Convergence of iterative split-operator approaches for approximating nonlinear reactive transport problems

Abstract Numerical solutions to nonlinear reactive solute transport problems (NRTPs) are often computed using split-operator (SO) approaches, which separate the transport and reaction processes. This uncoupling introduces an additional source of numerical error, known as the splitting error. The iterative split-operator (ISO) algorithm removes the splitting error through iteration. Although the ISO algorithm is often used, there has been very little analysis of its convergence behavior. This work uses theoretical analysis and numerical experiments to investigate the convergence rate of the ISO approach for solving NRTPs. We show that under certain assumptions regarding smoothness, the convergence rate of the ISO algorithm applied NRTPs is O(Δ ). We demonstrate that the theoretical convergence rate can be achieved in practice if the numerical solution of the transport and reaction steps are carried out with sufficient accuracy. We also show that accurate estimation of the lagged operator in each step is crucial to obtaining the theoretical convergence rate

An Examination of Prepartying and Drinking Game Playing During High School and Their Impact on Alcohol-Related Risk Upon Entrance into College

Prepartying and drinking game playing are associated with excessive alcohol consumption and alcohol-related negative consequences in college populations; however, research exploring the prevalence of these high risk drinking contexts among high school students, and how such engagement may impact both high school and subsequent college drinking risk, is lacking. The current study, which is the first study to assess prepartying during high school, examined how engaging in either prepartying or drinking game playing during high school was associated with risky high school drinking as well asalcohol use and consequences during the transitional first month of college. The study involved 477 first-year college students, the majority of whom were 18 years old (94%), female (66%), and Caucasian (59%). Prepartying was found to be highly prevalent in high school (45%). Further, students who prepartied or played drinking games during high school drank significantly more in high school than students who did not engage in these high risk activities. Finally, prepartying and game playing during high school were associated with greater collegiate alcohol consumption (controlling for high school drinking) and consequences (controlling for both high school and college drinking). This study establishes prepartying and drinking games as common high risk activities among both high school and incoming first-year college students, and addresses implications for prevention and targeted interventions

Differential Drinking Patterns of Family History Positive and Family History Negative First Semester College Females

Objective This study compares the natural drinking patterns of family history positive and family history negative women during their first semester of college, a transitional period known to coincide with considerable alcohol-related risks. Method Seventy-two incoming undergraduate females, approximately half of whom reported a family history of alcohol misuse, completed initial questionnaires as well as Timeline Followback assessments. In addition, participants completed five successive weeks of online behavioral diaries measuring three categories of prospective alcohol consumption: total drinks, maximum drinks, and heavy episodic drinking events. Repeated measures ANCOVA models, controlling for prior alcohol consumption, examined participants’ drinking behavior. Results Over the course of the five assessed weeks, first semester females with a genetic predisposition to alcohol problems were found to consume significantly more total drinks (p \u3c .05), maximum drinks (p \u3c .05), and were more likely to drink heavily (p \u3c .05) than family history negative peers. Conclusions Findings highlight increased alcohol-related risks faced by incoming first-year college females with a reported family history of problematic drinking and, thus, emphasize the need for early interventions targeted toward this at-risk group

Development and Validation of the Hookup Motives Questionnaire (HMQ)

Despite the high prevalence rates and growing research on hooking up among college students, no multidimensional inventory exists in the literature to assess motivations for hooking up. In the current study, we report on the development and validation of the Hookup Motives Questionnaire (HMQ), designed to assess the various reasons for hooking up. Exploratory and confirmatory factor analyses were conducted using 2 samples of college students (Campus 1, N = 401; Campus 2, N = 367). Exploratory factor analysis was undertaken to explore the psychometric properties of an initial set of 25 items, and confirmatory factor analysis was conducted to evaluate additional properties of the factor structure. The final factor structure of the HMQ contained 19 items that tapped 5 subscales representing social-sexual, social-relationship, enhancement, coping, and conformity motives. Results demonstrated good internal consistency and discriminant validity for the subscales. Moreover, criterion-related validity was satisfied by showing that HMQ subscales significantly correlated with hookup approval and behavior. Gender differences on the measures were found. The inventory offers considerable potential as a psychometrically sound instrument that may be administered to understand reasons for engaging in potentially risky hookup behaviors and used to inform the design of sexual health programs and interventions targeting young adults

Identifying Factors That Increase the Likelihood for Alcohol-Induced Blackouts in the Prepartying Context

The present study examined risk factors related to “blacking out” (e.g., temporary periods of memory loss during drinking) during preparty drinking events (i.e., pregaming, predrinking). Participants were students from two universities on the West Coast who reported past month prepartying (N = 2,546) in online surveys administered in the fall of 2008. Among these students, 25% (n = 636) reported blacking out during at least one occasion in which they prepartied in the past month. A logistic regression model underscored that Greek student affiliation, family history of alcohol abuse, frequency of prepartying, and both playing drinking games and consuming shots of liquor while prepartying increased the likelihood of blacking out. Limitations and implications for future research and collegiate prevention strategies are discussed

Global sleep quality as a moderator of alcohol consumption and consequences in college students

The authors examined the relationship between global sleep quality and alcohol risk, including the extent to which global sleep quality moderated the relationship between alcohol use and drinking-related consequences. Global sleep quality was measured using the Pittsburgh Sleep Quality Index (PSQI) and alcohol-related consequences were assessed using the Rutgers Alcohol Problem Index (RAPI). The sample consisted of 261 college students (61.3% female, 58.2% Caucasian) who completed online surveys. Using a four-step hierarchical multiple regression model, global sleep quality was found to predict alcohol consequences, over and above assessed covariates (demographics and weekly drinking). Further, global sleep quality emerged as a strong moderator in the drinking-consequences relationship such that among heavier drinkers, those with poorer global sleep quality experienced significantly greater alcohol-related harm. Campus health education and alcohol interventions may be adapted to address the importance of maintaining a healthy lifestyle, both in terms of healthful sleeping and drinking behaviors, which appear to play a strong synergistic role in alcohol-related risk

Hooking Up in the College Context: The Event-Level Effects of Alcohol Use and Partner Familiarity on Hookup Behaviors and Contentment

The current study examined hooking up experiences through event-level analyses, including the connections involving alcohol use, the extent of physical contact, and postevaluations of the hookup event. Participants were 828 college students (67.0% female). Of students who reported hooking up sometime within the past year (54.8%), chi-square analyses revealed that they were more likely to have been drinking when they met their partners the night of the hookup. Females who were drinking beforehand and females who met their partners that night were more likely to feel discontent with their hookup decisions. Among participants who consumed alcohol prior to their last hookup, a notable 30.7% of females and 27.9% of males indicated that they would likely not have hooked up with their partners had alcohol not been involved. Further, 34.4% of females and 27.9% of males indicated that they would not have gone as far physically if they had not been drinking. Among participants who reported both drinking beforehand and hooking up with unfamiliar partners, greater number of drinks consumed was associated with more advanced sexual behaviors. The current findings highlight the potential risks associated with alcohol use in the hooking up culture

Crystal structure of the Na+/H+ antiporter NhaA at active pH reveals the mechanistic basis for pH sensing.

The strict exchange of protons for sodium ions across cell membranes by Na+/H+ exchangers is a fundamental mechanism for cell homeostasis. At active pH, Na+/H+ exchange can be modelled as competition between H+ and Na+ to an ion-binding site, harbouring either one or two aspartic-acid residues. Nevertheless, extensive analysis on the model Na+/H+ antiporter NhaA from Escherichia coli, has shown that residues on the cytoplasmic surface, termed the pH sensor, shifts the pH at which NhaA becomes active. It was unclear how to incorporate the pH senor model into an alternating-access mechanism based on the NhaA structure at inactive pH 4. Here, we report the crystal structure of NhaA at active pH 6.5, and to an improved resolution of 2.2 Å. We show that at pH 6.5, residues in the pH sensor rearrange to form new salt-bridge interactions involving key histidine residues that widen the inward-facing cavity. What we now refer to as a pH gate, triggers a conformational change that enables water and Na+ to access the ion-binding site, as supported by molecular dynamics (MD) simulations. Our work highlights a unique, channel-like switch prior to substrate translocation in a secondary-active transporter

L-Edge Spectroscopy of Dilute, Radiation-Sensitive Systems Using a Transition-Edge-Sensor Array

We present X-ray absorption spectroscopy and resonant inelastic X-ray scattering (RIXS) measurements on the iron L-edge of 0.5 mM aqueous ferricyanide. These measurements demonstrate the ability of high-throughput transition-edge-sensor (TES) spectrometers to access the rich soft X-ray (100-2000eV) spectroscopy regime for dilute and radiation-sensitive samples. Our low-concentration data are in agreement with high-concentration measurements recorded by conventional grating-based spectrometers. These results show that soft X-ray RIXS spectroscopy acquired by high-throughput TES spectrometers can be used to study the local electronic structure of dilute metal-centered complexes relevant to biology, chemistry and catalysis. In particular, TES spectrometers have a unique ability to characterize frozen solutions of radiation- and temperature-sensitive samples.Comment: 19 pages, 4 figure

RCT of Web-based Personalized Normative Feedback for College Drinking Prevention: Are Typical Student Norms Good Enough?

Objectives Personalized normative feedback (PNF) interventions are generally effective at correcting normative misperceptions and reducing risky alcohol consumption among college students. However, research has yet to establish what level of reference group specificity is most efficacious in delivering PNF. This study compared the efficacy of a web-based PNF intervention employing eight increasingly-specific reference groups against a Web-BASICS intervention and a repeated-assessment control in reducing risky drinking and associated consequences. Method Participants were 1663 heavy drinking Caucasian and Asian undergraduates at two universities. The referent for web-based PNF was either the typical same-campus student, or a same-campus student at one (either gender, race, or Greek-affiliation), or a combination of two (e.g., gender and race), or all three levels of specificity (i.e., gender, race, and Greek-affiliation). Hypotheses were tested using quasi-Poisson generalized linear models fit by generalized estimating equations. Results The PNF intervention participants showed modest reductions in all four outcomes (average total drinks, peak drinking, drinking days, and drinking consequences) compared to control participants. No significant differences in drinking outcomes were found between the PNF group as a whole and the Web-BASICS group. Among the eight PNF conditions, participants receiving typical student PNF demonstrated greater reductions in all four outcomes compared to those receiving PNF for more specific reference groups. Perceived drinking norms and discrepancies between individual behavior and actual norms mediated the efficacy of the intervention. Conclusions Findings suggest a web-based PNF intervention using the typical student referent offers a parsimonious approach to reducing problematic alcohol use outcomes among college students