A GRASP/VND heuristic for the phylogeny problem using a new neighborhood structure

A phylogeny is a tree that relates taxonomic units, based on their similarity over a set of characters. The phylogeny problem consists in finding a phylogeny with the minimum number of evolutionary steps. We propose a new neighborhood structure for the phylogeny problem. A greedy randomized adaptive search procedure heuristic based on this neighborhood structure and using variable neighborhood descent for local search is described. Computational results on randomly generated and benchmark instances are reported, showing that the new heuristic is quite robust and outperforms the other algorithms in the literature in terms of solution quality and time‐to‐target value.     

Discontinuous Space-Vector Modulation for Three-Level PWM Rectifiers

This paper presents the implementation and experimental verification of two discontinuous pulsewidth modulation (DPWM) methods for three-phase, three-level rectifiers. DPWM's features, such as improved waveform quality, lower switching losses, reduced ac-side passive component size, are investigated and compared to the conventional continuous pulsewidth modulation (CPWM). These features allow higher power density and/or efficiency to be achieved and are important targets for the next generation of power rectifiers. The implementation of the two DPWM strategies is explained by means of space-vectors representation and modulation functions. A detailed analysis of both ac-side and dc-side current waveforms is presented, and there is excellent agreement between the analytical, simulated and experimental results for the mains current ripple amplitude and output center-point current over the practical modulation range. Finally, the control of the center-point voltage is discussed.     

Video coding scheme using DCT-pyramid vector quantization

A new and effective video coding scheme for contribution quality is proposed. The CMTT/2, a joint committee of CCIR and CCITT, has proposed a video coding scheme (already approved at European level by ETS) working at 34-45 Mbit/s. Basically this proposal includes a DCT transform for spatial correlation removal and motion compensation for temporal correlation removal. The individual transform coefficients are then scalar quantized with a non uniform bit assignment. Starting from the CMTT/2 proposal, the study presents a new video coding scheme designed using a vector quantizer solution instead of the scalar one. Specifically, the pyramid vector quantization (PVQ) has been chosen as the vector quantization method as it is able to reduce the DCT coefficients Laplacian distribution. Simulation results show that the proposed video coding scheme gives the same contribution quality at 22 Mbit/s as the one obtained with the CMTT/2 proposal at 45 Mbit/s.     

A parallel evolutionary algorithm for the vehicle routing problem with heterogeneous fleet

Nowadays genetic algorithms stand as a trend to solve NP-complete and NP-hard problems. In this paper, we present a new hybrid metaheuristic which uses parallel genetic algorithms and scatter search coupled with a decomposition-into-petals procedure for solving a class of vehicle routing and scheduling problems. The parallel genetic algorithm presented is based on the island model and its performance is evaluated for a heterogeneous fleet problem, which is considered a problem much harder to solve than the homogeneous vehicle routing problem.     

A hybrid genetic algorithm for the phylogeny problem using path-relinking as a progressive crossover strategy

A phylogenetic tree relates taxonomic units using their similarities over a set of characteristics. Given a set of taxonomic units and their characteristics, the phylogeny problem under the parsimony criterion consists in finding a phylogenetic tree with a minimum number of evolutionary steps. We developed a hybrid genetic algorithm for the problem of building a phylogenetic tree minimizing parsimony. The algorithm combines local search with a crossover strategy based on path-relinking, an intensification technique originally used in the context of other metaheuristics such as scatter search and GRASP. Computational experiments on benchmark and randomly generated instances show that the proposed algorithm is very robust and outperforms other heuristics in terms of solution quality and running times.     

Finite-element analysis of the frequency response of a metallic cantilever coupled with piezoelectric transducer

This paper is devoted to modeling the dynamic response of an electromechanical system consisting of a piezoelectric transducer glued on part of the upper surface of a metallic cantilever. The piezo works both as vibration sensor and as actuator, and the system is the basis of many vibration-control devices of current interest. A three-dimensional (3D) finite-element method (FEM) model that reproduces the physical system is proposed, and its advantages with respect to an analytical approach and to one-dimensional (1D) and two-dimensional (2D) FEM models are discussed. In sensor mode, the frequency response in terms of the voltage at the electrodes is drawn; while in actuator mode, the frequency response of acceleration and displacement at the free end of the cantilever is calculated. The 3D model has been verified through the comparison with the results from the experiment carried out at the University of L'Aquila, Italy. Furthermore, experimental inaccessible quantities such as stresses at the piezo-cantilever interface are computed in both modes as a preliminary step in the study of delamination phenomena and their impact on the performance of the system in vibration-control applications.     

Structural considerations for a Tokamak fusion reactor

Several preliminary structural analyses are presented which validate a design for the experimental power reactor. Three components are singled out as requiring special attention: the magnetic coils, the blanket support structure, and the blanket modules. Repeated loading of a coil structure by magnetic forces should produce only linear elastic deformation. An analysis for minimum preload necessary to ensure this is presented. Using axisymmetric thin shell theory, a stress analysis of the blanket support structure is described. To account for the welded ring structure, a perforated plate analysis is used to compute the structural displacements and the ligament stresses. Temperature distributions and thermal stresses in the blanket module are determined using both finite element and analytical analysis. The stresses are all acceptable, including the effects produced by creep and fatigue. Thermal stress in the liner produced by a nonlinear temperature gradient is also shown to be acceptable.     

Optimisation of biological and physical parameters for lycopene supercritical CO2 extraction from ordinary and high‐pigment tomato cultivars

BACKGROUND: Lycopene is used for several industrial applications. Supercritical CO₂ (SC‐CO₂) extraction from red‐ripe tomato fruits is an excellent technique to replace the use of harmful solvents. In this study, starting from red‐ripe tomatoes of ordinary and high‐lycopene cultivars, the effect of different agronomical and technical aspects on lycopene content, stability and yield was evaluated throughout the production process from fresh tomatoes to the final SC‐CO₂‐extracted oleoresin containing lycopene. RESULTS: Red‐ripe tomato cultivars differed in their lycopene content. Irrigation excess or deficit caused an increase in the amount of lycopene in the fruits. Fresh tomatoes were processed into a lyophilised matrix suitable for SC‐CO₂ extraction, which could be stored for more than 6 months at ? 20 °C without lycopene loss. Under the optimal extraction conditions, efficiencies of up to 80% were achieved, but the recovery of lycopene in the extracted oleoresin was very low (～24%). Co‐extraction of the tomato matrix mixed with a lipid co‐matrix allowed the recovery of ～90% of lycopene in the oleoresin. Using the high‐lycopene cultivars, the yield of total extracted lycopene increased by ～60% with respect to the ordinary cultivars. Lipids and other biologically active molecules were present in the oleoresin. CONCLUSION: A method for extracting, from a tomato matrix, a natural and solvent‐free oleoresin containing lycopene dissolved in a highly unsaturated vegetable oil has been described. The oleoresin represents an excellent product for testing on cancer and cardiovascular disease prevention. Copyright © 2010 Society of Chemical Industry     

Detection of rifampin resistance by single-strand conformation polymorphism analysis of cerebrospinal fluid of patients with tuberculosis of the central nervous system

Mutations in a 69-bp region of the rpoB gene of Mycobacterium tuberculosis are associated with rifampin resistance (Rif[r]). These have been detected with mycobacterial DNA extracted from bacterial suspensions or respiratory specimens that were acid-fast smear positive. We experimented with a strategy for the rapid detection of Rif(r) in cerebrospinal fluid (CSF) samples. The strategy involves the amplification of the 69-bp region of rpoB by means of PCR and the identification of nucleotide mutations by single-strand conformation polymorphism (SSCP) analysis of the amplification products. Sixty-five CSF specimens collected from 29 patients (19 patients were coinfected with human immunodeficiency virus) with culture or autopsy-confirmed (22 patients) or highly probable (7 patients) tuberculosis of the central nervous system (CNS-TB) were processed. Amplified products suitable for evaluation by SSCP analysis were obtained from 37 CSF specimens from 25 subjects (86.2%). PCR-SSCP of CSF correctly identified the rifampin susceptibility phenotype of isolates from all 17 patients for whom the results of susceptibility tests carried out with strains cultured from CSF or respiratory samples were available. Moreover, this assay revealed the rifampin susceptibility genotype of isolates from the eight patients (three patients with culture-confirmed CNS-TB and five patients in whom CNS-TB was highly probable) for whom no susceptibility test results were available; the PCR-SSCP data obtained for these patients were concordant with the outcome after a standard antituberculosis treatment. The evolution of a mutation in the rpoB gene was documented in a patient during the course of treatment. PCR-SSCP analysis of CSF seems to be an efficacious method of predicting Rif(r) and would reduce the time required for susceptibility testing from approximately 4 to 8 weeks to a few days.     

High-Performance Planar Isolated Current Sensor for Power Electronics Applications

A planar current sensor, comprised of a magnetic current transformer and a hall-effect element, is presented. The sensor has a broad frequency bandwidth from dc up to 30 MHz, a high current rating (40-A dc), superior linearity, high EMI immunity, small size, robustness, and low realization cost. The main design formulations are given analytically; simulations and finite-element results are presented for verification. Experimental results of current step response and dv/dt immunity are included.