Integrated Optimal Cell Site Selection and Frequency Allocation for Cellular Radio Networks

Two major planning problems are encountered when designing a cellular radio network. The initial question is where to locate the base transmitter stations such that full coverage is achieved at low interference. This is relevant for frequency division (FDMA) as well as code division multiple access (CDMA) technology. If the locations of base stations are given, then for an FDMA-system frequencies have to be assigned such that there is a sufficient number of channels per cell available at a low total interference level. Since cell site selection and frequency allocation have mutual influences on each other, the ultimate goal is to deal with both problems in a single design step. The main intention of this paper is to model the above planning issues as linear integer programs, and to discuss solution methods for the corresponding NP-hard problems. According to their increasing complexity we proceed from channel allocation via cell site selection to an integrated single setup.     

Corrosion of friction stir welded magnesium alloy AM50

The microstructure of a friction stir welded magnesium alloy AM50 was examined by means of optical light microscopy. The chemical composition, particularly the iron content, and morphology of the oxide film were analyzed and discerned via auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Corrosion behaviour of the welds and base materials were investigated by virtue of neutral salt spray tests and potentiodynamic polarization measurements in conventional cells and in a mini cell. The results demonstrate that minor increases in iron concentration as might be speculated to occur as a consequence of tool/work piece interaction during the welding process on the corrosion resistance of the weld can be ignored. The corrosion morphology was predominantly influenced by the distribution of the Mg₁₇Al₁₂ phase. Here, it was also found that the corrosion resistance of the friction stir weld varied in response to changes in the joint microstructure.     

Experimental determination of the jet effect for blowing oxygen into the melting bath of electric arc furnaces

Recent practice with electric arc furnaces has been the injection of oxygen through nozzle positioned on the bottom of the furnace. This type of furnace places certain requirements on bottom injection. To enable a constant coupling of the energy over the electrodes, a calm bath surface must be guaranteed. On the other hand, a good mixing of the bath is required to avoid any thermal lamination in the bath. The latter condition in particular is prerequisite for a maximum melting capacity. When judging the effect of the jet on the bath, it must be taken into account that the oxygen disintegrates directly after entering the bath and merely transfers its impulse to the liquid melt. This jet effect is described by the calculation method introduced below which is adjusted to the actual behaviour using simulation tests. In this connection, changes in the jet consistency caused by the formation of carbon monoxide have not yet been considered. Parallel to this, the mixing of the bath was determined by conductivity measurements. In these experiments, the bath level x_f, the vessel diameter D and the blown-in water mass-flux m_w were changed. A comparison of the results for fountain height and mixing time formed the basis for the development of an optimization concept for bottom-blowing nozzles in electric arc furnaces.     

Influence of oxide scales on heat transfer in secondary cooling zones in the continuous casting process,part 2: determination of material properties of oxide scales on steel under spray-water cooling conditions

In order to model heat transfer from the slab to the cooling agent in the continuous casting process the thermophysical properties of the surface layer must be taken into account. For this purpose thermal conductivities and thermal diffusivities of wustite as well as of two carbon steels were measured. The oxide scale growth for six steels was measured as a function of time and at temperatures between 900 and 1200°C in air and in steam. Complex heterogeneous oxide scales were examined by optical and scanning electron microscopy, by SIMS, as well as by Mössbauer spectroscopy. Segregation of alloying elements in the metal-oxide contact zone was found. Cracks due to thermal stresses result in spalling of the scale. Therefore, a straightforward use of the data for process modelling can principally not be recommended without restrictions.     

Life stressors, personal and social resources, and depression: A 4-year structural model.

By extending earlier stress-resistance research with a 1-yr time lag, findings with 254 adults show that adaptive personality characteristics and positive family support operate prospectively over 4 yrs in predicting reduced depression even when prior depression is controlled. By strengthening knowledge about the determinants and mediational role of coping, the results demonstrate in a 2-group LISREL analysis that the pattern of predictive relations differs under high and low stressors. Under high stressors, personal and social resources relate to future psychological health indirectly, through more adaptive coping strategies. Under low stressors, these resources relate directly to psychological health. The results support the idea that such resources play a causal role in maintaining psychological health, and they suggest the potential for a general, adaptively oriented framework applicable to adjustment under both high and low stressors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial Non-Cyclic Geometric Phase in Neutron Interferometry

We present a split-beam neutron interferometric experiment to test the non-cyclic geometric phase tied to the spatial evolution of the system: the subjacent two-dimensional Hilbert space is spanned by the two possible paths in the interferometer and the evolution of the state is controlled by phase shifters and absorbers. A related experiment was reported previously by some of the authors to verify the cyclic spatial geometric phase. The interpretation of this experiment, namely to ascribe a geometric phase to this particular state evolution, has met severe criticism. The extension to non-cyclic evolution manifests the correctness of the interpretation of the previous experiment by means of an explicit calculation of the non-cyclic geometric phase in terms of paths on the Bloch-sphere. The theoretical treatment comprises the cyclic geometric phase as a special case, which is confirmed by experiment.