用于双向WDM网络系统的新型大规模全光星形耦合器

首次提出了一种新型大规模星形耦合器.这种星形耦合器不但能提供巨大的端口数,满足未来超大规模双向WDM网络系统的需要;而且,由其构成的WDM网络具有极大的组网灵活性,可方便、平滑地实现网络的在线扩容、升级;同时,它也适用于目前广泛应用的单向WDM网络及其他光通信系统.这种大规模星形耦合器为WDM网络系统提供了一种理想的选择.     

Systematic variation of the stellar initial mass function in early-type galaxies

Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination, no consensus has emerged on whether it is universal among different types of galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS(3D) sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy's IMF depends intimately on the galaxy's formation history.     

A prokaryotic proton-gated ion channel from the nicotinic acetylcholine receptor family

Ligand-gated ion channels (LGICs) mediate excitatory and inhibitory transmission in the nervous system. Among them, the pentameric or 'Cys-loop' receptors (pLGICs) compose a family that until recently was found in only eukaryotes. Yet a recent genome search identified putative homologues of these proteins in several bacterial species. Here we report the cloning, expression and functional identification of one of these putative homologues from the cyanobacterium Gloeobacter violaceus. It was expressed as a homo-oligomer in HEK 293 cells and Xenopus oocytes, generating a transmembrane cationic channel that is opened by extracellular protons and shows slow kinetics of activation, no desensitization and a single channel conductance of 8 pS. Electron microscopy and cross-linking experiments of the protein fused to the maltose-binding protein and expressed in Escherichia coli are consistent with a homo-pentameric organization. Sequence comparison shows that it possesses a compact structure, with the absence of the amino-terminal helix, the canonical disulphide bridge and the large cytoplasmic domain found in eukaryotic pLGICs. Therefore it embodies a minimal structure required for signal transduction. These data establish the prokaryotic origin of the family. Because Gloeobacter violaceus carries out photosynthesis and proton transport at the cytoplasmic membrane, this new proton-gated ion channel might contribute to adaptation to pH change.     

Exchange of terminal portions of X- and Y-chromosomal short arms in human XX males

In most human 'XX males', DNA sequences normally found on Yp, the short arm of the Y chromosome, are present on Xp, the short arm of the X chromosome. To establish whether this transfer involves a terminal portion of Yp, and whether a terminal portion of Xp is lost in the process, we followed the inheritance of pseudoautosomal restriction fragment length polymorphisms in two XX-male families. One XX male apparently inherited the entire pseudoautosomal region of his father's Y chromosome and no part of the pseudoautosomal region of his father's X chromosome. The second XX male also inherited the entire pseudoautosomal region of his father's Y, but in addition inherited a proximal portion of the pseudoautosomal region of his father's X. These findings argue that XX males result from the transfer of a terminal portion of Yp onto Xp in exchange for a terminal portion of Xp (ref. 7). This implies that the testis-determining factor gene (TDF) maps distally in the strictly sex-linked portion of Yp, near the pseudoautosomal domain. The XX males described here appear to result from single (and, at least in the second case, unequal) crossovers proximal to the pseudoautosomal region on Yp and proximal to or within the pseudoautosomal region on Xp.     

The Combinatorial Approach to Asymmetric Hydrogenation: More Miles out of Monophos

1Introduction In custom manufacturing time-to-market is of overriding importance. Thus, asymmetric hydrogenation will be applied only if an appropriate catalyst can be found in a very short period of time. For this reason we have build up a full-scale capability for High Throughput Experimentation, encompassing several robot systems. As ligand synthesis was the last remaining barrier we have explored, together with the University of Groningen, the use of simple monodentate ligands, such as MonoPhosTM. These ligands can be synthesised in two chemical steps, from BINOL, PCl3 and an amine.Surprisingly, very high enantioselectivities can be obtained in the asymmetric hydrogenation of α-and β-dehydro-amino acids and esters, aromatic enamides, itaconic acid and ester[1]. See Scheme 1 and 2(at page 830).     

Depth of a strong jovian jet from a planetary-scale disturbance driven by storms

The atmospheres of the gas giant planets (Jupiter and Saturn) contain jets that dominate the circulation at visible levels. The power source for these jets (solar radiation, internal heat, or both) and their vertical structure below the upper cloud are major open questions in the atmospheric circulation and meteorology of giant planets. Several observations and in situ measurements found intense winds at a depth of 24 bar, and have been interpreted as supporting an internal heat source. This issue remains controversial, in part because of effects from the local meteorology. Here we report observations and modelling of two plumes in Jupiter's atmosphere that erupted at the same latitude as the strongest jet (23 degrees N). The plumes reached a height of 30 km above the surrounding clouds, moved faster than any other feature (169 m s(-1)), and left in their wake a turbulent planetary-scale disturbance containing red aerosols. On the basis of dynamical modelling, we conclude that the data are consistent only with a wind that extends well below the level where solar radiation is deposited.     

Phosphatidylglycerol is involved in protein translocation across Escherichia coli inner membranes

Newly synthesized proteins to be exported out of the cytoplasm of bacterial cells have to pass across the inner membrane. In Gram-negative bacteria ATP, a membrane potential, the products of the sec genes and leader peptidases (enzymes which cleave the N-terminal signal peptides of the precursor proteins) are required. The mechanism of translocation, however, remains elusive. Important additional roles for membrane lipids have been repeatedly suggested both on theoretical grounds and on the basis of experiments with model systems but no direct evidence had been obtained. We demonstrate here, using mutants of Escherichia coli defective in the synthesis of the major anionic membrane phospholipids, that phosphatidylglycerol is involved in the translocation of newly synthesized outer-membrane proteins across the inner membrane.     

Local destabilisation of a DNA double helix by a T--T wobble pair.

Nuclear magnetic resonance is a technique which permits direct observation of the Waton--Click hydrogen-bonded ring imino protons (guanine N1H and thymine N3H). As the formation and disruption of hydrogen bonds of double-helical RNA and DNA structures are key events during various biological processes, NMR thus provides a useful tool for studying the fluctuational mobility of the individual base pairs. Indeed, several NMR studies of oligo- and polynucleotides have been carried out to probe the structure and dynamics of nucleic acids in solution (for a review see ref. 1). The present study constitutes the first part of our attempt to assess the influence of non-complementary base pairs on the stability of nucleic acid double helices. We report the spectral assignment and temperature-dependent NMR profiles of the hydrogen-bonded imino protons of the two DNA fragments shown in Fig. 1. The assignment is based solely on experimental grounds using the principle of chemical modification. It will be demonstrated that the introduction of a non-complementary (wobble) base pair in a DNA duplex introduces an extra melting site in addition to the sequential melting which starts with the terminal base pairs in the double helix structure.     

Cloning of a gene that is rearranged in patients with choroideraemia

Choroideraemia (tapetochoroidal dystrophy, TCD), a common form of X-linked blindness, is characterized by progressive dystrophy of the choroid, retinal pigment epithelium and retina. Previous studies have assigned the TCD gene to a small segment of the Xq21 band. By making use of reverse genetics strategies we have isolated eight overlapping complementary DNA clones from the same chromosomal region. The corresponding gene is expressed in retina, choroid and retinal pigment epithelium. The cDNAs encompass an open reading frame of 948 base pairs that is structurally altered in eight TCD patients with deletions, and in a female patient with a balanced translocation involving Xq21. These findings provide strong evidence that we have cloned the gene underlying choroideraemia. Elucidation of its function should provide new insights into the molecular mechanisms responsible for this disorder and other hereditary retinopathies.