2,276 research outputs found

    Cesium plasma spectroscopy. Electron number density measured by Stark shift of spectral lines Final report

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    Electron density measurement from atomic spectral line widths and shifts in cesium plasma electric discharg

    Studying the potential of the [OII] emission line as a surrogate for stellar velocity dispersion in Active Galactic Nuclei

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    We study the emission profiles of 80 active galaxies to find a surrogate for stellar velocity dispersion. We focus on the width of the emission line of once ionized oxygen, [OII], and compare our results to previous work that used [OIII]. In previous research, [OIII] was found to be a good candidate for a surrogate for stellar velocity dispersion, but analysis of the line was complicated by the presence of wings caused by gas infall and outflow in the region. Emission lines with lower ionization levels, like [OII], are known to have less artificial line-broadening from wings. The study of [OIII] used a double Gaussian profile in an attempt to remove the wings. Here we simply fit the [OII] doublet line with two single Gaussian profiles at fixed separation and width. The main benefits of the [OII] line over the [OIII] line are the simpler fitting process, and the fact that [OII] is in a quiet region on the spectra with little interference from other emission lines. We found that the [OII] line still showed wings significant enough to require a fitting of these wings. [OIII] still appears to be the best candidate for a surrogate for stellar velocity dispersion

    An Aerodynamic Performance Evaluation of the NASA/Ames Research Center Advanced Concepts Flight Simulator

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    The results of an aerodynamic performance evaluation of the National Aeronautics and Space Administration (NASA)/Ames Research Center Advanced Concepts Flight Simulator (ACFS), conducted in association with the Navy-NASA Joint Institute of Aeronautics, are presented. The ACFS is a full-mission flight simulator which provides an excellent platform for the critical evaluation of emerging flight systems and aircrew performance. The propulsion and flight dynamics models were evaluated using classical flight test techniques. The aerodynamic performance model of the ACFS was found to realistically represent that of current day, medium range transport aircraft. Recommendations are provided to enhance the capabilities of the ACFS to a level forecast for 1995 transport aircraft. The graphical and tabular results of this study will establish a performance section of the ACFS Operation's Manual

    The Large N_c Baryon-Meson I_t = J_t Rule Holds for Three Flavors

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    It has long been known that nonstrange baryon-meson scattering in the 1/N_c expansion of QCD greatly simplifies when expressed in terms of t-channel exchanges: The leading-order amplitudes satisfy the selection rule I_t = J_t. We show that I_t = J_t, as well as Y_t = 0, also hold for the leading amplitudes when the baryon and/or meson contain strange quarks, and also characterize their 1/N_c corrections, thus opening a new front in the phenomenological study of baryon-meson scattering and baryon resonances.Comment: 12 pages, 0 figures, ReVTe

    Changing patterns in long-acting bronchodilator trials in chronic obstructive pulmonary disease

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    Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide. Developments in the understanding of COPD have led to standard guidelines for diagnosis, treatment, and spirometry assessments, which have in turn influenced trial designs and inclusion criteria. Substantial clinical evidence has been gained from clinical trials and supports a positive approach to COPD management. However, there appear to be changing trends in recent trials. Large bronchodilator studies have reported lower improvements in trough forced expiratory volume in 1 second (FEV1) values versus placebo than were observed in earlier studies, while the rate of FEV1 decline seems to be lower in more recent trials. In addition, recent evidence has called into question the usefulness of bronchodilator reversibility testing as a trial inclusion criterion. Baseline patient populations and use of concomitant medications have also changed over recent years due to increased treatment options. The impact of these many variables on clinical trial results is explored, with a particular focus on changes in inclusion criteria and patient baseline demographics

    Above- and belowground herbivory jointly impact defense and seed dispersal traits in Taraxacum officinale

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    Plants are able to cope with herbivores by inducing defensive traits or growth responses that allow them to reduce or avoid the impact of herbivores. Since above- and belowground herbivores differ substantially in life-history traits, for example feeding types, and their spatial distribution, it is likely that they induce different responses in plants. Moreover, strong interactive effects on defense and plant growth are expected when above- and belowground herbivores are jointly present. The strengths and directions of these responses have been scarcely addressed in the literature. Using Taraxacum officinale, the root-feeding nematode Meloidogyne hapla and the locust Schistocerca gregaria as a model species, we examined to what degree above- and belowground herbivory affect (1) plant growth responses, (2) the induction of plant defensive traits, that is, leaf trichomes, and (3) changes in dispersal-related seed traits and seed germination. We compared the performance of plants originating from different populations to address whether plant responses are conserved across putative different genotypes. Overall, aboveground herbivory resulted in increased plant biomass. Root herbivory had no effect on plant growth. Plants exposed to the two herbivores showed fewer leaf trichomes than plants challenged only by one herbivore and consequently experienced greater aboveground herbivory. In addition, herbivory had effects that reached beyond the individual plant by modifying seed morphology, producing seeds with longer pappus, and germination success

    Axial anomaly and magnetism of nuclear and quark matter

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    We consider the response of the QCD ground state at finite baryon density to a strong magnetic field B. We point out the dominant role played by the coupling of neutral Goldstone bosons, such as pi^0, to the magnetic field via the axial triangle anomaly. We show that, in vacuum, above a value of B ~ m_pi^2/e, a metastable object appears - the pi^0 domain wall. Because of the axial anomaly, the wall carries a baryon number surface density proportional to B. As a result, for B ~ 10^{19} G a stack of parallel pi^0 domain walls is energetically more favorable than nuclear matter at the same density. Similarly, at higher densities, somewhat weaker magnetic fields of order B ~ 10^{17}-10^{18} G transform the color-superconducting ground state of QCD into new phases containing stacks of axial isoscalar (eta or eta') domain walls. We also show that a quark-matter state known as ``Goldstone current state,'' in which a gradient of a Goldstone field is spontaneously generated, is ferromagnetic due to the axial anomaly. We estimate the size of the fields created by such a state in a typical neutron star to be of order 10^{14}-10^{15} G.Comment: 18 pages, v2: added a discussion of the energy cost of neutralizing the domain wall charg

    Structural Phase Transition in the Superconducting Pyrochlore Oxide Cd2Re2O7

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    We report a structural phase transition found at Ts = 200 K in a pyrochlore oxide Cd2Re2O7 which shows superconductivity at Tc = 1.0 K. X-ray diffractionexperiments indicate that the phase transition is of the second order, from a high-temperature phase with the ideal cubic pyrochlore structure (space group Fd-3m) to a low-temperature phase with another cubic structure (space group F-43m). It is accompanied by a dramatic change in the resistivity and magnetic susceptibility and thus must induce a significant change in the electronic structure of Cd2Re2O7.Comment: 4 pages, 4figures, proceeding for ISSP
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