9,107 research outputs found
High-fidelity simulations of CdTe vapor deposition from a new bond-order potential-based molecular dynamics method
CdTe has been a special semiconductor for constructing the lowest-cost solar
cells and the CdTe-based Cd1-xZnxTe alloy has been the leading semiconductor
for radiation detection applications. The performance currently achieved for
the materials, however, is still far below the theoretical expectations. This
is because the property-limiting nanoscale defects that are easily formed
during the growth of CdTe crystals are difficult to explore in experiments.
Here we demonstrate the capability of a bond order potential-based molecular
dynamics method for predicting the crystalline growth of CdTe films during
vapor deposition simulations. Such a method may begin to enable defects
generated during vapor deposition of CdTe crystals to be accurately explored
Nucleotide-binding oligomerization domain-containing protein 2 (Nod2) modulates T1DM susceptibility by gut microbiota
Nucleotide-binding oligomerization domain-containing protein 2 (Nod2) is an innate immune receptor. To investigate the role of Nod2 in susceptibility to the autoimmune disease, type 1 diabetes mellitus (T1DM), we generated Nod2-/- non-obese diabetic (NOD) mice. The Nod2-/-NOD mice had different composition of the gut microbiota compared to Nod2+/+NOD mice and were significantly protected from diabetes, but only when housed separately from Nod2+/+NOD mice. This suggested that T1DM susceptibility in Nod2-/-NOD mice is dependent on the alteration of gut microbiota, which modulated the frequency and function of IgA-secreting B-cells and IL-10 promoting T-regulatory cells. Finally, colonizing germ-free NOD mice with Nod2-/-NOD gut microbiota significantly reduced pro-inflammatory cytokine-secreting immune cells but increased T-regulatory cells. Thus, gut microbiota modulate the immune system and T1D susceptibility. Importantly, our study raises a critical question about the housing mode in the interpretation of the disease phenotype of genetically-modified mouse strains in T1DM studies
Single- and multi-walled carbon nanotubes viewed as elastic tubes with Young's moduli dependent on layer number
The complete energy expression of a deformed single-walled carbon nanotube
(SWNT) is derived in the continuum limit from the local density approximation
model proposed by Lenosky {\it et al.} \lbrack Nature (London) {\bf 355}, 333
(1992)\rbrack and shows to be content with the classic shell theory by which
the Young's modulus, the Poisson ratio and the effective wall thickness of
SWNTs are obtained as TPa, , , respectively.
The elasticity of a multi-walled carbon nanotube (MWNT) is investigated as the
combination of the above SWNTs of layer distance and the
Young's modulus of the MWNT is found to be an apparent function of the number
of layers, , varying from 4.70TPa to 1.04TPa for N=1 to .Comment: 4 pages, 1 figur
Statistical mechanics of image restoration and error-correcting codes
We develop a statistical-mechanical formulation for image restoration and
error-correcting codes. These problems are shown to be equivalent to the Ising
spin glass with ferromagnetic bias under random external fields. We prove that
the quality of restoration/decoding is maximized at a specific set of parameter
values determined by the source and channel properties. For image restoration
in mean-field system a line of optimal performance is shown to exist in the
parameter space. These results are illustrated by solving exactly the
infinite-range model. The solutions enable us to determine how precisely one
should estimate unknown parameters. Monte Carlo simulations are carried out to
see how far the conclusions from the infinite-range model are applicable to the
more realistic two-dimensional case in image restoration.Comment: 20 pages, 9 figures, ReVTe
Enhancing Transport Efficiency by Hybrid Routing Strategy
Traffic is essential for many dynamic processes on real networks, such as
internet and urban traffic systems. The transport efficiency of the traffic
system can be improved by taking full advantage of the resources in the system.
In this paper, we propose a dual-strategy routing model for network traffic
system, to realize the plenary utility of the whole network. The packets are
delivered according to different "efficient routing strategies" [Yan, et al,
Phys. Rev. E 73, 046108 (2006)]. We introduce the accumulate rate of packets,
{\eta} to measure the performance of traffic system in the congested phase, and
propose the so-called equivalent generation rate of packet to analyze the
jamming processes. From analytical and numerical results, we find that, for
suitable selection of strategies, the dual- strategy system performs better
than the single-strategy system in a broad region of strategy mixing ratio. The
analytical solution to the jamming processes is verified by estimating the
number of jammed nodes, which coincides well with the result from simulation.Comment: 6 pages, 3 figure
Electronic Properties of Vinylene-Linked Heterocyclic Conducting Polymers: Predictive Design and Rational Guidance from DFT Calculations
The band structure and electronic properties in a series of vinylene-linked
heterocyclic conducting polymers are investigated using density functional
theory (DFT). In order to accurately calculate electronic band gaps, we utilize
hybrid functionals with fully periodic boundary conditions to understand the
effect of chemical functionalization on the electronic structure of these
materials. The use of predictive first-principles calculations coupled with
simple chemical arguments highlights the critical role that aromaticity plays
in obtaining a low band gap polymer. Contrary to some approaches which
erroneously attempt to lower the band gap by increasing the aromaticity of the
polymer backbone, we show that being aromatic (or quinoidal) in itself does not
insure a low band gap. Rather, an iterative approach which destabilizes the
ground state of the parent polymer towards the aromatic \leftrightarrow
quinoidal level-crossing on the potential energy surface is a more effective
way of lowering the band gap in these conjugated systems. Our results highlight
the use of predictive calculations guided by rational chemical intuition for
designing low band gap polymers in photovoltaic materials.Comment: Accepted by the Journal of Physical Chemistry
Rotation Symmetry Spontaneous Breaking of Edge States in Zigzag Carbon Nanotubes
Analytical solutions of the edge states were obtained for the (N, 0) type
carbon nanotubes with distorted ending bonds. It was found that the edge states
are mixed via the distortion. The total energies for N=5 and N>=7 are lower in
the asymmetric configurations of ending bonds than those having axial rotation
symmetry. Thereby the symmetry is breaking spontaneously. The results imply
that the symmetry of electronic states at the apex depends on the occupation;
the electron density pattern at the apex could change dramatically and could be
controlled by applying an external field.Comment: 19 pages, 3 figure
Optoelectronic Properties of Carbon Nanorings: Excitonic Effects from Time-Dependent Density Functional Theory
The electronic structure and size-scaling of optoelectronic properties in
cycloparaphenylene carbon nanorings are investigated using time-dependent
density functional theory (TDDFT). The TDDFT calculations on these molecular
nanostructures indicate that the lowest excitation energy surprisingly becomes
larger as the carbon nanoring size is increased, in contradiction with typical
quantum confinement effects. In order to understand their unusual electronic
properties, I performed an extensive investigation of excitonic effects by
analyzing electron-hole transition density matrices and exciton binding
energies as a function of size in these nanoring systems. The transition
density matrices allow a global view of electronic coherence during an
electronic excitation, and the exciton binding energies give a quantitative
measure of electron-hole interaction energies in the nanorings. Based on
overall trends in exciton binding energies and their spatial delocalization, I
find that excitonic effects play a vital role in understanding the unique
photoinduced dynamics in these carbon nanoring systems.Comment: Accepted by the Journal of Physical Chemistry
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