Showing papers by "University of York published in 1975"
TL;DR: In this article, the complexity of simple first-order nonlinear difference equations has been studied in an ecological context and the complexity can also occur in the wider context of competition between two species.
Abstract: THE complicated dynamics associated with simple first-order, nonlinear difference equations have received considerable attention (refs 1–4 and R. M. May and G. F. Oster, unpublished). In an ecological context, equations of this type provide a powerful and realistic means of modelling the behaviour of animal populations with ron-overlapping generations, typified by many arthropods in temperate regions. May4 has shown that such models, incorporating density dependence, have three regimes of dynamic solution in their parameter space, namely (1) a stable equilibrium point; (2) bifurcating cycles of period 2n, 0
386 citations
TL;DR: In this article, the authors investigate the topology of two configuration spaces associated to a smooth manifold M. The first is the space C(M) of all finite subsets of M, and it is topologised so that particles cannot collide.
237 citations
TL;DR: In this paper, a bovine femur was loaded in tension at strain rates of from 0·00013 to 0·16 sec −1, and the ash content and amount of reconstruction (Haversian bone) of each specimen was determined.
180 citations
TL;DR: None of the proteins except L7/L12 is present at a level significantly different from one molecule per ribosome, suggesting that the ribosomes of Escherichia coli are homogeneous in vivo.
Abstract: A ribosome preparation from E. coli made without stringent washing procedures has been shown to contain the same relative amounts of nearly all the ribosomal proteins as ribosomes in intact cells. Stoichiometric measurements on all the proteins of this preparation except for L8, L20, L31 and L34 have been made using an isotope dilution technique. When the scatter of the values obtained, the uncertainty in the molecular weights, and the losses occurring during extraction are taken into account, none of the proteins except L7/L12 is present at a level significantly different from one molecule per ribosome. There are multiple copies of L7/L12. These data suggest that the ribosomes of Escherichia coli are homogeneous in vivo.
174 citations
TL;DR: In this paper, for a vintage model of capital equipment expressions for the implicit rental value and the optimal replacement policy are derived from the hypothesis of profit maximization, and the relationship of certain payoff period criteria to the optimal policy is also discussed.
161 citations
TL;DR: Insect wings are very light structures as mentioned in this paper, with a rotational moment of inertia about the wing base small enough to reduce as far as possible the energy expenditure involved in their repeated accelerations.
Abstract: SELECTION is likely to have resulted in the evolution of insect wings which combine aerodynamic efficiency with a rotational moment of inertia about the wing base small enough to reduce as far as possible the energy expenditure involved in their repeated accelerations. Their construction has to leave them stiff enough to remain aerodynamically efficient when under inertial or aerodynamic load, and free from buckling, however light they become. Insect wings are very light structures—11 g m−2 in the dragonfly Aeschna cyanea, 16.7 g m−2 in Locusta migratoria1 and 7.4 g m−2 in Tipula sp.2.
144 citations
TL;DR: Theoretical estimates in the LCAO approximation reveal that matrix elements for interatomic Auger processes are very strongly energy dependent, but that for very low energy Auger transitions they may be comparable with the competing intra-atomic processes as mentioned in this paper.
142 citations
TL;DR: Measurements of lift and drag forces acting on corrugated aerofoils are reported and an attempt is made to model the thick leading edge vein of the real wing by constructing the model leading edge from a stainless steel rod.
Abstract: IN this communication I report measurements of lift and drag forces acting on corrugated aerofoils. The chordal profile of the wings in many orders of insects is corrugated1 and I have used scale models of a wing section of this type found in the hover fly Syrphus balteatus (Diptera, Syrphidae). The experimental profile is shown in Fig. 1d. The life-size chord length is 2.9 mm, and occurs 3.7 mm distal to the wing-root hinge, in a total unilateral wing length of 11.5 mm. (There is no special reason either for selecting this particular section or for choosing S. balteatus.) The model profiles were 22 times life size (chord length = 6.4 cm) and were made of stainless steel 100 µm thick. They were built to uniform chordal profile, with spans of 7.17 cm or 3.39 cm, giving aspect ratios of 1.12 and 0.53, respectively—both very low. An attempt was made to model the thick leading edge vein of the real wing by constructing the model leading edge from a stainless steel rod (diameter 1.7 mm).
107 citations
TL;DR: In this paper, a measure of native labile P was first added to the sorption data, and this sum plotted against intensity, and the exponent from the isotherm was closely related to exchangeable A1 (in acid soils) and exchangeable Ca (in neutral and calcareous soils).
Abstract: Summary
Phosphate sorption data for twenty-nine soils were found to fit the Freundlich adsorption isotherm better if a measure of native labile P was first added to the sorption data, and this sum plotted against intensity. The exponent from the isotherm thus obtained was closely related to exchangeable A1 (in acid soils) and exchangeable Ca (in neutral and calcareous soils), with a mole ratio of one P to 6 A1 or Ca.
101 citations
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01 Jan 1975TL;DR: The kinetics of muscle contraction is studied in detail in the context of muscular dystrophy and its role in accidents and injuries.
Abstract: The kinetics of muscle contraction , The kinetics of muscle contraction , کتابخانه مرکزی دانشگاه علوم پزشکی ایران
99 citations
TL;DR: Colonoscopy and the contrast enema are best reported as completmentary rather than competitive approaches, and by their combined use, diagnostic accuracy is greatly enhanced.
Abstract: Endoscopic examination of the entire colon (colonoscopy) is an important new method of diagnosis and treatment of diseases of the colon and rectum, particularly cancer The records of 500 patients who had one or more contrast enemas and subsequent colonoscopy were analyzed in an attempt to evaluate the competitive and complementary features of the two methods The endoscopists had the advantage of having a radiologic report or radiographs available to them In general, when the level of abnormality could be reached, colonoscopy had a higher degree of accuracy, particularly since observation could be combined with biopsy This was particularly true in the case of polyps in which colonoscopy confirmed 166 radiologically described growths plus an additional 118 lesion, twenty-one of which were over 1 cm in diameter By endoscopic excision of these polyps via the colonoscope, malignant changes can be identified, a conclusion rarely reached by radiographic means alone With respect to cancer, exclusive of polyps, only twenty-four of thirty-two cases were diagnosed by x-ray study alone Another nine, interpreted aa demonstrating malignancy from the radiographs, had cancer excluded when subjected to endoscopic confirmation Colonoscopy has also proved valuable in identifying lesions of the cecum, notoriously a problem for the radiologist, and in identifying milder degrees of inflammatory change which are undetectable by radiographic means Colonoscopy and the contrast enema are best reported as completmentary rather than competitive approaches, and by their combined use, diagnostic accuracy is greatly enhanced
TL;DR: The synthetic pheromone and A. polyphemus females were not attractive to released Antheraea pernyi males and a 90 : 10 mixture of acetate and aldehyde was highly attractive to wild males in the field.
TL;DR: Rosenhan's study proves that pseudopatients are not detected by psychiatrists as having simulated signs of mental illness, and this rather unremarkable finding is not relevant to the real problems of the reliability and validity of psychiatric diagnosis.
Abstract: Rosenhan's "On Being Sane in Insane Places" is pseudoscience presented as science. Just as his pseudopatients were diagnosed at discharge as "schizophrenia in remission," so a careful examination of this study's methods, results, and conclusion leads to a diagnosis of "logic in remission." Rosenhan's study proves that pseudopatients are not detected by psychiatrists as having simulated signs of mental illness. This rather unremarkable finding is not relevant to the real problems of the reliability and validity of psychiatric diagnosis and only serves to obscure them. A correct interpretation of these data contradicts the conclusions that were drawn. In the setting of a psychiatric hospital, psychiatrists seem remarkably able to distinguish the "sane" from the "insane."
TL;DR: In this paper, the authors discuss three generalised accounts of the processes by which scientific knowledge develops: the "me)del of openness", the "model of dewure", and the "irujdel of branching".
Abstract: In this paper I am going to discuss three generalised accounts, or 'me)dels', of the processes by which sdence develops.' I shall call these the 'me)del of openness', the 'model of dewure', and the 'irujdel of branching'. The central concern of each is to show how social factors operating within the pure research communitycontribute to the developtnent of scientific knowledge. I shall argue that the third mexlel provides a more satisfacteny solution to this problem than either of the other two.
TL;DR: In this paper, it is shown that in the neighborhood of an unstable equilibrium point such time delays can slow the growth rate of instabilities, thus leading to a population spending longer times in the vicinity of such unstable points.
Abstract: It is well known that time delays in feedback mechanisms in the neighborhood of a stable equilibrium point tend to produce oscillatory overshooting, eventually leading to patterns of limit cycles for excessive time delays. It is less well appreciated that in the neighborhood of an unstable equilibrium point such time delays can slow the growth rate of instabilities, thus leading to a population spending longer times in the vicinity of such unstable points. These ideas are illustrated with a biologically motivated mathematical example. Some laboratory data are discussed in the light of the findings.
TL;DR: In this article, the frequency of occurrence of the pulsations as a function of Kp index and local time was analyzed from five stations; Eskdalemuir (L = 3.1), Lerwick (L= 4.0), St. Anthony, Sodankyla and Tromso.
TL;DR: This study shows that cathepsin D could be the endogenous enzyme responsible for the breakdown of basic protein to form smaller encephalitogenic fragments, some of which are known to be present in crude tissue extracts.
Abstract: Myelin basic protein, purified from bovine spinal cord, is cleaved by a purified bovine brain acid proteinase to yield three peptide fragments which were purified by gel filtration procedures combined with preparative gel electrophoresis. The purity of the fragments was established by end group analysis, amino acid analysis, polyacrylamide disc gel electrophoresis, and by their encephalitogenic activity. Chemical and biological characterization shows that one peptide, (peptide II), originates from the N-terminal end of the basic protein and contains residues 1–43; a second peptide, (peptide I), contains residues 44–89 and a third peptide (peptide III). originates from the C-terminal region with an N-terminal phenylalanine, residue 90, through arginine, residue 170, of the basic protein. The combined amino acid composition of the three fragments account for the amino acid content of the basic protein. The structure of the three peptides demonstrates that the purified brain acid proteinase selectively cleaves the two phenylalanine-phenylalanine linkages formed between residues 43–44 and 89–90 of the basic protein molecule. This study shows that cathepsin D could be the endogenous enzyme responsible for the breakdown of basic protein to form smaller encephalitogenic fragments, some of which are known to be present in crude tissue extracts.
TL;DR: In this article, the authors present a simple calculation which shows that one can account for the formation of three-dimensional islands of copper on nickel or gold on palladium if the energies associated with misfit strain and misfit dislocations are considered.
01 Dec 1975-Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology
TL;DR: The results suggest that satiation in Aplysia is due to activation of mechanoreceptors associated solely with the anterior gut, and the bulk stimulus that causes satiation is quantifying and localizing.
Abstract: The present study was concerned with quantifying and localizing the bulk stimulus that causes satiation inAplysia.
1.
Food-deprived animals were found to gain a mean of 15.4 ± 6.6 (S.D.) percent of body weight immediately following a meal of dried seaweed. The weight gain is largely accounted for by water ingested along with the dried seaweed (Fig. 3).
2.
Animals that were chronically food deprived required a larger amount of food to satiate, compared to animals that had been fed daily (Figs. 7, 8; Table 1); nevertheless, after satiation, the mean anterior gut contents were similar in all animals, regardless of the quantity of bulk consumed during the meal (Figs. 8, 9). The greater quantity of food eaten by the previously food-deprived animals can be quantitatively accounted for by the smaller amount of bulk present in their anterior gut before the meal (Fig. 8).
3.
Injection of high viscosity non-nutritive bulk which preferentially fills the anterior gut (Fig. 10) was capable of causing satiation (Figs. 11, 12), whereas injection of low viscosity bulk which preferentially fills the intestine did not cause satiation (Figs. 11, 12). Satiation also was not produced by injections of bulk into the hemocoel (Fig. 12).
TL;DR: It is reported that gamete release by one A. planci induces other ripe starfish to spawn; similar behaviour has been observed in certain other echinoderms1,2.
Abstract: LARGE aggregations of the crown-of-thorns starfish Acanthaster planci L have destroyed a high proportion of the coral on certain Indo-Pacific reefs. We report that gamete release by one A. planci induces other ripe starfish to spawn; similar behaviour has been observed in certain other echinoderms1,2. During natural spawning a pheromone is released from the gonad, which synchronises spawning in neighbouring animals and also induces starfish movement towards the spawning individual. Using a Y maze to study chemoattraction in spawning starfish, we have attempted to isolate and characterise the active gonad component.
TL;DR: Human polymorphonuclear neutrophil granule extract released 60 percent of the available 35SO4 from labeled rabbit articular cartilage in 0.5 hour at neutral pH, suggesting that the chymotrypsin-like esterases were responsible for proteoglycan degradation by this region of the gel.
Abstract: Human polymorphonuclear neutrophil (PMN) granule extract (25 mug of protein) released 60 percent of the available 35SO4 from labeled rabbit articular cartilage in 0.5 hour at neutral pH. N-acetyl-L-alanyl-L-alanyl-L-prolyl-L-alanine choloromethyl ketone (NAcAAPACK), a specific elastase inhibitor, was only minimally effective against whole granule extract, and N-alpha-tosyl-L-lysine chloromethyl ketone, which inhibits trypsin but not elastase, was completely ineffective. Preparative disc-gel electrophoresis of PMN granule extract revealed two separate regions with independent activity against 35SO4-labeled cartilage. One region contained elastases and when tested alone, was completely inhibited by NAcAAPACK. The other contained lysozyme and two esterases active against N-acetyl-L-phenylalanine-alpha-naphthol. Purified lysozyme proved inactive, suggesting that the chymotrypsin-like esterases were responsible for proteoglycan degradation by this region of the gel.
TL;DR: The name sub-apical necrosis is proposed to describe this condition, which was shown to be due to calcium deficiency and was fully controlled by frequent application of 0.01M calcium sulphate solution to the tips of the sprouts.
Abstract: Majestic potatoes sprouted in the dark at 20°C developed necrotic lesions in the elongating region of the sprout, about 3 to 5 mm below the apex. The name sub-apical necrosis is proposed to describe this condition. It was shown to be due to calcium deficiency and was fully controlled by frequent application of 0.01M calcium sulphate solution to the tips of the sprouts. The influence of several other factors was also studied. Calcium was necessary to maintain apical dominance of the sprout and prevent some of the changes which have been attributed to physiological ageing.
TL;DR: It is shown that for any n, there exist subsets of an n × n square array containing n points, of which no three lie in a line, and that for sufficiently large n there exist such subsets containing (32 − ϵ)n points.
TL;DR: In this paper, the authors compare the results of measurements of the M 45 N 45 N 46 N 45 Auger spectrum of cadmium with those of the vapour phase.
TL;DR: In this article, the authors argue that debates over the detailed aspects of energy analysis and its applications are misplaced in face of the absence of any real assessment of the purpose of energy analyses.
TL;DR: The epitaxial growth of thin copper films on (001) surfaces of nickel in ultra-high vacuum has been investigated using Auger electron spectroscopy and electron microscopy as discussed by the authors.
Abstract: The epitaxial growth of thin copper films on (001) surfaces of nickel in ultra-high vacuum has been investigated using Auger electron spectroscopy and electron microscopy. At room temperature, deposits tend to grow in layer-like fashion and are strained compressively to be coherent with the substrate up to a thickness of about 8 A. Above this thickness the elastic strain decreases with the introduction of misfit dislocations, but more rapidly than theories predict. At 300°C, copper grows by a Stranski–Krastenov mechanism.
TL;DR: This paper proposes models that characterise the effect of prey consumption on the components of the predator rate of increase that are specifically designed to relate the authors' hypotheses to field or laboratory data.
Abstract: CENTRAL to our understanding of predator–prey dynamics is the relationship between the death rate imposed on the prey by the predators and the rate of increase, or numerical response, of the predator population. Most of the familiar mathematical models of predator–prey systems involve the assumption that there is a simple linear relationship between the number of prey killed and predator reproduction1–4. Although this assumption is valid for most insect host–parasitoid systems2, the rate of increase of other predatory arthropods is a more complex function of the prey consumed. For successful reproduction, each instar must find and eat several prey to complete development. Thus the predator rate of increase will depend on the duration of, and the survival rate within each instar and the fecundity of the adults. Where models for the predator rate of increase have incorporated more complex nonlinear relationships5,6, these relationships are of too abstract a character to allow simple experimental corroboratiqn or refutation. In this paper we propose models that characterise the effect of prey consumption on the components of the predator rate of increase that are specifically designed to relate our hypotheses to field or laboratory data.
TL;DR: Wild snails yielding extracts containing more than two heavily staining zones were shown to possess only two such zones after three months under laboratory conditions, and a model is suggested which could account for this phenomenon.
Abstract: Hepatopancreatic extracts from the snail Cepaea nemoralis, assayed straight from the field, often contain three or four heavily staining esterase zones which migrate to the cathodal end of polyacrylamide disc gels during electrophoresis Previous breeding results showed that the heavily straining zones appeared allelic but to incorporate these multibanded phenotypes, a super gene of five closely linked loci was tentatively proposed Further breeding work again failed to demonstrate multiple zones in parents or offspring and so experiments were conducted to see whether the multi-zoned phenotypes in the wild were produced by secondary modification of single primary products Wild snails yielding extracts containing more than two heavily staining zones were shown to possess only two such zones after three months under laboratory conditions Also, the ingestion of nettle (Urtica dioica L) has been demonstrated to induce extra esterase zones in laboratory-reared animals Some of the secondarily induced zones appear identical in physical, biochemical and electrophoretic properties to the primary products of other alleles, and thus appear to be electrophoretic phenocopies A model is suggested which could account for this phenomenon
TL;DR: In this article, a statistical study using data from four geomagnetic recording stations with McIlwain parameters from L = 2.5 to 6.6, suggests that the general source location of Pc 1 micropulsations lies close to the plasmapause.
TL;DR: The intrinsic fluorescence characteristics of the purified basic protein have been determined and the results interpreted in terms of current ideas on the structure of the protein suggest that the basic protein can be used as a natural, non‐perturbing probe which will report on its environment after it has reacted with other membrane components.
Abstract: —The encephalitogenic basic protein has been isolated from the myelin sheath of ox brain white matter and the purity and amino acid composition have been verified. The intrinsic fluorescence characteristics of the purified basic protein have been determined and the results interpreted in terms of current ideas on the structure of the protein. Fluorescence data obtained from the basic protein in aqueous solution indicate that the tyrosine and tryptophan residues are largely exposed to the solvent and that resonance energy transfer from tyrosine to tryptophan is very inefficient. Denaturing conditions in 8 m-urea have little effect on the fluorescence properties of the protein. The ionic detergent, sodium dodecyl sulphate, interacts with the basic protein and alters the fluorescence properties in a manner which indicates that the tryptophan residue is in the hydrocarbon chain region of the detergent while the local positive charge around the tyrosine residues is neutralized by the negatively charged sulphate head-groups. The fluorescence results suggest that the basic protein can be used as a natural, non-perturbing probe which will report on its environment after it has reacted with other membrane components.