1,132 research outputs found
Heterogeneous aggregation in binary colloidal alloys
Molecular dynamics (MD) simulation has been employed to study the
nonequilibrium structure formation of two types of particles in a colloidal
suspension, driven by type-dependent forces. We examined the time evolution of
structure formation as well as the structural properties of the resulting
aggregation by studying the radial distribution function (RDF). The resulting
aggregation is well described by a binary colloidal gelation. We compared the
structural properties to those for one type of particles. From the MD results,
it is evident that there are significant differences between the RDF's of the
two cases. Moreover, we found that the average coordination number is generally
larger in the monodisperse case for all area fractions considered. Thus, by
means of heterogeneous aggregation, it is possible to obtain a wide variety of
structures while more close-packed structures are formed for monodisperse
colloidal aggregation.Comment: 15 pages, 5 eps figures; preliminary results have been reported at
the APS March Meeting 2002; accepted by Physica
Molecular beam epitaxy of highly mismatched N-rich GaNSb and InNAs alloys
GaN materials alloyed with group V anions form the so-called highly mismatched alloys (HMAs). Recently, the authors succeeded in growing N-rich GaNAs and GaNBi alloys over a large composition range by plasma-assisted molecular beam epitaxy (PA-MBE). Here, they present first results on PA-MBE growth and properties of N-rich GaNSb and InNAs alloys and compare these with GaNAs and GaNBi alloys. The enhanced incorporation of As and Sb was achieved by growing the layers at extremely low growth temperatures. Although layers become amorphous for high As, Sb, and Bi content, optical absorption measurements show a progressive shift of the optical absorption edge to lower energy. The large band gap range and controllable conduction and valence band positions of these HMAs make them promising materials for efficient solar energy conversion devices
Numerical Simulation of the Damage Behavior of a Concrete Beam with an Anisotropic Damage Model
An anisotropic damage model was proposed to describe the nonlinear behavior of concrete beams under monotonic and cyclic loading. The hysteresis effect of concrete is approximately modeled by employing nonlinear loading/linear reloading stress paths in the model, which was implemented into ABAQUS. Linear, bilinear, exponential and Reinhardt strain softening functions are introduced to investigate their influence on accuracy of calculations.Предложена модель анизотропного повреждения для описания нелинейного поведения бетонных балок в условиях монотонного и циклического нагружения. Поведение бетона при гистерезисе ориентировочно моделируют с использованием траектории напряжения при нелинейной нагрузке/линейной перегрузке с последующей реализацией модели в программе ABAQUS. Введены линейная, билинейная, экспоненциальная функции и функция Рейнхардта деформации разуплотнения для изучения их влияния на точность расчетов
Pseudogap and precursor superconductivity in underdoped cuprate high temperature superconductors: A far-infrared ellipsometry study
Abstract.: With the technique of infrared ellipsometry we performed a detailed study of the temperature- and doping dependence of the c-axis response of a series of YBa2Cu3O7−δ single crystals. In particular, we explored the anomalous electronic properties at temperatures above the macroscopic superconducting transition temperature, T c, whose conflicting explanations range from a precursor superconducting state to electronic correlations that compete with superconductivity. We show that the c-axis spectra provide evidence that both kinds of correlations are present and that their contributions can be disentangled based on an analysis with a so-called multilayer-model. We find that the onset temperature, T *, and the energy scale, ΔPG, of the competing pseudogap increase rapidly towards the underdoped side whereas they vanish on the overdoped side. In addition, we provide evidence that in a strongly underdoped sample the precursor superconducting correlations develop below an onset temperature, T ons, that is considerably lower than T * but still much higher than T
Neutral top-pion and lepton flavor violating processes
In the context of topcolor-assisted techicolor(TC2) models, we study the
contributions of the neutral top-pion to the lepton flavor
violating(LFV) processes and .
We find that the present experimental bound on gives severe
constraints on the free parameters of models. Taking into account these
constraints, we consider the processes generated by
top-pion exchange at the tree-level and the one loop level, and obtain
, , in most of
the parameter space.Comment: latex files,16 pages, 6 figures. Submitted to Phys. Rev.
1/f Noise in Electron Glasses
We show that 1/f noise is produced in a 3D electron glass by charge
fluctuations due to electrons hopping between isolated sites and a percolating
network at low temperatures. The low frequency noise spectrum goes as
\omega^{-\alpha} with \alpha slightly larger than 1. This result together with
the temperature dependence of \alpha and the noise amplitude are in good
agreement with the recent experiments. These results hold true both with a
flat, noninteracting density of states and with a density of states that
includes Coulomb interactions. In the latter case, the density of states has a
Coulomb gap that fills in with increasing temperature. For a large Coulomb gap
width, this density of states gives a dc conductivity with a hopping exponent
of approximately 0.75 which has been observed in recent experiments. For a
small Coulomb gap width, the hopping exponent approximately 0.5.Comment: 8 pages, Latex, 6 encapsulated postscript figures, to be published in
Phys. Rev.
Cubic and hexagonal InGaAsN dilute arsenides by unintentional homogeneous incorporation of As into InGaN
Arsenic alloying is observed for epitaxial layers nominally intended to be In0.75Ga0.25N. Voids form beneath their interfaces with GaAs substrates, acting as sources of Ga + As out-diffusion into the growing epilayers. As a result, heteroepitaxial single-phase quaternary InxGa1-xAsyN1-y, films are formed with x similar to 0.55 and 0.05 menor que y menor que 0,10. While an undoped epilayer retains the wurtzite structure, a Mn-doped sample showed randomly spaced dopant segregations, which, together with a slightly higher As concentration, led to a transformation from the hexagonal to the twinned cubic phase
Littlest Higgs model and associated ZH production at high energy collider
In the context of the littlest Higgs (LH) model, we consider the Higgs
strahlung process . We find that the correction effects on
this process mainly come from the heavy photon . If we take the mixing
angle parameter in the range of 0.75 - 1, the contributions of the heavy
gauge boson is larger than 6%. In most of the parameter space, the
deviation of the total production cross section from its SM
value is larger than 5%, which may be detected in the future high energy
collider (LC) experiments. The future LC experiments could test
the LH model by measuring the cross section of the process .Comment: 13 pages, 3 figure
A rapid and cheap protocol for preparation of PCR templates in peanut
This paper describes a simple, low cost and reliable DNA template
preparation protocol for polymerase chain reaction (PCR) using immature
leaves from peanut seeds or leaves from field-grown plants. The
technique may find wide utility in studies involving PCR-based
molecular markers, rapid screening for transformants and gene cloning
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