Effect of Si additions and heat treatment on the mechanical behaviour of an Al-5Mg casting alloy

Adding 1%Si to binary Al-5Mg alloy slightly increases the yield stress in comparison with the Si free alloy but dramatically reduces the ductility and tensile strength due to the formation of brittle eutectic Mg2Si and pi-Al8FeMg3Si6 particles. Adding 3%Si slightly reduces the yield stress, presumably due to some of the Mg being tied up in the Mg2Si, and further reduces the ductility due to the increased volume fraction of intermetallics. Solution heat treatment at 436degreesC decreases the yield stress of both Si containing alloys, and slightly increases the ductility in the alloy with 3%Si. Subsequent ageing at 180degreesC has no further effects on the strength or ductility. The loss in strength of the heat treated alloys seems to be due to overageing Of Mg2Si precipitates dispersed in the bulk of the alloy. (C) 2004 W. S. Maney Son Ltd.

Effects of combined additions of Sr and AlTiB grain refiners in hypoeutectic Al-Si foundry alloys

Strontium is the most widely used and a very effective element for modifying the morphology of eutectic silicon, while Ti and B are commonly present in the commercial grain refiners used for Al-Si alloys. Systematic studies on the effects of combined additions of Sr and different AlTiB grain refiners on the Al + Si eutectic and primary aluminium solidification have been performed. While slight coarsening of both eutectic Si and primary aluminium grains occurs during holding, no obvious interactions are observed between Sr and AlTiB grain refiners when the addition level of grain refiners is low. As a result, a well-modified and grain refined structure was obtained. However, strong negative interactions between Sr and Al1.5Ti1.5B3 were observed as the addition level of the grain refiner increases. It was found that these interactions have a much more profound impact on the eutectic solidification than the primary Al solidification. The melt treated with combined additions of Sr and Al1.5Ti1.5B still shows good grain refinement efficiency even after losing its modification completely. The mechanism responsible for such negative interactions is further discussed. (c) 2006 Elsevier B.V. All rights reserved.

As-cast morphology of iron-intermetallics in Al-Si foundry alloys

The as-cast three-dimensional morphologies of alpha-Al-15(Fe,Mn)(3)Si-2 and beta-Al5FeSi intermetallics were investigated by serial sectioning. Large beta-Al5FeSi intermetallics were observed to grow around pre-existing dendrite arms. The alpha-Al-15(Fe,Mn)(3)Si-2 intermetallic particle was observed to have a central polyhedral particle and an external highly convoluted three-dimensional structure. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Greenberger-Horne-Zeilinger-type and W-type entangled coherent states: Generation and Bell-type inequality tests without photon counting

We study Greenberger-Horne-Zeilinger-type (GHZ-type) and W-type three-mode entangled coherent states. Both types of entangled coherent states violate Mermin's version of the Bell inequality with threshold photon detection (i.e., without photon counting). Such an experiment can be performed using linear optics elements and threshold detectors with significant Bell violations for GHZ-type entangled coherent states. However, to demonstrate Bell-type inequality violations for W-type entangled coherent states, additional nonlinear interactions are needed. We also propose an optical scheme to generate W-type entangled coherent states in free-traveling optical fields. The required resources for the generation are a single-photon source, a coherent state source, beam splitters, phase shifters, photodetectors, and Kerr nonlinearities. Our scheme does not necessarily require strong Kerr nonlinear interactions; i.e., weak nonlinearities can be used for the generation of the W-type entangled coherent states. Furthermore, it is also robust against inefficiencies of the single-photon source and the photon detectors.

Volumetric and areal bone mineral density measures are associated with cardiovascular disease in older men and women: The health, aging, and body composition study

The associations of volumetric (vBMD) and areal (aBMD) bone mineral density measures with prevalent cardiovascular disease (CVD) and subclinical peripheral arterial disease (PAD) were investigated in a cohort of older men and women enrolled in the Health, Aging, and Body Composition Study. Participants were 3,075 well-functioning white and black men and women (42% black, 51% women), aged 68-80 years. Total hip, femoral neck, and trochanter aBMD were measured using dual-energy X-ray absorptiometry. Quantitative computed tomography was used to evaluate spine trabecular, integral, and cortical vBMD measures in a subgroup (n = 1,489). Logistic regression was performed to examine associations of BMD measures with CVD and PAD. The prevalence of CVD (defined by coronary heart disease, PAD, cerebrovascular disease, or congestive heart failure) was 29.8%. Among participants without CVD, 10% had subclinical PAD (defined as ankle-arm index < 0.9). Spine vBMD measures were inversely associated with CVD in men (odds ratio of integral [ORintegral] = 1.34, 95% confidence interval [CI] 1.10-1.63; ORtrabecular = 1.25, 95% CI 1.02-1.53; ORcortical = 1.36, 95% CI 1.11-1.65). In women, for each standard deviation decrease in integral vBMD, cortical vBMD, or trochanter aBMD, the odds of CVD were significantly increased by 28%, 27%, and 22%, respectively. Total hip aBMD was associated with subclinical PAD in men (OR = 1.39, 95% CI 1.03-1.84) but not in women. All associations were independent of age and shared risk factors between BMD and CVD and were not influenced by inflammatory cytokines (interleukin-6 and tumor necrosis factors-alpha). In conclusion, our results provide further evidence for an inverse association between BMD and CVD in men and women. Future research should investigate common pathophysiological links for osteoporosis and CVD.

A scheme for efficient quantum computation wtih linear optics

Quantum computers promise to increase greatly the efficiency of solving problems such as factoring large integers, combinatorial optimization and quantum physics simulation. One of the greatest challenges now is to implement the basic quantum-computational elements in a physical system and to demonstrate that they can be reliably and scalably controlled. One of the earliest proposals for quantum computation is based on implementing a quantum bit with two optical modes containing one photon. The proposal is appealing because of the ease with which photon interference can be observed. Until now, it suffered from the requirement for non-linear couplings between optical modes containing few photons. Here we show that efficient quantum computation is possible using only beam splitters, phase shifters, single photon sources and photo-detectors. Our methods exploit feedback from photo-detectors and are robust against errors from photon loss and detector inefficiency. The basic elements are accessible to experimental investigation with current technology.

The effects of time delays in adaptive phase measurements

It is not possible to make measurements of the phase of an optical mode using linear optics without introducing an extra phase uncertainty. This extra phase variance is quite large for heterodyne measurements, however it is possible to reduce it to the theoretical limit of log (n) over bar (4 (n) over bar (2)) using adaptive measurements. These measurements are quite sensitive to experimental inaccuracies, especially time delays and inefficient detectors. Here it is shown that the minimum introduced phase variance when there is a time delay of tau is tau/(8 (n) over bar). This result is verified numerically, showing that the phase variance introduced approaches this limit for most of the adaptive schemes using the best final phase estimate. The main exception is the adaptive mark II scheme with simplified feedback, which is extremely sensitive to time delays. The extra phase variance due to time delays is considered for the mark I case with simplified feedback, verifying the tau /2 result obtained by Wiseman and Killip both by a more rigorous analytic technique and numerically.

NMR study of the gamma radiolysis of poly(dimethyl siloxane) under vacuum at 303 K

The structural changes which occur on the gamma -radiolysis of poly(dimethyl siloxane) (PDMS) under vacuum at 303 K have been investigated using Si-29 and C-13 NMR. New structural units consistent with main chain scission and crosslinking through both H-linking and Y-linking reactions have been identified. The results obtained at various absorbed doses have been used to calculate the G-values for scission and crosslinking. G-values for scission of G(S) = 1.3 +/- 0.2, for H-linking of G(D-CH2-R) = 0.34 +/- 0.02 and for Y-Linking of G(Y) = 1.70 +/- 0.09 were obtained for radiolysis under vacuum at 303 K. Thus crosslinking predominates over scission for radiolysis of PDMS under these conditions, and, by contrast with previous studies, Y-links have been shown to be the predominant form of crosslinks. (C) 2001 Elsevier Science Ltd. All rights reserved.

Mechanical alloying of MoSi2 with ternary alloying elements. Part 2 - computer simulation

A computer model of the mechanical alloying process has been developed to simulate phase formation during the mechanical alloying of Mo and Si elemental powders with a ternary addition of Al, Mg, Ti or Zr. Using the Arhennius equation, the model balances the formation rates of the competing reactions that are observed during milling. These reactions include the formation of tetragonal C11(b) MOSi2 (t-MoSi2) by combustion, the formation of the hexagonal C40 MoSi2 polymorph (h-MoSi2), the transformation of the tetragonal to the hexagonal form, and the recovery of t-MoSi2 from h-MoSi2 and deformed t-MoSi2. The addition of the ternary additions changes the free energy of formation of the associated MoSi2 alloys, i.e. Mo(Si, Al)(2), Mo(Mg, Al)(2), (Mo, Ti)Si-2 (Mo, Zr)Si-2 and (Mo, Fe)Si-2, respectively. Variation of the energy of formation alone is sufficient for the simulation to accurately model the observed phase formation. (C) 2003 Elsevier B.V. All rights reserved.

The role of oxides in the formation of primary iron intermetallics in an Al-11.6Si-0.37Mg Alloy

Recent research suggest that the iron-rich intermetallic phases, such as alpha-FeAl15(Fe,Mn)(3)Si-2 and beta-Fe Al5FeSi, nucleate on oxide films entrained in aluminum casting alloys. This is evidenced by the presence of crack-like defects within these iron-rich intermetallics. In an attempt to verify the role of oxides in nucleating iron-rich intermetallics, experiments have been conducted under conditions where in-situ entrained oxide films and deliberately added oxide particles were present. Iron-rich intermetallics are observed to be associated with the oxides in the final microstructure, and crack-like defects are often observed in the beta-Fe plates. The physical association of the Fe-rich intermetallic phases with these solid oxides, either formed in situ or added, is in accordance with the mechanism suggesting that iron-rich intermetallics nucleate upon the wetted sides of double oxide films.

The effect of grain refinement and silicon content on grain formation in hypoeutectic Al-Si alloys

The effect of increasing the amount of added grain refiner on grain size and morphology has been investigated for a range of hypoeutectic Al-Si alloys. The results show a transition in grain size at a silicon concentration of about 3 wt% in unrefined alloys; the grain size decreasing with silicon content before the transition, and increasing beyond the transition point. A change in morphology also occurs with increased silicon content. The addition of grain refiner leads to greater refinement for silicon contents below the transition point than for those contents above the transition point, while the transition point seems to remain unchanged. The slope of the grain size versus silicon content curve after the transition seems to be unaffected by the degree of grain refinement. The results are related to the competitive processes of nucleation and constitutional effects during growth and their impact on nucleation kinetics. (C) 1999 Elsevier Science S.A. All rights reserved.

Influence of Mg content on the microstructure and solid solution chemistry of Al-7%Si-Mg casting alloys during solution treatment

The solution treatment stage of the T6 heat-treatment of Al-7%Si-Mg foundry alloys influences microstructural features such as Mg2Si dissolution, and eutectic silicon spheroidisation and coarsening. Microstructural and microanalytical studies have been conducted across a range of Sr-modified Al-7%Si alloys, with an Fe content of 0.12% and Mg contents ranging from 0.3-0.7wt%. Qualitative and quantitative metallography have shown that, in addition to the above changes, solution treatment also results in changes to the relative proportions of iron-containing intermetallic particles and that these changes are composition-dependent. While solution treatment causes a substantial transformation of pi phase to beta phase in low Mg alloys (0.3-0.4%), this change is not readily apparent at higher Mg levels (0.6-0.7%). The pi to beta transformation is accompanied by a release of Mg into the aluminum matrix over and above that which arises from the rapid dissolution of Mg2Si. Since the level of matrix Mg retained after quenching controls an alloy's subsequent precipitation hardening response, a proper understanding of this phase transformation is crucial if tensile properties are to be maximised.

Experimental study of phase equilibria in the systems Fe-Zn-O and Fe-Zn-Si-O at metallic iron saturation

The reported experimental work on the systems Fe-Zn-O and Fe-Zn-Si-O in equilibrium with metallic iron is part of a wider research program that combines experimental and thermodynamic computer modeling techniques to characterize zinc/lead industrial slags and sinters in the system PbO-ZnO-SiO2-CaO-FeO-Fe2O3. Extensive experimental,investigations using high-temperature equilibration and quenching techniques followed by electron probe X-ray microanalysis (EPMA) were carried out. Special experimental; procedures were developed to enable accurate measurements in these ZnO-containing systems to be performed in equilibrium with metallic iron; The systems Fe-Zn-O and FeZn-Si-O were experimentally investigated in equilibrium with metallic iron in the temperature ranges 900 degreesC to 1200 degreesC (1173 to 1473 K) and from 1000 degreesC to 1350 degreesC (1273 to 1623 K), respectively. The liquidus surface in the system Fe-Zn-Si-O in equilibrium with metallic iron was characterized in the composition ranges 0 to 33 wt pet ZnO and 0 to 40 wt pet SiO2. The wustite (Fe,Zn)O, zincite (Zn,Fe)O, willemite (Zn,Fe)(2)SiO4, arid fayalite: (Fe,Zn)(2)SiO4 solid solutions in equilibrium with metallic iron were measured.