Showing papers by "University of London published in 1976"

Radiation from a moving mirror in two-dimensional space-time conformal anomaly

Abstract: The energy-momentum tensor is calculated in the two dimensional quantum theory of a massless scalar field influenced by the motion of a perfectly reflecting boundary (mirror). This simple model system evidently can provide insight into more sophisticated processes, such as particle production in cosmological models and exploding black holes. In spite of the conformally static nature of the problem, the vacuum expectation value of the tensor for an arbitrary mirror trajectory exhibits a non-vanishing radiation flux (which may be readily computed). The expectation value of the instantaneous energy flux is negative when the proper acceleration of the mirror is increasing, but the total energy radiated during a bounded mirror motion is positive. A uniformly accelerating mirror does not radiate; however, our quantization does not coincide with the treatment of that system as a 'static universe'. The calculation of the expectation value requires a regularization procedure of covariant separation of points (in products of field operators) along time-like geodesics; more naive methods do not yield the same answers. A striking example involving two mirrors clarifies the significance of the conformal anomaly.

The adolescent growth spurt of boys and girls of the Harpenden growth study.

Abstract: Logistic curves have been fitted to the growth during puberty of the 55 boys and 35 girls of the Harpenden Growth Study who were measured every three months during puberty and thereafter until grow...

The relative importance of muscle protein synthesis and breakdown in the regulation of muscle mass.

Abstract: The effects of growth-suppressing and muscle-wasting treatments on muscle protein turnover and amino acid concentrations were determined in vivo. All treatments depressed protein synthesis and some treatments depressed protein breakdown. Only prolonged starvation increased protein breakdown. Muscle protein mass is regulated primarily through alterations in protein synthesis in all except emergency conditions. The increased concentrations of the branched-chain amino acids indicate that they are unlikely to be involved in this regulation.

Clinical pharmacology and pharmacokinetics of clonidine.

Abstract: A 300-mug oral dose of clonidine was administered to 5 normal volunteers and measurements of plasma concentration and effects upon blood pressure, heart rate, circulatory reflexes, sedation, and dry mouth were made for the following 8 hr. The plasma concentration rose to a peak of 1.02 +/- 0.52 ng/ml (SD) at 90 min and fell with a mean half-life of 12.7 hr. Blood pressure of the group fell from 111.0/77.0 to 87.2/60.4 after 3 hr and was 95.2/62.2 mm Hg at 8 hr. Heart rate in recumbency was slowed. Marked sedation and a fall in salivary flow followed the same time-course as the plasma concentration. The cold pressor response was reduced but the Valsalva overshoot was little affected.

Protection of mice against babesia and plasmodium with bcg.

Abstract: Babesia spp. are haemoprotozoans, and some cause diseases of considerable economic importance in cattle. Complete protection against challenge has been recorded only in animals recovered from artificial1 or natural infections with a virulent strain of the organism. We have achieved the same result with B.microti and B.rodhaini, two of the species which parasitise mice, by previous infection with Mycobacterium bovis strain BCG (Bacillus Calmette-Guerin). Evidence is provided that neither antibody specific for surface antigens of the parasites nor increased phagocytic capacity is responsible for this protection. We suggest that BCG protects by increasing the release of non-antibody soluble mediators of immunity postulated to cause the death of B.microti inside red cells2. Preliminary observations on protection against Plasmodium berghei yoelii and P.vinckei are also presented.

Enzyme immunoassays for parasitic diseases.

Abstract: It is only in recent years that serology has come to play a major role in parasitic diseases. At first complement fixation was most used but gradually more convenient and sensitive techniques such as gel precipitation (DRAPER, 1976), and agglutination methods (KAGAN, 1974) were introduced. Probably the serological test most used by parasitologists has been immunofluorescence, particularly the indirect fluorescent antibody method (KAGAN, 1974; AMBROISE-THOMAS, 1976). Certain factors must be taken into consideration when assessing the usefulness of serological methods for parasitic diseases. The major parasitoses such as malaria, schistosomiasis, trypanosomiasis, infect millions of people in poor areas of the world where technical expertise is, at present, very limited. In these areas serological methods can be of most use in establishing epidemiological indices and for monitoring disease control programmes. Tests for use in such areas should be suitable for mass screening, should be simple and cheap, and .the results should be available quickly. Under these conditions some degree of precision may have to be sacrificed in the interests of practicability. There is also a place for more sophisticated methods suitable for individual diagnosis of parasitic infections especially in the more privileged areas of the world. We feel that enzyme-immunoassays, especially the enzyme-linked immunosorbent assay, have a part to play in both the above situations.

Liposomes as Immunological Adjuvants

Abstract: Adjuvants can be defined as agents which non-specifically increase immune responses to specific antigens. Some adjuvants, such as alum or Freund’s incomplete adjuvant (FICA, a water-in-oil emulsion), increase the formation of antibodies against protein antigens without the development of delayed hypersensitivity. These can be termed type A (antibody-promoting) adjuvants. Others, such as Freund’s complete adjuvant (FCA, with killed mycobacteria added to the incomplete adjuvant), promote delayed hypersensitivity as well as increasing antibody formation against protein antigens. These can be termed type C (cellmediated immunity-promoting) adjuvants. Evidence has been summarized (1) that many adjuvants exert their effects initially on macrophages and then on helper T-lymphocytes; for these the term T-adjuvants has been proposed. However, some adjuvants, such as bacterial lipopolysaccharide, appear to be able to stimulate B-lymphocytes directly without the agency of T-lympho-cytes; these can be termed B-adjuvants.

Chromium uptake and transport in barley seedlings (Hordeum vulgare L.).

Abstract: Potassium chromate is more toxic to the growth of barley in solution culture than chromic chloride, though apparent uptake of the latter is much faster. Inhibitor studies indicate that CrO42- uptake is “active” whereas Cr3+ uptake is passive, demonstrating that the two forms do not share a common uptake mechanism. Studies on the form of Cr inside root cells show that in plants fed CrO42- the Cr remains largely unchanged whereas in plants fed Cr3+ a little CrO42- (0.5 per cent) is produced. This conversion is dependent on the presence of living material and is probably enzymatic. Chromate uptake follows Michaelis-Menten kinetics at low concentration and is competitively inhibited by sulphate. Transport of chromium up the root is very slow, accounting for the low levels of Cr in the shoots. Chromate is transported better than Cr3+ though still to a very limited extent. These experiments provide a physiological basis for previous observations.

Mineral Requirements for Growth and Callus Initiation of Tissue Explants Excised from Mature Coconut Palms (Cocos nucifera) and Cultured in vitro

Abstract: Growth of stem, leaf, and inflorescence explants from mature coconut (Cocos nucifera L.) palms on a new mineral formulation (Y3) was superior to that on the minerals of White, Heller, or Murashige and Skoog. Cell division in the upper part of cultured explants gave rise to a layer of white callus within a month. The effects of omitting entirely or altering the concentration of individual elements in the Y3 formulation were investigated. It was concluded that growth on White's and Heller's minerals was seriously limited by deficiencies in macro-elements, i.e. nitrogen (particularly ammonium), potassium and phosphorus, as well as micro-elements, i.e. iron, iodine and molybdenum. The Murashige and Skoog formulation, on the other hand, was deficient only in certain micro-elements (particularly iodine).

Exposure in vivo of agoraphobics: contributions of diazepam, group exposure, and anxiety evocation.

Abstract: Fifty-seven chronic agoraphobic outpatients were treated by 12 hours of exposure in vivo on four days over two weeks to check the effects of oral diazepam versus placebo during group exposure, group versus individual exposure, and high versus medium anxiety arousal during individual exposure. The controlled parallel design allowed comparative evaluation of each treatment condition to six months follow-up. Assessment was blind with respect to drug and psychological treatment. Patients in all treatment conditions improved significantly in phobias and in related life areas. Outcome to group exposure on phobias and other measures was similar in all three drug conditions (placebo, waning diazepam, peak diazepam) with no significant differences between them. Diazepam patients had significantly less discomfort than placebo patients during group exposure treatment. Group exposure patients improved slightly but significantly more than individual exposure patients on non-phobic measures, though group exposure was accompanied by more panics during treatment yet was easier to run by the therapist. Individual exposure under high anxiety arousal was no more therapeutic than with lower anxiety. Diazepam is a mild palliative during group exposure but does not facilitate outcome to treatment. Group exposure in vivo is mildly facilitatory for outcome compared with individual exposure. Anxiety evocation during treatment was not therapeutically helpful.

Immunodepression, high IgM levels and evasion of the immune response in murine trypanosomiasis.

Abstract: THERE is currently much interest in the devices evolved by parasites which enable them to evade the immune responses mounted by their hosts1. One such device is the phenomenon of antigenic variation associated with the salivarian trypano-some infections of man and animals in Africa2,3. Typically these infections show successive waves of blood parasitaemia. Each succeeding trypanosome population is characterised by a novel variant-specific glycoprotein antigen present in the parasite surface coat and not reactive with antibodies induced against preceding variants4,5. Antigenic variation has a clear role in the evasion of host immunity and leads to chronic and usually fatal infections. More recently we have become aware of a possible additional component of the evasion mechanism, generalised immunodepression.

Diffusion of Water in Composite Filling Materials

Abstract: The uptake of water by composite filling materials seems to be a diffusion-controlled process; the magnitudes of the diffusion coefficients obtained are consistent with the uptake base through the resin matrix. The diffusion coefficients measured show the diffusion coefficient to decrease with increasing water concentration, which accounts for the protracted nature of the attainment of equilibrium uptake. Diffusion coefficients are generally lower in these composites based on difunctional methacrylates, compared with methyl methacrylate, presumably because of the highly cross-linked nature of the former.

Metabolic aspects of selenium action and toxicity.

Abstract: The nutritional observations, on which the activity of selenium is based, are briefly reviewed, and the interactions of the trace element with vitamin E, polyunsaturated fatty acids, and sulfur amino acids at the dietary level highlighted. Brief mention is made of early morphological effects of vitamin E and selenium deficiency and of “classical” interpretations of these in biochemical terms. The concept is developed, based on recent observations in a number of laboratories, that selenium participates in enzyme systems that have an oxidation/reduction role. In this connection, work on glutathione peroxidase on a selenoenzyme of lamb nuscle, on certain bacterial reductases, and on rat liver electron-transfer systems is discussed.The toxicology of selenium is reviewed briefly, and interactions of the element with mercury, cadmium, silver, and arsenic are discussed. Mechanisms for selenium detoxication are considered, and probable biochemical pathways for treatment of toxic amounts of selenium are set out. F...

Finite Element Stress Analysis of the Crowns of Normal and Restored Teeth

Abstract: Stress distributions are presented for a normal and a restored mandibular second premolar under masticatory-type forces. These were obtained using the finite element method of stress analysis applied to two-dimensional models. The effect of the relative stiffness of the materials is examined in each instance.

Energy expenditure in small children of obese and non-obese parents

Abstract: SEVERAL recent studies have suggested the possibility of identifying some of the factors in infancy which contribute to the development of obesity in later life. For example, the abnormally rapid gain in weight of those infants who tend to become overweight later may be associated either with some genetic factor or with early overfeeding1,2. It is, however, highly probable that a child born to obese parents will itself become obese3. The main aim of this study was to see if it was possible to identify a difference in energy expenditure between children of ‘normal’ and ‘obese’ parents.

Selective inhibition of neuronal GABA uptake by cis-1,3-aminocyclohexane carboxylic acid.

Abstract: IT is now generally accepted that GABA is an important inhibitory synaptic transmitter in the vertebrate central nervous system. However, there remain many problems in elucidating the precise roles of GABA in the brain. One important problem is the existence of a glial pool of GABA which makes it difficult to determine the origin of GABA released during experiments designed to demonstrate the release of GABA after nervous stimulation. It was thought at one time that this problem might be overcome by utilising the uptake processes for GABA to label the neuronal GABA pools, with for example, 3H-GABA. However, it is now clear that in many areas of the brain, GABA is also taken up by glial cells and in some areas, this glial uptake may actually predominate. The transport processes for GABA in neurones and glia have remarkably similar properties but do appear to have slightly different structural requirements.

Benign adenomatous neoplasm (adenoma) of the middle ear

Abstract: This presentation is a study of the pathogenesis, clinical behaviour and therapeutic response of 20 cases of a primary adenomatous neoplasm confined to the middle ear cleft. The investigation supported origin of the tumour from the middle ear mucosal epithelium. Clinical behaviour was that of a benign, localized, non-metastasizing neoplasm. Simple localized surgical removal of the tumour afforded an excellent prognosis in all cases. The designation of the tumour entity as adenoma of middle ear is proposed.

Continuous conduction in demyelinated mammalian nerve fibres

Abstract: MYELINATED nerve fibres conduct in a saltatory fashion, with sites of inward membrane current restricted to the nodes of Ranvier1. Loss of myelin causes long delays in the inter nodal conduction time, extreme refractoriness and conduction block2. In the large rat ventral root fibres studied the slowed conduction always remained saltatory, with discrete sites of inward current, but the limited spatial resolution of the method used prevented conclusions about whether any membrane beyond that of the original nodes was excited. To find out more about the inter nodal axon membrane exposed by demyelination, we have used an improved technique of external longitudinal current analysis. A smaller electrode separation (120 µm as against 400–600 µm) has improved the spatial resolution3, and signal averaging has made possible recordings from smaller axons. We have found that in these fibres not only is internodal axon membrane electrically excitable, but that it can support continuous conduction across a demyelinated inter-node. This result provides a new basis for interpreting the effects of demyelinating disease.

The effects of starvation and force‐feeding on the metabolism of the Northern pike, Esox lucius L.

Abstract: The effects of starvation and force-feeding on certain tissue and blood constituents were studied in the Northern pike, Esox lucius L Starvation resulted in a reduction of liver and muscle glycogen and liver lipid Blood glucose concentration and haematocrit were reduced, total plasma cholesterol levels were increased, while the levels of plasma free fatty acids (FFA), amio acid nitrogen and protein remained unaltered No significant changes were observed in either muscle protein, muscle water or the response to amino acid loading during the starvation period The force-feeding of pike starved for 3 months resulted in liver lipid and muscle glycogen being increased to levels higher than those observed in freshly-captured fish Liver glycogen, however, increased to values only slightly higher than those of starved animals Furthermore, while force-feeding had little effect on plasma FFA or protein concentrations, blood glucose, plasma cholesterol and haematocrit returned to the levels found in freshlycaptured fish and those of amino acid nitrogen were higher The results indicate that pike are well adapted for periods of prolonged starvation and that hepatic and extra-hepatic lipid and glycogen stores serve for metabolic needs during food shortage, while body protein is conserved The endocrine basis for these changes in the tissue and blood constituents is discussed