Generating solitons by phase engineering of a bose-einstein condensate     

Denschlag J  Simsarian JE  Feder DL  Clark CW  Collins LA  Cubizolles J  Deng L  Hagley EW  Helmerson K  Reinhardt WP  Rolston SL  Schneider BI  Phillips WD 《Science (New York, N.Y.)》2000,287(5450):97-101

Quantum phase engineering is demonstrated with two techniques that allow the spatial phase distribution of a Bose-Einstein condensate (BEC) to be written and read out. A quantum state was designed and produced by optically imprinting a phase pattern onto a BEC of sodium atoms, and matter-wave interferometry with spatially resolved imaging was used to analyze the resultant phase distribution. An appropriate phase imprint created solitons, the first experimental realization of this nonlinear phenomenon in a BEC. The subsequent evolution of these excitations was investigated both experimentally and theoretically.  相似文献   

Seal lungs collapse during free diving: evidence from arterial nitrogen tensions   总被引：4，自引：0，他引：4  

K J Falke  R D Hill  J Qvist  R C Schneider  M Guppy  G C Liggins  P W Hochachka  R E Elliott  W M Zapol 《Science (New York, N.Y.)》1985,229(4713):556-558

Arterial blood nitrogen tensions of free-diving Weddell seals (Leptonychotes weddelli) were measured by attaching a microprocessor-controlled blood pump and drawing samples at depth to determine how these marine mammals dive to great depths and ascend rapidly without developing decompression sickness. Forty-seven samples of arterial blood were obtained from four Weddell seals during free dives lasting up to 23 minutes to depths of 230 meters beneath the sea ice of McMurdo Sound, Antarctica. Peak arterial blood nitrogen tensions of between 2000 and 2500 millimeters of mercury were recorded at depths of 40 to 80 meters during descent, indicating that the seal's lung collapses by 25 to 50 meters. Then arterial blood nitrogen tensions slowly decreased to about 1500 millimeters of mercury at the surface. In a single dive, alveolar collapse and redistribution of blood nitrogen allow the seal to avoid nitrogen narcosis and decompression sickness.  相似文献   

Conserved folding in retroviral proteases: crystal structure of a synthetic HIV-1 protease   总被引：57，自引：0，他引：57  

A Wlodawer  M Miller  M Jaskólski  B K Sathyanarayana  E Baldwin  I T Weber  L M Selk  L Clawson  J Schneider  S B Kent 《Science (New York, N.Y.)》1989,245(4918):616-621

The rational design of drugs that can inhibit the action of viral proteases depends on obtaining accurate structures of these enzymes. The crystal structure of chemically synthesized HIV-1 protease has been determined at 2.8 angstrom resolution (R factor of 0.184) with the use of a model based on the Rous sarcoma virus protease structure. In this enzymatically active protein, the cysteines were replaced by alpha-amino-n-butyric acid, a nongenetically coded amino acid. This structure, in which all 99 amino acids were located, differs in several important details from that reported previously by others. The interface between the identical subunits forming the active protease dimer is composed of four well-ordered beta strands from both the amino and carboxyl termini and residues 86 to 94 have a helical conformation. The observed arrangement of the dimer interface suggests possible designs for dimerization inhibitors.  相似文献   

Association of transfer RNA acceptor identity with a helical irregularity   总被引：8，自引：0，他引：8  

W H McClain  Y M Chen  K Foss  J Schneider 《Science (New York, N.Y.)》1988,242(4886):1681-1684

The aminoacylation specificity ("acceptor identity") of transfer RNAs (tRNAs) has previously been associated with the position of particular nucleotides, as opposed to distinctive elements of three-dimensional structure. The contribution of a G.U wobble pair in the acceptor helix of tRNA(Ala) to acceptor identity was examined with synthetic amber suppressor tRNAs in Escherichia coli. The acceptor identity was not affected by replacing the G.U wobble pair in tRNA(Ala) with a G.A, C.A, or U.U wobble pair. Furthermore, a tRNA(Ala) acceptor identity was conferred on tRNA(Lys) when the same site in the acceptor helix was replaced with any of several wobble pairs. Additional data with tRNA(Ala) show that a substantial acceptor identity was retained when the G.U wobble pair was translocated to another site in the acceptor helix. These results suggest that the G.U wobble pair induces an irregularity in the acceptor helix of tRNA(Ala) to match a complementary structure in the aminoacylating enzyme.  相似文献   

A Chemoautotrophically Based Cave Ecosystem   总被引：1，自引：0，他引：1  

SM Sarbu  TC Kane  BK Kinkle 《Science (New York, N.Y.)》1996,272(5270):1953-1955

Microbial mats discovered in a ground-water ecosystem in southern Romania contain chemoautotrophic bacteria that fix inorganic carbon, using hydrogen sulfide as an energy source. Analysis of stable carbon and nitrogen isotopes showed that this chemoautotrophic production is the food base for 48 species of cave-adapted terrestrial and aquatic invertebrates, 33 of which are endemic to this ecosystem. This is the only cave ecosystem known to be supported by in situ autotrophic production, and it contains the only terrestrial community known to be chemoautotrophically based.  相似文献   

Insect olfaction: deciphering system for chemical messages   总被引：11，自引：0，他引：11  

D Schneider 《Science (New York, N.Y.)》1969,163(871):1031-1037

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Gastrin antibodies: induction, demonstration, and specificity     

D R Schneider  G L Endahl  M C Dodd  J E Jesseph  N J Bigley  R M Zollinger 《Science (New York, N.Y.)》1967,156(773):391-392

Antibodies to the antral hormone gastrin have been induced in the rabbit and detected by passive hemagglutination. Specificity of the antibody, as determined by three methods, is directed to gastrins I and II, gastrin pentapeptide, and gastrin tetrapeptide, as well as to the stage-1 gastrin used for immunization.  相似文献   

Ultraviolet spectrometer observations of neptune and triton     

Broadfoot AL  Atreya SK  Bertaux JL  Blamont JE  Dessler AJ  Donahue TM  Forrester WT  Hall DT  Herbert F  Holberg JB  Hunter DM  Krasnopolsky VA  Linick S  Lunine JI  McConnell JC  Moos HW  Sandel BR  Schneider NM  Shemansky DE  Smith GR  Strobel DF  Yelle RV 《Science (New York, N.Y.)》1989,246(4936):1459-1466

Results from the occultation of the sun by Neptune imply a temperature of 750 +/- 150 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane, acetylene, and ethane at lower levels. The ultraviolet spectrum of the sunlit atmosphere of Neptune resembles the spectra of the Jupiter, Saturn, and Uranus atmospheres in that it is dominated by the emissions of H Lyman alpha (340 +/- 20 rayleighs) and molecular hydrogen. The extreme ultraviolet emissions in the range from 800 to 1100 angstroms at the four planets visited by Voyager scale approximately as the inverse square of their heliocentric distances. Weak auroral emissions have been tentatively identified on the night side of Neptune. Airglow and occultation observations of Triton's atmosphere show that it is composed mainly of molecular nitrogen, with a trace of methane near the surface. The temperature of Triton's upper atmosphere is 95 +/- 5 kelvins, and the surface pressure is roughly 14 microbars.  相似文献   

Scent organ development in creatonotos moths: regulation by pyrrolizidine alkaloids     

Schneider D  Boppré M  Zweig J  Horsley SB  Bell TW  Meinwald J  Hansen K  Diehl EW 《Science (New York, N.Y.)》1982,215(4537):1264-1265

7-Hydroxy-6,7-dihydro-5H-pyrolizine-1-carboxaldehyde is the major volatile component of the scent organs in males of two species of Creatonotos (Lepidoptera, Arctiidae). The biosynthesis of this presumed pheromone depends on the presence of pyrrolizidine alkaloids in plants that are ingested by the larvae. In addition, these secondary plant substances control the morphogenesis of the scent organs. This morphogenetic effect of an alkaloid has not been observed previously.  相似文献   

Growth of SiO2 at room temperature with the use of catalyzed sequential half-reactions     

JW Klaus  O Sneh  SM George 《Science (New York, N.Y.)》1997,278(5345):1934-1936

Films of silicon dioxide (SiO2) were deposited at room temperature by means of catalyzed binary reaction sequence chemistry. The binary reaction SiCl4 + 2H2O --> SiO2 + 4HCl was separated into SiCl4 and H2O half-reactions, and the half-reactions were then performed in an ABAB ellipsis sequence and catalyzed with pyridine. The pyridine catalyst lowered the deposition temperature from >600 to 300 kelvin and reduced the reactant flux required for complete reactions from approximately 10(9) to approximately 10(4) Langmuirs. Growth rates of approximately 2.1 angstroms per AB reaction cycle were obtained at room temperature for reactant pressures of 15 millitorr and 60-second exposure times with 200 millitorr of pyridine. This catalytic technique may be general and should facilitate the chemical vapor deposition of other oxide and nitride materials.  相似文献