6,781 research outputs found
Estimating root zone soil moisture using near-surface observations from SMOS
Satellite-derived soil moisture provides more spatially and temporally
extensive data than in situ observations. However, satellites can only measure
water in the top few centimeters of the soil. Root zone soil moisture is
more important, particularly in vegetated regions. Therefore estimates of
root zone soil moisture must be inferred from near-surface soil moisture
retrievals. The accuracy of this inference is contingent on the relationship
between soil moisture in the near-surface and the soil moisture at greater
depths. This study uses cross correlation analysis to quantify the
association between near-surface and root zone soil moisture using in situ data
from the United States Great Plains. Our analysis demonstrates that there is
generally a strong relationship between near-surface (5â10 cm) and root
zone (25â60 cm) soil moisture. An exponential decay filter is used to
estimate root zone soil moisture using near-surface soil moisture derived
from the Soil Moisture and Ocean Salinity (SMOS) satellite. Root zone soil
moisture derived from SMOS surface retrievals is compared to in situ soil moisture
observations in the United States Great Plains. The SMOS-based root zone
soil moisture had a mean R2 of 0.57 and a mean NashâSutcliffe score of
0.61 based on 33 stations in Oklahoma. In Nebraska, the SMOS-based root zone
soil moisture had a mean R2 of 0.24 and a mean NashâSutcliffe score of
0.22 based on 22 stations. Although the performance of the exponential
filter method varies over space and time, we conclude that it is a useful
approach for estimating root zone soil moisture from SMOS surface
retrievals
Socio-demographic factors, behaviour and personality: associations with psychological distress
Background: Anxiety, psychological distress and personality may not be independent risk factors for cardiovascular disease; however they may contribute via their relationship with unhealthy lifestyle behaviours. This study aimed to examine the association between psychological distress, risk behaviours and patient demographic characteristics in a sample of general practice patients aged 40â65 years with at least one risk factor for cardiovascular disease.
Design: Cross-sectional analytic study.
Methods: Patients, randomly selected from general practice records, completed a questionnaire about their behavioural risk factors and psychological health as part of a cluster randomized controlled trial of a general practice based intervention to prevent chronic vascular disease. The Kessler Psychological Distress Score (K10) was the main outcome measure for the multilevel, multivariate analysis.
Results: Single-level bi-variate analysis demonstrated a significant association between higher K10 and middle age (p = 0.001), high neuroticism (p = 0), current smoking (p = 0), physical inactivity (p = 0.003) and low fruit and vegetable consumption (p = 0.008). Socioeconomic (SES) indicators of deprivation (employment and accommodation status) were also significantly associated with higher K10 (p = 0). No individual behavioural risk factor was associated with K10 on multilevel multivariate analysis; however indicators of low SES remained significant (p < 0.001).
Conclusions: When all factors were considered, psychological distress was not associated with behavioural risk factors for cardiovascular disease. Other underlying factors, such as personality type and socioeconomic status, may be associated with both the behaviours and the distress
Effect of Scalar Mass in the Absorption and Emission Spectra of Schwarzschild Black Hole
Following Sanchez's approach we investigate the effect of scalar mass in the
absorption and emission problems of 4d Schwarzschild black hole. The absorption
cross sections for arbitrary angular momentum of the scalar field are computed
numerically in the full range of energy by making use of the analytic
near-horizon and asymptotic solutions and their analytic continuations. The
scalar mass makes an interesting effect in the low-energy absorption cross
section for S-wave. Unlike the massless case, the cross section decreases with
increasing energy in the extremely low-energy regime. As a result the
universality, {\it i.e.} low-energy cross section for S-wave is equal to the
horizon area, is broken in the presence of mass. If the scalar mass is larger
than a critical mass, the absorption cross section becomes monotonically
decreasing function in the entire range of energy. The Hawking emission is also
calculated numerically. It turns out that the Planck factor generally
suppresses the contribution of higher partial waves except S-wave. The scalar
mass in general tends to reduce the emission rate.Comment: 20 pages, 8 figures, V2: few comments are added. version to appear in
Classical and Quantum Gravit
Random tree growth by vertex splitting
We study a model of growing planar tree graphs where in each time step we
separate the tree into two components by splitting a vertex and then connect
the two pieces by inserting a new link between the daughter vertices. This
model generalises the preferential attachment model and Ford's -model
for phylogenetic trees. We develop a mean field theory for the vertex degree
distribution, prove that the mean field theory is exact in some special cases
and check that it agrees with numerical simulations in general. We calculate
various correlation functions and show that the intrinsic Hausdorff dimension
can vary from one to infinity, depending on the parameters of the model.Comment: 47 page
Gravitation: Global Formulation and Quantum Effects
A nonintegrable phase-factor global approach to gravitation is developed by
using the similarity of teleparallel gravity with electromagnetism. The phase
shifts of both the COW and the gravitational Aharonov-Bohm effects are
obtained. It is then shown, by considering a simple slit experiment, that in
the classical limit the global approach yields the same result as the
gravitational Lorentz force equation of teleparallel gravity. It represents,
therefore, the quantum mechanical version of the classical description provided
by the gravitational Lorentz force equation. As teleparallel gravity can be
formulated independently of the equivalence principle, it will consequently
require no generalization of this principle at the quantum level.Comment: Latex (IOP style), 14 pages, 3 figures. To appear in Classical and
Quantum Gravit
Morris-Thorne wormholes with a cosmological constant
First, the ideas introduced in the wormhole research field since the work of
Morris and Thorne are briefly reviewed, namely, the issues of energy
conditions, wormhole construction, stability, time machines and astrophysical
signatures. Then, spherically symmetric and static traversable Morris-Thorne
wormholes in the presence of a generic cosmological constant are analyzed. A
matching of an interior solution to the unique exterior vacuum solution is done
using directly the Einstein equations. The structure as well as several
physical properties and characteristics of traversable wormholes due to the
effects of the cosmological term are studied. Interesting equations appear in
the process of matching. For instance, one finds that for asymptotically flat
and anti-de Sitter spacetimes the surface tangential pressure of the
thin-shell, at the boundary of the interior and exterior solutions, is always
strictly positive, whereas for de Sitter spacetime it can take either sign as
one could expect, being negative (tension) for relatively high cosmological
constant and high wormhole radius, positive for relatively high mass and small
wormhole radius, and zero in-between. Finally, some specific solutions with
generic cosmological constant, based on the Morris-Thorne solutions, are
provided.Comment: latex, 49 pages, 8 figures. Expanded version of the paper published
in Physical Review
Semiclassical Casimir Energies at Finite Temperature
We study the dependence on the temperature T of Casimir effects for a range
of systems, and in particular for a pair of ideal parallel conducting plates,
separated by a vacuum. We study the Helmholtz free energy, combining
Matsubara's formalism, in which the temperature appears as a periodic Euclidean
fourth dimension of circumference 1/T, with the semiclassical periodic orbital
approximation of Gutzwiller. By inspecting the known results for the Casimir
energy at T=0 for a rectangular parallelepiped, one is led to guess at the
expression for the free energy of two ideal parallel conductors without
performing any calculation. The result is a new form for the free energy in
terms of the lengths of periodic classical paths on a two-dimensional cylinder
section. This expression for the free energy is equivalent to others that have
been obtained in the literature. Slightly extending the domain of applicability
of Gutzwiller's semiclassical periodic orbit approach, we evaluate the free
energy at T>0 in terms of periodic classical paths in a four-dimensional cavity
that is the tensor product of the original cavity and a circle. The validity of
this approach is at present restricted to particular systems. We also discuss
the origin of the classical form of the free energy at high temperatures.Comment: 17 pages, no figures, Late
Full Accounting of Diabetes and Pre-Diabetes in the U.S. Population in 1988â1994 and 2005â2006
OBJECTIVEâWe examined the prevalences of diagnosed diabetes, and undiagnosed diabetes and pre-diabetes using fasting and 2-h oral glucose tolerance test values, in the U.S. during 2005â2006. We then compared the prevalences of these conditions with those in 1988â1994
- âŠ