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Empirical Models (empirical + models)
Kinds of Empirical Models Selected AbstractsEmpirical Models and Policy-Making: Interaction and InstitutionsECONOMICA, Issue 286 2005Ruud A. De Mooij No abstract is available for this article. [source] Effects of Fiber Architecture on Matrix Cracking for Melt-Infiltrated SiC/SiC CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010Gregory N. Morscher The matrix cracking behavior of slurry cast melt-infiltrated SiC matrix composites consisting of Sylramic-iBN fibers with a wide variety of fiber architectures were compared. The fiber architectures included 2D woven, braided, 3D orthogonal, and angle interlock architectures. Acoustic emission was used to monitor in-plane matrix cracking during unload,reload tensile tests. Two key parameters were found to control matrix-cracking behavior: the fiber volume fraction in the loading direction and the area of the weakest portion of the structure, that is, the largest tow in the architecture perpendicular to the loading direction. Empirical models that support these results are presented and discussed. [source] Empirical models of UV total radiation and cloud effect studyINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2010David Mateos Villán Abstract Several empirical models of hourly ultraviolet total radiation (UVT) have been proposed in this study. Measurements of UVT radiation, 290,385 nm, have been recorded at ground level from February 2001 to June 2008 in Valladolid, Spain (latitude 41°40,N, longitude 4°50,W and 840 m a.s.l.). The empirical models have emerged due to the lack of some radiometric variables in measuring stations. Hence, good forecasts of them can be obtained from usual measures in these stations. Therefore, some advantages of the empirical models are that they allow the estimation of past missing data in the database and the forecast of future ultraviolet solar availability. In this study, reported models in the bibliography have been assessed and recalibrated. New expressions have been proposed that allow obtaining hourly values of ultraviolet radiation from global radiation measures and parameters as clearness index and relative optical air mass. The accuracy of these models has been assessed through the following statistical indices: mean bias, mean-absolute bias and root-mean-square errors whose values are close to zero, below 7% and below 10%, respectively. Two new clear sky models have been used to evaluate two new parameters: ultraviolet and global cloud modification factors, which can help to understand the role of the clouds on solar radiation. The ultraviolet cloud modification factor depends on cloudiness in such a way that its value under overcast skies is half of the cloudless skies one. Exponential and potential fits are the best relationships between both cloud factors. Finally, these parameters have been used to build new UV empirical models which show low values of the statistical indices mentioned above. Copyright © 2009 Royal Meteorological Society [source] Investigation of Pluronic© F127,Water solutions phase transitions by DSC and dielectric spectroscopyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009Anna Angela Barba Abstract The water solutions of the block copolymers PEOn -PPOm -PEOn, known as pluronics, show a complex thermal behavior, since they are liquid at low temperature (5°C), and they can give soft gel when heated at body temperature (37°C). These properties are of great interest in biomedical applications. To properly design these applications, a prerequisite is the knowledge of the thermodynamics,how much,and of the kinetics,how fast,with which these transformations take place. In this work, solutions of F127 (the copolymer for which n = 100 and m = 65) were studied by varying the concentration and the temperature and analyzing their behavior when heated under several heating rates. The studies were performed by differential scanning calorimetry (DCS) and dielectric spectroscopy. The investigations carried out under equilibrium conditions allowed us to determine the thermodynamics of the phase transitions, whereas the investigations carried out under varying conditions allowed us to quantify the kinetics of the phase transitions. Empirical models were also proposed to describe both the thermodynamics and the kinetics observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Disinfection of recycled red-meat-processing wastewater by ozoneJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2005Jiangning Wu Abstract Ozonation of a real red-meat-processing wastewater was conducted in a semi-batch reactor to explore the possibility of the water reuse. The experimental results revealed that ozone was very effective in disinfection of the red-meat-processing wastewater. After 8 min of ozonation with an applied ozone dose of 23.09 mg min,1 liter,1 of wastewater, 99% of aerobic bacteria, total coliforms and Escherichiacoli were inactivated. Empirical models were developed to predict the microbial inactivation efficacy of ozone from the CT values for the real red-meat-processing wastewater. A correlation was also derived to estimate the CT values from the applied ozone dose and the ozone contact time. The results also revealed that under the ozonation condition for 99% inactivation of aerobic bacteria, total coliforms and E coli, the decrease in the chemical oxygen demand and the 5-day biological oxygen demand of the wastewater were 10.7% and 23.6%, respectively. However, ozonation under this condition neither improved the light transmission nor reduced the total suspended solids (TSS) despite of the decolorization of the wastewater after ozonation. Copyright © 2005 Society of Chemical Industry [source] Detachment of sprayed colloidal copper oxychloride,metalaxyl fungicides by a shallow water flowPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 6 2009Eva Pose-Juan Abstract BACKGROUND: Flow shear stress induced by rainfall promotes the loss of the pesticides sprayed on crops. Some of the factors influencing the losses of colloidal-size particulate fungicides are quantified by using a rotating shear system model. With this device it was possible to analyse the flow shear influencing washoff of a commercial fungicide formulation based on a copper oxychloride,metalaxyl mixture that was sprayed on a polypropylene surface. A factor plan with four variables, i.e. water speed and volume (both variables determining flow boundary stress in the shear device), formulation dosage and drying temperature, was set up to monitor colloid detachment. RESULTS: This experimental design, together with sorption experiments of metalaxyl on copper oxychloride, and the study of the dynamics of metalaxyl and copper oxychloride washoff, made it possible to prove that metalaxyl washoff from a polypropylene surface is controlled by transport in solution, whereas that of copper oxychloride occurs by particle detachment and transport of particles. Average losses for metalaxyl and copper oxychloride were, respectively, 29 and 50% of the quantity applied at the usual recommended dosage for crops. CONCLUSION: The key factors affecting losses were flow shear and the applied dosage. Empirical models using these factors provided good estimates of the percentage of fungicide loss. From the factor analysis, the main mechanism for metalaxyl loss induced by a shallow water flow is solubilisation, whereas copper loss is controlled by erosion of copper oxychloride particles. Copyright © 2009 Society of Chemical Industry [source] Access to Land, Rural Development and Public Action: The When and the HowDEVELOPMENT POLICY REVIEW, Issue 1 2009Pablo Bandeira After being marginalised in the 1980s, land-reform policies came back to national and international development agendas during the 1990s, resulting in a revival of academic research on the subject. This article reviews the empirical literature on access to land, rural development and public action for evidence on when and how the state should intervene in the allocation of rural land. The review suggests that positive impacts are obtained if, and only if, public actions on the allocation of land are carried out under certain conditions and in a certain way. The article ends by highlighting the need to elaborate empirical models that take into consideration opportunity costs and interactions, and that integrate individual responses with aggregate effects. [source] An attenuation model for distant earthquakesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2004Adrian Chandler Abstract Large magnitude earthquakes generated at source,site distances exceeding 100km are typified by low-frequency (long-period) seismic waves. Such induced ground shaking can be disproportionately destructive due to its high displacement, and possibly high velocity, shaking characteristics. Distant earthquakes represent a potentially significant safety hazard in certain low and moderate seismic regions where seismic activity is governed by major distant sources as opposed to nearby (regional) background sources. Examples are parts of the Indian sub-continent, Eastern China and Indo-China. The majority of ground motion attenuation relationships currently available for applications in active seismic regions may not be suitable for handling long-distance attenuation, since the significance of distant earthquakes is mainly confined to certain low to moderate seismicity regions. Thus, the effects of distant earthquakes are often not accurately represented by conventional empirical models which were typically developed from curve-fitting earthquake strong-motion data from active seismic regions. Numerous well-known existing attenuation relationships are evaluated in this paper, to highlight their limitations in long-distance applications. In contrast, basic seismological parameters such as the Quality factor (Q -factor) could provide a far more accurate representation for the distant attenuation behaviour of a region, but such information is seldom used by engineers in any direct manner. The aim of this paper is to develop a set of relationships that provide a convenient link between the seismological Q -factor (amongst other factors) and response spectrum attenuation. The use of Q as an input parameter to the proposed model enables valuable local seismological information to be incorporated directly into response spectrum predictions. The application of this new modelling approach is demonstrated by examples based on the Chi-Chi earthquake (Taiwan and South China), Gujarat earthquake (Northwest India), Nisqually earthquake (region surrounding Seattle) and Sumatran-fault earthquake (recorded in Singapore). Field recordings have been obtained from these events for comparison with the proposed model. The accuracy of the stochastic simulations and the regression analysis have been confirmed by comparisons between the model calculations and the actual field observations. It is emphasized that obtaining representative estimates for Q for input into the model is equally important.Thus, this paper forms part of the long-term objective of the authors to develop more effective communications across the engineering and seismological disciplines. Copyright © 2003 John Wiley & Sons, Ltd. [source] An Evaluation of the Cod Fishing Policies of Denmark Iceland and NorwayEUROCHOICES, Issue 3 2004R. Arnason Summary An Evaluation of the Cod Fishing Policies of Denmark, Iceland and Norway Many ocean fisheries are subject to a fundamental economic problem generally referred to as the common property problem. This problem manifests itself as excessive fishing fleets and fishing effort, depressed fish stocks and little or no profitability of the fishing activity, irrespective of the richness of the underlying marine resources. European fisheries represent some of the most dramatic examples of the common property problem. This article employs simple empirical models and recently developed mathematical techniques to examine the economic efficiency of three European fisheries, namely the Danish, Icelandic and Norwegian cod fisheries, The optimal harvesting policies for each of these fisheries are calculated. Comparing these optimal policies with actual harvests provides a measure of the relative efficiency in these three cod fisheries. The comparison confirms the widely held impression that the cod harvesting policies of ail three countries have been hugely inefficient in the past. Moreover, it appears that the inefficiency has been increasing over time. Only during the last few years of our data are there indications that this negative trend may have been halted. Somewhat more surprisingly, in spite of radically different fisheries management systems, we find relatively little difference in the level of stock over-exploitation between these three countries. Politiques compareées de pêhe à la morue au Danemark, en Islande et en Norvège Beaucoup de pêcheries océaniques sont confrontées au problème nique fondamental de la "propriété collective". Celui-ci se manifeste par des flottes de taille excessive, au service d' efforts de péche exagérés, qui aboutissent à détruire les stocks de poisson et la rentabilité des pécheries, en dépit de la richesse des ressources marines sousjacentes. Les pêcheries européennes constituent actuellement l'un des exemples les plus dramatiques des problèmes associés a la propriété collective. On présente ici un modèle empirique assez simple mais associéà de nouvelles techniques mathématiques récemment développé es pour mesurer l' efficacitééconomique de trois types de politiques de pêche à la morue, au Danemark, en Norvège et en Islande. On commence par calculer le volume optimal des prises pour chacun de ces pays. La comparaison entre le niveau optimal et le niveau réel des prises permet de mesurer le degré d' efficacité des politiques suivies. Elle permet de confirmer l'opinion largement répandue selon laquelle les politiques passées ont été extrêmement peu efficaces. En outre, il apparaît que l'inefficacité est croissante avec le temps. C'est seulement dans les toutes dernières années des séries de données que l' on observe un infléchissement de cette tendance négative. Enfin, et c'est le plus surprenant, on trouve peu de differences entre les trois pays en ce qui conceme le degré de surexploitation du stock, et cela, bien que les principes de gestion des pêcheries y soient entiArement différents. Eine Bewertung der Kabeljaufischereipolitik in Dänemark, Island und Norwegen ahlreiche Hochseefischereien tehen einem grundlegenden ftliehen Problem gegenüber, das allgemein als Problem des kollektiven Eigentums bezeichnet wird. Dieses Problem zeigt sich in übermäßig großen Fangflotten und beträchtlichem Fischereiaufwand, geschrumpften Fischbeständen und geringer oder fehlender Rentabilität der Fischerei; dabei ist die Höhe der Fischressourcen unbedeutend für das Problem. Die europäischen Fischereien stellen einige der drastischsten Beispiele für das Problem des kollektiven Eigentums dar. In diesem Beitrag werden einfache empirische Modelle und kürzlich entwickelte mathematische Verfahren angewendet, um die wirtschaftliche Effizienz von drei europäischen Fischereien zu untersuchem der dänischen, der isländischen und der norwegischen Kabeljaufischerei. Für jede dieser Fischereien wird die optimale Nutzungsstrategie berechnet. Aus dem Vergleich dieser optimalen Nutzungsstrategie mit den tatsächlichen Erträgen ergibt sich ein Maß fur die relative Effizienz, die bei diesen drei Kabeljaufischereien vorliegt. Der Vergleich bestätigt den weit verbreiteten Eindruck, dass die Strategien zum Kabeljaufang in alien drei Ländern in der Vergangenheit enorm ineffizient waren. Darüber hinaus wird deutlich, dass die Ineffizienz im Laufe der Zeit zugenommen hat. Lediglich die Daten der letzten jahre enthalten Hinweise darauf, dass dieser negative Trend zum Stillstand gekommen sein könnte. Obwohl sich die Fischwirtschaft in jedem dieser drei Länder sehr stark unterscheidet, lassen sich erstaunlich wenige Unterschiede im Maß der Übernutzung des Fischbestandes finden. [source] Partitioning of metals (Cd, Co, Cu, Ni, Pb, Zn) in soils: concepts, methodologies, prediction and applications , a reviewEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009F. Degryse Summary Prediction of the fate of metals in soil requires knowledge of their solid,liquid partitioning. This paper reviews analytical methods and models for measuring or predicting the solid,liquid partitioning of metals in aerobic soils, and collates experimental data. The partitioning is often expressed with an empirical distribution coefficient or Kd, which gives the ratio of the concentration in the solid phase to that in the solution phase. The Kd value of a metal reflects the net effect of various reactions in the solid and liquid phases and varies by orders of magnitude among soils. The Kd value can be derived from the solid,liquid distribution of added metal or that of the soil-borne metal. Only part of the solid-phase metal is rapidly exchangeable with the solution phase. Various methods have been developed to quantify this ,labile' phase, and Kd values based on this phase often correlate better with soil properties than Kd values based on total concentration, and are more appropriate to express metal ion buffering in solute transport models. The in situ soil solution is the preferred solution phase for Kd determinations. Alternatively, water or dilute-salt extracts can be used, but these may underestimate in situ concentrations of dissolved metals because of dilution of metal-complexing ligands such as dissolved organic matter. Multi-surface models and empirical models have been proposed to predict metal partitioning from soil properties. Though soil pH is the most important soil property determining the retention of the free metal ion, Kd values based on total dissolved metal in solution may show little pH dependence for metal ions that have strong affinity for dissolved organic matter. The Kd coefficient is used as an equilibrium constant in risk assessment models. However, slow dissociation of metal complexes in solution and slow exchange of metals between labile and non-labile pools in the solid phase may invalidate this equilibrium assumption. [source] Spatial variation of ammonia volatilization from soil and its scale-dependent correlation with soil propertiesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2008R. Corstanje Summary Quantitative predictions of ammonia volatilization from soil are useful to environmental managers and policy makers and empirical models have been used with some success. Spatial analysis of the soil properties and their relationship to the ammonia volatilization process is important as predictions will be required at disparate scales from the field to the catchment and beyond. These relationships are known to change across scales and this may affect the performance of an empirical model. This study is concerned with the variation of ammonia volatilization and some controlling soil properties: bulk density, volumetric water content, pH, CEC, soil pH buffer power, and urease activity, over distances of 2, 50, 500, and >2000 m. We sampled a 16 km × 16 km region in eastern England and analyzed the results by a nested analysis of (co)variance, from which variance components and correlations for each scale were obtained. The overall correlations between ammonia volatilization and the soil properties were generally weak: ,0.09 for bulk density, 0.04 for volumetric water content, ,0.22 for CEC, ,0.08 for urease activity, ,0.22 for pH and 0.18 for the soil pH buffer power. Variation in ammonia volatilization was scale-dependent, with substantial variance components at the 2- and 500-m scales. The results from the analysis of covariance show that the relationships between ammonia volatilization and soil properties are complex. At the >2000 m scale, ammonia volatilization was strongly correlated with pH (,0.82) and CEC (,0.55), which is probably the result of differences in parent material. We also observed weaker correlations at the 500-m scale with bulk density (,0.61), volumetric water content (0.48), urease activity (,0.42), pH (,0.55) and soil pH buffer power (0.38). Nested analysis showed that overall correlations may mask relationships at scales of interest and the effect of soil variables on these soil processes is scale-dependent. [source] Determination of moisture content in a deformable soil using time-domain reflectometry (TDR)EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2000D. J. Kim Summary Time-domain reflectometry (TDR) is being used increasingly for measuring the moisture content of porous media. However, successful application for measuring water in soil has been limited to non-deformable soils, and it would be a valuable extension of the technique if it could be used for soils that shrink on drying. We have recently investigated its application to soils rich in clay and organic matter and peats. Here we propose a method for determining moisture content in deformable soils based on the relation between the dielectric constant, K, and the volumetric moisture content, ,, measured by TDR. Parallel TDR probes with a length of 15 cm and a spacing of 2 cm were placed horizontally in soil cores with a diameter of 20 cm and height of 10 cm taken from a forest. The soil is very porous with large proportions of both silt and clay. The sample weight and travel time of the electromagnetic wave guided by parallel TDR probes were simultaneously measured as a function of time, from saturation to oven-dryness during which the core samples shrank considerably. Vertical and horizontal components of shrinkage were also measured to take the air-exposed region of TDR probe into account in the determination of K. The effect of deformation on volumetric moisture content was formulated for two different expressions, namely actual volumetric moisture content (AVMC) and fictitious (uncorrected) volumetric moisture content (FVMC). The effects of air-exposure and expressions of volumetric moisture content on the relation between K and, were examined by fitting the observations with a third-order polynomial. Neglecting the travel time in the air-exposed part or use of the FVMC underestimated the , for a given K. The difference was more pronounced between AVMC and FVMC than between two different dielectric constants, i.e. accounting for air-exposure, Kac, and not accounting for air-exposure, Kau. When the existing empirical models were compared with the fitted results, most underestimated the relation based on the AVMC. This indicates that published empirical models do not reflect the effect of deformation on the determination of , in our forest soil. Correct use of the , expression has more impact on determining moisture content of a deformable soil than the accommodation of travel time through the air-exposed region of TDR probe. [source] Model complexity versus scatter in fatigueFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 11 2004T. SVENSSON ABSTRACT Fatigue assessment in industry is often based on simple empirical models, such as the Wöhler curve or the Paris' law. In contrast, fatigue research to a great extent works with very complex models, far from the engineering practice. One explanation for this discrepancy is that the scatter in service fatigue obscures many of the subtle phenomena that can be studied in a laboratory. Here we use a statistical theory for stepwise regression to investigate the role of scatter in the choice of model complexity in fatigue. The results suggest that the amount of complexity used in different design concepts reflects the appreciated knowledge about input parameters. The analysis also points out that even qualitative knowledge about the neglected complexity may be important in order to avoid systematic errors. [source] Predicting the impacts of an introduced species from its invasion history: an empirical approach applied to zebra mussel invasionsFRESHWATER BIOLOGY, Issue 6 2003Anthony Ricciardi SUMMARY 1.,Quantitative models of impact are lacking for the vast majority of known invasive species, particularly in aquatic ecosystems. Consequently, managers lack predictive tools to help them prioritise invasion threats and decide where they can most effectively allocate limited resources. Predictive tools would also enhance the accuracy of water quality assessments, so that impacts caused by an invader are not erroneously attributed to other anthropogenic stressors. 2.,The invasion history of a species is a valuable guide for predicting the consequences of its introduction into a new environment. Regression analysis of data from multiple invaded sites can generate empirical models of impact, as is shown here for the zebra mussel Dreissena polymorpha. Dreissena's impacts on benthic invertebrate abundance and diversity follow predictable patterns that are robust across a range of habitat types and geographic regions. Similar empirical models could be developed for other invaders with a documented invasion history. 3.,Because an invader's impact is correlated with its abundance, a surrogate model may be generated (when impact data are unavailable) by relating the invader's abundance to environmental variables. Such a model could help anticipate which habitats will be most affected by invasion. Lack of precision should not be a deterrent to developing predictive models where none exist. Crude predictions can be refined as additional data become available. Empirical modelling is a highly informative and inexpensive, but underused, approach in the management of aquatic invasive species. [source] Competition Tests with a Non-Structural Model: the Panzar,Rosse Method Applied to Germany's Savings BanksGERMAN ECONOMIC REVIEW, Issue 1 2009Horst Gischer Banking; competition; market behaviour Abstract. In this paper we adopt the Panzar,Rosse approach to assess the competitive conditions in the German banking market for the period from 1993 to 2002. We suggest several improvements to the empirical application of the approach and show that frequently used empirical models that apply price rather than revenue functions lead to biased results. Using disaggregated annual data from more than 400 savings banks (Sparkassen) the empirical findings indicate monopolistic competition, the cases of monopoly and perfect competition are strongly rejected. Furthermore, small banks seem to enjoy even more market power than larger institutions. [source] Estimating annual N2O emissions from agricultural soils in temperate climatesGLOBAL CHANGE BIOLOGY, Issue 10 2005Caroline Roelandt Abstract The Kyoto protocol requires countries to provide national inventories for a list of greenhouse gases including N2O. A standard methodology proposed by the Intergovernmental Panel on Climate Change (IPCC) estimates direct N2O emissions from soils as a constant fraction (1.25%) of the nitrogen input. This approach is insensitive to environmental variability. A more dynamic approach is needed to establish reliable N2O emission inventories and to propose efficient mitigation strategies. The objective of this paper is to develop a model that allows the spatial and temporal variation in environmental conditions to be taken into account in national inventories of direct N2O emissions. Observed annual N2O emission rates are used to establish statistical relationships between N2O emissions, seasonal climate and nitrogen-fertilization rate. Two empirical models, MCROPS and MGRASS, were developed for croplands and grasslands. Validated with an independent data set, MCROPS shows that spring temperature and summer precipitation explain 35% of the variance in annual N2O emissions from croplands. In MGRASS, nitrogen-fertilization rate and winter temperature explain 48% of the variance in annual N2O emissions from grasslands. Using long-term climate observations (1900,2000), the sensitivity of the models with climate variability is estimated by comparing the year-to-year prediction of the model to the precision obtained during the validation process. MCROPS is able to capture interannual variability of N2O emissions from croplands. However, grassland emissions show very small interannual variations, which are too small to be detectable by MGRASS. MCROPS and MGRASS improve the statistical reliability of direct N2O emissions compared with the IPCC default methodology. Furthermore, the models can be used to estimate the effects of interannual variation in climate, climate change on direct N2O emissions from soils at the regional scale. [source] Contrasting soil respiration in young and old-growth ponderosa pine forestsGLOBAL CHANGE BIOLOGY, Issue 12 2002J. IRVINE Abstract Three years of fully automated and manual measurements of soil CO2 efflux, soil moisture and temperature were used to explore the diel, seasonal and inter-annual patterns of soil efflux in an old-growth (250-year-old, O site) and recently regenerating (14-year-old, Y site) ponderosa pine forest in central Oregon. The data were used in conjunction with empirical models to determine which variables could be used to predict soil efflux in forests of contrasting ages and disturbance histories. Both stands experienced similar meteorological conditions with moderately cold wet winters and hot dry summers. Soil CO2 efflux at both sites showed large inter-annual variability that could be attributed to soil moisture availability in the deeper soil horizons (O site) and the quantity of summer rainfall (Y site). Seasonal patterns of soil CO2 efflux at the O site showed a strong positive correlation between diel mean soil CO2 efflux and soil temperature at 64 cm depth whereas diel mean soil efflux at the Y site declined before maximum soil temperature occurred during summer drought. The use of diel mean soil temperature and soil water potential inferred from predawn foliage water potential measurements could account for 80% of the variance of diel mean soil efflux across 3 years at both sites, however, the functional shape of the soil water potential constraint was site-specific. Based on the similarity of the decomposition rates of litter and fine roots between sites, but greater productivity and amount of fine litter detritus available for decomposition at the O site, we would expect higher rates of soil CO2 efflux at the O site. However, annual rates were only higher at the O site in one of the 3 years (597 ± 45 vs. 427 ± 80 g C m,2). Seasonal patterns of soil efflux at both sites showed influences of soil water limitations that were also reflected in patterns of canopy stomatal conductance, suggesting strong linkages between above and below ground processes. [source] When is Commuting Desirable to the Individual?GROWTH AND CHANGE, Issue 3 2004David T. Ory ABSTRACT Commuting is popularly viewed as a stressful, costly, time-wasting experience from the individual perspective, with the attendant congestion imposing major social costs as well. However, several authors have noted that commuting can also offer benefits to the individual, serving as a valued transition between the home and work realms of personal life. Using survey data collected from about 1,300 commuting workers in three San Francisco Bay Area neighborhoods, empirical models are developed for four key variables measured for commute travel, namely: Objective Mobility, Subjective Mobility, Travel Liking, and Relative Desired Mobility. Explanatory variables include measures of general travel-related attitudes, personality traits, lifestyle priorities, and sociodemographic characteristics. Both descriptive statistics and analytical models indicate that commuting is not the unmitigated burden that it is widely perceived to be. About half of the sample were relatively satisfied with the amount they commute, with a small segment actually wanting to increase that amount. Both the psychological impact of commuting, and the amounts people want to commute relative to what they are doing now, are strongly influenced by their liking for commuting. An implication for policy is that some people may be more resistant than expected toward approaches intended to induce reductions in commuting (including, for example, telecommuting). New creativity may be needed to devise policies that recognize the inherent positive utility of travel, while trying to find socially beneficial ways to fulfill desires to maintain or increase travel. [source] A comprehensive approach to characterization of the nonlinearity of runoff in the headwaters of the Tarim River, western ChinaHYDROLOGICAL PROCESSES, Issue 2 2010Jianhua Xu Abstract Nonlinear characteristics of the runoff processes in the headwaters of the Tarim River were identified and evaluated using several selected methods, including wavelet analysis, correlation dimension, and R/S analysis. Time-series of annual data describing runoff, average temperature, and precipitation from 1957 to 2005 were used to construct and test empirical models. The primary findings of this study were as follows: (1) The annual runoff of the headwaters are complex and nonlinear in nature, and they each presented periodic, nonlinear trends at the chosen time scales, chaotic dynamics, and long-memory characteristics. (2) These nonlinear trends appeared to have resulted from the regional climatic changes that occurred during the study period. The periodicity of changes in runoff occurred on an approximately 25-year cycle, which appeared to be correlated with temperature and precipitation cycles. In addition, the annual runoff exhibited a significant, positive correlation with the temperature and precipitation factors at the 4-, 8-, 16-, and 32-year temporal scales. (3) The correlation dimensions of the attractor derived from the runoff time series for the Hotan, Yarkand, and Aksu rivers were all greater than 3·0 and non-integral, implying that all three rivers are dynamic chaotic systems that are sensitive to initial conditions, and that the dynamic modelling of their annual runoff requires at least four independent variables. (4) The computed Hurst exponents indicate that a long-term memory characteristic exists in the annual runoff processes. However, there were some differences observed, with the Aksu and Yarkand rivers demonstrating a persistent trait, and the Hotan River exhibiting an anti-persistent feature. Copyright © 2009 John Wiley & Sons, Ltd. [source] Empirical models of UV total radiation and cloud effect studyINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 9 2010David Mateos Villán Abstract Several empirical models of hourly ultraviolet total radiation (UVT) have been proposed in this study. Measurements of UVT radiation, 290,385 nm, have been recorded at ground level from February 2001 to June 2008 in Valladolid, Spain (latitude 41°40,N, longitude 4°50,W and 840 m a.s.l.). The empirical models have emerged due to the lack of some radiometric variables in measuring stations. Hence, good forecasts of them can be obtained from usual measures in these stations. Therefore, some advantages of the empirical models are that they allow the estimation of past missing data in the database and the forecast of future ultraviolet solar availability. In this study, reported models in the bibliography have been assessed and recalibrated. New expressions have been proposed that allow obtaining hourly values of ultraviolet radiation from global radiation measures and parameters as clearness index and relative optical air mass. The accuracy of these models has been assessed through the following statistical indices: mean bias, mean-absolute bias and root-mean-square errors whose values are close to zero, below 7% and below 10%, respectively. Two new clear sky models have been used to evaluate two new parameters: ultraviolet and global cloud modification factors, which can help to understand the role of the clouds on solar radiation. The ultraviolet cloud modification factor depends on cloudiness in such a way that its value under overcast skies is half of the cloudless skies one. Exponential and potential fits are the best relationships between both cloud factors. Finally, these parameters have been used to build new UV empirical models which show low values of the statistical indices mentioned above. Copyright © 2009 Royal Meteorological Society [source] Monetary policy analysis and inflation targeting in a small open economy: a VAR approach*JOURNAL OF APPLIED ECONOMETRICS, Issue 4 2001Tor Jacobson Empirical monetary policy research has increased in the last decade, possibly because deregulation and explicit monetary targets have made monetary policy issues more interesting. In particular, within the inflation targeting framework it has been argued that inflation forecasts can be used as optimal intermediate targets for monetary policy, and the development of empirical models that have good forecasting properties is therefore important. This paper shows that a VAR model with long-run restrictions, justified by economic theory, is useful for both forecasting inflation and for analysing other issues that are central to the conduct of monetary policy. Copyright © 2001 John Wiley & Sons, Ltd. [source] Effect of autumn and winter meteorological variables on spring aphid populations in the Po valley, Northern ItalyJOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2001D. Rongai Prediction of aphid populations is crucial to the successful application of control strategies. In previous studies clear relationships between aphid catches and meteorological variables were highlighted. The primary objective of this study was to quantify the effects of autumn and winter meteorological variables on the aphid species populations the following spring. The data on all the species caught at two Italian sites (Ozzano Emilia and Budrio) up to 31 May from 1992 to 1999 were used for this study. Different models were found according to the aphid biological cycle (i.e. holocycle, anholocycle, holo-anholocycle). A fourth group of minor species, designated as ,others', was properly modelled as holo-anholocycle species. A satisfactory fit was observed when holocycle species were plotted against minimum temperature and precipitation in October, anholocycle species against minimum temperature and precipitation in December,January, holo-anholocycle species and ,others' against wind speed and number of frosty days in November, and minimum temperature and precipitation in December,January. Model response was more consistent at Budrio (open flat site) than at Ozzano Emilia (flat site delimited by a hill). A coherent pattern was found with an overall comparison of the estimates against observations. The possibility offered by these empirical models for forecasting spring aphid populations of all species at a given site is clearly of interest. This first study encouraged further investigation aimed at validating models before applying them in practice. [source] Tax Clientele Effects in the Term Structure of UK Interest RatesJOURNAL OF BUSINESS FINANCE & ACCOUNTING, Issue 3-4 2001Eric J. Levin This paper tests for tax clientele effects in the term structure of UK interest rates. Five empirical models of the term structure of interest rates, incorporating tax effects, are estimated with daily data covering the period 31 March, 1995 to 3 August, 1995. In May 1995, the British government announced its intention to eliminate the tax exemption on capital gains from government bonds, but subsequently in July 1995 backtracked on some of its initial proposals. This period therefore forms the basis of a crude natural experiment in the sense that it provides an opportunity to examine tax clientele effects ,before' and ,after' an event which should have levelled greatly the taxing of government bonds. The empirical analysis suggests large tax clientele effects. However, there is little evidence of tax-specific term structures of interest rates. [source] Econometric modelling of non-ferrous metal pricesJOURNAL OF ECONOMIC SURVEYS, Issue 5 2004Clinton Watkins Abstract., This article evaluates the significance of the empirical models and the distributional properties of prices in non-ferrous metal spots and futures markets published in leading refereed economics and finance journals between 1980 and 2002. The survey focuses on econometric analyses of pricing and return models applied to exchange-based spot and futures markets for the main industrially used non-ferrous metals, namely aluminium, copper, lead, nickel, tin and zinc. Published empirical research is evaluated in the light of the type of contract examined, frequency of data used, choice of both dependent and explanatory variables, use of proxy variables, type of model chosen, economic hypotheses tested, methods of estimation and calculation of SEs for inference, reported descriptive statistics, use of diagnostic tests of auxiliary assumptions, use of nested and non-nested tests, use of information criteria and empirical implications for non-ferrous metals. [source] Geographic Concentration and Increasing ReturnsJOURNAL OF ECONOMIC SURVEYS, Issue 5 2003Paolo Surico Abstract., Economic activities are highly clustered. Why is geographic concentration becoming a predominant feature of industrialized economies? On the basis of the empirical models developed by the new theories of international trade, our answer is that increasing returns are the driving force of economic geography in the US as well as in Europe. In so doing, we review several econometric methods proposed in the literature to separate and to test alternative theoretical paradigms. [source] DEHYDRATION CHARACTERISTICS OF PAPAYA (CARICA PUBENSCENS): DETERMINATION OF EQUILIBRIUM MOISTURE CONTENT AND DIFFUSION COEFFICIENTJOURNAL OF FOOD PROCESS ENGINEERING, Issue 5 2009R. LEMUS-MONDACA ABSTRACT This study determined the drying kinetics behavior of papaya at different temperatures (40, 50, 60, 70 and 80C). Desorption isotherms were determined at 5, 20 and 50C over a relative humidity range of 10,95%. The Guggenheim, Anderson and de Boer models were found to be suitable for description of the sorption data. The samples reached equilibrium moisture of 0.10 ± 0.01 g water/g dry matter. Fick's second law model was used to calculate the effective diffusivity (6.25,24.32 × 10 - 10 m2/s). In addition, experimental data were fitted by means of seven mathematical models. The kinetic parameters and the diffusion coefficient were temperature-dependent and were evaluated by an Arrhenius-type equation. The modified Page model obtained the best-fit quality on experimental data according to statistical tests applied. PRACTICAL APPLICATIONS The main utility of this study is the application of both different empirical models and the diffusional model in tropical fruits' dehydration, which can be considered a basis for a very accurate estimation of drying time and the optimization of the same process. Two newly mathematical models are proposed in this study, through which a good fit on the data of experimental moisture content was achieved. The study of drying of papaya cultivated in Chile engages a great technological interest, because this product is widely used in the development of different products such as candying, canning, juice, syrup and marmalade. In addition, papayas cultivated in Chile, along with other tropical fruits cultivated in Brazil, Colombia and the Caribbean, have become especially important in the exportations of these countries. The major markets for these products include the U.S.A., the European Community and Asia. [source] Empirical Distribution Models for Escherichia coli 57:H7 in Ground Beef Produced by a Mid-size Commercial GrinderJOURNAL OF FOOD SCIENCE, Issue 5 2004R.A. Flores ABSTRACT: The purpose of this research was to develop empirical models that describe the amount and distribution of ground beef contaminated with Escherichia coli O157:H7 when a contaminated beef trim is introduced into a batch of uncontaminated beef before processing in a mid-size commercial grinder (34 g/s). A beef trim was inoculated with a rifampacin-resistant strain of E. coli O157:H7 and added to a batch of noncontaminated trims at the grinding step. To study the distribution of the E. coli O157:H7rif in the ground beef, 6 treatments with different inoculum levels (1 to 6 log10 colony-forming units [CFU]) were tested. Removal or pick up of the residual contamination with E. coli O157:H7rif left in the grinder was evaluated. E. coli O157:H7rif was detected in 9% to 86% of the total ground beef for the 1 to 6 log10 CFU inoculum levels, respectively. E. coli O157:H7rif contamination was detected in the collar that fixes the grinder's die and blade to the hub. An exponential algorithm described the relationship between the quantities of ground beef containing E. coli O157:H7rif and the inoculum level (R2= 0.82). Distribution models based on a Chi-squared algorithm were developed for each inoculum level describing the contamination level as a function of the batch fraction processed (R2= 0.81 to 0.99). The results of this study corroborate that when beef processors test for pathogenic contamination in a mid-scale grinder, they should test the beef residues in the collar that fixes the grinder's die and blade to the hub. [source] Expansion and Validation of a Predictive Model for the Growth of Bacillus Stearothermophilus in Military RationsJOURNAL OF FOOD SCIENCE, Issue 5 2002T.M. Ng ABSTRACT: Predictive models for the exponential growth rate (EGR) and germination, outgrowth, and lag times (GOL) of Bacillus stearothermophilus previously developed in our laboratory were expanded to include higher salt (1.5%) formulations. The expanded models were validated in 7 military meals-ready-to-eat incubated at temperatures from 45 °C to 60 °C, and tryptic soy broth incubated from 37.5 °C to 70 °C. The 95% prediction intervals for EGR were fail-safe in all the military rations tested. The 95% prediction intervals for GOL were failsafe in 5 of the 7 rations. The TSB results illustrate the dangers of using empirical models to predict microbial behavior outside the range of conditions under which the models were developed. [source] A common model approach to macroeconomics: using panel data to reduce sampling errorJOURNAL OF FORECASTING, Issue 3 2005William T. Gavin Abstract Is there a common model inherent in macroeconomic data? Macroeconomic theory suggests that market economies of various nations should share many similar dynamic patterns; as a result, individual country empirical models, for a wide variety of countries, often include the same variables. Yet, empirical studies often find important roles for idiosyncratic shocks in the differing macroeconomic performance of countries. We use forecasting criteria to examine the macrodynamic behaviour of 15 OECD countries in terms of a small set of familiar, widely used core economic variables, omitting country-specific shocks. We find this small set of variables and a simple VAR ,common model' strongly support the hypothesis that many industrialized nations have similar macroeconomic dynamics. Copyright © 2005 John Wiley & Sons, Ltd. [source] Statistical analyses of freeway traffic flowsJOURNAL OF FORECASTING, Issue 1 2002Claudia Tebaldi Abstract This paper concerns the exploration of statistical models for the analysis of observational freeway flow data, and the development of empirical models to capture and predict short-term changes in traffic flow characteristics on sequences of links in a partially detectorized freeway network. A first set of analyses explores regression models for minute-by-minute traffic flows, taking into account time of day, day of the week, and recent upstream detector-based flows. Day- and link-specific random effects are used in a hierarchical statistical modelling framework. A second set of analyses captures day-specific idiosyncrasies in traffic patterns by including parameters that may vary throughout the day. Model fit and short-term predictions of flows are thus improved significantly. A third set of analyses includes recent downstream flows as additional predictors. These further improvements, though marginal in most cases, can be quite radically useful in cases of very marked breakdown of freeway flows on some links. These three modelling stages are described and developed in analyses of observational flow data from a set of links on Interstate Highway 5 (I-5) near Seattle. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||