Attention: Reaction Time and Accuracy Reveal Different Mechanisms.

The authors propose that there are 2 different mechanisms whereby spatial cues capture attention. The voluntary mechanism is the strategic allocation of perceptual resources to the location most likely to contain the target. The involuntary mechanism is a reflexive orienting response that occurs even when the spatial cue does not indicate the probable target location. Voluntary attention enhances the perceptual representation of the stimulus in the cued location relative to other locations. Hence, voluntary attention affects performance in experiments designed around both accuracy and reaction time. Involuntary attention affects a decision as to which location should be responded to. Because involuntary attention does not change the perceptual representation, it affects performance in reaction time experiments but not accuracy experiments. The authors obtained this pattern of results in 4 different versions of the spatial cuing paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Estimation of Weibull Parameters With Competing-Mode Censoring

Existing results are reviewed for the maximum likelihood (ML) estimation of the parameters of a 2-parameter Weibull life distribution for the case where the data are censored by failures due to an arbitrary number of independent 2-parameter Weibull failure modes. For the case where all distributions have a common but unknown shape parameter the joint ML estimators are derived for i) a general percentile of the j-th distribution, ii) the common shape parameter, and iii) the proportion of failures due to failure mode j. Exact interval estimates of the common shape parameter are constructable in terms of the ML estimates obtained by using i) the data without regard to failure mode, and ii) existing tables of the percentage points of a certain pivotal function. Exact interval estimates for a general percentile of failure-mode-j distribution are calculable when the failure proportion due to failure-mode-j is known; otherwise a joint s-confidence region for the percentile and failure proportion is calculable. It is shown that sudden death endurance test results can be analyzed as a special case of competing-mode censoring. Tabular values for the construction of interval estimates for the 10-th percentile of the failure-mode-j distribution are given for 17 combinations of sample size (from 5 to 30) and number of failures.     

Nanostructured thin palladium-silver membranes: Effects of grain size on gas permeation properties

Submicron-thick Pd-Ag alloy membranes, prepared on 4 nm pore -alumina support by magnetron sputter deposition, are nanocrystalline with a grain (crystallite) size of about 20 nm. The membranes show good selectivity for hydrogen over helium (about 4000 at 300°C). Hydrogen permeation is dominated by the surface reaction steps in 100–200°C with an activation energy of about 30 kJ/mol. Bulk diffusion resistance becomes important at higher temperatures (>200 °C). Grain size is the most critical parameter affecting the hydrogen permeance of the thin nanostructued Pd-Ag membranes. Increase in Pd-Ag grain size from about 20 to 60 nm results in a substantial improvement in hydrogen permeance with a higher apparent activation energy in 100–300°C. Grain growth appears to increase the hydrogen permeability in the bulk phase of the Pd-Ag membranes. Helium permeance through the grain boundary decreases with increasing temperature or hydrogen partial pressure due to grain expansion. Carbonation and the accompanied grain expansion have detrimental effects on the perm-selectivity of the Pd-Ag membranes.     

Amino‐Functionalized Silica Membranes for Enhanced Carbon Dioxide Permeation

Functionalization of silica membranes is important for enhancing surface interactions with specific chemicals in order to enhance separations. It is important to develop synthesis strategies that allow control over the density and the surface chemistry of the functional group in order to tailor the membrane separation properties. In this paper we investigate the ability of amino functionalization to enhance CO₂ transport in silica membranes. Specifically, we examine three synthesis techniques for functionalizing silica membranes with amino groups that result in different surface chemistries of the silica membranes. Silica membranes are amino‐functionalized by atomic layer deposition (ALD) with aminopropyldimethylethoxysilane (APDMES), ethylenediamine (EDA)‐assisted APDMES ALD, and direct attachment of aminopropyltriethoxysilane (APTES) from the liquid phase. Three different reaction schemes are presented and verified by using Fourier‐transform infrared (FTIR) spectroscopy. The FTIR measurements were performed on silica powders that were processed using the same reaction conditions as the membranes used in this study. The differences in reaction schemes are correlated with changes in the CO₂ facilitation characteristics. It is found that high loadings of amino groups, in which interaction with the silica surface is minimized, promote the highest CO₂ transport.     

Glycoprotein A is the immunodominant antigen of Pneumocystis carinii in mice following immunization

A rapid and simple dual enzyme-linked immunosorbent assay was developed to quantitate the relative frequency of monoclonal antibodies produced against Pneumocystis carinii glycoprotein A (gpA) or other antigens of P. carinii after immunization with whole organisms. In BALB/cj mice, P. carinii gpA was clearly the immunodominant antigen, with a quarter of all hybridomas secreting antibody directed against this molecule.     

Unbiased Maximum-Likelihood Estimation of a Weibull Percentile when the Shape Parameter is Known

The maximum-likelihood (ML) estimator for a percentile of a Weibull distribution with a known shape parameter is considered. Multiplicative correction factors are listed for rendering the ML estimator mean or median unbiased in the cases where the samples are type II censored with or without replacement. The correction factors depend upon the number of failures and the shape parameter but are independent of the sample size and the percentile being estimated.     

Gamma 3 gene-disrupted mice selectively deficient in the dominant IgG subclass made to bacterial polysaccharides undergo normal isotype switching after immunization with polysaccharide-protein conjugate vaccines

Bacterial polysaccharides (PS) are T-independent type 2 Ags that elicit restricted Ab responses of IgM and IgG3 in mice and IgM and predominantly IgG2 in humans. Immunodeficiency in the dominant IgG subclass made to PS is associated with chronic sinus and pulmonary infections with PS-encapsulated bacteria. To elucidate the biologic role of the dominant IgG subclass in the immune response to PS and to make an animal model of human IgG subclass deficiency, we generated mice with a targeted disruption of the exon encoding the CH1 domain of the gamma 3 heavy-chain constant region gene. Homozygotes had no detectable serum IgG3, and their splenocytes did not produce IgG3 after LPS stimulation. IgG3(-/-) mice immunized with PS from Pseudomonas aeruginosa LPS O-side chain or Streptococcus pneumoniae type 19F capsule did not produce any IgG3 anti-PS Abs, in contrast to wild-type mice in which IgG3 was the major IgG subclass. Immunizing both wild-type and IgG3(-/-) mice with 19F PS-protein conjugate elicited IgG1 Abs. We conclude that IgG3(-/-) mice have a selective deficiency in the dominant murine IgG subclass made to T-independent type 2 Ags and may be a useful animal model of IgG subclass deficiency. In addition, we show that the anti-PS Ab class switching to IgG1 that occurs when mice are immunized with a PS-protein conjugate vaccine does not require sequential Ig expression or an intact, upstream gamma 3 heavy-chain gene.     

Reverse osmosis desalting of inland brackish water of high gypsum scaling propensity: kinetics and mitigation of membrane mineral scaling

The potential for mineral scaling that may limit the generation of new potable water resources by reverse osmosis (RO), from inland brackish water of high gypsum scaling propensity, was experimentally explored via flux decline measurements and real-time RO membrane surface imaging. Antagonistic gypsum and calcium carbonate scaling kinetics were demonstrated for high-sulfate brackish water desalting. RO scaling studies with brackish water from the California San Joaquin Valley (approximately 10 000 mg/L total dissolved solids) revealed that membrane gypsum scaling was increasingly retarded with rising bicarbonate concentrations. Crystal growth rate, fractional membrane scale coverage, and flux decline decreased by up to about 63, 78, and 73%, respectively, as the bicarbonate concentration increased, at the membrane surface, from < 0.01 to 7.81 mM, for a gypsum saturation index of 2. Inhibition of gypsum crystal growth was attributed to bicarbonate adsorption onto the crystal surfaces, and CaCO3 scaling was undetected even up to a calcite saturation index of approximately 16. Given the suppression of gypsum scaling by bicarbonate, it is essential to considerthis effect in the conventional practice of pH adjustment to suppress CaCO3 scaling. The present results suggest that antagonistic and synergistic mineral crystallization kinetics effects are important for optimizing scale-control strategies (e.g., acid and antiscalants addition to the RO feed).     

Systematic and random errors in least squares estimation for circular contours

It is assumed that stochastically independent measurements are made of the distance from a reference centre to n points spaced at equi-angular intervals along an arc of length θ on the circular contour of a part. The least squares estimates of the radius of the circular contour and the coordinates of the true centre relative to the reference centre are derived assuming that the distance between the true and reference centres is small, relative to the radius of the part. These estimates are shown to be expressible as linear combinations of the measured distances with coefficients that are explicit functions of n and θ.

The estimates are shown to be systematically in error (biased) unless the true and reference centres coincide. Formulas are given for the calculation of the bias error in any situation. The random error of the estimated quantities is expressed in terms of the random error of an individual measurement and the values of n and θ. The correlation coefficient between the estimated quantities is also found. The results enable the determination, in advance of making measurements, of whether the likely random and systematic errors will be tolerable for a given choice of n and θ and a given centring accuracy