Local dielectric spectroscopy of near-surface glassy polymer dynamics

A non-contact scanning-probe-microscopy method was used to probe local near-surface dielectric susceptibility and dielectric relaxation in poly-vinyl-acetate (PVAc) near the glass transition. Dielectric spectra were measured from 10-4 Hz to 102 Hz as a function of temperature. The measurements probed a 20 nm thick layer below the free-surface of a bulk film. A small (4 K) reduction in glass transition temperature and moderate narrowing of the distribution of relaxation times was found. In contrast to results for ultra-thin-films confined on or between metallic electrodes, no reduction in the dielectric strength was found, inconsistent with the immobilization of slower modes.Comment: submitte

Synchrotron Radiation as the Source of Gamma-Ray Burst Spectra

We investigate synchrotron emission models as the source of gamma-ray burst spectra. We show that including the possibility for synchrotron self-absorption, a ``smooth cutoff'' to the electron energy distribution, and an anisotropic distribution for the electron pitch angles produces a whole range of low energy spectral behavior. In addition, we show that the procedure of spectral fitting to GRB data over a finite bandwidth can introduce a spurious correlation between spectral parameters - in particular, the value of the peak of the nu F_nu spectrum, E_p, and the low energy photon spectral index alpha (the lower E_p is, the lower (softer) the fitted value of alpha will be). From this correlation and knowledge of the E_p distribution, we show how to derive the expected distribution of alpha. We show that optically thin synchrotron models with an isotropic electron pitch angle distribution can explain the distribution of alpha below alpha=-2/3. This agreement is achieved if we relax the unrealistic assumption of the presence of a sharp low energy cutoff in the spectrum of accelerated electrons, and allow for a more gradual break. We show that this low energy portion of the electron spectrum can be at most flat. We also show that optically thin synchrotron models with an anisotropic electron pitch angle distribution can explain all bursts with -2/3 < alpha <= 0$. The very few bursts with low energy spectral indices that fall above alpha=0 may be due the presence of a the synchrotron self-absorption frequency entering the lower end of the BATSE window. Our results also predict a particular relationship between alpha and E_p during the temporal evolution of a GRB. We give examples of spectral evolution in GRBs and discuss how the behavior are consistent with the above models.Comment: 21 pages, including 10 postscript figures. To appear in the December 10, 2000 issue of Ap

Flash-Heating of Circumstellar Clouds by Gamma Ray Bursts

The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrisic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within ~ 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions.Comment: 9 pages, 1 figure, submitted to ApJ Letter

Effects of Climate Change on Phenology of Blackbirds and Orioles (Icterids) in Eastern South Dakota

Birds are among the first responders to climate change, often having clearly observable phenological responses to less perceptible levels of climate shift. Declines in populations of a number of bird species have been witnessed both in the United States and abroad, with up to a 48% decline in grassland birds of the Central U.S. Understanding changes in bird abundance and distribution is essential because birds supply a wide variety of critical ecosystem services, including pollination and pest control. While the effects of climate change on many bird species’ phenology have been studied intensely, research on the family Icteridae is limited. This study was conducted using spring bird presence and absence data and weather data from Oak Lake Field Station from 1995 to 2012. Linear regression analysis was applied against warmth sum days for the 30 days prior to each spring bird survey. Our analysis demonstrated significant increases in accumulated warmth sum days between 1999 and 2012 (P = 0.01). Icterid species richness also increased with increasing warmth sum days during the month leading up to surveys (P = 0.02). Trends in both habitat (open woodland, marsh, and grassland) and feeding guild (insectivores and omnivores) species richness were also observed with increasing warmth sum days. These findings suggest a shift towards earlier spring arrival of members of the family Icteridae in eastern South Dakota

Aircraft Loss of Control: Problem Analysis for the Development and Validation of Technology Solutions

Aircraft loss of control (LOC) is a leading cause of fatal accidents across all transport airplane and operational classes. LOC can result from a wide spectrum of precursors (or hazards), often occurring in combination. Technologies developed for LOC prevention and recovery must therefore be effective under a wide variety of conditions and uncertainties, including multiple hazards, and the validation process must provide a means of assessing system effectiveness and coverage of these hazards. This paper provides a detailed description of a methodology for analyzing LOC as a dynamics and control problem for the purpose of developing effective technology solutions. The paper includes a definition of LOC based on several recent publications, a detailed description of a refined LOC accident analysis process that is illustrated via selected example cases, and a description of planned follow-on activities for identifying future potential LOC risks and the development of LOC test scenarios. Some preliminary considerations for LOC of Unmanned Aircraft Systems (UAS) and for their safe integration into the National Airspace System (NAS) are also discussed

Preliminary Analysis of Aircraft Loss of Control Accidents: Worst Case Precursor Combinations and Temporal Sequencing

Aircraft loss of control (LOC) is a leading cause of fatal accidents across all transport airplane and operational classes, and can result from a wide spectrum of hazards, often occurring in combination. Technologies developed for LOC prevention and recovery must therefore be effective under a wide variety of conditions and uncertainties, including multiple hazards, and their validation must provide a means of assessing system effectiveness and coverage of these hazards. This requires the definition of a comprehensive set of LOC test scenarios based on accident and incident data as well as future risks. This paper defines a comprehensive set of accidents and incidents over a recent 15 year period, and presents preliminary analysis results to identify worst-case combinations of causal and contributing factors (i.e., accident precursors) and how they sequence in time. Such analyses can provide insight in developing effective solutions for LOC, and form the basis for developing test scenarios that can be used in evaluating them. Preliminary findings based on the results of this paper indicate that system failures or malfunctions, crew actions or inactions, vehicle impairment conditions, and vehicle upsets contributed the most to accidents and fatalities, followed by inclement weather or atmospheric disturbances and poor visibility. Follow-on research will include finalizing the analysis through a team consensus process, defining future risks, and developing a comprehensive set of test scenarios with correlation to the accidents, incidents, and future risks. Since enhanced engineering simulations are required for batch and piloted evaluations under realistic LOC precursor conditions, these test scenarios can also serve as a high-level requirement for defining the engineering simulation enhancements needed for generating them

“No-Spin” States and Low-Lying Structures in \u3csup\u3e130\u3c/sup\u3eXe and \u3csup\u3e136\u3c/sup\u3eXe

Inelastic neutron scattering on solid 130XeF2 and 136XeF2 targets was utilized to populate excited levels in 130Xe and 136Xe. When calculating nuclear matrix elements vital to the understanding of double-beta decay, it is important to have a clear understanding of the low-lying level structure of both the parent and daughter nucleus. Of particular relevance to double-beta decay searches are the assignments of 0+ states. We show here that in the case of 130Xe there are several discrepancies in the adopted level structure. We found that one previous 0+ candidate level (1590 keV) can be ruled out and assigned two additional candidates (2223 and 2242 keV). In 136Xe we question the previous assignment of a 0+ level at 2582 keV. Excitation function and angular distribution measurements were utilized to make spin and parity assignments of levels and place new transitions

Seniority Structure of \u3csup\u3e136\u3c/sup\u3eXe\u3csub\u3e82\u3c/sub\u3e

The level structure of the N = 82 nucleus 136Xe was studied with the inelastic neutron scattering reaction followed by γ-ray detection. A number of the spins and parities were reassigned, and many level lifetimes were determined for the first time using the Doppler-shift attenuation method. New shell-model calculations were also performed using both the full Z = 50–82 model space, and a reduced model space including only the 1d5/2 and 0g7/2 orbitals. This new information characterizing 136Xe was used to identify the seniority structure of the low-lying levels and to assign (π0g7/2)4υ=0, (π0g7/2)4υ=2, (π0g7/2)4υ=4, (π1d5/2)(π0g7/2)3υ=1, and (π1d5/2)2(π0g7/2)2υ=0 configurations to describe all observed states below 2.8 MeV

Inelastic Neutron Scattering Studies of \u3csup\u3e132,134\u3c/sup\u3eXe: Elucidating Structure in a Transitional Region and Possible Interferences for 0vββ Searches

Highly enriched (\u3e 99.9%) 132Xe and 134Xe gases were converted to solid 132XeF2 and 134XeF2 and were used as scattering samples for inelastic neutron scattering measurements at the University of Kentucky Accelerator Laboratory (UKAL). Lifetimes of levels up to 3.5MeV in excitation energy in these xenon isotopes were measured using the Doppler-shift attenuation method, allowing the determination of reduced transition probabilities. Gamma rays corresponding to new transitions and levels have been observed. In particular, tentative new excited 0+ states and associated decays have been examined in an effort to elucidate the structure of these nuclei in a transitional region, and comparisons have been drawn with models which seek to describe such nuclei, e.g., the E(5) critical-point symmetry of the IBM. Newly identified potential interferences for neutrinoless double-beta decay searches involving 136Xe are also discussed

Folate catabolites in spot urine as non-invasive biomarkers of folate status during habitual intake and folic acid supplementation.

Folate status, as reflected by red blood cell (RCF) and plasma folates (PF), is related to health and disease risk. Folate degradation products para-aminobenzoylglutamate (pABG) and para-acetamidobenzoylglutamate (apABG) in 24 hour urine have recently been shown to correlate with blood folate. Since blood sampling and collection of 24 hour urine are cumbersome, we investigated whether the determination of urinary folate catabolites in fasted spot urine is a suitable non-invasive biomarker for folate status in subjects before and during folic acid supplementation. Immediate effects of oral folic acid bolus intake on urinary folate catabolites were assessed in a short-term pre-study. In the main study we included 53 healthy men. Of these, 29 were selected for a 12 week folic acid supplementation (400 µg). Blood, 24 hour and spot urine were collected at baseline and after 6 and 12 weeks and PF, RCF, urinary apABG and pABG were determined. Intake of a 400 µg folic acid bolus resulted in immediate increase of urinary catabolites. In the main study pABG and apABG concentrations in spot urine correlated well with their excretion in 24 hour urine. In healthy men consuming habitual diet, pABG showed closer correlation with PF (rs = 0.676) and RCF (rs = 0.649) than apABG (rs = 0.264, ns and 0.543). Supplementation led to significantly increased folate in plasma and red cells as well as elevated urinary folate catabolites, while only pABG correlated significantly with PF (rs = 0.574) after 12 weeks. Quantification of folate catabolites in fasted spot urine seems suitable as a non-invasive alternative to blood or 24 hour urine analysis for evaluation of folate status in populations consuming habitual diet. In non-steady-state conditions (folic acid supplementation) correlations between folate marker (RCF, PF, urinary catabolites) decrease due to differing kinetics