A dynamically extending exclusion process

An extension of the totally asymmetric exclusion process, which incorporates a dynamically extending lattice is explored. Although originally inspired as a model for filamentous fungal growth, here the dynamically extending exclusion process (DEEP) is studied in its own right, as a nontrivial addition to the class of nonequilibrium exclusion process models. Here we discuss various mean-field approximation schemes and elucidate the steady state behaviour of the model and its associated phase diagram. Of particular note is that the dynamics of the extending lattice leads to a new region in the phase diagram in which a shock discontinuity in the density travels forward with a velocity that is lower than the velocity of the tip of the lattice. Thus in this region the shock recedes from both boundaries.Comment: 20 pages, 12 figure

Nuclear Dbf2-related protein kinases (NDRs) in isolated cardiac myocytes and the myocardium: activation by cellular stresses and by phosphoprotein serine-/threonine-phosphatase inhibitors

The nuclear Dbf2-related protein kinases 1 and 2 (NDR1/2) are closely-related AGC family kinases that are strongly conserved through evolution. In mammals, they are activated inter alia by phosphorylation of an hydrophobic domain threonine-residue [NDR1(Thr-444)/NDR2(Thr-442)] by an extrinsic protein kinase followed by autophosphorylation of a catalytic domain serine-residue [NDR1(Ser-281)/NDR2(Ser-282)]. We examined NDR1/2 expression and regulation in primary cultures of neonatal rat cardiac myocytes and in perfused adult rat hearts. In myocytes, transcripts for NDR2, but not NDR1, were induced by the hypertrophic agonist, endothelin-1. NDR1(Thr-444) and NDR2(Thr-442) were rapidly phosphorylated (maximal in 15-30 min) in myocytes exposed to some phosphoprotein Ser-/Thr-phosphatase 1/2 inhibitors (calyculin A, okadaic acid) and, to a lesser extent, by hyperosmotic shock, low concentrations of H(2)O(2), or chelerythrine. In myocytes adenovirally-transduced to express FLAG-NDR2 (which exhibited a mainly-cytoplasmic localisation), the same agents increased FLAG-NDR2 activity as assessed by in vitro protein kinase assays, indicative of FLAG-NDR2(Ser-282/Thr-442) phosphorylation. Calyculin A-induced phosphorylation of NDR1(Thr-444)/NDR2(Thr-442) and activation of FLAG-NDR2 were inhibited by staurosporine, but not by other protein kinase inhibitors tested. In ex vivo rat hearts, NDR1(Thr-444)/NDR2(Thr-442) were phosphorylated in response to ischaemia-reperfusion or calyculin A. From a pathological viewpoint, we conclude that activities of NDR1 and NDR2 are responsive to cytotoxic stresses in heart preparations and this may represent a previously-unidentified response to myocardial ischaemia in vivo

A model of hyphal tip growth involving microtubule-based transport

We propose a simple model for mass transport within a fungal hypha and its subsequent growth. Inspired by the role of microtubule-transported vesicles, we embody the internal dynamics of mass inside a hypha with mutually excluding particles progressing stochastically along a growing one-dimensional lattice. The connection between long range transport of materials for growth, and the resulting extension of the hyphal tip has not previously been addressed in the modelling literature. We derive and analyse mean-field equations for the model and present a phase diagram of its steady state behaviour, which we compare to simulations. We discuss our results in the context of the filamentous fungus, Neurospora crassa.Comment: 5 pages, 5 figure

Proprietary Reasons and Joint Action

Some of the reasons one acts on in joint action are shared with fellow participants. But others are proprietary: reasons of one’s own that have no direct practical significance for other participants. The compatibility of joint action with proprietary reasons serves to distinguish the former from other forms of collective agency; moreover, it is arguably a desirable feature of joint action. Advocates of “team reasoning” link the special collective intention individual participants have when acting together with a distinctive form of practical reasoning that purports to put individuals in touch with group or collective reasons. Such views entail the surprising conclusion that one cannot engage in joint action for proprietary reasons. Suppose we understand the contrast between minimal and robust forms of joint action in terms of the extent to which participants act on proprietary reasons as opposed to shared reasons. Then, if the team reasoning view of joint intention and action is correct, it makes no sense to talk of minimal joint action. As soon as the reason for which one participates is proprietary, then one is not, on this view, genuinely engaged in joint action

Public goods and decay in networks

We propose a simple behavioral model to analyze situations where (1) a group of agents repeatedly plays a public goods game within a network structure and (2) each agent only observes the past behavior of her neighbors, but is affected by the decisions of the whole group. The model assumes that agents are imperfect conditional cooperators, that they infer unobserved contributions assuming imperfect conditional cooperation by others, and that they have some degree of bounded rationality. We show that our model approximates quite accurately regularities derived from public goods game experiments

Adaptation and extension of the European recommendations (EACD) on Developmental Coordination Disorder (DCD) for the UK context

Background. Developmental Coordination Disorder (DCD) affects the learning and performance of everyday motor skills. It commonly co-occurs with other developmental disorders and a range of associated psycho-social impairments. Recent evidence-based guidelines on diagnosis, assessment and intervention provide valuable information for practitioners. However these are directed primarily at German-speaking countries and focus on work with children. Aim. The aim of this project was to consider the application of these guidelines in the UK and to extend them for use with adults with DCD. Methods. Individuals with DCD, parents and professionals from a wide range of disciplines were invited to two workshops to discuss and debate the guidelines, to adapt them for the UK and produce dissemination materials. Results. A working definition of DCD was agreed, minor revisions were made to the guidelines to reflect the UK context, an extension for adults was compiled and a series of leaflets was produced to disseminate this information to health and education professionals, parents and employers. Conclusions. This work will raise awareness of the condition across different professional groups. It provides information to help those working with children and adults with DCD in the UK to assist in the process of diagnosis, assessment and intervention

Awards, incentives and mutual benefit

Frey argues that if buyers and sellers of labour understand their relationship merely as exchange, workers’ intrinsic motivation can be impaired; this problem can be partially overcome by using awards as a supplementary reward mechanism. I argue that this proposal is self-defeating. In an economy that relies on the division of labour, it is an unavoidable fact that individuals are subject to the will of others; award-giving practices are merely camouflage. However, recognising this fact need not impair anyone’s sense of autonomy as a paid worker if participation in market exchanges is understood as expressing intentions for mutual benefit

Cooperation, Norms, and Revolutions: A Unified Game-Theoretical Approach

Cooperation is of utmost importance to society as a whole, but is often challenged by individual self-interests. While game theory has studied this problem extensively, there is little work on interactions within and across groups with different preferences or beliefs. Yet, people from different social or cultural backgrounds often meet and interact. This can yield conflict, since behavior that is considered cooperative by one population might be perceived as non-cooperative from the viewpoint of another. To understand the dynamics and outcome of the competitive interactions within and between groups, we study game-dynamical replicator equations for multiple populations with incompatible interests and different power (be this due to different population sizes, material resources, social capital, or other factors). These equations allow us to address various important questions: For example, can cooperation in the prisoner's dilemma be promoted, when two interacting groups have different preferences? Under what conditions can costly punishment, or other mechanisms, foster the evolution of norms? When does cooperation fail, leading to antagonistic behavior, conflict, or even revolutions? And what incentives are needed to reach peaceful agreements between groups with conflicting interests? Our detailed quantitative analysis reveals a large variety of interesting results, which are relevant for society, law and economics, and have implications for the evolution of language and culture as well

Phase diagram of two-lane driven diffusive systems

We consider a large class of two-lane driven diffusive systems in contact with reservoirs at their boundaries and develop a stability analysis as a method to derive the phase diagrams of such systems. We illustrate the method by deriving phase diagrams for the asymmetric exclusion process coupled to various second lanes: a diffusive lane; an asymmetric exclusion process with advection in the same direction as the first lane, and an asymmetric exclusion process with advection in the opposite direction. The competing currents on the two lanes naturally lead to a very rich phenomenology and we find a variety of phase diagrams. It is shown that the stability analysis is equivalent to an `extremal current principle' for the total current in the two lanes. We also point to classes of models where both the stability analysis and the extremal current principle fail