To delay once or twice: the effect of hypobiosis and free-living stages on the stability of host-parasite interactions.

The life cycle of many endoparasites can be delayed by free-living infective stages and a developmental arrestment in the host referred to as hypobiosis. We investigated the effects of hypobiosis and its interaction with delay in the free-living stages on host-parasite population dynamics by expanding a previous attempt by Dobson & Hudson. When the parasite life cycle does not include free-living stages, hypobiosis destabilizes the host-parasite interactions, irrespective of the assumptions about the regulation of the host population dynamics. Interestingly, the destabilizing effect varies in a nonlinear way with the duration of hypobiosis, the maximal effect being expected for three to five months delay. When the parasite life cycle involves free-living stages, hypobiosis of short or intermediate duration increases the destabilizing effect of the first time delay. However, hypobiosis of a duration of five months or more can stabilize interactions, irrespective of the regulation of the host population dynamics. Overall, we confirmed that hypobiosis is an unusual time delay as it can stabilize a two-way interaction. Contrary to the previous conclusions, such an atypical effect does not require self-regulation of the host population, but instead depends on the existence of free-living stages.     

Quantifying social distancing arising from pandemic influenza.

Local epidemic curves during the 1918-1919 influenza pandemic were often characterized by multiple epidemic waves. Identifying the underlying cause(s) of such waves may help manage future pandemics. We investigate the hypothesis that these waves were caused by people avoiding potentially infectious contacts-a behaviour termed 'social distancing'. We estimate the effective disease reproduction number and from it infer the maximum degree of social distancing that occurred during the course of the multiple-wave epidemic in Sydney, Australia. We estimate that, on average across the city, people reduced their infectious contact rate by as much as 38%, and that this was sufficient to explain the multiple waves of this epidemic. The basic reproduction number, R0, was estimated to be in the range of 1.6-2.0 with a preferred estimate of 1.8, in line with other recent estimates for the 1918-1919 influenza pandemic. The data are also consistent with a high proportion (more than 90%) of the population being initially susceptible to clinical infection, and the proportion of infections that were asymptomatic (if this occurs) being no higher than approximately 9%. The observed clinical attack rate of 36.6% was substantially lower than the 59% expected based on the estimated value of R0, implying that approximately 22% of the population were spared from clinical infection. This reduction in the clinical attack rate translates to an estimated 260 per 100000 lives having been saved, and suggests that social distancing interventions could play a major role in mitigating the public health impact of future influenza pandemics.     

Is there the potential for an epidemic of variant Creutzfeldt–Jakob disease via blood transfusion in the UK?

The discovery of three individuals suspected to have contracted variant Creutzfeldt-Jakob disease (vCJD) through blood transfusions has heightened concerns that a secondary epidemic via human-to-human transmission could occur in the UK. The Department of Health responded immediately to this threat by banning those who had received blood transfusions since 1980 from donating blood. In this paper, we conduct a sensitivity analysis to explore the potential size of a blood-borne vCJD epidemic and investigate the effectiveness of public health interventions. A mathematical model was developed together with an expression for the basic reproduction number (R0). The sensitivity of model predictions to unknown parameters determining the transmission of vCJD via infected blood was assessed under pessimistic modelling assumptions. We found that the size of the epidemic (up until 2080) was bounded above by 900 cases, with self-sustaining epidemics (R0>1) also possible; but the scenarios under which such epidemics could arise were found to be biologically implausible. Under optimistic assumptions, public health interventions reduced the upper bound to 250 and further still when only biologically plausible scenarios were considered. Our results support the belief that scenarios leading to large or self-sustaining epidemics are possible but unlikely, and that public health interventions were effective.     

The dynamic balance of import and export of zinc in Escherichia coli suggests a heterogeneous population response to stress

Zinc is essential for life, but toxic in excess. Thus all cells must control their internal zinc concentration. We used a systems approach, alternating rounds of experiments and models, to further elucidate the zinc control systems in Escherichia coli. We measured the response to zinc of the main specific zinc import and export systems in the wild-type, and a series of deletion mutant strains. We interpreted these data with a detailed mathematical model and Bayesian model fitting routines. There are three key findings: first, that alternate, non-inducible importers and exporters are important. Second, that an internal zinc reservoir is essential for maintaining the internal zinc concentration. Third, our data fitting led us to propose that the cells mount a heterogeneous response to zinc: some respond effectively, while others die or stop growing. In a further round of experiments, we demonstrated lower viable cell counts in the mutant strain tested exposed to excess zinc, consistent with this hypothesis. A stochastic model simulation demonstrated considerable fluctuations in the cellular levels of the ZntA exporter protein, reinforcing this proposal. We hypothesize that maintaining population heterogeneity could be a bet-hedging response allowing a population of cells to survive in varied and fluctuating environments.     

Cyclical parthenogenesis algorithm for layout optimization of truss structures with frequency constraints

Structural optimization with frequency constraints is seen as a challenging problem because it is associated with highly nonlinear, discontinuous and non-convex search spaces consisting of several local optima. Therefore, competent optimization algorithms are essential for addressing these problems. In this article, a newly developed metaheuristic method called the cyclical parthenogenesis algorithm (CPA) is used for layout optimization of truss structures subjected to frequency constraints. CPA is a nature-inspired, population-based metaheuristic algorithm, which imitates the reproductive and social behaviour of some animal species such as aphids, which alternate between sexual and asexual reproduction. The efficiency of the CPA is validated using four numerical examples.     

ELEVATED TEMPERATURE FATIGUE IN Ni3Al-BASED ALLOYS

Both high-cycle and low-cycle fatigue properties of hot-extruded powders of a Ni₃Al-based alloy, IC218, have been evaluated. High cycle fatigue measurements were performed under stress controlled conditions at temperatures ranging from 25°C to 850°C. Tests were made in both laboratory air and vacuum environments. Low cycle fatigue tests were conducted under total strain control in a laboratory air environment at 650°C. In high cycle fatigue, high ratios of the fatigue limit (Δσ at 10⁶ cycles) to monotonic yield strength (σ_ys), of approximately Δσ/σ_ys～1, were obtained in the powder extruded IC218 alloy for temperatures ranging from 25°C to 650°C. In low cycle fatigue, a substantial decrease in fatigue life occurred at 650°C, compared to results obtained previously at 25°C. High cycle fatigue performance at low stress/strain amplitudes is better than expected when compared to precipitation strengthened superalloys. The improved performance is explained in terms of the cyclic hardening behavior of the alloy.     

基于等效源法插值的声场重放方法

声场重放旨在保留声音内容与声场空间特性,创造或再现一个真实的空间声学环境.一套在真实"听音室"实现的声场重放听音系统,需要对扬声器阵列的声传递函数进行多次测量,这个过程繁琐且耗时.文章提出一种等效源法插值重放方法,在传声器采样率较低的情况下,实现了扬声器阵列声传递函数在整个目标重放空间内的插值.对比传统的声压匹配法,所...     

遗传算法中约束的凝聚选择和复合形处理方法

本文在实数编码的遗传算法中对约束条件提出一种凝聚选择和复合形法处理的方法。利用凝聚函数求出个体的约束违背值,在选择中不仅考虑适应度值而且考虑约束违背值,使有潜力的个体优先被选择。利用复合形法对违背约束的个体进行改进,从而改善整个种群的性能、增加可行个体数量,有利于最优解的搜索。算例表明本文方法是可行和有效的。     

Experimental demonstration of a two-phase population extinction hazard

Population extinction is a fundamental biological process with applications to ecology, epidemiology, immunology, conservation biology and genetics. Although a monotonic relationship between initial population size and mean extinction time is predicted by virtually all theoretical models, attempts at empirical demonstration have been equivocal. We suggest that this anomaly is best explained with reference to the transient properties of ensembles of populations. Specifically, we submit that under experimental conditions, many populations escape their initially vulnerable state to reach quasi-stationarity, where effects of initial conditions are erased. Thus, extinction of populations initialized far from quasi-stationarity may be exposed to a two-phase extinction hazard. An empirical prediction of this theory is that the fit Cox proportional hazards regression model for the observed survival time distribution of a group of populations will be shown to violate the proportional hazards assumption early in the experiment, but not at later times. We report results of two experiments with the cladoceran zooplankton Daphnia magna designed to exhibit this phenomenon. In one experiment, habitat size was also varied. Statistical analysis showed that in one of these experiments a transformation occurred so that very early in the experiment there existed a transient phase during which the extinction hazard was primarily owing to the initial population size, and that this was gradually replaced by a more stable quasi-stationary phase. In the second experiment, only habitat size unambiguously displayed an effect. Analysis of data pooled from both experiments suggests that the overall extinction time distribution in this system results from the mixture of extinctions during the initial rapid phase, during which the effects of initial population size can be considerable, and a longer quasi-stationary phase, during which only habitat size has an effect. These are the first results, to our knowledge, of a two-phase population extinction process.     

Estimating reproduction numbers for adults and children from case data

We present a method for estimating reproduction numbers for adults and children from daily onset data, using pandemic influenza A(H1N1) data as a case study. We investigate the impact of different underlying transmission assumptions on our estimates, and identify that asymmetric reproduction matrices are often appropriate. Under-reporting of cases can bias estimates of the reproduction numbers if reporting rates are not equal across the two age groups. However, we demonstrate that the estimate of the higher reproduction number is robust to disproportionate data-thinning. Applying the method to 2009 pandemic influenza H1N1 data from Japan, we demonstrate that the reproduction number for children was considerably higher than that of adults, and that our estimates are insensitive to our choice of reproduction matrix.     

Application of methods for assessing the geno- and cytotoxicity of Triclosan to C. ehrenbergii

The toxic effects of Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) on morphology and sexual and asexual reproduction of C. ehrenbergii were examined. In addition, the genotoxic effects of Triclosan were evaluated on the same alga using the microgel electrophoresis test, also-called Comet assay. Increasing Triclosan concentrations in the range 0.125-5 mg L(-1) did not affect size and shape of the cells but had relevant effects on both chloroplast morphology and dimension. Triclosan inhibited the vegetative growth of C. ehrenbergii at 0.5 mg L(-1). The effects on sexual reproduction indicate that the number of C. ehrenbergii zygospores was significantly reduced by the application of 0.937 mg L(-1). The Comet assay showed that Triclosan treatments led to a dose-dependent DNA damage of C. ehrenbergii; 0.25 mg L(-1)caused significant genotoxic effects and higher concentrations irreversibly altered the DNA strands. These results suggest that C. ehrenbergii could represent a useful organism to evaluate the whole toxicity of pharmaceuticals and personal care products (PPCPs), giving valuable information for a risk assessment.     

Cyclic oxidation – guidelines for test standardisation,aimed at the assessment of service behaviour†

Abstract

This paper reviews current procedures used for cyclic oxidation testing and their ability to simulate service behaviour for life time prediction modelling. Test complexity varies from a simple laboratory, slow cycle, furnace test to the use of high velocity dynamic combustion rigs. It is shown that the response of an alloy under cyclic oxidation testing varies, depending on the exact test conditions chosen and the length of test exposure, but for many alloy systems this response has common features. It is proposed that all alloys that are protected by a stable, slow growing oxide scale conform to a common, generic behaviour under cyclic oxidation conditions. This life cycle of such alloys involves first the formation of a stable, protective oxide. At a critical thickness this may start to spall, increasing the rate of scale forming element consumption. When the activity of such elements falls below a critical level, in the near surface region, internal oxidation results together with the formation of less protective scales. Ultimately, it is no longer possible for the alloy to self repair following a thermal cycle and then breakaway corrosion ensures, marking the end of the alloys life.

Thus the choice of cyclic test procedure must be tailored to the particular phase of the alloy life cycle under investigation.     

色貌模型在跨媒体图像复制中的应用研究

目的 研究CIECAM02和iCAM色貌模型颜色空间的均匀性,以及应用于不同观察条件下的图像复制效果。方法 利用均匀颜色数据集测试色貌模型颜色空间的均匀性,并通过视觉评价实验来测试2个色貌模型的图像复制效果。结果 CIECAM02的色貌空间具有更好的色差均匀性,iCAM的色貌空间具有更好的色相、明度和彩度均匀性。在不同观察条件下的图像复制中,CIECAM02有更好的表现。结论 iCAM的颜色空间适合于颜色色貌属性的计算,而CIECAM02的颜色空间更适合于颜色色差的计算,在不同观察条件下的图像复制中,CIECAM02有更稳定的表现,但并不是对所有图像都有更好的表现。     

基于网点结构形态的印刷色彩再现研究

以调幅网点和同心圆网点作为主要研究对象,分析了网点结构对网点呈色特性的影响,应用Clapper-Yule颜色预测模型和Lambert-Beer法则,解释了同心圆网点高饱和度色彩再现的机理,并通过实验对理论分析进行了验证。结果表明:网点内部结构的差异会影响色彩再现质量,同心圆网点环形内部结构是影响其印刷呈色的重要因素;同心圆网点的色彩表现力优于调幅网点,特别是在饱和度再现上优势明显。     

色彩高保真复制基色筛选算法的研究

基色的筛选与优化是多基色色彩高保真复制的关键技术。以显示器色域为扩展目标,提出了印刷色彩高保真复制基色筛选算法。研究表明,传统印刷所复制的红绿蓝在中间调红色、亮调绿色、暗调蓝色区域,相比显示器色彩再现具有最显著的不足,提出了以淡红色(Lr)、淡绿色(Lg)为新基色,与传统C,M,Y,K组成六色色彩高保真复制的基色向量,并筛选出了符合要求的Lr,Lg基色油墨。使用色彩预测模型对新的基色组合进行了色彩复制和色域的仿真。结果表明,提出的基色筛选机制所得到的六基色,能够有效扩大印刷复制的色域。     

基于改进K均值聚类的图像修复方法

目的 解决特定工艺条件下灰平衡数据的再现问题。方法 通过在一定工艺条件下,获得青、品、黄、黑等4色阶调复制曲线,并拟合曲线方程,根据方程求取同一密度(理论密度)条件下青、品和黄色的网点面积率,据所得青、品、黄网点面积率设计样本色,检测其色度和密度值(实际密度)。结果 经验证,样本色色度值趋近于0,即证明样本色块趋于中性灰。建立了理论密度值与实际密度值之间的数学模型,再通过该模型和阶调复制曲线方程,获得了该工艺条件下灰平衡数据参数。结论 该方法可以准确获得特定条件下的灰平衡数据参数,为特定工艺条件下灰平衡数据的数字化建模提供了理论依据。     

Life cycle risk assessment of bottom ash reuse

The life cycle thinking was integrated with risk assessment to develop the life cycle risk assessment (LCRA) methodology in this study. Because LCRA assessed risks from a life cycle perspective of the concerned policies, it was helpful to identify important sources, contaminants, receptors and exposure pathways along the life cycle of reuse activities. The case study showed that different reuse scenarios resulted in risk shift between different life stages and receptors, and using duration of pavement was an essential factor for risk management. When ash reuse strategies were made based on a focus on the stage of reuse, the rank of strategies were shown to be different from the one based on the total population risks over the entire life cycle. This demonstrated the importance of decision criteria used in selecting reuse strategies. The results also showed that when bottom ash was reused, the health risk was shifted to the laborers; the individual risks of laborers were higher than residents through exposure to Cr and Cd via inhalation and dermal contact. Although the population risk at the treatment stage was the highest, the smaller size of exposed population would make it quite effective to reduce the risk of the laborers.     

基于表单的网络印刷客户端色彩再现方法的研究

通过研究计算机网络技术和印刷色彩管理技术,提出了通过表单实现网络印刷客户端显示色彩再现的一种方法。以网络客户的显示色彩为基础,借助网络客户的视觉观察和表单数据,获取了客户端色彩显示数据;经计算再现色彩数据,实现了客户端显示色彩的所见即所得。实验表明,方法可以解决网络印刷客户端显示色彩的再现问题,提高网络印刷质量,缩短周期,降低成本,提高效率。     

The impact of prophylaxis of healthcare workers on influenza pandemic burden.

Several models have rationalized the use of antiviral drugs as an early control measure for delaying the progression and limiting the size of outbreaks during an influenza pandemic. However, the strategy for use of these drugs is still under debate. We evaluated the impact of prophylaxis of healthcare workers (HCWs) through a mathematical model that considers attack rates in a range of 25-35% in the general population and 25-50% among HCWs. Simulations and uncertainty analysis using the demographics of the province of Ontario, Canada show that increasing prophylaxis coverage of HCWs has little impact on reducing the reproduction number of disease transmission and may not prevent the occurrence of an outbreak if expected. However, it does enable a high level of treatment, which substantially reduces morbidity and mortality in the population as a whole. Therefore, prophylaxis of HCWs should be considered an important part of public health efforts for minimizing influenza pandemic burden and its socio-economic disruption.