Showing papers by "University of Reading published in 1992"

Effects of acute subcutaneous nicotine on attention, information processing and short-term memory in Alzheimer's disease.

Abstract: This single-blind, placebo controlled study reports on the effects of administering three acute doses of nicotine (0.4, 0.6 and 0.8 mg) subcutaneously to a group of Alzheimer's disease (DAT) patients (n=22), young adult controls (n=24), and normal aged controls (n=24). The study extends our previous findings obtained using smaller groups of subjects. Drug effects were examined on three computerised tests: the first measuring rapid visual information processing, sustained visual attention and reaction time (RVIP task); a delayed response matching to location-order task measuring sustained visual attention and visual short-term memory (DRMLO task); and a finger tapping test measuring simple reaction time (FT task). The critical flicker fusion test (CFF) was used as a measure of perception and the WAIS digit span forwards (DS), of auditory short-term memory. Tests were graded in difficulty, titrated to avoid floor and ceiling effects so that meaningful, direct comparisons between groups could be made. Nicotine significantly improved sustained visual attention (in both RVIP and DRMLO tasks), reaction time (in both FT and RVIP tasks), and perception (CFF task — both ascending and descending thresholds). Nicotine administration did not improve auditory and visual short-term memory. There were no consistent, overall patterns of difference in performance between smokers and non-smokers in the control groups, or between males and females in any group. Despite the absence of change in memory functioning, these results demonstrate that DAT patients have significant perceptual and visual attention deficits which are improved by nicotine administration. The importance of measuring multiple abilities in future drug studies is emphasized and results are discussed in terms of nicotine's actions on attention, information processing and short-term memory.

Estimating the locations and the sizes of the effects of quantitative trait loci using flanking markers.

Abstract: The use of information from flanking markers to estimate the position and size of the effect of a quantitative trait locus (QTL) lying between two markers is shown to be affected by QTLs lying in neighbouring regions of the chromosome. In some situations the effects of two QTLs lying outside the flanked region are reinforced in such a way that a ‘ghost’ QTL may be mistakenly identified as a real QTL. These problems are discussed in the framework of a backcross using a regression model as the analytical tool to present the theoretical results. Regression models that use information obtained from three or more nearby markers are shown to be useful in separating the effects of QTLs in neighbouring regions. A simulated data set exemplifies the problem and is analysed by the interval mapping method as well as by the regression model.

Calculating net primary production and annual input of organic matter to soil from the amount and radiocarbon content of soil organic matter

Abstract: Soil samples collected from four of the Rothamsted long-term field experiments over the last 100 yr were used to follow the effects of management on soil organic matter content. The experimental sites were:Broadbalk and Geescroft Wildernesses, both on old arable land that had been fenced off in the early 1880s and allowed to revert naturally to deciduous woodland; the unmanured plot in the Rothamsted Park Grass Continuous Hay Experiment, started in 1856; the unmanured and one of the NPK plots in the Broadbalk Continuous Wheat Experiment started in 1843. Total C, radiocarbon and (in some cases) soil microbial biomass C were measured in stored and contemporary soil samples. The current Rothamsted model for the turnover of organic C in soil was then used to calculate how the organic C content of the topsoils from the four sites would change with time for a range of annual inputs. The inputs that generated the best fit to the measured values were: Broadbalk Wilderness 3.5 t C ha−1 yr−1; Geescroft Wilderness 2.5 t C ha−1 yr−1;unmanured plot on Park Grass 3.01 t C ha−1 yr−1; unmanured plot on Broadbalk Wheat 1.3 t C ha−1 yr−1; NPK plot on Broadbalk Wheat 1.71 t C ha−1 yr−1. The model also generated the radiocarbon content of soil organic C for these inputs of C, knowing the 14C content of the atmosphere over the period 1840–1985. The marked increase in the 14C content of soil organic C brought about by thermonuclear testing during the 1960's was accurately represented by the model. The quantities of soil microbial biomass (measured by fumigation-incubation) in the top 23 cm of soil from the four sites were: Broadbalk Wilderness,1.571 t C ha−1; Geescroft Wilderness, 0.58 t C ha−1; unmanured plot on Park Grass,1.621C ha−1; unmanured plot on Broadbalk Wheat, 0.47 t C ha−1; NPK plot on Broadbalk Wheat, 0.76 t C−1.The values for soil microbial biomass C generated by the model for the above annual inputs agreed closely (with one exception) with the measured values. For a site under steady-state conditions, the annual input of organic matter to the soil plus the annual removal of organic matter from the site (if any) gives the Net Primary Production (NPP). NPP thus calculated was 4.0 t C ha−1 yr−1 for the unmanured plot on Park Grass, 2.2 for the unmanured plot on Broadbalk and 5.2 for the NPK plot on Broadbalk. The two Wilderness sites are still accumulating C in both soil and vegetation and here NPP is given by annual input to the soil, plus the annual increment of C in the trees. NPP calculated in this way was 4.8 t C ha−1 yr−1 for Broadbalk Wilderness and 3.3 for Geescroft Wilderness. This new way of estimating NPP, from measurements made on soil organic matter, needs to be tested on a wider range of soils, climates and vegetation types before it can be generally recommended. However, it has many potential advantages, not least that it can give a value for NPP that is integrated over many years from a single sampling. For sites under steady-state conditions it is not essential to have stored soil samples—the necessary measurements can be made on contemporary samples alone.

Iontophoretically administered drugs acting at the N‐methyl‐D‐aspartate receptor modulate burst firing in A9 dopamine neurons in the rat

Abstract: Extracellular single-unit recording and iontophoresis were used to examine the effect of N-methyl-D-aspartate (NMDA) and the competitive NMDA antagonist (+/-)-4-(3-phosphonopropyl)-2-piperazine carboxylic acid (CPP) on the firing rate and firing pattern of A9 dopamine (DA) neurons in the rat. Administration of NMDA produced a dose-dependent increase in firing rate (up to nearly 300% of baseline at the highest ejection current), which could be blocked by iontophoretic CPP. Low currents (less than 10 nA) were sufficient to induce apparent depolarisation inactivation in some neurons. In addition to this effect on firing rate, NMDA also caused a dramatic increase in burst firing, which was also dose dependent; cells made more bursts, and each burst consisted of more spikes. The only measured aspect of burst morphology that was not affected was the mean burst interspike interval. All nonbursting cells (n = 10) were converted to burst firing by the drug. CPP administered alone was found to reduce burst firing, without affecting the firing rate. These data suggest that a tonically active excitatory amino acid input to A9 DA neurons is responsible for inducing burst firing in vivo and that this input seems to operate via the NMDA receptor, possibly by virtue of its link to a Ca2+ ionophore.

Linear mixture modelling applied to AVHRR data for crop area estimation

Abstract: A technique for estimating crop coverage using linear mixture modelling of multi-temporal Advanced Very High Resolution Radiometer (AVHRR) data is presented for a study area in northern Greece. This paper identifies some of the problems associated with using satellite sensor data with coarse spatial resolution for crop area estimation. Using satellite sensor imagery with a high spatial resolution to extrapolate ground measurements to AVHRR scales, the paper shows how the mixture model can be applied to AVHRR data in a mixed agricultural system. Crop areas are estimated to an average accuracy of 89 percent on regional scale using this technique. The results show that this linear mixture modelling has potential for operational crop area monitoring on a regional basis.

Business Ethics Judgments: A Cross-Cultural-Comparison

Abstract: With the increased attention paid to ethical issues in business practice, there is interest in the ethics gap between the U.S. and the U.K. and in the ramifications for educating college students for business management positions. This paper examines the differences in ethics judgments between U.S. and U.K. business students. The results indicate that differences in their demographic profiles do not influence their ethics judgments. However, consistently higher business ethics of female students from both countries are discussed in relation to providing business ethics education.

Possibility of an Arctic ozone hole in a doubled-CO2 climate

Abstract: Increased atmospheric carbon dioxide concentrations are expected to cause cooling of the lower stratosphere. This could enhance the formation of polar stratospheric clouds, which convert potential ozone-depleting species to their active forms. In an idealized three-dimensional numerical simulation of the Northern Hemisphere winter stratosphere, doubling the CO2 concentration leads to the formation of an Arctic ozone hole comparable to that observed over Antarctica, with nearly 100% local depletion of lower-stratospheric ozone.

Radiative forcing of climate from halocarbon-induced global stratospheric ozone loss

Abstract: OBSERVATIONS from satellite and ground-based instruments1–3 indicate that between 1979 and 1990 there have been statistically significant losses of ozone in the lower stratosphere of the middle to high latitudes in both hemispheres. Here we determine the radiative forcing of the surface–troposphere system4–6 due to the observed decadal ozone losses, and compare it with that due to the increased concentrations of the other main radiatively active gases (CO2, CH4, N2O and chlorofluorocarbons) over the same time period. Our results indicate that a significant negative radiative forcing results from ozone losses in middle to high latitudes, in contrast to the positive forcing at all latitudes caused by the CFCs and other gases. As the anthropogenic emissions of CFCs and other halocarbons are thought to be largely responsible for the observed ozone depletions1, our results suggest that the net decadal contribution of CFCs to the greenhouse climate forcing is substantially less than previously estimated.

Palustrine Carbonates and the Florida Everglades: Towards an Exposure Index for the Fresh-Water Environment?

Abstract: Palustrine carbonates are shallow fresh-water deposits showing evidence of subaqueous deposition and subaerial exposure. These facies are common in the geological record. The intensity of modification is highly variable depending on the climate and the length of emergence. Palustrine limestones have previously been interpreted as marginal lacustrine deposits from fluctuating, low-salinity carbonate lakes, but several problems remain with existing facies models: 1) palustrine carbonates possess a lacustrine biota but commonly display fabrics similar to those of calcretes and peritidal carbonates; 2) the co-occurrence of calcrete horizons and karst-like cavities is somewhat unusual and appears to indicate contemporaneous carbonate precipitation and dissolution in the vadose zone; 3) the dominance of gray colors indicates water-saturation, apparently inconsistent with the evidence for strong desiccation overprint; 4) profundal lake deposits are generally absent from palustrine sequences, and sublittoral facies commonly make up only a small proportion of total thicknesses; 5) no good modern analogue has been identified for the palustrine environment. Analogy with the Florida Everglades suggests a re-interpretation of palustrine limestones, not as pedogenically modified lake margin facies but as the deposits of extensive, very shallow carbonate marshes. The distribution of environments in the Everglades is determined by the local hydrology, reflecting the control of seasonal water-level fluctuations and topography. Climate and topography were the main controls on deposition of ancient palustrine carbonates. As in peritidal sequences, aggradational cycles are capped by a range of lithologies (evaporites, desiccation and microkarst breccias, calcretes, lignite or coal horizons etc.), permitting interpretation of the climate. Careful analysis of lateral facies variations may permit reconstruction of subtle topography. Consideration of the Florida Everglades as a modern analogue for the palustrine environment has suggested the development of an exposure index for fresh-water carbonates.

Nicotine as a cognitive enhancer

Abstract: 1. Nicotine improves attention in a wide variety of tasks in healthy volunteers. 2. Nicotine improves immediate and longer term memory in healthy volunteers. 3. Nicotine improves attention in patients with probable Alzheimer's Disease. 4. While some of the memory effects of nicotine may be due to enhanced attention, others seem to be the result of improved consolidation as shown by post-trial dosing.

The Maillard Reaction

Abstract: The Maillard reaction is a type of non-enzymic browning which involves the reaction of carbonyl compounds, especially reducing sugars, with cornpounds which possess a free amino group, such as amino acids, amines and proteins. In most foods, the e-amino groups of the lysine residues of proteins are the most important source of free amino groups, and the ease with which they take part in the reaction explains why the Maillard reaction is the most important route to nutritional damage of food proteins. 1,2 The Maillard reaction in fact comprises a complex network of intertwining reactions and takes place during food processing, especially when heat treatment is involved, and also on storage. Apart from resulting in nutritional damage, the Maillard reaction is also primarily responsible for the development of aroma and colour, which may be desirable or undesirable, in heated foods. It also results in the formation of potentially toxic compounds and in the development of components with antioxidant properties.3 In addition, it occurs in vivo. The Maillard reaction and its ramifications are so important that four symposia have been devoted to it over the last 12 years.4–7

Seed and seedling vigour in relation to crop growth and yield

Abstract: In theory, seed germination, vigour and size (three aspects of seed quality) may influence crop yield through both indirect and direct effects. The indirect effects include those on percentage emergence and time from sowing to emergence. These influence yield by altering plant population density, spatial arrangement, and crop duration. Direct effects on subsequent plant performance are more difficult to discern. A number of different approaches to testing the hypothesis that seed quality affects subsequent plant performance (implicit in some definitions of vigour) are illustrated. The results show that it is possible to detect such effects in some circumstances.

Urban Structure and the Labour Market: Worker Mobility, Commuting, and Underemployment in Cities

Abstract: Theory of urban spatial structure information, search and matching - a survey job-worker matching in urban space job-worker matching and urban commuting job-worker matching and underemployment employment policies and urban redevelopment final thoughts...for now.

Molecular LEGO. 1. Substrate-directed synthesis via stereoregular Diels-Alder oligomerizations

Abstract: The diastereoselective synthesis and structural characterization of a wide range of wholly-synthesis cyclic and acyclic polyacene derivatives has been achieved. These novel compounds are notable for (i) their rigidity, (ii) their highly-ordered structures, and (iii) the high stereochemical precision which governs their formation. A key feature in the success of the synthetic methodology described is the development of a repetitive Diels-Alder reaction sequence in which three distinct levels of diastereoselectivity are expressed during each cycloaddition involving bisdiene and bisdienophilic building blocks

Visual interpretation of known objects in constrained scenes

Abstract: Recent work on the visual interpretation of traffic scenes is described which relies heavily on a priori knowledge of the scene and position of the cam era, and expectations about the shapes of vehicles and their likely movements in the scene. Knowledge is represented in the computer as explicit three-dimensional geometrical models, dynamic filters, and descriptions of behaviour. Model-based vision, based on reasoning with analogue models, avoids many of the classical problems in visual perception: recognition is robust against changes in the image of shape, size, colour and illumination. The three-dimensional understanding of the scene which results also deals naturally with occlusion, and allows the behaviour of vehicles to be interpreted. The experiments with machine vision raise questions about the part played by perceptual context for object recognition in natural vision, and the neural mechanisms which might serve such a role.

A comparison of root and shoot competition between spring cereals and Avena fatua L.

Abstract: Summary: Resume: Zusammenfassung Two cultivars of each of three spring cereals (wheat, barley and oats) were grown with Avena fatua in a box experiment, where the effects of root and shoot competition were separated using soil and aerial partitions. Measures of resource complementarity (RYT) and of the relative severity of competition indicated that competition for soil resources, particularly nitrogen, was more severe than competition for aerial resources, i.e. light. When both root and shoot competition occurred, oats and barley were generally more competitive than wheat, but there were significant differences in competitive ability between cultivars of all three cereals. Although competition between cereals and A. fatua occurred predominantly below-ground, the various cultivars only differed slightly in root competitive ability against weeds. Nitrogen fertilizer did not significantly change the ranking of competitive abilities of the cultivars. Although shoot competition had less effect than root competition, the various cereals differed markedly in shoot competitive ability. The two oat cultivars, and the barley cultivar Egmont, had higher shoot competitive abilities than the two wheat cultivars or the barley cultivar Goldmarker. There was little evidence that differences in shoot competitive ability were due to differences in plant height. Une comparaison de la competition racinaire et aerienne entre les cereales de printemps et Avena fatua L. Deux cultivars de chacune des 3 cereales de printemps (ble, orge et avoine) ont ete cultives avec de l'Avena fatua dans des boites experimentales ou les effets de la competition aerienne et ceux de la competition racinaire etaient separees en utilisant des partitions de sol et d'air. Des mesures de complementarite de ressources (RYT) et de la severite relative de la competition ont montre que la competition pour les ressources du sol, en particulier l'azote, etait plus forte que la competition pour les ressources aeriennes comme la lumiere. Quand a fois on avait une competition aerienne et racinaire, l'avoine et l'orge etaient generalement plus competitives que le ble, mais il y avait des differences significatives dans l'aptitude a la competition entre les cullivars des 3 cereales. Bien que la competition enlre cereales et A. fatua soit apparue pour la majeure partie sous le sol, les differents cultivars ont seulement legerement differe dans leur aptitude a la competition contre les adventices. Les engrais azotes n'ont pas change de facon significative le niveau de la competitivite des cullivars. Bien que la competition aerienne soit moins forte que la racinaire, les differentes cereales ont exprime des differences nettes dans leur aptitude a la competition aerienne. Les 2 avoines et l'orge ‘Egmont’ ont une plus grande capacite de competition que les 2 bles et l'orge ‘Goldmaker’. II n'est pas ressorti que les differences dans la competitive aerienne soient liees a des differences de hauleur de plantes. Konkurrenz im Wurzel- und im Sprosbereich zwischen Sommergetreide und Avena fatua L. Je 2 Sorten von Sommerweizen, Sommergerste und Hafer wuchsen mit Avena fatua in einem Topfversuch, wo durch Trennwande die Wirkung der Wurzel- und der Sproskonkurrenz unterschieden werden konnte. Messungen der Nahrstoffaufnahme und der relativen Starke der Konkurrenz zeigten, das die Konkurrenz um Nahrstoffe im Boden, besonders Stickstoff, heftiger war als die Konkurrenz im Sprosbereich, z. B. um Licht. Lag sowohl Wurzel- wie Sproskonkurrenz vor, waren Hafer und Gerste allgemein konkurrenzstarker als Weizen, aber es gab bei allen 3 Getreidearten signifikante Unterschiede zwischen den Sorten. Obwohl die Konkurrenz zwischen den Getreiden und A. fatua vor allem im Wurzelbereich lag, unterschieden sich die verschiedenen Sorten da in ihrer Konkurrenzkraft nur wenig, was auch durch Stickstoffdungung nicht signifikant geandert werden konnte. Trotz der geringeren Bedeutung der Konkurrenz im Sprosbereich unterschieden sich die Getreidearten hier in ihrer Konkurrenzkraft deutlich: Die beiden Hafersorten und die Gerstensorte ‘Egmont’ubertrafen hierin die beiden Weizensorten oder die Gerstensorte ‘Goldmaker’. Es gab keine Hinweise darauf, das die Unterschiede der Konkurrenzkraft im Sprosbereich auf die Halmlange zuruckzufuhren sei.

The development of seed quality in spring and winter cultivars of barley and wheat

Abstract: Seed development and changes in germination ability and longevity were monitored in two spring and two winter cultivars of each of barley (Hordeum vulgare L.) and wheat(Triticum aestivum L.). Physiological maturity (end of the seed-filling period) occurred between 31 and 41 d after 50% anthesis in the eight cultivars, at which time seed moisture contents had declined naturally to 40–49% (wet basis). Most seeds were able to germinate (in 28 d tests at 10°C) following enforced desiccation at this time (normal germination varied from 83% in one cultivar of winter wheat to 97% in one of spring wheat).Potential seed longevity continued to increase after physiological maturity. The intervalbetween physiological maturity and the time when seeds attained maximum potential longevity varied between 3 and 21 d; maturation drying had reduced seed moisture contents to 16–28% (wb) at this time. The results for all eight cultivars contradict the hypothesis that maximum seed quality is attained at physiological maturity and thereafter declines. The term physiological maturity is potentially misleading, therefore; mass maturity is more appropriate to describe this developmental stage. It is shown that the results of accelerated ageing or controlled deterioration tests may provide misleading conclusions in seed quality development studies if the single storage treatment chosen is inappropriate.

Changes in seed quality during seed development and maturation in tomato

Abstract: Changes in tomato (Lycopersicon esculentum Mill.) seed quality were monitored during seed development and maturation in glasshouse experiments in 2 years. The end of the seedfilling period (mass maturity) occurred 35–41 d after anthesis (differing among trusses) in 1989 and 42 d after anthesis in 1990. Seed moisture contents at this developmental stage were 53–72% (wet basis), while the onset of ability to germinate (during 21-d tests at 20°/30°C) and the onset of tolerance to rapid enforced desiccation occurred just before (1990) or just after (1989) mass maturity. In 1989, seed quality was assessed primarily by seedling size in a glasshouse experiment; maximum mean seedling dry weight 25 d after sowing was not achieved until 24–40 d after mass maturity. In 1990, seed quality was assessed primarily by germination following storage; maximum normal germination after 35 d in storage at 40 °C with 14 ± 0.5% moisture content was attained 23 d after mass maturity, but with little difference among seed lots harvested 10 d earlier or up to 30 d later. The results contradict the hypothesis that maximum seed quality is attained at the end of the seed-filling period and that seed viability and vigour begin to decline immediately thereafter.

Non‐Linear Three‐Dimensional Effects On Gravity‐Wave Drag: Splitting Flow and Breaking Waves

Abstract: A study has been made of some aspects of frictionless stratified flow past three-dimensional isolated mountains. the study uses a three-dimensional non-hydrostatic numerical model to investigate the behaviour of the flow as a function of the Froude number, and produces a picture of the dependence of the gravity-wave drag on the Froude number for a wide range of that parameter. At the same time, the results of the numerical experiments clarify the behaviour of the flow in the transition from high to low Froude number, showing the relative importance of wave breaking and flow splitting in the transitional regime.

Reactions of adult female parasitoids, particularly Aphidius rhopalosiphi, to volatile chemical cues from the host plants of their aphid prey

Abstract: . In Y-tube olfactometer tests, Aphidius ervi Hal., Trioxyssp., Praon sp., Aphelinus flavus (Nees), Lysiphlebus fabarum (Marsh.) and Aphidius rophalosiphi De Stef. responded positively to the odour of the plant on which aphid mummies containing them had been collected. The response to host plant odour was greater than the response to the odour of host aphids, their honeydew or a combination of the two. The strongest response was to a combination of plant and host aphids. A. rhopalosiphi showed a strong positive response to three wheat volatiles (cis-3-hexenyl acetate, cis-3-hexen-1-ol and trans-2-hexenal) as well as to indole-3-acetaldehyde (a breakdown product of tryptophan in aphid honeydew). In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphidistinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.

Groundwater dolocretes from the Upper Triassic of the Paris Basin, France: a case study of an arid, continental diagenetic facies

Abstract: Thick dolomite-cemented horizons (dolocretes) occur within a fluvial sandstone-mudstone sequence of Late Triassic age in the western part of the Paris Basin, France. Two types of dolomites can be distinguished: (a) nodular dolomitic beds less than a few metres thick, which formed within mottled overbank siltstones and mudstones; and (b) massive dolomite up to 16 m thick, which occurs in coarse grained channel sandstones and conglomerates. The majority of the dolomite consists of a finely crystalline groundmass of dolomicrospar and, less commonly, dolomicrite. Glaebules, irregular spar-filled cracks, spheroidal dolomite, silicification and vuggy porosity are locally abundant in the massive dolomite. In contrast, biologically induced micromorphological features such as rhizocretions and alveolar-septal fabrics were observed in the thin, nodular dolomite beds. The dolomite is near stoichiometric, well ordered and non-ferroan. 18O values range from −7·7 to −0·4%o PDB and 18O values range from −5·1 to + 1·8%0 PDB and no obvious difference in the stable isotopic composition between both types of dolomites was observed. Sr isotope ratios range from 0·7101 to 0·7126 and are invariably higher than the contemporary Triassic sea water. A vadose—pedogenic origin for the thin dolocrete layers is indicated by the occurrence of rhizocretions and other biological structures. Several features, however, argue against a pedogenic origin for the massive carbonates, most notably the absence of biologically induced structures, the occurrence in coarse grained channel (and not overbank) deposits, and the great thickness. These units are thus interpreted as groundwater in origin. Phreatic calcretes of Quaternary age, widespread in inland Australia, are regarded as a modern analogue for the Triassic Paris Basin dolocretes. Petrographic observations argue in favour of primary (proto)dolomite precipitation, although early diagenetic replacement of calcite by (proto)dolomite cannot be ruled out. Strontium and carbon isotope data of early diagenetic dolocrete cements and oxygen isotope data of early diagenetic silica indicate an entirely non-marine, continental origin for the groundwaters. The poorly ordered and non-stoichiometric protodolomite probably underwent stabilization upon further burial resulting in a near-stoichiometric, well ordered dolomite that clearly lacks evidence for pervasive recrystallization.