461 research outputs found
Kinetic Vlasov Simulations of collisionless magnetic Reconnection
A fully kinetic Vlasov simulation of the Geospace Environment Modeling (GEM)
Magnetic Reconnection Challenge is presented. Good agreement is found with
previous kinetic simulations using particle in cell (PIC) codes, confirming
both the PIC and the Vlasov code. In the latter the complete distribution
functions () are discretised on a numerical grid in phase space.
In contrast to PIC simulations, the Vlasov code does not suffer from numerical
noise and allows a more detailed investigation of the distribution functions.
The role of the different contributions of Ohm's law are compared by
calculating each of the terms from the moments of the . The important role
of the off--diagonal elements of the electron pressure tensor could be
confirmed. The inductive electric field at the X--Line is found to be dominated
by the non--gyrotropic electron pressure, while the bulk electron inertia is of
minor importance. Detailed analysis of the electron distribution function
within the diffusion region reveals the kinetic origin of the non--gyrotropic
terms
Waves and instability in a one-dimensional microfluidic array
Motion in a one-dimensional (1D) microfluidic array is simulated. Water
droplets, dragged by flowing oil, are arranged in a single row, and due to
their hydrodynamic interactions spacing between these droplets oscillates with
a wave-like motion that is longitudinal or transverse. The simulation yields
wave spectra that agree well with experiment. The wave-like motion has an
instability which is confirmed to arise from nonlinearities in the interaction
potential. The instability's growth is spatially localized. By selecting an
appropriate correlation function, the interaction between the longitudinal and
transverse waves is described
Revisiting the reaction of dicarbonyls in aerosol proxy solutions containing ammonia: the case of butenedial
Reactions in aqueous solutions containing dicarbonyls
(especially the α-dicarbonyls methylglyoxal, glyoxal, and biacetyl)
and reduced nitrogen (NHx) have been studied extensively. It has been
proposed that accretion reactions from dicarbonyls and NHx could be a
source of particulate matter and brown carbon in the atmosphere and
therefore have direct implications for human health and climate. Other
dicarbonyls, such as the 1,4-unsaturated dialdehyde butenedial, are also
produced from the atmospheric oxidation of volatile organic compounds,
especially aromatics and furans, but their aqueous-phase reactions with
NHx have not been characterized. In this work, we determine a
pH-dependent mechanism of butenedial reactions in aqueous solutions with
NHx that is compared to α-dicarbonyls, in particular the
dialdehyde glyoxal. Similar to glyoxal, butenedial is strongly hydrated in
aqueous solutions. Butenedial reaction with NHx also produces
nitrogen-containing rings and leads to accretion reactions that form brown
carbon. Despite glyoxal and butenedial both being dialdehydes, butenedial is
observed to have three significant differences in its chemical behavior: (1)Â as previously shown, butenedial does not substantially form acetal
oligomers, (2) the butenedial/OH− reaction leads to light-absorbing
compounds, and (3)Â the butenedial/NHx reaction is fast and first order
in the dialdehyde. Building off of a complementary study on butenedial
gas-particle partitioning, we suggest that the behavior of other reactive
dialdehydes and dicarbonyls may not always be adequately predicted by
α-dicarbonyls, even though their dominant functionalities are
closely related. The carbon skeleton (e.g., its hydrophobicity, length, and
bond structure) also governs the fate and climate-relevant properties of
dicarbonyls in the atmosphere. If other dicarbonyls behave like butenedial,
their reaction with NHx could constitute a regional source of brown
carbon to the atmosphere.</p
Statistical kinetic treatment of relativistic binary collisions
In particle-based algorithms, the effect of binary collisions is commonly
described in a statistical way, using Monte Carlo techniques. It is shown that,
in the relativistic regime, stringent constraints should be considered on the
sampling of particle pairs for collision, which are critical to ensure
physically meaningful results, and that nonrelativistic sampling criteria
(e.g., uniform random pairing) yield qualitatively wrong results, including
equilibrium distributions that differ from the theoretical J\"uttner
distribution. A general procedure for relativistically consistent algorithms is
provided, and verified with three-dimensional Monte Carlo simulations, thus
opening the way to the numerical exploration of the statistical properties of
collisional relativistic systems.Comment: Accepted for publication as a Rapid Communication in Phys. Rev.
A Semi-Kinetic Model of Plasmasphere Refilling Following Geomagnetic Storms and Comparison with Hydrodynamic Results
The objective of this paper is the development of a kinetic model for plasmasphere refilling following geomagnetic storms. The kinetic model is based on the ‘particle-in-cell’ method, a method based on the simulation of particle motion and thus well-suited to high altitude, low-density regimes, where the plasma transport equations are not valid. The model was validated with exact, analytical benchmarks, which are provided in this paper. The refilling results obtained from the kinetic model were then compared with results from a recently developed hydrodynamic solution methodology based on the ‘flux-corrected transport’ (FCT) method, and the limitations of hydrodynamic modeling for low-density flow at high altitudes were explored
Reaching Inward Not Outward: Marketing via the Internet at the UK 2010 General Election
The Internet has been to date used as a space for simple promotion by political parties; websites present an opportunity for the delivery of non-mediated communication directly to the online audience and nothing more. However, new patterns in usage during campaigns, particularly that of Barack Obama, aided by the technological innovations that fall under the umbrella of Web 2.0, offer new models of online political communication. Through an analysis of the websites and linked online presences of six parties that stood across the UK at the 2010 General Election, we find a dual strategy for Internet campaigning emerging. The persuasive traditions of electioneering remain a feature; however, the key emergent function is one of internal marketing to party supporters and activists. Large sections of party websites are being dedicated to harnessing supporters and converting them to being donators, promoters, and campaigners both online and offline. This suggests that the Internet is increasingly embedded within election communication and online communication strategies are becoming a feature of most of the parties' marketing communication mix. © 2013 Copyright Taylor and Francis Group, LLC
Simulations of beam-beam and beam-wire interactions in RHIC
The beam-beam interaction is one of the dominant sources of emittance growth
and luminosity lifetime deterioration. A current carrying wire has been
proposed to compensate long-range beam-beam effects in the LHC and strong
localized long-range beam-beam effects are experimentally investigated in the
RHIC collider. Tune shift, beam transfer function, and beam loss rate are
measured in dedicated experiments. In this paper, we report on simulations to
study the effect of beam-wire interactions based on diffusive apertures, beam
loss rates, and beam transfer function using a parallelized weak-strong beam
simulation code (bbsimc). The simulation results are compared with measurements
performed in RHIC during 2007 and 2008.Comment: 15 pages, 36 figures, submitted to HB2008 PRST-AB Special Editio
Quasi-stationary States of Two-Dimensional Electron Plasma Trapped in Magnetic Field
We have performed numerical simulations on a pure electron plasma system
under a strong magnetic field, in order to examine quasi-stationary states that
the system eventually evolves into. We use ring states as the initial states,
changing the width, and find that the system evolves into a vortex crystal
state from a thinner-ring state while a state with a single-peaked density
distribution is obtained from a thicker-ring initial state. For those
quasi-stationary states, density distribution and macroscopic observables are
defined on the basis of a coarse-grained density field. We compare our results
with experiments and some statistical theories, which include the
Gibbs-Boltzmann statistics, Tsallis statistics, the fluid entropy theory, and
the minimum enstrophy state. From some of those initial states, we obtain the
quasi-stationary states which are close to the minimum enstrophy state, but we
also find that the quasi-stationary states depend upon initial states, even if
the initial states have the same energy and angular momentum, which means the
ergodicity does not hold.Comment: 9 pages, 7 figure
Radio-frequency discharges in Oxygen. Part 1: Modeling
In this series of three papers we present results from a combined
experimental and theoretical effort to quantitatively describe capacitively
coupled radio-frequency discharges in oxygen. The particle-in-cell Monte-Carlo
model on which the theoretical description is based will be described in the
present paper. It treats space charge fields and transport processes on an
equal footing with the most important plasma-chemical reactions. For given
external voltage and pressure, the model determines the electric potential
within the discharge and the distribution functions for electrons, negatively
charged atomic oxygen, and positively charged molecular oxygen. Previously used
scattering and reaction cross section data are critically assessed and in some
cases modified. To validate our model, we compare the densities in the bulk of
the discharge with experimental data and find good agreement, indicating that
essential aspects of an oxygen discharge are captured.Comment: 11 pages, 10 figure
Molecular Dynamics for Low Temperature Plasma-Surface Interaction Studies
The mechanisms of physical and chemical interactions of low temperature
plasmas with surfaces can be fruitfully explored using molecular dynamics (MD)
simulations. MD simulations follow the detailed motion of sets of interacting
atoms through integration of atomic equations of motion, using inter-atomic
potentials that can account for bond breaking and formation that result when
energetic species from the plasma impact surfaces. This article summarizes the
current status of the technique for various applications of low temperature
plasmas to material processing technologies. The method is reviewed, and
commonly used inter-atomic potentials are described. Special attention is paid
to the use of MD in understanding various representative applications,
including tetrahedral amorphous carbon film deposition from energetic carbon
ions; the interactions of radical species with amorphous hydrogenated silicon
films; silicon nano-particles in plasmas; and plasma etching.Comment: Manuscript #271801, Accepted in J. Phys. D, November 10th, 200
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