A pattern-recognition theory of search in expert problem solving

Understanding how look-ahead search and pattern recognition interact is one of the important research questions in the study of expert problem-solving. This paper examines the implications of the template theory (Gobet & Simon, 1996a), a recent theory of expert memory, on the theory of problem solving in chess. Templates are "chunks" (Chase & Simon, 1973) that have evolved into more complex data structures and that possess slots allowing values to be encoded rapidly. Templates may facilitate search in three ways: (a) by allowing information to be stored into LTM rapidly; (b) by allowing a search in the template space in addition to a search in the move space; and (c) by compensating loss in the "mind's eye" due to interference and decay. A computer model implementing the main ideas of the theory is presented, and simulations of its search behaviour are discussed. The template theory accounts for the slight skill difference in average depth of search found in chess players, as well as for other empirical data

Generalized survival in equilibrium step fluctuations

We investigate the dynamics of a generalized survival probability $S(t,R)$ defined with respect to an arbitrary reference level $R$ (rather than the average) in equilibrium step fluctuations. The exponential decay at large time scales of the generalized survival probability is numerically analyzed. $S(t,R)$ is shown to exhibit simple scaling behavior as a function of system-size $L$, sampling time $\delta t$, and the reference level $R$. The generalized survival time scale, $\tau_s(R)$, associated with $S(t,R)$ is shown to decay exponentially as a function of $R$.Comment: 4 pages, 2 figure

Persistence of Manifolds in Nonequilibrium Critical Dynamics

We study the persistence P(t) of the magnetization of a d' dimensional manifold (i.e., the probability that the manifold magnetization does not flip up to time t, starting from a random initial condition) in a d-dimensional spin system at its critical point. We show analytically that there are three distinct late time decay forms for P(t) : exponential, stretched exponential and power law, depending on a single parameter \zeta=(D-2+\eta)/z where D=d-d' and \eta, z are standard critical exponents. In particular, our theory predicts that the persistence of a line magnetization decays as a power law in the d=2 Ising model at its critical point. For the d=3 critical Ising model, the persistence of the plane magnetization decays as a power law, while that of a line magnetization decays as a stretched exponential. Numerical results are consistent with these analytical predictions.Comment: 4 pages revtex, 1 eps figure include

Reflectionless analytic difference operators I. algebraic framework

We introduce and study a class of analytic difference operators admitting reflectionless eigenfunctions. Our construction of the class is patterned after the Inverse Scattering Transform for the reflectionless self-adjoint Schr\"odinger and Jacobi operators corresponding to KdV and Toda lattice solitons

Reflectionless analytic difference operators II. Relations to soliton systems

This is the second part of a series of papers dealing with an extensive class of analytic difference operators admitting reflectionless eigenfunctions. In the first part, the pertinent difference operators and their reflectionless eigenfunctions are constructed from given ``spectral data'', in analogy with the IST for reflectionless Schr\"odinger and Jacobi operators. In the present paper, we introduce a suitable time dependence in the data, arriving at explicit solutions to a nonlocal evolution equation of Toda type, which may be viewed as an analog of the KdV and Toda lattice equations for the latter operators. As a corollary, we reobtain various known results concerning reflectionless Schr\"odinger and Jacobi operators. Exploiting a reparametrization in terms of relativistic Calogero--Moser systems, we also present a detailed study of $N$-soliton solutions to our nonlocal evolution equation

Kink Arrays and Solitary Structures in Optically Biased Phase Transition

An interphase boundary may be immobilized due to nonlinear diffractional interactions in a feedback optical device. This effect reminds of the Turing mechanism, with the optical field playing the role of a diffusive inhibitor. Two examples of pattern formation are considered in detail: arrays of kinks in 1d, and solitary spots in 2d. In both cases, a large number of equilibrium solutions is possible due to the oscillatory character of diffractional interaction.Comment: RevTeX 13 pages, 3 PS-figure

HIV ascertainment through repeat home-based testing in the context of a treatment as prevention trial (ANRS 12249 TasP) in rural South Africa

International audienceBackgroundThe ANRS 12249 TasP cluster-randomised trial evaluates whether HIV testing of all members of a community, followed by immediate antiretroviral treatment (ART) for infected people, will prevent onward sexual transmission and reduce HIV incidence at population level. Ascertaining the HIV status of a high proportion of the population regularly and repeatedly is key to the success of any universal test and treat strategy, as the first step of the HIV cascade.MethodsBetween March 2012 and March 2014, we implemented three six-monthly rounds of home-based HIV counselling and testing in ten local communities (clusters). At each home visit, individual questionnaires were administered and a rapid HIV test offered to all trial participants. We report early results on rates of HIV ascertainment, defined as undergoing a rapid HIV test or HIV-positive self-report.ResultsOf 12,911 eligible individuals (resident in the trial area and ≥16 years), 10,007 were successfully contacted at least once. At first contact, HIV status was ascertained for 7,628 (76.2% [95% CI: 75.4-77.1]) individuals. At second contact, among the 5,885 individuals contacted a second time, HIV status was ascertained for 2,829 (85.0% [95% CI: 83.7-86.2]) of the 3,328 tested negative at first contact and for 543 (45.7% [95% CI: 42.9-48.6]) of the 1,188 who refused a rapid test at first contact. Overall, HIV ascertainment rate was 89.0% (5,239/5,885 [95% CI: 88.2-89.8]) among trial participants contacted twice.ConclusionsRepeat home-based HIV testing is acceptable and feasible in this rural area. Socio-demographic characteristics, behaviours, attitudes, household characteristics and experience of HIV infection and ART in the household will be explored for their association with HIV ascertainment uptake. This will inform whether this intervention reaches the individuals at higher risk in a rural South African region

Molecular evidence of synaptic pathology in the CA1 region in schizophrenia.

Alterations of postsynaptic density (PSD)95-complex proteins in schizophrenia ostensibly induce deficits in synaptic plasticity, the molecular process underlying cognitive functions. Although some PSD95-complex proteins have been previously examined in the hippocampus in schizophrenia, the status of other equally important molecules is unclear. This is especially true in the cornu ammonis (CA)1 hippocampal subfield, a region that is critically involved in the pathophysiology of the illness. We thus performed a quantitative immunoblot experiment to examine PSD95 and several of its associated proteins in the CA1 region, using post mortem brain samples derived from schizophrenia subjects with age-, sex-, and post mortem interval-matched controls (n=20/group). Our results indicate a substantial reduction in PSD95 protein expression (-61.8%). Further analysis showed additional alterations to the scaffold protein Homer1 (Homer1a: +42.9%, Homer1b/c: -24.6%), with a twofold reduction in the ratio of Homer1b/c:Homer1a isoforms (P=0.011). Metabotropic glutamate receptor 1 (mGluR1) protein levels were significantly reduced (-32.7%), and Preso, a protein that supports interactions between Homer1 or PSD95 with mGluR1, was elevated (+83.3%). Significant reduction in synaptophysin (-27.8%) was also detected, which is a validated marker of synaptic density. These findings support the presence of extensive molecular abnormalities to PSD95 and several of its associated proteins in the CA1 region in schizophrenia, offering a small but significant step toward understanding how proteins in the PSD are altered in the schizophrenia brain, and their relevance to overall hippocampal and cognitive dysfunction in the illness

Intra-individual movement variability during skill transitions: A useful marker?

Applied research suggests athletes and coaches need to be challenged in knowing when and how much a movement should be consciously attended to. This is exacerbated when the skill is in transition between two more stable states, such as when an already well learnt skill is being refined. Using existing theory and research, this paper highlights the potential application of movement variability as a tool to inform a coach’s decision-making process when implementing a systematic approach to technical refinement. Of particular interest is the structure of co-variability between mechanical degrees-of-freedom (e.g., joints) within the movement system’s entirety when undergoing a skill transition. Exemplar data from golf are presented, demonstrating the link between movement variability and mental effort as an important feature of automaticity, and thus intervention design throughout the different stages of refinement. Movement variability was shown to reduce when mental effort directed towards an individual aspect of the skill was high (target variable). The opposite pattern was apparent for variables unrelated to the technical refinement. Therefore, two related indicators, movement variability and mental effort, are offered as a basis through which the evaluation of automaticity during technical refinements may be made