Pulsed laser deposition of silicon nitride thin films by laser ablation of a Si target in low pressure ammonia

We report the deposition of Si-N films by multipulse excimer laser ( = 308 nm, _FWHM = 30 ns) ablation of Si wafers placed in a slow flow of NH₃ in the pressure range (1 bar-1 mbar). The films are deposited on to a Si collector placed parallel to the Si target. We succeeded in depositing pure amorphous Si₃N₄ films at a pressure of 1 mbar of NH₃. The deposition rate reached a maximum value of 0.2–0.3 nm per pulse. At lower pressures, the deposited films consist of a fine mixture of three amorphous phases (amorphous stoichiometric silicon nitride, amorphous non-stoichiometric silicon nitride and amorphous silicon). The amorphous silicon is prevalent in films deposited at a pressure of several to several tens of bars. Droplets of polycrystalline -Si are sometimes visible on the film surface. The experimental evidence, is analysed with a view to elucidating the participation in the chemical synthesis of the three main stages of the process: the substance expulsion from the target by laser ablation, the transition through the gas of the expulsed substance and it's final impact on the collector. We conclude that silicon nitride is mostly synthesized during the impact on the collector of the flow of the ablated substance.     

A participatory approach for the prevention of type 2 diabetes for francophone youth of New Brunswick]

Diabetes, a serious public health problem, is on the rise, claiming millions of victims. A considerable body of research exists on diabetes, but the development of effective primary prevention strategies is just beginning. This article presents the results of a project, based on an innovative approach where health professionals and community groups have come together to address the issue. The purpose of the project is to develop an intervention strategy for the prevention of type 2 diabetes directed at young francophones living in a minority environment in New Brunswick and adapted to their needs. Qualitative data were gathered from two focus groups and submitted for a content analysis. The process was evaluated. The young francophones have identified the school environment as ideal for intervention. According to them, the intervention should be adapted to the age of the youths. For the 5-to-13-year-old group, the intervention should target healthy eating habits and physical activity whereas for the 14-to-18-year-old group, the emphasis should be on preventing diabetes. The youth and the professionals acquired a greater understanding of the problem of diabetes and its prevention. Youth can now proceed to action, with appropriate guidance. The experience and knowledge of the professionals contributed to the development of the strategy. A shortage of dietitians in public health to work in the area of the prevention of diabetes has been noted.     

Psychiatric comorbidity, health status, and functional impairment associated with alcohol abuse and dependence in primary care patients: Findings of the PRIME MD-1000 study.

The psychiatric comorbidity, health, and functioning of primary care patients with alcohol abuse and dependence (AAD) was investigated in a sample of 1,000 patients. Psychiatric symptomatology was assessed with the Primary Care Evaluation of Mental Disorders (PRIME-MD) diagnostic system. Health and functional status was assessed with the Medical Outcomes Study Short Form General Health Survey (SF-20). Results indicated that use of the PRIME-MD system brought about a 71% increase in physician recognition of AAD. AAD patients were diagnosed with substantial psychiatric comorbidity, and they reported poorer health and functioning than did patients without any psychiatric disorders. However, they reported less impairment and psychiatric comorbidity than did patients with other psychiatric disorders. Results also indicated that AAD patients' health and functioning were associated with the presence or absence of psychiatric comorbidity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasonic Reflectivity Imaging in Three Dimensions: Exact Inverse Scattering Solutions for Plane, Cylindrical, and Spherical Apertures

The problem of reconstructing the reflectivity of a three-dimensional medium with density and compressibility variations is examined. For the special case of continuous-wave (CW) insonification, exact inversion formulas have recently been reported for recovering an unknown scattering parameter from scattering measurements. In this work, exact solutions, or inversion formulas, are obtained for the general case of arbitrary broad-band insonification where the incident wave is assumed to be a spherically diverging broad-bandwidth pulse of arbitrary shape. Solutions are derived under the assumption that the scattering is sufficiently weak for the Born approximation to hold. Exact inversion formulas are obtained for three aperture geometries: a plane, cylindrical, or spherical recording surface enclosing the scattering region. Under most practical conditions, the process of back projection and coherent summation over spherical surfaces in image space, without prior filtering, is shown to provide a close approximation to the exact inversion procedure. Finally, in the case of the spherical geometry, the mathematical equivalence between the three-dimensional inverse Radon transform and the far-field approximation to the exact solution is demonstrated.     

Le stress per?u et son influence sur le comportement alimentaire des étudiants de l'Université de Moncton, Campus de Moncton

Objectif. Mesurer et analyser le lien entre le stress per?u et le comportement alimentaire d'étudiants de première (Et1) et de quatrième année (Et4) à l'Université de Moncton au début (T1) et à la fin (T2) du trimestre universitaire. Méthodes. Quatre-vingt-quatorze sujets de divers programmes universitaires ont participé à l'étude. Le stress per?u a été mesuré à l'aide de la Perceived Stress Scale, la consommation alimentaire par un journal alimentaire de trois jours et la fréquence de consommation alimentaire par un questionnaire de fréquence. Résultats. Au début du trimestre, les Et1 et Et4 présentent un niveau de stress faible. Au T2, le stress per?u des Et4 augmente significativement (22,3+/-1,4; p=0,005). Le profil alimentaire mesuré selon le niveau de conformité au "Guide alimentaire canadien pour manger sainement" montre, avec l'accroissement du stress, une augmentation de la consommation de lait et produits laitiers (p=0,05) chez les Et1,T1 et de produits céréaliers (p=0,02) chez les Et4,T2. Une corrélation négative significative est observée chez les Et4 entre le stress per?u et l'ingestion de thiamine (r=-0,48, p=0,006) et de zinc (r=-0,42, p=0,02). Aucune corrélation n'est observée entre le stress, l'apport en calories et la consommation des autres nutriments étudiés. Conclusion. Ces résultats révèlent l'importance d'intervenir auprès des étudiants universitaires et d'implanter des sessions d'information favorisant la gestion du stress et l'adoption de comportements alimentaires sains.     

Iterative Toeplitz solvers with local quadratic convergence

We study an iterative, locally quadratically convergent algorithm for solving Toeplitz systems of equations from [R. P. Brent, F. G. Gustavson and D. Y. Y. Yun. “Fast solution of Toeplitz systems of equations and computation of Padé approximations”,J. Algorithms, 1:259–295, 1980]. We introduce a new iterative algorithm that is locally quadratically convergent when used to solve symmetric positive definite Toeplitz systems. We present a set of numerical experiments on randomly generated symmetric positive definite Toeplitz matrices. In these experiments, our algorithm performed significantly better than the previously proposed algorithm.     

Lexicographic Bit Allocation for MPEG Video

We consider the problem of allocating bits among pictures in an MPEG video coder to equalize the visual quality of the coded pictures, while meeting buffer and channel constraints imposed by the MPEG video buffering verifier. We address this problem within a framework that consists of three components: (1) a bit production model for the input pictures, (2) a set of bit-rate constraints imposed by the video buffering verifier, and (3) a novel lexicographic criterion for optimality. Under this framework, we derive simple necessary and sufficient conditions for optimality that lead to efficient algorithms.     

Optimal Energy Measurement in Nonlinear Systems: An Application of Differential Geometry

Design of TES microcalorimeters requires a tradeoff between resolution and dynamic range. Often, experimenters will require linearity for the highest energy signals, which requires additional heat capacity be added to the detector. This results in a reduction of low energy resolution in the detector. We derive and demonstrate an algorithm that allows operation far into the nonlinear regime with little loss in spectral resolution. We use a least squares optimal filter that varies with photon energy to accommodate the nonlinearity of the detector and the non-stationarity of the noise. The fitting process we use can be seen as an application of differential geometry. This recognition provides a set of well-developed tools to extend our work to more complex situations. The proper calibration of a nonlinear microcalorimeter requires a source with densely spaced narrow lines. A pulsed laser multi-photon source is used here, and is seen to be a powerful tool for allowing us to develop practical systems with significant detector nonlinearity. The combination of our analysis techniques and the multi-photon laser source create a powerful tool for increasing the performance of future TES microcalorimeters.     

13C‐NMR study on the structure of phenol‐urea‐formaldehyde resins prepared by methylolureas and phenol

Phenol‐urea‐formaldehyde (PUF) resins were synthesized by reacting mixture of methylolureas (MMU), phenol, and formaldehyde. The structure of PUF cocondensed resins at different stages of reaction were analyzed by liquid ¹³C nuclear magnetic resonance (NMR) spectroscopy. The liquid ¹³C‐NMR analysis indicated that methylolureas had the dominant content in MMU with the reaction between urea and formaldehyde under the alkaline condition. The PUF cocondensed resins had no free formaldehyde. methylolureas were well incorporated into the cocondensed resins by reacting with phenolic units to form cocondensed methylene bridges. The second formaldehyde influenced the further reaction and the structure of the PUF resins. The resins with the prepared method of PUFB possessed relatively high degree of polymerization and low proportion of unreacted methylol groups. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009