Observation of Interference Between Two Bose Condensates     

MR Andrews  CG Townsend  H Miesner  DS Durfee  DM Kurn  W Ketterle 《Science (New York, N.Y.)》1997,275(5300):637-641

Interference between two freely expanding Bose-Einstein condensates has been observed. Two condensates separated by approximately 40 micrometers were created by evaporatively cooling sodium atoms in a double-well potential formed by magnetic and optical forces. High-contrast matter-wave interference fringes with a period of approximately 15 micrometers were observed after switching off the potential and letting the condensates expand for 40 milliseconds and overlap. This demonstrates that Bose condensed atoms are "laser-like"; that is, they are coherent and show long-range correlations. These results have direct implications for the atom laser and the Josephson effect for atoms.  相似文献   

Effects of Monomer Structure on Their Organization and Polymerization in a Smectic Liquid Crystal     

CA Guymon  EN Hoggan  NA Clark  TP Rieker  DM Walba  CN Bowman 《Science (New York, N.Y.)》1997,275(5296):57-59

Photopolymerizable diacrylate monomers dissolved in fluid-layer smectic A and smectic C liquid crystal (LC) hosts exhibited significant spatial segregation and orientation that depend strongly on monomer structure. Small, flexible monomers such as 1,6-hexanediol diacrylate (HDDA) oriented parallel to the smectic layers and intercalated, whereas rod-shaped mesogen-like monomers such as 1,4-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)-2-methylbenzene (C6M) oriented normal to the smectic layers and collected within them. Such spatial segregation caused by the smectic layering dramatically enhanced photopolymerization rates; for HDDA, termination rates were reduced, whereas for C6M, both the termination and propagation rates were increased. These polymerization precursor structures suggest novel materials-design paradigms for gel LCs and nanophase-separated polymer systems.  相似文献   

Role of Gene Interactions in Hybrid Speciation: Evidence from Ancient and Experimental Hybrids   总被引：6，自引：0，他引：6  

LH Rieseberg  B Sinervo  CR Linder  MC Ungerer  DM Arias 《Science (New York, N.Y.)》1996,272(5262):741-745

The origin of a new diploid species by means of hybridization requires the successful merger of differentiated parental species' genomes. To study this process, the genomic composition of three experimentally synthesized hybrid lineages was compared with that of an ancient hybrid species. The genomic composition of the synthesized and ancient hybrids was concordant (rs = 0.68, P < 0.0001), indicating that selection to a large extent governs hybrid species formation. Further, nonrandom rates of introgression and significant associations among unlinked markers in each of the three synthesized hybrid lineages imply that interactions between coadapted parental species' genes constrain the genomic composition of hybrid species.  相似文献   

Chromosomal regions associated with barley yellow dwarf virus resistance in oat     

José F. Barbosa-Neto  Wilawan Siripoonwiwat  Louise S. O'Donoughue  Stewart M. Gray  Down M. Smith  Fred L. Kolb  Catherine Gourmet  Charlie M. Brown  Mark E. Sorrells 《Euphytica》2000,114(1):67-76

Immature embryos of the spring barley variety GoldenPromise, were bombarded with three different particledelivery systems and both transient and stabletransformation examined. In addition, a range oftechniques for the preparation of the DNA coated goldparticles was examined. Fertile transgenic barleyplants were obtained using three particle preparationtechniques which differed in the amount of gold andDNA used for each bombardment. However, only one ofthe particle delivery systems, the PDS 1000/He device,appeared to be effective in yielding transformedbarley plants.  相似文献   

Solar wind outflow and the chromospheric magnetic network     

DM Hassler  IE Dammasch  P Lemaire  P Brekke  W Curdt  HE Mason  JC Vial  K Wilhelm 《Science (New York, N.Y.)》1999,283(5403):810-813

Observations of outflow velocities in coronal holes (regions of open coronal magnetic field) have recently been obtained with the Solar and Heliospheric Observatory (SOHO) spacecraft. Velocity maps of Ne7+ from its bright resonance line at 770 angstroms, formed at the base of the corona, show a relationship between outflow velocity and chromospheric magnetic network structure, suggesting that the solar wind is rooted at its base to this structure, emanating from localized regions along boundaries and boundary intersections of magnetic network cells. This apparent relation to the chromospheric magnetic network and the relatively large outflow velocity signatures will improve understanding of the complex structure and dynamics at the base of the corona and the source region of the solar wind.  相似文献   

Die Stickstoffbilanz eines hochmontanen Bergwaldökosystems in den Tegernseer alpen in Abhängigkeit von der Jahreswitterung     

Eckart Kolb 《European Journal of Forest Research》1998,117(1-6):156-166

The nitrogen budget of a montane forest ecosystem in the Bavarian Alps was investigated from summer 1993 to winter 1995/96 in dependence on seasonal weather in the project “The influence of climate change on the nitrogen budget of forest soils”. The N-budgets were calculated by the nitrogen input via throughfall and the nitrogen output by seepage water, that has been sampled using suction cups. The hypothesis of a more positiv nitrogen budget of the ecosystem in warmer summers — nitrogen input is greater than nitrogen output — could neither be confirmed nor rejected, because there were no two summers differing solely in temperature. Rather, the variable precipitation regime during the summer season predominates a potentially changed nitrogen uptake by vegetation. In the investigated ecosystem, the nitrogen budget is less positive if the precipitation is higher and/or the average temperature of the air is lower. Also, for winter periods with higher precipitation we calculated a lower rate of nitrogen accumulation or even a nitrogen loss. On the other hand, higher temperatures will cause accelerated nitrogen accumulation. This is explained by the importance of high nitrogen inputs via throughfall in winter. The sequestration of potentially mobile nitrate-N in organic matter, and thus its retention in the ecosystem, demands a certain degree of humus activity. This activity is diminished at low temperatures.  相似文献   

Is GRO J1744-28 a strange star?     

KS Cheng  ZG Dai  DM Wei  T Lu 《Science (New York, N.Y.)》1998,280(5362):407-409

The unusual hard x-ray burster GRO J1744-28 recently discovered by the Compton Gamma-Ray Observatory can be modeled as a strange star with a dipolar magnetic field of 相似文献   

In situ measurements of organics, meteoritic material, mercury, and other elements in aerosols at 5 to 19 kilometers   总被引：1，自引：0，他引：1  

DM Murphy  DS Thomson  MJ Mahoney 《Science (New York, N.Y.)》1998,282(5394):1664-1669

In situ measurements of the chemical composition of individual aerosol particles at altitudes between 5 and 19 kilometers reveal that upper tropospheric aerosols often contained more organic material than sulfate. Although stratospheric aerosols primarily consisted of sulfuric acid and water, many also contained meteoritic material. Just above the tropopause, small amounts of mercury were found in over half of the aerosol particles that were analyzed. Overall, there was tremendous variety in aerosol composition. One measure of this diversity is that at least 45 elements were detected in aerosol particles. These results have wide implications for the complexity of aerosol sources and chemistry. They also offer possibilities for understanding the transport of atmospheric aerosols.  相似文献   

Presence and diversity of mixed avian Plasmodium spp. infections in introduced birds whose distribution overlapped with threatened New Zealand endemic birds     

ER Schoener  DM Tompkins  KA Parker  I Castro 《New Zealand veterinary journal》2020,68(2):101-106

ABSTRACT

Aims: To determine the presence of infection and co-infection of Plasmodium lineages in introduced birds at translocation sites for the North Island saddleback (Philesturnus rufusater), to investigate their role as Plasmodium spp. reservoirs.

Methods: Blood samples were collected from introduced bird species, with a special focus on blackbirds (Turdus merula) and song thrushes (Turdus philomelos), at six locations in the North Island of New Zealand that were the origin, or translocation sites, for North Island saddleback. Where available, blood smears were examined, and blood samples were tested using nested PCR with subsequent sequence analysis, for the presence of Plasmodium spp.

Results: Of the 55 samples tested using PCR analysis, 39 (71%) were positive for Plasmodium spp., and 28/40 (62%) blood smears were positive for Plasmodium spp. Overall, 31 blood samples were from blackbirds with 28/31 (90%) samples positive for Plasmodium spp. Six distinct avian Plasmodium lineages were identified, including three cosmopolitan lineages; Plasmodium vaughani SYAT05 was detected in 16 samples, Plasmodium matutinum Linn1 in 10 samples and Plasmodium elongatum GRW6 in eight samples. Mixed infections with more than one lineage were detected in 12 samples. Samples from two Australian magpies (Gymnorhina tibicen) were positive for Plasmodium. sp. lineage MYNA02, previously not identified in New Zealand.

Conclusions and clinical relevance: This is the first report from New Zealand in which specific Plasmodium spp. mixed infections have been found in introduced birds. Co-infections with several cosmopolitan Plasmodium lineages were identified, as well as the first report in New Zealand of an exotic avian Plasmodium sp. lineage, in Australian magpies. Whilst the role of introduced birds in maintaining and spreading pathogenic avian malaria in New Zealand is unclear, there is a potential infection risk to native birds, especially where distributions overlap.  相似文献