18,677 research outputs found
Comment on "PIC simulations of circularly polarised Alfv\'en wave phase mixing: A new mechanism for electron acceleration in collisionless plasmas" by Tsiklauri et al
Tsiklauri et al. recently published a theoretical model of electron
acceleration by Alfv\'en waves in a nonuniform collisionless plasmas. We
compare their work with a series of results published earlier by an another
team, of which Tsiklauri et al. were probably unaware. We show that these two
series of works, apparently conducted independently, lead to the same
conclusions. This reinforces the theoretical consistency of the model.Comment: 2 pages. Accepted at "Astronomy and Astrophysics
Evaluation of the effects of a freeze/thaw environment on cellular glass
Using the evaluation criteria of water vapor permeability and conformability, a protective butylrubber/silicone conformal coating system was selected for use on Foamglas substrates in a freeze/thaw environment. The selection of a specific freeze/thaw cycle which closely models field conditions is discussed. A sampling plan is described which allows independent evaluation of the effects of conformal coatings, cycle number and location within the environmental chamber. The results of visual examination, measurement of density, modulus of rupture and Young's modulus are reported. Based upon statistical evaluation of the experimental results, it is concluded that no degradation in mechanical properties of either coated or uncoated Foamglas occurred within the duration of the test (53 freeze/thaw cycles)
NMR Knight shifts and linewidths in the NiâPdâP and NiâPtâP metallic glasses: Composition and temperature dependences
NMR Knight shift and linewidth measurements are reported for the ^(31)P nuclei in the metallic glasses (Ni_(0.50)Pd_(0.50))100â_xP_x (where x=16 to 26.5) and (Ni_yPd_(1ây))_(80)P_(20) (where y=0.20 to 0.80), and both the ^(31)P and 195Pt nuclei in the metallic glass (Ni_yPt_(1ây))_(75)P_(25) (where y=0.20 to 0.68). The results are discussed in terms of the amorphous structure, electronic structure, and stability of transition metal + metalloid metallic glasses
Fermionic bright soliton in a boson-fermion mixture
We use a time-dependent dynamical mean-field-hydrodynamic model to study the
formation of fermionic bright solitons in a trapped degenerate Fermi gas mixed
with a Bose-Einstein condensate in a quasi-one-dimensional cigar-shaped
geometry. Due to a strong Pauli-blocking repulsion among spin-polarized
fermions at short distances there cannot be bright fermionic solitons in the
case of repulsive boson-fermion interactions. However, we demonstrate that
stable bright fermionic solitons can be formed for a sufficiently attractive
boson-fermion interaction in a boson-fermion mixture. We also consider the
formation of fermionic solitons in the presence of a periodic axial
optical-lattice potential. These solitons can be formed and studied in the
laboratory with present technology.Comment: 7 pages, 7 ps figure
Oblique amplitude modulation of dust-acoustic plasma waves
Theoretical and numerical studies are presented of the nonlinear amplitude
modulation of dust-acoustic (DA) waves propagating in an unmagnetized three
component, weakly-coupled, fully ionized plasma consisting of electrons,
positive ions and charged dust particles, considering perturbations oblique to
the carrier wave propagation direction. The stability analysis, based on a
nonlinear Schroedinger-type equation (NLSE), shows that the wave may become
unstable; the stability criteria depend on the angle between the
modulation and propagation directions. Explicit expressions for the instability
rate and threshold have been obtained in terms of the dispersion laws of the
system. The possibility and conditions for the existence of different types of
localized excitations have also been discussed.Comment: 21 pages, 6 figures, to appear in Physica Script
Spontaneous soliton formation and modulational instability in Bose-Einstein condensates
The dynamics of an elongated attractive Bose-Einstein condensate in an
axisymmetric harmonic trap is studied. It is shown that density fringes caused
by self-interference of the condensate order parameter seed modulational
instability. The latter has novel features in contradistinction to the usual
homogeneous case known from nonlinear fiber optics. Several open questions in
the interpretation of the recent creation of the first matter-wave bright
soliton train [Strecker {\it et al.} Nature {\bf 417} 150 (2002)] are
addressed. It is shown that primary transverse collapse, followed by secondary
collapse induced by soliton--soliton interactions, produce bursts of hot atoms
at different time scales.Comment: 4 pages, 3 figures. Phys. Rev. Lett. in pres
The Spin Mass of an Electron Liquid
We show that in order to calculate correctly the {\it spin current} carried
by a quasiparticle in an electron liquid one must use an effective "spin mass"
, that is larger than both the band mass, , which determines the
charge current, and the quasiparticle effective mass , which determines
the heat capacity. We present microscopic calculations of in a
paramagnetic electron liquid in three and two dimensions, showing that the mass
enhancement can be a very significant effect.Comment: 10 pages, 1 figur
Fluctuating noise drives Brownian transport
The transport properties of Brownian ratchet was studied in the presence of
stochastic intensity noise (SIN) in both overdamped and underdamped regimes. In
the overdamped case, analytical solution using the matrix continued fraction
method revealed the existence of a maximum current when the noise intensity
fluctuates on intermediate time scale regions. Similar effects were observed
for the underdamped case by Monte Carlo simulations. The optimal
time-correlation for the Brownian transport coincided with the experimentally
observed time-correlation of the extrinsic noise in Esherichia coli gene
expression and implied the importance of environmental noise for molecular
mechanisms.Comment: 22 pages, 8 figure
On the characterisation of paired monotone metrics
Hasegawa and Petz introduced the notion of dual statistically monotone
metrics. They also gave a characterisation theorem showing that
Wigner-Yanase-Dyson metrics are the only members of the dual family. In this
paper we show that the characterisation theorem holds true under more general
hypotheses.Comment: 12 pages, to appear on Ann. Inst. Stat. Math.; v2: changes made to
conform to accepted version, title changed as wel
- âŠ