Model bicategories and their homotopy bicategories

We give the definitions of model bicategory and $w$-homotopy, which are natural generalizations of the notions of model category and homotopy to the context of bicategories. For any model bicategory $\mathcal{C}$, denote by $\mathcal{C}_{fc}$ the full sub-bicategory of the fibrant-cofibrant objects. We prove that the 2-dimensional localization of $\mathcal{C}$ at the weak equivalences can be computed as a bicategory \mathcal{H}\mbox{o}(\mathcal{C}) whose objects and arrows are those of $\mathcal{C}_{fc}$ and whose 2-cells are classes of $w$-homotopies up to an equivalence relation. The pseudofunctor \mathcal{C} \stackrel{r}{\longrightarrow} \mathcal{H}\mbox{o}(\mathcal{C}) which yields the localization is constructed by using a notion of fibrant-cofibrant replacement in this context. When considered for a model category, the results in this article give in particular a bicategory whose reflection into categories is the usual homotopy category constructed by Quillen.Comment: 37 pages, many elevator calculus diagrams. This is a "preliminary version

Surface Studies of Calcium Oxalate Dihydrate Single Crystals During Dissolution in the Presence of Urine

Single crystals of Calcium Oxalate Dihydrate (COD) were grown from solution under controlled release of the reacting ions. Dissolution of COD was studied at different pH levels and in different dilutions of urine. The descriptors of the contour were determined during dissolution of COD using a quantitative morphological technique. The shape parameters and surface ruggedness were determined from Fourier and fractal analysis. The results obtained give quantitative information on the dissolution kinetics and the surface geometry of COD crystals in normal and diluted urine. Dissolution inhibition and morphological changes of COD crystals during dissolution were attributed to selective adsorption of urine non-ionic macromolecules on the crystal stepped surface. Surface etching of COD was found to depend on urine dilution and time of incubation. The data obtained suggest that the geometric structure of the surface is likely to be a potential factor in understanding crystal aggregation in stone formation

Experimental determination of microwave attenuation and electrical permittivity of double-walled carbon nanotubes

The attenuation and the electrical permittivity of the double-walled carbon nanotubes (DWCNTs) were determined in the frequency range of 1–65 GHz. A micromachined coplanar waveguide transmission line supported on a Si membrane with a thickness of 1.4 µm was filled with a mixture of DWCNTs. The propagation constants were then determined from the S parameter measurements. The DWCNTs mixture behaves like a dielectric in the range of 1–65 GHz with moderate losses and an abrupt change of the effective permittivity that is very useful for gas sensor detection. ©2006 American Institute of Physic

Exploring levels of student-athlete burnout at two Canadian universities

The purpose of the current study was to examine the levels of burnout among student-athletes at two Canadian universities and to investigate whether there were significant differences related to gender, sport, year of university sport participation, academic year, and academic program. Burnout was measured by administering Raedeke and Smith’s (2001) Athlete Burnout Questionnaire to 145 student-athletes from various sports. Overall, 1.4% of the student-athletes had elevated burnout scores on all three subscales, and 17% scored high on two of the three subscales. No significant differences emerged with regards to year of varsity sport participation, academic year, or program. However, women had significantly higher levels of emotional and physical exhaustion than men. Significant differences also emerged in relation to levels of emotional and physical exhaustion, and of sport devaluation, when comparing various sports.  Le but de cette étude était d’évaluer le niveau d’épuisement d’étudiants athlètes fréquentant deux universités canadiennes et de déterminer s’il y avait des différences significatives liées au sexe, au sport, au nombre d’années de participation au sport universitaire, ainsi qu’à l’année universitaire et au programme d’étude. L’épuisement a été mesuré en distribuant le « Athlete Burnout Questionnaire » (Raedeke & Smith, 2001) à 145 étudiants athlètes universitaires de différentes disciplines sportives. En somme, 1,4 % des participants ont affiché des scores élevés sur chacune des trois sous-échelles et 17 % ont fait de même sur deux d’entre elles. Aucune différence marquée n’a été identifiée quant au nombre d’années de participation au sport universitaire, ni à l’année universitaire ou au type de programme d’étude. Cependant, les femmes ont affiché un niveau d’épuisement émotif et physique significativement plus élevé que celui des hommes. En outre, on a noté des différences marquées en comparant les sports entre eux en ce qui a trait au niveau d’épuisement émotif et physique et au niveau de dévalorisation des disciplines

A localization of bicategories via homotopies

Given a bicategory C and a family W of arrows of C, we give conditions on the pair (C, W) that allow us to construct the bicategorical localization with respect to W by dealing only with the 2-cells, that is without adding objects or arrows to C. We show that in this case, the 2-cells of the localization can be given by the homotopies with respect to W, a notion defined in this article which is closely related to Quillen’s notion of homotopy for model categories but depends only on a single family of arrows. This localization result has a natural application to the construction of the homotopy bicategory of a model bicategory, which we develop elsewhere, as the pair (Cf c, W) given by the weak equivalences between fibrant-cofibrant objects satisfies the conditions given in the present article.Fil: Descotte, María Emilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Investigaciones Matemáticas "Luis A. Santaló". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Matemáticas "Luis A. Santaló"; ArgentinaFil: Dubuc, Eduardo Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Investigaciones Matemáticas "Luis A. Santaló". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Matemáticas "Luis A. Santaló"; ArgentinaFil: Szyld, M.. Dalhousie University Halifax; Canad

Evaluation of the Surface Roughness of Cystine Stones Using a Visible Laser Diode Scattering Approach

To understand the processes of fragmentation and the chemical reactivity of solids, proper characterization of surface topography is crucial. This paper describes a non-destructive technique of quantifying the surface roughness of cystine renal stones, using visible laser diode scattering and fractal geometry. Fragments of cystine stones were mounted on microscope slides and coated by a carbon-sputtering apparatus. The slides were placed under a dynamic active-vision system, using a visible laser diode to measure three-dimensional surface coordinates. The data obtained were analyzed by fractal geometry. Surface fractal dimensions were determined by the variation method. The results showed that the surface of a compact-size sample can be evaluated quantitatively. The technique is valuable for the accurate presentation of surfaces in three dimensions

Modulations of ongoing alpha oscillations predict successful short-term visual memory encoding

Alpha-frequency band oscillations have been shown to be one of the most prominent aspects of neuronal ongoing oscillatory activity, as reflected by electroencephalography (EEG) recordings. First thought to reflect an idling state, a recent framework indicates that alpha power reflects cortical inhibition. In the present study, the role of oscillations in the upper alpha-band (12 Hz) was investigated during a change-detection test of short-term visual memory. If alpha oscillations arise from a purely inhibitory process, higher alpha power before sample stimulus presentation would be expected to correlate with poorer performance. Instead, participants with faster reaction-times showed stronger alpha power before the sample stimulus in frontal and posterior regions. Additionally, faster participants showed stronger alpha desynchronization after the stimulus in a group of right frontal and left posterior electrodes. The same pattern of electrodes showed stronger alpha with higher working-memory load, so that when more items were processed, alpha power desynchronized faster after the stimulus. During memory maintenance, alpha power was greater when more items were held in memory, likely due to a faster resynchronization. These data are consistent with the hypothesis that the level of suppression of alpha power by stimulus presentation is an important factor for successfully encoding visual stimuli. The data are also consistent with a role for alpha as actively participating in attentional processes

Solution of the Euler Unsteady Equations Using Deforming Grids. G.U. Aero Report 9704.

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