We report on the evolution of the thickness-dependent electronic band structure of the two-dimensional layered-dichalcogenide molybdenum disulfide (MoS2). Micrometer-scale angle-resolved photoemission spectroscopy of ...
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We report on the evolution of the thickness-dependent electronic band structure of the two-dimensional layered-dichalcogenide molybdenum disulfide (MoS2). Micrometer-scale angle-resolved photoemission spectroscopy of mechanically exfoliated and chemical-vapor-deposition-grown crystals provides direct evidence for the shifting of the valence band maximum from Γ¯ to K¯, for the case of MoS2 having more than one layer, to the case of single-layer MoS2, as predicted by density functional theory. This evolution of the electronic structure from bulk to few-layer to monolayer MoS2 had earlier been predicted to arise from quantum confinement. Furthermore, one of the consequences of this progression in the electronic structure is the dramatic increase in the hole effective mass, in going from bulk to monolayer MoS2 at its Brillouin zone center, which is known as the cause for the decreased carrier mobility of the monolayer form compared to that of bulk MoS2.
We present a quantitative method for relating system matrices to the complete-data space in maximum likelihood expectation maximization (MLEM) using the Kullback-Leibler distance. We show that a more accurate system m...
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We present a quantitative method for relating system matrices to the complete-data space in maximum likelihood expectation maximization (MLEM) using the Kullback-Leibler distance. We show that a more accurate system matrix has a smaller Kullback-Leibler (KL) distance. System matrices of a coded aperture imaging system were used for comparison. The calculation of the KL distance is based on the Monte Carlo integral. We note that system matrices for the KL distance evaluation should be generated by underlying physics processes.
We consider the problem of finding steady states of the two-dimensional Euler equation from topology-preserving rearrangements of a given vorticity distribution. We begin by briefly reviewing a range of available nume...
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We consider the problem of finding steady states of the two-dimensional Euler equation from topology-preserving rearrangements of a given vorticity distribution. We begin by briefly reviewing a range of available numerical methodologies. We then focus on a recently introduced technique, which enables the computation of steady vortices with (1) compact vorticity support, (2) prescribed topology, (3) multiple scales, (4) arbitrary stability, and (5) arbitrary symmetry. We highlight a recent set of results, involving the branch of solutions originating at the first bifurcation of the Kirchhoff elliptical vortices. Remarkably, one finds that, as the end of the branch is approached, the family of solutions traces a spiral in a bifurcation diagram involving the rotational velocity and impulse of the configuration. We next show a new set of results, comprising the near-limiting states for a von Kármán street of uniform, finite-area vortices. Building the bifurcation diagram for this flow also reveals a spiral. These and other recent results hint at the possibility that such spirals may constitute a universal feature of families of uniform-vorticity flows.
A simple model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn is constructed and quantitatively compared to the results of recent measurements [A. H. Mack et al., J. Mol. Biol. 423...
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A simple model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn is constructed and quantitatively compared to the results of recent measurements [A. H. Mack et al., J. Mol. Biol. 423, 687 (2012)]. First, a coarse-grained model for the histone-DNA free-energy landscape that incorporates both an elastic free-energy barrier and specific histone-DNA bonds is developed. Next, a theoretical expression for the rate of transitions across a piecewise linear free-energy landscape with multiple minima and maxima is presented. Then, the model free-energy landscape, approximated as a piecewise linear function, and the theoretical expression for the transition rates are combined to construct a model for the force-dependent unwinding and rewinding rates of the nucleosome inner turn. Least-mean-squares fitting of the model rates to the rates observed in recent experiments rates demonstrates that this model is able to well describe the force-dependent unwinding and rewinding rates of the nucleosome inner turn, observed in the recent experiments, except at the highest forces studied, where an additional ad hoc term is required to describe the data, which may be interpreted as an indication of an alternate high-force nucleosome disassembly pathway, that bypasses simple unwinding. The good agreement between the measurements and the model at lower forces demonstrates that both specific histone-DNA contacts and an elastic free-energy barrier play essential roles for nucleosome winding and unwinding, and quantifies their relative contributions.
A class of double‐perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended s...
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A class of double‐perovskite compounds display fast oxygen ion diffusion and high catalytic activity toward oxygen reduction while maintaining excellent compatibility with the electrolyte. The astoundingly extended stability of NdBa 1− x Ca x Co 2 O 5+ δ (NBCaCO) under both air and CO 2 ‐containing atmosphere is reported along with excellent electrochemical performance by only Ca doping into the A site of NdBaCo 2 O 5+ δ (NBCO). The enhanced stability can be ascribed to both the increased electron affinity of mobile oxygen species with Ca, determined through density functional theory calculations and the increased redox stability from the coulometric titration.
Anomalous, vacancy-induced anisotropic thermal conductivity is one of the important properties in the recently discovered high-ZT In4Se3−x compound. In this work, the lattice thermal conductivity of In4Se3−x is invest...
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Anomalous, vacancy-induced anisotropic thermal conductivity is one of the important properties in the recently discovered high-ZT In4Se3−x compound. In this work, the lattice thermal conductivity of In4Se3−x is investigated using equilibrium molecular dynamics simulation, the point-defect model, and ab initio calculations. The charge density distribution shows highly anisotropic structure with strong bonding along In-Se-In chain direction. Se vacancy strongly suppresses the phonon propagation along the chain direction, with little change in other directions. We show that suppressed long-range acoustic phonon transport caused by the vacancy results in anisotropic change of lattice conductivity. We suggest controlling of vacancy in intrinsic low-dimensional compounds is critical in achieving optimal lattice thermal conductivity and other thermoelectric properties.
Nanopillar array is an indispensable functional structure for many scientific researches. In this paper, one kind of nanopillar structure array with the pillars’ diameter far smaller than Abbe’s diffraction limit is...
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Nanopillar array is an indispensable functional structure for many scientific researches. In this paper, one kind of nanopillar structure array with the pillars’ diameter far smaller than Abbe’s diffraction limit is realized on negative tone photoresist film with our developed donut-shaped 532nm visible CW laser direct system, the average diameter of nanopillars is about 65nm and the smallest diameter is 48nm, which is about 1/11 of the incident laser wavelength. In addition, the main factors such as the coma and astigmatism effect are studied in detail with numerical simulation for achieving high-quality prospective nanoscale patterns. This preliminary work demonstrates a novel, easy and effective method of CW laser direct writing system for fabricating nanopillar/pore arrays with sub-diffraction dimensions.
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