Reasonable Amount (reasonable + amount)

Distribution by Scientific Domains


Selected Abstracts


Optimal integrated code generation for VLIW architectures

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 11 2006
Christoph Kessler
Abstract We present a dynamic programming method for optimal integrated code generation for basic blocks that minimizes execution time. It can be applied to single-issue pipelined processors, in-order-issue superscalar processors, VLIW architectures with a single homogeneous register set, and clustered VLIW architectures with multiple register sets. For the case of a single register set, our method simultaneously copes with instruction selection, instruction scheduling, and register allocation. For clustered VLIW architectures, we also integrate the optimal partitioning of instructions, allocation of registers for temporary variables, and scheduling of data transfer operations between clusters. Our method is implemented in the prototype of a retargetable code generation framework for digital signal processors (DSPs), called OPTIMIST. We present results for the processors ARM9E, TI C62x, and a single-cluster variant of C62x. Our results show that the method can produce optimal solutions for small and (in the case of a single register set) medium-sized problem instances with a reasonable amount of time and space. For larger problem instances, our method can be seamlessly changed into a heuristic. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Augmenting LZ-77 with authentication and integrity assurance capabilities

CONCURRENCY AND COMPUTATION: PRACTICE & EXPERIENCE, Issue 11 2004
Mikhail J. Atallah
Abstract The formidable dissemination capability allowed by the current network technology makes it increasingly important to devise new methods to ensure authenticity and integrity. Nowadays it is common practice to distribute documents in compressed form. In this paper, we propose a simple variation on the classic LZ-77 algorithm that allows one to hide, within the compressed document, enough information to warrant its authenticity and integrity. The design is based on the unpredictability of a certain class of pseudo-random number generators, in such a way that the hidden data cannot be retrieved in a reasonable amount of time by an attacker (unless the secret bit-string key is known). Since it can still be decompressed by the original LZ-77 algorithm, the embedding is completely ,transparent' and backward-compatible, making it possible to deploy it without disrupting service. Experiments show that the degradation in compression due to the embedding is almost negligible. Copyright © 2004 John Wiley & Sons, Ltd. [source]


A Family of Location Models for Multiple-Type Discrete Dispersion

GEOGRAPHICAL ANALYSIS, Issue 3 2006
Kevin M. Curtin
One of the defining objectives in location science is to maximize dispersion. Facilities can be dispersed for a wide variety of purposes, including attempts to optimize competitive market advantage, disperse negative impacts, and optimize security. With one exception, all of the extant dispersion models consider only one type of facility, and ignore problems where multiple types of facilities must be located. We provide examples where multiple-type dispersion is appropriate and based on this develop a general class of facility location problems that optimize multiple-type dispersion. This family of models expands on the previously formulated definitions of dispersion for single types of facilities, by allowing the interactions among different types of facilities to determine the extent to which they will be spatially dispersed. We provide a set of integer-linear programming formulations for the principal models of this class and suggest a methodology for intelligent constraint elimination. We also present results of solving a range of multiple-type dispersion problems optimally and demonstrate that only the smallest versions of such problems can be solved in a reasonable amount of computer time using general-purpose optimization software. We conclude that the family of multiple-type dispersion models provides a more comprehensive, flexible, and realistic framework for locating facilities where weighted distances should be maximized, when compared with the special case of locating only a single type of facility. [source]


Portfolio management using value at risk: A comparison between genetic algorithms and particle swarm optimization

INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 7 2009
V. A. F. Dallagnol
In this paper, it is shown a comparison of the application of particle swarm optimization and genetic algorithms to portfolio management, in a constrained portfolio optimization problem where no short sales are allowed. The objective function to be minimized is the value at risk calculated using historical simulation where several strategies for handling the constraints of the problem were implemented. The results of the experiments performed show that, generally speaking, the methods are capable of consistently finding good solutions quite close to the best solution found in a reasonable amount of time. In addition, it is demonstrated statistically that the algorithms, on average, do not all consistently achieve the same best solution. PSO turned out to be faster than GA, both in terms of number of iterations and in terms of total running time. However, PSO appears to be much more sensitive to the initial position of the particles than GA. Tests were also made regarding the number of particles needed to solve the problem, and 50 particles/chromosomes seem to be enough for problems up to 20 assets. © 2009 Wiley Periodicals, Inc. [source]


The nature of high-redshift galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2001
Rachel S. Somerville
Using semi-analytic models of galaxy formation set within the cold dark matter (CDM) merging hierarchy, we investigate several scenarios for the nature of the high-redshift ) Lyman-break galaxies (LBGs). We consider a ,collisional starburst' model in which bursts of star formation are triggered by galaxy,galaxy mergers, and find that a significant fraction of LBGs are predicted to be starbursts. This model reproduces the observed comoving number density of bright LBGs as a function of redshift and the observed luminosity function at and with a reasonable amount of dust extinction. Model galaxies at have star formation rates, half-light radii, colours and internal velocity dispersions that are in good agreement with the data. Global quantities such as the star formation rate density and cold gas and metal content of the Universe as a function of redshift also agree well. Two ,quiescent' models without starbursts are also investigated. In one, the star formation efficiency in galaxies remains constant with redshift, while in the other, it scales inversely with disc dynamical time, and thus increases rapidly with redshift. The first quiescent model is strongly ruled out, as it does not produce enough high-redshift galaxies once realistic dust extinction is accounted for. The second quiescent model fits marginally, but underproduces cold gas and very bright galaxies at high redshift. A general conclusion is that star formation at high redshift must be more efficient than locally. The collisional starburst model appears to accomplish this naturally without violating other observational constraints. [source]


The Vibrational Behavior of Bladed Disks in Consideration of Friction Damping and Contact Elasticity

PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2005
Christian Siewert
Rotating turbine blading is subjected to fluctuating gas forces during operation that cause blade vibrations. One of the main tasks in the design of turbomachinery blading is the reduction of the vibration amplitudes of the blades to avoid high resonance stresses that could damage the blading. The vibration amplitudes of the blades can be reduced significantly to a reasonable amount by means of friction damping devices such as underplatform dampers. In the case of blade vibrations, relative displacements between the friction damping devices and the neighboring blades occur and friction forces are generated that provide additional damping to the structure due to the dry friction energy dissipation. In real turbomachinery applications, spatial blade vibrations caused by a complex blade geometry and distributed excitation forces acting on the airfoil accur. Therefore, a three dimensional model including an appropriate spatial contact model to predict the generalized contact forces is necessary to describe the vibrational behavior of the blading with sufficient accuracy, see [1] and [2]. In this paper the contact model presented in [2] is extended to include also local deformations in the contacts between underplatform dampers and the contact surfaces of the adjacent blades. The additional elasticity in the contact influences the resonance frequency of the coupled bladed disk assembly. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Designing an accelerated degradation experiment by optimizing the estimation of the percentile

QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2003
Hong-Fwu Yu
Abstract Degradation tests are widely used to assess the reliability of highly reliable products which are not likely to fail under traditional life tests or accelerated life tests. However, for some highly reliable products, the degradation may be very slow and hence it is impossible to have a precise assessment within a reasonable amount of testing time. In such cases, an alternative is to use higher stresses to extrapolate the product's reliability at the design stress. This is called an accelerated degradation test (ADT). In conducting an ADT, several decision variables, such s the inspection frequency, sample size and termination time, at each stress level are influential on the experimental efficiency. An inappropriate choice of these decision variables not only wastes experimental resources but also reduces the precision of the estimation of the product's reliability at the use condition. The main purpose of this paper is to deal with the problem of designing an ADT. By using the criterion of minimizing the mean-squared error of the estimated 100th percentile of the product's lifetime distribution at the use condition subject to the constraint that the total experimental cost does not exceed a predetermined budget, a nonlinear integer programming problem is built to derive the optimal combination of the sample size, inspection frequency and the termination time at each stress level. A numerical example is provided to illustrate the proposed method. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Optimization of a model IV fluidized catalytic cracking unit

THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2001
Rein Luus
Abstract Maximization of a profit function related to a fluidized catalytic cracking unit model was carried out by Luus-jaakola optimization procedure. A 7-dimensional search is carried out on a FCC unit described by 113 nonlinear algebraic equations and 9 differential equations. Despite the low sensitivity and the existence of several local optima, the global optimum was obtained with reasonable amount of computational effort. At the optimum, the profit function is 1% higher than when the air blowers are constrained to operate at their maximum capacity. On a réalisé par la méthode d'optimisation de Luus-jaakola la maximisation d'une fonction de profit relativement à un modèle d'unité de craquage catarytique fluidisé (FCC). Une recherche en sept dimensions est menée sur une unité FCC décrite par 113 équations algébriques non linéaires et 9 équations différentielles. Malgré la faible sensibilité et l'existence de plusieurs optimums locaux, l'optimum global a été atteint avec des efforts raisonnables en termes de calcul. À l'optimum, la fonction de profit est de 1% supérieure à celle obtenue lorsqu'on force les ventilateurs soufflants à fonctionner à leur capacité maximum. [source]


From Single-Molecule Precursors to Coupled Ag2S/TiO2 Nanocomposites

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 28 2008
Márcia C. Neves
Abstract A single-source approach using mild temperatures was applied to prepare morphological well-defined and coupled TiO2/metal,sulfide nanocomposites. Metal N -alkyldithiocarbamates were used as the precursors to the metal,sulfide nanophases and, in particular, Ag2S nanostructures were investigated in more detail. These were observed as nano-islands at the surface of TiO2 (anatase) particles, which were used as substrates. To explain the formation of these nanocomposite particulates, a tentative mechanism has been proposed which involves the controlled release of sulfide ions from an intermediate coordination compound. Because the growth of the metal sulfide can be controlled at the surface of a photoactive substrate, we anticipate the potential of this synthetic method to chemical design reasonable amounts of semiconductor-sensitized TiO2, such as Ag2S/TiO2 nanocomposites. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


Volatile compositions of two Asteraceae from the north-east of Brazil: Ageratum conyzoides and Acritopappus confertus (Eupatorieae)

FLAVOUR AND FRAGRANCE JOURNAL, Issue 6 2005
Mary Anne Sousa Lima
Abstract Essential oils obtained by hydrodistillation of leaves from specimens of Ageratum conyzoides and Acritopappus confertus were investigated by GC,MS. The leaf essential oil of A. conyzoides consisted exclusively of the chromenes precocene I (95.4%) and II (4.5%). The essential oil of A. confertus consisted predominantly of monoterpenes, representing 81.0% of the total. The main component was myrcene (52.0%), with reasonable amounts of , -pinene (16.8%) and limonene (8.2%). The essential oil of A. conyzoides from the north-east of Brazil has been reported as the major source of precocene I to date. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Optimisation study of gum extraction from Basil seeds (Ocimum basilicum L.)

INTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 9 2009
Seyed M. A. Razavi
Summary Basil seed (Ocimum basilicum L.) is cultivated in large quantities in different regions of Iran. This seed has reasonable amounts of gum with good functional properties which is comparable with commercial food hydrocolloids. A central composite rotatable design was applied to evaluate the effects of temperature, pH and water/seed ratio on the yield, apparent viscosity and protein content of water-extracted Basil seed gum. All of the variables significantly (P < 0.05) affected the extraction yield, whereas the effect of water/seed ratio on apparent viscosity and the effects of pH and water/seed ratio on protein content were not significant (P > 0.05). Numerical optimisation determined the optimum extraction conditions based on the highest yield and viscosity and the lowest protein content as being temperature 68.71 °C, pH 8.09 and water/seed ratio 65.98:1. Power law model well described non-Newtonian pseudoplastic behaviour of BSG. Flow behaviour index (n) and consistency index (K) of 1% crude and pure BSG samples were 0.306, 0.283 and 17.46, 20.22 Pa sn, respectively. [source]