This could easily be a condensed intro to Special Relativity. If you are not familiar with it, or want a quick historical overview, you might want to check out this article.
Zz
Thursday, February 28, 2013
Wednesday, February 27, 2013
RF Basics
This is the course material for class in RF fields used for particle accelerators, given at a CERN Particle Accelerator school.
Note the very important characteristics of this course. You'll see the beginning of the material looking like a typical E&M course for a physics major. But later on, you'll see the applications of it the way an electrical engineer would see it. This is a clear example of what I've been trying to emphasize so far, that this is one of those fields where physics and engineering smoothly merge! It is why the field of accelerator physics is one of the few areas of physics that still has a higher hiring rate and why graduates can find a wide-range of jobs to apply for beyond just academia.
Zz.
Note the very important characteristics of this course. You'll see the beginning of the material looking like a typical E&M course for a physics major. But later on, you'll see the applications of it the way an electrical engineer would see it. This is a clear example of what I've been trying to emphasize so far, that this is one of those fields where physics and engineering smoothly merge! It is why the field of accelerator physics is one of the few areas of physics that still has a higher hiring rate and why graduates can find a wide-range of jobs to apply for beyond just academia.
Zz.
Physicist Gave A Paper Marriage Proposal
I'll admit it. Physicists can be a bunch of rather weird, strange people. But hey, no one can ever accuse us of not being creative! After all, who would have come up with proposing to one's future wife by putting it into a physics paper?
I found a copy of the so-called paper elsewhere on the web. Best wishes to the happy couple!
Zz.
When Sydney physicist Brendan McMonigal got down on one knee to propose to his partner of seven years, Christie Nelan, he pulled out a physics paper, not a ring.It helps that the future bride is also a physicist, so she got the meaning.
His paper, Two Body Interactions: A Longitudinal Study, pictured right, is laden with science geek speak and tracks the couple's relationship, including a graph (''happiness over time'') and the all important question.
I found a copy of the so-called paper elsewhere on the web. Best wishes to the happy couple!
Zz.
Tuesday, February 26, 2013
How Big Is the Universe?
Check out the video. You are the center of the universe... the observable universe, that is.
Zz.
Zz.
Ernest Moniz Leading Candidate For DOE Post
The rumor that we have been getting is that MIT Physicist Ernest Moniz is the leading candidate to replace the retiring Steven Chu for the Secretary of the US Department of Energy (DOE). This makes for another physicist being selected to run that branch of the Federal Govt.
From that news article, it certainly appears that Moniz might be able to better navigate the politics of Washington, since he has had plenty of experience dealing with that kind of cra... err ... environment before.
If this comes true, I would be happy enough. I was dreading the idea of a non-scientist, a non-engineer, or worst still, a career bureaucrat, running what is essentially a science/engineering/technical branch of the govt. We have had those before with other administrations. I'd rather not have that again.
Zz.
The leading candidate to replace departing energy secretary Steven Chu is Ernest Moniz, director of the Energy Initiative at the Massachusetts Institute of Technology (MIT) in Cambridge. He would bring to the office a pragmatic support for nuclear power and natural gas, along with a candid desire to, in his own words, “innovate like hell” on basic energy technologies. Colleagues at MIT are waiting for a confirmation of the appointment, which could come as early as this week. “Ernie is a real people person, and he took us to a whole new level in terms of both size and visibility,” says Howard Herzog, a participant in the Energy Initiative who works on carbon capture and sequestration technologies at MIT.
From that news article, it certainly appears that Moniz might be able to better navigate the politics of Washington, since he has had plenty of experience dealing with that kind of cra... err ... environment before.
If this comes true, I would be happy enough. I was dreading the idea of a non-scientist, a non-engineer, or worst still, a career bureaucrat, running what is essentially a science/engineering/technical branch of the govt. We have had those before with other administrations. I'd rather not have that again.
Zz.
Monday, February 25, 2013
Possible Higgs Has Strong Even Parity
CMS and ATLAS continue to investigate the particle discovered last year that are strong candidates to be the Higgs. The latest result out of CMS is the study of the parity of this particle.
Turns out that the result points strongly towards the even-parity particle, which is consistent with the Standard Model Higgs.
Zz.
One important test is the parity of the particle: how its mirror image behaves. In a mirror, even-parity particles look the same, whereas odd-parity particles appear reversed. The standard model Higgs boson is a scalar, a spin-0 even-parity particle. But there are many models that include a spin-0 odd-parity particle known as a pseudoscalar.
Turns out that the result points strongly towards the even-parity particle, which is consistent with the Standard Model Higgs.
Zz.
Sunday, February 24, 2013
Open Access For All Federally-Funded Papers
The US White House has released a policy directing all federal agency to make available to the public all federally-funded research work.
Not sure how the for-profit journals would deal with this, but for many not-for-profit journals such as the Phys. Rev., authors are already allowed to put copies of their publications either on their own webpages or on arXiv.
Zz.
The six-page directive from the White House Office of Science and Technology Policy (OSTP) says that agencies that spend more than $100 million on research must "develop a plan to support increased public access to the results of research funded by the federal government," including papers published in peer-reviewed journals. Each agency must come up with a draft plan within 6 months that meets several requirements. For example, it must leverage existing archives, strive to partner with journals, make it possible to access digital data, optimize the ability to search and archive papers, describe how to enforce compliance, and find ways to carry out the plan within the agency's existing budget.
Not sure how the for-profit journals would deal with this, but for many not-for-profit journals such as the Phys. Rev., authors are already allowed to put copies of their publications either on their own webpages or on arXiv.
Zz.
Friday, February 22, 2013
ILC And CLIC Unite
Not a very surprising news since almost everyone saw it coming. The two groups that are working on the next generation of linear collider to follow the LHC as CERN have decided to join forces and share information in a new organization.
Of course, for ILC, this is certainly welcomed since the US is severely cutting back on its contribution to the ILC effort (some even say that the ILC in the US is dead). It also appears that if some form of the ILC is built, Japan appears to be the leading candidate for a site to build this facility. For those of us in the US, this means that the US will continue to have ZERO high energy physics particle collider if this comes true.
Zz.
The two most mature future particle physics projects, the International Linear Collider (ILC) and the Compact Linear Collider study (CLIC), have formed an official organisational partnership today. As the newly founded Linear Collider Collaboration, they will coordinate and advance the global development work for the linear collider, a global project to complement the Large Hadron Collider (LHC) at CERN and ultimately understand the deepest secrets of the universe. The Linear Collider Collaboration is headed by Lyn Evans, former Project Manager of CERN’s Large Hadron Collider (LHC). Hitoshi Murayama, Director of the Kavli Institute for the Physics and Mathematics of the Universe, will serve as a deputy director.
Of course, for ILC, this is certainly welcomed since the US is severely cutting back on its contribution to the ILC effort (some even say that the ILC in the US is dead). It also appears that if some form of the ILC is built, Japan appears to be the leading candidate for a site to build this facility. For those of us in the US, this means that the US will continue to have ZERO high energy physics particle collider if this comes true.
Zz.
A Tour Of MIT's Plasma Physics And Fusion Center
If you haven't seen the inside of it, here is a quick tour of MIT's Plasma Physics and Fusion Center.
Zz.
Zz.
New Limits On Possible (?) 5th Force
OK, I'll be honest. I am not quite sure how I would tackle this news release, because I could easily go off the deep end and just blast this thing to bits. First of all, this is a fine work, and I haven't finished reading the paper yet. So the issue here isn't with the published work. But I have issues with this press release.
This press release describes a very novel way of looking for a possible spin-spin force, using the entire earth (?) and invoking a multidisciplinary knowledge.
The way this has been titled, and the way it sounds, it makes it sounds as if there is a 5th force, and that we're just trying to hunt it down. All this experiment has done is put a severe limit on such a thing because of a non-detection at the level of accuracy that the experiment has. In other words, they didn't find any!
But what I found unbelievable is the comment from one of the authors.
Whoa! Is this really that surprising? We already have studies on geoneutrinos, among other things. It all came out of our knowledge from high energy physics.
Oh well, I guess we can add this to a GROWING list of practical applications of high energy physics.
Zz.
This press release describes a very novel way of looking for a possible spin-spin force, using the entire earth (?) and invoking a multidisciplinary knowledge.
Hunter -- along with emeritus Amherst physics professor Joel Gordon; postdoctoral fellow Stephen Peck; student researcher Daniel Ang '15; and Jung-Fu "Afu" Lin, associate professor of geosciences at UT Austin -- co-authored a paper about their work that appears in this week's issue of the journal Science. The highly interdisciplinary research relies on geophysics, atomic physics, particle physics, mineral physics, solid-state physics and nuclear physics to reach its conclusions.
The way this has been titled, and the way it sounds, it makes it sounds as if there is a 5th force, and that we're just trying to hunt it down. All this experiment has done is put a severe limit on such a thing because of a non-detection at the level of accuracy that the experiment has. In other words, they didn't find any!
But what I found unbelievable is the comment from one of the authors.
Lin had his own take: "The most rewarding and surprising thing about this project was realizing that particle physics could actually be used to study the deep Earth."
Whoa! Is this really that surprising? We already have studies on geoneutrinos, among other things. It all came out of our knowledge from high energy physics.
Oh well, I guess we can add this to a GROWING list of practical applications of high energy physics.
Zz.
Robert Richardson Dies at 74
This is on the news almost everywhere, but I'll report it here anyway in case anyone missed this. One of the giants in the world of condensed matter/low-temperature physics has passed away due to complications from a heart attack. Richardson won the Nobel Prize in Physics in 1996 along with Douglas Osheroff and David Lee for the discovery of superfluidity in He3.
You may also read the NY Times coverage of this here (link available for free only for a limited time).
Zz.
You may also read the NY Times coverage of this here (link available for free only for a limited time).
Zz.
Thursday, February 21, 2013
Incorporating Technology Into A Physics Lab Course
Quite a while back, I asked about useful physics apps that people are using on their smartphones and tablets. This blog entry covers something similar, but a bit more specific.
We all know that a lot of students in college (and even in high schools) nowadays have laptops, tablets, and smartphones. In fact, in some schools, they give out tablets to incoming freshmen as part of their registration package. Of course, these things are often used to browse the web, and maybe be even useful to take down notes in class. Still, I was thinking of some other ways that these items can be useful, and the one area that I think should be explored (if it hasn't already) is in the college physics laboratories.
There are already discussions going around on various research projects migrating to electronic lab books. I still haven't seen detailed description on how that is implemented, how it works in a collaborative environment, and how people keep them secure and archived. But the tell-tale signs are there, that this might easily be the wave of the future. So I believe that, as physics instructors, we should prepare the students for such an environment, and introduce the ability to migrate from our traditional pen-and-paper lab notebooks to the electronic version.
I have been exploring a few apps on my iPad on whether such a thing can be done in a college physics lab class. I first started out with a number of criteria that it must be able to do, based on what I expect from the students:
1. The students must keep their own lab notebook. They can scribble anything here, from notes taken during lab briefing, to notes taken during the experiment itself.
2. The record needs to be "permanent". In a traditional paper-and-pen lab book, all records must be written in ink. No erasing of anything.
3. The students will then use these notes to write a proper lab report that will be submitted (electronically, of course) along with the lab notes.
The only way that I can think of for the students to do their note-taking quickly and efficiently is to use apps that accept free-hand writing, using a stylus for convenience. It will allow them to quickly jot things down as if they are writing on paper, it allows them to make quick sketches, and also easily draw up a table when taking data. In other words, it will work just like a pen-and-paper situation.
However, the drawback here is that, unlike ink on paper, what they write and draw are not permanent, and there will always be a tendency to try and erase things off a page. While I can try to keep on drilling into their heads to not do that, there's nothing to absolutely prevent such an act. The only way I can think of to minimize them changing what they wrote in the lab is to require them to send whatever lab notes that they have done at the end of the laboratory session to me, via e-mail. That way, whatever they have written by the end of the experiment is now permanently stored in my record and can't be changed. I can always refer to these notes when reviewing/grading their lab reports.
So far, the apps that I've been testing and like the most is an iPad app Penultimate. With a stylus, it is quite easy to write notes, draw stuff, and make tables, all the things that I need to do in a lab. Each experiments can also be its own separate notes, so at the end of the lab, the students can easily just e-mail that to me. What is also nice about this app is that it can be synched to Evernote, another app. Evernote is an app that works under iOS, Android, and also a program that can be run under Windows and Mac. Once you synch items in Evernote, those items are accessible to all your devices that are running your Evernote. It is extremely convenient, you don't have to keep sending things around or e-mailing yourself documents. In this case, once you send your lab notes to Evernote, then when you get back home or to your room, if you have a desktop or laptop, you can always fire up Evernote, pull out your lab notes, and start writing your report. The apps is also useful when you have a collaborative effort with someone else, but I've yet to test that out extensively.
I haven't tested this out yet in a lab class because I am still trying it out on my own. But since the reader of this blog comes from such a varied background, I thought I throw this out in case some of you are already ahead of the curve and already are implementing such a scheme in your classes/laboratories. I would very much like to hear from you and what your experience is in doing something like this.
Edit: has anyone use LabGuru iPad app? This is something I'm interested in hearing and will be testing soon. But if you have used it, or are using it, I definitely want to hear from you.
Zz.
We all know that a lot of students in college (and even in high schools) nowadays have laptops, tablets, and smartphones. In fact, in some schools, they give out tablets to incoming freshmen as part of their registration package. Of course, these things are often used to browse the web, and maybe be even useful to take down notes in class. Still, I was thinking of some other ways that these items can be useful, and the one area that I think should be explored (if it hasn't already) is in the college physics laboratories.
There are already discussions going around on various research projects migrating to electronic lab books. I still haven't seen detailed description on how that is implemented, how it works in a collaborative environment, and how people keep them secure and archived. But the tell-tale signs are there, that this might easily be the wave of the future. So I believe that, as physics instructors, we should prepare the students for such an environment, and introduce the ability to migrate from our traditional pen-and-paper lab notebooks to the electronic version.
I have been exploring a few apps on my iPad on whether such a thing can be done in a college physics lab class. I first started out with a number of criteria that it must be able to do, based on what I expect from the students:
1. The students must keep their own lab notebook. They can scribble anything here, from notes taken during lab briefing, to notes taken during the experiment itself.
2. The record needs to be "permanent". In a traditional paper-and-pen lab book, all records must be written in ink. No erasing of anything.
3. The students will then use these notes to write a proper lab report that will be submitted (electronically, of course) along with the lab notes.
The only way that I can think of for the students to do their note-taking quickly and efficiently is to use apps that accept free-hand writing, using a stylus for convenience. It will allow them to quickly jot things down as if they are writing on paper, it allows them to make quick sketches, and also easily draw up a table when taking data. In other words, it will work just like a pen-and-paper situation.
However, the drawback here is that, unlike ink on paper, what they write and draw are not permanent, and there will always be a tendency to try and erase things off a page. While I can try to keep on drilling into their heads to not do that, there's nothing to absolutely prevent such an act. The only way I can think of to minimize them changing what they wrote in the lab is to require them to send whatever lab notes that they have done at the end of the laboratory session to me, via e-mail. That way, whatever they have written by the end of the experiment is now permanently stored in my record and can't be changed. I can always refer to these notes when reviewing/grading their lab reports.
So far, the apps that I've been testing and like the most is an iPad app Penultimate. With a stylus, it is quite easy to write notes, draw stuff, and make tables, all the things that I need to do in a lab. Each experiments can also be its own separate notes, so at the end of the lab, the students can easily just e-mail that to me. What is also nice about this app is that it can be synched to Evernote, another app. Evernote is an app that works under iOS, Android, and also a program that can be run under Windows and Mac. Once you synch items in Evernote, those items are accessible to all your devices that are running your Evernote. It is extremely convenient, you don't have to keep sending things around or e-mailing yourself documents. In this case, once you send your lab notes to Evernote, then when you get back home or to your room, if you have a desktop or laptop, you can always fire up Evernote, pull out your lab notes, and start writing your report. The apps is also useful when you have a collaborative effort with someone else, but I've yet to test that out extensively.
I haven't tested this out yet in a lab class because I am still trying it out on my own. But since the reader of this blog comes from such a varied background, I thought I throw this out in case some of you are already ahead of the curve and already are implementing such a scheme in your classes/laboratories. I would very much like to hear from you and what your experience is in doing something like this.
Edit: has anyone use LabGuru iPad app? This is something I'm interested in hearing and will be testing soon. But if you have used it, or are using it, I definitely want to hear from you.
Zz.
Tuesday, February 19, 2013
Physics Professor's Bizarre Behavior
Hey, I am all for engaging students attention in a physics class, but I think this went too far and was extremely bizarre. A professor at Columbia University pulled off a very strange stunt in front of his students, and apparently did not give any rational explanation on why.
Ok, that is downright creepy. But then again, if anyone tells you physicists are boring and uninteresting ........
Zz.
First-years in Frontiers of Science were supposed to hear a lecture on quantum mechanics from renowned physics professor Emlyn Hughes on Monday morning. But what they witnessed first was a bizarre performance from Hughes that left many of them baffled and confused.
As students filed into the lecture hall, all of the lights were off, except for two spotlights on stage where Hughes was sitting. With Lil Wayne's “Drop It Like It’s Hot” playing in the background, Hughes stripped down to his underwear, then proceeded to change into a black T-shirt and pants. Afterwards, he sat down on the chair, hugging his knees in a fetal position.
Then, as a jumbled video that included footage of the planes crashing into the Twin Towers on 9/11 continued to play on the screen, two figures dressed in black came on stage with long swords. One of them proceeded to chop a stuffed animal in half on a stool.
Ok, that is downright creepy. But then again, if anyone tells you physicists are boring and uninteresting ........
Zz.
Friday, February 15, 2013
Breaking Time-Reversal Symmetry Reduces Thermodynamic Efficiency
This was reported a few days ago, but I've only had a chance to read it recently. It is an interesting calculation for the thermodynamic efficiency of a thermoelectric engine in the presence of an external magnetic field, thereby breaking the time-reversal symmetry.
The rest of the article has a very good detail on why this is such an important study. You also get a free copy of the paper in the link.
Zz.
In this spirit, Kay Brandner at the University of Stuttgart, Germany, and colleagues report in Physical Review Letters their calculated efficiency of a simple thermoelectric device that converts heat to electrical current (Fig. 1). They show that when the device operates in an external magnetic field—a condition that breaks time-reversal symmetry for the motion of electrons—the efficiency is significantly lower than previous studies predicted. The lower bound on efficiency occurs, they argue, because in addition to the requirement that entropy be greater than or equal to zero, charge must be conserved—a point that was missed in earlier work. Their findings improve our understanding of thermoelectric efficiency and may one day influence the design of thermoelectric devices for real-world applications.
The rest of the article has a very good detail on why this is such an important study. You also get a free copy of the paper in the link.
Zz.
Thursday, February 14, 2013
It is Valentine's Day - Date A Scientist!
(A tip of the hat to Ryan at PF for finding this amusing article)
If you are single, and you find that you can't stand all this brouhaha about St. Valentine's day, then I found an article that is a perfect solution for you - date a scientist!
There ya go!
The article then went on to tell you a good way to snag one of these elusive scientists.
Happy hunting!
Zz.
If you are single, and you find that you can't stand all this brouhaha about St. Valentine's day, then I found an article that is a perfect solution for you - date a scientist!
Scientists are highly educated people with decent career prospects, but are also rarely associated with a fondness for romance and passion (or any other emotional state) so are likely to be apathetic towards Valentine's Day. Ergo, scientists are the ideal partners.
There ya go!
The article then went on to tell you a good way to snag one of these elusive scientists.
Happy hunting!
Zz.
Wednesday, February 13, 2013
Vote For Your Favorite PhotoWalk Photos
Voting has started for you to vote on your favorite Particle Physics PhotoWalk contest. There are some stunning photos in here, and I don't know how I can choose just 3.
So get your votes in!
Zz.
So get your votes in!
Zz.
Tuesday, February 12, 2013
Science At Work
A rather fascinating video out of Fermilab. In some ways, this is a "propaganda" video, but in other ways, it actually is a very informative look at not only what the Lab does (or will do), but also what "high energy physics" is. The personal angle that is included in the video provides some "emotional" content that the general public can relate to.
Here's the synopsis of the video:
Six days. Three frontiers. One amazing lab. From 2010 to 2012, a film crew followed a group of scientists at the Department of Energy's Fermilab and filmed them at work and at home. This 40-minute documentary shows the diversity of the people, research and work at Fermilab. Viewers catch a true behind-the-scenes look of the United States' premier particle physics laboratory while scientists explain why their research is important to them and the world.
It's a long, 40-minute video, though. But it is worth sitting down and watching it, especially if you want to learn a bit more about high energy physics here in the US, and what Fermilab did and will do.
Zz.
Here's the synopsis of the video:
Six days. Three frontiers. One amazing lab. From 2010 to 2012, a film crew followed a group of scientists at the Department of Energy's Fermilab and filmed them at work and at home. This 40-minute documentary shows the diversity of the people, research and work at Fermilab. Viewers catch a true behind-the-scenes look of the United States' premier particle physics laboratory while scientists explain why their research is important to them and the world.
It's a long, 40-minute video, though. But it is worth sitting down and watching it, especially if you want to learn a bit more about high energy physics here in the US, and what Fermilab did and will do.
Zz.
Monday, February 11, 2013
FFAG Review
I wrote quite a while back about this Fixed Field Alternating Gradient accelerator, including the unfortunate acronym that it has adopted. This document provides a good review of this area. It was presented at a 2011 CERN Accelerator school.
Zz.
Friday, February 08, 2013
"Quantum photonic devices in single-crystal diamond"
A very interesting report on the ability to control single-photons in photonic devices.
You can get free access to the paper at the New Journal of Physics website.
Notice that this work was partly funded by DARPA.
Zz.
Physicists in the US are the first to make an integrated device that extracts photons from a tiny piece of diamond before the light is sent through a waveguide to the outside world. The photons all have the same frequency and originate in a nitrogen vacancy (NV), which is a defect that occurs in diamond when two neighbouring carbon atoms are replaced by a nitrogen atom and an empty lattice site. According to the researchers, the chip could be used to create quantum-information technology such as quantum repeaters.
.
.
Researchers are particularly interested in extracting photons that do not interact with the surrounding lattice because these "zero phonon line" (ZPL) photons have a well defined frequency. Unfortunately, one challenge in building NV-based quantum systems is how to reliably get ZPL photons out of the diamond and into an integrated optical system, where it can be processed further. What Andrei Faraon and colleagues from Caltech, Hewlett Packard and the University of Washington have managed to do is to create an integrated optical system that does just that.
You can get free access to the paper at the New Journal of Physics website.
Notice that this work was partly funded by DARPA.
Zz.
Kelvin Probe
Hey, I'm an experimentalist. It may be a revelation to some because I see this blog linked to many different sites, and some of them referred to it as ".. written by a high energy theorist..."! Me? High energy theorist? :)
Anyhow, I think it is always good to highlight certain experimental techniques, especially the ones that I'm quite familiar with. So here's one.
Often, for most of us, our first encounter to measuring the work function of something is via the photoelectric effect. Later on, if some of us go into photoemission spectroscopy, we deal with the work function there as well. However, that is not the only means to measure the work function. A technique that does not require the use of any light source to perform such measurement is called the Kelvin probe.
If you understand the physics behind a pn junction in semiconductors, then you've already understood the physics used in a Kelvin probe. You have a metal (the probe) with a particular Fermi energy, in close proximity (or in contact) with another material that has a different Fermi energy. This creates a contact potential difference. The Kelvin probe measures this contact potential difference, which is the difference between the two Fermi energies.
The link that I gave above gives you more details on such a measurement. If you know the value of the Fermi energy of the probe, you get the value of the work function of the material being studied. The only caveat here is that if the sample you are looking at is a semiconductor, you do not get the "work function", but rather, the value of the Fermi energy with respect to the vacuum state. In many cases, this is called the work function (energy between the Fermi level and the vacuum state) of the semiconductor, but one should not confuse this with the photoemission threshold, because the Fermi level resides in the gap. The photoemission threshold is the energy between the top of the valence band and the vacuum level.
Confused? Let's go on.
A significant improvement in the Kelvin probe technique was introduced with the invention of the Atomic Force Microscopy (AFM). It turns out that one can adapt an AFM system to work in the Kelvin probe mode. This technique is now called Kelvin Probe Force Microscopy (KPFM). I've linked to a very nice review paper on the physics and capabilities of KPFM technique. This technique allows for the mapping of the surface potential (or work function if you know the work function of the tip) of a surface with spatial resolution of the order of 100 nm.
So why is this useful. Obviously, knowledge of the surface potential is crucial in the understanding of the behavior of many materials (read some of the references in the KPFM review paper). It is another parameter that is part of the characteristics of the material. It also provides another check to the value of the work function that are often obtained from photoemission experiments. In fact, some material actually react to the exposure of light (especially UV), and the value of the work function obtained may not be as accurate as it should be from photoemission measurement.
There. So now, if you haven't heard about this before, you've learned something new! :)
Zz.
Anyhow, I think it is always good to highlight certain experimental techniques, especially the ones that I'm quite familiar with. So here's one.
Often, for most of us, our first encounter to measuring the work function of something is via the photoelectric effect. Later on, if some of us go into photoemission spectroscopy, we deal with the work function there as well. However, that is not the only means to measure the work function. A technique that does not require the use of any light source to perform such measurement is called the Kelvin probe.
If you understand the physics behind a pn junction in semiconductors, then you've already understood the physics used in a Kelvin probe. You have a metal (the probe) with a particular Fermi energy, in close proximity (or in contact) with another material that has a different Fermi energy. This creates a contact potential difference. The Kelvin probe measures this contact potential difference, which is the difference between the two Fermi energies.
The link that I gave above gives you more details on such a measurement. If you know the value of the Fermi energy of the probe, you get the value of the work function of the material being studied. The only caveat here is that if the sample you are looking at is a semiconductor, you do not get the "work function", but rather, the value of the Fermi energy with respect to the vacuum state. In many cases, this is called the work function (energy between the Fermi level and the vacuum state) of the semiconductor, but one should not confuse this with the photoemission threshold, because the Fermi level resides in the gap. The photoemission threshold is the energy between the top of the valence band and the vacuum level.
Confused? Let's go on.
A significant improvement in the Kelvin probe technique was introduced with the invention of the Atomic Force Microscopy (AFM). It turns out that one can adapt an AFM system to work in the Kelvin probe mode. This technique is now called Kelvin Probe Force Microscopy (KPFM). I've linked to a very nice review paper on the physics and capabilities of KPFM technique. This technique allows for the mapping of the surface potential (or work function if you know the work function of the tip) of a surface with spatial resolution of the order of 100 nm.
So why is this useful. Obviously, knowledge of the surface potential is crucial in the understanding of the behavior of many materials (read some of the references in the KPFM review paper). It is another parameter that is part of the characteristics of the material. It also provides another check to the value of the work function that are often obtained from photoemission experiments. In fact, some material actually react to the exposure of light (especially UV), and the value of the work function obtained may not be as accurate as it should be from photoemission measurement.
There. So now, if you haven't heard about this before, you've learned something new! :)
Zz.
Thursday, February 07, 2013
No Ignition For National Ignition Facility
The soft whispers about issues and skepticism with the National Ignition Facility (NIF) got louder with the review reports on its failure to meet its milestone last year.
The gist of the conclusion given in the committee report is in this paragraph:
The ignition program certainly has a major task ahead of it, and this failure to initiate ignition certainly generates even strong skepticism of its program.
Zz.
The US$3.5 billion National Ignition Facility (NIF), at the Lawrence Livermore National Laboratory in Livermore, California, is designed to crush tiny pellets of hydrogen isotopes until they fuse into helium. The goal is to release more energy than goes into the pellet and in doing so roughly mimic conditions inside a modern nuclear warhead.
That was the goal, but a six-year “ignition campaign” came up short in September, sparking introspection amongst scientists, federal officials and congressional funders. Introspection in Washington inevitably leads to reports, and in November and December, a series of reviews of the project were released—including plans to shift the giant laser facility away from ignition work and towards weapons.
The gist of the conclusion given in the committee report is in this paragraph:
The important conclusion from the NIC is that the pressent understanding of the physics of the hahlraum and capsule implosion as embodied in modeling and computer simulation is insufficient to predict the results of the implosion experiments aimed at achieving ignition. Reviewers indicated that, while progress towards ignition had been made, a program of scientific experiments and modeling focused on understanding the various physical effects, in isolation, that impact the integrated implosion experiments provides the best approach to eventually either achieve ignition, or to understand definitively why it may not be achievable with indirect drive using the NIF laser. Executing such a program will also require enhancing the number of diagnostic measurements of both the future focused experiments and integrated implosion experiments.
The ignition program certainly has a major task ahead of it, and this failure to initiate ignition certainly generates even strong skepticism of its program.
Zz.
70 Years Of Schrodinger's "What Is Life?" Lectures
If you were not alive 70 years ago, this news article provides a very good summary of the landmark set of lectures by Erwin Schrodinger on a surprising topic for a physicists - What is Life?
I'm wondering if many crackpots and creationists got the idea of the evolution of life violating the 2nd law from this lecture. It might easily be the impetus for such misinformation to be passed on.
Anyhow, this is a very good news article to get a brief idea on that monumental lecture in the history of science.
Zz.
One of Schr̦dinger's key aims was to explain how living things apparently defy the second law of thermodynamics Рaccording to which all order in the universe tends to break down. It was this that led my colleague Professor Brian Cox to use Schr̦dinger as the starting point of his BBC series Wonders of Life, leading to What is Life? shooting up the Amazon sales chart.
But Schrödinger's book contains something far more important than his attempt to fuse physics and biology. In that lecture 70 years ago, he introduced some of the most important concepts in the history of biology, which continue to frame how we see life.
I'm wondering if many crackpots and creationists got the idea of the evolution of life violating the 2nd law from this lecture. It might easily be the impetus for such misinformation to be passed on.
Anyhow, this is a very good news article to get a brief idea on that monumental lecture in the history of science.
Zz.
Tuesday, February 05, 2013
Store Photons. Then Make Them Intract With Each Other
It's amazing to see the development in this area. Just a few years ago, we were amazed at the accomplishments coming out of Lene Hau's lab in being able to not only store photons, but also to "replay" them back. Now comes this, which is another step in refining and improving the capability of storing photons.
http://arxiv.org/pdf/1207.6007v3.pdf
Apparently, this is to be published in PRL.
Definitely a commendable accomplishment here in the evolution of our capability of using photons for quantum communications.
Zz.
What Charles Adams and colleagues at Durham University have now done is come up with a way of storing individual optical photons in highly excited states of an atomic gas. Once stored, the photons can be made to interact strongly, before being released again. An important feature of the technique is that it uses microwaves, which are also used to control some types of stationary qubit.
http://arxiv.org/pdf/1207.6007v3.pdf
Apparently, this is to be published in PRL.
Definitely a commendable accomplishment here in the evolution of our capability of using photons for quantum communications.
Zz.
Monday, February 04, 2013
The Emergence Of QCD
This is a nice review of how QCD came about and its role in the Standard Model, written by Nobel Laureates David Gross and Franck Wilczek.
Zz.
Zz.
Friday, February 01, 2013
Steven Chu Resigns
In case you didn't see this already, Steven Chu announced his resignation as the US Energy Secretary.
It will be interesting to see who President Obama will nominate to replace him. I'm hoping that it will be someone who is a scientist and not a science-challenged bureaucrat (cough bill richardson cough!).
Zz.
Chu will enter the record books as the longest-serving Secretary in DOE's 35-year history, and the first Nobel laureate to lead the sprawling, $27 billion department. Once a successor is named, Chu says that he plans to return to California. He spent 17 years on the faculty of Stanford University before moving to the University of California, Berkeley, and was director of DOE's Lawrence Berkeley National Laboratory before coming to Washington in January 2009.Despite the Solyndra debacle, I thought he did an admirable job considering that he was faced with a hostile congress that was determined to cut funding to the sciences regardless of the harm it will do not only to the advancement of knowledge, but also to the US economy.
It will be interesting to see who President Obama will nominate to replace him. I'm hoping that it will be someone who is a scientist and not a science-challenged bureaucrat (cough bill richardson cough!).
Zz.
Subscribe to:
Posts (Atom)