Charles Amos

Revealing the Reconstructed Surface of Li[Mn2]O4

The spinel Li[Mn2]O4 is a candidate cathode for a Li-ion battery, but its capacity fades over a charge/discharge cycle of Li1-x[Mn2]O4 (0 < x < 1) that is associated with a loss of Mn to the organic-liquid electrolyte. It is known that the disproportionation reaction 2Mn(3+) = Mn(2+) + Mn(4+) occurs at the surface of a Mn spinel, and it is important to understand the atomic structure and composition of the surface of Li[Mn2]O4 in order to understand how Mn loss occurs. We report a study of the surface reconstruction of Li[Mn2]O4 by aberration-corrected scanning transmission electron microscopy. The atomic structure coupled with Mn-valence and the distribution of the atomic ratio of oxygen obtained by electron energy loss spectroscopy reveals a thin, stable surface layer of Mn3O4, a subsurface region of Li1+x[Mn2]O4 with retention of bulk Li[Mn2]O4. This observation is compatible with the disproportionation reaction coupled with oxygen deficiency and a displacement of surface Li(+) from the Mn3O4 surface phase. These results provide a critical step toward understanding how Mn is lost from Li[Mn2]O4, once inside a battery.

The Relationship Between Perceived Exposure to Promotional Smoking Messages and Smoking Status among High School Students

Data on self-reported perceived exposure to pro-smoking messages were collected from 1,608 high school students surveyed through the ASPIRE (A Smoking Prevention Interactive Experience) Program in Houston, Texas, in 2003. Results indicated that high school smoking quitters had approximately twice the odds of perceived exposure to pro-smoking messages as nonsmokers through billboard advertisements (Adjusted Odds Ratio [AOR] = 2.04, 95% CI: 1.09, 3.81), newspapers & magazines (AOR: 1.97, 95% CI: 1.09, 3.56), and movies (AOR: 1.94, 95% CI: 1.03, 3.65). Smoking experimenters marginally perceived more exposure to pro-smoking radio messages (AOR = 1.31, 95% CI: 1.04, 1.67) and billboard advertisements (AOR = 1.28, 95% CI: 1.02, 1.61) compared to nonsmokers. Lastly, current smokers were 1.82 times as likely to report exposure to pro-smoking poster advertisements as nonsmokers (95% CI: 1.19, 2.79, p < or = .05). These findings suggest that experimenters and quitters may pay more attention to smoking advertisements than nonsmokers and current smokers.

The Association of Drug Use and Post-Traumatic Stress Reactions Due to Hurricane Ike Among Fifth Ward Houstonian Youth

This study shows the important link between higher drug use and self-medication among youth with higher reported posttraumatic stress reactions after natural disasters. The study offers secondary analysis of cross-sectional data collected on 170 predominately African American males through the Fifth Ward Enrichment program (FWEP) in Houston, Texas, between November and December 2009. Men who stated that in the last week they tried to keep from thinking or talking about the hurricane or things that remind them of what happen were significantly more likely to use alcohol (p < .05), marijuana (p < .01), codeine cough syrup (p < .00), anti-energy drinks (p < .00), crystal methamphetamines (p < .00), and Viagra (p < .00). Unadjusted logistic regression showed that they also experienced over twice the odds of reporting past 30 day use of alcohol (OR = 2.57, 95% CI = .98, 6.8), marijuana (OR = 4.31, 95% CI = 1.2, 15.3), codeine cough syrup (OR = 5.22, 95% CI = 1.4, 19.5), and anti-energy drinks (OR = 3.27, 95% CI = 1.0, 1.4). Adjusted logistic regression revealed that male youth post-traumatic stress reaction is a significant predictor of marijuana use (OR = 4.1, 95% CI = 1.0, 16.5). This study shows the important link of higher drug use and self-medication among youth with higher reported posttraumatic stress reactions after natural disasters.

Stigma Consciousness Concerns Related to Drug Use and Sexuality in a Sample of Street-Based Male Sex Workers

Abstract Measurement of, and response to, three different stigmas and their exposure (homosexual behavior, sex work, and drug use) were studied a group of 90 key-informant recruited male sex workers in Houston, Texas who were over 18 and had exchanged sex for money in the previous 7 days. Respondents reported on self-identified sexual orientation and were interviewed, including providing responses on a measure of perceived stigma relating to sexual behavior and drug use. Two thirds were white, almost all had used drugs (many in the past week), and half had ever injected. A fifth identified as heterosexual, with the remainder split between gay and bisexually-identified men. There was a high level of homelessness and contact with the criminal justice system for drug and property offences. Consciousness about drug-related stigma was moderately associated with concerns about drug-related exposure and sensitivity to rejection as a drug user, but not to exposure as homosexual or as a sex worker. Drug-using status is related to greater concern about exposure as a sex worker. Data suggest that stigma is domain-specific and that there are different patterns of response to different stigmata in the same individual. Measurement of stigmata and concern about exposure and rejection need to be specific to stigmatized behaviors, and not generalized to other stigmatized behaviors since the data suggest that they are minimally related.

The relationship between perceived youth exposure to anti-smoking advertisements: how perceptions differ by race.

Data on self-reported perceived exposure to anti-smoking messages were collected from 1,608 high school students surveyed through the ASPIRE (A Smoking Prevention Interactive Experience) Program in Houston, Texas. Data collection took place between October 2002 and March 2003. Logistic regression identified that African Americans perceived significantly less exposure to anti-smoking advertisements via television (OR = .50, p ≤ 0.05) and posters (OR = .61, p ≤ 0.05) than whites. However, they had nearly twice as much perceived exposure to anti-smoking advertisements at movies (OR = 1.79, p ≤ 0.05) and sporting events (OR = 2.1, p ≤ 0.05) than their white counterparts. Hispanic youth perceived significantly less exposure to anti-smoking posters (OR = .51, p ≤ 0.05) and significantly higher exposure to anti-smoking messages at sporting events (OR = 1.92, p ≤ 0.05) and school programs (OR = 3.44, p ≤ 0.05) compared to white youth. While the relationships tested in this study are exploratory, they provide initial evidence for an important nexus between race and communication channels that may impact perceived exposure to tobacco advertising.

Responsibility as a dimension of HIV prevention normative beliefs: Measurement in three drug-using samples

Abstract The concept of responsibility was derived originally from principles of morality, as part of a network of rights, duties and obligations. HIV risk-related studies have suggested that a sense of responsibility for condom use to protect a partner is a potentially important predictor of condom use in drug-using populations. We created a four-item scale measuring Self responsibility to use condoms and Partners responsibility to use condoms. Data were collected from three drug-using samples: crack smokers, HIV seropositive crack smokers in an intervention study in Houston, Texas, and Tanzanian heroin users in Dar es Salaam. Data indicated that the four responsibility items had high alpha coefficients in each sample, and that there were moderate to high intercorrelations between equivalent self and partner responsibility items. There were significant differences in scale scores between the crack smokers and the HIV positive crack smokers and the Tanzanian samples, but no significant differences between the HIV positive and Tanzanian samples. Comparing within the first crack-smoker sample those who were HIV positive and negative showed significant differences in the direction of higher beliefs in responsibility to use condoms in the HIV positive group. These data suggest that responsibility is measurable, holds similar psychometric properties across three samples differing in culture and HIV serostatus, and that condom use responsibility is conceptualized as a measure of general responsibility rather than as a reciprocal self/partner responsibility.

The Link Between Recent Sexual Abuse and Drug Use Among African American Male College Students : It's Not Just a Female Problem in and Around Campus

Abstract This study examined the relationship between sexual abuse in or around campus and drug use among young African-American males in college. It offers cross-sectional analysis of data collected from the Alcohol and Substance Abuse Awareness and Use Study (ASAAUS). Data collection took place in October 2004 via a self-administered survey among 181 African-American male students. Males who reported past sexual abuse in or around campus were significantly more likely than nonsexuallyabused males to have used tobacco (41% v. 19%, p < .05), alcohol (82% v. 49%, p < .05), marijuana (59% v. 30%,p < .05), and cocaine (18% v. 2%, p < .05) in the 30 day preceding the interview. Logistic regression analyses indicated that sexual abuse history in or around campus was significantly associated with past year (OR = 9.8, p ≤ 0.001) and past 30 day (OR = 5.0, p ≤ 0.001) drug use.

The impact of a situationally focused individual human immunodeficiency virus/sexually transmitted disease risk-reduction intervention on risk behavior in a 1-year cohort of Nigerian military personnel

Human immunodeficiency virus (HIV) and sexually transmitted disease (STD)-related risks in peacekeeping troops is a concern when they are stationed in areas of high HIV prevalence. We carried out an assessment of a situationally focused individual HIV/STD reduction intervention (where avoidance of risk situations, as well as risk behaviors, are emphasized) in one Nigerian military unit (N = 1,222), with a comparable unit from the same service as a waiting list control (N = 987). The intervention consisted of a possible five modules that were presented to groups of up to 50 personnel. Data were collected on reported sexual behaviors, condom beliefs, sexual risk behaviors with casual partners, and number of interventions attended. Data indicated significant increases in reported condom use with casual partners and positive condom beliefs at 6- and 12-month follow-up. Risk behavior was reduced 30% from baseline at 6 months and 23% from baseline at 12 months. There was also a significant dose-response effect for number of interventions attended. These data suggest that relatively brief situationally focused individual interventions are effective in military and West African contexts in reducing HIV/STD risk behaviors.

Understanding the Surface Structure of LiMn 2 O4 Spinel Cathodes with Aberration-Corrected HAADF STEM and EELS

As global energy consumption continues to rise, the importance of energy storage becomes increasingly important. Energy density, rate-capability, and cyclability must continually improve. This constant struggle for advancement is seen most easily in the high-density, electrical energy storage market, which is dominated by lithium-ion batteries. One of the most promising chemistries in lithium-ion batteries is LiMn2O4 (LMO), a spinel cathode material which has the advantage of both a high energy density and a high rate capability, but this chemistry is plagued with cyclability problems. In the LMO system the main contributor to cycling degradation is the Mn disproportionation reaction (2Mn = Mn + Mn) which creates soluble Mn that is lost to solution. This loss of active material from LMO leads to capacity degradation. In order to understand exactly how LMO loses active material from its surface, it is crucial to determine the surface’s atomic structure. This is because the surface structure dictates how the electrolyte will interact with the cathode.

Understanding the surface structure of LiNi0.45Mn1.55O4 spinel cathodes with aberration-corrected HAADF STEM

In order for Li-ion batteries to mature to a level useful for integration into the current or future energy infrastructure, basic problems such as cyclability, cost and rate capability must be overcome. LiNi0.5Mn1.5O4 (LNM), a spinel cathode material, has the advantage of being both cost-effective and a high-rate capable material, but it is plagued with cyclability problems. In the LNM system the main contributor to cycling degradation is the high operating voltage which leads to solid-electrolyte interphase (SEI) formation. We find that excess-Mn doping of this material (LiNi0.5-XMn1.5+XO4 where x=0.05) leads to increased cyclability through natural passivation [1]. To understand the exact role that excess Mn plays in the passivation of this cathode material, it is crucial to determine the surface’s atomic structure. This is because the surface structure determines how reactive the cathode will be with the electrolyte during oxidation and reduction cycles.