13,205 research outputs found
Numerical variational methods applied to cylinder buckling
We review and compare different computational variational methods applied to
a system of fourth order equations that arises as a model of cylinder buckling.
We describe both the discretization and implementation, in particular how to
deal with a 1 dimensional null space. We show that we can construct many
different solutions from a complex energy surface. We examine numerically
convergence in the spatial discretization and in the domain size. Finally we
give a physical interpretation of some of the solutions found.Comment: 23 pages, 12 figures, 6 table
Quantum Reciprocity Conjecture for the Non-Equilibrium Steady State
By considering the lack of history dependence in the non-equilibrium steady
state of a quantum system we are led to conjecture that in such a system, there
is a set of quantum mechanical observables whose retarded response functions
are insensitive to the arrow of time, and which consequently satisfy a quantum
analog of the Onsager reciprocity relations. Systems which satisfy this
conjecture can be described by an effective Free energy functional. We
demonstrate that the conjecture holds in a resonant level model of a multi-lead
quantum dot.Comment: References revised to take account of related work on Onsager
reciprocity in mesoscopics by Christen, and in hydrodynamics by Mclennan,
Dufty and Rub
Retrograde transport pathways utilised by viruses and protein toxins
A model has been presented for retrograde transport of certain toxins and viruses from the cell surface to the ER that suggests an obligatory interaction with a glycolipid receptor at the cell surface. Here we review studies on the ER trafficking cholera toxin, Shiga and Shiga-like toxins, Pseudomonas exotoxin A and ricin, and compare the retrograde routes followed by these protein toxins to those of the ER trafficking SV40 and polyoma viruses. We conclude that there is in fact no obligatory requirement for a glycolipid receptor, nor even with a protein receptor in a lipid-rich environment. Emerging data suggests instead that there is no common pathway utilised for retrograde transport by all of these pathogens, the choice of route being determined by the particular receptor utilised
Ion-induced nucleation in polar one-component fluids
We present a Ginzburg-Landau theory of ion-induced nucleation in a gas phase
of polar one-component fluids, where a liquid droplet grows with an ion at its
center. By calculating the density profile around an ion, we show that the
solvation free energy is larger in gas than in liquid at the same temperature
on the coexistence curve. This difference much reduces the nucleation barrier
in a metastable gas.Comment: 9 pagers, 9 figures, to be published in J. Chem. Phy
Capillary-gravity wave resistance in ordinary and magnetic fluids
Wave resistance is the drag force associated to the emission of waves by a
moving disturbance at a fluid free surface. In the case of capillary-gravity
waves it undergoes a transition from zero to a finite value as the speed of the
disturbance is increased. For the first time an experiment is designed in order
to obtain the wave resistance as a function of speed. The effect of viscosity
is explored, and a magnetic fluid is used to extend the available range of
critical speeds. The threshold values are in good agreement with the proposed
theory. Contrary to the theoretical model, however, the measured wave
resistance reveals a non monotonic speed dependence after the threshold.Comment: 12 pages, 4 figures, 1 table, submitted to Physical Review Letter
Large-Scale Magnetic-Field Generation by Randomly Forced Shearing Waves
A rigorous theory for the generation of a large-scale magnetic field by
random non-helically forced motions of a conducting fluid combined with a
linear shear is presented in the analytically tractable limit of low Rm and
weak shear. The dynamo is kinematic and due to fluctuations in the net
(volume-averaged) electromotive force. This is a minimal proof-of-concept
quasilinear calculation aiming to put the shear dynamo, a new effect recently
found in numerical experiments, on a firm theoretical footing. Numerically
observed scalings of the wavenumber and growth rate of the fastest growing
mode, previously not understood, are derived analytically. The simplicity of
the model suggests that shear dynamo action may be a generic property of
sheared magnetohydrodynamic turbulence.Comment: Paper substantially rewritten, results changed (relative to v1).
Revised versio
Herschel/HIFI discovery of interstellar chloronium (H_2Cl^+)
We report the first detection of chloronium, H_2Cl^+, in the interstellar medium, using the HIFI instrument aboard the Herschel Space Observatory.
The 2_(12)−1_(01) lines of ortho-H^(35)_2 Cl^+ and ortho-H^(37)_2 Cl^+ are detected in absorption towards NGC 6334I, and the 1_(11)−0_(00) transition of para-H^(35)_2 Cl^+ is
detected in absorption towards NGC 6334I and Sgr B2(S). The H_2Cl^+ column densities are compared to those of the chemically-related species
HCl. The derived HCl/H_2Cl^+ column density ratios, ~1–10, are within the range predicted by models of diffuse and dense photon dominated
regions (PDRs). However, the observed H_2Cl^+ column densities, in excess of 10^(13) cm^(−2), are significantly higher than the model predictions. Our
observations demonstrate the outstanding spectroscopic capabilities of HIFI for detecting new interstellar molecules and providing key constraints
for astrochemical models
Universal method to extract the average electron spin relaxation in organic semiconductors from muonium ALC resonances
Muon spin spectroscopy and in particular the avoid level crossing (ALC)
technique is a sensitive probe of electron spin relaxation (eSR) in organic
semiconductors. In complex ALC spectra, eSR can be challenging to extract, as
it requires the modelling of overlapping ALCs, where covariance between
parameters can result in significant uncertainties. Here we demonstrate a
general method to extract eSR rate, which is independent on the number of ALCs
resonances present, whether they overlap or not, and what the muonium hyperfine
(isotropic and anisotropic) parameters are. This can then be used to extract an
accurate value for eSR rate and as guidance for undertaking experiments
efficientl
Variational formulation of Eisenhart's unified theory
Eisenhart's classical unified field theory is based on a non-Riemannian
affine connection related to the covariant derivative of the electromagnetic
field tensor. The sourceless field equations of this theory arise from
vanishing of the torsion trace and the symmetrized Ricci tensor. We formulate
Eisenhart's theory from the metric-affine variational principle. In this
formulation, a Lagrange multiplier constraining the torsion becomes the source
for the Maxwell equations.Comment: 7 pages; published versio
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