The Effects of Emotional States and Traits on Time Perception

Background: Leading models of time perception share an important element of Scalar Expectancy Theory known as the internal clock, containing specific mechanisms by which the human mind is able to experience time passing and thus to function effectively within society. A major debate exists in the literature about whether to treat factors that influence these internal clock mechanisms (e.g., emotion, personality, executive functions such as inhibition, and related neurophysiological components) as arousal- or attentional-based factors. Purpose: The present study investigated behavioral and neurophysiological responses to an affective Go/NoGo task, taking into account personality correlates related to Behavioral Inhibition and Behavioral Activation Systems, which are major components of Reinforcement Sensitivity Theory. Methods: After completion of self-report inventories assessing personality traits, electroencephalogram (EEG) and behavioral recordings of 32 women and 13 men recruited from introductory psychology classes were made during an affective Go/NoGo task. The task consisted of three phases: 1. A learning phase, during which the participants were exposed to a neutral, visual standard duration ten times. 2. A practice phase, during which the participants practiced responding and inhibiting to "Go" and "NoGo" neutral visual stimuli of varying durations, respectively. For "Go" stimuli, participants' responses were based on their subsequent comparisons of the presented stimuli to the standard via button press (i.e., left button press means "shorter than standard duration", right button press means "longer than standard duration"). 3. A test phase, during which participants responded in the same manner as the practice phase, but "Go" and "NoGo" stimuli were defined according to positive and negative valence. Results: Findings indicated that higher BAS scores (especially BAS Drive) were associated with overestimation bias scores for both negative and positive stimuli presentation, while BIS scores were not significantly correlated with overestimation bias scores. N2 amplitudes were greater in response to "NoGo" stimuli than in response to "Go" stimuli. Furthermore, higher BIS Total scores were associated with higher N2d amplitudes during positive stimulus presentation for 280ms, while higher BAS Total scores were associated with higher N2d amplitudes during negative stimuli presentation for 910ms. BAS Drive scores were consistently and strongly correlated with greater relative left hemisphere asymmetry. Discussion: Findings are discussed in terms of arousal-based models of time perception, and suggestions for future research are considered.  M.A

PREDICTING TREATMENT ADHERENCE FROM ELECTROPHYSIOLOGICAL BIOMARKERS AND INDIVIDUAL DIFFERENCES IN BEHAVORIAL ACTIVATION (BAS) AND BEHAVIORAL INHIBITION (BIS) SYSTEMS

Obstructive sleep apnea (OSA) is a common chronic sleep disorder with a demanding and complex treatment regimen. Even though continuous positive airway pressure (CPAP) is a highly effective treatment for OSA, approximately 25% of those prescribed CPAP do not adhere. In accordance with a recent call for a biopsychosocial approach to address CPAP nonadherence, two studies were designed to investigate patient-centered factors of nonadherence. Study One was a laboratory-based experimental study with the aim to identify predictive variables of behavioral intentions to adhere to advantage- and disadvantage-framed health messages, which simulated receiving an OSA diagnosis and subsequent CPAP treatment recommendations. Multiple regression models indicated that higher behavioral intentions after viewing the advantage-framed message were expected from undergraduate participants endorsing higher positive emotional responses from the message and lower use of humor as a coping strategy. Higher behavioral intentions after viewing the disadvantage-framed health message were expected from undergraduate participants endorsing higher feelings of control, greater relative right hemisphere baseline cortical activity, higher levels of behavioral inhibition, and lower use of humor as a coping strategy. Study Two was a community-based study that aimed to identify predictive variables of CPAP adherence in a clinical sample of adult patients with OSA. Logistic regression analyses were employed in accordance with current adherence criteria at seven, thirty, sixty, and ninety day time-points. Age significantly predicted nonadherence at sixty days, while age and subjective severity rating predicted nonadherence at ninety days. Multiple regression analyses were used to predict total hours of CPAP use at the same time-points, and were able to identify additional predictors with clinical utility. Age, race, and reward responsiveness trait were significant predictors of total hours of CPAP use at sixty days, while age and race were significant predictors at ninety days. Important clinical implications are discussed in light of findings for enhancing likelihood of CPAP adherence.  Ph.D

An investigation of micro-mechanisms in hydrogen induced cracking in nickel-based superalloy 718

Hydrogen embrittlement of the nickel-iron based superalloy 718 has been investigated using slow strain rate tests for pre-charged material and also in-situ hydrogen charging during testing. Fractography analyses have been carried using scanning electron microscopy, electron back-scattering diffraction and orientation image microscopy concentrating on the influence of microstructural features and associated micro-mechanisms leading to hydrogen induced cracking and embrittlement. It was observed that hydrogen induced transgranular cracking initiates at micro-voids in the crystal lattice. Similar behaviour has been observed in multi-scale finite element chemo-mechanical numerical simulations. In contrast, hydrogen induced localized slip intergranular cracking was associated with the formation of micro-voids in intergranular regions. The effects of grain boundary and triple junction character on intergranular hydrogen embrittlement were also investigated. It was observed that low end high angle misorientations (LHAM), 15° 55°. Finally, the use of grain boundary engineering techniques to increase the resistance of super alloy 718 to hydrogen induced cracking and embrittlement is discussed

Precipitate Redistribution During Creep of Alloy 617

Nickel-based superalloys are being considered for applications within advanced nuclear power generation systems due to their high temperature strength and corrosion resistance. Alloy 617, a candidate for use in heat exchangers, derives its strength from both solid solution strengthening and the precipitation of carbide particles. However, during creep, carbides that are supposed to retard grain boundary motion are found to dissolve and re-precipitate on boundaries in tension. To quantify the redistribution, we have used electron backscatter diffraction and energy dispersive spectroscopy to analyze the microstructure of 617 after creep testing at 900 and 1000°C. The data were analyzed with respect to location of the carbides (e.g., intergranular vs. intragranular), grain boundary character, and precipitate type (i.e., Cr-rich or Mo-rich). We find that grain boundary character is the most important factor in carbide distribution; some evidence of preferential distribution to boundaries in tension is also observed at higher applied stresses. Finally, the results suggest that the observed redistribution is due to the migration of carbides to the boundaries and not the migration of boundaries to the precipitates

Influence of Grain Boundary Character on Creep Void Formation in Alloy 617

Alloy 617, a high temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP) which will operate at temperatures exceeding 760oC. Orientation imaging microscopy (OIM) is used to characterize the grain boundaries in the vicinity of creep voids that develop during high temperature creep tests (800-1000oC at creep stresses ranging from 20-85 MPa) terminated at creep strains ranging from 5-40%. Observations using optical microscopy indicate creep rate does not significantly influence the creep void fraction at a given creep strain. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular or 45o to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids while CSL-related grain boundaries did not appear to be consistently associated with void development

Evolution of grain boundary network topology in 316L austenitic stainless steel during powder hot isostatic pressing

The grain boundary network evolution of 316L austenitic steel powder during its densification by hot isostatic pressing (HIPing) was investigated. While the as-received powder contained a network of random high angle grain boundaries, the fully consolidated specimen had a large fraction of annealing twins, indicating that during densification, the microstructure evolves via recrystallization. By interrupting the HIPing process at different points in time, microstructural changes were tracked quantitatively at every stage using twin boundary fractions, distribution of different types of triple junctions, and the parameters associated with twin related domains (TRDs). Results revealed that, with increase in temperature, (i) the fraction of annealing twins increased steadily, but they mostly were not part of the grain boundary network in the fully consolidated specimen and (ii) the average number of grains within a TRD, the length of longest chain, and twinning polysynthetism increased during HIPing and (iii) the powder characteristics and the HIPing parameters have a strong influence on the development of grain boundary network. Based on the results obtained, possible alterations to the HIPing process are discussed, which could potentially allow twin induced grain boundary engineering

Effects of crystallographic anisotropy on fracture development and acoustic emission in quartz

Transgranular microcracking is fundamental for the initiation and propagation of all fractures in rocks. The geometry of these microcracks is primarily controlled by the interaction of the imposed stress field with the mineral elastic properties. However, the effects of anisotropic elastic properties of minerals on brittle fracture are not well understood. This study examines the effects of elastic anisotropy of quartz on the geometry of brittle fracture and related acoustic emissions (AE) developed during indentation experiments on single crystals at ambient pressure and temperature. A Hertzian cone crack developed during blunt indentation of a single crystal of flawless Brazilian quartz parallel to the c axis shows geometric deviation away from predictions based on the isotropic case, consistent with trigonal symmetry. The visible cone crack penetration depth varies from 3 to 5 mm and apical angle from 53 to 40. Electron backscatter diffraction (EBSD) mapping of the crack tip shows that fracturing initiates along a ~40 μm wide process zone, comprising damage along overlapping en echelon high-index crystallographic planes, shown by discrete bands of reduced electron backscatter pattern (EBSP) quality (band contrast).Coalescence of these surfaces results in a stepped fracture morphology. Monitoring of AE during indentation reveals that the elastic anisotropy of quartz has a significant effect on AE location and focal mechanisms. Ninety-four AE events were recorded during indentation and show an increasing frequency with increasing load. They correspond to the development of subsidiary concentric cracks peripheral to the main cone crack. The strong and complex anisotropy in seismic velocity (~28% Vp, ~43% Vs with trigonal symmetry) resulted in inaccurate and high uncertainty in AE locations using Geiger location routine with an isotropic velocity model. This problem was overcome by using a relative (master event) location algorithm that only requires a priori knowledge of the velocity structure within the source volume. The AE location results correlate reasonably well to the extent of the observed cone crack. Decomposition of AE source mechanisms of the Geiger relocated events shows dominantly end-member behavior between tensile and compressive vector dipole events, with some double-couple-dominated events and no purely tensile or compressive events. The same events located by the master event algorithm yield greater percentage of vector dipole components and no double-couple events, indicating that AE source mechanism solutions can depend on AE location accuracy, and therefore, relocation routine that is utilized. Calculations show that the crystallographic anisotropy of quartz causes apparent deviation of the moment tensors away from double-couple and pure tensile/compressive sources consistent with the observations. Preliminary modeling of calcite anisotropy shows a response distinct from quartz, indicating that the effects of anisotropy on interpreting AE are complex and require detailed further study