Does decision quality (always) increase with the size of information samples? Some vicissitudes in applying the law of large numbers.

Adaptive decision making requires that contingencies between decision options and their relative assets be assessed accurately and quickly. The present research addresses the challenging notion that contingencies may be more visible from small than from large samples of observations. An algorithmic account for such a seemingly paradoxical effect is offered within a satisficing-choice framework. Accordingly, a choice is only made when the sample contingency describing the relative evaluation of the 2 options exceeds a critical threshold. Small samples, because of the high dispersion of their sampling distribution, facilitate above-threshold contingencies. Across a broad range of parameters, the resulting small-sample advantage in terms of hits is stronger than their disadvantage in false alarms. Computer simulations and experiments support the model predictions. The relative advantage of small samples is most apparent when information loss is low, when the threshold is high relative to the ecological contingency, and when the sampling process is self-truncated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Endohedral metallofullerenes M@C82 (M=La, Y): synthesis and transport properties

Endohedral metallofullerenes M@C_2n (M=La, Y) were synthesized by the arc-discharge method using optimum electric arc parameters. It was also shown that an organic solvent (N,N-dimethylformamide) is successfully used in selective extraction of M@C_2n. We identified the resulting products by mass spectrometry, electron spectrophotometry, EPR and X-ray fluorescence spectroscopy. The resulting N,N-dimethylformamide extracts of La@C_2n and Y@C_2n are shown to be free of empty fullerenes and appear as a mixture of endometallofullerenes M@C_2n whose main ingredient is M@C₈₂ (∼80 wt%). Transport properties of the extracts of La@C₈₂ and Y@C₈₂ were studied using pressed pellets. It was found that oxygen and heat treatment affect conductivity of endometallofullerenes. Heat treatment results in a three-order increase of conductivity from 10⁻⁵ upto 10⁻² Ohm⁻¹ cm⁻¹     

Base rates, contingencies, and prediction behavior.

A skew in the base rate of upcoming events can often provide a better cue for accurate predictions than a contingency between signals and events. The authors study prediction behavior and test people's sensitivity to both base rate and contingency; they also examine people's ability to compare the benefits of both for prediction. They formalize these notions and propose a new measure of the regularity in the environment (ExpPA). In two experiments they test whether the notions underlying this measure capture prediction behavior. In the first experiment, they compare participants' prediction behavior, preference, and assessment of contingencies in two data sets that differ only in their base rate. In the second, in which the contribution of contingency over base rate is manipulated, they study participants' willingness to forgo a costly predictor. Results indicate a close correspondence between ExpPA and behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Through a narrow window: Sample size and the perception of correlation.

A theoretical analysis (Y. Kareev, 1995b) of the sampling distribution of correlations led to the surprising conclusion that the use of small samples has a potential advantage for the early detection of a correlation. This is so because the distribution is highly skewed, and the smaller the sample size, the more the distribution is skewed. This article describes 2 experiments that were designed as empirical tests of this conclusion. In Experiment 1 (N?=?112), the authors compared the predictions of participants differing in their working-memory capacity (hence in the size of the samples they were likely to consider). In Experiment 2 (N?=?144), the authors compared the predictions of participants who viewed samples of different sizes, whose size was determined by the authors. The results fully supported Y. Kareev's conclusion: In both experiments, participants with lower capacity (or smaller samples) indeed perceived the correlation as more extreme and were more accurate in their predictions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Antioxidant Potential of Aqueous Dispersions of Fullerenes C60, C70, and Gd@C82

The antioxidant potential (capacity and activity) of aqueous fullerene dispersions (AFD) of non-functionalized C₆₀, C₇₀, and Gd@C₈₂ endofullerene (in micromolar concentration range) was estimated based on chemiluminescence measurements of the model of luminol and generation of organic radicals by 2,2′-azobis(2-amidinopropane) dihydrochloride (ABAP). The antioxidant capacity was estimated by the TRAP method, from the concentration of half-suppression, and from the suppression area in the initial period. All three approaches agree and show that the antioxidant capacity of AFDs increased in the order Gd@C₈₂ < C₇₀ < C₆₀. Mathematical modeling of the long-term kinetics data was used for antioxidant activity estimation. The effect of C₆₀ and C₇₀ is found to be quenching of the excited product of luminol with ABAP-generated radical and not an actual antioxidant effect; quenching constants differ insignificantly. Apart from quenching with a similar constant, the AFD of Gd@C₈₂ exhibits actual antioxidant action. The antioxidant activity in Gd@C₈₂ is 300-fold higher than quenching constants.     

Ramp‐Reversal Memory and Phase‐Boundary Scarring in Transition Metal Oxides

Transition metal oxides are complex electronic systems that exhibit a multitude of collective phenomena. Two archetypal examples are VO₂ and NdNiO₃, which undergo a metal–insulator phase transition (MIT), the origin of which is still under debate. Here this study reports the discovery of a memory effect in both systems, manifested through an increase of resistance at a specific temperature, which is set by reversing the temperature ramp from heating to cooling during the MIT. The characteristics of this ramp‐reversal memory effect do not coincide with any previously reported history or memory effects in manganites, electron‐glass or magnetic systems. From a broad range of experimental features, supported by theoretical modelling, it is found that the main ingredients for the effect to arise are the spatial phase separation of metallic and insulating regions during the MIT and the coupling of lattice strain to the local transition temperature of the phase transition. We conclude that the emergent memory effect originates from phase boundaries at the reversal temperature leaving “scars” in the underlying lattice structure, giving rise to a local increase in the transition temperature. The universality and robustness of the effect shed new light on the MIT in complex oxides.     

Investigation of Composition of Endometallofullerene Extracts

Gases evolved upon heating endometallofullerene (EMF) extracts with La or Y have been investigated. It has been shown that solvent molecules used to release EMF are observed in extracts up to high temperatures. It has been found that in the dimethylformamide (DMF) extract the EMF molecules are present mainly as the [EMF]^- anions, which were observed in electrospray mass spectra. The treatment of such extracts with iodine results in the anion reduction to neutral molecules.