Some natural carbonates for magnetic cooling below 1°K

The natural minerals calcite, magnesite, and dolomite containing 0.1% Mn ²⁺ ions have been investigated to determine their usefulness as cooling agents for adiabatic demagnetization. Cooling curves below 1°K, obtained by a series of adiabatic demagnetizations, gave characteristic temperatures: 0.05°K for the pink and the white calcites and the magnesite, and 0.1°K for the dolomite, in fair agreement with the values predictable from the ESR data for Mn ²⁺ . As for the specific heat constant,cT ²/R, the agreement with the ESR was good below 0.4° K with values of 6×10 ^–3 (°K) ² for the pink and the white calcites and the magnesite, and 22×10 ^–3 (°K) ² for the dolomite. The static magnetic susceptibility was measured from 4.2 to 0.06° K and gave the values of Curie constant: 0.44×10 ^–3 , 0.27×10 ^–3 , and 0.05×10 ^–3 emu/cm ³ at high temperature, for the polycrystalline samples of pink calcite, magnesite, and dolomite, respectively. The pink calcite and the dolomite obey Curie's law down to 0.8°K and the magnesite to 0.3°K. The ordering temperatures for these samples are deduced to be lower than 0.06°K. Measurement of the thermal conductivityK(T) is reported for several types of samples between 4 and 0.2°K.K(T) of the Iceland spar is 15 times better than that of CrK alum as reported elsewhere, whereas that of the single crystal of white calcite is about two times higher. The polycrystalline samples are poor from this point of view.Work supported by a grant from the National Research Council of Canada.     

Natural Oxidant Demand of Aquifer Materials Using the Push-Pull Technique

The quantification of the natural oxidant demand (NOD) of aquifer materials is required to estimate the fate of reagents injected into contaminated aquifers during in situ chemical oxidation applications. Three push-pull tests were conducted at a horizontal spacing of 12–20 m within an uncontaminated region of the saturated zone in the Canadian Forces Base Borden aquifer located near Alliston, Ont., Canada to estimate the NOD for permanganate. Each test contacted a minimum of 270 kg of aquifer material. Upper estimates of NOD values from the three tests were 0.51–0.75 g/kg based on the initial mass of aquifer material contacted, and lower estimates were 0.29–0.42 g/kg based on additional aquifer material mass contacted during the drift or reaction phase. These results compared favorably to NOD values determined from bench-scale tests with high solids mass to solution volume ratios. If design and operational concerns can be overcome, the push-pull test offers significant advantages over the variety of bench-scale testing methods currently used to determine the NOD of aquifer materials.     

Crowd of Virtual Humans: a New Approach for Real Time Navigation in Complex and Structured Environments

The navigation activity is an every day practice for any human being capable of locomotion. Our objective in this work is to reproduce this crucial human activity inside virtual environments. Putting together the high complexity of a realistic environment such as a city, a big amount of virtual humans and the real‐time constraint requires to optimize each aspect of the animation process. In this paper, we present a suitable topological structuring of the geometric environment to allow fast path finding as well as an efficient reactive navigation algorithm for virtual humans evolving inside a crowd.     

Elaboration d'un instrument de mesure des habiletés socio-cognitives chez l'enfant de cinq à dix ans.

To assess social cognitive skills in children, a special test was constructed with cognitive and linguistic demands adapted to young children. The test consisted of 4 tasks that were submitted to 200 children, aged 5–10 yrs. Three tasks were devised to measure cognitive role-taking and the 4th to measure referential communication. Results show a significant increase in performance with age for each task and a significant increasing order of difficulty in the tasks. Thus, each task corresponded to specific levels in the development of role-taking skills. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Magnetic cooling and susceptibility of MgO: Mn2+

ESR, paramagnetic susceptibility, and adiabatic demagnetization studies of single crystals of MgO doped with about 0.14 % Mn²⁺ are presented. The results of the ESR measurements are in good agreement with that obtained by previous investigators on crystals with lower Mn²⁺ concentration, but the line widths observed are much wider. Also, the line widths are wider by 20 % at 4.2°K than those at room temperature. The paramagnetic susceptibility obeys Curie's law very accurately down to 0.3°K and may be used for thermometry down to 0.1°K. The crystal has a maximum specific heat between 0.03 and 0.04°K. Temperatures well below 0.1°K can be attained by adiabatic demagnetization with a moderate field at 1.3°K.Work supported by a grant from the National Research Council of Canada.     

L'integration de l'information en fonction de la poly?emie des stimuli.

Those who have studied impression (formation) have often observed what is called the positive context effect. Two opposite hypotheses have been formulated to explain this phenomenon. According to one, the traits are interacting in such a way that there is a meaning shift due to the context. The 2nd hypothesis explains the phenomenon by a quite different interpretation, the generalized halo effect. Up to now it has not been possible to confirm one hypothesis or the other, so a new experiment was carried out wherein 1 of the experimental conditions, the context, was comprised of 2 traits whose evaluation was conflicting, and the test trait was polysemic (ambiguous). Ss were 120 undergraduates. Results seem to favor the generalized halo effect hypothesis, but there are reasons to think that the meaning shift hypothesis might better explain what happens when the persons perceived are not fictitious. (French abstract) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Study of the structure and transport of asymmetric polyamide membranes for reverse osmosis using the electron spin resonance (ESR) method

The electron spin resonance technique (ESR) was used to study the structure and transport of asymmetric aromatic polyamide membranes. TEMPO (2,2,6,6-tetramethyl-1-piperridinyloxy free radical) was used as a spin probe that was brought into the membrane either by (a) immersion ofthe membranes in aqueous TEMPO solutions, (b) reverse osmosis (RO) experiments with feed solutions involving TEMPO or (c) blending TEMPO in casting solutions. The membranes were further tested for the separation of sodium chloride and TEMPO from water by RO. It was concluded that aromatic polyamide membranes contain water channels in the polymer matrix like cellulose acetate membranes. The presence of such water channels allows aromatic polyamide membranes to be used as RO membranes. The diffusion of organic solutes through the water channels seems much slower in aromatic polyamide membranes than in cellular acetate membranes, which probably causes a higher separation of organic solutes by aromatic polyamide membranes than cellulose acetate membranes. A comparison was made with other RO membranes (cellulose acetate, CA) and ultrafiltration membranes (polyethersulphone, PES). It was observed that the ESR technique can be used to study the structure of OF and RO membranes. The presence of water channels in the polymer matrix seems indispensable for the RO membrane.