Showing papers by "Stockholm University published in 1984"

Oxygen isotope calibration of the onset of ice-rafting and history of glaciation in the North Atlantic region

Abstract: We report here that DSDP Site 552A, cored with the hydraulic piston corer on the west flank of Rockall Bank, recovered an undisturbed sequence of alternating white deep-sea carbonate oozes and dark-coloured layers that are rich in glacial debris. Oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice-rafting occurred at about 2.4 Myr, and was preceded by a minor pulse of ice-rafting at about 2.5 Myr. The carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present-day North Atlantic deep water at least since 3.5 Myr.

Constructive mathematics and computer programming

Abstract: If programming is understood not as the writing of instructions for this or that computing machine but as the design of methods of computation that it is the computer’s duty to execute (a difference that Dijkstra has referred to as the difference between computer science and computing science), then it no longer seems possible to distinguish the discipline of programming from constructive mathematics. This explains why the intuitionistic theory of types (Martin-Lof 1975 In Logic Colloquium 1973 (ed. H. E. Rose & J. C. Shepherdson), pp. 73- 118. Amsterdam: North-Holland), which was originally developed as a symbolism for the precise codification of constructive mathematics, may equally well be viewed as a programming language. As such it provides a precise notation not only, like other programming languages, for the programs themselves but also for the tasks that the programs are supposed to perform. Moreover, the inference rules of the theory of types, which are again completely formal, appear as rules of correct program synthesis. Thus the correctness of a program written in the theory of types is proved formally at the same time as it is being synthesized.

Comparisons of nutrient uptake rates for Baltic macroalgae with different thallus morphologies

Abstract: In-situ experiments were performed during different seasons to determine uptake rates of PO3-4, NH+4 and NO-3 within ecologically representative ranges of nutrient concentrations, of dominant macroalgae in the Baltic Sea. Uptake rates were governed by nutrient concentrations, water temperature and thallus morphology, but not by the phylogenetic affinity of the species. Nitrogen uptake rates were always higher than those of phosphorus at the same concentrations, and NH+4−N uptake rates exceeded those of NO-3−N. The lowest uptake rates occurred among the late successional, long-lived, coarse species with low surface: volume ratios (Fucus vesiculosus, Furcellaria lumbricalis andPhyllophora truncata). The highest uptake rates were measured for short-lived, opportunistic algae, filamentous or with numerous hairs, (Cladophora glomerata, Enteromorpha ahlneriana, Scytosiphon lomentaria, Dictyosiphon foeniculaceus andCeramium tenuicorne). The latter group also had the highest Vmax:kmax ratios, which indicates a more competitive advantage for nutrient uptake at low concentrations.

Stress reactions in computerized administrative work

Abstract: SUMMARY Ninetyfive white-collar workers employed by an insurance company using visual display units (VDU) connected by telecommunication to a central computer filled in a questionnaire concerning psychosocial stressors in connection with work at the VDU. Eleven persons with extensive and ten with no work at VDUs were also studied during regular work, during breakdown of machinery, and in their leisure time. Self-reports on mood and alertness were recorded along with blood pressure, heart rate, and excretion of adrenaline and noradrenaline. Results indicate that (1) stress and mental strain occurred in association with delayed response times in the computer system and unpredicted interruptions of system operation, (2) such a temporary interruption caused an increase of blood pressure and adrenaline excretion, (3) complaints of stress and strain were reported mainly by data-entry staff, (4) data-entry groups displayed a higher level of physiological arousal during post-work hours than a control group, and (5) that a majority of those who worked continuously at a VDU reported physical discomfort within 1.5 hours. It is concluded that stress and strain in computerized work may be counteracted at the technological and the organizational level: by reducing the duration and frequency of breakdowns, by reducing response times in the system, and by eliminating pure data-entry tasks.

Strategy for the Measurement of Regional Cerebral Blood Flow Using Short-Lived Tracers and Emission Tomography

Abstract: This report describes a strategy for measurement of regional CBF that rigorously accounts for differing tracer partition coefficients and recirculation, and is convenient for use with positron emis...

Egg-laying patterns in butterflies in relation to their phenology and the visual apparency and abundance of their host plants

Abstract: 1. The egg-laying behaviour in the wild of 51 butterflies in Sweden is studied: three different patterns emerge. Firstly, although the majority of butterflies deposit their eggs on the plants on which their larvae later feed, butterflies that overwinter in the egg stage and use herbaceous host plants tend to avoid laying their egges on host plants 2. Secondly, butterflies which use host plants that are superabundant, notably the grass-feeding satyrids, also tend not to deposit their eggs on the leaves on which the larvae later feed. Among the Swedish satyrids, two of the three species which do deposit their eggs on the larval hosts overwinter in the pupal stage, thus necessitating rapid larval development. 3. Thirdly, butterflies which use visually apparent host plants seem to find their host plants without having to alight on non-hosts, whereas butterflies that use hosts that are visually non-apparent frequently alight on non-host plants during the oviposition search before they find the appropriate plants. 4. The possible adaptive significance of these egg-laying patterns is discussed.

Lack of correspondence between genetic and morphologic variability patterns in Atlantic herring (Clupea harengus)

Abstract: The Atlantic herring (Clupea harengus) stock complex is confusing from the perspectives of both evolutionary biology and systematics. There are numerous ecologically and morphologically divergent stocks classified as species, subspecies, races, tribes, etc. with an unknown degree of genetic differentiation and reproductive isolation between them. The genetic population structure of herring from the Scandinavian waters was analysed electrophoretically. The pattern for distribution of genetic variation was compared to that of the morphological characters most frequently used for stock classification, i.e., the number of vertebrae and keeled scales. Fish were collected from 17 locations distributed from the northern Gulf of Bothnia to the north-east Atlantic off the west coast of Norway. The genetic analysis was based on 17 electrophoretic loci, 13 of which were variable. There are statistically significant allele frequency heterogeneities, but there is a conspicuously small amount of genetic differentiation, even between stocks classified as representing different subspecies. More than 99 per cent of the total gene diversity was found within populations, and genetic distances are typically of the order of 0·001. The genotypic distribution of the total material is very similar to the one expected if all the samples had been drawn from a single panmictic population. There appears to be no association between the variation of morphological characters and that at electrophoretic loci, and this is true for the variation between as well as within samples. Data suggest that stocks either diverged rather recently or that the amount of gene flow between groups of fish classified as stocks has been large enough to prevent substantial differentiation, and that morphologic and ecologic divergence may to a large extent be environmentally induced.

Characterization of inhibitor A, a protease from Bacillus thuringiensis which degrades attacins and cecropins, two classes of antibacterial proteins in insects.

Abstract: The insect pathogen Bacillus thuringiensis produces an exoprotease, inhibitor A, at the beginning of the stationary growth phase. In vitro, the enzyme selectively destroys cecropins and attacins, two antibacterial proteins found in immune hemolymph from Hyalophora cecropia. The specificity of this enzyme was investigated using cecropin A(1–33) and HPLC for separation and characterization of the fragments obtained. A maximum of 12 different peptides were produced and their positions in the known sequence of cecropin A(1–33) were deduced from their amino acid compositions. The enzyme did not show a stringent requirement for a specific amino acid sequence at the cleavage site but prefers a hydrophobic residue on the C-terminal side. The specificity of the enzyme is explained in terms of the open structure of the cecropins and a pronounced inability of inhibitor A to attack globular proteins.

On the role of mechanical energy in maintaining subglacial water conduits at atmospheric pressure

Abstract: Recent theo retical studies of glacier hydrology have assumed that subglacial conduits are completely filled with water under steady-state conditions. This, however, is not necessarily the case. Where discharges are larger than a few tens of liters per second and the down-glacier slope of the bed is more than a few degrees, the potential energy released by water descending this slope may be capable of melting the walls of a subglacial conduit many times faster than the conduit can close by plastic flow of the ice. As a result, the pressure in such tunnels may normally be atmospheric, or possibly even at the triple-point pressure if there is no open connection to the glacier surface. Simple calcu lations suggest that such pressures in subglacial conduits may be more common than hercLOfore anticipated. The positions of such "open" conduits may be unstable to small per­ turbations in discharge or ice veloci ty. This is because the mechanical energy available in excess of that needed to balance closure can instead offset the gene ral flow of the ice. Cond ui ts can thus trend diago nally across the direction of ice Aow. If an increase in the angle which such a conduit makes with the ice flow direction also results in an increase in slope of (he conduit, more mechanical energy will become available, resulting in a positive feedback process. Subglacial channels at atmospheric pressure may inAuence the origin and morphology of certain glacial landforms, such as eskers and "plastically­ molded" features. RESUME. Sur le role de l'inergie newtonnienne dam le maintien du riseau aquiflrl sous-glaciaire cl la pression almosph irique. De recentes etudes theoriques d'hydrologie glaciaire ont suppose que le reseau sous glaci aire clait corn­ pletement rempli d'eau en condition d'cquil ibre stable. Ceci, neanmoins, n'est pas necess airement le cas. Lorsque les debits sonl superieurs a quelques dizaines de litres par seconde et que la pente dU lit dU glacier est superieure a quelques degres, I'energie potentielle mise en oeuvre par I'eau descendant celle pente peut "Ire capable de fondre les parois d'un chenal sous-glaciaire beaucoup plus vite que le chenal ne peut se refermer par le Auage plastique de la glace. Il en resuhe que la pression dans de tels chenaux peut nor­ rnalement etre atrnospherique

Emission of nitric oxide from arable land

Abstract: The flux of NO between arable land and atmosphere has been measured with a chamber technique. The net flux from the soil to the atmosphere varied from less than 0.1 up to 62 ng NO-N m -2 s -1 for a fertilized area (200 kg N ha -1 as calcium nitrate) and up to 17 ng NO-N m -2 s -1 for an unfertilized area. The emission was high in the summer when the temperature was high and the soil was dry and decreased to low values when the soil surface was thoroughly wetted by rain. Previously reported findings of equilibrium concentrations of NO (compensation point) have been verified. These concentrations ranged from 2 to more than 75 ppbv. At the rural site where the measurements were made, the atmospheric NO concentration was always below this compensation point and there was consequently a net emission of NO from the soil. Nitrogen gases, measured as the difference between NO and NO x (including NO 2 and possibly also HNO 3 and PAN), were found to be absorbed on soil and vegetation. The absorption of NO 2 was generally smaller than the emission of NO. The areal variability within an area of 100 m 2 was found to be moderate with a standard deviation of 25%, somewhat higher on recently fertilized soil (between 50 and 80%). The temperature dependence of NO emission could be described with an activation energy of 65 to 83 kJ mol -1 (Q 10 between 2.7 and 3.6). A more rapid increase of production than that predicted by the temperature increase was observed in morning hours. This is tentatively explained to be caused by nutrient dynamics in the soil. The yearly emission is estimated to be about 0.6 kg NO-N ha -1 and 0.2 kg NO-N ha -1 for the fertilized and unfertilized areas, respectively. During the vegetation period, NO emission from highly fertilized areas might be of some importance when compared with anthropogenic emission from combustion within Sweden. DOI: 10.1111/j.1600-0889.1984.tb00048.x

A novel clathrate design: selective inclusion of uncharged molecules via the binaphthyl hinge and appended coordinating groups. X-ray crystal structures and binding modes of 1,1'-binaphthyl-2,2'-dicarboxylic acid host/hydroxylic guest inclusions

Abstract: Etude de cinq clathrates du compose du titre (1) avec des alcools differents: 1.2 MeOH (P2 1 /n, Z=4), 1.2 EtOH (C2/c, Z=4), 1.2 (PrOH-2) (C2/c, Z=4), 1.(RuOH-2) (P2 1 /n, Z=4), 1.ethyleneglycol (P2 1 /n, Z=4). Affinements

Influence of in vitro lactic acidosis and hypercapnia on respiratory activity of isolated rat brain mitochondria.

Abstract: Respiratory activity and the ADP/O ratio of isolated rat brain mitochondria were measured following incubation with varying concentrations of lactic acid in reaction media buffered either with bicarbonate and CO2 or with phosphate alone, at a pH of 7.1. Increasing lactic acid levels caused a progressive decrease in substrate-, phosphate-, and ADP-stimulated (State 3) respiration and ADP/O ratios. Fifteen millimolar lactic acid, pH 6.4, caused approximately 50% inhibition of State 3 respiration (with malate + glutamate as substrate). At lower pH values (5.3-6.1), addition of ADP caused little or no increase in O2 consumption; i.e., ATP formation ceased. Addition of lactic acid at constant pH moderately affected respiratory control ratios but did not change State 3 respiration or ADP/O ratios. Thus, the effect of lactic acid was related to the pH change. Increasing CO2 concentrations in the reaction medium had similar effects on mitochondrial respiration, indicating that changes in extramitochondrial pH rather than in transmembrane H+ gradients determined the respiratory alterations. Following a 5-min incubation of mitochondria with lactic acid, pH 6.1, there was an incomplete recovery of State 3 respiration and respiratory control ratios. It is concluded that mitochondrial respiration is inhibited by a decrease in pH which, if excessive, may lead to a permanent suppression of ATP production. These results may, at least partly, explain the deleterious effects of enhanced lactic acidosis in brain ischemia.

Potential energy surfaces of MH2 (M=Co, Fe, and Cu)

Abstract: In many important catalytic processes, the dissociation of the hydrogen molecule is a fundamental step, and the chemisorption of dihydrogen by metal surfaces has been studied. However, quantitative results from theoretical treatments are not very encouraging. Blomberg and Siegbahn (1983) have found that the negative binding energy for NiH2 obtained with the aid of the commonly used Hartree-Fock approximation differs greatly from the result found on the basis of a more sophisticated calculation, including electron correlation. Another study showed the great importance of d orbitals in the dissociation process. A study, similar to the one on NH2, has been conducted for three other metals, including cobalt, iron, and copper. The present investigation is concerned with the results of this study. The potential surfaces of CoH2, FeH2, and CuH2 are discussed, taking into account the lowest atomic states, the bent low spin complex, the bent high spin saddle points, and the linear states.

Accurate atomic positions from electron microscopy

Abstract: Modern electron microscopes have resolutions in the range 1.8–2.4 A which is, in principle, sufficient for structure determination at atomic resolution. High-resolution electron microscopy (HREM) has been widely used for studies of inorganic materials1, and computerized image processing of electron micrographs has been used for structure determinations of biological macromolecules2,3. Klug4 suggested that image processing could also be applied to electron micrographs of inorganic crystals. By combining the two powerful methods, HREM and computerized image processing, we have determined atomic coordinates (in projection) of metal atoms in a thin inorganic crystal, to an accuracy of 0.1 A. This high accuracy is mainly due to the noise reduction achieved through averaging over many identical unit cells.

Field measurements of emission of nitric oxide from fertilized and unfertilized forest soils in Sweden

Abstract: Application of nitrate fertilizers on two types of forest soils led to a marked increase in the NO emission rate indicating a large potential for NO production in these soils. The largest fluxes on the fertilized plots were up to 60 ng NO−N m−2 s−1. About 0.35% of the applied nitrogen was lost as NO within about 14 days after fertilization. The fluxes from the unfertilized forest soils were in the range 0.1 to 0.8 ng NO−N m−2 s−1 with a median value of 0.3 ng NO−N m−2 s−1. If this value, obtained during June and August to September, is representative for the growing season (150 days), it corresponds to an annual emission of 0.04 kg NO−N ha−1. This is about 30% of the value obtained for an unfertilized agricultural soil. Because of the large areas occupied by forests in Sweden the flux of NO from forest soils represents a significant contribution to the total flux of NO from soils in Sweden. Earlier observations of equilibrium concentrations for NO have been verified. These were found to range from 0.2 to 2 ppbv for an unfertilized forest soil and up to 170 ppbv for a fertilized soil. At the rural site in Sweden where these measurements were performed the ambient concentrations where found to be less than this equilibrium concentration, and consequently there was generally a net emission of NO. There are still large uncertainties about the global flux of NO from soils. Using direct measurements on three different types of ecosystems and estimates based on a qualitative discussion for the remaining land areas, a global natural source for NO of the order of 1 Tg N a−1 was obtained. If 0.35% of the total annual production of fertilizer nitrogen is lost as NO, fertilization of soils may contribute with 20% to the natural flux from soils.

Determination of average individual dry weights and ash-free dry weights in different sieve fractions of marine meiofauna

Abstract: Individual dry weights and ash-free dry weights for different meiofauna taxa from two soft bottom localities (31 and 117 m depth) in Gullmar Fjord on the Swedish west coast were determined. Samples from August 1980 and February 1981 of about 100 to 600 formalin-preserved specimens of each of the different taxa from each of four sieve fractions were weighed on a microbalance. Individual dry weights ranging from 0.12 μg (nematodes in the 0.040-mm fraction) to 172 μg (polythalamous, arenaceous Foraminifera in the 0.500-mm fraction) and ash-free dry weights ranging from 0.10 μg (nematodes in the 0.040-mm fraction) to 37 μg (polychaetes in the 0.500-mm fraction) were obtained. Great similarities were noted between corresponding values from the two stations as well as between summer and winter values. The percentage of organic matter, determined by ashing, in the body weight differed greatly among taxa. Some standard individual dry weight and ash-free dry weight values, to be used for re-calculation of abundance values into biomass, are presented.

Insect immunity. Isolation and sequence of two cDNA clones corresponding to acidic and basic attacins from Hyalophora cecropia

Abstract: The Cecropia moth has three known classes of antibacterial immune proteins, attacins, lysozyme and cecropins (earlier referred to as P5, P7 and P9, respectively). Six attacins with different isoelectric points have been purified. The N-terminal sequences for five of these forms imply that only two different genes exist. We have now isolated and sequenced two cDNA clones, one for the basic attacin and one for the acidic form. The two mature proteins show 76% homology at the nucleotide level, while the regions beyond the stop codons are 36% homologous. The differences in the content of aspartic acid accounts for the difference in net charge between the acidic and basic attacin. Further differences in charge can be obtained by post-translational removal of a lysine-containing tetrapeptide at the C-terminal end of the two proteins. Evidence for a prepro form of the basic attacin is presented.