I want to power up 4-5 peltier elements TEC 12706 which have maximum voltage of 16.4V and max current of 6.4A (at 50 C). Will a power supply of 12V 30A do the job (I'm thinking about connecting them in parallel). Also in which case peltier is going to take it's maximum current? I have done experiments before, peltier does not sink more than 2A of current. Why so?
Maybe the underlying question is what the Voltage-Current curve looks like. Can I drive it from a voltage source (like you drive a heater) or from a current source (like you drive an LED)? Or even different than those two options?  ADDITIONAL1: Say (hypothetically) I have two commercially available identical Peltier's, they are spec'd 6V/3A. Can I connect these in series to a 12Vdc power supply without any worries?  CONCLUSION1: Current/Voltage load curve is reasonably linear, both driving from current or voltage source will do fine as long as the device is operated within its spec. (Olin Lathrop, Russell McMahon)  CONCLUSION2: Don't drive a Peltier from PWM, power loss due to current increase, grows more rapidly than cooling power. (Olin Lathrop)  CONCLUSION3: Beware the mechanical wear of the device with continues cycling. Eg. don't use a thermostat on/off controller. (Russell McMahon)
Intersection of three vector subspaces We say that two vector subspaces $U,W\subset V$ intersect transversally (written $U\pitchfork W$) if $U+W=V$.  Let $V_1,V_2,V_3$ be vector subspaces of $V$ where $\dim V=n$. We say they intersect normally if $V_i\pitchfork(V_k\cap V_l)$  for $i\ne k,l$. Prove that $V_1,V_2,V_3$ intersect normally if  the following condition holds:  $\operatorname{codim}(V_1\cap V_2\cap V_3)=\operatorname{codim} V_1+\operatorname{codim} V_2+\operatorname{codim} V_3,$   where $\operatorname{codim} V_i=n-\dim V_i$.  How to approach this problem? I tried to order dimensions of $V_i$ but I got that the LHS is $\ge n-\min (\dim V_i,i=1,2,3)$ and the RHS is $\le 3( n-\min (\dim V_i,i=1,2,3))$ which does not lead anywhere. What is the right way to do this? Why does Super User site appear twice in vote-to-close dialog? Super User appears in both the main Off-Topic list and the Migration list of the close dialog. Is this a bug or intentional?  I also don't really understand why Server Fault appears in the main Off-Topic list and not the Migration list, apart from it being new.  Here:    and: Normal ordering of the commutator between annihilation and creation operator According to the commutation relation of annihilation and creation operators,   $$[a,a^{\dagger}]=1. \tag{1}$$   I would like to calculate the vacuum expectation value of the normal order of this commutator. We claim that since this commutator is just a c-number, then there is no effect from the normal ordering. We therefore get   $$\langle 0|(:[a,a ^\dagger]:)|0 \rangle=1. \tag{2}$$  However, if we expand the commutator first and do normal order later, we will get something like   $$\langle0|(:[a,a^\dagger]:)|0\rangle=\langle0|(:aa^\dagger-a^\dagger a:)|0\rangle=\langle0|(a^\dagger a-a^\dagger a)|0\rangle=0.\tag{3}$$ Which is contradicting with itself. text-overflow: ellipsis in table-cell without width In the early '80s, I read a story about a Terran man on another planet, where the natives develop skin lesions and eventually die, but are happy, as they become part of the planet they live on. I remember that the protagonist is not developing the lesions, because he hates the planet. Once he starts loving the planet, he starts having the lesions as well. In this story, the planet is "alive".  I have read about "" and "". They do not match my memory. Thank you. Leaving Italy without paying a bus fine My wife and I got bus fines today in Bologna. We had only recently arrived and had purchased a ticket from where we were staying which was about 6 or 7 km from the city. The hotel receptionist explained the ticketing system to us and said that if we buy a ticket we could use it on as many journeys for 75 minutes.  We took the bus from our hotel to Bologna and then straight away got on another bus to get to central Bologna where all the sights are. When we got on this other bus we assumed that it was ok as we were still within the 75 minutes. However, when we tried to validate our tickets in the machine it flashed red like an error had occurred so we figured something wasn't right.   We tried to ask the driver about it or if we could buy a ticket but he just grunted and started to drive off. We therefore started to leave the bus at the next stop so we could try and buy another ticket but were ushered back on by a few men who turned out to be ticket inspectors!  They alleged that our tickets were not valid in the city and that we had to pay a 65 euro fine. They wanted to see our official documentation and so took details from our UK driving licences and issued us both with fines. They wanted us to pay there and then, but we explained we didn't have enough cash on us to do so and they then stated we could pay by card.   However, I still wasn't happy about doing that so he then said that we could pay later by going to an Italian post office; or if we don't pay within a certain time the fine will go up to 270 euros each and will be posted to us (he got our addresses off our UK driving licences)!  I am a bit miffed about this as we were noway trying to evade and as soon as we realised our mistake we tried to talk to the bus driver to buy a ticket or get off the bus, but he drove off and ignored us! I have a slight suspicion that it was a rouse as it is very strange that he did this and then out of nowhere bus inspectors got on and made a beeline for us!  If we go back to the UK without paying these fines and ignore the subsequent fines that they send us through the post (if they do send any), then what happens? Do they have any powers when we are back in the UK? a total fine of 500 euros for an honest mistake seems utterly outrageous.   Fine below I've recently installed Fedora 19.  is installed. But its own examples don't work. When I enter gedti the output is:  bash: gedti: command not found... Similar command is: 'gedit'   And it works correctly but when I enter powertop, the output is:  bash: powertop: command not found...   With no suggestion about the package. Why? Should I edit some configuration files or update some cache or ... ? Weather Resistant Outlets vs Weather Proof Box Reading input from text file to array in c++ Logarithm as limit lists this as a limit representation of the natural log:  $$\ln{z} = \lim_{\omega \to \infty} \omega(z^{1/\omega} - 1)$$  Is there a quick proof of this? Thanks animating an element's height using jquery Include the "People Reached" and "Helpful Flags (count)" data in SEDE I know the new profile design hasn't been updated for  on the network yet, so maybe this is a bit too early. Nonetheless, please include the &quot;People Reached&quot; data in  at your earliest convenience. Also, I was just made aware that users helpful flag counts are now publicly displayed on their  towards the top-right, underneath the people reached stat. So please include this data in SEDE as well. So I decided to install my copy of Ableton (v9.1) on my computer now that I've upgraded to a machine that isn't ancient. HOWEVER Despite WineHQ reporting that Ableton is platinum-certified, I can't get the dern thing to open.  It crashes out just as the splash screen pops up.  Sometimes I see it, sometimes not.  It tells me that some catastrophic error has occurred, and it needs to close.  I've tried this on two different systems running two different versions of wine  (One runs the up-to-date public distro 1.6.2, while the machine I actually want to install it on is running the 1.7.19)  I don't know what to do.  I'd really just like to get this working, as my friends really like the look and feel of Ableton, and I really don't like LMMS (Linux-y free Audio Software).  Any idea what's going on here? I've found a couple of other people who seem to be having the same problem as me, but no dice on any solutions.  None provided, really.  Specs: Ubuntu 14.04 LTS  8 Gig ram  i7-2670QM CPU @ 2.20GHz × 8  Lots of free space... yadda yadda yadda   Error message: Resampling GeoTIFF images to same resolution using QGIS I have two geotiff images that I would like to resample the same resolution. If I use ArcGIS Desktop this is easy to do but how do I do this using QGIS? I have a table similar to this:  CREATE TABLE example (   id integer primary key,   name char(200),   parentid integer,   value integer);   I can use the parentid field to arrange data into a tree structure.  Now here's the bit I can't work out. Given a parentid, is it possible to write an SQL statement to add up all the value fields under that parentid and recurse down the branch of the tree ?  UPDATE: I'm using posgreSQL so the fancy MS-SQL features are not available to me. In any case, I'd like this to be treated as a generic SQL question.  BTW, I'm very impressed to have 6 answers within 15 minutes of asking the question! Go stack overflow! Shared email on 2 Facebook accounts is stopping access to both accounts My husband wanted me to set up a Facebook account for him and I accidentally used our shared email address, which is set against my own account.  Since then, neither of us has been able to log in, so I can't alter any settings.  Can anyone advise how to resolve this please? Okay, this should be super easy to do but I just can't find the way.  I have a background image with a solid colour layer on top of it, and I would like to add text on top of everything in such a way that the filling of the text is the image in the background. I have tried selecting the text shape and deleting that selection shape in the solid colour layer, but it just looks wrong.   Can anyone help me with this? Many thanks in advance. What constitutes an observation/measurement in QM? Suppose that I have a group $G$ of order $p^{2}q$ for two distinct primes $p$ and $q$.  I need to first show that one of its Sylow subgroups is normal.  I start by letting $H$ be a Sylow $p$-subgroup and $K$ be a Sylow $q$-subgroup.  If $K$ is not normal, then letting $r$ denote the number of Sylow $q$-subgroups, I have that $r|p^{2}$ and $r\equiv 1$(mod $q$).  I also have by the second Sylow theorem that $r\neq 1$.  So $r = p$ or $p^{2}$.  If $r = p^{2}$, I can write out the Sylow $q$-subgroups, and count their combined elements to show that $H$ is uniquely determined and then again imply Sylow number $2$ to obtain that $H$ is normal.  But if $r = p$, then I cannot see how to proceed.  Can anyone give any advice?  Thank you.  ( I am happy to provide more detail for the $r = p^{2}$ case if it is desired or appropriate. ) Using conditional statements in ArcGIS Field Calculator? I have two fields, "P_Area" and "PC_Area", whose sizes I'd like to compare in a third field, "Areas_Equal". The "Areas_Equal" field should contain a "Yes" if the other two are equal and a "No" if they aren't.  How can I do this with Field Calculator and its Python Parser?