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排序方式: 共有906条查询结果,搜索用时 62 毫秒
61.
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
62.
The structure of ferrihydrite, a nanocrystalline material 总被引:2,自引:0,他引:2
Michel FM Ehm L Antao SM Lee PL Chupas PJ Liu G Strongin DR Schoonen MA Phillips BL Parise JB 《Science (New York, N.Y.)》2007,316(5832):1726-1729
Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, the nanocrystallinity of this iron oxyhydroxide has hampered accurate structure determination by traditional methods that rely on long-range order. We uncovered the atomic arrangement by real-space modeling of the pair distribution function (PDF) derived from direct Fourier transformation of the total x-ray scattering. The PDF for ferrihydrite synthesized with the use of different routes is consistent with a single phase (hexagonal space group P6(3)mc; a = approximately 5.95 angstroms, c = approximately 9.06 angstroms). In its ideal form, this structure contains 20% tetrahedrally and 80% octahedrally coordinated iron and has a basic structural motif closely related to the Baker-Figgis delta-Keggin cluster. Real-space fitting indicates structural relaxation with decreasing particle size and also suggests that second-order effects such as internal strain, stacking faults, and particle shape contribute to the PDFs. 相似文献
63.
Myxovirus antibody increases in human connective tissue disease 总被引:12,自引:0,他引:12
Antibodies to measles and parainfluenza type 1 viruses were significantly increased in systemic lupus erythematosus and Reiter's syndrome. Of the individuals with highest titers of measles antibody, 75 percent had neurologic illness. Persistent virus infection may be a factor in the pathogenesis of these diseases. 相似文献
64.
Phillips JC 《Science (New York, N.Y.)》1913,37(958):717-718
65.
Huntington's disease: two families with differing clinical features show linkage to the G8 probe 总被引:8,自引:0,他引:8
S E Folstein J A Phillips D A Meyers G A Chase M H Abbott M L Franz P G Waber H H Kazazian P M Conneally W Hobbs 《Science (New York, N.Y.)》1985,229(4715):776-779
To test the hypothesis that interfamily variability in Huntington's Disease (HD) is due to mutation at different loci, linkage analysis was undertaken in two large HD kindreds that differed in ethnicity, age-at-onset, and neurologic and psychiatric features. Both families showed linkage of the HD locus to the G8 probe. Several recombinants were documented in each family, and the best estimate of the recombination fraction for the two families was 6 percent with a 95 percent confidence interval of 0 to 12 percent. Although the data support the existence of a single HD locus, use of the G8 probe for presymptomatic testing in these kindreds would have resulted in a 12 percent error rate in genotype assignment at the HD locus. 相似文献
66.
Curran MA van Ommen TD Morgan VI Phillips KL Palmer AS 《Science (New York, N.Y.)》2003,302(5648):1203-1206
The instrumental record of Antarctic sea ice in recent decades does not reveal a clear signature of warming despite observational evidence from coastal Antarctica. Here we report a significant correlation (P < 0.002) between methanesulphonic acid (MSA) concentrations from a Law Dome ice core and 22 years of satellite-derived sea ice extent (SIE) for the 80 degrees E to 140 degrees E sector. Applying this instrumental calibration to longer term MSA data (1841 to 1995 A.D.) suggests that there has been a 20% decline in SIE since about 1950. The decline is not uniform, showing large cyclical variations, with periods of about 11 years, that confuse trend detection over the relatively short satellite era. 相似文献
67.
68.
Measurements have been made of the ratios of chlorine-36 to chlorine in five halite samples from Searles Lake sediments, previously dated by carbon-14, thorium-230, and magnetostratigraphic techniques. The ages calculated from the chlorine ratios are generally concordant with those from the other methods, implying the constancy of the chlorine input ratio over the last million years. 相似文献
69.
70.
Coal palynology and studies of petrified peat indicate major changes in coal-swamp floras and the botanical constituents of coal throughout Pennsylvanian time. The changes are the result of broad climatic shifts and local environmental factors. The most striking is the change from a lycopod-dominated flora to one in which tree ferns were the major element. This change occurred at the Desmoinesian-Missourian (Westphalian-Stephanian) boundary and is probably multicontinental in scope. 相似文献