The determination of the topological structure of skin friction lines on a rectangular wing-body combination

A short tutorial in the application of topological ideas to the intepretation of oil flow patterns is presented. Topological concepts such as critical points, phase portraits, topological stability, and indexing are discussed. These concepts are used in an ordered procedure to construct phase portraits of skin friction lines with oil flow patterns for a wing-body combination and two angles of attack. The relationship between the skin friction phase portrait and planar cuts of the velocity field is also discussed

ASTP chemical and microbiological analysis of potable water

The Apollo-Soyuz Test Project procedures for potable water system servicing and the results of preflight and postflight chemical and microbiological analyses of the water are discussed. Tables show results of the analyses. The effectiveness of the water system is evaluated

COLLECTIVE ACTION AND INFORMAL FINANCIAL INSTITUTIONS: AN EMPIRICAL ANALYSIS OF ROTATING AND SAVINGS CREDIT ASSOCIATIONS (ROSCAS) IN SENEGAL

This study analyzes how rotating savings and credit associations (ROSCAs) in Senegal were able to overcome the collective action dilemma, maintain institutional performance, and remain sustainable over time. This study models cooperation among members as well as the performance and sustainability of associations using data collected from field research conducted in Dakar, Senegal in 2001. The results show that factors such as homogeneity of individuals within an association, how long the association has existed, how defaults are covered, and rules such residency requirements, individual contributions, and rotation order are to various degree critical to the performance and sustainability of ROSCAs and to the fostering of cooperation among members of these associations.Financial Economics,

The Political and Economic Determinants of Trade Disputes under the WTO

Replaced with revised version of paper 02/25/08.democratization, system of government, trade disputes, World Trade Organization (WTO), economic strata, International Relations/Trade, P16, F13,

Detecting Differential Rotation and Starspot Evolution on the M dwarf GJ 1243 with Kepler

We present an analysis of the starspots on the active M4 dwarf GJ 1243, using four years of time series photometry from Kepler. A rapid $P = 0.592596\pm0.00021$ day rotation period is measured due to the $\sim$2.2\% starspot-induced flux modulations in the light curve. We first use a light curve modeling approach, using a Monte Carlo Markov Chain sampler to solve for the longitudes and radii of the two spots within 5-day windows of data. Within each window of time the starspots are assumed to be unchanging. Only a weak constraint on the starspot latitudes can be implied from our modeling. The primary spot is found to be very stable over many years. A secondary spot feature is present in three portions of the light curve, decays on 100-500 day timescales, and moves in longitude over time. We interpret this longitude shearing as the signature of differential rotation. Using our models we measure an average shear between the starspots of 0.0047 rad day$^{-1}$, which corresponds to a differential rotation rate of $\Delta\Omega = 0.012 \pm 0.002$ rad day$^{-1}$. We also fit this starspot phase evolution using a series of bivariate Gaussian functions, which provides a consistent shear measurement. This is among the slowest differential rotation shear measurements yet measured for a star in this temperature regime, and provides an important constraint for dynamo models of low mass stars.Comment: 13 pages, 7 figures, ApJ Accepte

The Role of Pregnancy Concerns in the Relationship between Substance Use and Unprotected Sex among Adolescents

BACKGROUND: Substance use and unprotected sex are prevalent among adolescents. The link between substance use and unprotected sex is well-established. Research has also highlighted how adolescents' attitudes and risk perceptions regarding unprotected sex, including concerns about pregnancy ("Getting pregnant would force me to grow up too fast"), are associated with unprotected sex and unplanned pregnancy. However, less research has examined the potential relationship between pregnancy concerns and substance use among adolescents. OBJECTIVES: The study prospectively examined (1) differences in pregnancy concerns across patterns of substance use and (2) whether pregnancy concerns mediate the relationship between substance use and later unprotected sex among a sample of middle and high school students. METHOD: 98 adolescents [M(SD) age = 14.28(1.68), 59.4% female, 59.4% black/African American] completed self-report measures of marijuana and alcohol use, pregnancy concerns, and unprotected sex across three time points over 6 months (T1-T3). RESULTS: Substance users (alcohol/marijuana) reported fewer pregnancy concerns compared to non-substance users (t = 2.99, p = .04). Pregnancy concerns at T2 mediated the relationship between T1 lifetime substance use and later unprotected sex (T3) (indirect effect: b = 0.10, CI[.01-.41]; direct effect: b = 0.15, p = .32), controlling for gender, age, and race. More frequent substance use (T1) was related to fewer pregnancy concerns at T2 (b = -0.10, p = .04); fewer pregnancy concerns were related to increased likelihood of later unprotected sex (b = -1.02, p = .02). CONCLUSIONS: Findings offer new insight into associations between substance use and unprotected sex and suggest that substance use and sexual health interventions should target pregnancy concerns

Predictor Aided Tracking in a System with Time Delay - Performance Involving Flat Surface, Roll, and Pitch Conditions

Predictor aided human tracking performance with time delay control under flat surface, roll, pitch, and roll and pitch condition