Influence of melt feeding scheme and casting parameters during direct-chill casting on microstructure of an AA7050 billet

© The Minerals, Metals & Materials Society and ASM International 2012Direct-chill (DC) casting billets of an AA7050 alloy produced with different melt feeding schemes and casting speeds were examined in order to reveal the effect of these factors on the evolution of microstructure. Experimental results show that grain size is strongly influenced by the casting speed. In addition, the distribution of grain sizes across the billet diameter is mostly determined by melt feeding scheme. Grains tend to coarsen towards the center of a billet cast with the semi-horizontal melt feeding, while upon vertical melt feeding the minimum grain size was observed in the center of the billet. Computer simulations were preformed to reveal sump profiles and flow patterns during casting under different melt feeding schemes and casting speeds. The results show that solidification front and velocity distribution of the melt in the liquid and slurry zones are very different under different melt feeding scheme. The final grain structure and the grain size distribution in a DC casting billet is a result of a combination of fragmentation effects in the slurry zone and the cooling rate in the solidification range

Electroweak Baryogenesis with dimension-6 Higgs interactions

We present the computation of the baryon asymmetry in the SM amplified by dimension-6 Higgs interactions using the WKB approximation. Analyzing the one-loop potential it turns out that the phase transition is strongly first order in a wide range of the parameters. It is ensured not to wash out the net baryon number gained previously even for Higgs masses up to at least 170 GeV. In addition dimension-6 operators induce new sources of CP violation. Novel source terms which enhance the generated baryon asymmetry emerge in the transport equations. This model predicts a baryon to entropy ratio close to the observed value for a large part of the parameter space.Comment: 10 pages, 4 figures, Talk given at the 8th International Moscow School of Physic

Magnetization reversal and magnetic anisotropy in Co network nanostructures

The magnetization reversal and magnetic anisotropy in Co network structures have been studied using magneto-optic Kerr effect (MOKE). An enhancement of the coercivity is observed in the network structures and is attributed to the pinning of domain walls by the hole edges in the vicinity of which the demagnetizing field spatially varies. We find that the magnetization reversal process is dominated by the intrinsic unaxial anisotropy (2K(u)/M(s)approximate to 200 Oe) in spite of the shape anisotropy induced by the hole edges. The influence of the cross-junction on the competition between the intrinsic uniaxial anisotropy and the induced shape anisotropy is discussed using micromagnetic simulations

Fabricating high performance conventional and inverted polymer solar cells by spray coating in air

We report bulk heterojunction organic solar cells utilising the electron-donating polymer PffBT4T-2OD blended with the fullerene acceptor PC71BM, with cells explored based on both conventional and inverted architectures. As charge-transporting layers, we utilise the hole-transporting polymer poly (2, 3-dihydrothieno-1, 4-dioxin)-poly (styrenesulfonate) (PEDOT:PSS) in conventional device architectures, and zinc oxide (ZnO) electron-transport in inverted devices. Critically, all charge-transporting layers and the poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt- (3,3‴-di(2-octyldodecyl) 2,2'; 5',2''; 5″,2‴ -quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD): [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) active layer blend were spray coated in air. We demonstrate champion devices having a power conversion efficiency of 8.13% and 8.43% for conventional and inverted architectures respectively

Pyrene- benzo[1,2,5]thiadiazole based conjugated polymers for application in BHJ solar cells

Ethylhexyloxy-functionalised pyrene (PEH) was prepared and copolymerised with both dithienyl-benzo[c]-[1], [2], [5]thiadiazole and dibithiophenyl-benzo[c]-[1], [2], [5]thiadiazole via a Stille coupling polymerisation method to yield PPEH-DTBT-8 and PPEH-DT2BT-8, respectively. A comparative study was conducted to assess the impact of substituting thiophene for bithiophene repeat units upon the resulting properties of the conjugated polymers. PPEH-DT2BT-8 which has bithiophene spacers between pyrene and benzothiadiazole repeat units, exhibited a narrower optical and electrochemical band gap relative to PPEH-DTBT-8; a consequence of the incorporating bithiophene spacer units which promote intramolecular charge transfer between the electron donating and electron accepting moieties. Both PPEH-DTBT-8 and PPEH-DT2BT-8 showed deep HOMO levels of -5.54 and -5.50 eV, respectively. The polymers possess good thermal stabilities with degradation temperatures in excess of 310 °C. The photovoltaic performance of the two polymers was studied by fabricating bulk heterojunction (BHJ) photovoltaic devices using PC70BM as the acceptor. PPEH-DTBT-8 and PPEH-DT2BT-8 demonstrated efficiencies of 0.33 and 1.83%, respectively. The higher efficiency of PPEH-DT2BT-8 can be attributed to vastly improved FF and Jsc values

High efficiency arrays of polymer solar cells fabricated by spray-coating in air

We present bulk heterojunction organic solar cells fabricated by spray-casting both the PEDOT:PSS hole-transport layer (HTL) and active PBDTTT-EFT:PC71BM layers in air. Devices were fabricated in a (6 × 6) array across a large-area substrate (25 cm2) with each pixel having an active area of 6.45 mm2. We show that the film uniformity and operational homogeneity of the devices are excellent. The champion device with spray cast active layer on spin cast PEDOT:PSS had an power conversion efficiency (PCE) of 8.75%, and the best device with spray cast active layer and PEDOT:PSS had a PCE of 8.06%. The impacts of air and light exposure of the active layer on device performance are investigated and found to be detrimental

Solid-State Nuclear Spin Quantum Computer Based on Magnetic Resonance Force Microscopy

We propose a nuclear spin quantum computer based on magnetic resonance force microscopy (MRFM). It is shown that an MRFM single-electron spin measurement provides three essential requirements for quantum computation in solids: (a) preparation of the ground state, (b) one- and two- qubit quantum logic gates, and (c) a measurement of the final state. The proposed quantum computer can operate at temperatures up to 1K.Comment: 16 pages, 5 figure

Modelling Deformations in Car Crash animation

In this paper, we present a prototype of a deformation engine to efficiently model and render the damaged structure of vehicles in crash scenarios. We introduce a novel system architecture to accelerate the computation, which is traditionally an extremely expensive task. We alter a rigid body simulator to predict trajectories of cars during a collision and formulate a correction procedure to estimate the deformations of the collapsed car structures within the contact area. Non-linear deformations are solved based on the principle of energy conservation. Large plastic deformations resulting from collisions are modelled as a weighted combination of deformation examples of beams which can be produced using classical mechanics