Efficiently solving quantified bit-vector formulas

In recent years, bit-precise reasoning has gained importance in hardware and software verification. Of renewed interest is the use of symbolic reasoning for synthesising loop invariants, ranking functions, or whole program fragments and hardware circuits. Solvers for the quantifier-free fragment of bit-vector logic exist and often rely on SAT solvers for efficiency. However, many techniques require quantifiers in bit-vector formulas to avoid an exponential blow-up during construction. Solvers for quantified formulas usually flatten the input to obtain a quantified Boolean formula, losing much of the word-level information in the formula. We present a new approach based on a set of effective word-level simplifications that are traditionally employed in automated theorem proving, heuristic quantifier instantiation methods used in SMT solvers, and model finding techniques based on skeletons/templates. Experimental results on two different types of benchmarks indicate that our method outperforms the traditional flattening approach by multiple orders of magnitude of runtime.     

The effect of copolymer composition on the surface properties of perfluoroalkylethyl acrylates

The surface properties of two perfluoroalkylethyl acrylic copolymers—aqueous, Zonyl^®329 and solvent‐based, Zonyl^®225—were studied. Zonyl^®329 is a water‐based dispersion and Zonyl^®225 a solvent‐based copolymer solution; both polymers have the same perfluoroalkyethyl side chains [F(CF₂)_nCH₂CH₂? ] but have different comonomer compositions. Thin films, prepared by dip coating onto mica and quartz, with and without annealing, were characterized by contact angle and by X‐ray photoelectron spectroscopy (XPS). The contact angle measurements showed little variation with polymer and with substrate, consistent with the supposition that the perfluoroalkylethyl chains aggregate on the surface and thus dominate surface properties, irrespective of the composition of the rest of the polymer. XPS revealed only small variations in surface chemistry for studied films. Annealed films showed improved segregation for solvent‐based Zonyl^®225, which has both hydrocarbon alkyl and perfluoroalkylethyl side chains; the presence of hydrocarbon alkyl chains enables the perfluoroalkylethyl chains to reorganize after annealing. Depending on the external conditions, this thermal treatment can enable more perfluoroalkylethyl chains to reach the film surface (solid/air interface), leading to a reduction in the dispersive‐dominant surface and enhancement in perfluoroalkylethyl segregation. This suggested that perfluoroalkylethyl side chains dominate the surface properties, which are thus not dependent on substrate, backbone composition, or formulation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Natural ageing of tri-layer polyethylene film: Evolution of properties and lifetime in North Africa region

The effects of natural ageing in the north Algeria of tri-layer films lay down hot greenhouse made of low-density polyethylene are presented in this work. Ageing was monitored by observing the changes of physical, mechanical and structural effects on the various greenhouse faces. It has been shown that the structural change occur on the outside face of the films, while the inside faces are protected by the dye. The study shows that the measured parameters are directly related to the criteria of evaluation of the greenhouse effectiveness. The lifetime of these films under natural conditions in north Algerian was estimated to be 10 months.     

A comparison of viscoplastic intermediate approaches for deformation texture evolution in face-centered cubic polycrystals

We present a comparison between two intermediate viscoplastic approaches: the self-consistent approach and the ?-model for the texture development in face-centered cubic polycrystals. In these models, the interactions between a grain and its surroundings are taken into account in different ways. We performed different tests to simulate axisymmetric tension/compression and plane-strain compression for different values of the parameter ? and for different formulations of the self-consistent model. Predicted results (stress–strain, texture, slip activity, local stress and strain rate deviations) are compared and conclusions are drawn. The ?-model allows for fairly good predictions, in comparison to existing experimental results, while it is much easier to formulate and to implement numerically. The ?-model is also able to predict texture transition from the copper type to the brass type. Using the same boundary conditions and spherical grains, the self-consistent model is unable to predict this texture transition and only a copper type texture is obtained.     

Microwave-assisted versus conventional synthesis of zeolite A from metakaolinite

This is a comparative study of the synthesis of zeolite A from metakaolinite using both conventional and microwave-assisted heating. The effects of reaction conditions on the rate of formation, crystallinity and actual % yield of zeolite A were investigated. Reaction parameters such as different NaOH molarities (1.0–5.0 M), temperatures (70 and 80 °C), durations (1–8 h) as well as the effect of seeding percentage (1–4%) were tested. The rate of zeolite A formation was found to increase by 2–3 times in microwave treated samples with a notable enhancement in the product crystallinity and % yield whether seeded or un-seeded.     

Optimized asset planning for minimizing latency in wireless sensor networks

Wireless Sensor Networks (WSNs) has been attracting lots of interest in recent years. In such networks sensors data are collected over multi-hop routes at one or multiple base-stations (gateway nodes) for processing. In many WSN applications such as disaster management and combat field surveillance, rapid response to detected events is necessary and thus data latency should be minimal. Given the sensor’s energy and radio range constraints, direct communication with the gateway is inefficient and often infeasible for most deployed sensors. An intuitive approach to limit data latency is to increase the population of gateways and place them in the vicinity of sensors. However, gateway nodes are typically costly and thus it is desired to limit their count. Therefore, there is a need to balance between such conflicting requirements. In this paper, we pursue an integrated approach to asset planning in WSNs so that the data latency is minimized. The goal is to determine the least number of gateways and identify where to place them in the network in order to achieve a certain delay bound on data delivery. We formulate an optimization model for the asset planning problem and present effective algorithms for solving it. The proposed solution scheme employs contemporary search heuristics such as k-means and genetic algorithms. Validation results confirm the effectiveness of our approach in achieving the desired design goals.