基因工程菌在活性污泥中的衰减及其影响因素

在间歇实验和连续运行的反应器中,考察了基因工程菌细胞密度在活性污泥中的衰减,进行了动力学模型拟合,求得模型参数,并分析了影响衰减的因素.结果表明,在间歇实验和连续运行反应器中,细胞密度在活性污泥中均呈现初期快速衰减而后趋于稳定的趋势.其衰减动力学可以用Logistic模型和Gompertz模型拟合,两个模型的拟合都有很好的相关性和显著性,拟合优度没有差异.在不同的条件下,间歇实验拟合得到的参数取值范围是：Logistic模型衰减系数r′=0.5～0.6 h^-1,稳定细胞密度K′=10⁴～10⁵ cfu·ml^-1;Gompertz模型初始衰减系数b=0.6～1.2 h^-1,比衰减系数a=0.02～0.09 h^-1.初始投加密度对衰减速率影响不大,但是显著影响稳定细胞密度.污泥浓度和温度对衰减速率和稳定密度均有显著影响. 污泥浓度越大,衰减越快,稳定密度越大;而温度越低,衰减越快,稳定密度也会越低.营养条件和微型动物捕食也是影响衰减的重要因素.基因工程菌在连续运行的膜生物反应器和活性污泥反应器中的细胞密度衰减,也可以用Logistic模型拟合,其参数在间歇实验的取值范围内.     

Green leaf area decline of wheat flag leaves: the influence of fungicides and relationships with mean grain weight and grain yield

A modified Gompertz model was derived to describe the fractional decline in green area of wheat flag leaves in field experiments where green leaf area at time t=100exp[‐exp(‐k(t‐m))]. Curves fitted over time to visual assessments of green leaf area (% of total leaf area) throughout flag leaf life accounted for more than 98% of variation in 45 of 48 wheat cultivar × fungicide treatment (+/?) comparisons. This data set spanned 17 yr and therefore included cultivars of contrasting parentage and age. In the absence of fungicide, green leaf area decline was associated with drought or infection with a number of foliar pathogens including Septoria tritici (sexual stage Mycospherella graminicola), Erysiphe graminis and Puccinia striiformis. Fungicides applied to the flag leaf included propiconazole, propiconazole plus tridemorph, flusilazole or azoxystrobin. Fungicide effects on m (i.e. time to 37% green area) were closely related to fungicide effects (% of untreated) on mean grain weight (variation accounted for (VAF) = 80%) and grain yield (VAF = 85%).     

论Richards增长曲线

本文给出了Ｒｉｃｈａｒｄｓ增长曲线一个很好的解析表达式,它使得Ｌｏｇｉｓｔｉｃ增长曲线、Ｇｏｍｐｅｒｔｚ增长曲线与Ｒｉｃｈａｒｄｓ增长曲线之间的关系清晰了,提示了著名的Ｌｏｇｉｓｔｉｃ增长曲线与Ｇｏｍｐｅｒｔｚ增长曲线是Ｒｉｃｈａｒｄｓ增长曲线的特殊情形,而且还给出了Ｒｉｃｈａｒｄｓ增长曲线一些很好的特性。     

Dietary restriction of rodents decreases aging rate without affecting initial mortality rate – a meta‐analysis

Dietary restriction (DR) extends lifespan in multiple species from various taxa. This effect can arise via two distinct but not mutually exclusive ways: a change in aging rate and/or vulnerability to the aging process (i.e. initial mortality rate). When DR affects vulnerability, this lowers mortality instantly, whereas a change in aging rate will gradually lower mortality risk over time. Unraveling how DR extends lifespan is of interest because it may guide toward understanding the mechanism(s) mediating lifespan extension and also has practical implications for the application of DR. We reanalyzed published survival data from 82 pairs of survival curves from DR experiments in rats and mice by fitting Gompertz and also Gompertz–Makeham models. The addition of the Makeham parameter has been reported to improve the estimation of Gompertz parameters. Both models separate initial mortality rate (vulnerability) from an age‐dependent increase in mortality (aging rate). We subjected the obtained Gompertz parameters to a meta‐analysis. We find that DR reduced aging rate without affecting vulnerability. The latter contrasts with the conclusion of a recent analysis of a largely overlapping data set, and we show how the earlier finding is due to a statistical artifact. Our analysis indicates that the biology underlying the life‐extending effect of DR in rodents likely involves attenuated accumulation of damage, which contrasts with the acute effect of DR on mortality reported for Drosophila. Moreover, our findings show that the often‐reported correlation between aging rate and vulnerability does not constrain changing aging rate without affecting vulnerability simultaneously.     

Modelling inactivation by aqueous chlorine dioxide of Dothiorella gregaria Sacc. and Fusarium tricinctum (Corda) Sacc. spores inoculated on fresh chestnut kernel

Aims: To model survival curves of Dothiorella gregaria Sacc. and Fusarium tricinctum (Corda) Sacc. spores inoculated on fresh chestnut kernel exposed to aqueous chlorine dioxide (ClO₂). Methods and Results: Spores of two dominant spoilage fungi, D. gregaria and F. tricinctum, were inoculated onto chestnut kernel and treated with ClO₂. The inactivation efficacy of ClO₂ treatment increased with ClO₂ concentration and treatment time. The Weibull model was the best model to describe the ClO₂ survival curves of D. gregaria, while the modified Gompertz model was most appropriate for fitting the survival curves of F. tricinctum. Within the range of ClO₂ concentration from 3 to 7 mg l^?1, the n values in the Weibull model were similar. The b value in the Weibull model and decimal logarithms of the M, B and C values in the modified Gompertz model had linear relationships with ClO₂ concentration. After simplification, these two models still provided acceptable predictions. Conclusion: Applying models for describing survival curves of fungal spores on chestnut kernel by aqueous ClO₂ was feasible. Significance and Impact of the Study: This work would promote the application of ClO₂ sanitizing technique and mathematical models when preventing the occurrence of chestnut kernel decay.     

Inferring the effect of therapy on tumors showing stochastic Gompertzian growth

The present work deals with a Gompertz-type diffusion process, which includes in the drift term a time-dependent function C(t) representing the effect of a therapy able to modify the dynamics of the underlying process. However, in experimental studies is not immediate to deduce the functional form of C(t) from a treatment protocol. So a statistical approach is proposed in order to estimate this function when a control group and one or more treated groups are observed. In order to validate the proposed strategy a simulation study for several interesting functional forms of C(t) has been carried out. Finally, an application to infer the net effect of cisplatin and doxorubicin+cyclophosphamide in actual murine models is presented.     

Modelling cacao pod growth: implications for disease control

Cacao trees are affected by diseases that attack either their vegetative parts, their fruits or both. In cacao pod diseases, several factors are involved in disease susceptibility, such as the fruiting cycle, fruit size, age, position on the tree and cacao genotype. To gain a clearer understanding of how these characteristics influence cacao pod diseases, four models describing pod growth in several cacao genotypes were evaluated. Three models used to estimate pod volume or surface area were also compared. Observed pod growth was of a sigmoid form and fitted best to the Richards model, well to the Logistic and Beta growth models, and least to the Gompertz model. Pod volume and probably pod surface area were best estimated using a prolate spheroid model. Pod growth models can help improve pod disease management and thereby cacao production. They can help to predict yield, as well as provide information for the timing and frequency of control operations. Information on pod size, surface area and susceptibility will help to improve dose transfer and spray deposit studies intended to optimise control efficiency.     

A stochastic model in tumor growth

A stochastic model of solid tumor growth based on deterministic Gompertz law is presented. Tumor cells evolution is described by a one-dimensional diffusion process limited by two absorbing boundaries representing healing threshold and patient death (carrying capacity), respectively. Via a numerical approach the first exit time problem is analysed for the process inside the region restricted by the boundaries. The proposed model is also implemented to simulate the effects of a time-dependent therapy. Finally, some numerical results are obtained for the specific case of a parathyroid tumor.     

Parallel lines: nothing has changed?

The exponential increase in mortality rate with age is a universal feature of aging and is described mathematically by the Gompertz equation. When this equation is transformed semilogarithmically, it conforms to a straight line, the slope of which is generally used to reflect the rate of senescence. Historical and contemporary data of human and nonhuman populations show that adverse environmental conditions do not always change the slope of the log mortality rate over age. From these latter observations it is sometimes mistakenly inferred that the rate of senescence is unaffected by environmental conditions. Current biological inference emphasizes that gene action is dependent on the environment in which it is expressed. Here, we propose using the tangent line of the Gompertz equation to assess whether the rate of senescence has altered. Such an approach unmasks different rates of senescence when parameter G has remained constant, an observation that is in line with the notion that a plastic life history trait such as the rate of senescence results from the interplay of both genes and environment.     

Many lifetime growth trajectories for a single mammal

Despite their importance in shaping life history tactics and population dynamics, individual growth trajectories have only been rarely explored in the wild because their analysis requires multiple measurements of individuals throughout their lifetime and some knowledge of age, a key timer of body growth. The availability of long‐term longitudinal studies of two wild boar populations subjected to contrasting environments (rich vs. poor) provided an opportunity to analyze individual growth trajectories. We quantified wild boar growth trajectories at both the population and the individual levels using standard growth models (i.e., Gompertz, logistic, and monomolecular models) that encompass the expected range of growth shapes in determinate growers. Wild boar is a rather altricial species, with a polygynous mating system and is strongly sexually dimorphic in size. According to current theories of life history evolution, we thus expect wild boar to display a sex‐specific Gompertz type growth trajectory and lower sexual size dimorphism in the poorer environment. While wild boar displayed the expected Gompertz type trajectory in the rich site at the population level, we found some evidence for potential differences in growth shapes between populations and individuals. Asymptotic body mass, growth rate and timing of maximum growth rate differed as well, which indicates a high flexibility of growth in wild boar. We also found a cohort effect on asymptotic body mass, which suggests that environmental conditions early in life shape body mass at adulthood in this species. Our findings demonstrate that body growth trajectories in wild boar are highly diverse in relation to differences of environmental context, sex and year of birth. Whether the intermediate ranking of wild boar along the precocial–altricial continuum of development at birth may explain the ability of this species to exhibit this high diversity of growth patterns remains to be investigated.