Showing papers by "University of Sussex published in 1973"

The Logic of Animal Conflict

Abstract: Conflicts between animals of the same species usually are of “limited war” type, not causing serious injury. This is often explained as due to group or species selection for behaviour benefiting the species rather than individuals. Game theory and computer simulation analyses show, however, that a “limited war” strategy benefits individual animals as well as the species.

Rate equation approaches to thin film nucleation kinetics

Abstract: The nucleation and growth of crystals on a substrate are discussed in terms of rate equations for the atom cluster concentrations as a function of time. Simple approximations allow this general set of equations to be reduced to three coupled equations. Many physical processes can be incorporated into these rate equations, including coalescence of clusters, and cluster mobility. The problem of increasing correlation between single atoms and stable clusters as growth proceeds is studied. It is shown that the problem can be solved self-consistently using an auxiliary diffusion equation and that approximations may be obtained which give upper and lower bounds for the cluster growth rates. These diffusion equations also give expressions which enable the cluster-cluster correlations and cluster size distributions to be discussed. With these approximations, expressions are derived for observable quantities and the expressions are compared with one experimental example. In this case, that of gold on alka...

Electron back-scattering patterns—A new technique for obtaining crystallographic information in the scanning electron microscope

Abstract: It is shown that the angular distribution of back-scattered electrons can be observed in a scanning electron microscope, and that the patterns observed can be used to obtain crystallographic information about the specimen. The patterns are termed electron back-scattering patterns (E.B.S.P.). The use of these patterns as a crystallographic techniques is shown to have several significant advantages over two other techniques currently in use in scanning electron microscopes.

Finding picture edges through collinearity of feature points

Abstract: The recovery of straight picture edges from digitisations of scenes containing polyhedra ('line finding') is central to the functioning of scene analysis programs. While recognising that recovery properly involves a computational mobilisation of a great deal of knowledge-supported context, there remain some "basic issues of representation which govern the way in which the primary data - grey levels - are addressed. The paper describes a parametric representation of straight picture edges and its procedural deployment in the recovery of edges from digitisations of scenes whose contents arc essentially polyhedra with strong visible shadows.

Interpreting pictures of polyhedral scenes

Abstract: A computer program that achieves the interpretation of line drawings as polyhedral scenes without using specific object prototypes is described. The method is primarily based on general coherence rules that the orientations of the surfaces and edges must satisfy, thereby dispensing with predetermined interpretations of particular categories of picture junctions as corners. The paper also comments on the relationship of this program to four other scene analysis programs.

Studies by electron paramagnetic resonance on the catalytic mechanism of nitrogenase of Klebsiella pneumoniae.

Abstract: The properties and catalytic reactions of the enzyme nitrogenase purified from Klebsiella pneumoniae were studied by electron-paramagnetic-resonance (e.p.r.) spectroscopy at temperatures down to 8 degrees K. The two protein fractions, Kp1 (the iron-molybdenum protein) and Kp2 (the iron protein), were examined alone and in steady-state mixtures and also in pre-steady-state experiments, by using the rapid-freezing method. Kp1 protein in dithionite solution shows a rhombic type of spectrum with g(1) 4.32, g(2) 3.63, g(3) 2.009 at pH6.8 (0 degrees C). Small changes in the spectrum produced by protons (pK=8.7 at 0 degrees C) or by acetylene indicate binding of these oxidizing substrates to this protein fraction. Kp2 protein shows a rhombic spectrum with g(1) 2.053, g(2) 1.942, g(3) 1.865, which integrates to about 0.45 electron/molecule. Binding of ATP, with a dissociation constant of 4x10(-4)m, changes the spectrum to an axial form with g( parallel) 2.036, g( perpendicular) 1.929, thus indicating a conformation change of Kp2 protein. The Kp2 protein spectrum disappears reversibly on cautious oxidation. The signals of both proteins are diminished in their steady-state mixtures, obtained in the presence of ATP and dithionite (with an ATP-generating system and Mg(2+) ions) and with protons, N(2) or acetylene as oxidizing substrate. At the same time as dithionite is consumed in such reactions, the Kp1 protein signal is gradually restored and the Kp2 protein signal diminishes to zero. In rapid-freezing experiments the signals from the two proteins decreased at indistinguishable rates (t((1/2)) about 10ms), then they remained constant. Results are interpreted in terms of a scheme in which reducing equivalents pass from dithionite to Kp2 protein, then, in an ATP-dependent reaction to Kp1 protein, this being finally reoxidized by N(2) or another oxidizing substrate. In this scheme Kp1 protein cycles between its signal-giving state and a very highly reduced signal-free state.

Describing Sequences of Behavior

Abstract: A review is given of the methods currently available for analyzing sequences of behavior. Simple flow diagrams based on the frequencies or conditional probabilities of individual transitions are considered to be of restricted usefulness except where the sequence is highly ordered and the different patterns occur at similar frequencies. It is more helpful to compare the data with a random model provided that repetitions of the same behavior, and any transitions which cannot occur, are excluded before the expected number of each type of transition is calculated. Such comparisons are most likely to be helpful if the behavior patterns included are closely related and fall into discrete homogeneous categories. The fact that most behavioral data are unlikely to be stationary is considered to be the main factor limiting this approach. It is suggested that first-order transition analysis and correlative techniques are the best current methods for examining such data. The search for higher-order dependencies is useful only in stationary data, where grouping of acts due to changing causal factors can be assumed to be unimportant. Additional difficulties involved in the analysis of sequences of interaction between individuals are briefly discussed. The major complicating factor here is that the behavior of an individual is likely to be dependent both on that of others and on its own previous behavior. Some ways of improving current techniques to take account of this are put forward. It is emphasized that sequence analysis provides only a description of the behavior under study and that there are dangers in making causal inferences on the basis of such descriptions alone.

Protein and nucleic acid metabolism in insect fat body

Abstract: Summary 1. The appearance of larval fat body as seen under the light or electron microscope depends on the nutritional state of the larva and on the stage of larval development at which the fat body is observed. 2. Early in the last larval instar the cells usually possess a well-developed endo-plasmic reticulum rich in ribosomes, numerous mitochondria, glycogen granules, a Golgi complex and fat droplets, while later in the instar the endoplasmic reticulum is much reduced and mitochondria are few, but glycogen and fat droplets are present in greater amount together with the appearance of large numbers of proteinaceous spheres. 3. Early in the last instar the fat body synthesizes proteins and exports them into the blood, while later in the instar proteins are sequestered from the blood into the fat body. 4. The rate of protein synthesis by the fat body is high in the early to mid part of the last instar, but then falls off rapidly to a low level, at which it remains until the larva pupates. In diapausing pupae, protein synthesis remains at this low level. 5. The similarity between the electrophoretic patterns of proteins from the fat body and those from the blood provides strong evidence that the fat body is the site of synthesis of many of the blood proteins. 6. Some of the blood proteins have been shown to possess enzymic properties, while others are thought to play a role in the transportation of various types of compounds. 7. Ecdysone and juvenile hormone both stimulate the rate of protein synthesis by larval fat body. Protein synthesis in fat body from diapausing pupae is stimulated after injury to the pupae. 8. The appearance of adult fat body and the amount of protein it contains is often closely linked with the nutritional and reproductive states of the insect. 9. An important role of the fat body in the adult female insect is the synthesis of yolk proteins, which are released into the blood and then taken up by the developing oocytes. This synthesis and uptake are under the control of hormones secreted by the corpora allata and by the median neurosecretory cells of the pars intercerebralis. 10. The RNA content of fat body in final-instar larvae is not constant throughout the instar. In some larvae it is at its highest level early in the instar, falling to a low level as the instar progresses, while in other larvae (e.g. Calliphora) the level of RNA in fat body does not decrease as the instar progresses. 11. In some dipterous insects the base composition of total RNA is DNA-like in that the guanine + cytosine content is low, accounting for 40 % of the bases. A similar composition is seen in rapidly labelled RNA isolated from insects of other orders (Coleoptera and Lepidoptera), but the base content of total RNA from these latter insects resembles ribosomal RNA from vertebrate tissues in that it has a high (ca. 60 %) guanine + cytosine content. 12. The RNA/DNA ratios in blowfly larval tissues are high compared with those found in any vertebrate tissue. 13. In larval fat body, RNA synthesis is low at the time of a moult, increases during the early and mid-instar period and subsequently falls during the latter part of the instar. During the pupal period, especially during pupal diapause, the rate of RNA synthesis is very low and then increases during the subsequent development of the pharate adult. Injury to diapausing pupae results in an increased rate of RNA synthesis in most of their tissues. 14. Ecdysone and juvenile hormone both stimulate RNA and DNA synthesis in larval and adult fat body and in other tissues, although there is evidence that in some tissues these two hormones may act antagonistically to each other. The insecticide DDT also has been shown to stimulate RNA synthesis in tissues of adult insects.

Head Movement of Flies during Visually Guided Flight

Abstract: MOST visually advanced animals are able to move their eyes relative to the body. This makes vision independent of body movements; in man it enables the eyes to keep the visual world stationary on the retinae, to scan the field of view, and to maintain fixation on moving objects1. The extent to which animals other than vertebrates are able to perform these activities is largely unknown; many, especially arthropods, make body movements tending either to stabilize the visual surroundings2,3 or to cause fixation of objects by the eyes4,5. In a very few cases, however, it has been shown that arthropod eyes may make directed movements independent of the body: examples are the fixation of prey by mantids6 and by salticid spiders7, and compensatory eye movements in a moving visual surround by crabs8 and locusts9. Here I describe the head movements (and therefore, in insects, eye movements) made by blowflies during sustained flight. I show these to be of two kinds: rapid saccadic flicks in which the head takes up a new angle with respect to the visual surroundings, and stabilization movements which keep the angular position of the head almost constant, in spite of body movements of up to 10° in either direction.

Pavlovian conditioning with heat reinforcement produces stimulus-directed pecking in chicks.

Abstract: In a cooled chamber, chicks approached and pecked a small disk whose illumination preceded heat lamp activation, even when pecks prevented heat lamp onset. These behaviors did not occur when the disk and heat stimuli were randomly presented. Approach and contact of conditioned stimuli may develop even though these behaviors are not (i) evoked by the reinforcing stimulus, (ii) necessary for reinforcer reception, or (iii) ever followed by the reinforcer.

Control of ornithine decarboxylase activity in stimulated human lymphocytes by putrescine and spermidine

Abstract: Ornithine decarboxylase activity in extracts of phytohaemagglutinin-stimulated human lymphocytes is rapidly and extensively inhibited by additions of micromolar concentrations of putrescine or spermidine to the culture medium. This inhibition is not due to feedback inhibition of the enzyme by putrescine, spermidine or their metabolites. Inhibition is dependent on the continuation of protein synthesis, but does not require RNA synthesis. The effect of putrescine is abolished when its conversion into spermidine by the cells is prevented.

A Study of Success and Failure in Industrial Innovation

Abstract: This paper discusses the main results of a recent project carried out at the Science Policy Research Unit of the University of Sussex.1 The project (SAPPHO) was an attempt to measure a large number of characteristics of successful attempts to innovate and to compare them with corresponding unsuccessful attempts.

The effect of salt on protein synthesis in the halophyte Suaeda maritima

Abstract: An amino acid-incorporating microsomal fraction has been isolated from the leaves of the halophyte Suaeda maritima and the characteristics of the incorporation described. There were no differences in the properties of the microsomes isolated from plants grown in saline and non-saline conditions. The incorporation was severely inhibited by high concentrations of sodium or potassium ions. The results are discussed in relation to the mechanism of salt tolerance in halophytes and the localization of salt in the cells.

Mutagenicity of dichlorvos and methyl methane-sulphonate for Escherichia coli WP2 and some derivatives deficient in DNA repair

Abstract: The mutagenic and lethal action of methyl methanesulphonate (MMS) and dichlorvos (DDVP) has been studied on Escherichia coli WP2 and some derivatives deficient in DNA repair genes. The exrA + and recA + alleles were necessary for significant mutagenesis by either compound, and the uvrA gene affected neither the lethal nor mutagenic responses. Increased sensitivity to both compounds was shown by the exrA and uvrAexrA strains and in a more pronounced way by the uvrApolA , recA , and uvrAexrApolA strains. Bacteria deficient at the polA locus were 2 and 3 times more mutable by DDVP and MMS respectively, consistent with the hypothesis that the absence of the polA system for the repair of single-strand gaps results in a greater proportion of the total repair being channelled through the error-prone exrA + / recA + -dependent system. Single-strand breaks were detectable by alkaline sucrose gradient centrifugation after both MMS and DDVP treatment of polA bacteria. Thus in all the tests carried out, both compounds showed similar patterns of activity, and the results are consistent with their known ability to alkylate DNA. The chief differences were quantitative; sensitivity increases were far more pronounced with MMS which was also a far more potent mutagen than DDVP.

Food and nutrition planning

Abstract: This paper discusses food and nutrition planning. It presents a planning schema in which static micro level analysis is incorporated into a dynamic general equilibrium framework. The paper is critical of conventional policy approaches based as they are on false notions of the nature of the nutrition problem. The problem is generally one of calorie rather than of protein deficiency, and it arises from inadequate effective demand for food rather than as a result of insufficient supply. If the continued existence of malnutrition is not simply to be accepted it will have to be treated as primarily a symptom of poverty. Thus, policies to end it will seek to generate incomes among the poor. Analytical and empirical work is needed to identify the nature of specific policy alternatives and to predict their effects. Practical criteria to reflect social objectives still need to be developed. Technological approaches to increasing food supplies overlook the poverty of the undernourished and the prediction of growing food ‘surpluses’. Resume PLANIFICATION DE L'ALIMENTATION ET LA NUTRITION L'auteur examine la question de l'alimentation et la nutrition planifiees. Il presente une methode de planification incorporant une microanalyse statique dans un cadre de travail equilibre, general et dynamique. Il s'eleve contre les methodes classiques utilisees pour apprehender le probleme de la nutrition et reposant sur des notions erronees de la nature de ce probleme. Selon lui, il s'agit en general d'un probleme de calories plutot que de carences proteiques, probleme qui decoule de l'insuffisance de la demande effective en matiere d'alimentation et non d'une insuffisance de production. A moins que l'on n'admette tout simplement la persistance du phenomene de la malnutrition, il faudra le traiter comme etant primordialement un symptome de pauvrete. Des lors, les systemes d'elimination de la malnutrition s'emploieront a engendrer des revenus parmi les categories sociales pauvres. Des travawc analytiques et empiriques sont necessaires pour definir la nature des differentes methodes d'action specifiques que l'on pourrait choisir et pour predire leurs effets. Un travail plus approfondi est encore necessaire pour determiner les criteres pratiques qui doivent refleter les objectifs sociaux. Les methodes technologiques employees en vue de parvenir a l'accroissement des approvisionnements alimentaires ne tiennent pas compte du pauperisme des sous-alimentes et de la prediction de l'augmentation des surplus alimentaires. Zusammenfassung NAHRUNGSMITTEL- UND ERNAHRUNGSPLANUNG Diese Arbeit behandelt Nahrungsmittel- und Ernahrungsplanung. Sie stellt ein Planungsschema dar, bei dem die statische Analyse auf der Mikroebene in einen dynamischen allgemeinen Gleichgewichtsrahmen einbezogen wird. Die Arbeit setzt sich kritisch mit konventionellen Verfahrensansatzen auseinander, die auf falschen Annahmen uber die Art des Ernahrungsproblems beruhen. Das Problem ist im allgemeinen eher eines von Kalorien- als von Proteinmangel und es ergibt sich in starkerem Mass aus einer unzureichend wirk-samen Nachfrage nach Nahrungsmitteln und ist weniger ein Ergebnis unzureichenden Angebots. Wenn man sich nicht mit der nach wie vor bestehenden Unterernahrung einfach abfinden will, wird sie vor allem als ein Symptom von Armut behandelt werden mussen. Daher werden Verfahren zu ihrer Beseitigung darauf abzielen, Einkommen unter den Armen zu schaffen. Analytische und empirische Arbeiten sind erforderlich, um die Art spezifischer Verfahrensalternativen zu erhellen und ihre Wirkungen vorauszusagen. Praktische Kriterien, die soziale Ziele einbeziehen, mussen noch entwickelt werden. Technologische Ansatze zur Erhohung der Nahrungsmittelversorgung ubersehen die Armut der Unterernahrten und die Voraussage der wachsenden Nahrungsmitteluberschusse.

Organometallic Complexes with Silicon-Transition Metal or Silicon-Carbon-Transition Metal Bonds

Abstract: Publisher Summary This chapter provides a guide to the literature on organometallic complexes with silicon–transition metal (Si–M) or silicon–carbon–transition metal bonds (Si–C–M). It discusses complexes having Si–transition metal (M) bonds, the role of transition metal complexes in hydrosilylation, and complexes having Si–C–M bonds. The work of Hein and his associates on Sn–Co derivatives established the possibility of forming bonds between a Group IVB metal and a transition element, but it was another 15 years before CpFe(CO) 2 SiMe 3 —the first of many silyl derivatives—was synthesized. Substantial advances have been made in the field of hydrosilylation since 1965, when a comprehensive mechanism for catalysis by noble metal complexes was first published. The mechanism for the hydrosilylation of olefins catalyzed by chloroplatinic acid is outlined in the chapter. In 1970, two groups of workers independently drew attention to a type of alkyl ligand that was expected to have significance in transition-metal chemistry. This may formally be regarded as a carbanion in which one or more α -H atoms have been replaced by an organometallic or organic group. Six methods have been used for the synthesis of Me 3 SiCH 2 M and related complexes. All these have counterparts in Me–M and related chemistry.

Amplified Spontaneous Emission and External Signal Amplification in an Inverted Medium

Abstract: An improved version of the theory of amplified spontaneous emission (ASE) is presented and shown to be satisfied by experimental data obtained using the 3.39-\ensuremath{\mu}m transition of He-Ne. The new approach allows the effect of an external signal injected at one end of the system to be investigated and its influence on both the positive-going and negative-going waves to be calculated for He-Ne. A special case occurs when the injected signal is replaced by a mirror which reflects the negative-going wave back into the medium and the theory of this commonly occurring laboratory system is experimentally verified at 3.39 \ensuremath{\mu}m. The treatment allows the importance of the interaction between spontaneous and stimulated emission to be considered. The beam divergence predicted by the theory is evaluated and compared with experiment. The spectral distribution for a pure ASE system is considered, as is the distribution of inversion which results from the positive- and negative-going waves and which is shown to have minima at the medium extremities. Finally the implications of this work for the problem of interstellar OH emission is considered.