Showing papers by "University of Dundee published in 1970"

Electronic Transport in Amorphous Silicon Films

Abstract: Drift mobility and conductivity measurements were made between 290 and 85\ifmmode^\circ\else\textdegree\fi{}K on amorphous silicon specimens prepared by glow-discharge decomposition of silane. The results suggest that excess electrons drift in the extended states with a mobility of about 10 ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{V}}^{\ensuremath{-}1}$. At lower temperatures, phonon-assisted hopping occurs through localized states occupying a range of 0.2 eV below the extended states. Conductivity results also suggest hopping transport near the Fermi energy.

Selective outgrowth of fimbriate bacteria in static liquid medium.

Abstract: Competitive mixed cultures were grown from inocula of a large number of bacteria of a genotypically nonfimbriate (fim−) strain of Salmonella typhimurium and a small number of a genotypically fimbriate (fim+) variant strain that formed type 1 fimbriae and had been derived from the fim− strain by phage transduction. The fim+ strain differed from the fim− strain in fermenting l-rhamnose (rha+), and the viable fim+ and fim− bacteria present in the cultures after different periods at 37 C were counted differentially in platings on rhamnose media. When the cultures were grown under aerobic static conditions in tubes of nutrient broth, the fim+ bacteria rapidly outgrew the fim− bacteria, so that, although starting as a small minority (e.g., 1 in 107), they approached or surpassed the number of the fim− in 48 hr. A pellicle consisting of fimbriate bacteria was formed on the surface of the broth between 6 and 24 hr, and it is thought that the advantage of access to atmospheric oxygen enjoyed by these bacteria in the pellicle enabled them to outgrow the fim− bacteria confined in the oxygen-depleted broth. The fim+ bacteria did not show selective outgrowth in mixed cultures grown in broth aerated by continuous shaking, in static broth incubated anaerobically in hydrogen, and on aerobic agar plates, i.e., under conditions not allowing an advantage from pellicle formation. The outgrowth of fim+ bacteria in aerobic static broth was prevented by the addition of α-methylmannoside, a substance that inhibits the adhesive and early pellicle-forming properties of bacteria with type 1 fimbriae. A motile flagellate (fla+) variant of a fim−fla− strain of S. typhimurium outgrew its parent strain in mixed cultures in aerobic static broth, but the selective advantage conferred by motility was weaker than that conferred by fimbriation.

Benlate-induced Instability of Aspergillus Diploids

Abstract: BENOMYL is the proprietary name of the fungicide in which the active ingredient is benlate (methyl 1-(butyl carbamoyl)-2-benzimidazole carbamate). After extensive trials over the past few years it has been widely reported to be effective in controlling many phytopathogenic fungi and was released for commercial use in 1969. I wish to draw attention to experiments with Aspergillus nidulans which show that benlate radically alters the stability of diploid strains.

Hopscotch: a Fast Second-order Partial Differential Equation Solver

Abstract: An idea of Gordon for the numerical solution of evolutionary problems is reformulated and shown to be equivalent to a Peaceman-Rachford process A fast computational process is then developed and applied to parabolic and elliptic problems, both linear and non-linear This algorithm is very efficient with regard to computing time, storage requirements and ease of programming Several fairly general conditions are given which ensure convergence for parabolic and elliptic problems

Nitrogenase activity in the blue-green alga Plectonema boryanum strain 594

Abstract: The non-heterocystous filamentous blue-green alga, Plectonema boryanum strain 594 reduces acetylene to ethylene, incorporates 15N2 into cell protoplasm, and grows readily in medium free of combined nitrogen, when incubated in a gas phase without added oxygen. Cells grown in the presence of 50 mg/l of ammonium-nitrogen do not reduce acetylene, and a concentration of 0.015 atm. CO in the gas phase inhibits nitrogenase activity completely but inhibits 14CO2 incorporation by only 28%. Nitrogenase activity is inhibited after 2 h treatment with 3×10-5 M DCMU and is inhibited completely in air.

Effects of Aerobic and Anaerobic Conditions on Growth and Metabolism of Blue-Green Algae

Abstract: The blue-green algae Anabaena flos-aquae and Nostoc muscorum may reduce acetylene to ethylene most actively at pO$_{2}$ levels below 0.2 atm. High pO$_{2}$ levels inhibit acetylene reduction, nitrogen fixation, respiration and $^{14}$CO$_{2}$ fixation in A. flos-aquae. The effect is not solely via an inhibition of nitrogenase activity because inhibition of $^{14}$CO$_{2}$ fixation by a species of Phormidium which does not fix nitrogen, and by A. flos-aquae grown on combined nitrogen also occurs. The inhibition of acetylene reduction in Anabaena is reversible in short-term experiments, the rate of recovery being rather similar irrespective of the pO$_{2}$ level to which the alga was subjected initially. 3(3,4-dichlorophenyl)-1-1-dimethyl urea (DCMU) at a concentration of 3 $\times $ 10$^{-5}$ M, which completely inhibits oxygen evolution and acetylene reduction but not respiration by aerobically grown Anabaena cultures also inhibits acetylene reduction in Na$_{2}$S-grown cultures. Salicylaldoxime at a concentration of 10$^{-4}$ M which partially inhibits electron flow from photosystem II inhibits acetylene reduction to a greater extent under aerobic conditions than in the presence of Na$_{2}$S. The presence of Na$_{2}$S also results in the removal of free oxygen from the medium in the pH range at which Anabaena normally grows. The data suggest that under our conditions (1) the photolysis of water, or photosystem II is essential for the growth of A. flos-aquae in the presence of H$_{2}$S; (2) H$_{2}$S may provide electrons when reducing power from the photolysis of water is reduced but not inhibited completely; (3) H$_{2}$S prevents an accumulation of oxygen in the medium during photosynthesis. These physiological findings from the laboratory may help to explain why blue-green algae live not only in aerobic environments but also in habitats where reducing conditions may prevail.

I.—A class of symmetric polynomials with a parameter*

Abstract: In an attempt to evaluate the integral (5) below, using a decomposition of an orthogonal matrix (Jack 1968), the author is led to define a set of polynomials, one for each partition of an integer k, which are invariant under the orthogonal group and which depend on a real parameter α. An explicit representation of these polynomials is given in an operational form. When α = − 1, these polynomials coincide with the augmented monomial symmetric functions. When α = 1, a systematic way of taking linear combinations of these polynomials is explained and it is shown that the resulting polynomials coincide with the Schur functions from the representation theory of the symmetric group. A similar procedure in the case α = 2 then appears to give the zonal polynomials as defined by James (1964, p. 478).

Variation in the plane of cell cleavage during the process of stratification in the mouse epidermis

Abstract: SUMMARY. The location and orientation of mitotic figures were recorded in the developing mouse epidermis from the initiation of stratification in the embryo to 32 days of post-natal age. It was found that in the single-layered stage mitotic figures were orientated to give a plane of cleavage at right angles to the epithelial surface to give daughter cells lying side by side, and that from the onset of stratification until the beginning of keratinization some 75–85% of mitotic figures in the basal layer were orientated to give horizontal cleavage, leaving one daughter cell on the basal layer and the other in the layer above. This contrasted with the orientation of the numerous mitotic figures in the supra-basal layer, where 75–85% were partitioning vertically. In the later stages of stratification up to 32 days of post-natal life, there was a progressive decline of mitotic figures outside the basal layer and a return of mitotic orientation in the basal layer to the vertical position. It was concluded that during the initiation of stratification superficial cells are recruited from the superficial daughter cells of horizontally cleaving basal cells whereas in the established keratinized epithelium these cells originate from upward migration of interphase basal cells.

The reactions between glutaraldehyde and various proteins. An investigation of their kinetics

Abstract: Glutaraldehyde reacts readily with various proteins in solution. With high concentrations of both, the solutions become yellow and many proteins form a gel. At low concentrations the reactions may be followed by the changes in the u.v. spectrum between 250 and 300 nm. The reverse reaction does not proceed to any detectable extent. The kinetics are pseudo-first-order. The activation energies for the reactions between proteins and glutaraldehyde were found to be about II kcal/mole. This suggests that the proteins have not been denatured to any marked extent by the glutaraldehyde fixation. The rates of reactions increase with pH. The rate of formation of glutaraldehyde-protein links per protein molecule glutarated is approximately I sec−1 mol−1 1.

Nitrogenase activity in extracts of heterocystous and non-heterocystous blue-green algae.

Abstract: Cell-free extracts capable of acetylene reduction and cyanide reduction have been prepared from heterocystous (Anabaena cylindrica) and non-heterocystous (Plectonema boryanum 594) blue-green algae. Extracts from Anabaena were obtained from cultures grown in blulk under aerobic conditions, while the Plectonema cultures were grown in bulk on nitrate-nitrogen, then washed free from nitrate and sparged with A/CO2 for 40 h after which time maximum nitrogenase activity was detected. The nitrogenases of both algae are similar and resemble in many respects nitrogenases from bacteria and legumes. Activity is located primarily in a 40,000xgx15 min supernatant fraction and the rate of C2H2 reduction observed is about 10 per cent of whole cell activity. ATP and a source of reducing power (Na2S2O4) are required for efficient functioning of the enzyme. ATP-dependent hydrogen evolution occurs, the extracts are cold labile and highly sensitive to oxygen and the oxygen inhibition is irreversible.

Host range, properties and purification of Raspberry bushy dwarf virus.

Abstract: SUMMARY Raspberry bushy dwarf virus (RBDV) was found in all plants of Lloyd George raspberry with bushy dwarf disease and occurred occasionally in plants of some other cultivars. It was transmitted by inoculation of sap to fifty-five other species in twelve families of flowering plants and infected most of them symptomlessly. It caused systemic symptoms in some species of Amaranthaceae, Chenopodiaceae and Cucurbitaceae, and necrotic local lesions in some Leguminosae. It did not induce bushy dwarf disease when returned to Lloyd George raspberry. Chenopodium quinoa was used for propagating the virus and Vigna cylindrica for local lesion assay. In C. quinoa sap, RBDV lost infectivity when diluted 10-4, heated for 10 min at 65 °C or stored for 4 days at 22 °C. Preparations made by twice precipitating the virus at pH 4·8 and resuspending it at pH 7·0, followed by ultracentrifugation and exclusion chromatography in columns of 2 % agarose beads, contained isometric particles about 33 nm in diameter, which sedimented as two components, with sedimentation coefficients of 111 and 116S. Only a few particles, all of them disrupted, were seen in preparations mounted in phosphotungstate, but the particles were well preserved in uranyl formate provided that they were first dispersed in a saxlt such as MgCl2 instead of distilled water. Many particles were oval in outline as though distorted during drying. No serological relationship was detected between RBDV and twenty-four other isometric viruses nor between RBDV and the filamentous virus apple chlorotic leafspot, to which it was previously thought to be related. An isolate of loganberry degeneration virus was serologically indistinguishable from RBDV.

Alternating direction methods for parabolic equations in two space dimensions with a mixed derivative

Abstract: Alternating direction implicit (A.D.I.) methods are proposed for solving the parabolic equation with variable coefficients in two and three space dimensions with mixed derivatives. The methods require the solution of two tridiagonal sets of equations at each time step in the two space dimensional case, and three tridiagonal sets of equations in the three space dimensional case. Several theorems are stated showing the methods to be unconditionally stable for certain ranges of an auxiliary parameter. Reference is made to other authors and numerical results are mentioned.

Host range and some properties of potato mop-top virus.

Abstract: SUMMARY Potato mop-top virus (PMTV) was transmitted by inoculation of sap to twenty-six species in the Solanaceae or Chenopodiaceae and to Tetragonia expansa; species in eleven other plant families were not infected. The virus was cultured in inoculated leaves of Nicotiana tabacum cv. Xanthi-nc or in N. debneyi. Diagnostic local lesions were produced in Chenopodium amaranticolor. In winter, ten solanaceous species were slowly invaded systemically but the first leaves infected were those immediately above inoculated leaves. When transmitted to Arran Pilot potato by the vector Spongospora subterranea, PMTV induced all the main types of shoot and tuber symptoms found in naturally infected plants. Isolates of PMTV from different sources differed considerably in virulence. PMTV-containing tobacco sap lost infectivity when heated for 10 min at 80 °C, diluted to 10-4, or stored at 20 °C for 14 weeks. Infectivity was partially stabilized by 0·02% sodium azide. When sap was centrifuged for 10 min at 8000 g, infectivity was mainly in the sediment. Infective sap contained straight rod-shaped particles about 20 nm wide, with lengths up to 900 nm and crossbands at intervals of 2·5 nm. Many of the particles were aggregated side-to-side, and the ends of most seemed damaged. The slight infectivity of phenol-treated leaf extracts was abolished by pancreatic ribonuclease. The present cryptogram of PMTV is R/*:*/*:E/E:S/Fu.

Sites of virus retention in the alimentary tract of the nematode vectors, Xiphinema diversicaudatum (Micol.) and X. index (Thorne and Allen)

Abstract: SUMMARY Electron microscopy of thin sections of Xiphinema diversicaudatum and X. index fed on plants infected respectively with arabis mosaic and grapevine fanleaf viruses showed that the viruses are retained as a monolayer of particles adsorbed on to the cuticle lining the lumina of the odontophore (stylet extension), anterior oesophagus and oesophageal bulb. During the moult of the nematode the cuticular lining is shed and together with the detached virus particles is ingested into the intestine through the oesophago-intestinal valve; this supports the limited experimental evidence that viruses transmitted by X. diversicaudatum and X. index are not retained through the moult.

Nitrogen fixation by blue-green algae in Yellowstone thermal areas*

Abstract: Potential nitrogen-fixing blue-green algae were common in three hot spring streams studied in Yellowstone National Park. In two streams, where the dominant nitrogen-fixing algae were species of Calothrix, nitrogen fixation, as measured by uptake of 15N2, was detected in situ in the temperature range 28–46 C. At higher temperatures nitrogen fixation was not detected, although the algae may have received fixed nitrogen from a growth of Calothrix, Nostoc, and unicellular algae which occurred at lower temperatures on the sides of the streams. In the third stream, where Mastigocladus was abundant, nitrogen fixation was detected at temperatures up to 54 C, although the optimum for fixation was near 42.5 C. The overall data imply that in situ nitrogen fixation contributes to the productivity of Yellowstone hot spring regions and that Mastigocladus and Calothrix are the most important nitrogen-fixing blue-green algae.

A virus of blue‐green algae from freshwater habitats in scotland

Abstract: Summary A virus which is pathogenic to certain blue-green algae belonging to the genera Plectonema, Phormidium and Lyngbya has been isolated from a variety of freshwater habitats in Scotland and has been detected over a 12-month period in one of these habitats. The virus (D-1) is a cyanophage, has an isohedral head and a short tail and is morphologically and serologically related to the LPP-1 virus isolated from the United States and the GIII virus isolated from Israel by other workers. The partially purified virus has an absorption spectrum characteristic of a nucleoprotein with a maximum at 260 nm and a minimum at 243 nm. D-1 is temperature sensitive being inactivated on heating at 60°C for 6 minutes. Its multiplication rate is fast, increasing from an initial titre of 103 to 1012PFU/ml within 40 hours. The lysis of the host cell results in a rapid loss of the phycobilin and chlorophyll pigments.

The evaluation of media used to enumerate sulphate reducing bacteria.

Abstract: Summary. Several media were used to enumerate bacteria in cultures of Desulfovibrio vulgaris, the most suitable being a modification of Iron Sulphite Agar (Oxoid). This medium was also suitable for the enumeration of D. desulfuricans and, with extra salt, D. salexigens. Cultures of D. africanus and D. gigas were enumerated in a lactate-sulphate agar medium which gave higher counts than similar media described in the literature. These media were suitable for counting the organisms in pure and mixed cultures. Neither of these media can be used successfully to enumerate Desulfotomaculum spp.

The Effect of Surface Microvilli on the Water Permeability of Single Toad Oocytes

Abstract: The water permeability of isolated toad ovarian oocytes was found from their rate of shrinkage in hypertonic Ringer's solution. Apparent membrane permeability coefficients, ( k ), calculated on the assumption that the cell surface was smooth, rose from about 20 µm s-1 in small cells 200 µm in diameter, to 35 µm s-1 in cells 800 µm in diameter and then fell to 5µm s-1 in large cells of 2000 µm diameter. The factor ( f ) by which microvilli extend the oocyte surface area beyond that of a smooth sphere was estimated from an analysis of electron micrographs of the cell surface. The value of f rose from 2 x at 200 µm diameter, to 11 x at 800 µm diameter and then fell to 5 x at 2000 µm diameter. The correlation coefficient between k and f was 0 474 (0 005 > P > 0.001). Corrected permeability coefficients, (k'), calculated so as to take account of the effects of the microvilli, ( k ' = k / f ), declined with increasing oocyte size, from 5 µm s-1 in small cells (200 µm) to 1 ,µm s-1 in large cells (2000 µm). The correlation between k and f indicates resistance to water flow by the cell membrane, while the decrease in k' as the cell grows suggests that diffusion in the cytoplasm may also be sufficiently slow to affect water flow out of the cell. It may be calculated that a surface membrane permeability coefficient in the range from 2 to 30 µm s-1 combined with an internal diffusion coefficient in the range from 6 x 10-8 to 10-6 cm2 s-1 could account for the effects found.

Effects of lytic enzymes and natural soil on the fine structure of conidia of Cochliobolus sativus

Abstract: The effects of natural soil and lytic enzymes on two wild-type, pigmented and two hyaline isolates of Cochliobolus sativus were studied. Pigmented isolates resisted lysis by enzymes and survived for more than 2 weeks on natural soil. Hyaline isolates lysed after a few hours in enzyme solutions and after a few days on natural soil. The fine structure of pigmented and hyaline isolates was compared before and after exposure to soil and enzymes. Resistance of wild-type conidia to lysis by soil bacteria and enzymes was associated with a broad electron-dense surface layer, corresponding to the distribution of pigment in the cell wall.

Electronic transport properties of some low mobility solids under high pressure

Abstract: The paper discusses results of drift mobility experiments in orthorhombic S, anthracene, trigonal and vitreous Se carried out under hydrostatic pressure p of up to 6 kbar. Some details of the experimental method are given. In the S crystals, where electrons propagate by an intermolecular hopping mechanism, the experiments show a remarkably large pressure dependence for the electron drift mobility (μe ∋ exp (αp)). It is concluded, on the basis of small polaron theory, that this is caused by the increase in overlap energy between hopping states on neighbouring molecules. In narrow band materials, a less pronounced pressure dependence of μ would be expected, which is borne out by Kepler's results for anthracene. In trigonal Se, ( μ h  c ≈ 26 cm 2 sec −1 V −1 ) we found that μh was substantially independent of p up to 5 kbar. The same applies to μe and μh in vitreous Se specimens and the implications of this result on the conduction mechanism are briefly discussed. It is also suggested that the pronounced pressure dependence of the steady dark- and photoconductivity in this material is primarily due to the effect of pressure on the injecting properties of the contacts.

The uptake of labelled thymidine by leucocytes of nickel sensitive patients.

Abstract: SUMMARY.— Thymidine uptake studies using a predominantly lymphocyte suspension of white blood cells in a series of 12 cases of nickel contact dermatitis and 14 controls are reported. In none of the controls was there any evidence of significant thymidine uptake. In 7 out of the 12 nickel hypersensitive subjects there was significant 14C thymidine uptake when the lymphocytes were stimulated by a concentration of nickel of 10–4 mEq/ml. culture. Possible explanations for failure of transformation in the other 5 subjects are discussed.

A method of monitoring drugs for adverse reactions II. Amitriptyline and cardiac disease

Abstract: A hospital based drug information system has been used to investigate a suspected association between unexpected death and the administration of the tricyclic antidepressant, amitriptyline in patients with a diagnosis of cardiac disease. The hospital information system made it possible to establish that 6 out of 53 such patients died suddenly and unexpectedly following the administration of the drug compared with no deaths in 53 control patients matched for age, sex, diagnosis and duration of stay. This high frequency of unexpected death was not found in patients without cardiac disease receiving amitriptyline nor in patients with cardiac disease receiving imipramine. It was observed that the cardiac patients receiving imipramine comprised a geriatric population occupying long stay beds whereas the amitriptyline patients occupied acute medical beds. It is concluded that amitriptyline should be used with caution in patients with cardiac disease. The importance of the accurate recording of medical information is stressed and the potentialities of hospital information systems are discussed.