激光技术在刚挠性HDI板的应用——微导通孔形成，图形成形，外型加工

概述了采用一个激光源能够加工刚性和挠性板的一种新型激光技术,PCB制造商可能采用最小的投资和提高生产率而进入HDI市场。     

A preamble-based approach for providing quality of service support in wireless sensor networks

Medium Access Control (MAC) protocols for Wireless Sensor Networks (WSN) are usually designed as random access protocols that apply different kinds of backoff strategies since Time Division Multiple Access (TDMA) based protocols with admission control are very complex and require additional mechanisms for synchronization. Without such mechanisms, fair or priority based medium access with Quality of Service (QoS) guarantees can hardly be achieved by existing protocols. Therefore, we developed a random access protocol which uses a new preamble-based medium access strategy that enables collision-free priority based access without the need of synchronization. In this paper we introduce different QoS strategies and their use cases. All strategies can be easily integrated in our protocol to meet the requirements of different target applications. Furthermore, we compare the performance of the strategies with a typical carrier-sense based protocol.     

Performance of PKI-based security mechanisms in mobile ad hoc networks

Security for ad hoc network environments has received a lot of attention as of today. Previous work has mainly been focussing on secure routing, fairness issues, and malicious node detection. However, the issue of introducing and conserving trust relationships has received considerably less attention. In this article, we present a scalable method for the use of public key certificates and their revocation in mobile ad hoc networks (MANETs). With the LKN-ad hoc security framework (LKN-ASF) a certificate management protocol has been introduced, bringing PKI technology to MANETs. In addition a performance analysis of two different revocation approaches for MANETs will be presented.     

Crystallization of 2D Hybrid Organic–Inorganic Perovskites Templated by Conductive Substrates

2D hybrid organic–inorganic perovskites are valued in optoelectronic applications for their tunable bandgap and excellent moisture and irradiation stability. These properties stem from both the chemical composition and crystallinity of the layer formed. Defects in the lattice, impurities, and crystal grain boundaries generally introduce trap states and surface energy pinning, limiting the ultimate performance of the perovskite; hence, an in-depth understanding of the crystallization process is indispensable. Here, a kinetic and thermodynamic study of 2D perovskite layer crystallization on transparent conductive substrates are provided—fluorine-doped tin oxide and graphene. Due to markedly different surface structure and chemistry, the two substrates interact differently with the perovskite layer. A time-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to monitor the crystallization on the two substrates. Molecular dynamics simulations are employed to explain the experimental data and to rationalize the perovskite layer formation. The findings assist substrate selection based on the required film morphology, revealing the structural dynamics during the crystallization process, thus helping to tackle the technological challenges of structure formation of 2D perovskites for optoelectronic devices.     

Spatio-temporal fMRI analysis using Markov random fields

Functional magnetic resonance images (fMRI's) provide high-resolution datasets which allow researchers to obtain accurate delineation and sensitive detection of activation areas involved in cognitive processes. To preserve the resolution of this noninvasive technique, refined methods are required in the analysis of the data. In this paper, we first discuss the widely used methods based on a statistical parameter map (SPM) analysis exposing the different shortcomings of this approach when considering high-resolution data. First, the often used Gaussian filtering results in a blurring effect and in delocalization of the activated area. Secondly, the SPM approach only considers false alarms due to noise but not rejections of activated voxels. We propose to embed the fMRI analysis problem into a Bayesian framework consisting of two steps: i) data restoration and ii) data analysis. We, therefore, propose two Markov random fields (MRF's) to solve these two problems. Results on three protocols (visual, motor and word recognition) are shown for two SPM approaches and compared with the proposed MRF approach.     

Dynamics of the transient buildup of emission inNd3+-doped fiber lasers

The two-stage process of the transient buildup of emission in Nd ⁴⁺-doped fiber lasers is described both experimentally and theoretically. After switching on the pump, spontaneous emission increases first until the gain becomes sufficient to compensate for the cavity losses; the laser field then develops and reaches the steady state after more or less regular oscillations. During this second stage, an almost chaotic spiking is obtained either for high pumping rates and/or at low temperatures. The whole set of these dynamical scenarios is not described under the usual assumptions of uniform cavity losses over the whole field spectrum and of pure homogeneous broadening for the transition line, but rather a modified form of the Maxwell-Bloch equations which retains some frequency dependence for the losses in the cavity and the inhomogeneous broadening as well is proposed     

Comparison of modelling approaches and layouts for solar chimney turbines

The turbogenerator is a core component of any solar chimney power plant. Various layouts for the turbogenerator have been proposed in the literature. In this paper the performance of these layouts is compared using analytical models and optimization techniques, and the important design parameters are discussed. The turbine layouts under consideration are single rotor and counter rotating turbines, both with or without inlet guide vanes.In contrast to similar investigations found in the literature, various radial sections along the blades are analysed in the turbine model. This approach is more appropriate than using a simple mean line analysis when dealing with turbines with high blade aspect ratio and low hub to tip ratio. Furthermore, a limit to the degree of reaction of the turbine has been introduced to avoid diffusion at the hub.It is shown in this paper that these slight changes in modelling approach have a significant impact on the performance prediction. Further it can be concluded that the single rotor layout without guide vanes performs very poorly; the efficiency of the other three layouts is much better and lies in a narrow band. The counter rotating layouts provide the highest peak efficiencies, but at relatively low speeds, which leads to an undesirable higher torque for the same power output.