Showing papers by "University of York published in 1979"

The existence, uniqueness and stability of traffic equilibria

Abstract: The paper formulates link-flow definitions of equilibrium and stability, and gives conditions which guarantee the existence, uniqueness and stability of traffic equilibria. Junction delays in towns usually depend on the traffic flow along intersecting links; the theory presented here is designed to be applicable when there are such junction interactions.

Management of multispecies fisheries.

Abstract: With the overexploitation of many conventional fish stcocks, and growing interest in harvesting new kinds of food from the sea, there is increasing need for managers of fisheries to take account of interactions among species. In particular, as Antarctic krill-fishing industries grow, there is a need to agree upon sound principles for managing the Southern Ocean ecosystem. Using simple models, we discuss the way multispecies food webs respond to the harvesting of species at differrent trophic levels. These biological and economic insights are applied to a discussion of fisheries in the Southern Otean and the North Sea and to enunciate some for harvesting in multispecies systems.

Crossing the border into borderline personality and borderline schizophrenia. The development of criteria.

Abstract: • Although there is a large psychiatric literature on various "borderline" conditions, there has been no agreement as to the definition of the concept. A review of the literature reviewed two major uses of the term: Borderline Schizophrenia and Borderline Personality. Two item sets were developed to provide diagnostic criteria for the two concepts. High sensitivity and specificity were demonstrated for both item sets using data describing 808 borderline and 808 control patients. These criteria will be used in the forthcoming DSM-III classification for the categories of Borderline Personality Disorder and Schizotypal Personality Disorder.

Approaches To the Analysis of Government Expenditure Growth

Abstract: The article surveys the literature on public expenditure growth, and makes some suggestions for possible future developments. At the theoretical level, it is argued that public choice and associate...

Use of the Research Diagnostic Criteria and the Schedule for Affective Disorders and Schizophrenia to study affective disorders.

Abstract: In a pilot study of 150 manic or depressive patients, the authors used the Research Diagnostic Criteria (RDC) and the Schedule for Affective Disorders and schizophrenia (SADS) to perform preliminary analysis of symptom pictures of the index episode of different diagnostic groups, joint diagnostic classification of the different subtypes of major depressive disorder, and differential outcome by diagnostic groups The results suggest that schizophrenic symptoms in affective disorders do have diagnostic and prognostic significance, that the term "psychotic depression" should be limited to impaired reality testing without reference to degree of incapacitation, that situational-nonsituational and endogenous-nonendogenous classifications are separate depressive subtypes, and that it may not be true that patients with endogenous major depressive disorder have a better prognosis than patients with nonendogenous depression

The marginal cost taxation of a transportation network

Abstract: The paper shows that if the cost and demand functions satisfy certain weak smoothness conditions then the marginal cost taxation of a transportation network is optimal in the usual local sense. Interactions between the cost of travel along a link and flow along other links and between the demand for travel along a route and flow along other routes are permitted.

Chloroplast Division and DNA Synthesis in Light-grown Wheat Leaves

Abstract: Light-grown 7-day-old wheat seedlings (Triticum aestivum, var. Maris Dove) showed an increase of 200% in plastids per cell between 1.7 and 4.5 centimeters from the leaf base. This increase was the result of divisions of young chloroplasts at various stages of development, and was well separated in distance, and therefore in time from the region of cell division in the basal meristem. [3H]Thymidine was incorporated into plastid DNA throughout the zone of plastid division, but not above it.

Traffic control and route-choice; a simple example

Abstract: The paper considers, in a simple case, the interaction between Webster's Method and drivers' route-choice decisions. In the example considered the overall network capacity is severely reduced by using Webster's Method. This shows that Webster's Method does not, in general, maximize the travel capacity of a road network. The analysis of this simple case suggests a signal-setting policy which does maximize the travel capacity of a general network.

The epidemiology of forcible rape

Abstract: Problems of measurement of the incidence of rape are considered, and empirical findings are summarized regarding prevalence, demographic and psychiatric characteristics of offenders, spatial and temporal distribution of offenses, victim-offender relationships, and evidence about recidivism and progression of crimes. Findings are discussed in the framework of blame models and their implications for treatment and prevention.

A study of the autotropic straightening reaction of a shoot previously curved during geotropism

Abstract: The growth of marked zones on horizontal sunflower and maize shoots was measured over long periods. Subsequent to a period of geocurvature, a period of autotropic straightening occurred in most zones of these shoots. The patterns of differential growth causing this straightening were determined. The straightening appeared in the more apical zones initially and subsequently in the basal zones. The magnitude of the differential growth causing the straightening in any zone was similar to that which caused geocurvature in the same zone. It was found that autotropic straightening became evident in some zones before those zones had reached a vertical orientation thus it is suggested that gravity is not directly involved in the initiation of autotropism.

The reinforcing value of several types of aggressive behavior: A review

Abstract: Field observations of “surplus killing” and laboratory studies of operant performance rewarded by prey-killing opportunities suggest that predatory behavior is positively reinforcing. Similarly, both repeated encounter and operant performance studies suggest that intraspecific aggression can be positively reinforcing for successful aggressors. While a few studies suggest that defensive aggression under aversive conditions may also be positively reinforcing, it appears that when appropriate response modes are available escape and/or avoidance are preferred to attack. Studies of the reinforcing properties of aggression-eliciting brain stimulation are in general agreement with these conclusions, but methodological problems with these latter observations render them less compelling. The progressive escalation of aggression seen in “warm-up effects” of birds and fish, “priming effects” of mice, and ecstatic violence of humans may be analogous processes based on the positively self-reinforcing characteristics of some kinds of aggression. The transient reductions of aggression which appear as refractory periods and satiation effects in a variety of species may reflect temporary reductions in the reinforcing value of aggression. All these temporal effects must be considered in the evaluation of experiments on the reinforcing value of aggression. More generally, it is possible that these temporal fluctuations reflect the operation of common motivational processes (aggressive states) which regulate overt aggression by changing its reinforcing value.

Structure and permeability of the epidermal/hypodermal layers of the sand sedge ( Carex arenaria , L.)

Abstract: During the normal course of development in the root of sand sedge (Carex arenaria), many of the cells in the central cortex degenerate to form an extensive aerenchyma. The epidermis and multi-layered hypodermis become heavily suberized and only remain attached to the stele by a few, thin, radial files of cortical cells that have not autolyzed. These changes make it possible for epidermal/hypodermal sleeves to be isolated so that their permeability can be determined. The coefficient of diffusive permeability for tritiated water is of the order of 20 nm s−1, while the permeability coefficient for self diffusion of labelled phosphate and calcium is approximately 5.0 and 4.0 nm s−1 respectively. These values are approximately 200 (water) and 500 (phosphate and calcium) times lower than similar determinations made on isolated sleeves of onion roots. The outer layers of the mature root ofC. arenaria are thus extremely impermeable: any significant absorptive function has been lost at the expense of a protective role provided by the modified cortex for the vascular stele.

Effects of prey‐size and predator‐instar on the predation of Daphnia by Notonecta

Abstract: 1 Attack rates and handling times are measured by a series of separate functional response experiments for each instar of Notonecta glauca attacking four size classes of Daphnia magna as prey The resulting attack rate and handling time surfaces are complex, with maximum attack rates for small predators attacking small prey, and large predators attacking large prey Adult Notonecta have lower attack rates than the two previous juvenile instars (4 and 5) 2 The literature on attack rates and handling times in other predator—prey interactions that involve a series of different predator and prey size or age classes is reviewed in the context of the Notonecta-Daphnia results The data suggest that small predator instars will usually compete with large instars for food, unless there is spatial or temporal separation between them 3 Complex attack rate and handling time surfaces are to be expected wherever a wide range of prey and predator sizes is involved 4 Size related changes in attack rates and handling times can introduce very complex dynamics into predator-prey interactions

Complex demodulation applied to Pi2 geomagnetic pulsations

Abstract: The spectral technique of complex demodulation is applied to Pi2 pulsations recorded along a meridional profile. The technique provides instantaneous values of amplitude and phase and allows frequency dispersion to be taken into account. The variations of magnetospheric wave polarization parameters are observed as a function of both space and time. The results are directly compared with recent theories of the resonance of geomagnetic field lines and the effects of the ionosphere on ground based observations. The theoretical predictions are tested and the experimental results indicate that the night-time ionosphere is capable of a controlling influence on the source characteristics of these magnetospheric waves in the plasmapause region.

The B-chromosome system of Allium schoenoprasum

Abstract: Nine morphologically distinct euchromatic B-chromosomes have been identified in Allium schoenoprasum from the River Wye, South Wales. The most common type (89%) is telocentric (Bt−1) and it is likely that the non-standard Bs are derivatives of Bt−1 by deletion, centric shift and/or centric misdivision. New B-types have also been produced from standard Bs in controlled crosses. In general, the Bs are mitotically extremely stable, although occasional plants, particularly those carrying non-standard Bs, are conspicuously variable in their B-constitution between root-tip cells. In addition, B-chromosome number is enhanced in some anthers of about one third of plants. Behaviour of B-chromosomes during meiosis is described. Although there is little bivalent formation, less than 5% of the Bs are lost during meiosis in anthers. There is, however, no evidence of B-chromosome accumulation in the offspring of controlled crosses, usually a slight loss, and Bs have deleterious effects on aspects of vigour and fertility. Thus, no satisfactory explanation for populations with up to 65% B-containing individuals has yet been found.

An analysis of the changes in growth rate occurring during the initial stages of geocurvature in shoots

Abstract: A detailed study of the changes in growth rate on the two sides of a shoot prior to, and following geostimulation has been undertaken. Data from etiolated Zea seedlings, and cucumber hypocotyls, and from light grown sunflower hypocotyls are presented. In all cases, the differential growth which brings about geocurvature begins simultaneously along the length of the organ. This is contrary to previous reports in the literature which suggested that curvature begins first at the tip of an organ and progresses basipetally. The feature which is common to all species investigated is that growth of the upper side of the shoot ceases following geostimulation. In some cases there is also a marked acceleration in growth rate on the lower side of the shoot (sunflower) but other species show no such acceleration of growth (cucumber). It has been assumed for many years that the major factor causing upward curvature was an acceleration of growth on the lower side of the organ. The data presented here show that the cessation of growth on the upper side is a major, and in some cases the only factor bringing about geocurvature. The data are discussed in relation to the mechanisms which might control geotropic curvature.

Evidence for parthenogenetic reproduction in the sea anemone Actinia equina L

Abstract: Contradictory evidence has led to contrasting hypotheses as regards the origin in Actinia equina. L. of the juvenile anemones which may be found being brooded within adults. We have found, in a North Yorkshire population, a very low proportion of males, but these, as well as individuals lacking gonads, often contained young. All young resembled in colour the adults from which they were obtained. Adults maintained in isolation so as to prevent fertilization continued to produce young. Also ova apparently undergoing cell division were found within female gonads. By contrast, small fragments of anemone, although adopting the appearance of larvae, when cultured, do not develop into juveniles. We conclude that within the population studied reproduction is most probably by parthenogenesis.

Purification and properties of brain cathepsin B. Evidence for cleavage of pituitary lipotropins.

Abstract: 1 CM-cellulose chromatography of calf brain extracts revealed the presence of several enzymes hydrolysing benzoyiarginyl-β-naphthylamide (Bz-Arg-Nap) one of which resembled cathepsin B (EC 3.4.22.1). The latter was purified to homogeneity and showed an absolute dependence on thiol compounds and was optimally active at pH 6.5. The molecular weight of the purified enzyme was 27000 ± 1500. 2 Purified enzyme was inhibited by leupeptin, antipain, iodoacetate, Hg2+, zn2+, and partially by chymostatin and phenylmethylsulfonyl fluoride but was unaffected by pepstatin, puromycin, bestatin and bacitracin. The Km with Bz-Arg-Nap was 0.53 mM, Kcat 4.5 min−1. Dipeptidyl and tripeptidyl-acrylamide substrates were hydrolysed also by the brain enzyme but with lower Kcat/Km ratios. 3 Comparison of the kinetics of inhibition using leupeptin (Ac-l-Leu-Leu-arginal) with Boc-d-Phe-Pro-arginal showed that the latter was non-competitive and the former competitive with Ki of 1.5*10−8 M and 8*10−7 M respectively. 4 Purified enzyme hydrolysed histones (lysine-rich and type-1), myelin basic protein, porcine β-lipotropin, human β-endorphin and protamine. Hydrolysis of β-lipotropin was accompanied by the generation of a 8000-Mr fragment. 5 Cathepsin-B-like enzymes were present in highest concentration in rat pituitary, and lower in cerebellum, hypothalamus, medulla oblongata, striatum and spinal cord.