Showing papers by "University of Reading published in 1990"

The Mechanism of Antioxidant Action in Vitro

Abstract: The spontaneous reaction of atmospheric oxygen with organic compounds leads to a number of degradative changes that reduce the lifetime of many products of interest to the chemical industry, especially polymers, as well as causing the deterioration of lipids in foods. The importance of oxygen in the deterioration of rubber was demonstrated over a century ago,1 and this finding led chemists to investigate the chemistry of oxidative deterioration and its inhibition.

The turnover of organic carbon and nitrogen in soil.

Abstract: Although the decomposition of plant material in soil is an extremely complex process, relatively simple models can give good fits to the decay process. Thus a two-compartment model gives a close representation, over the first few years, of the decay of 14 C-labelled plant material in soil. A model containing a single homogeneous humus compartment decomposing by a first-order process is surprisingly useful for soil organic nitrogen over periods measured in decades. More sophisticated multicompartmental models are now widely used to represent turnover in soil. One of these, the Rothamsted turnover model, is described in detail and shown to give a useful representation of data from the Rothamsted long-term field experiments.

On the Existence of Storm-Tracks.

Abstract: Given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth, it is perhaps surprising that concentrated regions of such eddy activity, i.e. storm-tracks, are found in the Northern Hemisphere winter. The existence and possible self-maintenance of storm-tracks is investigated using a linear, stationary wave model with storm-track region forcings taken from data averaged over a number of winters. It is found that the direct thermal effect of the eddies does indeed act against the existence of the storm-track. Their vorticity fluxes lead to some reduction of this effect. It is argued that the mean diabatic heating in the storm-track region is an indirect eddy effect. This heating is found to maintain the mean maximum in baroclinicity in the region. Further, the mean low-level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t...

An Intermediate Category of Seed Storage Behaviour? I. COFFEE

Abstract: Seeds of four cultivars of arabica coifee (Coffea arabica L.) were tested for germination following hermetic storage for up to 12 months at several different combinations of temperatures between —20 °C and 15 °C and moisture contents between 5% and 10% (wet basis). Most of the seeds from one cultivar withstood desiccation to between 5% and 6% moisture content, a seed water potential of approximately 250 MPa, but those of the remaining three cultivars were much more sensitive to desiccation damage. Moreover, in all four cultivars, seed longevity at cool and sub-zero temperatures, and at low moisture contents did not conform with orthodox seed storage behaviour: viability was lost more rapidly under these conditions than at either warmer temperatures or higher moisture contents. The results confirm that coffee seeds fail to satisfy the definitions of either typical orthodox or recalcitrant seed storage behaviour. These results, therefore, point to the possibility of a third category of storage behaviour intermediate between those of orthodox and recalcitrant seeds. One of the main features of this category is that dry seeds are injured by low temperatures.

Natural Antioxidants Not Exploited Commercially

Abstract: Reports in recent years both in the popular and scientific press have stressed the value and advantages of natural ingredients as food preservatives. There is an implied assumption of safety for compounds that occur naturally in foods and that have been consumed for many centuries. It is not the intent of the authors to debate the issue of superiority of either natural or synthetic food components as to the safety or functional properties. It is preferable, however, to use substances that do not pose problems of proof of safety. Caution should be employed in the use of natural compounds: except for the major commercial synthetic versions (tocopherols, ascorbic acid) they have not usually been subjected to scrutiny and scientific evaluation as have the artificial synthetic compounds (BHA, BHT). Their potential as mutagens, carcinogens, teratogens, or as other pathogens must be investigated.

Three‐Year‐Olds' Problems with False Belief: Conceptual Deficit or Linguistic Artifact?

Abstract: Researchers are divided over whether young children understand other people's minds. This study reexamines the main technique used to show a basic inability in 3-year-olds to make judgments about a person's thoughts when that person's knowledge happens to be false. 131 children, aged 3, 3 1/2, and 4, were shown the real, unexpected contents of a chocolate box and were required to say what a friend would think was in it and what their own previous expectations had been. Success in this task was compared between the 3 age groups and also according to the specificity of questions asked. It was found, in contrast to previous findings, that test questions that are temporally specific and syntactically straightforward enable most 3-year-olds to attribute false beliefs to others. These results suggest that 3-year-olds' access to information about others' mental states is bounded by the linguistic demands placed upon them, but long before their fourth birthday children have some understanding of others' mind.

Fracture Properties of Plants

Abstract: Publisher Summary There is a number of reasons for studying the mechanisms controlling the structural integrity (largely expressed as fracture properties) of plants. The first is in terms of the plant itself—the plant has to be able to withstand the mechanical effects of wind, water, and gravity and grow in such a way that its integral parts remain intact and do not split open unannounced. This may sound a trivial statement, but it is the experience of engineers that it is much easier to design something which breaks than something which does not especially when, as with plants, there is an upper limit (if only an implied one) to the amount of material available for construction. To survive, the plant must, therefore, have mechanisms for resisting fracture (the initiation and propagation of cracks). By contrast, the plant can encourage and direct fracture by laying down abcission and dehiscence layers, which are very brittle. The fracture properties of plants are also important for the animals that feed upon them. Mechanical properties constitute a significant factor in palatability, which, for man, extends to mechanical properties during and after various processes in preparing plants as food.

Formation of siderite-Mg-calcite-iron sulphide concretions in intertidal marsh and sandflat sediments, north Norfolk, England

Abstract: Concretions cemented mainly by siderite, Mg-calcite and iron monosulphide are common in late Holocene marsh and sandflat sediments on parts of the north Norfolk coast. Field experiments have shown that the concretions are actively forming in reduced sediments in which sulphate-reducing bacteria are active. δ13C values ranging from −3 to −11·8% (mean −5·9%0) suggest that the carbonate in the concretions is derived partly from marine sources and partly from microbial degradation of organic matter. δ18O values ranged from −6·4% to + 0·8% (mean −1·0%) suggesting that carbonate precipitated in porewaters ranging from pure sea water to-sea water diluted with meteoric water. Chemical analysis of porewaters showed no evidence of significant sulphate depletion at the depth of concretion formation. Some concretions have formed around fragments of wood or metal, but others contain no apparent nucleus. In field experiments siderite, FeS and Mg-calcite were precipitated around several different nuclei within a period of six months. We suggest that siderite may form wherever the rate of iron reduction exceeds the rate of sulphate reduction, such that insufficient dissolved sulphide is available to precipitate all the available dissolved ferrous iron.

The 1985/86 Intraseasonal Oscillation and the Role of the Extratropics

Abstract: An intraseasonal oscillation that occurred in the 1985/86 northern winter is documented in this study. The tropical convection of this event is dominated by the mixture of a standing oscillation over the maritime continent and an eastward moving feature from the Indian Ocean into the central Pacific. The time evolution of the upper tropospheric circulation patterns, instead of propagating eastward along the equator as suggested in the existing composites of the intraseasonal oscillation, is characterized by a series of wave patterns in the Northern Hemisphere and does not complete the cycle around the globe. The familiar moist Kelvin wave explanation for the intraseasonal oscillation receives little support from diagnosis of this event using zonal wind, height field, streamfunction, and potential vorticity. Only in the lower troposphere near the date line is the convincing evidence for its existence found. A scenario for the intraseasonal oscillation, which is suggested by the analysis, includes ...

Campylobacters associated with human diarrhoeal disease.

Abstract: In this review, the increasingly complex taxonomy of the genus Campylobacter was explored, and the various aspects of the physiology of the organisms of relevance in isolation, cultivation and survival were discussed. The isolation and identification techniques were considered for those campylobacters known to cause enteritis and the aspects of relevance to the control of the spread of campylobacter enteritis via foods and water were discussed.

Control of the Maillard reaction in food systems.

Abstract: The Maillard reaction is of primary importance to the food manufacturer, since it is frequently responsible for the aromas and colours that develop during heating or storage of food products. Our ability to control the reaction is still very limited, although recent studies have indicated how it may be manipulated, particularly with regard to aroma development. The introduction of new processing and cooking techniques, such as microwave heaving, presents a constant challenge to the manufacturer to find ways of manipulating the reaction. The chemistry of the reaction and the factors affecting it are reviewed.

The effect of new environment on adapted genetic architecture

Abstract: Central to the study of life cycle evolution is the concept of genetic trade-offs. Genetic trade-offs between life cycle characters develop as a result of the accumulation of genes with antagonistic pleiotropic effects. In the present study a comparison was made between the genetic architecture that had evolved in the ancestral environment and the way that this genetic architecture was disrupted following transfer to a new environment. It was predicted that, in the ancestral environment, genetic trade-offs should have evolved between each life cycle character and, as a result of these genetic trade-offs, significant levels of additive genetic variation should remain despite many generations of selection. Following transfer to a new environment different genes might be expressed. Therefore, it was predicted that in the new environment the levels of additive genetic variation should increase and that the genetic trade-offs should break down. The predictions were well supported by the data.

The standard deviation of luminance as a metric for contrast in random-dot images

Abstract: Michelson's contrast, C, is an excellent metric for contrast in images with periodic luminance profiles, such as gratings, but is not suitable for images consisting of isolated stimulus elements, eg single bars; other metrics have been devised for such stimuli But what metric should be used for random-dot images such as are commonly used in stereograms and kinematograms? Previously the standard deviation (SD) of the luminances (equivalent to the root mean square, RMS, of the amplitudes) has been taken as a measure of contrast, but on little more than intuitive grounds The validity of this speculative usage is tested Experiments are described in which a wide range of random-dot images of various compositions was used and the adapting power of these images measured This was taken as an index of their visual effectiveness The contrast and contrast-reducing effects of the stimuli were expressed in terms of six candidate metrics, including SD, to discover which would give the most lawful description of the experimental data The usefulness and generality of the SD measure were confirmed The effects of mean luminance were also measured and a general expression that would take them into account was derived Finally, on the basis of computational modelling in which spatial filters with properties approximating those of retinal ganglion cells were used, a possible theoretical account for the success of the SD metric is offered

A comparison of maturation drying, germination, and desiccation tolerance between developing seeds of Acer pseudoplatanus L. and Acer platanoides L

Abstract: SUMMARY Differences in maturation drying and desiccation tolerance during seed development were detected between the two contrasting Acer spp., Norway maple (Acer platanoides L.), which shows orthodox seed storage behaviour, and sycamore (A. pseudoplatanus L.), which shows recalcitrant seed storage behaviour. In both species, the onset of germinability (150 d tests at 5 °C) occurred after percentage seed moisture content had begun to decline, but before net loss in seed moisture. The onset of germinability in Norway maple occurred 4 wk before physiological maturity (i.e. 4 wk before the end of the increase in seed dry matter), whereas in sycamore it occurred some ten weeks before physiological maturity when the seeds were only 60 % filled. Seeds of Norway maple were able to tolerate enforced rapid desiccation to 10% moisture content (f. wt) at physiological maturity, when maturation-drying had reduced seed moisture content to 54 %. Between 2 and 4 wk later seed moisture content rapidly declined naturally to 25 %, at which value the fruits were shed. In contrast, a constant rate of maturation-drying was observed in sycamore. The seeds were shed at 58 % moisture content and, in almost all cases, the seeds were intolerant of rapid desiccation to c. 10 % moisture content throughout seed development. A very small proportion of sycamore seeds did survive rapid desiccation when harvested between 6 September and 4 October, but no seeds survived desiccation to 5 % moisture content or below. A comparison of the germination of sycamore seeds harvested on four dates and dried to various moisture contents showed that the seeds tolerated greater desiccation as they matured between 12 July and 20 September, but there was no further change thereafter. The results are therefore compatible with previous classifications of seed storage behaviour in each species, and with the view that the initial decline in seed moisture content stimulates the developmental switch which results in the onset of germinability in both orthodox and recalcitrant seeds.

Integral equations : a practical treatment, from spectral theory to applications

Abstract: Preface 1. Classification and examples of integral equations 2. Second order ordinary differential equations and integral equations 3. Integral equations of the second kind 4. Compact operators 5. The spectrum of a compact self-adjoint operator 6. Positive operators 7. Approximation methods for eigenvalues and eigenvectors of self-adjoint operators 8. Approximation methods for inhomogeneous integral equations 9. Some singular integral equations Appendixes Notation index Index.

Polymerase chain reaction for detection of Toxoplasma gondii.

Abstract: Summary A DNA-based assay has been developed for the detection of Toxoplasma gondii. The assay makes use of the polymerase chain reaction (PCR) to amplify part of the P30 gene on the parasite's DNA. Following gel electrophoresis, the amplified DNA can be detected either directly on the gel or by Southern hybridisation with radioactive or non-radioactive DNA probes. The assay has been used to detect the DNA from different isolates of T. gondii in a background of human or mouse DNA. Together with other information such as clinical data, CT scans and serology, the PCR assay should improve the diagnosis of toxoplasmosis in immunosuppressed and immunocompromised patients as well as in fetal tissues.

The role of hydrogen in methanol synthesis over copper catalysts

Abstract: The experimental observation that the activity of a series of zinc oxide supported copper catalysts is related to the surface area of the copper is examined in the light of recent evidence that hydrogen spillover from copper to zinc oxide is facile. A model is proposed which explains the effect of zinc oxide on copper in terms of a reversible transfer of hydrogen between copper and zinc oxide. It is suggested that therate determining step normally occurs on the surface of the copper but that therate of reaction can be dependent on the availability of spillover hydrogen from the zinc oxide.

Reversion of flowering

Abstract: Reversion from floral to vegetative growth is under environmental control in many plant species. However the factors regulating floral reversion, and the events at the shoot apex that take place when it occurs, have received less attention than those associated with the transition to flowering. Reversions may be categorized as flower reversion, in which the flower meristem resumes leaf production, or inflorescence reversions, in which the meristem ceases to initiate bracts with flowers in their axils and begins instead to make leaves with vegetative branches in their axils. Related to these two types of reversion, but distinct from them, are examples of partial flowering, when non-floral meristems grow out so that the plant begins to grow vegetatively again. Anomalous or proliferous flowers may form as a result of unfavourable growth conditions or viral infection, but these do not necessarily involve flower reversions. There are many examples of inflorescence reversion but fewer clearly defined cases of flower reversion. In flower reversion the meristem of the flower itself reverts to vegetative growth so that flowers with basal floral organs and distal leaves on the same axis are formed successively by the apical meristem. InPharbitis nil, Anagallis arvensis, andImpatiens balsamina flower reversions have been caused by defined environmental conditions. However, only inImpatiens has detailed study of the changes in growth and development at the shoot apex during reversion been carried out. These studies show that changes in apical growth and phyllotaxis that typically accompany flowering can be separated from the development of floral organs and suggest that the floral stimulus plays a role throughout flower morphogenesis. The occurrence of reverting organs intermediate between leaves and petals is of particular interest in allowing experiments to be done on the progress of determination at the cell, tissue and organ levels. Reversion indicates that the flowering process must be regarded as a continuum, with physiological stages such as commitment to flower, and even morphological stages such as different floral organ types, being to varying extents artificial. Further study of the regulation of floral morphogenesis, and of the events associated with reversion, may provide important information on the nature of the factors that bring about the onset of flowering itself.

A Micromorphological Classification of Fossil and Recent Calcic and Petrocalcic Microstructures

Abstract: Two end-member types of microstructures are recognised in calcic and petrocalcic horizons in both present day and fossil soils (paleosols). The first, alpha -type, consist of dense, continuous micritic to microsparitic groundmasses (K-fabrics), typically with crystallaria (including circum-granular forms), floating grains and intercalary crystals. The second, beta -type exhibits a variety of biogenically-formed features such as needle-fibre calcite, microbial tubes, alveolar-septal fabric and other types of rhizocretions, Microcodium and calcified fecal pellets. While many soils and paleosols contain mixtures of both types, some consist only of alpha-fabrics. Parent material and climate (influencing vegetation) may control the type which forms. University of Reading, P.R.I.S. Contr. No. 010.

The assumption of equilibrium in the analysis of migration and interregional differences: a review of some recent research.

Abstract: This paper questions the plausibility of the assumption of interregional equilibrium in recent research into migration and the valuation of amenities in the United States. It is shown that it is difficult to develop a satisfactory explanation for continuing net migration which is compatible with the equilibrium assumption and that recent relevant research generally fails to support the idea that the U.S. economy is in equilibrium. The association of higher rent levels with in-migration is explained as a short-run phenomenon. If the spatial economy is in disequilibrium then the valuations of amenities assuming equilibrium will be biased being probably too low in areas of net in-migration and too high in areas of net out-migration. (EXCERPT)

On-line recognition of handwritten Arabic characters

Abstract: Arabic characters are always in cursive script. Handwritten words were entered into an IBM PC via a graphics tablet and a segmentation process applied to the points; the length and the slope of each segment was then found, and the slope categorized into one of four directions. In the learning process, specifications on the strokes of each character are fed to the computer. In the recognition process, the parameters of each stroke are found and special rules applied to select the collection of strokes which best matches the features of one of the stored characters. The results are promising, and suggestions for improvements leading to 100% recognition are proposed. >