Analysis of enhanced diffusion in Taylor dispersion via a model problem

We consider a simple model of the evolution of the concentration of a tracer, subject to a background shear flow by a fluid with viscosity $\nu \ll 1$ in an infinite channel. Taylor observed in the 1950's that, in such a setting, the tracer diffuses at a rate proportional to $1/\nu$, rather than the expected rate proportional to $\nu$. We provide a mathematical explanation for this enhanced diffusion using a combination of Fourier analysis and center manifold theory. More precisely, we show that, while the high modes of the concentration decay exponentially, the low modes decay algebraically, but at an enhanced rate. Moreover, the behavior of the low modes is governed by finite-dimensional dynamics on an appropriate center manifold, which corresponds exactly to diffusion by a fluid with viscosity proportional to $1/\nu$

Is Fed Policy Still Relevant for Investors?

Using 38 years of data, we show that U.S. monetary policy has had, and continues to have, a strong relationship with security returns. Specifically, we find that U.S. stock returns are consistently higher and less volatile during periods when the Federal Reserve is following an expansive monetary policy. Further, firms considered to be more sensitive to changes in monetary conditions, such as small firms and cyclicals, exhibit monetary-policy-related return patterns that are much more pronounced than average. Lastly, the influence of U.S. monetary policy is shown to be a global phenomenon, as international indices have return patterns similar to those for the U.S. market. Overall, our evidence suggests that investment professionals should continue to use monetary conditions when performing fundamental analysis of both U.S. and international securities

Sexual function in 16- to 21-year-olds in Britain

Purpose: Concern about young people's sexuality is focused on the need to prevent harmful outcomes such as sexually transmitted infections and unplanned pregnancy. Although the benefit of a broader perspective is recognized, data on other aspects of sexuality, particularly sexual function, are scant. We sought to address this gap by measuring the population prevalence of sexual function problems, help seeking, and avoidance of sex in young people. Methods: A cross-sectional stratified probability sample survey (Natsal-3) of 15,162 women and men in Britain (response rate: 57.7%), using computer-assisted self-interviews. Data come from 1875 (71.9%) sexually active, and 517 sexually inactive (18.7%), participants aged 16–21 years. Measures were single items from a validated measure of sexual function (the Natsal-SF). Results: Among sexually active 16- to 21-year-old participants, 9.1% of men and 13.4% of women reported a distressing sexual problem lasting 3 months or more in the last year. Most common among men was reaching a climax too quickly (4.5%), and among women was difficulty in reaching climax (6.3%). Just over a third (35.5%) of men and 42.3% of women reporting a problem had sought help, but rarely from professional sources. Among those who had not had sex in the last year, just >10% of young men and women said they had avoided sex because of sexual difficulties. Conclusions: Distressing sexual function problems are reported by a sizeable minority of sexually active young people. Education is required, and counseling should be available, to prevent lack of knowledge, anxiety, and shame progressing into lifelong sexual difficulties

Forming new sex partnerships while overseas: findings from the third British national survey of sexual attitudes & lifestyles (Natsal-3)

Objectives: Travelling away from home presents opportunities for new sexual partnerships, which may be associated with sexually transmitted infection (STI) risk. We examined the prevalence of, and factors associated with, reporting new sexual partner(s) while overseas, and whether this differed by partners’ region of residence. Methods: We analysed data from 12 530 men and women aged 16–74 years reporting ≥1 sexual partner(s) in the past 5 years in Britain's third National Survey of Sexual Attitudes and Lifestyles (Natsal-3), a probability survey undertaken 2010–2012. Results: 9.2% (95% CI 8.3% to 10.1%) of men and 5.3% (4.8% to 5.8%) of women reported new sexual partner(s) while overseas in the past 5 years. This was strongly associated with higher partner numbers and other sexual and health risk behaviours. Among those with new partners while overseas, 72% of men and 58% of women reported partner(s) who were not UK residents. Compared with those having only UK partners while abroad, these people were more likely to identify as ‘White Other’ or ‘Non-White’ (vs White British ethnicity), report higher partner numbers, new partners from outside the UK while in the UK and paying for sex (men only) all in the past 5 years. There was no difference in reporting STI diagnosis/es during this time period. Conclusions: Reporting new partners while overseas was associated with a range of sexual risk behaviours. Advice on sexual health should be included as part of holistic health advice for all travellers, regardless of age, destination or reason for travel

The Journal of Comorbidity affiliates with the Society for Academic Primary Care

No abstract available

Supercritical maneuvering fighter configuration. Wind-tunnel investigation at Mach numbers of 0.60 to 0.95

A wind tunnel investigation was conducted to study the application of supercritical technology to highly maneuverable combat aircraft. The configuration studied has a leading-edge sweep of 45 deg and an aspect ratio of 3.28. Two supercritical-wing shapes were tested at Mach numbers from 0.60 to 0.95 with angles of attack from -2 deg to 17 deg. On supercritical wing was designed to achieve a high level of transonic maneuver performance at a Mach number of 0.90; however, excessive flow separation developed on this wing at a Mach number of 0.85. A second supercritical wing was tested which had significantly reduced flow separation and improved drag characteristics at a Mach number of 0.85 and maintained the performance of the original wing at the higher Mach numbers. Leading-edge vortex generators did not improve the performance of the second wing; however, a sharp leading-edge flap produced sizable drag reductions at Mach numbers from 0.60 to 0.90

Effective lifetime radiation risk for a number of national mammography screening programmes

Background and purpose: The performance of mammography screening programmes is focussed mainly on breast cancer detection rates. However, when the benefits and risks of mammography are considered, the risk of radiation-induced cancer is calculated for only the examined breast using Mean Glandular Dose (MGD). The risk from radiation during mammography is often described as low or minimal. This study aims to evaluate the effective lifetime risk from full field digital mammography (FFDM) for a number of national screening programmes. Material and Methods: Using an ATOM phantom, radiation doses to multiple organs were measured during standard screening mammography. Sixteen FFDM machines were used and the effective lifetime risk was calculated across the female lifespan for each machine. Once the risks were calculated using the phantom, the total effective lifetime risk across 48 national screening programmes was then calculated; this assumed that all these programmes use FFDM for screening. Results: Large differences exist in effective lifetime risk, varying from 42.21 [39.12 - 45.30] cases/106 (mean [95% CI]) in the Maltese screening programme to 1099.67 [1019.25 - 1180.09] cases/106 for high breast cancer risk women in the United States of America. These differences are mainly attributed to the commencement age of screening mammography and the time interval between successive screens. Conclusions: Effective risk should be considered as an additional parameter for the assessment of screening mammography programme performance, especially for those programmes which recommend an early onset and more frequent screening mammography

The Bubbling Galactic Disk

A visual examination of the images from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) has revealed 322 partial and closed rings that we propose represent partially or fully enclosed three-dimensional bubbles. We argue that the bubbles are primarily formed by hot young stars in massive star formation regions. We have found an average of about 1.5 bubbles per square degree. About 25% of the bubbles coincide with known radio H II regions, and about 13% enclose known star clusters. It appears that B4-B9 stars (too cool to produce detectable radio H II regions) probably produce about three-quarters of the bubbles in our sample, and the remainder are produced by young O-B3 stars that produce detectable radio H II regions. Some of the bubbles may be the outer edges of H II regions where PAH spectral features are excited and may not be dynamically formed by stellar winds. Only three of the bubbles are identified as known SNRs. No bubbles coincide with known planetary nebulae or W-R stars in the GLIMPSE survey area. The bubbles are small. The distribution of angular diameters peaks between 1' and 3' with over 98% having angular diameters less than 10' and 88% less than 4'. Almost 90% have shell thicknesses between 0.2 and 0.4 of their outer radii. Bubble shell thickness increases approximately linearly with shell radius. The eccentricities are rather large, peaking between 0.6 and 0.7; about 65% have eccentricities between 0.55 and 0.85