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91.
The analogy between free-space propagation of optical beams and light-pulse reflection from linearly chirped fiber gratings is used to analyze the Lau effect in the temporal domain. The coherence conditions that are satisfied in the spatial domain for obtaining, at certain fixed locations, periodic fringes patterns are reformulated for guided light propagation. In this analogy, spatial periodic irradiance distributions are transformed in periodic sequences of light pulses. An optical setup is proposed to produce sharp pulse trains, with minimal distortion effects, that have repetition frequencies that are different from those associated with the input periodic optical signal. Some numerical results are given to illustrate this approach. 相似文献
92.
Ezequiel?López-RubioEmail author José?Mu?oz-Pérez José Antonio?Gómez-Ruiz Enrique?Domínguez-Merino 《Neural computing & applications》2003,12(2):109-118
The ASSOM is a self-organising neural network with the capability of adapting to linear subspaces. Here we propose two new methods to train the ASSOM network. A nonlinear system of equations is derived for network training. This system can be solved by a gradient-based approach or by the Levenberg–Marquardt method. Each of these two approaches gives a different learning rule. A comparison is carried out among the original Kohonens method and the proposed learning rules. Experimental results are reported, including a convergence speed experiment and a speech processing application, which show that the new learning rules have better performance than the original one. 相似文献
93.
AC-coupled front-end for biopotential measurements 总被引:5,自引:0,他引:5
Spinelli EM Pallàs-Areny R Mayosky MA 《IEEE transactions on bio-medical engineering》2003,50(3):391-395
AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz. 相似文献
94.
The easy detection of biomolecular interactions in complex mixtures using a minimum amount of material is of prime interest in molecular and cellular biology research. In this work, a mass spectrometry MALDI-TOF based approach, which we call intensity-fading (IF MALDI-TOFMS), and which was designed for just such a purpose, is reported. This methodology is based on the use of the MALDI ion intensities to detect quickly the formation of complexes between nonimmobilized biomolecules in which a protein is one of the partners (protein-protein, protein-peptide, protein-organic molecule, and protein-nucleic acid complexes). The complex is detected through the decrease (fading) of the molecular ion intensities of the partners as directly compared to the MALDI mass spectrum of the mixture (problem and control molecules) following the addition of the target molecule. The potential of the approach is examined in several examples of model interactions, mainly involving small nonprotein and protein inhibitors of proteases, at both the qualitative and semiquantitative levels. Using this method, different protein ligands of proteolytic enzymes in total extracts of invertebrate organisms have been identified in a simple way. The proposed procedure should be easily applied to the high-throughput screening of biomolecules, opening a new experimental strategy in functional proteomics. 相似文献
95.
Escaja N Gómez-Pinto I Rico M Pedroso E González C 《Chembiochem : a European journal of chemical biology》2003,4(7):623-632
The structures and stabilities of cyclic DNA octamers of different sequences have been studied by NMR and CD spectroscopy and by restrained molecular dynamics. At low oligonucleotide concentrations, some of these molecules form stable monomeric structures consisting of a short stem of two base pairs connected by two mini-loops of two residues. To our knowledge, these dumbbell-like structures are the smallest observed to date. The relative stabilities of these cyclic dumbbells have been established by studying their melting transitions. Dumbbells made up purely of GC stems are more stable than those consisting purely of AT base pairs. The order of the base pairs closing the loops also has an important effect on the stabilities of these structures. The NMR data indicate that there are significant differences between the solution structures of dumbbells with G-C base pairs in the stem compared to those with A-T base pairs. In the case of dumbbells with G-C base pairs, the residues in the stem form a short segment of a BDNA helix stabilized by two Watson-Crick base pairs. In contrast, in the case of d, the stem is formed by two A-T base pairs with the glycosidic angles of the adenine bases in a syn conformation, most probably forming Hoogsteen base pairs. Although the conformations of the loop residues are not very well defined, the thymine residues at the first position of the loop are observed to fold back into the minor groove of the stem. 相似文献
96.
Juan-Carlos Amengual Alberto Sanchis Enrique Vidal José-Miguel Benedí 《Machine Learning》2001,44(1-2):143-159
In many language processing tasks, most of the sentences generally convey rather simple meanings. Moreover, these tasks have a limited semantic domain that can be properly covered with a simple lexicon and a restricted syntax. Nevertheless, casual users are by no means expected to comply with any kind of formal syntactic restrictions due to the inherent spontaneous nature of human language. In this work, the use of error-correcting-based learning techniques is proposed to cope with the complex syntactic variability which is generally exhibited by natural language. In our approach, a complex task is modeled in terms of a basic finite state model, F, and a stochastic error model, E. F should account for the basic (syntactic) structures underlying this task, which would convey the meaning. E should account for general vocabulary variations, word disappearance, superfluous words, and so on. Each natural user sentence is thus considered as a corrupted version (according to E) of some simple sentence of L(F). Adequate bootstrapping procedures are presented that incrementally improve the structure of F while estimating the probabilities for the operations of E. These techniques have been applied to a practical task of moderately high syntactic variability, and the results which show the potential of the proposed approach are presented. 相似文献
97.
MR imaging of baker cysts—prevalence and relation to internal derangements of the knee 总被引:3,自引:0,他引:3
Rationale and objectives: To evaluate the prevalence of popliteal cysts in patients studied with magnetic resonance (MR) imaging. Cyst presence and
volume will be related to other internal derangement of the knee.Materials and methods: Three hundred and eighty-two consecutive patients with a MR study of the knee were included. Images were obtained in the
three spatial orthogonal planes and evaluated through consensus. Four categories were established for the Baker cyst and synovial
fluid (absence, minimum, moderate and massive), and the presence of meniscal, cruciate ligaments and cartilage lesions were
recorded. Statistical analysis was carried out with bivariate analysis (χ2 of Pearson and Gamma tests).Results: From the 382 patients, 145 had Baker cysts (38.0%). Cyst content was minimum in 99, moderate in 34 and massive in 12. Joint
effusion was observed in 269 patients (70.4%), being minimal in 140 patients, moderate in 119 and massive in ten. Meniscal
lesions were observed in 195 patients (51%), while 58 patients (15%) had a cruciate ligament lesion. Baker cyst has a statistically
significant direct relationship with the presence and quantity of synovial fluid (P=0.002) and with the presence and type of meniscal lesion (P=0.01) but not with cruciate ligaments or cartilage lesions.Conclusions: The prevalence of Baker cysts in MR studies of the knee is high. Its presence and volume are related to the quantity of
synovial fluid, and to the presence and severity of meniscal lesions. 相似文献
98.
Learning finite-state models for machine translation 总被引:1,自引:0,他引:1
In formal language theory, finite-state transducers are well-know models for simple “input-output” mappings between two languages.
Even if more powerful, recursive models can be used to account for more complex mappings, it has been argued that the input-output
relations underlying most usual natural language pairs can essentially be modeled by finite-state devices. Moreover, the relative
simplicity of these mappings has recently led to the development of techniques for learning finite-state transducers from
a training set of input-output sentence pairs of the languages considered. In the last years, these techniques have lead to
the development of a number of machine translation systems. Under the statistical statement of machine translation, we overview
here how modeling, learning and search problems can be solved by using stochastic finite-state transducers. We also review
the results achieved by the systems we have developed under this paradigm. As a main conclusion of this review we argue that,
as task complexity and training data scarcity increase, those systems which rely more on statistical techniques tend produce
the best results.
This work was partially supported by the European Union project TT2 (IST-2001-32091) and by the Spanish project ITEFTE (TIC
2003-08681-C02-02).
Editor: Georgios Paliouras and Yasubumi Sakakibara 相似文献
99.
Group decision-making model with incomplete fuzzy preference relations based on additive consistency. 总被引:2,自引:0,他引:2
Enrique Herrera-Viedma Francisco Chiclana Francisco Herrera Sergio Alonso 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2007,37(1):176-189
In decision-making problems there may be cases in which experts do not have an in-depth knowledge of the problem to be solved. In such cases, experts may not put their opinion forward about certain aspects of the problem, and as a result they may present incomplete preferences, i.e., some preference values may not be given or may be missing. In this paper, we present a new model for group decision making in which experts' preferences can be expressed as incomplete fuzzy preference relations. As part of this decision model, we propose an iterative procedure to estimate the missing information in an expert's incomplete fuzzy preference relation. This procedure is guided by the additive-consistency (AC) property and only uses the preference values the expert provides. The AC property is also used to measure the level of consistency of the information provided by the experts and also to propose a new induced ordered weighted averaging (IOWA) operator, the AC-IOWA operator, which permits the aggregation of the experts' preferences in such a way that more importance is given to the most consistent ones. Finally, the selection of the solution set of alternatives according to the fuzzy majority of the experts is based on two quantifier-guided choice degrees: the dominance and the nondominance degree. 相似文献
100.
This work describes a framework that combines techniques from Adaptive Hypermedia and Natural Language processing in order to create, in a fully automated way, on-line information systems from linear texts in electronic format, such as textbooks. The process is divided into two steps: an off-line processing step, which analyses the source text, and an on-line step, which executes when a user connects to the system with a web browser, moment at which the contents and hyperlinks are generated. The framework has been implemented as the Welkin system, which has been used to build three adaptive on-line information sites in a quick and easy way. Some controlled experiments have been performed with real users aimed to provide positive feedback on the implementation of the system. 相似文献