Effects of orbital exposure on Halar during the LDEF mission

Thermomechanical Analysis (TMA), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) were performed on samples of Halar exposed on the LDEF Mission for 6 years in orbit and unexposed Halar control samples. Sections 10-100 microns thick were removed from the exposed surface down to a depth of 1,000 microns through the 3 mm thick samples. The TMA and DSC results, which arise from the entire slice and not just its surface, showed no differences between the LDEF and the control samples. TMA scans were run from ambient to 300 C; results were compared by a tabulation of the glass transition temperatures. DSC scans were run from ambient to 700 C; the enthalpy of melting was compared for the samples as a function of section depth with the sample. The TGA results, which arise from the surface of the sample initially, showed a sharp increase in the topmost 50 micron section (the exposed, discolored side) in the weight loss of 170 C in oxygen. This weight loss dropped to bulk values in the range of depth of 50-200 microns. The control sample showed only a slight increase in weight loss as the top surface was approached. The LDEF Halar sample appears to be mechanically undamaged, with a surface layer which oxidizes faster as a result of orbital exposure

Investigation of passive shock wave-boundary layer control for transonic airfoil drag reduction

The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data show an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity

The Barrow Symposium on Sea Ice, 2000: Evaluation of One Means of Exchanging Information between Subsistence Whalers and Scientists

A Barrow Symposium on Sea Ice (BSSI) was held in early winter 2000. The National Science Foundation (U.S.) funded this symposium as the keystone event in a project designed to ally traditional ecological knowledge (TEK) with formal ice research and remote sensing. The goal of the project was to stimulate substantive interactions between scientists and technicians who study sea ice on one hand, and Inupiat Eskimos (primarily whaling captains and their crews) who use the ice routinely for travel, camping, and hunting, on the other. From different perspectives, at different scales, and for different purposes, the two groups have accumulated extensive knowledge of ice characteristics and dynamics. We evaluate strengths and weaknesses of the workshop format as a means of exchanging information between scientific and traditional knowledge.... To continue to develop the interactions and shared purposes that characterized the BSSI, a core group of participants needs to meet periodically to review progress on sea ice research in the region, and to seek ways to promote further collaboration between ice observers from the subsistence community and scientists. Research on sea ice appears likely to continue to flourish near Barrow. Both whalers and scientists are eager to share information and insights. Facilitating that exchange is not a trivial task. To be successful in the long run, the promising start made by the BSSI needs to be followed up with refinements in collaborative field research, as well as by regular opportunities for scientists and whalers to learn from one another

Effects of orbital exposure on RTV during the LDEF mission

Thermomechanical analysis (TMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) were performed on samples of RTV 511 exposed on the Long Duration Exposure Facility (LDEF) mission for 6 years in orbit and unexposed RTV 511 control samples. Slices 20- to 400-microns thick were removed from the exposed surface down to a depth of 1,500 microns through the 3-mm thick samples. The TMA and DSC results, which arise from the entire slice and not just its surface, showed no significant differences between the LDEF exposed and the control samples. TMA scans were run from ambient to 500 C; results were compared by a tabulation of the onset temperatures for flow. DSC scans were run from ambient to 600 C; no endotherms or exotherms occurred over the range observed. What appear to be glass transition temperatures were compared for the samples as a function of section depth within the sample and between the exposed and control samples. The TGA scans from 25 to 900 C, which arise from the surface of the sample initially, showed a slight increase in the top most 105-micron slice (the exposed, discolored side) in the weight loss at 600 C in oxygen. This weight loss dropped to bulk values at the next slice below the top section, a mean depth of 258 microns. The control sample also showed an increase in weight loss as the top surface was approached, but the 600 C weight losses were very inconsistent. The LDEF RTV sample appears to be mechanically undamaged, with a surface layer which oxidizes slightly faster as a result of orbital exposure

Odderon in baryon-baryon scattering from the AdS/CFT correspondence

Based on the AdS/CFT correspondence, we present a holographic description of various C-odd exchanges in high energy baryon-baryon and baryon-antibaryon scattering, and calculate their respective contributions to the difference in the total cross sections. We predict that, due to the warp factor of AdS_5, the total cross section in pp collisions is larger than in p\bar{p} collisions at asymptotically high energies.Comment: 23 pages, v2: minor changes, to be published in JHE

Phase imaging systems for measurement of plasma density contours

During recent years, there has been considerable interest in obtaining spatially localized time resolved density measurements in fusion plasmas. However, the study of such phenomena requires many channels of information on a scale much finer than available with current discrete chordal view multichannel interferometers. These problems can be overcome by imaging an expanded probe beam occupying the entire plasma port crosssection onto a linear detector array [1], thereby significantly reducing the number of optical components and hence the cost and complexity of the system compared with a comparable discrete chord multichannel interferometer. Other more fundamental advantages of the imaging technique include compensation for phase errors due to plasma refraction, whilst the diffraction limited system resolution (typically ≃ 1cm for FIR probe wavelengths) allows the use of many detector channels for high spatial sampling rates. and hence accurate reconstruction of the density profiles

Dimensional Reduction of Fermions in Brane Worlds of the Gross-Neveu Model

We study the dimensional reduction of fermions, both in the symmetric and in the broken phase of the 3-d Gross-Neveu model at large N. In particular, in the broken phase we construct an exact solution for a stable brane world consisting of a domain wall and an anti-wall. A left-handed 2-d fermion localized on the domain wall and a right-handed fermion localized on the anti-wall communicate with each other through the 3-d bulk. In this way they are bound together to form a Dirac fermion of mass m. As a consequence of asymptotic freedom of the 2-d Gross-Neveu model, the 2-d correlation length \xi = 1/m increases exponentially with the brane separation. Hence, from the low-energy point of view of a 2-d observer, the separation of the branes appears very small and the world becomes indistinguishable from a 2-d space-time. Our toy model provides a mechanism for brane stabilization: branes made of fermions may be stable due to their baryon asymmetry. Ironically, our brane world is stable only if it has an extreme baryon asymmetry with all states in this ``world'' being completely filled.Comment: 26 pages, 7 figure

Hybrid speciation in Heliconius butterflies? A review and critique of the evidence

The evidence supporting the recent hypothesis of a homoploid hybrid origin for the butterfly species Heliconius heurippa is evaluated. Data from selective breeding experiments, mate-choice studies, and a wide variety of DNA markers are reviewed, and an alternative hypothesis for the origin of the species and its close relatives is proposed. A scenario of occasional red wing-pattern mutations in peripheral populations of Heliconius cydno with subsequent adaptive convergence towards sympatric mimicry rings involving H. melpomene and H. erato is offered as an alternative to the HHS hypothesis. Recent twists of this tale are addressed in a postscript

Failure of knee osteotomy in a case of neuropathic arthropathy of the knee

Neuropathic arthropathy (Charcot’s joint) is a degenerative process that affects peripheral or vertebral joints as a consequence of a disturbance in proprioception and pain perception. The knee is one of the most frequently affected joints, but even when the diagnosis is made at an early stage there is no consensus on the best treatment options. An early diagnosis of neurosyphilis was made in a 55-year-old woman presenting a delayed union of an asymptomatic Schatzker type IV fracture of the proximal tibia. A medial opening wedge tibial osteotomy was performed to achieve fracture healing, to correct the medial depression of the articular surface, and possibly to avoid an early arthritis typical of the disease. To our knowledge, a knee osteotomy has never been reported at an early stage of neuropathic arthropathy. Even though the clinical and radiographic evaluation performed at 4 months follow-up showed a good stage of healing of the osteotomy and no typical features of neuropathic joint degeneration, at 8 months follow-up the knee was markedly deranged

Wilson loops stability in the gauge/string correspondence

We study the stability of some classical string worldsheet solutions employed for computing the potential energy between two static fundamental quarks in confining and non-confining gravity duals. We discuss the fixing of the diffeomorphism invariance of the string action, its relation with the fluctuation orientation and the interpretation of the quark mass substraction worldsheet needed for computing the potential energy in smooth (confining) gravity background. We consider various dual gravity backgrounds and show by a numerical analysis the existence of instabilities under linear fluctuations for classical string embedding solutions having positive length function derivative $L'(r_0)>0$. Finally we make a brief discussion of 't Hooft loops in non-conformal backgrounds.Comment: 34 pages, 36 figures. Reference added. Final version JHEP accepte