1,299 research outputs found
Chrysomelidae of Arkansas
A list of Chrysomelidae of Arkansas is brought up to date by inclusion of species in the reference collection in the University of Arkansas, the collection in the Zoological Institute of Leningrad, and the private collection of L. Medvedev, as well as those reported in the literature. The list consists of 232 species, subspecies, and varieties and the ecological data where known. One new species and one new variety are included
On transition to bursting via deterministic chaos
We study statistical properties of the irregular bursting arising in a class
of neuronal models close to the transition from spiking to bursting. Prior to
the transition to bursting, the systems in this class develop chaotic
attractors, which generate irregular spiking. The chaotic spiking gives rise to
irregular bursting. The duration of bursts near the transition can be very
long. We describe the statistics of the number of spikes and the interspike
interval distributions within one burst as functions of the distance from
criticality.Comment: 8 pages, 6 figure
PIC Simulations of the Temperature Anisotropy-Driven Weibel Instability: Analyzing the perpendicular mode
An instability driven by the thermal anisotropy of a single electron species
is investigated in a 2D particle-in-cell (PIC) simulation. This instability is
the one considered by Weibel and it differs from the beam driven filamentation
instability. A comparison of the simulation results with analytic theory
provides similar exponential growth rates of the magnetic field during the
linear growth phase of the instability. We observe in accordance with previous
works the growth of electric fields during the saturation phase of the
instability. Some components of this electric field are not accounted for by
the linearized theory. A single-fluid-based theory is used to determine the
source of this nonlinear electric field. It is demonstrated that the magnetic
stress tensor, which vanishes in a 1D geometry, is more important in this
2-dimensional model used here. The electric field grows to an amplitude, which
yields a force on the electrons that is comparable to the magnetic one. The
peak energy density of each magnetic field component in the simulation plane
agrees with previous estimates. Eddy currents develop, which let the amplitude
of the third magnetic field component grow, which is not observed in a 1D
simulation.Comment: accepted by Plasma Physics and Controlled Fusio
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
The filamentation instability driven by warm electron beams: Statistics and electric field generation
The filamentation instability of counterpropagating symmetric beams of
electrons is examined with 1D and 2D particle-in-cell (PIC) simulations, which
are oriented orthogonally to the beam velocity vector. The beams are uniform,
warm and their relative speed is mildly relativistic. The dynamics of the
filaments is examined in 2D and it is confirmed that their characteristic size
increases linearly in time. Currents orthogonal to the beam velocity vector are
driven through the magnetic and electric fields in the simulation plane. The
fields are tied to the filament boundaries and the scale size of the
flow-aligned and the perpendicular currents are thus equal. It is confirmed
that the electrostatic and the magnetic forces are equally important, when the
filamentation instability saturates in 1D. Their balance is apparently the
saturation mechanism of the filamentation instability for our initial
conditions. The electric force is relatively weaker but not negligible in the
2D simulation, where the electron temperature is set higher to reduce the
computational cost. The magnetic pressure gradient is the principal source of
the electrostatic field, when and after the instability saturates in the 1D
simulation and in the 2D simulation.Comment: 10 pages, 6 figures, accepted by the Plasma Physics and Controlled
Fusion (Special Issue EPS 2009
Safe and complete contig assembly via omnitigs
Contig assembly is the first stage that most assemblers solve when
reconstructing a genome from a set of reads. Its output consists of contigs --
a set of strings that are promised to appear in any genome that could have
generated the reads. From the introduction of contigs 20 years ago, assemblers
have tried to obtain longer and longer contigs, but the following question was
never solved: given a genome graph (e.g. a de Bruijn, or a string graph),
what are all the strings that can be safely reported from as contigs? In
this paper we finally answer this question, and also give a polynomial time
algorithm to find them. Our experiments show that these strings, which we call
omnitigs, are 66% to 82% longer on average than the popular unitigs, and 29% of
dbSNP locations have more neighbors in omnitigs than in unitigs.Comment: Full version of the paper in the proceedings of RECOMB 201
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
Protein Dynamics Control of Electron Transfer in Photosynthetic Reaction Centers from Rps. Sulfoviridis
In the cycle of photosynthetic reaction centers, the initially oxidized special pair of bacteriochlorophyll molecules is subsequently reduced by an electron transferred over a chain of four hemes of the complex. Here, we examine the kinetics of electron transfer between the proximal heme c-559 of the chain and the oxidized special pair in the reaction center from Rps. sulfoviridis in the range of temperatures from 294 to 40 K. The experimental data were obtained for three redox states of the reaction center, in which one, two, or three nearest hemes of the chain are reduced prior to special pair oxidation. The experimental kinetic data are analyzed in terms of a Sumi–Marcus-type model developed in our previous paper,1 in which similar measurements were reported on the reaction centers from Rps. viridis. The model allows us to establish a connection between the observed nonexponential electron-transfer kinetics and the local structural relaxation dynamics of the reaction center protein on the microsecond time scale. The activation energy for relaxation dynamics of the protein medium has been found to be around 0.1 eV for all three redox states, which is in contrast to a value around 0.4–0.6 eV in Rps. viridis.1 The possible nature of the difference between the reaction centers from Rps. viridis and Rps. sulfoviridis, which are believed to be very similar, is discussed. The role of the protein glass transition at low temperatures and that of internal water molecules in the process are analyzed.España, Ministerio de Educación y Ciencia BFU2004-04914-C02-01/BMCJunta de Andalucía PAI CVI-26
Undoped sr2mmoo6 double perovskite molybdates (M = ni, mg, fe) as promising anode materials for solid oxide fuel cells
The chemical design of new functional materials for solid oxide fuel cells (SOFCs) is of great interest as a means for overcoming the disadvantages of traditional materials. Redox stability, carbon deposition and sulfur poisoning of the anodes are positioned as the main processes that result in the degradation of SOFC performance. In this regard, double perovskite molybdates are possible alternatives to conventional Ni-based cermets. The present review provides the fundamental properties of four members: Sr2NiMoO6-δ, Sr2MgMoO6-δ, Sr2FeMoO6-δ and Sr2Fe1.5Mo0.5O6-δ. These properties vary greatly depending on the type and concentration of the 3d-element occupying the B-position of A2BB’O6. The main emphasis is devoted to: (i) the synthesis features of undoped double molybdates, (ii) their electrical conductivity and thermal behaviors in both oxidizing and reducing atmospheres, as well as (iii) their chemical compatibility with respect to other functional SOFC materials and components of gas atmospheres. The information provided can serve as the basis for the design of efficient fuel electrodes prepared from complex oxides with layered structures. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.The work was funded by a grant from the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15-2019-1924)
Descent Relations in Cubic Superstring Field Theory
The descent relations between string field theory (SFT) vertices are
characteristic relations of the operator formulation of SFT and they provide
self-consistency of this theory. The descent relations and
in the NS fermionic string field theory in the kappa and discrete bases are
established. Different regularizations and schemes of calculations are
considered and relations between them are discussed.Comment: Replaced to JHEP styl
- …