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.     

Democracy in Arts Development 1

Too often in the arts, projects are undertaken without clear‐cut aims and ways of assessing whether these aims are accomplished. With regard to “Art for Social Change” projects, it is not difficult to identify activities that might be labelled “dishonest”, “ill‐conceived” or even “unethical”. It is argued here that it is possible, and necessary, to set clear aims, and also to devise effective assessment strategies. It is essential for artists to embrace evaluation in order to help them improve and better understand their work.

     

Outlier detection based on extreme value theory and applications

Whether an extreme observation is an outlier or not depends strongly on the corresponding tail behavior of the underlying distribution. We develop an automatic, data-driven method rooted in the mathematical theory of extremes to identify observations that deviate from the intermediate and central characteristics. The proposed algorithm is an extension of a method previously proposed in the literature for the specific case of heavy tailed Pareto-type distributions to all max-domains of attraction. We propose some applications such as a tail-adjusted boxplot which yields a more accurate representation of possible outliers, and the identification of outliers in a multivariate context through an analysis of associated random variables such as local outlier factors. Several examples and simulation results illustrate the finite sample behavior of the algorithm and its applications.     

From waterfall plots to spaghetti plots in early oncology clinical development

Waterfall plots are used to describe changes in tumor size observed in clinical studies. They are frequently used to illustrate the overall drug response in oncology clinical trials because of its simple representation of results. Unfortunately, this visual display suffers a number of limitations including (1) potential misguidance by masking the time dynamics of tumor size, (2) ambiguous labelling of the y‐axis, and (3) low data‐to‐ink ratio. We offer some alternatives to address these shortcomings and recommend moving away from waterfall plots to the benefit of plots showing the individual time profiles of sum of lesion diameters (according to RECIST). The spider plot presents the individual changes in tumor measurements over time relative to baseline tumor burden. Baseline tumor size is a well‐known confounding factor of drug effect which has to be accounted for when analyzing data in early clinical trials. While spider plots are conveniently correct for baseline tumor size, they cannot be presented in isolation. Indeed, percentage change from baseline has suboptimal statistical properties (including skewed distribution) and can be overly optimistic in favor of drug efficacy. We argued that plots of raw data (referred to as spaghetti plots) should always accompany spider plots to provide an equipoised illustration of the drug effect on lesion diameters.     

Risk Assessment of Listeria monocytogenes: Impact of Individual Cell Variability on the Exposure Assessment Step

Recently, the lag phase research in predictive microbiology is focusing more on the individual cell variability, especially for pathogenic microorganisms that typically occur in very low contamination levels, like Listeria monocytogenes. In this study, the effect of this individual cell lag phase variability was introduced in an exposure assessment study for L. monocytogenes in a liver paté. A basic framework was designed to estimate the contamination level of paté at the time of consumption, taking into account the frequency of contamination and the initial contamination levels of paté at retail. Growth was calculated on paté units of 150 g, comparing an individual-based approach with a classical population-based approach. The two different protocols were compared using simulations. If only the individual cell lag variability was taken into account, important differences were observed in cell density at the time of consumption between the individual-based approach and the classical approach, especially at low inoculum levels, resulting in high variability when using the individual-based approach. Although, when all variable factors were taken into account, no significant differences were observed between the different approaches, allowing the conclusion that the individual cell lag phase variability was overruled by the global variability of the exposure assessment framework. Even in more extreme conditions like a low inoculum level or a low water activity, no differences were created in cell density at the time of consumption between the individual-based approach and the classical approach. This means that the individual cell lag phase variability of L. monocytogenes has important consequences when studying specific growth cases, especially when the applied inoculum levels are low, but when performing more general exposure assessment studies, the variability between the individual cell lag phases is too limited to have a major impact on the total exposure assessment.     

Common ground: cultural action as a route to community development

Cultural action has been used to promote community developmentfor at least thirty years in the UK, often with good results.During that period, the theories, values, and approaches ofprofessionals have varied and evolved, but there has been anoticeable shift in focus – particularly in cultural policy– from collective to individual outcomes, in line withthe growing individualization of policy since the 1980s. Yetthe potential of cultural action to bring people together andto build a foundation for lasting community development workremains important. This article considers the processes by whicharts-based community projects can lead to the development ofboth informal and formal collective organization, and theirpotential in empowerment. Central to this process, it is argued,is culture's focus on people's strengths and interests, ratherthan on externally defined problems. The paper draws on twocontrasting examples to demonstrate the continuing importanceof cultural action in very different social and economic situations:the author's research into voluntary arts development in ruralEngland and Wales, and his experience of community culturalprojects in south-east Europe.     

Regularized Gaussian belief propagation

Belief propagation (BP) has been applied in a variety of inference problems as an approximation tool. BP does not necessarily converge in loopy graphs, and even if it does, is not guaranteed to provide exact inference. Even so, BP is useful in many applications due to its computational tractability. In this article, we investigate a regularized BP scheme by focusing on loopy Markov graphs (MGs) induced by a multivariate Gaussian distribution in canonical form. There is a rich literature surrounding BP on Gaussian MGs (labelled Gaussian belief propagation or GaBP), and this is known to experience the same problems as general BP on graphs. GaBP is known to provide the correct marginal means if it converges (this is not guaranteed), but it does not provide the exact marginal precisions. We show that our adjusted BP will always converge, with sufficient tuning, while maintaining the exact marginal means. As a further contribution we show, in an empirical study, that our GaBP variant can accelerate GaBP and compares well with other GaBP-type competitors in terms of convergence speed and accuracy of approximate marginal precisions. These improvements suggest that the principle of regularized BP should be investigated in other inference problems. The selection of the degree of regularization is addressed through the use of two heuristics. A by-product of GaBP is that it can be used to solve linear systems of equations; the same is true for our variant and we make an empirical comparison with the conjugate gradient method.     

Accuracy of the judgment of facial expression of emotions as a function of sex and level of education

The purpose of this study is to examine the recognition of facial expressions of six emotions as a function of sex and level of education (high school, college, university) of the subjects. Three hundred French-speaking citizens of Quebec had to judge which emotion was expressed in various facial stimuli presented on slides. Results show that overall, the recognition of emotions was very good. However, there were significant and strong differences between emotions and sex and levels of education did not have strong effects on the results.This research was supported by grant EQ-1717 from Fonds FCAC (Gouvernment du Quebec).     

Old friends and new acquaintances: Tie formation mechanisms in an interorganizational network generated by employee mobility

This study investigates mechanisms of tie formation in an interorganizational network generated by the mobility of employees between organizations. We analyze a data set that contains information on all organizations in the Stockholm metropolitan area between 1990 and 2003. We show that the formation of new ties is contingent upon the direction of past ties, and that most connections occur at an intermediate geodesic distance of 2 and 3. The findings highlight the importance of tie direction and indirect connections in research on network dynamics and knowledge exchanges stemming from the mobility of employees across organizations.     

Grief and Trauma Group Therapy for Children After Hurricane Katrina

Theoretical and evidence-based group therapy models that address the interplay of grief and trauma are needed for children postdisaster. This article describes a theoretically informed 10-week grief and trauma group model that was evaluated with children in schools after Hurricane Katrina. The foundation of the grief and trauma intervention includes utilizing developmentally specific methods, an ecological perspective, and culturally relevant approaches. The theoretical ordering of themes addressed occurs within three overlapping phases: (1) resilience and safety, (2) restorative retelling, (3) and reconnecting (Herman, 1997 Herman, J. L. 1997. Trauma and recovery, New York: Basic Books.  [Google Scholar]; Rynearson, 2001 Rynearson, R. 2001. Retelling violent death, Philadelphia: Brunner-Routledge.  [Google Scholar]). Techniques from cognitive behavioral therapy and narrative therapy are combined to address loss and trauma.