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排序方式: 共有273条查询结果,搜索用时 262 毫秒
231.
Abstract Concern regarding the potential for selective fisheries to degrade desirable characteristics of exploited fish populations is growing worldwide. Although the occurrence of fishery‐induced evolution in a wild population has not been irrefutably documented, considerable theoretical and empirical evidence for that possibility exists. Environmental conditions influence survival and growth in many species and may mask comparatively subtle trends induced by selective exploitation, especially given the evolutionarily short time series of data available from many fisheries. Modeling may be the most efficient investigative tool under such conditions. Motivated by public concern that large‐mesh gillnet fisheries may be altering Chinook salmon in western Alaska, we constructed a stochastic model of the population dynamics of Chinook salmon. The model contained several individually based components and incorporated size‐selective exploitation, assortative mating, size‐dependent female fecundity, density‐dependent survival, and the heritability of size and age. Substantial reductions in mean size and age were observed under all scenarios. Concurrently reducing directional selection and increasing spawning abundance was most effective in stimulating population recovery. Use of this model has potential to improve our ability to investigate the consequences of selective exploitation and aid development of improved management strategies to more effectively sustain fish and fisheries into the future. 相似文献
232.
Hao Wu Songyang Yao Tiankun Wang Jun Wang Kang Ren Hai Yang Wenkui Ma Pengyun Ji Yongqiang Lu Hui Ma Changwang He Wenjuan Wei Lu Zhang Guoshi Liu 《Molecules (Basel, Switzerland)》2021,26(4)
Mastitis is a common disease in cows breeding. The milk quality will be significantly reduced with increased milk somatic cells, which often occurs in cows with mastitis. In this study, the influence of seasonal changes, age and lactation stages in the Dairy Herd Improvement (DHI) of cows was investigated. Then, the Dairy Herd Improvement (DHI) of cows with high somatic cell score (SCS) after melatonin treatment was systemically investigated. The results showed that melatonin significantly suppressed the milk somatic cell score under all of the tested conditions. The melatonin treatment also improved the milk nutritional value by reducing its fat but increasing its lactose and protein contents. The application of melatonin significantly improved the DHI. The beneficial effects of melatonin on DHI are likely attributed to the antioxidant and anti-inflammatory activities of melatonin. 相似文献
233.
Kai Li Han‐Ting Fan Yan‐Fang Yu Fan‐Li Bu Ling‐Li Hu Jian‐Wen Wang Hao‐Fang Mu Steven Haigh Feng Chen 《Electrophoresis》2015,36(14):1633-1639
Previous studies have demonstrated that a large sample size is needed to reliably estimate population‐ and locus‐specific microsatellite mutation rates. Therefore, we conducted a long‐term collaboration study and performed a comprehensive analysis on the mutation characteristics of 19 autosomal short tandem repeat (STR) loci. The STR loci located on 15 of 22 autosomal chromosomes were analyzed in a total of 21 106 samples (11 468 parent–child meioses) in a Chinese population. This provided 217 892 allele transfers at 19 STR loci. An overall mutation rate of 1.20 × 10?3 (95% CI, 1.06–1.36 × 10?3) was observed in the populations across 18 of 19 STR loci, except for the TH01 locus with no mutation found. Most STR mutations (97.7%) were single‐step mutations, and only a few mutations (2.30%) comprised two and multiple steps. Interestingly, approximately 93% of mutation events occur in the male germline. The mutation ratios increased with the paternal age at child birth (r = 0.99, p<0.05), but not maternal age. Last, with the combination analysis of the data from the southern Chinese population, we drew a picture of 19 STR mutations in China. In conclusion, the data from this study will provide useful information in parentage testing, kinship analysis, and population genetics. 相似文献
234.
235.
Scheduling Strategy Design Framework for Cyber–Physical System with Non-Negligible Propagation Delay
Cyber–physical systems (CPS) have been widely employed as wireless control networks. There is a special type of CPS which is developed from the wireless networked control systems (WNCS). They usually include two communication links: Uplink transmission and downlink transmission. Those two links form a closed-loop. When such CPS are deployed for time-sensitive applications such as remote control, the uplink and downlink propagation delay are non-negligible. However, existing studies on CPS/WNCS usually ignore the propagation delay of the uplink and downlink channels. In order to achieve the best balance between uplink and downlink transmissions under such circumstances, we propose a heuristic framework to obtain the optimal scheduling strategy that can minimize the long-term average control cost. We model the optimization problem as a Markov decision process (MDP), and then give the sufficient conditions for the existence of the optimal scheduling strategy. We propose the semi-predictive framework to eliminate the impact of the coupling characteristic between the uplink and downlink data packets. Then we obtain the lookup table-based optimal offline strategy and the neural network-based suboptimal online strategy. Numerical simulation shows that the scheduling strategies obtained by this framework can bring significant performance improvements over the existing strategies. 相似文献
236.
密封容器中钚材料同位素丰度和年龄的测量 总被引:1,自引:0,他引:1
根据相对效率法的原理,利用PC/FRAM分析软件,开展了用高分辨γ谱仪测量密封容器中钚材料的同位素丰度和年龄的实验研究.研究结果表明,同位素丰度和年龄的分析精度随能谱测量精度的提高而提高,如果能谱的测量精度不够,通过PC/FRAM分析得出的钚材料的同位素丰度和年龄有偏低的可能.因此,在能谱测量过程中,建议通过监测某个特征峰的峰面积计数来判定239Pu丰度和年龄的测量精度是否已满足测量要求.Based on the concept of relative detection efficiency, some experiments have been conducted to measure the isotopic abundance and the age of the plutonium material in a sealed container by a high-resolution γ-ray spectrometer. The PC/FRAM software analyzes the spectra. The study shows that the analysis precision of the isotopic abundance and the age will rise as the spectral measurement precision increases, and that If the spectral measurement precision is not enough, the analyzed results by the PC/FRAM software might be lower. Hence, the study suggests that a spectral peak is monitored to show lights on the spectral measurement precision during the process of spectrum acquirement. 相似文献
237.
给出了1990年和2000年宁波市人口年龄结构的统计分析,以及相应人口年龄结构对比的统计分析。分析显示:在业、退休年龄结构具有明显的年龄段特征,相隔10年,在业率和退休率无显著变化,而失业率总体上有一定的增幅,应适当予以关注。 相似文献
238.
根据结核病的传染特征,建立了一个具有年龄结构的结核病微分方程模型,对模型的性态进行了分析,得到了该模型平衡解唯一存在的条件。 相似文献
239.
Inside Cover: Oxidation Monitoring by Fluorescence Spectroscopy Reveals the Age of Fingermarks (Angew. Chem. Int. Ed. 24/2014)
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240.
Antoni Leon Dawidowicz Anna Poskrobko 《Mathematical Methods in the Applied Sciences》2014,37(8):1240-1248
The paper deals with the problem of the stability for a model of a population with delayed dependence of the structure. We study an equilibrium age distribution. We also give conditions under which such distribution is exponentially asymptotically stable. The work continues authors’ research which begun in 2009. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献