The patient's family history remains a critical element in risk assessment for many conditions, but substantive barriers impede application in primary care practice, and evidence for its contribution to improved health outcomes is limited in this setting. Short of radical changes in reimbursement, new tools will be required to aid primary care physicians in the efficient collection and application of patient family history in the era of genetic testing.
This is a self-contained introductory textbook on the calculus of differential forms and modern differential geometry. The intended audience is physicists, so the author emphasises applications and geometrical reasoning in order to give results and concepts a precise but intuitive meaning without getting bogged down in analysis. The large number of diagrams helps elucidate the fundamental ideas. Mathematical topics covered include differentiable manifolds, differential forms and twisted forms, the Hodge star operator, exterior differential systems and symplectic geometry. All of the mathematics is motivated and illustrated by useful physical examples.
In this article, I introduce the user-written command craggit, which simultaneously fits both tiers of Cragg's (1971, Econometrica 39: 829-844) "twotier" (sometimes called "two-stage" or "double-hurdle") alternative to tobit for corner-solution models. A key limitation to the tobit model is that the probability of a positive value and the actual value, given that it is positive, are determined by the same underlying process (i.e., the same parameters). Cragg proposed a more flexible alternative that allows these outcomes to be determined by separate processes through the incorporation of a probit model in the first tier and a truncated normal model in the second. Also, tobit is nested in craggit, making the latter a popular choice among "two-tier" models. In the article, I also present postestimation syntax to facilitate the understanding and interpretation of results.
This paper treats the slow-motion approximation for radiating systems as a problem in singular perturbations. By using the method of matched asymptotic expansions, we can construct approximations valid both in the near zone and the wave zone. The outgoing-wave boundary condition applied to the wave-zone expansion leads, by matching, to a unique and easily calculable radiation resistance in the near zone. The method is developed and illustrated with model problems from mechanics and electromagnetism; these should form a useful and accessible introduction to the method of matched asymptotic expansions. The method is then applied to the general relativistic problem of gravitational radiation from gravitationally bound systems, where a significant part of the radiation can be attributed to nonlinear terms in the expansion of the metric. This analysis shows that the formulas derived from the standard linear approximation remain valid for gravitationally bound systems. In particular, it shows that, according to general relativity, bodies in free-fall motion do indeed radiate. These results do not depend upon any definition of gravitational field energy.
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