Showing papers by "University of Western Ontario published in 1986"

Reductions in arterial diameter produced by chronic decreases in blood flow are endothelium-dependent

Abstract: A 70 percent reduction in the rate of blood flow through the common carotid artery in rabbits caused a 21 percent decrease in the diameter of this artery within 2 weeks. The smooth muscle relaxant papaverine did not attenuate the response; therefore, such reductions in diameter probably reflect a structural modification of the arterial wall rather than sustained contraction of smooth muscle. This arterial response to reduced blood flow was abolished when the endothelium was removed from the vessels. It appears that the endothelium is essential for the compensatory arterial response to long-term changes in luminal blood flow rates.

Large adjustments in visually guided reaching do not depend on vision of the hand or perception of target displacement

Abstract: When we reach towards an object that suddenly appears in our peripheral visual field, not only does our arm extend towards the object, but our eyes, head and body also move in such a way that the image of the object falls on the fovea. Popular models of how reaching movements are programmed1,2 have argued that while the first part of the limb movement is ballistic, subsequent corrections to the trajectory are made on the basis of dynamic feedback about the relative positions of the hand and the target provided by central vision. These models have assumed that the adjustments are dependent on seeing the hand moving with respect to the target. Here we present evidence that a change in the position of a visual target during a reaching movement can modify the trajectory even when vision of the hand is prevented. Moreover, these dynamic corrections to the trajectory of the moving limb occur without the subject perceiving the change in target location. These findings demonstrate that (1) visual feedback about the relative position of the hand and target is not necessary for visually driven corrections in reaching to occur, and (2) the mechanisms that maintain the apparent stability of a target in space are dissociable from those that mediate the visuomotor outputdirected at that target.

Visual control of reaching movements without vision of the limb

Abstract: The spatial and temporal organization of hand and eye movements were studied in normal human subjects as they pointed toward small visual targets. The experiment was designed to assess the role of information about target position in correcting the trajectory of the hand when view of the hand was not available. To accomplish this, the duration of target presentation was systematically varied across blocks of trials. The results of this experiment showed that pointing movements were about 3 times more accurate when the target was present throughout the entire pointing movement, than when the target disappeared shortly after the hand movement had begun. These data indicate that pointing movements made without view of the limb are not purely preprogrammed but instead, are corrected during their execution. These modifications to the motor program are smoothly integrated into the ongoing movement and must depend upon comparing visual information about the position of the target with non-visual information about the position of the limb. The source of this non-visual information was not directly established in the present experiment but presumably must be derived from kinesthetic reafferences and/or efference copy.

An acute axonal form of Guillain-Barré polyneuropathy.

Abstract: Five patients with a clinical diagnosis of acute Guillain-Barre polyneuropathy (GBP) had electrically inexcitable motor nerves. All were quadriplegic. One patient died and 3 of the 4 survivors showed poor recovery. Autopsy studies on the patient who died showed severe axonal degeneration in nerve roots and distal nerves without inflammation or demyelination. Electrophysiological studies in these patients suggested that the predominant process was axonal degeneration. These cases may represent a separate clinicopathological entity, and constitute a variant of GBP characterized by an acute axonal neuropathy.

Generic business strategies, organizational context and performance: An empirical investigation

Abstract: Some of the common organizational requirements prescribed for generic business strategies of cost leadership and differentiation are empirically examined in a study consisting of 69 business units. The results suggest the fit between business unit strategy and the internal organization of multi-business companies does have an effect upon business unit performance.

Altruism and aggression: The heritability of individual differences.

Abstract: Five questionnaires measuring altruistic and aggressive tendencies were completed by 573 adult twin pairs of both sexes from the University of London Institute of Psychiatry Volunteer Twin Register. The questionnaires measured altruism, empathy, nurturance, aggressiveness, and assertiveness. The intraclass correlations for the five scales, respectively, were .53, .54, .49, .40, and .52 for 296 monozygotic pairs, and .25, .20, .14, .04, and .20 for 179 same-sex dizygotic pairs, resulting in broad heritability estimates of 56%, 68%, 70%, 72%, and 64%. Additional analyses, using maximum-likelihood model-fitting, revealed approximately 50% of the variance on each scale to be associated with genetic effects, virtually 0% with the twins' common environment, and the remaining 50% with each twins' specific environment and/or error associated with the test. Correcting for the unreliability in the tests raised the maximum-likelihood heritabilities to approximately 60%. Age and sex differences were also found: altruism increased over the age span from 19 to 60, whereas aggressiveness decreased, and, at each age, women had higher scores than men on altruism and lower scores on aggressiveness.

Acute patellar dislocations. The natural history.

Abstract: Of 27 patients sustaining primary patellar dislocations, 20 were treated with immobilization and subsequent physiotherapy (including nine patients who underwent arthroscopy) and seven with immediate surgical stabilization and lateral release. The patients with predisposing factors such as patellofemoral malalignment, abnormal patellar configuration, and a history of prior symptoms of instability were more prone to recurrent dislocation and may benefit from operative intervention. Although the incidence of recurrence among those individuals can be decreased, at least 30% to 50% of all patients having sustained a primary patellar dislocation will continue to have symptoms of instability and/or anterior knee pain.

Evaluation of amitriptyline in primary fibrositis. A double‐blind, placebo‐controlled study

Abstract: Seventy patients with primary fibrositis satisfying Smythe's criteria were studied in a 9-week double-blind trial comparing 50 mg amitriptyline with placebo. Fifty-nine patients completed the trial: 27 were treated with amitriptyline, and 32 took a placebo. The patients who received amitriptyline improved significantly in their morning stiffness and pain analog scores at 5 and 9 weeks, compared with baseline scores, whereas no changes were noted in these parameters in the placebo group. Fibrocytic point tenderness did not improve significantly in either of the treatment groups. When compared with the placebo group, the amitriptyline group improved significantly with respect to sleep pattern and patient and physician global assessments. Our data indicate that amitriptyline has some therapeutic benefit in patients with primary fibrositis.

Followup of the acute nonoperated isolated anterior cruciate ligament tear

Abstract: This report is an attempt to analyze what happens to an isolated ACL tear that is treated nonoperatively. The results of 40 patients treated initially by nonoperative means for this injury and followed an average of 4 years are reported. A very small percentage of these patients had associated meniscal pathology. Secondary reconstructive surgery was necessary in 12 patients (30%). Primary meniscal tears were present in 4 of 25 knees (16%) and secondary meniscal tears occurred in an additional four of the patients. Giving way was a problem for 36 (86%) of the nonoperated patients, but pain and swelling were not significant problems for most. Full return to unlimited athletic activities was possible for only four (14%) of the patients. Objective signs of ACL insufficiency could be demonstrated on all patients upon clinical examination at followup. Overall grading of the knees revealed 87.5% fair or poor results.

Similarities in behavioral and social maladjustment among child victims and witnesses to family violence

Abstract: This study examines the impact of exposure to family violence on school-aged boys. Boys who had witnessed violence between their parents were compared to boys who had been abused by their parents. The findings indicate that boys exposed to violence had a pattern of adjustment problems similar to those of abused boys and significantly different in severity and type from those of a community comparison group.

Factor structure of the dysfunctional attitude scale in a student population

Abstract: The Dysfunctional Attitude Scale-Form A (DAS-A) was completed by 664 university students and the results were factor-analyzed. Approximately 61% of the variance was accounted for by two factors, labelled Performance Evaluation and Approval by Others. Analyses conducted on two subsamples indicated that the obtained factor solution was stable. The present results are discussed with respect to personality subtypes hypothesized to be vulnerable to depression.

Iron-silica crystallite nucleation by bacteria in a geothermal sediment

Abstract: The recognition of microfossils in ancient sedimentary rocks has confirmed that microorganisms which strongly resemble presentday prokaryotes existed at least 3 × 109 years ago1. Identification of these structures is a difficult task, complicated not only by the simple morphology of microorganisms, but also by our limited understanding of the processes leading to the mineralization of individual cells and their component parts2–4. We have investigated these processes in a natural setting, by examining sediment samples from an acidic hot spring in Yellowstone National Park. Electron microscopy and energy-dispersive X-ray spectroscopy of thin-sectioned specimens revealed remains of bacteria inside accumulations of iron and silica. Bacterial-like forms in successive stages of mineral preservation by silica were also found

Dietary polyunsaturated fat in relation to mammary carcinogenesis in rats.

Abstract: High fat diets promote the development of mammary tumors induced in rats by 7,12-dimethylbenz(a)anthracene (DMBA), and polyunsaturated fats are more effective than saturated fats. This difference is related to the linoleic acid content of polyunsaturated vegetable oils, but the amount of linoleate required for maximum tumor promotion appears to be higher than indicated by earlier experiments. Comparison of the effects of a polyunsaturated vegetable oil (corn oil) containing linoleate with a fish oil (menhaden oil) containing polyunsaturated fatty acids derived from linolenic acid showed that higher dietary levels of corn oil increased the yield of DMBA-induced mammary tumors, while corresponding levels of menhaden oil had an inhibitory effect. This is further evidence that promotion of mammary tumorigenesis by polyunsaturated vegetable oils may be mediated by prostaglandins or other biologically active eicosanoids derived from n-6 fatty acids.

A preliminary evaluation of the dimensionality and clinical importance of pain and disability in osteoarthritis of the hip and knee

Abstract: Current methods of clinical assessment in osteoarthritis show a high degree of variability. By contrast, patients with rheumatoid arthritis may be evaluated using a number of standardised and validated indices. One hundred patients with primary osteoarthritis of the hip and knee were interviewed in order to determine the dimensionality of their discomfort and disability and to define the clinical importance of each component item. The symptomatology of osteoarthritis was captured by five pain, one stiffness, twenty-two physical, eight social and eleven emotional items. In spite of a high degree of variability in the frequency of involvement of the individual items, their clinical importance was similar both within as well as across dimensions. Further studies are indicated to determine the reliability, validity and responsiveness of each of the items identified as a prelude to developing a standardized method of assessing patients with osteoarthritis of the hip and knee.

Multivariate allometry and removal of size with principal components analysis

Abstract: A method is presented that constrains principal components analysis (PCA) to extract a first component that, by definition, summarizes isometric size alone. The remaining information is partitioned according to variation in shape. Size-constrained and conventional procedures are compared with analyses of data on sexual dimorphism in the painted turtle (Chrysemys picta marginata) and a crayfish (Cambarus bartoni). Contrary to results from standard analyses using covariance or correlation matrices, the size-constrained technique shows that turtles are dimorphic in isometric size but not in shape. Conventional methods do not com- pletely isolate variation in isometric size from variation in shape. Analysis of the crayfish data confirms that PCA with the correlation matrix separates size from shape more effectively than analysis with the covariance matrix. Secondary shape components (i.e., the third and subsequent components) differ markedly, suggesting that incomplete partitions of isometric size and shape by the traditional methods dramatically affect the results. (Size; shape; allometry; principal components analysis.)

Maintenance factors in coercive mother-child interactions: the compliance and predictability hypotheses

Abstract: Two stimulus control processes by which some parent-child dyads occasionally escalate their aversive exchanges into progressively more coercive interactions are described. The compliance hypothesis suggests that aversive actions have instructional properties for the dyad and that parent compliance with such child instructions maintains behavior chains of increasing aversiveness. The predictability hypothesis suggests that social interactions are most likely to function as aversive stimuli in the dyad when delivered in unpredictable fashion by either party and that responses instrumental in reducing dyadic unpredictability maintain aversive behavior chains. Expectations derived from both hypotheses are evaluated in a series of correlational analyses of mother-child interactions obtained in extended baseline observations of three dyads seeking psychological help for severe interactional problems. Results provide tentative support for the predictability hypothesis and suggest important avenues of further research.

Child witnesses to violence between parents: critical issues in behavioral and social adjustment.

Abstract: This study examined the impact of exposure to family violence on children's adjustment. Two groups of residents of shelters for battered women (current and former residents) were compared to a nonviolent control group. All three groups of mothers completed interviews and selfreport questionnaires related to both their own and their children's adjustment. Children recently witnessing violence tended to have the lowest levels of social competence ratings, and their mothers reported the most health and emotional difficulties. Former residents of shelters experienced the highest level of family/social disadvantage. The results are discussed in the context of previous research findings, and implications for intervention programs are outlined.

Hypersexuality or altered sexual preference following brain injury.

Abstract: Eight patients are described in whom either hypersexuality (four cases) or change in sexual preference (four cases) occurred following brain injury. In this series disinhibition of sexual activity and hypersexuality followed medial basal-frontal or diencephalic injury. This contrasted with the patients demonstrating altered sexual preference whose injuries involved limbic system structures. In some patients altered sexual behaviour may be the presenting or dominant feature of brain injury.

Imagery ability and the acquisition and retention of movements

Abstract: In this study, we examined the relationship between imagery ability, as measured by the Movement Imagery Questionnaire (MIQ), and the acquisition, retention, and reacquisition of movements. Based on their MIQ scores, 10 subjects were selected for the following imagery groups: high visual/high kinesthetic (HH), high visual/low kinesthetic (HL), and low visual/low kinesthetic (LL). The subjects learned four movements to a criterion level. Before each trial, subjects kinesthetically imaged the movement about to be produced. Following each acquisition trial, subjects were provided visual feedback. The acquisition phase was followed by a 2-day retention interval, a retention test consisting of three trials on each movement (no feedback provided), and a reacquisition phase. The HH group acquired the movements in the least number of trials, the LL group required the greatest number of trials, and the HL group required an intermediate number of trials. The data for the reacquisition phase showed the same trend. There was only weak evidence for a relationship between imagery ability and the retention of the movements. These findings support the position that high imagery ability facilitates the acquisition, but probably not the short term retention, of movements.

Fluid infiltration into fault zones: Chemical, isotopic, and mechanical effects

Abstract: Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments In the 27 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids Such fluids were characterised by δ18O=+6±2, δD=−50±20, δ13C=−4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism Hydrothermal fluids were more radiogenic (87Sr/86Sr=07010 to 07040) and possessed higher μ than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement A provinciality of87Sr/86Sr and δ13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W Fluids were characterised by XCO 2≈01, neutral to slightly acidic pH, low salinity ≤3 wt-%, K/Na=01, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression Clastic sediments occupy graben developed at fault flexures The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years At the Grenville front, translation was accommodated along two mylonite zones and an intervening boundary fault The high-temperature (580°C) and low-temperature (430 to 490°C) mylonite zones, formed in the presence of deep-level crust-equilibrated fluids of metamorphic origin Late brittle faults contain quartz veins precipitated from fluids with extemely negative δ18O (−14 per mil) at 200 to 300°C The water may have been derived from downward penetration into fault zones of precipitation of low18O on a mountain range induced by continental collision, with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults Archean gneisses overlie Proterozoic sediments along thrust surfaces at Lagoa Real, Brazil; the gneisses are transected by brittle-ductile shear zones locally occupied by uranium deposits Following deformation at 500 to 540°C, in the presence of metamorphic fluids and under conditions of low water-to-rock ratio, shear zones underwent local intense oxidation and desilication All minerals undergo a shift of −10 per mil, indicating discharge of meteoric-water-recharged formation brines in the underlying Proterozoic sediments up through the Archean gneisses, during overthrusting; ≈1000 km3 of solutions passed through these structures The shear zones and Proterozoic sediments are less radiogenic (87Sr/86Sr=0720) than contemporaneous Archean gneisses (0900), corroborating the transport of fluids and solutes through the structure from a large external reservoir Major crustal detachment faults of Tertiary age in the Picacho Cordilleran metamorphic core complex of Arizona show an upward transition from undeformed granitic basement through mylonitic to brecciated and hydrothermally altered counterparts The highest tectonic levels are allochthonous, oxidatively altered Miocene volcanics This transition is accompanied by an increase of 12 per mil in δ18O, from +7 to +19, and a 400°C decrease in temperature Lower tectonic levels acted as aquifers for the expulsion of large volumes of higher-temperature reduced metamorphic fluids and/or evolved formation brines The Miocene allochthon was influenced by a lower-temperature reservoir inducing oxidative potassic alteration; mixing occurred between cool downward-penetrating thermal waters and the hot, deeper aqueous reservoir In general, flow regimes in these fault and shear zones follow a sequence, from conditions of high temperature and pressure with locally derived fluids at low water-to-rock ratios, during initiation of the structures, to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs Later in the tectonic evolution and at shallower crustal levels there was incursion of oxidising fluids from near-surface reservoirs into the faults In general, magmatism, tectonics, and fluid motion are intimately related

Dissociative Recombination of Molecular Ions

Abstract: The dissociative recombination of molecular ions with electrons plays a central role in the physics and chemistry of ionized systems. Although simple in concept it displays an underlying complexity which has frustrated many attempts to obtain a clear understanding of its nature. In fact almost without exception it is impossible to say with confidence that the recombination of any molecular species is well understood. The problem lies partially within the inherent complexity of molecular systems with their infinite series of excited rydberg states which play an important role in the mechanism for recombination. An additional concern is the fact that as yet no absolute demonstration of the predicted mechanisms for recombination has been performed. Many experimental measurements relating to recombination have been made. All however have either inherent uncertainties concerning the identity of initial and final excitation states or have been performed on systems where recombination can proceed through a variety of channels so that no individual one can be singled out.