Aging and the detection of observer and moving object collisions.

The authors examined age-related differences in the detection of collision events. Older and younger observers were presented with displays simulating approaching objects that would either collide or pass by the observer. In 4 experiments, the authors found that older observers, as compared with younger observers, had less sensitivity in detecting collisions with an increase in speed, at shorter display durations, and with longer time-to-contact conditions. Older observers also had greater difficulty when the scenario simulated observer motion, suggesting that older observers have difficulty discriminating object motion expansion from background expansion from observer motion. The results of these studies support the expansion sensitivity hypothesis-that age-related decrements in detecting collision events involving moving objects are the result of a decreased sensitivity to recover expansion information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detecting and Characterizing Asphaltene Instability

Methods of detecting and characterizing asphaltenes abound in the literature, but most can raise significant levels of controversy. Because of real differences between samples, it can be difficult for one lab to validate the results of another. In this work, a suite of seven crude oil samples, including two with recognized asphaltene problems and a sequence of three hydrotreater product fluids, have been selected for comparative testing by relatively simple techniques at ambient conditions. The onset of flocculation in response to addition of heptane was identified in batch mode by microscopic observation with the onset solubility conditions calculated from refractive index measurements. These were compared to continuous heptane titrations of toluene solutions of oil with an optical detection system. At essentially infinite dilution, solubility parameter can be calculated from the known properties of toluene and heptane. Further characterization of some asphaltene fractions was provided by measurements of the amount of precipitate, by FTIR, and by elemental analysis. The results demonstrate similarities and differences in the properties measured by these different techniques and help to highlight some of the difficulties of such comparisons of asphaltenes and their stability.     

Efficient return algorithms for associated plasticity with multiple yield planes

A new return method for implicit integration of linear isotropic yield criteria is presented. The basic idea is to perform all the manipulations in the principal stress space and thereby achieve very simple formulae for calculating the plastic corrector stresses, based on the constant gradient of such criteria. The return formulae are in closed form and no iteration is required. The method accounts for three types of stress return: return to a single yield plane, to a discontinuity line at the intersection of two yield planes and to a discontinuity point at the intersection between three or more yield planes. The infinitesimal and the consistent elastoplastic constitutive matrix are calculated for each type of stress return, as are the conditions to ascertain which type of return is required. The method is exemplified with the Mohr–Coulomb yield criterion. Copyright © 2005 John Wiley & Sons, Ltd.     

Design of a time-efficient video-goniophotometer combining bidirectional functions assessment for transmission and reflection

A detailed knowledge of the light distribution characteristics through advanced window systems is required to improve the visual comfort of the building's occupants while controlling the propagation of daylight in rooms and the solar gains. An innovative bidirectional goniophotometer has recently been set up for this purpose, using digital image capture and the projection of the emerging light on a diffusing screen. It therefore provides a continuous investigation of the bidirectional transmission figures in a time-efficient way. This instrument was converted into a double-purpose device, allowing both transmission and reflection measurements, which induced several strong constraints due to the conflict of incident and emerging light flux in reflection mode: on one hand the incident beam had to be restricted to the sample area only; on the other hand, as the screen obstructed the incoming light flux in some positions, a special opening in the latter was required. The practical answer to these constraints, detailed in this paper, proved to be reliable, appropriate and efficient.