A multiphase series-resonant converter with a new topology and areduced number of thyristors

Multiphase series resonant (SR) power converters provide a flexible way to transform power between a utility grid and a multiphase load or source. The current implementations all suffer from a high component count, which makes the use of these power converters unattractive from an economical point of view. A new topology for multiphase SR power converters has been proposed in the literature in a simulation context. This topology uses half the number of power semiconductors compared to the existing multiphase SR power converters. The present paper addresses the implementation of the new topology in a prototype power converter. The old and new topologies are presented. The operation of the new topology is explained. In the new topology the resonant circuit is grounded at one side, which compared to the old topology imposes a restriction on the operation. The paper shows both simulation data and measured waveforms. It is explained that the economical gain due to the reduction in component count is offset by a lower power rating. The paper finishes with conclusions and acknowledgments     

Star‐Shaped Oligothiophenes for Solution‐Processible Organic Field‐Effect Transistors

We have designed and successfully synthesized star‐shaped oligothiophenes, which could be used as semiconducting materials for solution‐processible organic field‐effect transistors (FETs). By systematically changing the chemical structure of the star‐shaped oligothiophenes we obtained the structural requirements needed for making working FETs from them. UV‐vis fluorescence measurements showed that a molecule of the star‐shaped compounds under consideration is not a fully conjugated molecule, but it has three independently conjugated oligothienyl‐phenylene blocks. A possible scheme of molecular packing of the star‐shaped oligothiophenes in a lamellar structure was proposed and confirmed by atomic force microscopy (AFM) and X‐ray diffraction (XRD) measurements. Although the star‐shaped semiconductors show a somewhat lower mobility than their linear analogs, they possess better solubility and film‐forming properties, leading to improved spin‐coating processing. The best FETs were made by spin‐coating 1,3,5‐tris(5″‐decyl‐2,2′:5′,2″‐terthien‐5‐yl)benzene from a chloroform solution, which resulted in a mobility of 2 × 10^–4 cm² V ^–1s^–1, a 10² on/off ratio at gate voltages of 0 V and –20 V, and a threshold voltage close to 0 V.     

The application of inverse titania opals in nanostructured solar cells

The synthesis and characterization of nanostructured heterojunction solar cells based on inverse opal titanium dioxide (TiO₂) films is discussed. Photonic films with thicknesses of 0.9 and 3.7 μm are deposited using self-organisation of latex spheres with diameters of 400 and 100 nm. The voids between the spheres are filled with a TiO₂ precursor and a subsequent heat treatment yields a highly organized porous structure. Sensitization with Ru 535-dye (cis-[L₂Ru(SCN)₂] in which L is 2,2′-dipyridine-4,4′-dicarboxylic acid), yields solar cells with a power conversion efficiency of 0.6% under simulated solar light. At present, the small area of the ordered structure is limiting the performance of the cells. These cells may be promising for future applications, if improved fabrication techniques will enable an enlargement of the ordered area.     

The combined effect of rosemary (Rosmarinus officinalis L.) and modified atmosphere packaging as protection against warmed over flavour in cooked minced pork meat

Rosemary (dried leaves ofRosmarinus officinalis L.) added to cooked meat balls (minced pork) was found to retard the formation of warmed over flavour (WOF) during chill storage. The spice was added to pork meat (Longissimus dorsi) balls in an amount acceptable for the product, as evaluated by a sensory panel (0.05% of total weight). After cooking (water bath, internal temperature 80°C), the meat balls were packed using five atmosphere packaging conditions: (i) air; (ii) 5% O₂/95% N₂; (iii) 3% O₂/97% N₂; (iv) 1% O₂/99% N₂; and (v) 100% N₂. During chill storage (5°C), the sensory quality of the reheated meat balls was evaluated by a trained sensory panel, and lipid oxidation was followed by measurement of thiobarbituric acid reactive substances (TBARS). The combination of decreased O₂ atmosphere in the packages and addition of rosemary resulted in a significantly (p<0.05) lower amount of TBARS and a significantly (p<0.05) better sensory score.     

3D-GSIS geotechnical modelling of tunnel intersection in soft ground: the Second Heinenoord Tunnel, Netherlands

A 3D subsurface geotechnical model was developed for the Second Heinenoord Tunnel in a 3D-geo-scientific information systems (3D-GSIS) environment. The model is developed through the establishment of a 3D-subsurface model, a tunnel geometrical model, a 3D-grid (block) model, and the application of geostatistical modelling. The model was utilized for the analysis of tunnel boring machine geomechanical performance with a quantitative volumetric analysis. The study demonstrated the applicability of 3D-GSIS in modelling complex subsurface geological conditions, which is the case at the project site with soft heterogeneous Holocene top layers. The methodology followed is applicable for feasibility and engineering analysis, and may also be used for production estimation and model based simulation with a link to knowledge-based expert systems.     

Volumetric breast density estimation from full-field digital mammograms

A method is presented for estimation of dense breast tissue volume from mammograms obtained with full-field digital mammography (FFDM). The thickness of dense tissue mapping to a pixel is determined by using a physical model of image acquisition. This model is based on the assumption that the breast is composed of two types of tissue, fat and parenchyma. Effective linear attenuation coefficients of these tissues are derived from empirical data as a function of tube voltage (kVp), anode material, filtration, and compressed breast thickness. By employing these, tissue composition at a given pixel is computed after performing breast thickness compensation, using a reference value for fatty tissue determined by the maximum pixel value in the breast tissue projection. Validation has been performed using 22 FFDM cases acquired with a GE Senographe 2000D by comparing the volume estimates with volumes obtained by semi-automatic segmentation of breast magnetic resonance imaging (MRI) data. The correlation between MRI and mammography volumes was 0.94 on a per image basis and 0.97 on a per patient basis. Using the dense tissue volumes from MRI data as the gold standard, the average relative error of the volume estimates was 13.6%.     

Strategic technology investment under uncertainty

In this paper the technology investment decision of a firm is analyzed, while competition on the output market is explicitly taken into account. Technology choice is irreversible and the firms face a stochastic innovation process with uncertainty about the speed of arrival of new technologies. The innovation process is exogenous to the firms. For reasons of market saturation and the fact that more modern technologies are invented as time passes, the demand for a given technology decreases over time. This implies that also the sunk cost investment of each technology decreases over time. The investment decision problem is transformed into a timing game, in which the waiting curve is introduced as a new concopt. An algorithm is designed for solving this (more) general timing game. The algorithm is applied to an information technology investment problem. The most likely outcome exhibits diffusion with equfal payoffs for the firms. Received: December 16, 1999 / Accepted: February 7, 2001     

Phase-lock-loop operating ranges measurement

A measurement method is presented that quickly displays the operating ranges of phase-lock loops (PLLs) and acquisition aids under various input conditions such as noise and interference. The PLL measurement set-up is based on the use of normally available spectrum analyser/tracking generator equipment rather than on the common display of the control voltage of the oscillator. It is shown that in case of a narrow-band PLL the spectrum-analyser display can be more easily interpreted than the control-voltage display.     

Studies of the proporation and synthesis of haemoblogin C Philadelphia in red cells of heterozygotes, a homozygote, and a heterozygote for both haemoglobin G and alpha thalassaemia

This 9th Contribution concerns Cestodes obtained from: A Lamellibranchiata, B Gastropoda, C Pteropoda, D Cephalopoda, E Crustacea.     

Reaeration in sewers

The sewer system is a very dynamic system with an abundance of mass transfer processes and transformations. A key process is the mass exchange between the wastewater and the sewer atmosphere. An equation that describes the gas-liquid mass transfer under different hydrodynamic conditions is essential when sewer processes are to be quantified or modelled. In this work, a calibrated reaeration equation is proposed. It is based on the shear Reynolds and the Froude number to correct the increased gas-liquid interface roughness to higher flow rates. The equation was calibrated with previously published data and with new data. This data was obtained with a safe and environmentally friendly gas tracer method for gravity sewers based on the inert gas sulphur hexafluoride (SF6), a new method for the sewer system. Measurements were conducted in four channels under different conditions. The resulting equation will allow for more accurate simulations of the sewer system. Finally, the effect of reaeration with regard to the oxygen consuming processes for different hydrodynamic conditions is discussed.