Melting and crystallization of UHMWPE skived film

Commercial skived film from ultra-high molecular-weight polyethylene (UHMWPE) with considerable uniaxial orientation of lamellae is studied by ultra-small-angle X-ray scattering (USAXS) and wide-angle X-ray scattering (WAXS) during melting and crystallization in order to identify its mechanisms of crystallization. For the analysis of the nanostructure two-dimensional USAXS patterns are analyzed by means of the multidimensional chord distribution function (CDF) method. WAXS shows that crystallization is always isotropic and fast. WAXS reflections are observed before—under certain processing conditions—the SAXS pattern becomes anisotropic. Thus crystallization is decoupled from a slower process of oriented nanostructure formation (nanoforming). If nanoforming is performed isothermally at 105 °C, the evolving nanodomain layers obtain some preferential orientation, as long as the orientation of the melt has not previously been erased by melt-annealing at temperatures of 140 °C or above. Crystallization at temperatures ≥110 °C followed by quenching leads to isotropic nanostructure. Although crystallization is always observed early in the WAXS patterns, the USAXS patterns exhibit only weak discrete scattering during isothermal treatment at temperatures of 110 °C and higher. At 105 °C anisotropic isothermal nanoforming starts after 1.5 min. The melting of the original material resembles an inverted random car-parking mechanism. Only next-neighbor correlations are observed among the crystalline layers. The average nanodomain layer thickness is only slightly increasing (26–30 nm), whereas the long period increase is strong (from 60 nm to 140 nm).     

Integration of beamforming and uncertainty-of-observation techniques for robust ASR in multi-source environments

This paper presents a new approach for increasing the robustness of multi-channel automatic speech recognition in noisy and reverberant multi-source environments. The proposed method uses uncertainty propagation techniques to dynamically compensate the speech features and the acoustic models for the observation uncertainty determined at the beamforming stage. We present and analyze two methods that allow integrating classical multi-channel signal processing approaches like delay and sum beamformers or Zelinski-type Wiener filters, with uncertainty-of-observation techniques like uncertainty decoding or modified imputation. An analysis of the results on the PASCAL-CHiME task shows that this approach consistently outperforms conventional beamformers with a minimal increase in computational complexity. The use of dynamic compensation based on observation uncertainty also outperforms conventional static adaptation with no need of adaptation data.     

On time-triggered and event-based control of integrator systems over a shared communication system

When analyzing networked control systems, where the control loop is closed over a communication system, it is crucial to take the communication system into account. Hence, time-triggered and event-based control of an integrator system with noise over a shared communication system is analyzed. Thereby, analytical models of different communication systems are used and the analysis is focused on the effect of the communication system on the performance, as well as the interaction between control and communication. For time-triggered control, where the event times are known in advance, a deterministic communication protocol can be used. Hence, time-triggered control with the two most well-known deterministic communication protocols, time division multiple access (TDMA) and frequency division multiple access (FDMA), is analyzed. For event-based control, where the events appear at random times, a contention-based communication protocol should be used. Hence, event-based control is analyzed with different contention-based communication protocols: pure ALOHA, slotted ALOHA, a queueing system, and Erlang’s loss model. It turns out that time-triggered control with either TDMA or FDMA outperforms event-based control with pure or slotted ALOHA. However, event-based control with a properly designed queueing system gives an even better performance. Thus, we conclude that it is crucial to take the details of the communication system into account.     

Reconfigurable handling systems as an enabler for large components in mass customized production

Manufacturing companies today are exposed to increasingly dynamic market requirements. Particularly in high-wage countries, there is also a clear trend toward standing out from global competitors by means of product differentiation. At the same time, however, prices have to remain competitive. As a consequence, many companies choose a mass customization strategy to reconcile individualized products with advantages of the economies of scale. So far, this aim is mainly reached in the consumer goods sector by flexible production systems with a high degree of automation. The approach presented here is capable of transferring the benefits of mass customization to large products with lower production quantities such as aircraft by means of a highly reconfigurable automated handling system. Instead of manual operations or specific jigs and fixtures for each component, the new system is characterized by supporting large work pieces at several distributed points by multiple robotic arms. The individual robots are simple in design and very lightweight so that they can be easily switched in order to reconfigure the assembly system for different tasks. The development does not only comprise hardware construction, but also new methods for programming, commissioning and control of cooperating handling devices in a modular and reconfigurable system layout.     

Deriving fine-scale socioeconomic information of urban areas using very high-resolution satellite imagery

This article presents a new approach to derive fine-scale socioeconomic information of urban areas using very high resolution satellite data. The rationale behind the method is to use high resolution satellite data, capable of resolving urban morphology details, to derive a classification of the image. Thus, it is assumed that there is a relationship between the socioeconomic profile and the urban morphology of an area in terms of availability of green areas, sport facilities, private swimming pools or pavement conditions. The method is tested using a case study of Lima, Peru. Using a sample of ground data, a neural network classifier was applied to a pre-classified image in which entropy had been used to mask extensive, non-built up areas that would otherwise have inserted spurious information into the classifier. The result shows a high correlation (0.70 R ²) when compared with validation data. The good performances also show that a physiographic satellite view of the city reflects the socioeconomic layout of their inhabitants, thus making remote sensing a complementary tool for social research and urban planning. While the parameterization of the problem may differ from one area to another, it is shown that an a priori choice of a few parameters may help to automatically characterize large areas in social terms, thus allowing social inequality and its evolution to be mapped in those areas with limited availability of data. In order to make the method widely applicable, the possibilities and limitations of applying the procedure to other large cities are discussed.     

Schnelle optische Tomographie zum Nachweis von OH*‐Verteilungen in Flammen

A recently developed and patented fast tomographic reconstruction system has been applied to detect two‐dimensional distributions of the OH* chemiluminescence in laminar and turbulent flames. This could be achieved by the arrangement at exposure times down to 100 – 200 μs at a spatial resolution of < 1 – 2 mm, even though the concentration of OH* in flames is in the order of some ppb and, therefore, extremely small. Among other things the results provide important information regarding the determination of the heat release rate in flames to predict unstable operating points of gas turbines.     

德国汉堡的创意城市发展策略

从城市规划建设的实践角度入手,论文总结和归纳了创意城市汉堡通过弘扬文化创意产业、打造创意城区、吸引创意人群等途径推进城市发展的具体策略,如港城建设、传统工人街区改造、IBA项目、创意公司等,并综合评述了这些策略的成败得失.     

Experimental results of a compact thermally driven cooling system based on metal hydrides

In this paper a detailed experimental analysis of a metal hydride based cooling system is presented. For the high temperature side an AB₅ type alloy (LmNi_4.91Sn_0.15) was chosen, whereas an AB₂ type alloy (Ti_0.99Zr_0.01V_0.43Fe_0.09Cr_0.05Mn_1.5) is used for the low temperature side. Due to very good heat and also mass transfer characteristics (among others, large heat transfer surface area) of the utilized capillary tube bundle reaction bed, very short half-cycle times in the order of 100 s have been reached. Consequently, the specific cooling power of the system is up to 780 W per kg desorbing metal hydride – depending on the temperature boundary conditions. The system was experimentally analyzed for different cooling and ambient temperatures, whereas the heating temperature was fixed to 130 °C.