6,991 research outputs found
Thin-disk laser pump schemes for large number of passes and moderate pump source quality
Novel thin-disk laser pump layouts are proposed yielding an increased number
of passes for a given pump module size and pump source quality. These novel
layouts result from a general scheme which bases on merging two simpler pump
optics arrangements. Some peculiar examples can be realized by adapting
standard commercially available pump optics simply by intro ducing an
additional mirror-pair. More pump passes yield better efficiency, opening the
way for usage of active materials with low absorption. In a standard multi-pass
pump design, scaling of the number of beam passes brings ab out an increase of
the overall size of the optical arrangement or an increase of the pump source
quality requirements. Such increases are minimized in our scheme, making them
eligible for industrial applicationsComment: 16 pages, 9 figure
Pattern formation in the nonlinear Schrödinger equation with competing nonlocal nonlinearities
We study beam propagation in the framework of the nonlinear Schrödinger equation with competing Gaussian nonlocal nonlinearities. We demonstrate that such system can give rise to self-organization of light into stable states of trains or hexagonal arrays of filaments, depending on the transverse dimensionality. This long-range ordering can be achieved by mere unidirectional beam propagation. We discuss the dynamics of long-range ordering and the crucial role which the phase of the wavefunction plays for this phenomenon. Furthermore we discuss how transverse dimensionality affects the order of the phasetransition
On knotted streamtubes in incompressible hydrodynamical flow and a restricted conserved quantity
For certain families of fluid flow, a new conserved quantity --
stream-helicity -- has been established.Using examples of linked and knotted
streamtubes, it has been shown that stream-helicity does, in certain cases,
entertain itself with a very precise topological meaning viz, measure of the
degree of knottedness or linkage of streamtubes.As a consequence,
stream-helicity emerges as a robust topological invariant.Comment: This extended version is the basically a more clarified version of
the previous submission physics/0611166v
DNA loop statistics and torsional modulus
The modelling of DNA mechanics under external constraints is discussed. Two
analytical models are widely known, but disagree for instance on the value of
the torsional modulus. The origin of this embarassing situation is located in
the concept of writhe. This letter presents a unified model for DNA
establishing a relation between the different approaches. I show that the
writhe created by the loops of DNA is at the origin of the discrepancy. To take
this into account, I propose a new treatment of loop statistics based on
numerical simulations using the most general formula for the writhe, and on
analytic calculations with only one fit parameter. One can then compute the
value of the torsional modulus of DNA without the need of any cut-off.Comment: 8 pages, 1 figure. Accepted by Europhysics Letter
Enhanced transmission versus localization of a light pulse by a subwavelength metal slit: Can the pulse have both characteristics?
The existence of resonant enhanced transmission and collimation of light
waves by subwavelength slits in metal films [for example, see T.W. Ebbesen et
al., Nature (London) 391, 667 (1998) and H.J. Lezec et al., Science, 297, 820
(2002)] leads to the basic question: Can a light be enhanced and simultaneously
localized in space and time by a subwavelength slit? To address this question,
the spatial distribution of the energy flux of an ultrashort (femtosecond)
wave-packet diffracted by a subwavelength (nanometer-size) slit was analyzed by
using the conventional approach based on the Neerhoff and Mur solution of
Maxwell's equations. The results show that a light can be enhanced by orders of
magnitude and simultaneously localized in the near-field diffraction zone at
the nm- and fs-scales. Possible applications in nanophotonics are discussed.Comment: 5 figure
Higher dimensional abelian Chern-Simons theories and their link invariants
The role played by Deligne-Beilinson cohomology in establishing the relation
between Chern-Simons theory and link invariants in dimensions higher than three
is investigated. Deligne-Beilinson cohomology classes provide a natural abelian
Chern-Simons action, non trivial only in dimensions , whose parameter
is quantized. The generalized Wilson -loops are observables of the
theory and their charges are quantized. The Chern-Simons action is then used to
compute invariants for links of -loops, first on closed
-manifolds through a novel geometric computation, then on
through an unconventional field theoretic computation.Comment: 40 page
Imkeren met de Golzkast
Op 24 mei 2014 was Dr. Friedrich Pohl, bekend Duits imker en bijenauteur, in Rhenen om bij 'De Werkbij' samen met Jan Charpentier een dag te verzorgen over het imkeren met de Golzkast. Vanwege de belangstelling voor het imkeren met deze kast leek het een goed idee om een artikel van zijn hand te vertalen in het Nederlands. Het artikel is oorspronkelijk gepubliceerd in de Allgemeine Deutsche Imker Zeitung (ADIZ) 2012 nr. 1. Hier de eerste aflevering
Nonthermal Emission from the Arches Cluster (G0.121+0.017) and the Origin of -ray Emission from 3EG J1746-2851
High resolution VLA observations of the Arches cluster near the Galactic
center show evidence of continuum emission at 3.6, 6, 20 and 90cm. The
continuum emission at 90cm is particularly striking because thermal
sources generally become optically thick at longer wavelengths and fall off in
brightness whereas non-thermal sources increase in brightness. It is argued
that the radio emission from this unique source has compact and diffuse
components produced by thermal and nonthermal processes, respectively. Compact
sources within the cluster arise from stellar winds of mass-losing stars (Lang,
Goss & Rodriguez 2001a) whereas diffuse emission is likely to be due to
colliding wind shocks of the cluster flow generating relativistic particles due
to diffuse shock acceleration. We also discuss the possibility that
-ray emission from 3EG J1746--2851, located within 3.3 of the Arches
cluster, results from the inverse Compton scattering of the radiation field of
the cluster.Comment: 15 pages, four figures, ApJL (in press
3D Distribution of Molecular Gas in the Barred Milky Way
We present a new model of the three-dimensional distribution of molecular gas
in the Milky Way Galaxy, based on CO line data. Our analysis is based on a
gas-flow simulation of the inner Galaxy using smoothed-particle hydrodynamics
(SPH) using a realistic barred gravitional potential derived from the observed
COBE/DIRBE near-IR light distribution. The gas model prescribes the gas orbits
much better than a simple circular rotation model and is highly constrained by
observations, but it cannot predict local details. In this study, we provide a
3D map of the observed molecular gas distribution using the velocity field from
the SPH model. A comparison with studies of the Galactic Center region suggests
that the main structures are reproduced but somewhat stretched along the
line-of-sight, probably on account of limited resolution of the underlying SPH
simulation. The gas model will be publicly available and may prove useful in a
number of applications, among them the analysis of diffuse gamma-ray emission
as measured with GLAST.Comment: ApJ in pres
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