Statistical Properties of SGR 1806-20 Bursts     

Göğüş E  Woods PM  Kouveliotou C  van Paradijs J  Briggs MS  Duncan RC  Thompson C 《The Astrophysical journal》2000,532(2):L121-L124

We present statistics of SGR 1806-20 bursts, combining 290 events detected with the Rossi X-Ray Timing Explorer/Proportional Counter Array, 111 events detected with the Burst and Transient Source Experiment, and 134 events detected with the International Cometary Explorer. We find that the fluence distribution of bursts observed with each instrument are well described by power laws with indices 1.43, 1.76, and 1.67, respectively. The distribution of time intervals between successive bursts from SGR 1806-20 is described by a lognormal function with a peak at 103 s. There is no correlation between the burst intensity and either the waiting times until the next burst or the time elapsed since the previous burst. In all these statistical properties, SGR 1806-20 bursts resemble a self-organized critical system, similar to earthquakes and solar flares. Our results thus support the hypothesis that the energy source for soft gamma repeater bursts is crustquakes due to the evolving, strong magnetic field of the neutron star, rather than any accretion or nuclear power.  相似文献   

Seed supply for coastal brackishwater shrimp farming: environmental impacts and sustainability     

Islam MS  Wahab MA  Tanaka M 《Marine pollution bulletin》2004,48(1-2):7-11

Globally, shrimp farming has been a significant agro-based economic activity since the early 1970s. Because it offered a huge immediate economic return, shrimp farming showed a booming expansion and soon became a multimillion dollar industry. However, it has been under extreme criticism because of its devastating ecological and socio-economic impacts. Because seed is the primary input, the impact from farming has started from the source of seed supply, so that not only are natural stocks of shrimp seeds now overexploited worldwide but seed collection activities also significantly reduce stocks of other living resources. Although hatcheries were developed as potential alternative and have replaced the natural seed source to a great extent, large-scale hatchery productions provide a potential source of coastal pollution. However, this area is still poorly studied. The present paper provides a review of the environmental impacts of the wild shrimp seed fishery as well as the possibility of environmental degradation from artificial shrimp seed production in hatcheries.  相似文献   

A Peculiar Broad Line Radio Galaxy 1938-155： VLA Observation at 90 cm     

Tao An  Xiao-Yu Hong  Wen-Xia Feng  Jun-Hui Zhao Shanghai Astronomical Observatory  Chinese Academy of Sciences  Shanghai  National Astronomical Observatories  Chinese Academy of Sciences  Beijing Harvard-Smithsonian Center for Astrophysics  Garden Street  MS  Cambridge  MA 《中国天文和天体物理学报》2004,4(6):527-532

We observed 1938-155, a broad line radio galaxy (BLRG), with the Very Large Array (VLA) at 90cm with an angular resolution of 6.8" × 4.0". The source consists of two components separated by 4 arcsec (- 20kpc, for H0 = 65km s-1 Mpc-1, q0 = 0.5) along the SE-NW direction. Both components show steep-spectra with a similar spectral index α - 0.83 ± 0.07 (Sv ∝ v-α). The bright double components are surrounded by a low-brightness cocoon. The radio properties of the two bright components are consistent with the hot spots produced by twin jets. An upper limit of - 0.0008 for the core dominance parameter (R) is inferred, suggesting there is no prominent radio core in the source. Assuming a modest viewing angle 30f77, a jet velocity is estimated - 0.07 c, based on the jet to counter-jet brightness ratio (J). The lower limit in jet speed inferred is consistent with no Doppler beaming effect on the jet. The radio galaxy 1938-155 could be an exceptional BLRG with no prominent radio core or jet.  相似文献   

Genetic responses to metal contamination in two clams: Ruditapes decussatus and Ruditapes philippinarum   总被引：1，自引：0，他引：1  

Moraga D  Mdelgi-Lasram E  Romdhane MS  El Abed A  Boutet I  Tanguy A  Auffret M 《Marine environmental research》2002,54(3-5):521-525

Coastal ecosystems are subjected to a wide variety of disturbances, including those due to xenobiotics of agricultural and industrial origin. These pollutants as heavy metals can modify the genetic diversity of populations by favouring or counter-selecting certain alleles or genotypes by differential mortality. In the present study, two genetic markers (phosphoglucomutase and glucosephosphate isomerase) and a protein marker (metallothionein) were monitored in order to determine the impact of heavy metals in different clam populations. Analysis of the genetic structure of the clam populations examined reveals that those inhabiting environments contaminated by heavy metals exhibit a higher allelic diversity and possess alleles at PGM loci that could be selected by the presence of heavy metals. The evaluation of metallothionein levels using a specific polyclonal antibody developed in the Pacific oyster (Crassostrea gigas) demonstrated the existence of a relationship between metallothionein concentrations and the level of metal pollution for clam populations sampled from different sites. An inter-specific difference was also detected between Ruditapes decussatus and Ruditapes philippinarum living in sympatry at the same site, suggesting a differential response of these two species upon exposure to an identical heavy metal concentration.  相似文献   

Toxicopathic liver lesions in English sole and chemical contaminant exposure in Vancouver Harbour,Canada     

Stehr CM  Myers MS  Johnson LL  Spencer S  Stein JE 《Marine environmental research》2004,57(1-2):55-74

The prevalence of toxicopathic liver lesions in English sole (Pleuronectes vetulus) was determined along a presumed gradient of chemical contamination in Vancouver Harbour, Canada. Fish were captured from five sites in or near Vancouver Harbour, British Columbia, Canada. No toxicopathic lesions were observed in fish examined at the reference site (Howe Sound outside Vancouver Harbour), or at the outer harbour site. In contrast, 20-23% of the fish from three sites located in the central harbour, Indian Arm and Port Moody Arm had one or more types of toxicopathic lesions. Likewise, aromatic hydrocarbon (AH) metabolites measured in bile exhibited a gradient in levels from lower concentrations at the reference site to significantly higher levels in fish from Indian Arm and Port Moody Arm harbour sites. The occurrence of toxicopathic liver lesions was statistically associated with concentrations of AHs measured in sediment and AH metabolite levels measured in bile.  相似文献   

Colonization of mine tailings by marine invertebrates     

Kline ER  Stekoll MS 《Marine environmental research》2001,51(4):301-325

An experiment was conducted to determine if a tailings substrate would inhibit recolonization of benthic macrofauna upon closure of a submarine tailings disposal (STD) operation. Trays of defaunated marine sediment, serving as a reference, and trays of tailings from a proposed gold mine were placed at 21 m depth on the ocean floor to allow colonization via settlement from the water column. Trays of reference sediment and tailings, and cores of ambient sediment were collected 9, 17, and 22 months after tray placement. Probable tray effects, which were desirable given the objectives of this study, precluded direct comparison of ecological succession in the tray sediments to the ambient assemblage. The ambient macrofauna assemblage was distinguishable from the reference sediment and tailings assemblages throughout the experiment and displayed more pronounced seasonality. Differences between the reference sediment and tailings assemblages were generally insignificant, including total abundance, total biomass, number of taxa, average size of individuals, numerically dominant taxa, abundance by ecological guilds, and overall community composition. Upon cessation of STD, recolonization of a benthic macrofauna community should not be inhibited by the presence of these tailings as a benthic substrate.  相似文献   

海洋高技术现状     

Estab.  N 沈乃宏 《海洋信息》1996,(11):11-18

1 前言 载人潜水器、遥控潜水器、海洋能、遥感、水下成像和海洋仪器是世界海洋勘探、开发的工具,与海洋勘探、开发密切相关的这六个方面,最近取得迅速进展。本报告按高级海洋技术委员会给出的题目编写,每一部分扼要阐述  相似文献   

厄尔尼诺现象对美国天然气工业的影响     

Wils.  MS 沈乃宏 《海洋信息》1996,(11):7-10

1994～1995年非同寻常的温暖冬季给美国天然气工业以巨大冲击,1994年末天然气价格下跌,引起公司收益和股票价格的下降。另一轮的解雇、重组、兼并席卷1995年的美国天然气产业。1994～1995年冬是厄尔尼诺冬,那么,厄尔尼诺现象是否是问题的罪魁祸首呢? 对厄尔尼诺现象周期性、天然气价格和天  相似文献   

旅游潜艇业     

Jones  LB 沈乃宏 《海洋信息》1996,(11):1-6

1 前言 近些年来,由于遥控潜水器(ROV)的大量涌现,科学研究和商业用载人潜水器的建造已急剧下降,而一种新型水下潜水器——旅游潜艇的建造数量已剧增。 近10多年来,已建造约48艘专用旅游潜艇,并有7艘商用深水潜水器经改装后用来搭  相似文献   

Migration of scheduled caste population in rural Bist Doab (Punjab)     

Mehta S  Gill MS 《Population geography : a journal of the Association of Population Geographers of India》1984,6(1-2):26-38

Using primary data collected from 5 villages in the Bist Doab, this study analyzes migration patterns of the scheduled caste population in rural areas of this region of Punjab. During 1971-1981, the rural scheduled caste population recorded a growth rate of 28.37% as compared to the corresponding growth rate of 13.32% among the rural nonscheduled castes. The proportion of the scheduled caste population showed striking intervillage variations from 52.85% in Khark Balhra to 87.45% in Bhoyapur. It was found that the rate of in-migration of the general population was quite low; the scheduled castes were no exception. Male in-migration has been primarily due to economic reasons; female in-migration was due largely to the change of marital status. It is only in Bhoyapur that about 44% of male in-migrants came as a result of rehabilitation programs undertaken by the state government after 1947. In all the villages, the scheduled caste males have out-migrated at a far slower pace than their nonscheduled caste counterparts. Economic reasons for males and marriage for females are almost the only 2 determinants of out-migration. Scheduled caste males and females differ from each other not only in terms of their motives for migration, but also with respect to the distance of the move; compared to the short distance migration among females, males experience relatively long range migration. Scheduled caste and nonscheduled caste difference is widest in terms of gross emigration; emigration among the scheduled castes is small in volume and more recent in origin. This is directly related to their meager incomes, low literacy rates, and lack of awareness of opportunities.  相似文献