1,346 research outputs found
Non-linear Weibel-type Soliton Modes
Discussion is given of non-linear soliton behavior including coupling between
electrostatic and electromagnetic potentials for non-relativistic, weakly
relativistic, and fully relativistic plasmas. For plasma distribution functions
that are independent of the canonical momenta perpendicular to the soliton
spatial structure direction there are, in fact, no soliton behaviors allowed
because transverse currents are zero. Dependence on the transverse canonical
momenta is necessary. When such is the case, it is shown that the presence or
absence of a soliton is intimately connected to the functional form assumed for
the particle distribution functions. Except for simple situations, the coupled
non-linear equations for the electrostatic and electromagnetic potentials would
seem to require numerical solution procedures. Examples are given to illustrate
all of these points for non-relativistic, weakly relativistic, and fully
relativistic plasmas.Comment: Accepted for publication at Journal of Physics A: Mathematical and
Theoretica
Disaggregating non-volatile memory for throughput-oriented genomics workloads
Massive exploitation of next-generation sequencing technologies requires dealing with both: huge amounts of data and complex bioinformatics pipelines. Computing architectures have evolved to deal with these problems, enabling approaches that were unfeasible years ago: accelerators and Non-Volatile Memories (NVM) are becoming widely used to enhance the most demanding workloads. However, bioinformatics workloads are usually part of bigger pipelines with different and dynamic needs in terms of resources. The introduction of Software Defined Infrastructures (SDI) for data centers provides roots to dramatically increase the efficiency in the management of infrastructures. SDI enables new ways to structure hardware resources through disaggregation, and provides new hardware composability and sharing mechanisms to deploy workloads in more flexible ways. In this paper we study a state-of-the-art genomics application, SMUFIN, aiming to address the challenges of future HPC facilities.This work is partially supported by the European Research Council (ERC) under the EU Horizon 2020 programme (GA 639595), the Spanish Ministry of Economy, Industry and Competitivity (TIN2015-65316-P) and the Generalitat de Catalunya (2014-SGR-1051).Peer ReviewedPostprint (author's final draft
The theory of spectral evolution of the GRB prompt emission
We develop the theory of jitter radiation from GRB shocks containing
small-scale magnetic fields and propagating at an angle with respect to the
line of sight. We demonstrate that the spectra vary considerably: the
low-energy photon index, , ranges from 0 to -1 as the apparent viewing
angle goes from 0 to . Thus, we interpret the hard-to-soft evolution and
the correlation of with the photon flux observed in GRBs as a combined
effect of temporal variation of the viewing angle and relativistic aberration
of an individual thin, instantaneously illuminated shell. The model predicts
that about a quarter of time-resolved spectra should have hard spectra,
violating the synchrotron line of death. The model also naturally
explains why the peak of the distribution of is at .
The presence of a low-energy break in the jitter spectrum at oblique angles
also explains the appearance of a soft X-ray component in some GRBs and a
relatively small number of them. We emphasize that our theory is based solely
on the first principles and contains no {\it ad hoc} (phenomenological)
assumptions.Comment: 5 pages, 3 figures, accepted to Ap
Cluster magnetic fields from large-scale-structure and galaxy-cluster shocks
The origin of the micro-Gauss magnetic fields in galaxy clusters is one of
the outstanding problem of modern cosmology. We have performed
three-dimensional particle-in-cell simulations of the nonrelativistic Weibel
instability in an electron-proton plasma, in conditions typical of cosmological
shocks. These simulations indicate that cluster fields could have been produced
by shocks propagating through the intergalactic medium during the formation of
large-scale structure or by shocks within the cluster. The strengths of the
shock-generated fields range from tens of nano-Gauss in the intercluster medium
to a few micro-Gauss inside galaxy clusters.Comment: 4 pages, 2 color figure
Dissipative Dynamics of Collisionless Nonlinear Alfven Wave Trains
The nonlinear dynamics of collisionless Alfven trains, including resonant
particle effects is studied using the kinetic nonlinear Schroedinger (KNLS)
equation model. Numerical solutions of the KNLS reveal the dynamics of Alfven
waves to be sensitive to the sense of polarization as well as the angle of
propagation with respect to the ambient magnetic field. The combined effects of
both wave nonlinearity and Landau damping result in the evolutionary formation
of stationaryOA S- and arc-polarized directional and rotational
discontinuities. These waveforms are freqently observed in the interplanetary
plasma.Comment: REVTeX, 6 pages (including 5 figures). This and other papers may be
found at http://sdphpd.ucsd.edu/~medvedev/papers.htm
Field desorption of lithium
Absolute appearance energies of field-desorbed Li+ ions were obtained from mass-to-charge resolved retarding potential analyses of Li+ emitted from the first and second Li layer on W(111). Activation energies for Li+ field desorption were derived from desorption rate measurements. The field-independent binding energy of Li adatoms has been found from field-dependent Li+ appearance and activation energy values, indicating a negligible field-induced charge transfer in the applied field range. We use the cluster embedded in jellium model, based on density-functional theory, to interpret the data by calculating local field enhancements, surface potentials, and activation energies for Li field desorption as a function of field strength and surface coverage as well as geometry
Hot Settling Accretion Flow onto a Spinning Black Hole
We study the structure and properties of hot MHD accretion onto a Kerr black
hole. In such a system, the hole is magnetically coupled to the inflowing gas
and exerts a torque onto the accretion flow. A hot settling flow can form
around the hole and transport the angular momentum outward, to the outer edge
of the flow. Unlike other hot flows, such as advection- and
convection-dominated flows and inflow-outflow solutions (ADAFs, CDAFs, and
ADIOS), the properties of the hot settling flow are determined by the spin of
the central black hole, but are insensitive to the mass accretion rate.
Therefore, it may be possible to identify rapidly spinning BHs simply from
their broad-band spectra.
Observationally, the hot settling flow around a Kerr hole is somewhat similar
to other hot flows in that they all have hard, power-law spectra and relatively
low luminosities. Thus, most black hole candidates in the low/hard and,
perhaps, intermediate X-ray state may potentially accrete via the hot settling
flow. However, a settling flow will be somewhat more luminous than
ADAFs/CDAFs/ADIOS, will exhibit high variability in X-rays, and may have
relativistic jets. This suggests that galactic microquasars and active galactic
nuclei may be powered by hot settling flows. We identify several galactic X-ray
sources as the best candidates.Comment: 7 pages, 1 figure. Submitted to Ap
Density of Phonon States in Superconducting FeSe as a Function of Temperature and Pressure
The temperature and pressure dependence of the partial density of phonon
states of iron atoms in superconducting Fe1.01Se was studied by 57Fe nuclear
inelastic scattering (NIS). The high energy resolution allows for a detailed
observation of spectral properties. A sharpening of the optical phonon modes
and shift of all spectral features towards higher energies by ~4% with
decreasing temperature from 296 K to 10 K was found. However, no detectable
change at the tetragonal - orthorhombic phase transition around 100 K was
observed. Application of a pressure of 6.7 GPa, connected with an increase of
the superconducting temperature from 8 K to 34 K, results in an increase of the
optical phonon mode energies at 296 K by ~12%, and an even more pronounced
increase for the lowest-lying transversal acoustic mode. Despite these strong
pressure-induced modifications of the phonon-DOS we conclude that the
pronounced increase of Tc in Fe1.01Se with pressure cannot be described in the
framework of classical electron-phonon coupling. This result suggests the
importance of spin fluctuations to the observed superconductivity
Spatial transformation as an institutional factor of the public management of macroeconomic systems
Purpose: The article analyzes the issue of substantiating the impact of the spatial organization of the territory of the Russian Federation on the public management at the level of macroeconomic systems. Design/Methodology/Approach: The federal districts were chosen as the object of the study as macro-regional socio-economic systems, the Southern Federal District and its constituent regions (subjects of the Russian Federation). The article investigates the main transformational processes taking place in the RF spatial development, concerning the development of the regional systems of the public management and the necessity of their consistency at the supra-regional (macro-regional) level. Findings: The authors propose a set of measures to form supra-regional system to coordinate the regional development priorities considering the peculiarities of the spatial transformation of Russia's territory and the position of the Southern macro-region in the spatial system of the country. This system formation allows involving as many interested parties as possible. Practical Implications: The results may be implemented into macro-region public administration to maximize the advantages of the geo-economic and strategic position, natural and climatic conditions of Russian regions' development. Originality/Value: The main contribution of this study is a tailored approach to the public administration of the social and economic development of the macro-regions in the context of the spatial transformation.peer-reviewe
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