一种非均匀分簇的路由算法

在对经典的分簇路由算法进行分析的基础上,以延长网络生存时间为宗旨,从节点入簇、孤立节点的处理和簇间传输等方面进行设计,提出了一种非均匀分簇的路由算法。与EEUC和UCRA算法相比,该算法的节点能量利用率更高,有效延长了网络生存时间。     

The Timing of Household Events and Housing Events in the Netherlands: A Longitudinal Perspective

Research on the relationship between household events and housing events so far has largely ignored the role of timing. This study aims to uncover in what way the postponement of marriage and childbirth that took place in the second half of the 20th century in the Netherlands affected the timing of moving into 'long-stay housing' (single-family dwellings and owner occupied dwellings). This is done by analysing time lags between household events and housing events. Survival analysis shows that over cohorts, moving into long-stay housing happens consistently earlier, and increasingly frequently before first childbirth. This finding is most likely attributable to the increased economic prosperity and increased availability of long-stay housing. This allows young people to adjust their housing to the household situation they anticipate, rather than to wait until they actually experience the household event. However, this does not hold for single home leavers: they move into long-stay housing neither earlier, nor much more often over time. It is concluded that the level of commitment in the household situation is the fundamental explanation for housing choice, and that economic prosperity mainly facilitates advancement in the timing of adapting the housing situation to the (anticipated) household situation.     

The growth of Propionibacterium cyclohexanicum in fruit juices and its survival following elevated temperature treatments

This study investigated the growth of Propionibacterium cyclohexanicum in orange juice over a temperature range from 4 to 40 degrees C and its ability to multiply in tomato, grapefruit, apple, pineapple and cranberry juices at 30 and 35 degrees C. Survival after 10 min exposure to 50, 60, 70, 80, 85, 90 and 95 degrees C in culture medium and in orange juice was also assessed. In orange juice the organism was able to multiply by 2 logs at temperatures from 4 to 35 degrees C and survived for up to 52 days. However, at 40 degrees C viable counts were reduced after 6 days and no viable cells isolated after 17 days. The optimum growth temperature in orange juice over 6 days was 25 degrees C but over 4 days it was 35 degrees C. The growth of P. cyclohexanicum was monitored in tomato, grapefruit, cranberry, pineapple and apple juices at 30 and 35 degrees C over 29 days. Cranberry, grapefruit and apple juice did not support the growth of P. cyclohexanicum. At 30 degrees C no viable cells were detected after 8 days in cranberry juice or after 22 days in grapefruit juice while at 35 degrees C no viable cells were detected after 5 and 15 days, respectively. However, in apple juice, although a 5 log reduction occurred, viable cells could be detected after 29 days. P. cyclohexanicum was able to multiply in both tomato and pineapple juices. In tomato juice, there was a 2 log increase in viable counts after 8 days at 30 degrees C but no increase at 35 degrees C, while in pineapple juice there was a 1 log increase in numbers over 29 days with no significant difference between numbers of viable cells present at 30 and 35 degrees C. The organism survived at 50 degrees C for 10 min in culture medium without a significant loss of viability while similar treatment at 60, 70 and 80 degrees C resulted in approximately a 3-4 log reduction, with no viable cells detected after treatment at 85 or 90 or 95 degrees C but, when pre-treated at intermediate temperatures before exposure to higher temperatures, some cells survived. However, in orange juice a proportion of cells survived at 95 degrees C for 10 min without pre-treatment and there was no significant difference between numbers surviving with and without pre-treatment. The results from this study demonstrate that P. cyclohexanicum is able to grow in a number of juices, other than orange juice, and able to survive a number of high temperature procedures. Therefore, if initially present in the raw materials P. cyclohexanicum might survive the pasteurization procedures used in the fruit juice industry, contaminate and consequently spoil the final product.     

The influence of attachment to beef surfaces on the survival of cells of Salmonella enterica serovar Typhimurium DT104, at different a(w) values and at low storage temperatures

This study investigated the influence of attachment to beef surfaces on the survival, injury and death of stationary phase cells of Salmonella enterica serovar Typhimurium DT104, compared to cells free in solution. The effects on cells are considered at different a(w) values and low temperatures in relation to osmotic and cold temperature shock effects. Attachment of cells to meat surfaces prevented cell injury and death from hyperosmosis and low temperatures, compared to meat solutions. Storage of cells for 72h resulted in higher levels of cell death on cells attached to meat surfaces. The improved survival of cells in solutions was considered to be related to adaptation to osmotic stress as a result of exposure to a previous hyperosmotic shock and the ability of the cells to produce cold shock proteins. Pathogen cell growth at low temperatures is discussed in relation to the presence of low levels of NaCl. Finally the data is discussed in relation to pathogen survival on beef carcass surfaces during refrigeration.     

Evaluating multiple reliability indices of regional networks in wide area measurement system

The paper presents a hierarchical structure of Wide Area Measurement System (WAMS) that can satisfy requirements of reliable real-time data transfer. The methods of calculating multiple reliability indices of WAMS regional networks in the protection and recovery survival mechanisms are developed and an equivalent two-state model of a WAMS regional network is presented. The numerical results of an example indicate that the meshed WAMS regional network can provide a very high reliability level. The reliability of the regional network can be enhanced by selecting an appropriate location of Phasor Data Center (PDC) or by improving availability of crucial optic fiber links in the protection mechanism. In the dynamic recovery mechanism, however, these measures may not be effective and thus the key consideration should be put on how to timely restore data transfers after a communication contingency.     

Hazard based models for freeway traffic incident duration

Assessing and prioritising cost-effective strategies to mitigate the impacts of traffic incidents and accidents on non-recurrent congestion on major roads represents a significant challenge for road network managers. This research examines the influence of numerous factors associated with incidents of various types on their duration. It presents a comprehensive traffic incident data mining and analysis by developing an incident duration model based on twelve months of incident data obtained from the Australian freeway network. Parametric accelerated failure time (AFT) survival models of incident duration were developed, including log-logistic, lognormal, and Weibul—considering both fixed and random parameters, as well as a Weibull model with gamma heterogeneity. The Weibull AFT models with random parameters were appropriate for modelling incident duration arising from crashes and hazards. A Weibull model with gamma heterogeneity was most suitable for modelling incident duration of stationary vehicles. Significant variables affecting incident duration include characteristics of the incidents (severity, type, towing requirements, etc.), and location, time of day, and traffic characteristics of the incident. Moreover, the findings reveal no significant effects of infrastructure and weather on incident duration. A significant and unique contribution of this paper is that the durations of each type of incident are uniquely different and respond to different factors. The results of this study are useful for traffic incident management agencies to implement strategies to reduce incident duration, leading to reduced congestion, secondary incidents, and the associated human and economic losses.     

An application of nonparametric censored-data analysis to certain electrochemical observations

If a physical component or a device, employed in a process fails at a certain time instant T⁺, but due to an event unrelated to the evolution of the process, or its mechanism, the observed survival time is called censored. Since the true survival time T might have been found to be any time instant T > T⁺, had the process-independent event not occurred, analysis is different from purely uncensored-data analysis. The subject matter is numerically treated for an electrochemical system by estimating its survival function, and by two-sample observation sets of cathode failure in comparing tank-flow to tubular-flow electrolyzer performance.     

Modelling of growth, growth/no-growth interface and nonthermal inactivation areas of Listeria in foods

Growth, growth boundary and inactivation models have been extensively developed in predictive microbiology and are commonly applied in food research nowadays. Few studies though report the development of models which encompass all three areas together. A tiered modelling approach, based on the Gamma hypothesis, is proposed here to predict the behaviour of Listeria.Datasets of Listeria spp. behaviour in laboratory media, meat, dairy, seafood products and vegetables were collected from literature, unpublished sources and from the databases ComBase and Sym'Previus. The explanatory factors were temperature, pH, water activity, lactic and sorbic acids. For the growth part, 697 growth kinetic datasets were fitted. The estimated growth rates and 2021 additional growth primary datasets were used to fit the secondary growth models. In a second step, the fitted model was used to predict the growth/no-growth boundary. For the inactivation modelling phase, 535 inactivation curves were used.Gamma models with and without interactions between the explanatory factors were used for the growth and boundary models. The correct prediction percentage (predicted growth when growth is observed + predicted inactivation when inactivation is observed) varied from 62% to 81% for the models without interactions, and from 85% to 87% for the models with interactions. The median error for the predicted population size was less than 0.34 log₁₀(CFU/mL) for all models. The kinetics of inactivation were fitted with modified Weibull primary models and the estimated bacterial resistance was then modelled as a function of the explanatory factors. The error for the predicted microbial population size was less than 0.71 log₁₀(CFU/mL) with a median value of less than 0.21 for all foods.The model enables the quantification of the increase or decrease in the bacterial population for a given formulation or storage condition. It might also be used to optimise a food formulation or storage condition in the case of a targeted increase or decrease of the bacterial population.     

The first dairy product exclusively fermented by Propionibacterium freudenreichii: A new vector to study probiotic potentialities in vivo

Dairy propionibacteria display probiotic properties which require high populations of live and metabolically active propionibacteria in the colon. In this context, the probiotic vector determines probiotic efficiency. Fermented dairy products protect propionibacteria against digestive stresses and generally contain a complex mixture of lactic and propionic acid bacteria. This does not allow the identification of dairy propionibacteria specific beneficial effects. The aim of this study was to develop a dairy product exclusively fermented by dairy propionibacteria. As they grow poorly in milk, we determined their nutritional requirements concerning carbon and nitrogen by supplementing milk ultrafiltrate (UF) with different concentrations of lactate and casein hydrolysate. Milk or UF supplemented with 50 mM lactate and 5 g L⁻¹ casein hydrolysate allowed growth of all dairy propionibacteria studied. In these new fermented dairy products, dairy propionibacteria remained viable and stress-tolerant in vitro during minimum 15 days at 4 °C. The efficiency of milk fermented by the most tolerant Propionibacterium freudenreichii strain was evaluated in piglets. Viability and SCFA content in the colon evidenced survival and metabolic activity of P. freudenreichii. This work results in the design of a new food grade vector, which will allow preclinical and clinical trials.     

Arginine metabolism in sugar deprived Lactococcus lactis enhances survival and cellular activity, while supporting flavour production

Flavour development in cheese is affected by the integrity of Lactococcus lactis cells. Disintegrated cells enhance for instance the enzymatic degradation of casein to free amino acids, while integer cells are needed to produce specific flavour compounds from amino acids. The impact of the cellular activity of these integer cells on flavour production remains to be elucidated. In this study we investigated whether lactose-deprived L. lactis cells that use arginine as an alternative energy source can extend cellular activity and produce more specific flavours. In cheese experiments we demonstrated that arginine metabolising cells survived about 3 times longer than non-arginine metabolising cells, which suggests prolonged cellular activity. Cellular activity and flavour production of L. lactis was further studied in vitro to enable controlled arginine supplementation. Comparable with the results found in cheese, the survival rates of in vitro incubated cells improved when arginine was metabolised. Furthermore, elongated cellular activity was reflected in 3-4-fold increased activity of flavour generating enzymes. The observed prolonged cellular activity resulted in about 2-fold higher concentrations of typical Gouda cheese flavours. These findings provide new leads for composing starter cultures that will produce specific flavour compounds.