## Thursday, July 21, 2005

### A Public Service for Slashdot readers

Just in case anybody else without the forethought to click on the page edit button was interested in the story about the kids from Utah who came up with a "better car air conditioning system" I can offer a couple of things. Their link, on the day of their post, to the original story seems lost.... sorry. The description of the Peltier effect link, before someone decided they would like a visit from extremely serious looking guys with funky ear pieces read:

The '''Peltier-Seebeck effect''', or '''thermoelectric effect''', is the direct conversion of heat differentials to electric [[voltage]] and vice versa. Related effects are the '''Thomson effect''' and [[Joule heating]]. The Peltier, Seebeck, and Thomson effects are reversible; Joule heating is not, and cannot be, under the [[laws of thermodynamics]].

==Seebeck effect==
The '''Seebeck effect''' is the conversion of [[heat]] differences directly into [[electricity]].

This effect was first discovered, accidentally, by the [[Estonia]]n physicist [[Thomas Johann Seebeck]] in [[1821]], who found that a voltage existed between two ends of a [[metal]] bar when a temperature gradient $\nabla T$ existed in the bar.

He also discovered that a [[compass]] needle would be deflected when a closed loop was formed of two metals with a temperature difference between the junctions. This is because the metals respond differently to the heat difference, which creates a current loop, which produces a [[magnetic field]].

A [[voltage]], the thermoelectric [[Electromotive force|EMF]], is created in the presence of a [[temperature]] difference between two different metals or [[semiconductor]]s. This usually causes a continuous current to flow in the conductors. The voltage created is on the order of several μV per [[kelvin]] (or degree [[Celsius]]) of difference.

In the circuit:

[[Image:Seebeck_effect_circuit_2.png]]

(which can be in several different configurations and be governed by the same equations), the voltage developed can be derived from:

:$V = \int_\left\{T_1\right\}^\left\{T_2\right\} \left\left( S_B\left(T\right) - S_A\left(T\right) \right\right) \, dT$

''SA'' and ''SB'' are the [[Seebeck coefficient]]s (also called ''thermoelectric power'' or ''thermopower'') of the metals A and B, and ''T1'' and ''T2'' are the temperatures of the two junctions. The Seebeck coefficients are non-linear, and depend on the conductors' absolute temperature, material, and molecular structure. If the Seebeck coefficients are effectively constant for the measured temperature range, the above formula can be approximated as:

:$V = \left(S_B - S_A\right) \cdot \left(T_2 - T_1\right)$

Thus, a [[thermocouple]] works by measuring the difference in potential caused by the dissimilar wires. It can be used to measure a temperature difference directly, or to measure an absolute temperature, by setting one end to a known temperature. Several thermocouples in series are called a thermopile.

This is also the principle at work behind [[thermal diode]]s and [[thermoelectric generator]]s (such as [[radioisotope thermoelectric generator]]s or RTGs) which are used for creating power from heat differentials.

The Seebeck effect is due to two effects: ''charge carrier diffusion'' and ''phonon drag''.

=== Thermopower ===
If the temperature difference between the two nodes is small,

:$T_2 = T_1 + \Delta T \,$

and a voltage Δ''V'' is seen at the terminals, then the [[thermopower]] of the entire thermocouple is defined as:

:$S_\left\{AB\right\} = S_B-S_A = \lim_\left\{\Delta T \to 0\right\} \left\{\Delta V \over \Delta T\right\}$

This can also be written in relation to the electric field ''E'' and the temperature gradient
$\nabla T$, by the equation

:$S = \left\{E \over \left | \nabla T \right |\right\}$

[[Superconductor]]s have zero thermopower, and can be used to make thermocouples. This allows a direct measurement of the thermopower of the other material, since it is the thermopower of the entire thermocouple as well.

In [[semiconductor]]s the sign of the thermopower is used to decide whether the charge carriers are electrons or holes.

=== Charge carrier diffusion ===
Charge carriers in the materials (electrons in metals, electrons and holes in semiconductors, ions in ionic conductors) will diffuse when one end of a conductor is at a different temperature than the other. Hot carriers diffuse from the hot end to the cold end, since there is a lower density of hot carriers at the cold end of the conductor. Cold carriers diffuse from the cold end to the hot end for the same reason.

If the conductor were left to reach [[equilibrium]], this process would result in heat being distributed evenly throughout the conductor (see [[heat transfer]]). The movement of heat (in the form of hot charge carriers) from one end to the other is called a [[heat current]]. As charge carriers are moving, it is also an [[electrical current]].

In a system where both ends are kept at a constant temperature relative to each other (a constant heat current flows from one end to the other), there is a constant diffusion of carriers. If the rate of diffusion of hot and cold carriers were equal, there would be no net change in charge. However, the diffusing charges are [[scattering|scattered]] by impurities, imperfections, and lattice vibrations ([[phonon]]s). If the scattering is energy dependent, the hot and cold carriers will diffuse at different rates. This creates a higher density of carriers at one end of the material, and the distance between the positive and negative charges produces a potential difference; an electrostatic voltage.

This electric field, however, opposes the uneven scattering of carriers, and an equilibrium is reached where the net number of carriers diffusing in one direction is canceled by the net number of carriers moving in the opposite direction from the electrostatic field. This means the thermopower of a material depends greatly on impurities, imperfections, and structural changes (which often vary themselves with temperature and electric field), and the thermopower of a material is a collection of many different effects.

=== Phonon drag ===
[[Phonon]]s are not always in local thermal equilibrium; they move along the thermal gradient. They lose momentum by interacting with electrons (or other carriers) and imperfections in the crystal. If the phonon-electron interaction is predominant, the phonons will tend to push the electrons to one end of the material, losing momentum in the process. This contributes to the already present thermoelectric field. This contribution is most important in the temperature region where phonon-electron scattering is predominant. This happens for

:$T \approx \left\{1 \over 5\right\} \theta_D$

where ''θD'' is the [[Peter Debye|Debye]] temperature. At lower temperatures there are less phonons available for drag, and at higher temperatures they tend to lose momentum in phonon-phonon scattering instead of phonon-electron scattering.

This region of the thermopower versus temperature function is highly variable under a magnetic field.

==Peltier effect==
The '''Peltier effect''' is the reverse of the Seebeck effect; a creation of a heat difference from an electric voltage.

It occurs when a current is passed through two dissimilar metals or [[semiconductor]]s (n-type and p-type) that are connected to each other at two junctions ([[Peltier junction]]s). The current drives a transfer of heat from one junction to the other: one junction cools off while the other heats up. This effect was observed 13 years after Seebeck's initial discovery in 1834 by [[Jean Charles Athanase Peltier|Jean Peltier]].

[[Image:Peltier_effect_circuit.png]]

When a current ''I'' is made to flow through the circuit, heat is evolved at the upper junction (at T2), and absorbed at the lower junction (at T1). The Peltier heat absorbed by the lower junction per unit time, $\dot\left\{Q\right\}$ is equal to

:$\dot\left\{Q\right\} = \Pi_\left\{AB\right\} I = \left\left( \Pi_B - \Pi_A \right\right) I$

Where Π is the Peltier coefficient Π''AB'' of the entire thermocouple, and Π''A'' and Π''B'' are the coefficients of each material. P-type silicon typically has a positive Peltier coefficient (though not above ~550 K), and n-type silicon is typically negative.

The conductors are attempting to return to the electron equilibrium that existed before the current was applied by absorbing energy at one connector and releasing it at the other. The individual couples can be connected in series to enhance the effect.

The direction of heat transfer is controlled by the polarity of the current, reversing the polarity will change the direction of transfer and thus the sign of the heat absorbed/evolved.

A '''Peltier cooler'''/heater or thermoelectric [[heat pump]] is a solid-state active heat pump which transfers heat from one side of the device to the other. Peltier coolers are also called ''Thermo Electric Converter''s (TEC).

==Thomson effect==
'''Thomson effect''', named for [[William Thomson, 1st Baron Kelvin]], describes the heating or cooling of a current-carrying conductor with a temperature gradient.

Any current-carrying conductor, with a temperature difference between two points,
will either absorb or emit heat, depending on the material.

If a current density ''J'' is passed through a homogeneous conductor, heat production per unit volume is

:$q = \rho J^2 - \mu J dT/dx \,$

where

''ρ'' is the [[resistivity]] of the material

''dT''/''dx'' is the temperature gradient along the wire

''μ'' is the Thompson coefficient.

The first term ''ρ J'' is simply the [[Joule heating]], which is not reversible.

The second term is the Thomson heat, which changes sign when ''J'' changes directions.

The Peltier and Seebeck coefficients are related by the Thomson relation

:$\Pi = S \cdot T$

which predicted the Thomson effect before it was actually formalized. It can also be written

:$\mu = T dS/dT \,$

where ''T'' is the absolute temperature of the metal.

In metals such as [[zinc]] and [[copper]], which have a hotter end at a higher potential and a cooler end at a lower potential, when current moves from the hotter end to the colder end, it is moving from a high to a low potential, so there is an evolution of energy. When it moves from the colder to the hotter end, there is an energy absorption. This is called the '''positive Thomson effect'''.

In metals such as [[cobalt]], [[nickel]], and [[iron]], which have a cooler end at a higher potential and a hotter end at a lower potential, when current moves from the hotter end to the colder end, it is moving from a low to a high potential, there is an absorption of energy. When it moves from the colder to the hotter end, there is an energy evolution. This is called the '''negative Thomson effect'''.

In [[lead]], there is zero Thomson effect.

The Seebeck effect is actually a combination of the Peltier and Thomson effects.

*[[Thermoelectricity]]
*[[Joule's law]]
*[[Heat transfer]]
*[[Thermoelectric cooling]]
*[[Pyroelectric effect]] - the creation of an electric field in a crystal after uniform heating

==Patents==

* {{US patent|2510397}} - [[Clarence Hansell|Clarence W. Hansell]] - "''Heat-to-electrical energy converter''".
* {{US patent|2881384}} - [[Lyndon Durant|Lyndon A. Durant]] - "''Thermal electric alternator''"
* {{US patent|2915652}} - [[George Hatsopoulos|G. N. Hatsopoulos]] - "''Conversion of thermal energy into electrical energy''".
* {{US patent|3175105}} - [[John Creedon| John E. Creedon]] - "''Conversion of heat to electricity''"

=== General ===
*[http://www.nanothermel.org/public_main.htm Thermoelectricity, including equations and applications]
*[http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_2/backbone/r2_3_3.html General]
*[http://www.insa-lyon.fr/Laboratoires/GEMPPM/TEP/index.htm Has an explanation of carrier diffusion and phonon drag components of thermopower]

=== Semiconductors ===
*[http://www.coolworksinc.com/about_thermoelectric_technology.htm A brief explanation]
*[http://www.electronics-cooling.com/Resources/EC_Articles/SEP96/sep96_04.htm An introduction to thermoelectric coolers]
*[http://www.its.caltech.edu/~jsnyder/thermoelectrics/science_page.htm The science and materials of thermoelectrics]

=== Metals ===
*[http://www.uni-konstanz.de/physik/Jaeckle/papers/thermopower/thermopower.html The origin of the thermoelectric potential]

=== Related ===
*[http://www.peltier-info.com/info.html Directory of Peltier device information]
*[http://www.trnmag.com/Stories/2001/121901/Chips_turn_more_heat_to_power_121901.html A news article on the increases in thermal diode efficiency]
*[http://www.sii.co.jp/info/eg/thermic_main.html A wristwatch powered by thermocouples, using the heat difference between the human body and its surroundings]

[[Category:Thermodynamics]]
[[Category:HVAC]]
[[Category:Electricity]]

[[fr:Effet Peltier]]
[[ja:ペルチエ効果]]
[[nl:Peltier-effect]]
[[pl:Efekt Peltiera]]
[[pt:ForÃ§a eletromotriz de Peltier]]

good luck to the Department of Treasury folks in their tracking exercise :-)

### Kos kids lose reality grip: Part 2

After quoting this piece in the Washington Post:

A classified State Department memorandum central to a federal leak investigation contained information about CIA officer Valerie Plame in a paragraph marked "(S)" for secret, a clear indication that any Bush administration official who read it should have been aware the information was classified, according to current and former government officials.

Plame -- who is referred to by her married name, Valerie Wilson, in the memo -- is mentioned in the second paragraph of the three-page document, which was written on June 10, 2003, by an analyst in the State Department's Bureau of Intelligence and Research (INR), according to a source who described the memo to The Washington Post.

The paragraph identifying her as the wife of former ambassador Joseph C. Wilson IV was clearly marked to show that it contained classified material at the "secret" level, two sources said. The CIA classifies as "secret" the names of officers whose identities are covert, according to former senior agency officials.

Kos goes on to pontificate:

So who is singing to the WSJ and WaPo? This piece cites "two sources familiar with the investigation." The special prosecutor has been leak-free thus far, and would likely try to stay that way (especially one who has shown as much contempt for the press as this one). The Rovians, who have leaked like sieves (most of it lies), aren't going to leak this golden nugget. Powell? He did his damage yesterday, placing the memo right on the White House's lap. So who's left?

It's the CIA. Funny how those guys don't like their covers blown.

There are only 4 problems with all of this.

1. Just because a paragraph in a memo which contains a persons name is marked as secret doesn't mean that their identity is secret. If a paragraph on a CIA memo marked secret contained the DCIA's name or title would that lead one to believe that his name/position is secret.

2. We know full well that Wilson's wife was not a covert operative at the time of the "leak" and had not been for more than 5 years. We further know that her cover had been blown in the international intelligence community at least 10 years before the "leak".

3. It is not even implied that Karl Rove ever saw this memo. The "sources" quoted give us no reason to believe that this memo is important enough for the assistant chief of staff to have bothered to read it. I have to assume that there are hundreds if not thousands of such memos produced each day. To make a leap that because a "secret" memo was produced that a senior player read it is insane.

4. The sources quoted are clearly criminals. The investigation into this matter has a gag order in place. Further, to describe in any detail the contents of a top secret, not yet declassified memo, to the press is a crime. And you might notice that the sources are anonymous. Big shock.

## Wednesday, July 20, 2005

### Kos kids lose reality grip: Part 1

This post is most interesting. After pointing out that Justice Ginsburg refused to answer questions about her views on issues that were likely to come before the court:

This attitude begs the question, what does Judge Roberts need to hide? Why should he be afraid to state clearly and unequivocally his judicial views?

I tell you what I suspect - he does not want to discuss Roe. And that is unacceptable.

One of the very issues that Justice Ginsburg refused to answer was her views on Roe. In my view (and I am not a lawyer and don't play one on TV, nor did I stay in a Holiday Inn Express last night) that was entirely appropriate. There were several cases that did come before the court pertaining to Roe in the first few years of her term on the court.

With Roberts, or whomever Pres. Bush would have chosen, this decision is even easier. We know that in the next session of the court (assuming cert is granted, and I haven't heard anyone who thinks it won't be) a case challenging the constitutionality of the partial birth abortion ban will be heard.

Irrespective of which party was appointing a replacement I would argue that it would be inappropriate for the Senate to ask how a perspective justice would rule on a case that everyone assumes will be heard in the next 12 months.

If the Republicans had bought into the philosophy presented here neither of Clinton's appointees to the bench would have gotten out of committee or passed an up or down vote. Republicans had a majority in the Senate for both of his very Liberal choices. Both were passed overwhelmingly. That is what elections are about, even when we don't like the choices of the victor.

### Scotty, one to beam up.

And, unfortunately, dear friend it is you. James Doohan played the lively character on the original Star Trek and was, both to his frustration and his personal credit, typecast as that character for the next 30 years. As one of millions of young people who watched Star Trek avidly both in first run and in reruns (it went off the air when I was 2) I wish his family well in their time of mourning.

### Google shoots the Moon

On the anniversary of the first human moon landing Google has given us this (HT: Wizbang!). Select (A: Apollo 11) and zoom in slowly using the "+" icon. The detail gets more and more impressive as you zoom in. Very cool!

## Tuesday, July 19, 2005

### bloglines is cool

My list of interesting blogs had gotten unmanageable in a standard web browser so I went looking for a solution. I tried 20+ RSS/Atom tools for the Mac and was disappointed with all of them for one or more reasons. I went to Google and found bloglines and I am pretty impressed. The best feature it has that none of the fat clients have is that it allows me to switch between various computers without having to remark articles as having been read. This could be done on the Mac by tying into iSync but I don't expect to see that any time soon.

Many of the Mac fat clients were highly unstable. This may be a result of them not being updated for Tiger which has significant OS changes that might cause freeware/shareware to become unstable until updated. I don't know. The thing I found most interesting is that none of the ones I tried would actually cache the articles. I travel quite a bit so this is a big deal. If my laptop was just downloading the stuff I want to read while I was working I could just close it and go to the airport. Bloglines doesn't solve this problem either but since I don't get that feature with the fat clients it will do for now.

If anybody has found a better solution to this problem feel free to email me.

### More stupidity about spam filtering

I am not a lawyer and don't play one on TV. I do, however, know a lot about deploying large scale email solutions for ISPs. Therefore I know a lot about spam prevention at large providers, like Comcast. As a disclaimer, I do not know all the details about how Comcast is filtering at the moment. I know a fair bit and I won't reveal the details that I do know because the less the bad guys know about a particular provider the better.

The Brad Blog apparently knows next to nothing about spam filtering. I suspect I would have nothing but disdain for the content from afterdowningstreet.com that is/was getting filtered but I have seen overreactions like this from groups that I support as well. This is not a first amendment issue. Trust me, the big carriers have better things to worry about than political speech that they may or may not agree with.

The BRAD BLOG has learned that cable company and Internet service provider, Comcast Corporation has been automatically deleting email sent to Comcast customers with the text "www.afterdowningstreet.org" in the body of the email.

So far so good here. I did some checking and this appears to be accurate.

The discovery that email was being secretly filtered was made after an investigation conducted by ADS co-founder, David Swanson who reported that many coalition members did not seem to be receiving email alerts and others messages being sent by the group.

Bold emphasis mine and where the wheels start to come off.

In a statement released by People-Link.org, the Internet host for the AfterDowningStreet.org domain, the directors of the "progressive" firm charge that the filtering is politically motivated and both they and Swanson have requested people contact Comcast to complain. (Contact information at the bottom of this article.)...

The wheels are off. It's a conspiracy!!!!! No it isn't. It is a mistake in a filter somewhere. The filters are modified many times per day. Some of it is automated, some of it is manual based on statistical tracking. There are a lot of possibilities. There is some VERY small possibility that one right wing wacko with the right access did it but if he did he risked his job for it.

While it is not uncommon for Internet Service Providers, or ISP's, to filter out messages sent to their users by domains which are known to send large amounts of unrequested junkmail, or "spam", Comcast acknowledged to Swanson that AfterDowningStreet.org was not on their list of domains alleged to have sent such email.

And your point would be. In the article itself they point out that changing the referral URL in the body of the message was sufficient to get the mail through. ERGO... it is being hit by a body string match filter. These filters are often created automatically by scanning mail as it comes through and looking for things like identical referral URLs. All large ISPs now use a combination of IP and domain blocking, volume control or throttling, pattern matching in the subject line, sender id matching, body text pattern matching and a host of other technical methods to block spams and frustrate spammers. This one is clearly a body pattern match rule.

My best guess: There were a large number of emails being sent out in a wave that contained the same body. Some automated filter creation program detected the pattern and created a filter which blocked the content. Believe it or not this kind of thing happens pretty frequently. Remember that in excess of 60% of all messages being sent to any large US ISP is spam. In many cases that number exceeds 90%. There is no such thing as a spam filtering system which is 90% or more effective that can guarantee no false positives. We all wish there were, but there aren't.

Happy emailing and please double check before assuming the service providers do anything that is politically motivated unless they are getting paid to do it (advertising, etc). Their only politics is making money.

### Life Happened

Sorry no posts for a bit. Life happened..... End of fiscal year, a couple weddings, a sick dog, visiting friends, etc, etc. Rather than try to truly catch up on some of the things I noted for blogging over the last few weeks I will do a little speed blogging here.

Colorado Conservative on stupid criminals.

Colorado Conservative on funny things happening to stupid criminals.

BummerDietz on "Michael Smith" on the Downing Street memos.

A great Father's Day post from Major K.

A memorial from 365 and a Wakeup.... Keep tissues handy.

Wizbang on end of session court rulings.

HP World isn't happening.
Not surprising since Microsoft and the Linux community already have their own conferences.

More Plame game from Wizbang. This is one of the best laid out of this overblown non-story and spends a lot of time asking why the press is trying to make a story of it.

Mark Steyn on the Plame game.
Funny.

later.