Working memory, short-term memory, and general fluid intelligence: A latent-variable approach.

A study was conducted in which 133 participants performed 11 memory tasks (some thought to reflect working memory and some thought to reflect short-term memory), 2 tests of general fluid intelligence, and the Verbal and Quantitative Scholastic Aptitude Tests. Structural equation modeling suggested that short-term and working memories reflect separate but highly related constructs and that many of the tasks used in the literature as working memory tasks reflect a common construct. Working memory shows a strong connection to fluid intelligence, but short-term memory does not. A theory of working memory capacity and general fluid intelligence is proposed: The authors argue that working memory capacity and fluid intelligence reflect the ability to keep a representation active, particularly in the face of interference and distraction. The authors also discuss the relationship of this capability to controlled attention, and the functions of the prefrontal cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Benefits of direct-to tool in National Airspace System

Initiatives in air traffic management both in the United States and in Europe are aimed at providing air traffic controllers with automation tools to separate traffic, meet time constraints required for traffic flow and accommodate route preferences of users such as airlines. These efforts are expected to result in removal of restrictions on users preferred routes without compromising safety. Thus, aircraft will be able to fly optimal routes such as great circle and wind-optimal routes. NASA has developed the design for a new automation tool, referred to as the direct-to tool, which advises the controller on direct time-saving routes for any aircraft irrespective of levels of equipage. In contrast to earlier studies on the potential benefits of direct routes in the National Airspace System, the objective of the paper is to evaluate the benefits based on a controller tool. The paper describes the benefits of applying this algorithm to the 20 air route traffic control centers within the United States. Benefits are measured in terms of the total time savings accrued by flying the direct route. Results are described for three different implementations dependent on the search region bounding each air route traffic control center. The first region exactly encloses the air route traffic control center airspace, the second is the smallest rectangular bounding region while the third is a bigger rectangular bounding region approximately twice as large as the second region. It is shown that the application of the direct-to routing algorithm does not significantly alter the number of conflicts and their spatial distribution compared to the case in which the aircraft fly along the airways. The results presented in the paper suggest that the direct-to routing algorithm can provide significant cost savings to the users without adversely impacting the air traffic management functions     

Multivariate Statistical Differences of MRI Samples of the Human Brain

Multivariate statistical discrimination methods are suitable not only for classification but also for characterization of differences between a reference group of patterns and the population under investigation. In the last years, statistical methods have been proposed to classify and analyse morphological and anatomical structures of medical images. Most of these techniques work in high-dimensional spaces of particular features such as shapes or statistical parametric maps and have overcome the difficulty of dealing with the inherent high dimensionality of medical images by analysing segmented structures individually or performing hypothesis tests on each feature separately. In this paper, we present a general multivariate linear framework that addresses the small sample size problem in medical images. The goal is to identify and analyse the most discriminating hyper-plane separating two populations using all the intensity features simultaneously rather than segmented versions of the data separately or feature-by-feature. To demonstrate the performance of the multivariate linear framework we carry out experimental results on artificially generated data set and on a real medical data composed of magnetic resonance images (MRI) of subjects suffering from Alzheimer’s disease (AD) compared to an elderly healthy control group. To our knowledge this is the first multivariate statistical analysis of the human brain in AD that uses the whole features (texture + shapes) simultaneously rather than segmented version of the images. The conceptual and mathematical simplicity of the approach involves the same operations irrespective of the complexity of the experiment or nature of the spatially normalized data, giving multivariate results that are plausible and easy to interpret by the clinicians.     

Measurement of the force required to move a neurosurgical probethrough in vivo human brain tissue

The advent of high-precision magnetic and robotic computer-controlled neurosurgery systems makes it necessary to determine the range of forces that will be encountered by the probes of such devices as they are guided through the brain tissues to intraparenchymal targets. We have measured the penetration forces on 2.5-mm spheres and the drag forces on 3.0-mm ventricular shunt catheters advanced 2.0-3.5 cm deep into in vivo human brain tissues (in patients about to have those tissues resected during epilepsy surgery) at rates of approximately 0.33 mm s-1. Penetration forces of (8 +/- 2) grams were found for the spherical probe once it passed 0.5 cm below the cortical surface, and frictional drags of (2.8 +/- 0.3) grams cm-1 were exerted on the catheters. The variable nature of these forces is discussed and the results are compared with earlier studies on experimental animal tissues and brain phantom gelatins. The implications of these results for magnetic and robotic surgery systems are considered.     

Comprehensive Linkage of Defect and Phase Equilibria through Ferroelectric Transition Behavior in BaTiO3-Based Dielectrics: Part 1. Defect Energies Under Ambient Air Conditions

Defect and phase equilibria have been investigated via the ferroelectric phase transition behavior of pure and equilibrated nonstoichiometric BaTiO₃ powder samples. Through fabricating the BaTiO₃ materials under highly controlled conditions to preserve the equilibrium conditions with respect to Ba/Ti ratio, annealing temperature ( T ), and oxygen partial pressure ( P _O2), systematic variations in the phase transition temperature can be noted with respect to Ba/Ti ratio and T . From the data extracted, we can then determine solubility limits. Equilibrating the defect reactions at the solubility limits provides a direct approach to identify and calculate the defect energetics. The phase transition temperature decreased with increasing concentration of the TiO₂ partial-Schottky defects (BaTi_1−δO_3−2δ) and the BaO partial-Schottky defects (Ba_1−δTiO_3−δ), and showed discontinuous changes in the two-phase region. The formation enthalpy and entropy for the partial-Schottky defect reactions was evaluated to be 2.32±0.1 eV and 10.15±0.7 k _B for the BaO partial-Schottky defect, and 2.89±0.1 eV and 8.0±1.5 k _B for the TiO₂ partial-Schottky defects equilibrated under air annealing conditions.     

An Alternative to Cohen's Standardized Mean Difference Effect Size: A Robust Parameter and Confidence Interval in the Two Independent Groups Case.

The authors argue that a robust version of Cohen's effect size constructed by replacing population means with 20% trimmed means and the population standard deviation with the square root of a 20% Winsorized variance is a better measure of population separation than is Cohen's effect size. The authors investigated coverage probability for confidence intervals for the new effect size measure. The confidence intervals were constructed by using the noncentral t distribution and the percentile bootstrap. Over the range of distributions and effect sizes investigated in the study, coverage probability was better for the percentile bootstrap confidence interval. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Microstructural parameters related to liquid-phase sintering

Often, we need means to explain the effects of process variations with respect to the properties of sintered materials. Hence, quantification of microstructural parameters in the sintering process is an inherent part of liquid-phase sintering. A random grain distribution results in a random distribution of the distance between neighboring grains. This distribution determines most of the microstructural parameters, such as coordination number and contiguity. In this study, a statistical model based on an assumed Rayleigh distribution of the closest distance between neighboring grains is developed to establish the relations between microstructural parameters in liquid-phase sintering. A new grain-packing factor is derived to describe the grain arrangement. It is useful in quantifying the theoretical relations between microstructural parameters and describing the sintering process.     

Effect of Acceptor (Mg) Concentration on the Resistance Degradation Behavior in Acceptor (Mg)-Doped BaTiO3 Bulk Ceramics: II. Thermally Stimulated Depolarization Current Analysis

Thermally stimulated depolarization current (TSDC) of acceptor (Mg)-doped BaTiO₃ ceramics was analyzed with different acceptor concentrations for coarse-grained specimens with uniform grain sizes. In all specimens, the increase of the polarization temperature ( T _P) for a fixed condition of polarization field ( E _P) and polarization time ( t _P) increased TSDC peak associated with an oxygen vacancy ( V _O^••) relaxation. When the acceptor concentration is increased, both T _P to generate same magnitude of TSDC and the relaxation temperature ( T _m) of the TSDC peak systematically decreased. On the other hand, the activation energy of the oxygen vacancy relaxation showed roughly constant values of ∼0.9 eV, irrespective of acceptor concentration. Such behavior can be explained by a decrease in the relaxation time constant (τ₀), which is in turn associated with the shape of oxygen vacancy profile in the specimen after polarization. The decrease of T _P, T _m, τ₀, and the little change of activation energy from the TSDC data with the increase of acceptor concentration implies an increase in the oxygen vacancy concentration C ( V _O^••). The experimentally observed behavior of C ( V _O^••) vs acceptor concentration could be explained by the defect chemical model, and from these results, the acceptor ionization energy E _A was estimated to be about 1.0 eV.