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Structural Models (structural + models)
Selected AbstractsA Conditional Likelihood Ratio Test for Structural ModelsECONOMETRICA, Issue 4 2003Marcelo J. Moreira This paper develops a general method for constructing exactly similar tests based on the conditional distribution of nonpivotal statistics in a simultaneous equations model with normal errors and known reduced-form covariance matrix. These tests are shown to be similar under weak-instrument asymptotics when the reduced-form covariance matrix is estimated and the errors are non-normal. The conditional test based on the likelihood ratio statistic is particularly simple and has good power properties. Like the score test, it is optimal under the usual local-to-null asymptotics, but it has better power when identification is weak. [source] Beyond Conceptual Change: Using Representations to Integrate Domain-Specific Structural Models in Learning MathematicsMIND, BRAIN, AND EDUCATION, Issue 2 2007Florence Mihaela Singer ABSTRACT, Effective teaching should focus on representational change, which is fundamental to learning and education, rather than conceptual change, which involves transformation of theories in science rather than the gradual building of knowledge that occurs in students. This article addresses the question about how to develop more efficient strategies for promoting representational change across cognitive development. I provide an example of an integrated structural model that highlights the underlying cognitive structures that connect numbers, mathematical operations, and functions. The model emphasizes dynamic multiple representations that students can internalize within the number line and which lead to developing a dynamic mental structure. In teaching practice, the model focuses on a counting task format, which integrates a variety of activities, specifically addressing motor, visual, and verbal skills, as well as various types of learning transfer. [source] Structural Models and Binding Site Prediction of the C-terminal Domain of Human Hsp90: A New Target for Anticancer DrugsCHEMICAL BIOLOGY & DRUG DESIGN, Issue 5 2008Miriam Sgobba Heat shock protein 90 is a valuable target for anticancer drugs because of its role in the activation and stabilization of multiple oncogenic signalling proteins. While several compounds inhibit heat shock protein 90 by binding the N-terminal domain, recent studies have proved that the C-terminal domain is important for dimerization of the chaperone and contains an additional binding site for inhibitors. Heat shock protein 90 inhibition achieved with molecules binding to the C-terminal domain provides an additional and novel opportunity to design and develop drugs. Therefore, for the first time, we have investigated the structure and the dynamic behaviour of the C-terminal domain of human heat shock protein 90 with and without the small-middle domain, using homology modelling and molecular dynamics simulations. In addition, secondary structure predictions and peptide folding simulations proved useful to investigate a putative additional ,-helix located between H18 and ,20 of the C-terminal domain. Finally, we used the structural information to infer the location of the binding site located in the C-terminal domain by using a number of computational tools. The predicted pocket is formed by two grooves located between helix H18, the loop downstream of H18 and the loop connecting helices H20 and H21 of each monomer of the C-terminal domain, with only two amino acids contributing from each middle domain. [source] A Salmonella typhi OmpC fusion protein expressing the CD154 Trp140,Ser149 amino acid strand binds CD40 and activates a lymphoma B-cell lineIMMUNOLOGY, Issue 2 2003Mario I. Vega Summary CD154 is a type II glycoprotein member of the tumour necrosis factor (TNF) ligand family, which is expressed mainly on the surface of activated T lymphocytes. The interaction with its receptor CD40, plays a central role in the control of several functions of the immune system. Structural models based on the homology of CD154 with TNF and lymphotoxin indicate that binding to CD40 involves three regions surrounding amino acids K143, R203 and Q220, and that strands W140,S149 and S198,A210 are critical for such interactions. Also, it has been reported that two recombinant CD154 fragments, including amino acid residues Y45,L261 or E108,L261 are biologically active, whereas other polypeptides, including S149,L261, are not. Therefore, we decided to construct a fusion protein inserting the W140-S149 amino acid strand (WAEKGYYTMS) in an external loop of the outer membrane protein C (OmpC) from Salmonella enterica serovar Typhi and assess its ability to bind CD40 and activate B cells. The sodium dodecyl sulphate,polyacrylamide gel electrophoresis demonstrated that the chimeric OmpC,gp39 protein conserved its ability to form trimers. Binding to CD40 was established by three variants of enzyme-linked immunosorbent assay, a direct binding assay by coating plates with a recombinant CD40,Fc protein and through two competition assays between OmpC,gp39 and recombinant CD154 or soluble CD40,Fc. Flow cytometry analysis demonstrated that OmpC,gp39 increased the expression levels of major histocompatibility complex II, CD23, and CD80, in Raji human B-cell lymphoma similarly to an antibody against CD40. These results further support that the CD154/CD40 interaction is similar to the TNF/TNF receptor. This is the first report of a bacterial fusion protein containing a small amino acid strand form a ligand that is able to activate its cognate receptor. [source] What can we learn from tuberous sclerosis complex (TSC) about autism?JOURNAL OF INTELLECTUAL DISABILITY RESEARCH, Issue 10 2008P. J. De Vries Tuberous Sclerosis Complex (TSC) is now recognized as one of the medical conditions most commonly associated with autism. Between 1,5% of those with autism have TSC and up to 50% of people with TSC meet criteria for an autism spectrum disorder. The clinical characteristics of autism in TSC are qualitatively indistinguishable from those of idiopathic autism. So, what can TSC teach us about autism? We will present an overview of the neuropsychiatric features of TSC and will proceed with an examination of aetiological models of autism in TSC. Structural models (suggesting that autism is caused by brain lesions in specific neuroanatomical locations) and seizure models (suggesting that the age, type and control of seizures may predict autism) have both received some support, but with limited replication. More recently, molecular approaches have suggested that dysregulation of intracellular signalling through the TSC1/2-mTOR pathway may be sufficient to lead to socialization deficits and autism, and that drugs that act as mTOR inhibitors may reverse some aspects of the learning and social deficits in TSC. [source] Structural models for twin interfaces in Pd thin filmsJOURNAL OF MICROSCOPY, Issue 3 2006I. TSIAOUSSIS Summary In a Pd thin film grown on a 6H-SiC (0001) substrate, several twin interfaces have been observed, classified as (1) {111}, = 3 twin interfaces and (2) {}, = 3 twin interfaces. The first ones are coherent twin interfaces and in some cases exhibit steps of one or more atomic layers in height. The second ones are perpendicular to the first ones. They usually appear with a rigid-body displacement, but in some cases no displacement was observed. Models for the interfaces are proposed. [source] The Relationship Between Genetic Influences on Alcohol Dependence and on Patterns of Alcohol ConsumptionALCOHOLISM, Issue 6 2010Kenneth S. Kendler Background:, Genetic factors impact substantially both on alcohol consumption (AC) and on the risk for alcohol dependence (AD). However, we know little about the degree to which measures of AC index the genetic risk for AD. Methods:, We assessed a lifetime history of AD by DSM-IV criteria and four measures of AC at the time of heaviest drinking (drink frequency, regular quantity, maximum quantity, and drunk frequency) in 5,073 adult twins from same-sex pairs from the Virginia Twin Registry. Structural models were fitted using Mx. Results:, We found evidence for different genetic structure in the sexes. In women, genetic risk for AD and for the four measures of AC was entirely shared. In men, the AC measures captured 85% of the genetic risk for AD. In women, the genetic relationship with AD was strongest for drunk frequency and in men for both drunk frequency and regular quantity. Conclusions:, In a population-based sample of twins, four relatively simple measures of AC obtained for the time of lifetime heaviest drinking were able to capture all (in women) or a very large proportion (in men) of the genetic risk for the complex multi-dimensional construct of AD. If replicated, these results have practical implications for studies aiming to assess genetic risk for AD. [source] Functional analysis of the large periplasmic loop of the Escherichia coli K-12 WaaL O-antigen ligaseMOLECULAR MICROBIOLOGY, Issue 6 2008José M. Pérez Summary WaaL is a membrane enzyme implicated in ligating undecaprenyl-diphosphate (Und-PP)-linked O antigen to lipid A-core oligosaccharide. We determined the periplasmic location of a large (EL5) and small (EL4) adjacent loops in the Escherichia coli K-12 WaaL. Structural models of the EL5 from the K-12, R1 and R4 E. coli ligases were generated by molecular dynamics. Despite the poor amino acid sequence conservation among these proteins, the models afforded similar folds consisting of two pairs of almost perpendicular ,-helices. One ,-helix in each pair contributes a histidine and an arginine facing each other, which are highly conserved in WaaL homologues. Mutations in either residue rendered WaaL non-functional, since mutant proteins were unable to restore O antigen surface expression. Replacements of residues located away from the putative catalytic centre and non-conserved residues within the centre itself did not affect ligation. Furthermore, replacing a highly conserved arginine in EL4 with various amino acids inactivates WaaL function, but functionality reappears when the positive charge is restored by a replacement with lysine. These results lead us to propose that the conserved amino acids in the two adjacent periplasmic loops could interact with Und-PP, which is the common component in all WaaL substrates. [source] Metric spaces in NMR crystallographyCONCEPTS IN MAGNETIC RESONANCE, Issue 4 2009David M. Grant Abstract The anisotropic character of the chemical shift can be measured by experiments that provide shift tensor values and comparing these experimental components, obtained from microcrystalline powders, with 3D nuclear shielding tensor components, calculated with quantum chemistry, yields structural models of the analyzed molecules. The use of a metric tensor for evaluating the mean squared deviations, d2, between two or more tensors provides a statistical way to verify the molecular structure governing the theoretical shielding components. The sensitivity of the method is comparable with diffraction methods for the heavier organic atoms (i.e., C, O, N, etc.) but considerably better for the positions of H atoms. Thus, the method is especially powerful for H-bond structure, the position of water molecules in biomolecular species, and other proton important structural features, etc. Unfortunately, the traditional Cartesian tensor components appear as reducible metric representations and lack the orthogonality of irreducible icosahedral and irreducible spherical tensors, both of which are also easy to normalize. Metrics give weighting factors that carry important statistical significance in a structure determination. Details of the mathematical analysis are presented and examples given to illustrate the reason nuclear magnetic resonance are rapidly assuming an important synergistic relationship with diffraction methods (X-ray, neutron scattering, and high energy synchrotron irradiation). © 2009 Wiley Periodicals, Inc.Concepts Magn Reson Part A 34A: 217,237, 2009. [source] An Empirical Study of the Effect of Knowledge Management Processes at Individual, Group, and Organizational Levels,DECISION SCIENCES, Issue 2 2003Rajiv Sabherwal ABSTRACT To enhance our understanding of knowledge management, this paper focuses on a specific question: How do knowledge management processes influence perceived knowledge management effectiveness? Prior literature is used to develop the research model, including hypotheses about the effects of four knowledge management processes (internalization, externalization, socialization, and combination) on perceived individual-level, group-level, and organizational-level knowledge management effectiveness. The study was conducted at the John F. Kennedy Space Center of the National Aeronautics and Space Administration using a survey of 159 individuals and two rounds of personal interviews. Structural equation modeling was performed to test measurement and structural models using the survey data. The emergent model suggests that internalization and externalization impact perceived effectiveness of individual-level knowledge management. Socialization and combination influence perceived effectiveness of knowledge management at group and organizational levels, respectively. The results also support the expected upward impact in perceived effectiveness of knowledge management, from individual to group level, as well as from group level to organizational level. The study's limitations and implications for practice and future research are described. [source] Uniform hazard versus uniform risk bases for performance-based earthquake engineering of light-frame wood constructionEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 11 2010Yue Li Abstract This paper investigates the implications of designing for uniform hazard versus uniform risk for light-frame wood residential construction subjected to earthquakes in the United States. Using simple structural models of one-story residences with typical lateral force-resisting systems (shear walls) found in buildings in western, eastern and central regions of the United States as illustrations, the seismic demands are determined using nonlinear dynamic time-history analyses, whereas the collapse capacities are determined using incremental dynamic analyses. The probabilities of collapse, conditioned on the occurrence of the maximum considered earthquakes and design earthquakes stipulated in ASCE Standard 7-05, and the collapse margins of these typical residential structures are compared for typical construction practices in different regions in the United States. The calculated collapse inter-story drifts are compared with the limits stipulated in FEMA 356/ASCE Standard 41-06 and observed in the recent experimental testing. The results of this study provide insights into residential building risk assessment and the relation between building seismic performance implied by the current earthquake-resistant design and construction practices and performance levels in performance-based engineering of light-frame wood construction being considered by the SEI/ASCE committee on reliability-based design of wood structures. Further code developments are necessary to achieve the goal of uniform risk in earthquake-resistant residential construction. Copyright © 2010 John Wiley & Sons, Ltd. [source] Incremental dynamic analysis for estimating seismic performance sensitivity and uncertainty ,EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2010Dimitrios Vamvatsikos Abstract Incremental dynamic analysis (IDA) is presented as a powerful tool to evaluate the variability in the seismic demand and capacity of non-deterministic structural models, building upon existing methodologies of Monte Carlo simulation and approximate moment-estimation. A nine-story steel moment-resisting frame is used as a testbed, employing parameterized moment-rotation relationships with non-deterministic quadrilinear backbones for the beam plastic-hinges. The uncertain properties of the backbones include the yield moment, the post-yield hardening ratio, the end-of-hardening rotation, the slope of the descending branch, the residual moment capacity and the ultimate rotation reached. IDA is employed to accurately assess the seismic performance of the model for any combination of the parameters by performing multiple nonlinear timehistory analyses for a suite of ground motion records. Sensitivity analyses on both the IDA and the static pushover level reveal the yield moment and the two rotational-ductility parameters to be the most influential for the frame behavior. To propagate the parametric uncertainty to the actual seismic performance we employ (a) Monte Carlo simulation with latin hypercube sampling, (b) point-estimate and (c) first-order second-moment techniques, thus offering competing methods that represent different compromises between speed and accuracy. The final results provide firm ground for challenging current assumptions in seismic guidelines on using a median-parameter model to estimate the median seismic performance and employing the well-known square-root-sum-of-squares rule to combine aleatory randomness and epistemic uncertainty. Copyright © 2009 John Wiley & Sons, Ltd. [source] Shaking table tests on reinforced concrete frames without and with passive control systemsEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2005Mauro Dolce Abstract An extensive experimental program of shaking table tests on reduced-scale structural models was carried out within the activities of the MANSIDE project, for the development of new seismic isolation and energy dissipation devices based on shape memory alloys (SMAs). The aim of the experimental program was to compare the behaviour of structures endowed with innovative SMA-based devices to the behaviour of conventional structures and of structures endowed with currently used passive control systems. This paper presents a comprehensive overview of the main results of the shaking table tests carried out on the models with and without special braces. Two different types of energy dissipating and re-centring braces have been considered to enhance the seismic performances of the tested model. They are based on the hysteretic properties of steel elements and on the superelastic properties of SMAs, respectively. The addition of passive control braces in the reinforced concrete frame resulted in significant benefits on the overall seismic behaviour. The seismic intensity producing structural collapse was considerably raised, interstorey drifts and shear forces in columns were drastically reduced. Copyright © 2005 John Wiley & Sons, Ltd. [source] Evolutionary aseismic design and retrofit of structures with passive energy dissipationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 13 2005G. F. Dargush Abstract A new computational framework is developed for the design and retrofit of building structures by considering aseismic design as a complex adaptive process. For the initial phase of the development within this framework, genetic algorithms are employed for the discrete optimization of passively damped structural systems. The passive elements may include metallic plate dampers, viscous fluid dampers and viscoelastic solid dampers. The primary objective is to determine robust designs, including both the non-linearity of the structural system and the uncertainty of the seismic environment. Within the present paper, this computational design approach is applied to a series of model problems, involving sizing and placement of passive dampers for energy dissipation. In order to facilitate our investigations and provide a baseline for further study, we introduce several simplifications for these initial examples. In particular, we employ deterministic lumped parameter structural models, memoryless fitness function definitions and hypothetical seismic environments. Despite these restrictions, some interesting results are obtained from the simulations and we are able to gain an understanding of the potential for the proposed evolutionary aseismic design methodology. Copyright © 2005 John Wiley & Sons, Ltd. [source] Assessing alternative models of individualism and collectivism: a confirmatory factor analysisEUROPEAN JOURNAL OF PERSONALITY, Issue 2 2001Mark A. Freeman Six alternative structural models of individualism,collectivism are reviewed and empirically compared in a confirmatory factor analysis of questionnaire data from an Australian student sample (N,=,340). Central to the debate about the structure of this broad social attitude are the issues of (1) polarity (are individualism and collectivism bipolar opposites, or orthogonal factors?) and (2) dimensionality (are individualism and collectivism themselves higher-order constructs subsuming several more specific factors and, if so, what are they?). The data from this Australian sample support a model that represents individualism and collectivism as a higher-order bipolar factor hierarchically subsuming several bipolar reference-group-specific individualisms and collectivisms. Copyright © 2001 John Wiley & Sons, Ltd. [source] The product of the gene GEF1 of Saccharomyces cerevisiae transports Cl, across the plasma membraneFEMS YEAST RESEARCH, Issue 8 2007Angélica López-Rodríguez Abstract Expression of GEF1 in Xenopus laevis oocytes and HEK-293 cells gave rise to a Cl, channel that remained permanently open and was blocked by nitro-2-(3-phenylpropylamino) benzoic acid and niflumic acid. NPPB induced petite -like colonies, resembling the GEF1 knock-out. The fluorescent halide indicator SPQ was quenched in a wild-type strain, in contrast to both a GEF1 knock-out strain and yeast grown in the presence of NPPB. Immunogold and electron microscopy located Gef1p in the plasma membrane, vacuole, endoplasmic reticulum and Golgi apparatus. Eleven substitutions in five residues forming the ion channel of GEF1 were introduced; some of them (S186A, I188N, Y459D, Y459F, Y459V, I467A, I467N and F468N) did not rescue the pet phenotype, whereas F468A, A558F and A558Y formed normal colonies. All the pet mutants showed reduced O2 consumption, small mitochondria and mostly disrupted organelles. Finally, electron microscopy revealed that the plasma membrane of the mutants develop multiple foldings and highly ordered cylindrical protein-membrane complexes. All the experiments above suggest that Gef1p transports Cl, through the plasma membrane and reveal the importance of critical amino acids for the proper function of the protein as suggested by structural models. However, the mechanism of activation of the channel has yet to be defined. [source] A deterministic seismic hazard map of India and adjacent areasGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2003Imtiyaz A. Parvez SUMMARY A seismic hazard map of the territory of India and adjacent areas has been prepared using a deterministic approach based on the computation of synthetic seismograms complete with all main phases. The input data set consists of structural models, seismogenic zones, focal mechanisms and earthquake catalogues. There are few probabilistic hazard maps available for the Indian subcontinent, however, this is the first study aimed at producing a deterministic seismic hazard map for the Indian region using realistic strong ground motion modelling with the knowledge of the physical process of earthquake generation, the level of seismicity and wave propagation in anelastic media. Synthetic seismograms at a frequency of 1 Hz have been generated at a regular grid of 0.2°× 0.2° by the modal summation technique. The seismic hazard, expressed in terms of maximum displacement (Dmax), maximum velocity (Vmax), and design ground acceleration (DGA), has been extracted from the synthetic signals and mapped on a regular grid over the studied territory. The estimated values of the peak ground acceleration are compared with the observed data available for the Himalayan region and are found to be in agreement. Many parts of the Himalayan region have DGA values exceeding 0.6 g. The epicentral areas of the great Assam earthquakes of 1897 and 1950 in northeast India represent the maximum hazard with DGA values reaching 1.2,1.3 g. The peak velocity and displacement in the same region is estimated as 120,177 cm s,1 and 60,90 cm, respectively. [source] An efficient method for decomposition of regular structures using graph productsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2004A. Kaveh Abstract In this paper an efficient method is presented for calculating the eigenvalues of regular structural models. A structural model is called regular if they can be viewed as the direct or strong Cartesian product of some simple graphs known as their generators. The eigenvalues of the adjacency and Laplacian matrices for a regular graph model are easily obtained by the evaluation of eigenvalues of its generators. The second eigenvalue of the Laplacian of a graph is also obtained using a much faster and much simple approach than the existing methods. Copyright © 2004 John Wiley & Sons, Ltd. [source] Use of resampling to select among alternative error structure specifications for GLMM analyses of repeated measurements,INTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 1 2004Scott Tonidandel Abstract Autocorrelated error and missing data due to dropouts have fostered interest in the flexible general linear mixed model (GLMM) procedures for analysis of data from controlled clinical trials. The user of these adaptable statistical tools must, however, choose among alternative structural models to represent the correlated repeated measurements. The fit of the error structure model specification is important for validity of tests for differences in patterns of treatment effects across time, particularly when maximum likelihood procedures are relied upon. Results can be affected significantly by the error specification that is selected, so a principled basis for selecting the specification is important. As no theoretical grounds are usually available to guide this decision, empirical criteria have been developed that focus on model fit. The current report proposes alternative empirical criteria that focus on bootstrap estimates of actual type I error and power of tests for treatment effects. Results for model selection before and after the blind is broken are compared. Goodness-of-fit statistics also compare favourably for models fitted to the blinded or unblinded data, although the correspondence to actual type I error and power depends on the particular fit statistic that is considered. Copyright © 2004 Whurr Publishers Ltd. [source] mmLib Python toolkit for manipulating annotated structural models of biological macromoleculesJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2004Jay Painter The Python Macromolecular Library (mmLib) is a software toolkit and library of routines for the analysis and manipulation of macromolecular structural models, implemented in the Python programming language. It is accessed via a layered object-oriented application programming interface, and provides a range of useful software components for parsing mmCIF, PDB and MTZ files, a library of atomic elements and monomers, an object-oriented data structure describing biological macromolecules, and an OpenGL molecular viewer. The mmLib data model is designed to provide easy access to the various levels of detail needed to implement high-level application programs for macromolecular crystallography, NMR, modeling and visualization. We describe here the establishment of mmLib as a collaborative open-source code base, and the use of mmLib to implement several simple illustrative application programs. [source] A theoretical study on the structures and energetics of hypothetical TiM(NCN)3 compounds of the 3d transition metalsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2005Maxence Launay Abstract Quasi-ternary cyanamides and carbodiimides of general formula AB(NCN)3 with A , B have neither been predicted nor synthesized. Thus, hypothetical compounds of that kind containing 3d transition metals were considered (A = Ti, B = Mn, Fe, Co, Ni, Cu) by means of density-functional calculations on 34 structural models, most of which were derived from chemically related phases. After performing structure optimizations based on the local-density approximation, the relative energetic orderings are rationalized in terms of geometrical factors such as molar volumes and polyhedral connections. Total-energy generalized-gradient calculations evidence that the most stable models are enthalpically favored with respect to the elements. Even at ambient temperatures, the ternary phases are predicted as being thermodynamically stable in terms of their Gibbs free formation energies, especially if energetically competing and low-lying binaries (TiC, TiN) can be excluded by a kinetic reaction control. The best models are characterized by low-spin magnetic transition metals found in octahedral coordination, and the TiN6 and MN6 polyhedra either share faces or edges. © 2005 Wiley Periodicals, Inc. J Comput Chem 26: 1180,1188, 2005 [source] THE INFLUENCE OF FUNDAMENTALS ON EXCHANGE RATES: FINDINGS FROM ANALYSES OF NEWS EFFECTSJOURNAL OF ECONOMIC SURVEYS, Issue 4 2010Rafael R. Rebitzky Abstract As we survey the literature of macroeconomic news in the foreign exchange market, we can by now look back on nearly 30 years of research. The first studies which analysed news effects on exchange rates were established in the early 1990s (see, for example, Dornbusch). Almost at the same time Meese and Rogoff published their influential paper, revealing the forecasting inferiority in exchange rates of structural models against the random walk. This finding has shocked the pillars of exchange rate economics and thus cast general suspicion on research focusing on fundamentals in this field. The eventual rising popularity of event studies can partly be attributed to the re-establishment of the,raison d'ętre,of exchange rate economics. This work focuses on systematically surveying this literature with particular respect to its primary goal, i.e. shedding light on the analytical value of fundamental research. Thus, its major findings are, first, fundamental news does matter, whereas non-fundamental news matters to a lesser degree. Second, news influences exchange rates via two separated channels, i.e. incorporating common information into prices directly or indirectly based upon order flow. Third, with a few exceptions the impact of fundamental news on exchange rates is fairly stable over time. [source] Assessing the forecasting accuracy of alternative nominal exchange rate models: the case of long memoryJOURNAL OF FORECASTING, Issue 5 2006David Karemera Abstract This paper presents an autoregressive fractionally integrated moving-average (ARFIMA) model of nominal exchange rates and compares its forecasting capability with the monetary structural models and the random walk model. Monthly observations are used for Canada, France, Germany, Italy, Japan and the United Kingdom for the period of April 1973 through December 1998. The estimation method is Sowell's (1992) exact maximum likelihood estimation. The forecasting accuracy of the long-memory model is formally compared to the random walk and the monetary models, using the recently developed Harvey, Leybourne and Newbold (1997) test statistics. The results show that the long-memory model is more efficient than the random walk model in steps-ahead forecasts beyond 1 month for most currencies and more efficient than the monetary models in multi-step-ahead forecasts. This new finding strongly suggests that the long-memory model of nominal exchange rates be studied as a viable alternative to the conventional models.,,Copyright © 2006 John Wiley & Sons, Ltd. [source] Trait-Specific Dependence in Romantic RelationshipsJOURNAL OF PERSONALITY, Issue 5 2002Bruce J. Ellis ABSTRACT Informed by three theoretical frameworks,trait psychology, evolutionary psychology, and interdependence theory,we report four investigations designed to develop and test the reliability and validity of a new construct and accompanying multiscale inventory, the Trait-Specific Dependence Inventory (TSDI). The TSDI assesses comparisons between present and alternative romantic partners on major dimensions of mate value. In Study 1, principal components analyses revealed that the provisional pool of theory-generated TSDI items were represented by six factors: Agreeable/Committed, Resource Accruing Potential, Physical Prowess, Emotional Stability, Surgency, and Physical Attractiveness. In Study 2, confirmatory factor analysis replicated these results on a different sample and tested how well different structural models fit the data. Study 3 provided evidence for the convergent and discriminant validity of the six TSDI scales by correlating each one with a matched personality trait scale that did not explicitly incorporate comparisons between partners. Study 4 provided further validation evidence, revealing that the six TSDI scales successfully predicted three relationship outcome measures,love, time investment, and anger/upset,above and beyond matched sets of traditional personality trait measures. These results suggest that the TSDI is a reliable, valid, and unique construct that represents a new trait-specific method of assessing dependence in romantic relationships. The construct of trait-specific dependence is introduced and linked with other theories of mate value. [source] Lexical Studies of Indigenous Personality Factors: Premises, Products, and ProspectsJOURNAL OF PERSONALITY, Issue 6 2001Gerard Saucier The rationale for lexical studies rests on the assumption that the most meaningful personality attributes tend to become encoded in language as single-word descriptors. We articulate some key premises of the lexical approach and then review a number of studies that have been conducted examining the factor structure of personality descriptors extracted from dictionaries. We compare lexical studies in English and 12 other languages, with attention to delineating consistencies between the structures found in diverse languages. Our review suggests that the Anglo-Germanic Big Five is reproduced better in some languages than in others. We propose some organizing rules for lexical factor structures that may be more generalizable than the contemporary Big-Five model. And, we propose several candidate structural models that should be compared with the Big Five in future studies, including structures with one, two, and three very broad factors, an alternative five-factor structure identified in Italian and Hungarian studies, and a seven-factor structure represented in Hebrew and Philippine studies. We recommend that in future studies more attention be paid to middle-level personality constructs and to examining the effects of methodological variations on the resulting factor structures. [source] Acid,base behavior of triazoleporphyrazines in proton-donating mediaJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 4 2005O. G. Khelevina Abstract The acid,base properties of some peripheral substituted triazoleporphyrazines in proton-donating media with poor-donating character were experimentally studied. The substitution of one pyrrole moiety in the porphyrazine-like compounds by one triazole ring in the triazoleporphyrazines leads to an increase in the basicity. The protonation of the triazoleporphyrazines results in a hypsochromic shift of the Q-bands in the UV,visible spectra. A DFT study of some selected structural models of the unsubstituted triazoleporphyrazine shows that the protonation strongly influences on the molecular electron structure of this compound and that it occurs preferentially through the nitrogen atom located at position 4 of triazole ring. The protonation through the other basic centers (the triazoleporphyrazine is a multicenter conjugated base) leads to different protonated forms which differ notably in their aromatic character. Therefore, this compound could be considered an intramolecular switch of aromaticity. Copyright © 2004 John Wiley & Sons, Ltd. [source] EXAFS study of local atomic order about iodine in thyroxine, rat, human and sheep thyroidsJOURNAL OF SYNCHROTRON RADIATION, Issue 6 2008B. R. Orton Radioactive 125I emits short-range Auger electrons and represents a human health risk when incorporated in thyroglobulin of the thyroid. Quantitative evaluation of this risk can only be realised if local atomic order about iodine in the thyroid is known. Here, extended X-ray absorption fine structure (EXAFS) has been used to probe the local structure about iodine in pure thyroid hormone, thyroxine. These data are consistent with a model where iodine is bound to a single iodinated carbon ring linked to an oxygen atom, similar to a previously published model for monoiodotyrosine, a major iodinated residue in thyroglobulin. Several structural models for the local environment of iodine from rat, human and sheep have been tested and these data are found to be compatible with a slightly modified environment with respect to that found for thyroxine. The best-fit models include the following three components: (i) iodine covalently bonded to a tyrosine ring, as found for thyroxine; (ii) iodine bonded quasi-covalently to a carbonyl ligand in partially filled (50%) sites; (iii) partially filled sites (50,40%) of carbonyl ligands, with oxygen at van der Waals distances from iodine. Advantages of using Fourier-filtered EXAFS for complex crystal structures are discussed. [source] Structure of new porous compounds after annealing in vacuumJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001S. B. Erenburg Dehydration process in recently synthesized porous inorganic salts formed by large cluster anions [Re6X8(CN)6]4- (X= S, Se), transition metal cations and water molecules has been investigated. Desolvation process of the complex Co(DMF)6[Mo6Br8(NCS)6], where DMF - dimethylformamide, has been studied. CoK, MoK and ReL3 XAFS measurements of these new complicated compounds before and after annealing in vacuum at temperature up to 250°C were performed. Changes of electronic and spatial structure of these compounds under the heating process have been established and adequate structural models of the amorphous compounds obtained are suggested and discussed. [source] The Structure of Yttrialite and Its Identification Using Laboratory and Synchrotron-Based Powder X-Ray DiffractionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009William J. Heward A highly crystalline sample of the impurity stabilized phase y -Y2Si2O7, generally known as yttrialite, has been formed from the melt of a glass with a nominal composition of 62(SiO2),10(Al2O3),28(Y2O3) mol%. Powder X-ray diffraction patterns were collected using in-house instrumentation and the 11-BM diffractometer at the Advanced Photon Source, Argonne National Laboratory, Argonne, IL. Rietveld refinements were carried out on the patterns using two structural models. On patterns collected using in-house instrumentation the correct structure assignment was difficult to determine; however, the extremely high-quality data afforded by the 11-BM instrument showed conclusively that the sample was found to crystallize in the monoclinic system (SG=P21/m) with lattice parameters a=5.03032(6), b=8.06892(6), c=7.33620(6) Ĺ, and ,=108.673(1). Furthermore, simulations have shown that it is likely that this structure model can be used to describe natural yttrialite or yttrialite that is formed at low temperatures, though the possibility that such materials are paracrystalline is also discussed. [source] A Molecular Dynamic Study of Cementitious Calcium Silicate Hydrate (C,S,H) GelsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2007Jorge S. Dolado In this article, we study the polymerization of silicic acids (Si(OH)4) in the presence of calcium ions by molecular dynamics simulations. We focus on the formation and structure of cementitious calcium silicate hydrate (C,S,H) gels. Our simulations confirm that, in accordance with experiments, a larger content of calcium ions slows down the polymerization of the cementitious silicate chains and prevents them from forming rings and three-dimensional structures. Furthermore, by an analysis of the connectivity of our simulated silicate chains and by a count of the number of Ca,OH and Si,OH bonds formed, the relationship with commonly used structural models of C,S,H gels, such as 1.4 nm tobermorite and jennite, is discussed. [source] | ||||||||||||||||||||||||||||||||||||||||||||||