Continuous magnetic reconnection at Earth's magnetopause

The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar flares and magnetospheric substorms--two phenomena believed to be initiated by reconnection--are highly burst-like occurrences, raising the possibility that the reconnection process is intrinsically intermittent, storing and releasing magnetic energy in an explosive and uncontrolled manner. Here we show that reconnection at Earth's high-latitude magnetopause is driven directly by the solar wind, and can be continuous and even quasi-steady over an extended period of time. The dayside proton auroral spot in the ionosphere--the remote signature of high-latitude magnetopause reconnection--is present continuously for many hours. We infer that reconnection is not intrinsically intermittent; its steadiness depends on the way that the process is driven.     

A first-generation linkage disequilibrium map of human chromosome 22

DNA sequence variants in specific genes or regions of the human genome are responsible for a variety of phenotypes such as disease risk or variable drug response. These variants can be investigated directly, or through their non-random associations with neighbouring markers (called linkage disequilibrium (LD)). Here we report measurement of LD along the complete sequence of human chromosome 22. Duplicate genotyping and analysis of 1,504 markers in Centre d'Etude du Polymorphisme Humain (CEPH) reference families at a median spacing of 15 kilobases (kb) reveals a highly variable pattern of LD along the chromosome, in which extensive regions of nearly complete LD up to 804 kb in length are interspersed with regions of little or no detectable LD. The LD patterns are replicated in a panel of unrelated UK Caucasians. There is a strong correlation between high LD and low recombination frequency in the extant genetic map, suggesting that historical and contemporary recombination rates are similar. This study demonstrates the feasibility of developing genome-wide maps of LD.     

磁性肥料(诱导磁场)对种子萌发影响的试验研究

试验研究几种磁肥(诱导磁场)对种子萌发的影响,结果发现磁性微粒所产生的诱导磁场强度对种子萌发具有促进作用。     

A semi‐parametric time series approach in modeling hourly electricity loads

In this paper we develop a semi‐parametric approach to model nonlinear relationships in serially correlated data. To illustrate the usefulness of this approach, we apply it to a set of hourly electricity load data. This approach takes into consideration the effect of temperature combined with those of time‐of‐day and type‐of‐day via nonparametric estimation. In addition, an ARIMA model is used to model the serial correlation in the data. An iterative backfitting algorithm is used to estimate the model. Post‐sample forecasting performance is evaluated and comparative results are presented. Copyright © 2006 John Wiley & Sons, Ltd.     

Evaluating coverage of genome-wide association studies

Genome-wide association studies involving hundreds of thousands of SNPs in thousands of cases and controls are now underway. The first of many analytical challenges in these studies involves the choice of SNPs to genotype. It is not practical to construct a different panel of tag SNPs for each study, so the first generation of genome-wide scans will use predefined, commercially available marker panels, which will in part dictate their success or failure. We compare different approaches in use today, and show that although many of them provide substantial coverage of common variation in non-African populations, the precise extent is strongly dependent on the frequencies of alleles of interest and on specific considerations of study design. Overall, despite substantial differences in genotyping technologies, marker selection strategies and number of markers assayed, the first-generation high-throughput platforms all offer similar levels of genome coverage.     

Digestive physiology is a determinant of foraging bout frequency in hummingbirds

Hummingbirds are among the smallest endothermic vertebrates. Because they forage by energetically costly hovering, and because weight-specific basal metabolic rates increase with decreasing body size, their basal and active metabolic rates are among the highest recorded. Hummingbirds fuel these metabolic requirements mainly with highly concentrated sugar in nectar, which they extract rapidly and efficiently by an unknown mechanism. It is especially puzzling that, despite their high energy requirements, hummingbirds spend only approximately 20% of their waking hours feeding, but 75% perched and apparently doing nothing. Here we report the first measurement of nutrient absorption by hummingbird intestine and present a new method for measuring crop-emptying times. We find that hummingbird intestine has the highest active glucose transport rate and lowest passive glucose permeability reported for any vertebrate. Crop-emptying time may limit feeding-bout frequency and could largely account for the time spent perched.     

陕北高原蝗虫资源调查及区系分析

经调查，陕北高原共计蝗虫2总科8科14亚科27属51种(亚种)，其中对陕北地区农牧业危害严重的属有小车蝗属、星翅蝗属、负蝗属、尖翅蝗属、疣蝗属、稻蝗属等；对陕北高原蝗虫区系进行分析，结果表明：古北种为43种，占84．31％；东洋种1种，占1．96％；广布种为7种，占13．73％。标本保存于河北大学博物馆。     

The effects of human population structure on large genetic association studies

Large-scale association studies hold substantial promise for unraveling the genetic basis of common human diseases. A well-known problem with such studies is the presence of undetected population structure, which can lead to both false positive results and failures to detect genuine associations. Here we examine approximately 15,000 genome-wide single-nucleotide polymorphisms typed in three population groups to assess the consequences of population structure on the coming generation of association studies. The consequences of population structure on association outcomes increase markedly with sample size. For the size of study needed to detect typical genetic effects in common diseases, even the modest levels of population structure within population groups cannot safely be ignored. We also examine one method for correcting for population structure (Genomic Control). Although it often performs well, it may not correct for structure if too few loci are used and may overcorrect in other settings, leading to substantial loss of power. The results of our analysis can guide the design of large-scale association studies.