21,529 research outputs found
Introduction to Library Trends 55 (3) Winter 2007: Libraries in Times of War, Revolution and Social Change
published or submitted for publicatio
Two-peaked and flat-top perfect bright solitons in epsilon-near-zero nonlinear metamaterials: novel Kerr self-trapping mechanisms
We analytically investigate transverse magnetic (TM) spatial bright solitons,
as exact solutions of Maxwell's equations, propagating through nonlinear
metamaterials whose linear dielectric permittivity is very close to zero and
whose effective nonlinear Kerr parameters can be tailored to achieve values not
available in standard materials. Exploiting the fact that, in the considered
medium, linear and nonlinear polarization can be comparable at feasible and
realistic optical intensities, we identify two novel self-trapping mechanisms
able to support two-peaked and flat-top solitons, respectively. Specifically,
these two novel mechanisms are based on the occurrence of critical points at
which the effective nonlinear permittivity vanishes, the two mechanisms
differing in the way the compensation between linear and nonlinear polarization
is achieved through the non-standard values of the nonlinear parameters.Comment: 7 pages, 4 figure
Recording and Analysis of Head Movements, Interaural Level and Time Differences in Rooms and Real-World Listening Scenarios
The science of how we use interaural differences to localise sounds has been studied for over a century and in many ways is well understood. But in many of these psychophysical experiments listeners are required to keep their head still, as head movements cause changes in interaural level and time differences (ILD and ITD respectively). But a fixed head is unrealistic. Here we report an analysis of the actual ILDs and ITDs that occur as people naturally move and relate them to gyroscope measurements of the actual motion. We used recordings of binaural signals in a number of rooms and listening scenarios (home, office, busy street etc). The listener's head movements were also recorded in synchrony with the audio, using a micro-electromechanical gyroscope. We calculated the instantaneous ILD and ITDs and analysed them over time and frequency, comparing them with measurements of head movements. The results showed that instantaneous ITDs were widely distributed across time and frequency in some multi-source environments while ILDs were less widely distributed. The type of listening environment affected head motion. These findings suggest a complex interaction between interaural cues, egocentric head movement and the identification of sound sources in real-world listening situations
Integrated multi vector vortex beam generator
A novel method to generate and manipulate vector vortex beams in an
integrated, ring resonator based geometry is proposed. We show numerically that
a ring resonator, with an appropriate grating, addressed by a vertically
displaced access waveguide emits a complex optical field. The emitted beam
possesses a specific polarization topology, and consequently a transverse
intensity profile and orbital angular momentum. We propose a combination of
several concentric ring resonators, addressed with different bus guides, to
generate arbitrary orbital angular momentum qudit states, which could
potentially be used for classical and quantum communications. Finally, we
demonstrate numerically that this device works as an orbital angular momentum
sorter with an average cross-talk of -10 dB between different orbital angular
momentum channels.Comment: 8 pages, 7 figure
Thermocapillary effects in driven dewetting and self-assembly of pulsed laser-irradiated metallic films
In this paper the lubrication-type dynamical model is developed of a molten,
pulsed laser-irradiated metallic film. The heat transfer problem that
incorporates the absorbed heat from a single beam or interfering beams is
solved analytically. Using this temperature field, we derive the 3D long-wave
evolution PDE for the film height. To get insights into dynamics of dewetting,
we study the 2D version of the evolution equation by means of a linear
stability analysis and by numerical simulations. The stabilizing and
destabilizing effects of various system parameters, such as the peak laser beam
intensity, the film optical thickness, the Biot and Marangoni numbers, etc. are
elucidated. It is observed that the film stability is promoted for such
parameters variations that increase the heat production in the film. In the
numerical simulations the impacts of different irradiation modes are
investigated. In particular, we obtain that in the interference heating mode
the spatially periodic irradiation results in a spatially periodic film rupture
with the same, or nearly equal period. The 2D model qualitatively reproduces
the results of the experimental observations of a film stability and spatial
ordering of a re-solidified nanostructures
Variational analysis of self-focusing of intense ultrashort pulses in gases
By using perturbation theory we derive an expression for the electrical field
of a Gaussian laser pulse propagating in a gas medium. This expression is used
as a trial solution in a variational method to get quasianalytical solutions
for the width, intensity and self-focusing distance of ultrashort pulse. The
approximation gives an improved agreement with results of numerical simulations
for a broad range of values of the input power of the pulse than previous
analytical results available in the literature.Comment: 19 pages, 8 figure
The Action of Certain Organic Silver Compounds on the Potato Root Eelworm, Heterodera schachtii, Schmidt, With Notes on the Biology of the Parasite, and Additional Papers
Abstract Not Provided
Analytical model of brittle destruction based on hypothesis of scale similarity
The size distribution of dust particles in nuclear fusion devices is close to
the power function. A function of this kind can be the result of brittle
destruction. From the similarity assumption it follows that the size
distribution obeys the power law with the exponent between -4 and -1. The model
of destruction has much in common with the fractal theory. The power exponent
can be expressed in terms of the fractal dimension. Reasonable assumptions on
the shape of fragments concretize the power exponent, and vice versa possible
destruction laws can be inferred on the basis of measured size distributions.Comment: 10 pages, 3 figure
Magnetic models on Apollonian networks
Thermodynamic and magnetic properties of Ising models defined on the
triangular Apollonian network are investigated. This and other similar networks
are inspired by the problem of covering an Euclidian domain with circles of
maximal radii. Maps for the thermodynamic functions in two subsequent
generations of the construction of the network are obtained by formulating the
problem in terms of transfer matrices. Numerical iteration of this set of maps
leads to exact values for the thermodynamic properties of the model. Different
choices for the coupling constants between only nearest neighbors along the
lattice are taken into account. For both ferromagnetic and anti-ferromagnetic
constants, long range magnetic ordering is obtained. With exception of a size
dependent effective critical behavior of the correlation length, no evidence of
asymptotic criticality was detected.Comment: 21 pages, 5 figure
Extreme nonlinear electrodynamics in metamaterials with very small linear dielectric permittivity
We consider a sub-wavelength periodic layered medium whose slabs are filled
by arbitrary linear metamaterials and standard nonlinear Kerr media and we show
that the homogenized medium behaves as a Kerr medium whose parameters can
assume values not available in standard materials. Exploiting such a parameter
availability, we focus on the situation where the linear relative dielectric
permittivity is very small thus allowing the observation of the extreme
nonlinear regime where the nonlinear polarization is comparable with or even
greater than the linear part of the overall dielectric response. The behavior
of the electromagnetic field in the extreme nonlinear regime is very peculiar
and characterized by novel features as, for example, the transverse power flow
reversing. In order to probe the novel regime, we consider a class of fields
(transverse magnetic nonlinear guided waves) admitting full analytical
description and we show that these waves are allowed to propagate even in media
with since the nonlinear polarization produces a
positive overall effective permittivity. The considered nonlinear waves
exhibit, in addition to the mentioned features, a number of interesting
properties like hyper-focusing induced by the phase difference between the
field components.Comment: 12 pages, 7 figure
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