1,757 research outputs found
QED can explain the non-thermal emission from SGRs and AXPs : Variability
Owing to effects arising from quantum electrodynamics (QED),
magnetohydrodynamical fast modes of sufficient strength will break down to form
electron-positron pairs while traversing the magnetospheres of strongly
magnetised neutron stars. The bulk of the energy of the fast mode fuels the
development of an electron-positron fireball. However, a small, but potentially
observable, fraction of the energy ( ergs) can generate a
non-thermal distribution of electrons and positrons far from the star. This
paper examines the cooling and radiative output of these particles. Small-scale
waves may produce only the non-thermal emission. The properties of this
non-thermal emission in the absence of a fireball match those of the quiescent,
non-thermal radiation recently observed non-thermal emission from several
anomalous X-ray pulsars and soft-gamma repeaters. Initial estimates of the
emission as a function of angle indicate that the non-thermal emission should
be beamed and therefore one would expect this emission to be pulsed as well.
According to this model the pulsation of the non-thermal emission should be
between 90 and 180 degrees out of phase from the thermal emission from the
stellar surface.Comment: 7 pages, 5 figures, to appear in the proceedings of the conference
"Isolated Neutron Stars: from the Interior to the Surface" (April 2006,
London), eds. D. Page, R. Turolla, & S. Zane, Astrophysics & Space Scienc
Random wave loads on a long detached breakwater considering diffraction
Battjes (1982) found the loads of short-crested random waves on a long structure decrease with the structure length and also with the obliqueness of wave incidence. These decreases come from the spatial phase difference along the structure. Lee et al. (2010) found that obliquely incident random waves in a nearshore area become directionally asymmetric due to refraction. They also found the asymmetry becomes more significant in shallower waters. Recently, Jung et al. (2011) studied random wave loads on a long structure considering diffraction and directional asymmetry. In this study, we further study random wave loads on a detached breakwater considering diffraction of waves which propagate at both ends of the breakwater. We also consider directional asymmetry. The structure may be placed along the bottom contours in order to protect on-shore incoming waves. In that case, refraction induced random waves may become asymmetric, i.e., on-shore components are more dominant than along-shore ones. Therefore, directional obliqueness on the structure becomes less and thus the wave loads decrease in less degree than the symmetric waves. When waves are obliquely incident on a long structure, the diffract ing waves give forces on the lee side of the structure. The diffracting wave has a spatial phase variation along the lee side which is different from that the obliquely incident wave has on the front side. Thus, the wave loads decrease with the existence of diffract ing waves and also the phase difference between the incident and diffracting waves
Heavy Metal Contamination and Remediation of Paddy Soil in Korea(Frontiers in Rice Science -from Gene to Field-,The 100^<th> Anniversary of Tohoku University, International Symposium)
Boundary behavior in High Dimension, Low Sample Size asymptotics of PCA
In High Dimension, Low Sample Size (HDLSS) data situations, where the dimension d is much larger than the sample size n, principal component analysis (PCA) plays an important role in statistical analysis. Under which conditions does the sample PCA well reflect the population covariance structure? We answer this question in a relevant asymptotic context where d grows and n is fixed, under a generalized spiked covariance model. Specifically, we assume the largest population eigenvalues to be of the order dα, where α1. Earlier results show the conditions for consistency and strong inconsistency of eigenvectors of the sample covariance matrix. In the boundary case, α=1, where the sample PC directions are neither consistent nor strongly inconsistent, we show that eigenvalues and eigenvectors do not degenerate but have limiting distributions. The result smoothly bridges the phase transition represented by the other two cases, and thus gives a spectrum of limits for the sample PCA in the HDLSS asymptotics. While the results hold under a general situation, the limiting distributions under Gaussian assumption are illustrated in greater detail. In addition, the geometric representation of HDLSS data is extended to give three different representations, that depend on the magnitude of variances in the first few principal components
Boundary behavior in High Dimension, Low Sample Size asymptotics of PCA
In High Dimension, Low Sample Size (HDLSS) data situations, where the dimension d is much larger than the sample size n, principal component analysis (PCA) plays an important role in statistical analysis. Under which conditions does the sample PCA well reflect the population covariance structure? We answer this question in a relevant asymptotic context where d grows and n is fixed, under a generalized spiked covariance model. Specifically, we assume the largest population eigenvalues to be of the order dα, where α1. Earlier results show the conditions for consistency and strong inconsistency of eigenvectors of the sample covariance matrix. In the boundary case, α=1, where the sample PC directions are neither consistent nor strongly inconsistent, we show that eigenvalues and eigenvectors do not degenerate but have limiting distributions. The result smoothly bridges the phase transition represented by the other two cases, and thus gives a spectrum of limits for the sample PCA in the HDLSS asymptotics. While the results hold under a general situation, the limiting distributions under Gaussian assumption are illustrated in greater detail. In addition, the geometric representation of HDLSS data is extended to give three different representations, that depend on the magnitude of variances in the first few principal components
Prominent bulk pinning effect in the MgB_2 superconductor
We report the magnetic-field dependence of the irreversible magnetization of
the recently discovered binary superconductor MgB. For the temperature
region of , the contribution of the bulk pinning to the
magnetization overwhelms that of the surface pinning. This was evident from the
fact that the magnetization curves, , were well described by the
critical-state model without considering the surface pinning effect. It was
also found that the curves at various temperatures scaled when the field
and the magnetization were normalized by the characteristic scaling factors
and , respectively. This feature suggests that the
pinning mechanism determining the hysteresis in is unique below .Comment: 4pages and 4 figures. Phys. Rev. B (accepted
The in vitro effects of dehydroepiandrosterone on human osteoarthritic chondrocytes
AbstractObjective: To investigate the in vitro effects of dehydroepiandrosterone (DHEA) on human osteoarthritic chondrocytes.Design: Chondrocytes isolated from human osteoarthritic knee cartilage were three-dimensionally cultured in alginate beads, except for cell proliferation experiment. Cells were treated with DHEA in the presence or absence of IL-1β. The effects on chondrocytes were analyzed using a 3-(4,5-dimethylthiazol-2yl)-5-(3-carboxymethoxy-phenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS) assay (for chondrocyte proliferation), a dimethylmethylene blue (DMB) assay (for glycosaminoglycan (GAG) synthesis), and an indole assay (for DNA amount). Gene expressions of type I and II collagen, metalloproteinase-1 and -3 (MMP-1 and -3), and tissue inhibitor of metalloproteinase-1 (TIMP-1) as well as the IL-1β-induced gene expressions of MMP-1 and -3 were analyzed by reverse transcription-polymerase chain reaction (RT-PCR). The protein synthesis of MMP-1 and -3 and TIMP-1 was determined by Western blotting.Results: The treatment of chondrocytes with DHEA did not affect chondrocyte proliferation or GAG synthesis up to 100μM of concentration. The gene expression of type II collagen increased in a dose-dependent manner, while that of type I decreased. DHEA suppressed the expression of MMP-1 significantly at concentrations exceeding 50μM. The gene expression of MMP-3 was also suppressed, but this was without statistical significance. The expression of TIMP-1 was significantly increased by DHEA at concentrations exceeding 10μM. The effects of DHEA on the gene expressions of MMP-1 and -3 were more prominent in the presence of IL-1β, in which DHEA suppressed not only MMP-1, but also MMP-3 at the lower concentrations, 10 and 50μM, respectively. Western blotting results were in agreement with RT-PCR, which indicates that DHEA acts at the gene transcription level.Conclusions: Our study demonstrates that DHEA has no toxic effect on chondrocytes up to 100μM of concentration and has an ability to modulate the imbalance between MMPs and TIMP-1 during OA at the transcription level, which suggest that it has a protective role against articular cartilage loss
Improving the Quality of EEG Data in Patients With Alzheimers Disease Using ICA
Does Independent Component Analysis (ICA) denature EEG
signals? We applied ICA to two groups of subjects (mild Alzheimer
patients and control subjects). The aim of this study was to examine
whether or not the ICA method can reduce both group di®erences and
within-subject variability. We found that ICA diminished Leave-One-
Out root mean square error (RMSE) of validation (from 0.32 to 0.28),
indicative of the reduction of group di®erence. More interestingly, ICA
reduced the inter-subject variability within each group (¾ = 2:54 in the
± range before ICA, ¾ = 1:56 after, Bartlett p = 0.046 after Bonfer-
roni correction). Additionally, we present a method to limit the impact
of human error (' 13:8%, with 75.6% inter-cleaner agreement) during
ICA cleaning, and reduce human bias. These ¯ndings suggests the novel
usefulness of ICA in clinical EEG in Alzheimer's disease for reduction of
subject variability
Molecular epidemiology and genetic diversity of human astrovirus in South Korea from 2002 to 2007
AbstractThe present study was conducted to survey the prevalence and genotypic distribution of human astrovirus (HAstV) circulating in South Korea. Of 160,027 patients with acute gastroenteritis, 2,057 (1.3%) were positive for HAstV antigen. We determined the genotypes of 187 HAstV strains collected from laboratories across the country. Genetic analysis revealed genotype 1 to be the most prevalent, accounting for 72.19% of the strains, followed by genotypes 8 (9.63%), 6 (6.95%), 4 (6.42%), 2 (3.21%) and 3 (1.60%). Our findings indicate that HAstV is less common but, even so, a potentially important viral agent of gastroenteritis in South Korea, with significant genetic diversity among circulating HAstV strains
Optical investigation on the electronic structures of Y_{2}Ru_{2}O_{7}, CaRuO_{3}, SrRuO_{3}, and Bi_{2}Ru_{2}O_{7}
We investigated the electronic structures of the bandwidth-controlled
ruthenates, YRuO, CaRuO, SrRuO, and BiRuO, by optical conductivity analysis in a wide energy region of 5 meV
12 eV. We could assign optical transitions from the systematic changes
of the spectra and by comparison with the O 1 x-ray absorption data. We
estimated some physical parameters, such as the on-site Coulomb repulsion
energy and the crystal-field splitting energy. These parameters show that the
4 orbitals should be more extended than 3 ones. These results are also
discussed in terms of the Mott-Hubbard model.Comment: 12 pages (1 table), 3 figure
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