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Selected AbstractsThe inherent ,safety-net' of an Acrisol: measuring and modelling retarded leaching of mineral nitrogenEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2002D. Suprayogo Summary The inherent features of Acrisols with their increasing clay content with depth are conducive to reducing nutrient losses by nutrient adsorption on the matrix soil surfaces. Ammonium (NH4+) and nitrate (NO3,) adsorption by a Plinthic Acrisol from Lampung, Indonesia was studied in column experiments. The peak of the H218O breakthrough occurred at 1 pore volume, whereas the median pore volumes for NH4+ and NO3, ranged from 6.4 to 6.9 and 1.1 to 1.6, respectively. The adsorption coefficients (Ka in cm3 g,1) measured were 1.81, 1.51, 1.64 and 1.47 for NH4+ and 0.03, 0.09, 0.10 and 0.17 for NO3,, respectively, in the 0,0.2, 0.2,0.4, 0.4,0.6 and 0.6,0.8 m soil depth layers. The NH4+ and NO3, adsorption coefficients derived from this study were put in to the Water, Nutrient and Light Capture in Agroforestry Systems (WaNuLCAS) model to evaluate their effect on leaching in the context of several cropping systems in the humid tropics. The resulting simulations indicate that the inherent ,safety-net' (retardation mechanism) of a shallow (0.8,1 m) Plinthic Acrisol can reduce the leaching of mineral N by between 5 and 33% (or up to 2.1 g m,2), mainly due to the NH4+ retardation factor, and that the effectiveness in reducing N leaching increases with increasing depth. However, the inherent ,safety-net' is useful only if deep-rooted plants can recover the N subsequently. [source] Hydrologic and geochemical controls on soluble benzene migration in sedimentary basinsGEOFLUIDS (ELECTRONIC), Issue 2 2005Y. ZHANG Abstract The effects of groundwater flow and biodegradation on the long-distance migration of petroleum-derived benzene in oil-bearing sedimentary basins are evaluated. Using an idealized basin representation, a coupled groundwater flow and heat transfer model computes the hydraulic head, stream function, and temperature in the basin. A coupled mass transport model simulates water washing of benzene from an oil reservoir and its miscible, advective/dispersive transport by groundwater. Benzene mass transfer at the oil,water contact is computed assuming equilibrium partitioning. A first-order rate constant is used to represent aqueous benzene biodegradation. A sensitivity study is used to evaluate the effect of the variation in aquifer/geochemical parameters and oil reservoir location on benzene transport. Our results indicate that in a basin with active hydrodynamics, miscible benzene transport is dominated by advection. Diffusion may dominate within the cap rock when its permeability is less than 10,19 m2. Miscible benzene transport can form surface anomalies, sometimes adjacent to oil fields. Biodegradation controls the distance of transport down-gradient from a reservoir. We conclude that benzene detected in exploration wells may indicate an oil reservoir that lies hydraulically up-gradient. Geochemical sampling of hydrocarbons from springs and exploration wells can be useful only when the oil reservoir is located within about 20 km. Benzene soil gas anomalies may form due to regional hydrodynamics rather than separate phase migration. Diffusion alone cannot explain the elevated benzene concentration observed in carrier beds several km away from oil fields. [source] THE ,LITTLE ICE AGE': RE-EVALUATION OF AN EVOLVING CONCEPTGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2005JOHN A. MATTHEWS ABSTRACT. This review focuses on the development of the ,Little Ice Age' as a glaciological and climatic concept, and evaluates its current usefulness in the light of new data on the glacier and climatic variations of the last millennium and of the Holocene. ,Little Ice Age' glacierization occurred over about 650 years and can be defined most precisely in the European Alps (c. AD 1300,1950) when extended glaciers were larger than before or since. ,Little Ice Age' climate is defined as a shorter time interval of about 330 years (c. AD 1570,1900) when Northern Hemisphere summer temperatures (land areas north of 20°N) fell significantly below the AD 1961,1990 mean. This climatic definition overlaps the times when the Alpine glaciers attained their latest two highstands (AD 1650 and 1850). It is emphasized, however, that ,Little Ice Age' glacierization was highly dependent on winter precipitation and that ,Little Ice Age' climate was not simply a matter of summer temperatures. Both the glacier-centred and the climate-centred concepts necessarily encompass considerable spatial and temporal variability, which are investigated using maps of mean summer temperature variations over the Northern Hemisphere at 30-year intervals from AD 1571 to 1900. ,Little Ice Age'-type events occurred earlier in the Holocene as exemplified by at least seven glacier expansion episodes that have been identified in southern Norway. Such events provide a broader context and renewed relevance for the ,Little Ice Age', which may be viewed as a ,modern analogue' for the earlier events; and the likelihood that similar events will occur in the future has implications for climatic change in the twenty-first century. It is concluded that the concept of a ,Little Ice Age' will remain useful only by (1) continuing to incorporate the temporal and spatial complexities of glacier and climatic variations as they become better known, and (2) by reflecting improved understanding of the Earth-atmosphere-ocean system and its forcing factors through the interaction of palaeoclimatic reconstruction with climate modelling. [source] Novel mutations of the GLA gene in Japanese patients with Fabry disease and their functional characterization by active site specific chaperone,,HUMAN MUTATION, Issue 2 2008Masaaki Shimotori Abstract Fabry disease is an X-linked recessive inborn metabolic disorder caused by a deficiency of the lysosomal enzyme ,-galactosidase A (EC 3.2.1.22). The causative mutations are diverse, include both large rearrangements and single-base substitutions, and are dispersed throughout the 7 exons of the ,-galactosidase A gene (GLA). Mutation hotspots for Fabry disease do not exist. We examined 62 Fabry patients in Japan and found 24 GLA mutations, including 11 novel ones. A potential treatment reported for Fabry disease is active site specific chaperone (ASSC) therapy using 1-deoxygalactonojirimycin (DGJ), an inhibitor of ,-galactosidase A, at subinhibitory concentrations. We transfected COS-7 cells with the 24 mutant GLAs and analyzed the ,-galactosidase A activities. We then treated the transfected COS-7 cells with DGJ and analyzed its effect on the mutant enzyme activities. The activity of 11 missense mutants increased significantly with DGJ. Although ASSC therapy is useful only for misfolding mutants and therefore not applicable to all cases, it may be useful for treating many Japanese patients with Fabry disease. © 2007 Wiley-Liss, Inc. [source] An efficient diagonal preconditioner for finite element solution of Biot's consolidation equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 4 2002K. K. Phoon Abstract Finite element simulations of very large-scale soil,structure interaction problems (e.g. excavations, tunnelling, pile-rafts, etc.) typically involve the solution of a very large, ill-conditioned, and indefinite Biot system of equations. The traditional preconditioned conjugate gradient solver coupled with the standard Jacobi (SJ) preconditioner can be very inefficient for this class of problems. This paper presents a robust generalized Jacobi (GJ) preconditioner that is extremely effective for solving very large-scale Biot's finite element equations using the symmetric quasi-minimal residual method. The GJ preconditioner can be formed, inverted, and implemented within an ,element-by-element' framework as readily as the SJ preconditioner. It was derived as a diagonal approximation to a theoretical form, which can be proven mathematically to possess an attractive eigenvalue clustering property. The effectiveness of the GJ preconditioner over a wide range of soil stiffness and permeability was demonstrated numerically using a simple three-dimensional footing problem. This paper casts a new perspective on the potentialities of the simple diagonal preconditioner, which has been commonly perceived as being useful only in situations where it can serve as an approximate inverse to a diagonally dominant coefficient matrix. Copyright © 2002 John Wiley & Sons, Ltd. [source] The role of trout in stream food webs: integrating evidence from field surveys and experimentsJOURNAL OF ANIMAL ECOLOGY, Issue 2 2006KRISTIAN MEISSNER Summary 1We evaluated the effects of brown trout on boreal stream food webs using field surveys and enclosure/exclosure experiments. Experimental results were related to prey preference of uncaged trout in the same stream, as well as to a survey of macroinvertebrate densities in streams with vs. without trout. Finally, we assessed the generality of our findings by examining salmonid predation on three groups of macroinvertebrate prey (chironomid midges, epibenthic grazers, invertebrate predators) in a meta-analysis. 2In a preliminary experiment, invertebrate predators showed a strong negative response to trout, whereas chironomids benefited from trout presence. In the main experiment, trout impact increased with prey size. Trout had the strongest effect on invertebrate predators and cased caddis larvae, whereas Baetis mayfly and chironomid larvae were unaffected. Trout impact on the largest prey seemed mainly consumptive, because prey emigration rates were low and independent of fish presence. Despite strong effects on macroinvertebrates, trout did not induce a trophic cascade on periphyton. Uncaged trout showed a strong preference for the largest prey items (predatory invertebrates and aerial prey), whereas Baetis mayflies and chironomids were avoided by trout. 3Densities of invertebrate predators were significantly higher in troutless streams. Baetis mayflies also were less abundant in trout streams, whereas densities of chironomids were positively, although non-significantly, related to trout presence. Meta-analysis showed a strong negative impact of trout on invertebrate predators, a negative but variable impact on mobile grazers (mainly mayfly larvae) and a slightly positive impact on chironomid larvae. 4Being size-selective predators, salmonid fishes have a strong impact on the largest prey types available, and this effect spans several domains of scale. Discrepancies between our experimental findings and those from the field survey and meta-analysis show, however, that for most lotic prey, small-scale experiments do not reflect fish impact reliably at stream-wide scales. 5Our findings suggest that small-scale experiments will be useful only if the experimental results are evaluated carefully against natural history information about the experimental system and interacting species across a wide array of spatial scales. [source] Scan profiles for neutron spectrometers.JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 5 2003The recent development of neutron collimators with rectangular transmission profiles (intensity versus angular divergence) extends hope of improved count rates on neutron scattering instruments. It is usually assumed that a more effective use of beam angular spread in these devices should increase count rates by about a factor of two. However, real beams have both angular and wavevector spread and both these spreads are governed by the allowed collimation. In this extended view, the gains from ideal rectangular-profile elements (angle filters) are shown to be much larger (about a factor of four). The mirror reflections used to achieve the rectangular profiles in real devices complicate the resolution effects. Specifically, the reflections disturb the wavevector,angular divergence correlation in the beams, leading to unusual peak shapes characterized by triple peaks on powder diffractometers. Thus, these reflecting collimators are likely to be universally useful only before the monochromator and immediately preceding the detector, where wavevector,angle correlations have no effect. This reduces the potential gains to a factor of two or so. Note that the gains are as previously expected but for quite different reasons than imagined. This remains a very significant gain in a field where most work is intensity-limited. [source] The role of theory-constitutive metaphor in nursing scienceNURSING PHILOSOPHY, Issue 3 2008Jennifer Greenwood Abstract, The current view of theoretical statements in science is that they should be literal and precise; ambiguous and metaphorical statements are useful only as pre-theoretical, exegetical, and heuristic devices and as pedagogical tools. In this paper we argue that this view is mistaken. Literal, precise statements apply to those experiential phenomena which can be defined either conventionally by criterial attribution or by internal atomic constitution. Experiential phenomena which are defined relationally and/or functionally, like nursing, in virtue of their nature, require metaphorical description and explanation. In such cases, metaphor is theory-constitutive. Using insights from the philosophies of language and mind, and examples from nursing practice, education, and our own empirical research, we explore the nature of metaphor and its role in theory constitution. We argue that the apparent resistance of certain experiential phenomena to literal description and explanation is not necessarily indicative of pre-theoretic linguistic imprecision. We suggest, rather, that such resistance provides useful insights into the nature of such experiential phenomena. We also suggest that the aim of scientific theory should be methodological or epistemological precision and not merely linguistic precision. [source] Just how useless is an amblyopic eye?OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 1 2008Eve Panesar Purpose:, The extent to which individuals with amblyopia are visually disadvantaged has generated renewed research interest. Investigation of the contribution of the amblyopic eye to visual performance under habitual conditions is a key component of this issue. This study aims to evaluate the contribution of each eye to a simple light detection task when both eyes are open and in their habitual motor position. Methods:, A custom program on the Humphrey Field Analyzer (Carl Zeiss Meditec Inc., Dublin, CA, USA) was used to measure detection thresholds for a blue light on a yellow background along the horizontal meridian at two degree intervals to an eccentricity of 25 degrees either side of fixation. Three viewing conditions were used: (1) both eyes open, (2) a yellow filter in front of the amblyopic eye and (3) a yellow filter in front of the fellow eye. The purpose of the yellow filter was to produce minimal dissociation as it only prevented the eye behind the filter from seeing the blue stimulus; the fixation mark and the background remained visible to both eyes. Participants included 10 visual normals and 16 volunteers with amblyopia. Results:, Within the sample of amblyopes there were three basic patterns of results, and each applied to around one third of the group: (1) habitual sensitivity governed by the sensitivity of the fellow eye at each stimulus location, (2) habitual sensitivity exceeding the sensitivities of either eye at each stimulus location and (3) a pattern of contribution that varied across the range of eccentricities. Surprisingly, in one amblyope the habitual sensitivity appeared to be governed by the sensitivity of the amblyopic eye. The pattern of contribution of each eye to the habitual sensitivity did not vary in a manner that was predictable by the visual acuity deficit or the presumed aetiology of the amblyopia. The control sample showed either pattern 2 (70%) or pattern 3 (30%). Conclusions:, The amblyopic eye did not contribute to the habitual performance in approximately one-third of cases in this simple detection task. Thus, in many cases the amblyopic eye may be a useful contributor to visual performance in the binocular field. This challenges the traditional view that an amblyopic eye is useful only for peripheral vision. [source] Perspectives on polyploidy in plants , ancient and neoBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2004MICHAEL D. BENNETT It is timely to re-examine the phenomenon of polyploidy in plants. Indeed, the power of modern molecular technology to provide new insights, and the impetus of genomics, make polyploidy a fit, fashionable and futuristic topic for review. Some historical perspective is essential to understand the meaning of the terms, to recognize what is already known and what is dogma, and to frame incisive questions for future research. Polyploidy is important because life on earth is predominantly a polyploid phenomenon. Moreover, civilization is mainly powered by polyploid food , notably cereal endosperm. Ongoing uncertainty about the origin of triploid endosperm epitomizes our ignorance about somatic polyploidy. New molecular information makes it timely to reconsider how to identity polyploids and what is a polyploid state. A functional definition in terms of a minimal genome may be helpful. Genes are known that can raise or lower ploidy level. Molecular studies can test if, contrary to dogma, the relationship between diploids and polyploids is a dynamic two-way system. We still need to understand the mechanisms and roles of key genes controlling ploidy level and disomic inheritance. New evidence for genome duplications should be compared with old ideas about cryptopolyploidy, and new views of meiosis should not ignore premeiotic genome separation. In practice, new knowledge about polyploidy will be most useful only when it reliably predicts which crops can be usefully improved as stable autopolyploids and which genomes combined to create successful new allopolyloids. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 411,423. [source] Autologous or homologous transfusion in aortic surgery: randomized trialBRITISH JOURNAL OF SURGERY (NOW INCLUDES EUROPEAN JOURNAL OF SURGERY), Issue 4 2001F. Torella Background: Aortic surgery often requires blood transfusion, which may cause complications and postoperative infection. Autologous transfusion was evaluated in a multicentre clinical trial. Methods: Some 145 patients undergoing elective aortic surgery in eight hospitals were randomized to either ,homologous' or ,autologous' transfusion, a combination of acute normovolaemic haemodilution (ANH) and intraoperative cell salvage. Homologous blood was administered when the haemoglobin concentration fell below 8 g dl,1. Results: Median (interquartile range (i.q.r.)) blood loss was 668 (400,862) ml or 17 (10,24) per cent of blood volume in aortobifemoral bypass, and 1120 (765,1700) ml or 24 (17,36) per cent in aneurysm repair (P < 0·001). Autologous transfusion reduced homologous blood requirements from a median (i.q.r.) of 2 (0,4) units to 0 (0,2) units (P = 0·008). Independent predictors of blood transfusion were homologous transfusion strategy (odds ratio (OR) 2·3 (95 per cent confidence interval 1·1,5·0); P = 0·03), low preoperative haemoglobin concentration (OR 3·7 (1·7,8·2); P < 0·001), prolonged surgery (OR 2·1 (1·0,4·8); P = 0·05) and blood loss (OR 3·0 (1·4,6·5); P = 0·007). Patients with a preoperative haemoglobin concentration greater than 13·5 g dl,1 and who lost less than 20 per cent of their blood volume rarely required transfusion. There was no significant difference between the groups in terms of morbidity, mortality and postoperative hospital stay. Conclusion: Autologous transfusion reduced the need for homologous blood in aortic surgery, but was useful only in patients with low haemoglobin levels or when blood loss exceeded 20 per cent of the blood volume. ANH alone is indicated for patients undergoing aortobifemoral bypass and in those with a higher haemoglobin level and blood volume. © 2001 British Journal of Surgery Society Ltd [source] | ||||||||||||||||