A sceptic looks at "housing theory"

A sceptic looks at "housing theory

Foaming-electrolyte fuel cell

Foam structure feeds fuel gas solution into electrolyte. Fuel gas reacts at static, three-phase interface between fuel gas, electrolyte, and electrode material. The foam forms an electrical contact between main body of electrolyte and the electrode, and aids in removal of by-products of the chemical reaction

Pattern stabilization through parameter alternation in a nonlinear optical system

We report the first experimental realization of pattern formation in a spatially extended nonlinear system when the system is alternated between two states, neither of which exhibits patterning. Dynamical equations modeling the system are used for both numerical simulations and a weakly nonlinear analysis of the patterned states. The simulations show excellent agreement with the experiment. The nonlinear analysis provides an explanation of the patterning under alternation and accurately predicts both the observed dependence of the patterning on the frequency of alternation, and the measured spatial frequencies of the patterns.Comment: 12 pages, 5 figures. To appear in PR

Endoscopy : an evolving speciality

The practice of endoscopy has been rapidly changing due to new emerging technologies and novel techniques. There has been more focus on colonoscopy training with the development of structured programmes including simulators. Chromoendoscopy and magnification endoscopy have enabled improved diagnosis of small neoplastic lesions and will be important for the success of colorectal cancer screening programmes. The small bowel is now accessible to diagnostic modalities like capsule endoscopy and to therapeutic tools through the double balloon enteroscope. Endoscopic therapy has also become more sophisticated with endoscopic therapy of reflux disease now possible. Excision of large colorectal adenomatous polyps by endoscopic mucosal resection and dissection of submucosal tumours may reduce the need for surgical intervention. The practice of endoscopy has rapidly changed over the past few years. What was once a simple diagnostic procedure made possible by the development of fibre optics has become a speciality in its own right. This article will highlight some aspects of endoscopic practice that have undergone major changes over the past few years and that will shape endoscopy practice in the future.peer-reviewe

Development of dispersion-strengthened Ni-Cr-ThOz alloys for the space shuttle thermal protection system

Manufacturing processes were developed for TD-NiCr providing small sheet (45 x 90 cm), and larger sheet (60 x 150 cm) and foil. The alternate alloy, DS-NiCr, was produced by pack-chromizing Ni-ThO2 sheet. Formability criteria are being established for basic sheet forming processes, which are brake forming, corrugation forming, joggling, dimpling, and beading. Resistance spot welding (fusion and solid state), resistance seam welding, solid state diffusion welding, and brazing are included in the joining programs. Major emphasis is centered on an Al-modified Ni-Cr-ThO2 alloy development. These alloys, containing 3 to 5% Al, form the protective Al2O3 scale. This enhances oxidation resistance under reentry conditions. Both TD-NiCrAl and DS-NiCrAl alloys are included. A tentative composition of Ni-16Cr-3.5Al-2ThO2 was selected based on oxidation resistance and fabricability

Spin Freezing in Geometrically Frustrated Antiferromagnets with Weak Disorder

We investigate the consequences for geometrically frustrated antiferromagnets of weak disorder in the strength of exchange interactions. Taking as a model the classical Heisenberg antiferromagnet with nearest neighbour exchange on the pyrochlore lattice, we examine low-temperature behaviour. We show that random exchange generates long-range effective interactions within the extensively degenerate ground states of the clean system. Using Monte Carlo simulations, we find a spin glass transition at a temperature set by the disorder strength. Disorder of this type, which is generated by random strains in the presence of magnetoelastic coupling, may account for the spin freezing observed in many geometrically frustrated magnets.Comment: 4 pages, 5 figure

A3 Subscale Diffuser Test Article Design

This paper gives a detailed description of the design of the A3 Subscale Diffuser Test (SDT) Article Design. The subscale diffuser is a geometrically accurate scale model of the A3 altitude rocket facility. It was designed and built to support the SDT risk mitigation project located at the E3 facility at Stennis Space Center, MS (SSC) supporting the design and construction of the A3 facility at SSC. The subscale test article is outfitted with a large array of instrumentation to support the design verification of the A3 facility. The mechanical design of the subscale diffuser and test instrumentation are described her

Optimal slit orientation for long multi-object spectroscopic exposures

Historically, long-slit spectroscopic observations were carried out using the parallactic angle for the slit orientation if slit loss was an important consideration (either to maximize the signal-to-noise or to do spectrophotometry). This requires periodic realignment of the slit position angle as the parallactic angle changes. This is not possible for multi-slit observations where one slit position angle must be chosen for the entire exposure. Common wisdom suggests using the parallactic angle at the meridian (HA=0). In this paper, I examine what the best strategy is for long, multi-slit exposures. I find that in extreme cases (very long exposure time) the best choice is to orient the slit \emph{perpendicular} to the parallactic angle at the meridian. There are two effects to consider: the increasing dispersion with increasing airmass and the changing angle between the parallactic angle and the slit. In the case of \emph{traditional} slit orientation, the two effects amplify each other, thus rendering a significant fraction of the observation useless. Using the perpendicular orientation, the two processes work against each other, thus most of the observation remains useful. I will use, as an example, our 8 hour Lockman Hole observations using the Keck telescope, but generic methods are given to evaluate a particular observation. I also make the tools available to the community.Comment: Accepted by A&A (20/06/2005