Machine Discovery of Effective Admissible Heuristics

Admissible heuristics are an important class of heuristics worth discovering: they guarantee shortest path solutions in search algorithms such as A ^* and they guarantee less expensively produced, but boundedly longer solutions in search algorithms such as dynamic weighting. Unfortunately, effective (accurate and cheap to compute) admissible heuristics can take years for people to discover. Several researchers have suggested that certain transformations of a problem can be used to generate admissible heuristics. This article defines a more general class of transformations, called abstractions, that are guaranteed to generate only admissible heuristics. It also describes and evaluates an implemented program (Absolver II) that uses a means-ends analysis search control strategy to discover abstracted problems that result in effective admissible heuristics. Absolver II discovered several well-known and a few novel admissible heuristics, including the first known effective one for Rubik's Cube, thus concretely demonstrating that effective admissible heuristics can be tractably discovered by a machine.     

Psychosis proneness and clinical psychopathology: Examination of the correlates of schizotypy.

The present report examined the associations between the Perceptual Aberration Scale (PAS), a prominent psychometric index of hypothetical psychosis proneness, and several measures of clinical psychopathology in a nonpsychotic psychiatric sample (N?=?101). Patients were examined by experienced clinicians using structured psychiatric interviews to assess Diagnostic and Statistical Manual of Mental Disorders-III—Revised (DSM-III—R) Axis I and II conditions and rated for anxiety, depression, severity of illness, and current adult social competence. Elevated scores on the PAS were most closely associated with anxiety and depression as well as schizotypal, schizoid, avoidant, and obsessive–compulsive personality disorder symptomatology. Hierarchical regression analysis identified schizotypal symptoms and anxiety as the two underlying psychopathological processes most useful in explaining variance in PAS scores. Results are interpreted as supporting both the clinical relevance and research utility of the PAS and enhancing the construct validity of Meehl's model of schizotypy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Resistance to extinction in evaluative conditioning.

A well-demonstrated phenomenon in traditional Pavlovian conditioning research with humans is that of experimental extinction. In contrast, human evaluative conditioning research suggests that evaluative learning shows marked resistance to extinction. Here, the authors replicate both findings concurrently. Two differential fear conditioning experiments with an electrocutaneous stimulus as the unconditioned stimulus evidenced (a) sensitivity to extinction using an autonomic skin-conductance measure and (b) complete resistance to extinction using an affective-priming measure. The results corroborate the idea that evaluative conditioning is more resistant to extinction than is expectancy learning (F. Baeyens, P. Eelen, & G. Crombez, 1995). (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Kinetics and slurry-type reactor modelling during catalytic hydrogenation of o-cresol on Ni/SiO2

The effect of kinetic parameters (reactant concentrations, temperature) was investigated on the initial reaction rate for the catalytic hydrogenation of o-cresol on Ni/SiO₂, carried out in a batch or semi-batch agitated slurry-type reactor.

The data were interpreted by a kinetic model based on the Langmuir-Hinshelwood mechanism with non-dissociative and non-competitive adsorption of o-cresol and hydrogen on different sites, where the limiting step is due to the reaction of adsorbed reactants. The activation energy (E_a = 82 kJ/mol) is in good agreement with previous literature values reported for the catalytic hydrogenation of phenol.

Taking into account thermodynamic (solubilities) and mass transfer kinetics (k_La) data measured in situ, the integral reactor conversion rate of this three-phase catalytic reaction was simulated accurately in the physical regime by taking into account external and internal mass transfer resistances.     

Social comparison, self-stereotyping, and gender differences in self-construals.

Four studies examined gender differences in self-construals and the role of social comparison in generating these differences. Consistent with previous research, Study 1 (N=461) showed that women define themselves as higher in relational interdependence than men, and men define themselves as higher in independence/agency than women. Study 2 (N=301) showed that within-gender social comparison decreases gender differences in self-construals relative to a control condition, whereas between-genders comparison increases gender differences on both relational interdependence and independence/agency. Studies 3 (N=169) and 4 (N=278) confirmed these findings and showed that changing self-construal changes gender differences in social dominance orientation. Across the 4 studies, strong evidence for the role of in-group stereotyping as mediator of the effect of gender on self-construal was observed on the relational dimension but not on the agentic dimension. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adaptation of the sheet resistance of an YBaCuO layer to the substrate impedance,applications

We have studied the Far Infrared transmission spectra of an MgO plate covered with an YBaCuO film of thickness t=200 Å, at different temperatures. By cooling from room temperature to temperatures Θ < 140 K, the Far Infrared interference fringes are displaced by half a period. Explanation in terms of different adaptations of the YBaCuO sheet resistance to the MgO substrate impedance during cooling.     

Microwaves properties of MgO single crystals computed from the IR,and measured with a resonator technique

The dielectric properties of MgO single crystals are carefully measured in the microwaves and compared with the predictions given by a dynamical model made of 4 Lorentz oscillators with parameters fitting quite well the IR spectra. The microwave losses can be made very low (e.g. 4 × 10^?7 for T=80 K and f=8 GHz), with the same order of magnitude expected from the model. It is a hint that Debye relaxation of small amounts of impurities (e.g. Mn which is sometimes detected by ESR analysis), bring a negligible contribution, and MgO crystal plates are indeed a good support to grow High Tc superconducting films.     

Is soil quality improvement by legume cover crops a function of the initial soil chemical characteristics?

The aim of this study, which was conducted in a humid savannah zone of central Côte d’Ivoire, was to examine changes in the quality of soil cultivated with herbaceous legume cover crops as a function of initial soil characteristics. Mucuna pruriens var utilis and Pueraria phaseoloides were used in a two side-by-side location experiment: a shrubby savannah (the savannah site or “SAV”) and a natural fallow dominated by Chromolaena odorata (the fallow site or “FAL”). The latter was mainly characterized by higher organic matter [organic carbon (C) 10 vs. 7.5 mg kg^?1; total nitrogen (N) 0.8 vs. 0.5 mg kg^?1) and total phosphorus (P) (282.3 vs. 168.3 mg kg^?1) contents in the upper soil layer (0–10 cm). After 8 months of growth, biomass production by M. pruriens was found to be 6.5 and 4.9 t dry matter (DM) ha^?1 at FAL and SAV, respectively. For P. phaseoloides, the values were 7.2 and 6.4 t DM ha^?1, respectively, in approximately the same period. The quantities of nutrients released by decomposing legume litter were higher at FAL than at SAV. Between-site differences in soil quality improvement were most noticeable in terms of available P, microbial biomass carbon (MBC) and MBC:total carbon (TC) ratio. The FAL site experienced a faster improvement of soil parameters under both legume species: available P increased from 18 to 58 mg kg^?1 under M. pruriens, and from 19 to 52 mg kg^?1 under P. phaseoloides; MBC increased from 88 to 185 mg kg^?1 under M. pruriens, and from 127 to 192 mg kg^?1 under P. phaseoloides. In contrast, the parameters remained constant over time at SAV. Soil C and N contents as well as C mineralization showed similar trends at both sites. Based on these results, we conclude that soil quality improvement under cover crops appears to be faster when the initial soil organic C, total N and P contents are adequate. These findings will be useful in assisting governmental decision-making on approaches to be taken for restoring soil fertility in low-input agricultural systems in West Africa.     

Effects of silicone coating degradation on GaN MQW LEDs performances using physical and chemical analyses

This work presents a physics of failure (POF) methodology coupling failure signatures with physico-chemical analyses. The aim is to work out electro-optical failure signatures located in packaged InGaN/GaN Multiple Quantum Wells Light Emitting Diodes (MQW LEDs). Electrical and optical characteristics performed after accelerated ageing tests (30 mA/85 °C/1500 h), confirm a 65% drop of optical power and an increase of one decade of leakage current spreading at the silicone oil/chip interfaces. Through measurements of silicone coating fluorescence emission spectra, we demonstrate that the polymer enlarges the LED emission spectrum and shifts central wavelength. This shift is related to silicone oil spectral instability and the central wavelength of packaged LED appears to be temperature insensitive. In this paper, we discriminate the degradation of bulk silicone oil responsible for optical losses from the polymer/chip interface inducing larger leakage current.