5,415 research outputs found
An algorithm for calculating the Lorentz angle in silicon detectors
Future experiments will use silicon sensors in the harsh radiation
environment of the LHC (Large Hadron Collider) and high magnetic fields. The
drift direction of the charge carriers is affected by the Lorentz force due to
the high magnetic field. Also the resulting radiation damage changes the
properties of the drift.
In this paper measurements of the Lorentz angle of electrons and holes before
and after irradiation are reviewed and compared with a simple algorithm to
compute the Lorentz angle.Comment: 13 pages, 7 figures, final version accepted by NIMA. Mainly
clarifications included and slightly shortene
Higher order glass-transition singularities in colloidal systems with attractive interactions
The transition from a liquid to a glass in colloidal suspensions of particles
interacting through a hard core plus an attractive square-well potential is
studied within the mode-coupling-theory framework. When the width of the
attractive potential is much shorter than the hard-core diameter, a reentrant
behavior of the liquid-glass line, and a glass-glass-transition line are found
in the temperature-density plane of the model. For small well-width values, the
glass-glass-transition line terminates in a third order bifurcation point, i.e.
in a A_3 (cusp) singularity. On increasing the square-well width, the
glass-glass line disappears, giving rise to a fourth order A_4 (swallow-tail)
singularity at a critical well width. Close to the A_3 and A_4 singularities
the decay of the density correlators shows stretching of huge dynamical
windows, in particular logarithmic time dependence.Comment: 19 pages, 12 figures, Phys. Rev. E, in prin
Finite size effects on transport coefficients for models of atomic wires coupled to phonons
We consider models of quasi-1-d, planar atomic wires consisting of several,
laterally coupled rows of atoms, with mutually non-interacting electrons. This
electronic wire system is coupled to phonons, corresponding, e.g., to some
substrate. We aim at computing diffusion coefficients in dependence on the wire
widths and the lateral coupling. To this end we firstly construct a numerically
manageable linear collision term for the dynamics of the electronic occupation
numbers by following a certain projection operator approach. By means of this
collision term we set up a linear Boltzmann equation. A formula for extracting
diffusion coefficients from such Boltzmann equations is given. We find in the
regime of a few atomic rows and intermediate lateral coupling a significant and
non-trivial dependence of the diffusion coefficient on both, the width and the
lateral coupling. These results, in principle, suggest the possible
applicability of such atomic wires as electronic devices, such as, e.g.,
switches.Comment: 9 pages, 5 figures, accepted for publication in Eur. Phys. J.
How does the relaxation of a supercooled liquid depend on its microscopic dynamics?
Using molecular dynamics computer simulations we investigate how the
relaxation dynamics of a simple supercooled liquid with Newtonian dynamics
differs from the one with a stochastic dynamics. We find that, apart from the
early beta-relaxation regime, the two dynamics give rise to the same relaxation
behavior. The increase of the relaxation times of the system upon cooling, the
details of the alpha-relaxation, as well as the wave vector dependence of the
Edwards-Anderson-parameters are independent of the microscopic dynamics.Comment: 6 pages of Latex, 4 figure
Desingularization of vortices for the Euler equation
We study the existence of stationary classical solutions of the
incompressible Euler equation in the plane that approximate singular
stationnary solutions of this equation. The construction is performed by
studying the asymptotics of equation -\eps^2 \Delta
u^\eps=(u^\eps-q-\frac{\kappa}{2\pi} \log \frac{1}{\eps})_+^p with Dirichlet
boundary conditions and a given function. We also study the
desingularization of pairs of vortices by minimal energy nodal solutions and
the desingularization of rotating vortices.Comment: 40 page
Molecular dynamics simulation of the fragile glass former ortho-terphenyl: a flexible molecule model
We present a realistic model of the fragile glass former orthoterphenyl and
the results of extensive molecular dynamics simulations in which we
investigated its basic static and dynamic properties. In this model the
internal molecular interactions between the three rigid phenyl rings are
described by a set of force constants, including harmonic and anharmonic terms;
the interactions among different molecules are described by Lennard-Jones
site-site potentials. Self-diffusion properties are discussed in detail
together with the temperature and momentum dependencies of the
self-intermediate scattering function. The simulation data are compared with
existing experimental results and with the main predictions of the Mode
Coupling Theory.Comment: 20 pages and 28 postscript figure
Lorentz angle measurements in irradiated silicon detectors between 77 K and 300 K
Future experiments are using silicon detectors in a high radiation
environment and in high magnetic fields. The radiation tolerance of silicon
improves by cooling it to temperatures below 180 K. At low temperatures the
mobility increases, which leads to larger deflections of the charge carriers by
the Lorentz force. A good knowledge of the Lorentz angle is needed for design
and operation of silicon detectors. We present measurements of the Lorentz
angle between 77 K and 300 K before and after irradiation with a primary beam
of 21 MeV protons.Comment: 13 pages, 9 figures, submitted to ICHEP2000, Osaka, Japa
Comparative simulation study of colloidal gels and glasses
Using computer simulations, we identify the mechanisms causing aggregation
and structural arrest of colloidal suspensions interacting with a short-ranged
attraction at moderate and high densities. Two different non-ergodicity
transitions are observed. As the density is increased, a glass transition takes
place, driven by excluded volume effects. In contrast, at moderate densities,
gelation is approached as the strength of the attraction increases. At high
density and interaction strength, both transitions merge, and a logarithmic
decay in the correlation function is observed. All of these features are
correctly predicted by mode coupling theory
Adolescent brain cognitive development (ABCD) study: Overview of substance use assessment methods.
One of the objectives of the Adolescent Brain Cognitive Development (ABCD) Study (https://abcdstudy.org/) is to establish a national longitudinal cohort of 9 and 10 year olds that will be followed for 10 years in order to prospectively study the risk and protective factors influencing substance use and its consequences, examine the impact of substance use on neurocognitive, health and psychosocial outcomes, and to understand the relationship between substance use and psychopathology. This article provides an overview of the ABCD Study Substance Use Workgroup, provides the goals for the workgroup, rationale for the substance use battery, and includes details on the substance use module methods and measurement tools used during baseline, 6-month and 1-year follow-up assessment time-points. Prospective, longitudinal assessment of these substance use domains over a period of ten years in a nationwide sample of youth presents an unprecedented opportunity to further understand the timing and interactive relationships between substance use and neurocognitive, health, and psychopathology outcomes in youth living in the United States
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