44,197 research outputs found
Correlation of Low z Lyman-alpha Absorbers with HI-selected Galaxies
In this work, observational evidence for the connection between low column
density Lyman-alpha absorbers and large-scale structure traced by gas-rich
galaxies is investigated. The HI Parkes All Sky Survey (HIPASS) galaxy
catalogue is cross-correlated with known low redshift, low column density
Lyman-alpha absorbers from the literature. The absorber-galaxy
cross-correlation function shows that on scales from 1 to 10 h^-1 Mpc,
absorbers are imbedded in halos with masses similar to that of galaxy groups.
This statistical evidence suggests that galaxy groups could be the dominant
environment of low column density Lyman-alpha absorbers at z=0.Comment: 3 pages, 1 figure, to appear in IAU 199 conf. proc.: "Probing
Galaxies through Quasar Absorption Lines," eds. Williams, Shu, Menar
Cross correlation of Lyman-alpha absorbers with gas-rich galaxies
The HI Parkes All Sky Survey (HIPASS) galaxy catalogue is cross-correlated
with known low redshift, low column density (N_HI <10^15 cm^-2) Lyman-alpha
absorbers from the literature. The redshift-space correlation is found to be
similar in strength to HIPASS galaxy self-clustering (correlation length
s_0,ag=6+/-4 and s_0,gg=3.1+/-0.5 h^-1 Mpc respectively). In real-space the
cross-correlation is stronger than the galaxy auto-correlation (correlation
length r_0,ag=7.2+/-1.4 and r_0,gg=3.5+/-0.7 h^-1 Mpc respectively) on scales
from 1-10 h^-1 Mpc, ruling out the mini-halo model for the confinement
Lyman-alpha absorbers at the 99 percent confidence level. Provided that the
cause of the strong cross-correlation is purely gravitational, the ratio of
correlation lengths suggest that absorbers are embedded in dark matter haloes
with masses log(M/Msun)=14.2 h^-1, similar to those of galaxy groups. The
flattening of the cross-correlation at separations less than ~600 h^-1 kpc
could correspond to the thickness of filaments in which absorbers are embedded.
This work provides indirect statistical evidence for the notion that galaxy
groups and large-scale filaments, particularly those that comprise gas-rich
galaxies, are the dominant environments of low column density Lyman-alpha
absorbers at z=0.Comment: 10 pages, 10 figures, accepted for publication in MNRAS, minor typos
fixed and references update
Size effect and the quadratic temperature dependence of the transverse magnetoresistivity in "size-effect" tungsten single crystals
The transverse magnetoresistivity of pure tungsten single crystals with a residual resistivity ratio ρ293K/ρ4.2K of about 75000 was measured from 4.2 to 20 K and in magnetic fields of up to 15 T. The size effect, i.e. the linear dependence of the magnetoconductivity on the inverse cross sample dimensions, was studied in detail at high fields. We show that the size effect can be used for the separation of the contributions from the electron-surface and the electron-phonon scattering mechanisms to the full conductivity. We demonstrate that the electron-phonon scattering leads to the exponential temperature dependence of the conductivity, and the interference between the electron-phonon and the electron-surface processes leads to a new scattering mechanism "electron-phonon-surface" with a quadratic temperature dependence of the magnetoconductivity. © Published under licence by IOP Publishing Ltd
Voting on the choice of core languages in the European Union
This is the post-print version of the final paper published in European Journal of Political Economy. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2008 Elsevier B.V.Extensive multilingualism is one of the most important and fundamental principles of the European Union (EU). However, a large number of languages (currently 23) hinders communication and imposes substantial financial and legal costs. On the other hand, the reduction of the number of languages would disenfranchise some or many EU citizens. We use the results of a survey on languages and argue that even though a linguistic reform reducing the number of languages is unlikely to gain sufficient political support today, this may change in the future since young people are more proficient at speaking foreign languages
Asymptotic distributions for a class of generalized -statistics
We adapt the techniques in Stigler [Ann. Statist. 1 (1973) 472--477] to
obtain a new, general asymptotic result for trimmed -statistics via the
generalized -statistic representation introduced by Serfling [Ann. Statist.
12 (1984) 76--86]. Unlike existing results, we do not require continuity of an
associated distribution at the truncation points. Our results are quite general
and are expressed in terms of the quantile function associated with the
distribution of the -statistic summands. This approach leads to improved
conditions for the asymptotic normality of these trimmed -statistics.Comment: Published in at http://dx.doi.org/10.3150/09-BEJ240 the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Sidereal time analysis as a toll for the study of the space distribution of sources of gravitational waves
Gravitational wave (GW) detectors operating on a long time range can be used
for the study of space distribution of sources of GW bursts or to put strong
upper limits on the GW signal of a wide class of source candidates. For this
purpose we propose here a sidereal time analysis to analyze the output signal
of GW detectors. Using the characteristics of some existing detectors, we
demonstrate the capability of the sidereal time analysis to give a clear
signature of different localizations of GW sources: the Galactic Center, the
Galactic Plane, the Supergalactic plane, the Great Attractor. On the contrary,
a homogeneous 3D-distribution of GW sources gives a signal without features. In
this paper we consider tensor gravitational waves with randomly oriented
polarization. We consider GW detectors at fixed positions on the Earth, and a
fixed orientation of the antenna.Comment: 7 pages, 6 figure
Conductance oscillations in mesoscopic rings: microscopic versus macroscopic picture
The phase of Aharonov-Bohm oscillations in mesoscopic metal rings in the
presence of a magnetic field can be modulated by application of a DC-bias
current I_DC. We address the question of how a variation of I_DC and hence of
the microscopic phases of the electronic wave functions results in the
macroscopic phase of the conductance oscillations. Whereas the first one can be
varied continuously the latter has to be quantized for a ring in two-wire
configuration by virtue of the Onsager symmetry relations. We observe a
correlation between a phase flip by +/- pi and the amplitude of the
oscillations.Comment: 4 pages, 4 figure
Shape-induced phenomena in the finite size antiferromagnets
It is of common knowledge that the direction of easy axis in the finite-size
ferromagnetic sample is controlled by its shape. In the present paper we show
that a similar phenomenon should be observed in the compensated
antiferromagnets with strong magnetoelastic coupling. Destressing energy which
originates from the long-range magnetoelastic forces is analogous to
demagnetization energy in ferromagnetic materials and is responsible for the
formation of equilibrium domain structure and anisotropy of macroscopic
magnetic properties. In particular, crystal shape may be a source of additional
uniaxial magnetic anisotropy which removes degeneracy of antiferromagnetic
vector or artificial 4th order anisotropy in the case of a square cross-section
sample. In a special case of antiferromagnetic nanopillars shape-induced
anisotropy can be substantially enhanced due to lattice mismatch with the
substrate. These effects can be detected by the magnetic rotational torque and
antiferromagnetic resonance measurements.Comment: 7 pages, 5 figures, to appear in Phys. Rev. B, v.75, N17, 200
Evolution of damped Lyman alpha kinematics and the effect of spatial resolution on 21-cm measurements
We have investigated the effect of spatial resolution on determining
pencil-beam like velocity widths and column densities in galaxies. Three 21-cm
datasets are used, the HIPASS galaxy catalogue, a subset of HIPASS galaxies
with ATCA maps and a high-resolution image of the LMC. Velocity widths measured
from 21-cm emission in local galaxies are compared with those measured in
intermediate redshift Damped Lyman alpha (DLA) absorbers. We conclude that
spatial resolution has a severe effect on measuring pencil-beam like velocity
widths in galaxies. Spatial smoothing by a factor of 240 is shown to increase
the median velocity width by a factor of two. Thus any difference between
velocity widths measured from global profiles or low spatial resolution 21-cm
maps at z=0 and DLAs at z>1 cannot unambiguously be attributed to galaxy
evolution. The effect on column density measurements is less severe and the
values of dN/dz from local low-resolution 21-cm measurements are expected to be
overestimated by only ~10 per cent.Comment: 5 pages, 6 figures, accepted for publication in MNRAS letter
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