Living in the Fast Lane: The Role of Temporal Processing in ADHD Risk-taking Behaviors

Background: Attention Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder, prevalent in the college student population, that is associated with temporal processing deficits and functional impairments, namely engagement in risky behaviors (ERB; e.g., binge drinking). An existing theoretical framework purposes that aberrant temporal processing and subjective experience of time passing slowly, experienced in individuals with a fast internal clock (e.g., individuals with ADHD), increases the likelihood of ERB. The primary aim of this project is to improve our understanding of the relationship between objective temporal processing deficits and the subjective experience of time passage among people with elevated ADHD symptoms. Method: The present study used the Wittmann and Paulus (2008) theoretical framework to examine (a) relationships between objective and subjective temporal processing and ADHD symptoms and (b) associations between these variables and ERB. A novel measure of temporal processing (the Time Management and Estimation Scale, TiME) was revised from a pilot study and assessed via factor analysis and tested for reliability and validity to be used as a predictor variable in subsequent analyses. College student participants (N=215) completed measures of current ADHD symptoms, objective measures of temporal processing, ERB, the TiME, and relevant covariates (e.g., delay aversion, impulsivity). Linear regressions analyzed the associations between ADHD symptoms, objective temporal processing, and subjective (self-report) temporal processing, and negative binomial regressions analyzed the associations between these variables and ERB. Results: Factor analysis indicated a four-factor structure of the TiME. The TiME demonstrated good reliability to be used in subsequent analyses, but validity was only partially established for the TiME. Concurrent validity with the TiME and procrastination, but not objective measures of temporal processing or ADHD, was established. Overall, objective and subjective measures of temporal processing were not significantly associated with ADHD symptoms. ADHD symptom severity and temporal processing self-report were significantly associated with greater engagement in academic risk behaviors (e.g., missing class, not completing assignments). Time estimation accuracy was associated with lower engagement in risky sexual behavior (e.g., condomless sex) and aggressive behavior (e.g., hitting someone). No other significant associations were found between the predictor variables and ERB. The interaction between ADHD symptoms and subjective temporal processing was not associated with ERB. Discussion: The present study established preliminary evidence for the reliability of a novel self-report measure of temporal processing, yet there was a lack of concurrent validity evidence supporting associations between ADHD symptoms and subjective and objective temporal processing skills in college students. Objective time estimation accuracy was associated with decreased engagement in sexual or aggressive risky behaviors. Future research should continue to investigate if temporal processing deficits are present in college students with ADHD and clinically significant impairments associated with these deficits

Modification of the G-phonon mode of graphene by nitrogen doping

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We show that the bond length change and the long range interaction of point defects are possible mechanisms responsible for the oscillatory behavior of the G frequency as a function of nitrogen concentration. At the same time, Friedel charge oscillations are unlikely to contribute to this behavior

Modification of the G-phonon mode of graphene by nitrogen doping

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We show that the bond length change and the long range interaction of point defects are possible mechanisms responsible for the oscillatory behavior of the G frequency as a function of nitrogen concentration. At the same time, Friedel charge oscillations are unlikely to contribute to this behavior

Modification of the G-phonon mode of graphene by nitrogen doping

The effect of nitrogen doping on the phonon spectra of graphene is analyzed. In particular, we employ first-principles calculations and scanning Raman analysis to investigate the dependence of phonon frequencies in graphene on the concentration of nitrogen dopants. We demonstrate that the G phonon frequency shows oscillatory behavior as a function of nitrogen concentration. We analyze different mechanisms which could potentially be responsible for this behavior, such as Friedel charge oscillations around the localized nitrogen impurity atom, the bond length change between nitrogen impurity and its nearest neighbor carbon atoms, and the long-range interactions of the nitrogen point defects. We show that the bond length change and the long range interaction of point defects are possible mechanisms responsible for the oscillatory behavior of the G frequency as a function of nitrogen concentration. At the same time, Friedel charge oscillations are unlikely to contribute to this behavior

Visualizing Individual Nitrogen Dopants in Monolayer Graphene

In monolayer graphene, substitutional doping during growth can be used to alter its electronic properties. We used scanning tunneling microscopy (STM), Raman spectroscopy, x-ray spectroscopy, and first principles calculations to characterize individual nitrogen dopants in monolayer graphene grown on a copper substrate. Individual nitrogen atoms were incorporated as graphitic dopants, and a fraction of the extra electron on each nitrogen atom was delocalized into the graphene lattice. The electronic structure of nitrogen-doped graphene was strongly modified only within a few lattice spacings of the site of the nitrogen dopant. These findings show that chemical doping is a promising route to achieving high-quality graphene films with a large carrier concentration.Comment: Science 201