Energy-sharing asymmetries in ionization by positron impact

The triply differential cross section of molecular hydrogen for ionization by 50 eV positrons has been determined, for the first time, for both the ejected electron in coincidence with the remnant ion and for the scattered projectile. Asymmetries in the energy sharing between the two light particles in the final state are observed, with the electron spectrum being shifted to significantly lower (and the scattered positron to correspondingly higher) energies than expected. A similar shape is observed in the case of the ejected electron spectrum from a helium target at the same excess energy

Peer Effects in Medical School

Using data on the universe of students who graduated from U.S. medical schools between 1996 and 1998, we examine whether the abilities and specialty preferences of a medical school class affect a student's academic achievement in medical school and his choice of specialty. We mitigate the selection problem by including school-specific fixed effects, and show that this method yields an upper bound on peer effects for our data. We estimate positive peer effects that disappear when school-specific fixed effects are added to control for the endogeneity of a peer group. We find no evidence that peer effects are stronger for blacks, that peer groups are formed along racial lines, or that students with relatively low ability benefit more from their peers than students with relatively high ability. However, we do find some evidence that peer groups form along gender lines.

Present distribution of the threatened killifish Aphanius fasciatus (Actinopterygii, Cyprinodontidae) in the Maltese Islands

A survey of the nine localities from which the threatened Killifish Aphanius fasciatus has been recorded in the Maltese Islands showed that large and thriving populations exist at Salina, at the Simar and Ghadira bird sanctuaries and in reservoirs at Marsa and Ghadira. The Simar and Ghadira populations are introduced and originate from a mixture of animals collected from Salina and Marsa. The provenance of the Marsa population is unknown but it is possibly autochthonous to the Marsa area. The Salina and possibly the Marsa populations seem to be the only remaining natural populations of this species in the Maltese Islands.peer-reviewe

Living Rationally Under the Volcano? An Empirical Analysis of Heavy Drinking and Smoking

This study investigates whether models of forward-looking behavior explain the observed patterns of heavy drinking and smoking of men in late middle age in the Health and Retirement Study better than myopic models. We develop and estimate a sequence of nested models which differ by their degree of forward-looking behavior. We also study models which allow for heterogeneity in discounting, and thus test whether certain types of individuals are more likely to show forward-looking behavior than other types. Our empirical findings suggest that forward-looking models with an annual discount factor of approximately 0.78 fit the data the best. These models also dominate other behavioral models based on out-of-sample predictions using data of men aged 70 and over. Myopic models predict rates of smoking and drinking for old individuals which are significantly larger than those found in the data on elderly men.

The opto-mechanical alignment procedure of the VLT Survey Telescope

The VLT Survey Telescope is a f/5.5 modified Ritchey-Chretien imaging telescope, which is being installed at the ESO-Paranal Observatory. It will provide a one square degree corrected field of view to perform survey-projects in the wavelength range from UV to I band. In this paper we describe the opto-mechanical alignment procedure of the 2.61m primary mirror, the secondary and correctors lenses onto the mechanical structure of the telescope. The alignment procedure does not rely on the mechanical precision of the mirrors. It will be achieved using ad-hoc alignment tools, described in the paper, which allows the spatial determination of optical axes (and focuses where necessary) of the optical components with respect to the axis defined by the rotation of a laser beam mounted on the instrument bearing.Comment: 10 pages, 10 figures, Proceeding 773357 of the SPIE Conference "Ground-based and Airborne Telescopes III", Sunday 27 June 2010, San Diego, California, US

Modeling College Major Choices Using Elicited Measures of Expectations and Counterfactuals

The choice of a college major plays a critical role in determining the future earnings of college graduates. Students make their college major decisions in part due to the future earnings streams associated with the different majors. We survey students about what their expected earnings would be both in the major they have chosen and in counterfactual majors. We also elicit students' subjective assessments of their abilities in chosen and counterfactual majors. We estimate a model of college major choice that incorporates these subjective expectations and assessments. We show that both expected earnings and students' abilities in the different majors are important determinants of student's choice of a college major. We also show that students' forecast errors with respect to expected earnings in different majors is potentially important, with our estimates suggesting that 7.5% of students would switch majors if they made no forecast errors.choice of college major, subjective expectations