9,338 research outputs found
SIMDET - Version 4 A Parametric Monte Carlo for a TESLA Detector
A new release of the parametric detector Monte Carlo program \verb+SIMDET+
(version 4.01) is now available. We describe the principles of operation and
the usage of this program to simulate the response of a detector for the TESLA
linear collider. The detector components are implemented according to the TESLA
Technical Design Report. All detector component responses are treated in a
realistic way using a parametrisation of results from the {\em ab initio} Monte
Carlo program \verb+BRAHMS+. Pattern recognition is emulated using a complete
cross reference between generated particles and detector response. Also, for
charged particles, the covariance matrix and information are made
available. An idealised energy flow algorithm defines the output of the
program, consisting of particles generically classified as electrons, photons,
muons, charged and neutral hadrons as well as unresolved clusters. The program
parameters adjustable by the user are described in detail. User hooks inside
the program and the output data structure are documented.Comment: 30 pages, 7 figure
Two-step rocket engine bipropellant valve Patent
Solenoid two-step valve for bipropellant flow rate control to rocket engin
Two-step rocket engine bipropellant valve concept
Initiating combustion of altitude control rocket engines in a precombustion chamber of ductile material reduces high pressure surges generated by hypergolic propellants. Two-step bipropellant valve concepts control initial propellant flow into precombustion chamber and subsequent full flow into main chamber
Endoscopic Imaging of Clostridium diffìcile Colitis
AbstractClostridium difficile infection (CDI) is one of the most dreaded causes of hospital-acquired diarrhea with an increasing incidence. Frequently, CDI affects older and immunocompromised patients, but recent data suggests that even young and healthy persons who had previously not been exposed to an antimicrobial therapy are at risk. Although differential diagnosis of hospital-acquired diarrhea is broad, these patients are regularly committed to the endoscopy department. The video of this article focuses on typical endoscopic aspects of C. difficile colitis. This article is part of an expert video encyclopedia
Dielectrophoresis model for the colossal electroresistance of phase-separated manganites
We propose a dielectrophoresis model for phase-separated manganites. Without
increase of the fraction of metallic phase, an insulator-metal transition
occurs when a uniform electric field applied across the system exceeds a
threshold value. Driven by the dielectrophoretic force, the metallic clusters
reconfigure themselves into stripes along the direction of electric field,
leading to the filamentous percolation. This process, which is time-dependent,
irreversible and anisotropic, is a probable origin of the colossal
electroresistance in manganites.Comment: 4 pages, 5 figure
Patterning of dielectric nanoparticles using dielectrophoretic forces generated by ferroelectric polydomain films
A theoretical study of a dielectrophoretic force, i.e. the force acting on an
electrically neutral particle in the inhomogeneous electric field, which is
produced by a ferroelectric domain pattern, is presented. It has been shown by
several researchers that artificially prepared domain patterns with given
geometry in ferroelectric single crystals represent an easy and flexible method
for patterning dielectric nanoobjects using dielectrophoretic forces. The
source of the dielectrophoretic force is a strong and highly inhomogeneous
(stray) electric field, which exists in the vicinity of the ferroelectric
domain walls at the surface of the ferroelectric film. We analyzed
dielectrophoretic forces in the model of a ferroelectric film of a given
thickness with a lamellar 180 domain pattern. The analytical formula
for the spatial distribution of the stray field in the ionic liquid above the
top surface of the film is calculated including the effect of free charge
screening. The spatial distribution of the dielectrophoretic force produced by
the domain pattern is presented. The numerical simulations indicate that the
intersection of the ferroelectric domain wall and the surface of the
ferroelectric film represents a trap for dielectric nanoparticles in the case
of so called positive dielectrophoresis. The effects of electrical neutrality
of dielectric nanoparticles, free charge screening due to the ionic nature of
the liquid, domain pattern geometry, and the Brownian motion on the mechanism
of nanoparticle deposition and the stability of the deposited pattern are
discussed.Comment: Accepted in the Journal of Applied Physics, 10 pages, 5 figure
Coulomb crystallization in expanding laser-cooled neutral plasmas
We present long-time simulations of expanding ultracold neutral plasmas,
including a full treatment of the strongly coupled ion dynamics. Thereby, the
relaxation dynamics of the expanding laser-cooled plasma is studied, taking
into account elastic as well as inelastic collisions. It is demonstrated that,
depending on the initial conditions, the ionic component of the plasma may
exhibit short-range order or even a superimposed long-range order resulting in
concentric ion shells. In contrast to ionic plasmas confined in traps, the
shell structures are built up from the center of the plasma cloud rather than
from the periphery
On knotted streamtubes in incompressible hydrodynamical flow and a restricted conserved quantity
For certain families of fluid flow, a new conserved quantity --
stream-helicity -- has been established.Using examples of linked and knotted
streamtubes, it has been shown that stream-helicity does, in certain cases,
entertain itself with a very precise topological meaning viz, measure of the
degree of knottedness or linkage of streamtubes.As a consequence,
stream-helicity emerges as a robust topological invariant.Comment: This extended version is the basically a more clarified version of
the previous submission physics/0611166v
On the formation and decay of a molecular ultracold plasma
Double-resonant photoexcitation of nitric oxide in a molecular beam creates a
dense ensemble of Rydberg states, which evolves to form a plasma of
free electrons trapped in the potential well of an NO spacecharge. The
plasma travels at the velocity of the molecular beam, and, on passing through a
grounded grid, yields an electron time-of-flight signal that gauges the plasma
size and quantity of trapped electrons. This plasma expands at a rate that fits
with an electron temperature as low as 5 K, colder that typically observed for
atomic ultracold plasmas. The recombination of molecular NO cations with
electrons forms neutral molecules excited by more than twice the energy of the
NO chemical bond, and the question arises whether neutral fragmentation plays a
role in shaping the redistribution of energy and particle density that directs
the short-time evolution from Rydberg gas to plasma. To explore this question,
we adapt a coupled rate-equations model established for atomic ultracold
plasmas to describe the energy-grained avalanche of electron-Rydberg and
electron-ion collisions in our system. Adding channels of Rydberg
predissociation and two-body, electron- cation dissociative recombination to
the atomic formalism, we investigate the kinetics by which this relaxation
distributes particle density and energy over Rydberg states, free electrons and
neutral fragments. The results of this investigation suggest some mechanisms by
which molecular fragmentation channels can affect the state of the plasma
Electron Temperature Evolution in Expanding Ultracold Neutral Plasmas
We have used the free expansion of ultracold neutral plasmas as a
time-resolved probe of electron temperature. A combination of experimental
measurements of the ion expansion velocity and numerical simulations
characterize the crossover from an elastic-collision regime at low initial
Gamma_e, which is dominated by adiabatic cooling of the electrons, to the
regime of high Gamma_e in which inelastic processes drastically heat the
electrons. We identify the time scales and relative contributions of various
processes, and experimentally show the importance of radiative decay and
disorder-induced electron heating for the first time in ultracold neutral
plasmas
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