1,721,044 research outputs found
Understanding storm-time ring current sources: Data analysis and global modeling.
No full textWith the availability of abundant, high-quality recent observations (ground-based and space-borne) and the newly-developed Space Weather Modeling Framework (SWMF), the storm-time ring current sources are examined via extensive data analyses and global storm simulations. The results of this dissertation work improve our understanding of upstream solar wind conditions, immediate plasma-sheet sources, and ionospheric outflow effect during storms. It is found in the magnetic cloud-storm study that ∼76% of magnetic clouds cause storms, but only ∼30% of storms are caused by clouds. A storm can be driven by a cloud's leading field, axial field, trailing field, or the combination thereof. It is shown that the leading field is the most geoeffective region and the sheath is equally effective at causing storms during solar maximum compared to solar minimum. A new name, quasicloud, is proposed for those cloud-like solar wind structures. Superposed epoch analyses are performed to make comparisons of typical behaviors of upstream solar wind plasma and interplanetary magnetic field (IMF), geosynchronous-orbit hot ions, and geomagnetic indices in four storm categories: moderate and in tense storms at solar minimum and maximum. The long-known control of geomagnetic activity mainly by southward IMF Bz is supported in the investigations. The averaged interplanetary causes of intense storms at solar minimum are against the well-known empirical criteria (Bz ≤ -10 nT for ≥ 3 hrs). Around storm minimum in each category, hot ions at geosynchronous orbit are denser near dawn than dusk. In the second part of the dissertation work, high-performance storm simulations are performed with the actual and superposed solar wind as input to the SWMF, respectively. It is shown that the SWMF is reaching a sophistication level for allowing quantitative comparison with observations. Major storm characteristics except for the recovery phase are successfully reproduced. It is demonstrated that ionospheric outflow plays an important role in causing a storm. IMF Bz ≤ -5 nT for ≥ 2 hrs without large oscillations in the solar wind and an increased inner boundary mass density to compensate is not geoeffective enough to cause a moderate storm. 24 M virtual geostationary satellites are introduced to make data-model comparisons straightforward.PhDAtmospheric sciencesEarth SciencesGeophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125936/2/3224794.pd
Upper atmospheric geoeffectiveness of energetic proton precipitation with beam spreading.
No full textA 3-D Monte Carlo proton transport model has been developed to investigate the dynamic effects of high-energy magnetospheric ion precipitation on the Earth's Mesosphere and Lower Thermosphere/Ionosphere (MLTI) region from 60 to 300 km altitude. Interaction of fast particles with a three-species atmosphere (O, N2 and O2) is considered in the model through charge exchange, electron stripping, ionization, excitation, and elastic scattering collisions. Unlike electron injection, major difficulties in modeling ion precipitation arise from the coupling of ion and neutral transport through repeated electron capture from and loss to the ambient atmospheric constituents. The spreading effect is a unique feature for an incident energetic ion beam, and thus an important focus of our study. The beam spreading effect is extensively simulated using our 3-D Monte Carlo model for both a fine proton beam and a proton arc of longitudinal and latitudinal extent. Our model is validated through a variety of comparisons with observations and other model simulation results. In the comparison with 1-D calculations, it is found that a single correction factor, often introduced by 1-D models for incident ions with finite arc dimensions, cannot completely account for the spatial spreading effect. In general, ionization rates are overestimated at high altitudes and underestimated at low altitudes by 1-D models. The availability of the NOAA/POES satellite data helps to yield a global pattern of energetic ion precipitation. We have carried out 3-D Monte Carlo simulations for the energetic proton precipitation during the April 2002 magnetic storm events, and examined for the first time how the structure of the global proton energy input to the Earth's upper atmosphere varies with time in response to different types of solar and magnetospheric activities. In addition, our simulation results are fed into the Global Ionosphere and Thermosphere model (GITM) by providing ionization rates and atmospheric heating. Through the coupling with GITM, the impact of high-energy precipitating protons on the ionosphere-thermosphere system has been for the first time evaluated by assuming realistic global particle precipitation. It is shown that, in certain regions, electron and nitric oxide densities can be enhanced by an order of magnitude, and ion and neutral winds can be affected by tens of percent.PhDEarth SciencesGeophysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125648/2/3208453.pd
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation of global periodic sawtooth oscillations observed in energetic particle flux at geosynchronous orbit.
No full textSawtooth events are defined as quasi-periodic, large-amplitude particle flux oscillations with a periodicity about 2-4 hours observed by geosynchronous Los Alamos National Laboratory satellites. In this thesis, the periodicity of sawtooth events is examined statistically first. As each oscillation shows similar signatures with isolated magnetospheric substorms, there are different opinions about whether sawtooth events are just an intense periodic form of magnetospheric substorms or they are a different magnetospheric activity due to their global and quasi-periodic characters. To help answer this, we use 96 sawtooth events intervals, including 394 individual teeth, and 213 isolated magnetospheric substorms to statistically analyze the similarities and differences in the ground geomagnetic disturbance, plasma property and magnetic dipolarization at geosynchronous orbit between the two categories. We also examine the relationship between sawtooth events and other magnetosphere phenomena, i.e., steady magnetospheric convection events and magnetic storms. Further we investigate the solar wind driver conditions during sawtooth events to understand why the Earth's magnetosphere prefer sawtooth event mode than magnetospheric substorms and other magnetosphere phenomena.PhDAtmospheric sciencesEarth SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126633/2/3276103.pd
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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