1,130 research outputs found
Light Cone analysis of relativistic first-order in the gradients hydrodynamics
This work applies a Rayleigh-Brillouin light spectrum analysis in order to
establish a causality test by means of a frequency cone. This technique allows
to identify forbidden and unforbidden regions in light scattering experiments
and establishes if a set of linearized transport equations admits causal
solutions. It is shown that, when studying a relativistic fluid with its
acoustic modes interacting with light, Eckart's formalism yields a non causal
behavior. In this case the solutions describing temperature, density and
pressure fluctuations are located outside the frequency cone. In contrast, the
set of equations that arises from modified Eckart's theory (based on
relativistic kinetic theory) yields solutions that lie within the cone, so that
they are causal.Comment: 6 pages, no figure
The Kinematics and Metallicity of the M31 Globular Cluster System
With the ultimate aim of distinguishing between various models describing the
formation of galaxy halos (e.g. radial or multi-phase collapse, random
mergers), we have completed a spectroscopic study of the globular cluster
system of M31. We present the results of deep, intermediate-resolution,
fibre-optic spectroscopy of several hundred of the M31 globular clusters using
the Wide Field Fibre Optic Spectrograph (WYFFOS) at the William Herschel
Telescope in La Palma, Canary Islands. These observations have yielded precise
radial velocities (+/-12 km/s) and metallicities (+/-0.26 dex) for over 200
members of the M31 globular cluster population out to a radius of 1.5 degrees
from the galaxy center. Many of these clusters have no previous published
radial velocity or [Fe/H] estimates, and the remainder typically represent
significant improvements over earlier determinations. We present analyses of
the spatial, kinematic and metal abundance properties of the M31 globular
clusters. We find that the abundance distribution of the cluster system is
consistent with a bimodal distribution with peaks at [Fe/H] = -1.4 and -0.5.
The metal-rich clusters demonstrate a centrally concentrated spatial
distribution with a high rotation amplitude, although this population does not
appear significantly flattened and is consistent with a bulge population. The
metal-poor clusters tend to be less spatially concentrated and are also found
to have a strong rotation signature.Comment: 33 pages, 20 figure
Innovative 3-D Printing Processing Techniques for Flexible and Wearable Planar Rectennas
This work demonstrates the use of a low-cost, lossy, flexible substrate processed by novel 3-D printing techniques which significantly mitigate its intrinsic losses, thus providing performance comparable to those of traditional substrates. These processing techniques are applied to both microstrip and coplanar waveguide structures; they are first derived theoretically, starting from the electromagnetic theory of modes propagation, then numerically validated by full-wave analysis, and finally experimentally verified. The design of a miniaturized 868 MHz rectenna, adopting a coplanar-fed patch antenna based on the proposed fabrication approach, is presented. By means of nonlinear/electromagnetic co-design, the antenna is directly matched to the rectifier. A 30-dB power range starting from -20 dBm is considered. Direct matching allows to get rid of a dedicated matching network and its associated losses, resulting in a slight efficiency increase and a significant reduction of the overall dimensions. Finally, the 3-Dprinted prototype is presented: the overall rectenna performance proves that design freedom enabled by 3-D printing paves the way to the use of low-cost flexible dielectric materials, even with poor electromagnetic properties, to realize wearable battery-free wireless nodes
Spectral Energy Distributions and Age Estimates of 172 Globular Clusters in M31
In this paper we present CCD multicolor photometry for 172 globular clusters
(GCs), taken from the Bologna catalog (Battistini et al. 1987), in the nearby
spiral galaxy M31. The observations were carried out by using the National
Astronomical Observatories 60/90 cm Schmidt Telescope in 13 intermediate-band
filters, which covered a range of wavelength from 3800 to 10000A. This provides
a multicolor map of M31 in pixels of 1.7"*1.7". By aperture photometry, we
obtain the spectral energy distributions (SEDs) for these GCs. Using the
relationship between the BATC intermediate-band system used for the
observations and the UBVRI broad-band system, the magnitudes in the B and V
bands are derived. The computed V and B-V are in agreement with the values
given by Battistini et al. (1987) and Barmby et al. (2000). Finally, by
comparing the photometry of each GC with theoretical stellar population
synthesis models, we estimate ages of the sample GCs for different
metallicities. The results show that nearly all our sample GCs have ages more
than 10^{9} years, and most of them are around 10^{10} years old. Also, we find
that GCs fitted by the metal-poor model are generally older than ones fitted by
the metal-rich model.Comment: 38 pages, 7 figures will appear in the February 2003 issue of A
Wide-Field Survey of Globular Clusters in M31. I. A Catalog of New Clusters
We present the result of a wide-field survey of globular clusters (GCs) in
M31 covering a 3deg x 3deg field c. We have searched for GCs on CCD images
taken with Washington CMT1 filters at the KPNO 0.9 m telescope using steps: (1)
inspection of morphological parameters given by the SExtractor package such as
stellarity, full maximum, and ellipticity; (2) consulting the spectral types
and radial velocities obtained from spectra takena spectrograph at the WIYN 3.5
m telescope; and (3) visual inspection of the images of each object. We have
and GC candidates, of which 605 are newly found GCs and GC candidates and 559
are previously known GCs. Amoects there are 113 genuine GCs, 258 probable GCs,
and 234 possible GCs, according to our classification critee known objects
there are 383 genuine GCs, 109 probable GCs, and 67 possible GCs. In total
there are 496 genprobable GCs and 301 possible GCs. Most of these newly found
GCs have T1 magnitudes of 17.5 - 19.5 mag, [17.9 < V < 19.9 mag assuming (C-T1)
~ 1.5], and (C-T1) colors in the range 1 - 2.Comment: accepted by AJ, using emulateapj.cl
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