The identification of physical close galaxy pairs

A classification scheme for close pairs of galaxies is proposed. The scheme is motivated by the fact that the majority of apparent close pairs are in fact wide pairs in three-dimensional space. This is demonstrated by means of numerical simulations of random samples of binary galaxies and the scrutiny of the resulting projected and spatial separation distributions. Observational strategies for classifying close pairs according to the scheme are suggested. As a result, physical (i.e., bound and spatially) close pairs are identified.Comment: 16 pages, 5 figures, accepted for publication in The Astronomical Journal, added text corrections on proof

The art of fitting p-mode spectra: Part II. Leakage and noise covariance matrices

In Part I we have developed a theory for fitting p-mode Fourier spectra assuming that these spectra have a multi-normal distribution. We showed, using Monte-Carlo simulations, how one can obtain p-mode parameters using 'Maximum Likelihood Estimators'. In this article, hereafter Part II, we show how to use the theory developed in Part I for fitting real data. We introduce 4 new diagnostics in helioseismology: the $(m,\nu)$ echelle diagramme, the cross echelle diagramme, the inter echelle diagramme, and the ratio cross spectrum. These diagnostics are extremely powerful to visualize and understand the covariance matrices of the Fourier spectra, and also to find bugs in the data analysis code. These diagrammes can also be used to derive quantitative information on the mode leakage and noise covariance matrices. Numerous examples using the LOI/SOHO and GONG data are given.Comment: 17 pages with tex and ps files, submitted to A&A, [email protected]

The art of fitting p-mode spectra: Part I. Maximum Likelihood Estimation

In this article we present our state of the art of fitting helioseismic p-mode spectra. We give a step by step recipe for fitting the spectra: statistics of the spectra both for spatially unresolved and resolved data, the use of Maximum Likelihood estimates, the statistics of the p-mode parameters, the use of Monte-Carlo simulation and the significance of fitted parameters. The recipe is applied to synthetic low-resolution data, similar to those of the LOI, using Monte-Carlo simulations. For such spatially resolved data, the statistics of the Fourier spectrum is assumed to be a multi-normal distribution; the statistics of the power spectrum is \emph{not} a $\chi^{2}$ with 2 degrees of freedom. Results for $l=1$ shows that all parameters describing the p modes can be obtained without bias and with minimum variance provided that the leakage matrix is known. Systematic errors due to an imperfect knowledge of the leakage matrix are derived for all the p-mode parameters.Comment: 13 pages, ps file gzipped. Submitted to A&

Simulation or cohort models? Continuous time simulation and discretized Markov models to estimate cost-effectiveness

The choice of model design for decision analytic models in cost-effectiveness analysis has been the subject of discussion. The current work addresses this issue by noting that, when time is to be explicitly modelled, we need to represent phenomena occurring in continuous time. Multistate models evaluated in continuous time might be used but closed form solutions of expected time in each state may not exist or may be difficult to obtain. Two approximations can then be used for costeffectiveness estimation: (1) simulation models, where continuous time estimates are obtained through Monte Carlo simulation, and (2) discretized models. This work draws recommendations on their use by showing that, when these alternative models can be applied, it is preferable to implement a cohort discretized model than a simulation model. Whilst the bias from the first can be minimized by reducing the cycle length, the second is inherently stochastic. Even though specialized literature advocates this framework, the current practice in economic evaluation is to define clinically meaningful cycle lengths for discretized models, disregarding potential biases.

The Demographic Transition and the Sexual Division of Labor

This paper presents a theory where increases in female labor force participation and reductions in the gender wage-gap are generated as part of a single process of demographic transition, characterized by reductions in mortality and fertility. The paper suggests a link between changes in mortality and transformations in the role of women in society that has not been identified before in the literature. Mortality reductions affect the incentives of individuals to invest in human capital and to have children. Particularly, gains in adult longevity reduce fertility, increase investments in market human capital, increase female labor force participation, and reduce the wage differential between men and women. Child mortality reductions, though reducing fertility, do not generate this same pattern of changes. The model reconciles the increase in female labor market participation with the timing of age-specific mortality reductions observed during the demographic transition. It generates changes in fertility, labor market attachment, and the gender wage-gap as part of a single process of social transformation, triggered by reductions in mortality.

The Demographic Transition and the Sexual Division of Labor

This paper presents a theory where increases in female labor force participation and reductions in the gender wage-gap are generated as part of a single process of demographic transition, characterized by reductions in mortality and fertility. The paper suggests a link between changes in mortality and transformations in the role of women in society that has not been identified before in the literature. Mortality reductions affect the incentives of individuals to invest in human capital and to have children. Particularly, gains in adult longevity reduce fertility, increase investments in market human capital, increase female labor force participation, and reduce the wage differential between men and women. Child mortality reductions, though reducing fertility, do not generate this same pattern of changes. The model reconciles the increase in female labor market participation with the timing of age-specific mortality reductions observed during the demographic transition. It generates changes in fertility, labor market attachment, and the gender wage-gap as part of a single process of social transformation, triggered by reductions in mortality.