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191.
Hydrogen strongly affects the electronic and structural properties of many materials. It can bind to defects or to other impurities, often eliminating their electrical activity: this effect of defect passivation is crucial to the performance of many photovoltaic and electronic devices. A fuller understanding of hydrogen in solids is required to support development of improved hydrogen-storage systems, proton-exchange membranes for fuel cells, and high-permittivity dielectrics for integrated circuits. In chemistry and in biological systems, there have also been many efforts to correlate proton affinity and deprotonation with host properties. Here we report a systematic theoretical study (based on ab initio methods) of hydrogen in a wide range of hosts, which reveals the existence of a universal alignment for the electronic transition level of hydrogen in semiconductors, insulators and even aqueous solutions. This alignment allows the prediction of the electrical activity of hydrogen in any host material once some basic information about the band structure of that host is known. We present a physical explanation that connects the behaviour of hydrogen to the line-up of electronic band structures at heterojunctions. 相似文献
192.
Walter F Bertoldi F Carilli C Cox P Lo KY Neri R Fan X Omont A Strauss MA Menten KM 《Nature》2003,424(6947):406-408
Observations of molecular hydrogen in quasar host galaxies at high redshifts provide fundamental constraints on galaxy evolution, because it is out of this molecular gas that stars form. Molecular hydrogen is traced by emission from the carbon monoxide molecule, CO; cold H2 itself is generally not observable. Carbon monoxide has been detected in about ten quasar host galaxies with redshifts z > 2; the record-holder is at z = 4.69 (refs 1-3). Here we report CO emission from the quasar SDSS J114816.64 + 525150.3 (refs 5, 6) at z = 6.42. At that redshift, the Universe was only 1/16 of its present age, and the era of cosmic reionization was just ending. The presence of about 2 x 1010 M\circ of H2 in an object at this time demonstrates that molecular gas enriched with heavy elements can be generated rapidly in the youngest galaxies. 相似文献
193.
Raskin C Gérard C Donfut S Giannotta E Van Driessche G Van Beeumen J Dusart J 《Cellular and molecular life sciences : CMLS》2003,60(7):1460-1469
Streptomyces cacaoi -lactamase genes are controlled
by two regulators named blaA and
blaB. Whereas BlaA has been identified as a LysR-type activator,
the function of BlaB is still unknown. Its primary structure is similar to that of the serine
penicillin-recognizing enzymes (PREs). Indeed, the SXXK and KTG motifs are perfectly conserved in
BlaB, whereas the common SXN element found in PREs is replaced by a SDG motif. Site-directed
mutations were introduced in these motifs and they all disturb -lactamase regulation. A
water-soluble form of BlaB was also overexpressed in the
Streptomyces lividans TK24 cytoplasm and purified.
To elucidate the activity of BlaB, several compounds recognized by PREs were tested. BlaB could be
acylated by some of them, and it can therefore be considered as a penicillin-binding protein. BlaB
is devoid of -lactamase, D-aminopeptidase, DD-carboxypeptidase or thiolesterase activity.Received 13 January 2003; received after revision 9 April 2003; accepted 11 April 2003 相似文献
194.
Varon R Gooding R Steglich C Marns L Tang H Angelicheva D Yong KK Ambrugger P Reinhold A Morar B Baas F Kwa M Tournev I Guerguelcheva V Kremensky I Lochmüller H Müllner-Eidenböck A Merlini L Neumann L Bürger J Walter M Swoboda K Thomas PK von Moers A Risch N Kalaydjieva L 《Nature genetics》2003,35(2):185-189
195.
Stevens JA Ivison RJ Dunlop JS Smail IR Percival WJ Hughes DH Röttgering HJ Van Breugel WJ Reuland M 《Nature》2003,425(6955):264-267
The most massive galaxies in the present-day Universe are found to lie in the centres of rich clusters. They have old, coeval stellar populations suggesting that the bulk of their stars must have formed at early epochs in spectacular starbursts, which should be luminous phenomena when observed at submillimetre wavelengths. The most popular model of galaxy formation predicts that these galaxies form in proto-clusters at high-density peaks in the early Universe. Such peaks are indicated by massive high-redshift radio galaxies. Here we report deep submillimetre mapping of seven high-redshift radio galaxies and their environments. These data confirm not only the presence of spatially extended regions of massive star-formation activity in the radio galaxies themselves, but also in companion objects previously undetected at any wavelength. The prevalence, orientation, and inferred masses of these submillimetre companion galaxies suggest that we are witnessing the synchronous formation of the most luminous elliptical galaxies found today at the centres of rich clusters of galaxies. 相似文献
196.
197.
G. F. Van Went 《Cellular and molecular life sciences : CMLS》1978,34(3):324-325
Summary Using the micronucleus test as a screening method for mutagenic activity, no significant increase in the number of micronuclei was found when LSD, psilocybin or 9-THC were administered in 3 logarithmically increasing doses to mice. Azathioprine (Imuran®), given as a positive control, caused a statistically significant increase in micronucleated cells.Acknowledgment. The expert technical assistance of Mr Joop Branger is greatfully acknowledged. We thank Prof. Dr C. A. Salemink, University of Utrecht, for the supply of the THC, and Dr J. Fokkens, National Institute of Public Health, for preparing the solutions. 相似文献
198.
E. L. Van Alstyne Celia D. Sladek D. C. Smith 《Cellular and molecular life sciences : CMLS》1977,33(7):863-864
Summary The plasma concentration of L-carnitine in scalded rats was determined to be greater (p0.05) than that of control rats at 6 h following the administration of a 20% body surface, full-thickness burn produced by scalding in a 100°C water bath for 15 sec. 相似文献
199.
H. J. Wynne K. H. Van Buuren W. Wakelkamp 《Cellular and molecular life sciences : CMLS》1982,38(6):655-657
Summary Capacity factors in reversed-phase HPLC and distribution constants in octan-l-ol/water of N-acetyl-N-methylamino acid amides have been measured as a function of temperature. The HPLC capacity factors are proposed as estimates of the hydrophobicity of the amino acid side chains.We acknowledge the interest in this work of Dr H. van Rooy, Dr J. Kinkel, Prof. W. Soudijn and Prof. E. Tomlinson. 相似文献
200.
Anske Van den Abbeele Sarah De Clercq Ariane De Ganck Veerle De Corte Berlinda Van Loo Sameh Hamdy Soror Vasundara Srinivasan Jan Steyaert Joël Vandekerckhove Jan Gettemans 《Cellular and molecular life sciences : CMLS》2010,67(9):1519-1535
RNA interference has tremendously advanced our understanding of gene function but recent reports have exposed undesirable
side-effects. Recombinant Camelid single-domain antibodies (VHHs) provide an attractive means for studying protein function without affecting gene expression.
We raised VHHs against gelsolin (GsnVHHs), a multifunctional actin-binding protein that controls cellular actin organization
and migration. GsnVHH-induced delocalization of gelsolin to mitochondria or the nucleus in mammalian cells reveals distinct
subpopulations including free gelsolin and actin-bound gelsolin complexes. GsnVHH 13 specifically recognizes Ca2+-activated gelsolin (K
d ~10 nM) while GsnVHH 11 binds gelsolin irrespective of Ca2+ (K
d ~5 nM) but completely blocks its interaction with G-actin. Both GsnVHHs trace gelsolin in membrane ruffles of EGF-stimulated
MCF-7 cells and delay cell migration without affecting F-actin severing/capping or actin nucleation activities by gelsolin.
We conclude that VHHs represent a potent way of blocking structural proteins and that actin nucleation by gelsolin is more
complex than previously anticipated. 相似文献