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Empirical Relationships (empirical + relationships)
Selected AbstractsDisaggregate Wealth and Aggregate Consumption: an Investigation of Empirical Relationships for the G7*OXFORD BULLETIN OF ECONOMICS & STATISTICS, Issue 2 2003Joseph P. Byrne To date, studies of wealth effects on consumption have mainly used aggregate wealth definitions on a single-country basis. This study seeks to break new ground by analysing disaggregated financial wealth in consumption functions for G7 countries. Contrary to earlier empirical work, we find that illiquid financial wealth (i.e. securities, pensions and mortgage debt) tends to be a more important long-run determinant of consumption than liquid financial wealth. These results imply potential instability in consumption functions employing aggregate wealth. Our results are robust using SURE; when testing with a nested specification; and when using a linear model. [source] Agitation requirements for complete solid suspension in an unbaffled agitated vessel with an unsteadily forward,reverse rotating impellerJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2007Shuichi Tezura Abstract Background: To develop a new type of solid,liquid apparatus, we have proposed the application of an agitation system with an impeller whose rotation alternates direction unsteadily, i.e., a forward,reverse rotating impeller. For an unbaffled agitated vessel fitted with this system, the suspension of solid particles in a liquid was studied using a disk turbine impeller with six flat blades. Results: The effects of the solid,liquid conditions and geometrical conditions of the apparatus on the minimum rotation rate and the corresponding impeller power consumption were evaluated experimentally for a completely suspended solid. The power consumption for a just suspended solid with this type of vessel was comparable with that for a baffled vessel with a unidirectionally rotating impeller, taking the liquid flow along the vessel bottom into consideration. Conclusion: Empirical relationships to predict the parameters of agitation requirements were found. A comparative investigation demonstrated the usefulness of the forward,reverse rotation mode of the impeller for off-bottom suspension of solid particles. Copyright © 2007 Society of Chemical Industry [source] Design and operation of unbaffled aerated agitated vessels with unsteadily forward,reverse rotating impellers handling viscous Newtonian liquidsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2003Masanori Yoshida Abstract Design and operation of unbaffled aerated agitated vessels with multiple unsteadily forward,reverse rotating impellers (AJITERs) for viscous Newtonian liquids were studied. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, geometrical conditions such as the diameters of vessel and impeller, and the physical properties of liquids on the drag and added moment of inertia coefficients, necessary to predict the average and maximum power consumptions of the impellers in AJITERs, were evaluated and the empirical relationships which estimate values of each of these coefficients are presented. The effects of operating conditions, geometrical conditions and liquid physical properties on the gas hold-up, ,gD, and volumetric oxygen transfer coefficient, kLaD, were evaluated in relation to the total power input which is the sum of the average power consumption of impellers, ie average agitation power input, and aeration power input. Empirical relationships, useful for design and operation of AJITERs, were obtained for each viscosity range, where the dependences of ,gD and kLaD on the specific total power input and superficial gas velocity differed, to predict ,gD and kLaD respectively as a function of the specific total power input, superficial gas velocity and liquid physical properties. © 2003 Society of Chemical Industry [source] Flow and mass transfer in aerated viscous Newtonian liquids in an unbaffled agitated vessel having alternating forward,reverse rotating impellersJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 11 2001Masanori Yoshida Abstract Flow and mass transfer characteristics in aerated viscous Newtonian liquids were studied for an unbaffled aerated agitated vessel with alternating rotating impellers (AAVAI), ie with multiple forward,reverse rotating impellers having four delta blades. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, and the liquid physical properties (viscosity) on the gas hold-up, ,gD, and volumetric oxygen transfer coefficient, kLaD were evaluated experimentally. The dependences of ,gD and kLaD on the specific total power input and superficial gas velocity differed, depending on the ranges of liquid viscosity. Empirical relationships are presented for each viscosity range to predict ,gD and kLaD as a function of the specific total power input, superficial gas velocity and viscosity of liquid. Based on a comparative investigation of the volumetric coefficient in terms of the specific total power input between the AAVAI and conventional aerated agitated vessels (CAAVs) having unidirectionally rotating impellers, the usefulness of AAVAI as a gas,liquid agitator treating viscous Newtonian liquids is also discussed. © 2001 Society of Chemical Industry [source] Regionalisation of chemical variability in European mountain lakesFRESHWATER BIOLOGY, Issue 12 2009LLUÍS CAMARERO Summary 1. We carried out a coordinated survey of mountain lakes covering the main ranges across Europe (including Greenland), sampling 379 lakes above the local tree line in 2000. The objectives were to identify the main sources of chemical variability in mountain lakes, define a chemical classification of lakes, and develop tools to extrapolate our results to regional lake populations through an empirical regionalisation or upscaling of chemical properties. 2. We investigated the main causes of chemical variability using factor analysis (FA) and empirical relationships between chemistry and several environmental variables. Weathering, sea salt inputs, atmospheric deposition of N and S, and biological activity in soils of the catchment were identified as the major drivers of lake chemistry. 3. We tested discriminant analysis (DA) to predict the lake chemistry. It was possible to use the lithology of the catchments to predict the range of Ca2+ and SO42, into which a lake of unknown chemistry will decrease. Lakes with lower SO42, concentrations have little geologically derived S, and better reflect the variations in atmospheric S loading. The influence of marine aerosols on lakewater chemistry could also be predicted from the minimum distance to the sea and altitude of the lakes. 4. The most remarkable result of FA was to reveal a factor correlated to DOC (positively) and NO3, (negatively). This inverse relationship might be the result either of independent processes active in the catchment soils and acting in an opposite sense, or a direct interaction, e.g. limitation of denitrification by DOC availability. Such a relationship has been reported in the recent literature in many sites and at all scales, appearing to be a global pattern that could reflect the link between the C and N cycles. 5. The concentration of NO3, is determined by both atmospheric N deposition and the processing capacity of the catchments (i.e. N uptake by plants and soil microbes). The fraction of the variability in NO3, because of atmospheric deposition is captured by an independent factor in the FA. This is the only factor showing a clear pattern when mapped over Europe, indicating lower N deposition in the northernmost areas. 6. A classification has been derived which takes into account all the major chemical features of the mountain lakes in Europe. FA provided the criteria to establish the most important factors influencing lake water chemistry, define classes within them, and classify the surveyed lakes into each class. DA can be used as a tool to scale up the classification to unsurveyed lakes, regarding sensitivity to acidification, marine influence and sources of S. [source] Inflorescence characteristics, seed composition, and allometric relationships predicting seed yields in the biomass crop Cynara cardunculusGCB BIOENERGY, Issue 3 2010S. V. ARCHONTOULIS Abstract Cynara (Cynara cardunculus) is a perennial C3 herb that has its potential as bioenergy crop. This paper aims (a) to derive empirical relationships to predict cynara seed yield per head and per unit area, avoiding laborious extraction of seeds from the complex structure of its inflorescences; (b) to determine the head-weight distribution per unit area, the seed composition and the oil profile of cynara seeds; and (c) to estimate the range of cynara biomass, seed and oil yield in representative parts of Greece. We analyzed 16 field experiments, varying in crop age and environmental conditions in Greece. Seed yield per head (SYhead) can be accurately predicted as a linear function of dry head weight (Hw): SYhead=0.429·Hw,2.9 (r2=0.96; n=617). Based on this relationship, we developed a simple two-parameter equation to predict seed yield per unit area (SY): SY=HN·(0.429·,,2.9), where , is the mean head weight (g head,1) and HN is the total number of heads per unit area, respectively. The models were tested against current and published data (n=180 for head-level; n=35 for unit area-level models), and proved to be valid under diverse management and environmental conditions. Attainable cynara seed yields ranged from 190 to 480 g m,2 yr,1, on dry soils and on aquic soils (shallow ground water level). This variation in seed yield was sufficiently explained by the analyses of head-weight distribution per unit area (small, medium and large heads) and variability of seed/head weight ratio at head level. Seed oil concentration (average: 23%) and crude protein concentration (average: 18.7%) were rather invariant across different seed sizes (range: 26,56 mg seed,1) and growing environments. [source] Seismicity in a model governed by competing frictional weakening and healing mechanismsGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2009G. Hillers SUMMARY Observations from laboratory, field and numerical work spanning a wide range of space and time scales suggest a strain dependent progressive evolution of material properties that control the stability of earthquake faults. The associated weakening mechanisms are counterbalanced by a variety of restrengthening mechanisms. The efficiency of the healing processes depends on local material properties and on rheologic, temperature, and hydraulic conditions. We investigate the relative effects of these competing non-linear feedbacks on seismogenesis in the context of evolving frictional properties, using a mechanical earthquake model that is governed by slip weakening friction. Weakening and strengthening mechanisms are parametrized by the evolution of the frictional control variable,the slip weakening rate R,using empirical relationships obtained from laboratory experiments. In our model, weakening depends on the slip of an earthquake and tends to increase R, following the behaviour of real and simulated frictional interfaces. Healing causes R to decrease and depends on the time passed since the last slip. Results from models with these competing feedbacks are compared with simulations using non-evolving friction. Compared to fixed R conditions, evolving properties result in a significantly increased variability in the system dynamics. We find that for a given set of weakening parameters the resulting seismicity patterns are sensitive to details of the restrengthening process, such as the healing rate b and a lower cutoff time, tc, up to which no significant change in the friction parameter is observed. For relatively large and small cutoff times, the statistics are typical of fixed large and small R values, respectively. However, a wide range of intermediate values leads to significant fluctuations in the internal energy levels. The frequency-size statistics of earthquake occurrence show corresponding non-stationary characteristics on time scales over which negligible fluctuations are observed in the fixed- R case. The progressive evolution implies that,except for extreme weakening and healing rates,faults and fault networks possibly are not well characterized by steady states on typical catalogue time scales, thus highlighting the essential role of memory and history dependence in seismogenesis. The results suggest that an extrapolation to future seismicity occurrence based on temporally limited data may be misleading due to variability in seismicity patterns associated with competing mechanisms that affect fault stability. [source] Amazon drought and its implications for forest flammability and tree growth: a basin-wide analysisGLOBAL CHANGE BIOLOGY, Issue 5 2004Daniel Nepstad Abstract Severe drought in moist tropical forests provokes large carbon emissions by increasing forest flammability and tree mortality, and by suppressing tree growth. The frequency and severity of drought in the tropics may increase through stronger El Niño Southern Oscillation (ENSO) episodes, global warming, and rainfall inhibition by land use change. However, little is known about the spatial and temporal patterns of drought in moist tropical forests, and the complex relationships between patterns of drought and forest fire regimes, tree mortality, and productivity. We present a simple geographic information system soil water balance model, called RisQue (Risco de Queimada , Fire Risk) for the Amazon basin that we use to conduct an analysis of these patterns for 1996,2001. RisQue features a map of maximum plant-available soil water (PAWmax) developed using 1565 soil texture profiles and empirical relationships between soil texture and critical soil water parameters. PAW is depleted by monthly evapotranspiration (ET) fields estimated using the Penman,Monteith equation and satellite-derived radiation inputs and recharged by monthly rain fields estimated from 266 meteorological stations. Modeled PAW to 10 m depth (PAW10 m) was similar to field measurements made in two Amazon forests. During the severe drought of 2001, PAW10 m fell to below 25% of PAWmax in 31% of the region's forests and fell below 50% PAWmax in half of the forests. Field measurements and experimental forest fires indicate that soil moisture depletion below 25% PAWmax corresponds to a reduction in leaf area index of approximately 25%, increasing forest flammability. Hence, approximately one-third of Amazon forests became susceptible to fire during the 2001 ENSO period. Field measurements also suggest that the ENSO drought of 2001 reduced carbon storage by approximately 0.2 Pg relative to years without severe soil moisture deficits. RisQue is sensitive to spin-up time, rooting depth, and errors in ET estimates. Improvements in our ability to accurately model soil moisture content of Amazon forests will depend upon better understanding of forest rooting depths, which can extend to beyond 15 m. RisQue provides a tool for early detection of forest fire risk. [source] Vegetation structure characteristics and relationships of Kalahari woodlands and savannasGLOBAL CHANGE BIOLOGY, Issue 3 2004J.L. Privette Abstract The Kalahari Transect is one of several International Geosphere,Biosphere Programme (IGBP) transects designed to address global change questions at the regional scale, in particular by exploiting natural parameter gradients (Koch et al., 1995). In March 2000, we collected near-synoptic vegetation structural data at five sites spanning the Kalahari's large precipitation gradient (about 300,1000 mm yr,1) from southern Botswana (,24°S) to Zambia (,15°S). All sites were within the expansive Kalahari sandsheet. Common parameters, including plant area index (PAI), leaf area index (LAI) and canopy cover (CC), were measured or derived using several indirect instruments and at multiple spatial scales. Results show that CC and PAI increase with increasing mean annual precipitation. Canopy clumping, defined by the deviation of the gap size distribution from that of randomly distributed foliage, was fairly constant along the gradient. We provide empirical relationships relating these parameters to each other and to precipitation. These results, combined with those in companion Kalahari Transect studies, provide a unique and coherent test bed for ecological modeling. The data may be used to parameterize process models, as well as test internally predicted parameters and their variability in response to well-characterized climatological differences. [source] The relationships between local and regional species richness and spatial turnoverGLOBAL ECOLOGY, Issue 5 2002Patricia Koleff Abstract Aim To determine the empirical relationships between species richness and spatial turnover in species composition across spatial scales. These have remained little explored despite the fact that such relationships are fundamental to understanding spatial diversity patterns. Location South-east Scotland. Methods Defining local species richness simply as the total number of species at a finer resolution than regional species richness and spatial turnover as turnover in species identity between any two or more areas, we determined the empirical relationships between all three, and the influence of spatial scale upon them, using data on breeding bird distributions. We estimated spatial turnover using a measure independent of species richness gradients, a fundamental feature which has been neglected in theoretical studies. Results Local species richness and spatial turnover exhibited a negative relationship, which became stronger as larger neighbourhood sizes were considered in estimating the latter. Spatial turnover and regional species richness did not show any significant relationship, suggesting that spatial species replacement occurs independently of the size of the regional species pool. Local and regional species richness only showed the expected positive relationship when the size of the local scale was relatively large in relation to the regional scale. Conclusions Explanations for the relationships between spatial turnover and local and regional species richness can be found in the spatial patterns of species commonality, gain and loss between areas. [source] Simultaneous estimation of diffusive Volatile Organic Compound (VOC) fluxes and Non-Aqueous Phase Liquid (NAPL) saturation in the vadose zoneGROUND WATER MONITORING & REMEDIATION, Issue 2 2005David Werner Soil-gas monitoring is a widely used tool to observe the migration of volatile organic compounds (VOCs) at contaminated sites. By combining this technique with natural gradient tracer methods, diffusive contaminant fluxes can be measured in situ, and non,aqueous phase liquid (NAPL) can be detected and roughly quantified. This work describes the new approach and its application at a field site in Denmark with an emplaced NAPL contamination. Soil-gas probes with a low dead volume were installed at 1-m depths in the sandy vadose zone, and a small volume of gas containing conservative and partitioning tracers was injected. Soil-gas samples were withdrawn subsequently during 1 to 4 h and analyzed simultaneously for VOCs and tracers. Tracers detected the NAPL reliably, and the combined data allowed for a close delineation of the source zone. The calculated NAPL saturation deviated by up to a factor of 3 from the analyses of soil cores. Better agreement was found by taking the NAPL composition into consideration, which is, however, generally unknown at the actual field sites. In addition, the tracers were also used to estimate effective diffusion coefficients in situ, which varied by a factor of 2 between various locations. From these data, diffusive contaminant vapor fluxes were quantified without additional laboratory experiments or the use of empirical relationships. The new approach yields a better site investigation with a few additional measurements. [source] On morphometric properties of basins, scale effects and hydrological responseHYDROLOGICAL PROCESSES, Issue 1 2003Roger Moussa Abstract One of the important problems in hydrology is the quantitative description of river system structure and the identification of relationships between geomorphological properties and hydrological response. Digital elevation models (DEMs) generally are used to delineate the basin's limits and to extract the channel network considering pixels draining an area greater than a threshold area S. In this paper, new catchment shape descriptors, the geometric characteristics of an equivalent ellipse that has the same centre of gravity, the same principal inertia axes, the same area and the same ratio of minimal inertia moment to maximal inertia moment as the basin, are proposed. They are applied in order to compare and classify the structure of seven basins located in southern France. These descriptors were correlated to hydrological properties of the basins' responses such as the lag time and the maximum amplitude of a geomorphological unit hydrograph calculated at the basin outlet by routing an impulse function through the channel network using the diffusive wave model. Then, we analysed the effects of the threshold area S on the topological structure of the channel network and on the evolution of the source catchment's shape. Simple models based on empirical relationships between the threshold S and the morphometric properties were established and new catchment shape indexes, independent of the observation scale S, were defined. This methodology is useful for geomorphologists dealing with the shape of source basins and for hydrologists dealing with the problem of scale effects on basin topology and on relationships between the basin morphometric properties and the hydrological response. Copyright © 2002 John Wiley & Sons, Ltd. [source] Design and operation of unbaffled aerated agitated vessels with unsteadily forward,reverse rotating impellers handling viscous Newtonian liquidsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2003Masanori Yoshida Abstract Design and operation of unbaffled aerated agitated vessels with multiple unsteadily forward,reverse rotating impellers (AJITERs) for viscous Newtonian liquids were studied. The effects of operating conditions such as gas sparging rate, agitation rate and the number of impeller stages, geometrical conditions such as the diameters of vessel and impeller, and the physical properties of liquids on the drag and added moment of inertia coefficients, necessary to predict the average and maximum power consumptions of the impellers in AJITERs, were evaluated and the empirical relationships which estimate values of each of these coefficients are presented. The effects of operating conditions, geometrical conditions and liquid physical properties on the gas hold-up, ,gD, and volumetric oxygen transfer coefficient, kLaD, were evaluated in relation to the total power input which is the sum of the average power consumption of impellers, ie average agitation power input, and aeration power input. Empirical relationships, useful for design and operation of AJITERs, were obtained for each viscosity range, where the dependences of ,gD and kLaD on the specific total power input and superficial gas velocity differed, to predict ,gD and kLaD respectively as a function of the specific total power input, superficial gas velocity and liquid physical properties. © 2003 Society of Chemical Industry [source] Deliberation Quality: A Preliminary Examination in Criminal JuriesJOURNAL OF EMPIRICAL LEGAL STUDIES, Issue 2 2007Dennis J. Devine Large-scale studies of the deliberation process in actual juries have been surprisingly rare, and relatively little attention has been devoted to how well juries deliberate. This study identified a set of process-related criteria relevant to the quality of criminal jury deliberations and examined empirical relationships between indicators of these criteria and jury verdicts. Data were obtained via posttrial surveys from jurors and legal professionals associated with 179 criminal jury trials in Indiana. The quality of deliberations varied across the process criteria, with juries reportedly doing fairly well in terms of understanding their instructions and reviewing the evidence, but not as well with regard to systematically gathering input from their members, adopting an evidence-driven deliberation style, and avoiding factionalism. Several deliberation variables were also strongly related to jury verdicts, particularly the foreperson's initial verdict stance and the emergence of an identifiable pro-acquittal faction leader. Discussion of reasonable doubt and thoroughness of evidence review also tended to be negatively correlated with conviction even when strength of evidence was controlled. This study calls attention to the importance of deliberation quality. [source] Predicting Root Density in Streambanks,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2008Candice Piercy Abstract:, Roots of riparian vegetation increase streambank erosion resistance and structural stability; therefore, knowledge of root density and distribution in streambanks is useful for stream management and restoration. The objective of this study was to compare streambank root distributions for herbaceous and woody vegetation and to develop empirical models to predict root density. Root length density, root volume ratio, soil physical and chemical properties, and above-ground vegetation densities were measured at 25 sites on six streams in southwestern Virginia. The Mann-Whitney test was used to determine differences in root density along stream segments dominated by either woody or herbaceous vegetation. Multiple linear regression was used to develop relationships between root density and site characteristics. Study results showed that roots were evenly distributed across the bank face with the majority of roots having diameters less than 2 mm. Soil bulk density and above-ground vegetation were key factors influencing root density. While significant relationships were developed to predict root density, the predictive capabilities of the equations was low. Because of the highly variable nature of soil and vegetation properties, it is recommended at this time that soil erodibility and root density be measured in the field for design and modeling purposes, rather than estimated based on empirical relationships. [source] Stream Temperature Surges Under Urbanization and Climate Change: Data, Models, and Responses,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2007Kären C. Nelson ABSTRACT: Multiple anthropogenic stressors, including increased watershed imperviousness, destruction of the riparian vegetation, increased siltation, and changes in climate, will impact streams over the coming century. These stressors will alter water temperature, thus influencing ecological processes and stream biota. Quantitative tools are needed to predict the magnitude and direction of altered thermal regimes. Here, empirical relationships were derived to complement a simple model of in-stream temperature [developed by Caissie et al. Canadian Journal of Civil Engineering25 (1998) 250; Journal of Hydrology251 (2001) 14], including seasonal temperature shifts linked to land use, and temperature surges linked to localized rainstorms; surges in temperature averaged about 3.5°C and dissipated over about 3 h. These temperature surges occurred frequently at the most urbanized sites (up to 10% of summer days) and could briefly increase maximum temperature by >7°C. The combination of empirical relationships and model show that headwater streams may be more pervasively impacted by urbanization than by climate change, although the two stressors reinforce each other. A profound community shift, from common cold and coolwater species to some of the many warmwater species currently present in smaller numbers, may be expected, as shown by a count of days on which temperature exceeds the "good growth" range for coldwater species. [source] PREDICTION OF LOCAL SCOUR AROUND BRIDGE PIERS USING ARTIFICIAL NEURAL NETWORKS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2006Sung-Uk Choi ABSTRACT: This paper describes a method for predicting local scour around bridge piers using an artificial neural network (ANN). Methods for selecting input variables, calibrations of network control parameters, learning process, and verifications are also discussed. The ANN model trained by laboratory data is applied to both laboratory and field measurements. The results illustrate that the ANN model can be used to predict local scour in the laboratories and in the field better than other empirical relationships that are currently in use. A parameter study is also carried out to investigate the importance of each input variable as reflected in data. [source] What Determines Rule of Law?KYKLOS INTERNATIONAL REVIEW OF SOCIAL SCIENCES, Issue 3 2009An Empirical Investigation of Rival Models SUMMARY In the growing literature on the creation of institutions, the theories emphasizing colonial origin (Mauro, 1995), legal origin and religious affiliation (La Porta et al., 1999), Western European influence (Hall and Jones, 1999), and settler mortality (Acemoglu et al., 2001), have been especially influential. The validity and influence of these studies rests heavily on empirical modeling, which, since the theories are obviously closely related, might actually capture the same primary mechanism. It is therefore unclear whether the empirical relationships found are the same or if they are different. Therefore, this paper takes the empirical models seriously in order to discriminate among the existing models and to identify the model and variables that best explain the variation in institutional quality. The aim of this paper is thus to provide answers to the following questions: (i) Is there one model which explains more of the variation in institutional quality than the other models? (ii) Do these models capture the same information? And (iii), if we let the information in the data decide, which combination of variables would be selected? [source] Thermodynamic and spectroscopic study of the binding of dimethyltin(IV) by citrate at 25 °CAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2006Paola Cardiano Abstract Thermodynamic (potentiometric and calorimetric) and spectroscopic (1H NMR, 119Sn Mössbauer) studies were performed in aqueous solution in order to characterize the interaction of dimethyltin(IV) cation with citrate ligand. Six species {(CH3)2Sn(cit),; [(CH3)2Sn]2(cit)22,; (CH3)2Sn(cit)H0; (CH3)2Sn(cit)OH2,; [(CH3)2Sn]2(cit)OH0; [(CH3)2Sn]2(cit)(OH)2,} were found. All the species formed in this system are quite stable and formation percentages are fairly high. For example, at pH = 7.5 and C = Ccit = 10 mmol l,1, ,% for [(CH3)2Sn]2(cit)(OH)2, and (CH3)2Sn(cit)OH2, species reaches 65%. Overall thermodynamic parameters obtained show that the main contribution to stability is entropic in nature. Thermodynamic parameters were discussed in comparison with a simple tricarboxylate ligand (1,2,3-propanetricarboxylate). Two empirical relationships were derived from thermodynamic formation parameters. Spectroscopic results fully confirm the speciation model defined potentiometrically and show the mononuclear species to have an eq-(CH3)2Tbp structure with different arrangements around the metal, while for [(CH3)2Sn]2(cit)(OH)2, there are two different Sn(IV) environments, namely trans -(CH3)2 octahedral and cis -(CH3)2 Tbp. Copyright © 2005 John Wiley & Sons, Ltd. [source] Soil fertility, heterogeneity, and microbes: towards an integrated understanding of grassland structure and dynamicsAPPLIED VEGETATION SCIENCE, Issue 1 2009Heather L. Reynolds Abstract Objective: To highlight the need and the potential for an integrated understanding of three key soil-based drivers of plant community structure and dynamics , soil fertility, soil heterogeneity, and microbes. Location: European and North American grasslands. Methods: Review and discussion of conceptual models and empirical literature, including examples of observational and manipulative studies from both natural and restored grassland communities. Results and Conclusions: In general, the results of empirical studies on soil fertility, soil heterogeneity, and soil microbes in grassland communities do not support expectations of common conceptual models. Ecological theory assumes a unimodal relationship between soil fertility and plant community diversity, yet empirical relationships from grassland communities are variable, the mechanisms underlying these variable patterns are not yet well understood, and there is mixed success at manipulating soil fertility to facilitate restorations. While theory predicts that increased soil heterogeneity will lead to increased plant community diversity, results of experimental manipulations of soil heterogeneity often show the opposite. Of two major conceptual models proposed for how microbes structure plant communities, there is little support for the hypothesis of microbially mediated niche partitioning. Plant-microbe feedbacks do have significant empirical support to date and there is increasing application of positive feedback dynamics in restoration, yet field tests of feedback dynamics remain limited. We suggest that an understanding of interactions between these soil drivers may help to resolve discrepancies between conceptual models and empirical results, improving our understanding of grasslands and our ability to restore them. [source] Parametric Study of Blade Tip Clearance, Flow Rate, and Impeller Speed on Blood Damage in Rotary Blood PumpARTIFICIAL ORGANS, Issue 6 2009Nahn Ju Kim Abstract Phenomenological studies on mechanical hemolysis in rotary blood pumps have provided empirical relationships that predict hemoglobin release as an exponential function of shear rate and time. However, these relations are not universally valid in all flow circumstances, particularly in small gap clearances. The experiments in this study were conducted at multiple operating points based on flow rate, impeller speed, and tip gap clearance. Fresh bovine red blood cells were resuspended in phosphate-buffered saline at about 30% hematocrit, and circulated for 30 min in a centrifugal blood pump with a variable tip gap, designed specifically for these studies. Blood damage indices were found to increase with increased impeller speed or decreased flow rate. The hemolysis index for 50-µm tip gap was found to be less than 200-µm gap, despite increased shear rate. This is explained by a cell screening effect that prevents cells from entering the smaller gap. It is suggested that these parameters should be reflected in the hemolysis model not only for the design, but for the practical use of rotary blood pumps, and that further investigation is needed to explore other possible factors contributing to hemolysis. [source] | ||||||||||||||||||||||