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Search Results: 1 - 10 of 371191 matches for " C. D. Evans "
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Chemical trends at lakes and streams in the UK Acid Waters Monitoring Network, 1988-2000: Evidence for recent recovery at a national scale
C. D. Evans,D. T. Monteith
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2001,
Abstract: A detailed trend analysis of 12 years of data (1988-2000) for 22 surface waters in acid-sensitive regions of the United Kingdom, in which individual site data have been combined to identify national-scale trends, has shown strong common patterns of temporal variation. Results suggest a widespread reduction in sulphate concentrations, hydrogen ion and inorganic aluminium species, and increases in acid neutralising capacity. Many chemical changes have not been linear. However, the first five years were characterised by high concentrations of marine ions and relatively stable pollutant sulphate concentrations and the remaining period by lower concentrations of marine ions and declining sulphate. Genuine 'recovery', in terms of declining acidity in response to reduced anthropogenic sulphur deposition is only apparent, therefore, for the latter part of the monitoring period. Reductions in calcium concentrations appear to have partially offset the influence of sulphate reductions on acidity, as have increases in organic acidity associated with strong and widespread rising trends in dissolved organic carbon. Fluctuations in a number of climatic factors over the monitoring period have led to significant inter-annual variability in nitrate, which exhibits little long-term trend, marine ions and acidity, emphasising the need for long monitoring periods if underlying trends are to be correctly identified. Keywords: acidification, recovery, long-term trends, climate, Dissolved Organic Carbon, United Kingdom Acid Waters Monitoring Network
Characteristics and classification of A-type supergiants in the Small Magellanic Cloud
C. J. Evans,I. D. Howarth
Physics , 2003, DOI: 10.1046/j.1365-2966.2003.07038.x
Abstract: We address the relationship between spectral type and physical properties for A-type supergiants in the SMC. We first construct a self-consistent classification scheme for A supergiants, employing the calcium K to H epsilon line ratio as a temperature-sequence discriminant. Following the precepts of the `MK process', the same morphological criteria are applied to Galactic and SMC spectra with the understanding there may not be a correspondence in physical properties between spectral counterparts in different environments. We then discuss the temperature scale, concluding that A supergiants in the SMC are systematically cooler than their Galactic counterparts at the same spectral type, by up to ~10%. Considering the relative line strengths of H gamma and the CH G-band we extend our study to F and early G-type supergiants, for which similar effects are found. We note the implications for analyses of extragalactic luminous supergiants, for the flux-weighted gravity-luminosity relationship and for population synthesis studies in unresolved stellar systems.
Transfinite game values in infinite chess
C. D. A. Evans,Joel David Hamkins
Mathematics , 2013,
Abstract: We investigate the transfinite game values arising in infinite chess, providing both upper and lower bounds on the supremum of these values---the omega one of chess---with two senses depending on whether one considers only finite positions or also positions with infinitely many pieces. For lower bounds, we present specific infinite positions with transfinite game values of omega, omega^2, omega^2 times k, and omega^3. By embedding trees into chess, we show that there is a computable infinite chess position that is a win for white if the players are required to play according to a deterministic computable strategy, but which is a draw without that restriction. Finally, we prove that every countable ordinal arises as the game value of a position in infinite three-dimensional chess, and consequently the omega one of infinite three-dimensional chess is as large as it can be, namely, true omega one.
An Algorithm to Solve the Equal-Sum-Product Problem
M. A. Nyblom,C. D. Evans
Computer Science , 2013,
Abstract: A recursive algorithm is constructed which finds all solutions to a class of Diophantine equations connected to the problem of determining ordered n-tuples of positive integers satisfying the property that their sum is equal to their product. An examination of the use of Binary Search Trees in implementing the algorithm into a working program is given. In addition an application of the algorithm for searching possible extra exceptional values of the equal-sum-product problem is explored after demonstrating a link between these numbers and the Sophie Germain primes.
Predicting regional recovery from acidification; the MAGIC model applied to Scotland, England and Wales
C. D. Evans,A. Jenkins,R. C. Helliwell,R. Ferrier
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 1998,
Abstract: A dynamic, process-based model of surface water acidification, MAGIC, has been applied to over a thousand sites across the UK. The model is calibrated to surface water samples collected during a survey for the Critical Loads programme, and utilises the best available and consistent estimates of soil physical and chemical properties, rainfall and runoff volumes, and deposition chemistry. A total of 698 sites were calibrated successfully. At these sites, surface water chemistry was reconstructed from 1850 to the present day, and forecast to 2050 based on future decreases in sulphur (S) deposition in response to the Second S Protocol. Model outputs capture distinct regional patterns of acidification and recovery. the most acidic present-day conditions are found in acid-sensitive regions of Northern England (the Pennines, Lake District and North York Moors). Although a significant proportion of sites in these areas failed to calibrate, those that did are predicted to have experienced severe historic decreases in acidic neutralising capacity (ANC) in response to high levels of acidic deposition. The model also indicates significant acidification in the moderate deposition areas of Wales and Galloway, whereas in the low deposition region of northern Scotland, acidification has been minor even in areas of acid-sensitive geology. ANC is forecast to recover at virtually all sites, with the greatest recovery predicted for areas currently subject to high deposition. The model indicates that the Second S Protocol, however, will not be sufficient to produce full recovery, with average ANC increases to 2050 counteracting just 27% of the simulated decline from 1850 to present day. Acidic conditions (ANC < 0) are predicted to persist until 2050 at a significant number of sites in Northern England, Wales and Galloway.
Effects of decreasing acid deposition and climate change on acid extremes in an upland stream
C. D. Evans,B. Reynolds,C. Hinton,S. Hughes
Hydrology and Earth System Sciences Discussions , 2007,
Abstract: This study assesses the major chemical processes leading to acid extremes in a small, moorland stream in mid-Wales, UK, which has been monitored since 1979. Results suggest that base cation (mainly calcium) dilution, the "sea-salt effect", and elevated nitrate pulses, are the major causes of seasonal/episodic minima in acid neutralising capacity (ANC), and that the relative importance of these drivers has remained approximately constant during 25 years of decreasing acid deposition and associated long-term chemical recovery. Many of the chemical variations causing short-term reductions in stream acidity, particularly base cation dilution and organic acid increases, are closely related to changes in water-flowpath and therefore to stream discharge. Changes in the observed pH-discharge relationship over time indicate that high-flow pH has increased more rapidly than mean-flow pH, and therefore that episodes have decreased in magnitude since 1980. However a two-box application of the dynamic model MAGIC, whilst reproducing this trend, suggests that it will not persist in the long term, with mean ANC continuing to increase until 2100, but the ANC of the upper soil (the source of relatively acid water during high-flow episodes) stabilising close to zero beyond 2030. With climate change predicted to lead to an increase in maximum flows in the latter half of the century, high-flow related acid episodes may actually become more rather than less severe in the long term, although the model suggests that this effect may be small. Two other predicted climatic changes could also detrimentally impact on acid episodes: increased severity of winter "sea-salt" episodes due to higher wind speeds during winter storms; and larger sulphate pulses due to oxidation of reduced sulphur held in organic soils, during more extreme summer droughts. At the Gwy, the near-coastal location and relatively small extent of peat soils suggest that sea-salt episodes may have the greatest influence.
Are there signs of acidification reversal in freshwaters of the low mountain ranges in Germany?
C. Alewell,M. Armbruster,J. Bittersohl,C. D. Evans
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2001,
Abstract: The reversal of freshwater acidification in the low mountain ranges of Germany is of public, political and scientific concern, because these regions are near natural ecosystems and function as an important drinking water supply. The aim of this study was to evaluate the status and trends of acidification reversal after two decades of reduced anthropogenic deposition in selected freshwaters of the low mountain ranges in the Harz, the Fichtelgebirge, the Bavarian Forest, the Spessart and the Black Forest. In response to decreased sulphate deposition, seven out of nine streams investigated had significantly decreasing sulphate concentrations (all trends were calculated with the Seasonal Kendall Test). The decrease in sulphate concentration was only minor, however, due to the release of previously stored soil sulphur. No increase was found in pH and acid neutralising capacity (defined by Reuss and Johnson, 1986). Aluminum concentrations in the streams did not decrease. Thus, no major acidification reversal can currently be noted in spite of two decades of decreased acid deposition. Nevertheless, the first signs of improvement in water quality were detected as there was a decrease in the level and frequency of extreme values of pH, acid neutralising capacity and aluminium concentrations in streams. With respect to nitrogen, no change was determined for either nitrate or ammonium concentrations in precipitation or stream water. Base cation fluxes indicate increasing net loss of base cations from all ecosystems investigated, which could be interpreted as an increase in soil acidification. The latter was due to a combination of continued high anion leaching and significant reduction of base cation deposition. No major improvement was noted in biological recovery, however, initial signs of recovery were detectable as there was re-occurrence of some single macroinvertebrate species which were formerly extinct. The results of this study have important implications for water authorities, forest managers and policy makers: the delay in acidification reversal suggests a need for ongoing intensive amelioration of waters, a careful selection of management tools to guarantee sustainable management of forests and the reduction of nitrogen deposition to prevent further acidification of soils and waters. Keywords: freshwater, acidification reversal, drinking water supply, forested catchments, Germany
Gene therapy of the rheumatic diseases: 1998 to 2008
Christopher H Evans, Steven C Ghivizzani, Paul D Robbins
Arthritis Research & Therapy , 2009, DOI: 10.1186/ar2563
Abstract: When Arthritis Research was launched, the field of gene therapy was going from strength to strength. The preceding decade had seen the number of human gene therapy trials grow, since the first properly authorized gene transfer to a human in 1989, to a total of 368 by 1998. Despite the worst predictions of the skeptics, there had been no serious adverse events and the field looked forward, like the economy that was fuelling much speculation in the area, to continued rapid growth. Optimists predicted that the first genetic medicines would be on the market within a few years. Rheumatoid arthritis (RA) had become an early target for gene therapy (Figure 1), capturing the optimism of the early 1990s and beginning clinical trials in 1996. The first International Meeting on the Gene Therapy of Arthritis and Related Disorders (GTARD) was held at the National Institutes of Health (NIH) (Bethesda, MD, USA) in 1998 [1] and attracted over 200 participants.Matters then changed abruptly. The 1999 death of Jesse Gelsinger [2] reopened safety concerns. This, in turn, made it more difficult to obtain funding from traditional sources, such as the NIH, as well as the biotechnology industry, which was also dealing with a rapidly slowing economy. Many rheumatic diseases, though serious, are not considered to be life-threatening, a factor that further reduced enthusiasm for gene therapy research in this area under these circumstances.Although the first flush of enthusiasm is over, the past decade has seen steady progress in developing genetic therapies for several conditions, and the number of clinical trials worldwide is approaching 1,500. The first commercial gene therapeutic, Gendicin for cancer of the head and neck, has been launched in China [3], and gene therapy for familial lipoprotein lipase deficiency is available as an orphan drug in Europe and the US. Cures have been reported for X-linked severe combined immunodeficiency disease (SCID) [4], adenosine deaminase-SCID [5], and X-
Arthritis gene therapy's first death
Christopher H Evans, Steven C Ghivizzani, Paul D Robbins
Arthritis Research & Therapy , 2008, DOI: 10.1186/ar2411
Abstract: On 24 July 2007 a 36-year-old woman with rheumatoid arthritis (RA) died, 22 days after receiving a second dose of an experimental, arthritis gene therapeutic [1]. The Food and Drug Administration (FDA) placed the trial on hold while the circumstances of the participant's death were investigated; the National Institutes of Health Recombinant DNA Advisory Committee (RAC) launched a similar enquiry. At the beginning of December 2007 the FDA allowed the trial to proceed, suggesting that it did not attribute the subject's death to the gene treatment. A few days later, however, the RAC concluded that a possible role of the gene transfer in this clinical course cannot definitively be excluded due to the lack of data (RAC Minutes of Meeting, December 3–5, 2007).As the clinical trial restarts, we review the circumstances of this tragedy in the larger gene therapy context and consider the lessons to be learned.For much of its short history, gene therapy has suffered huge mood swings. Enthusiasm ran high after the first properly authorized gene transfer to a human in 1989 [2], but was stilled instantly by the 1999 death of Jesse Gelsinger in a gene therapy trial at the University of Pennsylvania [3]. A more measured optimism returned when the first apparent gene cures of X-linked severe combined immunodeficiency were reported in the early 2000s [4], only to be dashed again by the occurrence of leukemia in several of these subjects [5]. Similar technology has been applied successfully to treat X-linked chronic granulomatous disease [6], and the death of a subject in a Swiss–German trial in 2006 was attributed to the disease, not to the gene transfer [7].Matters have been improving since then, with apparent cures in several cases of X-linked severe combined immunodeficiency, adenosine deaminase severe combined immunodeficiency [8] and melanoma [9], and promising clinical responses reported for Parkinson's disease [10]. Thirty-two phase III clinical trials are underway [11], and
Fluvial organic carbon losses from a Bornean blackwater river
S. Moore, V. Gauci, C. D. Evans,S. E. Page
Biogeosciences (BG) & Discussions (BGD) , 2011,
Abstract: Concentrations of dissolved organic carbon (DOC) and particulate organic carbon (POC) were analysed from the source to the mouth of the River Sebangau in Central Kalimantan, Indonesia during the dry and wet seasons in 2008/2009 and an annual total organic carbon (TOC) flux estimated. DOC concentrations were higher and POC concentrations lower in the wet season compared to the dry season. As seen in other tropical blackwater rivers, DOC concentration is consistently around 10 times greater than POC concentration. We estimate the annual TOC flux discharged to the Java Sea to be 0.46 Tg year 1 comprising of 93% (0.43 Tg) DOC and 7% (0.03 Tg) POC. This equates to a fluvial TOC loss flux per unit area over the entire Sebangau catchment of 88 g C m 2 yr 1. When extrapolating the River Sebangau DOC loss flux (83 g C m 2 yr 1) to the peat covered area of Indonesia (206 950 km2), we estimate a DOC loss of 17.2 Tg C yr 1 or ~10% of current estimates of the global annual riverine DOC discharge into the ocean.
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