Further Tests of Abortion and Crime: A Response to Donohue and Levitt (2001,2004, 2006)

The association between legalized abortion and crime remains a contentious finding with major implications for social policy. In this paper, I replicate analyses of Donohue and Levitt (2001, 2004, 2006) in which they regress age-specific arrests and homicides on cohort-specific abortion rates. I find that the coefficient on the abortion rate in a regression of age-specific homicide or arrest rates has either the wrong sign or is small in magnitude and statistically insignificant when adjusted for serial correlation. Efforts to instrument for measurement error are flawed and attempts to identify cohort from selection effects are mis-specified. Nor are their findings robust to alternative identification strategies. A convincing test of abortion and crime should be based on an exogenous change in abortion that had a demonstrable effect on fertility. Thus, I analyze changes in abortion rates before and after Roe to identify changes in unwanted fertility. I use within-state comparison groups to net out hard to measure period effects. I also follow Donohue and Levitt (2004) and average the effects of abortion on crime over 15 to 20 years of the life of a cohort to lessen the impact of the crack epidemic. I find little support for a credible association between legalized abortion and crime.

A Time-Series Analysis of Unemployment and Health: The Case of Birth Outcomes in New York City

Lifetime income is less variable than annual household income, since the latter reflects transitory shocks to wages, family status, and employment. The paper presents an aggregate time-series analysis of unemployment and infant health that improves on previous work in several ways. First, the data is monthly as opposed to annual and pertains to New York City from January, 1970 to December, 1986. Second, a structural production function is estimated in which the race-specific percentage of low-birthweight births is the health outcome. Because we are able to control for the race-specific percentage of women who begin care in the first trimester as well as the percentage of births to unmarried mothers, the unemployment rate as a proxy for maternal stress enters the production function as one among a set of well-defined health Inputs. Third, because a pregnancy is limited to at most ten months, we can specify a lag length with confidence. Fourth. the data is tested for stationarity and the production function is estimated in levels as well as in deviations from trend. We find no cyclical variation in the percentage of low-birthweight births. The results are insensitive to changes in lag length. the omission of relevant inputs, and the functional form of the coefficients on the distributed lag.

The Impact of Induced Abortion on Birth Outcomes in the U.S.

This paper examines the impact of induced abortion on birth outcomes by treating abortion as an endogenous input into the production of infant health. To gauge the direct and indirect effect of abortion, three measures of infant health are considered simultaneously: the neonatal sortality rate, the percentage of low-birth weight births, and the percentage of pretera births. All three are race-specific and all pertain to large counties in the U.S. in 1977. Because the utilization of health inputs nay be conditioned on the expected birth outcome, estimates obtained by two-stage least squares are emphasized. The results sake clear that abortion is an important determinant of infant health. This suggests that by reducing the number of unwanted births, abortion enhances the healthiness of newborns of a given weight and gestational age, as well as improving the distribution of births among high-risk groups. Moreover, these direct and indirect effects differ by race.

The Demand for Health Inputs and Their Impact on the Black Neonatal Mortality Rate in the U.S.

Relatively high birth rates among black adolescents and unmarried women as well as inadequate access to medical care are considered primary reasons why the black neonatal mortality rate is almost double that of whites. Using household production theory, this paper examines the determinants of input utilization and estimates the impact of utilization on the survival of black infants across large counties in the U.S. in 1977. The results indicate that expanding the availability of family planning clinics increases the number of teenagers served resulting in a lower neonatal mortality rate. Accessibility to abortion services operates in a similar manner. Moreover, the use of neonatal intensive care, which is strongly related to its availability, is an important determinant of newborn survivability whereas the initiation of early prenatal care is not. Overall, the results suggest that lowering the incidence of low weight and preterm births among blacks by helping women to avoid an unwanted birth, may be the moat cost-effective way of improving black infant health.

Interactive lectures: Clickers or personal devices?

Audience response systems (‘clickers’) are frequently used to promote participation in large lecture classes, and evidence suggests that they convey a number of benefits to students, including improved academic performance and student satisfaction. The limitations of these systems (such as limited access and cost) can be overcome using students’ personal electronic devices, such as mobile phones, tablets and laptops together with text message, web- or app-based polling systems. Using questionnaires, we compare student perceptions of clicker and smartphone based polling systems. We find that students prefer interactive lectures generally, but those that used their own device preferred those lectures over lectures using clickers. However, device users were more likely to report using their devices for other purposes (checking email, social media etc.) when they were available to answer polling questions. These students did not feel that this distracted them from the lecture, instead, concerns over the use of smartphones centred around increased battery usage and inclusivity for students without access to suitable technology. Our results suggest that students generally preferred to use their own devices over clickers, and that this may be a sensible way to overcome some of the limitations associated with clickers, although issues surrounding levels of distraction and the implications for retention and recall of information need further investigation

Supersymmetric Electroweak Baryogenesis in the WKB approximation

We calculate the baryon asymmetry generated at the electroweak phase transition in the minimal supersymmetric standard model, treating the particles in a WKB approximation in the bubble wall background. A set of diffusion equations for the particle species relevant to baryon generation, including source terms arising from the CP violation associated with the complex phase $\delta$ of the $\mu$ parameter, are derived from Boltzmann equations, and solved. The conclusion is that $\delta$ must be \gsim 0.1 to generate a baryon asymmetry consistent with nucleosynthesis. We compare our results to several other recent computations of the effect, arguing that some are overestimates.Comment: 12 pages, 1 figure, corrected some criticisms of hep-ph/9702409; to appear in Phys. Lett.

Supersymmetry of Noncompact MQCD-like Membrane Instantons and Heat Kernel Asymptotics

We perform a heat kernel asymptotics analysis of the nonperturbative superpotential obtained from wrapping of an M2-brane around a supersymmetric noncompact three-fold embedded in a (noncompact) G_2-manifold as obtained in [1], the three-fold being the one relevant to domain walls in Witten's MQCD [2], in the limit of small "zeta", a complex constant that appears in the Riemann surfaces relevant to defining the boundary conditions for the domain wall in MQCD. The MQCD-like configuration is interpretable, for small but non-zero zeta as a noncompact/"large" open membrane instanton, and for vanishing zeta, as the type IIA D0-brane (for vanishing M-theory cicle radius). We find that the eta-function Seeley de-Witt coefficients vanish, and we get a perfect match between the zeta-function Seeley de-Witt coefficients (up to terms quadratic in zeta) between the Dirac-type operator and one of the two Laplace-type operators figuring in the superpotential. This is an extremely strong signature of residual supersymmetry for the nonperturbative configurations in M-theory considered in this work.Comment: 21 pages, LaTeX; v3: several clarifying remarks added, to appear in JHE

Wear of a chute in a rice sorting machine

In a rice sorting machine, rice grains drop onto and slide down an anodised aluminium chute. The purpose of the chute is to separate the grains and provide a controlled distribution. At the bottom of the chute the grains are examined optically and contaminants or defective grains are removed from the stream by jets of air. The machine has the ability to sort low quality rice which contains a large element of contaminants such as husk. The husk is extremely abrasive and this, along with other factors, can lead to a reduction in the life of the chute by wear of the surface. In this work a failure analysis process was undertaken to establish the nature and causes of the chute surface wear and the mechanisms of material removal. Wear occurs initially at the location where the grains first strike the chute and at subsequent regions down the chute where bounce occurs. An experimental and analytical examination of the rice motion on impacting the chute was also carried out along with some friction testing of potential replacement chute materials. The evidence gathered during the failure analysis along with the experimental analysis was used to propose possible material/design improvements

Wheel/Rail Contact Isolation Due to Track Contamination

An experimental study has been carried out to investigate the effect of sanding on the electrical isolation of a wheel/rail contact. Sand is applied to the wheel/rail interface to increase adhesion in both braking and traction. Train detection, for signalling purposes, can be by means of track circuits. Signalling block occupancy is triggered by the wheelset of the train ‘shorting out’ the track circuit. Sand in the wheel/rail interface means that contact between the wheelsets and the track may be compromised, inhibiting train identification. Static tests were performed using sections cut from wheels and rail and dynamic tests on a twin disc machine where rail and wheel steel discs are loaded together and driven under controlled conditions of rolling and slip. The electrical circuit used was a simplified simulation of the TI21 track circuit. The application of sand was carried out under a range of mild and severe test conditions. The results indicated that a transition exists in the amount of sand applied, below which there is a measurable, but not severe, change in voltage, but above which the contact conductance decreases by an order of magnitude. A model of electrical isolation has been developed assuming either full disc separation by a sand layer or partial disc contact with some sand present. Idealisations inherent in both test methods mean that they represent a severe case. Given these limitations, it is likely that the test methods, at their present stage of development, should be used as a means to qualitatively assess the relative effects on electrical isolation of different contaminants