How Does Adolescent Fertility Affect the Human Capital and Wages of Young Women?

The consequences of teen childbearing for the future well-being of young women remain controversial. In this paper, we model and estimate the relationship between early childbearing and human capital investment, and its effect on wages in early adulthood. Taking advantage of a large set of potential instruments for fertility—principally state- and county-level indicators of the costs of fertility and fertility control—we use instrumental variables procedures to generate unbiased estimates of the effects of early fertility on education and work experience, and the effects of these outcomes on adult wages. For both black and white women, adolescent fertility substantially reduces years of formal education and teenage work experience. White teenage mothers also obtain less early adult work experience than young women who delay childbearing. We also find that, through these human capital effects, teenage childbearing has a significant effect on a young woman’s market wage at age 25. Our results, unlike those of recent “revisionist” studies, suggest that public policies that reduce teenage childbearing are likely to have positive effects on the economic well-being of many young mothers and their families.

Multistep integration formulas for the numerical integration of the satellite problem

The use of two Class 2/fixed mesh/fixed order/multistep integration packages of the PECE type for the numerical integration of the second order, nonlinear, ordinary differential equation of the satellite orbit problem. These two methods are referred to as the general and the second sum formulations. The derivation of the basic equations which characterize each formulation and the role of the basic equations in the PECE algorithm are discussed. Possible starting procedures are examined which may be used to supply the initial set of values required by the fixed mesh/multistep integrators. The results of the general and second sum integrators are compared to the results of various fixed step and variable step integrators

Instrument selection: The case of teenage childbearing and women's educational attainment

Recent research has identified situations in which instrumental variables (IV) estimators are severely biased and has suggested diagnostic tests to identify such situations. We suggest a number of alternative techniques for choosing a set of instruments that satisfy these tests from a universe of a priori plausible candidates, and we apply them to a study of the effects of adolescent childbearing on the educational attainment of young women. We find that substantive results are sensitive to instrument choice, and make two recommendations to the practical researcher: First, it is prudent to begin with a large set of potential instruments, when possible, and pare it down through formal testing rather than to rely on a minimal instrument set justified on a priori grounds. Second, the application of more restrictive tests of instrument validity and relevance can yield results very different from those based on less restrictive tests that produce a more inclusive set of instruments, and is the preferred, conservative approach when improper instrument choice can lead to biased estimates.

Studies of an orbital gradiometer mission

The goal of using an orbital gradiometer mission to provide an accurate (1 to 2 mgal), high resolution (1 by 1 deg), global map of the earth's geopotential is currently being investigated. This investigation involves the simulation of the satellite ephemeris and the corresponding gradiometer measurements which can be used in the study of various techniques and methodologies that were proposed to recover the parameters used in modeling the geopotential. Also, the effects on the mission of various time varying forces acting on the spacecraft were included in the studies

Reversible plasticity in amorphous materials

A fundamental assumption in our understanding of material rheology is that when microscopic deformations are reversible, the material responds elastically to external loads. Plasticity, i.e. dissipative and irreversible macroscopic changes in a material, is assumed to be the consequence of irreversible microscopic events. Here we show direct evidence for reversible plastic events at the microscopic scale in both experiments and simulations of two-dimensional foam. In the simulations, we demonstrate a link between reversible plastic rearrangement events and pathways in the potential energy landscape of the system. These findings represent a fundamental change in our understanding of materials--microscopic reversibility does not necessarily imply elasticity.Comment: Revised pape

Experimental f-value and isotopic structure for the Ni I line blended with [OI] at 6300A

We have measured the oscillator strength of the Ni I line at 6300.34 \AA, which is known to be blended with the forbidden [O I] $\lambda$6300 line, used for determination of the oxygen abundance in cool stars. We give also wavelengths of the two isotopic line components of $^{58}$Ni and $^{60}$Ni derived from the asymmetric laboratory line profile. These two line components of Ni I have to be considered when calculating a line profile of the 6300 \AA\ feature observed in stellar and solar spectra. We also discuss the labelling of the energy levels involved in the Ni I line, as level mixing makes the theoretical predictions uncertain.Comment: Accepted for publication in ApJLetter

How to Rescue American Football

Abstract Blows to the head damage the brain. American football is a contact/collision sport that produces many injuries, including to the brain. Football has many supporters who cite important redeeming characteristics of the activity. Public attention to the hazards of children and adults playing football has heightend recently due to many new scientific discoveries, not least of which is the frequency with which players are seriously harmed and do not recover. It is now incumbent on all interested parties to invent and implement far better safety practices, equipment, rules, and processes or the sport must cease to exist in its current form. This paper presents several safety proposals for consideration and study. Categories: Pathology, Neurosurgery, Public Health Keywords: football, brain damage, chronic traumatic encephalopathy, concussions, punch-drunk, helmets, safety rules, contact sports, tau protein, prevention Editorial American football is a great sport. It offers, requires, nurtures, and rewards speed, skill, strength, cunning, offensive and defensive strategic thinking, courage, judgment under pressure, competitive spirit, reliance on teamwork, a requirement for exquisite timing, and resolve. Football teaches a participant how to get up and get back at it after being knocked down again and again, a great life lesson. And football has the capacity to engender huge dedicated fan bases. Unfortunately, as the supreme contact sport, it is also a collision sport and thrives on a degree of inherent violence. Thus, injuries are expected and common. Most heal, usually without any disability. Some do not. Studies by US government agencies, the Centers for Disease Control (CDC) and the National Institute for Occupational Safety and Health (NIOSH), have found that those football players exposed to the ultimate of potential violence, professionals in the National Football League (NFL), live longer lives, on average, than men of their birth cohort, but that they have greater likelihood of chronic dementia than does their age cohort. Kickoffs should be eliminated, except perhaps at the beginning of each half, and instead, the ball should be placed at the 20-yard line after touchdowns and field goals, and at the 35-yard line after safeties. The most violent collisions occur when the players are traveling at full speed 1 2 Open Access Editoria