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Comment Another useful vacuum tube: Thermionic converter. (Score 1) 94

Another vacuum tube technology with current applications and substantial advantages over semiconductor approaches to the same problems is the Thermionic Converter. This is a vacuum-tube technology heat engine that turns temperature differences into electric power - by boiling electrons off a hot electrode and collecting them, at a somewhat more negative voltage (like 0.5 to 1 volt), at a cooler electrode.

Semiconductor approaches such as the Peltier Cell tend to be limited in operating temperature due to the materials involved, and lose a major fraction of the available power to non-power-producing heat conduction from the hot to the cold side of the device. Thermionic converters, by contrast are vacuum devices, and inherently insulating (with the heat conducted almost entirely by the working electrons, where it is doing the generation, or parasitic infrared radiation, which can be reflected rater than absorbed at the cold side.) They work very well at temperatures of a couple thousand degrees, a good match to combustion, point-focused solar, and nuclear thermal sources.

Thermionic converters have been the subject to recent improvements, such as graphine electrodes. The power density limitation of space charge has been solved, by using a "control grid" to encourage to charge to move along from the emitter to the collector and magnetic fields to guide it (so it doesn't discharge the control grid and waste the power used to charge it).

Current thermionic technology can convert better than 30% of the available thermal energy to electrical power and achieves power densities in the ballpark of a kilowatt per 100 square cm (i.e. a disk about 4 1/2 inches in diameter). That's a reasonably respectable carnot engine. This makes it very useful for things like topping cycles in steam plants: You run it with the flame against the hot side so it is at the combustion temperature, and the "cold" side at the temperature of the superheated steam for your steam cycle. Rather than wasting the energy of that temperature drop (as you would with a pure steam cycle) you collect about a third of it as electricity.

It also beats the efficiency of currently available solar cell technology (and the 33.4% Shockleyâ"Queisser theoretical limit for single-junction cells), if you don't mind mounting it on a sun-tracker. Not only that, but you can capture the "waste heat" at a useful temperature without substantial impairment to the electrical generation or heat collection, and thus use the same surface area for both generation and solar heating. (Doing this with semiconductor solar cells doesn't work well, because they become far less efficient when running a couple tens of degrees above room temparature.)

Comment Re:Original Metal Detectors Used Vacuum Tubes (Score 1) 94

No. A TWT relies on the velocity of electrons inside the tube and bunches up the electrons. At least a full cycle of the signal has to be present inside the tube at once. If the velocity is about c/10 (I'm guessing this is a reasonable low end) the tube would have to be 150 meters long for a 200 kHz signal.Precision machining is required, so TWTs are expensive.

Metal detectors operate at frequencies where semiconductors can be extremely efficient -- I'm guessing better than 90% using PWM and LC filtering. There's not much utility in trying for more.

Comment Re:Many a young engineer.... (Score 2) 94

... every schematic drawn by every semiconductor engineer got the arrow backwards.

As I heard it, The arrow is "backward" because Benjamin Franklin, when doing his work unifying "vitreous" and "resinous" electricity as surplus and deficit of a single charge carrier (and identifying the "electrical pressure" later named "voltage"), took a guess at which corresponded to a surplus of a movable charge carrier. He had a 50% chance to assign "positive" to the TYPICAL moving charge carrier in the situations being experimented with (charge transfer by friction between different substances, currents in metallic conductors, and high voltage discharges in air and water-in-air aerosols) and happened to guess "wrong".

Thus we say electrons have a negative charge, "classical current" corresponds to the sum of the flow of moving positive charge minus the flow of negative charge (i.e. the negative of the electron current, which is all there is in normal-matter metallic conductors), the arrowhead on diodes (and junction transistors) points in the direction of classical current across a junction, and so on.

But though it's the charge carrier in metallic conduction and (hard) vacuum tubes, the electron ISN'T the only charge carrier. Even in the above list of phenomena, positive ion flow is a substantial part of electrical discharge currents in air - static sparks and lightning. Positive moving charge carriers are substantial contributors to current as you get to other plasma phenomena and technologies - gas-filled "vacuum" tubes (such as thyratons), gas an LIQUID filled "vacuum" tubes (ignatrons), gas discharge lighting, arc lighting, arc welding, prototype nuclear fusion reactors, ...

Move on to electrochemistry and ALL the charge carriers are ions - atoms or molecular groups with an unequal electron and proton count, and thus a net charge - which may be either positive or negative (and you're usually working wit a mix of both).

And then there's semiconductors, where you have both electrons and "holes" participating in metallic conduction. Yes, you can argue that hole propagation is actually electron movement. But holes act like a coherent physical entity in SO many ways that it's easier to treat them as charge carriers in their own right, with their own properties, than to drill down to the electron hops that underlie them. For starters, they're the only entity in "hole current" that maintains a long-term association with the movement of a bit of charge - any given electron is only involved in a single hop, while the hole exists from its creation (by an electron being ejected from a place in the semiconductor that an electron should be, by doping or excitation, leaving a hole) to their destruction (by a free electron falling into them and releasing the energy of electron-hole-pair separation). They move around - like a charge carrier with a very short (like usually just to the next atom of the solid material) mean free path.

For me the big tell is that they participate in the Hall Effect just as if they were a positive charge carrier being deflected by a magnetic field. The hall voltage tells you the difference between the fraction of the current carried by electrons excited into a conduction band and that carried by holes - whether you think of them as actual moving positive charge carriers or a coordinated hopping phenomenon among electrons that are still in a lower energy state. Further, much of interesting semiconductor behavior is mediated by whether electrons or holes are the "majority carrier" in a given region - exactly what the hall effect tells you about it.

So, as with many engineering phenomena, the sign for charge and current is arbitrary, and there are both real and virtual current carriers with positive charge. Saying "they got it wrong" when classical current is the reverse of electron current is just metallic/thermionic conduction chauvinism. B

Comment Re:Vacuum tubes handle EMP's better (Score 1) 94

"No point progressing since the bombs are gonna fall any day now. Then where will your fancy silicon highways and databases be?"

Given that the Internet Protocol and much of the rest of the networking technology that still underpins the Internet were developed as part of a cold-war program to create a communication system that could survive a nuclear attack that destroyed most of it, and still reorganize itself to pass messages quickly, efficiently, and automatically among any nodes that still had SOME path between them, your post seems to come from some alternate universe to the one I inhabit.

Comment Re:I have an idea (Score 1) 566

ISIS is essentially an Al-Queda in Iraq splinter that set up shop on its own.

Yes, except it "set up shop" due to failures in the 0bama foreign policy.

The last "I" stands for Iraq. They wouldn't exist today without that mess having happened.

No, the last "I" stands for "In". ISIS stands for "Islamic State In Syria". President 0 favors ISIL, "Islamic State In the Levant".

They wouldn't exist today without that mess having happened.

They wouldn't exist today if the current administration hadn't thrown away all the blood and treasure expended on Iraq by cutting and running. Regardless of his dislike for the war, he should have acted in the best interests of both America and Iraq.

Comment Re:Good (Score 1) 780

The rights of children are not the same as the rights of adults. The parents' responsibility for their children gives them special proper powers over their children, a subset of which, in loco parentis, are temporarily extended to schools.

Using their best judgement, parents may spank their children to prevent them from running in front of cars or kicking the neighbor's pitbull. This is not a violation of a child's rights.

Comment Re:Dad of Ahmed is an Islamic Supremacist (Score 1) 780

All that is necessary for the triumph of evil is that good men do nothing. (Edmund Burke)

Ignoring loud people with dangerous stands gives ignorant bystanders the impression that there's nothing wrong. There's no requirement that I actively oppose villains, but I'm not improving the world when i fail to do so.

Comment The IRS keeps its hooks in US citizens who leave. (Score 2) 359

I'd also move my operation to Ireland if I could.

What's stopping you?

The US tax code. The US keeps its hooks in its citizens and companies, for decades, if they try to leave, even if they move out and renounce their citizenship.

The US does this to a far greater extent than other countries who generally don't tax their citizens if they're out of the country for more than half a year. (This is where "The Jet Set" came from: Citizens of various non-US countries who had found a way to earn a living that let them split their time among three or more countries every year and avoid enough income tax to live high-on-the-hog, even on an income that otherwise might be middle-class.)

Only really big companies, with armies of lawyers, can find loopholes that let them effectively move out of the US to a lower-taxing alternative. You'll note that TFA is a lament about how one managed to escape, and how the US might "close THIS loophole" to prevent others from using it.

Comment Re:This is only true (Score 2) 359

When what's legal and what's sustainable for the society are not aligned, there are likely one of two results: 1) Law is changed to be more sustainable or 2) the society suffers.

But hey, more power to those who can screw over everyone else for their tax free money!

If what the company is doing is not sustainable, the company will fail, as it should. If what society is doing is unsustainable, it will fail, as it should. It's called capitalism and if you leave it alone, you'd be surprised at how good it works.

What would you propose? We block companies from doing these kinds of inversions? They'd just transfer their entire operation overseas and then the US would see zero percent of that income. There are any number of other countries that would LOVE to have them, as is evidenced by their lower tax rates and success in luring said companies.

The stupidity is the assumption you can somehow control these companies, or punish them for their actions. Controlling them is impossible so long as there are other places to do business. Punishing them does nothing but punish those who consume their products or services. Putting them out of business adds to unemployment. Banning their products or services from the US market would damage consumers *and* employees. You know...employees...those people who work hard every day to take home a paycheck to their families. Not everyone at a corporation is Scrooge McDuck burning hundred dollar bills to warm their gold-plated mansion.

No, the answer is to lower our corporate tax burdens and win this business back to US shores and the US tax system. It doesn't take a genius to realize that 15% of something is better than 26% of nothing.

Take your work seriously but never take yourself seriously; and do not take what happens either to yourself or your work seriously. -- Booth Tarkington