty$ as its velocity approaches the speed of light. Thus, in order for the particle to move faster than the speed of light would require it to attain infinite kinetic energy, which can't happen.
Comment: -1: KE for relativistic speed is NOT $\gamma mc^2$!  This expression gives the total energy.  The kinetic energy is $\gamma mc^2 - mc^2$; the total energy minus the rest energy.
Comment: Ahh yes, I'll correct that. Thanks for the correction.
Comment: Great answer, i didn't knew that KE for relativistic speeds is $\gamma mc^2$
Answer: To complete bclifford's answer, our current equation for energy-momentum of a particle is $E^2=p^2c^2+m^2c^4$ which is the final expression for $E=\gamma mc^2$, where $\gamma$ is the Lorentz factor obtained from his transformations.
Hence, for a particle like the photon - this equation is valid throwing $E=pc$, which says that the photon has momentum.
For particles at rest, $p=0$ which gives the rest energy $mc^2$ of the massive object.
The great necessity of this equation is that it restricts massive objects to be accelerated above $c$ as it requires infinite energy, massless particles to travel at $c$ always and also faster-than-light hypothetical particles to travel above $c$ always...

You can consider $pc$ and $mc^2$ as the opposite and adjacent sides of a right-angled triangle and the energy along the hypotenuse. No matter how fast a massive object moves, the hypotenuse is always greater than the other two sides, (i.e.) it can never quite reach $c$...
Answer: It doesn't. The equation $E = mc^2$ and the fact that no physical object can be accelerated past the speed of light are two entirely separate conclusions of special relativity.
The reason $c$ is an upper bound on the speed of an object has to do with the Lorentz transformations. These are the mathematical expressions that relate positions and times as measured by one observer to positions and times as measured by another observer. Now, suppose an object starts at rest with respect to observer A, and then accelerates until it is at rest with respect to observer B, which is moving at a speed $v$ relative to A. There has to be some Lorentz transformation you can use to convert between A's measurements and B's measurements, or equivalently, between the reference frame of the object pre-acceleration and its reference frame post-acceleration. But there is no Lorentz transformation that will take you from a reference frame in which an object is going slower than light to a reference frame where the same object is going faster than light or at the speed of light.
(Technically, that argument is a little hand-wavy, but it should get the main point across.)
Comment: This is not really a satisfactory argument. It is possible to extend the Lorentz transformations to $v>c$ (but not $v=c$); see Recami, Riv Nuovo Cimento 9 (1986) 1. This works in $m+n$ dimensions only if $m=n$; otherwise there is a no-go theorem, V. Gorini, "Linear Kinematical Groups," Commun Math Phys 21 (1971) 150. A better argument would be that regardless of the existence or nonexistence of Lorentz-like transformations for $v>c$, no sequence of Lorentz transformations with $vc$, so no continuous process of acceleration can boost a bradyon past $c$.
Comment: @BenCrowell That's exactly why I said my argument is a little hand-wavy. The question didn't seem to be looking for a rigorous proof. Although what you're saying is what I meant to write, so let me clarify my answer a little bit.
Answer: Just to visualise the other answers, here is a plot of the kinetic energy of a body in relativistic and nonrelativistic mechanics (note the log scale on the vertical axis):

You can see that as the speed approaches the speed of light the energy required according to special relativity shoots up compared to what nonrelativistic mechanics would say. It requires an infinite amount of energy for any massive body to reach the speed of light.
Comment: The first time I looked at that chart, it appeared that the kinetic energy is zero when $v \approx 0.05c$. Then I looked again. `:)`


PreUpgradeCheck Error How to locate reference of Missing Feature

Question: I am migrating sharepoint 2007 publishing site to sharepoint 2010. For migration process I have followed the steps
1. Backup the content database from the SP2007 machine.
2. Restore that database in sql server 2008 (SP2010 machine).
3. Create a new web application in SP2010.
4. I have run the following stsadm command for PreUpgradeCheck in SP2007

I am getting the error log as follows
Error: Missing server file or server configuration issues
Server side files are referenced in the content databases, but are not installed on the server. Without these files, the sites may not function completely or the content may not render correctly. Also, upgrade or post upgrade issues may occur if these files are not available in the new version environment.
The following feature(s) are referenced by the content, but they are not installed on the web server
Name = Unknown, Feature id = f3dc6c9a-ea83-4c22-bdb9-1a3a178717cf, Reference count = 1, Scope = Web, Status = Missing
Name = Unknown, Feature id = a5977882-1fbc-4b94-a345-c9f3dac1b18c, Reference count = 1, Scope = Web, Status = Missing

The link provided below the error explains the issue but doesn't provide any instruction on how to search through the content to find the reference in order to fix it.
For more information about this rule, see KB article 976218 in the rule article list at http://go.microsoft.com/fwlink/?LinkID=120257.
Could anyone provide a solution for this issue ?
Answer: You can search the 12 hive location in your 2007 machine to find the missing feature. Do a text search on f3dc6c9a-ea83-4c22-bdb9-1a3a178717cf and the other feature and install it in SharePoint 2010.
You can also use a tool such as SharePoint Manager 2007 to browse all the features and inspect their ID's but doing a text search will allow you to find the missing feature quickly.


Is it safe to re-use drill holes in a wall?

Question: I've just mounted a 42" TV with a new wall mount that uses 3/16" bolts into some studs on the wall.  I now want to use an articulating one, which means I'll need to replace the old mount.  The new mount also uses the same size bolts.  Is it safe to re-use the holes from the old mount with the new mount, or should I drill new ones?
Answer: If you didn't strip the holes when removing the old bolts, then you PROBABLY should be able to re-use the same holes, but to be safe, I would inject a little Elmer's wood glue (just a few drops) into each hole before you insert the bolts.  This is just to reinforce the wood in the hole and help ensure it stays locked in place.
But honestly, I think you'd be wise to drill new pilot holes 1" above or below the old ones, and fill the old ones in with wood putty capped w/ a little dab of plaster (or toothpaste).  The old holes will end up hidden by the mounting plate anyway, and better safe than sorry.
Comment: Would sticking a short length of very thin dowel rod into the hole make for a tight hold when a new screw of the same size is driven into it?  And by thin, I mean toothpick-sized.
Answer: Put a dab of wood glue in the hole and push it all the way in with an appropriately sized nail, and then jam wood-glue-coated toothpicks into the hole.  You might need to give them a tap with a hammer to get them all the way in.
Give it 30 minutes to harden, and then you're good to go.
Answer: One trick I've seen someone do when reusing a hole is to put a small piece of copper wire in there so the screw has something to tighten up against.
Answer: If the screws go back in and hold tight, it should be OK, however, the worst case scenario of a TV falling off the wall is pretty bad, so sometimes it is better to be safe.
The best solution is to drill new holes a couple inches away from the existing holes.  If space and positioning allows, you can even re-use one row of the existing holes and drill new holes for the other row of screws (most brackets have 2 rows of holes).
If you are set on re-using the same holes, I would suggest that you either use a lag that is 1/2" longer than the previous lag (so it grabs new wood at the back of the stud; make sure its not too long or you might be in for a surprise on the other side of the wall), or use a lag that is one size larger in diameter.
I don't love the glue/dowel/toothpick solution. It might work on door hinges, but you are now putting all of your money on the strength of the glue and toothpicks - neither of these were designed to hold large loads.
I always hang on a TV mount with as much weight as I can to ensure it is secure. If it will hold me, it will hold a TV!  If it comes off the wall then better that it happens without an expensive TV attached and a child under it.
Comment: The bond of wood glue is often stronger than what's between individual wood fibers.
Comment: @Bmitch With a good wood glue sure, but I'd bet someone will try this with crazy glue, arts & crafts glue sticks, etc. Also wood glues usually require clamping, moisture, etc. to get a good bond, correct?


What is the equation of the gravitational potential in general relativity?

Question: How is the gravitational potential replaced by the metric tensor in general relativity?
$$U_G=\frac {GMm}{r}$$
What is its equation?
Comment: You might want to start here: http://en.wikipedia.org/wiki/Einstein%27s_equations
Comment: Related: https://physics.stackexchange.com/q/19796/2451
Answer: The other answers are correct, but for all reasonable situations which are nonrelativistic and slow moving, you can use
$$ g_{00} = (1- 2U(x)/c^2)$$
With all other components negligible. In this approximation, Einstein's equations reduce to Laplace's equation, and the geodesic equation reduces to Newton's law of motion for gravity.
Comment: Short and precise!
Answer: Like Jerry said, carrying over concepts from Newtonian gravity to general relativity isn't that simple. If you assume that spacetime is stationary, it is possible to define something similar to the gravitational potential.  A stationary spacetime is one where the metric tensor is independent of time, i.e. the gravitational field doesn't change.  Technically speaking, a stationary spacetime is one that posses a timelike Killing vector field.
If velocities are low, mass is low, and distances are macroscopic, then general relativity reduces to Newtonian gravity.  In this case, the Newtonian potential can be retrieved from general relativity.  To see how this works, you can see section 5 of this paper:
http://www.math.uchicago.edu/~may/VIGRE/VIGRE2010/REUPapers/Tolish.pdf
In GR, there is an 'effective' potential that allows you to calculate orbits, particularly in the Schwarzschild solution.  The SS is the solution to the Einstein field equations for a spherically symmetric gravitational field (it is a good approximation for the solar system), and it is also unchanging in time.  For the SS, the effective potential is $$\tilde V^{2}\left(\tilde L, r\right)= {\left(1-\frac {2M}{r}\right)} {\left(1+ \frac {\tilde L^{2}} {r^{2}}\right)} $$ Where $\tilde L$ is the angular momentum.
With it, you can calculate orbits by using the derivative of the radius with respect to proper time (the time measured by someone on the orbiting body), with $${\left(\frac {dr}{d\tau}\right)}^{2}+\tilde V^{2}(\tilde L, r) = \tilde E^{2}$$ $\tilde E$ is the potential energy per rest mass.
Comment: To be more precise, the Schwarzschild metric does change with some timelike coordinate within the event horizon; that is, it doesn't have a timelike Killing vector field there. But in the outside region there is a timelike Killing vector field.
Answer: This isn't a useful question to ask--General Relativity is a completely different framework from Newtonian mechanics, and often, questions can't directly map over.  In particular, the potential energy required to separate two masses depends on the spins of the masses, and in a nontrivial way on the mass ratio between the masses.
However, in the special case of a spherically symmetric unspinning case and an orbiting mass of negligible mass, you do find an equation of motion much like Newton's, which does, in fact, have a form with gravitational "potential" $U=-G\frac{Mm}{r}$, with the only modifications to Newton coming from extra terms in the "kinetic potential" of the orbit.


How do I complete "This Ain't My First Rodeo" Badass Challenge?

Question: The challenge states:

Explore your way to the top of the Happy Pig Motel sign

I've tried various forms of parkour off the nearby tower and rooftops and can't make it up.
Answer: A friend pointed out that there are nearby geysers that shoot you way up in the air.  By properly timing a run into the closest geyser (or simply standing in the right place), it is possible to land on top of the big pig, which will net you challenge success.
This YouTube video pretty much sums it up:
Answer: The closest geyser just needs to be stood on at the correct spot. It will launch you high enough that you will have ample time to adjust your decent onto the pig. You don't have to run at the geyser.
It took me 10-15 minutes to find the sweet spot on the geyser but after that it could be done with ~90% accuracy.
Answer: you need to use the geyser in front of the motel to get to the top of the pig sign. you have to stand on the edge(nearest to pig sign) of the geyser. Standing on center wont help you.
Answer: This can't be done with Krieg. His mass is increased so he doesn't get knocked around much, especially while using his action skill, and it keeps the geyser from lifting him enough. As of yet, I don't think Krieg can complete this challenge.


What are the benefits of venturing into The End?

Question: In simple terms, what can I get out of journeying to the End?
Answer: The biggest incentive for going there has to be the Enderdragon. Killing it is required for "winning" the game, gives you a ton of XP (the equivalent of 4000 zombies), and drops the Dragon Egg block, which is in itself useless other than as a trophy. Bragging rights, I suppose.
You can also get a material found nowhere else, the End Stone that the place is made out of. It also serves no purpose and isn't particularly pleasant to look at, though.
Other than that, it's crawling with Endermen. You can use this for XP grinders — from holes in the ground from where you hack away at Ender-shins, to huge spawning platforms that automatically drop the Endermen to ½ hearts of health.
Example of such a grinder setup:
Answer: Endermen grinders are useful, as well as the obsidian pillars, they could be destroyed for bunkers.  If you want to see one, look at etho plays minecraft videos. He has one set, his channel name is ethoslab.


Swipe To Delete songs in a playlist

Question: Is it possible to delete a song from a playlist with a 'swipe to delete'? I thought this was possible, but I am not able to do this. I'm running iOS 5.0.1.
Answer: Swipe to delete only appears to happen in the 'Songs' tab of the Music app. To remove songs from a playlist I only get the option of hitting Edit at the top of the playlist, then using the red icon on the left of the song name. - iOS 5.1
Answer: You're right. You can't delete songs in a playlist with a swipe. Only the way Nathan described. Hit the "Edit" button on top of the window, and remove the songs with the familiar red road sign.

You should be able to do this with a swipe on a whole Playlists, Artists, Songs, Albums, …

And make note you can't delete songs with a swipe from iCloud.

Swipe To Delete songs in a playlist


Who did Cal Weaver remind Jacob of in Crazy Stupid Love?

Question: In the bar Cal and Jacob meet for the first time in Crazy, Stupid, Love. Cal asks Jacob why he is helping him (Cal), to which Jacob replies

Maybe you remind me of someone

Who is Jacob referring to? Is it his father?
Answer: I imagine that Jacob is referring to some aspect of himself. It could either be his 'past self' - i.e. Jacob before he learned to be a stylish womanizer, perhaps - or it could be the nice and sentimental part of him that still exists in his character. (We know that some part of him like that exists because he falls in love with Cal's daughter.)
I imagine it is some combination of the two.
Answer: Nobody realises this, but Jacob fell in love with Hannah instantly and helps Cal because he reminds Jacob of Hannah.
Jacob never thinks "you remind me of Hannah," but he just feels some sort of connection to him. Hannah doesn't display any qualities of Cal but it's some sort of psychic thing.
Answer: If I remember right, Jacob once said that his dad was kind of too honest, too fair or something. That is why his wife (Jacob's mom) treated him not in a good way (maybe cheated too)
Maybe it was the scene where Hannah and him are chatting in his bedroom.
Answer: This is something I too pondered, however thanks to DVR and rewind/replay you can see that Gossling's character Jacob actually answers Carrell's character Cal's question "Why are you doing this?" with "Maybe you remind me of ME" - the Audio track was edited in post production to what we all hear, "Maybe you remind me of SOMEONE".
Because Gossling's facial expression and limited mouth movement when he speaks... it was an easy edit to make and unless your looking for it will probably easily miss.  As for my theory for the change... I understand a fair amount of Gossling's lines were ad libbed. To that end, When he's in bed with Stone's character Emma and they're talking and Jacob asks for 'a kindness' and reveals his fathers softness and that his mother easily took advantage of him is part one element.
My additional association is that when Hanna blows him off in the bar and he gives her the long stare... I think he also see's Hanna in Cal. My reason for the latter is Jacob says the same line when he 'honks' both of their noses. I realize Jacob's character is shocked when he ultimately meets Cal in the back yard 'meet the Mother & daughters - however, I still think there is some subliminal and intriguing tie between what he sees in Father Weaver and Daughter Weaver characters.
Answer: I too also pondered this, I even found this website looking for the answer. However, I think I've solved it. Jacob describes his parents at one point in the evening with Hannah, he says his mother was cold and vain and his father couldn't handle her. It makes for a strong argument that Jacob's parents got a divorce, and his father either died shortly after from that broken heart syndrome, or committed suicide. Realistically Jacob in this movie can't be older then early thirties. So for him to have had all this wealth and time to "try and buy happiness" his father must have died some time ago. id say at least a few years, if not more.
Answer: It's not Hannah, it's Jacob's father. He describes Cal when he is in the bedroom with Hannah. He calls him for fatherly advice when he is about to meet Hannah's mother. Cal gives off a fatherly vibe. From the moment that Jacob meets him he's devastated about his family falling apart, showing Jacob how important family is to him. Jacob was looking for a father figure and he saw it in Cal and wanted to help him and have him play a key role in his life. That's why it's so difficult for Jacob to have Cal angry with him and Hannah, it's why he craves his approval and why he's so hurt when Cal doesn't give it to him. I don't think that Jacob was ever any different than he is in the movie- I think he was always a womanizer. Even if the line was originally "Maybe you remind me of me" then they would have changed it to suit the purpose of Cal being a father figure.
Answer: Cal reminds Jacob of his father. The qualities  of being kind and sweet he describes to Hanna in the bedroom are traits that I believe Cal has. Proof of this is when the kids stay up and Jessica talks to Emily. Jessica told Emily "That when she babysits most kids will stay up late for moms but not for dad." He also said his father was very successful in business. Cal works for a business firm in the movie. Jacob stated that his mother was very vain and that his father "couldn't handle her." Cal's progression in the movie though Jacob's help is evident. Cal is devastated by Emily in the beginning of the movie. Cal throughout the moviel is more vocal with Emily expressing how he feels about the situation. This adds to what Jacob says to him when coming out of the fitting room, "Your wife cheated on you because you lost sight as who you are as  husband, a father, and even a lover." Cal admits towards the end of the movie he did not fight for his relationship.  Jacob lost his father very young according to the movie. Perhaps he helps Cal because he sees him headed down the same potential path as his father.
Answer: It is meant to mean Cal reminds him of himself. It's not that hard, this line makes you immediately think that Jacob is talking about himself, not his father. He didn't even mention his father until later.


Gas Fireplace Pilot

Question: I have a Heatilator NB4842I gas fireplace. When I turn on the switch on the wall, the pilot lights the burner. When I turn off the switch, the burner goes off but pilot is staying on until I tap on gas valve. It's never done this before, and the unit is only 4 years old and not used often. Any ideas for diagnosing the cause of the problem?
Answer: look at page 22 of the manual: http://www.heatilator.com/downloads/installManuals/4031-551.pdf
using a multimeter, check the voltage being sent to the valve while the fireplace is on, which should be the green and orange wires. the re-check it after you turn it off and the pilot is still on. if the on and off voltages are different, then your gas valve is faulty. if the voltages are the same, then your controller is faulty.
if the it's valve, do not replace it yourself. in nearly every jurisdiction, it is illegal for non-licensed people to do work on gas fixtures.
note that it might also be that you just never noticed that the pilot remains on for a brief time as it burns the residual gas in the line.
Answer: I'm not sure about your model, but in my experience (I have gas heating stoves and a gas fireplace) the pilot should stay lit at all times to prevent the build-up of gas in the case of a small leak. It also protects against the case of a power outage.
I know this is the DIY site, but I'd still recommend having it looked at by a licensed professional. You don't want to screw up with gas and blow up your house.
Comment: this model of fireplace does not have a continuous burning pilot.

Gas Fireplace Pilot


Facebook fan page - search keywords

Question: Apparently Facebook doesn't allow you to change the name of a fan page with more than 100 fans
This is causing problems for one of my clients, as they've recently gone through this whole rebranding phase which basically means they're now known under a different name.
Now they want to show up in Facebook's autocomplete search results for this new name, but as far as I can tell Facebook are basing these results on the fan page name — and nothing else.
Is there no other way to make Facebook pages recognize search keywords outside of the fan page name?
Answer: As stated in the help section, you need to provide insight for Facebook to understand your problem under their feedback form: Page Name Change Feedback

Facebook fan page - search keywords


Where can I buy Prime Beef?

Question: Does anyone know the type of place I can buy prime beef? Will I typically have to go to butcher or could I get it from a super market somewhere? Also, does anyone have an idea of what the price for an 8 oz cut would be?
Comment: We can buy it here in Canada at Costco sometimes. *shrug*
Comment: This doesn't make much sense if you don't tell us where you live (which country, if it is a large one, also the region).
Comment: Costco also sells prime beef in the US, at least in Colorado.
Comment: Sourcing questions meta:  http://meta.cooking.stackexchange.com/questions/1292/what-types-of-sourcing-questions-should-be-allowed-revisit-march-2013-plea
Answer: The price of a cut of meat depends on what cut it is (oyster blade vs fillet, for example) and where in what country you are buying it.
Prime Beef is an American designation for high grade meat. You will have to go to a butcher or high end specialty shop, if you can get it at all, as such quality of meat is generally bought by restaurants and other purchasers in the wholesale markets rather than making it to retail outlets where individuals can purchase. You might be able to get it through whatever Markets are in your area.
The best quality meat I have purchased here in Australia has been from cattle grown by hobby farmer friends and slaughtered on their property to their specifications (so hung for optimum flavour). If I wanted to buy similar meat from commercial suppliers, I would go to a couple of specialty stores in the area who would order it for me if they didn't have any, or I might have to visit the Growers Markets at 3-4am, or one of the local Farmer's Markets and know who I was looking for.
Answer: As @Freya points out most beef that is graded as "Prime" is sold into the restaurant industry. But there is a way to get "Prime or Better" that you may wish to consider.
I have both raised my own beef and bought from small ranches where they were custom finished. If you are in the US (based on your reference to "Prime") you can contact into local FFA (Future Farmers of America) or 4H groups (Check out the Ag buildings at your state fair) and you can probably find someone who is raising a few head that they might be willing to sell you one of them after they are done showing him. Because these cattle are being raised as show animals as a project they are usually superior to "Prime". If you buy such an animal and take it to a butcher the butcher will probably charge you to have it 'graded' but if you are dealing with a single beef it probably isn't worth the cost to have the meat officially blessed as "Prime", but that is your call.
You will also need to find a butcher who will also slaughter and hang for you. Such a butcher will work with you to custom cut your beef. Depending on the size of your family, you may want to find someone to split a beef with you...but that is a different matter.
Answer: Like others have said, Costco is the only place I have seen USDA prime steaks. I just picked some up for $11.99 a pound, here in Phoenix.

Where can I buy Prime Beef?


Will MATE ever be in the official repos?

Question: I was wondering if mate will ever show up in the official repos and be installable without the ppa?
Answer: Mate is in the process of being submitted to the Debian repositories, so it is just a matter of time really.
The biggest hurdle is having someone (preferably multiple people) to manage and maintain the packages (and to handle bug reports etc). Another problem is that the Debian people don't like the fact that MATE uses deprecated technologies forked from GNOME 2 - this problem is getting better with each MATE release. Once these are sorted, Mate will probably land in the Debian repositories like any other Desktop Environment. Then, it will automatically become part of the Ubuntu repositories, too.
Answer: Technically it can happen, because there is not any conflict between "Mate Desktop" packages and "Ubuntu Repository" packages.
I think it depends on Ubuntu development team and its relation to "Mate Desktop" development team, but i believe that it is not matter because a software popularity will lead to add a it's packages into official Ubuntu repository.
Answer: MATE 1.8 is in the official repositories beginning with Ubuntu 14.10, "Utopic Unicorn." See http://wiki.mate-desktop.org/download.


I live in a place where it frequently floods. How can I keep my chain from rusting?

Question: My poor bike's chain lasted all of three months before it gave in to the winter floods where I live. Storing it indoors is not an option, and despite my maintenance efforts, the knee-deep floods that come once a month or so, rain every other day, and ocean only a quarter of a mile away has made it pretty much impossible to keep my chain dry. It's deteriorated beyond a useable point, so I have to buy a new one now. I'm new to bike maintenance on this level so I'd really like some advice on how to avoid replacing it again in three months.
Comment: Interesting situation. A few questions that may help us give better answers: Can you describe the options that do exist for storage? i.e., what outdoor areas are available, and do you have the option to install hooks or what have you out of doors in these places?) Why can't you bring the bike inside? And is spending a little money on the problem an option, or do you need a cheap/free solution?
Answer: If you're getting knee-deep floods it's destroying the bearings along with the chain.  You need to hang the bike up somehow.
Comment: Seems a little unfair that you should get 8 upvotes for an answer that is the same as my earlier one.  :-P I know, I shouldn't care. :-)
Comment: @JamesBradbury - That's because I have such a pretty face.
Answer: While I agree with cherouvim that wet lube is a good thing for rust prevention, I would also ask if it's possible to store the bike higher up, perhaps with some kind of simple cover to prevent the rain and salt-spray from getting to it. Perhaps a couple of hooks on the wall and some rope or a simple bench or couple of large stones to stand the bike on.
Whatever magical product you treat it with, all parts of a bike are going to suffer from being repeatedly immersed in salt-water.
Answer: You need to start using a "wet" chain lube.
<code>"Wet" chain lubes are recommended for wet riding conditions. They are generally
made from oils and are not easily washed off by water.
</code>
Have a look at http://www.pinkbike.com/news/To-the-Point-Chain-Lube-2013.html for detailed chain maintenance information.
Answer: You can get stainless steel chains, but that won't stop the other components from failing, and they are typically not all stainless so will still rust a bit.
Have a read of This answer as it has useful information on rust resistant chains.
Answer: You could remove the chain from the sprockets while it's not being used. If you have quick release wheels removing it and putting it back on should take no longer than 5 minutes.  Removed the back wheel, disengage the chain, and wrap it up around the seat post. If you have a single speed or fixed gear bike, this will be easy but it gets more complicated with derailleurs, but depending on their design it still might be possible with about 10 minutes of work. But it probably doesn't flood every day, so you should watch your weather forecast and only do this if you think there's a chance of a flood.
I would second @Daniel's recommendation of getting the bike up off the ground.  If you have a derrailleur, yoo will at least have part of that sitting in the water along with the chain, and depending on the depth of the water, your bottom bracket and wheel hubs also.  You can also purchase a stainless steel or nickel plated chain which might hold up to the water a bit better.  If your spokes and wheels aren't rusted out then a stainless chain might be an easy solution.
Comment: Essentially disassembling the bike after each use probably isn't practical, but a folding bike *would* solve the problem if storing it indoors is an option. Just sayin'... :)
Comment: It's not really "disassembling", especially if you have a fixed gear/ single speed. Sure you can't just get on it and ride, but it's not that big of a deal, and if it saves you buying a new chain every three months, it's probably worth it.  With a quick link, you could probably just remove the chain completely, although I'm not sure how well they stand up to repeated opening and closing.


Optimization of annealing temperature

Question: I am trying to optimize annealing temperature for some primer pairs. I have tried optimization using cDNA, genomic DNA, Taq polymerase, phusion polymerase etc., but every time I am either getting non-specific amplification, a band of larger size than expected or no amplification. Every time I am getting a primer-dimer. Can anybody help me optimize the annealing temperature?
Comment: Posting the primer sequences and what genome they are designed against would be helpful.  Furthermore, have you double checked that your primers are in the correct orientation?
Comment: I've heard of people using single stand binding protein to reduce primer dimers.
Comment: Most PCR enzymes come with a manual (which can also be found online) that has a troubleshooting section, often dealing exactly with you problem. It may be more fruitful to first follow these steps, and include the outcome in your question.
Answer: I'm going to give this question a blind attempt, assuming you are talking about PCR (since you are talking about genomic DNA and cDNA) and not RT-PCR or qPCR, since I know very little about them. This answer is not necessarily optimisation for annealing but checking some basics and potential solutions. In my work I had to do a lot of site directed mutagenesis and genotyping and there are some important rules you have to follow in your primer design. First try to keep your primer length between 25-30 for sequencing (at least thats what I do) and for site-directed mutagenesis between 25-45 since anything above 45 bases increases the likelihood of secondary structure formation. Primer melting temperature (Tm) should be >=78 oC (Tm= 81.5 + 0.41(%GC)-675/N [with N being primer length in bases]). Also primers should have a minimum CG content of 40% and should ideally start and end with a C or G. So check your primer CG% since if its too high then it will make a few problems including increased Tm and possibility of primer-dimer formation due to CG triple hydrogen binding. This document has some nice information (http://www.genomics.agilent.com/files/Manual/210518.pdf)
In my opinion if all else fails and you are still struggling with your primers, then re-design a new primer set, if possible. Now getting back to the annealing temperature issue, in my experience for cDNA, annealing temp of 50 oC works best and for genomic DNA, annealing temp of 55 oC works best, which is about the range most people work with and I have so far had no problems. I'm more than happy to share my genomic DNA PCR cycle information with you if you wish through an edit.
Hope this helps!

Optimization of annealing temperature


Is there a way to scroll the toolbar icons of an application?

Question: On a 24" display, there is enough space to display all the toolbar icons of my applications.
But on the MacBook 13" display some of them are not displayed.
Is there a way to scroll the tools bar in order to see the entire set of icons?
Answer: I use AccessMenubarApps which works on the basic principle of temporarily replacing the current menubar with a shorter one to allow all the menubar icons to be visible. It can be accessed by clicking on the icon, via mouse gestures, or a configurable hotkey.
Answer: Not exactly what you are looking for (not a scrolling solution), but you could have a look at Bartender. By putting the least important icons in there, and leaving the most important ones in place, you could have 2 levels of icons, hopefully giving enough real estate to display all of them in your 13" display.


What is the difference between using varchar(100) and varchar(255)?

Question: I want to know difference between varchar(100) and varchar(255) in terms of memory usage and programming problems of using more memory.
Answer: The difference is going to be in how much data you are allowed to store there.  The memory and disk space will depend on how much is actually stored, not what limits you put in place.
Most db's (MySQL included) store varchar fields with a length identifier and then a variable length data string.  This means that the size of the field on disk goes up more or less linearly with the actual data stored.  Similarly in memory, you aren't going to be allocating a large amount of memory for a small string unless it is padded (so varchar uses a lot less memory than char does regardless of underlying storage of the latter).  In fact some db's like PostgreSQL store VARCHAR() and TEXT fields the same (and there is a 1GB compressed size limit there) and try to optimize storage based on actual requirements of the data being used.
In general these decisions should be made based on what your data retention and collection needs are, not based on the performance considerations.  The performance can be tuned and that's the lovely thing about an RDBMS.
Answer: Since varchar takes disk space proportional to the size of the field, so
the length of a field should be appropriate to the data that is being stored there, not least because there is a limit to the length of single record in each database e.g. SQL Server (it's ~8000 bytes).


May one put cut flowers in a vase of water on Chol HaMoed?

Question: I know certain agricultural activities are prohibited on Chol HaMoed -- it's not the recommended time to do gardening or lawn-mowing (if there's sudden pressing need, talk with your rabbi). What about putting cut flowers into water? Is that "agricultural work"? (I know it would be prohibited on shabbos ...)
Comment: Never heard that it is a problem on Chol HaMoed.
Answer: Shulchan Aruch (Orach Chaim 336:11) permits putting branches into water on Shabbos, "as long as they don't have buds or flowers that will open because of the moisture from the water." Shulchan Aruch Harav (ibid. :18) and Mishnah Berurah (ibid. :54) clarify that this means putting them into a vase that already had water in it, but that one may not fill a vase on Shabbos and put the branches in it.
Elsewhere (654:1) the Mechaber adds that on Yom Tov water may even be added to the vase in which the lulav is kept, but that the water may not be changed; "but on Chol Hamoed it is a mitzvah to change the water so that the lulav stays fresh and beautiful."
Now it is true that a lulav doesn't have flowers on it. Nevertheless, if you're allowed even to change the water on Chol Hamoed and that's not considered "too much trouble" (טירחא יתירא), then it would seem logical that you can do the same for cut flowers, and that it wouldn't matter whether the flowers are going to open or not - it should be no worse than watering a field that needs it, which is permitted on Chol Hamoed (ibid. 537:1).
Answer: I'm not a Rabbi and this is not Rabbinic advice, BUT:
I'm certain that putting cut flowers into water is permitted on Chol HaMo`ed.  Flowers presumably enhance one's enjoyment of the holiday, which would indicate that one can obtain them and put them in one's house.  And if they're not put in water, they will wither and die, so not putting them in water would cause a loss.
To me, it doesn't sound like "work" at all, either, and takes no skill or effort to do.
The Rambam (Sh'vitat Yom Tov 7:20) permits all forms of personal makeup and beautification on Chol HaMo`ed, and putting flowers into water is, I think, similar but with less work.
Comment: Feel free to downvote, but let me know what can be improved!
Comment: I did not feel the need to downvote, but additional sources would help.


Choosing a open source licence for embedded system library

Question: I'm writing a few libraries that I want to release as open source projects, but I want to find a licence that means I'll receive the credit when it is used in a project. Im not fussed about anything else, if people want to profit off of it then thats fine. So what licence is most appropriate? The only factor for me is that I receive the credit for producing the library if it is ever used.
Answer: The original four-clause BSD license is most probably what you are looking for. It allows (not forbids) commercial use, but both source and binary distributions have to show your copyright. In contrast to other variants of this license (e.g. the three-clause variant), it contains an "advertising clause" requiring users of this code to name you as a contributor.
However, this four-clause BSD license is considered not compatible to the GPL due to the advertising clause, so you may want to use the three-clause variant (which still requires acknowledging your copyright).
Comment: The four clause BSD is a bit ugly, but not just because of compatibility with the GPL.  IMO, the real issue is what happens to a 4-clause BSD application after lots of folk have contributed and made revisions.  You end up with lots and lots and lots of attributions, some of which may no longer be all that relevant because the code has changed dramatically.
Answer: Have a look at this Wikipedia article regarding Free and OSS licenses and that should get you started in the right direction.
Creative Commons has a number of licenses you may be interested in since attribution seems to be your biggest concern.
Answer: Pretty well all permissive licenses (eg BSD and MIT) would suffice-  they all require the license bearing copyright owners name to be distributed with any copy of the software. Most software released under BSD uses New BSD License (3 clause).
Comparability with other licenses becomes an issue if someone uses your library in another open source package.  Also remember, if you used GPL in your code, then you must release it under GPL.


How can I leverage multiple iTunes libraries in a LAN to create an office jukebox?

Question: Well, we all have Macs, we all have iTunes, and we want to be able to democratically enqueue songs on one of our Macs while being able to choose from everyone's iTunes libraries.
Is there such a tool?
Answer: You should be able to do this using shared libraries, which would probably be the easiest way and not cause any problems with permissions or anything like that, however it would probably end up with number of separate libraries rather than just having a one large library.
UPDATE:
Having had a bit of a look into the shared libraries feature it could be a decent option if combined with iTunes DJ - which can be turned on in preferences if currently off.
Essentially you would require everyone to turn sharing on for their iTunes library (or specific playlists) then have one of your computers acting as a master which has iTunes DJ setup. You can then add tracks from any of the libraries and have requests and votes for next tracks sent via the Remote app for iPhone or just shouted across the office.
May still not be quite what you're after, but essentially uses features already available in iTunes rather than a 3rd Party app to do it for you.
--
You could try having one folder for music and all linking to it, but you may hit permission issues or DRM or something silly like that.
http://support.apple.com/kb/ht1203
This tells you how to move the library to a shared folder for one computer to allow multiple users to connect to it, the actual library is still per user, so you may get duplicate files or have to update the library if new files are added. In theory this would allow multiple computers to connect to one collection of music, add to it and play the files others have added. Though my theory is untested and may be flawed (like all good theories).
On a different note:
I was able to have one library (so viewing the same apps, podcasts, music etc. without the need to update it each time you logged in or downloaded new stuff) for multiple users on one computer by copying the whole iTunes folder to the shared folder and then adding an alias to the shared iTunes folder in the Music folder for each users Home folder - which is a bit of a convoluted sentence - which may be of some help, but probably not as the library gets locked when it's accessed by a user, so i can't imagine it'd help for multiple computers. Just another way of doing things.
Hope that helps in some way, let me know id it's absolute guff though.
Comment: I was looking for something simpler, like an app, so I'll wait for more answers before accepting yours.
Comment: no worries - I didn't come across any apps like that while I was searching for an answer to my own combined library problem, but I wasn't specifically looking for one, so maybe there is something like that.
Comment: cheers - did it help at all? did you manage to get something setup?
Answer: Would MediaRover solve your problem? It creates a shared repository of all your songs, and allows them to be synced, but i don't see why songs couldn't be played from there directly. I'm guessing it might not strictly solve your problem (as i suspect you don't want to have to copy the songs to a new 'library', only enqueue them), but if you want to add them, then it would work.
Comment: Problem is, I need to get everyone to enqueue songs on the same playlist on the same mac.


Lowering the gearing on a Shimano biopace double

Question: My bike has a 52/38 Biopace pair on a 5 bolt 130 crank (Shimano 105). I want to reduce the pedal load because I'm getting older and live in hilly Wales, UK.  I have bought a 42/28 Biopace pair. Unfortunately the smaller ring has a bcd of 74. I would like to know how to fix the smaller ring. Presumably I need a spider or a new crank. I am expecting to use the existing Shimano front derailleur (FD 1055) which has a 14-tooth capacity. Is this feasible ?
Answer: I don't know of a crankset that has one 130 mm bcd chainring and one 74 mm bcd chainring.  However most Shimano triples have two 130 and one 74 chainring.  So you can use this and only populate the inner and middle chainring positions.  A used one shouldn't cost much.
There's a couple of quirks about using only the inner and middle chainring position.  You may need a longer bottom bracket to get the chain-line correct.  Also, you'll need either single speed chainring bolts for the 42t ring or some spacers (the standard chainring bolts assume you have two chainrings).  Your local bike shop should be able to supply you with all of these.
This will work, I've done this on several bikes.
As an alternative you could ditch the Biopace rings and get a 110 mm bcd triple.  (Sugino makes a nice one for about $80 US with 26-36-46 rings).  The 110 bcd will give you a wider range of chainrings you can install.


How to deploy Zencart on live environment

Question:
I have to deploy my zencart on my live server , when I deployed it on stage it was very painful.
I had to do everything step by step again , because of lots of customization it takes lots of time , effort and testing .
Can anyone tell me better way to do this?
Answer: If your live environment is a mirror of staging area you should be able to copy your completed copy of your site from your staging area to your live server when you are done developing it. You shouldn't need to go through the steps of reassembling it piece-by-piece on the live server. That kind of defeats the purpose of having a staging area in the first place.
Comment: There are some config files , which need to be changed.I dont how many are there.I know 2 of them , will work on them & find out.Also I wanted to know is here any change in db or not.But your post was helpful.Thanks.
Answer: As John states, the purpose of a staging area is to replicate your production environment so you can get the kinks out before you deploy to your production server(s). Ideally, you'd use the same VM image to ensure the two environments are identical, but if you can't then you should at least use the same OS and software versions.
Secondly, many of the repetitive manual tasks required in deployment can be automated. CI software like Capistrano, Puppet, etc. let you script your deployment tasks, such as fetching the latest files from your revision control server, uploading them to your production servers, running database migrations, regression testing, and automatically rollback to the previous revision if the deployment fails.
If you can't get your staging server identical to your production environment, then I would just set up a staging subdomain on the production server. Your deployment script can deploy to this subdomain, and if everything tests out, use a symlink to make it live.


Difference of the maximum eigenvalue of a graph with the one of one-edge-deleted subgraph

Question: Let $G$ be a graph and $e$ be an edge of the graph $G$ such that the subgraph $G\setminus e$
is connected. The subgraph $G\setminus e$ is the subgraph of $G$ obtained by deletion of the edge $e$ of $G$.
Assume that $G$ has $n$ vertices.
Is it true that $\lambda(G)-\lambda(G\setminus e)\geq \frac{1}{n}$?
Here $\lambda(G)$ denotes the maximum eigenvalue of adjacency matrix of $G$.
Answer: It's always useful to test these questions on actual examples. The largest eigenvalue of the cycle $C_n$ is 2 and the largest eigenvalue of the path $P_n$ on $n$ vertices is $2\cos(\pi/(n+1))$. When $n=8$, this is 1.879385 and $2-1.8793852=0.120615 <1/8$.
In fact it is not hard to see that for large $n$ the difference $2-2\cos(\pi/(n+1))$ is
of order $\pi^2/(n+1)^2$, and so your lower bound is not even of the right order.
Answer: This conjecture is not true in general. For example, let $G$ be a graph that obtained from joining the end vertex of $P_3$, $P_3$ and $P_4$, where it is an star-like tree. This graph has largest eigenvalue equal to $2.02852$. Now join the end vertex of $P_4$ to the end vertex of $P_3$. Therefore we added an edge to the previous graph. The largest eigenvalue of this graph is $2.13578$. Then the difference of this values is $0.10726$. But this graph has $8$ vertices and $1/8=0.125$. It is a counter example.
Also, we can construct a family of star-like tree that does not have this property. Also, I think for any polynomial $f(n)$, we can construct a graph $G$ such that $\lambda(G)-\lambda(G-e)\geq \frac{1}{f(n)}$ is not true.


Fourier transform vs Fourier series

Question: Why are Fourier series considered to be the subset of Fourier transform? It should have been other way around. Because a non periodic pulse is a subset of periodic pulse with period infinite. So Fourier transform (non periodic signals) is a subset of Fourier series (periodic signals).
Comment: no physics, please flag for migration to math stack exchange.
Answer: The set of periodic functions is surely a subset of the set of all functions (most of which are aperiodic). So the Fourier series – which allow us to describe periodic functions differently – are a "subset" (in this sentence, the word "subset" is stranger than before) of the Fourier transform – which is a tool to encode an arbitrary function.
Alternatively, we may see the "subset" relationship in the frequency representation, too. Fourier series may be written as a special case of the Fourier transform in which only the frequencies that are multiply of the basic angular frequency $2\pi/T$ where $T$ is the periodicity are allowed. The Fourier transform of a periodic function is a very special kind of a function, a combination of delta-functions
$$\tilde f(\omega) = \sum_{n\in{\mathbb Z}} c_n \delta(\omega-n\omega_0) $$
and functions that are a combination of delta-functions like that (determining Fourier series) are a subset of all functions, including distributions (which may be identified with the Fourier transform of the original function).
Answer: I would say that neither is more general, they're different things.
Fourier transform can be defined in a very abstract way, for arbitrary locally compact abelian groups, and sometimes even more general objects. In case of locally compact abelian groups, it turns a function defined on a group into a function defined on its dual, and the formula is quite simple: $\hat f(\xi)=\langle f\mid \xi\rangle=\int_G f \cdot \overline{\xi} \, d\mu$ with $\mu$ the Haar measure.
Fourier series are the instance of Fourier transform where the group considered is the circle group $S^1={\mathbb T}$ (or its finite power), and it so happens that its dual is the group of functions of the form $e^{ikx}$, isomorphic to the group $\bf Z$ of integers (and the Haar measure is just the counting measure); in that way, Fourier transforms are far more general, but that's probably not what you meant to ask about.
What you know as Fourier transform (and what is most commonly referred to when Fourier transforms are invoked) is probably the Fourier transform of a function on the additive group of real numbers $\bf R$ or ${\bf R}^n$, which happen to be isomorphic to their duals, consisting of  the functions of the form $e^{i\xi x}$.
Answer: I'm not quite sure I understand what you're saying about periodic versus non-periodic pulses, but you can think of a Fourier transform as a projection of a function onto a basis of functions. The same way you can project a vector onto the x, y, or z axes, you can project a function $f(x)$ onto the sine basis or the cosine basis. The Fourier transform projects functions onto the plane wave basis - basically a collection of sines and cosines. A Fourier series is also a projection, but it's not continuous - you sum over $\sin(nx) + \cos(nx)$, whereas in a Fourier transform you preform an integral - a continuous sum.
$$ \int_{-\infty}^{\infty} \;dx\; e^{ikx} f(x) = \int_{-\infty}^{\infty} \;dx\; (\cos(kx) + i\sin(kx)) f(x) \quad\quad x\in\mathbb{R}$$
I think it makes sense that a Fourier series is a subset of a Fourier transform, as the transform takes into account all the same sines and cosines that the series does, but adds in all the noninteger sines and cosines as well.
Hope that helps.
Comment: What my understanding was- Fourier series is used for analyzing periodic signals and Fourier transform for non-periodic signals. Now, Consider f(t)=f(T+t). In this if the period T-> ∞ then we get aperiodic version of periodic signal f(t). So I thought Fourier transform is a subset of Fourier series. The mistake I did was I differentiated this two based on the input signals not based on the output frequency spectrum or the explanation u have given above. I think now you might have understood what I thought previously. Anyway Thanks for yourreply.
Comment: @Inquisitive Thanks for the comment, now I understand it too
Answer: You can zero-extend a period of a periodic function to $\mathbb{R}$ and calculate the Fourier transform of the extension. This is done within pointwise function definition $f:\mathbb{R} \rightarrow \mathbb{C}$ and doesn't need the use of distributions. The zero-extension method has also the property that Fourier coefficients of the original periodic function can be read directly from the values of the transform of the extension. With suitable assumptions on the function also the inverse transform gives correct values within the interior of the period. That's why Fourier series is considered as a subset of Fourier transform.
The other way round it is not as easy. That's because Fourier series handles periodic functions only. A mapping that maps an infinite period to finite nonzero period violates the algebraical structure of the domain and values of the transform of the original aperiodic function cannot be read from the coefficients of the series anymore in a straightforward way. The countable domain $\mathbb{Z}$ of the coefficients isn't the problem because it can be extended to $\mathbb{R}$ by $f(\omega) = \sum_{k=-\infty}^\infty c_k \textrm{sinc}(\omega-k)$,  where $\textrm{sinc}(x) = \bigg\{ \begin{eqnarray} & \frac{\sin(\pi x)}{\pi x} & , \ x\neq 0 \\ & 1 & , \ x = 0 \end{eqnarray}$. Now the obvious way to calculate the values of the transform of the original function is to form the Fourier series of the mapped version of the original function. Then it can be inverse mapped to obtain the original function. Values of the transform of the original function can be now obtained by just calculating all the values of the transform of the original function. The procedure consisted of inverse transformation, inverse mapping and transformation, that is not easy to do. However, that kind of procedure exists.

Fourier transform vs Fourier series


Is there a plugin to integrate Face FX with Blender?

Question: Is there a plugin to integrate Face FX with Blender? I only see plugins for Maya, Max, SoftImage, and MotionBuilder on the Face FX website.
Answer: Well, I haven't used FaceFX myself, but I do recall FaceFX uses Ogre for its editor/viewer (here is a forum post about it), and there is an excellent Ogre exporter for Blender available here (for versions 2.4.x I believe). So you could export from blender into Ogre's format, then load that into FaceFX. It's not a plugin or direct integration, but I suspect that's as good as it's going to get unless the FaceFX devs decide make a plugin (maybe contact them about it?).
Answer: you can get facefx data out to fbx format, and it looks like you might be able to find an fbx importer for blender.  that is probably your best bet.


GIS professionals working from home

Question: How many of you out there work from home?
What kind of company / organization do you work for (private, government, municipal, institution..)?
How did you convince your employer it was a good idea?
What are the major drawbacks to working in a GIS position at home?
Answer: It's a very visual industry, and it is hard to walk people through your work on a telephone line.  It's also hard for the opposite to happen, people walking you through work they want you to do.  However, that depends on the role.  I work in most facets of GIS, and in development, as long as you have a project plan and a clear idea of what you have to produce, you can very easily work from home.  However, I have also been in charge of producing ad hoc maps, produced from rapidly evolving data models, and you can't do that offsite.
It depends.  I asked a question not long ago about the impact of the Cloud on GIS and one of the main ones, will be the ability to do almost anything on the cloud, freeing up the labour, but in some parts, you'll always have to be on site.
I thought I'd edit this and add my tuppence on benefits etc:
Pros.
Pretty much as mapperz has suggested.
I like the flexibility of taking the kids ot school, having lunch with my wife, sometimes just plopping out of bed and going to the office in my pj's with a saucepan of coffee (cautioned by the next comment).
I work better if I dress for work as I normally would and, yes, this does include a tie.  If I don't dress up, I am lethargic, and look for ways not to work.
I work a lot harder from home, I get an awful lot more done.
Don't have the radio on, it distracts you, and once, when I hooked up Sky Sports onto the laptop and watched cricket, I got nothing done.  The best part of working from home is the absolute lack of distraction you have, if you are disciplined and it's this that frees up your time; for me, 7 hours at home is worth a lot more than 9 in the office.
I hate the travel that comes wrapped with my work.  Not doing the soul destroying commute makes me smile a little more inside.
Cons:
Very easy to get distracted.
You will work harder, sometimes at the cost of your own personal life.  For me, I don't mind this so much, as it is outweighed, imo, by the other benefits.
And pretty much as what Mapperz said.
My choice, however, is as it is.  Keep this away from my wife, but I love being able to work away, as I get more sleep (3 kids, all young).  But I also like working from home 2 days a week too.  I think it is the best of both worlds.  But then, I would, wouldn't I!
Answer: Have in the past. Freelance (GIS Consultant) - Private
Advantages, by far is the eliminating the commute (saving a huge amount on fuel).
(one job was 1hr each way costing over £120 ($186.66) weekly, trains/buses are not cheaper and take much longer) Though some contracts require you to travel to win the initial work.
No office noise (third party noise) and can concentrate.
Your own choices or music/drinks/snacks and when you want them.
With technology today (high speed broadband a must) most can work from home.
Super-flexi time - get up at 4am - finish by 12am (unless a pending deadline).
You can go to appointments with out needing to ask/tell Manager permission
Disadvantages
Unless your able to focus without distraction - it is easily to be side-tracked off paid/incoming generating work.
(to avoid this it is good to set up a dedicated area or room to work from.)
kids and animals want your undivided attention.
[Freelance] Chasing up unpaid for work can be real time-consuming up to 20% of your time, which could be used to generate more revenue/work.
no real banter - only via email/social media.
But if had the choice would do office (small commute) mainly for the interaction with others.
Answer: I think this is an important psychogeographical issue.
It's hard to have a 3rd Place, when you don't have a 2nd place.  I've found it helpful to go out (maybe taking the kids to school) and come back with a view of the home as a workplace.  The harder part though, is being able to "leave the work at the office".  I'm not sure if there is some sort of psycho-GIS technology that could remedy this, short of an invisible fence electroshock collar triggered upon entering the room where my desk is.  Maybe Esri needs something like spArcGIS.
Answer: I do some work on the side from home, and Hairy is right, communication and ad-hoc, rapid on-the-fly tasks are probably the most difficult things I deal with. It is often easier to communicate something visually in person. Deployments and trouble-shooting can also be difficult. Luckily, there are plenty of technologies out there now that can help with remote access. I use ReadyTalk to remote into client machines to do deployments and to trouble shoot issues. Dropbox is great for sharing files (keep in mind security and size limitations).
Making yourself available for communication is key. Stay in touch with others on your team and/or your clients.
With many organizations, security is paramount, so you might run into issues with your IT security folks wondering who this person is that needs remote access to company resources - feel that out too.
As far as convincing your boss to let you work from home - maybe see if they would go for a test run, a trial period, where of course you would blow them away with the increased productivity you gain from working from home :)

GIS professionals working from home


edge distribution of random Young's tableaux from Okounkov's "random matrices and random permutations"

Question: I am reading the paper "random matrices and random permutations" by Andrei Okounkov, which is very beautifully written. I just have several technical questions about some of the computations:
1. in section 2.1.2, why is it clear that only the eigenvalues near the edges of the Wigner's semicircle contribute to the asymptotics of (2.1)? In the same spirit, on page 8, section 2.1.3, the author claims that it is easy to see that by taking a suitable linear combination we can single out hte contribution of only the maximal eigenvalues in formula (2.1). I don't quite see how a winner takes all argument can be applied.
Answer: In the expression below equation 2.1 the as n goes to infinity the expression tends towards
an exponent of $y_i$ times a positive expression. The $y_i$'s from expression 1.3 are negative
except in the range of 2n^.5 where they are close to zero. If they are substantially less
than this then the entire expression of 1.3 is roughly -n^1/3 which which as n goes to
infinity will make the exponential expression relatively small.
As for the contribution of maximimum eignenvalues in
2.1 there is more than one representation of 2.1
and a combination of these representations allows
the elimination of the contributions of all but the
maximum eigenvalues.
These are the lecture notes from a course on random matrices:
http://www.math.wisc.edu/~valko/courses/833/833.html


Gmail: Add 'mailed-by' domain to safe list?

Question: Gmail keeps marking emails coming from my site as spam. Is there any way to set up a filter that will send any emails coming from that domain to my inbox?
Answer: You can check for common issues with mxtoolbox http://www.mxtoolbox.com/?
Try the blacklist and spf test first, and fix those if they are not defined.
Answer: You can try clicking 'Not Spam' button. Gmail may not send it to spam anymore.
Another way is to click 'Filter messages like this' under More Actions and click 'Next' in first step after making necessary entries if necessary. In the 2nd step, put a check mark on Never send it to Spam. You will also get an option to Also apply filter to ? conversations below. This will enable you to move other mails from same address out of spam.
Answer: Actually, you can create a filter with just the domain and tell Gmail to always mark as important. This'll mean that anything coming from that domain will not only be delivered to your inbox but be in your "Importnat" emails list.


"Balky", "restive" and "stubborn" - what are the differences here?

Question: Please, share your understanding of the hues in meanings of these three words. American English is preferred, but British input would also be appreciated.
Answer: Broadly speaking, a stubborn person/animal insists on doing something despite all advice/evidence/exhortation to the contrary, while a balky person/animal insists on not doing something, despite exhortations. Balky is also used more with animals or inanimate objects than with people, while stubborn can be used with anything, but if it's applied to animals, it's usually with a meaning closer to "balky". (A stubborn donkey, for example, is so insistent on not going anywhere that it practically sits down.)
Restive is quite different in my usage - it's closer to impatient. (Though I note that the dictionary gives both "stubborn" and "balky" as alternative definitions.)
Answer: If somebody is stubborn, it has an idea or many ideas on how to do something, refusing anything else. On the other hand, restive person is just generally impatient and hard to be controlled. Restiveness can be a temporary state of a person caused by something embarrassing him. Alternatively, restiveness can be caused by lack of respect or culture. In contrast to that, stubbornness is usually caused by fervent beliefs in the ideas and/or deep wish to be always right.
As far as I know, the word "balky" is usually applied to animals or things, rather than persons and it can be applied to persons only in informal speech. If you say that someone is balky, you pretend to control his behavior (like you can control a dog or device or computer program) but the person refuses to do what you want him to do.
Disclaimer
Don't rely on my answer too much since I'm not a native English speaker.