249 research outputs found
Determination of the levitation limits of dust particles within the sheath in complex plasma experiments
Experiments are performed in which dust particles are levitated at varying
heights above the powered electrode in a RF plasma discharge by changing the
discharge power. The trajectories of particles dropped from the top of the
discharge chamber are used to reconstruct the vertical electric force acting on
the particles. The resulting data, together with the results from a
selfconsistent fluid model, are used to determine the lower levitation limit
for dust particles in the discharge and the approximate height above the lower
electrode where quasineutrality is attained, locating the sheath edge. These
results are then compared with current sheath models. It is also shown that
particles levitated within a few electron Debye lengths of the sheath edge are
located outside the linearly increasing portion of the electric field
The Effect of Industrial Tax Exemptions on School Board Revenues in Selected Parishes of Louisiana.
Landau-Zener-St\"uckelberg interferometry in pair production from counterpropagating lasers
The rate of electron-positron pair production in linearly polarized
counter-propagating lasers is evaluated from a recently discovered solution of
the time-dependent Dirac equation. The latter is solved in momentum space where
it is formally equivalent to the Schr\"odinger equation describing a strongly
driven two-level system. The solution is found from a simple transformation of
the Dirac equation and is given in compact form in terms of the
doubly-confluent Heun's function. By using the analogy with the two-level
system, it is shown that for high-intensity lasers, pair production occurs
through periodic non-adiabatic transitions when the adiabatic energy gap is
minimal. These transitions give rise to an intricate interference pattern in
the pair spectrum, reminiscent of the Landau-Zener-St\"uckelberg phenomenon in
molecular physics: the accumulated phase result in constructive or destructive
interference. The adiabatic-impulse model is used to study this phenomenon and
shows an excellent agreement with the exact result.Comment: 22 pages, 7 figure
The effect of thermophoresis on the discharge parameters in complex plasma experiments
Thermophoresis is a tool often applied in complex plasma experiments. One of
the usual stated benefits over other experimental tools is that changes induced
by thermophoresis neither directly depend on, nor directly influence, the
plasma parameters. From electronic data, plasma emission profiles in the
sheath, and Langmuir probe data in the plasma bulk, we conclude that this
assumption does not hold. An important effect on the levitation of dust
particles in argon plasma is observed as well. The reason behind the changes in
plasma parameters seems to be the change in neutral atom density accompanying
the increased gas temperature while running at constant pressure.Comment: 14 pages, 12 figure
Experimental and computational characterization of a modified GEC cell for dusty plasma experiments
A self-consistent fluid model developed for simulations of micro- gravity
dusty plasma experiments has for the first time been used to model asymmetric
dusty plasma experiments in a modified GEC reference cell with gravity. The
numerical results are directly compared with experimental data and the
experimentally determined dependence of global discharge parameters on the
applied driving potential and neutral gas pressure is found to be well matched
by the model. The local profiles important for dust particle transport are
studied and compared with experimentally determined profiles. The radial forces
in the midplane are presented for the different discharge settings. The
differences between the results obtained in the modified GEC cell and the
results first reported for the original GEC reference cell are pointed out
Models and experimental results from the wide aperture Nb-Ti magnets for the LHC upgrade
MQXC is a Nb-Ti quadrupole designed to meet the accelerator quality
requirements needed for the phase-1 LHC upgrade, now superseded by the high
luminosity upgrade foreseen in 2021. The 2-m-long model magnet was tested at
room temperature and 1.9 K. The technology developed for this magnet is
relevant for other magnets currently under development for the high-luminosity
upgrade, namely D1 (at KEK) and the large aperture twin quadrupole Q4 (at CEA).
In this paper we present MQXC test results, some of the specialized heat
extraction features, spot heaters, temperature sensor mounting and voltage tap
development for the special open cable insulation. We look at some problem
solving with noisy signals, give an overview of electrical testing, look at how
we calculate the coil resistance during at quench and show that the heaters are
not working We describe the quench signals and its timing, the development of
the quench heaters and give an explanation of an Excel quench calculation and
its comparison including the good agreement with the MQXC test results. We
propose an improvement to the magnet circuit design to reduce voltage to ground
values by factor 2. The program is then used to predict quench Hot-Spot and
Voltages values for the D1 dipole and the Q4 quadrupole.Comment: 8 pages, Contribution to WAMSDO 2013: Workshop on Accelerator Magnet,
Superconductor, Design and Optimization; 15 - 16 Jan 2013, CERN, Geneva,
Switzerlan
A Pilot Study to Evaluate Development Effort for High Performance Computing
The ability to write programs that execute efficiently on modern parallel computers has not been
fully studied. In a DARPA-sponsored project, we are looking at measuring the development time
for programs written for high performance computers (HPC). To attack this relatively novel
measurement problem, our goal is to initially measure such development time in student
programming to evaluate our own experimental protocols. Based on these results, we will
generate a set of feasible experimental methods that can then be applied with more confidence to
professional expert programmers.
This paper describes a first pilot study addressing those goals. We ran an observational study
with 15 students in a graduate level High Performance Computing class at the University of
Maryland. We collected data concerning development effort, developer activities and
chronology, and resulting code performance, for two programming assignments using different
HPC development approaches. While we did not find strong correlations between the expected
factors, the primary outputs of this study are a set of experimental lessons learned and 12 wellformed
hypotheses that will guard future study
A human coronavirus responsible for the common cold massively kills dendritic cells but not monocytes
Copyright @ 2012, American Society for Microbiology.Human coronaviruses are associated with upper respiratory tract infections that occasionally spread to the lungs and other organs. Although airway epithelial cells represent an important target for infection, the respiratory epithelium is also composed of an elaborate network of dendritic cells (DCs) that are essential sentinels of the immune system, sensing pathogens and presenting foreign antigens to T lymphocytes. In this report, we show that in vitro infection by human coronavirus 229E (HCoV-229E) induces massive cytopathic effects in DCs, including the formation of large syncytia and cell death within only few hours. In contrast, monocytes are much more resistant to infection and cytopathic effects despite similar expression levels of CD13, the membrane receptor for HCoV-229E. While the differentiation of monocytes into DCs in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4 requires 5 days, only 24 h are sufficient for these cytokines to sensitize monocytes to cell death and cytopathic effects when infected by HCoV-229E. Cell death induced by HCoV-229E is independent of TRAIL, FasL, tumor necrosis factor alpha, and caspase activity, indicating that viral replication is directly responsible for the observed cytopathic effects. The consequence of DC death at the early stage of HCoV-229E infection may have an impact on the early control of viral dissemination and on the establishment of long-lasting immune memory, since people can be reinfected multiple times by HCoV-229E
An Environment of Conducting Families of Software Engineering Experiments
The classroom is a valuable resource for conducting software engineering experiments. However, coordinating a family of experiments in classroom environments presents a number of challenges to researchers. This paper describes an environment that simplifies the process of collecting, managing and sanitizing data from classroom experiments, while minimizing disruption to natural subject behavior. We have successfully used this environment to study the impact of parallel programming languages on programmer productivity at multiple universities across the United States
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