5,833 research outputs found
A simple model for the kinetics of packaging of DNA in to a capsid against an external force
We propose a simple model for the kinetics of packaging of viral DNA in to a
capsid against an external force trying to prevent it. The model leads to a
Butler-Volmer type dependence of the rate of packaging on the pulling force F
Gyrations: The Missing Link Between Classical Mechanics with its Underlying Euclidean Geometry and Relativistic Mechanics with its Underlying Hyperbolic Geometry
Being neither commutative nor associative, Einstein velocity addition of
relativistically admissible velocities gives rise to gyrations. Gyrations, in
turn, measure the extent to which Einstein addition deviates from commutativity
and from associativity. Gyrations are geometric automorphisms abstracted from
the relativistic mechanical effect known as Thomas precession
Absence of singular superconducting fluctuation corrections to thermal conductivity
We evaluate the superconducting fluctuation corrections to thermal
conductivity in the normal state which diverge as T approaches T_c. We find
zero total contribution for one, two and three-dimensional superconductors for
arbitrary impurity concentration. The method used is diagrammatic many-body
theory, and all contributions -- Aslamazov-Larkin (AL), Maki-Thompson (MT), and
density-of-states (DOS) -- are considered. The AL contribution is convergent,
whilst the divergences of the DOS and MT diagrams exactly cancel.Comment: 4 pages text; 2 figure
Homeless population
The aim was to derive and analyze a model for numbers of homeless and non-homeless people in a borough, in particular to see how these figures might be affected by different policies regarding housing various categories of people. Most attention was focused on steady populations although the stability of these and possible timescales of dynamic problems were also discussed.
The main outcome of this brief study is the identification of the key role played by the constant k_1 - the constant which fixes the speed at which the homeless are rehoused in permanent council property. Reducing this constant, i.e. making the system "fairer" with less priority to accommodating homeless families, appears to have little effect on the sizes of other categories on the waiting list but there is a marked increase in the number of households in temporary accommodation.
The model, indicated by the size of its longest time-scale, should be modified to allow for births etc.
It could be varied by allowing people to remove themselves from the register or by allowing the rates at which registered and unregistered people become homeless to differ, but these modifications are unlikely to substantially change the main result.
The inclusion of movement from the homeless to the general population would have the effect of limiting the numbers in temporary accommodation. However, it is thought this effect is very small so a great reduction in k_1 would be needed for this flow to become significant
Refraction of Electromagnetic Energy for Wave Packets Incident on a Negative Index Medium is Always Negative
We analyze refraction of electromagnetic wave packets on passing from an
isotropic positive to an isotropic negative refractive index medium. We
definitively show that in all cases the energy is always refracted negatively.
For localized wave packets, the group refraction is also always negative.Comment: 5 pages, 3 figure
Gravitational waves from self-ordering scalar fields
Gravitational waves were copiously produced in the early Universe whenever
the processes taking place were sufficiently violent. The spectra of several of
these gravitational wave backgrounds on subhorizon scales have been extensively
studied in the literature. In this paper we analyze the shape and amplitude of
the gravitational wave spectrum on scales which are superhorizon at the time of
production. Such gravitational waves are expected from the self ordering of
randomly oriented scalar fields which can be present during a thermal phase
transition or during preheating after hybrid inflation. We find that, if the
gravitational wave source acts only during a small fraction of the Hubble time,
the gravitational wave spectrum at frequencies lower than the expansion rate at
the time of production behaves as with an
amplitude much too small to be observable by gravitational wave observatories
like LIGO, LISA or BBO. On the other hand, if the source is active for a much
longer time, until a given mode which is initially superhorizon (), enters the horizon, for , we find that the gravitational
wave energy density is frequency independent, i.e. scale invariant. Moreover,
its amplitude for a GUT scale scenario turns out to be within the range and
sensitivity of BBO and marginally detectable by LIGO and LISA. This new
gravitational wave background can compete with the one generated during
inflation, and distinguishing both may require extra information.Comment: 21 pages, 2 figures, added discussion about numerical integration and
a new figure to illustrate the scale-invariance of the GW power spectrum,
conclusions unchange
Effect of Background Evolution on the Curvaton Non-Gaussianity
We investigate how the background evolution affects the curvature
perturbations generated by the curvaton, assuming a curvaton potential that may
deviate slightly from the quadratic one, and parameterizing the background
fluid density as \rho\propto a^{-\alpha}, where a is the scale factor, and
\alpha depends on the background fluid. It turns out that the more there is
deviation from the quadratic case, the more pronounced is the dependence of the
curvature perturbation on \alpha. We also show that the background can have a
significant effect on the nonlinearity parameters f_NL and g_NL. As an example,
if at the onset of the curvaton oscillation there is a dimension 6 contribution
to the potential at 5 % level and the energy fraction of the curvaton to the
total one at the time of its decay is at 1 %, we find variations \Delta f_NL
\sim \mathcal{O}(10) and \Delta g_NL \sim \mathcal{O}(10^4) between matter and
radiation dominated backgrounds. Moreover, we demonstrate that there is a
relation between f_NL and g_NL that can be used to probe the form of the
curvaton potential and the equation of state of the background fluid.Comment: 14 pages, 8 figure
A GIS of the extent of historical mining activities in Scotland: explanatory notes
As part of the secondment of BGS staff to SEPA to help implement the Water Framework
Directive (WFD) in Scotland, BGS have been asked to provide an approximate outline of the
extent of historical mining in Scotland. This will be used to help characterize pressures on
Scottish groundwater as part of the initial characterization of groundwater bodies for the WFD.
Initial characterization has to be completed by December 2004; for bodies deemed to be at risk
there will be further characterization after 2004. A team of BGS geologists carried out the work
during September 2003.
The aim of the study was:
“To delineate the extent of known and inferred historical and current shallow and dee
A Brane Teaser
In this note we study the puzzle posed by two M5-branes intersecting on a
string (or equivalently, a single M5-brane wrapping a holomorphic four-cycle in
C^4). It has been known for a while that this system is different from all
other configurations built using self-intersecting M-branes; in particular the
corresponding supergravity solution exhibits various curious features which
have remained unexplained. We propose that the resolution to these puzzles lies
in the existence of a non-zero two-form on the M5-brane world-volume.Comment: 21 pages. References adde
The Upper Critical Field in Disordered Two-Dimensional Superconductors
We present calculations of the upper critical field in superconducting films
as a function of increasing disorder (as measured by the normal state
resistance per square). In contradiction to previous work, we find that there
is no anomalous low-temperature positive curvature in the upper critical field
as disorder is increased. We show that the previous prediction of this effect
is due to an unjustified analytical approximation of sums occuring in the
perturbative calculation. Our treatment includes both a careful analysis of
first-order perturbation theory, and a non-perturbative resummation technique.
No anomalous curvature is found in either case. We present our results in
graphical form.Comment: 11 pages, 8 figure
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