10,855 research outputs found
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
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
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
Provenance and geochemistry of exotic clasts in conglomerates of the Oligocene Torehina Formation, Coromandel Peninsula, New Zealand
Non-marine pebble to cobble conglomerates of the lower Torehina Formation (Oligocene) crop out along western Coromandel Peninsula and overlie, with strong angular discordance, continental-margin metasedimentary rocks (Manaia Hill Group) of Mesozoic (Late Jurassic to ?Early Cretaceous) age. The conglomerates contain provenance information that identifies a pre-Oligocene depositional history obscured by the unconformable juxtaposition of these Tertiary and Mesozoic strata. Most clasts in the lower Torehina Formation are visually similar to local bedrock lithologies, including metamorphosed sandstones and argillites, but are kaolinitic and contain more detrital and authigenic chert, quartz, and potash feldspar. Local derivation of these clasts seems unlikely. By comparing geochemical ratios with those defined for continental margin sandstones, and well characterised New Zealand tectonic terranes, we interpret the majority of clasts in the lower Torehina Formation to have been derived from a dissected orogen, with mixtures of felsic and volcanogenic-derived sediment. The most likely sources are the Waipapa and Torlesse Terranes. The remaining 20â30% of the clasts in the lower Torehina Formation were originally friable, are coarse grained, and appear to be lithologically exotic relative to known metamorphosed sandstones in basement terrane sources on North Island. Some clasts contain coal laminae and particles, and all contain detrital kaolinite as lithic fragments and matrix. Such characteristics imply a non-marine to marginal-marine source containing sediment derived from strongly weathered granite or granodiorite. Mechanical fragility implies a likely proximal, easily erodible source. We propose that this group of clasts was derived from an Upper Cretaceous sedimentary cover, either part of a locally developed basin fill or part of a once regionally extensive cover on North Island. Either case defines a more widely distributed Cretaceous source than found today
Shock tunnel studies of scramjet phenomena, supplement 5
A series of reports are presented on SCRAMjet studies, shock tunnel studies, and expansion tube studies. The SCRAMjet studies include: (1) Investigation of a Supersonic Combustion Layer; (2) Wall Injected SCRAMjet Experiments; (3) Supersonic Combustion with Transvers, Circular, Wall Jets; (4) Dissociated Test Gas Effects on SCRAMjet Combustors; (5) Use of Silane as a Fuel Additive for Hypersonic Thrust Production, (6) Pressure-length Correlations in Supersonic Combustion; (7) Hot Hydrogen Injection Technique for Shock Tunnels; (8) Heat Release - Wave Interaction Phenomena in Hypersonic Flows; (9) A Study of the Wave Drag in Hypersonic SCRAMjets; (10) Parametric Study of Thrust Production in the Two Dimensional SCRAMjet; (11) The Design of a Mass Spectrometer for use in Hypersonic Impulse Facilities; and (12) Development of a Skin Friction Gauge for use in an Impulse Facility. The shock tunnel studies include: (1) Hypervelocity flow in Axisymmetric Nozzles; (2) Shock Tunnel Development; and (3) Real Gas Efects in Hypervelocity Flows over an Inclined Cone. The expansion tube studies include: (1) Investigation of Flow Characteristics in TQ Expansion Tube; and (2) Disturbances in the Driver Gas of a Shock Tube
Direct UV observations of the circumstellar envelope of alpha Orionis
Observations were made in the IUE LWP camera, low dispersion mode, with alpha Ori being offset various distances from the center of the Long Wavelength Large Aperture along its major axis. Signal was acquired at all offset positions and is comprised of unequal components of background/dark counts, telescope-scattered light, and scattered light emanating from the extended circumstellar shell. The star is known from optical and infrared observations to possess an extended, arc-minute sized, shell of cool material. Attempts to observe this shell with the IUE are described, although the deconvolution of the stellar signal from the telescope scattered light requires further calibration effort
Mental States Are Like Diseases
While Quineâs linguistic behaviorism is well-known, his Kant Lectures contain one of his most detailed discussions of behaviorism in psychology and the philosophy of mind. Quine clarifies the nature of his psychological commitments by arguing for a modest view that is against âexcessively restrictiveâ variants of behaviorism while maintaining âa good measure of behaviorist disciplineâŠto keep [our mental] terms under controlâ. In this paper, I use Quineâs Kant Lectures to reconstruct his position. I distinguish three types of behaviorism in psychology and the philosophy of mind: ontological behaviorism, logical behaviorism, and epistemological behaviorism. I then consider Quineâs perspective on each of these views and argue that he does not fully accept any of them. By combining these perspectives we arrive at Quineâs surprisingly subtle view about behaviorism in psychology
Unbiased bases (Hadamards) for 6-level systems: Four ways from Fourier
In quantum mechanics some properties are maximally incompatible, such as the
position and momentum of a particle or the vertical and horizontal projections
of a 2-level spin. Given any definite state of one property the other property
is completely random, or unbiased. For N-level systems, the 6-level ones are
the smallest for which a tomographically efficient set of N+1 mutually unbiased
bases (MUBs) has not been found. To facilitate the search, we numerically
extend the classification of unbiased bases, or Hadamards, by incrementally
adjusting relative phases in a standard basis. We consider the non-unitarity
caused by small adjustments with a second order Taylor expansion, and choose
incremental steps within the 4-dimensional nullspace of the curvature. In this
way we prescribe a numerical integration of a 4-parameter set of Hadamards of
order 6.Comment: 5 pages, 2 figure
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