High-aspect-ratio nanoporous membranes made by reactive ion etching and e-beam and interference lithography

Nanoporous membranes engineered to mimic natural filtration systems can be used in “smart” implantable drug delivery systems, hemodialysis membranes, bio-artificial organs, and other novel nano-enabled medical devices. Conventional membranes exhibit several limitations, including broad pore size distributions and low pore densities. To overcome these problems, lithographic approaches were used to develop porous silicon, silicon nitride, ultrananocrystalline diamond (UNCD), and polymer film membranes. Here we report processing of high porosity, high-aspect-ratio membranes by two techniques: UNCD fabricated by reactive ion etching after e-beam lithography and epoxy fabricated by interference lithography.     

Identification of the cleavage site involved in production of plasma soluble Fc gamma receptor type III (CD16)

CD16 (FcgammaR type III) is a low-affinity IgG Fc receptor (R) that exists in two isoforms, a transmembrane FcgammaRIIIa expressed by NK cells and monocytes, and a phosphatidylinositol-linked FcgammaRIIIb expressed by neutrophils. A soluble form of CD16 (sCD16) circulates in plasma. The cleavage site and the nature of the enzyme(s) involved in production of sCD16 were investigated. Soluble CD16 was purified to apparent homogeneity from human serum by eight steps, including anion exchange and immunoaffinity chromatography. Serum sCD16 was sequenced at both ends, as well as a recombinant form of sCD16 used as control. N-terminal sequencing demonstrated that serum sCD16 originates from neutrophil FcgammaRIIIb and C-terminal sequencing suggested that the cleavage site is between Val 196 and Ser 197, close to the membrane anchor. Addition of a hydroxamate-based inhibitor of Zn2+ metalloproteinases (RU36156) led to a dramatic decrease of sCD16 production by phorbol 12-myristate 13-acetate-activated neutrophils, whereas inhibitors of serine proteinases had no significant effect, showing the metalloproteinase dependence of this cleavage process.     

A hierarchical knowledge based system for airplane classification

Airplane classification is used as an application domain to illustrate how hierarchical reasoning on large knowledge bases can be implemented. The knowledge base is organized as a two-dimensional hierarchy: one dimension corresponds to the levels of complexity often seen in computer vision, and the other dimension corresponds to the complexity of hypothesis used in the reasoning process. Reasoning proceeds top-down, from more abstract levels with fewer details toward levels with more details. Whenever possible, with the help of domain knowledge, decision is taken at a higher level, which significantly reduces processing time. A software package called RuBICS (Rule-Based Image Classification System) is described, and some examples of airplane classification are shown     

Combined atomistic and mesoscale simulation of grain growth in nanocrystalline thin films

We have combined molecular-dynamics (MD) simulations with mesoscale simulations to elucidate the mechanism and kinetics of grain growth in nanocrystalline palladium with a columnar grain structure. The conventional picture of grain growth assumes that the process is governed by curvature-driven grain-boundary (GB) migration. Our MD simulations demonstrate that, at least in a nanocrystalline material, grain growth can also be triggered by the coordinated rotations of neighboring grains so as to eliminate the common GB between them. Such rotation–coalescence events result in the formation of highly elongated, unstable grains which then grow via the GB migration mechanism. These insights can be incorporated into mesoscale simulations in which, instead of the atoms, the objects that evolve in space and time are discretized GBs, grain junctions and the grain orientations, with a time scale controlled by that associated with grain rotation and GB migration and with a length scale given by the grain size. These mesoscale simulations, with physical insight and input materials parameters obtained by MD simulation, enable the investigation of the topology and long-time grain-growth behavior in a physically more realistic manner than via mesoscale simulations alone.     

Optimum system availability and spare allocation

This paper presents a method for optimizing the number of spare units in order to maximize the steady-state availability of a repairable system with cold standbys and non-zero replacement time under constraints of “costs”. The problem is formulated as a non-linear integer programming problem and a new algorithm named Multiple Gradient is used for the constrained optimization. The practical calculation is carried out on a computer, the results being presented in a form of a list of necessary spare units. At the same time, information is received concerning the steady-state availability of the system and the “costs” of the maintenance philosophy.     

Environmental risk of particulate and soluble platinum group elements released from gasoline and diesel engine catalytic converters

A comparison of platinum-group element (PGE) emission between gasoline and diesel engine catalytic converters is reported within this work. Whole raw exhaust fumes from four catalysts of three different types were examined during their useful lifetime, from fresh to 80,000 km. Two were gasoline engine catalysts (Pt-Pd-Rh and Pd-Rh), while the other two were diesel engine catalysts (Pt). Samples were collected following the 91441 EUDC driving cycle for light-duty vehicle testing, and the sample collection device used allowed differentiation between the particulate and soluble fractions, the latter being the most relevant from an environmental point of view. Analyses were performed by inductively coupled plasma-mass spectrometry (ICP-MS) (quadrupole and high resolution), and special attention was paid to the control of spectral interference, especially in the case of Pd and Rh. The results obtained show that, for fresh catalysts, the release of particulate PGE through car exhaust fumes does not follow any particular trend, with a wide range (one-two orders of magnitude) for the content of noble metals emitted. The samples collected from 30,000-80,000 km present a more homogeneous PGE release for all catalysts studied. A decrease of approximately one order of magnitude is observed with respect to the release from fresh catalysts, except in the case of the diesel engine catalyst, for which PGE emission continued to be higher than in the case of gasoline engines. The fraction of soluble PGE was found to represent less than 10% of the total amount released from fresh catalysts. For aged catalysts, the figures are significantly higher, especially for Pd and Rh. Particulate PGE can be considered as virtually biologically inert, while soluble PGE forms can represent an environmental risk due to their bioavailability, which leads them to accumulate in the environment.     

Shedding light onto the nano- and micro-structures of B-containing SiOC glasses using high resolution TEM 3D imaging

The internal structure of nanostructured pyrolyzed SiBOC glasses has been analyzed using a combination of transmission electron microscopy techniques including high resolution imaging, EELS spectroscopy and 3D imaging. For the first time, we provide direct information on the 3D architecture within such complex glasses containing SiC nanograins, silica-rich and carbon nanodomains. Their sizes and relative 3D distribution have been precisely quantified. It was shown that the SiC nanocrystals and the silica-rich domains exhibit different types of connectivities with the graphitic carbon network. A direct evidence of the existence of “covalent” bridges between the edges of graphitic nanoplatelets and the SiC nanocrystals is provided. In addition, it was demonstrated that the silica rich domains are not covalently bonded to the graphitic platelets. As a consequence, this amorphous phase can be dissolved into HF and may generate a bimodal porosity, in strong relationship with the initial nanostructure of the SiBOC glass specimen.     

ZnO/NiO heterostructure-based microsensors used in formaldehyde detection at room temperature: Influence of the sensor operating voltage

Journal of Materials Science: Materials in Electronics - Recently the emissions of volatile organic compounds (VOCs) in the atmosphere have increased dramatically with rapid development of...     

Low-voltage cross-sectional EBIC for characterisation of GaN-based light emitting devices

Electron beam induced current (EBIC) characterisation can provide detailed information on the influence of crystalline defects on the diffusion and recombination of minority carriers in semiconductors. New developments are required for GaN light emitting devices, which need a cross-sectional approach to provide access to their complex multi-layered structures. A sample preparation approach based on low-voltage Ar ion milling is proposed here and shown to produce a flat cross-section with very limited surface recombination, which enables low-voltage high resolution EBIC characterisation. Dark defects are observed in EBIC images and correlation with cathodoluminescence images identify them as threading dislocations. Emphasis is placed on one-dimensional quantification which is used to show that junction delineation with very good spatial resolution can be achieved, revealing significant roughening of this GaN p-n junction. Furthermore, longer minority carrier diffusion lengths along the c-axis are found at dislocation sites, in both p-GaN and the multi-quantum well (MQW) region. This is attributed to gettering of point defects at threading dislocations in p-GaN and higher escape rate from quantum wells at dislocation sites in the MQW region, respectively. These developments show considerable promise for the use of low-voltage cross-sectional EBIC in the characterisation of point and extended defects in GaN-based devices and it is suggested that this technique will be particularly useful for degradation analysis.