嵌入式数字课桌进入校园

在巴西,嵌入式数字课桌以其动态的交互式界面和海量信息传载,已经取代传统课桌遍布校园,并得到了广泛应用。     

Effect of solvent nature in casting-based carbon nanofiber/poly(methyl-methacrylate) nanocomposites

Eight different solvents, of different polarities, were used to prepare carbon nanofiber (CNF)/poly(methyl methacrylate nanocomposites by solvent casting. Selected solvents ranged from organic acetone to nonpolar toluene, passing through N-containing solvents. In addition, pristine and oxygen and nitrogen-functionalized CNFs were used. Two objectives were pursued: (1) the role of the solvent in the dispersion of the CNFs and (2) the benefit of the functionalization on the dispersion through the stability in the solvent and compatibility with the matrix. The dispersion analysis of the materials leads to the conclusion that solvents containing oxygen groups work better with the oxidized CNFs, similarly solvents containing nitrogen groups with the nitrogen-functionalized CNFs. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Design of pH Sensors in Long-Period Fiber Gratings Using Polymeric Nanocoatings

In this paper, two different pH sensors based on the deposition of nanometric scale polymeric films onto the surface of a long-period fiber grating (LPFG) have been studied and compared. An electrostatic self-assembled (ESA) method has been used to create sensitive films with an optimal overlay thickness. Two types of sensors have been designed: The first one is based on polyallylamine hydrochloride (PAH), polyacrylic acid (PAA), and the second one was done incorporating the pigment Prussian blue (PB) in the PAH/PAA matrix. A theoretical model of multilayer cylindrical waveguides based on coupled-mode theory has been used to predict the position of the attenuation bands as a function of the overlay thickness. Both sensors were tested and compared in terms of sensitivity and response time. A faster response was obtained with the introduction of PB particles in the polymeric matrix. Linear sensors in the pH range 4-7 were obtained, showing good repeatability and high sensitivity     

Fissure analysis in one-directional slabs with on-site concrete rib by continuous formwork

This article presents a detailed analysis of a common pathology in concrete one-directional slabs with on-site rib and prefabricated concrete hollow blocks. This pathology is causing complaints from the users and tenants of the buildings affected by it pressing charges against the construction companies.This pathology consists of very thin fissures marked on the claddings, and parallel to the slab ribs. The cracks usually begin to be detected a few days after the slab is in service, after partitions and floor paving are placed and they normally appear much quicker in dry and warm weather. These fissures occur in isolation and are distanced according to the width of the slab. In addition, although the cracking lines show an apparent fixed repetition, there does not seem to be a correlation between this modulation and the frame geometry/modulation.This work analyzes the causes for this pathology type proposing some solutions to avoid it.     

An improved piecewise outer-approximation algorithm for the global optimization of MINLP models involving concave and bilinear terms

In this paper a new version of the Outer Approximation for Global Optimization Algorithm by Bergamini et al. [Bergamini, M.L., Aguirre, P., & Grossmann, I.E. (2005a). Logic based outer approximation for global optimization of synthesis of process networks. Computers and Chemical Engineering 29, 1914] is proposed, in order to speed up the convergence in nonconvex MINLP models that involve bilinear and concave terms. Bounding problems are constructed replacing these nonconvex terms by piecewise linear underestimators. These problems, which correspond to mixed-integer linear programs, are solved to generate approximate solutions with improved objective value. When no further feasible solution can be found, this guarantees that the upper bound cannot be improved in the nonconvex problem, thus providing a termination criterion. The new algorithm is applied to five different synthesis problems in the areas of water networks, heat exchanger networks and distillation sequences. The results show a significant reduction in the computational cost compared with the previous version of the algorithm.     

Balancing responsiveness and economics in process supply chain design with multi‐echelon stochastic inventory

This article is concerned with the optimal design of multi‐echelon process supply chains (PSCs) under economic and responsive criteria with considerations of inventory management and demand uncertainty. The multi‐echelon inventory systems are modeled with the guaranteed service approach to handle the uncertain demands at each echelon. The maximum guaranteed service time of the last echelon of the PSC is proposed as a measure of a PSC's responsiveness. The problem is formulated as a bi‐criterion mixed‐integer nonlinear program (MINLP) with the objectives of minimizing the annualized cost (economic objective) and minimizing the maximum guaranteed service times of the markets (responsiveness objective). The model simultaneously predicts the optimal network structure, transportation amounts, and inventory levels under different specifications of the PSC responsiveness. An example on acetic acid supply chain is presented to illustrate the application of the proposed model and to comprehensively compare different measures of PSC responsiveness. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Cross-Entropy Optimization for Scaling Factors of a Fuzzy Controller: A See-and-Avoid Approach for Unmanned Aerial Systems

The Cross-Entropy (CE) is an efficient method for the estimation of rare-event probabilities and combinatorial optimization. This work presents a novel approach of the CE for optimization of a Soft-Computing controller. A Fuzzy controller was designed to command an unmanned aerial system (UAS) for avoiding collision task. The only sensor used to accomplish this task was a forward camera. The CE is used to reach a near-optimal controller by modifying the scaling factors of the controller inputs. The optimization was realized using the ROS-Gazebo simulation system. In order to evaluate the optimization a big amount of tests were carried out with a real quadcopter.     

Unit load and material-handling considerations in facility layout design

The effectiveness of a layout design cannot be completely measured if the operational characteristics of the manufacturing system are ignored. There is, therefore, a need to develop integrated manufacturing system design models. In this paper, the integration of unit load and material-handling considerations in a facility layout design is presented. This integration is based on a stochastic model that captures the operational characteristics of the manufacturing system and a nonlinear mixed-integer program that incorporates a department formation and facility layout. The non-linear mixed-integer program is solved using a simulated annealing-based algorithm. Analytical results for different manufacturing system scenarios are presented and compared with results obtained using alternative QAP-type formulations. Based on our experiments and the characteristics of the different formulations, key observations are presented and discussed.     

Polyphase FIR Networks Based on Frequency Sampling for Multirate DSP Applications

It is well known that the frequency sampling approach to the design of Finite Impulse Response digital filters allows recursive implementations which are computationally efficient when most of the frequency samples are integers, powers of 2 or null. The design and implementation of decimation (or interpolation) filters using this approach is studied herein. Firstly, a procedure is described which optimizes the tradeoff between the stopband energy and the deviation of the passband from the ideal filter. The search space is limited to a small number of samples (in the transition band), imposing the condition that the resulting filter have a large number of zeros in the stopband. Secondly, three different structures to implement the decimation (or interpolation) filter are proposed. The implementation complexity, i.e., the number of multiplications and additions per input sample, are derived for each structure. The results show that, without taking into account finite word-length effects, the most efficient implementation depends on the filter length to decimation (or interpolation) ratio.