New ⁴⁰Ar/³⁹Ar dating of the Grande Ronde lavas, Columbia River Basalts, USA: Implications for duration of flood basalt eruption episodes

Grande Ronde Basalt (GRB) lavas represent the most voluminous eruptive pulse of the Columbia River-Snake River-Yellowstone hotspot volcanism. With an estimated eruptive volume of 150,000 km3, GRB lavas form at least 66% of the total volume of the Columbia River Basalt Group. New 40Ar/39Ar dates for GRB lavas reveal they were emplaced within a maximum period of 0.42 ± 0.18 My. A well-documented stratigraphy indicates at least 110 GRB flow fields (or individual eruptions), and on this basis suggests an average inter-eruption hiatus of less than 4,000 years. Isotopic age-dating cannot resolve time gaps between GRB eruptions, and it is difficult to otherwise form a picture of the durations of eruptions because of non-uniform weathering in the top of flow fields and a general paucity of sediments between GR lavas. Where sediment has formed on top of the GRB, it varies in thickness from zero to 20-30 cm of silty to fine-sandy material, with occasional diatomaceous sediment. Individual GRB eruptions varied considerably in volume but many were greater than 1000 km3 in size. Most probably eruptive events were not equally spaced in time; some eruptions may have followed short periods of volcanic repose (perhaps 102 to 103 of yrs), whilst others could have been considerably longer (many 1000 s to > 104 yrs). Recent improvements in age-dating for other continental flood basalt (CFB) lava sequences have yielded estimates of total eruptive durations of less than 1 My for high-volume pulses of lava production. The GRB appears to be a similar example, where the main pulse occupied a brief period. Even allowing for moderate to long-duration pahoehoe flow field production, the amount of time the system spends in active lava-producing mode is small – less than c. 2.6% (based on eruption durations of approximately 10,000 yrs, as compared to the duration of the entire eruptive pulse of c. 420,000 yrs). A review of available 40Ar/39Ar data for the major voluminous phases of the Columbia River Basalt Group suggests that activity of the Steens Basalt-Imnaha Basalt-GRB may have, at times, been simultaneous, with obvious implications for climatic effects. Resolving intervals between successive eruptions during CFB province construction, and durations of main eruptive pulses, remains vital to determining the environmental impact of these huge eruptions

Self-steepening of light pulses

Self-steepening of light pulses due to propagation in medium with intensity-dependent index of refractio

SDL and Technology: Implications for Adult Education

As SDL is embraced and technology continually advances in organizations, new and improved skills and learning strategies will be required. This session will explore the anticipated change necessary for adult educators and related scholarly practitioners to be able to effectively support the learners in their organizations

Oxygen-related traps in pentacene thin films: Energetic position and implications for transistor performance

We studied the influence of oxygen on the electronic trap states in a pentacene thin film. This was done by carrying out gated four-terminal measurements on thin-film transistors as a function of temperature and without ever exposing the samples to ambient air. Photooxidation of pentacene is shown to lead to a peak of trap states centered at 0.28 eV from the mobility edge, with trap densities of the order of 10(18) cm(-3). These trap states need to be occupied at first and cause a reduction in the number of free carriers, i.e. a consistent shift of the density of free holes as a function of gate voltage. Moreover, the exposure to oxygen reduces the mobility of the charge carriers above the mobility edge. We correlate the change of these transport parameters with the change of the essential device parameters, i.e. subthreshold performance and effective field-effect mobility. This study supports the assumption of a mobility edge for charge transport, and contributes to a detailed understanding of an important degradation mechanism of organic field-effect transistors. Deep traps in an organic field-effect transistor reduce the effective field-effect mobility by reducing the number of free carriers and their mobility above the mobility edge.Comment: 13 pages, 14 figures, to be published in Phys. Rev.

Bone Turnover Response to Acute Exercise with Varying Impact Levels: A preliminary investigation

International Journal of Exercise Science 8(2): 154-163, 2015. The purpose of this investigation was to determine if there are changes in metabolic markers of bone turnover within the 24-hour period following an acute bout of jogging or water exercise. Ten healthy females (22-30 yr.) underwent three trials with different ground impact forces: jogging, water aerobics and control. For the jogging and water aerobics trials, subjects exercised for 30 min at 60-70% of predicted maximal heart rate in addition to a 5 min warm up and cool down. For the control trial, subjects rested for 40 min, i.e., the total exercise time of the other trials. For each trial, blood samples were collected pre, immediately post, 1 hr. post, and 24 hr. post exercise. All samples were analyzed for levels of osteocalcin, bone specific alkaline phosphatase and cross-linked N telopeptides. A repeated-measure ANOVA was used to determine if there were differences between impact levels or over time. There were no significant differences over time, or between impact levels of exercise. Therefore these results indicate that healthy young women demonstrate no changes in bone turnover within 24 hr. of a single bout of exercise. Due to biochemical markers of bone turnover responding in a similar manner regardless of activity type, these findings suggest that water aerobics can be seen as a beneficial form of exercise for maintenance of bone density

Geometry-induced pulse instability in microdesigned catalysts: the effect of boundary curvature

We explore the effect of boundary curvature on the instability of reactive pulses in the catalytic oxidation of CO on microdesigned Pt catalysts. Using ring-shaped domains of various radii, we find that the pulses disappear (decollate from the inert boundary) at a turning point bifurcation, and trace this boundary in both physical and geometrical parameter space. These computations corroborate experimental observations of pulse decollation.Comment: submitted to Phys. Rev.