Evolution of structure of SiO2 nanoparticles upon cooling from the melt

Evolution of structure of spherical SiO2 nanoparticles upon cooling from the melt has been investigated via molecular-dynamics (MD) simulations under non-periodic boundary conditions (NPBC). We use the pair interatomic potentials which have weak Coulomb interaction and Morse type short-range interaction. The change in structure of SiO2 nanoparticles upon cooling process has been studied through the partial radial distribution functions (PRDFs), coordination number and bond-angle distributions at different temperatures. The core and surface structures of nanoparticles have been studied in details. Our results show significant temperature dependence of structure of nanoparticles. Moreover, temperature dependence of concentration of structural defects in nanoparticles upon cooling from the melt toward glassy state has been found and discussed.Comment: 12 pages, 6 figure

An isogeometric analysis for elliptic homogenization problems

A novel and efficient approach which is based on the framework of isogeometric analysis for elliptic homogenization problems is proposed. These problems possess highly oscillating coefficients leading to extremely high computational expenses while using traditional finite element methods. The isogeometric analysis heterogeneous multiscale method (IGA-HMM) investigated in this paper is regarded as an alternative approach to the standard Finite Element Heterogeneous Multiscale Method (FE-HMM) which is currently an effective framework to solve these problems. The method utilizes non-uniform rational B-splines (NURBS) in both macro and micro levels instead of standard Lagrange basis. Beside the ability to describe exactly the geometry, it tremendously facilitates high-order macroscopic/microscopic discretizations thanks to the flexibility of refinement and degree elevation with an arbitrary continuity level provided by NURBS basis functions. A priori error estimates of the discretization error coming from macro and micro meshes and optimal micro refinement strategies for macro/micro NURBS basis functions of arbitrary orders are derived. Numerical results show the excellent performance of the proposed method

A Renormalization Group Improved Calculation of Top Quark Production near Threshold

The top quark cross section close to threshold in $e^+e^-$ annihilation is computed including the summation of logarithms of the velocity at next-to-next-to-leading-logarithmic order in QCD. The remaining theoretical uncertainty in the normalization of the total cross section is at the few percent level, an order of magnitude smaller than in previous next-to-next-to-leading order calculations. This uncertainty is smaller than the effects of a light standard model Higgs boson.Comment: changed figures, added reference

A new scenario of dynamical heterogeneity in supercooled liquid and glassy states of 2D monatomic system

Via analysis of spatio-temporal arrangements of atoms based on their dynamics in supercooled liquid and glassy states of 2D monatomic system with a double-well Lennard-Jones-Gauss (LJG) interaction potential, we find a new scenario of dynamical heterogeneity. Atoms with the same or very close mobility have a tendency to aggregate into clusters. Number of atoms with high mobility (and size of their clusters) increases with decreasing temperature passing over a maximum before decreasing downto zero. Position of the peak moves toward a lower temperature if mobility of atoms in clusters is lower together with an enhancement of height of the peak. In contrast, number of atoms with very low mobility or solidlike atoms (and size of their clusters) has a tendency to increase with decreasing temperature and then it suddenly increases in the vicinity of glass transition temperature leading to the formation of a glassy state. A sudden increase in the number of strongly correlated solidlike atoms in the vicinity of a glass transition temperature ( ) may be an origin of a drastical increase in viscosity of the glass-forming systems approaching glass transition. The fact, we find that diffusion coefficient decays exponentially with fraction of solidlike atoms exhibiting a sudden decrease in the vicinity of glass transition region

A High Efficiency Lateral Light Emitting Device on SOI

The infrared light emission of lateral p/sup +/-p-n/sup +/ diodes realized on SIMOX-SOI (separation by implantation of oxygen - silicon on insulator) substrates has been studied. The confinement of the free carriers in one dimension due to the buried oxide was suggested to be a key point to increase the band-to-band recombination probability in silicon light emitters. We found in our devices an external quantum efficiency comparable to previous results presented in the literature. The wavelength range of the emission was found to be 900-1300 nm which is common for indirect band to band recombination in Si. The SOI technology incorporates an insulating layer between the thin single crystal silicon layer and the much thicker substrate. This electrically insulating layer is also a thermal isolator and so self-heating effects are common in devices fabricated on SOI wafers. Investigation of its influence on the light emission and the light distribution in the device has been carried out in our research. In this paper, the characteristics of the device with different active region lengths were investigated and explained quantitatively based on the recombination rate of carriers inside the active area by using the simulation model in Silvaco

Online user behavioural modeling with applications to price steering

Price steering is the practice of “changing the order of search results to highlight specific products” and products prices. In this paper, we show an initial investigation to quantify the price steering level in search results shown to different kind of users on Google Shopping. We mimic the category of affluent users. Affluent users visit websites offering expensive services, search for luxury goods and always click on the most costly items results at Google Shopping. The goal is checking if users trained in specific ways get different search results, based on the price of the products in the results. Evaluation is based on well known metrics to measure page results differences and similarities. Experiments are automised, rendering large-scale investigations feasible. Results of our experiments, based on a preliminary experimental setting, show that users trained on some particular topics are not always influenced by previous search and click activities. However, different trained users actually achieve different search results, thus paving the way for further investigation

Selection and reconstruction of the top quarks in the all-hadronic decays at a Linear Collider

A method of reconstruction of the top quarks produced in the process E+E- -> t\bar{t} -> 6 jets at a Linear Collider (LC) is proposed. The approach does not involve a kinematic fit, as well as assumptions on the invariant masses of the dijets originating from the decays of W bosons and, therefore, the method is expected to be less sensitive to theoretical and experimental uncertainties on the top-mass measurement than traditional reconstruction methods. For the first time, the reconstruction of the top quarks was investigated using the full LC detector simulation after taking into account the background arising from QCD multi-jet production.Comment: 22 pages, including 13 figures and 3 table