Showing papers by "Université de Sherbrooke published in 1990"

Efficient molecular dissociation by a chirped ultrashort infrared laser pulse.

Abstract: Dissociation probabilities and populations of excited vibrational states are calculated numerically for interaction of a Morse oscillator with a chirped, ultrashort (${\mathit{t}}_{\mathit{p}}$${10}^{\mathrm{\ensuremath{-}}11}$ sec), intense laser pulse. It is shown that if the pulse frequency \ensuremath{\omega}(t) decreases at a specific rate adapted to the molecular anharmonicity, the dissociation probability is many orders of magnitude higher than for a monochromatic pulse of the same intensity. Such pulses should be useful for more efficient multiphoton dissociation of molecular bonds.

Influence of temperature and pressure on the electronic transitions in SnS and SnSe semiconductors.

Abstract: Optical-absorption measurements in the near infrared have enabled us to determine the direct and indirect band gaps of SnS and SnSe layered compounds, in the a and b polarizations, at temperatures ranging from 7 to 295 K (at P=0 kbar) and pressures up to 40 kbar (at T=295 K) At T=295 K and P=0 kbar, we obtain, for SnS, ${\mathit{E}}_{\mathrm{ind}}$${\mathrm{i}}_{\mathrm{a}}$ a=1076 eV, ${\mathit{E}}_{\mathrm{ind}\mathbf{b}}$=1049 eV, and ${\mathit{E}}_{\mathrm{dir}}$ b=1296 eV; and for SnSe, ${\mathit{E}}_{\mathrm{ind}\mathbf{a}}$=0898 eV, ${\mathit{E}}_{\mathrm{ind}\mathbf{b}}$=0903 eV, ${\mathit{E}}_{\mathrm{dir}\mathbf{a}}$=1238 eV, and ${\mathit{E}}_{\mathrm{dir}\mathbf{b}}$=1047 eV For both crystals, an additional structure, associated with an impurity level, is observed in the a polarization Its shape reveals the three-dimensional nature of the electronic properties in these compounds The measured pressure coefficients for the transitions ${\mathit{E}}_{\mathrm{inda}}$, ${\mathit{E}}_{\mathrm{ind}\mathbf{b}}$, ${\mathit{E}}_{\mathrm{dir}\mathbf{a}}$, and ${\mathit{E}}_{\mathrm{dir}\mathbf{b}}$ are, for SnS, -56, -60, -83, and -73 meV/kbar, respectively; and for SnSe, -52, -89, -36, and -112 meV/kbar, respectively The corresponding temperature coefficients are, for SnS, -024, -036, (undetermined), and -0563 meV/K; and for SnSe, -032, -029, -043, and -043 meV/K The behavior of the transition energies with temperature is explained by a self-energy correction attributed to the interaction between electrons and nonpolar phonons Concerning this temperature dependence, we find that the effect of volume dilatation is opposite in sign to that of the electron-phonon interactions The latter effect dominates

Competitive antagonists discriminate between NK2 tachykinin receptor subtypes.

Abstract: 1. We have compared the ability of various tachykinins and selective tachykinin receptor agonists to induce contraction of the endothelium-denuded rabbit pulmonary artery (RPA) and hamster trachea (HT) and have estimated the affinity of some newly developed NK2 selective antagonists in the same tissues. 2. In confirmation of previous findings, experiments with the agonists indicated that NK2 receptors are the main if not the sole mediators of the response to tachykinins in both RPA and HT. No evidence for significant degradation of neurokinin A (NKA) was found in either tissue when experiments were repeated in the presence of a mixture of peptidase inhibitors (thiorphan, captopril and bestatin, 1 microM each). 3. The peptide antagonists tested were: Peptide I = [Tyr5, D-Trp6,8,9, Arg10]-NKA(4-10); Peptide II = [Tyr5, D-Trp6,8,9, Arg10]-NKA(3-10); Peptide III = Ac-Leu-Asp-Gln-Trp-Phe-Gly-NH2. The three peptides produced a concentration-dependent rightward shift of the concentration-response curve to NKA in both RPA and HT with no significant depression of the maximal response attainable. The slopes of the Schild plots were not significantly different from unity, indicating a competitive antagonism. Peptides I and II were about 100 times more potent in the RPA than in the HT, while Peptide III was about 100 times more potent in the HT than RPA. 4. The pA2 values obtained in these two tissues with the three antagonists were not significantly different when tested in the absence or presence of peptidase inhibitors, or when a selective NK2 receptor agonist, [beta Ala8]-NKA(4-10) was used instead of NKA.(ABSTRACT TRUNCATED AT 250 WORDS)

Photosensitizing activity of water- and lipid-soluble phthalocyanines on Escherichia coli.

Abstract: Escherichia coli, as most Gram-negative bacteria, is insensitive to the photosensitizing action of both lipid-soluble Zinc-phthalocyanine (Zn-Pc) and water-soluble Zinc-mono/disulfonated phthalocyanine (Zn-PcS). Photosensitivity can be induced by alteration of the outer membrane, as obtained by either induction of competence or treatment with Tris-EDTA. Both phthalocyanines largely bind at the level of the cytoplasmic membrane; however, Zn-PcS shows a superior photosensitizing activity as compared with Zn-Pc. Biochemical analyses performed on irradiated cells suggest that the cytoplasmic membrane is an important target of the photoprocess, while DNA is not involved.

SAR observations and modeling of the C-band backscatter variability due to multiscale geometry and soil moisture

Abstract: The effect of the multiscale surface geometry on the sensitivity of C band synthetic aperture radar (SAR) data to soil moisture is studied. The experimental data consist of C-band SAR images of an agricultural site, including fields with various combinations of three distinct roughness components from small to large scale. The backscatter variability due to surface roughness has been analyzed. The effect of random roughness associated with soil clods is never less than 2 dB, and the effect of a row pattern can be as strong as 10 dB. In addition, the periodic drainage topography induces a backscatter variability due to soil moisture variation and drainage relief. The results indicate that airborne C-band SAR data cannot be easily inverted into soil moisture data. However, with ERS-1 or Radarsat data at an incidence angle of about 20 degrees , the effect of random and periodic roughness can be reduced to about 2 dB if the look angle is less than 50 degrees . >

On reducing computational complexity of codebook search in CELP coder through the use of algebraic codes

Abstract: A general framework is introduced which allows both fast search and freedom in designing codebooks with good statistical properties. Several previously proposed schemes are compared from this viewpoint. A backward filtering formulation is given to show that sparse algebraic codes (SACs) (i.e., with few nonzero components) offer distinct advantages. It is shown that they reduce the optimal-search computation per codeword. They also allow control of the statistical properties of the codebook in the time and frequency domains. This control can be dynamic in the sense that it can be made to evolve as a function of the linear predictive coding model A(z). The algebraic-code excited linear prediction (ACELP) technology which allows full duplex operation on a single TMS320C25 at rates between 4.8 and 16 kb/s and which is based on SAC-driven dynamic codebooks is described. >

pH modulates conducting and gating behaviour of single calcium release channels

Abstract: Intracellular pH changes affect excitation-contraction coupling in skeletal and cardiac muscles. However the proton implication in modulating the sarcoplasmic reticulum Ca2+ release channel activity has never been visualized at single channel level. A large conducting Ca2+ release pathway has previously been characterized after incorporation of skeletal and cardiac sarcoplasmic reticulum vesicles into planar lipid bilayers. This channel has been activated by micromolar and millimolar concentrations of Ca2+ and ATP, respectively. The pH was independently varied on each side of the channels. Acidification of the cis-chamber (7.4 to 6.6) induced a modification of the gating behaviour, resulting in a decrease of the open probability. This effect was completely reversible. On the other hand, acidification of the trans-chamber (7.4 to 6.8) induced a reduction of the unitary conductance of the sarcoplasmic reticulum Ca2+ release channel.

Studies on inflammatory response induced by Ehrlich tumor in mice peritoneal cavity.

Abstract: In the present study we investigated the inflammatory response induced by the inoculation of Ehrlich tumor cells (EAT) into the peritoneal cavity of mice. It was found that after inoculation of 103 EAT cells, the number of peritoneal leukocytes remained unchanged till the sixth day. Subsequently, the number of cells increased as a consequence of tumor growth. EAT cells did not induce influx of PMN leukocytes till six days after tumor implantation, but a significant influx was observed on the tenth day. Inoculation of the tumor cells did not induce production of H2O2 by peritoneal cells at any time examined and induced low levels of macrophage spreading only until the third day after tumor implantation but not later on. The levels of thromboxane in the peritoneal cavity were not affected by the presence of the tumor, whereas prostaglandin E2 levels were significantly increased at all times examined. The biological significance of these results on the evolution and escape of the tumor from host defense mechanisms is under investigation.

Kinin receptor subtypes.

Abstract: Bradykinin, kallidin, and some of their metabolites exert potent biological effects in a variety of organs and tissues These effects are mediated by specific receptors, of two different types B1 and B2, according to the classification proposed in 1980 by Regoli and Barabe This classification has recently been challenged by several authors on the basis of data obtained with a variety of synthetic analogs (both agonists and antagonists) of bradykinin and kallidin B2-receptor subtypes and even a new receptor type, B3 have been considered Other workers have shown that some of the kinins' biological effects, such as the activation of prostaglandins or histamine release, may occur through nonreceptor mechanisms Recently, a variety of new kinin-related peptides have been prepared and tested In particular, new selective agonists for both B1 and B2 receptors have been identified and used for receptor characterization, particularly in complex biological systems Antagonists are critically reviewed, because several of them are in effect partial agonists Pure antagonists have been obtained and used for receptor characterization in various organs Activation of receptors and nonreceptor mechanisms by kinins bring about direct effects on smooth muscles and other cells and indirect effects mediated by endothelium-derived relaxing factor, or by prostacyclin, prostaglandins, leukotrienes, histamine, etc Interaction of kinins with their receptors activates second messengers that may be different from one cell to another (in the same tissue) and that are activated either by kinins or by other endogenous mediators released by kinins(ABSTRACT TRUNCATED AT 250 WORDS)

Chitin/chitosan transformation by thermo-mechano-chemical treatment including characterization by enzymatic depolymerization.

Abstract: Chitosan, the deacetylated derivative of chitin, was until recently produced by hydrolysis in 50% (w/v) NaOH. Application of thermo-mechano-chemical technology to chitin deacetylation was evaluated as an alternative method of chitosan production. This process consists of a cascade reactor unit operating under reduced alkaline conditions of 10% (w/v) NaOH. Prior mercerization of chitin at 4 degrees C for 24 h was required for high deacetylation yields. Sudden decompression of the aqueous alkaline suspension of mercerized chitin resulted in near complete deacetylation of chitin. Reactor residence time was 90 s at 230 degrees C prior to decompression. The chitosan produced was characterized by elemental analysis, (13)C-NMR and enzymatic depolymerization. Enzymatic determination of the degree of acetylation of chitin/chitosan mixtures was also investigated. Relative chitinase and/or chitosanase digestibilities were shown to be strongly dependent on chitin deacetylation. Based on enzymatic digestibilities, the alkaline aqueous high shear process does not appear to produce significant secondary products. Correlation of chitosanase digestibility with percentage of deacetylation provides a simple biological assay to study chitosan composition.

Quinone sensitized electron transfer photooxidation of nucleic acids: chemistry of thymine and thymidine radical cations in aqueous solution.

Abstract: — The 2-methyl-l,4-naphthoquinone (MQ) sensitized photooxidation of nucleic acid derivatives has been studied by laser flash photolysis and steady state methods. Thymine and thymidine, as well as other DNA model compounds, quench triplet MQ by electron transfer to give MQ radical anions and pyrimidine or purine radical cations. Although the pyrimidine radical cations cannot be directly observed by flash photolysis, the addition of N,N,N',N'-tetramethyl-l,4-phenylenediamine (TMPD) results in the formation of the TMPD radical cation via scavenging of the pyrimidine radical cation. The photooxidation products for thymine and thymidine are shown to result from subsequent chemical reactions of the radical cations in oxygenated aqueous solution. The quantum yield for substrate loss at limiting substrate concentrations is 0.38 for thymine and 0.66 for thymidine. The chemistry of the radical cations involves hydration by water leading to C(6)-OH adduct radicals of the pyrimidine and deprotonation from the N(l) position in thymine and the C(5) methyl group for thymidine. Superoxide ions produced via quenching of the quinone radical anion with oxygen appear to be involved in the formation of thymine and thymidine hydroperoxides and in the reaction with N(l)-thyminyl radicals to regenerate thymine. The effects of pH were examined in the range pH 5–8 in both the presence and absence of superoxide dismutase. Initial C(6)-OH thymine adducts are suggested to dehydrate to give N(l)-thyminyl radicals.

Dynamic codebook for efficient speech coding based on algebraic codes

Abstract: A method of encoding a speech signal is presented. This method improves the excitation codebook and search procedure of the conventional Code Excited Linear Prediction (CELP) speech encoders. Use is made of a dynamic codebook (201, 202) based on the combination of two modules: a sparse algebraic code generator (201) associated to a filter (202) having a transfer function varying in time. The generator (102) is a structured codebook with codewords having very few non zero components. The filter (202) shapes the spectral characteristics whereby the resulting excitation codebook (201, 202) exhibits favorable perceptual properties. The search complexity in finding the best codeword is greatly reduced by bringing the search back to the algebraic code domain thereby allowing the sparsity of the algebraic code to speed up the necessary computations.

Migration of fetal intestinal intervillous cells in neonatal mice.

Abstract: The migration of intestinal intervillous epithelial cells labeled in the fetus was followed in neonatal mice. At 17 days of gestation, a first group of pregnant mice received three intraperitoneal injections of 3H-thymidine (150 microCi/injection) administered at 30 min intervals. Two mothers were sacrificed 3 hours after the first injection. Mice from different litters were also sacrificed on days 0, 2, 4, 8, 12, 14, and 16 after birth. A second group of pregnant mice was injected at 18 1/2 days of gestation and offspring were sacrificed on days 6, 8, 10, 12, 14, and 16 after birth. Segments of duodenum and ileum were fixed in glutaraldehyde, postfixed in osmium tetroxide, dehydrated, and embedded in Epon. Sections were stained with aldehyde fuchsin and processed for radioautography. By following the leading front and trailing edge of labeled cells in the longest villi of the duodenum and ileum, we observed that 1) extrusion zones become active immediately after birth and 2) the longest villi do not elongate until 10 days after birth in the duodenum and 14 days in the ileum, that is, when all labeled epithelial cells originally present in the fetus have been extruded. Moreover, by measuring the distance between the internal limit of the inner circular layer of smooth muscle and the intervillous epithelium at 17 days of gestation (12.95 +/- 1.18 microns) or the bottom of the crypts at day 3 (14.81 +/- 0.91 microns), we propose that crypts do not develop as downgrowths: rather the intervillous epithelium is reshaped and the crypt-villus junction moves upward, away from the muscularis externa.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological activities of phthalocyanines. XII: Synthesis tumor uptake and biodistribution of 14C-labeled disulfonated and trisulfonated gallium phthalocyanine in C3H mice.

Abstract: The biodistribution and metabolism of 14C-labeled disulfonated and trisulfonated gallium phthalocyanine (Ga-PcS) was studied in radiation-induced fibrosarcoma tumor-bearing C3H mice. The [14C]Ga-PcS compounds were prepared via the condensation of [14C]phthalic acid and sulfophthalic acid in the presence of gallium chloride and characterized by their spectroscopic and chromatographic properties. The tissue concentrations of the dyes was measured by scintillation counting of the 14C and by extraction and fluorescence measurements. Elevated dye levels were found in the liver, lungs, kidneys and spleen as well as in the tumor. Lower sulfonation of Ga-PcS favored liver and spleen uptake whereas higher dye sulfonation resulted in greater kidney uptake. Both dyes showed high tumor uptake with peak concentrations exceeding those of most tissues except for the liver in the case of Ga-PcS2. The highest tumor uptake was observed with Ga-PcS3. Both dyes were slowly excreted from the body. The liver—feces pathway was favored in the case of Ga-PcS2 with high activities persisting in the liver, even after 21 days. The Ga-PcS3 was preferentially excreted via the kidney—urine pathway. High performance liquid chromatography analysis of the liver and tumor extracts of [14C]Ga-PcS3-treated animals did not reveal desulfonation of the dye.

Motion and coalescense of gas bubbles in non-Newtonian polymer solutions

Abstract: In this paper, we report new results of an experimental study concerning the motion and coalescense of bubbles in viscoelastic polymer solutions. In particular, the shapes and velocity-volume characteristics of air nitrogen and carbon dioxide bubbles have been examined in solutions of polyacrylamide in 50/50 glycerine/water mixtures under a wide range of conditions. Furthermore, the possible effects of surface-active agents and of the aging characteristics of polymer solutions were also explored. Under no conditions did we observe an abrupt discontinuity in bubble velocity-volume data, and the fluid viscoelasticity is known to exert a significant influence in governing the shapes of bubbles moving in viscoelastic media. Finally, the coalescence of two bubbles simultaneously released from different orifices was studied in terms of the volume of one bubble required to achieve coalescence with a second bubble of fixed volume at predetermined heights above the orifices. Coalescence was studied with different polymer solutions for air, N 2 and CO 2 for a range of (initial) orifice separations. It is shown that the fluid viscoelasticity influences the coalescence via the shapes and wake characteristics of bubbles.

The 'stretched'-Golay and other codes for high-SNR finite-delay quantization of the Gaussian source at 1/2 bit per sample

Abstract: Error-correcting codes are considered as codebooks for high-performance vector quantization (VQ) of the IID Gaussian source at fractional bit rate. A family of good rate-one-half codes is introduced: the stretched Golay codes. The performance of these codes is compared to other good block codes, trellis-coded quantization, and other techniques. The stretched Golay codes are shown to outperform previously published results for block lengths 32, 40, 56, and 64. The good performance, together with fast decoding make these techniques attractive for applications such as low-bit-rate coding of speech. >