3,778 research outputs found
Light capsules shaped by curvilinear meta-surfaces
We propose a simple yet efficient method for generating in-plane hollow beams
with a nearly-full circular light shell without the contribution of backward
propagating waves. The method relies on modulating the phase in the near field
of a centro-symmetric optical wavefront, such as that from a
high-numericalaperture focused wave field. We illustrate how beam acceleration
may be carried out by using an ultranarrow non-flat meta-surface formed by
engineered plasmonic nanoslits. A mirrorsymmetric, with respect to the optical
axis, circular caustic surface is numerically demonstrated that can be used as
an optical bottle
A dense micro-cluster of Class 0 protostars in NGC 2264 D-MM1
We present sensitive and high angular resolution (~1") 1.3 mm continuum
observations of the dusty core D-MM1 in the Spokes cluster in NGC 2264 using
the Submillimeter Array. A dense micro-cluster of seven Class 0 sources was
detected in a 20" x 20" region with masses between 0.4 to 1.2 solar masses and
deconvolved sizes of about 600 AU. We interpret the 1.3 mm emission as arising
from the envelopes of the Class 0 protostellar sources. The mean separation of
the 11 known sources (SMA Class 0 and previously known infrared sources) within
D-MM1 is considerably smaller than the characteristic spacing between sources
in the larger Spokes cluster and is consistent with hierarchical thermal
fragmentation of the dense molecular gas in this region.Comment: Accepted for publication in the Astrophysical Journal Letter
In situ conservation of crop wild relatives
Poster presented at 13. Meeting of the Subsidiary Body on Scientific, Technical and Technological Advice (SBSTTA) held in FAO, Rome (Italy), 18-22 Feb 200
Spectroscopic measurements of solar wind generation
Spectroscopically observable quantities are described which are sensitive to the primary plasma parameters of the solar wind's source region. The method is discussed in which those observable quantities are used as constraints in the construction of empirical models of various coronal structures. Simulated observations are used to examine the fractional contributions to observed spectral intensities from coronal structures of interest which co-exist with other coronal structures along simulated lines-of-sight. The sensitivity of spectroscopic observables to the physical parameters within each of those structures is discussed
Comment on ``Phase and Phase Diffusion of a Split Bose-Einstein Condensate''
Recently Javanainen and Wilkens [Phys. Rev. Lett. 78, 4675 (1997)] have
analysed an experiment in which an interacting Bose condensate, after being
allowed to form in a single potential well, is "cut" by splitting the well
adiabatically with a very high potential barrier, and estimate the rate at
which, following the cut, the two halves of the condensate lose the "memory" of
their relative phase. We argue that, by neglecting the effect of interactions
in the initial state before the separation, they have overestimated the rate of
phase randomization by a numerical factor which grows with the interaction
strength and with the slowness of the separation process.Comment: 2 pages, no figures, to appear in Phys. Rev. Let
Andreev reflection in bosonic condensates
We study the bosonic analog of Andreev reflection at a normal-superfluid
interface where the superfluid is a boson condensate. We model the normal
region as a zone where nonlinear effects can be neglected. Against the
background of a decaying condensate, we identify a novel contribution to the
current of reflected atoms. The group velocity of this Andreev reflected
component differs from that of the normally reflected one. For a
three-dimensional planar or two-dimensional linear interface Andreev reflection
is neither specular nor conjugate.Comment: 5 pages, 3 figures. Text revise
Geometrical Shape Optimization of a Cavity Receiver Using Coupled Radiative and Hydrodynamic Modeling
AbstractBy using a two-stage optimisation process we maximise the heat rate output of afour-parameter axisymmetric direct steam generation cavity receiver. The model includes radiative and hydrodynamic considerations. We show that a significant range of geometrical shapes show similar efficiencies while having different wall flux and temperature profiles
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