12,221 research outputs found
Glass fiber addition strengthens low-density ablative compositions
Approximately 15% of E-glass fibers was added to compositions under test and greatly improved char stability. Use of these fibers also reduced thermal strains which, in turn, minimized char shrinkage and associated cracks, subsurface voids, and disbonds. Increased strength allows honeycomb core reinforcement to be replaced by equivalent amount of glass fibers
Ion-implanted lanthanum fluoride waveguides
The effects of He+ and H+ implantation into LaF3 substrates have been investigated at both room temperature and 77 K. At room temperature the surface of the samples becomes black, possibly due to chemical reduction effects, but at low temperature the crystals remain clear and a refractive index change is observed which produces a surface waveguide. The dark mode spectra of these guides have been recorded using the prism coupling technique, and their refractive index profiles have been deduced from the spacing of these modes. The ion implantation produces a thin optical barrier layer of low refractive index at the end of the ion range. This paper discusses the use of multiple-energy implantation to produce a broad optical barrier in order to reduce the tunnelling losses of the guides, and subsequent thermal annealing to reduce absorption and scattering losses caused by colour centre formation in the electronic stopping surface region of the guides. It is concluded that either single- or multiple-energy He+ implants can be ideally used to form waveguides, for applications in the blue/UV or red/IR wavelength regions, respectively, with losses of a few dB/cm
Japanese Rice Protectionism: A Challenge for the Development of Agricultural Trade Laws
The Japanese government has failed to contribute meaningfully to agricultural trade negotiations. Japanâs extreme negotiation posture primarily stems from a disinclination to make concessions in its domestic rice market. It is also a result of the ability of Japan, and other developed nations, to take advantage of the rule structure outlined by the Agreement on Agriculture. Under current agricultural laws, Japan is able to maintain many domestic measures that provide support for rice farmers while also charging prohibitively high tariffs. Japanâs reluctance to limit its support for domestic rice farmers is based on the premise that rice plays a central role in Japanese culture, and without protection, the industry would collapse. What Japan has failed to realize, however, is that the bases of its arguments have little merit today. Perhaps more importantly, Japanese resistance to agricultural trade reform seriously undermines the legitimacy of the WTO
Nongovernmental Organizations and African Governments: Seeking an Effective International Legal Framework in a New Era of Heath and Development Aid
International and domestic nongovernmental organizations (NGOs) have multiplied on the African continent as both public and private donors have shifted their funding away from ineffective governments. Many African nations, including Zimbabwe and Sudan, have responded by expelling international NGOs and enacting laws that severely limit their ability to function. In most cases, NGOs are without recourse because of their precarious position in international law. Some scholars have posited that NGOs should be granted legal personality to make them full or partial subjects in international law. This Note argues that such a solution would not promote important goals NGOs advance in Africa. It would also ignore the important role that African governments must play in health and development issues. Instead, the international community should reinforce the existing international legal framework, allow NGOs to remain independent, and create mechanisms to foster communication between NGOs and host governments
Influence of gaseous hydrogen on metals Interim report
Gaseous hydrogen embrittlement in Inconel 718, Inconel 625, AISI 321 stainless steel, Ti-5Al-25Sn ELI, and OFHC coppe
A complete checklist with new records and geographical distribution of the rove beetles (Coleoptera, Staphylinidae) of Brazil
This paper presents the first comprehensive list of 2,688 species of Staphylinidae (Coleoptera) recorded from Brazil. The list is based on the taxonomic and ecological literature, and new records from some insect collections, and includes locality references for each species. In addition, Brazilian localities and the country-level distribution outside of Brazil are provided for each species. Brazilian localities are organized by state, and include the bibliographic reference and page number where each locality was reported. All localities are geo-referenced, organized by state, and listed in an Appendix.Este trabalho apresenta a primeira lista completa das 2.688 espĂ©cies de Staphylinidae (Coleoptera) registradas para o Brasil. A lista inclui todas as localidades citadas para cada espĂ©cie e baseia-se na literatura taxonĂŽmica e ecolĂłgica disponĂveis. Cada localidade inclui a referĂȘncia bibliogrĂĄfica e o nĂșmero da pĂĄgina onde foram citadas. TambĂ©m sĂŁo apresentados registros inĂ©ditos obtidos de algumas coleçÔes de insetos. AlĂ©m das localidades brasileiras sĂŁo citados todos os paĂses com ocorrĂȘncia conhecida para cada espĂ©cie. As localidades brasileiras, listadas no ApĂȘndice, estĂŁo organizadas por estado e georreferenciadas
Perturbation theory of the mass enhancement for a polaron coupled to acoustic phonons
We use both a perturbative Green's function analysis and standard
perturbative quantum mechanics to calculate the decrease in energy and the
effective mass for an electron interacting with acoustic phonons. The
interaction is between the difference in lattice displacements for neighbouring
ions, and the hopping amplitude for an electron between those two sites. The
calculations are performed in one, two, and three dimensions, and comparisons
are made with results from other electron-phonon models. We also compute the
spectral function and quasiparticle residue, as a function of characteristic
phonon frequency. There are strong indications that this model is always
polaronic on one dimension, where an unusual relation between the effective
mass and the quasiparticle residue is also found.Comment: 9 pages, 5 figures, submitted to PR
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