A simple variational method for calculating energy and quantum capacitance of an electron gas with screened interactions

We describe a variational procedure for calculating the energy of an electron gas in which the long-range Coulomb interaction is truncated by the screening effect of a nearby metallic gate. We use this procedure to compute the quantum capacitance of the system as a function of electron density and spin polarization. The accuracy of the method is verified against published Monte-Carlo data. The results compare favorably with a recent experiment.Comment: 4 pages, 3 figure

A model of large volumetric capacitance in graphene supercapacitors based on ion clustering

Electric double layer supercapacitors are promising devices for high-power energy storage based on the reversible absorption of ions into porous, conducting electrodes. Graphene is a particularly good candidate for the electrode material in supercapacitors due to its high conductivity and large surface area. In this paper we consider supercapacitor electrodes made from a stack of graphene sheets with randomly-inserted "spacer" molecules. We show that the large volumetric capacitances C > 100 F/cm^3 observed experimentally can be understood as a result of collective intercalation of ions into the graphene stack and the accompanying nonlinear screening by graphene electrons that renormalizes the charge of the ion clusters.Comment: 13 pages, 5 figures; additional discussion and supporting calculations adde

Take It to the eTeam: Improving ERA Troubleshooting Management and Communications with LibAnswers

This presentation was given during the Springshare SpringyCamp Virtual Conference

A Persistent High-Energy Flux from the Heart of the Milky Way : Integral's view of the Galactic Center

The Ibis/Isgri imager on Integral detected for the first time a hard X-ray source, IGR J17456-2901, located within 1' of Sgr A* over the energy range 20-100 keV. Here we present the results of a detailed analysis of ~7 Ms of Integral observations of the GC. With an effective exposure of 4.7 Ms we have obtained more stringent positional constraints on this HE source and constructed its spectrum in the range 20-400 keV. Furthermore, by combining the Isgri spectrum with the total X-ray spectrum corresponding to the same physical region around SgrA* from XMM data, and collected during part of the Integral observations, we constructed and present the first accurate wide band HE spectrum for the central arcmins of the Galaxy. Our complete analysis of the emission properties of IGR shows that it is faint but persistent with no variability above 3 sigma contrary to what was alluded to in our first paper. This result, in conjunction with the spectral characteristics of the X-ray emission from this region, suggests that the source is most likely not point-like but, rather, that it is a compact, yet diffuse, non-thermal emission region. The centroid of IGR is estimated to be R.A.=17h45m42.5, decl.=-28deg59'28'', offset by 1' from the radio position of Sgr A* and with a positional uncertainty of 1'. Its 20-400 keV luminosity at 8 kpc is L=5.4x10^35 erg/sec. Very recently, Hess detected of a source of ~TeV g-rays also located within 1' of Sgr A*. We present arguments in favor of an interpretation according to which the photons detected by Integral and Hess arise from the same compact region of diffuse emission near the central BH and that the supernova remnant Sgr A East could play an important role as a contributor of very HE g-rays to the overall spectrum from this region.Comment: 14 pages, 11 figures, Accepted for publication in Ap

Bridging the Gap: Providing a Marketing and Support Framework for Institutional Repository Services

Institutional Repositories require continuous promotion and support to attract and retain campus collections. However, balancing promotion with a clear representation of repository offerings, policies, and procedures is challenging, especially for institutions that rely on public services personnel for front-line promotion. This poster presents Georgia Southern University\u27s recently-developed IR Services LibGuide as a model for providing such a framework (http://georgiasouthern.libguides.com/irservices/). This portal provides 1) a front-line promotional tool; 2) a client-management tool for support consultations; and 3) a storehouse for repository-related forms and licenses. It further integrates with the library\u27s other scholarly communications-related guides, providing seamless representation of these services to patrons

Discover...Books, Articles, Everything in a Single Search!

This presentation was given during Georgia Southern University\u27s Eagle Techxpo

Choosing the Right Discovery Tool: Making a Discovery Task Force Function Effectively

This presentation describes a systematic way to go about selecting the best Discovery Tool for your institution. Selection is much more than pricing, vendor demonstrations or recommendations from a few colleagues. How do you go from an administrative decision to add a discovery service to the final decision? This presentation will outline the steps taken by the Discovery Task Force at Georgia Southern University which included selecting a service based on a set of criteria, implementation, as well as faculty and staff training

Very High Resolution Solar X-ray Imaging Using Diffractive Optics

This paper describes the development of X-ray diffractive optics for imaging solar flares with better than 0.1 arcsec angular resolution. X-ray images with this resolution of the \geq10 MK plasma in solar active regions and solar flares would allow the cross-sectional area of magnetic loops to be resolved and the coronal flare energy release region itself to be probed. The objective of this work is to obtain X-ray images in the iron-line complex at 6.7 keV observed during solar flares with an angular resolution as fine as 0.1 arcsec - over an order of magnitude finer than is now possible. This line emission is from highly ionized iron atoms, primarily Fe xxv, in the hottest flare plasma at temperatures in excess of \approx10 MK. It provides information on the flare morphology, the iron abundance, and the distribution of the hot plasma. Studying how this plasma is heated to such high temperatures in such short times during solar flares is of critical importance in understanding these powerful transient events, one of the major objectives of solar physics. We describe the design, fabrication, and testing of phase zone plate X-ray lenses with focal lengths of \approx100 m at these energies that would be capable of achieving these objectives. We show how such lenses could be included on a two-spacecraft formation-flying mission with the lenses on the spacecraft closest to the Sun and an X-ray imaging array on the second spacecraft in the focal plane \approx100 m away. High resolution X-ray images could be obtained when the two spacecraft are aligned with the region of interest on the Sun. Requirements and constraints for the control of the two spacecraft are discussed together with the overall feasibility of such a formation-flying mission

Shock tunnel studies of scramjet phenomena, supplement 6

Reports by the staff of the University of Queensland on various research studies related to the advancement of scramjet technology are presented. These reports document the tests conducted in the reflected shock tunnel T4 and supporting research facilities that have been used to study the injection, mixing, and combustion of hydrogen fuel in generic scramjets at flow conditions typical of hypersonic flight. In addition, topics include the development of instrumentation and measurement technology, such as combustor wall shear and stream composition in pulse facilities, and numerical studies and analyses of the scramjet combustor process and the test facility operation