Free‐Standing Photonic Glasses Fabricated in a Centrifugal Field

One efficient method to obtain disordered colloidal packing is to reduce the stability of colloidal particles by adding electrolytes to the colloidal dispersions. But the correct amount of additional electrolytes must be found empirically. Here, the effect of CaCl₂ on polystyrene colloidal dispersions is studied, and a link between the amount of CaCl₂ and the corresponding glassy colloidal structure is quantitatively built. A threshold concentration of CaCl₂ is found by dynamic light scattering. When exceeding this threshold, different nanoparticle oligomers are observed in the dispersions by analytical ultracentrifugation. The second objective is to achieve free‐standing samples, which is required for many optical measurements. A universal method is established, using a centrifugal field to produce robust samples by polymerizing coassembled hydrophilic monomers to form a network, which traps the glassy colloidal structures. Photon time of flight measurements shows that the CaCl₂ concentration threshold should not be exceeded. Otherwise an optical shortcut may take place. Thus, the work provides a feasible universal route to prepare macroscopic free‐standing photonic glasses from electrostatically stabilized nanoparticles, suitable for further optical investigation.     

Approximate motion planning and the complexity of the boundary of the union of simple geometric figures

We study rigid motions of a rectangle amidst polygonal obstacles. The best known algorithms for this problem have a running time of (n ²), wheren is the number of obstacle corners. We introduce thetightness of a motion-planning problem as a measure of the difficulty of a planning problem in an intuitive sense and describe an algorithm with a running time ofO((a/b · 1/_crit + 1)n(logn)²), wherea b are the lengths of the sides of a rectangle and _crit is the tightness of the problem. We show further that the complexity (= number of vertices) of the boundary ofn bow ties (see Figure 1) isO(n). Similar results for the union of other simple geometric figures such as triangles and wedges are also presented.This work was supported partially by the DFG Schwerpunkt Datenstrukturen und Algorithmen, Grants Me 620/6 and Al 253/1, and by the ESPRIT II Basic Research Actions Program of the EC under Contract No. 3075 (project ALCOM).     

Physical properties of (La,Sr)Ti(O,N)3 thin films grown by pulsed laser deposition

Thin films of La_xSr_1−xTiO_3+x/2 (x = 0, 0.25, 0.5, 0.75, 1) were grown by laser ablation on two different kinds of substrates (SrTiO₃ (STO) and MgO) and were subsequently ammonolysed to yield the corresponding oxynitrides La_xSr_1−xTi(O,N)₃. For both substrates all films were found to grow epitaxially to the (1 0 0) direction of the cubic perovskite structure, except for x = 0.5 that grew parallel to the (1 1 0) direction. For some of the films TiN was detected as impurity phase. Scanning electron microscopy revealed that the films are dense and homogeneous with thicknesses around 350 nm. Atomic force microscopy showed that the surface roughness of the films varied between 4.2 and 14.1 nm. The employed substrate had a strong influence on the electrical properties. Films grown on STO exhibited a metallic behaviour, in contrast to the films grown on MgO, which were insulating.     

改造当前国内污水管网需要综合考虑的四个因素

研究了国内污水管网的现状并参考欧洲的经验和教训,提出外来水入侵、管网里含外来水混合污水的处理量(污水处理厂的处理能力)、城市用水效率和污水收集率是影响污水管网性能和效率的四个因素.以维也纳和苏黎世合流式污水管网系统和维也纳主污水处理厂(VMWWTP)和苏黎世Werdh(o)lzli污水处理厂为例,比较国内和一些欧洲国家...     

Ripple dynamics over various microtopographical roughness elements and their implications for river management

Specific problems in connection with the sediment regime have arisen in the granite and gneiss area in the northern part of Austria due to the increased sediment supply of coarse sand and fine gravel as a product of rock weathering. One of the physical characteristics of these sediments is their high mobility in form of ripple bedforms along the surface. In these rivers, the microtopographical structures of the bed surface are hydraulically active, especially in the initial stages when ripples have not overtopped the largest elements of the bed's roughness elements. There is a lack of detailed studies of the impacts of these microtopographical structures on ripple dynamics. Thus, the aim of the present study was to investigate the impact of various microtopographic roughness elements on ripple movement. This study was performed using a 1:1‐scaled physical laboratory experiment. The results showed, in all repetitions of the experiment with variable grain sizes, that the higher the microtopographical variability of the river substrate and turbulence was, the higher the measured transport velocities of the ripples were. The expected hidden impacts on sediment transport were not documented. Important implications for sediment management were discussed, as river sections with high accumulation rates of coarse sand and fine gravel are prone to additional degradation as downstream transport decreases over smooth ripple–dune morphologies. Additionally, structural elements such as exposed rocks may increase the downstream transport due to the increased variability in turbulence.     

Mobility in wireless networks

Ohne Zusammenfassung     

Analytical and Numerical Modifications of Transonic Nozzle Flows

Classical transonic hodograph-based design methods are employed and revitalized using modern numerical tools to illustrate the design of a symmetrical accelerating-decelerating nozzle throat design. The concept of Elliptic Continuation is applied to solve transonic boundary value problems avoiding the inherently nonlinear nature of the basic equations and obtaining transonic flow examples using the Method of Characteristics in an inverse mode. Purpose of the present paper, besides describing a new special flow example, is to keep these classical methods alive for education of a new generation of creative engineers.     

Criteria for Selecting Cloud Service Providers: A Delphi Study of Quality-of-Service Attributes

Customers of cloud service providers (CSPs) use different criteria to judge the quality of cloud services. Based on managerial and technical Quality-of-Service (QoS) attributes, these criteria provide information on service quality and the CSP itself. Thus, it is important to identify relevant QoS to assure success of customers. Using a Delphi study, 16 professionals characterized by different cloud service models, company sizes, and industries identified and ranked QoS according to their relative importance. Our results show consensus on QoS. We identify functionality, legal compliance, contract, geolocation of servers, and flexibility as top QoS and observe increasing importance of managerial QoS.