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Search Results: 1 - 10 of 55 matches for " Hehn "
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Compara o de três sistemas digitais em rela o à densidade óptica de cimentos de ion metro de vidro
Hehn, Lisiane et al.
Revista Odonto Ciência , 2007,
Abstract: Objetivo: O objetivo deste estudo foi comparar três sistemas digitais, dois do tipo placas ópticas e um sensor, quanto à densidade óptica de três cimentos de ion mero de vidro restauradores. Materiais e Método: Foram obtidas imagens radiográficas dos corpos de prova confeccionados com cada um dos materiais, em espessuras de 1, 2, 3 e 4 mm, posicionados entre as metades de um pré-molar humano, extraído e seccionado no sentido mésio-distal. As medidas de densidade óptica, em valores de pixels, foram realizadas de acordo com as especifica es do sistema correspondente ao receptor de imagem utilizado e analisadas por meio do teste n o-paramétrico de Friedman (α = 1%). Resultados: Os resultados mostraram diferen as significativas nas médias dos valores de densidade óptica entre os sistemas digitais. As maiores médias foram determinadas no sistema CYGNUS, seguido pelo DENOPTIX e menores valores para o DIGORA (p ≤ 0,01). Entretanto, n o se observou diferen as estatísticas quando comparadas as médias das varia es de densidade óptica decorrentes do aumento na espessura do corpo de prova. Conclus o: Portanto, pode-se concluir que, apesar de diferirem quanto aos valores de densidade óptica, os sistemas testados apresentam padr es semelhantes quando expressam a varia o em fun o da espessura do material utilizado.
The lowest-possible BER and FER for any discrete memoryless channel with given capacity
Johannes B. Huber,Thorsten Hehn
Mathematics , 2008,
Abstract: We investigate properties of a channel coding scheme leading to the minimum-possible frame error ratio when transmitting over a memoryless channel with rate R>C. The results are compared to the well-known properties of a channel coding scheme leading to minimum bit error ratio. It is concluded that these two optimization requests are contradicting. A valuable application of the derived results is presented.
MBBP for improved iterative channel decoding in 802.16e WiMAX systems
Thorsten Hehn,Johannes B. Huber,Stefan Laendner
Mathematics , 2008,
Abstract: We propose the application of multiple-bases belief-propagation, an optimized iterative decoding method, to a set of rate-1/2 LDPC codes from the IEEE 802.16e WiMAX standard. The presented approach allows for improved decoding performance when signaling over the AWGN channel. As all required operations for this method can be run in parallel, the decoding delay of this method and standard belief-propagation decoding are equal. The obtained results are compared to the performance of LDPC codes optimized with the progressive edge-growth algorithm and to bounds from information theory. It will be shown that the discussed method mitigates the gap to the well-known random coding bound by about 20 percent.
Conservation and diversity of gene families explored using the CODEHOP strategy in higher plants
Marc Morant, Alain Hehn, Danièle Werck-Reichhart
BMC Plant Biology , 2002, DOI: 10.1186/1471-2229-2-7
Abstract: The method was tested with two different objectives. The first was to analyze the evolution of the CYP98 family of cytochrome P450 genes involved in 3-hydroxylation of phenolic compounds and lignification in a broad range of plant species. The second was to isolate an orthologue of the sorghum glucosyl transferase UGT85B1 and to determine the complexity of the UGT85 family in wheat. P450s of the CYP98 family or closely related sequences were found in all vascular plants. No related sequence was found in moss. Neither extensive duplication of the CYP98 genes nor an orthologue of UGT85B1 were found in wheat. The UGT85A subfamily was however found to be highly variable in wheat.Our data are in agreement with the implication of CYP98s in lignification and the evolution of 3-hydroxylation of lignin precursors with vascular plants. High conservation of the CYP98 family strongly argues in favour of an essential function in plant development. Conversely, high duplication and diversification of the UGT85A gene family in wheat suggests its involvement in adaptative response and provides a valuable pool of genes for biotechnological applications. This work demonstrates the high potential of the CODEHOP strategy for the exploration of large gene families in plants.Plants have evolved extremely diversified gene families as tools to cope with a harsh environment. Some of these families such as cytochromes P450 and UDP-glycosyltransferases (UGT) reflect the extraordinary biochemical versatility of plants and across plant species, and represent a very valuable source of genes for biotechnologies. Both gene families offer a huge potential for bioremediation and control of crop and weed pesticide tolerance [1-3], but obviously also for industrial applications. P450s, considered as the most versatile catalysts known [4], usually activate dioxygen and transfer one of its atoms into various substrates, but also catalyze a great diversity of reactions ranging from C-C and C=N bond cleava
Highly efficient integrated rectifier and voltage boosting circuits for energy harvesting applications
D. Maurath,C. Peters,T. Hehn,M. Ortmanns
Advances in Radio Science : Kleinheubacher Berichte , 2008,
Abstract: This paper presents novel circuit concepts for integrated rectifiers and voltage converting interfaces for energy harvesting micro-generators. In the context of energy harvesting, usually only small voltages are supplied by vibration-driven generators. Therefore, rectification with minimum voltage losses and low reverse currents is an important issue. This is realized by novel integrated rectifiers which were fabricated and are presented in this article. Additionally, there is a crucial need for dynamic load adaptation as well as voltage up-conversion. A circuit concept is presented, which is able to obtain both requirements. This generator interface adapts its input impedance for an optimal energy transfer efficiency. Furthermore, this generator interface provides implicit voltage up-conversion, whereas the generator output energy is stored on a buffer, which is connected to the output of the voltage converting interface. As simulations express, this fully integrated converter is able to boost ac-voltages greater than |0.35 V| to an output dc-voltage of 2.0 V–2.5 V. Thereby, high harvesting efficiencies above 80% are possible within the entire operational range.
Local magnetic anisotropy controlled by a surface nano-modulation
J. Briones,F. Montaigne,G. Lengaigne,D. Lacour,M. Hehn
Physics , 2009,
Abstract: A topological modulation of magnetic thin films can induce a magnetic anisotropy of magnetostatic origin. In this letter, we report on the magnetic properties of NiFe layers deposited on wavy shaped Si substrates. Without any modulation, our films always present an intrinsic anisotropy. We show unambiguously that patterning the substrate can overcome this anisotropy and even impose a different easy axis of magnetization. This allows the definition of two orthogonal easy axes at different places on the same substrate. This control of anisotropy both in direction and intensity paves the way to the realization of high precision bidimensional magnetic sensors.
Permutation Decoding and the Stopping Redundancy Hierarchy of Cyclic and Extended Cyclic Codes
Thorsten Hehn,Olgica Milenkovic,Stefan Laendner,Johannes B. Huber
Mathematics , 2007,
Abstract: We introduce the notion of the stopping redundancy hierarchy of a linear block code as a measure of the trade-off between performance and complexity of iterative decoding for the binary erasure channel. We derive lower and upper bounds for the stopping redundancy hierarchy via Lovasz's Local Lemma and Bonferroni-type inequalities, and specialize them for codes with cyclic parity-check matrices. Based on the observed properties of parity-check matrices with good stopping redundancy characteristics, we develop a novel decoding technique, termed automorphism group decoding, that combines iterative message passing and permutation decoding. We also present bounds on the smallest number of permutations of an automorphism group decoder needed to correct any set of erasures up to a prescribed size. Simulation results demonstrate that for a large number of algebraic codes, the performance of the new decoding method is close to that of maximum likelihood decoding.
The Trapping Redundancy of Linear Block Codes
Stefan Laendner,Thorsten Hehn,Olgica Milenkovic,Johannes B. Huber
Mathematics , 2006,
Abstract: We generalize the notion of the stopping redundancy in order to study the smallest size of a trapping set in Tanner graphs of linear block codes. In this context, we introduce the notion of the trapping redundancy of a code, which quantifies the relationship between the number of redundant rows in any parity-check matrix of a given code and the size of its smallest trapping set. Trapping sets with certain parameter sizes are known to cause error-floors in the performance curves of iterative belief propagation decoders, and it is therefore important to identify decoding matrices that avoid such sets. Bounds on the trapping redundancy are obtained using probabilistic and constructive methods, and the analysis covers both general and elementary trapping sets. Numerical values for these bounds are computed for the [2640,1320] Margulis code and the class of projective geometry codes, and compared with some new code-specific trapping set size estimates.
Permutation Decoding and the Stopping Redundancy Hierarchy of Linear Block Codes
Thorsten Hehn,Olgica Milenkovic,Stefan Laendner,Johannes B. Huber
Mathematics , 2007,
Abstract: We investigate the stopping redundancy hierarchy of linear block codes and its connection to permutation decoding techniques. An element in the ordered list of stopping redundancy values represents the smallest number of possibly linearly dependent rows in any parity-check matrix of a code that avoids stopping sets of a given size. Redundant parity-check equations can be shown to have a similar effect on decoding performance as permuting the coordinates of the received codeword according to a selected set of automorphisms of the code. Based on this finding we develop new decoding strategies for data transmission over the binary erasure channel that combine iterative message passing and permutation decoding in order to avoid errors confined to stopping sets. We also introduce the notion of s-SAD sets, containing the smallest number of automorphisms of a code with the property that they move any set of not more than s erasures into positions that do not correspond to stopping sets within a judiciously chosen parity-check matrix.
Multiple-Bases Belief-Propagation Decoding of High-Density Cyclic Codes
Thorsten Hehn,Johannes B. Huber,Olgica Milenkovic,Stefan Laendner
Mathematics , 2009,
Abstract: We introduce a new method for decoding short and moderate length linear block codes with dense parity-check matrix representations of cyclic form, termed multiple-bases belief-propagation (MBBP). The proposed iterative scheme makes use of the fact that a code has many structurally diverse parity-check matrices, capable of detecting different error patterns. We show that this inherent code property leads to decoding algorithms with significantly better performance when compared to standard BP decoding. Furthermore, we describe how to choose sets of parity-check matrices of cyclic form amenable for multiple-bases decoding, based on analytical studies performed for the binary erasure channel. For several cyclic and extended cyclic codes, the MBBP decoding performance can be shown to closely follow that of maximum-likelihood decoders.
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