Showing papers by "York University published in 1969"
TL;DR: The possibility that the action of these substances on the uterus may depend on the conversion of the analogs of DDT to estrogenic metabolites is suggested.
307 citations
287 citations
TL;DR: It is concluded that premeiotic DNA synthesis is completed well in advance of pairing of homologous chromosomes, as marked by the formation of synaptinemal complexes.
Abstract: At the leptotene stage of meiotic prophase in Locusta spermatocytes (2n=22 telocentric autosomes + X-chromosome), each chromosome forms an axial core. The 44 ends of the autosomal cores are all attached to the nuclear membrane in a small region opposite the two pairs of centrioles of the juxtanuclear mitochondrial mass. At later stages of meiotic prophase, the cores of homologous chromosomes synapse into synaptinemal complexes. Synapsis is initiated near the nuclear membrane, in the centromeric and the non-centromeric ends of the chromosomes. Homologous cores have their attachment points close together and some cores are co-aligned prior to synapsis. At subsequent stages of zygotene, the number of synaptinemal complexes at the membrane increases, while the number of unpaired axial cores diminishes. At pachytene, all 11 bivalents are attached to the membrane at both ends, so that there are 22 synaptinemal complexes at the membrane near the centrioles. Because each bivalent makes a complete loop, the configuration of the classic Bouquet stage is produced. The X-chromosome has a poorly defined single core at pachytene which also attaches to the nuclear membrane. These observations are based on consecutive serial sections (50 to 100) through the centriolar zone of the spermatocytes. Labeling experiments demonstrated that tritiated thymidine was incorporated in the chromatin of young spermatocytes prior to the formation of the axial cores at leptotene. It is concluded that premeiotic DNA synthesis is completed well in advance of pairing of homologous chromosomes, as marked by the formation of synaptinemal complexes.
185 citations
TL;DR: In this paper, the optical and magnetic properties of tetramethyl ammonium manganese trichloride (TAMM) were investigated and it was shown that the system approximates very closely a Heisenberg linear-chain antiferromagnet with interchain interactions many orders of magnitude smaller than intrachain exchange.
Abstract: This paper reports optical and magnetic properties of tetramethyl ammonium manganese trichloride, [${(\mathrm{C}{\mathrm{H}}_{3})}_{4}$N][Mn${\mathrm{Cl}}_{3}$]. Magnetically, the system is one of very weakly interacting chains of ${\mathrm{Mn}}^{++}$ ions. Magnetic-susceptibility measurements are given from room temperature to below 1\ifmmode^\circ\else\textdegree\fi{}K and show a possible phase transition at 0.84\ifmmode^\circ\else\textdegree\fi{}K. Theoretical analysis reveals that the system approximates very closely a Heisenberg linear-chain antiferromagnet with interchain interactions many orders of magnitude smaller than intrachain exchange $J$. We find $J=6.3\ifmmode^\circ\else\textdegree\fi{}$K and a susceptibility maximum at 55\ifmmode^\circ\else\textdegree\fi{}K. The optical spectrum shows certain features that are not easily accounted for by an isolated Mn${\mathrm{Cl}}_{6}$ cluster, and may contain information concerning the nature of low-temperature dynamics of the Heisenberg linear chain, although no positive identification of magnon sidebands has yet been made.
182 citations
Journal Article•
TL;DR: The data establish that the selective action of pyrimethamine in malaria is due to the greater sensitivity to this drug of the plasmodial enzyme as compared to the host enzyme and reflect the unique, potent binding of P. berghei H 2 -folate reductase.
Abstract: Dihydrofolate reductase has been isolated from cells of the rodent malarial organism Plasmodium berghei by separation from the host cells with saponin and extraction by rupture in a French pressure cell. The enzyme exhibits certain distinctive properties which clearly distinguish it from the dihydrofolate (H 2 -folate) reductase isolated from the host cells (mouse erythrocytes) and from H 2 -folate reductases obtained from other sources, as reported in the literature. The molecular weight determined by gel filtration (190,000 ± 10%) is 9-10-fold higher than reported for most other H 2 -folate reductases. This value was not significantly decreased when the enzyme was passed over Sephadex G-100 columns in the presence of KCl, urea + 2-mercaptoethanol, or the substrate, H 2 -folate. The plasmodial H 2 -folate reductase is unlike bacterial enzymes in its stimulation by high concentrations of KCl and urea, and its approximately 10-fold lower K m value for NADPH (1.3 µM). The enzyme from P. berghei differs markedly from other dihydrofolate reductases in its sensitivity to several diaminoheterocyclic inhibitors. Most striking is the inhibition by pyrimethamine; it exhibits a 50% inhibitory concentration of approximately 0.5 nM compared with 1 µM for the mouse erythrocyte enzyme. The binding of pyrimethamine to P. berghei dihydrofolate reductase is stoichiometric when enzyme and drug have been incubated for 5-10 min prior to the addition of H 2 -folate, and reversible in the absence of prior incubation. A positive correlation was observed between the binding of pyrimethamine and three dihydrotriazines by the enzyme and the activity of these compounds in vivo against P. berghei infections. These data establish that the selective action of pyrimethamine in malaria is due to the greater sensitivity to this drug of the plasmodial enzyme as compared to the host enzyme and reflect the unique, potent binding of pyrimethamine to plasmodial H 2 -folate reductase.
171 citations
TL;DR: In this paper, the authors argue that No Borders is a necessary part of a global system of common rights and contemporary struggle for the commons, and argue that no-borders is a practical political project.
Abstract: This editorial article argues for No Borders as a practical political project. We first critically examine borders as ideological, generating and reinforcing inequality. We consider some responses to injustices produced by borders: the call for “human rights”; attempts to make immigration controls more “humanitarian”; and trade unions’ organizing and campaigning with undocumented workers. Recognizing the important contributions of some of these responses, we argue that nevertheless they have often been limited because they do not question sovereignty, the territorializing of people’s subjectivities, and nationalism. No Borders politics rejects notions of citizenship and statehood, and clarifies the centrality of borders to capitalism. We argue that No Borders is a necessary part of a global system of common rights and contemporary struggle for the commons. The article concludes by highlighting the main themes of the papers that make up the Special Issue, a number of which explore practical instances of the instantiation of No Borders politics.
138 citations
TL;DR: In this article, a comparative study of executive heads of international organizations is presented, focusing on how the executive head protects and develops his position as top man and how, by doing so, he may be the creator of a new (if yet slender) world power base.
Abstract: The quality of executive leadership may prove to be the most critical single determinant of the growth in scope and authority of international organization. Now sufficiently long and varied to allow a comparative approach, the history of international organization may provide elements for a theory of leadership. This essay is but a preliminary effort in that direction. It is concerned not only with how the executive head protects and develops his position as top man but also with how, by doing so, he may be the creator of a new (if yet slender) world power base. The origin of the comparative study of executive heads of international organizations was the observation that Albert Thomas was a very different kind of man from Sir Eric Drummond and had very different ideas about how to carry out his job. From this observation stemmed a number of speculations. The failure of the League of Nations in the late thirties was contrasted with the apparent success of the International Labor Organization (ILO). Would the story have been different had a Thomas been secretary-general of the League? Or would – as seems to have been Sir Eric Drummond's view – the nature of the job have led a Thomas to fail in the League? Whatever disagreement surrounds this speculation there is a greater measure of agreement that with the Drummond approach the ILO would have become nothing more than a technical information bureau.
132 citations
121 citations
111 citations
TL;DR: A curious problem arises in connexion with the notion of the participant observer, a problem partly ethical and partly methodological It seems not to have been clearly seen and stated, although solutions to it exist in practice as discussed by the authors.
Abstract: A curious problem arises in connexion with the notion of the participant observer, a problem partly ethical and partly methodological It seems not to have been clearly seen and stated, although solutions to it exist — in practice, as it were The problem arises like this Standard accounts of the method of participant observation require, I would argue, an anthropological observer to be both a stranger and a friend among the people he is studying Yet one person cannot be a stranger and a friend at the same time: the roles are mutually exclusive This being so, it is a fortiori impossible to play either role in integrity while trying to combine them, with the result that an uneasy compromise is liable to be forged
TL;DR: In this article, the effects of different patterns and degrees of openness in superior-subordinate communication on subordinate job satisfaction were investigated. But they did not consider the effect of different types of communication.
Abstract: The article presents a comment on an earlier article titled “Effects of Different Patterns and Degrees of Openness in Superior-Subordinate Communication on Subordinate Job Satisfaction” by R. Burke...
TL;DR: A tentative working model of sentence production is proposed with emphasis more on content than on structure, which serves as a container of content, and is more or less automatically produced to suit a particular content.
TL;DR: It is questionable whether the lesions underlying ‘soft signs’ are a sufficient cause for psychiatric disorder and community survey and case finding techniques are indicated to investigate this area.
TL;DR: It is suggested that a single component in liver microsomes cannot alone determine the specificity in the 6β-, 7α- and 16α-hydroxylation of testosterone.
TL;DR: This chapter describes some characteristics of enzymic catalysis, reaction rates in solutions of long-chain macromolecules, catalysis and inhibition in micellar solutions, and critique of the use of synthetic polymers and micelles as enzyme models.
Abstract: Publisher Summary This chapter describes some characteristics of enzymic catalysis, reaction rates in solutions of long-chain macromolecules, catalysis and inhibition in micellar solutions, and critique of the use of synthetic polymers and micelles as enzyme models. The catalysis of various reactions in the solutions exhibits a number of characteristics normally associated with heterogeneous catalysis. An inhibition of the catalytic effect may result, when the reagent has to compete with an inert species for the available catalytic sites. The analogy between the high reactivity of the enzyme-substrate complex and the reactivity of substrates bound to polymers or micelles is even less satisfactory. Kinetic effects based on long-range electrostatic effects, particularly the concentration of catalytic hydrogen or hydroxyl ions in the vicinity of a polyion or the micellar surface, have no counterpart in enzyme chemistry. An inhibition of the catalytic effect may result, when the reagent has to compete with an inert species for the available catalytic sites.
TL;DR: Tritium-labelled haemolymph protein and [3H]-leucine were used to study haemarymph protein economy during the fifth instar of Locusta and the results are discussed in terms of protein synthesis, uptake, and turnover.
TL;DR: In this article, the Schr\"odinger equation for a bound electron in an attractive screened Coulomb potential is investigated using the large-$Z$ ($Z$ is nuclear charge) asymptotic expansion theory.
Abstract: The solution to the nonrelativistic Schr\"odinger equation for a bound electron in an attractive screened Coulomb potential is investigated using the large-$Z$ ($Z$ is nuclear charge) asymptotic expansion theory. Both the basic asymptotic and perturbation solutions are found. The problem of finding the $k\mathrm{th}$ order perturbation wave function and energy for any state is reduced to solving, recursively, a set of $k$ linear algebraic equations in $k$ unknowns. The asymptotic expansions for the energy and wave functions are presented to the tenth order in perturbation theory for the $1S$ state and to fifth order for the general $n$, $l=n\ensuremath{-}1$ quantum state. Results for the $2S$ states are also given. Comparison of the perturbation-theory results with those of numerical integrations for the energy show excellent agreement. It is shown that a finite screening radius gives rise to a finite number of bound states, a result which contradicts some recently published work. Application of the screened Coulomb potential model to intensity cutoffs in the spectra of solar and laboratory hydrogen plasmas is discussed.
TL;DR: The results suggest that the variation in UV sensitivity of E. coli B/r as a function of time of harvesting of the cells from batch cultures is related to the varying capacities of these populations to repair UV-damaged deoxyribonucleic acid.
Abstract: The ultraviolet (UV) sensitivity of Escherichia coli B/r harvested at various times during growth in batch cultures was measured. The results showed a period of increased UV sensitivity in late log phase, just before the cultures entered stationary phase. This increase in sensitivity was associated with a decreased shoulder in the UV survival curves. The postirradiation division delay of survivors was shortest for cells harvested during the period of maximal sensitivity. This period of increased UV sensitivity during late log phase was not found in the radiation-sensitive, repair-deficient mutant B(s-1) (a strain which is unable to excise pyrimidine dimers from UV-damaged deoxyribonucleic acid). These results suggest that the variation in UV sensitivity of E. coli B/r as a function of time of harvesting of the cells from batch cultures is related to the varying capacities of these populations to repair UV-damaged deoxyribonucleic acid. Further experiments designed to elucidate the mechanism underlying this variation in UV sensitivity indicated that it arises from the partial depletion of nutrients in the medium during late log phase. We suggest that growth in such depleted media leads to a depression in the intercellular concentration or activity of one or more of the repair enzymes concerned with the repair of damaged deoxyribonucleic acid.
TL;DR: In this paper, the authors used the annual census of full-time faculty at all Canadian universities, between 1984 to 1999, to measure the effect of gender, discipline, and institution on promotion from assistant to associate professor and from associate to full professor.
Abstract: Statistics Canada’s annual census of full-time faculty at all Canadian universities, between 1984 to 1999, is used to measure the effect of gender, discipline, and institution on promotion from assistant to associate professor and from associate to full professor. Accelerated failure time models show that gender has some effect on rates of promotion, but that disciplinary and institutional variation are much greater. Generally, departments in science, engineering, and professional schools promote their faculty more rapidly, while disciplines strongly oriented to training practitioners are slowest. There is considerable variationamong institutions, but this is not strongly linked to institutional characteristics such as size and prestige. All these factors more strongly affect the length of time for promotion from associate to full professor, than for promotion from assistant to associate professor. Nous utilisons le recensement annuel des professeures et professeurs a temps plein des universites canadiennes de Statistiques Canada (1984 a 1999) afi n de mesurer la variation du temps necessaire a la promotion (d’adjoint a agrege puis d’agrege a titulaire) en fonction du sexe, de la discipline et de l’institution. Des modeles statistiques (accelerated failure time models) demontrent que le sexe a un leger effet sur la vitesse de la promotion mais que cet effet est moindre que celui de la discipline et de l’institution. Regle generale, les departements de sciences et de genie ainsi que les ecoles professionnelles (medecine, droit, etc.) promeuvent plus rapidement leurs professeurs, tandis que les domaines de formation pratique (soins infi rmiers, travail social, etc.) sont plus lents. La variation entre institutions est considerable mais n’est associee ni a leur taille, ni a leur prestige. Ces deux facteurs affectent davantage la vitesse de promotion du rang de professeur adjoint a celui de professeur agrege que la titularisation.
TL;DR: The fate of haemolymph proteins during the fifth instar of Locusta has been investigated autoradiographically using tritiated blood protein and the fate of [ 3 H]-leucine was also studied.
TL;DR: Treatment of immature male rats with phenobarbital or chlordane for several days prior to an injection of testosterone or testosterone propionate inhibits the growth-promoting effect of these androgens on the seminal vesicles.
TL;DR: At meiotic prophase, the grasshopper Chorthippus longicornis has normal synaptinemal complexes inside paired homologous chromosomes, and evidence is presented that short single cores and small multiple core complexes occur inside metaphase I chromosomes.
Abstract: At meiotic prophase, the grasshopper Chorthippus longicornis has normal synaptinemal complexes inside paired homologous chromosomes. Evidence is presented that short single cores and small multiple core complexes occur inside metaphase I chromosomes. At first anaphase, interphase, and early spermatid stage, large multiple core complexes are located in the cytoplasm. It is speculated that the multiple core complexes have some structural elements in common with the synaptinemal complexes, but that different forms of pairing behavior are exhibited by the different complexes.
TL;DR: The differential effects of storage of liver microsomal preparations on the hydroxylation of testosterone in the 6β, 7α- and 16α-positions suggest that a single cytochrome cannot alone determine the specificity of the three hydroxyation reactions.
[...]
TL;DR: Gibson as discussed by the authors argued that sensory information consists of cognitive facts about the environment and that these invariants correspond to the permanent properties of the environment, hence the realism of perception.
Abstract: Philosophers should welcome scientists who bother to put their theories and data at the disposal of philosophical debate. When such a distinguished psychologist as J. J. Gibson calls our attention to features of his most recent work which he thinks lend new support for realism, philosophers of perception should pay close attention. 1 The most interesting aspect of Gibson's important new book is not, however, support or non-support for realism, but rather the particular way in which Gibson now views sensation and perception. Gibson is concerned to place the senses in their total environmental context, to consider them as parts of a system of information-extraction, rather than as separate atoms of impulseor sensation-production. He distinguishes \"the input to the nervous system that evokes conscious sensation from the input that evokes perception\" (p. 2). A notion of'sensationless perception' as the source of information replaces all notions of sensations as the basic unit of perception. There are invariants of energy accessible to our sensory receptors which yield information without producing sensations. These invariants \"correspond to the permanent properties of the environment\", hence the realism (p. 3). Before I get round to commenting upon Gibson's realism, I want to discuss a number of questions which a philosopher must raise about Gibson's 'information'. Gibson recognizes, of course, that physiological studies (behavioural ones, too) may be of some relevance to understanding perception, but he insists that perception has to be understood in terms of information pick-up. The stress upon information pick-up is Gibson's way of recognizing what some philosophers have been saying, that perception, can be analyzed and understood only in perceptual terms. Gibson's 'information' consists of cognitive facts about our environment. What he likes to call his 'ecological' study places the organism in its experiential and cognitive environment and then seeks to discover how the organism learns about that environment. It is because of this stress upon the cognitive, conscious features of perception that Gibson likes to remind us that sensing or the
TL;DR: In general terms, the basic significance of the synaptinemal complex has been confirmed by its regular occurrence in sexually reproducing plants and animals and the involvement of the complex in genetic exchange was confirmed by Meyer (3, 4).
Abstract: The elongate tripartite structure of synapsed homologous chromosomes at meiotic prophase was described by Moses (7) and by Fawcett (2) in 1956. A functional interpretation of this synaptinemal complex was put forward by Moses in 1958 (8) and by Coleman and Moses in 1964 (1). They proposed that the complex is \"the morphological expression of the specific function of the pairing of homologous chromosomes that is a prerequisite of genetic crossing-over and cytological chiasma formation.\" In general terms, the basic significance of the complex has been confirmed by its regular occurrence in sexually reproducing plants and animals. The involvement of the complex in genetic exchange was confirmed by Meyer (3, 4). Meyer reports that in two cases where genetic exchange does not take place (Drosophila melanogaster males and c3G females) no synaptinemal complexes occur. Similarly, no complexes were found in achiasmatic Tipula ceasia and Phryne fenestralis males. Chiasmatic T. oleracea males had normal complexes. Of direct relevance to this note is Meyer's observation (4) that in triploid Drosophila females normal synaptinemal complexes occur, but there are no indications that the third chromosome forms an individual single axial core. The unpaired leptotene chromosomes