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691.
Radioecological conditions have been estimated in Lake Chervyanoe located on the central axis of the Eastern Ural Radioactive Trace (EURT) about 100–110 km northeast of the Mayak Production Association. Data on the 90Sr and 137Cs contents in the main components of the lake, the distribution of these radionuclides over the profile of bottom sediments, and their amounts in the lake are presented. The experimental data have been used to construct mathematical models for estimating changes in the radionuclide concentrations and amounts in the water and bottom sediments of the lake over a long period after the nuclear accident, as well as the tritium content of the lake water in different periods of time.  相似文献   
692.
 Liquid phase hydrocarbon oxidation is one of the principal routes towards industrial organic chemicals. However, low product selectivity and associated by-product formation are major problems in several oxidation processes. As a result of the increasingly stringent environmental regulations, the development of oxidation catalysts has been a major challenge in the last decade. An overview of novel selective and clean oxidation catalysts and processes is presented. Received: 27 July 1998 / Accepted: 8 September 1998  相似文献   
693.
The structural-temporal organization of a murine rodent community in the taiga has been studied near Lake Teletskoe, Mountain Altai. The results show that the long-term dynamics of indices characterizing community diversity depend mainly on changes in the structure of dominance rather than on the population dynamics of species. The distribution of species in the factor space corresponds to their preference for certain biotopes, from dry to relatively moist. An analysis of relationships within the rodent community has revealed the synchronous dynamics of species abundance and antiphase pattern of changes in the structural indices of dominant species.  相似文献   
694.
Ultrasonographic features suggestive of esophageal atresia with or without tracheo-esophageal fistula (EA/TEF) are only in a small minority of fetuses with EA/TEF (<10%) identifiable on prenatal scans. The prenatal diagnosis of EA/TEF relies in principle, on two nonspecific signs: polyhydramnios and absent or small stomach bubble. Polyhydramnios is associated with a wide range of fetal abnormalities, but most commonly it pursues a benign course. Similarly the sonographic absence of a stomach bubble may point to a variety of fetal anomalies. The combination of polyhydramnios and absent stomach bubble in two small series offers a modest positive predictive value of 44 and 56% respectively. Prenatal scanning for EA/TEF identifies a larger proportion of fetuses with Edwards syndrome; there is also a higher proportion of isolated EA in comparison to postnatal studies. Current ultrasound technology does not allow for a definite diagnosis of EA/TEF and therefore, counseling of parents should be guarded. Postnatal diagnosis of EA is confirmed by the failure to pass a firm nasogastric tube into the stomach; on chest X-ray, the tube is seen curling in the upper esophageal pouch. Corrective surgery for EA/TEF is well established and survival rates of over 90% can be expected. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   
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