Showing papers by "University of Leicester published in 1978"

Concretions, isotopes, and the diagenetic history of the Oxford Clay (Jurassic) of central England

Abstract: In interpreting the results of a petrographic and isotopic study of concretions, a range of subjects is discussed including the original texture of the Oxford Clay sediment, Jurassic palaeotemperatures, the diagenetic history of pore-waters and the palaeo-hydrology of central England. The concretions are all composed predominantly of calcite. They include precompactional, pyrite-rich concretions that later suffered an eposide of brecciation, and others that only commenced to form after compaction had crushed ammonite shells included in the bituminous clay sediment. Petrographic, chemical, and especially carbon isotope data demonstrate a dominantly organic source for the carbon in the early formed concretions. Oxygen isotopes indicate formation at the same temperatures (13-16°C) at which benthic molluscs were living. Concretion growth in pelleted, anaerobic mud proceeded concurrently with bacterial sulphate reduction and pyrite precipitation. Cracking of the concretions started at this stage: in a few concretions, the cracks were also partially filled with brown calcite. During post-compactional growth, δ13C increased and pyrite content decreased, showing waning organic influence; δ18O decreased. The brecciated concretions were intruded by clay in which baryte crystals grew; finally, most remaining voids were filled with strongly-ferroan calcite of δ18O about—7 PDB and δ13C about O PDB. This must indicate strong depletion of the pore waters in 18O. Mechanisms that might lead to this are reviewed. It is concluded that the sequence of mineralogical and chemical changes is most readily explained if originally marine porewaters, first modified by bacterial activity, were flushed from the compacting clays by water of ultimately meteoric origin. This had its source in palaeo-aquifers beneath the Oxford Clay. Speculative attempts are made to relate this history to the geology of the region.

Coexistence of beta1 and beta2 adrenoceptors in mammalian lung: evidence from direct binding studies.

Abstract: [3H]Dihydroalprenolol ([3H]DHA) binds to rat and rabbit lung membranes with a dissociation equilibrium constant (Kd) of about 0.5 nM and displays binding characteristics indicative of an interaction with beta adrenoceptors. The density of beta adrenoceptor binding sites was greater in rat than rabbit lung membranes, though the binding sites from both species had very similar affinities for nonselective agents such as (-)isoproterenol, (-)epinephrine, and (-)timolol, and exerted a similar degree of stereoselectivity between the isomers of propranolol. On the other hand, the affinity of beta1 selective agents such as (±)practolol, (±)atenolol, and (-)norepinephrine was greater in rabbit lung membranes whereas the beta2 agonist (-)erythro procaterol (OPC-2009) was considerably more potent on membranes prepared from rat lung. However, detailed analysis of the competition curves displayed by the beta1 and beta2 selective drugs strongly suggest that beta1 and beta2 adrenoceptor binding sites coexist in different proportions within lung tissue in the two species (rat 25%, beta1; 75% beta2; rabbit 60%, beta1; 40% beta2). The significance of these findings to the effects of catecholamines on pulmonary function is discussed.

A Simple Method for Storage of Bacteria at — 76°C

Abstract: 1 A safe, reliable and simple procedure for storing bacteria on beads at –76 °C is described. 2 The most suitable cryoprotectant for a wide variety of bacteria appears to be 10–15% (v/v) glycerol.

Drainage basin morphometry: review and assessment

Abstract: The increasing rate of geographical publication has confronted contemporary geographers with a voluminous literature. Familiarity with increasing amounts of relevant material is particularly crucial when geography is struggling to reconcile greater internal specialization and differentiation with growing demands for applied solutions to integrated problems. The remorseless ’information explosion’ apparent in geography (Stoddart, 1967) manifests itself on at least three subsidiary levels. In geomorphology the breadth and depth of literature available in the 1960s necessitated the production of a bibliography of British Geomorphology (Clayton, 1964), and Geomorphological Abstracts (later to become Geographical Abstracts); within geomorphology, 1973 was found an appropriate time for publication of a comprehensive 928 item review of drainage basin studies (Gregory and Walling, 1973), whilst within fluvial geomorphology methods of drainage basin morphometric analysis have been reviewed and assessed (Gardiner, 1975). Stream morphometry has become a fundamental focal point of much post-war geomorphological research in the United

Direct evidence of two types of beta adrenoceptor binding site in lung tissue.

Abstract: THERE is much evidence to suggest that β adrenoceptors are not homogeneous—pharmacological data on the actions of β adrenoceptor agonists and antagonists in intact tissues indicate the presence of two broad subclasses β1 β2 (refs 1, 2), although there is some controversy regarding this strict subdivision3,4. The receptors found in heart and adipose tissue have been classified as β1 whereas those in liver, skeletal muscle, trachea and uterus have been designated β2. This classification has been supported by biochemical studies examining β adrenoceptor-mediated cyclic AMP formation in various tissues5–7, although the characterisation of the β adrenoceptor in lung tissue using this approach has been the subject of some debate6,8. The direct binding of radiolabelled β–adrenoceptor antagonists to tissue membrane preparations has been studied by several workers in an attempt to overcome some of the problems that may arise when examining this receptor indirectly9. We have examined the direct binding of the specific β adrenoceptor ligand 3H-dihydroalprenolol (DHA) to rat lung membranes and here we present evidence for the presence of both β1 and β2 adrenoceptor subtypes in this tissue in a ratio of approximately 1 : 3.

Discrete properties of random surfaces

Abstract: The problem of measuring surface parameters of tribological importance such as peak curvature has been considerably simplified. Using discrete random process analysis tribological parameters of a wide range of surfaces can now be expressed and measured in terms of just two points on the measured autocorrelation function and the r.m.s. value of the surface. In addition, the contribution each 9 scale of size ’ of asperity makes to an overall parameter can be assessed quantitatively. Many new expressions relating tribological parameters to the autocorrelation function have been derived using a limiting procedure which produces results entirely consistent with equivalent continuous theory. Using this theory it is now possible to predict ‘gap’ parameters between two surfaces in contact in terms of simple additive parameters of each surface. Finally a new statistical model of the surface has been developed which encompasses many types of engineering surface.

Theories of Communication and Theories of Society

Abstract: Mass communication research has grown into a vast academic enterprise. Our current conventions are testimony to its emer. gence as a fully fledged occupation, replete with the institutional apparatus of a mature discipline. University departments and schools of mass communications, journals devoted to communications, mass communications, human communication, and the media constantly spring up as the field grows, becomes specialised and differentiated. In our view this growth has be-

The role of hydrogen sulphide in environmental transport of mercury

Abstract: HYDROGEN SULPHIDE may be evolved in anoxic sulphur-containing river or lake sediments1. The effect of the presence of sulphide on the availability of inorganic mercury for biological methylation has been considered previously. Essentially mercury in the form of Hg(0) or Hg(II) may be converted into mercuric sulphide in anoxic sediments2. It might seem that this very insoluble material would not, in practice, be available for methylation and that sulphide formation would act as a method of removing mercury from availability to the general environment (that is, it would act as a mercury sink). However in a complex natural system (aquarium sediment) it has been shown that HgS may, in fact, be methylated in the sediments although to produce quantities of methyl mercury substantially less than those produced using a more soluble mercury substrate2. Therefore, although H2S in a sediment would be expected to reduce the rate of mercury methylation considerably by the formation of HgS, it would not be expected to prevent formation of methyl mercury entirely. The effect of H2S on methyl mercury itself has also been investigated using a purely inorganic model3. An aqueous solution of methyl mercuric chloride (1 mg dm−3) loses methyl mercury steadily over 3 days after initial exposure to H2S. A volatile product was evolved into the space above the solution. This product was trapped in a sodium carbonate–disodium phosphate solution, extracted with toluene and shown to co-migrate with methyl mercury on thin layer plates of silica gel. It was concluded that the evolved product of the reaction system was a volatile organo-sulphur derivative of mercury that reverted to methyl mercury on extraction. These observations suggest that reaction between methyl mercury and H2S generated in sediments reduces the amount of methyl mercury available for accumulation by fish and shellfish and represents a powerful mechanism adding to the general mobility of mercury compounds in the environment. It is therefore important to identify the unknown mercury compound evolved from the system described above. We have now investigated the interaction of H2S with River Mersey (England) inter-tidal estuary sediment samples in order to determine its effect on methyl mercury levels in real systems. We have also investigated similar reactions in a model system, leading to the identification of the previously unknown volatile mercury species responsible for the transport of mercury in the work of Rowland et al.3

Mechanism of resistance to thiostrepton in the producing-organism Streptomyces azureus.

Abstract: An antibiotic-producing organism, Streptomyces azureus, defends itself against its own toxic product by methylating the RNA of its ribosomes.

Control of DNA Replication in Bacteria

Abstract: The rate of DNA synthesis by a bacterial culture under steady state growth conditions is determined by the rate of initiation of rounds of chromosome replication. It is independent of the rate of DNA chain elongation. (For an extensive elaboration of the point see Pritchard, 1974). The process of initiation of a round of replication can be considered from at least two points of view. One can ask about the biochemistry of the process; what elements are involved and what they do. Alternatively it is possible to ask about the regulation of initiation; how the rate of initiation is matched to the rate of accumulation of mass by the culture. This article is concerned primarily with the latter question.

Escherichia coli resistance to β-lactam antibiotics through a decrease in the affinity of a target for lethality

Abstract: CLINICAL isolates of bacteria that have gained resistance to β-lactam antibiotics (penicillins, cephalosporins and related compounds) often arise by the acquisition of a plasmid that produces a β-lactamase1,2. An increase in β-lactamase activity has also been shown to cause resistance in some mutants isolated in the laboratory3. In other cases, β-lactamase activity is not the cause of resistance and, at least in Gram-negative bacteria, alteration of the cell envelope resulting in decreased penetration of the antibiotic to the targets responsible for lethality in the cytoplasmic membrane has been proposed3,4. For several groups of antibiotics resistance has been shown to occur by a decrease in the affinity of the target for lethality for the antibiotic5–9 but, although this mechanism has been suggested as a possible cause of resistance to β-lactam antibiotics, no examples have been reported. The lethality targets for β-lactam antibiotics in Escherichia coli have recently been identified and I report here the characterisation of a mutant that has gained resistance to some β-lactams by a decrease in the affinity of such a target.

Surfaces — A Link between Manufacture and Function:

Abstract: The role of surface texture as a control of the manufacturing process and its importance are discussed. It is shown that it is only recently, since the advent of digital methods and random process analysis, that its real significance has been realized.

Effects of tobacco smoking on plaque development and gingivitis.

Abstract: A study was undertaken to test the hypothesis that patients who smoke tobacco have a more rapid rate of plaque deposition and development of gingivitis than those patients who do not smoke tobacco. Twenty subjects participated in this study, their age range was 17 to 30 years. Ten were smokers and 10 were nonsmokers. After an initial thorough removal of all deposits, oral hygiene measures were stopped for 10 days. On days 3, 7 and 10, plaque levels were evaluated using the Plaque Index and the gingival status was evaluated using the Gingival Index. Samples of plaque were stained by the Gram technique and examined microscopically. Plaque levels appeared to be higher in smokers than nonsmokers but the differences were not statistically significant. No consistent differences were evident in the gingival status of the two groups. Microbiological analysis showed a statistically significant increase in the percentage of Gram-positive bacteria to Gram-negative bacteria in the smokers as compared to the nonsmokers on day 3, however these differences were not maintained in the plaque samples taken after the 3rd day.

The hydration of monosaccharides—an NMR study

Abstract: At temperatures close to 0°C proton exchange between sugar hydroxyl groups and water is slow, and separate proton resonance peaks can be detected for the hydroxyl protons. All are shifted downfield of the water resonance, the anomeric hydroxyl proton shift being the greatest. Axial anomeric hydroxyl protons are shifted less than corresponding equatorial protons. Proton exchange with water is strongly acid and base catalyzed, but, at least in some cases, there seems to be an additional pH-independent mechanism involved. From the temperature effect on the shifts, and the effect of added dimethyl sulfoxide, we conclude that each hydroxyl group is bonded on average to two water molecules. This estimate of the hydration number for monosaccharides is far greater than those previously deduced from relaxation studies. It is suggested that the source of this difference lies in the residence times of the bound water molecules. Shifts of the hydroxyl proton resonances for sugars in methanol are compared with those for aqueous solutions and are found to be very similar. Hence it is concluded that these shifts do not reveal any special effects due to water structure. There are quite marked differences in the shifts for different sugars, and, in particular, the anomeric hydroxyl proton shifts for ketoses are smaller than those for aldoses.

Plasmid-Mediated Mechanisms of Resistance to Aminoglycoside-Aminocyclitol Antibiotics and to Chloramphenicol in Group D Streptococci

Abstract: Genes conferring resistance to aminoglycoside-aminocyclitol antibiotics in three group D streptococcal strains, Streptococcus faecalis JH1 and JH6 and S. faecium JH7, and to chloramphenicol in JH6 are carried by plasmids that can transfer to other S. faecalis cells. The aminoglycoside resistance is mediated by constitutively synthesized phosphotransferase enzymes that have substrate profiles very similar to those of aminoglycoside phosphotransferases found in gram-negative bacteria. Phosphorylation probably occurs at the aminoglycoside 3′-hydroxyl group. Plasmid-borne streptomycin resistance is due to production of the enzyme streptomycin adenylyltransferase, which, as in staphylococci and in contrast to that detected in gram-negative bacteria, is less effective against spectinomycin as substrate. Resistance to chloramphenicol is by enzymatic acetylation. The chloramphenicol acetyltransferase is inducible and bears a close resemblance to the type D chloramphenicol acetyltransferase variant from staphylococci. Images

The constitutive equations of continuum creep damage mechanics

Abstract: When load-bearing metallic components operate at temperatures in excess of approximately one third of the melting temperature Tm consideration must be given to the effects of creep deformations and rupture. In some components such as those in use in the nuclear industry limitations are placed on the amount of creep strain which may be accumulated. In other components such as those occurring in the process industries less consideration need be given to deformation and the life is only terminated when rupture takes place and some form of leakage becomes evident. Rupture can be the consequence of thinning induced by large strains but it can also occur at small strains as the result of growth of damage in the metal. Metallographic inspection reveals that the damage normally occurs in the form of fissures and voids which coincide with grain boundaries. In some metals such as copper it is easy to observe the damage by visual inspection, while in others such as aluminium alloys the damage is difficult to observe in the optical microscope. In this paper attention is given to the means of describing metallic creep rupture behaviour by suitable constitutive equations which can be used to predict the creep life of components with complex geometries. This branch of mechanics is often referred to as continuum creep damage mechanics because damage is observed to be smoothly distributed, in contrast to classical fracture when damage appears to propagate along a well-defined line. An example illustrating the continuous distribution of creep rupture damage is that of a plate penetrated by a circular hole and subjected to constant load. The damage in a copper plate tested at 250 ?C is shown in figure 1, plate 1, from which it can be seen that the damage varies continuously with the greatest concentration of damage at the edge of the hole. This test was

The Isostatic Compensation of East Africa

Abstract: By means of the methods of Lewis & Dorman (1970), the isostatic response has been computed for an area 800 km square of East Africa, surrounding the Kenya rift valley. By applying linear programming to the inversion of these data, it can be shown that local compensation models involving only negative density contrasts fit the response data at confidence levels of up to 80%. Comparison of the gravity anomalies of the compensation with the results of seismic array measurements made by Long & Backhouse (1976) shows that the East African plateau is compensated differently from the highland region around the rift valley known as the Kenya dome. The dome is supported by a region of the mantle with low density, low seismic P velocity, and high electrical conductivity, almost certainly a zone of partial melting. The linear programming technique can be used to show that, to satisfy the data, the top of the anomalous zone must be no deeper than 55 km. If the density anomaly is entirely due to melting, the average melt concentration in the uppermost 50 km of the mantle must exceed 6%.

Creep Rupture of Notched Bars

Abstract: The creep rupture of circumferentially notched, circular tension bars which are subjected to constant load for long periods at constant tem ¬ perature is studied by the approximate calculation of stress and damage histories which result from tertiary creep. Stationary-state creep solutions which have been previously obtained by Hayhurst & Henderson (1977) are used in a continuum damage mechanics study of rupture at the minimum sections of circular (Bridgman 1952) and British Standard notched specimens (B.S. no. 3500, 1969). Notch strengthening and weakening are explained in terms of the multi-axial stress rupture criterion satisfied by the material. It is shown how the circular notch may be used as a materials test and that the British Standard notch is a good means of assessing the sensitivity of structural behaviour to the multi-axial stress rupture criterion of the material.

Chloramphenicol Resistance in Streptococcus pneumoniae: Enzymatic Acetylation and Possible Plasmid Linkage

Abstract: Clinical isolates of Streptococcus pneumoniae resistant to chloramphenicol were observed in France for the first time in 1973. During a 4-year survey, these strains were found to represent 6% of a total of 564 isolates of S. pneumoniae in a general hospital and to belong to 13 different serotypes. One such strain, referred to as BM 6001, was shown to inactivate chloramphenicol, and the process was found to be inducible. The inactivated products were demonstrated to be O -acetoxy esters of chloramphenicol. The synthesis of an inducible chloramphenicol acetyltransferase was shown to be responsible for the inactivation of the drug. The resistant strain was able to transfer the chloramphenicol marker by transformation to competent strains of pneumococci at a frequency of 1% of that observed for control chromosomal markers. The loss of resistance was enhanced by ethidium bromide treatment, but no chloramphenicol-resistant mutant was isolated by mutagenesis of a “cured” clone or naturally susceptible isolates. All attempts to isolate plasmid deoxyribonucleic acid as covalently closed circular molecules from strain BM 6001 have been unsuccessful, but epidemiological evidence and the fact that the genes specifying chloramphenicol acetyltransferase synthesis are usually located on plasmids suggest that this marker may be plasmid-borne in S. pneumoniae . Images

Inward rectification in skeletal muscle: a blocking particle model.

Abstract: Inwardly rectifying otassium currents were measured in resting frog skeletal muscle in different [K]. A model is presented for inward rectification which supposes that the potassium conductance depends on the K+ concentration within a channel and is reduced by a blocking particle which is driven into the channel by depolarization.

Identification of ancient heat treatment in flint artefacts by ESR spectroscopy

Abstract: IT is of archaeological importance to be able to determine whether or not a particular sample of flint has been subjected to heating, either intentionally or accidentally, during its utilisation by man We report here on the use of ESR spectroscopy for the study of flint, and show that heated material can be readily identified by the appearance of a characteristic ESR signal which is absent from the unheated flint This signal is considered to be stable over an indefinite period of time We have also explored other implications of this technique in the examination of flint, including its possible use for dating purposes

Genetic Factors Determining the Growth of Physarum polycephalum Amoebae in Axenic Medium

Abstract: Summary: Evidence is presented that in the true slime mould Physarum polycephalum the ability of the amoebal strain CLd-AXE to grow in axenic medium is determined by mutations in two genes axeA and axeB and that the axenic growth of RSD4-AXE amoebae is also under genetic control. Mutant amoebal strains are also able to grow on bacterial lawns and the ability to grow in axenic media persists during prolonged culture on bacteria. However, some of the mutant strains grow less well on bacteria than strains of similar genetic background which are unable to grow in axenic media. CLd-AXE has the same nuclear DNA content (0.59 pg per nucleus) as CLd, the strain from which it was derived. Amoebae able to grow in axenic media were also derived from strains E27 and LU858 which carry mutations for temperature sensitivity and leucine requirement expressed in the plasmodial phase. Tests in axenic media showed that these mutations were expressed in the amoebal phase. The elucidation of the genetic basis of axenic growth will allow the construction of a range of amoebal strains able to grow in axenic media and this will greatly facilitate the isolation and analysis of mutants in this organism.