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Quantifica o da falha na madeira em juntas coladas utilizando técnicas de vis o artificial
Abrah?o Christov?o Pereira,Varella Carlos Alberto Alves,Pinto Francisco de Assis de Carvalho,Khoury Junior Joseph Kalil
Revista árvore , 2003,
Abstract: Com o emprego de adesivos pode-se obter um grande número de produtos derivados da madeira. Para confec o industrial de produtos de madeira colada, normas reconhecidas internacionalmente exigem que a ades o da madeira seja testada segundo procedimentos padronizados e que nos resultados destes testes seja reportado, além da resistência das juntas, o porcentual de falha na madeira. Para avalia o da falha a norma ASTM D5266-99 recomenda o emprego de uma rede de quadrículas tra ada sobre um material transparente. Contudo, esta avalia o, além de demandar muito tempo, ainda é realizada com muita subjetividade. A hipótese do presente trabalho é que se pode quantificar a falha na madeira com um sistema de vis o artificial, tornando o procedimento mais rápido e menos sujeito à subjetividade. Foram testados dois tipos de algoritmos de limiariza o automática em imagens adquiridas com digitalizadores de mesa. Concluiu-se que a falha na madeira pode ser quantificada por limiariza o automática em substitui o ao método convencional das quadrículas. Os algoritmos testados apresentaram erro médio absoluto menor que 3% em rela o ao sistema convencional da rede quadriculada.
Quantifica??o da falha na madeira em juntas coladas utilizando técnicas de vis?o artificial
Abrah?o, Christov?o Pereira;Varella, Carlos Alberto Alves;Pinto, Francisco de Assis de Carvalho;Khoury Junior, Joseph Kalil;
Revista árvore , 2003, DOI: 10.1590/S0100-67622003000100010
Abstract: it is possible to obtain several products by glueing wood. internationally approved standards require wood adhesion to be tested according to standardized procedures, including in the results, shear stress and wood failure percentages. in order to estimate wood failure percentage, the astm d5266-99 standard suggests the use of a grid template printed on a transparent sheet. however, this evaluation is not only time-consuming but also subjective. this work developed and tested an algorithm to quantify the flawed wood areas by using a machine vision system, a faster and less subjective procedure. two types of automatic threshold algorithms were tested. the glued wood samples were scanned after the shear tests under compression. it was concluded that automatic measurement can replace the manual grid method. the proposed algorithms presented an average absolute error of 3%, as compared to the manual grid method.
Local Correction of Juntas  [PDF]
Noga Alon,Amit Weinstein
Mathematics , 2011,
Abstract: A Boolean function f over n variables is said to be q-locally correctable if, given a black-box access to a function g which is "close" to an isomorphism f_sigma of f, we can compute f_sigma(x) for any x in Z_2^n with good probability using q queries to g. We observe that any k-junta, that is, any function which depends only on k of its input variables, is O(2^k)-locally correctable. Moreover, we show that there are examples where this is essentially best possible, and locally correcting some k-juntas requires a number of queries which is exponential in k. These examples, however, are far from being typical, and indeed we prove that for almost every k-junta, O(k log k) queries suffice.
Quantum Algorithms for Learning and Testing Juntas  [PDF]
Alp Atici,Rocco A. Servedio
Computer Science , 2007, DOI: 10.1007/s11128-007-0061-6
Abstract: In this article we develop quantum algorithms for learning and testing juntas, i.e. Boolean functions which depend only on an unknown set of k out of n input variables. Our aim is to develop efficient algorithms: - whose sample complexity has no dependence on n, the dimension of the domain the Boolean functions are defined over; - with no access to any classical or quantum membership ("black-box") queries. Instead, our algorithms use only classical examples generated uniformly at random and fixed quantum superpositions of such classical examples; - which require only a few quantum examples but possibly many classical random examples (which are considered quite "cheap" relative to quantum examples). Our quantum algorithms are based on a subroutine FS which enables sampling according to the Fourier spectrum of f; the FS subroutine was used in earlier work of Bshouty and Jackson on quantum learning. Our results are as follows: - We give an algorithm for testing k-juntas to accuracy $\epsilon$ that uses $O(k/\epsilon)$ quantum examples. This improves on the number of examples used by the best known classical algorithm. - We establish the following lower bound: any FS-based k-junta testing algorithm requires $\Omega(\sqrt{k})$ queries. - We give an algorithm for learning $k$-juntas to accuracy $\epsilon$ that uses $O(\epsilon^{-1} k\log k)$ quantum examples and $O(2^k \log(1/\epsilon))$ random examples. We show that this learning algorithms is close to optimal by giving a related lower bound.
Comportamiento dieléctrico de compuestos epoxi/aluminio/BaTiO3  [cached]
Ramajo, L.,Reboredo, M. M.,Castro, M. S.
Boletín de la Sociedad Espa?ola de Cerámica y Vidrio , 2009,
Abstract: In order to improve the dielectric behaviour of epoxi/BaTiO3, in this work the influence of micrometric aluminum metal flakes (Al), on the dielectric properties of epoxy / BaTiO3 composites was studied. Epoxy resin, Al and BaTiO3 were mixed using an ultrasonic mixer and composites were deposited onto glass substrates by dipping technique. Obtained materials presented good dielectric properties at room temperature, and relaxation process appeared due to the resin behaviour. Obtained results were compared with those reported in literature for similar systems. Con el objetivo de mejorar el comportamiento dieléctrico de los compuestos epoxi/BaTiO3, en este trabajo se estudió la influencia de partículas metálicas de aluminio (Al), con forma de escamas y tama o micrométrico, sobre las propiedades dieléctricas de sistemas epoxi / BaTiO3. El material compuesto fue obtenido por la técnica de inmersión o “dipping”. La mezcla de los componentes fue llevado a cabo en mezclador ultrasónica y la deposición se realizó sobre sustratos de vidrio. Los materiales obtenidos presentaron buenas propiedades dieléctricas a temperatura ambiente, sin alcanzar el límite de percolación, y los fenómenos de relajación fueron generados por los dominios de la resina. Los valores obtenidos fueron comparados con los reportados en la bibliografía para sistemas similares.
Agnostically Learning Juntas from Random Walks  [PDF]
Jan Arpe,Elchanan Mossel
Computer Science , 2008,
Abstract: We prove that the class of functions g:{-1,+1}^n -> {-1,+1} that only depend on an unknown subset of k< 0 and access to a random walk on {-1,+1}^n labeled by an arbitrary function f:{-1,+1}^n -> {-1,+1}, finds with probability at least 1-delta a k-junta that is (opt(f)+epsilon)-close to f, where opt(f) denotes the distance of a closest k-junta to f.
Learning symmetric k-juntas in time n^o(k)  [PDF]
Mihail N. Kolountzakis,Evangelos Markakis,Aranyak Mehta
Mathematics , 2005,
Abstract: We give an algorithm for learning symmetric k-juntas (boolean functions of $n$ boolean variables which depend only on an unknown set of $k$ of these variables) in the PAC model under the uniform distribution, which runs in time n^{O(k/\log k)}. Our bound is obtained by proving the following result: Every symmetric boolean function on k variables, except for the parity and the constant functions, has a non-zero Fourier coefficient of order at least 1 and at most O(k/\log k). This improves the previously best known bound of (3/31)k, and provides the first n^{o(k)} time algorithm for learning symmetric juntas.
Aten o aos defeitos congênitos no Brasil: panorama atual  [cached]
Horovitz Dafne Dain Gandelman,Llerena Jr. Juan Clinton,Mattos Ruben Araújo de
Cadernos de Saúde Pública , 2005,
Abstract: O impacto dos defeitos congênitos no Brasil vem aumentando progressivamente, tendo passado da quinta para a segunda causa dos óbitos em menores de um ano entre 1980 e 2000, apontando para a necessidade de estratégias específicas na política de saúde. Foram localizadas, no Brasil, direcionadas aos defeitos congênitos, a es governamentais e n o-governamentais. Estas envolvem servi os de informa o sobre agentes teratogênicos na gravidez e sobre doen as metabólicas geneticamente determinadas, monitoriza o de defeitos congênitos, programa de triagem neonatal e tratamento de algumas doen as genéticas, imuniza o contra rubéola, além da fortifica o de farinhas com ácido fólico como a o preventiva de certos defeitos congênitos. Apesar da importancia de tais iniciativas, é pouco provável que seja possível atender à quest o dos defeitos congênitos de forma integrada. Para a efetiva o de um sistema de aten o voltado aos defeitos congênitos, deverá ser formulada política específica, de ambito nacional, com a participa o ativa do Ministério da Saúde, utilizando, como espinha dorsal, os servi os de genética existentes. Só assim, será possível a estrutura o de uma rede regionalizada, hierarquizada e funcional voltada à aten o aos defeitos congênitos no Brasil.
Avalia??o do comportamento em fadiga de juntas estruturais de ligas de Al2024T3 coladas com adesivo epóxi
Marchezin, E.;Pardini, L.C.;Guimar?es, V.A.;
Matéria (Rio de Janeiro) , 2012, DOI: 10.1590/S1517-70762012000100002
Abstract: aluminum alloys are widely used in aeronautical parts due to their good mechanical properties and low densities. these parts must be joined together to form larger assemblies. a structural joint is defined as a segment of structure that provides a means of transferring load from one structural member to another. the majority of aircraft joints are mechanically fastened with multiple fasteners. these joints present a high concentration of stresses around the fastener, because the load transfer between elements of the joint has to take place over a fraction of the available area. by contrast, the applied loads in the adhesive joints are distributed over the entire bonded area and reduce points of stress concentration. joints are the most common source of structural failures in aircraft and almost all repairs involve joints. therefore, it is important to understand all aspects of joint design and analysis. the aim of the present work was to perform a comparative evaluation of the structural joints of al2024-t3 alloy in three conditions: mechanically fastened joint, bonded joints and a hybrid configuration of bonded-riveted joint. the standard test method for determining strength properties of mechanically fastened sheet metal lap joints (nasm 1312-4) was used in all specimen configurations. besides, fatigue tests were conducted in specimens under constant amplitude loading at a stress ratio of 0.1 to evaluate the efficiency of the structural elements during their service life. the results showed that when metal-to-metal adhesive bond procedures are used with a mechanically fastened technique, the static strength and fatigue life of the joint will increase.
Ensaios de tra??o uniaxial com varia??o de temperatura em adesivo utilizado em juntas coladas de tubula??es de PRFV aplicado em plataformas marítimas
Pessanha, M.C.R.;Dias, D.P.;Filgueira, M.;Paranhos, R.P.R.;De Farias, O.L.;
Matéria (Rio de Janeiro) , 2008, DOI: 10.1590/S1517-70762008000100023
Abstract: this work has as objective to evaluate the thermo-mechanical behavior of adhesives used in bonded joints of pipes made of glass fiber reinforced plastics (gfrp). these bonded pipes, initially used in desalinization and effluent treatments installations, today are applied in the oil industry, both in oil drilling and production platforms, due to the necessity of lighter and higher corrosion resistance materials. it must be pointed out that in brazil these pipes are submitted at service temperature of approximately 85oc, with thermal transient until 115oc, while other applications of these pipes are designed to work at room temperature. so, the adhesive was evaluated by means of uniaxial tensile tests carried out at temperatures of 25, 55, 85 e 115oc, and there were determined the yield tension, the rupture tension, the elasticity modulus in the deformation associated to theses tensions. the obtained results show that, with the increase of the temperature, there is a high drop in the yield tension, the rupture tension and the elasticity modulus of the adhesive, while deformation associated to theses tensions significantly increase. it was possible to conclude that the adhesive operates with security until the temperature of 55oc. above this temperature the bonded joints produced with this adhesive would be subjected to fails.
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