Do Teens Make Rational Choices? The Case of Teen Nonmarital Childbearing

With emphasis on the role of economic incentives, we explore the determinants of a woman’s choice of whether or not to give birth as an unmarried teenager. Our data are taken from the Panel Study of Income Dynamics. Guided by a simple utility-maximization model, we represent the income possibilities available to teenaged women if they do and do not give birth out of wedlock. We estimate these choice-conditioned income possibilities through a two-stage probit procedure, relying on the observed incomes of a secondary sample of somewhat older women. The response of the young women in our primary sample to these income expectations is measured after controlling for the effects of a variety of other factors, including the characteristics of the girl’s family, the social and economic environment in which she lives (including such policy-related factors as expenditures by states on family planning programs and education), and her own prior choices. We use the estimated structural parameters from our model to simulate the effects of a variety of policy interventions on the probability of becoming an unmarried teen mother. Our estimations provide evidence that income expectations have a persistent influence on the childbearing decision. They also provide evidence that the provision of public family planning expenditures and increases in parental education could reduce the prevalence of teen nonmarital births.

Stability of the Submillimeter Brightness of the Atmosphere Above Mauna Kea, Chajnantor and the South Pole

The summit of Mauna Kea in Hawaii, the area near Cerro Chajnantor in Chile, and the South Pole are sites of large millimeter or submillimeter wavelength telescopes. We have placed 860 GHz sky brightness monitors at all three sites and present a comparative study of the measured submillimeter brightness due to atmospheric thermal emission. We report the stability of that quantity at each site.Comment: 6 figure

Design concepts for bioreactors in space

Microbial food sources are becoming viable and more efficient alternatives to conventional food sources especially in the context of Closed Ecological Life Support Systems (CELSS) in space habitats. Since bioreactor designs for terrestrial operation will not readily apply to conditions of microgravity, there is an urgent need to learn about the differences. These differences cannot be easily estimated due to the complex nature of the mass transport and mixing mechanisms in fermenters. Therefore, a systematic and expeditious experimental program must be undertaken to obtain the engineering data necessary to lay down the foundations of designing bioreactors for microgravity. Two bioreactor design concepts presented represent two dissimilar approaches to grappling with the absence of gravity in space habitats and deserve to be tested for adoption as important components of the life support function aboard spacecrafts, space stations and other extra-terrestrial habitats

Design concepts for bioreactors in space

Microbial food sources are becoming viable and more efficient alternatives to conventional food sources, especially in the context of closed ecological life support systems (CELSS) in space habitats. Two bioreactor design concepts presented represent two dissimilar approaches to grappling with the absence of gravity in space habitats and deserve to be tested for adoption as important components of the life support function aboard spacecraft, space stations and other extra-terrestrial habitats

Application of Risk Informed Decision Making to Highly Reliable Three Dimensionally Woven Thermal Protection System for Mars Sample Return

The NASA Risk Informed Decision Making process is used to assess a trade space of three dimensionally woven thermal protection systems for application to the Mars Sample Return Earth Entry Vehicle. Candidate architectures are assessed based on mission assurance, technical development, cost, and schedule risk. Assessment methodology differed between the architectures, utilizing a four-point quantitative scale for mission assurance and technical development and highly tailored PERT techniques for cost and schedule. Risk results are presented, in addition to a review of RIDM effectiveness for this application

Degenerative marrow (modic) changes on cervical spine MRI scans: prevalence, inter- and intra-examiner reliability and link to disc herniation

ABSTRACT: Study Design. A prevalence and reliability study of Modic changes in the cervical spine.Objective. To assess the prevalence and reliability of diagnosing and classifying Modic changes and their relationship to disc herniations in the cervical spine.Summary of Background Data. Degenerative marrow (Modic) changes in the spine can be seen on MRI with some evidence linking them to pain. Many studies have been published on Modic changes in the lumbar spine, but only 1 small prevalence study focusing on Modic changes in the cervical spine has been reported.Methods. The cervical MRI scans of 500 patients over the age of 50 were retrospectively evaluated for the prevalence, type and location of Modic changes and disc herniations. 200 of these same scans were independently analyzed by a second observer to evaluate interobserver reliability of diagnosis with 100 re-evaluated by the same observer 1 month later to assess intraobserver reliability. The SPSS program and Kappa statistics were used to assess prevalence and reliability. The risk ratio comparison of DH and MC was calculated.Results. 426 patients (85.2 %) met the inclusion criteria. Modic changes were observed in 40.4% of patients (14.4% of all motion segments). 4.3% were type 1 and 10.1% were type 2. Disc herniations were seen in 78.2% of patients (13.3% of motion segments). Both MC and DH were most frequently observed at C5/6 and C6/7. Disc extrusions were positively associated with MC (RR = 2.4). The reliability demonstrated an upper moderate interobserver (k = 0.54) and an almost perfect intraobserver agreement (k = 0.82).Conclusions. A high prevalence of Modic changes was observed with type 2 predominating. The C5/6 and C6/7 levels are most effected. Patients with MC are more likely to have a disc herniation at the same level. MC type 2 predominates. The classification is reliable