It's not just "more difficult", it's scientifically impossible to capture all of the power from temperature differentials. The maximum possible efficiency of such a heat engine is described by Carnot's Theorem and is (1-Tc/Th) where Tc and Th are the absolute temperatures of the cold and hot reservoir. So if 100MJ of heat flows from a hot water reservoir into a cold water reservoir through a heat engine you can only capture a single digit percentage of that energy for the temperature differences under discussion

So taking a 25 degree heat difference as 275K cold water and 300K hot water then the optimum efficiency of the heat enginer is only 8.3%, and the actual efficiency will of course be less.

This printer would work extremely well for MEMS devices since the complex structures such sensors can now just be printed rather than deposited and etched over and over again in a microchip fab.

I'm not sure how printing MEMs devices serially is going to be faster than parallel mass production on 12" or 18" silicon wafers. Printing them is analogous to laboriously machining a part in a CNC mill compared to stamping in a forge. Photolithography and etching are pretty fast processes. Well, etching can be slow but it can be done very well in parallel to multiple large wafers at once so per-device it's fast. Doing the printing as a prototype for a standard MEMs process production run won't work well since the material properties would be different.

And you still need to connect your MEMs devices to a circuit, so now you have to do a tricky hybrid integration process to pick up your tiny polymer MEMs devices and connect them to a chip and package your now non-planar device. Plus you need to be able to selectively metallize some of your surface for many MEMs applications - not sure how you do that given that stereolithography "printing" works on photohardening polymers not metals.

Right now it can take weeks to make complete microchip with the current fabrication methods. The fabrication size of this printer isn't that great however since most of what is seen in the TFA looks to be around 100 nanometers compared to the 28 nanometers a modern fab can make. However, it would be great to have for rapid prototypes of processors or be used to make devices that fabricate well at large sizes like flash memory.

It's a big leap going from hardening a polymer to printing full complex semiconductor circuits with dielectrics and metal interconnect. Unless you're just thinking of using this stereolithography process to replace the standard mask-based planar photolithography in the foundry, which might be a valid point if the stereolithography is faster or cheaper than electron-beam lithography or ordering a mask of the dimensions that this machine is actually capable of. Right now e-beam lithography can do this but it's slow and expensive.

For something like this to be applied to semiconductor processing another thought would be construction of stamps for nano-imprint lithography. Printing them might be cheaper or faster than the standard techniques of e-beam or optical lithography and etching at least for short runs.

What I don't understand about the plastic bag banning movement is why they turn straight to banning instead of a more capitalistic approach: Mandated charges for plastic bags. Suppose the total cost of a bag is 5 cents, including production, transportation (which are swallowed by the store), and the negative environmental externality. If this cost is passed on fully to customers then they will understand the true cost of choosing a disposable plastic bag over a re-usable one and they can then make an informed economic choice on how to proceed, and many, but not all, will choose re-usable bags. Right now the costs are hidden so consumers take the convenient choice rather than the informed choice.

The average US house uses about 1.3kW averaged over time. Obviously it can spike up to several kW or over 10kW when lots of appliances and any heating/cooling is turned on, but the batteries can handle spikes in load.

Source: http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3

It's 10 kilowatt hours not kilowatts per hour. A kilowatt hour is a unit of energy which could supply a 1kW load for 10 hours, or equivalently a 10kW load for one hour, or any other load at power P [kW] for a time t [hours] where t=E/P where E is the energy in kilowatt hours. Power is the rate of consumption of energy, where a watt is 1 joule per second, and energy is what's actually needed to do a given unit of work.

kW/h is basically a nonsense unit which means 10,000 joules per second per hour. This would be a power "acceleration" unit if you actually wanted to use it. Calling kWh kilowatts per hour is a pretty common misunderstanding that you see a lot in the news so as a EE I feel compelled to clarify when possible.

I haven't seen the numbers, but I have heard that a big part of the cost difference between running STEM and humanities degree programs is the higher cost of the faculty. STEM professors, especially full professors at a research university, can command very high salaries outside of academia, so naturally the academic salaries have to be at least somewhat comparable in order to attract qualified candidates. Some of this salary will be payed for by grants and research contracts, endowed positions, and so on, but it is still an expense for the university.

I know you're probably joking, but Apple buys chipsets and analog hardware for their cellphones from companies like Qualcomm, Triquint, and so on, so I think that these researchers are safe.

For wide bandwidth modulation formats this is a bit of a pain since you need a very wideband, high current, power supply. so they are doing an A/theta modulator but trying to simplify the bias control on the PA to avoid that.

No, they're doing something more complicated than A/theta modulation (aka envelope tracking aka envelope elimination and restorataion aka ...). They are doing an outphasing amplifier which splits the original signal into two constant amplitude variable phase signals which will reproduce the original signal when they are recombined, but they are adding some envelope tracking elements to further improve efficiency since wideband combiners will absorb the differential section of the input signals as loss.

What I'm not clear on is why they are doing this when they have a predistortion loop anyway. a pure predistortion loop should be able to achieve very similar results without any need for the PA bias adjust. you can also do it with 1 PA instead of two.

A predistorter doesn't have much of anything to do with PA efficiency (the point of this MIT research), PD's are for linearity. High efficiency PA topologies typically take a hit to linearity. Fancy techniques like outphasing and envelope tracking are better than some but they still reduce linearity. Poor linearity means increased distortion. Distortion increases error rates in digital transmissions, and it also leads to signal leaking into adjacent signal bands, which isn't allowed in the tight cellular spectral environment. So they put a PD in there to linearize things a bit further. That's probably why they are using discrete bias levels instead of continuously variable - they can optimize their PD loop to work best in these four well-characterized states which gets most of the efficiency gain while making the linearization easier.

I don't know, looks like somebody's thesis to me. Doesn't look like it's particular practical. Also, first rule of looking at schemes like this. How much of that power they saved is being used in the more complicated digital circuitry. That's the reason you don't see PD loops in cell phones. It's a wash, you spend so much power analyzing the signal to do PD that you burn up the savings . Now if you have a 10W transmitter, PD makes lots of sense.

These are not fundamental limitations. It's making more and more sense as digital processing and DSP chips get faster, cheaper, and lower power. The point of research is to try to push the state of the art and it may not be "practical" when the research paper is hot off the press. If it's good enough then it will be practical some time down the road, and if it isn't good enough then it will be left aside as a lesson learned. Apparently the researchers think its good enough to found a startup company, so they're either foolish or they understand it better than you. Time will tell.

Do you have an estimate of how much it does cost you as a percentage of the cash revenue?

This is a duplicate story posted on Slashdot on Oct 31: http://hardware.slashdot.org/story/12/11/01/0021213/breakthrough-promises-smartphones-that-use-half-the-power

Luckily this time the summary includes a link to an actual technical paper. The summary and the news article make it sound like this is an Envelope Tracking amplifier, but if you read the paper this is actually something different, it is more complicated and more interesting.

They are starting from an outphasing amplifier which divides a variable envelope signal into two constant amplitude but variable phase signals which can be amplified more efficiently since the amplifier doesn't need to output both large and small signals. But combining the signals is inefficient because the combiner must absorb some of the power when the two halves of the signal are very out of phase with each other. What the MIT researchers are doing is extending the outphasing technique to allow multiple discrete amplitudes on each amplifier to minimize the combiner inefficiency. It's more efficient than plain outphasing, I'm not sure how it compares to envelope tracking since the authors did not compare it to this in their paper.

Of course people really pay for porn. It costs money to create it, so somebody somewhere is paying for it to be made. Advertising doesn't add much to the industry revenue since most ads on free porn sites are for the paid porn sites and other adult sites. The free sites tend to have (in my opinion) pretty low quality in terms of the selection of content, and the display quality can be pretty bad. Some of the content there is placed by the entity who owns it, but much of it is surely pirated.

It's simply an entertainment expense and many people have no problem paying a fair price for something that they want. With a paid site you generally have a better selection of content in a genre that interests you, higher quality picture/video, and regularly added new content. In addition to people being cheap I think that there is some kind of guilt or shame that some people associate with paying for porn that they can sidestep if they only look at free porn.

Of course one problem is that many paid porn sites tend to be fairly expensive, probably because of the massive amount of marketing that they paid for on the free sites and the fact that a lot of people expect porn to be free these days, so there's a smaller number of paying customers.

Based on the article it sounds a lot like envelope tracking:

The new advance is essentially a blazingly fast electronic gearbox. It chooses among different voltages that can be sent across the transistor, and selects the one that minimizes power consumption, and it does this as many as 20 million times per second. The company calls the technology asymmetric multilevel outphasing.

But looking back at one of their papers: http://www-mtl.mit.edu/~jldawson/Dawson_digest2009.pdf it is not exactly envelope tracking. They are starting out with an outphasing amplifier (dividing the signal into two constant amplitude variable phase signals which can then be amplified with an efficient nonlinear amp and recombined into the original signal) and then adding a discretely variable drain bias (much like an envelope tracker) but the purpose of the variable drain voltage is actually to minimize power dissipation in the combiner's isolation resistor. Thus they compare their efficiency and linearity only to outphasing types of amplifiers. I would be curious to see how this stacks up to pure envelope tracking amplifiers.

I used a Graph Gear 1000 for a while. It has incredible style points, feels solidly built, and the retracting tip is a nice feature for when you keep the pencil in a bag or pocket. However after around 6 months of regular use with storage in a backpack the springiness in the clip was lost, and due to the unusual tip-retracting mechanism this mean that the tip would not stay retracted. Also I found that I was not a big fan of the narrow and hard metal grip, the heavy weight during long use, and the narrow eraser.

Nowadays my preferred pencil is the Pentel "Quicker Clicker" series, specifically the .7mm model, PD347. The wide body with a thin layer of rubber on the grip (enough to soften without being squishy) is very comfortable for me, and the large and easily accessible eraser is very handy. The non-retracting tip means I don't like to carry it around in my pocket, but since I only use it at my desk(s) and it's much cheaper than the Graph Gear I simply bought enough to cover all of the places where I'll need one.

Rather than simply modding you up I decided to try this out, and it works! Which is kind of creepy.

Since you dismiss the Newcastle University study only on the basis of Mark Bittman being a biased columnist (fair enough, he probably is), you may be interested to read the recent NY Times article which also explains some of the methodology differences between the studies which lead to different conclusions. In any case, I'm reserving judgement on both studies for now.

http://www.nytimes.com/2012/10/16/science/stanford-organic-food-study-and-vagaries-of-meta-analyses.html