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Showing posts with label Physics. Show all posts
Showing posts with label Physics. Show all posts
Monday, October 26, 2009
Sunday, October 25, 2009
Melbourne
SRI conference in down under was great. Apart from the travel the conference was a very focused one. I really like the way one of the speaker ended this talk at SRI. I could only get the last minute or so of his conclusion.
Tuesday, November 25, 2008
Physicist getting inspired!!
Here is something interesting... this is an absract from a paper in PNAS on doped ceria by D.A. Anderson et. al. (published date 12/2005)
"Oxides with the cubic fluorite structure, e.g., ceria (CeO2), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present a quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy–dopant interactions, represented by association (binding) energies of vacancy–dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd/Sm and Pr/Gd show enhanced ionic conductivity, as compared with that for each element separately."
And here is a paper in Journal of Materials science on doped ceria again published by Selladurai (Anna Univ).Well I guess the first author might have been a graduate student but I am pointing out the corresponding author. The paper was out sometime last year (2007).
"Oxides with the cubic fluorite structure, e.g., ceria (CeO2), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy–dopant interactions, represented by association (binding) energies of vacancy–dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd/Sm and Pr/Gd show enhanced ionic conductivity, as compared with that for each element separately."
simply amazing... what are the odds that two people came to the exact same conclusions !! well I went over the entire paper and believe it or not they even had the exact same data, plot everything. Talk about reproducibility. This is the awesome I have heard people say reproducible data but Dr S. Selladurai's group took a giant leap and reproduced the entire paper.
"Oxides with the cubic fluorite structure, e.g., ceria (CeO2), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present a quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy–dopant interactions, represented by association (binding) energies of vacancy–dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd/Sm and Pr/Gd show enhanced ionic conductivity, as compared with that for each element separately."
And here is a paper in Journal of Materials science on doped ceria again published by Selladurai (Anna Univ).Well I guess the first author might have been a graduate student but I am pointing out the corresponding author. The paper was out sometime last year (2007).
"Oxides with the cubic fluorite structure, e.g., ceria (CeO2), are known to be good solid electrolytes when they are doped with cations of lower valence than the host cations. The high ionic conductivity of doped ceria makes it an attractive electrolyte for solid oxide fuel cells, whose prospects as an environmentally friendly power source are very promising. In these electrolytes, the current is carried by oxygen ions that are transported by oxygen vacancies, present to compensate for the lower charge of the dopant cations. Ionic conductivity in ceria is closely related to oxygen-vacancy formation and migration properties. A clear physical picture of the connection between the choice of a dopant and the improvement of ionic conductivity in ceria is still lacking. Here we present quantum-mechanical first-principles study of the influence of different trivalent impurities on these properties. Our results reveal a remarkable correspondence between vacancy properties at the atomic level and the macroscopic ionic conductivity. The key parameters comprise migration barriers for bulk diffusion and vacancy–dopant interactions, represented by association (binding) energies of vacancy–dopant clusters. The interactions can be divided into repulsive elastic and attractive electronic parts. In the optimal electrolyte, these parts should balance. This finding offers a simple and clear way to narrow the search for superior dopants and combinations of dopants. The ideal dopant should have an effective atomic number between 61 (Pm) and 62 (Sm), and we elaborate that combinations of Nd/Sm and Pr/Gd show enhanced ionic conductivity, as compared with that for each element separately."
simply amazing... what are the odds that two people came to the exact same conclusions !! well I went over the entire paper and believe it or not they even had the exact same data, plot everything. Talk about reproducibility. This is the awesome I have heard people say reproducible data but Dr S. Selladurai's group took a giant leap and reproduced the entire paper.
Friday, November 14, 2008
Interesting read
I came across this interview with Peter Higgs (of the legendary Higgs Boson) and it was very interesting to note that he mainly credits his theory to Phillip Anderson. Infact to here are some interesting snippets from this article
"Once more help arrived from the condensed-matter community when, in 1963, Phil Anderson pointed out that the equivalent of a Goldstone boson in a superconductor could become massive due to its electromagnetic interactions. But did Anderson's argument apply in the relativistic case? No, said a paper by Walter Gilbert in an issue of Physical Review Letters that arrived in Edinburgh the middle of July. Yes, said Higgs, after thinking about it over the weekend."
and here is an quote from Higgs
""Anderson should have done basically the two things that I did," says Higgs. "He should have shown the flaw in the Goldstone theorem, and he should have produced a simple relativistic model to show it happened. However, whenever I give a lecture on the so-called Higgs mechanism I start off with Anderson, who really got it right, but nobody understood him."
You can read the complete articlehere
Well it is friday had a couple of interesting seminars which I attended to but it is one of those day where after the talk you do feel a bit dumb/frustrated. On the good note atleast it made me go back and read about Kondo effect. In most pure metals the resistance is supposed to go down as temperature. It has the usual t power 2 and 5 dependence with an addition phonon contribution. In certain impure metals (impurity being magnetic) however the resistance shoots up at some region. This was first observed in 30s and I think a few decades later Jun Kondo explained it. Simplifying the work of Kondo we could explain the data by adding a log{1/T} dependense. This should give rise to a divergent term at T approches 0 but I guess Kondo effect only comes it for a particular region.It is one of interesting and the very first example of asymptotic freedom discovered in nature. I guess much earlier than the same description was applied to strong forces in elementary particles. Its odd than Jun Kondo has not been awarded Nobel proze yet.... For a good reading on Kondo effect there is a good article
here
"Once more help arrived from the condensed-matter community when, in 1963, Phil Anderson pointed out that the equivalent of a Goldstone boson in a superconductor could become massive due to its electromagnetic interactions. But did Anderson's argument apply in the relativistic case? No, said a paper by Walter Gilbert in an issue of Physical Review Letters that arrived in Edinburgh the middle of July. Yes, said Higgs, after thinking about it over the weekend."
and here is an quote from Higgs
""Anderson should have done basically the two things that I did," says Higgs. "He should have shown the flaw in the Goldstone theorem, and he should have produced a simple relativistic model to show it happened. However, whenever I give a lecture on the so-called Higgs mechanism I start off with Anderson, who really got it right, but nobody understood him."
You can read the complete article
Well it is friday had a couple of interesting seminars which I attended to but it is one of those day where after the talk you do feel a bit dumb/frustrated. On the good note atleast it made me go back and read about Kondo effect. In most pure metals the resistance is supposed to go down as temperature. It has the usual t power 2 and 5 dependence with an addition phonon contribution. In certain impure metals (impurity being magnetic) however the resistance shoots up at some region. This was first observed in 30s and I think a few decades later Jun Kondo explained it. Simplifying the work of Kondo we could explain the data by adding a log{1/T} dependense. This should give rise to a divergent term at T approches 0 but I guess Kondo effect only comes it for a particular region.It is one of interesting and the very first example of asymptotic freedom discovered in nature. I guess much earlier than the same description was applied to strong forces in elementary particles. Its odd than Jun Kondo has not been awarded Nobel proze yet.... For a good reading on Kondo effect there is a good article
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