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

Preparation of a Resorbable Osteoinductive Tricalcium Phosphate Ceramic

Over the past decade we have demonstrated numerous times that calcium phosphates can be rendered with osteoinductive properties by introducing specific surface microstructures1. Since most of these calcium phosphates contained hydroxyapatite, they are either slowly or not resorbable2. Resorbability is an often sought after characteristic of calcium phosphates so that they can be gradually replaced by newly formed bone. The objective of this study was to prepare a resorbable surface microstructured tricalcium phosphate (TCP) ceramic and evaluate its osteoinductive property and resorption rate after intramuscular implantation in dogs. This material was then compared to the established and slowly resorbable osteoinductive biphasic calcium phosphate ceramic (BCP)

Relativistic Nucleus-Nucleus Collisions: Zone of Reactions and Space-Time Structure of a Fireball

A zone of reactions is determined and then exploited as a tool in studying the space-time structure of an interacting system formed in a collision of relativistic nuclei. The time dependence of the reaction rates integrated over spatial coordinates is also considered. Evaluations are made with the help of the microscopic transport model UrQMD. The relation of the boundaries of different zones of reactions and the hypersurfaces of sharp chemical and kinetic freeze-outs is discussed.Comment: 6 pages, 5 figure

Scattering Theory of Charge-Current Induced Magnetization Dynamics

In ferromagnets, charge currents can excite magnons via the spin-orbit coupling. We develop a novel and general scattering theory of charge current induced macrospin magnetization torques in normal metal$|$ferromagnet$|$normal metal layers. We apply the formalism to a dirty GaAs$|$(Ga,Mn)As$|$GaAs system. By computing the charge current induced magnetization torques and solving the Landau-Lifshitz-Gilbert equation, we find magnetization switching for current densities as low as $5\times 10^{6}$~A/cm$^2$. Our results are in agreement with a recent experimental observation of charge-current induced magnetization switching in (Ga,Mn)As.Comment: Final version accepted by EP

Onsager approach to 1D solidification problem and its relation to phase field description

We give a general phenomenological description of the steady state 1D front propagation problem in two cases: the solidification of a pure material and the isothermal solidification of two component dilute alloys. The solidification of a pure material is controlled by the heat transport in the bulk and the interface kinetics. The isothermal solidification of two component alloys is controlled by the diffusion in the bulk and the interface kinetics. We find that the condition of positive-definiteness of the symmetric Onsager matrix of interface kinetic coefficients still allows an arbitrary sign of the slope of the velocity-concentration line near the solidus in the alloy problem or of the velocity-temperature line in the case of solidification of a pure material. This result offers a very simple and elegant way to describe the interesting phenomenon of a possible non-single-value behavior of velocity versus concentration which has previously been discussed by different approaches. We also discuss the relation of this Onsager approach to the thin interface limit of the phase field description.Comment: 5 pages, 1 figure, submitted to Physical Review

Dissipative hydrodynamics in 2+1 dimension

In 2+1 dimension, we have simulated the hydrodynamic evolution of QGP fluid with dissipation due to shear viscosity. Comparison of evolution of ideal and viscous fluid, both initialised under the same conditions e.g. same equilibration time, energy density and velocity profile, reveal that the dissipative fluid evolves slowly, cooling at a slower rate. Cooling get still slower for higher viscosity. The fluid velocities on the otherhand evolve faster in a dissipative fluid than in an ideal fluid. The transverse expansion is also enhanced in dissipative evolution. For the same decoupling temperature, freeze-out surface for a dissipative fluid is more extended than an ideal fluid. Dissipation produces entropy as a result of which particle production is increased. Particle production is increased due to (i) extension of the freeze-out surface and (ii) change of the equilibrium distribution function to a non-equilibrium one, the last effect being prominent at large transverse momentum. Compared to ideal fluid, transverse momentum distribution of pion production is considerably enhanced. Enhancement is more at high $p_T$ than at low $p_T$. Pion production also increases with viscosity, larger the viscosity, more is the pion production. Dissipation also modifies the elliptic flow. Elliptic flow is reduced in viscous dynamics. Also, contrary to ideal dynamics where elliptic flow continues to increase with transverse momentum, in viscous dynamics, elliptic flow tends to saturate at large transverse momentum. The analysis suggest that initial conditions of the hot, dense matter produced in Au+Au collisions at RHIC, as extracted from ideal fluid analysis can be changed significantly if the QGP fluid is viscous.Comment: 11 pages, 10 figures (revised). In the revised version, calculations are redone with ADS/CFT and perurbative estimate of viscosity. Comments on the unphysical effects like early reheating of the fluid, in 1st order dissipative theories are added. The particle spectra calculations are redone with modified programm

On the origin dependence of multipole moments in electromagnetism

The standard description of material media in electromagnetism is based on multipoles. It is well known that these moments depend on the point of reference chosen, except for the lowest order. It is shown that this "origin dependence" is not unphysical as has been claimed in the literature but forms only part of the effect of moving the point of reference. When also the complementary part is taken into account then different points of reference lead to different but equivalent descriptions of the same physical reality. This is shown at the microscopic as well as at the macroscopic level. A similar interpretation is valid regarding the "origin dependence" of the reflection coefficients for reflection on a semi infinite medium. We show that the "transformation theory" which has been proposed to remedy this situation (and which is thus not needed) is unphysical since the transformation considered does not leave the boundary conditions invariant.Comment: 14 pages, 0 figure

Do dietary patterns in older men influence change in homocysteine through folate fortification? The Normative Aging Study

Objective We aimed to describe the difference in B-vitamin intake and in plasma B-vitamin and homocysteine concentrations before and after folic acid fortification, in relation to dietary patterns. Design The Normative Aging Study (NAS) is a longitudinal study on ageing. Between 1961 and 1970, 2280 male volunteers aged 21¿80 years (mean 42 years) were recruited. Dietary intake data have been collected since 1987 and assessment of plasma B vitamins and homocysteine was added in 1993. Setting Boston, Massachusetts, USA. Subjects In the present study, 354 men who had completed at least one FFQ and one measurement of homocysteine, both before and after the fortification period, were included. Results Three dietary patterns were identified by cluster analysis: (i) a prudent pattern, with relatively high intakes of fruit, vegetables, low-fat milk and breakfast cereals; (ii) an unhealthy pattern, with high intakes of baked products, sweets and added fats; and (iii) a low fruit and vegetable but relatively high alcohol intake pattern. Dietary intake and plasma concentrations of folate increased significantly (P <0·05) among all dietary patterns after the fortification period. Homocysteine tended to decrease in supplement non-users and in subjects in the high alcohol, low fruit and vegetable dietary pattern (both P = 0·08). Conclusions After fortification with folic acid, folate intake and plasma folate concentration increased significantly in all dietary patterns. There was a trend towards greatest homocysteine lowering in the high alcohol, low fruit and vegetable grou

Collision Thermalization of Nucleons in Relativistic Heavy-Ion Collisions

We consider a possible mechanism of thermalization of nucleons in relativistic heavy-ion collisions. Our model belongs, to a certain degree, to the transport ones; we investigate the evolution of the system created in nucleus-nucleus collision, but we parametrize this development by the number of collisions of every particle during evolution rather than by the time variable. We based on the assumption that the nucleon momentum transfer after several nucleon-nucleon (-hadron) elastic and inelastic collisions becomes a random quantity driven by a proper distribution. This randomization results in a smearing of the nucleon momenta about their initial values and, as a consequence, in their partial isotropization and thermalization. The trial evaluation is made in the framework of a toy model. We show that the proposed scheme can be used for extraction of the physical information from experimental data on nucleon rapidity distribution.Comment: 13 pages, 8 figure

Relaxed States in Relativistic Multi-Fluid Plasmas

The evolution equations for a plasma comprising multiple species of charged fluids with relativistic bulk and thermal motion are derived. It is shown that a minimal fluid coupling model allows a natural casting of the evolution equations in terms of generalized vorticity which treats the fluid motion and electromagnetic fields equally. Equilibria can be found using a variational principle based on minimizing the total enstrophy subject to energy and helicity constraints. A subset of these equilibria correspond to minimum energy. The equations for these states are presented with example solutions showing the structure of the relaxed states.Comment: 8 pages, 2 figure