Current and thermohaline characteristics of the Arabian Sea during January 1998

Based on a ship survey during January 1998, the characteristics of the flow, the thermohaline properties and the volume transport of the Arabian Sea are discussed. A strong westward flow exists between 10.5?N and 11?N, part of which turns to the south as the Somali current near the coast at about 10?N and the rest turns north. At the passage between the African continent and the So- cotra Island, the northern branch separates into two flows: the left one enters the passage and the right one flows eastward along the southern slope of the island. Off the island the flow separates once more, most of it meandering northeast and a small fraction flow- ing southeast. Volume transport calculation suggests that the tidal transport is one or two orders of magnitude smaller than the total transport in this region and it becomes more important near the coast. The average velocity of the flow in the upper layer (0-150 m) is about 20 cm s-1, with a maximum of 53 cm s-1 appearing east of the Socotra Island, and the subsurface layer (200-800 m) has an aver- age velocity of 8.6 cm s-1; the velocity becomes smaller at greater depths. The depth of the seasonal thermocline is about 100 m, above which there is a layer with well mixed temperature and dissolved oxygen. High-salinity and oxygen-rich water appears near the surface of the northern Arabian Sea; a salinity maximum and oxygen minimum at 100 m depth along 8?N testifies the subduction of surface water from the northern Arabian Sea. Waters from the Red Sea and the Persian Gulf also influence the salinity of the area.     

CLOBAL CHARM OF THE CHANGJIANG RIVER DELTA

1SPLENDOROFHISTORICALCULTURE InChina,theChangjiang(Yangtze)RiverDelta①gen-erallymeansanadvancedproductivityandculture,whichaffectsdeeplynotonlythewholeChinabutal-sotheAsian-Pacificregion,evenEuropeandAfrica. 1.1CradlefortheCommunicationandPropagationofCivilization ThedevelopmentcourseoftheChangjiangRiverDelta'scultureisdevious,buttheNeolithicHemuduCultureexcavatedinYuyaoCityofZhejiangProvinceindicatestheadvancedpaddyriceculture;MajiabangCulture5000aB.P.andEastBridgeRuin…     

A Measurement of Omega from the North American Test Flight of Boomerang

We use the angular power spectrum of the cosmic microwave background, measured during the North American test flight of the Boomerang experiment, to constrain the geometry of the universe. Within the class of cold dark matter models, we find that the overall fractional energy density of the universe Omega is constrained to be 0.85相似文献   

A High-Eccentricity Low-Mass Companion to HD 89744

We present deep Hubble Space Telescope (HST) imaging, as well as ground-based imaging and spectroscopy, of the optical afterglow associated with the long-duration gamma-ray burst GRB 990712 and its host galaxy. The data were obtained 48-123 days after the burst occurred. The magnitudes of the host (R=21.9, V=22.5) and optical afterglow (R=25.4, V=25.8, 47.7 days after the burst) favor a scenario in which the optical light follows a pure power-law decay with an index of alpha approximately -1.0. We find no evidence for a contribution from a supernova like SN 1998bw. This suggests that either there are multiple classes of long-duration gamma-ray bursts or that the peak luminosity of the supernova was more than 1.5 mag fainter than SN 1998bw. The HST images and EFOSC2 spectra indicate that the gamma-ray burst was located in a bright, extended feature (possibly a star-forming region) 1.4 kpc from the nucleus of a 0.2L*B galaxy at z=0.434, possibly a Seyfert 2 galaxy. The late-time afterglow and host galaxy of GRB 990712 bear some resemblance to those of GRB 970508.     

Radio Detection of a Rapid Disturbance Launched by a Solar Flare

We report the direct observation of motion associated with a solar flare at a speed of 26,000 km s-1. The motion is seen from a radio source at 0.33 GHz, which suddenly starts moving during the flare. At its peak, the radio source covers a quiet region of dimension 500&arcsec;. Emission from any given location is sporadic. The disturbance itself does not seem to radiate, but it excites coronal features that continue to radiate after it passes. The inferred velocity is larger than any previously inferred velocity of a disturbance in the solar atmosphere apart from freely streaming beams of accelerated electrons. The observed motion of the source at a fixed frequency, low polarization, and moderate bandwidth are more consistent with the typical properties of moving type IV radio bursts than with classical coronal shock-associated type II bursts, but any disturbance at such a high velocity must be highly supersonic and should drive a shock. We speculate that the disturbance is associated with the realignment of magnetic fields connecting different portions of an active region.     

ASCA Observation of the Quiescent X-Ray Counterpart to SGR 1627-41

We present a 2-10 keV ASCA observation of the field around the soft gamma repeater SGR 1627-41. A quiescent X-ray source, whose position is consistent both with that of a recently discovered BeppoSAX X-ray source and with the Interplanetary Network localization for this soft gamma repeater, was detected in this observation. In 2-10 keV X-rays, the spectrum of the X-ray source may be fit equally well by a power-law, blackbody, or bremsstrahlung function, with unabsorbed flux approximately 5x10-12 ergs cm-2 s-1. We do not confirm a continuation of a fading trend in the flux, and we find no evidence for periodicity, both of which were noted in the earlier BeppoSAX observations.     

巨早型星系的近红外谱合成

在8000至8670的波长范围内,利用一个由144颗恒星光谱组成的光谱厍,我们对57个巨椭圆和S0星系(M_B<-21)的光谱和它们的平均光谱进行了光谱合成.这个光谐库包括了光谱型为G,K和M的巨星和矮星,它具有的金属丰度[Fe/H]覆盖了-0.1到-0.5的范围,表面重力log g为1.0至5.0.光谱合成的结果表明:巨椭圆和S0星系的金属丰度约为太阳的一倍半;有效表面重力分布在3.2—4.1的范围内;矮星在8400附近光的贡献可与巨星相比较.     

身为菜鸟的岁月

大年初一,和父母一起到乡下外婆家拜年。南方气候湿润,过年这几天都是满天的云,不见蓝天。但初一晚上,云却奇迹般地散去一大片,露出了最灿烂的一片星空。     

Metabolic plasticity of nitrogen assimilation by Porphyra umbilicalis (Linnaeus) Kützing

The physical stresses associated with emersion have long been considered major factors determining the vertical zonation of intertidal seaweeds.We examined Porphyra umbilicalis(Linnaeus) Kützing thalli from the vertical extremes in elevation of an intertidal population(i.e.upper and lower intertidal zones) to determine whether Porphyra thalli acclimate to different vertical elevations on the shore with different patterns of nitrate uptake and nitrate reductase(NR) and glutamine synthetase(GS) activities in response to different degrees of emersion stress.We found that the nitrate uptake and NR recovery in the emersed tissues took longer in lower intertidal sub-population than in upper intertidal sub-population;and GS activity was also significantly affected by emersion and,interestingly,such an activity was enhanced by emersion of thalli from both upper and lower intertidal zones.These results suggested that intra-population variability in post-emersion recovery of physiological functions such as nutrient uptake and NR activity enables local adaptation and contributes to the wide vertical distribution of P.umbilicalis.The high GS activity during periodic emersion stress may be a protective mechanism enabling P.umbilicalis to assimilate nitrogen quickly when it again becomes available,and may also be an evidence of photorespiration during emersion.     

Effect of Matching Algorithm and Profile Shape on Pulsar Pulse Time of Arrival Uncertainties

For high-precision pulsar timing analysis and low-frequency gravitational wave detection, it is essential to accurately determine pulsar pulse times of arrival(ToAs) and associated uncertainties. To measure the ToAs and their uncertainties, various cross-correlation-based techniques can be employed. We develop methodologies to investigate the impact of the template-matching method, profile shape, signal-to-noise ratio of both template and observation on ToA uncertainties. These methodologies are...