Quantitative localized proton-promoted dissolution kinetics of calcite using scanning electrochemical microscopy (SECM)

Scanning electrochemical microscopy (SECM) has been used to determine quantitatively the kinetics of proton-promoted dissolution of the calcite (101̅4) cleavage surface (from natural “Iceland Spar”) at the microscopic scale. By working under conditions where the probe size is much less than the characteristic dislocation spacing (as revealed from etching), it has been possible to measure kinetics mainly in regions of the surface which are free from dislocations, for the first time. To clearly reveal the locations of measurements, studies focused on cleaved “mirror” surfaces, where one of the two faces produced by cleavage was etched freely to reveal defects intersecting the surface, while the other (mirror) face was etched locally (and quantitatively) using SECM to generate high proton fluxes with a 25 μm diameter Pt disk ultramicroelectrode (UME) positioned at a defined (known) distance from a crystal surface. The etch pits formed at various etch times were measured using white light interferometry to ascertain pit dimensions. To determine quantitative dissolution kinetics, a moving boundary finite element model was formulated in which experimental time-dependent pit expansion data formed the input for simulations, from which solution and interfacial concentrations of key chemical species, and interfacial fluxes, could then be determined and visualized. This novel analysis allowed the rate constant for proton attack on calcite, and the order of the reaction with respect to the interfacial proton concentration, to be determined unambiguously. The process was found to be first order in terms of interfacial proton concentration with a rate constant k = 6.3 (± 1.3) × 10–4 m s–1. Significantly, this value is similar to previous macroscopic rate measurements of calcite dissolution which averaged over large areas and many dislocation sites, and where such sites provided a continuous source of steps for dissolution. Since the local measurements reported herein are mainly made in regions without dislocations, this study demonstrates that dislocations and steps that arise from such sites are not needed for fast proton-promoted calcite dissolution. Other sites, such as point defects, which are naturally abundant in calcite, are likely to be key reaction sites

Learning object relationships which determine the outcome of actions

Peer reviewedPublisher PD

Problem opioid use and HIV primary care engagement among hospitalized people who use drugs and/or alcohol

Background There is growing public health concern around the potential impact of the opioid crisis on efforts to eradicate HIV. This secondary analysis seeks to determine if those who report opioids as their primary problem drug compared to those who report other drugs and/or alcohol differ in engagement in HIV primary care among a sample of hospitalized people with HIV (PWH) who use drugs and/or alcohol, a traditionally marginalized and difficult to engage population key to ending the HIV epidemic. Setting and participants A total of 801 participants (67% male; 75% Black, non-Hispanic; mean age 44.2) with uncontrolled HIV and reported drug and/or alcohol use were recruited from 11 hospitals around the U.S. in cities with high HIV prevalence from 2012 to 2014 for a multisite clinical trial to improve HIV viral suppression. Methods A generalized linear model compared those who reported opioids as their primary problem drug to those who reported other problem drugs and/or alcohol on their previous engagement in HIV primary care, controlling for age, sex, race, education, income, any previous drug and/or alcohol treatment, length of time since diagnosis, and study site. Results A total of 95 (11.9%) participants reported opioids as their primary problem drug. In adjusted models, those who reported opioids were significantly less likely to have ever engaged in HIV primary care than those who reported no problem drug use (adjusted risk ratio, ARR = 0.84, 95% Confidence Interval, CI 0.73, 0.98), stimulants (ARR = 0.84, 95% CI 0.74, 0.95), and polydrug use but no alcohol (ARR = 0.79, 95% CI 0.68, 0.93). While not statistically significant, the trend in the estimates of the remaining drug and/or alcohol categories (alcohol, cannabis, polydrug use with alcohol, and [but excluding the estimate for] other), point to a similar phenomena—those who identify opioids as their primary problem drug are engaging in HIV primary care less. Conclusions These findings suggest that for hospitalized PWH who use drugs and/or alcohol, tailored and expanded efforts are especially needed to link those who report problem opioid use to HIV primary care. Trial registration This study was funded by National Institutes of Health (NIH) grant: U10-DA01372011 (Project HOPE—Hospital Visit as Opportunity for Prevention and Engagement for HIV-Infected Drug Users; Metsch); which is also a registered clinical trial under the Clinical Trials Network (CTN-0049). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH

Team reasoning and the rational choice of payoff-dominant outcomes in games

Standard game theory cannot explain the selection of payoff-dominant outcomes that are best for all players in common-interest games. Theories of team reasoning can explain why such mutualistic cooperation is rational. They propose that teams can be agents and that individuals in teams can adopt a distinctive mode of reasoning that enables them to do their part in achieving Pareto-dominant outcomes. We show that it can be rational to play payoff-dominant outcomes, given that an agent group identifies. We compare team reasoning to other theories that have been proposed to explain how people can achieve payoff-dominant outcomes, especially with respect to rationality. Some authors have hoped that it would be possible to develop an argument that it is rational to group identify. We identify some large—probably insuperable—problems with this project and sketch some more promising approaches, whereby the normativity of group identification rests on morality

Self-Cognitions in Antisocial Alcohol Dependence and Recovery

Cross-sectional relationships between content and structural properties of the self-concept and alcohol use in young adults with antisocial alcohol dependence (AAD) (n = 24), those in recovery from AAD (n = 18), and controls (n = 23) were examined using the schema model of the self-concept. Persons with AAD had a trend toward fewer positive self-schemas than did controls, and had more negative self-schemas and a trend toward higher interrelatedness than did those in recovery and controls. They also showed evidence of a drinking-related self-schema, whereas those in recovery showed evidence of a recovery-related self-schema. Finally, evidence to support a model using properties of the self-concept to predict high levels of alcohol use was found. These findings provide a beginning empirical foundation for the development of nursing interventions aimed at altering self-structure to prevent the development of and promote recovery from antisocial alcohol dependence.http://deepblue.lib.umich.edu/bitstream/2027.42/65124/1/Corte & Stein 07.pd

Charlie-is-so-“English”-like: Nationality and the branded-celebrity person in the age of YouTube

The YouTube celebrity is a novel social phenomenon. YouTube celebrities have implications for the social and cultural study of celebrity more generally but in order to illustrate the features of vlogging celebrity and its wider dimensions, this article focuses upon one case-study – Charlie McDonnell and his video ‘How to be English’. The premise of YouTube – ‘Broadcast Yourself’ – begs the question ‘but what self?’ The article argues the YouTube celebrity is able to construct a celebrity persona by appealing to aspects of identity, such as nationality, and use them as a mask(s) to perform with. By situating Charlie’s ‘How to be English’ in the context of establishing celebrity, the article argues that the processes of celebrification and ‘self-branding’ utilise the power of identity myths to help assist the construction of a celebrity persona. Use of masks and myths allows for one to develop various aspects of their persona into personae. One such persona for Charlie is his ‘Englishness’. As the social experience of ‘Broadcasting Yourself’ necessarily asks one to turn ordinary aspects of their person into extra-ordinary qualities, Charlie’s use of Englishness allows ‘being English’ to become a mythological device to overcome the problem of ‘self-promotion’

The notion of contextual locking: Previously learnt items are not accessible as such when appearing in a less common context

We examined the effect of context on the learning of spatial coding in four experiments. Two partially overlapping sets of stimuli, which had the very same stimulus–response spatial coding, were presented in unique contexts. Results show contextual locking—that is, response times to the very same item in a more common context (80%) were significantly shorter than those in a less common context (20%). Contextual locking was obtained both when the context was more salient (Experiments 1 and 2) and less salient (Experiments 3 and 4). In addition, results were obtained even when contextualization seemed less necessary (Experiments 2 and 4). Binding of information to context is discussed in relation to chunking, transfer effects, and practical applications pertaining to professional training