Combining knowledge with many-valued logics

We compare EER and OO data models from the point of view of design quality. Quality is measured in terms of (a) correctness of the conceptual schemas being designed, (b) time to complete the design task, and (c) designers' preferences of the models. Result of an experimental comparison of the two models reveal that the EER model surpasses the OO model for designing unary and ternary relationships, it takes less time to design EER schemas, and the EER model is preferred by designers. We conclude that even if the objective is to implement an OO database schema, the recommended procedure is to: (1) create an EER conceptual scheme, (2) map it to an OO schema, and augment the target schema with behavioral constructs that are unique to the OO approach.     

Improved Fracture Behavior of Alumina Microstructural Composites with Highly Textured Compressive Layers

Alumina‐based microstructural composites combining equiaxed and textured layers were fabricated to examine how cracks propagate and the mechanical properties are affected as a function of the residual stress and volume fraction of texture in a multilayer structure. By combining equiaxed and highly textured alumina layers of varying thermal expansion, the embedded textured layers were placed under compressive residual stresses as high as ?670 MPa. Composites with a near constant maximum failure stress of up to 300 MPa were shown to be almost independent of the initial defect size as result of the compressive residual stress in the textured layers. An apparent fracture toughness of up to 10.1 MPa·m^1/2 was obtained for composites with an equiaxed to textured volume ratio of 7.4:1. The high compressive stress in the textured layers arrested cracks, whereas the weak bonding parallel to the basal surfaces of the textured alumina grains caused cracks to deflect within the textured layers. The coupling of these two mechanisms resulted in crack arrest and a maximum work of fracture of ~1200 J/m² or almost 50 times higher than equiaxed alumina. We believe that embedding textured layers having compressive stresses below the surface of multilayer composites represent an important strategy for designing flaw‐tolerant materials with pronounced crack growth resistance and a high work of fracture.     

Increased sensitivity to the aversive effects of ethanol in PKCε null mice revealed by place conditioning.

Determining the intracellular signaling pathways that mediate the rewarding effects of ethanol may help identify drug targets to curb excessive alcohol consumption. Mice lacking the epsilon isoform of protein kinase C (PKCε) voluntarily consumed less ethanol than wild-type mice in two-bottle choice and operant self-administration assays. Decreased consumption may reflect either increased or decreased sensitivity to the rewarding effects of ethanol. Alternatively, decreased voluntary consumption may reflect a change in sensitivity to the aversive effects of ethanol. The authors used place conditioning to determine that PKCε null mice have an increased sensitivity to the aversive effects of ethanol but a decreased sensitivity to the rewarding effects of ethanol. Together these data suggest that PKCε null mice voluntarily consume less ethanol because they derive less reward and are more sensitive to the aversive effects of ethanol. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Processing and Microstructure Development in Alumina–Silicon Carbide Intragranular Particulate Composites

Al₂O₃–SiC particulate composites were fabricated by hot-pressing mixtures of 5–30 vol% SiC with either α-Al₂O₃, γ-Al₂O₃, or boehmite (γ-AlOOH) to determine whether grain growth or the α-alumina phase transformation could be used to fabricate intragranular particulate composites. Samples starting with α-alumina resulted in primarily intergranular SiC of 0.3 μ and an alumina grain size of 1.5–4.1 μm. Heat treatments resulted in SiC coarsening but no entrapment of SiC by grain boundary breakaway. The α-alumina transformation in the samples starting with γ-alumina resulted in the entrapment of ∼48% of the 5 vol% of SiC added whereas 79% of the SiC was entrapped in the α-alumina grains in samples starting with boehmite. Only SiC particles ≤0.2 SmUm were entrapped in the α-alumina grains during the phase transformation. With increasing SiC content, the relative volume of intragranular SiC decreased, but the amount of intragranular SiC was constant and independent of the amount of SiC added before transformation. The formation of intragranular composites from γ-alumina and boehmite samples was explained with a model that attributes particle entrapment to the vermicular growth of α-alumina into the transition alumina matrix during the α-alumina phase transformation. Seeding the boehmite-based samples did not affect the concentration of entrapped SiC, but did lower the hot-pressing densification temperature by as much as 150°C.     

Preparation of Unsupported Metal Organic and Ceramic Thin Film Specimens for TEM Observation

A method for preparing TEM specimens from fragile metal organic resin and metal-organic-derived ceramic films is described. Unsupported films can be easily prepared by spin coating a metal organic solution onto a camphor substrate followed by separating the film by subliming the substrate. The method involves encapsulating the fragile film fragments in a low-viscosity, thermosetting, epoxy-hardener solution to obtain mechanical integrity. The encapsulated film can be easily hand polished to approximately 20-μm thickness in less than 1 h. Electron-transparent TEM specimens can then be prepared by ion-beam thinning the encapsulated film, after mounting it on a slotted copper grid.     

Synthesis and magnetic characterization of MnAs nanoparticles via nanoparticle conversion

We report on the synthesis of ferromagnetic manganese arsenide (MnAs) nanoparticles via the conversion of primary Mn particles which are generated in an aerosol process in a spark discharge generator. After sintering and size selection in an aerosol setup, the particles are deposited on GaAs(100)B and Si(111) substrates. Subsequent conversion to MnAs particles takes place in an annealing process under a hydrogen atmosphere with an arsine background pressure. The magnetic properties are studied using a SQUID magnetometer. The annealed MnAs particles exhibit hexagonal facets and show anisotropic magnetic behaviour on GaAs(100)B substrates, whereas on Si(111) they remain spherical and show isotropic magnetic behaviour. Scanning transmission electron microscopy studies are used to confirm the conversion from Mn to MnAs.     

Mn- and Mn/Cu-doped PIN-PMN-PT piezoelectric ceramics for high-power transducers

The effects of acceptor doping with manganese as either MnO₂ or MnNb₂O₆ (MnN) with CuO on the dielectric, ferroelectric, and piezoelectric properties of PIN-PMN-PT ceramics were investigated. The 2% MnNb₂O₆-doped PIN-PMN-PT (6Pb(Mn_1/3Nb_2/3)O₃-25Pb(In_1/2Nb_1/2)O₃-34Pb(Mg_1/3Nb_2/3)O₃-35PbTiO₃) ceramics possessed hard properties such as high coercive field (E_C) of 11.7 kV/cm, low dielectric loss (tan δ) of 0.7%, and high electromechanical quality factor (Q_M) of 1011. These properties were diminished in MnO₂-doped ceramics because of lower oxygen vacancy defect concentration, and exaggerated grain growth resulted in >20 µm grain size. Co-doping with 2 mol% MnNb₂O₆ and 0.5 mol% CuO retained hardened properties such as high E_C of 9.6 kV/cm, low tan δ of 0.6%, and high Q_M of 1029. MnNb₂O₆-doped and MnNb₂O₆ + Cu co-doped ceramics display excellent figures of merit for resonance and off-resonance applications as well as high energy conversion efficiencies which make them promising candidates for high-power transducer elements.     

Templated Grain Growth of <001> Textured PMN-28PT Using SrTiO3 Templates

Highly textured PMN-28PT (0.72Pb(Mg_1/3Nb_2/3)O₃–0.28PbTiO₃) ceramics were produced by templated grain growth on <001> oriented platelet-shaped SrTiO₃ template particles with an aspect ratio of 10–15. The templates were aligned in PMN-28PT matrix powder via tape casting and fired in an O₂–PbO atmosphere at 1150°C for up to 15 h. This resulted in textured ceramics with a 40 micrometer grain size and without residual templates. The volume fraction of textured material (  f  ) and the orientation parameter ( r ) were quantified by fitting X-ray diffraction rocking curve data to the March–Dollase equation. Processing conditions were optimized to achieve the best possible values of f and r for the chosen templates and matrix powder. A texture fraction of at least 81 vol% and an orientation parameter of 0.2 were achieved when all random matrix grains were consumed (a perfect textured ceramic would show a texture fraction of 100 vol% and an orientation parameter of 0).     

Conditional ablation of cerebellar astrocytes in postnatal transgenic mice

Astrocytes have been proposed to have multiple roles in the development and maintenance of the vertebrate CNS. To facilitate documentation of these roles, we designed a transgene to enable their ablation at selectable times. The transgene consists of the coding region for the herpes simplex virus-thymidine kinase (HSV-TK) under the control of the human glial fibrillary acidic protein gene promoter. The HSV-TK is innocuous but converts the antiherpetic agent ganciclovir (GCV) to a toxic product that interferes with DNA replication in proliferating cells. In a developmental study, transgenic mice were treated with GCV during the first postnatal week, with evaluation at P19. Treated mice displayed severe ataxia. Histological examination revealed disrupted astrocyte development, particularly in the cerebellum, with marked secondary effects on other cell types. Cerebellar defects included a loss in the numbers of astrocytes and an overall reduction in cerebellar size and disruption of the normally well defined cellular layers. Radial glia were disordered, Purkinje cells were ectopically distributed and displayed abnormal dendritic trees, and granule cells were markedly depleted. These effects were more severe in animals treated on postnatal day 1 versus treatment at day 5. A major factor causing granule cell death was excitotoxicity attributable to activation of NMDA receptors. These results suggest a critical role for astrocytes in cerebellar development.     

Consolidation of Nano-Crystalline Alumina

Dense alpha alumina was fabricated from seeded nano-crystalline boehmites. The intrinsic problem of boehmite solubility and hard agglomerate formation was avoided by dispersing gel agglomerates in ethanol. Homogeneous green microstructure and high sintered density were obtained by dry pressing. The superplasticity of nano-crystalline transition alumina was utilized to obtain fully dense, transparent alpha alumina by sinter forging. The effects of seeding and pressure are correlated with the microstructural evolution and densification of alumina.