Back and forth between continuous and discrete for the working computer scientist

This paper gives a perfect, ideal, discretization of continuous notions. This is a very convenient frame to treat continuous problems or theories with the help of a computer. This is illustrated by the conversion of algorithms using real numbers into algorithms using integers only and the founding of discrete geometry.     

Twelve-Nitrogen-Atom Cyclic Structure Stabilized by 3d-Element Atoms: Quantum Chemical Modeling

Using various versions of density functional theory (DFT), DFT M06/TZVP, DFT B3PW91/TZVP, DFT OPBE/TZVP, and, partially, the MP2 method, the possibility of the existence of 3d-element (M) compounds with nitrogen having unusual M: nitrogen ratio 1:12, unknown for these elements at the present, was shown. Structural parameter data were presented. It was shown that all MN4 groupings have tetragonal-pyramidal structure. It was noted that the bond lengths formed by nitrogen atoms and an M atom were equal to each other only in the case of M = Ti, V, Cr and Co, whereas for other Ms, they were slightly different; moreover, the bond angles formed by nitrogen atoms and an M atom were equal to 90.0°, or practically did not differ from this value. Thermodynamic parameters, NBO analysis data and HOMO/LUMO images for this compound were also presented. Good agreement between the calculated data obtained using the above three quantum chemical methods was also noted.     

Analyse des problemes de geometrie et apprentissage de la preuve au secondaire

Résumé

Le présent article rend compte de l'élaboration d'une grille d'analyse des problèmes de géométrie, et de sa mise à l'épreuve par la classification des problèmes et exercices de géométrie synthétique dans une collection de manuels du secondaire parmi les plus utilisées au Québec. Le cadre conceptuel sur lequel s'appuie cette élaboration s'inspire principalement des travaux de Balacheff (1987), Barbin (1988), Brousseau (1998), Hanna (1995) et Rouche (1989), et débouche sur une typologie des preuves de géométrie. La classification des problèmes à partir de cette grille et l'analyse qui en découle nous a permis de conclure sur les aspects de l'apprentissage de la preuve que nous évaluons comme mal ? gérés ? dans la collection : transition non suffisamment graduelle du sensible au formel (peu de problèmes qui sollicitent une validation hybride, niveau de formalisation trop longtemps stationnaire), prépondérance des applications directes et des déductions locales sur les séquences déductives, intérêt et mode de présentation des résultats qui ne favorisent pas une ? attitude de preuve ?.     

Temporal Regionalization of 7-Day Low Flows in the St. Lawrence Watershed in Quebec (Canada)

Winter and summer 7-day low flows of eighteen natural rivers in the St. Lawrence River watershed of Quebec were analyzed over the period from 1934 to 2000. The rivers were first subdivided into three modes using principal component analysis. Two of these modes are located on the south shore of the St. Lawrence River, respectively south (Southeast mode) and north (East mode) of the 47°N, and the third (Southwest mode) is located on the north shore. The Southeast mode shows a significant increase in 7-day low flows in winter and summer due to increasing summer and fall precipitation, whereas the Southwest mode shows a significant decrease in summer 7-day low flows due to an increase in evapotranspiration. No significant change in winter and summer 7-day low flows is observed in the East mode. Results show that the variability of 7-day low flows and their link with climate indices are mainly seasonally dependent. The North Atlantic Oscillation (NAO) is the only index which is correlated to 7-day low flows in all three modes. This correlation is positive for north shore rivers and negative for south shore rivers. Furthermore, only north shore rivers are correlated to NAO in both winter and summer.     

Using Superconducting Magnet to Reproduce Quick Variations of Gravity in Liquid Oxygen

A ground based facility (OLGA), providing magnetic compensation of gravity in oxygen, has been developed. A 2-T superconducting magnetic solenoid is used to create the required magnetic field. A novel electrical supply permits to quickly vary the magnetic field, leading to rapid variation of the acceleration forces applied to oxygen. These variations can be made from overcompensation of gravity (−0.5g) to zero gravity or from zero gravity to reduced gravity (0.4g) with a time constant of 340 ms. This time is typical of the cutoff or reignition of spacecraft engines. Preliminary results on the transient flows induced by these acceleration variations in a reservoir filled with liquid and gaseous oxygen are presented.     

Individual and area socioeconomic inequalities in cause-specific unintentional injury mortality: 11-Year follow-up study of 2.7 million Canadians

This study investigated the association between individual and area socioeconomic status (SES) and leading causes of unintentional injury mortality in Canadian adults. Using the 1991–2001 Canadian Census Mortality Follow-up Study cohort (N = 2,735,152), Cox proportional hazard regression was used to calculate hazard ratios and 95% confidence intervals for all-cause unintentional injury, motor vehicle collision (MVC), fall, poisoning, suffocation, fire/burn, and drowning deaths. Results indicated that associations with SES differed by cause of injury, and were generally more pronounced for males. Low education was associated with an elevated risk of mortality from all-cause unintentional injury and MVC (males only) and poisoning and drowning (both sexes). Low income was strongly associated with most causes of injury mortality, particularly fire/burn and poisoning. Having no occupation or low occupational status was associated with higher risks of all-cause injury, fall, poisoning and suffocation (both sexes) and MVC deaths among men. Associations with area deprivation were weak, and only areas with high deprivation had elevated risk of all-cause injury, MVC (males only), poisoning and drowning (both sexes). This study reveals the importance of examining SES differentials by cause of death from a multilevel perspective. Future research is needed to clarify the mechanisms underlying these differences to implement equity-oriented approaches for reducing differential exposures, vulnerability or consequences of injury mortality.     

Lignite oxidative desulphurization: notice 3—process technological aspects and application of products

International Journal of Coal Science & Technology - The study reviews the process of oxidative desulphurization of high-sulphur Ukrainian lignite, which was performed by coal treatment using...     

Implicit Contact Handling for Deformable Objects

We present an algorithm for robust and efficient contact handling of deformable objects. By being aware of the internal dynamics of the colliding objects, our algorithm provides smooth rolling and sliding, stable stacking, robust impact handling, and seamless coupling of heterogeneous objects, all in a unified manner. We achieve dynamicsawareness through a constrained dynamics formulation with implicit complementarity constraints, and we present two major contributions that enable an efficient solution of the constrained dynamics problem: a time stepping algorithm that robustly ensures non-penetration and progressively refines the formulation of constrained dynamics, and a new solver for large mixed linear complementarity problems, based on iterative constraint anticipation. We show the application of our algorithm in challenging scenarios such as multi-layered cloth moving at high velocities, or colliding deformable solids simulated with large time steps.