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排序方式: 共有1325条查询结果,搜索用时 15 毫秒
81.
Thorpe KL Cummings RI Hutchinson TH Scholze M Brighty G Sumpter JP Tyler CR 《Environmental science & technology》2003,37(6):1142-1149
The natural steroids estradiol-17beta (E2) and estrone (E1) and the synthetic steroid ethynylestradiol-17alpha (EE2) have frequently been measured in waters receiving domestic effluents. All of these steroids bind to the estrogen receptor(s) and have been shown to elicit a range of estrogenic responses in fish at environmentally relevant concentrations. At present, however, no relative potency estimates have been derived for either the individual steroidal estrogens or their mixtures in vivo. In this study the estrogenic activity of E2, E1, and EE2, and the combination effects of a mixture of E2 and EE2 (equi-potent fixed-ratio mixture), were assessed using vitellogenin induction in a 14-day in vivo juvenile rainbow trout screening assay. Median effective concentrations, relative to E2, for induction of vitellogenin were determined from the concentration-response curves and the relative estrogenic potencies of each of the test chemicals calculated. Median effective concentrations were between 19 and 26 ng L(-1) for E2, 60 ng L(-1) for E1, and between 0.95 and 1.8 ng L(-1) for EE2, implying that EE2 was approximately 11 to 27 times more potent than E2, while E2 was 2.3 to 3.2 times more potent than E1. The median effective concentration, relative to E2, for the binary mixture of E2 and EE2 was 15 ng L(-1) (comprising 14.4 ng L(-1) E2 and 0.6 ng L(-1) EE2). Using the model of concentration addition it was shown that this activity of the binary mixture could be predicted from the activity of the individual chemicals. The ability of each individual steroid to contribute to the overall effect of a mixture, even at individual no-effect concentrations, combined with the high estrogenic potency of the steroids, particularly the synthetic steroid EE2, emphasizes the need to consider the total estrogenic load of these chemicals in our waterways. 相似文献
82.
JL Cummings 《Canadian Metallurgical Quarterly》1999,281(4):376-378
83.
We have carried out a physicochemical and computational analysis on the stability of the intercalated structures formed by cytosine-rich DNA strands. In the computational study, the electrostatic energy components have been calculated using a Poisson-Boltzmann model, and the non-polar energy components have been computed with a van der Waals function and/or a term dependent on the solvent-accessible surface area of the molecules. The results have been compared with those obtained for Watson-Crick duplexes and with thermodynamic data derived from UV experiments. We have found that intercalated DNA is mainly stabilized by very favorable electrostatic interactions between hydrogen-bonded protonated and neutral cytosines, and by non-polar forces including the hydrophobic effect and enhanced van der Waals contacts. Cytosine protonation electrostatically promotes the association of DNA strands into a tetrameric structure. The electrostatic interactions between stacked C.C+ pairs are strongly attenuated by the reaction field of the solvent, and are modulated by a complex interplay of geometric and protonation factors. The forces stabilizing intercalated DNA must offset an entropic penalty due to the uptake of protons for cytosine protonation, at neutral pH, and also the electrostatic contribution to the solvation free energy. The latter energy component is less favorable for protonated DNA due to the partial neutralization of the negative charge of the molecule, and probably affects other protonated DNA and RNA structures such as C+-containing triplexes. 相似文献
84.
The void electromigration process in the strip geometry is investigated analytically and numerically. The void is assumed to travel either along the axis of symmetry of the metal strip or at the boundary. In each case, the shape, the velocity of the void and the characteristic electrical current are predicted. 相似文献
85.
86.
87.
Software radios for airborne platforms 总被引:1,自引:0,他引:1
Defense contributions to the Programmable Modular Communications System (PMCS) Integrated Product Team (IPT) included designs for an RF module based on software radio configurations useful in airborne systems. Several configurations were examined, analyzers were consolidated, and concepts of operation (CONOPS) were evaluated. Geographic separation of platforms and on-board separation of radio modules have consequences for the remote control of reconfigurable radios. This paper identifies organizational roles in software radio development, characterizes the need for software radios in airborne applications, and highlights those configurations found to be attractive. The methodology, CONOPS, and conclusions are summarized 相似文献
88.
HS Ruchlin EB Elkin CR MacKenzie P Williams-Russo JP Allegrante 《Canadian Metallurgical Quarterly》1997,10(5):343-351
This article reviews the scientific literature in several areas important to the delivery of palliative care: multicultural issues, education, comprehensive outcome measures and ethics. Most of the research can be classified as fundamental rather than intervention research according to the Cancer Control Framework of the National Cancer Institute of Canada. Desired outcomes of interventions are most often defined from the health care professional's perspective but need to be defined from the patient's perspective. In areas such as multicultural issues and the effect of the volunteer on the patient, there is almost no research. The complexity of studying the best way to deliver palliative care would benefit from the input of colleagues who have experience addressing these issues in other patient populations. 相似文献
89.
MB Elam J Heckman JR Crouse DB Hunninghake JA Herd M Davidson IL Gordon EB Bortey WP Forbes 《Canadian Metallurgical Quarterly》1998,18(12):1942-1947
Cilostazol is an antiplatelet agent and vasodilator marketed in Japan for treatment of ischemic symptoms of peripheral vascular disease. It is currently being evaluated in the United States for treatment of symptomatic intermittent claudication (IC). Cilostazol has been shown to improve walking distance in patients with IC. In addition to its reported vasodilator and antiplatelet effects, cilostazol has been proposed to have beneficial effects on plasma lipoproteins. We examined the effect of cilostazol versus placebo on plasma lipoproteins in 189 patients with IC. After 12 weeks of therapy with 100 mg cilostazol BID, plasma triglycerides decreased 15% (P<0.001). Cilostazol also increased plasma high density lipoprotein cholesterol (HDL-C) (10%) and apolipoprotein (apo) A1 (5.7%) significantly (P<0.001 and P<0.01, respectively). Both HDL3 and HDL2 subfractions were increased by cilostazol; however, the greatest percentage increase was observed in HDL2. Individuals with baseline hypertriglyceridemia (>140 mg/dL) experienced the greatest changes in both HDL-C and triglycerides with cilostazol treatment. In that subset of patients, HDL-C was increased 12.2% and triglycerides were decreased 23%. With cilostazol, there was a trend (3%) toward decreased apoB as well as increased apoA1, resulting in a significant (9.8%, P<0.002) increase in the apoA1 to apoB ratio. Low density lipoprotein cholesterol and lipoprotein(a) concentrations were unaffected. Cilostazol treatment resulted in a 35% increase in treadmill walking time (P=0.0015) and a 9.03% increase in ankle-brachial index (P<0.001). These results indicate that in addition to improving the symptoms of IC, cilostazol also favorably modifies plasma lipoproteins in patients with peripheral arterial disease. The mechanism of this effect is currently unknown. 相似文献
90.
K Yoshizawa WC Willett SJ Morris MJ Stampfer D Spiegelman EB Rimm E Giovannucci 《Canadian Metallurgical Quarterly》1998,90(16):1219-1224
BACKGROUND: In a recent randomized intervention trial, the risk of prostate cancer for men receiving a daily supplement of 200 microg selenium was one third of that for men receiving placebo. By use of a nested case-control design within a prospective study, i.e., the Health Professionals Follow-Up Study, we investigated the association between risk of prostate cancer and prediagnostic level of selenium in toenails, a measure of long-term selenium intake. METHODS: In 1986, 51,529 male health professionals aged 40-75 years responded to a mailed questionnaire to form the prospective study. In 1987, 33,737 cohort members provided toenail clippings. In 1988, 1990, 1992, and 1994, follow-up questionnaires were mailed. From 1989 through 1994, 181 new cases of advanced prostate cancer were reported. Case and control subjects were matched by age, smoking status, and month of toenail return. Selenium levels were determined by neutron activation. All P values are two-sided. RESULTS: The selenium level in toenails varied substantially among men, with quintile medians ranging from 0.66 to 1.14 microg/g for control subjects. When matched case-control data were analyzed, higher selenium levels were associated with a reduced risk of advanced prostate cancer (odds ratio [OR] for comparison of highest to lowest quintile = 0.49; 95% confidence interval [CI] = 0.25-0.96; P for trend = .11). After additionally controlling for family history of prostate cancer, body mass index, calcium intake, lycopene intake, saturated fat intake, vasectomy, and geographical region, the OR was 0.35 (95% CI = 0.16-0.78; P for trend = .03). CONCLUSIONS: Our results support earlier findings that higher selenium intakes may reduce the risk of prostate cancer. Further prospective studies and randomized trials of this relationship should be conducted. 相似文献