Showing papers by "Université de Sherbrooke published in 1984"

Interaction of low-energy electrons (1—30 eV) with condensed molecules: II. Vibrational-librational excitation and shape resonances in thin N 2 and CO films

Abstract: Low-energy [(1-30)-eV] electron scattering in multilayer films of ${\mathrm{N}}_{2}$ and CO, and in Ar matrices containing ${\mathrm{N}}_{2}$, was investigated using high-resolution electron-energy-loss spectroscopy (HREELS) and one-dimensional multiple scattering theory. The films were formed by condensing the gases on a polycrystalline platinum substrate held near a temperature of 20 K. Comparisons of experimental electron-energy-loss spectra in the range 0-2.4 eV with those generated theoretically indicated that the former are composed of peaks which result from single and multiple vibrational losses broadened by multiple phonon losses. The excitation function of the $v=1\ensuremath{-}3$ vibrational levels of ground-state ${\mathrm{N}}_{2}$ and CO were measured under different film conditions and angles of incidence of the primary beam. In CO the excitation functions exhibited broad peaks at 2.5 and 20 eV due to the formation of $^{2}\ensuremath{\Pi}$ and $^{2}\ensuremath{\Sigma}$ transient anions, respectively, similar to those previously found in ${\mathrm{N}}_{2}$ films. From measurements of the intensity of the fundamental vibrational loss in ${\mathrm{N}}_{2}$ as a function of film thickness, the total cross section for excitation of all possible vibrational levels of ${\mathrm{N}}_{2}$ was found to be 3.3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$ at resonance, and the sum of all phonon cross sections was found to be about 5 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}16}$ ${\mathrm{cm}}^{2}$.

Parametric study of the flow and temperature fields in an inductively coupled r.f. plasma torch

Abstract: A theoretical investigation of the effect of different parameters on the flow and the temperature fields in a radiofrequency inductively coupled plasma is carried out. The parameters studied are: central injection gas flow rate, total gas flow rate, input power, and the type of plasma gas. The results obtained for argon and nitrogen plasmas at atmospheric pressure indicate that the flow and the temperature fields in the coil region, as well as the heat flux to the wall of the plasma confinement tube, are considerably altered by the changes in the torch operating conditions.

Geometry Study of a High Resolution PET Detection System Using Small Detectors

Abstract: The current trend in positron emission tomography (PET) towards very high spatial resolution tomographs raises the problem of detecting high energy gamma-rays with a high spatial accuracy while preserving the overall sensitivity of the camera It is the purpose of this paper to investigate the effects of some geometrical parameters on the detection efficiency and intrinsic spatial resolution of a circular array of narrow closely packed detectors Two approaches were employed: the first one uses the Monte-Carlo technique to simulate the interactions of gamma-rays in the detectors; the second one is based on the linear attenuation on a beam of gamma-rays impinging on a detector array Aperture functions and modulation transfer functions were obtained for various configurations of the detectors and septas Expressions for the resolution and the spectral signal-to-noise ratio were derived It is shown that minor modifications to the geometry can improve both the efficiency and intrinsic resolution of the detector array

a.c. response of fractal networks

Abstract: We calculate the a.c. frequency response of Sierpinski-gasket networks, in which the bonds consist of resistors R (or of impedances Z h ) and all nodes are connected to the circuit ground by identical capacitors C (or by impedances Z v ). The resulting complex, size-dependent admittance between any of the «principal» nodes and the circuit ground can be accurately described at all frequencies less than 1/RC by a finite-size scaling function whose exponents are combinations of the fractal dimension d f and the spectral or «fracton» dimension d s of the Sierpinski gasket. The response function also bears a striking similarity to experimental observations of the a.c. response of a random mixture of conducting and insulating particles Nous avons calcule la reponse en frequence en courant alternatif pour un reseau du type Sierpinski dans lequel les liens sont soit des resistances R (ou des impedances Z h ) et ou tous les nœuds sont relies a la terre par l'intermediaire de capacites C identiques (ou d'impedances Z v ). Pour toutes les frequences plus petites que 1/RC, l'admittance complexe resultante entre chacun des nœuds «principaux» et la terre peut etre exprimee avec precision au moyen d'une fonction d'echelle avec effet de taille finie, tous les exposants de cette fonction etant des combinaisons des dimensions fractale d f et spectrale d s du tamis de Sierpinski. La dependance en frequence de la fonction de reponse presente une tres forte ressemblance avec celle d'un melange aleatoire de particules conductrices et isolantes

Effects of metallic vapor on the properties of an argon arc plasma

Abstract: During thermal plasma processing of materials, vapor generated from injected particulate matter will enter the plasma. Even traces of metallic vapors may have a strong effect on the properties and the behavior of the plasma and on the associated heat flux to the injected particles. In this paper a model system is considered in which an argon plasma at atmospheric pressure is “contaminated” by small amounts of copper vapor. By using the Chapman-Enskog approximation for a multicomponent gas mixture the transport properties are calculated for such a contaminated argon plasma. The results show that there is a drastic effect on the electrical properties. For temperatures below 104 K, the electrical conductivity, for example, increases by more than an order of magnitude if metallic vapor is present. The presence of metallic contaminants is also somewhat felt by the reactional thermal conductivity. In contrast, there is no effect on the heavy-particle properties as long as the percentage of the contaminants remains small.

Chemical equilibrium model for the thermodynamic properties of mixed aqueous micellar systems: Application to thermodynamic functions of transfer

Abstract: Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems.

Insulin receptors in isolated adult mouse intestinal cells: studies in vivo and in organ culture.

Abstract: Isolated intestinal cells from adult mice possess a high concentration of insulin receptors. The binding capacity and the number of binding sites are higher in duodenum than in jejunum or ileum and in the upper part of the villus than in the crypts. The specific binding is, respectively, 11.8 ± 1.0±, 9.1 ± 4.0±, and 5.5 ± 0.3±/mg·protein for duodenum, jejunum, and ileum. The number of high affinity sites per cell is, respectively, 11.0 × 103, 3 × 103, and 2.5 × 103. The number of low affinity sites per cell is, respectively, 11.0 × 104, 4.1 × 103, and 3.9 × 103. This specific binding increases to 15.9 + 0.9± after 24 h of fasting and to 24.5 ± 2.2± mg protein after 48 h of fasting. This increase is due not only to an increment in the number of sites but also to alterations in affinity constants (K1, control, 0.380, 48-h fasting, 0.044 × 109 m−1; K2, control, 1.20, 48-h fasting; 2.61 × 107 m−1). The receptors are mainly located on the basolateral and internal membranes (P1, 9.4 ± 0.7±/mg protein), but are ...

The snow ploughing problem solved by a graph theory algorithm

Abstract: An algorithm to trace the itinerary of a snow ploughing truck that respects street priorities is developed. It is based on the notion of an Eulerian circuit in a directed graph, the existence of which is guaranteed due to the nature of the snow ploughing problem. The algorithm can be easily programmed in an interactive form on a micro-computer. The computer output presents the truck itinerary, each street given with its priority and the cumulative percentage of the street length with the same priority already ploughed with respect to the total length for that priority.

A Comparison between Chevron and Mitchell Osteotomies for Hallux Valgus

Abstract: A retrospective study of 15 Mitchell and 15 Chevron osteotomies was undertaken in order to compare the efficacy of these two procedures in the correction of hallux valgus. Patient satisfaction, clinical findings, and roentgenographic measurements were all carefully evaluated after follow-up periods of 21 +/- 5 months for the Chevron and 34 +/- 8 months for the Mitchell procedures. Differences observed were a better correction of the angle between the first and second metatarsals by the Mitchell osteotomy (2.3 vs 5.5 degrees) and a tendency to loose the correction in the immediate postoperative period for the Chevron osteotomy. However, no clinical superiority could be demonstrated, nor did patient satisfaction differ in the two techniques. The authors conclude that these procedures give essentially equivalent results. Although the outcome was generally considered satisfactory by the patient, nearly 40% of both groups had metatarsalgia in the lateral rays, which stresses the importance of carefully considering load distribution across the foot in planning any corrective surgery.

Scintillation Detection with Large-Area Reach-Through Avalanche Photodiodes

Abstract: Silicon avalanche photodiodes of the "reach-through" type have been used as scintillation detectors with device performance closely approaching that of PMT's. The device consists of a 6 × 6mm diode with a 5 × 5mm photosensitive area in a 6.7 × 6.7 × 2.0mm package which is suitable for mounting in an array. Typical characteristics at room temperature are: quantum efficiency ?50% at ?=415nm; surface dark current <200nA; bulk dark-current (before gain) <1nA; noise current (at optimum gain of 20 to 50) <1pA/Hz?; response time <5ns; capacitance ?21pF; biasing voltage ?200-400 Volts. When coupled to a NaI(Tl) scintillator (9 × 9 × 38mm) photo-peak resolutions (FWHM) for 662keV radiation of 10.4% at 21°C and 9.8% at 0°C were measured. The measured noise equivalent primary charge of one detector at a gain of 50 was 121 electrons (51 electrons rms) at room temperature. The significance of this new detector to high resolution imaging systems and detector arrays is discussed.

Baseband speech coding at 2400 bps using "Spherical vector quantization"

Abstract: This paper concerns a new Quantization Scheme for efficient encoding of waveforms below or about one bit per sample. This technique is then applied to the encoding of baseband residual signals to demonstrate the feasibility of (baseband) Residual Excited LPC at 2400 hit/sec. The technique called "Spherical Vector Quantization" is described in which a block of n consecutive samples is quantized as a vector. The magnitude of the vector is transmitted independently of the vector's orientation. This vector's orientation is vector quantized using a codebook which can be seen as representing a set of N points on a unit hypersphere. The cases for blocks of n = 8 and 24 are discussed which make use of results by Conway and Sloane on regular point lattices. For n = 8, the algorithm is detailed which solves both the problem of finding the closest point on the hypersphere and the problem of determining the index of that point. Experiments involving SVQ in coding the speech baseband residual are described which show in particular that subband coding does not contribute any quality improvement when SVQ is used.

Acute necrosis of the intestinal mucosa with high serum levels of diamine oxidase

Abstract: A patient with acute necrosis of the intestinal mucosa and high serum diamine oxidase activity is described. The 71-year-old woman, with a history of hypertension and cardiovascular and peripheral arteriosclerotic disease, presented with acute epigastric pain, vomiting, and a deteriorating hemodynamic condition. Serum level of the intestinal enzyme diamine oxidase (DAO) obtained on admission, approximately 24 hr after the onset of symptoms, was 7.4 times above the normal value. An exploratory laparotomy performed 6 hr later revealed cyanosis and areas of transmural necrosis involving the entire small bowel. The bowel was not resected because of the extent of lesion. Thirty hours after the first sample was taken and 2 hr before death, the serum DAO level was only slightly above normal. It is suggested that this biochemical marker could provide a valuable tool for the early diagnosis of intestinal ischemia.

Phthalocyanine and naphthalocyanine photosensitized oxidation of 2′‐deoxyguanosine: distinct type i and type ii products

Abstract: The photodynamic properties of the di-and tetrasulfonated zinc and aluminium phthalocyanines and a tetrasulfonated aluminium napththalocyanine were studied using 2′-deoxyguanosine as a DNA model compound. The major photooxidation products of this nucleoside were identified and classified according to their formation through a radical mechanism (type I) or a singlet oxygen mediated mechanism (type II). The major type I product was obtained and identified as 2,2-diamino [(2-deoxy-β-d-erythropentofuranosyl)-4-amino]-5(2H)-oxazolone. Two major type II products were characterized as the 4R* and 4S* diastereomers of 9-(2-deoxy-β-d-erythropentofuranosyl)-7,8-dihydro-4-hydroxy-8-oxoguanine. In addition a third product, also resulting from a type II photooxidation, was identified as 8-oxo-7,8-dihydro-2′-deoxyguanosine. Quantification of these products provided a means to estimate the contribution of type I and type II pathways during the phthalocyanine and naphthalocyanine mediated photooxidation of 2′-deoxyguanosine, confirming the major role of singlet oxygen in these processes.

On the identification and design of single amplifier single resistance controlled oscillators

Abstract: Some interesting observations are made on eight recently reported single-amplifier single-resistance-controlled (SRCO) oscillators. We show that those 8 circuits can be regrouped into two families qualified as modified Deliyannis-Friend Bridge- T and modified RC: CR dual of the Deliyannis-Friend Bridge- T . We, furthermore, show that only two circuits need be identified and present a synthesis method which preserves the nature and value of all admittances in each circuit belonging to a given family.