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My advice is not comprehensive as I am no expert and there are other websites with such information (see list below). Below I will share some of my family's experiences in accommodating those with GF diets. I have thought it over, talked with my family, and written some suggestions for Sarah's friend here. I hope it might also be useful for other GF beginners or those like me who are cooking for friends and family who are GF.
It will get easier
When you start out eating gluten free or even cooking gluten free for friends and family, it seems like a huge task. Just remember this too shall pass. It will not always be this hard. When my sister first started a GF diet, she found GF bread inedible. After looking around she found a bread that she liked and she has started to appreciate the taste. Looking around the web, you will see everyone cooking GF has different preferences so you need to find your own way - what foods are you most comfortable with.
Be vigilant
Gluten is sneaky and gets into all manner of foods. It lurks where you would leak expect - baking powder, icing sugar, soy sauce, spice mixes. Familiarising yourself with what is and is not GF and then reading labels vigilantly is important in the beginning. We have found that some regular ingredients are GF but only in some brands so it is a matter of getting to know which ones. After a while, you will feel more confident and not need to read labels quite as much.
Embrace the range of grains available to you:
People I know who have gone gluten free will mourn the foods they can't have but learn to embrace many new foods. When life revolves around wheat, it is hard to believe just how many grain, legume and nut flours are available to us. I personally am intimidated by the huge range of flours that some of the experienced GF bloggers use but I have gradually started using some of these (see below photo of my stash that is taking over the fridge).
I prefer using a few tried and trusted GF flours such as besan, soy, buckwheat and cornflour. For example Ilva kindly shared her discovery that besan flour (also known as chickpea flour) can be used as a substitute for wheat flour in brownies. Almost as good are the Awesomely Delicious GF Pumpkin Brownies which are also vegan and use only cornflour and rice flour.
I love the diversity of flours and that they all taste different. I found the Gluten Free Goddess most helpful in getting to know the different sort of flours and being able to balance heavy, rich and light flours (and have recently discovered Gluten Free Girl's guide to GF flours). This knowledge has helped me substitute the flours I have for those in recipes rather than running out to buy new flours for every new recipe. It doesn't always work but GF baking is still a bit of trial and error for me. More recently I love the idea of Ricki's mix and match GF flours (grains, starches and beans) in her pancake recipe.
I have also seen bloggers using nut flours. I have yet to come across nut flours but what what I have read, it seems they are different to ground nuts because the oil is taken our to dry them out more.
Get to know your GF flour mixes
I know some like my sister prefer using just a commercial GF flour mix. A word of advice about GF flour mixes. Wheat flour has one type of flour. GF flour mixes are all different because there are so many flours to choose from. I suggest you read the labels so you know what flours you are eating if you buy a commercial mix. You may need to try different commercial mixes (or even mixes at home) to find what you prefer. My sister's favourite is Orgran.
Get to know what you are missing in Gluten flours
I was told by someone (I don't know who so it could be just an urban myth) that wheat flour is far richer than many gluten flours. So you might want to think about extra flavouring (such as vanilla or cinnamon) or some rich flour (such as soy) to make sure that your baking still has this richness. Or check your GF flour mix has a comparable nutritional profile to wheat flour.
Or are you missing the binding powers of gluten strands and need to think about some xanthum gum like Kim found. Dan Lepard adds the psyllium husk to his GF White Bread. Or you may just accept that your gluten free bread will be dense as Breadchick did when making a GF no-knead hearty sandwich loaf.
Identify GF friendly cuisines
If you live in Australia like me, or a Western country, you might find that wheat bread is the staff of life. Fortunately it is not so in every part of the world and you will find some cuisines are very GF friendly. Japan has a lot of rice and soba noodles (made of buckwheat - but beware soba noodles with wheat). India has lots of rice dishes. Mexican dishes have a lot of corn based tortillas and tacos. South East Asian dishes often have rice, rice paper rolls and rice noodles. Even in our Western cuisine - many soups and salads are GF and potatoes can often give the substance that wheat provides.
Think about eating out strategies
Friends of mine on a GF diet will suggest which sort of restaurant is better for them if we are eating out (see Identify Different Cuisines section above). But they also often have risotto in an Italian restaurant and flourless chocolate or flourless orange cake off the cake display. They might get a little tired of the same old thing but at least they know they can order something substantial. This is particularly important when there are still many restaurant staff with a poor knowledge of GF foods. I have even had friends who are quite bold in suggesting dishes to the waiters. Ringing ahead and finding 'safe' places to eat out is advisable but not always practical.
Take food to social gatherings
When going to a social gathering, remind the host the you are GF and ask if you can bring some food. Be selfish and suggest taking along something you want to eat. Eg if you are tired of never having a dessert at a dinner party, suggest you bring a dessert.
Educate your family and friends
You might find that those around you have good intentions but that gluten gets in under the radar. Always check if you are unsure and be gracious when others get it wrong. Warn people in advance and let them know some common pitfalls. (eg see Kristy's advice to those coming to a gluten free potluck.) It gets tiring reminding people that you are GF but those close to you will get better at it.
Some of the foods that are helpful to us
It sounds obvious, but we have found there are foods we eat regularly that are already GF or need very little alteration to be so. Here are some foods that appear in our family a lot.
- Made at home: My mum often does roast meat and roast vegies. Susie makes a cauliflower cheese with GF flour in the cheese sauce. Barbecues with salads are also quite regular and easy to make GF and substantial with a good potato salad. Dips with corn chips or rice crackers and vegetable sticks. Tacos. Pavlova, sponge cake, flourless chocolate cakes, fruit salads.
- Prepackaged: orgran little cakes packet mix, basco vanilla cupcakes mix, chocolate cake packet mix, Arnotts rice cookies, rice crackers, baked beans. (NB Check the labels!)
- My sister lets my niece have lollies which have glucose syrup in them - the doctor has told her that, although this is a wheat product, the amount of gluten in these is negligible and it is one childhood treat that Grace doesn't have to miss out on. Of course, some children are more sensitive to gluten than others so this doesn't suit everyone.
- Birthday cakes: my mum often makes sponge cakes that are mostly egg and sugar with a little cornflour but no flour. If I make a kids novelty birthday cake I usually take a bit of cake mixture out before adding the flour. I add a little GF flour to this mixture and make a little cake that I decorate with lots of sprinkle and lollies and have as a cake for the candle to sit in. (I have also found this GF chocolate cake works well for novelty cakes)
- Kinder and school: My mum has made GF bread from a packet mix to take to the kindergarten when there is a special bread baking day.
- Special occasions: My mum found a recipe for GF hot cross buns this Easter so that Susie and Grace could eat them.
- Keeping meals simple helps to avoid gluten. The less processed food is, the less chance of gluten sneaking in. For example plain salted potato crisps or corn chips can be GF but when they have flavourings often these will have some gluten in them.
- My mum has found that recipes which have very little flour in them are good for substituting GF flour mix for wheat flour. For example pancakes are excellent with GF flour - probably even better because they are meant to be light and a lot of GF flours are quite light.
- Both my mum and I have found that following a tried and true recipe that calls for GF flour mix usually works better than just substituting GF flour mix in any recipe. (eg my favourite GF Apricot and Cranberry Cake that is pictured above)
- It is good to find ways to make a fuss of a GF child who can feel she is missing out (eg such a decorating the GF cakes with lots of fancy colours and sprinkles, or giving a special role in party games).
- I've never seen GF oats in Australia but you can buy them over the internet.
- My mum often goes to a GF cafe/bakery in Northcote Melbourne called SACS Gluten Free for the Silly Yaks Bread - the cafe is at 105 High St, Northcote, 3070. Ph: (03) 9482-3999. If you are interested in the cafe or the baked goods, check out Silly Yaks website which includes the history of the cafe. Black Ruby in Rathdowne Street Carlton also sells v good GF bread.
- My mum has a gluten free pastry recipe with mashed potato in it. I have tried them in gf vegetarian sausage rolls and it tasted great but was quite delicate to work with. My sister now says she loves the Pastry Pantry gf puff pastry that you can find in the local supermarekts.
So to Sarah's friends, I say give it time, it will be hard sometimes but the more you find (or fight) your way in the maze of GF foods, the easier it will become.
I am not listing my gf recipes but if you look in my index you will see that I have marked those that are GF and/or GF friendly with (gf) and I have a list of favourite GF recipes in my index of favourites. Here are a few other blogs with good info and good recipes:
- Crispy Cook's list of GF blogs
- The Book of Yum - with lots of great GF links
- 50 incredibly useful links for gluten free living
- Gluten Schmooten - gf reviews of eating out in Melbourne
- Interesting post by GF Girl about using chia and flax rather than xanthum gum
- Oh She Glows asks for GF advice and gets lots of info
- My real food life post on understanding GF flours
- Gluten free baking tips and tricks - GF Diet
- Diet Dessert and Dogs GF flour mix
- Gluten Free Girl's all purpose GF flour mix
- Ginger Lemon Girl's GF master baking mix
- Simply Sugar and Gluten Free's flour blend


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subset: commoncrawl


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VIMS professor leads mission to underwater research station
Professor Mark Patterson of the Virginia Institute of Marine Science, College of William and Mary, will next week team with National Geographic's Explorer-in-Residence Sylvia Earle on what might be the last expedition to NOAA's Aquarius Undersea Laboratory, the world's only underwater research station.
Their weeklong mission is a celebration of 50 years of human habitation of the ocean floor. Human "aquanauts" have been living on the seafloor for purposes of science, innovation, and exploration since Jacques Cousteau launched the Conshelf I project in 1962.
Aquarius—aka America's Inner Space Station—is located 8 miles off Key Largo, Florida, 60 feet below the surface of the Florida Keys National Marine Sanctuary. Since its deployment at the site in 1993, the school-bus-sized lab has supported more than 115 missions, which have generated upwards of 300 peer-reviewed scientific publications and provided knowledge and long-term data to help guide the management and conservation of coral reefs in the U.S. and around the world. The lab is owned by NOAA and operated by the University of North Carolina Wilmington.
During the upcoming mission, scheduled for July 15-21, Patterson and Earle will focus their research on the nearby coral reefs. To share the excitement and inspiration of living beneath the sea, the mission will be available worldwide via a Ustream video feed (www.ustream.tv/aquariusreefbase) generated by the Aquarius Reef Base, the onshore command center for the undersea habitat.
Broadcasts from the mission will also be available to schools, science camps, aquariums, and other educational facilities, including the Science Museum of Virginia in Richmond and teams of "Research Experience for Undergraduate" students at VIMS, the Woods Hole Oceanographic Institution, and Mote Marine Laboratory in Sarasota, Florida.
Patterson and Earle are also scheduled for underwater interviews with reporters from ABC's Nightline and NPR's Science Friday, among other media outlets. One World One Ocean, a project of IMAX pioneer MacGillivray Freeman Films, will host social-media outreach during the mission at www.oneworldoneocean.org/expeditions/aquarius.
A special video feed on Thursday, July 12th will allow previous Aquarius aquanauts attending the 12th International Coral Reef Symposium in Cairns, Australia, to share their Aquarius research highlights with the public and the current Aquarius team. NOAA Chief Jane Lubchenco primed the pump for Thursday's live feed during her keynote address to the ICRS attendees, calling ocean acidification the "osteoporosis of the sea" and noting that it has emerged as one of the biggest threats to coral-reef ecosystems and the people that depend on them for food and jobs.
Patterson, head of the Autonomous Systems Laboratory at VIMS, has a long history of living and working underwater. He introduced the use of computer technology to NOAA's Hydrolab—the predecessor of Aquarius—in 1984, and has participated in 7 previous Aquarius missions. With support from the National Science Foundation and NOAA, he continues to develop and deploy advanced instrumentation and robotic submarines to study how corals cope with environmental stress from global warming and ocean acidification.
Earle—an internationally renowned oceanographer and Time magazine's inaugural "Hero for the Planet" in 1998—is a pioneer in the use of advanced technology for human exploration of the seas. She has led more than 60 expeditions worldwide involving more than 7,000 hours underwater in connection with her research—including the first visit by a team of women to an undersea habitat during the Tektite mission of 1970.
The continued operation of Aquarius is under serious question due to an Obama Administration plan to eliminate the $4 million National Undersea Research Program (NURP) under which the lab and several other undersea research programs operate. In April, a U.S. Senate spending panel threw further doubt on the future of Aquarius when it proposed to fold NURP into NOAA's Office of Ocean Exploration and Research. The fate of Aquarius within these budget-cutting and reorganization proposals remains unclear.
Saul Rosser, Operations Director of the Aquarius Reef Base, says "There's been some budgetary questions within Congress related to Aquarius, which definitely has us concerned. This mission is an opportunity to engage people with the habitat and understand the benefits it brings."
Otto Rutten, Associate Director of the Aquarius Reef Base, says "If the Aquarius program is ever shut down, what's going to be lost is a national asset, losing the world's only underwater laboratory. Fifty plus years of a legacy, and it's not easy to restart that if it were ever lost."
Patterson says the habitat's value lies in its facilitation of underwater research. "Aquarius has allowed me to do experiments that can't be done in the lab," he says, "and makes underwater research much easier than when diving from the surface." By living in Aquarius, the scientists' body tissues "saturate" with nitrogen gas, allowing them to spend much longer on each SCUBA dive than a surface-based diver.
Thomas Potts, Aquarius Reef Base director, says "The real benefit of Aquarius—science wise—is that you get about a 9-fold increase in productivity. You can spend 9 hours per day diving, at about 65 feet, where you'd be lucky to spend an hour a day diving from the surface. It gives you the opportunity to live on the bottom and actually concentrate on your research.
"Being able to study the animals and plants in their home using an underwater habitat gives me the gift of time," adds Earle. "Time to see what these magnificent life forms are actually doing on the reef, time to notice the small and seemingly insignificant that later turn out to be a sea secret. Every time I live underwater I come back with new insights and a hundred new questions."
Joining Patterson and Earle on the expedition is DJ Roller, a fellow aquanaut, underwater explorer, and award-winning filmmaker who uses his custom-designed 3-D underwater digital camera system to capture images in resolutions high enough for 5-story-tall IMAX screens. Roller and his production team will capture an entirely new view of science and living underwater.
Roller says, "Living underwater and exploring the ocean as an aquanaut is a life- changing experience that has given me a whole new perspective. The 3-D camera system creates a window into another world and has scientific merit as the determination of scale and distance isn't possible from 2D cameras."
During the upcoming mission, the aquanauts will illustrate the advantages of living and working on the seafloor by experiments on different corals and algae that cannot be conducted diving from a boat, or from a shore-based lab.
"We'll use sophisticated instruments to measure the health of coral colonies on the nearby reef," says Patterson. "I'll be conducting measurements on coral and sponge respiration and photosynthesis using a PAM fluorometer and a micro-electrode system. Our results will help predict how corals will cope, or not, as the oceans change."
Rounding out the Aquarius dive team is M. Dale Stokes—an internationally known marine scientist from Scripps Institution of Oceanography and a veteran of 4 previous saturation science missions at Aquarius. Stokes is an expert in underwater instrumentation, coral reef biology, and the physical and chemical oceanography of reefs. He will be collaborating with Patterson on planned experiments on corals and sponges.


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Create a Website Account - Manage notification subscriptions, save form progress and more.
We offer an education and support program (Juvenile Firesetter Program) for youth firesetters and their parents. For more information contact Lieutenant Dan Albertz at 513-922-2011.
Show All Answers
Yes. We offer car seat installation by our personnel who have been trained through Cincinnati Children's Hospital. Car seats are installed by appointment only, generally between the hours of 7 am to 7 pm, however, appointment requests at other times may be accommodated for special circumstances. Please note, it is important that you call for an appointment because there are times when a certified car seat installer is not available.
Please call 513-922-2011 for more information or to make an appointment.
Yes, for both! Please visit our Community Risk Reduction page to find out more all of our programs.
Periodic beeping (one short chirp every 15 to 20 minutes) is usually indicative of a low battery. Delhi Township Fire Department recommends changing batteries every spring and fall on the same day you change your clocks.
In a ranch-style home, one smoke detector should be placed in the hall outside the bedrooms and one at the bottom of the stairway in the lower level.
In a two story home, one smoke detector should be installed on each floor. On the second floor, place one in the hallway outside the bedrooms, on the first floor position a detector in a central location (preferably a hallway), and finally one at the bottom of the stairway in the basement.
Delhi Township Fire Department is for emergency transports only. Transporting patients in non-emergency cases are handled by private medical transport companies. Their numbers can be found in the Yellow Pages under "Ambulance Service."
If the EMS run report is for yourself or your minor dependent, a copy of the report can be obtained by stopping by the Delhi Township Fire Department Fire Headquarters located at 697 Neeb Road. Due to HIPAA law, there are forms that must be filled out and you must provide picture identification as proof of identity. Once the paperwork is filled out and approved, a copy of the report will be released to you. Because of HIPAA law, you cannot obtain copies of reports for relatives, friends, etc.
There is a fee of $0.05 per page for each report requested.
Please call 911 for any type of fire or medical emergency, or for medical non-emergencies. For other types of calls, call the administrative offices at 513-922-2011 or, if it is not during regular business hours, call the Hamilton County Communications Center non-emergency line at 513-825-2260. Do not call the fire station, as crews are not always at the station. They may be out doing training or at another emergency.
Charges for ambulance fees help cover the cost of equipment, supplies, and medicines used during the transport, as well as the transport itself. Most insurance carriers have a payment for EMS transports built into their plans, which should cover the costs. If you are a resident of Delhi Township any balance remaining is written off.
Routine fire hydrant maintenance is (in the spring and fall) is handled by the department. If a hydrant is leaking in your neighborhood, please call Fire Headquarters at 513-922-2011 and we will send personnel out to assess the problem.
No. Open burning is not permitted in Delhi Township. If you have questions, please call Delhi Township Fire Department at 513-922-2011.
No, they do not. The pool owner is responsible for filling their swimming pool.
A Knox Box is a secure rapid entry system for emergency services. It is a secure box containing master keys and information about contact persons, materials on the property or and special information that will aid the emergency service.
Yes, you can visit the Knox Box Rapid Entry Systems website or pick up a form at Fire Department Headquarters at 697 Neeb Road. Once the form is filled out, return it with your payment to the Fire Department for processing. When you receive your Knox Box, a Fire Inspector will help you find the best location for installation at your address. After the box is properly installed, Fire Department staff member with the master key to the Knox Box will come and place your Master keys into the box and lock it.
There are many things that give off carbon monoxide. They include gas appliances such as furnaces, water heaters and stoves. Fuel burning space heaters and wood burning fireplaces can give off carbon monoxide. Even warming up your car or barbecuing in your garage can fill your house with carbon monoxide. The problem is that it is an odorless, colorless gas so until you begin to see symptoms, you don't know it's there. People experiencing carbon monoxide poisoning feel like they have a flu that came on suddenly. This also affects small pets and even plants.
Carbon monoxide detectors will sense excessive levels of the gas early and warn you to leave. If your family is having symptoms or your detector is sounding an alarm, call 911 and the fire department will respond. We can take readings and provide medical help. Sometimes we can shut off the source of the problem but you will need to call out a technician to check the appliance and make repairs. For more information on carbon monoxide and detectors visit our Carbon Monoxide Safety page or contact Delhi Township Fire Department at 513-922-2011.
Complete, print and mail a copy of the Run Report Form and applicable fee or contact the Delhi Township Fire Department Administration office at 513-922-2011. There is a fee of $5 per report.
View the contact information for Fire Department Headquarters to learn more about contacting the Fire Chief.


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Omicron Delta Epsilon is one of the world′s largest academic honor societies. The objectives of Omicron Delta Epsilon are recognition of scholastic attainment and the honoring of outstanding achievements in economics; the establishment of closer ties between students and faculty in economics within colleges and universities, and among colleges and universities; the publication of its official journal The American Economist; and sponsoring of panels at professional meetings as well as the Irving Fisher and Frank W. Taussig competitions. The minimum requirements for admission for undergraduates are:
- Completion of 12 semester hours of economics courses; and
- Attainment of at least a 3.50 in economics courses and an overall 3.50 in all classes.
Students do not have to be economics majors, but must have a genuine interest in economics in addition to meeting the above requirements.
Please contact Professor Marshall Gramm for more information.


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After spending the better part of the year on this site I am seeing how big the open source GIS community is. I used to just think it was ESRI and nothing else. That said, how do you begin to nudge or convince others that open source programs might be more beneficial than ESRI products?
I'm not specifically asking about features in one vs the other, but actually trying to convince higher ups that a move to a similar product that would provide comparable results in terms of productivity, efficiency and end product.
I guess what it boils down to in the end, is, at the end of the day, does the cost savings outweigh the time that it might take to get GIS staff acclimated to open source software?


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Art for Seniors
The Benefits of Creativity for Seniors
People are living longer and embracing new activities well into their older years. Living longer begs the question, what can be done to age well? There's more to it than staying physically active, regular check-ups, and eating the right food. More and more seniors are finding a new hobby or pursuing arts and crafts to enhance their quality of life. Creative activities, such as writing, painting, sculpting or knitting, encourage a sense of purpose and competence—all of which contribute to aging well.
Here are a few ways that being creative—even if you're not artistically inclined—can have a positive impact on your life.
Reduces stress and anxiety
Did you know the average person has 60,000 thoughts per day, and 95% are the same thoughts being repeated day in and day out? ( 1 ) Creative activities can distract your brain from the usual and habitual thoughts reducing stress levels and anxiety.
Increases hand-eye coordination
Hand-eye coordination decreases with age. Holding knitting needles, a pencil or paintbrush can help stimulate the brain and improve hand-eye coordination.
Aids in communication and encourages socialization
Being involved in creative activities can help us connect with others, reducing the feelings of isolation, loneliness and depression. Working on projects together can grow friendships and provide a social network. For those that have difficulty expressing themselves verbally due to a condition or stroke, art can be a great way to communicate through visual means.
Improves fine motor skills
Doing an art project requires coordination. Through small and purposeful movements, fine motor skills can improve.
Reduces boredom
Being creative is a great way to increase motivation and combat boredom.
The hardest part is choosing what to do—the possibilities are endless. There are so many arts and craft projects to choose from. Here are a few ideas to get you started.
- Adult coloring books
- Polymer clay
- Mosaics
- Photography
- Painting
- Faux stained glass
- Decoupage
- Fabric Crafts
- Knitting
- Beading
- Scrapbooking
- Creative writing
- Gardening
It's never too late to create! Be creative—write, draw, build, color, paint, knit or attend an art class. So, it's up to you! Whatever you choose to do, it will positively impact your health and your happiness.


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In modern physics, the double-slit experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles; moreover, it displays the fundamentally probabilistic nature of quantum mechanical phenomena. This type of experiment was first performed, using light, by Thomas Young in 1801, as a demonstration of the wave behavior of light. At that time it was thought that light consisted of either waves or particles. With the beginning of modern physics, about a hundred years later, it was realized that light could in fact show behavior characteristic of both waves and particles. In 1927, Davisson and Germer demonstrated that electrons show the same behavior, which was later extended to atoms and molecules.[1][2] Thomas Young's experiment with light was part of classical physics well before quantum mechanics, and the concept of wave-particle duality. He believed it demonstrated that the wave theory of light was correct, and his experiment is sometimes referred to as Young's experiment[3] or Young's slits.
The experiment belongs to a general class of "double path" experiments, in which a wave is split into two separate waves that later combine into a single wave. Changes in the path lengths of both waves result in a phase shift, creating an interference pattern. Another version is the Mach–Zehnder interferometer, which splits the beam with a
In the basic version of this experiment, a coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate.[4][5] The wave nature of light causes the light waves passing through the two slits to interfere, producing bright and dark bands on the screen – a result that would not be expected if light consisted of classical particles.[4][6] However, the light is always found to be absorbed at the screen at discrete points, as individual particles (not waves); the interference pattern appears via the varying density of these particle hits on the screen.[7] Furthermore, versions of the experiment that include detectors at the slits find that each detected photon passes through one slit (as would a classical particle), and not through both slits (as would a wave).[8][9][10][11][12] However, such experiments demonstrate that particles do not form the interference pattern if one detects which slit they pass through. These results demonstrate the principle of wave–particle duality.[13][14]
Other atomic-scale entities, such as electrons, are found to exhibit the same behavior when fired towards a double slit.[5] Additionally, the detection of individual discrete impacts is observed to be inherently probabilistic, which is inexplicable using classical mechanics.[5]
The experiment can be done with entities much larger than electrons and photons, although it becomes more difficult as size increases. The largest entities for which the double-slit experiment has been performed were molecules that each comprised 810 atoms (whose total mass was over 10,000 atomic mass units).[1][2]
The double-slit experiment (and its variations) has become a classic thought experiment, for its clarity in expressing the central puzzles of quantum mechanics. Because it demonstrates the fundamental limitation of the ability of the observer to predict experimental results, Richard Feynman called it "a phenomenon which is impossible […] to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery [of quantum mechanics]."[5]
Numerical simulation of the double-slit experiment with electrons. Figure on the left: evolution (from left to right) of the intensity of the electron beam at the exit of the slits (left) up to the detection screen located 10cm after the slits (right). The higher the intensity is important, the more the color is light blue - Figure in the center: impacts of the electrons observed on the screen - Figure on the right: intensity of the electrons in the far field approximation (on the screen). Numerical data from Claus Jönsson's experiment (1961). Photons, atoms and molecules follow a similar evolution.
Same double-slit assembly (0.7 mm between slits); in top image, one slit is closed. In the single-slit image, a diffraction pattern (the faint spots on either side of the main band) forms due to the nonzero width of the slit. This diffraction pattern is also seen in the double-slit image, but with many smaller interference fringes.
If light consisted strictly of ordinary or classical particles, and these particles were fired in a straight line through a slit and allowed to strike a screen on the other side, we would expect to see a pattern corresponding to the size and shape of the slit. However, when this "single-slit experiment" is actually performed, the pattern on the screen is a diffraction pattern in which the light is spread out. The smaller the slit, the greater the angle of spread. The top portion of the image shows the central portion of the pattern formed when a red laser illuminates a slit and, if one looks carefully, two faint side bands. More bands can be seen with a more highly refined apparatus. Diffraction explains the pattern as being the result of the interference of light waves from the slit.
Simulation of a particle wave function: double slit experiment. The white blur represents the wave. The whiter the pixel, the greater the probability of finding a particle in that place if measured.
If one illuminates two parallel slits, the light from the two slits again interferes. Here the interference is a more pronounced pattern with a series of alternating light and dark bands. The width of the bands is a property of the frequency of the illuminating light.[15] (See the bottom photograph to the right.) When Thomas Young (1773–1829) first demonstrated this phenomenon, it indicated that light consists of waves, as the distribution of brightness can be explained by the alternately additive and subtractive interference of wavefronts.[5] Young's experiment, performed in the early 1800s, played a vital part in the acceptance of the wave theory of light, vanquishing the corpuscular theory of light proposed by Isaac Newton, which had been the accepted model of light propagation in the 17th and 18th centuries. However, the later discovery of the photoelectric effect demonstrated that under different circumstances, light can behave as if it is composed of discrete particles. These seemingly contradictory discoveries made it necessary to go beyond classical physics and take the quantum nature of light into account.
Feynman was fond of saying that all of quantum mechanics can be gleaned from carefully thinking through the implications of this single experiment.[16] He also proposed (as a thought experiment) that if detectors were placed before each slit, the interference pattern would disappear.[17]
The Englert–Greenberger duality relation provides a detailed treatment of the mathematics of double-slit interference in the context of quantum mechanics.
A low-intensity double-slit experiment was first performed by G. I. Taylor in 1909,[18] by reducing the level of incident light until photon emission/absorption events were mostly non-overlapping. A double-slit experiment was not performed with anything other than light until 1961, when Claus Jönsson of the University of Tübingen performed it with electron beams.[19][20] In 1974, the Italian physicists Pier Giorgio Merli, Gian Franco Missiroli, and Giulio Pozzi repeated the experiment using single electrons and biprism (instead of slits), showing that each electron interferes with itself as predicted by quantum theory.[21][22] In 2002, the single-electron version of the experiment was voted "the most beautiful experiment" by readers of Physics World.[23]
In 2012, Stefano Frabboni and co-workers eventually performed the double-slit experiment with electrons and real slits, following the original scheme proposed by Feynman. They sent single electrons onto nanofabricated slits (about 100 nm wide) and, by collecting the transmitted electrons with a single-electron detector, they could show the build-up of a double-slit interference pattern.[24]
In 2019, single particle interference was demonstrated for antimatter by Marco Giammarchi and coworkers.[25]
Variations of the experiment
Interference of individual particles
Electron buildup over time
An important version of this experiment involves single particles (or waves—for consistency, they are called particles here). Sending particles through a double-slit apparatus one at a time results in single particles appearing on the screen, as expected. Remarkably, however, an interference pattern emerges when these particles are allowed to build up one by one (see the adjacent image). This demonstrates the wave–particle duality, which states that all matter exhibits both wave and particle properties: the particle is measured as a single pulse at a single position, while the wave describes the probability of absorbing the particle at a specific place on the screen.[26] This phenomenon has been shown to occur with photons, electrons, atoms and even some molecules, including buckyballs.[27][28][29][30][31] So experiments with electrons add confirmatory evidence to the view that electrons, protons, neutrons, and even larger entities that are ordinarily called particles nevertheless have their own wave nature and even a wavelength (related to their momentum).
The probability of detection is the square of the amplitude of the wave and can be calculated with classical waves (see below). The particles do not arrive at the screen in a predictable order, so knowing where all the previous particles appeared on the screen and in what order tells nothing about where a future particle will be detected.[32] If there is a cancellation of waves at some point, that does not mean that a particle disappears; it will appear somewhere else. Ever since the origination of quantum mechanics, some theorists have searched for ways to incorporate additional determinants or "hidden variables" that, were they to become known, would account for the location of each individual impact with the target.[33]
More complicated systems that involve two or more particles in superposition are not amenable to the above explanation.[34]
"Which-way" experiments and the principle of complementarity
A well-known thought experiment predicts that if particle detectors are positioned at the slits, showing through which slit a photon goes, the interference pattern will disappear.[5] This which-way experiment illustrates the complementarity principle that photons can behave as either particles or waves, but cannot be observed as both at the same time.[35][36][37] Despite the importance of this thought experiment in the history of quantum mechanics (for example, see the discussion on Einstein's version of this experiment), technically feasible realizations of this experiment were not proposed until the 1970s.[38] (Naive implementations of the textbook gedanken experiment are not possible because photons cannot be detected without absorbing the photon.) Currently, multiple experiments have been performed illustrating various aspects of complementarity.[39]
An experiment performed in 1987[40][41] produced results that demonstrated that information could be obtained regarding which path a particle had taken without destroying the interference altogether. This showed the effect of measurements that disturbed the particles in transit to a lesser degree and thereby influenced the interference pattern only to a comparable extent. In other words, if one does not insist that the method used to determine which slit each photon passes through be completely reliable, one can still detect a (degraded) interference pattern.[42]
Delayed choice and quantum eraser variations
Main article: Delayed choice quantum eraser
Wheeler's Delayed Choice Experiment
A diagram of Wheeler's delayed choice experiment, showing the principle of determining the path of the photon after it passes through the slit
Wheeler's delayed choice experiments demonstrate that extracting "which path" information after a particle passes through the slits can seem to retroactively alter its previous behavior at the slits.
Quantum eraser experiments demonstrate that wave behavior can be restored by erasing or otherwise making permanently unavailable the "which path" information.
A simple do-it-at-home illustration of the quantum eraser phenomenon was given in an article in Scientific American.[43] If one sets polarizers before each slit with their axes orthogonal to each other, the interference pattern will be eliminated. The polarizers can be considered as introducing which-path information to each beam. Introducing a third polarizer in front of the detector with an axis of 45° relative to the other polarizers "erases" this information, allowing the interference pattern to reappear. This can also be accounted for by considering the light to be a classical wave,[43]:91 and also when using circular polarizers and single photons.[44]:6 Implementations of the polarizers using entangled photon pairs have no classical explanation.[44]
Weak measurement
Main article: Weak measurement
In a highly publicized experiment in 2012, researchers claimed to have identified the path each particle had taken without any adverse effects at all on the interference pattern generated by the particles.[45] In order to do this, they used a setup such that particles coming to the screen were not from a point-like source, but from a source with two intensity maxima. However, commentators such as Svensson[46] have pointed out that there is in fact no conflict between the weak measurements performed in this variant of the double-slit experiment and the Heisenberg uncertainty principle. Weak measurement followed by post-selection did not allow simultaneous position and momentum measurements for each individual particle, but rather allowed measurement of the average trajectory of the particles that arrived at different positions. In other words, the experimenters were creating a statistical map of the full trajectory landscape.[46]
Other variations
A laboratory double-slit assembly; distance between top posts approximately 2.5 cm (one inch).
Near-field intensity distribution patterns for plasmonic slits with equal widths (A) and non-equal widths (B).
In 1967, Pfleegor and Mandel demonstrated two-source interference using two separate lasers as light sources.[47][48]
It was shown experimentally in 1972 that in a double-slit system where only one slit was open at any time, interference was nonetheless observed provided the path difference was such that the detected photon could have come from either slit.[49][50] The experimental conditions were such that the photon density in the system was much less than unity.
In 1999, the double-slit experiment was successfully performed with buckyball molecules (each of which comprises 60 carbon atoms).[28][51] A buckyball is large enough (diameter about 0.7 nm, nearly half a million times larger than a proton) to be seen under an electron microscope.
In 2005, E. R. Eliel presented an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam.[52]
In 2012, researchers at the University of Nebraska–Lincoln performed the double-slit experiment with electrons as described by Richard Feynman, using new instruments that allowed control of the transmission of the two slits and the monitoring of single-electron detection events. Electrons were fired by an electron gun and passed through one or two slits of 62 nm wide × 4 μm tall.[53]
In 2013, the double-slit experiment was successfully performed with molecules that each comprised 810 atoms (whose total mass was over 10,000 atomic mass units).[1][2] The record was raised to 2000 atoms (25,000 amu) in 2019.[54]
Hydrodynamic pilot wave analogs
Hydrodynamic analogs have been developed that can recreate various aspects of quantum mechanical systems, including single-particle interference through a double-slit.[55] A silicone oil droplet, bouncing along the surface of a liquid, self-propels via resonant interactions with its own wave field. The droplet gently sloshes the liquid with every bounce. At the same time, ripples from past bounces affect its course. The droplet's interaction with its own ripples, which form what is known as a pilot wave, causes it to exhibit behaviors previously thought to be peculiar to elementary particles – including behaviors customarily taken as evidence that elementary particles are spread through space like waves, without any specific location, until they are measured.[56][57]
Behaviors mimicked via this hydrodynamic pilot-wave system include quantum single particle diffraction,[58] tunneling, quantized orbits, orbital level splitting, spin, and multimodal statistics. It is also possible to infer uncertainty relations and exclusion principles. Videos are available illustrating various features of this system. (See the External links.)
However, more complicated systems that involve two or more particles in superposition are not amenable to such a simple, classically intuitive explanation.[34] Accordingly, no hydrodynamic analog of entanglement has been developed.[55] Nevertheless, optical analogs are possible.[59]
Classical wave-optics formulation
Two-slit diffraction pattern by a plane wave
Photo of the double-slit interference of sunlight.
Two slits are illuminated by a plane wave.
Much of the behaviour of light can be modelled using classical wave theory. The Huygens–Fresnel principle is one such model; it states that each point on a wavefront generates a secondary wavelet, and that the disturbance at any subsequent point can be found by summing the contributions of the individual wavelets at that point. This summation needs to take into account the phase as well as the amplitude of the individual wavelets. Only the intensity of a light field can be measured—this is proportional to the square of the amplitude.
In the double-slit experiment, the two slits are illuminated by a single laser beam. If the width of the slits is small enough (less than the wavelength of the laser light), the slits diffract the light into cylindrical waves. These two cylindrical wavefronts are superimposed, and the amplitude, and therefore the intensity, at any point in the combined wavefronts depends on both the magnitude and the phase of the two wavefronts. The difference in phase between the two waves is determined by the difference in the distance travelled by the two waves.
If the viewing distance is large compared with the separation of the slits (the far field), the phase difference can be found using the geometry shown in the figure below right. The path difference between two waves travelling at an angle θ is given by:
\( d\sin \theta \approx d\theta \)
Where d is the distance between the two slits. When the two waves are in phase, i.e. the path difference is equal to an integral number of wavelengths, the summed amplitude, and therefore the summed intensity is maximum, and when they are in anti-phase, i.e. the path difference is equal to half a wavelength, one and a half wavelengths, etc., then the two waves cancel and the summed intensity is zero. This effect is known as interference. The interference fringe maxima occur at angles
\( ~d\theta _{n}=n\lambda ,~n=0,1,2,\ldots \)
where λ is the wavelength of the light. The angular spacing of the fringes, θf, is given by
\( \theta _{f}\approx \lambda /d \)
The spacing of the fringes at a distance z from the slits is given by
\( ~w=z\theta _{f}=z\lambda /d \)
For example, if two slits are separated by 0.5 mm (d), and are illuminated with a 0.6μm wavelength laser (λ), then at a distance of 1m (z), the spacing of the fringes will be 1.2 mm.
If the width of the slits b is greater than the wavelength, the Fraunhofer diffraction equation gives the intensity of the diffracted light as:[60]
\({\begin{aligned}I(\theta )&\propto \cos ^{2}\left[{\frac {\pi d\sin \theta }{\lambda }}\right]~\mathrm {sinc} ^{2}\left[{\frac {\pi b\sin \theta }{\lambda }}\right]\end{aligned}} \)
Where the sinc function is defined as sinc(x) = sin(x)/x for x ≠ 0, and sinc(0) = 1.
This is illustrated in the figure above, where the first pattern is the diffraction pattern of a single slit, given by the sinc function in this equation, and the second figure shows the combined intensity of the light diffracted from the two slits, where the cos function represent the fine structure, and the coarser structure represents diffraction by the individual slits as described by the sinc function.
Similar calculations for the near field can be done using the Fresnel diffraction equation. As the plane of observation gets closer to the plane in which the slits are located, the diffraction patterns associated with each slit decrease in size, so that the area in which interference occurs is reduced, and may vanish altogether when there is no overlap in the two diffracted patterns.[61]
Interpretations of the experiment
Like the Schrödinger's cat thought experiment, the double-slit experiment is often used to highlight the differences and similarities between the various interpretations of quantum mechanics.
Copenhagen interpretation
The Copenhagen interpretation, put forth by some of the pioneers in the field of quantum mechanics, asserts that it is undesirable to posit anything that goes beyond the mathematical formulae and the kinds of physical apparatus and reactions that enable us to gain some knowledge of what goes on at the atomic scale. One of the mathematical constructs that enables experimenters to predict very accurately certain experimental results is sometimes called a probability wave. In its mathematical form it is analogous to the description of a physical wave, but its "crests" and "troughs" indicate levels of probability for the occurrence of certain phenomena (e.g., a spark of light at a certain point on a detector screen) that can be observed in the macro world of ordinary human experience.
The probability "wave" can be said to "pass through space" because the probability values that one can compute from its mathematical representation are dependent on time. One cannot speak of the location of any particle such as a photon between the time it is emitted and the time it is detected simply because in order to say that something is located somewhere at a certain time one has to detect it. The requirement for the eventual appearance of an interference pattern is that particles be emitted, and that there be a screen with at least two distinct paths for the particle to take from the emitter to the detection screen. Experiments observe nothing whatsoever between the time of emission of the particle and its arrival at the detection screen. If a ray tracing is next made as if a light wave (as understood in classical physics) is wide enough to take both paths, then that ray tracing will accurately predict the appearance of maxima and minima on the detector screen when many particles pass through the apparatus and gradually "paint" the expected interference pattern.
Path-integral formulation
One of an infinite number of equally likely paths used in the Feynman path integral (see also: Wiener process)
The Copenhagen interpretation is similar to the path integral formulation of quantum mechanics provided by Feynman. The path integral formulation replaces the classical notion of a single, unique trajectory for a system, with a sum over all possible trajectories. The trajectories are added together by using functional integration.
Each path is considered equally likely, and thus contributes the same amount. However, the phase of this contribution at any given point along the path is determined by the action along the path:
\( A_{\text{path}}(x,y,z,t)=e^{iS(x,y,z,t)} \)
All these contributions are then added together, and the magnitude of the final result is squared, to get the probability distribution for the position of a particle:
\( p(x,y,z,t)\propto \left\vert \int _{\text{all paths}}e^{iS(x,y,z,t)}\right\vert ^{2} \)
As is always the case when calculating probability, the results must then be normalized by imposing:
\( \iiint _{\text{all space}}p(x,y,z,t)\,\mathrm {d} V=1 \)
To summarize, the probability distribution of the outcome is the normalized square of the norm of the superposition, over all paths from the point of origin to the final point, of waves propagating proportionally to the action along each path. The differences in the cumulative action along the different paths (and thus the relative phases of the contributions) produces the interference pattern observed by the double-slit experiment. Feynman stressed that his formulation is merely a mathematical description, not an attempt to describe a real process that we can measure.
Relational interpretation
Uncertainty Momentum
An example of the uncertainty principle related to the relational interpretation. The more that is known about the position of a particle, the less is known about the velocity, and vice versa
According to the relational interpretation of quantum mechanics, first proposed by Carlo Rovelli,[62] observations such as those in the double-slit experiment result specifically from the interaction between the observer (measuring device) and the object being observed (physically interacted with), not any absolute property possessed by the object. In the case of an electron, if it is initially "observed" at a particular slit, then the observer–particle (photon–electron) interaction includes information about the electron's position. This partially constrains the particle's eventual location at the screen. If it is "observed" (measured with a photon) not at a particular slit but rather at the screen, then there is no "which path" information as part of the interaction, so the electron's "observed" position on the screen is determined strictly by its probability function. This makes the resulting pattern on the screen the same as if each individual electron had passed through both slits. It has also been suggested that space and distance themselves are relational, and that an electron can appear to be in "two places at once"—for example, at both slits—because its spatial relations to particular points on the screen remain identical from both slit locations.[63]
Many-worlds interpretation
Physicist David Deutsch argues in his book The Fabric of Reality that the double-slit experiment is evidence for the many-worlds interpretation. However, since every interpretation of quantum mechanics is empirically indistinguishable, some scientists are skeptical of this claim.
De Broglie–Bohm theory
Bohmian trajectories
Trajectories of particles under De Broglie–Bohm theory in the double-slit experiment.
An alternative to the standard understanding of quantum mechanics, the De Broglie–Bohm theory states that particles have precise locations at all times, and that their velocities are influenced by the wave-function. So while a single particle will travel through one particular slit in the double-slit experiment, the so-called "pilot wave" that influences it will travel through both. The two slit de Broglie-Bohm trajectories were first calculated by Chris Dewdney whilst working with Chris Philippidis and Basil Hiley at Birkbeck College (London).[64] The de Broglie-Bohm theory produces the same statistical results as standard quantum mechanics, but dispenses with many of its conceptual difficulties.[65]
See also
Complementarity (physics)
Delayed choice quantum eraser
Dual-polarization interferometry
Elitzur–Vaidman bomb tester
N-slit interferometer
Photon polarization
Quantum coherence
Schrödinger's cat
Young's interference experiment
Measurement problem
"Physicists Smash Record For Wave-Particle Duality"
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Bach, Roger; et al. (March 2013). "Controlled double-slit electron diffraction". New Journal of Physics. 15 (3): 033018. arXiv:1210.6243. Bibcode:2013NJPh...15c3018B. doi:10.1088/1367-2630/15/3/033018. S2CID 832961.
Yaakov Y. Fein; Philipp Geyer; Patrick Zwick; Filip Kiałka; Sebastian Pedalino; Marcel Mayor; Stefan Gerlich; Markus Arndt (September 2019). "Quantum superposition of molecules beyond 25 kDa". Nature Physics. 15 (12): 1242–1245. Bibcode:2019NatPh..15.1242F. doi:10.1038/s41567-019-0663-9. S2CID 203638258.
Bush, John WM (2015). "Pilot-wave hydrodynamics" (PDF). Annual Review of Fluid Mechanics. 47 (1): 269–292. Bibcode:2015AnRFM..47..269B. doi:10.1146/annurev-fluid-010814-014506. hdl:1721.1/89790. Retrieved 21 June 2015.
Bush, John W. M. (2010). "Quantum mechanics writ large". PNAS. 107 (41): 17455–17456. Bibcode:2010PNAS..10717455B. doi:10.1073/pnas.1012399107. PMC 2955131.
Natalie Wolchover (30 June 2014). "Have We Been Interpreting Quantum Mechanics Wrong This Whole Time?". Wired.
Couder, Y.; Fort, E. (2012). "Probabilities and trajectories in a classical wave-particle duality". Journal of Physics: Conference Series. 361 (1): 012001. Bibcode:2012JPhCS.361a2001C. doi:10.1088/1742-6596/361/1/012001.
Li, Pengyun; Sun, Yifan; Yang, Zhenwei; Song, Xinbing; Zhang, Xiangdong (2016). "Classical hypercorrelation and wave-optics analogy of quantum superdense coding". Scientific Reports. 5: 18574. Bibcode:2015NatSR...518574L. doi:10.1038/srep18574. PMC 4686973. PMID 26689679.
Jenkins FA and White HE, Fundamentals of Optics, 1967, McGraw Hill, New York
Longhurst RS, Physical and Geometrical Optics, 1967, 2nd Edition, Longmans
Rovelli, Carlo (1996). "Relational Quantum Mechanics". International Journal of Theoretical Physics. 35 (8): 1637–1678. arXiv:quant-ph/9609002. Bibcode:1996IJTP...35.1637R. doi:10.1007/BF02302261. S2CID 16325959.
Filk, Thomas (2006). "Relational Interpretation of the Wave Function and a Possible Way Around Bell's Theorem". International Journal of Theoretical Physics. 45 (6): 1205–1219.arXiv:quant-ph/0602060. Bibcode:2006IJTP...45.1166F. doi:10.1007/s10773-006-9125-0. S2CID 10743236.
Philippidis, C.; Dewdney, C.; Hiley, B. J. (1979). "Quantum interference and the quantum potential". Il Nuovo Cimento B. 52 (1): 15–28. Bibcode:1979NCimB..52...15P. doi:10.1007/bf02743566. ISSN 1826-9877. S2CID 53575967.
"Bohmian Mechanics". The Stanford Encyclopedia of Philosophy. Metaphysics Research Lab, Stanford University. 2017.
Further reading
Al-Khalili, Jim (2003). Quantum: A Guide for the Perplexed. London: Weidenfeld & Nicolson. ISBN 978-0-297-84305-4.
Ananthaswamy, Anil (2018). Through Two Doors at Once: The Elegant Experiment That Captures the Enigma of Our Quantum Reality. Dutton/Penguin. ISBN 978-1-101-98609-7.
Feynman, Richard P. (1988). QED: The Strange Theory of Light and Matter. Princeton University Press. ISBN 978-0-691-02417-2.
Frank, Philipp (1957). Philosophy of Science. Prentice-Hall.
French, A.P.; Taylor, Edwin F. (1978). An Introduction to Quantum Physics. Norton. ISBN 978-0-393-09106-9.
Quznetsov, Gunn (2011). Final Book on Fundamental Theoretical Physics. American Research Press. ISBN 978-1-59973-172-8.
Greene, Brian (2000). The Elegant Universe. Vintage. ISBN 978-0-375-70811-4.
Greene, Brian (2005). The Fabric of the Cosmos. Vintage. ISBN 978-0-375-72720-7.
Gribbin, John (1999). Q is for Quantum: Particle Physics from A to Z. Weidenfeld & Nicolson. ISBN 978-0-7538-0685-2.
Hey, Tony (2003). The New Quantum Universe. Cambridge University Press. Bibcode:2003nqu..book.....H. ISBN 978-0-521-56457-1.
Sears, Francis Weston (1949). Optics. Addison Wesley.
Tipler, Paul (2004). Physics for Scientists and Engineers: Electricity, Magnetism, Light, and Elementary Modern Physics (5th ed.). W. H. Freeman. ISBN 978-0-7167-0810-0.
External links
Interactive animations
Huygens and interference
Single particle experiments
Website with the movie and other information from the first single electron experiment by Merli, Missiroli, and Pozzi.
Movie showing single electron events build up to form an interference pattern in double-slit experiments. Several versions with and without narration (File size = 3.6 to 10.4 MB) (Movie Length = 1m 8s)
Freeview video 'Electron Waves Unveil the Microcosmos' A Royal Institution Discourse by Akira Tonomura provided by the Vega Science Trust
Hitachi website that provides background on Tonomura video and link to the video
Hydrodynamic analog
"Single-particle interference observed for macroscopic objects"
Pilot-Wave Hydrodynamics: Supplemental Video
Through the Wormhole: Yves Couder . Explains Wave/Particle Duality via Silicon Droplets
Computer simulations
Java demonstration of Young's double slit interference
A simulation that runs in Mathematica Player, in which the number of quantum particles, the frequency of the particles, and the slit separation can be independently varied
Quantum mechanics
Introduction History
timeline Glossary Classical mechanics Old quantum theory
Bra–ket notation Casimir effect Coherence Coherent control Complementarity Density matrix Energy level
degenerate levels excited state ground state QED vacuum QCD vacuum Vacuum state Zero-point energy Hamiltonian Heisenberg uncertainty principle Pauli exclusion principle Measurement Observable Operator Probability distribution Quantum Qubit Qutrit Scattering theory Spin Spontaneous parametric down-conversion Symmetry Symmetry breaking
Spontaneous symmetry breaking No-go theorem No-cloning theorem Von Neumann entropy Wave interference Wave function
collapse Universal wavefunction Wave–particle duality
Matter wave Wave propagation Virtual particle
quantum coherence annealing decoherence entanglement fluctuation foam levitation noise nonlocality number realm state superposition system tunnelling Quantum vacuum state
Dirac Klein–Gordon Pauli Rydberg Schrödinger
Heisenberg Interaction Matrix mechanics Path integral formulation Phase space Schrödinger
algebra calculus
differential stochastic geometry group Q-analog
Bayesian Consistent histories Cosmological Copenhagen de Broglie–Bohm Ensemble Hidden variables Many worlds Objective collapse Quantum logic Relational Stochastic Transactional
Afshar Bell's inequality Cold Atom Laboratory Davisson–Germer Delayed-choice quantum eraser Double-slit Elitzur–Vaidman Franck–Hertz experiment Leggett–Garg inequality Mach-Zehnder inter. Popper Quantum eraser Quantum suicide and immortality Schrödinger's cat Stern–Gerlach Wheeler's delayed choice
biology chemistry chaos cognition complexity theory computing
Timeline cosmology dynamics economics finance foundations game theory information nanoscience metrology mind optics probability social science spacetime
Quantum technology
links Matrix isolation Phase qubit Quantum dot
cellular automaton display laser single-photon source solar cell Quantum well
Dirac sea Fractional quantum mechanics Quantum electrodynamics
links Quantum geometry Quantum field theory
links Quantum gravity
links Quantum information science
links Quantum statistical mechanics Relativistic quantum mechanics De Broglie–Bohm theory Stochastic electrodynamics
Quantum mechanics of time travel Textbooks
Hellenica World - Scientific Library
Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License


text:
You are a prisoner in a room with 2 doors and 2 guards. One of the doors will guide you to freedom and behind the other is a hangman –you don't know which is which.
One of the guards always tells the truth and the other always lies. You don't know which one is the truth-teller or the liar either.
You have to choose and open one of these doors, but you can only ask a single question to one of the guards.
What do you ask so you can pick the door to freedom?
Car Park


text:
Nov 3, 2011 – Visit to Grandma
When our SQL Server Interview Questions and Answers book got published I ran to my grandma with a copy of the book for her blessings. Well, just like every grandma, she loves me, her grandson, unconditionally. She is not into the technology domain (obviously), but she loved the book. She read the first few pages where I was mentioned and read about my co-author Vinod Kumar. After reading the introduction she looked at me and said "When I was young we used to read books, now all those good books are converted into the movies, when do you think this book will be converted into a movie?"
Silence. A very long silence.
I just could not answer her right away. As a matter of fact, I went into a deep thought. I never thought that she could actually ask me such question. It may be a very simple question, but I felt that it was very important to me. I was just stunned and speechless. I returned home from my grandma's place, with her blessings and an interesting thought of a "Movie from the Book". I just could not get this out of my mind.
Jan 24, 2012 – Movie from Book
I talked to my grandma very often, but since the last conversation my wife called her often and I did not talk to her at all. There was no reason to talk to her maybe because I constantly felt that she is with me. Her blessings were with me. I could not get her question out of my mind, still. I was extremely motivated and inspired from my last conversation with her. I called her early morning on January 24. Her very first questions were how I was doing and how was her great granddaughter. I told her that regarding our last conversation, there is actually a movie which is inspired from the book. Her very first reaction was that she knew this would happen as she was confident that my book would reach milestones. We talked for long hours.
Today – Fast Forward
Well, the book was an inspiration for the course, but the video course was developed using totally different angle. We made sure that we'd take the broader idea from the book but wanted present something unique and novel. Vinod Kumar and I thought about it for a long time. We wanted to decide on the format of our course. We spent hours talking about the course – how we could make it unique and give a different experience to every attendee. We wanted to keep the subject light enough to digest, yet deep enough to satisfy everyone's learning eagerness. After spending some days and efforts for the preparation of the unique content and exceptional demos, the course has become a reality for us.
SQL Server Questions and Answers
This course is designed to help you have a better understanding on how to use SQL Server effectively. The course presents many of the common misconceptions about SQL Server, and then carefully debunks those misconceptions with clear explanations and short but compelling demos, showing you how SQL Server really works. This course is for anyone who works in SQL Server databases, and basically for those who want to improve their knowledge and understanding of this complex platform.
In this course, each topic starts with a question and ends with an answer which is supplemented with a demo. Every question has an exercise file and a demo associated with it. Additionally, in the very last session, we have covered lots of SSMS tips and tricks. Here are the topics we have covered in this course:
- Introduction
- Retrieving IDENTITY value using @@IDENTITY
- Concepts Related to Identity Values
- Difference between WHERE and HAVING
- Order in WHERE clause
- Concepts Around Temporary Tables and Table Variables
- Are stored procedures pre-compiled?
- UNIQUE INDEX and NULLs problem
- Locks and Duration of Transactions
- Nested Transaction and Rollback
- Understanding Date/Time Datatypes
- Differences between VARCHAR and NVARCHAR datatypes
- Precedence of DENY and GRANT security permissions
- Identify Blocking Process
- NULLS usage with Dynamic SQL
- Appendix Tips and Tricks with Tools
Today we are very happy that our course is out. The journey from the book to the Training Course took 80 days and the experience was wonderful. In a future post, I will share the experience of writing book and building the training course.
In the end, we just want to thank YOU, our dear reader, who made this experience possible.
Reference: Pinal Dave (https://blog.sqlauthority.com)


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White House officials are revealing details of President Barack Obama's initial plans for protecting the computer networks of crucial American industries from cyberattacks.
Their description of Obama's executive order was planned for Wednesday, a day after the president signed it. The announcement was also coming hours after the president urged Congress in his annual State of the Union address to pass legislation taking even tougher steps.
In his speech, Obama said America's enemies are "seeking the ability to sabotage our power grid, our financial institutions and our air traffic control systems. We cannot look back years from now and wonder why we did nothing in the face of real threats to our security and our economy."
He added, "Now, Congress must act as well by passing legislation to give our government a greater capacity to secure our networks and deter attacks."
On Tuesday, senior administration officials said Obama's order starts the development of voluntary standards to protect the computer systems that run critical sectors of the economy like the banking, power and transportation industries. It also directs U.S. defense and intelligence agencies to share classified threat data with those companies.
Obama's executive order has been months in the making and is the product of often-difficult negotiations with private sector companies that oppose any increased government regulation.
While largely symbolic, the plan leaves several practical questions unanswered:
— Should a business be required to tell the government if it's been hacked and U.S. interests are at stake?
— Can a person sue her bank or water treatment facility if those companies don't take reasonable steps to protect her?
— If a private company's systems are breached, should the government swoop in to stop the attacks — and pick up the tab?
Under the president's new order, the National Institute of Standards and Technology has a year to finalize a package of voluntary standards and procedures that will help companies address their cybersecurity risks. The package must include flexible, performance-based and cost-effective steps that critical infrastructure companies can take to identify the risks to their networks and systems and ways they can manage those risks.
There also must be incentives the government can use to encourage companies to meet the standards, and the Pentagon will have four months to recommend whether cybersecurity standards should be considered when the department makes contracting decisions.
The order also calls for agencies to review their existing regulations to determine whether the rules adequately address cybersecurity risks.
Congress has been struggling for more than three years to reach a consensus on cybersecurity legislation. Given that failure and the escalating risks to critical systems, Obama turned to the order as a stopgap measure with the hope that lawmakers will be able to pass a bill this year. Leaders of the House Intelligence Committee said they plan to reintroduce their bill that encourages the government to share classified threat information, empowers companies to also share data and provides privacy and liability protections.
The process has exposed how difficult and complex the issue is, turning the long-awaited executive order into a bureaucratic scramble aimed at showing countries like China and Iran that the U.S. takes seriously the protection of business secrets. It has been an intensive effort by White House staff and industry lobbyists wary of government intervention but fearful about their bottom line.
The cyberthreat to the U.S. has been heavily debated since the 1990s, when much of American commerce shifted online and critical systems began to rely increasingly on networked computers.


text:
You are here
News Release
Sunday, July 23, 2006
Shared Ancestor to Humans, Present-day Non-human Primates May Be Linchpin in the Evolution of Language
When contemplating the coos and screams of a fellow member of its species, the rhesus monkey, or macaque, makes use of brain regions that correspond to the two principal language centers in the human brain, according to research conducted by scientists at the National Institute on Deafness and Other Communication Disorders (NIDCD) and the National Institute of Mental Health (NIMH), two of the National Institutes of Health. The finding, published July 23 in the advance online issue of Nature Neuroscience, bolsters the hypothesis that a shared ancestor to humans and present-day non-human primates may have possessed the key neural mechanisms upon which language was built. Principal collaborators on the study are Allen Braun, M.D., chief of NIDCD's Language Section, Alex Martin, Ph.D., chief of NIMH's Cognitive Neuropsychology Section, and Ricardo Gil-da-Costa, Gulbenkian Science Institute, Oeiras, Portugal, who conducted the study during a three-year joint appointment at the NIDCD and NIMH.
"This intriguing finding brings us closer to understanding the point at which the building blocks of language appeared on the evolutionary timeline," says James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. "While the fossil record cannot answer this question for us, we can turn to the here and now — through brain imaging of living non-human primates — for a glimpse into how language, or at least the neural circuitry required for language, came to be."
While non-human primates do not possess language, they are able to communicate about such things as food, identity, or danger to members of their species by way of vocalizations that are interpreted and acted upon. In humans, the two main regions of the brain that are involved in encoding this type of information in language are known as Broca's area and Wernicke's area, named for the physician-researchers who discovered them. Both areas are located along the Sylvian fissure (and are therefore referred to as perisylvian areas) with Broca's area located in the frontal lobe and Wernicke's area located behind it in the temporal and parietal lobes. Scientists once believed that Broca's area was chiefly involved in language production while Wernicke's area dealt more with comprehension, however current thinking suggests that the two areas work in tandem with one another. Although monkeys are not able to perform the mental activities required for language, their brains possess regions that are structurally similar to the perisylvian areas in humans in both hemispheres. The functional significance of such similarities, however, has been unclear up to this point.
To measure brain activity, the researchers injected water labeled with oxygen-15, a biologically safe, fast-degrading radioisotope, into the bloodstream of three adult macaques. As neural activity increases in a given region of the brain, blood — and the radioactive water it carries — rushes into that region. Using the brain imaging technology known as positron emission tomography (PET), researchers capture an image of the radioactive areas, thus highlighting the regions of heightened activity. In this way, brain scans were taken of the monkeys as they listened to three types of sounds: the recorded coos and screams of other rhesus monkeys, and assorted non-biological sounds, such as musical instruments and computer-synthesized sounds, which matched the vocalizations in frequency, rate, scale, and duration. For each monkey, 16 scans were recorded for each sound type and compared.
Although the coo of a monkey is acoustically very different from a high-pitched scream, the researchers found that both of these meaningful species-specific sounds elicited significantly more activity than the non-biological control stimuli in the same three regions of the macaque's brain. Moreover, these regions correspond to the key language centers in humans, with the ventral premotor cortex (PMv) corresponding to Broca's area, and the temporoparietal area (Tpt) and posterior parietal cortex (PPC) corresponding to Wernicke's area. In contrast, the non-biological sounds — which were acoustically similar to the coos and screams but had no meaning for the animals — elicited significantly less activity in these regions; rather, they were associated with greater activation of the brain's primary auditory areas. (The reason for this, the researchers suggest, is that these sounds were new to the monkeys and the primary auditory areas may be especially attuned to novel stimuli.)
Based on these findings, the researchers suggest that the communication centers in the brain of the last common ancestor to macaques and humans — particularly those centers used for interpreting species-specific vocalizations — may have been recruited during the evolution of language in humans. In the macaque, these areas may currently play a parallel, prelinguistic function, in which monkeys are able to assign meaning to species-specific sounds. In addition, in light of an earlier study published by the same group, in which species-specific vocalizations of macaques activated brain regions that process higher-order visual and emotional information, the researchers suggest that the language areas of the brain may have evolved from a much larger system used to extract meaning from socially relevant situations — a system in which humans and non-human primates may share similar neural pathways.
Further studies to be conducted include investigating which regions of the non-human primate brain are activated when animals listen to meaningful auditory stimuli other than species-specific vocalizations, such as a predators' calls, sounds made by humans, or other relevant environmental stimuli. In addition, they are interested in studying the pattern of brain activation elicited by non-auditory stimuli that convey the same meaning, such as visual images of monkeys producing vocalizations.
Other institutions represented on the study include Harvard University, Cambridge, MA; University College London/Institute of Child Health, London; and the University of Maryland, College Park. The work was supported by NIDCD, NIMH, and Fundação para a Ciência e Tecnologia, Portugal.
NIDCD supports and conducts research and research training on the normal and disordered processes of hearing, balance, smell, taste, voice, speech and language and provides health information, based upon scientific discovery, to the public. For more information about NIDCD programs, see the Web site at www.nidcd.nih.gov.
The National Institute of Mental Health (NIMH) mission is to reduce the burden of mental and behavioral disorders through research on mind, brain, and behavior. More information is available at the NIMH website, http://www.nimh.nih.gov.
About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
NIH…Turning Discovery Into Health®


text:
Faviana style 7904 is a perfect bridesmaid dress for a fall wedding. Minimal draping gives it a touch of elegance. The cut of the halter top gives it a classy and modern look while the doubled straps counterblanace the modest neckline. It has an understated charm, and the color will fit wonderfully in a fall color palette.
- Cut for a close fit
- Great for hourglass figures to accentuate curves
- Closure includes zipper, hook & eye
- Skirt length is 48"/ 121.92cm
- Model is 6'/ 183cm and is wearing a US Faviana size 6


text:
Some problems in business can be solved with money; many cannot.
When you're pitching to an investor, one of the best things you can do is to show how the important problems facing your business are those that can be solved with money, because money is what they're providing.
Even if you're not pitching this is a useful exercise, because if you're good at the things money can't buy, you'll remain competitive even when confronted by a well-funded competitor.
So it's useful to separate what aspects of your business could be improved with money alone from what you need to address with time, attention, and intelligence.
Finding good people is almost impossible. I have this blog, a nice Twitter following, attention in my local community, and social "favors" I can call in, and it's still almost impossible. And the thing about good people is they always have options: Existing job, other excellent offers, the freedom to not work for a while, etc..
If someone handed me a million dollars it wouldn't help me find an awesome person; they're just scarce.
Once I find someone, however, then money helps a lot, because I could satisfy any salary requirement, handle relocation, provide a signing bonus, lease a car, or whatever else is necessary to make money "not the issue."
So if you're raising money and you don't have your team assembled, the investor knows that handing you $200,000 won't change that. But if you have the team, but they've had to work in their spare time because everyone needs a day job to pay mortgages, that's a good reason to raise money.
Marketing of most sorts can be solved with money. Money means you can spray ads everywhere. Money means you can try 20 different campaigns even if most utterly fail. Money means you can try 50 titles/descriptions/landing pages through AdWords until you find one that converts decently.
One big exception is anything that requires authority, like blogging and other social media stuff. You can't buy authority. You can't buy that kind of attention, where people listen because they want to listen, not because they're interrupted, where they interact with you because they respect your opinion.
Social media marketeers (like mouse-katteers but with larger Twitter followings) have already beat this point to death; no reason to repeat it. But if your business requires the modern "tell-your-friends" social-media-style punditry to succeed, you'll have to do that without money. If it's just a matter of pouring more marketing dollars in the top so you can crank out more revenue in the bottom, that's a machine investors like to power.
And so forth
You see where this is going, so let's accelerate:
- Writing more code, faster, yes. Knowing what to write, no.
- Acquiring more leads, yes. Know how to convert them, no.
- A prettier website, yes. What text to put on the website, no.
- Leeway to make mistakes, yes. Philosophy of learning and using mistakes to improve, no.
- A QA team to improve quality, yes. Knowing when a bug isn't important enough to prevent shipping, no.
- Time to outlive a recession, yes.
The pattern: Concepts, behaviors, knowledge, and process cannot be fabricated with money, and possibly cannot even be accelerated. Once you know what to do or, more likely, you know how to learn quickly, then money becomes an accelerant.
Now therefore…
Supposing you're about to raise money, in light of this discussion what should your pitch include?
- Emphasize how spending money will improve specific things which, today, are broken or missing only because money is lacking.
- Show proof of your ability to master the things money cannot buy — your ability to learn, change, and improve.
- For those things money can accelerate, and for which you've spent a teeny amount of money, show how well you've done with that. It's easy to imagine more money bringing more results.
- For those things money can't solve and which you haven't mastered, bring it up before the investors do and have a plan, which in itself proves you're cognizant and thorough. If you don't have a clear, plausible plan, don't raise money yet.
- Specifically, don't raise money if you haven't assembled the core team.
Let me make point #2 tangible.
I cannot count the times I've heard someone proclaim how adaptable they are. "I'm in love with A/B testing." "I'm not afraid to admit when I'm wrong." "I listen to my customers." "I'm a big fan of Eric Ries."
Yeah, you and 60,000 other people. I'm supposed to be impressed?
Since everyone and their dog is now an expert in Lean Startup, you need to demonstrate, not regurgitate platitudes. Tell me about how and why your pitch changed when you vetted your idea with potential customers. Walk me through a screenshot of your app, revealing the customer feedback that lead to each part. Show me your company dashboard with the numbers that matter, explaining why each number is there, what you expect those numbers to do, and what you do when they don't go as expected. Tell me about your first idea which turned out to be wrong but lead to the second, and how much easier it was to sell the second. Tell me what happened when you tried different price points, and why you settled on the current one. Show me which part of your landing pages improved with A/B testing and which required old-fashioned creative thought. Tell me in your customers' own words why they're willing to pay you for any of this.
When you demonstrate that you can do these things, what you're really saying is that you know how to think, how to overcome roadblocks, how to figure out what to do.
All things money can't buy, but exactly the things which, when combined with money, make companies most likely to succeed.
If you're not raising money, you still need these skills, exactly because you don't have the money to waste!
Things money cannot buy are still the most valuable things.
Let's continue the discussion in the comments: What else can/can't money buy?