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VAN Horn HM 《Science (New York, N.Y.)》1991,252(5004):384-389
Degenerate bodies composed primarily of dense hydrogen and helium plasmas range from giant planets to the so far hypothetical brown dwarfs. More massive objects begin their lives as nondegenerate stars and may end as white dwarfs, composed primarily of carbon and oxygen, or as neutron stars, with solid crusts of iron or heavier elements and cores of neutron matter. The physical properties of dense plasmas that are necessary to construct theoretical models of such degenerate stars include the equation of state, transport properties, and nuclear reaction rates. 相似文献
64.
Well-preserved plant remains in packrat middens chronicle vegetation change in Chaco Canyon over the past 11,000 years. Early Holocene evidence of communities dominated by Douglas fir, Rocky Mountain juniper, and limber pine in the San Juan Basin calls for revision of traditional constructs based on fossil pollen. Middle and late Holocene vegetation in the canyon was pinyon-juniper woodland up until Anasazi occupation between 1000 and 800 years ago. Instead of climate, Anasazi fuel needs may explain the drastic reduction of pinyon and juniper after 1230 years ago. The lack of pinyon-juniper recovery over the past millennium has implications for contemporary forest and range ecology. 相似文献
65.
We investigated the regional and temporal variation of the composition stream of bed sediments of the Langbroekerwetering, The Netherlands, in particular the effect of effluent discharges of sewage treatment plants on the sediment composition. Before we could map the chemistry of the bed sediments we had to examine two aspects which might obscure regional variation, namely variation due to differences in clay and organic matter content and short range variation. To remove the effect of clay and organic matter, the concentrations in the bed sediment were normalized to a standard sediment with 7% clay and 5% organic matter. By means of a nested sampling we ascertained that the sediments were highly variable within short distances. By increasing the effective support size by collecting composite samples, the regional differences can be mapped. The number of subsamples needed for a composite sample was established at 25. From the mapping of the study area it appears that the two existing effluent discharges affect the sediment composition locally. In particular, concentrations of N, P, K, Na, Zn, and Cu are raised due to the discharge of effluent. Inlet of water from the River Rhine and the occurence of flood waves are the main sources of temporal variation in the bed sediment composition in the Langbroekerwetering. 相似文献
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D.C. GOODDY P. SHAND D.G. KINNIBURGH W.H. VAN RIEMSDIJK 《European Journal of Soil Science》1995,46(2):265-285
A total of 48 elements was detected in the soil solutions centrifuged from two acid sandy (humus-iron podzol) profiles from southern England. Concentrations ranged from mm for the major ions to mm for trace metals such as U and the rare earth elements. Field-based solid/solution partition coefficients, Kd, were determined by calculating the ratio of the amount of an element extracted by 0.43 m HNO3 or a neutral salt (0.01 m CaCl2 or 0.1 m Ba(NO3)2) to the concentration in the soil solution. These partition coefficients did not show the expected trend in selectivity. For example, Cd consistently had one of the highest Kd values, higher even than Cu. This was thought to be due in part to the nature of the Kd which reflects a balance between binding to the soil solids and to the dissolved organic carbon (DOC), which is present at relatively high concentrations (1–20 mm ) in the soil solutions. Because of the underlying functional similarity between metal binding by the solid and dissolved organic matter, the partition coefficient (and hence element mobility) will be relatively insensitive to changes in pH and metal-ion activity in the soil solution. 相似文献
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GARY W. ELLISON DVM MS Diplomate ACVS JAMIE R. BELLAH DVM Diplomate ACVS W. PRESTON STUBBS DVM JAMES VAN GILDER BS 《Veterinary surgery : VS》1995,24(2):140-147
Excision of perianal fistulas using a 1.064 micron wavelength neodymium:yttrium aluminum garnet (ND:YAG) contact tipped laser with primary wound closure was used to treat 20 dogs with perianal fistulas. Overall, 19 of 20 (95%) dogs had resolution of fistulas after one or more ND:YAG treatments. The period of resolution ranged from 10 to 42 months with a mean of 22.9 months. Sixteen of 20 (80%) dogs had resolved fistulas after one laser excision. Three of the four recurrences underwent additional laser treatments with successful results. The total number of laser procedures ranged from one to three with a mean of 1.2 procedures. Postoperatively, anal tone as judged by digital rectal examination was reduced in about 60% of the cases, but clinical evidence of fecal incontinence only occurred in four of 20 cases. This was managed effectively with diet modification. The tendency toward loss of anal tone or fecal incontinence depended on the severity of preexisting anal stenosis. On a client survey, 19 of 20 owners believed that their animals experienced less pain during defecation after surgery and rated the results as excellent or good. The overall success rate using ND:YAG laser excision compared very favorably with previously reported studies of other methods of treatment for perianal fistulas in dogs. 相似文献
70.
The life history of Tenualosa macrura in Sarawak, further notes on protandry in the genus and management strategies 总被引:1,自引:0,他引:1
S. J. M. BLABER G. FRY D.A. MILTON T. VAN DER VELDE O. BOON-TECK J. PANG & P. WONG 《Fisheries Management and Ecology》2005,12(3):201-210
Abstract The contraction of Tenualosa macrura (Bleeker) to the Sarawak coast and a small part of Sumatra, and the decline in its fishery mirror what has happened to three other species in the genus. Little was known of this species in its last stronghold in Sarawak where it is important for management and conservation reasons to understand its biology and life history. It forms part of a multispecies fishery where effort is uniform, but catches follow a lunar cycle. Tenualosa macrura is protandrous, but low numbers of small females suggest diandry. In Sumatra Tenualosa macrura spawn throughout the year, but in Sarawak have a seasonal peak in the NE monsoon (December). This has management implications because the Sarawak fishery ceases at this time because of adverse weather, hence reducing fishing pressure on spawning T. macrura . Management measures introduced in Sarawak for Tenualosa toli (Valenciennes) may therefore not be required for T. macrura . 相似文献