Lower Bounds for Runtime Complexity of Term Rewriting

We present the first approach to deduce lower bounds for (worst-case) runtime complexity of term rewrite systems (TRSs) automatically. Inferring lower runtime bounds is useful to detect bugs and to complement existing methods that compute upper complexity bounds. Our approach is based on two techniques: the induction technique generates suitable families of rewrite sequences and uses induction proofs to find a relation between the length of a rewrite sequence and the size of the first term in the sequence. The loop detection technique searches for “decreasing loops”. Decreasing loops generalize the notion of loops for TRSs, and allow us to detect families of rewrite sequences with linear, exponential, or infinite length. We implemented our approach in the tool AProVE and evaluated it by extensive experiments.     

Bioinspired Underwater Adhesion to Rough Substrates by Cavity Collapse of Cupped Microstructures

Underwater or wet adhesion is highly desirable for numerous applications but is counteracted by the liquids in the contact which weaken intermolecular attraction. The problem is exacerbated in conjunction with surface roughness when liquids partially remain in grooves or dimples of the substrate. In the present study, a cupped microstructure with a cavity inspired by suction organs of aquatic animals is proposed. The microstructures (cup radius of 100 µm) are made from polyurethane using two-photon lithography followed by replica molding. Adhesion to rough substrates is emulated experimentally by a micropatterned model substrate with varying channel widths. Pull-off stresses are found to be about 200 kPa, i.e., twice atmospheric pressure. Evaluation of force–displacement curves together with in situ observations reveal the adhesion mechanism, which involves adaptation to surface roughness and an elastic force induced by the collapse of the cavity that holds sealed contact with the substrate during retraction. This new microarchitecture may pave the way for next generation microstructures applicable to real, rough surfaces under wet conditions.     

Method for the Optimization of Kinematic and Dynamic Properties of Parallel Kinematic Machines

The following paper introduces an approach, which allows the consideration of the kinematic as well as the dynamic properties of parallel kinematic machines. Based on the results of a preceding kinematic optimization, a FEM-model with arbitrary input parameters is designed. The full kinematic functionality of struts and joints used is ensured. By coupling the FEM-model to the GNU Octave numerical program system, a variety of movements including machining forces can be simulated. A Broyden-Fletcher-Goldfarb-Shanno optimization algorithm, using GNU Octave, was written and coupled to the FEM-system. Now, this algorithm is able to influence the model's arbitrary input parameters during the optimization process. Thus, the model is optimized automatically for a certain machining process and/or dynamic behavior. This procedure is demonstrated using the example of a delta robot structure originally designed by Raymond Clavel [7].     

Monitoring concept for structural integration of PZT-fiber arrays in metal sheets: a numerical and experimental study

ABSTRACT

The technique joining by forming allows the structural integration of piezoceramic fibers into locally microstructured metal sheets without any elastic interlayers. A high-volume production of the joining partners causes in statistical deviations from the nominal dimensions. A numerical simulation on geometric process sensitivity shows that the deviations have a high significant influence on the resulting fiber stresses after the joining by forming operation and demonstrate the necessity of a monitoring concept. On this basis, the electromechanical behavior of piezoceramic array transducers is investigated experimentally before, during and after the joining process. The piezoceramic array transducer consists of an arrangement of five electrical interconnected piezoceramic fibers. The findings show that the impedance spectrum depends on the fiber stresses and can be used for in-process monitoring during the joining process. Based on the impedance values the preload state of the interconnected piezoceramic fibers can be specifically controlled and a fiber overload.     

Fast patterning of poly(methyl methacrylate) by a novel soft molding approach and its application to the fabrication of silver structures

A novel single-step approach for the fabrication of poly(methyl methacrylate) structures by soft molding of a 5 wt% solution in acetone is reported. The use of a low weight solution and of a solvent with high volatility ensures a very fast patterning, down to 10 s. In addition, the process is extremely simple and cost-effective, since just one elastomeric mold is needed, and areas as large as 1 cm² were patterned uniformly and defect-free. The process was applied to the fabrication of silver structures by silver deposition via electroless plating or evaporation followed by poly(methyl methacrylate) removal. Structures of various shapes and sizes, with dimensions in the micrometer and submicrometer range were successfully fabricated, showing the versatility of the process. This silver patterning process is particularly well suited for applications in microelectronics and optoelectronics, such as the fabrication of transparent electrodes for solar cells and displays, manufacturing of metal etching masks and wiring of printed circuits.     

采用特殊加工助剂改善绿色轮胎胎面胶性能

混炼白炭黑补强的S－SBR／BR轿车轮胎胎面胶料时,采用特殊的混炼程序可以获得最佳硅烷偶联的效果,在此混炼程序中,一段混炼仅加入生胶、填料、硅烷和油,二段混炼添加氧化锌、硬脂酸、防老剂和蜡,采用这种程序虽然可以获得最佳硅烷偶联效果,但可能会引起填料分散差和硅烷降解,而且还有添加的低熔点材料的润滑效应引起返炼初始胶料包辊性差的问题。分别采用常规混炼程序和特殊混程序制备了胶料,在一段混炼中分别添加和不添加特殊加工助剂,采用特殊程序混炼的胶料,在二段混炼中分别添加和不添加表面活性剂类加工助剂。一段混炼加的加工助剂是专为不影响硅烷偶联效果而开发的。由于添加剂的润滑作用使返炼时混炼效果差,可以通过用表面活性剂类加工助剂代替硬脂酸加以改善。对未硫化胶的粘弹动态试验可以使混炼质量各个方面的单独量化成为可能,试验数据清楚地表明,在一段和二段混炼中添加的加工助剂对于白炭黑分散和硅烷偶联有积极的作用,而且它们的作用是叠加的。物理性能数据还显示出这些加工助剂的优点,对硫化样品进行的粘弹动态试验可用于预测轮胎使用性能,而且也再次证明了使用这些加工助剂的优越性。     

Computing self-organisation: environmentally sensitive growth modelling

The self-organisation processes underlying the growth of living organisms can provide important lessons for architects. Natural systems display higher-level integration and functionality evolving from a dynamic feedback relation with a specific host environment. Biologists, biomimetic engineers and computer scientists have begun to tackle research in this field and there is much to learn from their work. Here, Michael Hensel examines the work undertaken by Professor Przemyslaw Prusinkiewicz and his collaborators at the Department of Computer Science at the University of Calgary in Alberta, Canada,1 outlining its potential application for architectural design. Copyright © 2006 John Wiley & Sons, Ltd.     

A review on emulsification via microfluidic processes

Emulsion is a disperse system with two immiscible liquids, which demonstrates wide applications in diverse industries. Emulsification technology has advanced well with the development of microfluidic process. Compared to conventional methods, the microfluidics-based process can produce controllable droplet size and distribution. The droplet formation or breakup is the result of combined effects resulting from interfacial tension, viscous, and inertial forces as well as the forces generated due to hydrodynamic pressure and external stimuli. In the current study, typical microfluidic systems, including microchannel array, T-shape, flow-focusing, co-flowing, and membrane systems, are reviewed and the corresponding mechanisms, flow regimes, and main parameters are compared and summarized.     

16th International Drying Symposium (IDS2008)

This study introduces sensor psychrometrics, as opposed to the physically constrained static gravimetric experimentation, for the characterisation of cobed maize drying. Simultaneous spreadsheet integration and Solver analytics were used to interpret the digital drying curve from sensor-sampled psychrometric data. The results were validated gravimetrically at dryer settings of 37, 43, and 53°C. The ear drying curves were reproduced with a goodness-of-fit consistency of 0.997–0.999 across the different calibration settings. The new methodology, presented along with its uncertainty, exploits advances in computing and instrumentation to digitize empirical drying, moving experimentation beyond the rigid confines of the lab to the desktop.