Secondary emission conductivity of high purity silica fabric

High purity silica fabrics were proposed for use as a material to control the effects of electrostatic charging of satellites at synchronous altitudes. These materials exhibited very quiet behavior when placed in simulated charging environments as opposed to other dielectrics used for passive thermal control which exhibit varying degrees of electrical arcing. Secondary emission conductivity is proposed as a mechanism for this superior behavior. Design of experiments to measure this phenomena and data taken on silica fabrics are discussed as they relate to electrostatic discharge (ESD) control on geosynchronous orbit spacecraft. Studies include the apparent change in resistivity of the material as a function of the electron beam energy, flux intensity, and the effect of varying electric fields impressed across the material under test

Materials and techniques for spacecraft static charge control

An overview of the design, development, fabrication, and testing of transparent conductive coatings and conductive lattices deposited or formed on high resistivity spacecraft dielectric materials to obtain control static charge buildup on spacecraft external surfaces is presented. Fabrication techniques for the deposition of indium/tin oxide coatings and copper grid networks on Kapton and FEP Teflon films and special frit coatings for OSR and solar cell cover glasses are discussed. The techniques include sputtering, photoetching, silkscreening, and mechanical processes. A facility designed and built to simulate the electron plasma at geosynchronous altitudes is described along with test procedures. The results of material characterizations as well as electron irradiation aging effects in this facility for spacecraft polymers treated to control static charge are presented. The data presents results for electron beam energies up to 30 kV and electron current densities of 30 nA/cm squared. Parameters measured include secondary emission, surface leakage, and through the sample currents as a function of primary beam energy and voltage

Optical conductivity of polaronic charge carriers

The optical conductivity of charge carriers coupled to quantum phonons is studied in the framework of the one-dimensional spinless Holstein model. For one electron, variational diagonalisation yields exact results in the thermodynamic limit, whereas at finite carrier density analytical approximations based on previous work on single-particle spectral functions are obtained. Particular emphasis is put on deviations from weak-coupling, small-polaron or one-electron theories occurring at intermediate coupling and/or finite carrier density. The analytical results are in surprisingly good agreement with exact data, and exhibit the characteristic polaronic excitations observed in experiments on manganites.Comment: 23 pages, 11 figure

Mobile small polaron

Extending the Froehlich polaron problem to a discrete ionic lattice we study a polaronic state with a small radius of the wave function but a large size of the lattice distortion. We calculate the energy dispersion and the effective mass of the polaron with the 1/\lambda perturbation theory and with the exact Monte Carlo method in the nonadiabatic and adiabatic regimes, respectively. The ``small'' Froehlich polaron is found to be lighter than the small Holstein polaron by one or more orders of magnitude.Comment: 4 pages, 4 figures, published versio

Signatures of Superfluidity in Dilute Fermi Gases near a Feshbach Resonance

We present a brief account of the most salient properties of vortices in dilute atomic Fermi superfluids near a Feshbach resonance.Comment: 6 pages, 1 figure, and jltp.cls. Several typos and a couple of inaccuracies have been correcte

Expressive and Instrumental Offending: Reconciling the Paradox of Specialisation and Versatility

Although previous research into specialisation has been dominated by the debate over the existence of specialisation versus versatility, it is suggested that research needs to move beyond the restrictions of this dispute. The current study explores the criminal careers of 200 offenders based on their criminal records, obtained from a police database in the North West of England, aiming to understand the patterns and nature of specialisation by determining the presence of differentiation within their general offending behaviours and examining whether the framework of Expressive and Instrumental offending styles can account for any specialised tendencies that emerge. Fifty-eight offences were subjected to Smallest Space Analysis. Results revealed that a model of criminal differentiation could be identified and that any specialisation is represented in terms of Expressive and Instrumental offending styles

Intraplate strike-slip faulting in East Antarctica: new geophysical views from the Rennick Graben and Wilkes Subglacial Basin

Intraplate strike-slip faulting can occur in association with different geodynamic settings, ranging from subduction-related to collision and extension. Geological and geophysical research in Northern Victoria Land (NVL) in East Antarctica, has led to the interpretation that major fault systems that were active during the early Paleozoic Ross Orogen were reactivated much later as right-lateral intraplate strike-slip fault systems from ca 48 Ma, and that these faults may have accomodated differential shear along evolving oceanic transform faults located between southeastern Australia and Tasmania. One of the main structures in NVL that has been inferred to relate to this unusual geodynamic process is the Rennick Graben (RG), but its age, extent and kinematics have remained both poorly constrained and controversial. Even less well-understood are the potential tectonic linkages between the RG and the deep sub-basins that lie within the much broader Wilkes Subglacial Basin (WSB), in the hinterland of the Transantarctic Mountains. Here, we present new interpretations of enhanced potential field images derived from aeromagnetic and airborne and land-gravity observations to help constrain the extent and architecture of the RG and the sub-basins within the WSB. We show that the RG is a composite pull-part basin that extends from the Oates Coast towards the margin of the Ross Sea Rift, part of the West Antarctic Rift System. We suggest that the more cratonic WSB region was also affected by extensional and transtensional processes, the latter potentially linked to an evolving and distributed left-lateral Paleogene(?) strike-slip plate boundary between East Antarctica and Australia

Non-interacting Cooper pairs inside a pseudogap

I present a simple analytical model describing the normal state of a superconductor with a pseudogap in the density of states, such as in underdoped cuprates. In nearly two-dimensional systems, where the superconducting transition temperature is reduced from the mean-field BCS value, Cooper pairs may be present as slow fluctuations of the BCS pairing field. Using the self-consistent T-matrix (fluctuation exchange) approach I find that the fermion spectral weight exhibits two BCS-like peaks, broadened by fluctuations of the pairing field amplitude. The density of states becomes suppressed near the Fermi energy, which allows for long-lived low-energy Cooper pairs that propagate as a sound-like mode with a mass. A self-consistency requirement, linking the width of the pseudogap to the intensity of the pairing field, determines the pair condensation temperature. In nearly two-dimensional systems, it is proportional to the degeneracy temperature of the fermions, with a small prefactor that vanishes in two dimensions.Comment: LaTeX (prbbib.sty included), 24 pages, 4 PostScript figures To appear in Phys.Rev.