Amplitude-modulation detection in single-stage negative-feedback amplifiers due to interfering out-of-band signals

The electromagnetic-interference effects of out-of-band signals on negative-feedback amplifiers are investigated. It is assumed that the interfering signals picked up at the input of the amplifier are dominant. Due to the nonlinear behavior of the active devices in the amplifier, unwanted dc shifts and amplitude-modulation (AM) detection may occur. Describing these effects is usually done by using the Volterra series. Although providing good results when used for analysis, methods to use the Volterra series for the design process are not yet mature enough. A simple procedure for calculating AM detection is presented. An equivalent source at the input of the amplifier is introduced that accounts for the nonlinear effects. Because the characteristics of this source are computed as a function of design parameters, this procedure facilitates a synthesis approach for designing amplifiers with a lower susceptibility to AM detection. It is shown that the root locus of the amplifier transfer function has a large influence on the amount of AM detection and, therefore, on the electromagnetic compatibility. Measurements made on a single-stage negative-feedback amplifier support the presented procedure.     

Unsteady two-film model for mass transfer

The classical two-film model for mass transfer between two fluid phases can only be used to describe the steady state mass transfer mechanism. Both the penetration and the film-penetration model are also valid solely when only one diffusion boundary layer exists at the interface between the phases. With a view to surmounting the limitations of the above models a new model has been developed for the mass transfer between two fluid phases with two diffusion boundary layers at the interface. The new model is based on the two-film concept and the Danckwerts distribution function, and is also able to simulate the unsteady state mass transfer mechanism between two fluid phases with two different boundary layers.     

Brain-computer communication: motivation, aim, and impact of exploring a virtual apartment.

The step away from a synchronized or cue-based brain-computer interface (BCI) and from laboratory conditions towards real world applications is very important and crucial in BCI research. This work shows that ten naive subjects can be trained in a synchronous paradigm within three sessions to navigate freely through a virtual apartment, whereby at every junction the subjects could decide by their own, how they wanted to explore the virtual environment (VE). This virtual apartment was designed similar to a real world application, with a goal-oriented task, a high mental workload, and a variable decision period for the subject. All subjects were able to perform long and stable motor imagery over a minimum time of 2 s. Using only three electroencephalogram (EEG) channels to analyze these imaginations, we were able to convert them into navigation commands. Additionally, it could be demonstrated that motivation is a very crucial factor in BCI research; motivated subjects perform much better than unmotivated ones.     

An integer concave minimization approach for the minimum concave cost capacitated flow problem on networks

Formulating the minimum concave cost capacitated network flow problem as an integer concave minimization problem, we establish finite branch and bound algorithms, in which the branching operation is the so–called integral rectangular partition and the bounding procedure is performed by the classical minimum linear cost flow problem on subnetworks. For the special case that the flow cost function is concave on a fixed number of arcs and linear on the others, an upper bound of the running time is given. Received: 19 July 1996 / Accepted: 8 July 1997     

Development and characterization of a biocompatible OH-modified copolymer based on polyurethane

Different polyurethanes were synthesized by varying the diol as well as the diisocyanate components and chain extenders. Polyurethanes with OH-groups were obtained by photo- and thermoinitiation of the radical polymerization of hydroxy alkyl acrylates in the presence of the polyurethanes. The polymers were evaluated with respect to their biocompatibility by measuring the cell spreading, the rates of DNA- and protein synthesis and the swelling behaviour. The differences in the surfaces and the bulks between the selected basic polyurethane and the functionalized modification were determined and characterized by XPS, FTIR-ATR and ¹³C-FT-NMR-spectroscopy. The mechanical data of Tecoflex EG 60D® and Pellethane 2363–80AE® were compared with the data of the synthesized polyurethanes.     

Membranen in der Verfahrenstechnik

Membranes in chemical engineering . In the last 10 years membranes and membrane processes have evolved from a useful laboratory tool to an industrial product of significant technical and commercial impact. In some applications membrane processes have today not only replaced some conventional separation procedures in the chemical process industry, because they are often more economical and yield better quality products, but they have also successfully been utilized to solve mass separation problems where conventional procedures failed or are too expensive. This contribution discusses the state of the art of membranes and membrane processes as well as their major applications, with the main emphasis being placed on more recent developments.     

Physical gelation of crystallizing metallocene and Ziegler-Natta ethylene-hexene copolymers

The effect of molecular architecture on the evolution of viscoelastic properties during crystallization was investigated using ethylene-hexene copolymers manufactured via metallocene (M-LLDPE) and Ziegler-Natta (ZN-LLDPE) processes. Differences in branching distribution were shown to have a drastic effect on the viscoelastic properties near the gel point. It is shown that the branching distribution rather than branch content is the determining parameter for the evolution of the rheological properties during isothermal and non-isothermal crystallization, and for the width of the solidification interval. We developed a partial melting technique for the preparation of stable critical gels of LLDPE whose viscoelastic properties correspond to the intermediate state between melt and solid. Local molecular conformation and crystallinity in these gels were characterized by Raman spectroscopy, which shows that the transition from melt-like to solid-like rheological behavior (physical gelation) in LLDPE occurs at a very low overall crystallinity of less than 5%.