Thermal formation of corundum from aluminium hydroxides prepared from various aluminium salts

Aluminium hydroxides have been precipitated from various aluminium salts and the differences in their thermal behaviour have been investigated. Pseudoboehmite derived from the nitrate, sulfate and chloride all form γ-Al₂O₃ at ∼ 400°C but the formation of α-A1₂O₃ at 1200°C occurs more readily in the material derived from the sulfate. This contains a higher concentration of anionic impurities related to differences in the solubility of the original aluminium salts. The sulfate is retained in the gel to higher temperatures at which its eventual decomposition may lead to the formation of a reactive pore structure which facilitates the nucleation of α-A1₂O₃.     

Determination of the percentage of homopolymer component in Ziegler/Natta catalyst linear low-density polyethylene resins using high-temperature cell Fourier transform infrared and partial least squares quantitative analysis technique

A new method for the determination of the percentage of homopolymer component, using high-temperature cell Fourier transform infrared (FT-IR) by partial least squares (PLS) quantitative analysis technique, was developed and applied to Ziegler Natta linear low-density polyethylene (LLDPE). The method is based on the IR spectrum changes between the 730 cm(-1) band and 720 cm(-1) band at the temperature of 110 degrees C, which is near the melting point of the polyethylene. The HD % (the percentage of high-density component, i.e., the percentage of homopolymer component) results obtained by CTREF (CRYSTAF in TREF mode) technique are used as the input data together with the respective FT-IR spectra for PLS analyses to establish a calibration curve. The PLS quality is characterized by a correlation coefficient of 0.997 (cross-validation) using four factors and a root mean square error of calibration (RMSEC) of 0.772. The HD% of the unknown can then be predicted by the PLS software from the unknown FT-IR spectrum. A control resin was tested seven times by CTREF and FT-IR. The HD% of the control resin was 28.59+/-0.88% by CTREF and 29.05+/-2.37% by FT-IR. It was found that the method was applicable for the same comonomer type of LLDPE within a melt index range and density.     

Chest radiography: a comparison of image quality and effective dose using four digital systems

Image quality (IQ) and effective dose for chest radiography was compared for four digital imaging systems that used three different detector technologies: a-Si/TFT flat-panel detector (FPD), scanning-slot/charge-coupled device (CCD) and photostimuable phosphor (PSP). On each system a phantom was exposed at 125 kV(p) for automatic exposure control (AEC) and 2, 4 and 8 Gy receptor dose using identical geometrical conditions. All images were scored as softcopy images by three observers. The effective dose was calculated for each exposure condition. For AEC, superior IQ was observed for the GE FPD compared with all the other systems, which showed similar IQ performance. For all systems the entrance surface dose associated with AEC was within the European recommendations but variations in the effective dose were observed between the four systems. For identical receptor dose levels superior IQ was observed with the FPDs. Thorascan was noted for its low effective dose and Agfa CR was associated with the highest effective dose. FPD systems showed a better overall performance, followed by the CCD and PSP systems.     

A framework for evaluating business lead users’ virtual reality innovations in Second Life

This paper extends von Hippel’s (Manag. Sci. 32(7):791–805, 1986) concept of lead users to a virtual reality environment. Three lead user groups, site developers, business firms and avatars, have a synergistic role to play in extending virtual reality from a social networking platform to a commercial one. The paper proposes a framework for assessing the extent to which innovative practices have been demonstrated by lead user business firms in a virtual setting. It applies the framework to twenty pioneering firms that operated within Second Life in 2007, from an avatar’s perspective. The study’s findings indicate that business firms made little use of digital agents, and provided few examples of bricolage. However, they exhibited higher levels of innovation in their use of telepresence and interactivity, which contributed to the achievement of flow. As a single-avatar study, the paper has limited generalizability, however studies with a wider scope will enable further development of this framework.     

Stampede: a cluster programming middleware for interactive stream-oriented applications

Emerging application domains such as interactive vision, animation, and multimedia collaboration display dynamic scalable parallelism and high-computational requirements, making them good candidates for executing on parallel architectures such as SMPs and clusters of SMPs. Stampede is a programming system that has many of the needed functionalities such as high-level data sharing, dynamic cluster-wide threads and their synchronization, support for task and data parallelism, handling of time-sequenced data items, and automatic buffer management. We present an overview of Stampede, the primary data abstractions, the algorithmic basis of garbage collection, and the issues in implementing these abstractions on a cluster of SMPs. We also present a set of micromeasurements along with two multimedia applications implemented on top of Stampede, through which we demonstrate the low overhead of this runtime and that it is suitable for the streaming multimedia applications.     

A glass-bonded ceramic material from chrysotile (white asbestos)

A process has been developed for bonding chrysotile asbestos into a robust, dimensionally-stable lightweight ceramic material by fusing it with sodium silicate and/or ground waste glass. The chrysotile can retain its desirable properties of fibrous morphology and porosity, but the fibre bundles are stabilized by fusion into a glassy matrix, reducing the respirable fibre concentration. The glass-bonded materials have good resistance to mechanical abrasion, and any resulting dust is found by SEM to be particularly free of fibres. The thermal treatment also converts the chrysotile into crystalline forsterite, which should destroy its cell toxicity. Other methods of glass-bonding chrysotile compacts (hot pressing and impregnating with glaze) were also investigated, and the properties of the resulting materials are reported.     

Hardness and low-temperature deformation of silica glass

Vickers diamond pyramid hardness measurements have been made on silica glass with varying thermal history using loads up to 1000 g. Hardness was independent of load and source. From interference photographs and subsequent anneal of the indentations at temperatures belowT _g, it was concluded that indentation leads primarily to densification of a volume of glass in the vicinity of the indenter. A portion of the densification which is recoverable at relatively low temperatures is attributed to molecular entanglement of the glassy network due to high pressure and shear. The other portion which is not recoverable belowT _g represents an approach to the final equilibrium density of the glass. Hardness of silica glass as determined by this method is thus defined as a resistance of the material to densification.This paper is based on part of a thesis submitted by J. E. Neely in partial fulfilment of the requirements for the degree of Master of Science in Materials Engineering, Rensselaer Polytechnic Institute, August 1967.     

Evanescent wave cavity ring-down spectroscopy in a thin-layer electrochemical cell

The application of evanescent wave cavity ring-down spectroscopy (EW-CRDS) in monitoring electrogenerated species within a thin-layer electrochemical cell is demonstrated. In the proof-of-concept experiments described, ferricyanide, Fe(CN)6(3-), was produced by the transport-limited oxidation of ferrocyanide, Fe(CN)6(4-), in a thin-layer solution cell (25-250 microm) formed between an electrode and the hypotenuse of a fused-silica prism. The prism constituted one element of a high-finesse optical cavity arranged in a triangular ring geometry with light being totally internally reflected at the silica/solution interface. The cavity was pumped with the output (approximately 417 nm) of a single-mode external cavity diode laser, which was continuously scanned across the cavity modes. The presence of electrogenerated ferricyanide within the resulting evanescent field, beyond the optical interface, was detected by the enhanced loss of light trapped within the cavity, as measured by the characteristic cavity ring down. In this way, the EW-CRDS technique is sensitive to absorption in only the first few hundred nanometers of solution above the silica surface. The cavity ring-down response accompanying both cyclic voltammetric and step potential chronoamperometry experiments at a variety of electrode-surface distances is presented, and the results are shown to be well reproduced in modeling by finite element methods. The studies herein thus provide a foundation for further applications of EW-CRDS combined with electrochemistry.     

Low bias dry etching of III-nitrides in Cl2-based inductively coupled plasmas

Cl₂-based inductively coupled plasmas (ICP) with low additional dc self-biases (?100V) produce convenient etch rates (500–1500Å·min^?1) for III-nitride electronic device structures. A systematic study of the effects of additive gas (Ar, N₂, H₂), discharge composition, process pressure, and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent Cl₂ in the discharge for all three mixtures, and to have an increase (decrease) in etch rate with source power (pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately six for InN over the other nitrides were obtained.