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1 - 9 of 9
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(2006)Journal ArticleWe have used a bioinformatics approach to evaluate the completeness and functionality of the reported human immunoglobulin heavy-chain IGHD gene repertoire. Using the hidden Markov-model-based iHMMune-align program, 1,080 relatively unmutated heavy-chain sequences were aligned against the reported repertoire. These alignments were compared with alignments to 1,639 more highly mutated sequences. Comparisons of the frequencies of gene utilization in the two databases, and analysis of features of aligned IGHD gene segments, including their length, the frequency with which they appear to mutate, and the frequency with which specific mutations were seen, were used to determine the reliability of alignments to the less commonly seen IGHD genes. Analysis demonstrates that IGHD4-23 and IGHD5-24, which have been reported to be open reading frames of uncertain functionality, are represented in the expressed gene repertoire; however, the functionality of IGHD6-25 must be questioned. Sequence similarities make the unequivocal identification of members of the IGHD1 gene family problematic, although all genes except IGHD1-14*01 appear to be functional. On the other hand, reported allelic variants of IGHD2-2 and of the IGHD3 gene family appear to be nonfunctional, very rare, or nonexistent. Analysis also suggests that the reported repertoire is relatively complete, although one new putative polymorphism (IGHD3-10*p03) was identified. This study therefore confirms a surprising lack of diversity in the available IGHD gene repertoire, and restriction of the germline sequence databases to the functional set described here will substantially improve the accuracy of IGHD gene alignments and therefore the accuracy of analysis of the V-D-J junction.
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(2000)Journal ArticleIn-plane fluctuations of superconductivity have been investigated for Al-doped Bi-2212 single crystals with different resistivity anisotropy. The experimental results of in-plane paraconductivity are in good agreement with the Lawrence and Doniach model. The interlayer coupling is found to decrease with the resistivity anisotropy.
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(2000)Journal ArticleHigh quality, large size Bi2Sr2CaCu2O8 (Bi-2212) single crystals have been grown by a self-flux method in a horizontal temperature gradient. We found that the presence of the horizontal temperature gradient is helpful for the crystal growing along the ab-plane direction. However, non-uniform distribution of temperature in the vertical direction in the furnace often causes imperfections along the c direction. This may be one of the critical reasons why crystals produced by flux method are very thin and easy to cleave along the ab-plane, compared with the crystals grown by the floating zone method. The influence of the growth conditions and post-heat treatment on the resistivity anisotropy of the crystals has been investigated. Crystals grown in the condition where the temperature is non-uniformly distributed along the vertical direction often have higher anisotropy in resistivity. In addition, the post-heat treatment in the nitrogen atmosphere reduces the anisotropy of the resistivity of the crystal. Possible mechanisms are discussed.
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(2008)Journal ArticleThe concept that macrophages can become foam cells as a result of a disturbed balance between the uptake of cholesterol from lipoproteins and cholesterol efflux is generally accepted. ABCA1 and ABCG1 are two cholesterol transporters that may act sequentially to remove cellular cholesterol, but currently their combined role in vivo is unknown. We report here that targeted disruption of both ABCA1 and ABCG1 in mice, despite severe plasma hypocholesterolemia, leads to massive lipid accumulation and foam cell formation of tissue macrophages. A complete ablation of cellular cholesterol efflux in vitro is observed, whereas in vivo macrophage-specific reverse cholesterol transport to the feces is markedly decreased. Despite the massive foam cell formation of tissue macrophages, no lipid accumulation was observed in the vascular wall, even in mice of 1 year old, indicating that the double knockout mice, possibly because of their hypocholesterolemia, lack the trigger to attract macrophages to the vessel wall. In conclusion, even under hypocholesterolemic conditions macrophages can be converted into foam cells, and ABCA1 and ABCG1 play an essential role in the prevention of foam cell formation.
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(2008)Journal ArticleFire activity has varied globally and continuously since the last glacial maximum (LGM) in response to long-term changes in global climate and shorter-term regional changes in climate, vegetation, and human land use. We have synthesized sedimentary charcoal records of biomass burning since the LGM and present global maps showing changes in fire activity for time slices during the past 21,000 years (as differences in charcoal accumulation values compared to pre-industrial). There is strong broad-scale coherence in fire activity after the LGM, but spatial heterogeneity in the signals increases thereafter. In North America, Europe and southern South America, charcoal records indicate less-than-present fire activity during the deglacial period, from 21,000 to ∼11,000 cal yr BP. In contrast, the tropical latitudes of South America and Africa show greater-than-present fire activity from ∼19,000 to ∼17,000 cal yr BP and most sites from Indochina and Australia show greater-than-present fire activity from 16,000 to ∼13,000 cal yr BP. Many sites indicate greater-than-present or near-present activity during the Holocene with the exception of eastern North America and eastern Asia from 8,000 to ∼3,000 cal yr BP, Indonesia and Australia from 11,000 to 4,000 cal yr BP, and southern South America from 6,000 to 3,000 cal yr BP where fire activity was less than present. Regional coherence in the patterns of change in fire activity was evident throughout the post-glacial period. These complex patterns can largely be explained in terms of large-scale climate controls modulated by local changes in vegetation and fuel load.
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(2008)Journal ArticleTwo-phase composites La0.7Sr0.3MnO3/Ta2O5 are synthesized and their magnetization and low-field magnetoresistance (LFMR) characteristics are investigated. It is found that a small amount of Ta ions enter into LSMO grains near the grain surface region, resulting in the reduction of the cell volume, and consequently, an extra reduction of the saturate magnetization. The paramagnetism-to-ferromagnetism transition temperature, TC, does not show significant change. The LFMR enhancement is observed over a wide range of temperature from 50 to 350K when the second phase material (Ta2O5) is introduced. The magnetic disorder caused by the secondary phase at grain boundaries and the Ta doping effect on the surface of LSMO grains are believed to contribute to the enhanced MR.
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(2008)Journal ArticleThe designers of a large scale video-on-demand system face an optimization problem of deciding how to assign movies to multiple disks (servers) such that the request blocking probability is minimized subject to capacity constraints. To solve this problem, it is essential to develop scalable and accurate analytical means to evaluate the blocking performance of the system for a given file assignment. The performance analysis is made more complicated by the fact that the request blocking probability depends also on how disks are selected to serve user requests for multicopy movies. In this paper, we analyze several efficient resource selection schemes. Numerical results demonstrate that our analysis is scalable and sufficiently accurate to support the task of file assignment optimization in such a system. © 2008 IEEE.
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(2000)Journal ArticleGas flame and modified melt-textured-growth (MTG) are used to grow textured YBa2Cu3Oy (123) crystals and to control the particle size of Y2BaCuO5 (211) inclusions. The size of 211 particles is reduced from 10 μm in conventional MTG samples to 0.2 μm in the crystals grown by the new processing technique. The new technique also has advantages such as a relatively low working temperature and a short reaction time compared with the conventional MTG method. The flux pinning force is significantly enhanced by the nanoparticles that act as effective flux pinning centers. The best sample shows a Jc as high as 5×104 A/cm2 at 77 K and 4 T.