共查询到20条相似文献,搜索用时 187 毫秒
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Haidet G. C.; Musch T. I.; Ordway G. A.; Mitchell J. H. 《Journal of applied physiology》1985,58(6):2047-2053
We compared the cardiovascular effects evoked in conscious dogs by 1) submaximal exercise; 2) infusion of dobutamine (40 micrograms X kg-1 X min-1); and 3) infusion of a combination of atropine (0.15 mg/kg), norepinephrine (0.19 micrograms X kg-1 X min-1), and epinephrine (0.05 micrograms X kg-1 X min-1). Myocardial O2 demand, as estimated by the double product (heart rate X systolic blood pressure), was similar during all three interventions. Cardiac output and heart rate increased significantly (P less than 0.05) during each of the three interventions. Arteriovenous O2 difference and total body O2 consumption, however, increased only during submaximal exercise. Although myocardial blood flow increased similarly during each of the three interventions, blood flow to skeletal muscle and the tongue increased only during exercise. Exercise and the combined infusion of atropine, norepinephrine, and epinephrine produced similar increases in blood flow to the diaphragm and similar decreases in blood flow to the stomach. These changes in blood flow were associated with appropriate changes in vascular resistance. Additionally, blood flow to the brain, kidney, adrenal glands, liver, and intestine did not change during any of the three interventions. Thus, in dogs, submaximal exercise, infusion of dobutamine, and infusion of a combination of atropine, norepinephrine, and epinephrine to evoke a given level of estimated myocardial O2 consumption produce similar increases in cardiac output, heart rate, and myocardial blood flow. In contrast, the changes in total body O2 consumption, arteriovenous O2 difference, regional blood flow, and regional vascular resistance that occur during each of these three interventions are different. 相似文献
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Lawrence A. Pervin 《Human ecology: an interdisciplinary journal》1978,6(1):71-105
A review is presented of issues relevant to the definition, measurement, and classification of stimuli, situations, and environments. Problems such as the lack of adequate definitions of concepts, error and bias in measurement procedures, confusion between measurement of a concept and measurement of its behavioral effects, and the lack of agreement among alternative measures are emphasized. It is suggested that concepts be defined in terms of objective characteristics while allowing for the study of the transactional relationship between organism and environment. The work of the ethologists in defining stimuli while studying their relationship to different organismic states and situational contexts is emphasized in this regard. Following Brunswik, it is also suggested that wherever possible there be a representative sampling of variables in natural settings.
Note from the editors: From time to time, Human Ecology will publish a review article. Our first in this series is a review by a psychologist of basic definitional and conceptual problems in environmental studies.This paper was prepared while the author was a Visiting Research Fellow at the Educational Testing Service. The support of ETS and my colleagues in the Division of Psychological Studies is gratefully acknowledged. The review was also supported in part by a grant from the Rutgers University Research Council. 相似文献
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A. Peter Castro 《American anthropologist》2003,105(1):187-189
Indians, Markets, and Rainforests: Theory, Methods, and Analysis. Ricardo A. Godoy. New York: Columbia University Press, 2001. 274 pp. 相似文献
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2-Dimethylaminomethylene-1-benzosuberone 1 was coupled with diazotized aniline derivatives to afford a series of the hitherto unreported 2-arylazo-1-benzosuberones 3a–i. The tautomeric structure and the effect of substituents on the tautomeric form (s) of the products 3a–i were discussed. Similar coupling of the enaminone 1 with diazonium salts of heterocyclic amines gave the respective fused azolotriazino-benzosuberones. Some of the newly synthesized compounds showed potent antimicrobial, anti-HCV, antioxidant, antitumor (as topoisomerase I inhibitors), and antimicrobial activities. 相似文献
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Loren A. Zech 《Mathematical biosciences》1984,72(2):407-414
Mones Berman's untimely death on 12 August 1982 put an end to his work in the development of theoretical biology. Arguments are examined, and it is concluded that a formal theory of lipoprotein metabolism flourished and expanded under the guidance of Dr. Berman. Not many scientists in the field of biology spend a major portion of their energies on theoretical work xxx was outstanding because of his early decision to follow the theoretical path. 相似文献
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Pericytes: developmental, physiological, and pathological perspectives, problems, and promises 总被引:3,自引:0,他引:3
Pericytes, the mural cells of blood microvessels, have recently come into focus as regulators of vascular morphogenesis and function during development, cardiovascular homeostasis, and disease. Pericytes are implicated in the development of diabetic retinopathy and tissue fibrosis, and they are potential stromal targets for cancer therapy. Some pericytes are probably mesenchymal stem or progenitor cells, which give rise to adipocytes, cartilage, bone, and muscle. However, there is still confusion about the identity, ontogeny, and progeny of pericytes. Here, we review the history of these investigations, indicate emerging concepts, and point out problems and promise in the field of pericyte biology. 相似文献
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Cadmium is an important environmental pollutant and a potent toxicant to bacteria, algae, and fungi. Mechanisms of Cd toxicity and resistance are variable, depending on the organism. It is very clear that the form of the metal and the environment it is studied in, play an important role in how Cd exerts its effect and how the organism(s) responds. A wide range of Cd concentrations have been used to designate resistance in organisms. To date, no concentration has been specified that is applicable to all species studied under standardized conditions. Cadmium exerts its toxic effect(s) over a wide range of concentrations. In most cases, algae and cyanobacteria are the most sensitive organisms, whereas bacteria and fungi appear to be more resistant. In some bacteria, plasmid-encoded resistance can lead to reduced Cd2+ uptake. However, some Gram-negative bacteria without plasmids are just as resistant to Cd as are bacteria containing plasmids encoding for Cd resistance. According to Silver and Misra (1984), there is no evidence for enzymatic or chemical transformations associated with Cd resistance. Insufficient information is available on the genetics of Cd uptake and resistance in cyanobacteria and algae. Mechanisms remain largely unknown at this point in time. Cadmium is toxic to these organisms, causing severe inhibition of such physiological processes as growth, photosynthesis, and nitrogen fixation at concentrations less than 2 ppm, and often in the ppb range (Tables 2 and 3). Cadmium also causes pronounced morphological aberrations in these organisms, which are probably related to deleterious effects on cell division. This may be direct or indirect, as a result of Cd effects on protein synthesis and cellular organelles such as mitochondria and chloroplasts. Cadmium is accumulated internally in algae (Table 4) as a result of a two-phase uptake process. The first phase involves a rapid physicochemical adsorption of Cd onto cell wall binding sites, which are probably proteins and (or) polysaccharides. This is followed by a lag period and then a slow, steady intracellular uptake. This latter phase is energy dependent and may involve transport systems used to accumulate other divalent cations, such as Mn2+ and Ca2+. Some data indicate that Cd resistance, and possibly uptake, in algae and cyanobacteria is controlled by a plasmid-encoded gene(s). Although considerable information is available on Cd toxicity to, and uptake in fungi, further work is clearly needed in several areas. There is little information about Cd uptake by filamentous fungi, and even in yeasts, information on the specificity, kinetics, and mechanisms of Cd uptake is limited.(ABSTRACT TRUNCATED AT 400 WORDS) 相似文献
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Friends play important roles throughout our lives by providing expressive, instrumental, and companionate support. We examined sexual orientation, gender, and age differences in the number of friends people can rely on for expressive, instrumental, and companionate support. Additionally, we examined the extent to which people relied on same-gender versus cross-gender friends for these types of support. Participants (N = 25,185) completed a survey via a popular news website. Sexual orientation differences in number of same-gender and cross-gender friends were generally small or non-existent, and satisfaction with friends was equally important to overall life satisfaction for all groups. However, the extent to which people’s friendship patterns demonstrated gender-based homophily varied by sexual orientation, gender, and age. Young adult gay and bisexual men, and to some extent bisexual women and older bisexual men, did not conform to gendered expectations that people affiliate primarily with their own gender. 相似文献
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Nicholas A. Ashford 《人类与生态风险评估》2005,11(1):85-96
The Precautionary Principle is in sharp political focus today because (1) the nature of scientific uncertainty is changing and (2) there is increasing pressure to base governmental action on more “rational” schemes, such as cost-benefit analysis and quantitative risk assessment, the former being an embodiment of ‘rational choice theory’ promoted by the Chicago school of law and economics. The Precautionary Principle has been criticized as being both too vague and too arbitrary to form a basis for rational decision making. The assumption underlying this criticism is that any scheme not based on cost-benefit analysis and risk assessment is both irrational and without secure foundation in either science or economics. This paper contests that view and makes explicit the rational tenets of the Precautionary Principle within an analytical framework as rigorous as uncertainties permit, and one that mirrors democratic values embodied in regulatory, compensatory, and common law. Unlike other formulations that reject risk assessment, this paper argues that risk assessment can be used within the formalism of tradeoff analysis—a more appropriate alternative to traditional cost-benefit analysis and one that satisfies the need for well-grounded public policy decision making. This paper will argue that the precautionary approach is the most appropriate basis for policy, even when large uncertainties do not exist, especially where the fairness of the distributions of costs and benefits of hazardous activities and products are a concern. Furthermore, it will offer an approach to making decisions within an analytic framework, based on equity and justice, to replace the economic paradigm of utilitarian cost-benefit analysis. 相似文献
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Wineries,drosophila, alcohol,and Adh 总被引:1,自引:0,他引:1
R. William Marks John G. Brittnacher John F. McDonald T. Prout F. J. Ayala 《Oecologia》1980,47(1):141-144
Summary Previous workers (McKenzie and Parsons, 1972, 1974; McKenzie, 1974; Briscoe et al., 1975) have found anomalous distributions of species of Drosophila, of sexes of D. melanogaster, and of Adh alleles in and around wineries in Australia and Spain. Field studies in California's Sonoma Valley provide evidence that the explanations advanced for these distributions may incorrect. The anomalous distribution of species was attributed to alcohol, either as a selective agent or as a behavioral stimulus. We find a virtually identical species distribution in the absence of environmental alcohol. The anomalous sex ratio was attributedd to differential survivall of the sexes when raised on alcohol. We present crude evidence thatehe difference may simply be a behavioral response to some product of fermentation, which need not be alcohol. Finally, the allele frequency difference reported from Spain was attributed to differential adult mortality on alcohol. We do not find an allele frequency difference even when alcohol is exposed, and therefore suggest that selection is occurring in pre-adult stages. 相似文献
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This paper seeks to understand what it means to live 'in the open'. It begins with an account of experiments that test whether children have acquired a scientifically correct understanding of the shape of the earth, according to which people live all around on the outside of a solid sphere. This understanding cannot accommodate the phenomenon of the sky, in relation to which the earth can appear only as the ground of human habitation. James Gibson's ecological approach to perception offers a possible alternative, depicting earth and sky as complementary hemispheres. Yet for Gibson, this earth-sky can be inhabited only insofar as it is furnished with objects. To that extent, it ceases to be open. Drawing on elements of Merleau-Ponty's phenomenology, it is argued that in the open world persons and things relate not as closed forms but by virtue of their common immersion in the generative fluxes of the medium – in wind and weather. Fundamental to life is the process of respiration, by which organisms continually disrupt any boundary between earth and sky, binding substance and medium together in forging their own growth and movement. Thus to inhabit the open is not to be stranded on the outer surface of the earth but to be caught up in the transformations of the weather-world. 相似文献
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Ari Helenius 《Molecular biology of the cell》2012,23(21):4157-4159
The fluid mosaic model for biological membranes was formulated 40 years ago. Ten years later endosomes were discovered as important prelysosomal organelles. At the outset of my research career, I was fortunate to witness both these turning points in biochemistry and cell biology from close up, and to participate in some of the studies. In this short essay, I will describe how this came about, and also try to provide some background as to the general starting situation in those not so distant pioneering years of membrane biology. 相似文献