bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new synthetic loading of induction machines based on phase modulation
Authors: Soltani J. , Szabados B. 
Published: July 2007

AbstractSynthetic loading of induction machines are used to test machines for temperature rise and total losses without the need for attaching mechanical load to the shaft. A new phase modulation technique of the voltage is proposed in lieu of the traditional two‐frequency method. A simple bang‐bang DC switch is used to modulate the excitation current of an induction generator. System modeling was performed using the traditional two‐axis method, and has proven that the method is feasible. Practical test results are shown to validate the simulated performance. It is shown that the only constraint of this synthetic loading is to maintain the RMS values of the current and voltage at rated values.
The determination of the stability regions and sequential transient stability analysis of integrated AC‐DC power system consisting of bipolar dc lines via the controlling unstable equilibrium points
Authors: Ayan K. , Arifoǧlu U. 
Published: July 2007

AbstractIn this paper, a sequential transient stability analysis of an integrated AC‐DC power system consisting of bipolar MTDC is accomplished by taking into account the variation of the amplitude of the bus voltages during transient. This variation of the bus voltages is provided by the sequential AC‐DC load flow algorithm of the AC‐DC power system with respect to the active power modified at each integration step. The algorithm has two superiority. Firstly, as DC system variables are not included in Jacobian matrix the convergence time of the algorithm and necessity of computer memory is little. Secondly, both this algorithm has been developed for bipolar system and this algorithm also can be run with current controlled, voltage controlled and power controlled terminals without making any changes in proposed method. Thus, the AC‐DC transient stability analysis is accomplished considering the true value of the ratio of the reactive power absorbed from the converters to the active power transferred through DC line by the sequential approach. In the transient analysis of the system, the DC lines loads are represented as the current injections to the buses where they are connected and its effect is reflected at the internal buses in the form of additional bus power injections. The effect of these is again reflected at the internal buses in the form of additional bus power injections. Thus, the problem in constructing a valid Lyapunov function due to the transfer conductance is eliminated.
Transforming growth factor-β and substrate stiffness regulate portal fibroblast activation in culture
Authors: Li Zhaodong , Dranoff Jonathan A. , Chan Erick P. , Uemura Masayuki , Sévigny Jean , Wells Rebecca G. 
Published: July 2007

Abstract

Myofibroblasts derived from portal fibroblasts are important fibrogenic cells in the early stages of biliary fibrosis. In contrast to hepatic stellate cells, portal fibroblasts have not been well studied

in vitro,

and little is known about their myofibroblastic differentiation. In this article we report the isolation and characterization of rat portal fibroblasts in culture. We demonstrate that primary portal fibroblasts undergo differentiation to α-smooth muscle actin–expressing myofibroblasts over 10–14 days. Marker analysis comparing portal fibroblasts to hepatic stellate cells demonstrated that these are distinct populations and that staining with elastin and desmin can differentiate between them. Portal fibroblasts expressed elastin at all stages in culture but never expressed desmin, whereas hepatic stellate cells consistently expressed desmin but never elastin. Immunostaining of rat liver tissue confirmed these results

in vivo.

Characterization of portal fibroblast differentiation in culture demonstrated that these cells required transforming growth factor-β (TGF-β): cells remained quiescent in the presence of a TGF-β receptor kinase inhibitor, whereas exogenous TGF-β1 enhanced portal fibroblast α-smooth muscle actin expression and stress fiber formation. In contrast, platelet-derived growth factor inhibited myofibroblastic differentiation. Portal fibroblasts were also dependent on mechanical tension for myofibroblastic differentiation, and cells cultured on polyacrylamide supports of variable stiffness demonstrated an increasingly myofibroblastic phenotype as stiffness increased.

Conclusion:

Portal fibroblasts are morphologically and functionally distinct from hepatic stellate cells. Portal fibroblast myofibroblastic differentiation can be modeled in culture and requires both TGF-β and mechanical tension. (HEPATOLOGY 2007.)
Econometric models based on count data. Comparisons and applications of some estimators and tests
Authors: Cameron A. Colin , Trivedi Pravin K. 
Published: July 2007

AbstractThis paper deals with specification, estimation and tests of single equation reduced form type equations in which the dependent variable takes only non‐negative integer values. Beginning with Poisson and compound Poisson models, which involve strong assumptions, a variety of possible stochastic models and their implications are discussed. A number of estimators and their properties are considered in the light of uncertainty about the data generation process. The paper also considers the role of tests in sequential revision of the model specification beginr ing with the Poisson case and provides a detailed application of the estimators and tests to a model of the number of doctor consultations.
An empirical analysis of self‐employment in the U.K.
Authors: Rees Hedley , Shah Anup 
Published: July 2007

AbstractThe paper formulates a self‐employment/paid‐employment choice problem that draws upon Knight's notion that the individual responds to the risk‐adjusted relative earnings opportunities in each sector. Based on a development of such choice‐theoretic considerations, an econometric model is developed with the purpose of empirically examining the determinants of self‐employment. The model features simultaneous determination of employment status and earnings, which allows for self‐selectivity. The model is estimated using a sample of 4762 individuals from the General Household Survey for 1978. The estimation of the earnings equation enables a calculation of the self‐employment/paid‐employment earnings differential and the estimated probit equation for self‐employment/paid‐employment status facilitates the prediction of the probability of self‐employment. The paper finds that there is positive selection bias in the observed earnings of employees, that the probability of self‐employment depends positively on the earnings difference between the two sectors and that education and age are significant determinants of self‐employment.
Formulating wald tests of the restrictions implied by the rational expectations hypothesis
Authors: Gregory Allan W. , Veall Michael R. 
Published: July 2007

AbstractIn this paper, we examine the small sample properties of alternative formulations of Wald tests of non‐linear restrictions implied by the rational expectations hypothesis. A Monte Carlo analysis is presented as well as an example using Canadian aggregate time series data. The evidence indicates that Wald test results are extremely sensitive in small samples to the way in which the non‐linear restrictions in such models are parameterized, with a multiplicative form yielding tests of most accurate size. Least squares degrees of freedom adjustments also improve the sample performance of the tests.
An empirical model of a household's choice of activities
Authors: Montmarquette Claude , Monty Luc 
Published: July 2007

AbstractThis paper analyses how households of school‐age children choose to participate in the labour force, volunteer work, democratic assemblies, and child‐related leisure activities. Contrary to previous studies, the model presented in this paper treats all of these household's choice of activities involving time allocation decisions as simultaneously determined. The empirical section uses qualitative data estimation techniques which permit a wide range of joint and interaction effects among the variables of the model. The results confirm the importance of time‐opportunity cost variables as major determinants of household's choice of activities with the mother's education consituting a particularly important factor.
A micro‐econometric analysis of vacation behaviour
Authors: Van Soest Arthur , Kooreman Peter 
Published: July 2007

AbstractWe present a micro‐econometric limited dependent variable model, which simultaneously explains the decision whether to go on vacation or not, the choice of destination and the decision on the level of the vacation expenditures. The model has been estimated on the basis of a cross‐section of Dutch households; we find a striking difference in income elasticity between domestic vacations and vacations abroad, and a large impact of owning certain durables (such as a boat) on the choice of destination. To illustrate the potential of the model, some simulations are performed.
In pursuit of monopoly power: Recent quantitative work in industrial: Economics
Authors: Geroski P. A. 
Published: July 2007

AbstractThis paper reviews empirical work in industrial organization devoted to the question of inferring the existence of monopoly power from data on observed market outcomes like profits and prices. The discussion covers inter‐industry work long conventional in the area, newer developments in intra‐industry analysis and case studies, and concludes with some remarks on a small but growing body of work assessing market dynamics. The wide range of studies reviewed all generally reveal that market power exists in many industries.
The dynamics of exchange rate volatility: A multivariate latent factor ARCH model
Authors: Diebold Francis X. , Nerlove Marc 
Published: July 2007

AbstractWe study temporal volatility patterns in seven nominal dollar spot exchange rates, all of which display strong evidence of autoregressive conditional heteroskedasticity (ARCH). We first formulate and estimate univariate models, the results of which are subsequently used to guide specification of a multivariate model. The key element of our multivariate approach is exploitation of factor structure, which facilitates tractable estimation via a substantial reduction in the number of parameters to be estimated. Such a latent‐variable model is shown to provide a good description of multivariate exchange rate movements: the ARCH effects capture volatility clustering, and the factor structure captures commonality in volatility movements across exchange rates.
Production of public safety: Are socioeconomic characteristics of local communities important factors?
Authors: Gyimah‐Brempong Kwabena 
Published: July 2007

AbstractThis paper uses the translog cost function and cross section data from Florida to investigate the importance of socioeconomic characteristics (SEC) of local communities in the production of public safety. The approach used is noteworthy in four respects: (1) the underlying production function is specified as an AGEM production function; (2) SEC are treated as non‐purchased fixed inputs; (3) two variables are used to proxy SEC in estimation; and (4) the paper test for the existence of endogenous quality differences in safety. It is shown that exclusion of SEC from the production (cost) function of safety leads to misspecification; and hence they provide a misleading guide to policy.
Tests of international CAPM with time‐varying covariances
Authors: Engel Charles , Rodrigues Anthony P. 
Published: July 2007

AbstractWe perform maximum‐likelihood estimation of a model of international asset pricing based on CAPM. We test the restrictions imposed by CAPM against a more general asset pricing model. The ‘betas’ in our CAPM vary over time as the supplies of assets change and as the conditional covariances or returns on those assets change. We let the covariances change over time as a function of macroeconomic data, and an alternative model allows the covariances to follow a multivariate ARCH process. We also can identify a modified CAPM model with measurement error. We find that the estimated CAPM performs much better when variances are not constant over time. Nonetheless, CAPM is rejected in favour of the lessrestricted model of asset pricing.
Fiscal and monetary policy co‐ordination: A differential game approach
Authors: Petit Maria Luisa 
Published: July 2007

AbstractIn this paper the interaction between the Treasury and the central bank is examined in the case of both cooperative and non‐cooperative behaviour. Differential games are used in the framework of a continuous‐time econometric model of the Italian economy. The Nash and the Stackelberg non‐cooperative equilibrium solutions are computed, and the case for cooperation is analysed by considering the Nash and the Kalai‐Smorodinsky bargaining models. It is shown that, in the Italian case, the government has a stronger bargaining position than the central bank. A comparison is then made between the different solutions to show that the drawbacks that emerge from non‐cooperation are not simply those depending on the players' payoffs. Other features are in fact considered which constitute a further argument for policy co‐ordination.
Output and unemployment dynamics in the United States: 1950–1985
Authors: Evans George W. 
Published: July 2007

AbstractFor US data over 1950–1985 the stochastic components of GNP growth and the unemployment rate appear to be stationary, and there is substantial feedback between these variables. The unconditional mean rate of unemployment in a joint model thus provides a natural benchmark in discussions of the ‘business cycle’. A bivariate VAR model is used to describe output–unemployment dynamics, to estimate the degree of persistence of output innovations, and to decompose output into trend and cycle. The bivariate results are interpreted using a restricted VAR and it is shown that a closely related cyclical measure can be obtained directly from the Okun's Law equation.
Models of military expenditure
Authors: Smith R. P. 
Published: July 2007

AbstractA brief review of the extensive empirical literature devoted to explaining levels of military expenditure indicates a wide variety of unreconciled results. However, comparing the alternative models is not straightforward. This paper uses British post‐war military expenditures to illustrate some of the methodological issues involved in model comparison, evaluation and selection. Starting from two published models for the UK, a systematic specification search leads to a new model, which dominates alternative specifications, passes a wide range of misspecification tests, and also fits well to French data.
Seasonal adjustment and measuring persistence in output
Authors: Jaeger Albert , Kunst Robert M. 
Published: July 2007

AbstractWe examine the robustness of persistence measurement to different seasonal adjustment procedures. The empirical analysis is based on US data for real gross national product (GNP). Officially published data on US GNP are seasonally adjusted by Census X‐11. We find that this series gives significantly higher measures of persistence than GNP data adjusted by alternative seasonal adjustment methods. Some Monte Carlo evidence in support of this conclusion is also presented.
On measuring economic efficiency
Authors: Kalirajan K. P. 
Published: July 2007

AbstractThis paper considers a system consisting of a production frontier and factor share equations to measure firm‐specific technical efficiency and input‐specific allocative efficiency simulataneously. In estimating the system as a whole, the joint distribution of all errors in the equations is used. This is more efficient than using the marginal distribution of a function of the errors as one does by estimating either the profit function of the production function alone. The workability of the method is illustrated by applying it to farm‐level data from Philippines agriculture.
The measurement of rationing and the treatment of structural change in the uk mortgage market
Authors: Meen Geoffrey P. 
Published: July 2007

AbstractUK mortgage markets have undergone major structural changes in the past few years, resulting in mortgages no longer being rationed. The ending of rationing has implications for the specification of empirical models of housing demand. Housing models have never adequately resolved how to incorporate unobservable mortgage rationing. Conventional proxy methods are particularly unsuitable, when rationing ceases. In this paper, we propose a new way of measuring rationing directly, which incorporates regime switching. The model of rationing is extensively tested and estimates of rationing for the period 1963–1988 are provided; these may be easily incorporated into housing demand studies.
The dynamics of job separation: The case of federal employees
Authors: Black Matthew , Moffitt Robert , Warner John T. 
Published: July 2007

AbstractIn this paper we develop a model of workers' quit decisions. Using panel data on a sample of US Federal government employees we use maximum‐likelihood techniques to determine how much of the observed decline in quits with job tenure is a result of declining individual quit propensities (‘state dependence’) rather than dynamic sample self‐selection (‘heterogeneity’). The latter is found to be much more important than the former. The effects of relative Federal government wages and other variables on quits are also estimated. The results are useful for analysing Federal compensation policies.
Purchasing power parity as a long‐run relation
Authors: Patel Jayendu 
Published: July 2007

AbstractDickey–Fuller and Stock–Watson tests of purchasing power parity (PPP) as a long‐run proposition are provided within the cointegration framework proposed by Granger. Since different countries use different weights to construct price indices, the traditional constraint that the coefficients on the price indices should be unity in the log‐linear PPP relation is relaxed. The absence of a general PPP relation cannot be rejected. At most, a PPP relation is indicated in five out of fifteen country pairs that are examined. Even if a long‐run PPP relation exists, it is not found to be useful in predicting future nominal exchange rates, which is consistent with efficient speculative markets.
Wage and price adjustment in a multimarket disequilibrium model
Authors: Salanie Bernard 
Published: July 2007

AbstractThe estimation of wage and price adjustment equations rests heavily on the use of tension variables that aim at capturing the disequilibria in the labour and goods markets. Disequilibrium models therefore provide a natural way of endogenizing these tension variables. This paper estimates jointly a two‐market disequilibrium model and a wage and price adjustment block where price and wage growth react to excess effective demands. The estimation is carried out using the simulated pseudo‐maximum‐likelihood methods developed by Laroque and Salaniè (1989); the results look promising as regards the estimation of even more sophisticated models.
The effect of parameter uncertainty on forecast variances and confidence intervals for unit root and trend stationary time‐series models
Authors: Sampson Michael 
Published: July 2007

AbstractIn this paper I describe the effect of parameter uncertainty on the way conditional forecast variances grow as the forecast horizon increases. Without parameter uncertainty, forecast variances for the unit root model grow linearly with the forecast horizon while with the trend stationary model they are bounded. With parameter uncertainty, however, I find that for both the unit root and the trend stationary models, forecast variances grow with the square of the forecast horizon so that uncertainty grows at a much faster rate than without parameter uncertainty.
An application and test for a random coefficient model in Bangladesh agriculture
Authors: Hoque Asraul 
Published: July 2007

AbstractThis paper deals with efficiency question by estimating four production functions for four different regions in connection with Bangladesh agriculture. Hildreth and Houck's (1968) random coefficient method was found more suitable than OLS after conducting an appropriate test for this. In contrast to earlier studies, 24 piece‐wise regressions have been fitted for each index of efficiency considering all four regions and six different ranges of farm size instead of a single regression so that the relationship could be studied more closely. The study clearly indicates higher efficiency for smaller farms.
Term structure of interest rates in the Singapore Asian dollar market
Authors: Lee Tom K. Y. , Tse Y. K. 
Published: July 2007

AbstractThis paper investigates empirically the term structure of interest rates in the Singapore Asian Dollar Market. We consider extended versions of the ARCH‐M model of Engle, Lilien, and Robins (1987). The extended models permit autocorrelation, skewness and leptokurtosis in the residuals. The robustness of the empirical tests with respect to alternative specifications of the ARCH process is examined. It turns out that there is significant time‐varying term premium, and this conclusion is independent of the hypothesized ARCH model.
Expenditure allocation across nondurables, services, durables and savings: An empirical study of separability in the long run
Authors: Anderson G. J. 
Published: July 2007

AbstractThe separability of categories of consumption expenditures and savings are empirically examined in the context of an error‐correction model of aggregate quarterly expenditure allocations in Canada. Some evidence is found for separability of consumption allocations from savings in both the long run structure and short run dynamics of the model lending some support to the use of the assumption in modelling consumption behaviour.
Models for truncated counts
Authors: Grogger J. T. , Carson R. T. 
Published: July 2007

AbstractThis paper examines a class of maximum‐likelihood regression estimators for count data from truncated samples. Estimators for the truncated Poisson and negative binomial distributions are illustrated. Simulation results are given to illustrate the magnitude of the bias that may result from the failure to account for overdispersion in truncated samples. An empirical application based upon the number of recreational fishing trips taken by a sample of Alaskan fishermen is provided.
The limiting distribution of extremal exchange rate returns
Authors: Hols Martien C. A. B. , De Vries Casper G. 
Published: July 2007

AbstractSeveral nonnested fat‐tailed distributions have been advocated for modelling exchange rate returns. Instead of directly estimating these nonnested distributions we investigate the extremal distribution of the returns. The advantage is that the parameter which characterizes the amount of tail fatness can be estimated without maintaining a specific distribution, and hence enables one to test hypotheses. The parameter of the limit law is estimated by employing nonparametric procedures based on order statistics. The appropriateness of these procedures is assessed. Given this estimate one can derive bounds on the returns for very low probabilities on an excess. Such information is useful in evaluating the volatility of exchange rates.
Time aggregation and the distributional shape of unemployment duration
Authors: Bergström R. , Edin P.‐A. 
Published: July 2007

AbstractThis paper reports empirical evidence on the sensitivity of unemployment duration regression estimates to distributional assumptions and to time aggregation. The results indicate that parameter estimates are robust to distributional assumptions, while estimates of duration dependence are not. Time aggregation does not seem to have drastic effects on the estimates in a simple parametric model like the Weibull, but can produce dramatic changes in the more complicated extended generalized gamma model. Semiparametric models for grouped data produce stable estimates, and perform much better than continuous‐time models in terms of significance at high levels of time aggregation.