Validation of a nonlinear transistor model by power spectrumcharacteristics of HEMT's and MESFET's

The bias dependence of the power output spectrum and the generation of intermodulation products from different HEMT's and MESFET's at large signal excitation is studied and compared with simulated values. An extended HEMT/FET model suitable for small and and negative V_ds (with a drain voltage dependence of the peak transconductance in the unsaturated drain current region, and at negative drain voltage), is also proposed. Good agreement between simulated and measured power spectrum up to at least the fourth harmonic is demonstrated for HEMT and MESFET devices from different manufacturers. Measured and simulated intermodulation products are also in good agreement, which confirm the validity of the model     

Finite-element analysis of a hot-rolling problem with nonlinear friction

An isotermal, steady-state, hot-rolling problem of a workpiece with rectangular profile is considered. The workpiece material is assumed to be rigid-plastic, strain-rate sensitive and slightly compressible. The existence of a thin layer is supposed, where nonlinear Siebel's type friction is assumed to hold. Several examples of rolling problems at different rolling conditions are solved numerically by an finite-element-secant-modulus method. Comparisons with experimental results are performed. The effect of the friction factor, workpiece reduction and rolling velocity on the relative contact velocity, roll pressure and effective strain rates is illustrated and discussed.     

Reactions of a bituminous coal with metal chlorides in carbon tetrachloride

The interaction of a bituminous coal (87.2% C) with several metal chlorides in carbon tetrachloride was studied using the conditions under which graphite forms intercalation compounds. Adducts with SbCl₅, AlCl₃, FeCl₃ and MoCl₅ were isolated by filtration and washing with carbon tetrachloride. Atomic ratios versus coal carbon are as follows: C_10.0SbCl_7.4; C_6.2AlCl_4.1; C_6.3FeCl_3.3; and C_11.3MoCl_3.8. X-ray diffraction patterns of the adducts show no 002-band, the latter being partially recovered after extraction with diluted hydrochloric acid. The g-value of the e.s.r. signal of the coal vitrain shows a characteristic increase because of adduct formation with SbCl₅ and AlCl₃ and is reversible by hydrolysis extraction. The results obtained indicate that the bonding with SbCl₅ and AlCl₃ is mainly due to formation of chloro-complexes and with FeCl₃ and MoCl₅ — to formation of organo-metal complexes.     

Hold-up within two-phase countercurrent pulsed columns via Eulerian simulations

The computational fluid dynamics (CFD) has been recently recognised to be a very powerful tool for analysis of contactor behaviour or for reactor design, both being of considerable interest to chemical engineers. In this paper, a model of turbulent two-fluid flow is applied to the simulation of hydrodynamics in discs and doughnuts pulsed columns. The task concerns a two-phase countercurrent turbulent non-stationary flow in a complex geometry with high volume fraction of the dispersed phase in some areas resulting in global hold-up up to 30%. The simulations have been performed using the CFD software ASTRID developed by Electricité de France (EDF). Concerning hydrodynamic parameters (continuous phase velocity, turbulent kinetic energy, hold-up), the results follow the tendencies of the experimental knowledge. The model validation is based on the mean hold-up determination upon a representative column compartment, which is compared to experimental data. The work demonstrates a possibility for prediction of the mean column hold-up using the Eulerian approach.     

Component-based analysis of embedded control applications

The widespread use of embedded systems requires the creation of industrial software technology that will make it possible to engineer systems being correct by construction. That can be achieved through the use of validated (trusted) components, verification of design models, and automatic configuration of applications from validated design models and trusted components. This design philosophy has been instrumental for developing COMDES—a component-based framework for distributed embedded control systems. A COMDES application is conceived as a network of embedded actors that are configured from instances of reusable, executable components—function blocks (FBs). System actors operate in accordance with a timed multitasking model of computation, whereby I/O signals are exchanged with the controlled plant at precisely specified time instants, resulting in the elimination of I/O jitter. The paper presents an analysis technique that can be used to validate COMDES design models in SIMULINK. It is based on a transformation of the COMDES design model into a SIMULINK analysis model, which preserves the functional and timing behaviour of the application. This technique has been employed to develop a feasible (light-weight) analysis method based on runtime observers. The latter are conceived as special-purpose actors running in parallel with the application actors, while checking system properties specified in Linear Temporal Logic. Observers are configured from reusable FBs that can be exported to SIMULINK in the same way as application components, making it possible to analyze system properties via simulation. The discussion is illustrated with an industrial case study—a Medical Ventilator Control System, which has been used to validate the developed design and analysis methods.     

Development of a new oat-based probiotic drink

In the present work, a whole-grain oat substrate was fermented with lactic acid bacteria to obtain a drink, combining the health benefits of a probiotic culture with the oat prebiotic beta-glucan. The levels of several factors, such as starter culture concentration, oat flour and sucrose content, affecting the fermentation process, were established for completing a controlled fermentation for 8 h. The viable cell counts reached at the end of the process were about 7.5 x 10(10) cfu ml(-1). It was found that the addition of sweeteners aspartame, sodium cyclamate, saccharine and Huxol (12% cyclamate and 1.2% saccharine) had no effect on the dynamics of the fermentation process and on the viability of the starter culture during product storage. Beta-glucan content in the drink (0.31-0.36%) remained unchanged both throughout fermentation and storage of the drink. The shelf life of the oat drink was estimated to 21 days under refrigerated storage.     

Mineral composition of Bulgarian wheat bread

The micronutrient composition of the flour, dough and the bread has been investigated by means of inductively coupled plasma atomic emission spectrometer (AES-ICP). The obtained experimental data demonstrate the existence of a low micronutrient content in bread and the necessity for its fortification to provide a really wholesome diet.     

Reductive alkylation of a phenanthrene—formaldehyde resin

A model insoluble oxygen-free phenanthrene—formaldehyde resin has been reductively alkylated by means of potassium—naphthalene in THF and subsequent treatment with alkyl halide. The extractability of the resultant alkylated products by benzene reaches 50% and depends on the size of the groups introduced. The polydispersity of the benzene-soluble portions and the presence of methyl groups in them indicate that decomposition processes are taking place at the methylene bridges as well. Mainly on the basis of n.m.r. analysis of the benzene-soluble fraction of a reductively trimethylsilylated resin, quantitative information about the silylation and decomposition processes was derived. The results obtained are of interest to the study of reductive alkylation of coals.