Large time behavior and asymptotic stability of the two-dimensional Euler and linearized Euler equations

We study the asymptotic behavior and the asymptotic stability of the two-dimensional Euler equations and of the two-dimensional linearized Euler equations close to parallel flows. We focus on spectrally stable jet profiles $U(y)$ with stationary streamlines $y_{0}$ such that $U'(y_{0})=0$, a case that has not been studied previously. We describe a new dynamical phenomenon: the depletion of the vorticity at the stationary streamlines. An unexpected consequence, is that the velocity decays for large times with power laws, similarly to what happens in the case of the Orr mechanism for base flows without stationary streamlines. The asymptotic behaviors of velocity and the asymptotic profiles of vorticity are theoretically predicted and compared with direct numerical simulations. We argue on the asymptotic stability of these flow velocities even in the absence of any dissipative mechanisms.Comment: To be published in Physica D, nonlinear phenomena (accepted January 2010

Serum Dioxin, Testosterone, and Subsequent Risk of Benign Prostatic Hyperplasia: A Prospective Cohort Study of Air Force Veterans

BACKGROUND: Operation Ranch Hand veterans were involved in spraying herbicides, including Agent Orange, during the Vietnam War in 1962–1971; Agent Orange was contaminated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). It has been hypothesized that dioxins may be partially responsible for an increase of male reproductive tract disorders such as testicular cancer, cryptorchidism, and hypospadias. OBJECTIVES: In this study, our objective was to assess the effect of serum TCDD concentration on the risk of development of benign prostatic hyperplasia (BPH) and on serum testosterone levels. METHODS: This study was a longitudinal, prospective cohort study made up of U.S. Air Force veterans involved in Operation Ranch Hand. Other Air Force veterans who did not spray herbicides were included as comparisons. BPH was determined by medical record review and by medical examinations conducted during the study. Data were available for 971 Ranch Hand and 1,266 comparison veterans. We investigated the relationship between BPH and serum TCDD level using the Cox proportional hazards models adjusted for testosterone levels, body mass index (BMI), and the percentage change in BMI per year. RESULTS: In univariate and multivariate analyses, the risk of BPH decreased with increasing serum TCDD in the comparison group. The multivariate risk ratio for BPH in the comparison group was 0.84 (95% confidence interval, 0.73–0.98). Excluding men with prostate cancer, inflammatory or other prostatic diseases did not substantially alter the association. Serum testosterone levels were inversely associated with serum TCDD levels in both Ranch Hand and comparison groups. CONCLUSIONS: TCDD exposure at general population levels is associated with a decreasing risk of BPH with higher exposure levels. TCDD exposure is also negatively associated with serum testosterone levels

Polybrominated Diphenyl Ether (PBDE) Levels in an Expanded Market Basket Survey of U.S. Food and Estimated PBDE Dietary Intake by Age and Sex

OBJECTIVES: Our objectives in this study were to expand a previously reported U.S. market basket survey using a larger sample size and to estimate levels of PBDE intake from food for the U.S. general population by sex and age. METHODS: We measured concentrations of 13 polybrominated diphenyl ether (PBDE) congeners in food in 62 food samples. In addition, we estimated levels of PBDE intake from food for the U.S. general population by age (birth through ≥60 years of age) and sex. RESULTS: In food samples, concentrations of total PBDEs varied from 7.9 pg/g (parts per trillion) in milk to 3,726 pg/g in canned sardines. Fish were highest in PBDEs (mean, 1,120 pg/g; median, 616 pg/g; range, 11.14–3,726 pg/g). This was followed by meat (mean, 383 pg/g; median, 190 pg/g; range, 39–1,426 pg/g) and dairy products (mean, 116 pg/g; median, 32.2 pg/g; range, 7.9–683 pg/g). However, using estimates for food consumption (excluding nursing infants), meat accounted for the highest U.S. dietary PBDE intake, followed by dairy and fish, with almost equal contributions. Adult females had lower dietary intake of PBDEs than did adult males, based on body weight. We estimated PBDE intake from food to be 307 ng/kg/day for nursing infants and from 2 ng/kg/day at 2–5 years of age for both males and females to 0.9 ng/kg/day in adult females. CONCLUSION: Dietary exposure alone does not appear to account for the very high body burdens measured. The indoor environment (dust, air) may play an important role in PBDE body burdens in addition to food

Three-dimensional coherent X-ray diffraction imaging of a ceramic nanofoam: determination of structural deformation mechanisms

Ultra-low density polymers, metals, and ceramic nanofoams are valued for their high strength-to-weight ratio, high surface area and insulating properties ascribed to their structural geometry. We obtain the labrynthine internal structure of a tantalum oxide nanofoam by X-ray diffractive imaging. Finite element analysis from the structure reveals mechanical properties consistent with bulk samples and with a diffusion limited cluster aggregation model, while excess mass on the nodes discounts the dangling fragments hypothesis of percolation theory.Comment: 8 pages, 5 figures, 30 reference

Polyfluoroalkyl Compounds in Texas Children from Birth through 12 Years of Age

Background: For > 50 years, polyfluoroalkyl compounds (PFCs) have been used worldwide, mainly as surfactants and emulsifiers, and human exposure to some PFCs is widespread