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R. Ocampo H. J. Callot P. Albrecht B. N. Popp M. R. Horowitz J. M. Hayes 《Die Naturwissenschaften》1989,76(9):419-421
The authors thank Dr. J. Connan [Société Nationale Elf Aquitaine (Production), Pau, France] for a sample of Julia Creek oil shale and helpful discussions; they also thank the Petroleum Research Fund (PRF 19791-AC2) for financial support. 相似文献
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Vanessa L. Bonanno Albrecht I. Schulte-Hostedde 《Behavioral ecology and sociobiology》2009,63(6):835-846
Sperm competition is widespread in mammals and occurs when ejaculates from two or more males compete within the female’s reproductive
tract to fertilize the ova. Enlarged testes are associated with sperm competition because they produce sperm, but the accessory
glands produce fluids and proteins that are also important for fertilization success. Sperm morphology can also have consequences
for fertilization success because of its influence on sperm motility. Red squirrels engage in multiple mating, and thus sperm
competition is likely. Here, we assess levels of multiple paternity in a natural population of red squirrels, test the prediction
that testis size is correlated with size of the accessory glands and sperm morphometry, and test the prediction that ejaculate
investment is condition-dependent. Five of six litters (83%) showed evidence of multiple paternity, indicating that sperm
competition is likely to have occurred. Testis size was correlated with the size of all three accessory glands (prostate,
seminal vesicle, epididymides), and there was a generally positive relationship between the size of the accessory glands and
sperm length. Sperm morphology showed significant variation in size and shape among individual male squirrels. There was no
evidence of condition dependence of testis size or the size of the accessory glands, but sperm midpiece length was negatively
related to body condition. Further work should include determining the fitness consequence of variation in sperm morphometry,
testis size, and accessory gland size, and determining the effects of variation in ejaculate investment on sperm motility. 相似文献
137.
Burnout is considered to be a long‐term reaction to occupational stress. It is characterized by emotional exhaustion, depersonalization, and diminished personal accomplishment. The most widely used instrument to measure burnout is the Maslach Burnout Inventory (MBI), developed by Maslach and Jackson (1986). From this instrument, Schaufeli and van Dierendonck (1995a) developed a somewhat modified Dutch version: the MBI‐NL. Burnout among dentists has hardly been studied. Since the professions that the MBI‐NL was developed upon are quite different from dentistry, the aim of this study was to test the three‐factor structure of the MBI‐NL against alternative structures among dentists. Both principal components analysis (PCA) and confirmatory factor analysis (CFA) were examined in a representative sample of 709 Dutch general dental practitioners (75 per cent response rate). The three‐factor structure shows the best fit to the underlying data, while other psychometric qualities are very satisfactory. It is concluded that the three‐factor structure of the MBI‐NL is superior to alternative structures, and that the MBI‐NL is a highly suitable instrument to measure burnout among dentists. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
138.
Nitrous Oxide Concentrations in the Soil of a Mown Grassland: Comparison of Model Results with Soil Profile Measurements 总被引:1,自引:0,他引:1
Nitrous oxide (N2O) concentrations in the soilprofile of a fertilized grassland on the Swiss plateauwere measured at irregular intervals during one year.Air samples were taken from air-permeable tubesinstalled at depths between 2 and 100 cm belowthe surface. Highest concentrations in thetopsoil were observed following precipitationafter fertilization. In the subsoil,concentrations were highest when the soil watercontent fell below about 92% after a wet periodand mineral nitrogen was available from priorfertilization. N2O concentrations in thetopsoil were simulated with the process-basedgrassland ecosystem model PaSim 2.5 (PastureSimulation Model) and compared with measured soilN2O concentrations. The model simulated wellthe concentration peaks after fertilizeradditions and the concentrations in winter. Butthe simulated baseline concentrations during thegrowing season were overestimated. Possiblecauses for this discrepancy are discussed andsuggestions are made to improve the model. 相似文献
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Albrecht Penck 《Die Naturwissenschaften》1926,14(41):933-935