3,013 research outputs found
A new method of measuring the cluster peculiar velocity power spectrum
We propose to use spatial correlations of the kinetic Sunyaev-Zeldovich (KSZ)
flux as an estimator of the peculiar velocity power spectrum. In contrast with
conventional techniques, our new method does not require measurements of the
thermal SZ signal or the X-ray temperature. Moreover, this method has the
special advantage that the expected systematic errors are always sub-dominant
to statistical errors on all scales and redshifts of interest. We show that
future large sky coverage KSZ surveys may allow a peculiar velocity power
spectrum estimates of an accuracy reaching ~10%.Comment: 5 pages, 2 figures, MNRAS in Press (doi:
10.1111/j.1365-2966.2008.13454.x
Cosmic Flows on 100 Mpc/h Scales: Standardized Minimum Variance Bulk Flow, Shear and Octupole Moments
The low order moments, such as the bulk flow and shear, of the large scale
peculiar velocity field are sensitive probes of the matter density fluctuations
on very large scales. In practice, however, peculiar velocity surveys are
usually sparse and noisy, which can lead to the aliasing of small scale power
into what is meant to be a probe of the largest scales. Previously, we
developed an optimal ``minimum variance'' (MV) weighting scheme, designed to
overcome this problem by minimizing the difference between the measured bulk
flow (BF) and that which would be measured by an ideal survey. Here we extend
this MV analysis to include the shear and octupole moments, which are designed
to have almost no correlations between them so that they are virtually
orthogonal. We apply this MV analysis to a compilation of all major peculiar
velocity surveys, consisting of 4536 measurements. Our estimate of the BF on
scales of ~ 100 Mpc/h has a magnitude of |v|= 416 +/- 78 km/s towards Galactic
l = 282 degree +/- 11 degree and b = 6 degree +/- 6 degree. This result is in
disagreement with LCDM with WMAP5 cosmological parameters at a high confidence
level, but is in good agreement with our previous MV result without an
orthogonality constraint, showing that the shear and octupole moments did not
contaminate the previous BF measurement. The shear and octupole moments are
consistent with WMAP5 power spectrum, although the measurement noise is larger
for these moments than for the BF. The relatively low shear moments suggest
that the sources responsible for the BF are at large distances.Comment: 13 Pages, 7 figures, 4 tables. Some changes to reflect the published
versio
Association of Subjective Global Assessment and adductor pollicis muscle thickness with the Sarcopenia in older patients with type 2 diabetes
Background and Aim: Sarcopenia is prevalent in older patients and increases the risk for negative outcomes during hospitalization and after hospital discharge. In patients with type 2 diabetes (T2D) this association may be even worse. Upon hospital admission, it is often difficult to identify sarcopenia, so the objective of this study was to assess whether the subjective global assessment (SGA), the European Society for Clinical Nutrition and Metabolism (ESPEN) and Global Leadership Initiative on Malnutrition (GLIM) criteria and/or usual anthropometric measures can predict sarcopenia. A secondary objective, to evaluate the accuracy of variables in the prediction of sarcopenia. Methodology: Patients 60 years old and with T2D were included. Malnutrition was evaluated in accordance with the guidelines of ESPEN and GLIM, and SGA. Anthropometric measurements were performed by Mid-arm circumference (MAC), mid-upper arm muscle circumference (MUAMC), and adductor pollicis muscle thickness (APMT) was performed. The sarcopenia was evaluated by handgrip strength, timed Up and Go (TUG) test and muscle mass by measuring the calf circumference (CC). Logistic regression was performed to assess the association of variables with Sarcopenia. Results: A total of 311 patients were included. The prevalence of malnutrition in accordance to ESPEN, GLIM and SGA was 18 (5.8%), 65 (21%) and 15 (4%), respectively. The MAC and MUAMC showed a negative relationship with sarcopenia (HR: 0.92 CI95% 0.85-0.99). However, patients with overweight had a 66% reduction in the risk of sarcopenia (HR: 0.34 CI95% 0.19-0.59). After adjustments, malnourished patients according to the SGA had a risk of HR: 5.65 (CI95% 1.64-19.38) of sarcopenia, similarly to patients with APMT <5 th HR: 2.81 (CI95% 1.53-5.13), ESPEN and GLIM criteria presented HR:3.10 (CI95%1.12-8.22) and HR:2.94 (CI95%1.64-5.27), respectively. The interaction between SGA and APMT after adjusting the model has been significant (HR: 7.23 CI95% 2.98-17.67). In the area under the curve (ROC), only SGA and APMT showed greater accuracy in the prediction of sarcopenia (AUC: 0.713 CI95% 0.650-0.803). Conclusion: In our sample, it was possible to predict sarcopenia through the malnutrition criteria of ESPEN and GLIM, SGA, MAC and APMT. Measures such as APMT associated with the SGA tool seem to better predict sarcopenia in older patients with T2D
Critical Hysteresis from Random Anisotropy
Critical hysteresis in ferromagnets is investigated through a -component
spin model with random anisotropies, more prevalent experimentally than the
random fields used in most theoretical studies. Metastability, and the
tensorial nature of anisotropy, dictate its physics. Generically, random field
Ising criticality occurs, but other universality classes exist. In particular,
proximity to criticality may explain the discrepancy between
experiment and earlier theories. The uniaxial anisotropy constant, which can be
controlled in magnetostrictive materials by an applied stress, emerges as a
natural tuning parameter.Comment: four pages, revtex4; minor corrections in the text and typos
corrected (published version
An estimate of \Omega_m without priors
Using mean relative peculiar velocity measurements for pairs of galaxies, we
estimate the cosmological density parameter and the amplitude of
density fluctuations . Our results suggest that our statistic is a
robust and reproducible measure of the mean pairwise velocity and thereby the
parameter. We get and . These estimates do not depend on prior assumptions on
the adiabaticity of the initial density fluctuations, the ionization history,
or the values of other cosmological parameters.Comment: 12 pages, 4 figures, slight changes to reflect published versio
R-parity Conservation via the Stueckelberg Mechanism: LHC and Dark Matter Signals
We investigate the connection between the conservation of R-parity in
supersymmetry and the Stueckelberg mechanism for the mass generation of the B-L
vector gauge boson. It is shown that with universal boundary conditions for
soft terms of sfermions in each family at the high scale and with the
Stueckelberg mechanism for generating mass for the B-L gauge boson present in
the theory, electric charge conservation guarantees the conservation of
R-parity in the minimal B-L extended supersymmetric standard model. We also
discuss non-minimal extensions. This includes extensions where the gauge
symmetries arise with an additional U(1)_{B-L} x U(1)_X, where U(1)_X is a
hidden sector gauge group. In this case the presence of the additional U(1)_X
allows for a Z' gauge boson mass with B-L interactions to lie in the sub-TeV
region overcoming the multi-TeV LEP constraints. The possible tests of the
models at colliders and in dark matter experiments are analyzed including
signals of a low mass Z' resonance and the production of spin zero bosons and
their decays into two photons. In this model two types of dark matter
candidates emerge which are Majorana and Dirac particles. Predictions are made
for a possible simultaneous observation of new physics events in dark matter
experiments and at the LHC.Comment: 38 pages, 7 fig
Consistently Large Cosmic Flows on Scales of 100 Mpc/h: a Challenge for the Standard LCDM Cosmology
Peculiar velocity surveys have non-uniform spatial distributions of tracers,
so that the bulk flow estimated from them does not correspond to that of a
simple volume such as a sphere. Thus bulk flow estimates are generally not
strictly comparable between surveys, even those whose effective depths are
similar. In addition, the sparseness of typical surveys can lead to aliasing of
small scale power into what is meant to be a probe of the largest scales. Here
we introduce a new method of calculating bulk flow moments where velocities are
weighted to give an optimal estimate of the bulk flow of an idealized survey,
with the variance of the difference between the estimate and the actual flow
being minimized. These "minimum variance" estimates can be designed to estimate
the bulk flow on a particular scale with minimal sensitivity to small scale
power, and are comparable between surveys. We compile all major peculiar
velocity surveys and apply this new method to them. We find that most surveys
we studied are highly consistent with each other. Taken together the data
suggest that the bulk flow within a Gaussian window of radius 50 Mpc/h is 407
km/s toward l=287 and b=8. The large-scale bulk motion is consistent with
predictions from the local density field. This indicates that there are
significant density fluctuations on very large scales. A flow of this amplitude
on such a large scale is not expected in the WMAP5-normalized LCDM cosmology,
for which the predicted one-dimensional r.m.s. velocity is ~110 km/s. The large
amplitude of the observed bulk flow favors the upper values of the WMAP5
error-ellipse, but even the point at the top of the WMAP5 95% confidence
ellipse predicts a bulk flow which is too low compared to that observed at >98%
confidence level.Comment: 19 Pages, 7 Figures, MNRAS in Press. Added some references and text
to reflect post proofs manuscrip
A comparison of the galaxy peculiar velocity field with the PSCz gravity field-- A Bayesian hyper-parameter method
We constructed a Bayesian hyper-parameter statistical method to quantify the
difference between predicted velocities derived from the observed galaxy
distribution in the \textit{IRAS}-PSC redshift survey and peculiar
velocities measured using different distance indicators. In our analysis we
find that the model--data comparison becomes unreliable beyond 70 \hmpc
because of the inadequate sampling by \textit{IRAS} survey of prominent,
distant superclusters, like the Shapley Concentration. On the other hand, the
analysis of the velocity residuals show that the PSC gravity field provides
an adequate model to the local, \le 70 \hmpc, peculiar velocity field. The
hyper-parameter combination of ENEAR, SN, A1SN and SFI++ catalogues in the
Bayesian framework constrains the amplitude of the linear flow to be
. For an rms density fluctuations in the PSC galaxy
number density , we obtain an estimate of the
growth rate of density fluctuations ,
which is in excellent agreement with independent estimates based on different
techniques.Comment: 14 pages, 32 figures, MNRAS in press, matched the MNRAS published
versio
Broken symmetry states and divergent resistance in suspended bilayer graphene
Graphene [1] and its bilayer have generated tremendous excitement in the
physics community due to their unique electronic properties [2]. The intrinsic
physics of these materials, however, is partially masked by disorder, which can
arise from various sources such as ripples [3] or charged impurities [4].
Recent improvements in quality have been achieved by suspending graphene flakes
[5,6], yielding samples with very high mobilities and little charge
inhomogeneity. Here we report the fabrication of suspended bilayer graphene
devices with very little disorder. We observe fully developed quantized Hall
states at magnetic fields of 0.2 T, as well as broken symmetry states at
intermediate filling factors , , and . The
devices exhibit extremely high resistance in the state that grows
with magnetic field and scales as magnetic field divided by temperature. This
resistance is predominantly affected by the perpendicular component of the
applied field, indicating that the broken symmetry states arise from many-body
interactions.Comment: 23 pages, including 4 figures and supplementary information; accepted
to Nature Physic
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