Active slip systems and their contribution to deformation phenomena by indentation of the cube face of face-centered cubic metals

New models are proposed for the distributions of active slip systems induced by a cone and a ball indentation on the (001) plane of f.c.c. metals. By employing modified elastic stress fields, three or four primary slip systems are predicted to be individually active in the octant bounded by the [110] and [010] axes.The observed slip traces, surface topography and the shape of dislocation clustering zones are shown to be in reasonable agreement with those expected by the activation of the predicted slip systems. It is also shown that the anisotropy of the extent of this plastic region can be related to that of the elastic stress field.     

THERMOELECTRIC CHARACTERISTICS OF MICROSCALE THIN-FILM THERMOCOUPLES

Microscale thin-film thermocouples (TFTCs), which can be fabricated using existing microelectronics technology on the surfaces of electronic de vices with film thicknesses as small as tens of angstroms, ha ve smaller thermoelectric potential compared to thick-film cases. The qualititati ve characteristics of TFTCs, which ha ve not yet been modeled successfully, ha ve been analyzed based on the model of distributed electric potential across the interface of two metals. The steady-state solution of the electron distribution and the electric potential distribution by solving the one-dimensional Schrodinger equation and the Poisson equation simultaneously show the decrease in the thermoeleectric potential quantitatively.     

Liquid flow circulating within an unbaffled vessel agitated with an unsteady forward–reverse rotating impeller

Liquid‐phase mixing is a common operation, often performed in vessels using mechanically rotating impellers. To enhance axial mixing the vessels are generally equipped with baffles; however, in industries where cleaning the vessel interior is a major concern, i.e. food and pharmaceuticals, and crystallization, where baffles can disturb particle growth, unbaffled vessels are preferred. One method of agitation in unbaffled vessels is an impeller that periodically changes either the direction or rate of rotation: so‐called unsteady rotation. For use in an enhanced agitation vessel, an agitation technology using an unsteady forward–reverse rotating impeller in an unbaffled vessel was investigated. Such unsteady agitation is expected to enhance mixing. However, knowledge of the liquid flows in such an apparatus remains elusive. Thus an aim of this work was to characterize the circulation flow in such a system. Circulation by a disk turbine impeller with six flat blades was studied through examination of tracer particle trajectories. Images showing flow patterns with the forward–reverse rotating impeller resembled those obtained with a unidirectionally rotating impeller in a baffled vessel. The pattern was characterized by a circulation loop whose pathway exits from the impeller rotational region and returns to that region past the wall and bottom of the vessel. Time‐series particle tracking velocimetry (PTV) images obtained during one forward–reverse rotation of the impeller showed that the flow near the vessel wall reduced the periodic fluctuation downstream and that a flow that was almost independent of time was induced near the vessel bottom. For the flow from the bottom to the impeller, unsteadiness was provided by proximity to the impeller. Based on the intensity distribution of the unsteady flow produced by this type of forward–reverse rotating impeller within the vessel, the unsteady flow was shown to have the potential to reach the region near the vessel wall. Copyright © 2010 Society of Chemical Industry     

Preparation of novel soluble poly(ester imide)s containing a trimellitimide moiety and their use as modifiers for aromatic diamine‐cured epoxy resin

Poly(ester imide)s, prepared by the reaction of phthalic anhydride, N‐(4‐carboxyphenyl) trimellitimide and 1,2‐ethanediol, were used to improve the toughness of bisphenol‐A diglycidyl ether epoxy resin cured with 4,4′‐diaminodiphenyl sulfone (DDS). The poly(ester imide)s include poly(ethylene phthalate‐co‐ethylene N‐(1,4‐phenylene) trimellitimide dicarboxylate)s (PESIs) having 10, 20 and 30 mol% trimellitimide (TI) units, respectively. PESIs having 10 and 20 mol% TI units were effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt% of PESI (20 mol% TI unit, M _W 19300 g mol^?1) led to a 55% increase in the fracture toughness (K_IC) of the cured resin (with an increase in flexural strength and modulus) and the modified resin had a particulate morphology. PESI having 30 mol% TI units was not effective because of degradation of the modifier by DDS. The toughening mechanism is discussed in terms of morphological and dynamic viscoelastic behaviour of the modified epoxy resin system. © 2001 Society of Chemical Industry     

Synthesis and characterization of ABA‐type triblock copolymers derived from polyimide and poly(2‐methyl‐2‐adamantyl methacrylate)

ABA‐type triblock copolymers derived from 4,4‐(hexafluoroisopropylidene)diphthalic anhydride‐2,3,5,6‐tetramethyl‐1,4‐phenylenediamine and 2‐methyl‐2‐adamantyl methacrylate (2‐MAdMA) were synthesized via atom transfer radical polymerization. The component ratios of polyimide (PI) and poly(2‐MAdMA) (PMAdMA) were about 8/2, 6/4 and 3/7, as determined using ¹H NMR spectroscopy and thermogravimetric analysis (TGA). The film structure of the triblock copolymers was dependent on the PI structure. Hydrophobicity increased as the component ratio of PMAdMA increased. Based on TGA, three‐step decomposition behaviors of all triblock copolymers derived from PI and PMAdMA in nitrogen and air atmosphere were observed. The gas permeability of the triblock copolymers was lower than that of PI. This finding can be attributed to the decrease in fractional free volume by the adamantane component and the decrease in permeability of the triblock copolymers compared with PI. The dielectric constant of the triblock copolymers was lower than that of PI. The dielectric constant was dependent on molar volume and molar porlarizability, and the dielectric constant derived from the symmetric structure of adamantane was reduced. The ABA‐type triblock copolymers derived from PI and PMAdMA can be considered as new polymer materials with high hydrophobicity, high H₂/CO₂ selectivity and low dielectric constant. © 2013 Society of Chemical Industry     

Effect of Re and Mo addition upon liquid phase methanol reforming with water over SiO2, ZrO2 and TiO2 supported Ir catalysts

Two different enhancement manners of Re and Mo additives have been studied in liquid phase methanol reforming with water over SiO₂, ZrO₂ and TiO₂ supported Ir catalysts. In the cases of Ir–Re/SiO₂ and Ir–Re/ZrO₂, hydrogen formation rate was accelerated remarkably by the formation of some nanocomposites between Ir and Re. On the other hand, in the case of Ir–Mo/TiO₂, the formation of thin monolayer-like structure of MoO₂ on TiO₂ surface was important for the acceleration of hydration process of partially dehydrogenated methanol with adsorbed water which was activated over thin MoO₂ overlayer.     

Identification of the odour-active cyclic diketone cis-2,6-dimethyl-1,4-cyclohexanedione in roasted Arabica coffee brew

We investigated odour-active trace compounds in roasted Brazilian Arabica coffee. Aroma dilution extract analysis (AEDA) applied to the volatile oil extracted from roasted coffee brew revealed 34 odour-active compounds. Among these, a pungent-smelling unknown odour-active compound was determined. The volatile oil was fractioned by silica gel column chromatography. Gas chromatography–olfactometry (GC–O) and multidimensional gas chromatography–mass spectrometry (MDGC–MS) of the fraction which contained a significant amount of the target unknown compound revealed the cyclic 1,4-diketone, cis-2,6-dimethyl-1,4-cyclohexanedione, which had a pungent odour, and was thus first identified in roasted coffee. Model experiments revealed that cis-2,6-dimethyl-1,4-cyclohexanedione was formed via thermal degradation of sugars, especially monosaccharides, under alkaline conditions. Further, we demonstrated that 2-hydroxy-3-pentanone and 1-hydroxy-2-propanone, thermal degradation products of monosaccharides, were closely related to the formation of cis-2,6-dimethyl-1,4-cyclohexanedione.