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921.
A single population of short-beaked common dolphins (Delphinus delphis Linnaeus) occurs in the western North Atlantic from Florida to Newfoundland. Dolphins killed in a swordfish driftnet fishery
between 1989 and 1998 provided samples for the present study. These were combined with additional observations from carcasses
collected from stranding programs. Samples were examined from 74 female and 161 male short-beaked common dolphins. A highly
significant male bias in the sex ratio of both the bycatch and stranding samples suggests that sex-based habitat partitioning
or school segregation occurs in this population. Age was estimated from decalcified thin sections of teeth and testis and
ovarian samples were examined both macro- and microscopically. Analyses showed that reproduction was both seasonal and synchronized.
Females reached sexual maturation at approximately age eight; males matured at 9.5 years. Conception occurred during July
and August (mean day 24 July). Gestation was estimated to last just under a year, so most females gave birth during July and
August (mean day 15 July). Annual pregnancy rate was estimated to be between 25 and 33%. Males undergo a fivefold seasonal
increase in testes mass and a twofold increase in seminiferous tubule diameter. Peak sperm production potential was observed
in July. At the end of the breeding season testis size and activity decreased after August. Male dolphins in this population
are hypothesized to engage in some form of sperm competition. 相似文献
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925.
The oxidation of trace organic impurities in ultrapure water by ultraviolet light (UV), ozone, and the combination of UV/ozone
is investigated. The emphasis is on the development of a global model to simulate the process that take place in the typical
oxidation reactors used in ultrapure water plants. The study also focuses on reaction mechanism for oxidation of multi-component
organic impurities. Eighteen organic model compounds are chosen as representative contaminants. The results demonstrate and
confirm a significant synergistic effect between UV and ozone oxidation. A mechanism for the synergistic oxidation of organic
impurities is proposed and validated with experimental data. The combination of the reaction and the reactor models is used
to determine the fundamental kinetic parameters involved in the three oxidation processes.
Received: 3 July 1998 / Accepted: 4 September 1998 相似文献
926.
Aquarius paludum inhabits a wide variety of water surfaces, ranging from temporary to permanent ponds and lakes throughout the Palearctic. Thus, some larvae of A. paludum will be exposed to habitats that dry out. We assess here the influence of drying on water strider growth and development. When exposed to drying-out in the larval stage, the growth period was prolonged. Drying-out during one of the first three instars was associated with longer maintenance of flight muscles without histolysis and reduced the number of eggs laid by long-winged (LW) adults that shifted to a "flyer" strategy. Alternatively, adults exposed to dry habitats during whole larval period expressed shorter preoviposition periods and shifted to a "non-flying, reproducer" strategy. These contrasting responses to drying can be understood as flexible physiological functions depending on the drying history to which larvae are exposed. This flexibility may be a significant factor in allowing A. paludum to occupy such a wide range of habitats in Eurasia. 相似文献
927.
Steen Smidt-Jensen John Philip Julia M. Zachary Sarah E. Fowler Bent Nørgaard-Pedersen 《黑龙江环境通报》1994,14(1):35-45
Of 2882 women allocated to either transabdominal CVS (TA) or transcervical CVS (TC) at two large obstetric centres in Denmark, 2707 had blood samples drawn before and 30 min after CVS for maternal serum-alpha-fetoprotein (MSAFP) measurement. 2535 of these women had cytogenetically normal pregnancies and 2091 of them went on to have samples drawn at the 18–20 week follow-up. Post-procedure MSAFP values were correlated to the biopsy method used, with mean MSAFP values significantly higher after TA than TC, 33 and 15 kU/l, respectively (P<0·001). Following TA procedures, 18 per cent of cases had feto-maternal transfusion higher than 0·1 ml; this occurred in only 5 per cent of TC cases. MSAFP levels were associated with spontaneous fetal loss in the TA group but not in the TC group. TC, however, was followed by more losses than TA. The post-CVS MSAFP value was positively correlated with the amount of villi aspirated. The difference in post-procedure elevation in MSAFP 30 min later (average 18 kU/l higher for TA than for TC) was not reflected in raised levels at the 18–20 week follow-up. Study medians at mid-trimester did not differ from reference group medians established from a group of singleton pregnancies with sonographically determined gestational age who did not experience invasive procedures and delivered normal infants. Our findings suggest that CVS does not compromise mid-trimester MSAFP for screening for neural tube defects (NTDs). Extremely high mid-trimester MSAFP values in the TC group could predict imminent loss. 相似文献
928.
Integrated environmental assessment: an urban perspective 总被引:2,自引:0,他引:2
John Murlis 《环境科学学报(英文版)》1999,11(3):264-271
1 IntroductionUrbanareasthroughouttheworldareincreasinglyafocusofenvironmentalconcern.Theyareplacesofintenseandgrowingeconomicactivity.Inresponse,urbanpopulationsaregrowingrapidly.Itisestimatedthat,by2000,morethanhalftheworld○spopulationwillliveintow… 相似文献
929.
Arsenic, a carcinogenic trace element, threatens not only the health of millions of humans and other living organisms, but also global sustainability. We present here, for the first time, the global industrial-age cumulative anthropogenic arsenic production and its potential accumulation and risks in the environment. In 2000, the world cumulative industrial-age anthropogenic arsenic production was 4.53 million tonnes. The world-wide coal and petroleum industries accounted for 46% of global annual gross arsenic production, and their overall contribution to industrial-age gross arsenic production was 27% in 2000. Global industrial-age anthropogenic As sources (as As cumulative production) follow the order: As mining production >As generated from coal >As generated from petroleum. The potential industrial-age anthropogenic arsenic input in world arable surface in 2000 was 2.18 mg arsenic kg–1, which is 1.2 times that in the lithosphere. The development of substitute materials for arsenic applications in the agricultural and forestry industries and controls of arsenic emissions from the coal industry may be possible strategies to significantly decrease arsenic pollution sources and dissipation rates into the environment. 相似文献
930.
Imhoff PT Jakubowitch A Briening ML Chiu PC 《Journal of the Air & Waste Management Association (1995)》2003,53(11):1391-1400
A key component in the operation of almost all bioreactor landfills is the addition of water to maintain optimal moisture conditions. To determine how much water is needed and where to add it, in situ methods are required to measure water within solid waste. Existing technologies often result in measurements of unknown accuracy, because of the variability of solid waste materials and time-dependent changes in packing density, both of which influence most measurement methods. To overcome these problems, a new technology recently developed by hydrologists for measuring water in the vadose zone--the partitioning gas tracer test--was tested. In this technology, the transport behavior of two gas tracers within solid waste is used to measure the fraction of the void space filled with water. One tracer is conservative and does not react with solids or liquids, while a second tracer partitions into the water and is separated from the conservative tracer during transport. This technology was tested in four different solid waste packings and was capable of determining the volumetric water content to within 48% of actual values, with most measurement errors less than 15%. This technology and the factors that affect its applicability to landfills are discussed in this paper. 相似文献