Modeling Individual Cell Lag Time Distributions for Listeria monocytogenes

The food industry faces two paradoxical demands: on the one hand, foods need to be microbiologically safe for consumption and on the other hand, consumers want fresh, minimally processed foods. To meet these demands, more insight into the mechanisms of microbial growth is needed, which includes, among others, the microbial lag phase. This is the time needed by bacterial cells to adapt to a new environment (for example, after food product contamination) before starting an exponential growth regime. Since food products are often contaminated with low amounts of pathogenic microorganisms, it is important to know the distribution of these individual cell lag times to make accurate predictions concerning food safety. More precisely, cells with the shortest lag times (i.e., appearing in the left tail of the distribution) are largely decisive for the outgrowth of the population. In this study, an integrated modeling approach is proposed and applied to an existing data set of individual cell lag time measurements of Listeria monocytogenes. In a first step, a logistic modeling approach is applied to predict the fraction of zero-lag cells (which start growing immediately) as a function of temperature, pH, and water activity. For the nonzero-lag cells, the mean and variance of the lag time distribution are modeled with a hyperbolic-type model structure. This mean and variance allow identification of the parameters of a two-parameter Weibull distribution, representing the nonzero-lag cell lag time distribution. The integration of the developed models allows prediction of a global distribution of individual cell lag times for any combination of environmental conditions in the interpolation domain of the original temperature, pH, and water activity settings. The global fitting quality of the model is quantified using several measures indicating that the model gives accurate predictions, erring slightly on the fail-safe side when predicting the shortest lag times.     

Benefit dependency: The pros and cons of using “caseload” data for national and international comparisons

Policy‐makers in advanced welfare states have increasingly expressed concerns over large numbers of working‐age people claiming social security support. Accordingly, policies aimed at reducing the level of “benefit dependency” have gained prominence. However, such policies rest on shaky empirical evidence. Systematic collections of national “caseload” data are rare, social security programmes overlap and administrative categories vary over time. The internationally inconsistent treatment of national transfer programmes provides a further challenge for cross‐national comparisons. This article first identifies and discusses several of these problems, and ways in which they may be addressed. It then employs administrative claimant data from six European countries as a way of illustrating trends over time and across countries. The underlying aim is to explore the scientific potential of benefit recipient numbers as an indicator for welfare state change over time and across countries.     

The state and use of municipal tree inventories in Swedish municipalities – results from a national survey

Urban trees are an essential component of urban ecosystems, and management of this resource constitutes an essential element of urban open space management. However, municipal tree inventories in Sweden and elsewhere have received limited attention. It is unknown how common municipal tree inventories are in Sweden, factors governing whether a municipality has an inventory and what the inventories are used for. This study therefore sought to: Create an overview of the state of Swedish municipal tree inventories and determine how municipality size, green space budget and management organisation affect the presence and scope of municipal tree inventories. The research questions examined were: What is the current state of Swedish municipal tree inventories? and what affects the status of these municipal tree inventories? A survey with questions related to strategic and operational perspectives of municipal tree inventories, e.g. how they are conducted and used, together with questions relating to budget and potential use of consultants, was sent to all 290 Swedish municipalities. The response rate was 55.5%. The main findings were that municipality size affects whether a municipality has an urban tree inventory and that the municipal organisation form affects how inventories are used. The existence of an inventory also increased the probability of the municipality having a tree management plan. Based on these results we recommend further research related to strategic management perspectives of tree inventories.     

Effects of ground surface permeability on the growth of urban linden trees

Street trees are an important part of urban vegetation due to their provisioning of different types of ecosystem services such as local climate regulation and contribution to aesthetical and recreational values. In order to provide these services, urban trees need to endure many stress factors not present in natural environments, such as the widespread use of impervious surfaces in the vicinity of street trees. However, few studies have evaluated the effect of this potential stress factor on urban tree growth. The aim of this study was therefore to investigate how ground surface permeability affects stem and current-year shoot growth of linden (Tilia europaea) street trees in Gothenburg, Sweden. We found that a small fraction of permeable ground surface in the vertically projected tree crown area caused lower stem growth and strongly suppressed current-year shoot growth. This finding can guide future city planning, demonstrating that the vitality of street trees is compromised when the permeable surface area in the vicinity of the tree is small.     

Consequences of governance restructuring for quality of urban living in the transformation era in Beijing: A view of job accessibility

One of the major issues concerning present-day public policy in a transitional and developing country is its ability to enhance the quality of urban living and individual social well-being in the context of rapid urban growth. A dramatic decline in overall job accessibility due to increases in commuting time is already a serious problem affecting the quality of urban living in Beijing. Understanding the impact of governance restructuring on overall job accessibility is of primary importance if politicians are to make policy innovations in development management. This paper applies the institutionalist approach to analyse the impact of governance restructuring on job accessibility. The analysis shows that current governance restructuring has a negative effect on overall job accessibility due to competition between different local governments increasing the degree of spatial fragmentation; revenue-enhancing development introducing constraints affecting the local jobs-housing balance; and the coexistence of the old planning system alongside the new market system leading to a fragmented land-use right transfer mechanism, intensifying scattered and low-density development. With respect to future policy, stronger municipal development management might be one direction in implementing public policy to enhance overall job accessibility, insofar as it addresses the negative impact of fragmented development management in the current transformation process.     

Building successful strategic alliances

In this paper we will discuss (1) why a firm would want to go into a strategic alliance, (2) the different types of alliance, and (3) guidelines to follow when forming an alliance.