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Mass Point (mass + point)

Distribution by Scientific Domains
Business, Economics, Finance and Accounting57%
Mathematics and Statistics28%

Selected Abstracts

Equilibrium Wage-Tenure Contracts

ECONOMETRICA, Issue 5 2003
Ken Burdett
In this study we consider a labor market matching model where firms post wage-tenure contracts and workers, both employed and unemployed, search for new job opportunities. Given workers are risk averse, we establish there is a unique equilibrium in the environment considered. Although firms in the market make different offers in equilibrium, all post a wage-tenure contract that implies a worker's wage increases smoothly with tenure at the firm. As firms make different offers, there is job turnover, as employed workers move jobs as the opportunity arises. This implies the increase in a worker's wage can be due to job-to-job movements as well as wage-tenure effects. Further, there is a nondegenerate equilibrium distribution of initial wage offers that is differentiable on its support except for a mass point at the lowest initial wage. We also show that relevant characteristics of the equilibrium can be written as explicit functions of preferences and the other market parameters. [source]

Economic aspects of human cloning and reprogenetics

ECONOMIC POLICY, Issue 36 2003
Gilles Saint-Paul
SUMMARY While most discussions of human cloning start and end with ethics, this paper analyses the economics of human cloning. I analyse the incentives for cloning and its implications for the long-run distribution of skills and income. I discuss models of human cloning for different motives, focusing on those that tend to produce new human beings with improved ability. I distinguish three cases: cloning as a means of assisted reproduction for infertile couples, cloning by fertile couples aimed at producing high ability offspring and, finally, financially motivated cloning. The third case supposes that the creator of a clone can appropriate some fraction of the clone's future income. Even if this fraction is small, the possibility of producing exceptionally talented clones with correspondingly high incomes might make it profitable, and thus turn cloning into a form of financial investment. An important consequence of these models is that to the extent that ability is genetically determined and cloners prefer to make high-ability clones, cloning will act as a form of what might be called ,unnatural selection'. Following standard Darwinian logic, such selection will tend to increase the proportion of high ability people in society. Indeed, under some assumptions the distribution of ability eventually converges to a mass point at the highest possible ability level. Under weaker assumptions, it is shown that ability-reducing genes are eventually eliminated. These results do not depend on cloning displacing sexual reproduction or even being widespread; they hold even if a small, or even negligible number of top ability workers are cloned at a small (but not negligible) number of copies. The paper discusses the plausibility of the models and their results in light on the evidence on marriage markets, child selection, human assisted reproduction and animal husbandry. Finally, it is shown how the analysis can be used to help formulate policies toward cloning, whether they aim at preventing it or managing its external effects. , Gilles Saint-Paul [source]

Space,time modeling of rainfall data

ENVIRONMETRICS, Issue 6 2004
Luis Guillermo Coca Velarde
Abstract Climate variables assume non-negative values and are often measured as zero. This is just the case when the rainfall level, in the dry season, is measured in a specified place. Then, the stochastic modeling demands the inclusion of a probability mass point at the zero level, and the resulting model is a mixture of a continuous and a Bernoulli distribution. In this article, spatial conditional autoregressive effects dealing with the idea that neighbors present similar responses is considered and the response level is modeled in two stages. The aim is to consider spatial interpolation and prediction of levels in a Bayesian context. Data on weekly rainfall levels measured in different stations at the central region of Brazil, an area with two well-marked seasons, will be used as an example. A method for comparing models, based on the deviance function, is also implemented. The main conclusion is that the use of space,time models improves the modeling of hydrological and climatological variables, allowing the inclusion of real life considerations such as the influence of other covariates, space dependence and time effects such as seasonality. Copyright © 2004 John Wiley & Sons, Ltd. [source]

A lumped mass numerical model for cellular materials deformed by impact

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2001
Z. H. Tu
Abstract When impacted by a relatively rigid body, cellular materials undergo severe deformation and extensive material failure. However, such behaviour may not be well described using traditional numerical approaches such as the finite element method. This paper presents a lumped mass numerical model which can accommodate high degrees of deformation and material failure. The essence of this model is to discretize a block of material into contiguous element volumes, each represented by a mass point. Interactions between a node and its neighbours are accounted for by defining ,connections' that represent their interfaces which transmit stresses. Strains at a node are calculated from the co-ordinates of the surrounding nodes; these also determine the stresses on the interfaces. The governing equations for the entire solution domain are then converted into a system of equations of motion with nodal positions as unknowns. Failure criteria and possible combinations of ,connection' breakage are incorporated to model the occurrence of damage. A practical contact algorithm is also developed to describe the contact interactions between cellular materials and rigid bodies. Simulations for normal and oblique impacts of rigid rectangular, cylindrical and wedge-tipped impactors on crushable foam blocks are presented to substantiate the validity of the model. The generally good correlation between the numerical and experimental results demonstrates that the proposed numerical approach is able to model the impact response of the crushable foam. However, some limitations in modelling crack propagation in oblique impacts by a rigid impactor on foam blocks are observed. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Asymptotic solution to the restricted three-body problem with a mass point moving near a small-mass body

MATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 15 2010
Alexander El'bert
Abstract The motion of a mass point in the gravitational field of two bodies traveling along arbitrary orbits about their center of mass is considered. The mass ratio of the two bodies is equal to ,,1. When the mass point passes close to the smaller mass, the character of its trajectory changes abruptly, and the trajectory asymptotics as ,,0 is complex. The uniform asymptotic expansion of the entire trajectory up to any power of , is constructed and justified. In particular, an algorithm is presented for finding the limiting turning angle of the trajectory after the mass point passes a neighbourhood of the smaller mass. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Incentive Problems With Unidimensional Hidden Characteristics: A Unified Approach

ECONOMETRICA, Issue 4 2010
Martin F. Hellwig
This paper develops a technique for studying incentive problems with unidimensional hidden characteristics in a way that is independent of whether the type set is finite, the type distribution has a continuous density, or the type distribution has both mass points and an atomless part. By this technique, the proposition that optimal incentive schemes induce no distortion "at the top" and downward distortions "below the top" is extended to arbitrary type distributions. However, mass points in the interior of the type set require pooling with adjacent higher types and, unless there are other complications, a discontinuous jump in the transition from adjacent lower types. [source]

Unobserved Heterogeneity in Models of Competing Mortgage Termination Risks

REAL ESTATE ECONOMICS, Issue 2 2006
John M. Clapp
This article extends unobserved heterogeneity to the multinomial logit (MNL) model framework in the context of mortgages terminated by refinance, move or default. It tests for the importance of unobserved heterogeneity when borrower characteristics such as income, age and credit score are included to capture lender-observed heterogeneity. It does this by comparing the proportional hazard model to MNL with and without mass-point estimates of unobserved heterogeneous groups of borrowers. The mass-point mixed hazard (MMH) model yields larger and more significant coefficients for several important variables in the move model, whereas the MNL model without unobserved heterogeneity performs well with the refinance estimates. The MMH clearly dominates the alternative models in sample and out of sample. However, it is sometimes difficult to obtain convergence for the models estimated jointly with mass points. [source]