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Selected AbstractsSignificance testing of synergistic/antagonistic, dose level-dependent, or dose ratio-dependent effects in mixture dose-response analysisENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2005Martijs J. Jonker Abstract In ecotoxicology, the state of the art for effect assessment of chemical mixtures is through multiple dose,response analysis of single compounds and their combinations. Investigating whether such data deviate from the reference models of concentration addition and/or independent action to identify overall synergism or antagonism is becoming routine. However, recent data show that more complex deviation patterns, such as dose ratio,dependent deviation and dose level,dependent deviation, need to be addressed. For concentration addition, methods to detect such deviation patterns exist, but they are stand-alone methods developed separately in literature, and conclusions derived from these analyses are therefore difficult to compare. For independent action, hardly any methods to detect such deviations from this reference model exist. This paper describes how these well-established mixture toxicity principles have been incorporated in a coherent data analysis procedure enabling detection and quantification of dose level,and dose ratio,specific synergism or antagonism from both the concentration addition and the independent action models. Significance testing of which deviation pattern describes the data best is carried out through maximum likelihood analysis. This analysis procedure is demonstrated through various data sets, and its applicability and limitations in mixture research are discussed. [source] GENETIC DISSECTION OF HYBRID INCOMPATIBILITIES BETWEEN DROSOPHILA SIMULANS AND D. MAURITIANA.: III.EVOLUTION, Issue 11 2003AND IMPLICATIONS FOR HALDANE, DEGREE OF DOMINANCE, HETEROGENEOUS ACCUMULATION OF HYBRID INCOMPATIBILITIES Abstract The genetic basis of Haldane,rule was investigated through estimating the accumulation of hybrid incompatibilities between Drosophila simulans and D. mauritiana by means of introgression. The accumulation of hybrid male sterility (HMS) is at least 10 times greater than that of hybrid female sterility (HFS) or hybrid lethality (HL). The degree of dominance for HMS and HL in a pure D. simulans background is estimated as 0.23,0.29 and 0.33,0.39, respectively; that for HL in an F1 background is unlikely to be very small. Evidence obtained here was used to test the Turelli-Orr model of Haldane's rule. Composite causes, especially, faster-male evolution and recessive hybrid incompatibilities, underlie Haldane's rule in heterogametic male taxa such as Drosophila (XY male and XX female). However, if faster-male evolution is driven by sexual selection, it contradicts Haldane's rule for sterility in hetero-gametic-female taxa such as Lepidoptera (ZW female and ZZ male). The hypothesis of a faster-heterogametic-sex evolution seems to fit the current data best. This hypothesis states that gametogenesis in the heterogametic sex, instead of in males per se, evolves much faster than in the homogametic sex, in part because of sex-ratio selection. This hypothesis not only explains Haldane's rule in a simple way, but also suggests that genomic conflicts play a major role in evolution and speciation. [source] Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmonJOURNAL OF FISH BIOLOGY, Issue 4 2003D. R. Geist Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O2 h,1 at 30 cm s,1 (c. 0·5 BL s,1) to 3347 mg O2 h,1 at 170 cm s,1 (c. 2·3 BL s,1). Corrected for fish mass, these values ranged from 122 to 670 mg O2 kg,1 h,1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s,1, and a third-order polynomial regression model fitted the data best. The upper critical swim speed (Ucrit) of fish tested at two laboratories averaged 155 cm s,1 (2·1 BL s,1), but Ucrit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s,1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s,1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s,1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the Ucrit for the fish used in the EMG trials (mean Ucrit 168·2 cm s,1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ,80% of the Ucrit. [source] Ab initio energy calculations and macroscopic rate modeling of hydroformylation of higher alkenes by Rh-based catalystAICHE JOURNAL, Issue 12 2009Maizatul S. Shaharun Abstract Ab initio quantum chemical computations have been done to determine the energetics and reaction pathways of hydroformylation of higher alkenes using a rhodium complex homogeneous catalyst. Calculation of fragments of the potential energy surfaces of the HRh(CO)(PPh3)3 -catalyzed hydroformylation of 1-decene, 1-dodecene, and styrene were performed by the restricted Hartree-Fock method at the second-order MØller-Plesset (MP2) level of perturbation theory and basis set of 6-31++G(d,p). Geometrically optimized structures of the intermediates and transition states were identified. Three generalized rate models were developed on the basis of above reaction path analysis as well as experimental findings reported in the literature. The kinetic and equilibrium parameters of the models were estimated by nonlinear least square regression of available literature data. The model based on H2 -oxidative addition fitted the data best; it predicts the conversion of all the alkenes quite satisfactorily with an average deviation of 7.6% and a maximum deviation of 13%. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Planning behavior and perceived control of time at workJOURNAL OF ORGANIZATIONAL BEHAVIOR, Issue 8 2004Brigitte J. C. Claessens This study investigated two mediation models of time management. The first model consisted of parts of Macan's (1994) model. The second model combined this model with Karasek's (1998) Job Demand,Control model. Two sets of self-report questionnaires were collected and were analyzed using structural equation modeling. The first model, in which perceived control of time was hypothesized to fully mediate the relation between planning behavior and work strain, job satisfaction, and job performance, was found to be less adequate than the second model, which added workload and job autonomy as independent variables. Results also indicated that partial, rather than full, mediation of perceived control of time fitted the data best. The study demonstrated the importance of studying both planning behavior and job characteristics, which was not part of past research. Copyright © 2004 John Wiley & Sons, Ltd. [source] The impact of case specificity and generalisable skills on clinical performance: a correlated traits,correlated methods approachMEDICAL EDUCATION, Issue 6 2008Paul F Wimmers Context, The finding of case or content specificity in medical problem solving moved the focus of research away from generalisable skills towards the importance of content knowledge. However, controversy about the content dependency of clinical performance and the generalisability of skills remains. Objectives, This study aimed to explore the relative impact of both perspectives (case specificity and generalisable skills) on different components (history taking, physical examination, communication) of clinical performance within and across cases. Methods, Data from a clinical performance examination (CPX) taken by 350 Year 3 students were used in a correlated traits,correlated methods (CTCM) approach using confirmatory factor analysis, whereby ,traits' refers to generalisable skills and ,methods' to individual cases. The baseline CTCM model was analysed and compared with four nested models using structural equation modelling techniques. The CPX consisted of three skills components and five cases. Results, Comparison of the four different models with the least-restricted baseline CTCM model revealed that a model with uncorrelated generalisable skills factors and correlated case-specific knowledge factors represented the data best. The generalisable processes found in history taking, physical examination and communication were responsible for half the explained variance, in comparison with the variance related to case specificity. Conclusions, Pure knowledge-based and pure skill-based perspectives on clinical performance both seem too one-dimensional and new evidence supports the idea that a substantial amount of variance contributes to both aspects of performance. It could be concluded that generalisable skills and specialised knowledge go hand in hand: both are essential aspects of clinical performance. [source] Managerial Quality, Administrative Performance and Trust in Governance: Can We Point to Causality?AUSTRALIAN JOURNAL OF PUBLIC ADMINISTRATION, Issue 3 2003Eran Vigoda The relationship between managerial quality, administrative performance and citizens' trust in government and in public administration systems is a field of study that so far has not received adequate scholarly attention. This article explores some interrelationships between these variables and empirically tests between causality, if it exists, between performance and trust. Applying a technique of structural equation modelling (SEM) with LISREL 8.3 the study examined a sample of 345 Israeli citizens and compared three alternative models. The second model that showed a quality , performance , trust relationship fitted the data best. However, the third model also had some advantages worthy of elaboration. Thus, we concluded that administrative performance may be treated as a precondition to trust in governance rather than trust serving as the precondition to performance. The article ends with further discussion of the findings and their meaning in light of the democratic, bureaucratic and new public management theory. [source] | |||||||||||||