Search results for "Metallurgy"
showing 10 items of 1419 documents
Post UV irradiation annealing of E’ centers in silica controlled by H2 diffusion
2004
Abstract We investigate the isothermal annealing of E′ centers generated by UV photons (266 nm) of a pulsed Nd:YAG laser in two natural silica types differing for their OH content. Electron spin resonance and absorption spectra recorded at room temperature at different delays from the laser exposure evidenced a partial reduction of E′ centers, more pronounced in the wet silica. These post irradiation kinetics complete within 10 5 s, regardless the silica type, and they are consistent with a diffusion limited reaction between the E′ centers and the molecular hydrogen H 2 . Analysis of our data is done by theoretical fits using the Waite's equation and compared with the H 2 diffusion paramete…
In-process tool force and rotation variation to control sheet thickness change in friction stir welding of magnesium alloys
2016
Two different in-process control strategies, developed in order to produce sound joints in AZ31 magnesium alloy by Friction Stir Welding on sheet blanks with a non-uniform thickness, are presented and compared. To this purpose, sheets with dip or hump were machined and welded by either changing the rotational speed or the tool plunging in order to keep constant the vertical force occurring during welding. The mechanical strength of the joints was measured in the zones where the sheets before welding were characterised by different thicknesses. The sheets welded by the two different strategies are characterized by very similar ultimate tensile strength values. Finally, the results showed tha…
AGingaObservation of the X‐Ray Pulsar 4U 0352+30
1996
4U 0352 + 30 (X Persei) is a low-luminosity binary X-ray pulsar with a pulse period of 835 s. We present timing and spectral analysis of a Ginga observation of X Persei from 1990 January 26 to January 29. The observation shows the peculiar spectral behavior of X Persei: the pulse-averaged hardness ratio exhibits a sharp hardening episode at phase minimum of the light curve. In order to explain the shape of the observed hardness ratio, we discuss the possible geometry of the emitting region. Simple models of fan emission from a hollow accretion column can reproduce the qualitative features of the observed light curve and hardness ratio.
Actinic Flux and Net Flux Calculations in Radiative Transfer—A Comparative Study of Computational Efficiency
2001
Abstract The accuracy and speed of three well-known computational techniques (DISORT, the δ–four-stream approximation, and the two-stream approximation), and the matrix inversion method, which is less well known, have been investigated. Results are presented for both broadband actinic and net fluxes over a range of parameters including solar zenith cosine, relative humidity, and altitude for two different surface/aerosol systems: terrestrial and oceanic. The matrix inversion method can only calculate actinic fluxes; therefore, this is the main focus of this paper. Investigations into the comparative accuracy of the four techniques for the oceanic model with and without a cloud layer include…
Flux expressions and NEMD perturbations for models of semi-flexible molecules
2001
We derive energy and momentum flux expressions, for systems composed of a general class of semi-flexible molecules, in the Ciccotti-Ferrario-Ryckaert linear constraint formalism. According to this formalism, the whole set of Cartesian coordinates is divided into basic (independent) and secondary (dependent) subsets. It is found that energy and momentum flux vectors have a simple and general expression using both basic and secondary coordinates. In the case of non-equilibrium molecular dynamics, we give general and simple heat and shear flow algorithms, deriving the dissipative fluxes in the space of all Cartesian coordinates. In comparison with previous derivations for some models of flexib…
Influence ofsp−dhybridization on the electronic structure of Al-Mn alloys
2008
The influence of $sp\text{\ensuremath{-}}d$ hybridization on the electronic structure of different Al-Mn alloys has been studied by photoelectron spectroscopy. Experimental evidence of a pseudogap in a crystalline binary Hume-Rothery alloy is provided. The pseudogap varies systematically with Mn concentration. The $sp\text{\ensuremath{-}}d$ hybridization alone, even in the absence of Hume-Rothery mechanism, can produce the pseudogap. Existence of the pseudogap, suppression of the $\mathrm{Mn}\phantom{\rule{0.2em}{0ex}}2p$ satellite, and decrease in the Doniach-\ifmmode \check{S}\else \v{S}\fi{}unji\ifmmode \acute{c}\else \'{c}\fi{} asymmetry parameter are the consequences of the $sp\text{\e…
Role of B diffusion in the interfacial Dzyaloshinskii-Moriya interaction inTa/Co20Fe60B20/MgOnanowires
2015
We report on current-induced domain wall motion in $\mathrm{Ta}/\mathrm{C}{\mathrm{o}}_{20}\mathrm{F}{\mathrm{e}}_{60}{\mathrm{B}}_{20}/\mathrm{MgO}$ nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient $D=+0.06\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta bu…
The Scherk-Schwarz mechanism as a flux compactification with internal torsion
2005
The aim of this paper is to make progress in the understanding of the Scherk-Schwarz dimensional reduction in terms of a compactification in the presence of background fluxes and torsion. From the eleven dimensional supergravity point of view, we find that a general E6(6) S-S phase may be obtained by turning on an appropriate background torsion, together with suitable fluxes, some of which can be directly identified with certain components of the four-form field-strength. Furthermore, we introduce a novel (four dimensional) approach to the study of dualities between flux/torsion compactifications of Type II/M-theory. This approach defines the action that duality should have on the backgroun…
Radiation defects and transition ions interaction in magnesium oxide
2007
Abstract The absorption spectra of nickel and manganese doped and pure MgO single crystals were investigated before and after fast neutron irradiation and after annealing. It is shown that the fast neutron irradiation leads to the formation of two types complex center: “Me 2+ –F + (or F) center” and “Me 3+ –V Mg ”. From the behavior of the ∼570 and ∼357 nm absorption bands during annealing the activation energies of the corresponding defects are determined. The obtained activation energy values ( E a
Backings and targets for chemical and nuclear studies of transactinides with TASCA
2008
Abstract At GSI the gas-filled separator TASCA (TransActinide Separator and Chemistry Apparatus) was set up to investigate the chemical and physical properties of the heaviest elements making use of the highest beam intensities available [ www.gsi.de/tasca ; M. Schadel, D. Ackermann, A. Semchenkov, A. Turler, GSI Scientific Report 2005, GSI Report 2006-1, p. 262]. Appropriate backings and targets have to be developed. Conceivable backing materials are aluminium, titanium, and carbon. Aluminium backings and titanium backings in different thickness and from different companies are produced by cold rolling. Deposition by resistance heating is applied for carbon backings. For experiments in a c…