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Externally driven plasmaspheric ULF waves observed by the Van Allen Probes
Get PDFWe analyze data acquired by the Van Allen Probes on 8 November 2012, during a period of extended low geomagnetic activity, to gain new insight into plasmaspheric ultralow frequency (ULF) waves. The waves exhibited strong spectral power in the 5-40 mHz band and included multiharmonic toroidal waves visible up to the eleventh harmonic, unprecedented in the plasmasphere. During this wave activity, the interplanetary magnetic field cone angle was small, suggesting that the waves were driven by broadband compressional ULF waves originating in the foreshock region. This source mechanism is supported by the tailward propagation of the compressional magnetic field perturbations at a phase velocity of a few hundred kilometers per second that is determined by the cross-phase analysis of data from the two spacecraft. We also find that the coherence and phase delay of the azimuthal components of the magnetic field from the two spacecraft strongly depend on the radial separation of the spacecraft and attribute this feature to field line resonance effects. Finally, using the observed toroidal wave frequencies, we estimate the plasma mass density for L = 2.6-5.8. By comparing the mass density with the electron number density that is estimated from the spectrum of plasma waves, we infer that the plasma was dominated by H+ ions and was distributed uniformly along the magnetic field lines. The electron density is higher than the prediction of saturated plasmasphere models, and this super saturated plasmasphere and the uniform ion distribution are consistent with the low geomagnetic activity that prevailed.Publishe
Microsatellite and mating type markers reveal unexpected patterns of genetic diversity in the pine root‐infecting fungus Grosmannia alacris
Get PDFGrosmannia alacris is a fungus commonly associated with root‐infesting bark beetles occurring on Pinus spp. The fungus has been recorded in South Africa, the USA, France, Portugal and Spain and importantly, has been associated with pine root diseases in South Africa and the USA. Nothing is known regarding the population genetics or origin of G. alacris, although its association with root‐infesting beetles native to Europe suggests that it is an invasive alien in South Africa. In this study, microsatellite markers together with newly developed mating type markers were used to characterize a total of 170 isolates of G. alacris from South Africa and the USA. The results showed that the genotypic diversity of the South African population of G. alacris was very high when compared to the USA populations. Two mating types were also present in South African isolates and the MAT1‐1/MAT1‐2 ratio did not differ from 1:1 (χ2 = 1·39, P = 0·24). This suggests that sexual reproduction most probably occurs in the fungus in South Africa, although a sexual state has never been seen in nature. In contrast, the large collection of USA isolates harboured only a single mating type. The results suggest that multiple introductions, followed by random mating, have influenced the population structure in South Africa. In contrast, limited introductions of probably a single mating type (MAT1‐2) may best explain the clonality of USA populations.Ye
Study of EMIC wave excitation using direct ion measurements
Get PDFWith data from Van Allen Probes, we investigate electromagnetic ion cyclotron (EMIC) wave excitation using simultaneously observed ion distributions. Strong He band waves occurred while the spacecraft was moving through an enhanced density region. We extract from helium, oxygen, proton, and electron mass spectrometer measurement the velocity distributions of warm heavy ions as well as anisotropic energetic protons that drive wave growth through the ion cyclotron instability. Fitting the measured ion fluxes to multiple sin(m)-type distribution functions, we find that the observed ions make up about 15% of the total ions, but about 85% of them are still missing. By making legitimate estimates of the unseen cold (below approximate to 2eV) ion composition from cutoff frequencies suggested by the observed wave spectrum, a series of linear instability analyses and hybrid simulations are carried out. The simulated waves generally vary as predicted by linear theory. They are more sensitive to the cold O+ concentration than the cold He+ concentration. Increasing the cold O+ concentration weakens the He band waves but enhances the O band waves. Finally, the exact cold ion composition is suggested to be in a range when the simulated wave spectrum best matches the observed one.Publishe
Two-photon imaging of Zn2+ dynamics in mossy fiber boutons of adult hippocampal slices
Get PDFMossy fiber termini in the hippocampus accumulate Zn2+, which is released with glutamate from synaptic vesicles upon neural excitation. Understanding the spatiotemporal regulation of mobile Zn2+ at the synaptic level is challenging owing to the difficulty of visualizing Zn2+ at individual synapses. Here we describe the use of zinc-responsive fluorescent probes together with two-photon microscopy to image Zn2+ dynamics mediated by NMDA receptor-dependent long-term potentiation induction at single mossy fiber termini of dentate gyrus neurons in adult mouse hippocampal slices. The membrane-impermeant fluorescent Zn2+ probe, 6-CO2H-ZAP4, was loaded into presynaptic vesicles in hippocampal mossy fiber termini upon KCl-induced depolarization, which triggers subsequent endocytosis and vesicular restoration. Local tetanic stimulation decreased the Zn2+ signal observed at individual presynaptic sites, indicating release of the Zn2+ from vesicles in synaptic potentiation. This synapse-level two-photon Zn2+ imaging method enables monitoring of presynaptic Zn2+ dynamics for improving the understanding of physiological roles of mobile Zn2+ in regular and aberrant neurologic function.Published
Assessment and Change Leadership in an Academic Library Department: A Case Study
Get PDFThe purpose of this paper is to report an academic library’s efforts to introduce
course-integrated assessment into its library instruction program. Applying a leadership change
model to the process allows for a step-by-step examination of both organizational change and the
creation of cultures of assessment.PublishedYe
Innovations for Access in Alabama: 1) Testing VuFind as an Index for AlabamaMosaic; 2) New Membership Structure for Alabama Digital Preservation Network
Get PDFIn the last decade, the Network of Alabama Academic Libraries (NAAL) has launched two statewide initiatives dealing with digitized cultural heritage materials. The first, AlabamaMosaic, is a digital library of materials from 21 institutions. Up until now, it has been necessary that all participants publish their materials using the same content management software (CMS). Most recently, this CMS has been CONTENTdm, with OCLC’s Multi-Site Server (MSS) software being used to index the collections and provide the search interface.
Although members have been exploring the use of alternative CMSs, these non-CONTENTdm collections cannot be indexed by MSS and thus could not be included in AlabamaMosaic before now. This past year, we have been testing the use of VuFind, an open-source next-generation catalog software, to index AlabamaMosaic collections. VuFind index records are created from OAI metadata harvesting feeds. Thus far, collections in three CMSs -- CONTENTdm, dSpace, and Acumen -- have been harvested into the VuFind index. Like MSS, VuFind allows searching across all indexed collections. Unlike MSS, VuFind facets then allow these search results to be narrowed by institution, collection, author, and/or subject term.
NAAL’s second statewide digital initiative is the Alabama Digital Preservation Network (ADPNet), a Private LOCKSS Network (PLN). Many of the digital collections indexed by AlabamaMosaic are also preserved in ADPNet. The original configuration for ADPNet involved seven server nodes, one each at the state archives and at six colleges and universities scattered around the state. Recently, a new membership model (presented here by Tom Wilson in 2011) was established with four tiers of membership. This new model allows smaller institutions to join without being required to host a server node and has resulted in the addition of two new ADPNet members, both public libraries
Atterburg Limits
No full textAtterberg Limits describe the water contents at which clays change behavior. The water content indicating the division between the liquid and plastic state is the liquid limit. The Liquid Limit is determined using a brass liquid limit device cup. The clay is sieved to #40. The clay is added to the cup. A groove of standard depth is made. The brass cup is subjected to a series of small drops that are counted. The groove slowly closes with each blow. The liquid limit is detremined when the groove closes 1 in. at 25 blows.N
The Comprehensive Inner Magnetosphere-Ionosphere Model
Get PDFSimulation studies of the Earth's radiation belts and ring current are very useful in understanding the acceleration, transport, and loss of energetic particles. Recently, the Comprehensive Ring Current Model (CRCM) and the Radiation Belt Environment (RBE) model were merged to form a Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model. CIMI solves for many essential quantities in the inner magnetosphere, including ion and electron distributions in the ring current and radiation belts, plasmaspheric density, Region 2 currents, convection potential, and precipitation in the ionosphere. It incorporates whistler mode chorus and hiss wave diffusion of energetic electrons in energy, pitch angle, and cross terms. CIMI thus represents a comprehensive model that considers the effects of the ring current and plasmasphere on the radiation belts. We have performed a CIMI simulation for the storm on 5-9 April 2010 and then compared our results with data from the Two Wide-angle Imaging Neutral-atom Spectrometers and Akebono satellites. We identify the dominant energization and loss processes for the ring current and radiation belts. We find that the interactions with the whistler mode chorus waves are the main cause of the flux increase of MeV electrons during the recovery phase of this particular storm. When a self-consistent electric field from the CRCM is used, the enhancement of MeV electrons is higher than when an empirical convection model is applied. We also demonstrate how CIMI can be a powerful tool for analyzing and interpreting data from the new Van Allen Probes mission.Publishe
Use What You Have: Authentic Assessment of In-Class Activities
Get PDFThe purpose of this paper is to share a practical approach to formative, authentic
assessment of Association of College and Research Libraries (ACRL) outcomes within individual
sessions of course-integrated information literacy. This method does not require extra class time
and assists librarians in modifying their teaching techniques to improve student learning.PublishedYe
Modeling the loss of inner belt protons by magnetic field line curvature scattering
Get PDFThe sudden loss of energetic protons in the inner radiation belt has been observed during geomagnetic storms. It is hypothesized that this sudden loss occurs because of changes in the geomagnetic field configuration which lead to a breakdown of the first adiabatic invariant, mu, in a process called magnetic field line curvature scattering or mu scattering. Comparison of observations to various analytic model predictions for mu scattering induced loss has, however, yielded discrepancies. To better understand how well the analytic models predict the proton loss, test particle simulations are carried out for various magnetic field configurations. Although our simulation results agree well with the analytic models for single-scattering events, the results after cumulative mu scattering can show significant disagreement with the theoretical predictions based on analytic models. In particular, we find the assumption that protons with predicted initial delta mu/mu 0.01 or epsilon > 0.1 are ultimately lost overestimates the proton loss. Based on the test particle simulation results, we develop a new empirical model, called the "epsilon-onset" model, to predict the minimum value of e at which all protons of a given pitch angle and energy can be assumed to be lost due to mu scattering. By applying our epsilon-onset model as the variable cutoff condition between trapping and detrapping, we obtain very good agreement between theoretical predictions and the simulation results for a range of Kp, suggesting that the epsilon-onset model can potentially serve as an easy-to-use and more reliable predictor of inner belt proton loss due to mu scattering than the previously used fixed-valued cutoff conditions.Publishe