Use of continuous viscometer and light scattering detectors in characterization of polyolefins: Comparisons of data from individual and combined detectors

Molecular weights of polyethylenes have been characterized using differential refractometer (DRI), continuous viscometer (CV), and low-angle laser light (LALLS) detection. In normal operation with the latter two detectors, the DRI is also employed as a concentration detector. The intrinsic viscosity of the whole polymer can be derived from the CV without use of a DRI concentration detector. If one calibrates the size exclusion chromatography (SEC) columns using the CV detector, it is possible to use this universal calibration relation and the CV detector to calculate number average molecular weight (M_n) of the polymer. Weight average molecular weight (M_w) of the sample can be calculated using data from the LALLS alone, without reference to the DRI. These variations of the analysis were tested and the advantages and limitations of the different detectors were compared using standard reference polyethylene samples in solution in 1,2,4-trichlorobenzene at 145°C. © 1992 John Wiley & Sons, Inc.     

Dynamische Belastungen von Zyklonabscheidern bei Anwendung in Blowdown-Systemen

Transient Loading of Cyclone Separators on Use in Blowdown Systems. On use of cyclone separators for phase separation in blowdown systems, pressure-discharge systems, and flaring units, considerable momentary liquid forces are often encountered. Only few details are known about the transient loading and dimensioning of such systems. Thus the behaviour of the entering surge of liquid and its effect on cyclone separators has now been studied experimentally and theoretically. Water/glycerol mixtures of various viscosities were used in these model experiments. After entering the separator the liquid immediately forms a compact wall film. It rapidly expands sideways under the action of the centrifugal force and simultaneously decelerates. A two-dimensional planar mathematical model serves for stepwise calculation of the experimental results with regard to film extension, deceleration, and the resulting transient forces. The results are summarised in the form of design criteria.     

Prediction of the concentration dependence of diffusion coefficients of polymers in solution

The hydrodynamic volumes of solvated polymers shrink with increasing concentrations in solution until a concentration (c_x) is reached at which the effective dimensions are those of a Theta solvent. A simple model (Ref. 7) can be used to calculate the volume fraction of solvated polymer coils as a function of concentration. From this, the concentration dependence of diffusion coefficients can be estimated (Ref. 5). Calculated data are in very good agreement with experimental values except for some lower molecular weight polymers in poor solvents.     

WLAN-GPRS Tight Coupling Based Interworking Architecture with Vertical Handoff Support

There have been parallel technological developments in wireless local network (WLAN) and cellular wide area network (WAN) technologies. This is evidenced by the boom in fast WLANs enabled devices, the spread of 2.5 G networks and the increasing emergence 3 G communication networks, applications and terminals. The prospects of integrating WLAN and cellular WAN technologies with support for seamless handoffs between the two heterogeneous have changed the mentality of researchers from considering WLAN technology as a threat to the future of wide area cellular networks to accepting the technology as a complementary solution. A number of architectures for interworking the two different network types have been proposed mainly based on the loose coupling interworking approach recommended by the ETSI. One of the main weaknesses anticipated with loose coupling architecture is excessive handoff latency, which may lead to data loss, traffic congestion and handoff failure. In this paper an architecture for interworking WLAN and the GPRS networks, based on the ETSI tight coupling approach, is proposed. Fredson Alfred Phiri holds a Master of Engineering Science (MEngSc) degree obtained from Multimedia University, Malaysia in 2005 and a Bachelor of Science degree in Electrical Engineering from the University of Malawi where he graduated in 2001. Mr. Phiri is currently working as a lecturer at the Polytechnic of Namibia (Namibia’s University of Science and Technology) where he also chairs the Electronics and Telecommunications (E-TEL) Research Group. He has previously worked as a lecturer at the University of Malawi, as a Telecommunications Engineer at Technocentre (Malawi), and as a Telecommunication Technician at the Malawi Telecommunications Limited (MTL). Mr. Phiri’s research interests include Integration of Mobile Data Networks, Network Programming and Powerline Communication. M.B.R. Murthy has obtained his B.E. (Electrical) from Andhra University, College of Engineering, Waltair, India, M.Sc (Engg) in Communication Systems from Regional Engineering College-Rourkela, India and PhD from Karnatak University, Dharwad, India. He has over 32 years of academic experience teaching under graduates and graduate students. He has vast research experience and has 43 publications in reputed journals and international conferences. He is a senior member at IEEE. He had six years of teaching and research experience at Multi Media University Malaysia. Currently he is Professor ECE and Dean PG engineering and R&D in GEC Gudlavalleru, India.     

Editorial

Ohne Zusammenfassung     

Integration von Energiemarkt und Verteilnetzbetrieb durch einen Flexibility Operator

The growing share of volatile distributed generation in the electric power grids results in increased local network utilisation and challenges the conventional strategies for maintaining the system balance. While grid extensions and smart grid solutions are considered for network utilisation issues, new market mechanisms are in focus for the balancing challenge. It can be expected that distributed generators on one hand will be able to supply only part of their available power to the grid in peak times, and on the other hand will have (potentially changing) contracts with different trans-regional virtual power plants. Against this background it will be necessary to define rules dealing with expected network access conflicts. One strategy also followed in this work is to find market mechanisms that support economically efficient network extension. Such mechanisms will have to include local flexibility markets that allow for compensating network bottlenecks. This work proposes strategies and technical interfaces for coordinating market and grid operation by means of a “Flexibility Operator”. Its integration into a holistic smart grid concept is discussed.