增长区域上斑图形成的自由边界问题

研究一个在增长区域上斑图形成的自由边界问题,首先利用不动点定理证明解的局部存在性,然后通过扰动分析方法得到斑图形成的参数条件,区域指一块生物组织,该组织由活的细胞组成．细胞的再生和死亡引起细胞间局部压力的变化,从而产生了一个细胞速度场,推动区域的增长．细胞的再生和死亡由2种化学物质决定,区域的增长影响这2种化学物质的空间分布．反过来,这2种化学物质的空间不均匀分布也会影响区域增长．生物斑图的形成由这2种化学物质的空间不均匀分布引起．     

Time from dosage to death in beetles, Tribolium castaneum, treated with pyrethrins or DDT,and its bearing on dose-mortality relations

Times from dosage to death were studied in adult beetles, Tribolium castaneum (Herbst), sprayed with pyrethrins or DDT in Risella 17 oil. Preliminary experiments with pyrethrins showed that if beetles were unfed, the usual method for correcting for control mortality was unsuitable. Hence in the main experiments all beetles were given access to food, eliminating control mortality, and further measures were taken to ensure that stable levels of mortality were finally reached in sprayed groups.Time operated as a time for response (not a dose factor). The statistical distributions of times to death due to insecticide were skewed to the right, but less so than if log-normal, and were normalized by power transformations. The main conclusion was that there was no evidence that dose influenced the mean or spread of the distribution. A specially designed experiment with pyrethrins indicated that this was not due to a combination of two opposing (hypothetical) effects, namely decreasing time to death with increasing dose above individual tolerance, and increasing time to death with increasing individual tolerance at fixed dose. In one experiment with pyrethrins, the mean transformed time to death was significantly greater for females than for males. Estimates of median times to death for the set of experiments ranged from 2·67 to 3·25 days. Those for pyrethrins and DDT were much the same. As judged by probit analysis of end-point mortalities, female beetles were about 1·3 and 1·6 times as tolerant as males to pyrethrins and DDT respectively.It is pointed out that when the distribution of time to death is not influenced by dose, only at one time after dosage up to or at end-point can probit mortality logically be taken as linear in log-dose. At other times of observation, the relation must be taken as curvilinear, in order to avoid the contradiction of assuming a percentage mortality falling with increasing period from dosage. Diagrams given illustrate this. Further statistical methods need to be developed for analysing in a fully satisfactory manner data relating mortality to dose and time for response.     

射频场内孔分散结构对物料温度分布及其杀虫效果的影响

为解决射频杀虫时加热不均匀而导致杀虫不彻底的问题,从孔方向、空实心、孔数量、孔径和分布方式方面研究孔分散结构在提升射频加热速率和加热均匀性方面的作用以及在杀虫方面的应用.以大米为材料,试验发现在促进加热效果上竖向分散结构优于横向,空心优于实心.当孔径相同时,孔数量越多效果越好.当孔数量相同时,孔径越大效果越好.等距分布...     

Determination of amatoxins in different tissues and development stages of Amanita exitialis

BACKGROUND: Mushroom poisoning is the main cause of human death by food poisoning in China. Most lethal mushrooms belong to the Amanita genus, whose amatoxins are responsible for the death of humans. Amanita exitialis is a lethal white mushroom commonly found in Guangdong Province, China. In this study the contents and distribution of the major amatoxins in different tissues and development stages of A. exitialis were systematically analysed. RESULTS: The amatoxin contents and distribution in six different mushroom tissues of A. exitialis were analysed by reverse phase high‐performance liquid chromatography. The highest concentrations of amatoxins were found in the gills and pileus, followed by the stipe and annulus, with the lowest concentrations in the volva and spores. Further analysis of mushrooms in different development stages showed that the amatoxin content was relatively high and steady during early development, reached its peak when the fruit body was in the vigorous growth stage and then decreased sharply when the mushroom entered its mature stage. Furthermore, the α‐amanitin/β‐amanitin ratio varied significantly in different tissues but remained constant within a specific tissue throughout development. CONCLUSION: The contents and distribution of amatoxins in different tissues and development stages of A. exitialis are markedly different. The distribution of α‐amanitin and β‐amanitin varies in different tissues but remains constant throughout development. Copyright © 2012 Society of Chemical Industry     

Mathematical modelling and numerical simulation of phosphine flow during grain fumigation in leaky cylindrical silos

The phosphine distribution in a cylindrical silo containing grain is predicted. A three-dimensional mathematical model, which accounts for multicomponent gas phase transport and the sorption of phosphine into the grain kernel is developed. In addition, a simple model is presented to describe the death of insects within the grain as a function of their exposure to phosphine gas. The proposed model is solved using the commercially available computational fluid dynamics (CFD) software, FLUENT, together with our own C code to customize the solver in order to incorporate the models for sorption and insect extinction. Two types of fumigation delivery are studied, namely, fan-forced from the base of the silo and tablet from the top of the silo. An analysis of the predicted phosphine distribution shows that during fan forced fumigation, the position of the leaky area is very important to the development of the gas flow field and the phosphine distribution in the silo. If the leak is in the lower section of the silo, insects that exist near the top of the silo may not be eradicated. However, the position of a leak does not affect phosphine distribution during tablet fumigation. For such fumigation in a typical silo configuration, phosphine concentrations remain low near the base of the silo. Furthermore, we find that half-life pressure test readings are not an indicator of phosphine distribution during tablet fumigation.     

具有阶段结构与随机扰动的酗酒模型

研究一类具有阶段结构与随机扰动的酗酒模型,分析饮酒平衡点附近的随机扰动.通过建立Lyapunov函数及应用伊藤公式,证明饮酒平衡点附近的随机全局渐近稳定性.当确定性模型基本再生数R_01,随机模型的解是平均持续的,说明饮酒行为持续存在.另外,饮酒的传播率,自然死亡率及复发率对饮酒平衡点附近的随机全局渐近稳定性起着决定性作用.     

Comparison between the measured and predicted sterilization performance of a laboratory-scale, direct heated UHT plant

The sterilizing efficiency of a small scale direct heating UHT sterilizer has been measured using Bacillus stearothormophilus spores suspended in water and milk. A special technique was used for accurate measurement of the correct concentration of heat resistant spores in the fluid before passage through the sterilizer. The results were compared with the values calculated from the thermal death kinetics of the same spore batch measured in the laboratory, together with the residence time distribution of the liquid in the sterilizer. The two sets of data were found to compare well for a wide range of operating temperatures, confirming that the performance of a continuous sterilizer in practice could be predicted, given accurate information for the spores and the equipment.     

Evaluation of the Weibull and log normal distribution functions as survival models of Escherichia coli under isothermal and non isothermal conditions

Published survival curves of Escherichia coli in two growth media, with and without the presence of salt, at various temperatures and in a Greek eggplant salad having various levels of essential oil, all had a characteristic downward concavity when plotted on semi logarithmic coordinates. Some also exhibited what appeared as a 'shoulder' of considerable length. Regardless of whether a shoulder was noticed, the survival pattern could be considered as a manifestation of an underlying unimodal distribution of the cells' death times. Mathematically, the data could be described equally well by the Weibull and log normal distribution functions, which had similar modes, means, standard deviations and coefficients of skewness. When plotted in their probability density function (PDF) form, the curves also appeared very similar visually. This enabled us to quantify and compare the effect of temperature or essential oil concentration on the organism's survival in terms of these temporal distributions' characteristics. Increased lethality was generally expressed in a shorter mean and mode, a smaller standard deviation and increased overall symmetry as judged by the distributions' degree of skewness. The 'shoulder', as expected, simply indicated that the distribution's standard deviation was much smaller than its mode. Rate models based on the two distribution functions could be used to predict non isothermal survival patterns. They were derived on the assumption that the momentary inactivation rate is the isothermal rate at the momentary temperature at a time that corresponds to the momentary survival ratio. In this application, however, the Weibullian model with a fixed power was not only simpler and more convenient mathematically than the one based on the log normal distribution, but it also provided more accurate estimates of the dynamic inactivation patterns.     

Dynamics of culling risk with disposal codes reported by Dairy Herd Improvement dairy herds

The objective was to describe the dynamics of culling risk with disposal codes for Holstein dairy cows reported by herds enrolled in the Dairy Herd Improvement program. Dairy producers could report 1 of 9 possible disposal codes or forego reporting a code. After edits, 3,629,002 lactation records were available for cows calving between 2001 and 2006 in 2,054 herds located in 38 states primarily east of the Mississippi river. The distribution of culled cows by disposal code was estimated by parity, days after calving, pregnancy status, cow-relative 305-d mature equivalent milk yield, herd-relative 305-d mature equivalent milk yield, and season. Of all herds, 57% reported all 8 different disposal codes excluding the codes dairy purposes and reason not reported. Hazard (risk) functions were calculated by parity, from 1 to 520 d since calving for open cows and from 1 to 280 d since conception for pregnant cows. Annualized live culling rate and death rate (reported code was death) were 25.1 and 6.6%, respectively. The primary disposal code was died (20.6% of all culling), followed by reproduction (17.7%), injury/other (14.3%), and low production and mastitis (both 12.1%). The risk of culling with various disposal codes varied with stage of lactation. Died and reproduction were the most frequently reported codes for cows leaving the herd during early and late lactation, respectively. Early lactation was also a critical period for culling with the disposal codes injury/other and disease, and the risk increased with days after calving for the codes low production and reproduction. The risk of culling with the disposal code died showed the greatest seasonal pattern with increased risk of death in spring and summer. A negative association was found between annualized live culling and death rates within herds. Compared with open cows, pregnant cows had a lower risk of culling with all reported disposal codes. In addition, the risk of culling was lower in high-producing cows with all disposal codes. In conclusion, the risk for culling by disposal code varied by parity, stage of lactation, season, pregnancy status, and milk yield.     

Microbial survival curves — the reality of flat “shoulders” and absolute thermal death times

Occasionally, experimental survival curves of micro-organisms exposed to a lethal agent have a flat region and traditionally it has been interpreted as evidence of the existence of a “shoulder”. However, if the survival curve is considered the cumulative distribution of lethal events, which reflects a spectrum of resistances, or sensitivities, then when the distribution's mean, or mode, is large relative to its spread, a region resembling a “shoulder” will be observed irrespective of whether the distribution is symmetric or skewed. Computer simulated survival curves generated with the Fermi and Weibull distributions as models demonstrate that the shape of the survival curve alone is, therefore, insufficient to confirm any specific inactivation mechanisms at the cellular and molecular level, although it can refute the existence of some. Microbial mortality has also been assumed to be a process following an exponential decay and hence that a certain degree of survival is inevitable. It is not inconceivable, however, that there can be an absolute thermal death time if the survivors are being progressively weakened by a prolonged exposure to the lethal agent. This testable possibility is demonstrated with simulated survival curves generated with two mathematical models.     

Predictive Models for the Survival/death of Campylobacter jejuni and Salmonella Typhimurium in Poultry Scalding and Chilling

ABSTRACT: Predictive models for the survival/death of Campylobacter jejuni and Salmonella Typhimurium during poultry scalding and chilling, as functions of temperature (50 to 60 °C), chlorine level (0 to 50 ppm) and water age (0, 10 h for scalding; 0, 8 h for chilling), were evaluated and developed using the data from previous study. As primary models, the Weibull distribution, exponential, logistic, and Gompertz models were compared. The secondary models were developed by modifying the Davey and polynomial models. Mean Square Errors ( MSE ) and the plots of predicted in contrast to observed survivors showed a good fit and prediction. The Weibull distribution-based secondary model was selected due to its fewer parameters and better prediction ( MSE s < 0.4) compared to the other models.     

Proposed dairy calf birth certificate data and death loss categorization scheme

The majority of dairy heifer calves in the United States are destined to be dairy replacements. However, many dairy heifer and bull calves die before 6 mo of age. Of these calves, about 6% (more than 500,000 calves) die at birth or shortly after (i.e., currently termed “stillbirth”). An additional 6% of dairy heifers die during the preweaning period. Death loss in dairy calves is primarily due to stillbirths, failure to adapt to extrauterine life, and infectious disease processes. The reasons for preweaning heifer calf deaths caused by infectious diseases are generally categorized based on easily recognizable clinical signs such as digestive disease/scours or respiratory disease. Most causes of calf death can be mitigated by appropriate preventive care or well-tailored treatments, meaning that the typical death loss percentage could be decreased with better management. Producers could gather information on the circumstances near birth and at death if they had appropriate guidance on what details to record and monitor. This paper provides recommendations on data to collect at the time of birth (i.e., calf birth certificate data). The recording of these critical pieces of information is valuable in evaluating trends over time in morbidity and mortality events in dairy calves. Ideally, necropsy examination would substantially improve the identification of cause of death, but even without necropsy, attribution of cause of death can be improved by more carefully defining death loss categories in on-farm record systems. We propose a death loss categorization scheme that more clearly delineates causes of death. Recommendations are provided for additional data to be collected at the time of death. Recording and analyzing birth certificate and death loss data will allow producers and veterinarians to better evaluate associations between calf risk factors and death, with the goal of reducing dairy calf mortality.     

The effect of recurrent episodes of clinical mastitis caused by gram-positive and gram-negative bacteria and other organisms on mortality and culling in Holstein dairy cows

The objective of this study was to estimate the effects of recurrent episodes of different types of clinical mastitis (CM) caused by gram-positive (Streptococcus spp., Staphylococcus aureus, Staphylococcus spp.) and gram-negative (Escherichia coli, Klebsiella, Citrobacter, Enterobacter, Pseudomonas) bacteria, and other organisms (Arcanobacterium pyogenes, Mycoplasma, Corynebacterium bovis, yeast, miscellaneous) on the probability of mortality and culling in Holstein dairy cows. Data from 30,233 lactations in cows of 7 dairy farms in New York State were analyzed. Cows were followed for the first 10 mo in lactation, or until death or culling occurred, or until the end of our study period. Generalized linear mixed models with a Poisson error distribution were used to study the effects of recurrent cases of the different types of CM and several other factors (herd, parity, month of lactation, current year and season, profitability, net replacement cost, other diseases) on cows’ probability of death (model 1) or being culled (model 2). Primiparous and multiparous cows were modeled separately because they had different risks of mortality and culling and potentially different CM effects on mortality and culling. Approximately 30% of multiparous cows had at least one case of CM in lactation compared with 16.6% of primiparous cows. Multipara also had higher lactational incidence risks of second (10.7%) and third (4.4%) cases than primipara (3.7% and 1.1%, respectively). For primipara, CM increased the probability of death, with each successive case occurring in a month being increasingly lethal. In multipara, gram-negative CM increased the probability of death, especially when the gram-negative case was the first or second CM case in lactation. Primiparous cows with CM were more likely to be culled after CM than if they did not have CM, particularly after a second or third case. In multipara, any type of CM increased the probability of being culled. Gram-negative CM cases were associated with the numerically highest risk of culling.     

Necropsy as a means to gain additional information about causes of dairy cow deaths

High mortality among dairy cows constitutes a problem both financially and in relation to animal welfare. Knowledge about causes of death is a fundamental step toward reducing cow mortality. Several studies have evaluated causes of dairy cow deaths. However, the vast majority of studies describing causes of death are based on questionnaires with farmers or veterinarians. It is uncertain to what degree such information is sufficient and reflects the true cause of death or euthanasia. In this study, proximate causes of death were evaluated based on a thorough necropsy of a random sample of 79 Danish dairy cows at an incineration plant. The necropsy was combined with information about the farmer’s perception regarding the cause of death and information about disease treatments from the Danish Cattle Database. Pneumonia and locomotor disorders were found to be the most predominant proximate causes of death. Often the death occurred after a prolonged period during which the cow suffered several different disorders, even though this was often not noticed by the farmer. Causes of death stated by the farmers agreed with the necropsy results in 50 to 64% of cases. Information about disease treatments from the Danish Cattle Database agreed with the necropsy results in 34 to 39% of cases. All 3 sources of information about cause of death agreed in only 1 out of 4 cases, and even when the farmer and the disease recordings did agree with the necropsy results, the latter often gave additional information about the cause of death. In many situations, therefore, a necropsy may be a valuable tool when trying to control excessive cow mortality in a herd.     

Heat tolerance of Salmonella enterica serovars Agona, Enteritidis, and Typhimurium in peanut butter

Recent large foodborne outbreaks caused by Salmonella enterica serovars have been associated with consumption of foods with high fat content and reduced water activity, even though their ingredients usually undergo pasteurization. The present study was focused on the heat tolerance of Salmonella enterica serovars Agona, Enteritidis, and Typhimurium in peanut butter. The Salmonella serovars in the peanut butter were resistant to heat, and even at a temperature as high as 90 degrees C only 3.2-log reduction in CFU was observed. The obtained thermal inactivation curves were upwardly concave, indicating rapid death at the beginning (10 min) followed by lower death rates and an asymptotic tail. The curves fitted the nonlinear Weibull model with beta parameters < 1, indicating that the remaining cells have a lower probability of dying. beta at 70 degrees C (0.40 +/- 0.04) was significantly lower than beta at 80 degrees C (0.73 +/- 0.19) and 90 degrees C (0.69 +/- 0.17). Very little decrease in the viable population (less than 2-log decrease) was noted in cultures that were exposed to a second thermal treatment. Peanut butter is a highly concentrated colloidal suspension of lipid and water in a peanut meal phase. We hypothesized that differences in the local environments of the bacteria, with respect to fat content or water activity, explained the observed distribution and high portion of surviving cells (0.1%, independent of the initial cell number). These results demonstrate that thermal treatments are inadequate to consistently destroy Salmonella in highly contaminated peanut butter and that the pasteurization process cannot be improved significantly by longer treatment or higher temperatures.     

Anthocyanin-rich Mulberry extract inhibit the gastric cancer cell growth in vitro and xenograft mice by inducing signals of p38/p53 and c-jun

Anthocyanins have been well characterized by various bioactive properties. In previous studies, Mulberry anthocyanins (MACs) have proven to prevent atherosclerosis and inhibit melanoma metastasis. Here, AGS cells demonstrated an increase in the distribution of hypodiploid phase (apoptotic peak) after treatment with MACs. Further investigation revealed that MACs exerted their influence by inducing intrinsic and extrinsic apoptosis through p38/p53 and p38/c-jun signaling pathways. In addition, the caspase-related protein, such as caspase-3, was activated from pro-caspase to cleaved-caspase by treating MACs to AGS cells. We also used the experimental AGS gastric cancer xenograft model to verify the inhibitory effect of MACs. These findings suggest that, by targeting p38/p53 and the c-jun pathways, MACs suppressed cell survival and tumorigenesis, but induced apoptotic death in AGS cells. MACs can potentially prevent the growth of AGS cells for ineffective conventional chemotherapy of gastric carcinoma.     

畜禽屠宰后肌肉细胞死亡机制研究进展

畜禽宰后肌肉变化为食肉是一个极为复杂的的过程。宰前应激、击晕方式(电击、CO2致晕等)以及宰后放血都会使畜禽肌肉细胞处于极端生存环境(缺氧、ATP消耗、H+积累等)中,不可避免地对细胞代谢产生重大影响,最终导致其死亡。凋亡、坏死、自噬性死亡以及最近提出的凋亡性坏死都是已经阐明的细胞死亡方式。对caspase活性的深入研究结果表明畜禽宰后肌肉细胞死亡可能涉及了凋亡过程。坏死作为一种突发性的非程序化死亡过程,由于具有胞浆中Ca2+升高、ATP快速消耗、线粒体膜通透性增加等特征,可能更适于解释宰后肌肉细胞变化过程。最近凋亡性坏死学说的提出又增加了宰后肌肉细胞死亡机制的复杂性。对畜禽宰后肌肉细胞死亡机制的研究任重而道远。