Showing papers by "University of Dundee published in 1972"

Investigation of the localised state distribution in amorphous Si films

Abstract: Field effect techniques have been used to determine the distribution function N (ϵ3) of the localised states in amorphous Si films prepared by glow discharge decomposition of silane. It was found possible to sweep the surface potential through about 0.5 eV and to determine N (e) to within 0.18 eV of the extended states. N (e) curves show a pronounced structure which largely depends on the substrate temperature during deposition of the films (400–630 K). Localised state densities increase with decreasing substrate temperatures. The equilibrium Fermi level generally lies close to a peak in the distribution and N (eF) ∼ 17 cm−3 eV−1. The analysis of the field effect experiments is described in some detail and relevant information from drift mobility and conductivity measurements are discussed. In particular it is found that the distribution of occupied states calculated from the N (e) curves agrees with predictions from the transport experiments. This supports our contention that the N (e) curves represent a volume rather than a surface property of the films.

Electronic transport and state distribution in amorphous Si films

Abstract: The specimens used in this investigation were prepared by the decomposition of silane in an r.f. glow discharge. Substrate temperatures, Td, between 310 K and 670 K were used during deposition. The temperature dependence of both the conductivity and the drift mobility was measured on the same specimens and was studied as a function of Td. An electron beam technique was used in the mobility experiments. In specimens prepared at Td>350 K, current flow above 250 K is associated with electron transport in the extended states near ec. An electron mobility of about 10 cm2 s−1 V−1 is deduced from the experiments. Below 250 K, phonon-assisted hopping of electrons through localized states, about 0.18 eV below ec, becomes the predominant transport mechanism. When specimens are deposited at Td⪝350 K, the Fermi energy satisfies ec−eF⪞0.8 eV and a transition to predominant hopping transport by holes occurs. Based on the transport results and previous field effect measurements, a model for the electronic state distribution is put forward, which also appears to be applicable to the interpretation of transport results in amorphous Si specimens prepared by vacuum evaporation or sputtering.

Codimension and analytic spread

Abstract: In this paper, I shall establish the sufficiency of certain conditions on an ideal A of a local ring Q, and on a set {g1 …,gk} of elements of Q generating a proper ideal G, for the ideals A and G to be analytically disjoint. Hence I shall establish an upper bound for the analytic spread of A.The maximal ideal of Q will be denoted throughout by M, and it will be assumed that the field Q/M is infinite.

The effects of water stress on nitrogen‐fixing root nodules

Abstract: Summary The effects of osmotic stress on nitrogen fixation and respiration of soybean root nodules were investigated. Non-electrolytes, such as mannitol, depressed acetylene reduction when given to detached nodules in sufficient concentration to withdraw water from them. When given to the root systems of whole plants, hypotonic concentrations of mannitol had a depressing effect after 1–2 hours, the exact time depending on the size of the nodules. Equivalent concentrations of salts had a much more rapid effect on whole root systems and on detached nodules (less than 5 minutes); 100 m-equiv./l almost stopped acetylene reduction by small nodules. These effects could not be transmitted via the roots and needed contact between salt solution and nodules. They were accompanied by a decrease in respiratory activity and were fully reversible if the root systems were flushed with water within a few hours of treatment. High salt concentrations, as in sea water, had a rapid (1–2 minutes) effect, which after 20 minutes became irreversible. The effects of salt stress are interpreted as resulting from alterations in the metabolism of the cortical cells of the nodules.

Impairment of human drug metabolism by oral contraceptive steroids.

Abstract: The effect of oral contraceptive steroids on drug‐metabolizing capacity was determined by the use of plasma antipyrine and phenylbutazone half‐lifes as indices. Drug‐metabolizing capacity seemed to be impaired in women taking oral contraceptive steroids since the mean plasma antipyrine half‐life in female control subjects was 10.8 ± 2.4 hours (N = 36) while that in the “pill” group was 14.1 ± 3.1 hours (N = 26). The difference between the groups was significant (p < 0.001). With phenylbutazone, the mean control value was 70.6 ± 30.1 hours (N = 18) and that for the subjects taking oral contraceptives 80.2 ± 30.6 hours (N = 18). In this case the difference was not statistically significant (p > 0.05).

Photorespiration and Nitrogenase Activity in the Blue-Green Alga, Anabaena cylindrica

Abstract: Oxygen uptake in the light (photorespiration) by the nitrogen-fixing blue-green alga Anabaena cylindrica may be up to twenty times the dark respiration rate. The rate of uptake in the light increases linearly with increasing p O 2 while dark respiration is saturated at a p O 2 near 0.05 atm. Photorespiration is inhibited rapidly and completely by DCMU (3 x 10 -5 m) but KCN (10 -4 m) has little effect. Exogenously supplied hydroxyethane sulphonate (10 -5 m), an inhibitor of glycollate oxidase activity, and glycollate do not affect respiration, although 14 C-labelled glycollate is assimilated in the light and in the dark. Photorespiration is highly sensitive to p CO 2 and to NaHCO 3 concentration and approaches true photosynthetic oxygen production at the CO 2 compensation point of 10 parts/10 6 . A CO 2 concentration of 0.02 atm completely inhibits photorespiration whereas true photosynthesis is scarcely affected. Conditions which stimulate photorespiration (low p CO 2 and high p O 2 ) progressively inhibit acetylene reduction. In short-term studies DCMU inhibits acetylene reduction under condi­tions which stimulate photorespiration but has little effect under conditions which inhibit photorespiration. The results suggest that photorespiration and nitrogenase activity com­pete indirectly for reducing power and that at least one mechanism of oxygen inhibition of nitrogenase activity is via a stimulation of photorespiration.

Melanin and cellular reactions to ultraviolet radiation.

Abstract: THERE has been much discussion about the importance of melanin in protecting skin against the damaging effects of sunlight and/or ultraviolet radiation1–4; absorption and scattering by melanin protect intracellular organelles and cells in vitro5,6. But we now believe that a number of the so-called “sunburn cells”, the dyskeratotic cells present in epidermis 12–48 h after irradiation7–9, contain granules of melanin. Furthermore, they contain more granules than neighbouring, apparently undamaged cells. Thus paradoxically, cells containing what should be a protective compound are killed, while those containing less or none are apparently undamaged.

The extent and survival of contamination of potato stocks in Scotland by Erwinia carotovora var. carotovora and E. carotovora var.atroseptica

Abstract: SUMMARY The following results were obtained when fifty-seven bulk and crate-stored commercial seed potato stocks from the East of Scotland were examined in 1966-8 for contamination by pectolytic Erwinia spp. (1) Most tubers of all the cultivars and stocks examined, irrespective of whether they were obtained from blackleg-infected or blackleg-free crops, were contaminated with E. carotovora; (2) some 80% of the Erwinia isolates obtained were identified as var. atroseptica, the rest being var. carotovora; (3) the organisms survived in and on tubers for 6–7 months of bulk storage over the winter and up to planting time the following spring; (4) contrary to what is generally thought, the high incidence of contamination of all stocks, while suggesting that the seed itself is the major source of E. carotovora for the growing crop, emphasizes that other factors affect manifestation of blackleg in the field and soft rot in store.

Ecological studies on potato mop-top virus in Scotland

Abstract: SUMMARY Plants with symptoms of potato mop-top virus (PMTV) occurred in many commercial seed stocks of Arran Pilot and Red Craig's Royal potato in Scotland, but their incidence rarely exceeded 5%. In nuclear stocks of seed potatoes, most varieties examined in 1967 and 1968 were infected at one or more locality, but infected plants did not occur in all clones or at all stages of propagation of any one variety. infection of nuclear stocks resulted both from propagation on virus-infested land and from unwitting selection of infected plants to start new clones. PMTV was detected in farm soils ranging from light sands to heavy loams, in five Scottish counties. Soil was infested throughout the ploughed layer but the severity of infestation varied greatly within any one field; some sites of former potato clamps were heavily infested. PMTV was detected in field soil 12 years after potatoes were grown. In glasshouse tests many British crop and wild plants were colonized by Spongospora subterranea. Within some families all species tested were moderate to good hosts. (Solanaceae, Chenopodiaceae and Cruciferae), in others, species differed greatly in susceptibility (Compositae and Umbelliferae), and in a few, species were poor hosts or were not infected (Caryophyllaceae and Gramineae). Of the British crop and weed species that were moderate to good zoosporangial hosts of S. subterranea, only Solanum nigrum, potato, spinach and sugar beet were hosts of vector-borne PMTV. Potato probably survives between potato crops mainly in the resting spores of S. subterranea. PMTV was probably first brought to Europe with potatoes from South or Central America.

Proton translocation coupled to quinone reduction by reduced nicotinamide--adenine dinucleotide in rat liver and ox heart mitochondria.

Abstract: Measurements were made of the stoicheiometry of proton-translocation coupled to NAD(P)H oxidation by several quinones (duroquinone, ubiquinone0, ubiquinone1, ubiquinone2) in mitochondria from rat liver and ox heart. Observed stoicheiometries of protons translocated per mol of NADH oxidized (→H+/2e− ratios; Mitchell, 1966) ranged from 0.75 (rat liver mitochondria with ubiquinone1) to 1.55 (ox heart mitochondria with ubiquinone1 or ubiquinone2). Only the rotenone-sensitive pathway of NADH oxidation by quinone was able to support proton translocation. Correction of the observed →H+/2e− ratios for the loss of reducing equivalents to the rotenone-insensitive pathway increased their value to approx. 2.0. It is concluded that the rotenone-sensitive NADH– ubiquinone reductase activity of the respiratory chain may be organized in the mitochondrial membrane as a proton-translocating oxidoreduction loop. The number of such loops between NADH and ubiquinone is one, and not two, as initially proposed by Mitchell (1966).

Simple metric sedimentary statistics used to recognize different environments

Abstract: Statistical data computed from analyses of present-day sediments may be useful for the recognition of ancient environments. Phi-based measures may be used for the separation of sands. An arithmetic technique is suitable for suites of samples with a considerable range of grain sizes. This paper presents a re-exploration of arithmetic scales and statistical measures which may facilitate environmental recognition. To test this technique, analyses from approximately 800 samples were used. Quar-tile and median values were substituted into Trask's arithmetic measures of quartile deviation QDa and skewness Ska. Values of QDa were plotted against the median M/d mm on double-log paper for four environments. On each graph the plots indicate a linear trend and both the positions and slopes of the individual trend curves are different. There is a decrease of gradient of the curves in the sequence: aeolian-fluviatile-beach- “quiet-water”. Values of QDa against Ska were plotted similarly, the gradients of the curves decreasing in the reverse sequence. Thus each set of curves (QDa vs. Md mm; QDa vs. Ska) establishes a method for comparing and differentiating sediments from these environments.

Some inequalities associated with certain ordinary differential operators

Abstract: F r o m such inequalities we are able to obtain certain so-called " separa t ion" results for the differential expression M [. ] similar to those considered in [-3] but with point-wise restrictions on the coefficients p and q rather than the global conditions previously required. In w 2 we give the basic conditions which the coefficients p and q are required to satisfy and then classify the differential expression M [ ' ] . This leads in w 3 to a determinat ion of the linear manifolds in L 2 (a, b) for which inequalities of the form (1.1) are valid. The inequalities are given in w167 4 and 8 and the separation results in w167 and 8. In w 9 we use inequalities of the form (l . l) and the theory of relatively bounded operators to consider certain per turbat ions of the differential operators in L2(a, b) generated by M [ . ] . A supplementary result is given in w 10 of this paper.

The effect of vagotomy on the human pancreatic response to direct and indirect stimulation.

Abstract: The pancreatic exocrine response to stimulation with secretin and pancreozymin, and to acid in the small intestine, has been studied in 29 patients with duodenal ulcer, before and after vagotomy and pyloroplasty. The bicarbonate response to the hormones decreased significantly postoperatively, while enzyme secretion was much less affected. The bicarbonate response to jejunal acidification also decreased postoperatively, although not as much as bicarbonate secretory capacity.

The interrelations of faecal ammonia, pH and bicarbonate: evidence of colonic absorption of ammonia by non-ionic diffusion.

Abstract: 1. Ammonia, bicarbonate and pH were measured in samples of faecal dialysate from thirteen healthy subjects taking free diets. To observe the effect of marked changes in faecal pH, three subjects were also studied while taking 25 mmol/day of MgCO 3 or Na 2 SO 4 by mouth. Both salts increased stool weight without causing diarrhoea, but stool pH was significantly increased by MgCO 3 and decreased by Na 2 SO 4 . 2. The total ammonia concentration and pH of faecal dialysate were very variable, but showed a highly significant negative correlation similar to that already established in man between urinary excretion of ammonia and urine pH. This relationship was more marked when individual subjects were studied while faecal pH was deliberately varied by administration of MgCO 3 and Na 2 SO 4 . 3. Faecal bicarbonate concentrations were positively correlated with pH. Faecal P co 2 was usually in the range 40–120 mmHg, the higher P co 2 values being found in the more acid samples. Faecal total ammonia concentrations were negatively correlated with faecal bicarbonate. 4. These findings suggest that passive non-ionic diffusion is the main mechanism by which ammonia is absorbed by the colon, but do not exclude a minor contribution from diffusion of ionized ammonium. Colonic secretion of bicarbonate facilitates non-ionic diffusion of ammonia by providing an anion which is also absorbed by non-ionic diffusion, so maintaining an alkaline intraluminal reaction that continues to generate unionized ammonia.

The Development of Morphological Rules in Children.

Abstract: Summary. The present study made use of Berko's ‘Wug Test’ to investigate the development of morphological rules in children aged from 4 to 14. The results suggest that the main usefulness of this procedure should be between the ages of 4 and 12, approximately. Within this range, most of the rules tested show a steady improvement towards a ceiling value. The two exceptions are derivation and the use of the comparative and superlative which show a slower and later development.

Drug‐metabolizing capacity in states of drug dependence and withdrawal

Abstract: Summary 1 Drug-metabolizing capacity was assessed in 8 barbiturate-dependent and in 3 Mandrax-dependent patients using, as indices, plasma antipyrine half-life and in some cases urinary output of 6β-hydroxycortisol. For comparison, antipyrine half-life was also measured in volunteers before and after a period of taking hypnotic doses of these agents. 2 Both indices indicated a very high drug-metabolizing capacity in the dependent subjects on admission, the antipyrine half-life value in the barbiturate patients being the shortest reported to date for any drug-exposed group. The urinary output of 6β-hydroxycortisol was approximately three times that in a control population. 3 This induction of drug-metabolizing capacity presumably contributed to the marked drug tolerance observed in the dependent patients. 4 It appeared that drug-metabolizing capacity eventually returned to normal levels after withdrawal of the barbiturate. 5 It is concluded that the abnormal drug-metabolizing capacity of dependent patients must be taken into account in assessing dose requirements for other drugs.

Charge Transport in the Diatomic Molecular Solids and Liquids: N 2 , O 2 , and CO

Abstract: The paper reports an investigation of the drift mobility of electronic charge carriers in several phases of the diatomic solids ${\mathrm{N}}_{2}$, ${\mathrm{O}}_{2}$, and CO. It also includes similar measurements on positive and negative ions in the corresponding liquids. Thin crystal specimens (20-400 \ensuremath{\mu}m thick) were grown from the liquid between parallel electrodes in a chamber attached to a miniature cryostat after careful purification of the starting gas. As in previous work on the rare-gas solids and liquids, an electron-beam technique was used for the generation of excess carriers near one of the electrodes. Measurement of the transit time led directly to the drift mobility $\ensuremath{\mu}$. In $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-${\mathrm{N}}_{2}$, $\ensuremath{\beta}$-${\mathrm{O}}_{2}$, and $\ensuremath{\beta}$-CO electron mobilities between ${10}^{\ensuremath{-}3}$ and ${10}^{\ensuremath{-}2}$ ${\mathrm{cm}}^{2}$ ${\mathrm{sec}}^{\ensuremath{-}1}$ ${\mathrm{V}}^{\ensuremath{-}1}$ were obtained; a similar value was found for the hole mobility in $\ensuremath{\gamma}$-${\mathrm{O}}_{2}$. The temperature dependence of $\ensuremath{\mu}$ has been analyzed in terms of the nonadiabatic small-polaron theory. It is found that low-energy phonons (10 meV) are involved in the hopping transport. The implications of these results are discussed. In the liquids, Walden's rule is obeyed. With small electrode spacings, the observed transit signals suggest the existence of two mobile species.

Mercury in marine organisms of the Tay region.

Abstract: THERE has been increasing concern recently about the quantities of heavy metals, such as mercury, which may accumulate in many organisms. In spite of studies in Japan1, Sweden2–4 and North America5,6, concentrations of mercury in populations of marine algae and invertebrates have received little attention, notably in the United Kingdom. Klein and Goldberg6 reported average mercury concentrations in epibenthic animals from near La Jolla, California, of 0.9 p.p.m. dry weight with a maximum of 21 p.p.m. in a cowry (Cypraea sp.) and values of 0.037 p.p.m. and 0.023 p.p.m. have been recorded in the algae Laminaria hyperborea and Fucus vesiculosus7. We present here data on mercury concentrations which were found in some organisms collected from the Tay region. These vary according to the sampling area examined and are highest in organisms receiving direct discharge from the Tay.

Nitrogenase activity, amino acid pool patterns and amination in blue-green algae

Abstract: The free amino acid pools in the nitrogen-fixing blue-green algae Anabaena cylindrica, A. flos-aquae and Westiellopsis prolifica contain a variety of amino acids with aspartic acid, glutamic acid and the amide glutamine being present in much higher concentrations than the others. This pattern is characteristic of that found in organisms having glutamine synthetage/glutamate synthetase [glutamine amide-2-oxoglutarate amino transferase (oxido-reductase)] as an important pathway of ammonia incorporation. Under nitrogen-starved conditions the level of acetylene reduction (nitrogen fixation) and the glutamine pool both increase but the free ammonia pool decreases, suggesting that ammonia rather than glutamine regulates nitrogen fixation.Glutamine synthetase has been demonstrated in Anabaena cylindrica using the γ-glutamyl transferase assay and also using a biosynthetic assay in which Pi release from ATP during glutamine synthesis was measured. The enzyme (γ-glutamyl transferase assay) is present in nitrogen-fixing cultures and activity is higher in aerobic than in microaerophilic cultures. Ammonium-grown cultures have lowest levels of all and activity in the presence of nitrate-nitrogen (150 mg nitrogen 1(-1)) is lower than in aerobic cultures growing on elemental nitrogen. Ammonium-nitrogen and nitrate-nitrogen have no effect on glutamine synthetase in vitro. Glutamate synthetase also operates in nitrogen-fixing cultures of Anabaena cylindrica.