A model for co-clusters and their strengthening in Al-Cu-Mg based alloys: a comparison with experimental data

A model for the thermodynamics of and strengthening due to Cu–Mg co-clusters in Al–Cu–Mg based alloys is analysed and tested. The formulation uses a single interaction enthalpy between dissimilar alloying elements (e.g. Cu and Mg atoms in an Al–Cu–Mg based alloy) combined with the configurational entropy. The metastable solvus in Al–Cu–Mg based alloys is calculated. Recently published small angle X-ray scattering experiments, 3 dimensional atom probe and yield strength data on these type of alloys support the model. The small angle X-ray scattering and hardness experiments, as well as calorimetry experiments, are sensitive to the main free energy (or enthalpy) changes, which are dominated by Cu–Mg bonds formed by the dimers and the local electron densities related to these bonds. 3 dimensional atom probe is less sensitive to dimers, and will detect agglomeration of dimers to form larger clusters

The influence of indenter tip rounding on the indentation size effect

A model was developed to interpret the indentation size effect. The model considers the tip wear effect, causing a rounded tip, the plastic zone size and various strengthening contributions, including geometrically necessary dislocations, preexisting statistically stored dislocations and grain size. It is shown that the shape of the worn tip can be effectively determined through calibration experiments. The model is applied to predict dislocation densities, and shows a good correspondence with published data on dislocation densities in copper single crystals. Predicted ISE is shown to be in good correspondence with published data on a range of metals, and an improvement over existing models is demonstrated

Microembossing of ultrafine grained Al: microstructural analysis and finite element modelling

Ultra fine grained (UFG) Al-1050 processed by equal channel angular pressing (ECAP) and UFG Al-Mg-Cu-Mn processed by high pressure torsion (HPT) were embossed at both room temperature and 300 °C, with the aim of producing micro-channels. The behaviour of Al alloys during the embossing process was analysed using finite element (FE) modelling. The cold embossing of both Al alloys is characterised by a partial pattern transfer, a large embossing force, channels with oblique sidewalls and a large failure rate of the mould. The hot embossing is characterised by straight channel sidewalls, fully transferred patterns and reduced loads which decrease the failure rate of the mould. Hot embossing of UFG Al-Mg-Cu-Mn produced by HPT shows a potential of fabrication of microelectromechanical system (MEMS) components with micro channels

Al-Mg-Cu based alloys and pure Al processed by high pressure torsion: the influence of alloying additions on strengthening

The influence of alloying additions on strengthening on high pressure torsion (HPT) processed alloys was investigated using commercially pure Al (Al-1050 alloy) and five Al-(1-3)Mg-(0-4)Cu alloys (in wt%). Microhardness was measured on cross sections. For Al-1050 the microhardness reaches a peak at an effective strain of about 3 and subsequently decreases. The microhardness of Al-Mg-Cu alloys increases strongly and continuously with increasing equivalent strain. This workhardening rate is enhanced by increasing Mg content over the entire range of strain. Furthermore, the workhardening rates were higher in Cu-free and low Cu-containing (? 0.4%) Al-Mg alloys as compared to high Cu-containing Al-Mg alloy at strains less than 3. A model is presented that describes the experimental results well. The strengthening model indicates that dislocation-solute and dislocation-cluster interactions play an important role

Acremonium phylogenetic overview and revision of Gliomastix, Sarocladium, and Trichothecium

AbstractOver 200 new sequences are generated for members of the genus Acremonium and related taxa including ribosomal small subunit sequences (SSU) for phylogenetic analysis and large subunit (LSU) sequences for phylogeny and DNA-based identification. Phylogenetic analysis reveals that within the Hypocreales, there are two major clusters containing multiple Acremonium species. One clade contains Acremonium sclerotigenum, the genus Emericellopsis, and the genus Geosmithia as prominent elements. The second clade contains the genera Gliomastix sensu stricto and Bionectria. In addition, there are numerous smaller clades plus two multi-species clades, one containing Acremonium strictum and the type species of the genus Sarocladium, and, as seen in the combined SSU/LSU analysis, one associated subclade containing Acremonium breve and related species plus Acremonium curvulum and related species. This sequence information allows the revision of three genera. Gliomastix is revived for five species, G. murorum, G. polychroma, G. tumulicola, G. roseogrisea, and G. masseei. Sarocladium is extended to include all members of the phylogenetically distinct A. strictum clade including the medically important A. kiliense and the protective maize endophyte A. zeae. Also included in Sarocladium are members of the phylogenetically delimited Acremonium bacillisporum clade, closely linked to the A. strictum clade. The genus Trichothecium is revised following the principles of unitary nomenclature based on the oldest valid anamorph or teleomorph name, and new combinations are made in Trichothecium for the tightly interrelated Acremonium crotocinigenum, Spicellum roseum, and teleomorph Leucosphaerina indica. Outside the Hypocreales, numerous Acremonium-like species fall into the Plectosphaerellaceae, and A. atrogriseum falls into the Cephalothecaceae

Proton recoil polarization in exclusive (e,e'pp) reactions

The general formalism of nucleon recoil polarization in the (${\vec e},e'{\vec N}N$) reaction is given. Numerical predictions are presented for the components of the outgoing proton polarization and of the polarization transfer coefficient in the specific case of the exclusive $^{16}$O(${\vec e},e'{\vec p}p$)$^{14}$C knockout reaction leading to discrete states in the residual nucleus. Reaction calculations are performed in a direct knockout framework where final-state interactions and one-body and two-body currents are included. The two-nucleon overlap integrals are obtained from a calculation of the two-proton spectral function of $^{16}$O where long-range and short-range correlations are consistently included. The comparison of results obtained in different kinematics confirms that resolution of different final states in the $^{16}$O(${\vec e},e'{\vec p}p$)$^{14}$C reaction may act as a filter to disentangle and separately investigate the reaction processes due to short-range correlations and two-body currents and indicates that measurements of the components of the outgoing proton polarization may offer good opportunities to study short-range correlations.Comment: 12 pages, 6 figure

Morphology control via dual solvent crystallization for high-mobility functionalized pentacene-blend thin film transistors

We present an approach to improving the performance of solution processed organic semiconductor transistors based on a dual solvent system. We here apply this to a blend containing the ?-conjugated small molecule 6,13 bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) and polystyrene, which acts as an inert binder. Using a semiconductor-binder solution of two solvents, where the main solvent is a better solvent of the small molecule and second solvent is a better solvent of the polymer, crystal morphologies can be altered and transistor mobilities increased by almost an order of magnitude. In this way, air-ambient and solution-processed transistors with linear and saturation mobilities higher than 1 cm2 V?1 s?1 have been fabricated. We discuss how the solubility properties of the formulation components can be used to identify solvent candidates that promote an efficient self-assembly of the small molecule

Species and ecological diversity within the Cladosporium cladosporioides complex (Davidiellaceae, Capnodiales)

The genus Cladosporium is one of the largest genera of dematiaceous hyphomycetes, and is characterised by a coronate scar structure, conidia in acropetal chains and Davidiella teleomorphs. Based on morphology and DNA phylogeny, the species complexes of C. herbarum and C. sphaerospermum have been resolved, resulting in the elucidation of numerous new taxa. In the present study, more than 200 isolates belonging to the C. cladosporioides complex were examined and phylogenetically analysed on the basis of DNA sequences of the nuclear ribosomal RNA gene operon, including the internal transcribed spacer regions ITS1 and ITS2, the 5.8S nrDNA, as well as partial actin and translation elongation factor 1-α gene sequences. For the saprobic, widely distributed species Cladosporium cladosporioides, both a neotype and epitype are designated in order to specify a well established circumscription and concept of this species. Cladosporium tenuissimum and C. oxysporum, two saprobes abundant in the tropics, are epitypified and shown to be allied to, but distinct from C. cladosporioides. Twenty-two species are newly described on the basis of phylogenetic characters and cryptic morphological differences. The most important phenotypic characters for distinguishing species within the C. cladosporioides complex, which represents a monophyletic subclade within the genus, are shape, width, length, septation and surface ornamentation of conidia and conidiophores; length and branching patterns of conidial chains and hyphal shape, width and arrangement. Many of the treated species, e.g., C. acalyphae, C. angustisporum, C. australiense, C. basiinflatum, C. chalastosporoides, C. colocasiae, C. cucumerinum, C. exasperatum, C. exile, C. flabelliforme, C. gamsianum, and C. globisporum are currently known only from specific hosts, or have a restricted geographical distribution. A key to all species recognised within the C. cladosporioides complex is provided