Showing papers by "University of Exeter published in 1994"

Perceived locus of causality, goal orientations, and perceived competence in school physical education classes

Abstract: Ryan & Connell (1989) have demonstrated that different types of behavioural regulation can be located on a continuum of perceived autonomy or perceived locus of causality. The present study applied their formulation in the context of school physical education (PE) and examined the relationships of perceived autonomy, perceived competence and goal orientations with intrinsic interest across two PE activities. School students aged 12-14 years (N = 85) completed an adapted version of the Self-Regulation Questionnaire (Ryan & Connell, 1989) and measures of perceived competence and intrinsic interest separately for two PE activities. They also completed the British version of the Task and Ego Orientation in Sport Questionnaire (Duda, Fox, Biddle & Armstrong, 1992). Students appeared to be differentially motivated for the two activities due to different perceptions of autonomy. Structural equation modelling analysis showed that perceived autonomy and task orientation had direct effects on intrinsic interest for both the activities. Perceived competence, however, was positively associated with intrinsic interest only for one of the activities. The implications of the results for the practice of physical education are discussed.

Assessment and Interpretation of Aerobic Fitness in Children and Adolescents

Abstract: Our understanding of the development of children and adolescents' aerobic fitness is limited by ethical considerations and methodological constraints. Protocols, apparatus, and criteria of maximal effort used with adults are often unsuitable for use with children. In normal children and adolescents, peak VO2 increases with growth and maturation, although there are indications that girls' peak VO2 may level off around 14 years of age. Males exhibit higher values of peak VO2 than females, and the sex difference increases as they progress through adolescence. The difference between males and females has been attributed to the boys' greater muscle mass and hemoglobin concentration. It appears that boys experience an adolescent growth spurt in peak VO2, which reaches a maximum gain near the time of PHV, but data are insufficient to offer any generalization for girls. Peak VO2 has usually been expressed in relation to body mass, and with this convention it appears that boys' values are consistent throughout the developmental period, whereas girls' values decrease as they get older. This type of analysis may, however, have clouded our understanding of growth and maturational changes in peak VO2, and scaling for differences in body size may provide further clarification. If differences are shown where none were previously thought to exist, then physiological explanations must be sought. Methodological issues have also hindered the understanding of how children's blood lactate responses to exercise develop. The actual lactate level recorded during an exercise test is influenced by the site of sampling and the blood handling and assay techniques. Valid interstudy comparisons can only be made where similar procedures have been employed. In general, children demonstrate lower blood lactate levels at peak VO2 than adults, although individual variation is wide. Therefore the use of blood lactate measures to confirm the attainment of peak VO2 cannot be supported. Exercise at the same relative submaximal intensity elicits a lower blood lactate in children than in adults, but interpretation and identification of developmental and maturational patterns of response are limited by the use of different testing conditions and reference points (e.g., lactate threshold and fixed level reference points). There is growing evidence that the 2.5 mM reference level should be used in preference to the 4.0 mM level, as the adult criterion occurs close to maximal exercise in many children and adolescents. Explanations for child-adult differences in blood lactate responses to exercise are difficult to elucidate.(ABSTRACT TRUNCATED AT 400 WORDS)

Perceived motivational climate and intrinsic motivation in school physical education classes

Abstract: Research has shown that dispositional achievement goal orientations have important effects on motivation, affect and behaviour in sport and physical activity. However, rather less is known about the relationship between perceived ethos, or climate, of physical education (P.E.) classes and subsequent motivation. The purpose of this study, therefore, was to investigate the psychometric properties of an inventory assessing P.E. class climate and the relationship of subscales of the inventory with intrinsic motivation. Second order factor analysis revealed class climate dimensions of ‘mastery’ and ‘performance’, confirming prior research. The mastery dimension scores were found to significantly enhance the prediction of intrinsic motivation beyond that accounted for by perceived competence, whereas this was not the case for performance climate scores. MANOVA showed that children perceiving their P. E. class to be high inboth mastery and performance climate reported greater intrinsic motivation and perceived competence.

Generation of defects in superfluid 4He as an analogue of the formation of cosmic strings

Abstract: ALTHOUGH the birth of the Universe is inaccessible to experimental study, aspects of cosmological theories can nonetheless be explored in the laboratory. Tiny inhomogeneities in the mix of particles and radiation produced in the Big Bang grew into the clusters of galaxies that we see today, but how those inhomogeneities arose and grew is still unclear. Cosmologies based on grand unified theories suggest that a symmetry-breaking phase transition occurred via the Higgs mechanism about 10−34 after the Big Bang as the Universe cooled through a critical temperature of 1027 K. It has been proposed by Kibble1 that this transition may have generated defects in the geometry of space-time (such as cosmic strings), which provided the inhomogeneities on which galaxies subsequently condensed. Zurek2–4 has suggested that it might be possible to model this cosmological phase transition by a laboratory analogue, the superfluid transition of liquid 4He induced by fast adiabatic expansion through the critical density. Here we report the results of such an experiment. We observe copious production of quantized vortices5, the superfluid analogue of cosmic strings. These results support Kibble's contention that such defects were available in the early Universe to seed galaxy formation.

Visual perception of intentional motion.

Abstract: A series of experiments were performed to investigate how motion sequences provide information about the intentional structure of moving figures or actors. Observers had to detect simulations of biologically meaningful motion within a set of moving letters. In the first two experiments a factorial design was used, with type of instruction as a between-subject factor and six movement parameters (number of items, speed and directness of target and distractors, and ‘relentlessness’ of target movement) as within-subject factor; in the final two experiments, the visibility of the goal towards which the target moved and the use of a tracking movement to distinguish the target were varied. In such displays search time increases with increasing number of stimuli. It was found that (a) the more direct the motion, the more likely it was to be interpreted as intentional; (b) intentional motion was much easier to detect when the target moved faster than the distractors than when it moved more slowly; (c) recognition ...

Self, Silence and Invisibility as a Beginning Teacher: a life history of lesbian experience

Abstract: This paper draws upon data from an ongoing series of life history interviews with a young lesbian PE teacher, called Jessica (a pseudonym), who has recently started her career in a secondary school. Various moments from her life as told and written are provided in order to present a view of schooling from a particular standpoint that, for the most part, has been repressed. Therefore, how Jessica experiences homophobia and heterosexism in educational institutions, how she relates these experiences to other moments in her life, and the identity management strategies she adopts to cope with specific situations, provide important insights into a reality that is oppositional to the taken‐for‐granted reality of the dominant and privileged sexual class in schools, that is, heterosexuals. These insights illustrate how Jessica is systematically denied an essential freedom that is systematically granted to heterosexual teachers in a way that legitimises a distinction between her private and public lives th...

Deindividuation, power relations between groups and the expression of social identity: The effects of visibility to the out‐group

Abstract: This paper builds upon Reicher's (1984a) model of deindividuation by arguing that manipulations of identifiability do not only affect the salience of social identity but also have strategic consequences for the expression of in-group stereotypes. Increasing the visibility of group members to a powerful out-group should decrease the ability of those members to express any aspects of their identity which would meet resistance from the out-group. A preliminary study found that making supporters of the Campaign for Nuclear Disarmament individually identifiable to a powerful out-group only affects the incidence of stereotypic behaviours which would be punishable by that out-group. In the main study, science students taking a psychology course are either defined as ‘scientists’ or as ‘students’. They are then asked to complete a questionnaire about the psychology course consisting of items where difference from a staff norm would either be unpunishable or punishable. On the punishable items, the ‘science’ stereotype is compatible with the staff position, while the ‘student’ stereotype is incompatible. As expected, increased visibility of subjects to academic staff decreases conformity to the in-group stereotype for those defined as students but does not affect the behaviour of those defined as scientists. What is more, this pattern of results only holds for the punishable items. However, contrary to expectations, on the unpunishable items, increased visibility increases conformity to the in-group stereotype for both groups. Taken together, the two experiments confirm that immersing individuals in a group where they are anonymous to outsiders not only predisposes them to act in terms of social identity but also blunts out-group power in such a way as to allow full expression of that identity.

Children's task and ego goal profiles in sport

Abstract: The purpose of this study was to examine the combined effects of task and ego goal orientations on children's sport motivation. Participants were 115 boys and 116 girls (mean age = 11.12 yrs). Unlike previous research, where the correlates of the two orientations have been examined separately, this study examined the motivational consequences of different task and ego combinations. Four groups were created based on mean splits on the task and ego scales of the Task and Ego Orientation in Sport Questionnaire. These were low task/low ego, low task/high ego, high task/low ego, and high task/high ego. The hi/hi group emerged as the most motivated and the lo/lo group least motivated in measures of sport enjoyment and perceived sport competence. The lo/lo group, made up primarily of girls, appear to be at high risk for non-participation in sport. Children dominated by a task orientation were more motivated than those dominated by an ego orientation. A similar pattern emerged whether children were in the lower or upper third of the perceived sport competence distribution. A high task orientation appears to provide the vital element for sport motivation. The addition of ego involvement to task involvement may enhance sport enjoyment and does not appear to be motivationally detrimental. Task and ego profile analysis seems to offer important insight into the achievement motivation of children of this age.

The Performance of Ethical Unit Trusts: Choosing an Appropriate Benchmark

Abstract: In recent years a growing emphasis has been given to the moral dimension of financial investment. This has been evidenced by the growth in 'socially responsible' managed funds. This paper addresses the question of the appropriate benchmark against which to measure the performance of ethical trusts. In a previous paper (Luther et al. (1992)) the authors show that 'ethical' unit trusts in the UK have investment portfolios concentrated in low market capitalisation companies. This paper examines the characteristics of the returns realised by 'ethical' trusts, using a comprehensive unit trust price database. In particular, empirical results show that over the period studied 'ethical' trusts: i) had returns which were, in general, at least as highly correlated with a small-company index as with a comprehensive market index; ii) are more appropriately evaluated, in terms of financial performance, by reference to a model which recognises that their returns are influenced both by general market movements and by factors specific to smaller companies; iii) points out that because of high correlation between indices, estimation of separate small company and market sensitivities is unstable.

Health and development

Abstract: Health and Development presents a broad and detailed description of the multifaceted aspects of health and development across the globe. People are living longer, their lifestyles are changing and so too are the diseases from which they suffer. Recession in the North and debt servicing in the South have reduced public expenditure on health and welfare. The links between regional, economic and environmental factors and the health of a population are becoming clearer. Does development mean a longer life of lower quality? Always alive to both the global and the local implications, the authors focus in particular on the critical issues surrounding environmental impact, the interaction of poverty and health, socio-cultural factors in HIV/AIDS transmission, the use of traditional and community health care resources and women's health.

Fungal endophytes from the leaves and twigs of Quercus ilex L. from England, Majorca and Switzerland

Abstract: SUMMARY Leaves of Quercus ilex taken from sites in England, Majorca and Switzerland have been studied to detect the influence of the geographic position of the host within and outside its native range on the composition of its endophytic fungal assemblages. Samples of stem tissue of Q. ilex collected from the Swiss trees were also studied to confirm tissue-specific differences. Sixty different fungal taxa were isolated, but only 28 were frequent. Of the total number of isolates from the leaves from the Swiss, British and Spanish sites 87%, 31% and 63%, respectively, were coelomycetes. Four species of Phomopsis, which includes Phyllosticta ilicina (=Phomopsis ilicina v. d. Aa, ined.), were the most frequent endophytes of leaves and were either absent or rare in the twig units. Two distinct kinds of sterile mycelia were common in twigs. Swiss and Spanish trees possessed fungal assemblages distinct from those present in Britain. Naturalized stands were distinguished from native stands by the presence of rather cosmopolitan and non-specific fungal taxa, rare or absent in the samples collected in the native stands. Samples derived from the native stands were colonized by more host-specific fungi. The relative frequency of two sterile mycelia in the Swiss and Spanish sites determined their separation. Phyllosticta (Phomopsis) ilicina, the most numerous leaf colonizer, was virtually absent from the bark and the xylem. The frequent occurrence of coelomycetes as endophytes of woody trees is briefly discussed.

Using reservoir deposits to reconstruct changing sediment yields and sources in the catchment of the Old Mill Reservoir, South Devon, UK, over the past 50 years

Abstract: In the absence of long-term records of sediment transport by UK rivers, sediment deposits in lakes and reservoirs offer considerable potential for estimating sediment yields and reconstructing changing patterns of sediment yield and sediment sources during the past century in response to environmental change. An investigation of the sediment deposits within the Old Mill Reservoir, located in the East Hams region of South Devon, UK, has shown that suspended sediment yields from the 1.58 km2 catchment have averaged ca. 54 t km−2 year−1 over the period 1942 to 1991. Bedload transport from the catchment during the same period averaged 15 t km−2 year−1. The sediment record also provided evidence of increasing productivity in the reservoir during recent years and of the impact of a single extreme event. The availability of several dateable horizons within the sediment cores made it possible to subdivide further the reconstructed record of sediment yield into four periods. This subdivision indicated tha...

On the consequences of deindividuation manipulations for the strategic communication of self: Identifiability and the presentation of social identity.

Abstract: According to traditional models of deindividuation, lowered personal identifiability leads to a loss of identity and a loss of internalized control over behaviour This account has been challenged by arguing that manipulations of identifiability affect the relative salience of personal or social identity and hence the choice of standards to control behaviour The present study contributes to an extension of this argument according to which identifiability manipulations do not only affect the salience of social identity but also the strategic communication of social identity. Reicher and Lvine (1993) have shown that subjects who are more identifiable to a powerful outgroup will moderate the expression of those aspects of ingroup identity which differ from the outgroup position and which would be punished by the outgroup. Here we seek to show that in addition, subjects who are more identifiable to a powerful outgroup will accentuate the expression of those aspects of ingroup identity which differ from the outgroup position but which would not be punished by the outgroup. This is because, when identifiable, subjects may use such responses as a means of publicly presenting their adherence to group norms and hence as a means of establishing their right to group membership. A study is reported in which 102 physical education students are either identifiable (I) or not identifiable (NI) to their academic tutors. They are asked to respond on a number of dimensions where pilot interviews show the ingroup stereotype to differ from outgroup norms. Expressions of difference from the outgroup position would lead to punishment on some of these dimensions (P items) but would not lead to punishment for others (NP items) The predicted interaction between identifiability and item type is highly significant. As expected, for NP items identifiability accentuates responses which differentiate the ingroup stereotype from outgroup norms. All these results occur independently of shifts in the salience of social identity. The one unexpectedfinding is that, for P items, identifiability does lead to decreased expression of the ingroup stereotype, but the diference does not reach significance. Nonetheless, overall the results do provide further evidence for the complex effects of identifiability on strategic considerations underlying the expression of social identity in intergroup contexts.

Life histories and the issue of voice: reflections on an emerging relationship

Abstract: As part of the revival of interest in life history research, this paper problematizes the issue of voice in this form of enquiry. It does so by acknowledging the differences between life stories and life histories while emphasizing their essential linkage within a developmental process grounded in the relationships that can emerge between researcher and subject. Issues of voice, and the potential for individual and social change in the transition from life story to life history are highlighted. An emerging relationship between a white, lesbian physical educator and a white, male heterosexual is discussed in terms of biographical positioning, sharing stories and building trust, collaboration, researcher as therapist, friendship, and the postmodern dilemmas of representation and authorship. It is suggested that the transition from life story to life history should not be viewed as a linear process but one that can have unpredictable consequences for those involved. A range of ethical and methodological dile...

Algorithms for the Nonclassical Method of Symmetry Reductions

Abstract: In this article we present first an algorithm for calculating the determining equations associated with so-called ``nonclassical method'' of symmetry reductions (a la Bluman and Cole) for systems of partial differentail equations. This algorithm requires significantly less computation time than that standardly used, and avoids many of the difficulties commonly encountered. The proof of correctness of the algorithm is a simple application of the theory of Grobner bases. In the second part we demonstrate some algorithms which may be used to analyse, and often to solve, the resulting systems of overdetermined nonlinear PDEs. We take as our principal example a generalised Boussinesq equation, which arises in shallow water theory. Although the equation appears to be non-integrable, we obtain an exact ``two-soliton'' solution from a nonclassical reduction.

The Performance Of Ethical Unit Trusts: Choosing An Appropriate Benchmark

Abstract: In recent years a growing emphasis has been given to the moral dimension of financial investment. This has been evidenced by the growth in 'socially responsible' managed funds. This paper addresses the question of the appropriate benchmark against which to measure the performance of ethical trusts. In a previous paper (Luther et al., 1992) the authors show that 'ethical' unit trusts in the UK have investment portfolios concentrated in low market capitalisation companies. This paper examines the characteristics of the returns realised by 'ethical' trusts, using a comprehensive unit trust price database. In particular, empirical results show that over the period studied 'ethical' trusts: i) had returns which were, in general, at least as highly correlated with a small-company index as with a comprehensive market index; ii) are more appropriately evaluated, in terms of financial performance, by reference to a model which recognises that their returns are influenced both by general market movements and by factors specific to smaller companies; iii) points out that because of high correlation between indices, estimation of separate small company and market sensitivities is unstable.

Evaluation of an easy, cost-effective strategy for cutting benzodiazepine use in general practice.

Abstract: AIM. This study set out to assess the effect of a letter from the general practitioner, suggesting a reduction in the use of benzodiazepines, and whether the impact of the letter could be increased by the addition of information on how to tackle drug reduction. METHOD. Two hundred and nine long-term users of benzodiazepines in general practice were divided into three groups: two intervention groups and a control group. The first intervention group received a letter from their general practitioner asking that benzodiazepine use be gradually reduced and perhaps, in time, stopped. The second intervention group received the same letter plus four information sheets at monthly intervals, designed to assist drug reduction: The mean age of the 209 people was 69 years (age range 34-102 years). RESULTS. After six months, both intervention groups had reduced their consumption to approximately two thirds of the original intake of benzodiazepines and there was a statistically significant difference between the intervention groups and the control group. Eighteen per cent of those receiving the interventions received no prescriptions at all during the six month monitoring period. CONCLUSION. The results indicate that a simple intervention can have a considerable effect on the use of hypnotic and anxiolytic drugs, even with a sample of elderly users.

Reduced microvascular hyperaemia in subjects at risk of developing type 2 (non-insulin-dependent) diabetes mellitus

Abstract: Abnormalities of microvascular function may be important in the pathogenesis of diabetic microangiopathy. As such changes are already present at diagnosis in patients with Type 2 (non-insulin-dependent) diabetes mellitus, subjects at risk of developing the disease, who had elevated fasting plasma glucose concentrations below the diabetic range, were studied. The maximal microvascular hyperaemic response to local heating was determined in the feet of 11 subjects with fasting hyperglycaemia and 11 age- and sex-matched control subjects. There was reduced maximal hyperaemia in the subjects with fasting hyperglycaemia (1.01 [0.71-1.57]V, median and range), when compared to control subjects (1.41 [1.32-2.13]V, p < 0.001). It is unlikely that this limited vasodilation is a result of the mild degree of hyperglycaemia observed in the subjects included in this study. Further studies are therefore required to address the possible mechanisms of limited microvascular reactivity in subjects at risk of developing Type 2 diabetes.

Demography, Extinction and Intervention in a Small Population: the Case of the Serengeti Wild Dogs

Abstract: The effects of ecological factors (prey, competitors, predators and disease) and intervention (immobilization, radio-collaring, and vaccination) on population size and demography were investigated in Serengeti wild dogs (Lycaon pictus), an endangered canid, between 1965 and 1991. Variation in ecological factors explained most changes in demography, but did not explain a decline in adult longevity. A significant reduction in pack life and individual longevity was coincident with the introduction of routine intervention and consistent with pathogen-induced mortality. Survival varied significantly between categories of intervention, and between individuals likely to have been exposed to different degrees of social stress before intervention. The loss of all study packs in 1991 contrasted with the persistence of breeding packs outside the study area. The cause of the demise of most study packs is unknown. Monte Carlo simulations demonstrated that population extinction was unlikely to be the consequence of chance events alone. One explanation compatible with the evidence is an outbreak of viral disease induced by stress, possibly caused by intervention.

UK Directors' Trading: The Impact of Dealings in Smaller Firms

Abstract: This paper reasesses the U.K. results of significant abnormal returns from directors' trading for a new sample of directors' trades, 1984-86, and finds that abnormal returns tend to be concentrated in smaller firms. When an appropriate benchmark portfolio is used, it is found that the significance of the abnormal returns is substantially reduced, with the implication that directors' trading does not yield particularly high profits to either the directors themselves or to an outside investor mimicking those trades. Coauthors are John Matatko, Ian Tonks, and Richard Purkis. Copyright 1994 by Royal Economic Society.

Siblings of a child with cancer.

Abstract: Summary A total of 21 healthy siblings were interviewed about their experiences when a brother or sister is diagnosed with cancer. Information about the illness, opinions about who should inform siblings, social support, specific worries and worst memories were studied, as well as perceptions of any differences in the way they were treated by their parents. A short General Impact Scale was developed to assess the extent to which the siblings felt their lives had been disrupted by the illness. Results on these measures were compared with scores on four dimensions of the Sibling Perception Questionnaire (Carpenter & Sahler 1991). Siblings who reported some positive effects as a consequence of the illness (they had become more empathic toward others, or valued life more) perceived their interpersonal relations to be more negatively affected, i.e. there were greater difficulties in their relationships with others especially their parents. Higher scores on communication were related to less of an impact of the illness on life generally. However, these siblings also reported heightened concerns that their brother or sister might die. The data suggested that siblings should have opportunities to talk about implications of the disease, especially worries about death, and more efforts should be made to prepare siblings for visits to hospital and seeing the sick child.

The quantitative genetics of floral characters in Mimulus guttatus

Abstract: We examined the quantitative genetics of 20 floral traits in Mimulus guttatus including flowering time, autofertility, flower size, the spatial arrangement of flower parts, pollen and ovule production and seed number and size. A six by six diallel crossing design including selfs was performed in the glasshouse between plants derived from one population of M. guttatus from California. All characters with the exception of pollen number showed significant amounts of additive genetic variance indicating a potential to respond to selection. A principal components analysis revealed that some variation in many characters could be explained by general flower size. However, most characters still displayed heritable variation after the flower size effect was removed by analysis of covariance. Families snowed considerable variation in the ability to self in glasshouse conditions. Only a weak relationship between autofertility and herkogamy was detected, suggesting that an unidentified mechanism was responsible for differences in selfing ability. Pollen quality and ovule production were also strongly heritable, suggesting the potential for gender specialization of plants but no trade-off between male and female function could be detected. Inbreeding depression was evident in flower size and pollen and ovule production. It is postulated that the heritable variation observed is maintained in this population through disruptive selection on autofertility in response to seasonal variation in the onset of spring drought and pollinator availability.

Dynamics of reduction enzymes involved in the denitrification process in pasture soil

Abstract: When oxygen is depleted in soil, reduction enzymes involved in the denitrification process are activated and de novo synthesis of enzymes starts within a few hours. The dynamics of these enzymes and the effect on the concentration of inorganic N formed were investigated for a soil from permanent pasture. Soil was incubated aerobically for 5 days and then amended with 100 mg NO3−-N kg−1. Treatments were with or without C2H2 and with or without chloramphenicol (found to inhibit de novo synthesis of reduction enzymes), purged of all O2, shaken and anaerobically incubated for 48 h while CO2 and N2O production and no3− and NO2− concentrations were monitored. Chloramphenicol was found to have no inhibitory effects on nitrate reduction indicating that nitrate reductase activity persisted in the absence of de novo synthesis. The persistence of nitrite reductase and nitrous oxide reductase was lower as the application of chloramphenicol increased NO2− concentrations and reduced N2 production. In the absence of chloramphenicol, de novo synthesis of nitrite reductase started 5 h and that of nitrous oxide 16 h after anaerobiosis was imposed. It is concluded that the dynamics of nitrite reductase have only a small effect on the N2O production as NO2− concentrations remained below l mg N kg−1 but the low persistence of N2O reductase in combination with its retarded de-repression results in a high N2O-to-N2 ratio when anaerobic conditions are rapidly induced.

Development of a prototype gas sensor using surface plasmon resonance on gratings

Abstract: A good basis has been established for the development of a prototype gas sensor using the phenomenon of surface plasmon resonance. By exciting a surface plasmon on a metallic diffraction grating that is twisted azimuthally so its grooves are not perpendicular to the plane of incidence, and with suitable choice of input and output polarization, a resonance maximum is detected (as opposed to the usual resonance minimum). the operation of the sensor is based on the measurement of this resonance maximum on a background of weak signal and incorporates a sensing head made remote from both the source and detector by means of fibre optics. Its use is demonstrated by sensing remotely the condensation of ≈0.9 nm of isopropyl alcohol onto a silver-coated grating surface.

Soil erosion and redistribution on cultivated and uncultivated land near las bardenas in the central Ebro river Basin, Spain

Abstract: The semiarid regions of Spain, including the central part of the Ebro River basin, are under threat due to desertification. Severe erosion, as a result of poor land management, has led to degradation of the soil resource, and there is a clear need for quantitative erosion rate data to evaluate the problem. This study aimed to examine the potential for using caesium-137 to identify the patterns and rates of soil erosion and redistribution within this semiarid environment. Samples for the determination of caesium-137 were collected from uncultivated slopes and cultivated valley floor sites near the head and outlet of a small representative basin in the Las Bardenas area. The measured patterns of caesium-137 mobilization, redistribution and export provide a semiquantitative indication of the variation in erosion within the study site. Calibration of the caesium-137 measurements, taking account of the differing behaviour of radiocaesium on cultivated and uncultivated land, allows estimation of the actual rates of erosion and deposition involved. The results show (1) the erosion rates on the cultivated land (1.6–2.5 kg m−2 yr−1) are typically more than five times those seen on the uncultivated land (0.2–0.4 kg m−2 yr−1), and (2) erosion on the uncultivated land is significantly less severe at the head of the basin than at the outlet. Study of the vegetation cover suggests that lower growing shrubs and grasses may be more effective in reducing erosion in this environment than trees.

Residue fractionation and decomposition: the significance of the active fraction.

Abstract: This paper describes an incubation experiment with homogeneously 14C labeled maize-straw and its insoluble fraction. The role of the soluble fraction in the decomposition process was assessed, using three independently measured characteristics: (1) fractionation of the maize-straw, resulting in kinetically different fractions; (2) microbial biomass C and its 14C activity determined by a fumigation extraction method, and (3) the 14C activity of the released CO2-C. The fumigation extraction method was proved to be useful from 9 days after the application of the maize-straw onwards. The fractionation method yielded a soluble (48%), a (hemi) cellulosic (47%), and a lignin fraction (1%). Nine days after addition of either the complete residue or its insoluble fraction, the microbial biomass C increased from 53 to 337 and 217 mg C kg-1 dry soil, respectively. Similar values were maintained up to day 40. The large increase in microbial activity was accompanied by a N-immobilization of 65 and 29 mg N Kg-1 dry soil for the maize-straw treatment and its insoluble fraction, respectively, resulting in biomass C/N values of 5.5 and 5.6 A genuine priming effect (10 and 7% of the total CO2-C production) on the mineralization of native soil organic C was caused by an increase in decomposition of the native C rather than by an increase in turnover of the microbial biomass in the soil amended with maize straw. The soluble fraction caused a ‘priming effect’ on the decomposition of the less decomposable cell-wall fraction. Calculations by nonlinear regression confirmed this observation.

Analysis of a histone H2A variant from fission yeast: evidence for a role in chromosome stability.

Abstract: We have isolated and characterised the pht1 gene from the fission yeast Schizosaccharomyces pombe. The sequence of the predicted translation product has revealed a striking similarity to the family of H2A.F/Z histone variant proteins, which have been found in a variety of different organisms. Cells deleted for the pht1 gene locus grow slowly, exhibit an altered colony morphology, increased resistance to heat shock and show a significant decrease in the fidelity of segregation of an S. pombe minichromosome. We propose that the histone H2A variant encoded by the pht1 gene is important for chromosomal structure and function, possibly including a role in controlling the fidelity of chromosomal segregation during mitosis.