Crystallographic electron microscopy

We present a family of techniques for the transmission electron microscope that generate surface zone-axis patterns. These patterns display the variation of the diffracted-beam intensity as a function of the angle of the incident electrons. The conditions of the experiments are those of reflection high-energy electron diffraction at near grazing incidence. The techniques are: surface convergent-beam diffraction, a surface analogue of the Tanaka method and a modified double-rocking scheme. Experimental results are presented for diffraction from surfaces of MgO and MoS₂. We anticipate that surface zone-axis patterns (surface ZAPs) will become established as an important tool for surface characterization, especially when used in conjunction with high-resolution surface imaging and surface energy loss spectroscopy; surface ZAPs may be expected to play, in surface analysis, a role analogous to that played by convergent-beam diffraction in normal transmission electron microscopy.     

Putting it all together – Formal verification of the VAMP

In the verified architecture microprocessor (VAMP) project we have designed, functionally verified, and synthesized a processor with full DLX instruction set, delayed branch, Tomasulo scheduler, maskable nested precise interrupts, pipelined fully IEEE compatible dual precision floating point unit with variable latency, and separate instruction and data caches. The verification has been carried out in the theorem proving system PVS. The processor has been implemented on a Xilinx FPGA. A shorter version of this article with the title “Instantiating uninterpreted functional units and memory system: functional verification of the VAMP” appeared in [8]. The work reported here was done while all the authors were with Saarland University.     

Screening of South African Food Plants for Antioxidant Activity

ABSTRACT: In a screening of South African indigenous food plants for antioxidant activity by testing for inhibition of lipid peroxidation, the "potherbs" Amaranthus sp., Sisymbrium thellungii , and Urtica dioica had very high activity. This activity was greatest in the boiled extract of Amaranthus sp. and the boilet and aqueous extracts of Sisymbrium thellungii and Urtica dioica. The activity in the aqueous extract of Nasturtium aquatica was lost by boiling. High activity was also obtained with the teas Galium aparine and Aspalathus linearis (Rooibos) and with the tuber Colocasia esculenta.     

Hydrogenation of canola oil in the presence of nickel and the methyl benzoate-chrome carbonyl complex

Canola oil was hydrogenated using a mixture of homogeneous methyl benzoate-Cr(CO)₃ and heterogeneous nickel catalysts. The effect of the methyl benzoate-Cr(CO)₃_to-nickel ratio on the activity, specific isomerization index, linoleate and linolenate selectivities, and fatty acid composition was evaluated, and the results compared with those obtained with commercial nickel catalyst and methyl benzoate-Cr(CO)₃ used individually. At higher chromium-to-nickel ratios the activity of nickel was inhibited and the system behaved essentially like the pure chrome complex, while at low chromium-to-nickel ratios the characteristics of the nickel predominated. In a short transition zone relatively high reaction rates were obtained with significantly reducedtrans-isomer levels in the product. In a broader sense, it may be possible to combine a homogeneous and heterogeneous catalyst while retaining the advantages of both. We may thus be able to design catalyst systems for specific applications.     

Effect of specimen size and loading conditions on spalling of concrete

Different qualities of concrete have been fire tested using different geometries of the specimens as well as different load levels and load configurations. The main objective with the study was to examine a test methodology consisting of a full‐scale test and different small scale‐tests for determining the probability of spalling and the amount of spalling of fire exposed concrete structures. A reference specimen was defined as a one‐sided fire exposed slab with the dimensions 1800 × 1200 mm² giving an exposed area of 1500 × 1200 mm². A number of concrete qualities with different probabilities for spalling, were tested using the reference specimen. These tests showed that the reference specimens worked well giving the expected test results. Small specimens were manufactured in different shapes with the same concrete as the one used in the reference tests. These small specimens were tested either at the same time as the reference specimens in the large furnace or afterwards on a small‐scale furnace where the fire exposed surface was 450 × 360 mm². The test results clearly show the increased probability and the increased amount of spalling by using external compressive loading. The results also show that by using pre‐stress through bars or wires the load can be lost due to heating of the bars/wires which results in a decreased amount of spalling. The boundary of the specimen also affects the amount of spalling. The spalling around the edges was in all tests less than the spalling on the central parts of the exposed area. It could also be noted that the spalling did not pass completely through any of the specimens. The reason for this is probably that the water/vapour could migrate out from the unexposed surface of the specimen. Copyright © 2006 John Wiley & Sons, Ltd.     

The microscopy cell (MicCell), a versatile modular flowthrough system for cell biology, biomaterial research, and nanotechnology

We describe a novel microfluidic perfusion system for high-resolution microscopes. Its modular design allows pre-coating of the coverslip surface with reagents, biomolecules, or cells. A poly(dimethylsiloxane) (PDMS) layer is cast in a special molding station, using masters made by photolithography and dry etching of silicon or by photoresist patterning on glass or silicon. This channel system can be reused while the coverslip is exchanged between experiments. As normal fluidic connectors are used, the link to external, computer-programmable syringe pumps is standardized and various fluidic channel networks can be used in the same setup. The system can house hydrogel microvalves and microelectrodes close to the imaging area to control the influx of reaction partners. We present a range of applications, including single-molecule analysis by fluorescence correlation spectroscopy (FCS), manipulation of single molecules for nanostructuring by hydrodynamic flow fields or the action of motor proteins, generation of concentration gradients, trapping and stretching of live cells using optical fibers precisely mounted in the PDMS layer, and the integration of microelectrodes for actuation and sensing.     

Some spatial equilibria in facility investment under uncertain demand

This paper describes the spatial distribution of customer demand, supply of customer services and facility investment, as the outcome of a three-level game-like interaction between customers (e.g., shoppers), suppliers (e.g., retailers) and developers (e.g., landlords). Treating both the suppliers and developers at each centre as competitors, oligopolistic equilibria of the Nash-Stackelberg type are developed, and conditions for their existence and uniqueness established. Uncertain customer demand is specified in probabilistic terms, representing the suppliers' perception of expected customer behaviour.