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571.
The air-dust samples collected from petro-chemical industrial region in the suburb of Lanzhou and from a certain rural region 64 km away from the city were extracted, with a mixed solvent (benzene: hexane: isopropanol=7:2:1) for 8 hours. A strong free radical signal at g= 2.00 of air-dust itself and a hyperfine splitting EPR signal of extract from air-dust have been detected. The sister chromatid exchange frequency (SCE) was increased by extracts of both dusts from the industrial region and from the rural region. If a chemical is able to increase SCE up to twice as high as the control, this chemical is considered to be mutagenic and/or carcinogenic. The double SCE frequency concentration is 23 μg/ml for the dust extract obtained from the industrial region and 47μg/ml for that from the rural region. Extracts were able to damage to DNA template. Results indicated that the mutagenicity and/or carcinogenicity of the extracts obtained from the petro-chemical industrial region were stronger than that of the 相似文献
572.
茶多酚清除自由基和抗氧化作用的研究 总被引:13,自引:0,他引:13
本文用化学发光法和TBA法测定了GTP对不同反应体系产生的氧自由基的清除作用,结果表明,GTP对X/XO和PMA刺激的PMN体系中产生的化学发光强度的清除作用均有量效关系,GTP对PMA刺激的PMN和红细胞膜体系在TBA反应中产生的MDA的抑制作用亦均有量效关系。 相似文献
573.
574.
Uganda kob mating success does not increase on larger leks 总被引:2,自引:0,他引:2
James C. Deutsch 《Behavioral ecology and sociobiology》1994,34(6):451-459
One explanation for the movement of sexually receptive females to clusters of male territories in lek-breeding species is that larger clusters provide females with higher-quality mating partners, as would be the case if males were distributed between leks in an ideal free distribution for unequal competitors. This ideal free model of lek evolution predicts that male competitive ability and mating success will be greater on larger leks than smaller ones. I tested these predictions by comparing the mean number of males on 19 different Uganda kob leks with the sex ratio, the availability of oestrous females, mating rates, male fighting rates and male turnover rates. Contrary to the predictions of the model, numbers of females, receptive females and fights increased proportionally with lek size, but were no greater per male on larger leks. Multivariate analyses of male and female numbers on leks showed that male numbers were associated with female numbers, female numbers in the past, and a variety of habitat variables which may have related to the costs of holding a lek territory, but female numbers varied only with male numbers and female density in the area. These data do not provide evidence that females gain access to superior males by mating on larger leks, though they do support the possibility that lekking may be promoted by a tendency for larger leks to retain females longer. 相似文献
575.
James N. Macri Kevin Spencer Kenneth Garver Philip D. Buchanan Burhan Say Nancy J. Carpenter Francoise Muller Andre Boué 《黑龙江环境通报》1994,14(2):97-103
The median maternal serum free beta human chorionic gonadotropin (hCG) multiple of the median (MOM) of 480 Down syndrome cases in the second trimester was 2·64, significantly greater than the reported median MOM of intact hCG (p<0·0001). In 234 of these cases from retrospective and prospective studies, the effectiveness of maternal serum free beta hCG was evaluated in combination with alpha-fetoprotein (AFP) and maternal age in second-trimester Down syndrome screening. Down syndrome detection in the gestational age range of 14–16 weeks was 82 per cent. In all gestational weeks (14–22), a 77·7 per cent Down syndrome detection rate was achieved. In prospective screening of 44 272 patients under the age of 35 years, 69 per cent of Down syndrome cases were detected (73 per cent in gestational weeks 14–16). The false-positive rate for the prospective study was 3·8 per cent. The use of free beta hCG combined with maternal serum AFP and maternal age-related risk for Down syndrome in a screening population (i.e., women under 35 years) yields an improved detection efficiency over other protocols. 相似文献
576.
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578.
秸秆与游离发酵液接触比例对产沼气特性的影响 总被引:1,自引:0,他引:1
在中温(37±1)℃条件下,以破碎麦秸为原料,采用批次进料和消化液每天回流方式(发酵固含率为10%),通过在反应器底部设置不同高度的多孔滤板使秸秆与游离发酵液接触比例分别为100%(T1)、50%(T2)和0%(T3),研究秸秆与游离发酵液接触比例对产沼气特性的影响.结果表明:从产气特征和发酵前后VS变化来看,各处理均无明显差异,表明减少秸秆与游离发酵液的接触比例,对秸秆产沼气效果无影响,即通过渗滤液每天回流方式,未浸没于游离发酵液中的秸秆可以达到与浸没秸秆相同的传质效果,此结果为秸秆厌氧发酵工程中提高秸秆有效发酵浓度提供了理论依据.此外,试验还发现,T3处理中消化液与秸秆接触比例随发酵进程呈逐渐降低趋势,并于发酵第6d基本稳定,表明发酵系统中实际的游离发酵液量逐渐减少,分析认为秸秆物料对消化液有吸收和截持作用,发酵第6d后已达秸秆物料吸持水饱和状态(秸秆物料含固率为16.42%). 相似文献
579.
以甲酸为活化剂,耦合热活化过硫酸钠技术产生还原性二氧化碳阴离子自由基(CO2·-),从而还原去除水溶液中四氯化碳(CT)和Cr(VI),考察过硫酸钠和甲酸初始浓度的影响以及复合污染处理效果.结果表明:当过硫酸钠与甲酸浓度均为100mmol/L时,单独CT或Cr(VI)分别在120min、60min内基本完全去除(50℃),且污染物去除效率随过硫酸钠及甲酸浓度升高而增强.在CT和Cr(VI)复合污染体系中,Cr(VI)的存在能够抑制CT降解,且抑制程度随Cr(VI)初始浓度升高而提高,但Cr(VI)去除率随CT初始浓度增大而升高.加入CO2·-猝灭剂(甲基紫精)能够抑制CT降解,但促进Cr(VI)去除,表明有机物的存在能够增强Cr(VI)去除效率. 相似文献
580.