Integration of telomere sequences with the draft human genome sequence

Telomeres are the ends of linear eukaryotic chromosomes. To ensure that no large stretches of uncharacterized DNA remain between the ends of the human working draft sequence and the ends of each chromosome, we would need to connect the sequences of the telomeres to the working draft sequence. But telomeres have an unusual DNA sequence composition and organization that makes them particularly difficult to isolate and analyse. Here we use specialized linear yeast artificial chromosome clones, each carrying a large telomere-terminal fragment of human DNA, to integrate most human telomeres with the working draft sequence. Subtelomeric sequence structure appears to vary widely, mainly as a result of large differences in subtelomeric repeat sequence abundance and organization at individual telomeres. Many subtelomeric regions appear to be gene-rich, matching both known and unknown expressed genes. This indicates that human subtelomeric regions are not simply buffers of nonfunctional 'junk DNA' next to the molecular telomere, but are instead functional parts of the expressed genome.     

Quasi-phase-matched generation of coherent extreme-ultraviolet light

High-harmonic generation is a well-known method of producing coherent extreme-ultraviolet (EUV) light, with photon energies up to about 0.5 keV (refs 1, 2). This is achieved by focusing a femtosecond laser into a gas, and high harmonics of the fundamental laser frequency are radiated in the forward direction. However, although this process can generate high-energy photons, efficient high-harmonic generation has been demonstrated only for photon energies of the order 50-100 eV (ref. 5). Ionization of the gas prevents the laser and the EUV light from propagating at the same speed, which severely limits the conversion efficiency. Here we report a technique to overcome this problem, and demonstrate quasi-phase-matched frequency conversion of laser light into EUV. Using a modulated hollow-core waveguide to periodically vary the intensity of the laser light driving the conversion, we efficiently generate EUV light even in the presence of substantial ionization. The use of a modulated fibre shifts the energy spectrum of the high-harmonic light to significantly higher photon energies than would otherwise be possible. We expect that this technique could form the basis of coherent EUV sources for advanced lithography and high-resolution imaging applications. In future work, it might also be possible to generate isolated attosecond pulses.     

Dysregulation of TGF-beta activation contributes to pathogenesis in Marfan syndrome

Marfan syndrome is an autosomal dominant disorder of connective tissue caused by mutations in fibrillin-1 (encoded by FBN1 in humans and Fbn1 in mice), a matrix component of extracellular microfibrils. A distinct subgroup of individuals with Marfan syndrome have distal airspace enlargement, historically described as emphysema, which frequently results in spontaneous lung rupture (pneumothorax; refs. 1-3). To investigate the pathogenesis of genetically imposed emphysema, we analyzed the lung phenotype of mice deficient in fibrillin-1, an accepted model of Marfan syndrome. Lung abnormalities are evident in the immediate postnatal period and manifest as a developmental impairment of distal alveolar septation. Aged mice deficient in fibrillin-1 develop destructive emphysema consistent with the view that early developmental perturbations can predispose to late-onset, seemingly acquired phenotypes. We show that mice deficient in fibrillin-1 have marked dysregulation of transforming growth factor-beta (TGF-beta) activation and signaling, resulting in apoptosis in the developing lung. Perinatal antagonism of TGF-beta attenuates apoptosis and rescues alveolar septation in vivo. These data indicate that matrix sequestration of cytokines is crucial to their regulated activation and signaling and that perturbation of this function can contribute to the pathogenesis of disease.     

A class of compact dwarf galaxies from disruptive processes in galaxy clusters

Dwarf galaxies have attracted increased attention in recent years, because of their susceptibility to galaxy transformation processes within rich galaxy clusters. Direct evidence for these processes, however, has been difficult to obtain, with a small number of diffuse light trails and intra-cluster stars being the only signs of galaxy disruption. Furthermore, our current knowledge of dwarf galaxy populations may be very incomplete, because traditional galaxy surveys are insensitive to extremely diffuse or compact galaxies. Aware of these concerns, we recently undertook an all-object survey of the Fornax galaxy cluster. This revealed a new population of compact members, overlooked in previous conventional surveys. Here we demonstrate that these 'ultra-compact' dwarf galaxies are structurally and dynamically distinct from both globular star clusters and known types of dwarf galaxy, and thus represent a new class of dwarf galaxy. Our data are consistent with the interpretation that these are the remnant nuclei of disrupted dwarf galaxies, making them an easily observed tracer of galaxy disruption.     

照片影调的尝试

一张平凡的照片经过影调加工,会使之沾染上艺术的气息.在这里笔者抛砖引玉,希望带给您一点启示,更多的效果还有待大家的多种尝试.     

两栖汽车

英国一家公司建造一种Ford Fiesta1.8升柴油发动机的两栖汽车。该型车有五个变速档，在陆地上行驶速度为每小时95英里，在水面上的行驶速度为每小时8英里。 驱动轴和驾驶杆是具有双层橡胶密封垫的防水不锈钢轴承。排气阀和热交换器也是用适合海上活动性能的不锈钢材制造，而且用抗海水腐蚀的多种涂料保护着其它部件。前车灯由具有高抗冲击性能的透明塑料制成。四个座位由坚固且柔软的材料制做。这种被称为“司令官”的车有一个1.3升的汽油发动机或者1.9升涡轮柴油发动机，五个变速档，四轮驱动。司机座后面的一条内置滚动杆可起到支撑软面的作用，而且一旦水越过玻璃风屏进入车蓬时，还能起到进气或排气的功能，以保持发动机处于干燥状态。 (法森译自美刊《机械设计》2000.6.15.)     

多源信息融合的配电网重复多发性停电在线监测与预警技术

针对配电网重复多发性停电问题，基于面向服务架构的多源停电信息融合技术，分析影响配电网重复多发性停电风险和停电分级预警的因素，并结合德尔菲法建立指标评价体系，分别得出各个因数指标的评分标准和权重，建立配电网重复多发性停电风险和停电分级预警模型。针对某实际停电实例进行了分析，得出重复多发性停电综合概率值和分级预警级别，为治理重复多发性停电提供了一种新思路。