Psychophysical estimation of speed discrimination. II. Aging effects

We studied the effects of aging on a speed discrimination task using a pair of first-order drifting luminance gratings. Two reference speeds of 2 and 8 deg/s were presented at stimulus durations of 500 ms and 1000 ms. The choice of stimulus parameters, etc., was determined in preliminary experiments and described in Part I. Thresholds were estimated using a two-alternative-forced-choice staircase methodology. Data were collected from 16 younger subjects (mean age 24 years) and 17 older subjects (mean age 71 years). Results showed that thresholds for speed discrimination were higher for the older age group. This was especially true at stimulus duration of 500 ms for both slower and faster speeds. This could be attributed to differences in temporal integration of speed with age. Visual acuity and contrast sensitivity were not statistically observed to mediate age differences in the speed discrimination thresholds. Gender differences were observed in the older age group, with older women having higher thresholds.     

A Griffith crack problem for a nonhomogeneous medium

A boundary value problem of two bonded nonhomogeneous similar planes containing a crack is considered. Poisson's ratio is supposed to be uniform whereas the shear modulus varies and is a function of the distance from the plane of the crack. Using Fourier transforms the original problem is reduced to a singular integral equation with a weakly singular kernel. The integral equation is then solved numerically and crack energy and stress intensity factors are calculated.     

Characteristics of holding, patterns of play, and social behaviors between parents and infants in New Delhi, India.

Characteristics of holding, play, and social behaviors between 54 mothers and fathers and their 1-year-old infants were observed within the context of their extended families in New Delhi, India. Mothers picked up and held infants more than did fathers, and were more likely to feed and comfort them and to invest more time feeding and displaying affection to them than were fathers. When parents held infants they were more likely to display affection than to feed, comfort, or play with them. Fathers engaged in more rough play than did mothers, and mothers engaged in more peek-a-boo than did fathers. Mothers and fathers treated boys and girls quite similarly. Infants smiled at, vocalized to, and followed mothers more than they did fathers. Parents were generally preferred over relatives as social partners. The data point to the cultural specificity of certain parent–child activities. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Experimental and first-principles studies of BiVO4/BiV1-xMnxO4-y n-n+ homojunction for efficient charge carrier separation in sunlight induced water splitting

Though bismuth vanadate (BiVO₄) is extensively used as a photoactive material, its performance in harnessing solar energy is limited by ineffective separation of photo-excited charge carriers. We demonstrate here a concept of n-n⁺ homojunction of BiVO₄/BiV_1-xMn_xO_4-y, which improves its charge separation efficiency. Using first-principles theoretical calculations, we determine the effect of Mn substitution on oxygen vacancy formation energies and associated changes in the electronic structure of BiVO₄. Showing that Mn substitution pushes the Fermi level of BiVO₄ towards its conduction band, we predict that the associated enhanced bending of bands at the homojunction (BiVO₄/BiV_1-xMn_xO_4-y) facilitates efficient separation of charge carriers. With Mott-Schottky experiments, we verify the increased band bending at the n-n⁺ homojunction, and show that the maximum photocurrent density measured in a sample with n-n⁺ homojunction is ten times higher than that obtained of the pristine sample. Secondly, Mn substitution in BiVO₄ also reduces the oxygen vacancy formation energy, promoting higher concentration of O-vacancies, further enhancing the photoelectrochemical response.     

Dynamics of Jacobi elliptic and soliton solutions for the modified quadratic-cubic nonlinear Schrödinger equation

We consider the quadratic-cubic nonlinear Schrödinger equation in the presence of external source, as an approximate model for a relatively quasi-1D Bose-Einstein condensate coupled to a waveguide. A scaling transformation is used to obtain a wide class of exact solutions for this model. It possesses fractional transform Jacobi elliptic solutions whose dynamics can be controlled by judicious choice of source and nonlinearity parameters. For other parametric conditions, this model exhibits bright/dark, Lorentzian-type and rational dark solitons. The presence of quadratic nonlinear term introduces a constant background and thus amplified the propagating wave. Further, the phase of the propagating wave is locked to the source and can be made either in- or out of-phase to the source wave through sign reversal of source parameter.