10,304 research outputs found

    On the nature of spectral line broadening in solar coronal dimmings

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    We analyze the profiles of iron emission lines observed in solar coronal dimmings associated with coronal mass ejections, using the EUV Imaging Spectrometer on board Hinode. We quantify line profile distortions with empirical coefficients (asymmetry and peakedness) that compare the fitted Gaussian to the data. We find that the apparent line broadenings reported in previous studies are likely to be caused by inhomogeneities of flow velocities along the line of sight, or at scales smaller than the resolution scale, or by velocity fluctuations during the exposure time. The increase in the amplitude of Alfv\'en waves cannot, alone, explain the observed features. A double-Gaussian fit of the line profiles shows that, both for dimmings and active region loops, one component is nearly at rest while the second component presents a larger Doppler shift than that derived from a single-Gaussian fit.Comment: 16 pages, 11 figures - Accepted for publication in Ap

    Resaca ecosystem development: colonization and succession of the macroinvertebrate community

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    Freshwater wetlands in the Lower Rio Grande Valley of Texas are locally known as resacas. Resacas are remnants of the Rio Grande River channel that were cut off by sedimentation and erosion of river banks. Many are maintained as permanent wetlands through intermittent water pumping from the river; and provide valuable habitat for fish, invertebrates, migratory birds and a diverse floral community in the semi-arid environment of South Texas. Three resacas in different stages of ecosystem development were studied, including one from day zero after re-flooding. The objectives were to document the colonization process of the re-flooded resaca and the macroinvertebrate community of all three sites to differentiate successional stages of the studied resacas. Two invertebrate collection methods were used, benthic corer and sweep net, in order to gather a representative sample from the entire community. Results indicated that environmental factors (i.e. water, sediment) varied little between resacas, but there were significant differences in the benthic and water column invertebrate communities among the sites studied. The most developed site exhibited the lowest diversity and richness, and the highest dominance. The intermediate site exhibited the greatest diversity and richness, and a low level of dominance. The new site fell between the other two, but was most similar to the intermediate site. Composition of the functional feeding groups did not follow expected trends within this community, but is still a useful metric for differentiating the study sites, particularly the predator and scraper taxa. The invertebrate community in the studied resacas did not follow successional trends that were expected based on other studies and the community was strongly influenced by the presence of an invasive gastropod. Based on the results of this baseline study, the invertebrate community may be useful in discriminating between successional stages of resacas

    A ground track control algorithm for the Topographic Mapping Laser Altimeter (TMLA)

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    The results of an analysis of an algorithm that will provide autonomous onboard orbit control using orbits determined with Global Positioning System (GPS) data. The algorithm uses the GPS data to (1) compute the ground track error relative to a fixed longitude grid, and (2) determine the altitude adjustment required to correct the longitude error. A program was written on a personal computer (PC) to test the concept for numerous altitudes and values of solar flux using a simplified orbit model including only the J sub 2 zonal harmonic and simple orbit decay computations. The algorithm was then implemented in a precision orbit propagation program having a full range of perturbations. The analysis showed that, even with all perturbations (including actual time histories of solar flux variation), the algorithm could effectively control the spacecraft ground track and yield more than 99 percent Earth coverage in the time required to complete one coverage cycle on the fixed grid (220 to 230 days depending on altitude and overlap allowance)

    Campus Environment 2008: A National Report Card on Sustainability in Higher Education

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    Presents survey findings on national and regional trends among colleges in environmental leadership in management, academic courses in sustainability, and conservation efforts in operations. Profiles exemplary programs and notes areas for improvement

    Correlations of the IR Luminosity and Eddington Ratio with a Hard X-ray Selected Sample of AGN

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    We use the SWIFT Burst Alert Telescope (BAT) sample of hard x-ray selected active galactic nuclei (AGN) with a median redshift of 0.03 and the 2MASS J and K band photometry to examine the correlation of hard x-ray emission to Eddington ratio as well as the relationship of the J and K band nuclear luminosity to the hard x-ray luminosity. The BAT sample is almost unbiased by the effects of obscuration and thus offers the first large unbiased sample for the examination of correlations between different wavelength bands. We find that the near-IR nuclear J and K band luminosity is related to the BAT (14 - 195 keV) luminosity over a factor of 10310^3 in luminosity (LIR≈LBAT1.25L_{IR} \approx L_{BAT}^{1.25})and thus is unlikely to be due to dust. We also find that the Eddington ratio is proportional to the x-ray luminosity. This new result should be a strong constraint on models of the formation of the broad band continuum.Comment: accepted to ApJ

    Introduction

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    A binding investigation of fluorescence\probes and cyclodextrin derivatives

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    Cyclodextrins (CDs) are cyclical carbohydrates composed of repeating glucopyranose units. The three most common CDs, α-, β-, or y-, contain 6, 7 and 8 glucopyranose units, respectively, and have hydrophilic exteriors, which makes them water soluble. CD polymers (CDPs) have been synthesized, containing glyceryl link, between CD units. These polymers are more water soluble than their monomer counterparts. CDs and CDPs, because of their hydrophobic interior cavities, form inclusion complexes with various molecules, including aromatics. This latter property is one we have investigated using fluorophores, including naphthalenes and pyrene. We have shown, through absorption spectral and fluorescence lifetime data, that naphthalene forms a different type of complex with α-CDP than α-CD. We suggest this complex is 1:1, as the α-CD/naphthalene complex has been reported to be 2:1. We have also studied the binding of pyrene with β-CD derivatives. These derivatives have different substitution patterns, with substitution on the smaller rim of the β-CD cavity, the larger rim of the cavity, and on both rims of the cavity. We have shown, through steady-state fluorescence and fluorescence lifetime measurements, that the derivative with substitution on the smaller rim behaves similarly to β-CD. This suggests that a 2:1 complex is still forming, as reported in the literature. On the other hand, derivatives with at least some substitution on the larger rim behave more like the β-CDP. We suggest that larger rim substitution has two effects: A) the groups extend the hydrophobic cavity and B) a 1:1 complex is likely, as the groups seem to sterically hinder a 2:1 complex from forming

    Introduction

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    A Response to Myung-Soo Park

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    Allow me to respond in two parts. First, I will comment on the direct connection between Dr. Park’s findings and traditional Church Growth principles. Second, I will note some concerns and questions that may be of help in focusing future research on this important issue of spiritual leadership and church growth
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