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511.
Krystyna Piotrowska Deborah Edwards Alan Mitch Ralph C. Dougherty 《Die Naturwissenschaften》1980,67(9):442-445
Experiments are reported in which three prochiral organic reactions were conducted in the presence of a ca. 1T magnetic field which was oriented with reference to the earth's geometric axes. The sign and magnitude of the rotation varied with the macroscopic orientation of the magnetic field and the time that the reaction was performed. Control measurements were in accord with expectations. The fact that the sign of the observed optical rotation of the product was reversed for all three reported reactions when the magnetic field was reversed for reactions conducted on the same day suggests that either the observed asymmetric synthesis was due to the reactions being conducted in a chiral physical field or extremely unusual stochastic processes were involved. 相似文献
512.
Jan A. Derecki Lieutenant Alan J. Potok 《Journal of the American Water Resources Association》1979,15(5):1418-1429
ABSTRACT: The feasibility of simulating monthly runoff for southeast Michigan, which comprises four major river basins, was evaluated with the Streamflow Synthesis and Reservoir Regulation watershed model. The evaluation covered a 13-year period (1961–73), which encompassed a complete runoff cycle. Results indicate it is feasible to simulate monthly runoff volumes on a regional scale with a single equivalent watershed by using daily precipitation and temperature data. Simulation of regional flows appears particularly attractive for the Great Lakes basin, since the basin consists of many relatively small watersheds. This method also appears promising for development of monthly runoff forecasts by employing average monthly meteorological data distributed on a daily basis. Tests of six-month runoff forecasts show relatively small deterioration with time and offer considerable improvement over climatology. 相似文献
513.
514.
Denise M. Cutillo MS Elizabeth A. Hammond Suzanne L. Reeser Melissa A. Kershner Barbara Lukin Lynn Godmilow Alan E. Donnenfeld 《黑龙江环境通报》1994,14(5):327-332
Prenatal diagnosis choices were reviewed in 473 women who presented for genetic counselling prior to 11 weeks' gestation for the indication of advanced maternal age. Group A consisted of 336 patients who were unaware of a possible association between chorionic villus sampling (CVS) and limb defects. Group B consisted of 137 patients who were provided this information. Fifty-one per cent of patients in group A and 45 per cent of patients in group B chose CVS. This difference was not significant by χ2 analysis (P = 0·7). Patterns of prenatal diagnosis procedure utilization from 1987 to 1992 revealed a significant reduction in CVS utilization accompanied by a corresponding increase in amniocentesis after the association between CVS and limb defects was publicized. Referrals for CVS counselling also significantly declined. However, acceptance rates did not change for those patients who received genetic counselling. First-trimester genetic counselling, including a discussion regarding a possible association between CVS and limb defects, helps patients make informed decisions concerning prenatal diagnosis options, and, in our population, resulted in no change in CVS acceptance rates. 相似文献
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517.
Casparus J. R. Verbeek Talia Hicks Alan Langdon 《Journal of Polymers and the Environment》2012,20(1):53-62
Polymers that are compostable and manufactured from renewable resources have gained significant importance in recent years.
The objective of this work was to assess the biodegradability of bloodmeal-based thermoplastics in a commercial green-waste
composting situation. Materials plasticised with tri-ethylene–glycol lost about 45% of their original mass after 12 weeks
composting while unplasticised samples lost 35%. Degradation appeared to have been in two phases; an initial loss of soluble,
low molecular compounds in the mesophilic phase followed by degradation of high molecular compounds as the temperature exceeded
about 40 °C in the thermophilic phase. It was found that as degradation proceeded materials became more soluble. In addition,
plasticised and unplasticized samples contained about 60 wt% moisture after 4 weeks of composting conditioning at 50% relative
humidity resulted in approximately 8–10 wt% moisture, unaffected by the extent of degradation. FTIR revealed that proteins
underwent hydrolytic cleavage resulting in the formation of primary amines. A significant reduction in combustion temperature
was observed, indicative of a reduction in covalent bonding, likely due to shorter chains lengths or less cross-linking. 相似文献
518.
The relationship between anemones and anemonefishes is an oft-cited and endearing example of a mutualistic symbiosis. Current
research on mutualistic symbioses suggests these relationships are more commonplace and have greater importance at the ecosystem
level on nutrient dynamics and evolutionary processes than previously thought. Using stable isotopes 15N and 13C, both field and laboratory experiments were designed to investigate whether nutrient transfer from two species of resident
anemonefishes (Amphiprion perideraion and A. clarkii) to host anemones (Heteractis crispa) occurs. Mass spectroscopy indicated that both 15N and 13C were significantly elevated in the tissues of anemonefishes and in both host anemone and zooxanthellae fractions. These
experiments provide the first direct empirical evidence of nitrogen and carbon transfer from resident anemonefishes to host
anemones and endosymbiotic zooxanthellae. Such transfer of elements within this intriguing tripartite association underscores
the central role that nutrient dynamics contributes to the evolutionary processes of these marine symbioses. 相似文献
519.
Burkey KO Neufeld HS Souza L Chappelka AH Davison AW 《Environmental pollution (Barking, Essex : 1987)》2006,143(3):427-434
Cutleaf coneflower (Rudbeckia laciniata L.), crown-beard (Verbesina occidentalis Walt.), and tall milkweed (Asclepias exaltata L.) are wildflower species native to Great Smoky Mountains National Park (U.S.A.). Natural populations of each species were analyzed for leaf ascorbic acid (AA) and dehydroascorbic acid (DHA) to assess the role of ascorbate in protecting the plants from ozone stress. Tall milkweed contained greater quantities of AA (7-10 micromol g(-1) fresh weight) than crown-beard (2-4 micromol g(-1) fresh weight) or cutleaf coneflower (0.5-2 micromol g(-1) fresh weight). DHA was elevated in crown-beard and cutleaf coneflower relative to tall milkweed suggesting a diminished capacity for converting DHA into AA. Tall milkweed accumulated AA in the leaf apoplast (30-100 nmol g(-1) fresh weight) with individuals expressing ozone foliar injury symptoms late in the season having less apoplast AA. In contrast, AA was not present in the leaf apoplast of either crown-beard or cutleaf coneflower. Unidentified antioxidant compounds were present in the leaf apoplast of all three species. Overall, distinct differences in antioxidant metabolism were found in the wildflower species that corresponded with differences in ozone sensitivity. 相似文献
520.
Abu-Allaban M Hamasha S Gertler A 《Journal of the Air & Waste Management Association (1995)》2006,56(10):1440-1444
Many areas in Jordan suffer from elevated levels of coarse particulate matter (PM10). One potentially significant source of the observed PM is the resuspension of road dust in the vicinity of limestone quarries. To obtain data to assess the impact from this source, PM10 road dust resuspension factors near Abusiiah, a town to the north east of Amman surrounded by many quarries and brick factories, were measured. Measurements included PM10 mass, particle size distributions, wind speed, and wind direction. The results showed that PM10 concentrations could be as high as 600 microg/m3, and most of the airborne PM is in the coarse fraction. Loading trucks play a major role in resuspending road dust, with an observed PM10 emission rate of >6000 mg/km. 相似文献