11,262 research outputs found
Forces on Bins - The Effect of Random Friction
In this note we re-examine the classic Janssen theory for stresses in bins,
including a randomness in the friction coefficient. The Janssen analysis relies
on assumptions not met in practice; for this reason, we numerically solve the
PDEs expressing balance of momentum in a bin, again including randomness in
friction.Comment: 11 pages, LaTeX, with 9 figures encoded, gzippe
Long lasting instabilities in granular mixtures
We have performed experiments of axial segregation in the Oyama's drum. We
have tested binary granular mixtures during very long times. The segregation
patterns have been captured by a CCD camera and spatio-temporal graphs are
created. We report the occurence of instabilities which can last several hours.
We stress that those instabilities originate from the competition between axial
and radial segregations. We put into evidence the occurence of giant
fluctuations in the fraction of grain species along the surface during the
unstable periods.Comment: 10 pages, 10 figures, (2002
The Variable Stars of the Draco Dwarf Spheroidal Galaxy - Revisited
We present a CCD survey of variable stars in the Draco dwarf spheroidal
galaxy. This survey, which has the largest areal coverage since the original
variable star survey by Baade & Swope, includes photometry for 270 RR Lyrae
stars, 9 anomalous Cepheids, 2 eclipsing binaries, and 12 slow, irregular red
variables, as well as 30 background QSOs. Twenty-six probable double-mode RR
Lyrae stars were identified. Observed parameters, including mean V and I
magnitudes, V amplitudes, and periods, have been derived. Photometric
metallicities of the ab-type RR Lyrae stars were calculated according to the
method of Jurcsik & Kovacs, yielding a mean metallicity of = -2.19 +/-
0.03. The well known Oosterhoff intermediate nature of the RR Lyrae stars in
Draco is reconfirmed, although the double-mode RR Lyrae stars with one
exception have properties similar to those found in Oosterhoff type II globular
clusters. The period-luminosity relation of the anomalous Cepheids is
rediscussed with the addition of the new Draco anomalous Cepheids.Comment: Accepted to AJ. 61 pages, 14 figures, 10 table
Nature of -wave interaction and dibaryon production at nucleonic resonance thresholds
Phase shifts and inelasticity parameters for scattering in the
partial-wave channels -- and at energies from zero to about 1 GeV are described within a unified potential
model assuming the formation of isoscalar and isovector dibaryon resonances
near the threshold. Evidence for these near-threshold resonances
is actually found in the recent WASA experiments on single- and double-pion
production in collisions. There, the excitation of the Roper resonance
exhibits a structure in the energy dependence of the total cross
section, which corresponds to the formation of dibaryon states with
and at the threshold. These two
-wave dibaryon resonances may provide a new insight into the nature of the
strong interaction at low and intermediate energies.Comment: 10 pages, 8 figure
The first Frontier Fields cluster: 4.5{\mu}m excess in a z~8 galaxy candidate in Abell 2744
We present in this letter the first analysis of a z~8 galaxy candidate found
in the Hubble and Spitzer imaging data of Abell 2744, as part of the Hubble
Frontier Fields legacy program. We applied the most commonly-used methods to
select exceptionally high-z galaxies by combining non-detection and
color-criteria using seven HST bands. We used GALFIT on IRAC images for fitting
and subtracting contamination of bright nearby sources. The physical properties
have been inferred from SED-fitting using templates with and without nebular
emission. This letter is focussed on the brightest candidate we found
(m=26.2) over the 4.9 arcmin field of view covered by the WFC3.
It shows a non-detection in the ACS bands and at 3.6{\mu}m whereas it is
clearly detected at 4.5{\mu}m with rather similar depths. This break in the
IRAC data could be explained by strong [OIII]+H{\beta} lines at z~8 which
contribute to the 4.5{\mu}m photometry. The best photo-z is found at
z~8.0, although solutions at low-redshift (z~1.9) cannot be
completely excluded, but they are strongly disfavoured by the SED-fitting work.
The amplification factor is relatively small at {\mu}=1.490.02. The Star
Formation Rate in this object is ranging from 8 to 60 Mo/yr, the stellar mass
is in the order of M=(2.5-10) x 10Mo and the size is
r~0.350.15 kpc. This object is one of the first z~8 LBG candidates showing
a clear break between 3.6{\mu}m and 4.5{\mu}m which is consistent with the IRAC
properties of the first spectroscopically confirmed galaxy at a similar
redshift. Due to its brightness, the redshift of this object could potentially
be confirmed by near infrared spectroscopy with current 8-10m telescopes. The
nature of this candidate will be revealed in the coming months with the arrival
of new ACS and Spitzer data, increasing the depth at optical and near-IR
wavelengths.Comment: 4 pages, 2 figures, Accepted for publication in Astronomy and
Astrophysics Letter
Deforestation and capital accumulation : lessons from the Upper Kerinci Region, Indonesia.
This study outlines a case where the behaviour of farmers in accumulating capital, rather than their poverty as commonly assumed, results in deforestation. Fieldwork was undertaken in the Upper Kerinci region of the island of Sumatera, Indonesia. A financial analysis of the "net income" streams received by farmers from deforestation is performed. Because forest lands can be "captured" and privatised through clearing, forest clearing and the subsequent agriculture have the capacity to produce high financial returns for farmers as well as to provide adequate capital to finance the next forest clearing. Such a capacity enables landless farmers to become land owners. Forest clearing also enables farmers to own a "long-term maturity bond" in the form of a cinnamon plantation. Poverty precludes poorer farmers from deforestation, and decisions to clear a forest rest mostly with more established farmers. Financial surpluses from outside the forestry and agricultural sectors are also used to finance forest clearing
All stationary axi-symmetric local solutions of topologically massive gravity
We classify all stationary axi-symmetric solutions of topologically massive
gravity into Einstein, Schr\"odinger, warped and generic solutions. We
construct explicitly all local solutions in the first three sectors and present
an algorithm for the numerical construction of all local solutions in the
generic sector. The only input for this algorithm is the value of one constant
of motion if the solution has an analytic centre, and three constants of motion
otherwise. We present several examples, including soliton solutions that
asymptote to warped AdS.Comment: 42 pages, 9 figures. v2: Changed potentially confusing labelling of
one sector, added references. v3: Minor changes, matches published versio
Possible observation sequences of Brans-Dicke wormholes
The purpose of this study is to investigate observational features of
Brans-Dicke wormholes in a case if they exist in our Universe. The energy flux
from accretion onto a Brans-Dicke wormhole and the so-called "maximum impact
parameter" are studied (the last one might allow to observe light sources
through a wormhole throat). The computed values were compared with the
corresponding ones for GR-wormholes and Schwarzschild black holes. We shown
that Brans-Dicke wormholes are quasi-Schwarzschild objects and should differ
from GR wormholes by about one order of magnitude in the accretion energy flux.Comment: 5 pages, 6 figure
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