4,768 research outputs found
The Impact of Halo Properties, Energy Feedback and Projection Effects on the Mass-SZ Flux Relation
We present a detailed analysis of the intrinsic scatter in the integrated SZ
effect - cluster mass (Y-M) relation, using semi-analytic and simulated cluster
samples. Specifically, we investigate the impact on the Y-M relation of energy
feedback, variations in the host halo concentration and substructure
populations, and projection effects due to unresolved clusters along the line
of sight (the SZ background). Furthermore, we investigate at what radius (or
overdensity) one should measure the integrated SZE and define cluster mass so
as to achieve the tightest possible scaling. We find that the measure of Y with
the least scatter is always obtained within a smaller radius than that at which
the mass is defined; e.g. for M_{200} (M_{500}) the scatter is least for
Y_{500} (Y_{1100}). The inclusion of energy feedback in the gas model
significantly increases the intrinsic scatter in the Y-M relation due to larger
variations in the gas mass fraction compared to models without feedback. We
also find that variations in halo concentration for clusters of a given mass
may partly explain why the integrated SZE provides a better mass proxy than the
central decrement. Substructure is found to account for approximately 20% of
the observed scatter in the Y-M relation. Above M_{200} = 2x10^{14} h^{-1}
msun, the SZ background does not significantly effect cluster mass
measurements; below this mass, variations in the background signal reduce the
optimal angular radius within which one should measure Y to achieve the
tightest scaling with M_{200}.Comment: 12 pages, 6 figures, to be submitted to Ap
Intrinsic and structural isotope effects in Fe-based superconductors
The currently available results of the isotope effect on the superconducting
transition temperature T_c in Fe-based high-temperature superconductors (HTS)
are highly controversial. The values of the Fe isotope effect (Fe-IE) exponent
\alpha_Fe for various families of Fe-based HTS were found to be as well
positive, as negative, or even be exceedingly larger than the BCS value
\alpha_BCS=0.5. Here we demonstrate that the Fe isotope substitution causes
small structural modifications which, in turn, affect T_c. Upon correcting the
isotope effect exponent for these structural effects, an almost unique value of
\alpha~0.35-0.4 is observed for at least three different families of Fe-based
HTS.Comment: 4 pages, 2 figure
Possible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals
International audiencePossible configurations of the magnetic field in the outer magnetosphere during geomagnetic polarity reversals are investigated by considering the idealized problem of a magnetic multipole of order m and degree n located at the centre of a spherical cavity surrounded by a boundless perfect diamagnetic medium. In this illustrative idealization, the fixed spherical (magnetopause) boundary layer behaves as a perfectly conducting surface that shields the external diamagnetic medium from the compressed multipole magnetic field, which is therefore confined within the spherical cavity. For a general magnetic multipole of degree n, the non-radial components of magnetic induction just inside the magnetopause are increased by the factor {1 + [(n + 1)/n]} relative to their corresponding values in the absence of the perfectly conducting spherical magnetopause. An exact equation is derived for the magnetic field lines of an individual zonal (m = 0), or axisymmetric, magnetic multipole of arbitrary degree n located at the centre of the magnetospheric cavity. For such a zonal magnetic multipole, there are always two neutral points and n-1 neutral rings on the spherical magnetopause surface. The two neutral points are located at the poles of the spherical magnetopause. If n is even, one of the neutral rings is coincident with the equator; otherwise, the neutral rings are located symmetrically with respect to the equator. The actual existence of idealized higher-degree (n>1) axisymmetric magnetospheres would necessarily imply multiple (n + 1) magnetospheric cusps and multiple (n) ring currents. Exact equations are also derived for the magnetic field lines of an individual non-axisymmetric magnetic multipole, confined by a perfectly conducting spherical magnetopause, in two special cases; namely, a symmetric sectorial multipole (m = n) and an antisymmetric sectorial multipole (m = n-1). For both these non-axisymmetric magnetic multipoles, there exists on the spherical magnetopause surface a set of neutral points linked by a network of magnetic field lines. Novel magnetospheric processes are likely to arise from the existence of magnetic neutral lines that extend from the magnetopause to the surface of the Earth. Finally, magnetic field lines that are confined to, or perpendicular to, either special meridional planes or the equatorial plane, when the multipole is in free space, continue to be confined to, or perpendicular to, these same planes when the perfectly conducting magnetopause is present
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Revised classification of the soils of Belize
The soil classification of Belize is revised and updated, starting from the system devised for 'Land in British Honduras' by A. C. S. Wright and his colleagues in the 1950s, the only previous country-wide survey of soils and land resources. The revised classification is a three-tiered system consisting of soil suites, subsuites and series. The suites are based on rock type, and the subsuites on soil profile characteristics. The main groups of soils, the soil suites, and the soil subsuites are described separately at progressively increasing levels of detail. There are insufficient data to describe soil series as yet, but guidelines for the definition and naming of new series are indicated. The classes of the revised system are correlated with all of the soil classifications previously used in Belize, and with the two main international systems of soil classification. Important chemical features of the-main soil groups are summarized and compared. The comparisons vindicate the revised classification
Predictions of the causal entropic principle for environmental conditions of the universe
The causal entropic principle has been proposed as a superior alternative to
the anthropic principle for understanding the magnitude of the cosmological
constant. In this approach, the probability to create observers is assumed to
be proportional to the entropy production \Delta S in a maximal causally
connected region -- the causal diamond. We improve on the original treatment by
better quantifying the entropy production due to stars, using an analytic model
for the star formation history which accurately accounts for changes in
cosmological parameters. We calculate the dependence of \Delta S on the density
contrast Q=\delta\rho/\rho, and find that our universe is much closer to the
most probable value of Q than in the usual anthropic approach and that
probabilities are relatively weakly dependent on this amplitude. In addition,
we make first estimates of the dependence of \Delta S on the baryon fraction
and overall matter abundance. Finally, we also explore the possibility that
decays of dark matter, suggested by various observed gamma ray excesses, might
produce a comparable amount of entropy to stars.Comment: RevTeX4, 13pp, 10 figures; v2. clarified introduction, added ref
Students as neighbors: utilizing dialogue and deliberation to manage town-gown tensions
The integration of the university and its students into the broader Harrisonburg community has promoted increased interaction amongst JMU students, JMU faculty and staff, and community members. Navigating this complex relationship can be challenging and, in recent years, this relationship has become increasingly strained. The following research seeks to cultivate processes that aid in its improvement. The research finds that utilizing dialogue and deliberation as an approach to designing public process is a promising approach to mending and maintaining the relationship between JMU students and the broader Harrisonburg community, as well as to addressing town-gown tension at large. The research also employs a unique, flexible, methodology to allow for ongoing learning in developing a multi-phased, responsive process that helps participants move from understanding to finding sustainable solutions. The research offers insights into how information and perceptions that emerge in dialogic conversation can be used to design processes that transition into collaborative solutions for town-gown tensions
The polarizability model for ferroelectricity in perovskite oxides
This article reviews the polarizability model and its applications to
ferroelectric perovskite oxides. The motivation for the introduction of the
model is discussed and nonlinear oxygen ion polarizability effects and their
lattice dynamical implementation outlined. While a large part of this work is
dedicated to results obtained within the self-consistent-phonon approximation
(SPA), also nonlinear solutions of the model are handled which are of interest
to the physics of relaxor ferroelectrics, domain wall motions, incommensurate
phase transitions. The main emphasis is to compare the results of the model
with experimental data and to predict novel phenomena.Comment: 55 pages, 35 figure
Constraints on Cosmological Parameters from Future Galaxy Cluster Surveys
We study the expected redshift evolution of galaxy cluster abundance between
0 < z < 3 in different cosmologies, including the effects of the cosmic
equation of state parameter w=p/rho. Using the halo mass function obtained in
recent large scale numerical simulations, we model the expected cluster yields
in a 12 deg^2 Sunyaev-Zeldovich Effect (SZE) survey and a deep 10^4 deg^2 X-ray
survey over a wide range of cosmological parameters. We quantify the
statistical differences among cosmologies using both the total number and
redshift distribution of clusters. Provided that the local cluster abundance is
known to a few percent accuracy, we find only mild degeneracies between w and
either Omega_m or h. As a result, both surveys will provide improved
constraints on Omega_m and w. The Omega_m-w degeneracy from both surveys is
complementary to those found either in studies of CMB anisotropies or of
high-redshift Supernovae (SNe). As a result, combining these surveys together
with either CMB or SNe studies can reduce the statistical uncertainty on both w
and Omega_m to levels below what could be obtained by combining only the latter
two data sets. Our results indicate a formal statistical uncertainty of about
3% (68% confidence) on both Omega_m and w when the SZE survey is combined with
either the CMB or SN data; the large number of clusters in the X-ray survey
further suppresses the degeneracy between w and both Omega_m and h. Systematics
and internal evolution of cluster structure at the present pose uncertainties
above these levels. We briefly discuss and quantify the relevant systematic
errors. By focusing on clusters with measured temperatures in the X-ray survey,
we reduce our sensitivity to systematics such as non-standard evolution of
internal cluster structure.Comment: ApJ, revised version. Expanded discussion of systematics;
Press-Schechter mass function replaced by fit from simulation
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