Showing papers by "Instituto Politécnico Nacional published in 2001"
30 Sep 2001
TL;DR: In this article, a step-by-step procedure for designing the LCL filter of a front-end three-phase active rectifier is proposed to reduce the switching frequency ripple at a reasonable cost, while at the same time achieving a high-performance front end rectifier.
Abstract: This paper proposes a step-by-step procedure for designing the LCL filter of a front-end three-phase active rectifier. The primary goal is to reduce the switching frequency ripple at a reasonable cost, while at the same time achieving a high-performance front-end rectifier (as characterized by a rapid dynamic response and good stability margin). An example LCL filter design is reported and a filter has been built and tested using the values obtained from this design. The experimental results demonstrate the performance of the design procedure both for the LCL filter and for the rectifier controller. The system is stable and the grid current harmonic content is low both in the lowand high-frequency ranges. Moreover, the good agreement that was obtained between simulation and experimental results validates the proposed approach. Hence, the design procedure and the simulation model provide a powerful tool to design an LCL-filter-based active rectifier while avoiding trial-and-error procedures that can result in having to build several filter prototypes.
2,147 citations
16 Jul 2001
TL;DR: TP Westwood is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks and is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed.
Abstract: TCP Westwood (TCPW) is a sender-side modification of the TCP congestion window algorithm that improves upon the performance of TCP Reno in wired as well as wireless networks. The improvement is most significant in wireless networks with lossy links, since TCP Westwood relies on end-to-end bandwidth estimation to discriminate the cause of packet loss (congestion or wireless channel effect) which is a major problem in TCP Reno. An important distinguishing feature of TCP Westwood with respect to previous wireless TCP “extensions” is that it does not require inspection and/or interception of TCP packets at intermediate (proxy) nodes. Rather, it fully complies with the end-to-end TCP design principle. The key innovative idea is to continuously measure at the TCP source the rate of the connection by monitoring the rate of returning ACKs. The estimate is then used to compute congestion window and slow start threshold after a congestion episode, that is, after three duplicate acknowledgments or after a timeout. The rationale of this strategy is simple: in contrast with TCP Reno, which “blindly” halves the congestion window after three duplicate ACKs, TCP Westwood attempts to select a slow start threshold and a congestion window which are consistent with the effective bandwidth used at the time congestion is experienced. We call this mechanism faster recovery. The proposed mechanism is particularly effective over wireless links where sporadic losses due to radio channel problems are often misinterpreted as a symptom of congestion by current TCP schemes and thus lead to an unnecessary window reduction. Experimental studies reveal improvements in throughput performance, as well as in fairness. In addition, friendliness with TCP Reno was observed in a set of experiments showing that TCP Reno connections are not starved by TCPW connections. Most importantly, TCPW is extremely effective in mixed wired and wireless networks where throughput improvements of up to 550% are observed. Finally, TCPW performs almost as well as localized link layer approaches such as the popular Snoop scheme, without incurring the O/H of a specialized link layer protocol.
993 citations
TL;DR: In this article, an ultrafast spectroscopic study using an optical excitation of a conjugated polymer by sub-10-fs pulses is reported. And the authors were able to time resolve for the first time the kinetics of this charge transfer process with a forward transfer time of around τ ct ∼45 fs.
589 citations
TL;DR: In this paper, a comprehensive study of the transport dynamics of electrons in the ternary compounds, Al/sub x/Ga/sub 1-x/N and In/sub ng/g/ng/s/n g/n/g n/g 1.x/n, is presented, which includes all of the major scattering mechanisms.
Abstract: We present a comprehensive study of the transport dynamics of electrons in the ternary compounds, Al/sub x/Ga/sub 1-x/N and In/sub x/Ga/sub 1-x/N. Calculations are made using a nonparabolic effective mass energy band model. Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab initio band models. The effects of alloy scattering on the electron transport physics are examined. The steady state velocity field curves and low field mobilities are calculated for representative compositions of these alloys at different temperatures and ionized impurity concentrations. A field dependent mobility model is provided for both ternary compounds AlGaN and InGaN. The parameters for the low and high field mobility models for these ternary compounds are extracted and presented. The mobility models can be employed in simulations of devices that incorporate the ternary III-nitrides.
421 citations
TL;DR: In this article, a transient study on the NOx storage-reduction properties of a PtBaO/γ-Al2O3 catalyst is performed by using a synthetic exhaust gas containing oxygen and nitrogen oxides (storage phase) and a reducing gas containing hydrogen (reduction phase).
347 citations
TL;DR: The complex mechanical interaction between blood flow and wall dynamics in a three dimensional custom model of a patient AAA was studied by means of computational coupled fluid-structure interaction analysis, providing a quantitative local evaluation of the stresses due to local structural and fluid dynamic conditions.
346 citations
TL;DR: In this article, an ultrasonic sensor that is able to measure the distance from the ground of selected points of a motor vehicle is described, which is based on the measurement of the time of flight of a ultrasonic pulse which is reflected by the ground.
Abstract: This paper describes an ultrasonic sensor that is able to measure the distance from the ground of selected points of a motor vehicle. The sensor is based on the measurement of the time of flight of an ultrasonic pulse, which is reflected by the ground. A constrained optimization technique is employed to obtain reflected pulses that are easily detectable by means of a threshold comparator. Such a technique, which takes the frequency response of the ultrasonic transducers into account, allows a sub-wavelength detection to be obtained. Experimental tests, performed with a 40 kHz piezoelectric-transducer based sensor, showed a standard uncertainty of 1 mm at rest or at low speeds; the sensor still works at speeds of up to 30 m/s, although at higher uncertainty. The sensor is composed of only low cost components, thus being apt for first car equipment in many cases, and is able to self-adapt to different conditions in order to give the best results.
298 citations
TL;DR: A critical review of the capacity of arsenicals to modulate the expression and/or accumulation of stress proteins is offered, finding that the stress response appears to be useful to monitor the sublethal toxicity resulting from a single exposure to arsenite.
282 citations
TL;DR: The main result is that a minimal confidence ellipsoid for the state, consistent with the measured output and the uncertainty description, may be recursively computed in polynomial time, using interior-point methods for convex optimization.
Abstract: This note presents a new approach to finite-horizon guaranteed state prediction for discrete-time systems affected by bounded noise and unknown-but-bounded parameter uncertainty. Our framework handles possibly nonlinear dependence of the state-space matrices on the uncertain parameters. The main result is that a minimal confidence ellipsoid for the state, consistent with the measured output and the uncertainty description, may be recursively computed in polynomial time, using interior-point methods for convex optimization. With n states, l uncertain parameters appearing linearly in the state-space matrices, with rank-one matrix coefficients, the worst-case complexity grows as O(l(n + l)/sup 3.5/) With unstructured uncertainty in all system matrices, the worst-case complexity reduces to O(n/sup 3.5/).
277 citations
TL;DR: Results indicate that the variability of the instantaneous median frequency is related to the repeatability of the biomechanics of the exercise, and a novel approach is proposed for calculating spectral parameters from the surface myoelectric signal during cyclic dynamic contractions.
Abstract: The time-dependent shift in the spectral content of the surface myoelectric signal to lower frequencies has proven to be a useful tool for assessing localized muscle fatigue. Unfortunately, the technique has been restricted to constant-force, isometric contractions because of limitations in the processing methods used to obtain spectral estimates. A novel approach is proposed for calculating spectral parameters from the surface myoelectric signal during cyclic dynamic contractions. The procedure was developed using Cohen class time-frequency transforms to define the instantaneous median and mean frequency during cyclic dynamic contractions. Changes in muscle length, force, and electrode position contribute to the nonstationarity of the surface myoelectric signal. These factors, unrelated to localized fatigue, can be constrained and isolated for cyclic dynamic contractions, where they are assumed to be constant for identical phases of each cycle. Estimation errors for the instantaneous median and mean frequency are calculated from synthesized signals. It is shown that the instantaneous median frequency is affected by an error slightly lower than that related to the instantaneous mean frequency. In addition, the authors present a sample application to surface myoelectric signals recorded from the first dorsal interosseous muscle during repetitive abduction/adduction of the index finger against resistance. Results indicate that the variability of the instantaneous median frequency is related to the repeatability of the biomechanics of the exercise.
272 citations
TL;DR: A new electromyogram generation and detection model, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties.
Abstract: The authors propose a new electromyogram generation and detection model. The volume conductor is described as a nonhomogeneous (layered) and anisotropic medium constituted by muscle, fat and skin tissues. The surface potential detected in space domain is obtained from the application of a two-dimensional spatial filter to the input current density source. The effects of electrode configuration, electrode size and inclination of the fibers with respect to the detection system are included in the transfer function of the filter. Computation of the signal in space domain is performed by applying the Radon transform; this permits to draw considerations about spectral dips and clear misunderstandings in previous theoretical derivations. The effects of generation and extinction of the action potentials at the fiber end plate and at the tendons are included by modeling the source current, without any approximation of its shape, as a function of space and time and by using again the Radon transform. The approach, based on the separation of the temporal and spatial properties of the muscle fiber action potential and of the volume conductor, includes the capacitive tissue properties.
TL;DR: The convergence and divergence regions for some algorithms are given, and the new algorithms are applied to solve the Stokes equations as well.
Abstract: Several SOR-like methods are proposed for solving augmented systems. These have many different applications in scientific computing, for example, constrained optimization and the finite element method for solving the Stokes equation. The convergence and the choice of optimal parameter for these algorithms are studied. The convergence and divergence regions for some algorithms are given, and the new algorithms are applied to solve the Stokes equations as well.
07 Mar 2001
TL;DR: The most commonly used evolutionary multiobjective optimization techniques will be described and criticized, including some of their applications, and Theory, test functions and metrics will be discussed.
Abstract: This tutorial will review some of the basic concepts related to evolutionary multiobjective optimization (i.e., the use of evolutionary algorithms to handle more than one objective function at a time). The most commonly used evolutionary multiobjective optimization techniques will be described and criticized, including some of their applications. Theory, test functions and metrics will be also discussed. Finally, we will provide some possible paths of future research in this area.
TL;DR: In this article, an isotropic damage model for concrete is presented, where the main features of the model are: limited number of constitutive parameters required; independent modelling of tension and compression behaviour by means of two damage variables and two separate activation criteria (bi-dissipative model); independent definition of tension/compression fracture energies; consistent modelling of the unilateral effect upon transition from tension to compression; and the effectiveness of fracture energy based regularization strategy.
TL;DR: A new algorithm is presented for computing the free distance d/sub free/ of parallel and serially concatenated codes with interleavers, the parameter that dominates the code performance at very high signal-to-noise ratios (SNRs).
Abstract: We present a new algorithm for computing the free distance d/sub free/ of parallel and serially concatenated codes with interleavers, the parameter that dominates the code performance at very high signal-to-noise ratios (SNRs). The knowledge of d/sub free/ allows one to analytically estimate the error floor, which may prevent the use of concatenated codes in applications requiring very low error rates. The algorithm is based on the new notion of constrained subcodes, and permits the computation of large distances for large interleavers without a constraint on the input sequence weight (e.g., up to d/sub free/=40 for a rate-1/3 turbo code with interleaver length N=3568). Applications to practical cases of relevant interest, i.e., (1) the new Consultative Committee for Space Data Systems (CCSDS) standard for deep-space telemetry and (2) the new UMTS/3GPP standard for third-generation personal communications, are presented for the first time. Other related aspects, like a study on the free distance distribution of turbo codes with small/medium interleaver length, and a comparison between parallel and serial concatenation behavior, are also discussed.
TL;DR: In this paper, an extensive cross section database for electron-impact inelastic processes of vibrationally excited molecules of hydrogen and its isotopes is presented, including electronic excitation, direct ionization, excitation-radiative decay vibrational excitation and dissociation and dissociative electron attachment.
Proceedings Article•
07 Jul 2001TL;DR: It is shown how this relatively simple algorithm coupled with an external file and a diversity approach based on geographical distribution can generate efficiently the Pareto fronts of several difficult test functions.
Abstract: In this paper, we propose a micro genetic algorithm with three forms of elitism for multiobjective optimization. We show how this relatively simple algorithm coupled with an external file and a diversity approach based on geographical distribution can generate efficiently the Pareto fronts of several difficult test functions (both constrained and unconstrained). A metric based on the average distance to the Pareto optimal set is used to compare our results against two evolutionary multiobjective optimization techniques recently proposed in the literature.
TL;DR: In this paper, the authors proposed a new ''pseudo-logarithmic'' rate of damage, which has the advantage of exhibiting a simple and meaningful conjugate force with very convenient properties.
TL;DR: In this paper, a catalytic amount of Mn(II)-Co(II) or Mn(III)-Cu(III) nitrates in combination with TEMPO allows the selective oxidation of primary and secondary alcohols to aldehydes and ketones by oxygen under very mild conditions.
TL;DR: In this paper, a procedure for the numerical evaluation of the mechanical properties of woven fabric laminates is presented, where three-dimensional finite element models are used in two steps to predict both the stiffness and the strength of woven fabrics.
Abstract: The paper presents a procedure for the numerical evaluation of the mechanical properties of woven fabric laminates. Woven fabrics usually present orthogonal interlaced yarns (warp and weft) and distribution of the fibers in the yarns and of the yarns in the composite may be considered regular. This allows us to apply the homogenization theory for periodic media both to the yarn and to the fabric. Three-dimensional finite element models are used in two steps to predict both the stiffness and the strength of woven fabric laminates. The model includes all the important parameters that influence the mechanical behavior: the lamina thickness, the yarn orientation, the fiber volume fraction and the mechanical characteristics of the components. The capabilities of the numerical model were verified studying the elastic behavior of a woven fabric laminate available in the literature and the ultimate strength of a glass fabric laminate experimentally investigated. The procedure, that can be implemented into commercial finite element codes, appears to be an efficient tool for the design of textile composites.
TL;DR: Application of both tissue culture and genetic transformation techniques have led to the development of chili pepper plants more resistant to at least one type of virus.
Abstract: Chili pepper is an important horticultural crop that can surely benefit from plant biotechnology. However, although it is a Solanaceous member, developments in plant cell, tissue, and organ culture, as well as on plant genetic transformation, have lagged far behind those achieved for other members of the same family, such as tobacco (Nicotiana tabacum), tomato (Lycopersicon esculentum), and potato (Solanum tuberosum), species frequently used as model systems because of their facility to regenerate organs and eventually whole plants in vitro, and also for their ability to be genetically engineered by the currently available transformation methods. Capsicum members have been shown to be recalcitrant to differentiation and plant regeneration under in vitro conditions, which in turn makes it very difficult or inefficient to apply recombinant DNA technologies via genetic transformation aimed at genetic improvement against pests and diseases. Some approaches, however, have made possible the regeneration of chili pepper plants from in vitro-cultured cells, tissues, and organs through organogenesis or embryogenesis. Anther culture has been successfully applied to obtain haploid and doubledhaploid plants. Organogenic systems have been used for in vitro micropropagation as well as for genetic transformation. Application of both tissue culture and genetic transformation techniques have led to the development of chili pepper plants more resistant to at least one type of virus. Cell and tissue cultures have been applied successfully to the selection of variant cells exhibiting increased resistance to abiotic stresses, but no plants exhibiting the selected traits have been regenerated. Production of capsaicinoids, the hot principle of chili pepper fruits, by cells and callus tissues has been another area of intense research. The advances, limitations, and applications of chili pepper biotechnology are discussed.
TL;DR: A new methodology to design pasteurization processes for high acidic fruit products is presented, using detection and identification methods for A. acidoterrestris and data regarding heat resistance of spores and growth in fruits were collected.
Abstract: Alicyclobacillus acidoterrestris is a thermoacidophilic, non-pathogenic and sporeforming bacterium which has been found in commercial pasteurized fruit juices in the past. Only few and recent studies were available in the literature, since only in 1984 Cerny et al. [Cerny, G., Hennlich, W., & Poralla, K. (1984). Fruchtsaftverderb durch bacillen: isolierung und charakterisierung des verderbserregers. Z. Lebensmitt. Unters. Forsch. 179, 224–227] reported a spoiled aseptically packaged apple juice with A. acidoterrestris and in 1987 Deinhard et al. [Deinhard, G., Blanz, P., Poralla, K., & Altan, E. (1987). Bacillus acidoterrestris sp. nov., a new thermotolerant acidophile isolated from different soils. Systematic and Applied Microbiology, 10, 47–53] named first this species. Detection and identification methods for A. acidoterrestris were reviewed and data regarding heat resistance of spores and growth in fruits were collected. Finally, a new methodology to design pasteurization processes for high acidic fruit products is presented.
TL;DR: In this paper, the authors investigated the role of thermal, intrinsic and extrinsic stresses in the formation of physical vapour deposition (PVD) films and found that tensile intrinsic stresses are usually observed in not fully dense films deposited by thermal evaporation from non-energetic particles.
TL;DR: The crystalline properties of zirconia synthesized by the precipitation and sol-gel methods were comparatively studied in this article, where samples were characterized with thermoanalysis and X-ray powder diffraction techniques.
TL;DR: The striking spatial and temporal differences found in the structure, dynamics, and life history traits of the clonal cactus, Opuntia rastrera, are aptly summarized by the periodic analyses.
Abstract: Spatial and temporal variability influence the structure and dynamics of perennial plant populations. In order to investigate the consequences of this environmental heterogeneity on population and life history traits of a perennial plant with a complex life history, four size-classified population matrix models were employed (i.e., annual, mean, periodic, and stochastic simulations) in a clonal cactus, Opuntia rastrera, in the Chihuahuan Desert, Mexico. This species was studied over a seven-year period in two contrasting, neighboring habitats (nopalera and grassland). The specific aims were: (a) to assess the effect of annual environmental variability on the long-term dynamics of both populations; and (b) to estimate the relative contribution of sexual reproduction and clonal propagation to the populations' rates of increase. Projections from each model provided complementary information on population dynamics and life history in the two habitats. The finite rate of population growth (A) varied among matrix projections. Mean, periodic, and stochastic projections yielded A > 1 for nopalera and A 1 for grassland. The relative contributions of size classes and demographic processes to changes in A differed widely between years and habitats for annual matrices. In contrast, elasticities of periodic matrices showed a stable habitat-dependent pattern. The proportional change in A produced by sexual recruit- ment and clonal propagation showed wide spatial variation in which the most distinctive difference between habitats was the predominance of clonal recruitment at the nopalera and seedling recruitment at the grassland. Elasticities also showed temporal variation where- by clonal propagation decreased as precipitation increased, while sexual reproduction and growth tended to increase with precipitation. The striking spatial and temporal differences found in the structure, dynamics, and life history traits of 0. rastrera are aptly summarized by the periodic analyses. These differences reflect both the varying influence of the selective pressures operating on this species and the ways in which demographic plasticity deals with them.
04 Apr 2001
TL;DR: The paper explores the possibility of generating a multi-organisational software cost estimation model by analysing the software cost data collected by the International Software Benchmarking Standards Group, based on a statistical technique which has been proposed as alternative to the standard regression approach.
Abstract: The paper explores the possibility of generating a multi-organisational software cost estimation model by analysing the software cost data collected by the International Software Benchmarking Standards Group. This database contains data about recently developed projects characterised mostly by attributes of categorical nature such as the project business area, organisation type, application domain and usage of certain tools or methods. The generation of the model is based on a statistical technique which has been proposed as alternative to the standard regression approach, namely the categorical regression or regression with optimal scaling. This technique starts with the quantification of the qualitative attributes (expressed either on nominal or ordinal scale), that appear frequently within such data, and proceeds by using the obtained scores as independent variables of a regression model. The generated model is validated by measuring certain indicators of accuracy.
TL;DR: The generalized pseudo-Rankine model as discussed by the authors is a generalization of the second-order tensors model for anisotropic tensile damage, and it is shown that the loading surface in pseudo-log space may assume shapes which vary gradually between a πplane and a Rankine-type criterion.
TL;DR: The effects of quantization on the performance of the iterative decoding algorithm of concatenated codes with interleavers is discussed, and it is shown that a suitable rescaling of the extrinsic information yields almost ideal performance with the same number of bits representing both log-likelihood ratios and extrinsics information at any decoder stage.
Abstract: We discuss the effects of quantization on the performance of the iterative decoding algorithm of concatenated codes with interleavers. Quantization refers here to the log-likelihood ratios coming from the soft demodulator and to the extrinsic information passed from one stage of the decoder to the next. We discuss the cases of a single soft-input soft-output (SISO) module, in its additive log-likelihood version (L-SISO), performing sequentially all iterations (an implementation solution coping with medium-low data rate as compared with the hardware clock), and that of a pipelined structure in which a dedicated hardware is in charge of each SISO operation (an implementation suitable for high data rates). We give design rules in both cases, and show that a suitable rescaling of the extrinsic information yields almost ideal performance with the same number of bits (five) representing both log-likelihood ratios and extrinsic information at any decoder stage.
01 Jan 2001
TL;DR: In this article, the authors discuss the monomial algebras and its connections to combinatorics, graph theory, and polyhedral geometry, and illustrate the interplay between several areas of mathematics and the power of combinatorial commutative algebra techniques.
Abstract: Publisher Summary This chapter discusses the monomial algebras and its connections to combinatorics, graph theory, and polyhedral geometry. Some important notions from commutative algebra that have played a role in the development of the theory, such as Cohen-Macaulay ring, normal ring, Gorenstein ring, integral closure, Hilbert series, and local cohomology are introduced. The upper bound theorem for the number of faces of a simplicial sphere, a description of the integral closure of an edge subring, a generalized marriage theorem for a certain family of graphs, and a study of systems of binomials in the ideal of an affine toric variety are provided as applications. It illustrates the interplay between several areas of mathematics and the power of combinatorial commutative algebra techniques. There is a connection between monomial rings and monomial subrings due to the fact that the initial ideal of a toric ideal is a monomial ideal. This allows computing several invariants of projective varieties using algebraic systems such as CoCoA and Macaulay2. An important tool to study monomial subrings is Normaliz, which is effective in practice and can be used to find normalizations, Hilbert series, Ehrhart rings, and volumes of lattice polytopes.
TL;DR: In this paper, the authors analyzed the impact of plane fretting fatigue contact problems and derived new consequences for FF damage, showing that the surface damage parameters decrease, but the tensile stress concentration increases, suggesting that for cracks eventually initiated, the likelihood of self-arrest is higher than in the equivalent Hertzian case with same loads.