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EUV emissions from solar wind charge exchange in the Earth's magnetosheath: Three-dimensional global hybrid simulation
Get PDFIn this paper, a three-dimensional (3-D) global hybrid simulation code and a 3-D geocoronal hydrogen model are used to systematically study the extreme ultraviolet (EUV) emissions at 30.4nm produced by solar wind charge exchange (SWCX) in the Earth's magnetosheath, associated with different solar wind-interplanetary magnetic field (SW-IMF) conditions and different imaging perspectives. We have found that the EUV emission intensities in the magnetosheath are highly variable from several mR to similar to 1200 mR and increase with the flow speed, the density, the temperature, and the He2+/H+ density ratio of the solar wind; the northward IMF leads to a minimum emission in the magnetosheath, whereas the southward IMF generates a maximum emission; with the increase of the magnitude of IMF, the emission pattern in the nightside splits from single field-aligned shape into a butterfly shape around the magnetic equator; and the EUV emissions vary with the imaging positions, reflecting different latitudinal and longitudinal information of the magnetosheath. It is noted that the SWCX EUV emissions in the magnetosheath for highly disturbed solar wind conditions should be considered in processing the Moon-based plasmaspheric EUV images. We suggest that EUV imaging of the global magnetosheath requires an EUV imager with large field-of-view, high-sensitivity, large dynamic range, and low intrinsic dark count rate. This investigation could provide us with an overall understanding on SWCX EUV emissions in the magnetosheath which can potentially be used to image the global magnetosheath to study the solar wind-magnetosphere coupling in the future.PublishedYe
Maskelynite formation via solid-state transformation: Evidence of infrared and X-ray anisotropy
Get PDFWe present the results of a combined study of shocked labradorite from the Lonar crater, India, using optical microscopy, micro-Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, high-energy X-ray total scattering experiments, and micro-Fourier transform infrared (micro-FTIR) spectroscopy. We show that maskelynite of shock class 2 is structurally more similar to fused glass than to crystalline plagioclase. However, there are slight but significant differencespreservation of original preimpact igneous zoning, anisotropy at infrared wavelengths, X-ray anisotropy, and preservation of some intermediate range orderwhich are all consistent with a solid-state transformation from plagioclase to maskelynite.PublishedYe
Embargo Periods: How Do They Affect the Use of Electronic Theses and Dissertations?
No full textEmbargo periods for Electronic Thesis and Dissertations (ETDs) collections are usually discussed from the point of view of publishers and/or submitters, not that of digital library end-users. This poster examines the impact of embargos on use patterns for a university ETDs collection. Data obtained from Google Analytics are compared for individual item page views and item downloads for both in-state and out-of-state end-users. The impact of global vs. university-only embargos is also examined.Presente
Dipolarization fronts as earthward propagating flux ropes: A three-dimensional global hybrid simulation
Get PDFDipolarization fronts (DFs) as earthward propagating flux ropes (FRs) in the Earth's magnetotail are presented and investigated with a three-dimensional (3-D) global hybrid simulation for the first time. In the simulation, several small-scale earthward propagating FRs are found to be formed by multiple X line reconnection in the near tail. During their earthward propagation, the magnetic field B-z of the FRs becomes highly asymmetric due to the imbalance of the reconnection rates between the multiple X lines. At the later stage, when the FRs approach the near-Earth dipole-like region, the antireconnection between the southward/negative B-z of the FRs and the northward geomagnetic field leads to the erosion of the southward magnetic flux of the FRs, which further aggravates the B-z asymmetry. Eventually, the FRs merge into the near-Earth region through the antireconnection. These earthward propagating FRs can fully reproduce the observational features of the DFs, e.g., a sharp enhancement of B-z preceded by a smaller amplitude B-z dip, an earthward flow enhancement, the presence of the electric field components in the normal and dawn-dusk directions, and ion energization. Our results show that the earthward propagating FRs can be used to explain the DFs observed in the magnetotail. The thickness of the DFs is on the order of several ion inertial lengths, and the electric field normal to the front is found to be dominated by the Hall physics. During the earthward propagation from the near-tail to the near-Earth region, the speed of the FR/DFs increases from similar to 150km/s to similar to 1000km/s. The FR/DFs can be tilted in the GSM (x,y) plane with respect to the y (dawn-dusk) axis and only extend several Earth radii in this direction. Moreover, the structure and evolution of the FRs/DFs are nonuniform in the dawn-dusk direction, which indicates that the DFs are essentially 3-D.PublishedYe
Getting to the Bottom Line: 20 Digital Preservation Cost Questions
Get PDFGetting to the Bottom Line: 20 Cost Questions for Digital Preservation is a cost-gathering resource created by the Outreach Committee of the MetaArchive Cooperative in Spring 2015. Launched during an Association of Southeastern Research Libraries (ASERL) webinar (https://vimeo.com/121926212) on March 11, 2015, this resource has been shared broadly with libraries, archives, and other institutions that have an interest in procuring digital preservation services. The easy-to-use resource is designed to equip institutions with questions that they can use to identify the full range of costs that might be associated with any particular digital preservation service--proprietary, community-sourced, or otherwise. For a variety of reasons, services of all types do not always make their costs as transparent as institutions might prefer. Using the Getting to the Bottom Line question-set will help ensure that institutions do not leave any stones unturned when evaluating their options and that they gather the information that they need to make informed choices that lead to sustainable solutions. Institutions are encouraged to make free use of the questions, adapt them as needed, and provide feedback on their usefulness. Going forward, the resource will serve as a foundation for building additional and more sophisticated cost transparency resources targeted toward the digital preservation community.N
The Information-Seeking Habits of In-Service Educators
Get PDFResearch on information literacy and educators has focused on preservice educators and learning information literacy skills. Little research exists on in-service educators and their information literacy skills. Purposes of this study were to identify information sources that in-service educators used; to determine relationships between information sources used and in-service educators’ professional position, age groups, experience, and information format preference; and to determine relationships between in-service educators’ information-seeking habits and prior library instruction. Results of this study indicated statistically significant relationships between information-seeking habits and prior library instruction. Other statistically significant in relationships were indicated between information-seeking habits and the age groups and current professional positions of sample population.PublishedYe
An efficient auxiliary variable method for quantification of spin density, R2* decay and field inhomogeneity maps in magnetic resonance imaging
Get PDFQuantification of spin density, decay and off-resonance frequency maps is very important in some applications of magnetic resonance imaging (MRI). To reconstruct these parameter maps, a time-varying model such as mono-exponentials must be used to represent the signal from each voxel. When only a single-shot trajectory is adopted, the underlying reconstruction problem is significantly nonlinear and therefore requires an iterative algorithm. The regularized trust region method previously proposed to address this problem is stable but lacks speed. In this paper, we propose a novel auxiliary variable method that is very efficient in solving the underlying optimization problem. This method introduces an auxiliary variable in the spatial-temporal domain that separates the data fidelity term and the structure fidelity term. The algorithm then alternately optimizes the data fidelity and the structure fidelity to reach the solution. The data fidelity optimization has a closed-form solution and can be solved very efficiently. The structure fidelity optimization fits the exponential model with the auxiliary variable and can also be rapidly computed. Some preliminary comparisons between the auxiliary variable method and the trust region method show that the new method is 10 times faster than the trust region method at a reasonable reconstruction precision.In pres
Felix Holt: The Radical and the Gusset of Cryptic Futurity
No full textArticle from the George Eliot Review, digitized and hosted by the George Eliot Review Online.Publishe
Dipolarization fronts as earthward propagating flux ropes: A three-dimensional global hybrid simulation
Get PDFDipolarization fronts (DFs) as earthward propagating flux ropes (FRs) in the Earth's magnetotail are presented and investigated with a three-dimensional (3-D) global hybrid simulation for the first time. In the simulation, several small-scale earthward propagating FRs are found to be formed by multiple X line reconnection in the near tail. During their earthward propagation, the magnetic field B-z of the FRs becomes highly asymmetric due to the imbalance of the reconnection rates between the multiple X lines. At the later stage, when the FRs approach the near-Earth dipole-like region, the antireconnection between the southward/negative B-z of the FRs and the northward geomagnetic field leads to the erosion of the southward magnetic flux of the FRs, which further aggravates the B-z asymmetry. Eventually, the FRs merge into the near-Earth region through the antireconnection. These earthward propagating FRs can fully reproduce the observational features of the DFs, e.g., a sharp enhancement of B-z preceded by a smaller amplitude B-z dip, an earthward flow enhancement, the presence of the electric field components in the normal and dawn-dusk directions, and ion energization. Our results show that the earthward propagating FRs can be used to explain the DFs observed in the magnetotail. The thickness of the DFs is on the order of several ion inertial lengths, and the electric field normal to the front is found to be dominated by the Hall physics. During the earthward propagation from the near-tail to the near-Earth region, the speed of the FR/DFs increases from similar to 150km/s to similar to 1000km/s. The FR/DFs can be tilted in the GSM (x,y) plane with respect to the y (dawn-dusk) axis and only extend several Earth radii in this direction. Moreover, the structure and evolution of the FRs/DFs are nonuniform in the dawn-dusk direction, which indicates that the DFs are essentially 3-D.Publishe
Search Engine Queries Used to Locate Electronic Theses and Dissertations: Differences for Local and Non-Local Users
Get PDFThis study examines two research questions: (1) What search engine queries lead users to the Auburn University Electronic Theses and Dissertations (AUETDs) collection? (2) Do these queries vary for users in different locations and, if so, how? Search engine queries used to locate the AUETDs collection were obtained from Google Analytics and were separated into groups based on user location. These queries were assigned to empirically-derived categories based on their content. Most local users' queries contained person names, variants for thesis or dissertation, and variants for Auburn University. Over a third were queries for the AUETDs collection, while the remainder were seeking theses and/or dissertations from specific Auburn researchers. Most out-of-state users' queries contained title and subject keywords and appeared to be seeking specific research studies. Queries from users located within the state but outside of the local area were intermediate between these two groups. Over two-thirds of visits to the AUETDs collection were made by search engine users which reinforces the importance of having repository content indexed by search engines such as Google. The specificity of their queries indicates that full-text indexing will be more helpful to users than metadata indexing alone. This is the first detailed analysis of search engine queries used to locate an ETDs collection. It may also be the last, as query content for the major search engines is no longer available from Google Analytics.PublishedYe