157 research outputs found
Effects of Interface Disorder on Valley Splitting in SiGe/Si/SiGe Quantum Wells
A sharp potential barrier at the Si/SiGe interface introduces valley
splitting (VS), which lifts the 2-fold valley degeneracy in strained
SiGe/Si/SiGe quantum wells (QWs). This work examines in detail the effects of
Si/SiGe interface disorder on the VS in an atomistic tight binding approach
based on statistical sampling. VS is analyzed as a function of electric field,
QW thickness, and simulation domain size. Strong electric fields push the
electron wavefunctions into the SiGe buffer and introduce significant VS
fluctuations from device to device. A Gedankenexperiment with ordered alloys
sheds light on the importance of different bonding configurations on VS. We
conclude that a single SiGe band offset and effective mass cannot comprehend
the complex Si/SiGe interface interactions that dominate VS.Comment: 5 figure
Million Atom Electronic Structure and Device Calculations on Peta-Scale Computers
Semiconductor devices are scaled down to the level which constituent
materials are no longer considered continuous. To account for atomistic
randomness, surface effects and quantum mechanical effects, an atomistic
modeling approach needs to be pursued. The Nanoelectronic Modeling Tool (NEMO
3-D) has satisfied the requirement by including emprical and
tight binding models and considering strain to successfully
simulate various semiconductor material systems. Computationally, however, NEMO
3-D needs significant improvements to utilize increasing supply of processors.
This paper introduces the new modeling tool, OMEN 3-D, and discusses the major
computational improvements, the 3-D domain decomposition and the multi-level
parallelism. As a featured application, a full 3-D parallelized
Schr\"odinger-Poisson solver and its application to calculate the bandstructure
of doped phosphorus(P) layer in silicon is demonstrated. Impurity
bands due to the donor ion potentials are computed.Comment: 4 pages, 6 figures, IEEE proceedings of the 13th International
Workshop on Computational Electronics, Tsinghua University, Beijing, May
27-29 200
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PAXX promotes KU accumulation at DNA breaks and is essential for end-joining in XLF-deficient mice
Non-homologous end-joining (NHEJ) is the most prominent DNA double strand break (DSB) repair pathway in mammalian cells. PAXX is the newest NHEJ factor, which shares structural similarity with known NHEJ factorsâXRCC4 and XLF. Here we report that PAXX is dispensable for physiological NHEJ in otherwise wild-type mice. Yet Paxxâ/â mice require XLF and Xlfâ/â mice require PAXX for end-ligation. As such, Xlfâ/âPaxxâ/â mice display severe genomic instability and neuronal apoptosis, which eventually lead to embryonic lethality. Despite their structural similarities, only Xlfâ/â cells, but not Paxxâ/â cells require ATM/DNA-PK kinase activity for end-ligation. Mechanistically, PAXX promotes the accumulation of KU at DSBs, while XLF enhances LIG4 recruitment without affecting KU dynamics at DNA breaks in vivo. Together these findings identify the molecular functions of PAXX in KU accumulation at DNA ends and reveal distinct, yet critically complementary functions of PAXX and XLF during NHEJ
Multiple solutions for a nonhomogeneous Schr\"odinger-Maxwell system in
The paper considers the following nonhomogeneous Schr\"odinger-Maxwell system
-\Delta u + u+\lambda\phi (x) u =|u|^{p-1}u+g(x),\ x\in \mathbb{R}^3,
-\Delta\phi = u^2, \ x\in \mathbb{R}^3, . \leqno{(SM)} where ,
and .
There seems no any results on the existence of multiple solutions to problem
(SM) for . In this paper, we find that there is a constant
such that problem (SM) has at least two solutions for all provided
, but only for we need is
small. Moreover, ,
where is the Sobolev constant.Comment: 12 page
Atomic-scale insights into the low-temperature oxidation of methanol over a single-atom Pt1-Co3O4 catalyst
Heterogeneous catalysts with singleâatom active sites offer a means of expanding the industrial application of noble metal catalysts. Herein, an atomically dispersed Pt1âCo3O4 catalyst is presented, which exhibits an exceptionally high efficiency for the total oxidation of methanol. Experimental and theoretical investigations indicate that this catalyst consists of Pt sites with a large proportion of occupied high electronic states. These sites possess a strong affinity for inactive Co2+ sites and anchor over the surface of (111) crystal plane, which increases the metalâsupport interaction of the Pt1âCo3O4 material and accelerates the rate of oxygen vacancies regeneration. In turn, this is determined to promote the coadsorption of the probe methanol molecule and O2. Density functional theory calculations confirm that the electron transfer over the oxygen vacancies reduces both the methanol adsorption energy and activation barriers for methanol oxidation, which is proposed to significantly enhance the dissociation of the CH bond in the methanol decomposition reaction. This investigation serves as a solid foundation for characterizing and understanding singleâatom catalysts for heterogeneous oxidation reactions
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