Microstructure and Fracture Toughness of Yttria-Daped Tetragonal Zirconia Polycrystal/Mullite Composites Prepared by an in Situ Method

Yttria-daped tetragonal zirconia polycrystal (Y-TZP)/ mullite composites were prepared by three methods: in situ whisker growth (IS), physical mixing (PM) of zirconia powder and mullite whiskers, and reaction sintering (RS). Microstructures and fracture toughness values were compared. All the composites with 15 vol% of mullite could be densified to more than 95% relative density by firing at 1500° to 1500°C for 10 h. The fracture toughness of the composites as measured by the indentation method showed a clear enhancement compared with that of pure Y-TZP; the ranking was Y-TZP ≦ RS composite < PM composite < IS composite. Enhancement of the fracture toughness in composites was found to relte strongly to the aspect ratio of mullite particles.     

Domain transfer multiple kernel learning

Cross-domain learning methods have shown promising results by leveraging labeled patterns from the auxiliary domain to learn a robust classifier for the target domain which has only a limited number of labeled samples. To cope with the considerable change between feature distributions of different domains, we propose a new cross-domain kernel learning framework into which many existing kernel methods can be readily incorporated. Our framework, referred to as Domain Transfer Multiple Kernel Learning (DTMKL), simultaneously learns a kernel function and a robust classifier by minimizing both the structural risk functional and the distribution mismatch between the labeled and unlabeled samples from the auxiliary and target domains. Under the DTMKL framework, we also propose two novel methods by using SVM and prelearned classifiers, respectively. Comprehensive experiments on three domain adaptation data sets (i.e., TRECVID, 20 Newsgroups, and email spam data sets) demonstrate that DTMKL-based methods outperform existing cross-domain learning and multiple kernel learning methods.     

Nanoindentation and tribology of a (Hf-Ta-Zr-Nb-Ti)C high-entropy carbide

A (Hf-Ta-Zr-Nb-Ti)C high-entropy carbide was prepared by ball milling and a two-step Spark Plasma Sintering process, achieving a single-phase ceramic sample with a high relative density of 99.4 %. The wear resistance of the sample was measured by tribology and micro-scale mechanical behaviour was studied by nanoindentation on both the non-deformed and worn surfaces. Grains and the vicinity of grain boundaries exhibited high hardness values of 38.5 ± 0.5 GPa and 35.5 ± 1.0 GPa with similar Young’s moduli of 562 ± 11 GPa and 547 ± 16 GPa, respectively. The dominant wear mechanism was mechanical wear with limited grain pull-out and fracture, and with a localized and thin tribo-layer formation. The specific wear rate exhibited an increase with the increasing load from 2.53·10^?6 mm³/Nm at 5 N to 9.03·10^?6 mm³/Nm at 50 N. This was correlated to the decrease of nanohardness of the worn surfaces with increasing wear load, which is attributed to the increased number of microcracks.     

A mechanism for the nitridation of silicon powder compacts

A mechanism for the nitridation of silicon powder is proposed, based on an interpretation of the microstructure of partially reacted compacts. It is observed that the reaction does not occur at the solid-state interface between the silicon and the nitride product layer. Both silicon and nitrogen are transported through this layer and the removal of silicon results in the formation of pores in the silicon crystals at the nitride-silicon interface. The nitridation reaction takes place within these pores, which subsequently migrate into the silicon grains, and within the original voidage of the compact.     

Some failures of intermanual and cross-lateral transfer in chronic schizophrenia.

The suggestion that split-brain symptoms are present in schizophrenia was investigated by using tests of intermanual and cross-lateral transfer. Ss were 24 chronic schizophrenics (mean age 52.1 yrs), 6 matched depressive and anxious patients, and 6 normal controls. All Ss were right-handed. Disconnections were seen on a variety of manual and cross-lateral transfer tasks involving position location on the hands, the arms, and the body as well as on tasks of manual tapping transfer. These are interpreted as communication failures of the brain related to callosal disturbance. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Photoresponsive effects in azo polymers

Photoresponsive effects associated with two photochromic polyamides [poly(3,3′-azo dibenzoyl-trans-2,5-dimethylpiperazene) (I) and poly(4,4′-azo dibenzoyl-trans-dimethylpiperazene) (II)] are reported. (i) Langmuir film balance measurements show a reduction in area/monomer unit on changing from dark to light conditions and this is interpreted as being the result of trans→cis isomerization. From detailed consideration of pressure-area curves for I and II, it is postulated that I exists as a helical structure whereas the structure of II is linear. (ii) I and II are also shown to exhibit a photoviscosity effect where the viscosity is reduced upon irradiation. This effect is discussed in terms of the postulated structures. (iii) The polymers also exhibit photomechanical properties. The photocontractile effect observed on switching off the radiation is attributed to incomplete isomerization of a fraction of the azo residues in locations within the polymer matrix.     

Photomechanical effects in polymers containing 6′-nitro-1,3,3-trimethyl-spiro-(2′H-1′-benzopyran-2,2′-indoline)

The photomechanical response of polystyrene and polymethyl methacrylate containing 6′-1,3,3-trimethyl-spiro-(2H-1-benzopyran-2,2′indoline), were investigated. The effects of the concentrations of the photochrome and of the initial stress were studied and the rates of the dark relaxation responses compared with the rates of decolouration of the photochrome.