pH-Dependent surface charge at the interfaces between aluminum gallium nitride (AlGaN) and aqueous solution revealed by surfactant adsorption.

HYPOTHESIS: The net surface charge of AlGaN/GaN structures, where AlGaN is in contact with the solution, is controlled by the pH-dependent protonation and deprotonation of the surface hydroxyl groups and possibly the electron-deficient surface electronic states. We hypothesize that atomic force microscopy (AFM) force measurements of ionic surfactant adsorption can reveal how the AlGaN surface properties vary with pH. EXPERIMENTS: AFM force curves and images were used to probe the AlGaN/solution interface in water as a function of pH, and with added cationic surfactant cetyltrimethylammonium bromide (CTAB) or anionic surfactant sodium dodecylsulfate (SDS). FINDINGS: The AlGaN/solution interface is negatively charged at pH 12, has an isoelectric point near pH 5.5, and is positively charged at pH values less than 5.5. Surfactant adsorption data suggests AlGaN surface is somewhat hydrophobic at acidic pH. Compared to gallium nitride (GaN), at pH 2, AlGaN has a lower charge density and hydrophobicity, but at other values of pH, the surface properties of AlGaN and GaN are similar.

pH-dependent surface properties of the gallium nitride - Solution interface mapped by surfactant adsorption.

HYPOTHESIS: The surface charge of gallium nitride (GaN) in contact with solution is controlled by pH via surface protonation and deprotonation, similar to silica. Ionic surfactants adsorb on surfaces via electrostatic and hydrophobic interactions and can be utilized to reflect the surface charge of GaN. EXPERIMENTS: The surface charge properties of Ga-polar GaN in solution were probed as a function of pH using atomic force microscopy (AFM). AFM soft-contact images and force curves were used to study the pH-dependent adsorption of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecylsulfate (SDS) on GaN surfaces. To further confirm the AFM results, GaN/AlGaN/GaN heterostructure-based ion sensing devices were used to measure the surfactant adsorption over the same pH range. FINDINGS: SDS aggregates adsorb on GaN below pH 2.75 while CTAB aggregates adsorb above pH 10. This shows that the GaN surface carries substantial net positive charge at low pH, and negative charge at high pH. There is no clear SDS or CTAB adsorption on the GaN surface between pH 3 and 9.75, which indicates the surface is weakly charged. GaN/AlGaN/GaN heterostructure-based devices confirm these results, and demonstrate the utility of these devices for measuring surfactant adsorption.

Risk Profiles for Falls among Older Adults: New Directions for Prevention.

OBJECTIVE: To address whether neighborhood factors, together with older adults' levels of health and functioning, suggest new combinations of risk factors for falls and new directions for prevention. To explore the utility of Grade-of-Membership (GoM) analysis to conduct this descriptive analysis. METHOD: This is a cross-sectional, descriptive study of 884 people aged ≥65 years from Alameda County, CA, Cook County, IL, Allegheny County, PA, and Wake and Durham counties, NC. Interviews focused on neighborhood characteristics, physical and cognitive function, walking, and falls and injuries. Four risk profiles (higher order interactions of individual and neighborhood factors) were derived from GoM analysis. RESULTS: Profiles 1 and 2 reflect previous results showing that frail older adults are likely to fall indoors (Profile 1); healthy older adults are likely to fall outdoors (Profile 2). Profile 3 identifies the falls risk for older with mild cognitive impairment living in moderately walkable neighborhoods. Profile 4 identifies the risk found for healthy older adults living in neighborhoods with low walkability. DISCUSSION: Neighborhood walkability, in combination with levels of health and functioning, is associated with both indoor and outdoor falls. Descriptive results suggest possible research hypotheses and new directions for prevention, based on individual and neighborhood factors.

Age, period, and cohort effects on gastric cancer mortality.

BACKGROUND: The incidence of gastric cancer varies both within and among populations and can change rapidly without a corresponding decline in Helicobacter pylori prevalence. Here, we describe the changes in gastric cancer mortality in Japan in relation to age-period-cohort effects as well as the decline in H. pylori prevalence. METHODS: We used data from Japanese for men and women aged 30-94 for birth years 1875-1970 (calendar time 1950-2000) to observe the age, period and cohort effects on gastric cancer mortality rates. Additionally, we used Poisson regression to simultaneously adjust for concurrent age, period and cohort effects as well as for declining H. pylori prevalence in the Japanese population. RESULTS: There was an approximate 60 % decline in gastric cancer mortality between 1965 and 1995. Detailed age, period and cohort analyses and Poisson regression analysis showed these factors interact in complex ways, analyses focused on one or two of these effects, such as birth cohort without considering concurrent age and period would obscure important interactions that affected different age groups at different times to produce this composite effect. CONCLUSION: The underlying complexity in population-disease dynamics requires population-specific descriptions of trends using multiple methods to provide an in-depth analysis while simultaneously allowing for necessary statistical adjustments as well as identification of interactions. More thorough descriptions of the population-specific general trends in relation to changes in the population structure (age-period-cohort) enable better prevention and health care policy planning, and further, the descriptions enable hypothesis generation regarding causes of population-specific disease patterns.

Adolescent risk taking under stressed and nonstressed conditions: conservative, calculating, and impulsive types.

PURPOSE: Adolescent risk taking may result from heightened susceptibility to environmental cues, particularly emotion and potential rewards. This study evaluated the impact of social stress on adolescent risk taking, accounting for individual differences in risk taking under nonstressed conditions. METHODS: Eighty-nine older adolescents completed a computerized risk-taking and decision-making battery at baseline. At follow-up, participants were randomized to a control condition, which repeated this battery, or an experimental condition, which included a social and cognitive stressor before the battery. Baseline risk-taking data were cluster-analyzed to create groups of adolescents with similar risk-taking tendencies. The degree to which these risk-taking tendencies predicted risk taking by stress condition was assessed at follow-up. RESULTS: Participants in the stress condition took more risks than those in the no-stress condition. However, differences in risk taking under stress were related to baseline risk-taking tendencies. We observed three types of risk-takers: conservative, calculated, and impulsive. Impulsives were less accurate and planful under stress; calculated risk takers took fewer risks; and conservatives engaged in low risk taking regardless of stress. CONCLUSIONS: As a group, adolescents are more likely to take risks in "hot cognitive" than in "cold cognitive" situations. However, there is significant variability in adolescents' behavioral responses to stress related to trait-level risk-taking tendencies.

Why do adolescents say they are less healthy than their parents think they are? The importance of mental health varies by social class in a nationally representative sample.

OBJECTIVE: We sought to (1) confirm the discrepancy between parent-reported and youth-reported adolescent health in a nationally representative sample, (2) compare the predictors of parent-reported and adolescent self-reported health, and (3) determine whether the discrepancy between the 2 ratings differed by sociodemographic characteristics, particularly income. METHODS: Data were from the 2001-2002 National Health and Nutrition Examination Survey. A total of 1157 adolescents aged 12 to 15 years, representative of 16,227,827 US youth, were included. Youth and their parents reported on the youth's health status along with other indicators of health and illness and sociodemographic characteristics. To examine predictors of self-rated and parent-rated adolescent health (excellent to poor), bivariate analyses were conducted, followed by multiple linear regression adjusted for relevant covariates. All of the analyses were stratified by income (standardized poverty income index: < or = 1 vs > 1). RESULTS: Parents and youth differed in subjective judgments regarding the child's health, even when these differences were not supported by other health indicators (days of school missed because of illness or injury or days of poor mental or physical health). Poor adolescents reported worse self-rated health than higher-income youth, and their parents did also. In income-stratified multiple regression models, higher-income adolescents' and their parents' ratings were predicted by indicators of physical health. In contrast, poor youth and parent ratings were better predicted by mental health care use. Poor youth with a mental health visit in the last year reported better health, but their parents saw these mental health visits as an indication of poor health. CONCLUSIONS: The findings suggest that social class differences in subjective ratings of adolescents' health are related to the differential ways that youth and parents determine what constitutes health and are not simply a reflection of objective health status.

Self-rated current and future health independently predict subsequent mortality in an aging population.

BACKGROUND: Self-rated current health is an independent, robust predictor of subsequent mortality in older adults. Investigators hypothesize that individuals likely take into account their future health when reporting their current health. However, few have measured and examined self-rated future health in relation to mortality. METHODS: We investigate the effect of three self-rated health measures on 10-year mortality in 2091 men and women in an aging cohort: (i) self-rated current health, (ii) self-rated future health (1 year in the future), and (iii) a combined measure of current and future health. Vital status at follow-up year 10 was the outcome. We used data from SPPARCS (Study of Physical Performance and Age-Related Changes in Sonomans), a population-based, census-sampled, study of the epidemiology of aging, health, and functioning. RESULTS: Compared to those reporting their future health as better/same, participants reporting their future health as worse or unknown (don't know) experienced elevated 10-year mortality (adjusted rate ratio [RR]=1.6, 95% confidence interval [CI], 1.2-2.1, p=.01), after adjustment for self-rated current health and other relevant covariates. The combined measure of current and future health also contributed important information. Compared to the referent (the best combination, current health excellent/good and future health better/same), participants reporting the worst combination, fair/poor current health and worse/unknown future health, experienced the highest 10-year mortality in the cohort (adjusted RR=3.2, 95% CI, 2.2-4.7, p=.00). CONCLUSIONS: Self-rated future health is an independent, robust predictor of mortality. It is as predictive of subsequent mortality in older adults as the standard measure of self-rated current health. Furthermore, a measure that combines self-reports of current health with future health was most useful in the identification of older adults with the highest mortality rates. Thus, the combined measure of current and future health may be most useful in practice, in distinguishing the differential mortality rates among persons reporting fair or poor self-rated current overall health.

Pathways to health: a framework for health-focused research and practice.

Public health research and practice is faced with three problems: 1) a focus on disease instead of health, 2) consideration of risk factor/disease relationships one at a time, and 3) attention to individuals with limited regard for the communities in which they live. We propose a framework for health-focused research and practice. This framework encompasses individual and community pathways to health while incorporating the dynamics of context and overall population vulnerability and resilience. Individual pathways to health may differ, but commonalities will exist. By understanding these commonalities, communities can work to support health-promoting pathways in addition to removing barriers. The perspective afforded by viewing health as a dynamic process instead of as a collection of risk factors and diseases expands the number of approaches to improving health globally. Using this approach, multidisciplinary research teams working with active community participants have the potential to reshape health and intervention sciences.

Dynamics of Helicobacter pylori infection in a US-Mexico cohort during the first two years of life.

BACKGROUND: The Pasitos Cohort Study has followed children in El Paso, Texas and Ciudad Juarez, Mexico since 1998 to identify determinants of Helicobacter pylori infection. This paper describes patterns of acquisition and elimination of H. pylori infection in 468 children from birth to 24 months. METHODS: Mothers were recruited during pregnancy at maternal-child clinics; children were targeted for follow-up examinations every 6 months after birth. H. pylori infection was detected using the 13C-urea breath test, corrected for age-dependent variation in CO2 production. RESULTS: Test results were available for 359, 341, 269, and 215 children around target ages of 6, 12, 18, and 24 months, respectively. The person-time at risk of a first detectable infection was 7742 person-months; 128 first infections were detected, thus the incidence rate was 1.7% per month (95% confidence interval 1.4-2.0%). Rates were similar in boys and girls and on both sides of the border; evidence suggests, however, that this similarity could be due to selection bias. Among children with follow-up after a positive test, 77% tested negative at a later visit. CONCLUSIONS: The initial acquisition of detectable H. pylori infection occurred at a rate of 20% per year among Pasitos Cohort children from birth to 24 months of age. A key finding, with implications for clinical, community health, and research settings, is that most of these infections did not persist. The transient nature of early H. pylori infection should be considered when designing research or contemplating therapeutic intervention for this age group.

You might as well smoke; the misleading and harmful public message about smokeless tobacco.

BACKGROUND: Compared to smoking cigarettes, use of Western smokeless tobacco (ST) products is associated with a very small risk of life-threatening disease (with estimates in the range of a few percent of the risk from smoking, or even less). This means that smokers can realize substantial health benefits by switching to ST, an obvious substitute. But consumers and policy makers have little chance of learning that ST is much less dangerous than smoking because popular information provided by experts and advocates overstates the health risks from ST relative to cigarettes. METHODS: To examine the extent of this overstatement in one medium, we conducted a systematic review of websites containing information about ST and health risks. We examined the content of 316 relevant websites identified by a Google search. RESULTS: We found that when any substantive information about the risk from ST is given, the risk is almost universally conflated with the risk from cigarettes. Accurate comparative risk information was quite rare, provided by only a handful of websites, all appearing low in our search results (i.e., of low popularity and thus unlikely to be found by someone searching for information). About 1/3 of the websites, including various authoritative entities, explicitly claimed that ST is as bad as or worse than cigarettes. Most of the other sites made statements that imply the risks are comparable. CONCLUSION: Through these websites, and presumably other information provided by the same government, advocacy, and educational organizations, ST users are told, in effect, that they might as well switch to smoking if they like it a bit more. Smokers and policy makers are told there is no potential for harm reduction. These messages are clearly false and likely harmful, representing violations of ethical standards.

Helicobacter pylori infection in pregnant women from a U.S.-Mexico border population.

Helicobacter pylori infection causes chronic digestive diseases that disproportionately affect Hispanics and other immigrant groups in the United States. Information on the epidemiology of H. pylori infection in pregnant women who reside along the U.S.-Mexico border is critical to understanding the dynamics of current H. pylori transmission patterns within families along the border. We describe the epidemiology of H. pylori infection in pregnant women recruited from Women, Infants, and Children (WIC) clinics in El Paso, Texas, and Mexican Social Security Institute maternal-child clinics in Ciudad Juarez, Mexico, from April 1998 to October 2000. We interviewed participants regarding environmental factors and tested their serum for IgG antibodies. We used logistic regression to estimate associations between environmental exposures and the odds of H. pylori prevalence. Definitive serological tests were available from 751 women. Seroprevalence was 74% in Juarez women and 56% in El Paso women. Prevalence increased with age, crowding, poor sanitation, and residence in Mexico, decreased with education, and was not associated with the woman's number of living children. In the U.S.-Mexico border region, women of reproductive age have a high prevalence of H. pylori infection, apparently related to poor socioeconomic conditions.

Establishment of a binational cohort to study Helicobacter pylori infection in children.

Chronic Helicobacter (H.) pylori infection, typically of childhood onset, causes upper digestive tract diseases of major impact among socioeconomically marginalized populations. This infection is common in children from ethnic minorities in the United States, and particularly so in immigrant children from Mexico. Prevention measures for H. pylori infection do not yet exist, given limited understanding of what causes either acute or persistent infection. To address this gap, we initiated the Pasitos Cohort Study to follow children from low-income families in the border region that includes El Paso County, Texas, and Ciudad Juarez, Chihuahua. The children were enrolled prior to birth, and are examined at 6-month intervals to observe the natural history of H. pylori infection, and to identify risk factors for acquisition, recurrence, and persistence. This report details the study methods, describes how the cohort was established, and discusses the challenges of compliance with follow up in the border setting. Between April 1998 and October 2000, 1,288 pregnant women were screened for eligibility; 807 of 994 eligible women consented to participate. Birth documentation was obtained for 615 infants, and 472 entered follow up. Successful follow up of this cohort requires resources, including a well-trained, dedicated staff, and incentives, to facilitate and motivate long-term participation. Future findings from this ongoing study will help to fill critical gaps in knowledge regarding the epidemiology of H. pylori infection, and will contribute to the identification of prevention strategies.