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The complex relationships among composition, roartensite start and finish temperatures, morphology of the martensite, residual stress distribution, and quenching conditions produce significant microstructural changes through a carburized case. Variations in the amount of retained austenite, the diffracting-particle size, and hardness were measured every 50μm in depth through a one percent carbon case on AISI-SAE 4320 steel. Measurement were made to a total depth of 2 mm. The percent retained austenite decreases from a maximum of 26% near the surface to a few percent in the bulk. It is shown that the x-ray diffracting-particle size of the martenaite phase is a structure parameter that changes when the martensite morphology goes from plate to lath type. The austenite phase diffracting-particle size is controlled hy the deformatioxis induced by the martensite formation.
The mechanical alloying process continually deforms, cold welds, and breaks apart metal powder particles. During the process of mechanical alloying elemental crystalline powders can produce an amorphous alloyed powder. Consolidation of these powders by powder metallurgy techniques can produce amorphous bulk metals.
Two Alloys 62.24 Zr-10.89 Ti-9.71 Ni-13.14 Cu-4.02 B and 64.84 Zr-11.35 Ti-11.12 Nt-13.69 Cu weight percent were mechanically alloyed for 45 hours by a SPEX 800 high energy ball-mill. The changes in structure were monitored by X-ray diffraction after every 5 hours of milling. Both powder compositions became amorphous after 15 hours of milling. New compounds began to form during milling to 35 hours. Milling for longer times produced no further structure changes. The milled samples were annealed at 950°C for 1 hour which produced a complex set of crystalline materials. The crystalline phases containing boron have larger lattice parameters and less tendency for grain growth.
Discussions exist in the literature concerning the application of single x-ray diffraction profile analysis to determine the average particle size, particle size distribution and root mean squared strain in catalytic systems. Nandi et al. have shown that the single order analysis can give erroneous strain results and is subject to error in the large particle size range. They further indicated that the initial slope of Stokes corrected Fourier coefficients gives more reliable average p article size than that which is calculated from single order peak shape analysis. There is apparent agreement that the average particle size and the particle size distribution measured by single order profile analysis, in small metal particle systems, are reliable.
Synchrotron-based micro-X-ray fluorescence (μXRF) equipment has been used to analyze impurities in polar ice. A customized sample holder has been developed and the μXRF equipment has been adapted with a thermal control system to keep samples unaltered during analyses. Artificial ice samples prepared from ultra-pure water were analyzed to investigate possible contamination and/or experimental artefacts. Analyses of polar ice from Antarctica (Dome C and Vostok) confirm this μXRF technique is non-destructive and sensitive. Experiments can be reproduced to confirm or refine results by focusing on interesting spots such as crystal grain boundaries or specific inclusions. Integration times and resolution can be adjusted to optimize sensitivity. Investigation of unstable particles is possible due to the short analysis time. In addition to identification of elements in impurities, μXRF is able to determine their speciations. The accuracy and reliability of the results confirm the potential of this technique for research in glaciology.
The development of high-intensity lasers has opened the field of nuclear reactions initiated by laser-accelerated particles. One possible application is the production of aneutronic fusion reactions for clean fusion energy production. We propose an innovative scheme based on the use of two targets and present the first results obtained with the ELFIE facility (at the LULI Laboratory) for the proton–boron-11 (p–11B) fusion reaction. A proton beam, accelerated by the Target Normal Sheat Acceleration mechanism using a short laser pulse (12 J, 350 fs, 1.056 µm, 1019 W cm−2), is sent onto a boron target to initiate fusion reactions. The number of reactions is measured with particle diagnostics such as CR39 track-detectors, active nuclear diagnostic, Thomson Parabola, magnetic spectrometer, and time-of-flight detectors that collect the fusion products: the α-particles. Our experiment shows promising results for this scheme. In the present paper, we discuss its principle and advantages compared with another scheme that uses a single target and heating mechanisms directly with photons to initiate the same p–11B fusion reaction.
X-ray and extreme ultraviolet emission from galaxy clusters can be interpreted as thermal emission from a hot plasma gravitationally bound to the cluster and constituting a significant amount of the mass of the cluster. The origin of this plasma and its thermal energy content can be linked to the formation process through the theory of self-organization of these structures.
In developed countries the majority of hepatitis C virus (HCV) infections occur in injecting drug users (IDUs) with prevalence in IDUs often high, but with wide geographical differences within countries. Estimates of local prevalence are needed for planning services for IDUs, but it is not practical to conduct HCV seroprevalence surveys in all areas. In this study survey data from IDUs attending specialist services were collected in 52/149 sites in England between 2006 and 2008. Spatially correlated random-effects models were used to estimate HCV prevalence for all sites, using auxiliary data to aid prediction. Estimates ranged from 14% to 82%, with larger cities, London and the North West having the highest HCV prevalence. The methods used generated robust estimates for each area, with a well-identified spatial pattern that improved predictions. Such models may be of use in other areas of study where surveillance data are sparse.
The thermal stresses induced by temperature variations that exist during steady-state Czochralski growth produce plastic deformations in the crystal by dislocation motion and generation. The temperature variations in the crystal are calculated numerically by the finite element method (FEM). Employing the Haasen-Sumino viscoplastic response function for silicon and the calculated temperature profile, the thermal stresses, the dislocation densities, and the residual stresses in the crystal are also calculated. Only low dislocation densities are of interest and hence the associated viscoplastic deformations are found to be small. The assumption is made that there is a very low dislocation density along the solid-melt interface. The Haasen-Sumino material model is modified to include a back-stress to account for the locking effects due to the impurity concentration in the crystal. This analysis provides guidance for growing large diameter crystal of materials with known constitutive relations which have a low dislocation density and low thermal stresses.
The morphology of nickel-containing phases at each stage during the treatment of a 12%Ni/SiO2 catalyst was studied. Liquid impregnated catalyst initially shows nickel nitrate uniformly dispersed on the surface of the silica in the form of a film. After calcining, large rafts of NiO with faceted surface pits are seen. The reduced catalyst contains bunched nickel particles or large rafts on the surface of the silica.
Metal powders of the composition 70 at% Cu and 30 at% Fe were produced by high energy mechanical alloying of the elemental powders. The powders were processed in a Spex 8000 mixer/mill for various times to investigate the potential of the mechanical alloying process for producing nano-composite structures with modified magnetic properties. Optical microscopy revealed a layered structure of alternating copper and iron that developed upon milling. The spacing between the layers decreased with milling time, becoming optically unresolvable (< 1 μm) after four hours of milling. A single profile x-ray diffraction profile shape analysis technique was used to determine the average diffracting particle size of the copper and iron phases. The diffracting particle size decreases with alloying time reaching values of 7.5 nm and 2 nm, for copper and iron respectively, after eight hours of alloying. The magnetic coercivity increased with milling time initially, reaching a maximum value above 300 Oe after six hours of milling. These results are discussed and compared to results obtained in Ag/Fe and Cu/Fe nano-composite films.
Characterization of the incubation time from infection to onset is important for understanding the natural history of infectious diseases. Attempts to estimate the incubation time distribution for novel A(H1N1v) have been, up to now, based on limited data or peculiar samples. We characterized this distribution for a generic group of symptomatic cases using laboratory-confirmed swine influenza case-information. Estimates of the incubation distribution for the pandemic influenza were derived through parametric time-to-event analyses of data on onset of symptoms and exposure dates, accounting for interval censoring. We estimated a mean of about 1·6–1·7 days with a standard deviation of 2 days for the incubation time distribution in those who became symptomatic after infection with the A(H1N1v) virus strain. Separate analyses for the <15 years and ⩾15 years age groups showed a significant (P<0·02) difference with a longer mean incubation time in the older age group.
Most stars are formed in a cluster or association, where the number density of stars can be high. This means that a large fraction of initially-single stars will undergo close encounters with other stars and/or exchange into binaries. We describe how such close encounters and exchange encounters can affect the properties of a planetary system around a single star. We define a singleton as a single star which has never suffered close encounters with other stars or spent time within a binary system. It may be that planetary systems similar to our own solar system can only survive around singletons. Close encounters or the presence of a stellar companion will perturb the planetary system, often leaving planets on tighter and more eccentric orbits. Thus planetary systems which initially resembled our own solar system may later more closely resemble some of the observed exoplanet systems.