10,214 research outputs found
GNSS troposphere tomography based on two-step reconstructions using GPS observations and COSMIC profiles
Traditionally, balloon-based radiosonde soundings are
used to study the spatial distribution of atmospheric water vapour. However,
this approach cannot be frequently employed due to its high cost. In
contrast, GPS tomography technique can obtain water vapour in a high temporal
resolution. In the tomography technique, an iterative or non-iterative
reconstruction algorithm is usually utilised to overcome rank deficiency of
observation equations for water vapour inversion. However, the single
iterative or non-iterative reconstruction algorithm has their limitations.
For instance, the iterative reconstruction algorithm requires accurate
initial values of water vapour while the non-iterative reconstruction
algorithm needs proper constraint conditions. To overcome these drawbacks,
we present a combined iterative and non-iterative reconstruction approach
for the three-dimensional (3-D) water vapour inversion using GPS observations
and COSMIC profiles. In this approach, the non-iterative reconstruction
algorithm is first used to estimate water vapour density based on a priori
water vapour information derived from COSMIC radio occultation data. The
estimates are then employed as initial values in the iterative
reconstruction algorithm. The largest advantage of this approach is that
precise initial values of water vapour density that are essential in the
iterative reconstruction algorithm can be obtained. This combined
reconstruction algorithm (CRA) is evaluated using 10-day GPS observations in
Hong Kong and COSMIC profiles. The test results indicate that the water
vapor accuracy from CRA is 16 and 14% higher than that of iterative
and non-iterative reconstruction approaches, respectively. In addition, the
tomography results obtained from the CRA are further validated using
radiosonde data. Results indicate that water vapour densities derived from
the CRA agree with radiosonde results very well at altitudes above 2.5 km.
The average RMS value of their differences above 2.5 km is 0.44 g m<sup>−3</sup>
Two-Sample Covariance Matrix Testing and Support Recovery
This paper proposes a new test for testing the equality of two covariance matrices Σ1 and Σ2 in the high-dimensional setting and investigates its theoretical and numerical properties. The limiting null distribution of the test statistic is derived. The test is shown to enjoy certain optimality and to be especially powerful against sparse alternatives. The simulation results show that the test significantly outperforms the existing methods both in terms of size and power. Analysis of prostate cancer datasets is carried out to demonstrate the application of the testing procedures. When the null hypothesis of equal covariance matrices is rejected, it is often of significant interest to further investigate in which way they differ. Motivated by applications in genomics, we also consider two related problems, recovering the support of Σ1 − Σ2 and testing the equality of the two covariance matrices row by row. New testing procedures are introduced and their properties are studied. Applications to gene selection is also discussed
Cold Dark Matter Isocurvature Perturbations: Cosmological Constraints and Applications
In this paper we present the constraints on cold dark matter (CDM)
isocurvature contributions to the cosmological perturbations. By employing
Markov Chain Monte Carlo method (MCMC), we perform a global analysis for
cosmological parameters using the latest astronomical data, such as 7-year
Wilkinson Microwave Anisotropy Probe (WMAP7) observations, matter power
spectrum from the Sloan Digital Sky Survey (SDSS) luminous red galaxies (LRG),
and "Union2" type Ia Supernovae (SNIa) sample. We find that the correlated
mixture of adiabatic and isocurvature modes are mildly better fitting to the
current data than the pure adiabatic ones, with the minimal given by
the likelihood analysis being reduced by 3.5. We also obtain a tight limit on
the fraction of the CDM isocurvature contributions, which should be less than
14.6% at 95% confidence level. With the presence of the isocurvature modes, the
adiabatic spectral index becomes slightly bigger, n_s^{\rm
adi}=0.972\pm0.014~(1\,\sigma), and the tilt for isocurvature spectrum could be
large, namely, the best fit value is n_s^{\rm iso}=3.020. Finally, we discuss
the effect on WMAP normalization priors, shift parameter R, acoustic scale l_A
and z_{*}, from the CDM isocurvaure perturbation. By fitting the mixed initial
condition to the combined data, we find the mean values of R, l_A and z_{*} can
be changed about 2.9\sigma, 2.8\sigma and 1.5\sigma respectively, comparing
with those obtained in the pure adiabatic condition.Comment: 9 pages, 5 figures, 3 tables, references adde
Cardiac Response to Chronic Intermittent Hypoxia with a Transition from Adaptation to Maladaptation: The Role of Hydrogen Peroxide
Obstructive sleep apnea (OSA) is a highly prevalent respiratory disorder of sleep, and associated with chronic intermittent hypoxia (CIH). Experimental evidence indicates that CIH is a unique physiological state with potentially “adaptive” and “maladaptive” consequences for cardio-respiratory homeostasis. CIH is also a critical element accounting for most of cardiovascular complications of OSA. Cardiac response to CIH is time-dependent, showing a transition from cardiac compensative (such as hypertrophy) to decompensating changes (such as failure). CIH-provoked mild and transient oxidative stress can induce adaptation, but severe and persistent oxidative stress may provoke maladaptation. Hydrogen peroxide as one of major reactive oxygen species plays an important role in the transition of adaptive to maladaptive response to OSA-associated CIH. This may account for the fact that although oxidative stress has been recognized as a driver of cardiac disease progression, clinical interventions with antioxidants have had little or no impact on heart disease and progression. Here we focus on the role of hydrogen peroxide in CIH and OSA, trying to outline the potential of antioxidative therapy in preventing CIH-induced cardiac damage
Bis[2-(2-furyl)-1-(2-furylmethyl)-1H-benzimidazole-κN 3]diiodidocadmium
In the title complex, [CdI2(C16H12N2O2)2], the CdII atom is located on a twofold rotation axis and is four-coordinated by two N atoms from symmetry-related 2-(2-furyl)-1-(2-furylmethyl)-1H-benzimidazole ligands and two I atoms in a distorted tetrahedral configuration. The benzimidazole rings in adjacent molecules are parallel, with an average interplanar distance of 3.486 Å. The I atom is disordered over two sites in a 0.85 (5):0.15 (5) ratio
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