DDFSGEN

This paper presents a functional compiler for the automatic design of Direct Digital Frequency Synthesizer (DDFS) integrated circuits (ICs) using a ROM based table look-up architecture. The compiler allows the user to specify high-level specifications such as the acceptable spurious response and it generates the IC architecture, floorplan, and layout. To construct the layout for different specifications, a library of parameterized macrocells has been developed in 1.2 m CMOS technology.A test chip with a quadrature DDFS module has been generated, using the compiler, and fabricated. The chip has two input signals: one is for frequency control while the other is for phase initialization. Input and output word lengths are 16 bits and 6 bits respectively. The chip complexity is approximately 12,000 transistors (DDFS core) and the die size is 4.8×2.9mm ². A maximum sample rate of 80 MHz has been attained implying a maximum sine (cosine) output frequency of 40 MHz and a frequency resolution of 1.22 kHz. The maximum spurious level measured is –46 dB.     

Determination of particle size distribution in a modified hop extract emulsion by electrical resistivity

A procedure has been developed which is suitable for the evaluation of particle size distribution in emulsions of modified hop extracts. A Coulter Counter Model A and a Coulter Counter Model B equipped with a Model M Data Converter were used to assess the weight percent distribution of particles smaller than 10 μm in diameter. The influences of electrolyte concentration, length of analysis, and concentration of the hop extract particles were factors affecting the reproducibility of the study. It was found that identical distribution curves could be obtained with either instrument. The Model B Coulter Counter with the Model M Data Converter is preferred since weight fractions are provided directly and lengthy calculation procedures are eliminated. Coincidence correction on particle counts was unnecessary under the controlled conditions of the analysis.     

Influence of structure and counterions on physicochemical properties of linear alkylbenzene sulfonates

The effects of different inorganic and organic counterions on the physicochemical behavior of three commercial linear alkylbenzene sulfonates (LAS) have been studied. It has been found that the counterion hydration radius of the corresponding commercial linear alkylbenzene sulfonates has great influence on solubility, viscosity, surface tension and critical micelle concentration (CMC). The counterion has no influence on the detergency performance of the finished formulation. The alkyl chain length and the presence of tetralines have an important influence on solubility, viscosity and surface tension.     

Structure formation during spinning of poly(p-phenylenebenzobisthiazole) fiber

The structure formed in the coagulation stage of the spinning process of poly(p-phenylene benzobisthiazole) fiber is studied by electron microscopy. An oriented network of microfibrils with typical fibril diameters of about 80-100Å is observed. We suggest that these microfibrils are the fundamental structural elements of the fiber. Thus, knowledge of the mechanism by which this initial structure is formed may allow for better control of final fiber properties. The relation of structure formation during coagulation to the phase diagram of a rigid polymer solution and to the kinetic mechanism of the phase transition is discussed.     

Parallelised production of fine and calibrated emulsions by coupling flow-focusing technique and partial wetting phenomenon

The capacity of microfluidic technology to fabricate monodisperse emulsion droplets is well established. Parallelisation of droplet production is a prerequisite for using such an approach for making high-quality materials for either fundamental or industrial applications where product quantity matters. Here, we investigate the emulsification efficiency of parallelised drop generators based on a flow-focusing geometry when incorporating the role of partial wetting in order to make emulsion droplets with a diameter below 10 μm. Confinement intrinsically encountered in microsystems intensifies the role played by interfaces between liquids and solids. We thus take advantage of partial wetting to enhance the maximum confinement accessible due to liquid flow focusing. We compare the performances brought by partial wetting to more established routes such as step emulsification. We show that the step configuration and the partial wetting regime are both well suited for being parallelised and thus open the way to the production of fine and calibrated emulsions for further applications. Finally, this new route of emulsification that exploits partial wetting between the fluids and the channel walls opens possibilities to the formation of substantially smaller droplets, as required in many fields of application.