348 research outputs found
Complex refraction metasurfaces for locally enhanced propagation through opaque media
Metasurfaces with linear phase gradients can redirect light beams. We propose
controlling both phase and amplitude of a metasurface to extend Snell's law to
the realm of complex angles, enabling a non-decaying transmission through
opaque media with complex refractive indices. This leads to the discovery of
non-diffracting and non-decaying solutions to the wave equation in opaque
media, in the form of generalised cosine and Bessel-beams with a complex
argument. While these solutions present nonphysical exponentially growing side
tails, we address this via a windowing process, removing the side tails of the
field profile while preserving significant transmission enhancement through an
opaque slab on a small localized region. Such refined beam profiles may be
synthesized by passive metasurfaces with phase and amplitude control at the
opaque material's interface. Our findings, derived from rigorous solutions of
the wave equation, promise new insights and enhanced control of light
propagation in opaque media.Comment: 9 pages, 3 figure
Anomalous temperature dependence of the first diffraction peak in vitreous boron trioxide
11 págs.; 9 figs.The temperature dependence of the parameters characterizing the first peak in the S(Q) and S(Q,E=0) diffraction patterns of vitreous boron trioxide is considered in some detail. The analysis of the experimental spectra is aided by results derived from molecular-dynamics simulations, which enable us to isolate the most relevant features driving the variation with temperature of both structure factors. The relevance of the present results regarding some recent phenomenological approaches developed towards the understanding of the dynamics of glasses at intermediate temperatures is finally discussed. ©1996 American Physical SocietyWork was performed in part under D.G.I.C.Y.T (Spain)
Grant No. PB92-0114-C03-01. Financial support from the
Large Scale Facilities Programme of the European Union for
the measurements carried at Risoe National Laboratory
(Denmark) is acknowledged. J.D. wishes to thank CONICET
(Argentina) and CSIC (Spain) for financial support.Peer Reviewe
Microscopic structure of Fe-Ni and Fe-Ni-S molten alloys of geophysical interest
9 págs.; 9 figs.; 2 tabs. ; PACS number(s): 61.25.Mv, 62.60.1v, 96.35.2jThe static S(Q) liquid structure factors for binary FexNi 1-x, x=0.90, 0.85, and ternary Fe0.85Ni 0.05S0.15 molten alloys are investigated by means of the concurrent use of neutron diffraction and reverse Monte Carlo simulations. The measured G(r) radial distributions reveal atomic orderings varying from that present in the Fe0.90Ni0.10 alloy, reminiscent of the ideal bcc structure of solid Fe, to a far more open structure found in Fe 0.85Ni0.05S0.15. From data at hand no clear evidence of the clustering of sulfur within the Fe-Ni matrix is found. In contrast, the addition of sulfur leads to significant changes in structural and some dynamical properties that can be inferred from knowledge of the static structure factors. Such dynamical changes seem to arise as a result of a strong decrease of the elastic moduli of the alloys resulting from interactions with a light element rather than from a density effect. ©2004 American Physical SocietyWe thank the Institut Laue Langevin for neutron beam
time.We are grateful to Pierre Palleau and to Dr. J. Campo of
ILL for his technical support during the diffraction experiments,
and Carlos Ayala of Centro Atómico Bariloche for the
sample preparationPeer Reviewe
Static structure factor of liquid parahydrogen
7 págs.; 5 figs. ; PACS number~s!: 61.20.2p, 61.12.2q, 78.70.2gThe single-differential neutron-scattering cross section of liquid parahydrogen has been measured at 15.2 K and 2 bars of applied pressure by means of low-energy neutron diffraction. Our experimental conditions enable the direct observation of the peak of the liquid structure factor and therefore largely improve the signal-to-noise ratio with respect to measurements carried out using higher-energy neutron diffraction. This avoids the need of performing corrections of approximate nature to the measured cross section that is dominated by molecular rotational components if measured by conventional neutron diffraction. ©2004 American Physical SocietyPeer Reviewe
Anharmonic dynamics in crystalline, glassy, and supercooled-liquid glycerol: A case study on the onset of relaxational behavior
10 págs.; 8 figs.The temperature dependence of the spectral distributions of the glass, crystalline, and supercooled-liquid phases of glycerol is investigated by means of neutron inelastic scattering. The importance of anharmonic effects is quantified by the temperature dependence of reduced spectral frequency moments. The onset of relaxational (i.e., stochastic, zero-frequency) motions in the supercooled liquid state is monitored by neutron quasielastic scattering. A substantial deviation of the observed linewidths from the hydrodynaimc prescription is observed and is interpreted at a microscopic level, by comparison with the crystalline phase. ©1998 American Physical SocietyWork supported in part by DGICYT ~Spain! Grant No.
PB95-0075-c03-01. Dr. O. Randl of the Institute Laue
Langevin is acknowledged for the help given during the
measurements at the IN10 spectrometer. The work at ANL
was supported by the U.S. Department of Energy, BESMaterials
Sciences, under Contract No. W-31-109-ENG-38.Peer Reviewe
Galaxy clusters and groups in the ALHAMBRA Survey
We present a catalogue of 348 galaxy clusters and groups with
selected in the 2.78 ALHAMBRA Survey. The high precision of our
photometric redshifts, close to , and the wide spread of the seven
ALHAMBRA pointings ensure that this catalogue has better mass sensitivity and
is less affected by cosmic variance than comparable samples.
The detection has been carried out with the Bayesian Cluster Finder (BCF),
whose performance has been checked in ALHAMBRA-like light-cone mock catalogues.
Great care has been taken to ensure that the observable properties of the mocks
photometry accurately correspond to those of real catalogues. From our
simulations, we expect to detect galaxy clusters and groups with both
completeness and purity down to dark matter halo masses of
for . Cluster redshifts are
expected to be recovered with precision for . We also expect
to measure cluster masses with
precision down to , masses which are
smaller than those reached by similar work.
We have compared these detections with previous optical, spectroscopic and
X-rays work, finding an excellent agreement with the rates reported from the
simulations. We have also explored the overall properties of these detections
such as the presence of a colour-magnitude relation, the evolution of the
photometric blue fraction and the clustering of these sources in the different
ALHAMBRA fields. Despite the small numbers, we observe tentative evidence that,
for a fixed stellar mass, the environment is playing a crucial role at lower
redshifts (z0.5).Comment: Accepted for publication in MNRAS. Catalogues and figures available
online and under the following link:
http://bascaso.net46.net/ALHAMBRA_clusters.htm
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