Dispersion curves in the diffusional instability of reaction fronts

A (linear) stability analysis of planar reaction fronts to transverse perturbations is considered for systems based on cubic autocatalysis and a model for the chlorite-tetrathionate reaction. Dispersion curves (plots of the growth rate sigma against a transverse wave-number k) are obtained. In both cases it is seen that there is a nonzero value D-0 of D (the ratio of the diffusion coefficients of autocatalyst and substrate) at which sigma(max), the maximum value of sigma for a given value of D, achieves its largest value, with sigma(max) being less for other values of D and becoming small as D decreases to zero. The existence of the optimum value D-0 for initiating a diffusional instability is confirmed, in the cubic autocatalysis case, by an asymptotic analysis for small wave numbers

Effects of constant electric fields on the buoyant stability of reaction fronts

The effects that applying constant electric fields have on the buoyant instability of reaction fronts propagating vertically in a Hele-Shaw cell are investigated for a range of electric field strengths and fluid parameters. The reaction produces a decrease in density across the front such that upwards propagating fronts are buoyantly unstable in the field-free situation. The reaction kinetics are modeled by cubic autocatalysis. A linear stability analysis reveals that a positive electric field increases the stability of a reaction front and can stabilize an otherwise unstable front. A negative field has the opposite effect, making the reaction front more unstable. Numerical simulations of the full nonlinear problem confirm these predictions and show the development of cellular fingers on unstable fronts. These simulations show that the electric field effects on the reaction within the front can alter the fluid density so as to give the possibility of destabilizing an otherwise stable downward propagating front

Homogenization induced by chaotic mixing and diffusion in an oscillatory chemical reaction

A model for an imperfectly mixed batch reactor with the chlorine dioxide-iodine-malonic acid (CDIMA) reaction, with the mixing being modelled by chaotic advection, is considered. The reactor is assumed to be operating in oscillatory mode and the way in which an initial spatial perturbation becomes homogenized is examined. When the kinetics are such that the only stable homogeneous state is oscillatory then the perturbation is always entrained into these oscillations. The rate at which this occurs is relatively insensitive to the chemical effects, measured by the Damkohler number, and is comparable to the rate of homogenization of a passive contaminant. When both steady and oscillatory states are stable, spatially homogeneous states, two possibilities can occur. For the smaller Damkohler numbers, a localized perturbation at the steady state is homogenized within the background oscillations. For larger Damkohler numbers, regions of both oscillatory and steady behavior can co-exist for relatively long times before the system collapses to having the steady state everywhere. An interpretation of this behavior is provided by the one-dimensional Lagrangian filament model, which is analyzed in detail

Association of Childhood Psychosocial Environment With 30-Year Cardiovascular Disease Incidence and Mortality in Middle Age

Background Childhood adversity and trauma have been shown to be associated with poorer cardiovascular disease (CVD) outcomes in adulthood. However, longitudinal studies of this association are rare. Methods and Results Our study used the CARDIA (Coronary Artery Risk Development in Young Adults) Study, a longitudinal cohort that has followed participants from recruitment in 1985-1986 through 2018, to determine how childhood psychosocial environment relates to CVD incidence and all-cause mortality in middle age. Participants (n=3646) completed the Childhood Family Environment (CFE) questionnaire at the year 15 (2000-2001) CARDIA examination and were grouped by high, moderate, or low relative CFE adversity scores. We used sequential multivariable regression models to estimate hazard ratios of incident (CVD) and all-cause mortality. Participants were 25.1+/-3.6 years old, 47% black, and 56% female at baseline and 198 participants developed CVD (17.9 per 10 000 person-years) during follow-up. CVD incidence was \u3e 50% higher for those in the high CFE adversity group compared with those in the low CFE adversity group. In fully adjusted models, CVD hazard ratios (95% CI) for participants who reported high and moderate CFE adversity versus those reporting low CFE adversity were 1.40 (0.98-2.11) and 1.25 (0.89-1.75), respectively. The adjusted hazard ratios for all-cause mortality was 1.68 (1.17-2.41) for those with high CFE adversity scores and 1.55 (1.11-2.17) for those with moderate CFE adversity scores. Conclusions Adverse CFE was associated with CVD incidence and all-cause mortality later in life, even after controlling for CVD risk factors in young adulthood

Effective dynamics of an electrically charged string with a current

Equations of motion for an electrically charged string with a current in an external electromagnetic field with regard to the first correction due to the self-action are derived. It is shown that the reparametrization invariance of the free action of the string imposes constraints on the possible form of the current. The effective equations of motion are obtained for an absolutely elastic charged string in the form of a ring (circle). Equations for the external electromagnetic fields that admit stationary states of such a ring are revealed. Solutions to the effective equations of motion of an absolutely elastic charged ring in the absence of external fields as well as in an external uniform magnetic field are obtained. In the latter case, the frequency at which one can observe radiation emitted by the ring is evaluated. A model of an absolutely nonstretchable charged string with a current is proposed. The effective equations of motion are derived within this model, and a class of solutions to these equations is found.Comment: 14 pages, 3 figures, format changed, minor change

Stagnation-point flow and heat transfer over an exponentially stretching/shrinking cylinder

The stagnation-point boundary-layer flow and heat transfer over an exponentially stretching/shrinking cylinder is studied. The governing partial differential equations in cylindrical form are first transformed into ordinary differential equations which are then solved numerically using a shooting method. Results for the skin friction coefficient, local Nusselt number, velocity and temperature profiles are presented and discussed in detail. The effects of the stretching/shrinking parameter ɛ and the curvature parameter γ on the fluid flow and heat transfer characteristics are also examined. It is found that the solutions for a shrinking cylinder are non-unique and that the surface shear stress and the heat transfer rate at the surface increase as the curvature parameter increases

Socioeconomic status and polycystic ovary syndrome

BACKGROUND: Polycystic ovary syndrome (PCOS) is a common metabolic-endocrine disorder in women and is associated with a number of metabolic morbidities. We examined the association of PCOS and its components with socioeconomic status (SES) over the life course to explore the role of the environment on the development of PCOS. METHODS: Participants included 1163 women, aged 34-39, from the Coronary Artery Risk Development in Young Adults (CARDIA) Women\u27s Study, examined at year 16 of the CARDIA study (2001). PCOS was defined according to the 1990 National Institutes of Health (NIH) criteria. RESULTS: Logistic regression models, adjusted for age, body mass index (BMI), waist circumference, and oral contraceptive (OC) use, demonstrated a statistically significant association between those women with low parental education/high personal education and PCOS (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.4-4.4). CONCLUSIONS: Our results indicate that women who experienced low childhood SES are at increased risk of PCOS, but this risk is limited to those who have personally attained a high level of education. More research is needed to determine the childhood socioeconomic factors that might influence this risk and whether conditions associated with upward life mobility play a role or if this group of at-risk women is simply more likely to recall the symptoms that define PCOS

Artificial Intelligence to Enhance Mission Science Output for In-situ Observations: Dealing with the Sparse Data Challenge

In the Earth's magnetosphere, there are fewer than a dozen dedicated probes beyond low-Earth orbit making in-situ observations at any given time. As a result, we poorly understand its global structure and evolution, the mechanisms of its main activity processes, magnetic storms, and substorms. New Artificial Intelligence (AI) methods, including machine learning, data mining, and data assimilation, as well as new AI-enabled missions will need to be developed to meet this Sparse Data challenge.Comment: 4 pages, 1 figure; Heliophysics 2050 White Pape

Area characteristics, individual-level socioeconomic indicators, and smoking in young adults: the coronary artery disease risk development in young adults study

The 10-year follow-up examination in 1995-1996 to the population-based Coronary Artery Disease Risk Development in Young Adults Study was used to compare the strength with which socioeconomic indicators at the individual and area levels are related to smoking prevalence and to investigate contextual effects of area characteristics. When categories based on similar percentile cutoffs were compared, differences across area categories in the odds of smoking were smaller than differences across categories based on individual-level indicators. In Whites, there was evidence of a significant contextual effect of area characteristics on smoking: Living in the most disadvantaged area quartiles was associated with 50-110% higher odds of smoking, even after controlling for individual-level socioeconomic indicators. Clear contextual effects of area characteristics were not present in Blacks, but there was evidence that contextual effects may emerge at higher levels of individual-level socioeconomic position. Similar results were obtained for census tracts and block groups. Even in the presence of contextual effects, area measures may underestimate associations of individual-level variables with health outcomes. On the other hand, as illustrated by the presence of contextual effects, area- and individual-level measures are likely to tap into different constructs.http://deepblue.lib.umich.edu/bitstream/2027.42/78991/1/DiezRouxMerkin2003_AJE.pd