Showing papers by "Concordia University published in 1989"

Brain dopamine and reward.

Abstract: While the evidence is strong that dopamine plays some fundamental and special role in the rewarding effects of brain stimulation, psychomotor stimulants, opiates, and food, the exact nature of that role is not clear. One thing is clear: Dopamine is not the only reward transmitter, and dopaminergic neurons are not the final common path for all rewards. Dopamine antagonists and lesions of the dopamine systems appear to spare the rewarding effects of nucleus accumbens and frontal cortex brain stimulation (Simon et al 1979) and certainly spare the rewarding effects of apomorphine (Roberts & Vickers 1988). It is clear that reward circuitry is multisynaptic, and since dopamine cells do not send axons to each other or receive axons from each other, dopamine can at best serve as but a single link in this circuitry. If dopamine is not a final common path for all rewards, could it be an intermediate common path for most rewards? Some workers have argued against such a view, but at present they must do so on incomplete evidence. For example, Phillips (1984) has argued that there must be multiple reward systems, functionally independent and organized in parallel with one another. His primary evidence, however, is the fact that brain stimulation is rewarding at different levels of the nervous system. As we have seen in the case of midline mesencephalic stimulation, the location of the electrode tip in relation to the dopamine cells and fibers tells us little about the role of dopamine in brain stimulation reward. It seems clear that the ventral tegmental dopamine system plays a critical role in midline mesencephalic reward, despite the distance from the electrode tip to the dopamine cells where morphine causes its dopamine-dependent facilitory effects or to the dopamine terminals where low-dose neuroleptics presumably cause theirs. Until pharmacological challenge has been extended to the cases discussed by Phillips, we can only speculate as to the role of dopamine in each of those cases. In the cases where pharmacological challenge has been examined, only nucleus accumbens and frontal cortex have been found to have dopamine-independent reward sites. It is not consistent with the dopamine hypothesis that dopamine-independent reward sites should exist in these areas, since any reward signals carried to nucleus accumbens or frontal cortex by dopamine fibers would-unless we are to believe that reward "happens" at these sites-have to be carried to the next stage of the circuit by nondopaminergic fibers (there are no dopaminergic cell bodies in any of the dopamine terminal areas).(ABSTRACT TRUNCATED AT 400 WORDS)

An active power factor correction technique for three-phase diode rectifiers

Abstract: A novel active power factor correction method for power supplies with three-phase front-end diode rectifiers is proposed and analyzed. The implementation of this method requires the use of an additional single switch boost chopper. The combined front-end converter draws sinusoidal AC currents from the AC source with nearly unity input power factor while operating at a fixed switching frequency. It is shown that when the active input power factor correction stage is also used to regulate the converter DC bus voltage, the converter performance can improve substantially in comparison with the conventional three-phase AC-to-DC converters. These improvements include component count reduction, simplified input synchronization logic requirements, and smaller filter refractive components. Theoretical results are verified experimentally. The proposed method has the disadvantage of substantially increasing the current stresses of the switching devices and the high-frequency ripple content of the prefiltered AC input currents. >

Calculation of initial yields of single- and double-strand breaks in cell nuclei from electrons, protons and alpha particles.

Abstract: A model of the DNA and electron and ion track structure computer codes are used to model damage in the DNA by direct action. This damage is converted into single-strand breaks using the method described by Charlton and Humm (1988) in which a minimum energy deposited in a critical volume of the DNA is correlated with the production of single-strand breaks. It is then assumed that if these single-strand breaks lie on opposite strands and are separated by less than a few base pairs they produce double-strand breaks. Absolute yields of both single- and double-strand breaks expressed in breaks/Gy-dalton are calculated and compared to measured yields. Good agreement is obtained for single-strand breaks while the calculated yields for double-strand breaks are greater than those measured.

Design aspects of synchronous PWM rectifier-inverter systems under unbalanced input voltage conditions

Abstract: A complete analysis of a synchronous front-end PWM rectifier-inverter system under unbalanced input voltage conditions is presented. The analysis includes the harmonic assessment of input/output current and voltage waveforms. It is shown both theoretically and experimentally that input voltage unbalance generates uncharacteristic low-frequency harmonic components in the input and output currents. Special emphasis is given to the generation of a DC component in the inverter output voltage in the case in which the output frequency is twice the input frequency. System design curves for different degrees of unbalance for all major system components are reported. Key predicted results are confirmed experimentally. >

Multiple broad-band source location using steered covariance matrices

Abstract: The authors present an approach for reducing the threshold observation time required to achieve high-resolution localization of multiple broadband sources. The proposed techniques are based on a space-time statistic called the steered covariance matrix (STCM). The STCM, like the well-known cross-spectral density matrix (CSDM), has asymptotic properties which facilitate high-resolution source localization. In broadband settings, however, the STCM has the advantage that it can be estimated with much greater statistical stability than the CSDM. The STCM is used in conjunction with minimum variance and linear predictive spectral estimation to obtain the steered minimum variance (STMV) and steered linear prediction (STLP) methods. Analytical and simulation results are presented that indicate that the STMV and STLP methods exhibit lower threshold observation times than their CSDM-based counterparts. >

Influence of Housing Conditions on the Acquisition of Intravenous Heroin and Cocaine Self-Administration in Rats

Abstract: Group-housed and individually housed rats were tested for the acquisition of a lever-pressing response reinforced by intravenous heroin or cocaine; animals in each housing condition quickly learned to self-administer drug. In the first experiment the isolated rats learned to self-administer heroin earlier than the group-housed animals, but the two groups self-administered similar levels of heroin by the fifth week of testing. In the second experiment cocaine self-administration was learned with equal speed in the two groups, and similar levels of cocaine were self-administered by both groups throughout the experiment. These data indicate that while social isolation can influence levels of heroin self-administration, isolation is not a necessary condition for heroin or cocaine injections to be reinforcing.

Analysis and design of a three-phase synchronous solid-state VAr compensator

Abstract: A three-phase synchronous solid-state VAr compensator (SSVC) system that uses a three-phase pulsewidth-modulated (PWM) voltage-source inverter is presented and analyzed. The proposed SSVC system can compensate for leading and lagging displacement power factor. Pulsewidth modulation is used as a means of reducing the size of reactive components. The SSVC system is analyzed under self- and independently-controlled DC bus voltage operating conditions. Other areas of investigation include the design of SSVC filter components for both approaches and the closing of the loop around the reactive power command signal. Predicted results are verified experimentally for the case of the SSVC working with a self-controlled DC bus. >

Influence of ultra-high strains at elevated temperatures on the microstructure of aluminium. Part I

Abstract: A1 (purity, 99·7%) with 0·1 or 2 mm grains was torsionally deformed at 400°C and 0·2s-1 up to equivalent strains of 60. Tangential sections were examined by polarized light, transmission electron microscopy and scanning electron microscopy. The grains wound into helicoids with an axial thickness varying inversely with the strain. Subgrains persisted at a constant size (about 7 μm) and equiaxed throughout the straining from 0·5 to 60. Relative misorientations, of structural units were determined by scanning transmission electron microscopy channelling patterns, which confirmed the X-ray diffraction textures. The grains, with their boundaries strongly serrated, retained their distinctness up to strains of 10 for 0·1 mm grains and up to 60 for 2 mm grains, while their thickness was greater than the subgrain diameter. For the former at strains of 20-60, the microstructure consists of subgrains having a mixture of small- and large-angle boundaries; this development is called geometric dynamic recrysta...

Recognition and shape synthesis of 3-D objects based on attributed hypergraphs

Abstract: A computer vision system is presented for shape synthesis and recognition of three-dimensional objects using an attributed hypergraph representation. The vision system is capable of: (1) constructing an attributed hypergraph representation (AHR) based on the information extracted from an image with range data; (2) synthesizing several AHRs obtained from various views of an object to form a complete AHR of the object; and (3) recognizing any view of an object of finding the graph monomorphism between the AHR of that view and the complete AHR of a prototype object. This system is implemented on a Grinnell imaging system driven by a VAX 11/750 running VMS. >

Pharmacological regulation of intravenous cocaine and heroin self-administration in rats: a variable dose paradigm

Abstract: Rats were trained to intravenously self-administer unit doses of cocaine or heroin. Constant supplemental infusion of a portion of each rat's mean hourly intake increased the mean time between successive infusions, but the effect was not statistically reliable from the data of a small sample of animals. A variable dose per infusion (VDI) paradigm was developed which enabled testing of several unit doses of cocaine or heroin within single test sessions. Unit doses of 0.5, 1.0, and 2.0 mg/kg of cocaine or 0.025, 0.05, and 0.1 mg/kg of heroin were made available with equal frequency but in unpredictable sequence to independent groups of rats. The mean time between successive infusions was linearly related to the log dose of the preceding infusion in each case. Pimozide, a drug thought to attenuate the reinforcing effects of both cocaine and heroin, shifted the functions without disturbing the dose-response relations; pimozide reliably decreased the time between successive cocaine infusions across a 4-fold range of pimozide doses. The effect of pimozide on heroin self-administration was not statistically significant and disrupted responding at the highest dose tested. This paradigm thus offers a within-session assessment of the dose-dependent duration of reinforcing actions of cocaine and heroin, and this assessment is sensitive to at least one challenge of intravenous drug reinforcement.

Absolutely continuous invariant measures for piecewise expandingC 2 transformations inR N

Abstract: LetS be a bounded region inR N and let ℊ={S i} =1/ be a partition ofS into a finite number of subsets having piecewiseC 2 boundaries. We assume that whereC 2 segments of the boundaries meet, the angle subtended by tangents to these segments at the point of contact is bounded away from 0. Letτ:S →S be piecewiseC 2 on ℊ and expanding in the sense that there exists 0<σ< 1 such that for anyi=1, 2, ...,m, ‖Dτ −1 ‖<σ, whereDτ −1 is the derivative matrix ofτ −1 and ‖ ‖ is the euclidean matrix norm. The main result provides an upper bound onσ which guarantees the existence of an absolutely continuous invariant measure forτ.

How Should We Use Student Ratings to Evaluate Teaching

Abstract: The proper use of student ratings to evaluate teaching is the subject matter of this paper. In particular, two divergent views are contrasted: the multidimensional view of evaluation and the unidimensional. Marsh (Int. J. Ed. Res., 1987, v.11, pp. 253–388) is the most outspoken advocate of the multidimensional view of evaluation based on factor scores. Because we disagree over such an important use of ratings, I explain the position I have adopted, summarize Marsh's most recent position, and respond to his concerns.

Running-related injury prevention through innate impact-moderating behavior.

Abstract: The purpose of these experiments was to test the Robbins and Hanna hypothesis, which relates differences in discomfort from localized deformation at certain positions on the plantar surface to protective behavior (intrinsic foot shock absorption). A penetrometer was used to quantify the relations between localized load and pain and between load and depth of deformation. The magnitude of load required to elicit pain varied significantly (P less than 0.005) in relation to position on the plantar surface. With a load of 9 kg and a 10 mm spherical end on the penetrometer, 6% of the sample reported pain at the heelpad, 32% at the distal first digit, and 66% at the first metatarsal-phalangeal joint. This pattern was predicted by the Robbins and Hanna thesis. Two deformation patterns were observed which were best explained by deformation constraint by tight trabecular tethering of the epithelial membrane at the heelpad and distal first digit and unrestricted deformation due to loose trabecular tethering of the epithelial membrane at the first metatarsal-phalangeal joint. These data provide insight into how, when barefoot, the plantar surface resists perforation yet provides protection to local bony structures. These data further support the notion that plantar sensory feedback plays a central role in safe and effective locomotion.

An analytical least square solution to the design problem of two-dimensional FIR filters with quadrantally symmetric or antisymmetric frequency response

Abstract: A closed-form least-squares solution to the design problem of two-dimensional real zero-phase finite-impulse-response (FIR) filters with quadrantally symmetric or antisymmetric frequency response is obtained. An in-depth study of the matrices involved in the development of the design technique reveals a number of useful properties. It is shown that these properties lead to an optimal analytical solution for the filter coefficients, making it unnecessary to use the time-consuming methods of optimization, matrix inversion, and iteration. Because of the reduced order of the matrices involved, their specific characteristics, and the analytical approach, the computational complexity is greatly reduced. Simplicity and efficiency of the design technique is illustrated through examples. The results in terms of error in frequency response compare favorably with those obtained by using other techniques. It is shown that the design time using the proposed technique is significantly smaller than that required by the I/sub p/-optimization technique or weighted least-squares technique using Harris' ascent algorithm or modified Lawson's algorithm. >

The arithmetic connection

Abstract: From test and interview data obtained during an investigation into Grade 10 students' conceptions of algebraic generalisation and justification, we have extracted evidence of the extent to which these students have coordinated the “worlds” of arithmetic and algebra, and can move freely between them. The data show more dissociation than we expected, even among students who were successful at standard algebraic tasks. Conceiving algebra as “generalised arithmetic” may obscure the many genuine obstacles that the learner has to overcome in moving from fluent performance in arithmetic to fluent performance in algebra while achieving and maintaining a smooth coordination of both modes of action.

All digital phase-locked loop: concepts, design and applications

Abstract: The concepts of an all digital phase-locked loop (DPLL), which contains a purely digital phase detector, loop filter and voltage-controlled oscillator, are explained. A second order DPLL is considered and analysed using the Z-transform technique. Implementation of the DPLL, based on the CMOS digital signal processor TMS 320C25, and the experimental results, are presented. Potential applications are also discussed.

O(n/sup 2/) algorithms for graph planarization

Abstract: The authors present two O(n/sup 2/) planarization algorithms, PLANARIZE and MAXIMAL-PLANARIZE. These algorithms are based on A. Lempel, S. Even, and I. Cederbaum's (1967) planarity testing algorithm and its implementation using PQ-trees. Algorithm PLANARIZE is for the construction of a spanning planar subgraph of an n-vertex nonplanar graph. The algorithm proceeds by embedding one vertex at a time and, at each step, adds the maximum number of edges possible without creating nonplanarity of the resultant graph. Given a biconnected spanning planar subgraph G/sub p/ of a nonplanar graph G, the MAXIMAL-PLANARIZE algorithm constructs a maximal planar subgraph of G which contains G/sub p/. This latter algorithm can also be used to planarize maximally a biconnected planar graph. >

L-serine degradation in Escherichia coli K-12: cloning and sequencing of the sdaA gene.

Abstract: A new mutant of Escherichia coli K-12 unable to grow with L-serine, glycine, and L-leucine has been isolated by lambda plac Mu insertion and shown to be deficient in L-serine deaminase activity. The corresponding gene, sdaA, has been cloned from a prototrophic strain, and the clone has been characterized and sequenced. The evidence is consistent with the hypothesis that sdaA is the structural gene for L-serine deaminase. However, other possibilities are also considered. No significant homology with previously reported DNA or protein sequences was detected.

Serotonin Uptake Blockers and Voluntary Alcohol Consumption

Abstract: Previous research demonstrated that serotonin uptake blockers (e g, zimeldine, sertraline, fluoxetine) reduce voluntary ethanol consumption in rats and humans However, the mechanism of action of these compounds is not well understood It has been suggested, for example, that serotonin uptake blockade interferes with the processes that mediate the reinforcement derived from ethanol ingestion On the other hand, there is considerable experimental evidence that suggests that the effects on alcohol intake may be an expression of a more general inhibitory role that serotonin plays in consummatory behavior This chapter presents evidence that suggests that serotonin uptake blockers may affect ethanol intake, in part via a reduction of food intake Current issues concerning the central versus pheripheral mediation of these effects, receptor specificity, as well as alternate mechanisms of action are considered