Slow Coarsening in a Class of Driven Systems

The coarsening process in a class of driven systems is studied. These systems have previously been shown to exhibit phase separation and slow coarsening in one dimension. We consider generalizations of this class of models to higher dimensions. In particular we study a system of three types of particles that diffuse under local conserving dynamics in two dimensions. Arguments and numerical studies are presented indicating that the coarsening process in any number of dimensions is logarithmically slow in time. A key feature of this behavior is that the interfaces separating the various growing domains are smooth (well approximated by a Fermi function). This implies that the coarsening mechanism in one dimension is readily extendible to higher dimensions.Comment: submitted to EPJB, 13 page

Molecular Model of the Contractile Ring

We present a model for the actin contractile ring of adherent animal cells. The model suggests that the actin concentration within the ring and consequently the power that the ring exerts both increase during contraction. We demonstrate the crucial role of actin polymerization and depolymerization throughout cytokinesis, and the dominance of viscous dissipation in the dynamics. The physical origin of two phases in cytokinesis dynamics ("biphasic cytokinesis") follows from a limitation on the actin density. The model is consistent with a wide range of measurements of the midzone of dividing animal cells.Comment: PACS numbers: 87.16.Ka, 87.16.Ac http://www.ncbi.nlm.nih.gov/pubmed/16197254 http://www.weizmann.ac.il/complex/tlusty/papers/PhysRevLett2005.pd

A scalable method for automatically measuring pharyngeal pumping in C. elegans

Background: The nematode Caenorhabditis elegans is widely used for studying small neural circuits underlying behavior. In particular, the rhythmic feeding motions collectively termed pharyngeal pumping are regulated by a nearly autonomous network of 20 neurons of 14 types. Despite much progress achieved through laser ablation, genetics, electrophysiology, and optogenetics, key questions regarding the regulation of pumping remain open. New method: We describe the implementation and application of a scalable automated method for measuring pumping in controlled environments. Our implementation is affordable and flexible: key hardware and software elements can be modified to accommodate different requirements. Results: We demonstrate prolonged measurements under controlled conditions and the resulting high quality data. We show the scalability of our method, enabling high throughput, and its suitability for maintaining static and dynamic conditions. When food availability was oscillated, pumping rates were low as compared to steady conditions and pumping activity was not reliably modulated in response to changes in food concentration. Comparison with existing method: The prevailing method for measuring rates of pumping relies on scoring by visual inspection of short recordings. Our automated method compares well with manual scoring. It enables detailed statistical characterization under experimental conditions not previously accessible and minimizes unintentional bias. Conclusions: Our approach adds a powerful tool for studying pharyngeal pumping. It enhances the experimental versatility of assaying genetic and pharmacological manipulations and the ability to characterize the resulting behavior. Both the experimental setup and the analysis can be readily adapted to additional challenging motion detection problems

Algebraic analysis of quantum search with pure and mixed states

An algebraic analysis of Grover's quantum search algorithm is presented for the case in which the initial state is an arbitrary pure quantum state of n qubits. This approach reveals the geometrical structure of the quantum search process, which turns out to be confined to a four-dimensional subspace of the Hilbert space. This work unifies and generalizes earlier results on the time evolution of the amplitudes during the quantum search, the optimal number of iterations and the success probability. Furthermore, it enables a direct generalization to the case in which the initial state is a mixed state, providing an exact formula for the success probability.Comment: 13 page

Editorial: Roles and mechanisms of parasitism in aquatic microbial communities

International audienc

Theory of Initialization-Free Decoherence-Free Subspaces and Subsystems

We introduce a generalized theory of decoherence-free subspaces and subsystems (DFSs), which do not require accurate initialization. We derive a new set of conditions for the existence of DFSs within this generalized framework. By relaxing the initialization requirement we show that a DFS can tolerate arbitrarily large preparation errors. This has potentially significant implications for experiments involving DFSs, in particular for the experimental implementation, over DFSs, of the large class of quantum algorithms which can function with arbitrary input states

Sickness presenteeism determines job satisfaction via affective-motivational states

Research on the consequences of sickness presenteeism, or the phenomenon of attending work whilst ill, has focused predominantly on identifying its economic, health, and absenteeism outcomes, neglecting important attitudinal-motivational outcomes. A mediation model of sickness presenteeism as a determinant of job satisfaction via affective-motivational states (specifically engagement with work and addiction to work) is proposed. This model adds to the current literature, by focusing on (i) job satisfaction as an outcome of presenteeism, and (ii) the psychological processes associated with this. It posits presenteeism as psychological absence and work engagement and work addiction as motivational states that originate in that. An online survey was completed by 158 office workers on sickness presenteeism, work engagement, work addiction, and job satisfaction. The results of bootstrapped mediation analysis with observable variables supported the model. Sickness presenteeism was negatively associated with job satisfaction. This relationship was fully mediated by both engagement with work and addiction to work, explaining a total of 48.07% of the variance in job satisfaction. Despite the small sample, the data provide preliminary support for the model. Given that there is currently no available research on the attitudinal consequences of presenteeism, these findings offer promise for advancing theorising in this area

Lighting of end of lay broiler breeders: fluorescent versus incandescent.

An 18-week experiment was conducted to investigate the effects of changing from incandescent to fluorescent lighting on egg production, egg weight, fertility, and hatchability of end of lay broiler breeders housed in an open-sided house. Forty-eight-week-old Cobb feather-sexed broiler breeders were housed, 30 females and 3 males per pen, in a total of 28 pens. Incandescent lights had been used previously, so pens were randomly assigned to either fluorescent or incandescent lights giving 20 lx of light at bird level. Lights used were 60 W incandescent and 22 W fluorescent cool-white circular. Body weight and egg production were measured weekly, and fertility, hatchability, and egg weight were determined monthly from 48 to 65 weeks of age. No significant treatment effects were observed on body weight, fertility, hatchability, or egg weight. A significant reduction in egg production was observed with fluorescent lighting from Weeks 58 to 65. The reduced egg production indicated it was detrimental to change from incandescent to cool-white fluorescent lighting

Senior entrepreneurs: The impact of temporal perception on the entrepreneurial process

Abstract Purpose Longer life expectancy brings a new phenomenon: senior entrepreneurship. Whereas starting a business involves investing energy, time, money or other types of resources, ageing is somewhat incompatible with these terms. Research on the impact of time perception on the entrepreneurial process is rather scarce. Considering the lack of knowledge related to the impact of time perception on the entrepreneurship process, this study aims to answer the following research question: how does temporal perception influence the entrepreneurial process? Design/methodology/approach Senior entrepreneurs are the most relevant category of individuals from which the impact of time perception could be observed, as they are objectively closer to the end of their careers than younger entrepreneurs. Therefore, longitudinal research was conducted by interviewing five senior entrepreneurs at 4-year intervals. Findings Results show that there are two types of temporal perception in entrepreneurship: temporal perception of the entrepreneur's career and temporal perception of the enterprise's development. When these two-time perspectives are not synchronized with the entrepreneur's vision, the entrepreneur develops strategies for seeking to re-establish synchronicity between the temporal perspective (TP) of their entrepreneurial career and that of the business development. The senior entrepreneur is distinguished from a traditional entrepreneur by a limited TP of their entrepreneurial career combined with the notions of bridge employment and generativity. Research limitations/implications The number of cases under study did not allow us to examine every possible type of situation. The sampling of the cases under study did not offer great diversity in terms of gender, as the study had only men. However, the range of ages at startup, from 50 to 65 years, provides greater diversity, as does the range of business segments that included the service, manufacturing and retail food industries. Originality/value Entrepreneurs with a limited career time perspective correspond to senior entrepreneurs, while others who have an open career prospect, regardless of their age, correspond to any other form of an entrepreneur. This study has also been able to identify that an entrepreneur who realizes their limited entrepreneurial career horizon and perceives a temporal purpose of their company in the service of the involved parties tends to plan the entrepreneurial exit phase