Showing papers by "Université de Sherbrooke published in 1995"

A review of vegetation indices

Abstract: In the field of remote sensing applications, scientists have developed vegetation indices (VI) for qualitatively and quantitatively evaluating vegetative covers using spectral measurements. The spectral response of vegetated areas presents a complex mixture of vegetation, soil brightness, environmental effects, shadow, soil color and moisture. Moreover, the VI is affected by spatial‐temporal variations of the atmosphere. Over forty vegetation indices have been developed during the last two decades in order to enhance vegetation response and minimize the effects of the factors described above. This paper summarizes, refers and discusses most of the vegetation indices found in the literature. It presents different existing classifications of indices and proposes to group them in a new classification.

Charge-resonance-enhanced ionization of diatomic molecular ions by intense lasers.

Abstract: We study the ionization of the ${\mathrm{H}}_{2}^{+}$ molecular ion in intense, short-pulse laser fields by numerically solving the three-dimensional time-dependent Schr\"odinger equation as a function of internuclear distance $R$. Anomalously high ionization for the molecular ion at large internuclear separations is observed for orientations parallel to the linearly polarized laser field. The ionization rate is found to exhibit maxima at large $R$, exceeding the atom limit by an order of magnitude. This is attributed to transitions between pairs of chargeresonant states which are strongly coupled by the field in diatomic molecular ions. The effect is shown to also occur in higher odd-charge diatomic molecular ions and can be attributed to field-induced nonadiabatic transitions between the charge-resonant states and electron tunneling suppression by the instantaneous Stark field of the laser.

Molecules in Laser Fields

Abstract: Current laser technology is capable of generating laser fields from the IR to visible wavelength regions in the form of well-tailored sequences of pulses with controllable phase and envelopes (pulse shape) [1–2]. Such pulses can be used for the efficient preparation of ensembles of atoms or molecules in specific states. This is of considerable interest not only in spectroscopy but also in studies of chemical dynamics [2–4]. Furthermore short pulses allow one to attain electric field strengths e (V cm-1) or equivalently laser intensities I (W/cm2) = ce 2 /8π (c = velocity of light) which are comparable or greater than atomic fields. An important consequence of the progress in this area is that one can greatly enhance radiative transition rates and even ionize molecules. Clearly strong field science and short pulse science are two fields which will become increasingly intertwined. Efficient rapid excitation requires increasingly higher intensities as can be seen from the simple example of a resonantly driven two-level system [6–7].

Consumer evaluations of sponsorship programmes

Abstract: Presents the results of a study of consumer reactions to various sponsorship programmes. The programmes differed in terms of four factors: the nature of the sponsorship (philanthropic versus commercial), its origin (pre‐existing versus event created by the sponsor), its frequency (continuous versus one‐shot) and the strength of the link between the entity (or the event) and the sponsor (weak versus strong). The results show that philanthropic sponsorship has a more positive impact on corporate image than commercial sponsorship. Also, the link between the sponsor and the event has a non‐linear effect on corporate image. Consumer interest in the sponsored event has a positive impact on perceptions of the sponsor′s image. In addition, it was found that the factors have interactive effects on consumer evaluations. Strategic implications for sponsorship management are derived from these results.

Normative Data for Grip Strength of Elderly Men and Women

Abstract: Objectives Grip strength is an important prerequisite for good performance of the upper limb, hence it is important to evaluate it correctly However, one of the main difficulties in evaluating the grip strength of elderly patients is the absence of valid norms Therefore, the objective of this study was to develop normative data for maximum grip strength of persons aged 60 years and older Method The grip strength of 360 subjects aged 60 years and older, randomly recruited by age and gender strata, was evaluated with the Jamar dynamometer and the Martin vigorimeter according to the protocol of the American Society of Hand Therapists Results Grip strength diminishes curvilinearly with age, and men are consistently stronger than women The data are presented by the means, standard deviations, and range, and as predictive equations obtained by regression analysis In addition to age and gender, hand circumference and body height proved to be the best indicators of grip strength for this population of elderly subjects Conclusion The random recruitment of subjects, the high participation rate in the study, and the comparability of the subjects who agreed to participate and those who refused give this study the high external validity that is essential to any norm study The predictive equations will help occupational therapists to better estimate the expected grip strength of elderly patients than they could if using only age and gender

Dissociation, ionization, and Coulomb explosion of H + 2 in an intense laser field by numerical integration of the time-dependent Schrödinger equation

Abstract: The time-dependent Schr\"odinger equation for ${\mathrm{H}}_{2}^{+}$ in a strong laser field is solved numerically for a model that uses the exact three-body Hamiltonian with one-dimensional nuclear motion restricted to the direction of the laser electric field. The influence of ionization on possible stabilization against dissociation is investigated. Unexpectedly high ionization rates from high vibrational states, exceeding those of neutral atomic hydrogen, are found. The ionization rates as functions of the internuclear distance R were also calculated for fixed nuclei, and these exhibit two strong maxima at large R, which explain the full dynamical results. A series of peaks seen in the calculated proton energy spectra can therefore be interpreted as occurring preferentially at (i) turning points of laser-induced vibrationally trapped states, and (ii) at the ionization maxima that occur at large internuclear distances of ${\mathrm{H}}_{2}^{+}$.

Routes to control of intense-field atomic polarizability.

Abstract: When atoms or molecules interact with intense bichromatic laser light, the relative optical phase between the two colors influences the formation of an electron wave packet in the continuum, further motion of the wave packet, and the phase accumulated by the wave packet on its trajectory. We show how the control over the wave packet motion can be used to generate single subfemtosecond pulses in the extreme ultraviolet spectral region. We also demonstrate control over the phase of the atomic polarizability.

Two-step Coulomb explosions of diatoms in intense laser fields

Abstract: A two-step model of Coulomb explosions of diatoms in intense laser fields is presented. In this model the molecule loses several electrons when the atoms are at the equilibrium internuclear distance and then fast Coulomb explosions occur until the products reach a critical distance Rc approximately=9 Bohr, at which several additional electrons are lost due to a recently discovered maxima of ionization rates occurring at R=Rc. Then the subsequent Coulomb explosion for the higher-charged ions takes place. The total combined Coulomb explosion energy agrees well with experimental results, showing striking regularities. The origin and intensity dependence of unexpectedly high ionization rates of dissociating nuclei at preferential, large internuclear distances R=Rc is also discussed and an analytic expression for Rc is derived.

Life History Consequences of Variation in Age of Primiparity in Bighorn Ewes

Abstract: We investigated the life history consequences of age at primiparity in two marked populations of bighorn sheep (Ovis canadensis), studied for 19 and 12 yr. Some ewes first lambed at 2 yr of age, others at 3 or 4 yr. Lambs of 2-yr-old ewes were smaller and less viable than lambs of older ewes. Lactation at 2 yr did not affect survival to 3 yr, but in one population it was associated with reduced survival from 3 to 4 yr. Two yr olds that weaned lambs gained less mass during summer than other 2 yr olds. Overwinter mass loss from 2 to 3 yr was correlated with autumn body mass, and was lower for parous than for nonporous ewes. Reproductive success at 3 yr was independent of reproductive status at 2 yr. At 4 yr, ewes that lactated as 2 yr olds were smaller than ewes that had not lactated as 2 yr olds. In one population, negative effects of early maturation upon mass gain and subsequent reproductive success became evident at high density, and very few 2 yr olds lambed when population density was high. The lifetime reproductive success of early- maturing ewes was not lower than that of late-maturing ewes. To account for individual variation in initial reproductive potential, we controlled body mass as a yearling, a variable that affected reproductive success. Mass as a yearling, however, did not interact with age of primiparity to affect survival, growth, or reproductive success. Uncertainties about re- source availability and possible effects of genotype and body fat may explain why many ewes postponed their first reproduction despite apparently low life history costs of early maturation.

Clara cell protein (CC-16) induces a phospholipase A2-mediated inhibition of fibroblast migration in vitro.

Abstract: Clara cell protein (CC-16, also designated CC-10) is synthesized by the bronchiolar epithelium and has been suggested as an inhibitor of phospholipase A(2) (PLA(2)) activity. Therefore, CC-16 is a candidate for controlling inflammatory events in the lung. Because CC-16 amounts and function may be altered in fibrosing lung diseases in which bronchiolar injury has been reported, it was measured in alveolar fluids and sera. Secretory PLA(2) activity in alveolar fluids and the influence of CC-16 on platelet-derived growth factor-induced human fibroblast chemotaxis and cytosolic PLA(2) activity were also explored. CC-16 content was decreased in alveolar fluids from idiopathic pulmonary fibrosis (IPF: 1.3 +/- 0.1 mg/L) and bleomycin lung (1.1 +/- 0.2 versus 2.1 +/- 0.2 mg/L in controls, p < 0.05), whereas there was a three- to ninefold increase in secretory PLA(2) activity (p < 0.05 versus controls). CC-16 inhibited fibroblast chemotaxis in a dose-dependent manner (90% inhibition at 30 mu g/ml CC-16). This inhibition was reversed by reducing CC-16. CC-16 was also able to lower fibroblastic cytosolic PLA(2) activity by 50% in vitro. In summary, CC-16 is able to inhibit fibroblast chemotaxis in vitro by mechanisms that may be related to a blockage of cytosolic PLA(2) activity. It can be postulated that CC-16 deficiency may contribute to fibroblast burden activity in fibrosing lung diseases.

Skyrme crystal in a two-dimensional electron gas.

Abstract: The ground state of a two-dimensional electron gas at Landau level filling factors near $\ensuremath{ u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ is a Skyrme crystal with long-range order in the positions and orientations of the topologically and electrically charged elementary excitations of the $\ensuremath{ u}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ ferromagnetic ground state. The lowest energy Skyrme crystal is a square lattice with opposing postures for topological excitations on opposite sublattices. The filling factor dependence of the electron spin polarization, calculated for the square lattice Skyrme crystal, is in excellent agreement with recent experiments.

Randomized Clinical Trial of Nutritional Supplementation Shows Little Effect on Functional Status among Free-Living Frail Elderly

Abstract: Nutritional deficiencies, frequently observed among the frail elderly, have been associated with increased morbidity and dependency. A randomized clinical trial was conducted to assess the impact of nutritional supplementation on the functional status of frail elderly living at home. Subjects (n = 50) over age 60 (mean 78 y) requiring community services and at elevated risk of undernutrition (excessive weight loss or body mass index < 24 kg/m2) were randomized to a high energy nutrient dense supplement provided by a dietitian or a control group receiving visits only. Outcome measures, including changes in handgrip strength, general well-being score, perception of health and number of falls, were measured by an investigator who was unaware of treatment assignment. After 12 wk, weight gain was greater in the supplemented group (2.1 +/- 2.3 vs. 0.6 +/- 1.6 kg; P < 0.01). Despite adequate statistical power, no functional measures differed except that the number of falls was lower among treated subjects vs. controls (0% vs. 21%; P = 0.05). Frail elderly can gain weight through oral supplementation, indicating the reversibility of weight loss in this group, but changes in functional status indicators may require a longer period of supplementation.

Hibernating Bats are Sensitive to Nontactile Human Disturbance

Abstract: I measured natural baseline activity and the response of hibernating bats to human presence in a hibernaculum containing ca. 1,300 bats of the species Myotis lucifugus and Myotis septentrionalis . Infrared detectors registered baseline flight movements in the hibernaculum over 62 days in January to March and over 8 days in April, when no observer was present, and they also registered the increase in flight movements following six visits of 1–2 h each to the hibernaculum. Visits to the mine resulted in a dramatic increase in flight activity of bats beginning within 30 min of the visit, peaking 1.0–7.5 h later, and remaining signifi-candy above baseline level for 2.5–8.5 h. These results show that, contrary to previously published studies, hibernating bats are sensitive to nontactile stimuli and arouse and fly following human visits. To avoid increased mortality due to the premature depletion of fat reserves, human visits to hibernacula should be kept to a minimum.

Wave packet structure and dynamics measured by Coulomb explosion.

Abstract: The motion and dimension of molecular nuclear wave packets produced by an ultrashort laser pulse are measured by Coulomb explosion induced by a delayed intense fs laser pulse. Two different continuum wave packets in ${\mathrm{I}}_{2}$ are observed as they move from an internuclear separation of $\ensuremath{\sim}7$ to $g100$ \AA{}. The ultimate spatial resolution is limited by the pulse duration of the probe laser. For 485 nm excitation of $B$-state wave packets the resolution limit is $\ensuremath{\sim}0.5$ \AA{}.

Risk factors for encephalopathy and mortality during melarsoprol treatment of Trypanosoma brucei gambiense sleeping sickness.

Abstract: This paper reviews the incidence of, and risk factors for, drug-induced encephalopathy and mortality (from all causes) during treatment with melarsoprol of 1083 patients with Trypanosoma brucei gambiense sleeping sickness in Nioki hospital (Zaire) between 1983 and 1990 Sixty-four patients (59%) developed encephalopathy and 62 (57%) died: 43 from reactive encephalopathy and 19 from other causes Univariate and multivariate analyses showed that the administration of prednisolone reduced significantly the incidence of encephalopathy and mortality during treatment, especially in patients with trypanosomes observed in the cerebrospinal fluid (CSF) and/or with a CSF white blood cell (WBC) count of 100 or more per mm3 The risk of encephalopathy was associated more strongly with the CSF WBC count than with the presence of CSF trypanosomes In the subgroup of patients with a CSF WBC count of 100 or more mm3, changing the melarsoprol regimen to 3 series of 3 injections instead of 3 series of 4 injections halved the mortality rate during treatment Treatment of patients who do develop reactive encephalopathy with the heavy metal chelator dimercaprol, in addition to intravenous steroids and anticonvulsants, may be harmful The data suggest that a further reduction of the total dose of melarsoprol may decrease toxicity without jeopardizing efficacy

Reaction mechanism of chitosanase from streptomyces sp. n174

Abstract: Chitosanase was produced by the strain of Streptomyces lividans TK24 bearing the csn gene from Streptomyces sp. N174, and purified by S-Sepharose and Bio-Gel A column chromatography. Partially (25-35%) N-acetylated chitosan was digested by the purified chitosanase, and structures of the products were analysed by NMR spectroscopy. The chitosanase produced heterooligosaccharides consisting of D-GlcN and GlcNAc in addition to glucosamine oligosaccharides [(GlcN)n, n = 1, 2 and 3]. The reducing- and non-reducing-end residues of the heterooligosaccharide products were GlcNAc and GlcN respectively, indicating that the chitosanase can split the GlcNAc-GlcN linkage in addition to that of GlcN-GlcN. Time-dependent 1H-NMR spectra showing hydrolysis of (GlcN)6 by the chitosanase were obtained in order to determine the anomeric form of the reaction products. The chitosanase was found to produce only the alpha-form; therefore it is an inverting enzyme. Separation and quantification of (GlcN)n was achieved by HPLC, and the time course of the reaction catalysed by the chitosanase was studied using (GlcN)n (n = 4, 5 and 6) as the substrate. The chitosanase hydrolysed (GlcN)6 in an endo-splitting manner producing (GlcN)2, (GlcN)3 and (GlcN)4, and did not catalyse transglycosylation. Product distribution was (GlcN)3 >> (GlcN)2 > (GlcN)4. Cleavage to (GlcN)3 + (GlcN)3 predominated over that to (GlcN)2 + (GlcN)4. Time courses showed a decrease in rate of substrate degradation from (GlcN)6 to (GlcN)5 to (GlcN)4. It is most likely that the substrate-binding cleft of the chitosanase can accommodate at least six GlcN residues, and that the cleavage point is located at the midpoint of the binding cleft.

High-order harmonic generation in intense laser and magnetic fields

Abstract: The effect of strong magnetic fields on high-order harmonic generation is considered for the molecule and a two-dimensional hydrogen atom in intense laser fields. Exact solutions of the time-dependent Schrodinger equation reveals: (i) strong magnetic fields parallel to the laser polarization confine the ionized electron wavepacket thereby enhancing the intensity and extending the harmonic generation spectrum; (ii) strong magnetic fields in combination with intense circularly polarized laser pulses can be used to control even and odd harmonic generation in two-dimensional atoms.

Rapid washout of technetium-99m-MIBI from a large parathyroid adenoma.

Abstract: The authors report a case of rapid {sup 99m}Tc-methoxyisobutylisonitrile (MIBI) clearance from a parathyroid adenoma. A double-phase {sup 99m}Tc-MIBI parathyroid scintigraphy was performed on a 62-yr-old female evaluated for primary hyperparathyroidism. A large parathyroid adenoma was visualized caudal to the left lobe of the thyroid gland with an unusually rapid washout of the tracer from tumor tissue. Histologic tissue examination confirmed the presence of a parathyroid adenoma and the absence of oxyphil cells. Care should be taken in interpretation of {sup 99m}Tc-MiBI parathyroid scintigrams because some adenomas can present a rapid release of the radiotracer in a double-phase study. Technitium-99m-MIBI retention could be related to the number of mitochondria-rich cells in parathyroid adenomas or to hyperplasia. 7 refs., 2 figs.

Stochastic McKean-Vlasov equations

Abstract: We prove the existence and uniqueness of solution to the nonlinear local martingale problems for a large class of infinite systems of interacting diffusions. These systems, which we call the stochastic McKean-Vlasov limits for the approximating finite systems, are described as stochastic evolutions in a space of probability measures onR d and are obtained as weak limits of the sequence of empirical measures for the finite systems, which are highly correlated and driven by dependent Brownian motions. Existence is shown to hold under a weak growth condition, while uniqueness is proved using only a weak monotonicity condition on the coefficients. The proof of the latter involves a coupling argument carried out in the context of associated stochastic evolution equations in Hilbert spaces. As a side result, these evolution equations are shown to be positivity preserving. In the case where a dual process exists, uniqueness is proved under continuity of the coefficients alone. Finally, we prove that strong continuity of paths holds with respect to various Sobolev norms, provided the appropriate stronger growth condition is verified. Strong solutions are obtained when a coercivity condition is added on to the growth condition guaranteeing existence.