44,641 research outputs found
Inflation, Renormalization, and CMB Anisotropies
In single-field, slow-roll inflationary models, scalar and tensorial
(Gaussian) perturbations are both characterized by a zero mean and a non-zero
variance. In position space, the corresponding variance of those fields
diverges in the ultraviolet. The requirement of a finite variance in position
space forces its regularization via quantum field renormalization in an
expanding universe. This has an important impact on the predicted scalar and
tensorial power spectra for wavelengths that today are at observable scales. In
particular, we find a non-trivial change in the consistency condition that
relates the tensor-to-scalar ratio "r" to the spectral indices. For instance,
an exact scale-invariant tensorial power spectrum, n_t=0, is now compatible
with a non-zero ratio r= 0.12 +/- 0.06, which is forbidden by the standard
prediction (r=-8n_t). Forthcoming observations of the influence of relic
gravitational waves on the CMB will offer a non-trivial test of the new
predictions.Comment: 4 pages, jpconf.cls, to appear in the Proceedings of Spanish
Relativity Meeting 2009 (ERE 09), Bilbao (Spain
Rural Employment At A Glance
Rural Employment At A Glance is a six-page brochure that highlights the most recent indicators of employment and unemployment in rural areas. It documents changes and differences in metro and nonmetro employment growth, unemployment, earnings per job, and occupational mix, as well as differences across nonmetro areas by location and county type.employment, unemployment, metro, nonmetro, rural, urban, earnings, occupation, employment growth, unemployment rate, Community/Rural/Urban Development, Crop Production/Industries,
South Asian Regional Workshop on Groundwater Farmer-Managed Irrigation Systems and Sustainable Groundwater Management, Dhaka, Bangladesh 18-21 May 1992
Farmer managed irrigation systems, Groundwater management, Sustainability, Bangladesh
Effect of doping and pressure on magnetism and lattice structure of Fe-based superconductors
Using first principles calculations, we analyze structural and magnetic
trends as a function of charge doping and pressure in BaFeAs, and
compare to experimentally established facts. We find that density functional
theory, while accurately reproducing the structural and magnetic ordering at
ambient pressure, fails to reproduce some structural trends as pressure is
increased. Most notably, the Fe-As bondlength which is a gauge of the magnitude
of the magnetic moment, , is rigid in experiment, but soft in calculation,
indicating residual local Coulomb interactions. By calculating the magnitude of
the magnetic ordering energy, we show that the disruption of magnetic order as
a function of pressure or doping can be qualitatively reproduced, but that in
calculation, it is achieved through diminishment of , and therefore
likely does not reflect the same physics as detected in experiment. We also
find that the strength of the stripe order as a function of doping is strongly
site-dependent: magnetism decreases monotonically with the number of electrons
doped at the Fe site, but increases monotonically with the number of electrons
doped at the Ba site. Intra-planar magnetic ordering energy (the difference
between checkerboard and stripe orderings) and interplanar coupling both follow
a similar trend. We also investigate the evolution of the orthorhombic
distortion, as a function of , and find that in the
regime where experiment finds a linear relationship, our calculations are
impossible to converge, indicating that in density functional theory, the
transition is first order, signalling anomalously large higher order terms in
the Landau functional
BCS theory of nodal superconductors
This course has a dual purpose. First we review the successes of the
weak-coupling BCS theory in describing new classes of superconductors
discovered since 1979. They include the heavy-fermion superconductors, high-Tc
cuprate superconductors, organic superconductors, Sr2RuO4, etc. Second, we
present the quasiclassical approximation introduced by Volovik, which we extend
to describe the thermodynamics and the thermal conductivity of the vortex state
in nodal superconductors. This approach provides the most powerful tool to
identify the symmetry of the energy gap function Delta(k) in these new
superconductors.Comment: 31 pages, 33 figure
Radio-continuum detections of Galactic Planetary Nebulae I. MASH PNe detected in large-scale radio surveys
We present an updated and newly compiled radio-continuum data-base for MASH
PNe detected in the extant large scale "blind" radio-continuum surveys (NVSS,
SUMSS/MGPS-2 and PMN) and, for a small number of MASH PNe, observed and
detected in targeted radio-continuum observations. We found radio counterparts
for approximately 250 MASH PNe. In comparison with the percentage of previously
known Galactic PNe detected in the NVSS and MGPS-2 radio-continuum surveys and
according to their position on the flux density-angular diameter and the radio
brightness temperature evolutionary diagrams we conclude, unsurprisingly, that
the MASH sample presents the radio-faint end of the known Galactic PNe
population. Also, we present radio-continuum spectral properties of a small
sub-sample of MASH PNe located in the strip between declinations -30arcdeg and
-40arcdeg, that are detected in both the NVSS and MGPS-2 radio surveys.Comment: 13 figures and 7 tables, accepted for publication in MNRA
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