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101.
Fisher CR MacDonald IR Sassen R Young CM Macko SA Hourdez S Carney RS Joye S McMullin E 《Die Naturwissenschaften》2000,87(4):184-187
During a research cruise in July 1997 in the Gulf of Mexico we discovered a gas hydrate approximately 1 m thick and over
2 m in diameter which had recently breached the sea floor at a depth of 540 m. The hydrate surface visible from the submarine
was considerably greater than that of any other reported hydrate. Two distinct color bands of hydrate were present in the
same mound, and the entire exposed surface of the hydrate was infested (2500 individuals/m2) with 2 to 4 cm-long worms, since described as a new species, Hesiocaeca
methanicola, in the polychaete family Hesionidae (Desbruyères and Toulmond 1998). H.
methanicola tissue stable isotope values are consistent with a chemoautotrophic food source. No evidence of chemoautotrophic symbionts
was detected, but geochemical data support the presence of abundant free living bacteria on the hydrate. The activities of
the polychaetes, grazing on the hydrate bacteria and supplying oxygen to their habitats, appears to contribute to the dissolution
of hydrates in surface sediments.
Received: 16 August 1999 / Accepted in revised form: 19 January 2000 相似文献
102.
Oliveira RS Koskinen WC Werdin NR Yen PY 《Journal of environmental science and health. Part. B》2000,35(1):39-49
The sorption of imidacloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolid-inimine ) (IMI) and its metabolites imidacloprid-urea (1-[(6-chloro-3-pyridinyl)-methyl]-2-imidazol-idinone) (IU), imidacloprid-guanidine (1-[(6-chloro-3-pyridinyl)-methyl]-4,5-dihydro-1H-imidazol-2-amine) (IG), and imidacloprid-guanidine-olefin (1-[(6-chloro-3-pyridinyl)methyl]-1H-imidazol-2-amine) (IGO) was determined on six typical Brazilian soils. Sorption of the chemicals on the soil was characterized using the batch equilibration method. The range and order of sorption (Kd) on the six soils was IG (4.75-134) > or = IGO (2.87-72.3) > IMI (0.55-16.9) > IU (0.31-9.50). For IMI and IU, Kd was correlated with soil organic carbon (OC) content and CEC, the latter due to the high correlation between OC and cation exchange capacity (CEC) (R2 = 0.98). For IG and IGO, there was no correlation of sorption to clay, pH, OC or CEC due to the high sorption on all soils. Average Koc values were IU = 170, IMI = 362, IGO = 2433, and IG = 3500. Although Kd and Koc values found were consistently lower than those found in soils developed in non-tropical climates, imidacloprid and its metabolites were still considered to be slightly mobile to immobile in Brazilian soils. 相似文献
103.
Smith BR Begeman PC Leland R Meehan R Levine RS Yang KH King AI 《Traffic injury prevention》2005,6(2):156-169
OBJECTIVE: The purpose of this study was to determine a mechanism of injury of the forefoot due to impact loads and accelerations as noted in some frontal offset car crashes. METHODS: The impact tests conducted simulated knee-leg-foot entrapment, floor pan intrusions, whole-body deceleration, muscle tension, and foot/pedal interaction. Specimens were impacted at speeds of up to 16 m/s. To verify this injury mechanism research was conducted in an effort to produce Lisfranc type injuries and metatarsal fractures. A total of 54 lower legs of post-mortem human subjects were tested. Two possible mechanisms of injury were investigated. For the first mechanism the driver was assumed to be braking hard with the foot on the brake pedal and at 0 deg plantar flexion (Plantar Nominal Configuration) and the brake pedal was in contact with the foot behind the ball of the foot. The second mechanism was studied by having the ball of the foot either on the brake pedal or on the floorboard with the foot plantar-flexed 35 to 50 deg (Plantar Flexed Configuration). RESULTS: The Plantar Nominal injury mechanism yielded few injuries of the type the study set out to produce. Out of 13 specimens tested at speeds of 16 m/s, three had injuries of the metatarsal (MT) and tarsometatarsal joints. The Plantar Flexed Configuration injury mechanism yielded 65% injuries at high (12.5-16 m/s) and moderate (6-12 m/s) speeds. CONCLUSION: It is concluded that Lisfranc type foot injuries are the result of impacting the forefoot in the Plantar Flexed Configuration. The injuries were consistent with those reported by physicians treating accident victims and were verified by an orthopedic surgeon during post impact x-ray and autopsy. They included Lisfranc fractures, ligamentous disruptions, and metatarsal fractures. 相似文献
104.
Shankar DS Kulkarni RS 《Journal of environmental biology / Academy of Environmental Biology, India》2005,26(1):49-53
The study on the mathematical relationship between length and weight of fishes has considerable importance in fishery research especially for the study of fish population dynamics and patterns of growth in fish stocks. This aspect is useful in rationally managing the population of fishes, and is an index of relative robustness of the fish). Variations from expected weight or length of an individual fish or group of fish indicate the general well being and state of gonadal development. The condition of fish can be influenced by the onset of maturity. The results indicate that the overall condition of the female and male fish seems to get improved towards the approach of maturing and mature stages of the gonads during pre-spawning phases. The reduction in the condition factor (K) and somatic condition factor (Ks) during spawning phase may be because of the fish becoming exhausted due to spawning activity. Although improvement in the condition of the fish was observed on the approach of breeding period, the overall condition seems to be better in the aquatic body from which the fish was collected. 相似文献
105.
Use of protein phosphatase inhibition assay to detect microcystins in Donghu Lake and a fish pond in China 总被引:6,自引:0,他引:6
Seasonal variations in the level of total microcystins in water samples collected from Donghu Lake and a fish pond in Wuhan, China, were studied between March 1995 and February 1996 using a protein phosphatase inhibition assay involving a radioactive 32P-labelled substrate. The assay is highly reliable and repeatable, and is probably the most sensitive assay for microcystin detection to date. Results of the survey indicated the presence of microcystins in the water samples, and the concentration of microcystins appeared to be related to the degree of eutrophication and water temperature. There is also a correlative relationship between the quantity of microcystins and the abundance of microcystin-producing cyanobacteria (Anabaena and Oscillatoria) in the water bodies over a year cycle. In the present study, the positive detection of microcystins in water bodies having no signs of algal bloom warns of considerable potential threat of these waters to public health. 相似文献
106.
The effect of cadmium on stage II naupliar larvae of barnacle (Balanus amphitrite Darwin) was investigated. Barnacle larvae were exposed to 0-15 microM CdCl(2) for 24 h. Apoptotic cells were stained by the terminal deoxyribonucleotidyl transferase mediated dUTP nick end labelling (TUNEL) method. Incidence of apoptosis, as measured by numbers of animals with ectopic pattern of apoptosis as well as numbers of apoptotic cells per animal, was assessed using confocal microscopy. An increase in incidence of apoptosis was observed in the experimental animals with an increase in cadmium concentration. Mortality increased, and motility decreased, when barnacle larvae were exposed to an increasing concentration of cadmium. The relationship between the occurrence of apoptosis and swimming behaviour was investigated in larvae exposed to 10 microM CdCl(2). Significant increases in apoptosis were detected in the non-motile and dead nauplii. This study suggested that whole-mount in situ TUNEL method may be used to study increased occurrence of apoptotic cells in crustacean larvae. 相似文献
107.
Chronic pollution may impair the reproductive success of adult organisms through a decrease in the quality of gametes. Our parallel study on gamete quality, showed that male sea urchins were more sensitive than the females towards cadmium pollution. The effects of chronic exposure to 0.01 and 1 ppm Cd2+ on sperm development of the sea urchin Anthocidaris crassispina were studied. Despite the fact that no significant change in gonad index was observed when sea urchins were exposed to both levels of Cd2+ for 4 weeks, deposition of electron-dense materials was conspicuous at the wall and intracellular space of male gonads. Apparent cytological alterations were observed in sperm cells, including changes in morphology of nuage in spermatogonia. The discrete, granular bodies of nuage were replaced by a large electron-dense body. Spermatozoa with short, incomplete 'broken' tails (scanning electron microscope observation) or tails of spermatids/spermatozoa with extraordinary electron-density (transmission electron microscope observation) were more abundant in gonads exposed to both levels of Cd2+. Mitochondrial cristae deformation was observed for sperm cells at all stages of development. Sperm plasma membrane also became more convoluted but acrosome remained intact. The observed cytological distortion of sperm tails and mitochondria/midpiece could help to explain the decline in motility as well as poor perseverance in sperm produced by sea urchins exposed to cadmium observed in our earlier study. 相似文献
108.
小应变硬化(HSS)模型考虑了土体在非常小的应变条件下刚度的高度非线性,在深基坑工程变形分析中得到广泛应用,其中如何确定土体的各个模型参数是应用该模型的关键。针对武汉软土地区,结合国内外文献中对HSS模型的研究成果,总结了HSS模型中各个参数的确定方法,并以武汉市两个软土深基坑工程为背景,利用三轴固结剪切仪和GDS动三轴仪进行了三轴固结排水剪切试验和动三轴试验研究,获得了HSS模型所需的土体强度、小应变刚度等参数。在此基础上,构建了HSS模型中各个参数的经验关系,并根据国内外学者的研究成果,结合本文室内试验的结果,提出了一套完整的武汉市软土深基坑工程HSS模型参数的获取方法。研究成果可为武汉市类似工程地质条件下的深基坑工程变形分析提供参数和技术支撑。 相似文献
109.
Estimating parameters of neutral communities: from one single large to several small samples 总被引:3,自引:0,他引:3
The neutral theory of S. P. Hubbell postulates a two-scale hierarchical framework consisting of a metacommunity following the speciation-drift equilibrium characterized by the "biodiversity number" theta, and local communities following the migration-drift equilibrium characterized by the "migration rate" m (or the "fundamental dispersal number" I). While Etienne's sampling formula allows simultaneous estimation of theta and m from a single sample of a local community, its applicability to a network of (rather small) samples is questionable. We define here an alternative two-stage approach estimating theta from an adequate subset of the individuals sampled in the field (using Ewens' sampling formula) and m from community samples (using Etienne's sampling formula). We compare its results with the simultaneous estimation of theta and m (one-stage estimation), for simulated neutral samples and for 50 1-ha plots of evergreen forest in South India. The one-stage approach exhibits problems of bias and of poor differentiability between high-theta, low-m and low-theta, high-m solution domains. Conversely, the two-stage approach yielded reasonable estimates and is to be preferred when several small, scattered plots are available instead of a single large one. 相似文献
110.
Shankar DS Kulkarni RS 《Journal of environmental biology / Academy of Environmental Biology, India》2007,28(1):137-139
In the present study tissue cholesterol and serum cortisol changes during two reproductive phases have been correlated in the freshwater fish Notopterus notopterus. The reproductive cycle of N. notopterus has two phases such as breeding phase (April - August) and non breading phase (October - December). The cholesterol content of the ovary and liver increased during breeding phase. The serum cortisol estimated by radio immuno assay (RIA) technique indicates that the level of the hormone was high during breeding phase compared to non breading phase. The increase in cholesterol during breeding phase may be because of increase in cortisol synthesis needed for ovarian growth and vitellogenesis. The gonadosomatic index (GSI) also increases during breeding phase. 相似文献