Transient characteristics of small salient-pole alternators

The use of small alternators, other than for standby purposes, is increasing and this has focused attention on the reliability and utility of the parameters normally quoted for such machines. Test procedures are described and methods used for parameter estimation discussed, with particular emphasis on the difficulties presented by small brushless machines     

Ammoxidation of methylaromatics over vanadium phosphate catalysts II. Catalyst formation, active sites and reaction mechanism

The interactions of VOHPO₄· 0.5H₂O and (VO)₂P₂O₇ with the ammoxidation feed and the single components such as ammonia, oxygen, water and component mixtures were studied in detail using XRD and temperature-programmed reaction spectroscopy. The aim of this work was to improve the knowledge of the formation of the active phases or active sites of the catalysts from their precursors under the condition of the ammoxidation reaction. Similar catalytic properties of various applied VPO materials were discussed in terms of the presence of similar structure elements (domains of adjacent edge-sharing VO₆ octahedra-units and P-O-NH₄ groups).     

Effect of stepper lens operating conditions on proximity effects in DUV optical lithography down to 250nm

Reduction of optical proximity effects (OPE), at deep uv wavelength of 248nm, caused by the variation of stepper lens operating conditions is investigated. It is shown that many of these effects, which increase as the Rayleigh limit is approached, can be minimised, and in many cases eliminated, by suitable choice of lens numerical aperture (NA) and partial coherence (sigma, σ).

Application of these results should enable the user of advanced wafer steppers to carry out high resolution lithography with a minimum of time consuming optical proximity correction (OPC).     

Cataract and high-pass resolution perimetry

The present study describes the influence of cataract on high-pass resolution perimetry results. Twenty-five otherwise healthy patients were examined before and after cataract surgery. Their preoperative visual acuities ranged from 0.1 to 0.8 and their mean resolution thresholds from 3.9 to 12.3 dB. Both elevated mean thresholds and local visual fields defects were observed. In patients with low-grade cataract, i.e. preoperative visual acuity 0.3 to 0.65, the mean improvement in perimetric results after operation was approximately 1 dB. In patients with higher degrees of lens opacity, visual acuity 0.1 to 0.25, the difference between pre- and postoperative perimetry results showed a wide range, 1.4-6.2 dB. In conclusion, cataract induced different types of visual field defects. The general threshold increase due to low-grade cataract (VA > or = 0.3) could be compensated for by subtracting 1 dB from the measured value.     

In situ FTIR spectroscopy on rhodium-exchanged NaX zeolite with different metal dispersion during syngas reaction

In situ FTIR spectroscopy has been applied to study the reason of the different selectivity behaviour of rhodium in the CO hydrogenation reaction in dependence on the different particle size. Several forms of molecularly adsorbed CO are observed, such as linearly- and bridgedbonded CO on metallic rhodium as well as dicarbonyl species with Rh(I) centres formed by oxidation of Rh(0) with protons in presence of CO. Furthermore, non-reactive formate, acetate, and carbonate species are produced as side products of the reaction. The higher selectivity to oxygenates, particularly to methanol, is explained by the existence of multiple-bonded CO present only on small rhodium crystallites. The multiple-bonded CO formed at low temperatures is converted at higher temperatures to the highly reactive formyl species, which is hydrogenated to methanol.     

APPLICATION OF SITE-SPECIFIC NATURAL ISOTOPE FRACTIONATION (SNIF-NMR) OF HYDROGEN TO THE CHARACTERIZATION OF EUROPEAN BEERS

More than one hundred samples of European beers have been investigated by the new SNIF-NMR method which is based on 2H NMR at the natural abundance level and enables site-specific natural isotope fractionation factors in ethanol to be determined. The relative (R) and absolute (D/H)_i, parameters are shown to be characteristic of the country where the beers are brewed and the observed variations are explained in terms of cereal composition, water resource, and manufacturing processing (fermentation, yeast, temperature cycle). These new parameters find analytical and mechanistic applications in the identification of a beer and in the investigation of a fermentation process.     

Parallel associative combinator evaluation II

A new evaluation model for SK combinator expressions is presented and used as a basis for the design of a novel processor. The resulting machine architecture resembles a dataflow ring, but executions are constrained to be fully lazy. An automatic dynamic load sharing mechanism for a distributed multiprocessor architecture is suggested, and initial simulation results are presented.     

Rate-distortion optimized tree-structured compression algorithms for piecewise polynomial images.

This paper presents novel coding algorithms based on tree-structured segmentation, which achieve the correct asymptotic rate-distortion (R-D) behavior for a simple class of signals, known as piecewise polynomials, by using an R-D based prune and join scheme. For the one-dimensional case, our scheme is based on binary-tree segmentation of the signal. This scheme approximates the signal segments using polynomial models and utilizes an R-D optimal bit allocation strategy among the different signal segments. The scheme further encodes similar neighbors jointly to achieve the correct exponentially decaying R-D behavior (D(R) - c(o)2(-c1R)), thus improving over classic wavelet schemes. We also prove that the computational complexity of the scheme is of O(N log N). We then show the extension of this scheme to the two-dimensional case using a quadtree. This quadtree-coding scheme also achieves an exponentially decaying R-D behavior, for the polygonal image model composed of a white polygon-shaped object against a uniform black background, with low computational cost of O(N log N). Again, the key is an R-D optimized prune and join strategy. Finally, we conclude with numerical results, which show that the proposed quadtree-coding scheme outperforms JPEG2000 by about 1 dB for real images, like cameraman, at low rates of around 0.15 bpp.     

Thermal fatigue effects on the temperature distribution inside IGBT modules for zone engine aeronautical applications

This work examines the thermal fatigue effects on the temperature distribution inside IGBT modules for aeronautical applications. Exactly, they are used in a very different application where temperature cycling due to the working environment is the most limiting fact. In this case, it is concluded that solder delamination does not present any restriction to module lifetime at short term (up to 60% of total delaminated area). In addition, it is proposed only determining the delaminated area behind devices, which is the main responsible of the thermal temperature increase.