25,702 research outputs found
A comparison of spectral element and finite difference methods using statically refined nonconforming grids for the MHD island coalescence instability problem
A recently developed spectral-element adaptive refinement incompressible
magnetohydrodynamic (MHD) code [Rosenberg, Fournier, Fischer, Pouquet, J. Comp.
Phys. 215, 59-80 (2006)] is applied to simulate the problem of MHD island
coalescence instability (MICI) in two dimensions. MICI is a fundamental MHD
process that can produce sharp current layers and subsequent reconnection and
heating in a high-Lundquist number plasma such as the solar corona [Ng and
Bhattacharjee, Phys. Plasmas, 5, 4028 (1998)]. Due to the formation of thin
current layers, it is highly desirable to use adaptively or statically refined
grids to resolve them, and to maintain accuracy at the same time. The output of
the spectral-element static adaptive refinement simulations are compared with
simulations using a finite difference method on the same refinement grids, and
both methods are compared to pseudo-spectral simulations with uniform grids as
baselines. It is shown that with the statically refined grids roughly scaling
linearly with effective resolution, spectral element runs can maintain accuracy
significantly higher than that of the finite difference runs, in some cases
achieving close to full spectral accuracy.Comment: 19 pages, 17 figures, submitted to Astrophys. J. Supp
Self-similar structure and experimental signatures of suprathermal ion distribution in inertial confinement fusion implosions
The distribution function of suprathermal ions is found to be self-similar
under conditions relevant to inertial confinement fusion hot-spots. By
utilizing this feature, interference between the hydro-instabilities and
kinetic effects is for the first time assessed quantitatively to find that the
instabilities substantially aggravate the fusion reactivity reduction. The ion
tail depletion is also shown to lower the experimentally inferred ion
temperature, a novel kinetic effect that may explain the discrepancy between
the exploding pusher experiments and rad-hydro simulations and contribute to
the observation that temperature inferred from DD reaction products is lower
than from DT at National Ignition Facility.Comment: Revised version accepted for publication in PRL. "Copyright (2015) by
the American Physical Society.
Attractive Potential around a Thermionically Emitting Microparticle
We present a simulation study of the charging of a dust grain immersed in a
plasma, considering the effect of electron emission from the grain (thermionic
effect). It is shown that the OML theory is no longer reliable when electron
emission becomes large: screening can no longer be treated within the
Debye-Huckel approach and an attractive potential well forms, leading to the
possibility of attractive forces on other grains with the same polarity. We
suggest to perform laboratory experiments where emitting dust grains could be
used to create non-conventional dust crystals or macro-molecules.Comment: 3 figures. To appear on Physical Review Letter
Dynamics of glycine receptor insertion in the neuronal plasma membrane
The exocytosis site of newly synthesized glycine receptor was defined by means of a morphological assay to characterize its export from the trans-Golgi Network to the plasma membrane. This was achieved by expressing in transfected neurons an alpha1 subunit bearing an N-terminal tag selectively cleavable from outside the cell by thrombin. This was combined with a transient temperature-induced block of exocytic transport that creates a synchronized exocytic wave. Immunofluorescence microscopy analysis of the cell surface appearance of newly synthesized receptor revealed that exocytosis mainly occurred at nonsynaptic sites in the cell body and the initial portion of dendrites. At the time of cell surface insertion, the receptors existed as discrete clusters. Quantitative analysis showed that glycine receptor clusters are stable in size and subsequently appeared in more distal dendritic regions. This localization resulted from diffusion in the plasma membrane and not from exocytosis of transport vesicles directed to dendrites. Kinetic analysis established a direct substrate-product relationship between pools of somatic and dendritic receptors. This indicated that clusters represent intermediates between newly synthesized and synaptic receptors. These results support a diffusion-retention model for the formation of receptor-enriched postsynaptic domains and not that of a vectorial intracellular targeting to synapses
Negotiated Development Denial Meets People\u27s Court: Del Monte Dunes Brings New Wildcards to Exactions Law
The United States Supreme Court Answered YES to the $1.45 million over exaction question for 1999. In City of Monterey v. Del Monte Dunes at Monterey Ltd., a unanimous court extended the scope of compensatory takings review beyond land dedication conditions into the realm of regulatory denial. Justice Kennedy\u27s opinion vitalized the legitimate state interests test from Agins v. City of Tiburon to sustain an inverse condemnation conclusion and damage award to the frustrated developer. A majority of the court also concurred that the trial court may delegate this takings conclusion to the jury under federal civil rights law. The activation of Agins\u27 substantive takings test in such challenges and the prospect of continued lay application of constitutional law to development restrictions add uncertain dimensions to exactions litigation at the millennium. In Del Monte Dunes, the Court also distinguished the instant development denial of an inverse condemnation claim from the land dedication conditions at issue in Dolan v. City of Tigard. This distinction enabled the unanimous Court to uphold the trial verdict based on Agins and avoid elements of the Ninth Circuit\u27s reasoning invoking the Dolan rough proportionality test. Other recent federal and state decisions also decline to extend Dolan\u27s applicability beyond individual land dedication development conditions to other forms of economic exactions. This year\u27s exactions and impact fee report focuses on Del Monte Dunes, namely its effects on negotiated development, trial practice, and on regulatory takings doctrine as defined by judges and juries in civil rights litigation
Negotiated Development Denial Meets People\u27s Court: Del Monte Dunes Brings New Wildcards to Exactions Law
The United States Supreme Court Answered YES to the $1.45 million over exaction question for 1999. In City of Monterey v. Del Monte Dunes at Monterey Ltd., a unanimous court extended the scope of compensatory takings review beyond land dedication conditions into the realm of regulatory denial. Justice Kennedy\u27s opinion vitalized the legitimate state interests test from Agins v. City of Tiburon to sustain an inverse condemnation conclusion and damage award to the frustrated developer. A majority of the court also concurred that the trial court may delegate this takings conclusion to the jury under federal civil rights law. The activation of Agins\u27 substantive takings test in such challenges and the prospect of continued lay application of constitutional law to development restrictions add uncertain dimensions to exactions litigation at the millennium. In Del Monte Dunes, the Court also distinguished the instant development denial of an inverse condemnation claim from the land dedication conditions at issue in Dolan v. City of Tigard. This distinction enabled the unanimous Court to uphold the trial verdict based on Agins and avoid elements of the Ninth Circuit\u27s reasoning invoking the Dolan rough proportionality test. Other recent federal and state decisions also decline to extend Dolan\u27s applicability beyond individual land dedication development conditions to other forms of economic exactions. This year\u27s exactions and impact fee report focuses on Del Monte Dunes, namely its effects on negotiated development, trial practice, and on regulatory takings doctrine as defined by judges and juries in civil rights litigation
Adaptive mesh refinement with spectral accuracy for magnetohydrodynamics in two space dimensions
We examine the effect of accuracy of high-order spectral element methods,
with or without adaptive mesh refinement (AMR), in the context of a classical
configuration of magnetic reconnection in two space dimensions, the so-called
Orszag-Tang vortex made up of a magnetic X-point centered on a stagnation point
of the velocity. A recently developed spectral-element adaptive refinement
incompressible magnetohydrodynamic (MHD) code is applied to simulate this
problem. The MHD solver is explicit, and uses the Elsasser formulation on
high-order elements. It automatically takes advantage of the adaptive grid
mechanics that have been described elsewhere in the fluid context [Rosenberg,
Fournier, Fischer, Pouquet, J. Comp. Phys. 215, 59-80 (2006)]; the code allows
both statically refined and dynamically refined grids. Tests of the algorithm
using analytic solutions are described, and comparisons of the Orszag-Tang
solutions with pseudo-spectral computations are performed. We demonstrate for
moderate Reynolds numbers that the algorithms using both static and refined
grids reproduce the pseudo--spectral solutions quite well. We show that
low-order truncation--even with a comparable number of global degrees of
freedom--fails to correctly model some strong (sup--norm) quantities in this
problem, even though it satisfies adequately the weak (integrated) balance
diagnostics.Comment: 19 pages, 10 figures, 1 table. Submitted to New Journal of Physic
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Simulations of Electron Cloud Build Up and Saturation in the APS
In studies with positron beams in the Advanced Photon Source, a dramatic amplification was observed in the electron cloud for certain bunch current and bunch spacings. In modeling presented previously, we found qualitative agreement with the observed beam-induced multipacting condition, provided reasonable values were chosen for the secondary electron yield parameters, including the energy distribution. In this paper, we model and discuss the build-up and saturation process observed over long bunch trains at the resonance condition. Understanding this saturation mechanism in more detail may have implications for predicting electron cloud amplification, multipacting, and instabilities in future rings
Contribution of Matrix Metalloproteinase-9 to Cerebral Edema and Functional Outcome following Experimental Subarachnoid Hemorrhage
Background: Cerebral edema is an important risk factor for death and poor outcome following subarachnoid hemorrhage (SAH). However, underlying mechanisms are still poorly understood. Matrix metalloproteinase (MMP)-9 is held responsible for the degradation of microvascular basal lamina proteins leading to blood-brain barrier dysfunction and, thus, formation of vasogenic cerebral edema. The current study was conducted to clarify the role of MMP-9 for the development of cerebral edema and for functional outcome after SAH. Methods: SAH was induced in FVB/N wild-type (WT) or MMP-9 knockout (MMP-9(-/-)) mice by endovascular puncture. Intracranial pressure (ICP), regional cerebral blood flow (rCBF), and mean arterial blood pressure (MABP) were continuously monitored up to 30 min after SAH. Mortality was quantified for 7 days after SAH. In an additional series neurological function and body weight were assessed for 3 days after SAH. Subsequently, ICP and brain water content were quantified. Results: Acute ICP, rCBF, and MABP did not differ between WT and MMP-9(-/-) mice, while 7 days' mortality was lower in MMP-9(-/-) mice (p = 0.03; 20 vs. 60%). MMP-9(-/-) mice also exhibited better neurological recovery, less brain edema formation, and lower chronic ICP. Conclusions: The results of the current study suggest that MMP-9 contributes to the development of early brain damage after SAH by promoting cerebral edema formation. Hence, MMP-9 may represent a novel molecular target for the treatment of SAH. Copyright (C) 2011 S. Karger AG, Base
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