Community-based alternative breeding plans for indigenous sheep breeds in four agro-ecological zones of Ethiopia

Based on the results of participatory approaches to define traits in the breeding objectives, four scenarios of ram selection and ram use were compared via deterministic modelling of breeding plans for community-based sheep breeding programmes in four diverse agro-ecological regions of Ethiopia. The regions (and production systems) were Afar (pastoral/agro-pastoral), Bonga and Horro (both mixed crop-livestock) and Menz (sheep-barley). The schemes or scenarios differed in terms of selection intensity and duration of ram use. The predicted genetic gains per year in yearling weight (kilograms) were comparable across the schemes but differed among the breeds and ranged from 0.399 to 0.440 in Afar, 0.813 to 0.894 in Bonga, 0.850 to 0.940 in Horro, and 0.616 to 0.699 in Menz. The genetic gains per year in number of lambs born per ewe bred ranged from 0.009 to 0.010 in both Bonga and Horro. The predicted genetic gain in the proportion of lambs weaned per ewe joined was nearly comparable in all breeds ranging from 0.008 to 0.011. The genetic gain per year in milk yield of Afar breed was in the order of 0.018 to 0.020 kg, while the genetic gain per generation for greasy fleece weight (kg) ranged from 0.016 to 0.024 in Menz. Generally, strong selection and shorter duration of ram use for breeding were the preferred options. The expected genetic gains are satisfactory but largely rely on accurate and continuous pedigree and performance recording.     

先锋精神：从新诗的民族神话、传说写作 看中国新诗用典出路

研究了多态不确定性环境下的城市垃圾处理问题.在一定假设条件下, 建立了一类固废管理问题的区间模糊优化模型. 提出了区间大小关系可能度算子的公理化定义,并基于这种可能度算子的方法, 对给定的权重系数和置信水平, 推导了原模型的确定型等价类, 从而把区间模糊优化问题转化为普通的线性规划问题求解.将所建立的模型和求解方法用于解决一个实际固废管理问题, 结果证实了该模型及其求解方法的有效性.     

Current hypotheses for the evolution of sex and recombination

The evolution of sex is one of the most important and controversial problems in evolutionary biology. Although sex is almost universal in higher animals and plants, its inherent costs have made its maintenance difficult to explain. The most famous of these is the twofold cost of males, which can greatly reduce the fecundity of a sexual population, compared to a population of asexual females. Over the past century, multiple hypotheses, along with experimental evidence to support these, have been put forward to explain widespread costly sex. In this review, we outline some of the most prominent theories, along with the experimental and observational evidence supporting these. Historically, there have been 4 classes of theories: the ability of sex to fix multiple novel advantageous mutants (Fisher-Muller hypothesis); sex as a mechanism to stop the build-up of deleterious mutations in finite populations (Muller's ratchet); recombination creating novel genotypes that can resist infection by parasites (Red Queen hypothesis); and the ability of sex to purge bad genomes if deleterious mutations act synergistically (mutational deterministic hypothesis). Current theoretical and experimental evidence seems to favor the hypothesis that sex breaks down selection interference between new mutants, or it acts as a mechanism to shuffle genotypes in order to repel parasitic invasion. However, there is still a need to collect more data from natural populations and experimental studies, which can be used to test different hypotheses.     

Multi-mycotoxin exposure and risk assessments for Chinese consumption of nuts and dried fruits

In this study, 15 mycotoxins were detected in 233 nut and dried fruit samples from China. The 15 mycotoxins included aflatoxins(AFs: AFB_1, AFB_2, AFG_1 and AFG_2), trichothecene toxins(TCs: T-2, ZEA, ENA, ENA_1, ENB, ENB_1 and BEA), Alternaria toxins(ATs: TEN, AOH and AME) and ochratoxin A(OTA). The mycotoxins were detected in 47.6% of the samples and all 15 of the mycotoxins were found. Two samples were positive for AFB_1 and exceeded the maximum tolerable levels allowed in China. The contamination levels of the mycotoxins found in nuts, dried jujubes, raisins, dried figs and dried longans were in the ranges of 0.1–462.7, 0.2–247.3, 0.8–10.1, 0.2–384.1 and 0.1–89.2 μg kg–1, respectively. Dried figs(80.0%) had the highest incidence of mycotoxins, followed by dried longans(60.0%), dried jujubes(57.1%), nuts(43.6%) and raisins(26.7%). The estimated daily intake(EDI) values of each individual mycotoxin and all of the mycotoxins collectively were calculated by both the deterministic approach(DA) and the probability approach(PA). For risk characterization, dietary exposure to TCs, ATs and OTA through consumption of nuts and dried fruits according to both approaches, showed no health risk to Chinese adults by exposure to either individual mycotoxins or in combination. To the best of our knowledge, this is the first work in which risk assessment of multimycotoxins is performed, specifically including the emerging ENNs and BEA, in nuts and dried fruits of China.     

Pesticide residues in food--acute dietary exposure

Consumer risk assessment is a crucial step in the regulatory approval of pesticide use on food crops. Recently, an additional hurdle has been added to the formal consumer risk assessment process with the introduction of short-term intake or exposure assessment and a comparable short-term toxicity reference, the acute reference dose. Exposure to residues during one meal or over one day is important for short-term or acute intake. Exposure in the short term can be substantially higher than average because the consumption of a food on a single occasion can be very large compared with typical long-term or mean consumption and the food may have a much larger residue than average. Furthermore, the residue level in a single unit of a fruit or vegetable may be higher by a factor (defined as the variability factor, which we have shown to be typically x3 for the 97.5th percentile unit) than the average residue in the lot. Available marketplace data and supervised residue trial data are examined in an investigation of the variability of residues in units of fruit and vegetables. A method is described for estimating the 97.5th percentile value from sets of unit residue data. Variability appears to be generally independent of the pesticide, the crop, crop unit size and the residue level. The deposition of pesticide on the individual unit during application is probably the most significant factor. The diets used in the calculations ideally come from individual and household surveys with enough consumers of each specific food to determine large portion sizes. The diets should distinguish the different forms of a food consumed, eg canned, frozen or fresh, because the residue levels associated with the different forms may be quite different. Dietary intakes may be calculated by a deterministic method or a probabilistic method. In the deterministic method the intake is estimated with the assumptions of large portion consumption of a 'high residue' food (high residue in the sense that the pesticide was used at the highest recommended label rate, the crop was harvested at the smallest interval after treatment and the residue in the edible portion was the highest found in any of the supervised trials in line with these use conditions). The deterministic calculation also includes a variability factor for those foods consumed as units (eg apples, carrots) to allow for the elevated residue in some single units which may not be seen in composited samples. In the probabilistic method the distribution of dietary consumption and the distribution of possible residues are combined in repeated probabilistic calculations to yield a distribution of possible residue intakes. Additional information such as percentage commodity treated and combination of residues from multiple commodities may be incorporated into probabilistic calculations. The IUPAC Advisory Committee on Crop Protection Chemistry has made 11 recommendations relating to acute dietary exposure.     

基于点评估方法的渤海湾产区苹果中农药残留膳食暴露风险研究

为评估渤海湾产区苹果中主要农药的残留情况及其产生的风险,在山东、辽宁及河北3个主要省份的150个生产基地进行了苹果样品采集与测定分析,并对我国不同人群的膳食暴露风险进行了评估。结果表明:93.3%的苹果样品检出有低浓度农药残留,经最大残留限量值(MRL)判定后100%合格,82.0%的样品中农药残留种类在3种及以下;共检出17种农药残留,大多为低毒或无毒农药,无禁用和高毒农药。采用点评估方法,选择检出率在20%以上的多菌灵、毒死蜱、啶虫脒和戊唑醇进行不同消费人群暴露点评估。结果显示:4种农药的急性和慢性摄入风险均为儿童高于成年人,绝大多数女性人群的摄入风险高于男性;4种农药急性摄入风险均高于慢性摄入风险,风险水平由高到低为多菌灵毒死蜱戊唑醇啶虫脒,但点评估结果均远低于100%,说明通过食用苹果摄入的农药残留极其微量,不会对人体产生急性或慢性风险。     

基于分步迁移策略的苹果采摘机械臂轨迹规划方法

针对非结构化自然环境使基于深度强化学习的采摘轨迹规划训练效率低的问题,提出了基于分步迁移策略的深度确定性策略梯度算法(DDPG),并进行了苹果采摘轨迹规划。首先,提出了基于DDPG的渐进空间约束分步训练策略;其次,利用迁移学习思想,将轨迹规划的最优策略由无障碍场景迁移到单一障碍场景、由单一障碍场景迁移到混杂障碍场景;最后,对多自由度苹果采摘机械臂进行了采摘轨迹规划仿真实验,结果表明,分步迁移策略能够提高DDPG算法的训练效率与网络性能,仿真实验验证了本文方法的有效性。     

应用确定性优化算法求解多目标气动设计问题的Pareto阵面

将确定性优化算法和Pareto阵面概念结合起来处理了多目标优化设计问题；给出了结合算法及数值过程的细节，并将其应用到了气动优化设计中；描述了如何用确定性优化算法快速抓获多目标优化问题的Pareto阵面以及能够抓获哪些类型的Pareto阵面。数值实验结果表明，确定性优化算法可以准确高效地抓获任意凸的和某些凹的Pareto阵面，故对于此类多目标气动优化问题，可用确定性算法代替进化算法。