Foraging as an evidence accumulation process

A canonical foraging task is the patch-leaving problem, in which a forager must decide to leave a current resource in search for another. Theoretical work has derived optimal strategies for when to leave a patch, and experiments have tested for conditions where animals do or do not follow an optimal strategy. Nevertheless, models of patch-leaving decisions do not consider the imperfect and noisy sampling process through which an animal gathers information, and how this process is constrained by neurobiological mechanisms. In this theoretical study, we formulate an evidence accumulation model of patch-leaving decisions where the animal averages over noisy measurements to estimate the state of the current patch and the overall environment. Evidence accumulation models belong to the class of drift diffusion processes and have been used to model decision making in different contexts. We solve the model for conditions where foraging decisions are optimal and equivalent to the marginal value theorem, and perform simulations to analyze deviations from optimal when these conditions are not met. By adjusting the drift rate and decision threshold, the model can represent different strategies, for example an increment-decrement or counting strategy. These strategies yield identical decisions in the limiting case but differ in how patch residence times adapt when the foraging environment is uncertain. To account for sub-optimal decisions, we introduce an energy-dependent utility function that predicts longer than optimal patch residence times when food is plentiful. Our model provides a quantitative connection between ecological models of foraging behavior and evidence accumulation models of decision making. Moreover, it provides a theoretical framework for potential experiments which seek to identify neural circuits underlying patch leaving decisions

Step-Indexed Logical Relations for Probability (long version)

It is well-known that constructing models of higher-order probabilistic programming languages is challenging. We show how to construct step-indexed logical relations for a probabilistic extension of a higher-order programming language with impredicative polymorphism and recursive types. We show that the resulting logical relation is sound and complete with respect to the contextual preorder and, moreover, that it is convenient for reasoning about concrete program equivalences. Finally, we extend the language with dynamically allocated first-order references and show how to extend the logical relation to this language. We show that the resulting relation remains useful for reasoning about examples involving both state and probabilistic choice.Comment: Extended version with appendix of a FoSSaCS'15 pape

Association Between Joint Hypermobility Syndrome and Developmental Coordination Disorder – A Review.

Introduction: The term joint hypermobility syndrome (JHS) was adopted after clinicians became aware of the myriad of symptoms associated with this multisystemic condition. JHS is an inherited disorder of connective tissues affecting the musculoskeletal and visceral systems which may contribute to a reduction in health related physical fitness. Pain associated with JHS may be influenced by hypermobility and biomechanical dysfunction. Biomechanical dysfunction observed in patients with JHS may be as a result of impaired motor control and in particular developmental coordination disorder (DCD). DCD (described in the literature utilising the terms clumsy child syndrome; perceptual motor dysfunction; dyspraxia) is a neurodevelopmental condition characterised by coordination difficulties affecting function. The objective of this review is to examine the association between hypermobility, JHS, motor control impairment and DCD. Methods and data sources: EMBASE, MEDLINE, CINAHL, ASSIA, PsychARTICLES, SPORTDiscus and PsycINFO from 1989 - 2009. Research articles written in English and peer reviewed were included. Results: Five research papers were identified. The studies employed a variety of methodologies and assessment tools for reporting joint hypermobility, JHS, motor delay, motor impairments and DCD. All five studies reported on children between the ages of six months and 12 years. Three out of four studies reported on association between impaired motor development, motor delay and joint hypermobility. There was no consensus as to whether motor delay, impaired motor development and joint hypermobility continued as the child matured. One study ascertained that children with JHS reported similar functional difficulties as children with DCD. Conclusion: There was a paucity of literature relating to an association between joint hypermobility, JHS, impaired motor control, motor delay and DCD in children, there was no literature pertaining to adults. This association requires further exploration if professionals are to understand, nurture and manage those reporting these associated conditions

Analysis and hardware testing of cell capacitor discharge currents during DC faults in half-bridge modular multilevel converters

This paper focuses on the behaviour of the cell capacitor discharge currents during DC faults in half-bridge modular multilevel converters. Active switches, not designed for fault conditions, are tripped to minimize discharge currents effect on the semiconductor switches. Two levels of device protection are commonly in place; driver level protection monitoring collector-emitter voltage and overcurrent protection with feedback measurement and control. However, unavoidable tripping delay times, arising from factors such as sensor lags, controller sampling delays and hardware propagation delays, impact transient current shape and hence affect the selection of semiconductor device ratings as well as arm inductance. Analytical expressions are obtained for current slew rate, peak transient current and resultant I2t for the cell capacitor discharge current taking into account such delays. The study is backed by experimental testing on discharge of a 900V MMC capacitor

Centralized Versus Decentralized Team Games of Distributed Stochastic Differential Decision Systems with Noiseless Information Structures-Part II: Applications

In this second part of our two-part paper, we invoke the stochastic maximum principle, conditional Hamiltonian and the coupled backward-forward stochastic differential equations of the first part [1] to derive team optimal decentralized strategies for distributed stochastic differential systems with noiseless information structures. We present examples of such team games of nonlinear as well as linear quadratic forms. In some cases we obtain closed form expressions of the optimal decentralized strategies. Through the examples, we illustrate the effect of information signaling among the decision makers in reducing the computational complexity of optimal decentralized decision strategies.Comment: 39 pages Submitted to IEEE Transaction on Automatic Contro

Stochastic Minimum Principle for Partially Observed Systems Subject to Continuous and Jump Diffusion Processes and Driven by Relaxed Controls

In this paper we consider non convex control problems of stochastic differential equations driven by relaxed controls. We present existence of optimal controls and then develop necessary conditions of optimality. We cover both continuous diffusion and Jump processes.Comment: Pages 23, Submitted to SIAM Journal on Control and Optimizatio

Confined Dirac Particles in Constant and Tilted Magnetic Field

We study the confinement of charged Dirac particles in 3+1 space-time due to the presence of a constant and tilted magnetic field. We focus on the nature of the solutions of the Dirac equation and on how they depend on the choice of vector potential that gives rise to the magnetic field. In particular, we select a "Landau gauge" such that the momentum is conserved along the direction of the vector potential yielding spinor wavefunctions, which are localized in the plane containing the magnetic field and normal to the vector potential. These wave functions are expressed in terms of the Hermite polynomials. We point out the relevance of these findings to the relativistic quantum Hall effect and compare with the results obtained for a constant magnetic field normal to the plane in 2+1 dimensions.Comment: 10 page

Haemoglobinopathies and health care provision for ethnic minorities

The level of training and competence in dealing with haemoglobinopathies (which mainly affect ethnic minorities in the UK) may not be totally adequate among nurses. Nurses indicated that they received little or no information in their teaching for working from a multiracial perspective and what they had learned was through experience and personal research since qualifying as nurses. Knowledge of the biological basis of inheritance, methods of acquisition of thalassaemia and sicklecell anaemia and the ethnic profile of people affected by these conditions may not be totally adequate among nurses. Many nurses wanted more training, including those who had already received instruction, since this was described as ‘far too vague’, ‘not constructive’, ‘minimal’, or ‘embarrassingly insufficient’, recommending that instruction be given by a sickle-cell anaemia/thalassaemia counsellor with a contribution from patients. A combination of poor quality, or lack, of instruction, together with time and resource pressures, is responsible for this limited understanding, resulting in insufficient awareness of the health needs of ethnic minorities leading to inequalities in healthcare provision