Showing papers by "McGill University published in 1982"

LSQR: An Algorithm for Sparse Linear Equations and Sparse Least Squares

Abstract: An iterative method is given for solving Ax ~ffi b and minU Ax b 112, where the matrix A is large and sparse. The method is based on the bidiagonalization procedure of Golub and Kahan. It is analytically equivalent to the standard method of conjugate gradients, but possesses more favorable numerical properties. Reliable stopping criteria are derived, along with estimates of standard errors for x and the condition number of A. These are used in the FORTRAN implementation of the method, subroutine LSQR. Numerical tests are described comparing I~QR with several other conjugate-gradient algorithms, indicating that I~QR is the most reliable algorithm when A is ill-conditioned.

Innovation in Conservative and Entrepreneurial Firms: Two Models of Strategic Momentum

Abstract: Summary Two very difJerent nmodels oJ pr-oduct innovation ar-e postulated and tested. The con rvative m-odel assumes that ininov-ation is peijormed reluictanitly-, mainl/ in r-esponise to serious challenges. It therefore pr-edic-ts that innoration will co rrelate positively with environmental, injformation processing, structlural and decision nmaking variables that represent, or help to recognize antd cope with these challenges. In conitrast, the entrepreneurial modlel supposes that innovation is alwavys aggressiv-ely plursued and w-vill be very high unless decision makers are warned to slow down. Thus negative correlations are predicted between innovation and the v-ariables that cant provide such warning. Co}rrelationial and curv ilinear regression anialyses revealed that each mi1odel wvas suppor ted by conservative and entrepreneurial sub-samples, respectively, in a diverse sanmple oj 52 Canadian firmns.

Measurement of job and work involvement

Abstract: Developed separate measures of job and work constructs using 3 techniques: semantic differential, questionnaire, and graphic. Assessment measures included the Job Involvement and Work Involvement Questionnaires, Job Involvement and Work Involvement Semantic Differentials, and Job Involvement and Wor

Top Executive Locus of Control and Its Relationship to Strategy-Making, Structure, and Environment

Abstract: In a Canadian study the locus of control of top executives was found to bear a direct and significant relationship to the nature of corporate strategy but an indirect relationship to environment an...

Algorithm 583: LSQR: Sparse Linear Equations and Least Squares Problems

Abstract: Received 4 June 1980; revised 23 September 1981, accepted 28 February 1982 This work was supported by Natural Sciences and Engineering Research Council of Canada Grant A8652, by the New Zealand Department of Scientific and Industrial Research; and by U S. National Science Foundation Grants MCS-7926009 and ECS-8012974, the Department of Energy under Contract AM03-76SF00326, PA No. DE-AT03-76ER72018, the Office of Naval Research under Contract N00014-75-C-0267, and the Army Research Office under Contract DAA29-79-C-0U0, Authors' addresses: C. C. Paige, School of Computer Science, McGill University, Montreal, Quebec, Canada H3A 2K6; M. A Saundem, Department of Operations Research, Stanford University, Stanford, CA 94305. Permmsion to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notme is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. © 1982 ACM 0098-3500/82/0600-0[95 $00 75

Tracking Strategy in an Entrepreneurial Firm1

Abstract: This study tracks the strategies of a retail chain over 60 years of its history to show how that vague concept called strategy can be operationalized and to draw conclusions about strategy formatio...

The cerebral balance of power: confrontation or cooperation?

Abstract: Two visual search experiments were carried out using as stimuli large letters made of small identical letters presented in right, or left, or central visual fields. Considering the spatial frequency contents of the stimuli as the critical variable, Experiment 1 showed that a left-field superiority could be obtained whenever a decision had to be made on a large (low frequency) letter alone, and a right-field advantage emerged when a small (high frequency) letter had to be processed. Experiment 2 showed that the two levels of structure of the stimulus were not encoded at the same rate and that at very brief exposure, only the large letter could be accurately identified. This was accompanied by a left-field superiority, whether or not the stimulus contained the target. These results are interpreted as revealing a differential sensitivity of the hemispheres to the spatial frequency contents of a visual image, the right hemisphere being more adept at processing early-available low frequencies and the left hemisphere operating more efficiently on later-available low frequencies. From these and other experiments reviewed, it is suggested that (a) cerebral lateralization of cognitive functions results from differences in sensorimotor resolution capacities of the hemispheres; (b) both hemispheres can process verbal and visuospatial information, analytically and holistically; (c) respective hemispheric competence is a function of the level of sensorimotor resolution required for processing the information available. Language: en

The sampling characteristics of electivity indices

Abstract: Electivity indices measure the utilization of food types (r) in relation to their abundance or availability in the environment (p). Foods that constitute a larger proportion of the diet than of the available foods are considered preferred; conversely those proportionately underrepresented in the diet are avoided. A food is eaten at random if its proportion in the diet equals its proportion in the environment. A family of electivity indices stemming from Ivlev's (1961) classic monograph exist and differ only in the particular algorithm used to calculate electivity from r and p.For each available index I graphed the values of electivity as contours for all combinations of r and p. These graphs are compared to illustrate the strengths and weaknesses of each index on the basis of the following criteria: 1) the value of the index when r=p for a food, 2) the symmetry of the electivity value as feeding deviates from random, 3) the possible range of index values, 4) the linearity of changes in electivity over the full range of r and p, 5) the sensitivity of the index to sampling errors, 6) the statistical testability of the electivity, and 7) the stability of the electivity value for a food type that changes relative abundance or occurs in combination with different food types. No one index ideally satisfies all the criteria.The host preferences of gypsy moth, Lymantria dispar, feeding on tree foliage in an undisturbed deciduous forest in southwestern Quebec, Canada were used to compare the available indices: Ivlev's electivity, E; Ivlev's forage ratio, E'; Jacob's modified electivity, D; Jacob's modified forage ratio, log Q; Chesson's alpha; Strauss' linear index, L; and Vanderploeg and Scavia's relativized electivity, E *. The electivity values calculated by each index differ one from another; host trees shown as preferred by one index will frequently appear avoided according to an alternative index. The rank order electivities for the 19 available host trees, however, are remarkably similar for all but Strauss' linear index, L. Populus grandidentata, Quercus rubra, Ostrya virginiana, and Amelanchier were the most preferred host trees in the sampled forest; Prunus serotina, Acer pensylvanicum, A. rubrum, Betula lutea, and Fraxinus americana were most avoided. The use of Vanderploeg and Scavia's E * index is recommended.

Extensive elongation of axons from rat brain into peripheral nerve grafts

Abstract: The failure of axons to elongate in the injured central nervous system (CNS) of adult mammals restricts drastically the establishment of connections with target tissues situated more than a few millimetres away. Mechanisms that include a primary inability of some nerve cells to support renewed axonal growth, a premature formation of synapses on nearby neurones1, an obstruction caused by the formation of a glial scar2,3 and other influences of the microenvironment4–7 are presumed to contribute to the failure of nerve fibres to regenerate as effectively in the CNS as in the peripheral nervous system (PNS). Support for the hypothesis that conditions in the glial environment of injured fibres have a decisive role in successful axonal elongation has recently come from studies using transplants containing either central glia or peripheral nerve segments as conduits of axon growth7,8. While CNS glial grafts have been shown to prevent growth of PNS fibres7–9, experiments which used labelling techniques to trace the source of axons growing into PNS grafts provided evidence that processes from nerve cells in the spinal cord and medulla oblongata of adult rats may increase in length by 1 or more centimetres when the CNS glial environment is replaced by that of peripheral nerves10,11. Here we report for the first time the extensive elongation of axons from neurones in the brain of adult rats through PNS grafts introduced into the cerebral hemispheres.

On the need for the rare disease assumption in case-control studies.

Abstract: The conditions under which matched and unmatched odds ratios are consistent estimators of the incidence-density ratio in case-control studies are examined. Under "incidence-density" sampling, in which controls are selected from those at risk at the time of onset of each case, the matched estimator is shown to be consistent. In contrast, the unmatched estimator is biased unless the proportion exposed in the population at risk is constant over the study period; the bias is, however, negligible unless there is very large variation in the proportion exposed. No assumption of rarity of the disease is needed for these results. On the other hand, when the risk ratio is the parameter of interest, the assumption of rarity is needed for the odds ratio to be a consistent estimator. In such situations, the odds ratio obtained under "incidence-density" sampling will in general provide a better approximation to the risk ratio than will the odds ratio obtained under "cumulative-incidence" sampling, in which controls are selected from those still unaffected at the end of the study period. Even if the disease is rare, however, the odds ratio obtained under cumulative sampling need not consistently estimate any parameter of interest unless the proportion exposed is approximately constant.

Genetic regulation of resistance to intracellular pathogens

Abstract: Natural resistance of mice to infections with Salmonella typhimurium and Leishmania donovani is regulated by chromosome 1 gene(s) designated Ity and Lsh, respectively1,2. Given the fact that these two microorganisms are taxonomically and antigenically distinct, and yet the host response to them is regulated by the same locus or complex3,4, one might expect that the resistance to other intracellular pathogens would be controlled similarly. Innate resistance of inbred mice to infection with Mycobacterium bovis (BCG) is regulated by a single, dominant, autosomal gene designated Bcg which is known to exist in two allelic forms: resistant Bcgr and susceptible Bcgs (ref. 5). The distribution of Bcgr and Bcgs alleles, among a total of 14 inbred and 38 recombinant inbred (BXD and BXH) strains, matches exactly that established for resistant and susceptible alleles of Lsh (gene controlling resistance to Leishmania donovani) and Ity (gene controlling resistance to Salmonella typhimurium), suggesting that resistance to all these pathogens is controlled by the same chromosome 1 locus. The existence of such a chromosomal locus is further supported by the Bcg–Lsh and Bcg–Ity linkage as established by formal backcross analysis.

Chromosome aberration assays in Allium. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

Abstract: The common onion (Allium cepa) is an excellent plant for the assay of chromosome aberrations after chemical treatment. Other species of allium (A. cepa var. proliferum, A. carinatum, A. fistulosum and A. sativum) have also been used but to a much lesser extent. Protocols have been given for using root tips from either bulbs or seeds of Allium cepa to study the cytological end-points, such as chromosome breaks and exchanges, which follow the testing of chemicals in somatic cells. It is considered that both mitotic and meiotic end-points should be used to a greater extent in assaying the cytogenetic effects of a chemical. From a literature survey, 148 chemicals are tabulated that have been assayed in 164 Allium tests for the clastogenic effect. Of the 164 assays which have been carried out, 75 are reported as giving a positive reaction (i.e., causing chromosome aberrations), 49 positive and with a dose response, 1 positive and temperature-related, 9 borderline positive, and 30 negative; 76% of the chemicals gave a definite positive response. It is proposed that the Allium test be included among those tests routinely used for assessing chromosomal damage induced by chemicals.

Crossing-Free Subgraphs

Abstract: If m⩾4 then every planar drawing of a graph with n vertices and m edges contains more than m3/100n2 edge-crossings and fewer than 1013n crossing-free subgraphs. The first result settles a conjecture of Erdos and Guy and the second result settles a conjecture of Newborn and Moser.

Is Sperm Cheap? Limited Male Fertility and Female Choice in the Lemon Tetra (Pisces, Characidae)

Abstract: In the laboratory, fertilization rates achieved by male lemon tetras decline with spawning frequency. Even when the number of females is not limited, males can produce only four times as many offspring as females. Females show a preference for males that have not recently spawned as opposed to those that have. The cost of producing sufficient sperm to maximize fertilization rates may therefore reduce the intensity of sexual selection in this polygamous fish species.

The mechanism of uranium biosorption by Rhizopus arrhizus.

Abstract: Biosorption of elements is a little understood phenomenon exhibited by some types of even nonliving microbial biomass. A common fungus Rhizopus arrhizus has been reported to take up uranium from aqueous solutions to the extent of 180 mg U(6+)/g. The mechanism of uranium sequestering by this type of biomass was studied by using experimental techniques such as electron microscopy, x-ray energy dispersion analysis, IR spectroscopy, and supporting evidence was obtained for a biosorption mechanism consisting of at least three processes. Uranium coordination and adsorption in the cell-wall chitin structure occur simultaneously and rapidly whereas precipitation of uranylhydroxide within the chitin microcrystalline cell-wall structure takes place at a lower rate. Interference of Fe(2+) and Zn(2+) coions with uranium biosorption is indicated.

Tumor growth inhibition in patients with prostatic carcinoma treated with luteinizing hormone-releasing hormone agonists

Abstract: Ten patients with prostatic carcinoma--six with stage C and four with stage D disease--were treated for 6 weeks to 12 months with agonistic analogues of luteinizing hormone-releasing hormone (LH-RH). [D-Trp6]LH-RH was given subcutaneously once daily at a dose of 100 microgram and [D-Ser(But)6]des-GlyNH2(10)-LH-RH ethylamide (HOE 766) was given subcutaneously (50 microgram once daily) or intranasally (500 microgram twice daily). In all patients, mean plasma testosterone levels showed a 75% suppression by the third week of treatment and remained low thereafter. This was followed by a decrease or normalization of plasma acid phosphatase levels by the second month of treatment and a 47% decrease in serum alkaline phosphatase by the 10th week of treatment in all but one patient. In patients with stage C disease presenting with prostatism or urinary outflow obstruction, there was a noticeable clinical improvement. In two such patients, a decrease in the size of the prostate was confirmed by ultrasonography. In patients with stage D disease manifested by diffuse bone metastases, there was relief of bone pain, and in one patient treated for greater than 12 months the improvement was documented by radioisotope bone imaging. It is concluded that superactive agonistic LH-RH analogues hold promise as therapeutic agents in patients with androgen-sensitive prostatic adenocarcinoma. Furthermore, the analogous of LH-RH may be used to assess the responsiveness of patients to surgical castration. Long-term administration of LH-RH analogues could become an alternative to surgical castration and estrogen therapy for the treatment of hormone-dependent prostatic carcinoma.

Myelin-Associated Glycoprotein Is the Antigen for a Monoclonal IgM in Polyneuropathy

Abstract: Recent studies show that IgM monoclonal antibody from patients with IgM paraproteinemia and peripheral neuropathy reacts with a protein component of human PNS myelin and an analogous component or components of human CNS myelin. We have now demonstrated that the antigen for this antibody is a specific glycoprotein component of myelin, referred to as myelin-associated glycoprotein (MAG). Human PNS and CNS myelin proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis on pore-gradient slabs, and MAG was identified by the immuno-electroblot procedure with rabbit anti-MAG (rat). The identical band(s) were stained by an analogous procedure with patient serum as the first antibody. Human PNS MAG had an apparent molecular weight of 107,000. Human CNS MAG appeared as three bands: 113,000, 107,000, and 92,000. Passage of myelin proteins through a concanavalin A-Sepharose column removed the staining component. Purified patient IgM, added to a lithium diiodosalicylate extract of myelin, immunoprecipitated MAG. This antibody also cross-reacted with MAG from bovine CNS, but not from rabbit, rat, or mouse.

Structural Change and Performance: Quantum Versus Piecemeal-Incremental Approaches

Abstract: The effectiveness of different approaches to changing organization structure is examined. Two dimensions of structural change are explored. The findings show a tendency for quantum change, that is,...

Association of hyperapobetalipoproteinemia with endogenous hypertriglyceridemia and atherosclerosis.

Abstract: Researchers disagree on whether plasma triglyceride levels are an independent risk factor for atherosclerotic coronary artery disease We hypothesized that patients with endogenous hypertriglyceridemia would differ: Some would have normal values of plasma low-density lipoprotein (LDL) B protein; others, despite their normal level of LDL cholesterol, would have increased levels of LDL B protein We believe the latter patients--those with hyperapobetalipoproteinemia--would be the ones at risk for atherosclerosis We studied two populations Group 1, consisting of 162 patients with type IV lipoprotein patterns, was divided into two groups One subgroup (A), which included 38 patients with elevated plasma LDL B atherosclerotic disease than the other subgroup (B) of 36 patients with normal levels of plasma LDL B protein (10 patients versus two, p less than 002) Group 2 consisted of 100 patients who had had myocardial infarction Eighty-one percent of the 47 hypertriglyceridemic and 70% of the 53 normotriglyceridemic patients had elevated plasma LDL B protein levels (129 mg/dL or greater)--a proportion significantly higher than that in Group 1 (p less than 0001) Thus, an elevated plasma level of LDL B protein not only identifies subgroups of patients with type IV lipoprotein patterns, but also may be an important marker for atherosclerotic disease

Phase locking, period doubling bifurcations and chaos in a mathematical model of a periodically driven oscillator: a theory for the entrainment of biological oscillators and the generation of cardiac dysrhythmias.

Abstract: A mathematical model for the perturbation of a biological oscillator by single and periodic impulses is analyzed. In response to a single stimulus the phase of the oscillator is changed. If the new phase following a stimulus is plotted against the old phase the resulting curve is called the phase transition curve or PTC (Pavlidis, 1973). There are two qualitatively different types of phase resetting. Using the terminology of Winfree (1977, 1980), large perturbations give a type 0 PTC (average slope of the PTC equals zero), whereas small perturbations give a type 1 PTC. The effects of periodic inputs can be analyzed by using the PTC to construct the Poincare or phase advance map. Over a limited range of stimulation frequency and amplitude, the Poincare map can be reduced to an interval map possessing a single maximum. Over this range there are period doubling bifurcations as well as chaotic dynamics. Numerical and analytical studies of the Poincare map show that both phase locked and non-phase locked dynamics occur. We propose that cardiac dysrhythmias may arise from desynchronization of two or more spontaneously oscillating regions of the heart. This hypothesis serves to account for the various forms of atrioventricular (AV) block clinically observed. In particular 2∶2 and 4∶2 AV block can arise by period doubling bifurcations, and intermittent or variable AV block may be due to the complex irregular behavior associated with chaotic dynamics.