87 research outputs found
On momentum conservation and thermionic emission cooling
The question of whether relaxing momentum conservation can increase the
performance of thermionic cooling device is examined. Both homojunctions and
heterojunctions are considered. It is shown that for many cases, a
non-conserved lateral momentum model overestimates the current. For the case of
heterojunctions with a much heavier effective mass in the barrier and with a
low barrier height, however, non-conservation of lateral momentum may increase
the current. These results may be simply understood from the general principle
that the current is limited by the location, well or barrier, with the smallest
number of conducting channels. These results also show that within thermionic
emission framework, the possibilities of increasing thermionic cooling by
relaxing momentum conservation are limited. More generally, however, when the
connection to the source is weak or in the presence of scattering, the
situation may be different. Issues that deserve further study are identified.Comment: 36 pages, 1 table, 9 figure
On Electronic Structure Engineering and Thermoelectric Performance
In this paper, we address the question of how to engineer the electronic structure to enhance the performance of a thermoelectric material. We examine several different materials and show that all of them, even those for which giant Seebeck coefficients have been predicted, display a value that is expected from conventional thermoelectric theory. For molecular thermoelectrics, we show that the detailed lineshape plays an important role. Finally, using III-V alloy semiconductors as a model system, we explore the role of electronic structure in the Seebeck coefficient, electrical conductivity, and power factor. In the process, some general guidelines for engineering the electronic component of thermoelectric performance are identified
On the Best Bandstructure for Thermoelectric Performance
The conventional understanding that a bandstructure that produces a Dirac
delta function transport distribution (or transmission in the Landauer
framework) maximizes the thermoelectric figure of merit, ZT, is revisited.
Thermoelectric (TE) performance is evaluated using a simple tight binding (TB)
model for electron dispersion and three different scattering models: 1) a
constant scattering time, 2) a constant mean-free-path, and 3) a scattering
rate proportional to the density-of-states. We found that a Dirac
delta-function transmission never produces the maximum ZT. The best
bandstructure for maximizing ZT depends on the scattering physics. These
results demonstrate that the selection of bandstructure to maximize TE
performance is more complex than previously thought and that a high
density-of-states near the band edge does not necessarily improve TE
performance
Full Dispersion vs. Debye Model Evaluation of Lattice Thermal Conductivity with a Landauer approach
Using a full dispersion description of phonons, the thermal conductivities of bulk Si and Bi2Te3 are evaluated using a Landauer approach and related to the conventional approach based on the Boltzmann transport equation. A procedure to extract a well-defined average phonon mean-free-path from the measured thermal conductivity and given phonon-dispersion is presented. The extracted mean-free-path has strong physical significance and differs greatly from simple estimates. The use of simplified dispersion models for phonons is discussed, and it is shown that two different Debye temperatures must be used to treat the specific heat and thermal conductivity (analogous to the two different effective masses needed to describe the electron density and conductivity). A simple technique to extract these two Debye temperatures is presented and the limitations of the method are discussed
Restructuring TCAD System: Teaching Traditional TCAD New Tricks
Traditional TCAD simulation has succeeded in predicting and optimizing the
device performance; however, it still faces a massive challenge - a high
computational cost. There have been many attempts to replace TCAD with deep
learning, but it has not yet been completely replaced. This paper presents a
novel algorithm restructuring the traditional TCAD system. The proposed
algorithm predicts three-dimensional (3-D) TCAD simulation in real-time while
capturing a variance, enables deep learning and TCAD to complement each other,
and fully resolves convergence errors.Comment: In Proceedings of 2021 IEEE International Electron Devices Meeting
(IEDM
Quaternary structures of Vac8 differentially regulate the Cvt and PMN pathways.
Armadillo (ARM) repeat proteins constitute a large protein family with diverse and fundamental functions in all organisms, and armadillo repeat domains share high structural similarity. However, exactly how these structurally similar proteins can mediate diverse functions remains a long-standing question. Vac8 (vacuole related 8) is a multifunctional protein that plays pivotal roles in various autophagic pathways, including piecemeal microautophagy of the nucleus (PMN) and cytoplasm-to-vacuole targeting (Cvt) pathways in the budding yeast Saccharomyces cerevisiae. Vac8 comprises an H1 helix at the N terminus, followed by 12 armadillo repeats. Herein, we report the crystal structure of Vac8 bound to Atg13, a key component of autophagic machinery. The 70-angstrom extended loop of Atg13 binds to the ARM domain of Vac8 in an antiparallel manner. Structural, biochemical, and in vivo experiments demonstrated that the H1 helix of Vac8 intramolecularly associates with the first ARM and regulates its self-association, which is crucial for Cvt and PMN pathways. The structure of H1 helix-deleted Vac8 complexed with Atg13 reveals that Vac8[Delta 19-33]-Atg13 forms a heterotetramer and adopts an extended superhelical structure exclusively employed in the Cvt pathway. Most importantly, comparison of Vac8-Nvj1 and Vac8-Atg13 provides a molecular understanding of how a single ARM domain protein adopts different quaternary structures depending on its associated proteins to differentially regulate 2 closely related but distinct cellular pathways
Proximity-Directed Labeling Reveals a New Rapamycin-Induced Heterodimer of FKBP25 and FRB in Live Cells
Mammalian target of rapamycin (mTOR) signaling is a core pathway in cellular metabolism, and control of the mTOR pathway by rapamycin shows potential for the treatment of metabolic diseases. In this study, we employed a new proximity biotin-labeling method using promiscuous biotin ligase (pBirA) to identify unknown elements in the rapamycin-induced interactome on the FK506-rapamycin binding (FRB) domain in living cells. FKBP25 showed the strongest biotin labeling by FRB-pBirA in the presence of rapamycin. Immunoprecipitation and immunofluorescence experiments confirmed that endogenous FKBP25 has a rapamycin-induced physical interaction with the FRB domain. Furthermore, the crystal structure of the ternary complex of FRB-rapamycin-FKBP25 was determined at 1.67-angstrom resolution. In this crystal structure we found that the conformational changes of FRB generate a hole where there is a methionine-rich space, and covalent metalloid coordination was observed at C2085 of FRB located at the bottom of the hole. Our results imply that FKBP25 might have a unique physiological role related to metallomics in mTOR signaling.ope
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