831 research outputs found
Computing the set of Epsilon-efficient solutions in multiobjective space mission design
In this work, we consider multiobjective space mission design problems. We will start from the need, from a practical point of view, to consider in addition to the (Pareto) optimal solutions also nearly optimal ones. In fact, extending the set of solutions for a given mission to those nearly optimal signiïŹcantly increases the number of options for the decision maker and gives a measure of the size of the launch windows corresponding to each optimal solution, i.e., a measure of its robustness. Whereas the possible loss of such approximate solutions compared to optimalâand possibly even âbetterââones is dispensable. For this, we will examine several typical problems in space trajectory designâa biimpulsive transfer from the Earth to the asteroid Apophis and two low-thrust multigravity assist transfersâand demonstrate the possible beneïŹt of the novel approach. Further, we will present a multiobjective evolutionary algorithm which is designed for this purpose
The Gradient Free Directed Search Method as Local Search within Multi-objective Evolutionary Algorithms
Recently, the Directed Search Method has been proposed as a point-wise iterative search procedure that allows to steer the search, in any direction given in objective space, of a multi-objective optimization problem. While the original version requires the objectivesâ gradients, we consider here a possible modification that allows to realize the method without gradient information. This makes the novel algorithm in particular interesting for hybridization with set oriented search procedures, such as multi-objective evolutionary algorithms. In this paper, we propose the DDS, a gradient free Directed Search method, and make a first attempt to demonstrate its benefit, as a local search procedure within a memetic strategy, by integrating the DDS into the well-known algorithmMOEA/D. Numerical results on some benchmark models indicate the advantage of the resulting hybrid
A study on using genetic niching for query optimisation in document retrieval
International audienceThis paper presents a new genetic approach for query optimisation in document retrieval. The main contribution of the paper is to show the effectiveness of the genetic niching technique to reach multiple relevant regions of the document space. Moreover, suitable merging procedures have been proposed in order to improve the retrieval evaluation. Experimental results obtained using a TREC sub-collection indicate that the proposed approach is promising for applications
Household Contamination with Salmonella enterica1
Household contamination with Salmonella enterica increases when occupational exposure exists (cattle farms with known salmonellosis in cattle, a salmonella research laboratory, or a veterinary clinic experiencing an outbreak of salmonellosis). Fifteen of 55 (27.2%) vacuum cleaner bags from households with occupational exposure to S. enterica were positive versus 1 of 24 (4.2% without known exposure. Use of a carpet cleaner and several cleaners/disinfectants reduced, but failed to eliminate, S. enterica from artificially contaminated carpet
Suscetibilidade de Anastrepha fraterculus (Diptera: Tephritidae) a iscas tĂłxicas formuladas com espinosinas.
A mosca-das-frutas Anastrepha fraterculus Ă© a principal praga da fruticultura de clima temperado. Para o manejo da praga, uma alternativa Ă© o emprego de iscas tĂłxicas que consiste na associação de um atrativo alimentar com um agente letal. No Brasil, as formulaçÔes de iscas tĂłxicas utilizam principalmente inseticidas fosforados como agente letal sendo as espinosinas uma alternativa. Nesse trabalho, foi avaliada a suscetibilidade de adultos de A. fraterculus a iscas tĂłxicas formuladas com inseticidas espinosade (Tracer? 480 SC) e espinetoram (Delegate? 250 WG) em mistura com os atrativos alimentares a base de proteĂna hidrolisada de milho (Biofruit? 3%) e melaço de cana-de-açĂșcar (7%).(Embrapa Uva e Vinho. Documentos, 99
Efeito de iscas tĂłxicas sobre o parasitoide Diachasmimorpha longicaudata (Hymenoptera: Braconidae) em laboratĂłrio.
As moscas-das-frutas causam prejuĂzos significativos aos fruticultores. A liberação de parasitoides da famĂlia Braconidae (Hymenoptera) Ă© uma estratĂ©gia de Manejo Integrado da Praga que pode ser associada ao controle quĂmico. Diachasmimorpha longicaudata Ă© a espĂ©cie de parasitoide mais utilizada pela facilidade de multiplicação em laboratĂłrio e por ser efetivo sobre vĂĄrias espĂ©cies de tefritĂdeos de importĂąncia econĂŽmica. Neste trabalho, foi avaliado em laboratĂłrio (temperatura: 24±2°C, UR: 70±10%) o efeito de iscas tĂłxicas sobre D. longicaudata.(Embrapa Uva e Vinho. Documentos, 99
Kinetics of the ureaâurease clock reaction with urease immobilized in hydrogel beads
Feedback driven by enzyme catalyzed reactions occurs widely in biology and has been well characterized in single celled organisms such as yeast. There are still few examples of robust enzyme oscillators in vitro that might be used to study nonlinear dynamical behavior. One of the simplest is the ureaâurease reaction that displays autocatalysis driven by the increase in pH accompanying the production of ammonia. A clock reaction was obtained from low to high pH in batch reactor and bistability and oscillations were reported in a continuous flow rector. However, the oscillations were found to be irreproducible and one contributing factor may be the lack of stability of the enzyme in solution at room temperature. Here, we investigated the effect of immobilizing urease in thiol-poly(ethylene glycol) acrylate (PEGDA) hydrogel beads, prepared using emulsion polymerization, on the ureaâurease reaction. The resultant mm-sized beads were found to reproduce the pH clock and, under the conditions employed here, the stability of the enzyme was increased from hours to days
Machine Learning in Automated Text Categorization
The automated categorization (or classification) of texts into predefined
categories has witnessed a booming interest in the last ten years, due to the
increased availability of documents in digital form and the ensuing need to
organize them. In the research community the dominant approach to this problem
is based on machine learning techniques: a general inductive process
automatically builds a classifier by learning, from a set of preclassified
documents, the characteristics of the categories. The advantages of this
approach over the knowledge engineering approach (consisting in the manual
definition of a classifier by domain experts) are a very good effectiveness,
considerable savings in terms of expert manpower, and straightforward
portability to different domains. This survey discusses the main approaches to
text categorization that fall within the machine learning paradigm. We will
discuss in detail issues pertaining to three different problems, namely
document representation, classifier construction, and classifier evaluation.Comment: Accepted for publication on ACM Computing Survey
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