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Transitions in neural oscillations reflect prediction errors generated in audiovisual speech

NATURE NEUROSCIENCE 2011年第6期14卷 797-U164页

作者： Arnal, Luc H. Wyart, Valentin Giraud, Anne-Lise Ecole Normale Super INSERM U960 F-75231 Paris France Univ Paris 06 Ctr Rech Ctr Natl Rech SciUnite Mixte Rech 7225 Inst Cerveau & Moelle EpiniereINSERMU975 Paris France Hop La Pitie Salpetriere Ctr Neuroimagerie Rech Paris France

According to the predictive coding theory, top-down predictions are conveyed by backward connections and prediction errors are propagated forward across the cortical hierarchy. Using MEG in humans, we show that violating multisensory predictions causes a fundamental and qualitative change in both the frequency and spatial distribution of cortical activity. When visual speech input correctly predicted auditory speech signals, a slow delta regime (3-4 Hz) developed in higher-order speech areas. In contrast, when auditory signals invalidated predictions inferred from vision, a low-beta (14-15 Hz) / high-gamma (60-80 Hz) coupling regime appeared locally in a multisensory area (area STS). This frequency shift in oscillatory responses scaled with the degree of audio-visual congruence and was accompanied by increased gamma activity in lower sensory regions. These findings are consistent with the notion that bottom-up prediction errors are communicated in predominantly high (gamma) frequency ranges, whereas top-down predictions are mediated by slower (beta) frequencies.

关键词： NEUROPHYSIOLOGY OSCILLATING chemical reactions coding theory PREDICTIVE control MAGNETOENCEPHALOGRAPHY AUDITORY perception

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Uncertainty and sensitivity analyses as a validation tool for BWR bundle thermal-hydraulic predictions

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NUCLEAR ENGINEERING AND DESIGN 2011年第9期241卷 3697-3706页

作者： Hernandez-Solis, Augusto Ekberg, Christian Demaziere, Christophe Jensen, Arvid Odegard Bredolt, Ulf Chalmers Univ Technol Dept Nucl Engn SE-41296 Gothenburg Sweden Chalmers Univ Technol Dept Chem & Biol Engn SE-41296 Gothenburg Sweden Westinghouse Elect Sweden AB Nucl Serv SE-72163 Vasteras Sweden

In recent years, more realistic safety analyses of nuclear reactors have been based on best estimate (BE) computer codes. The need to validate and refine BE codes that are used in the predictions of relevant reactor safety parameters, led to the organization of international benchmarks based on high quality experimental data. The OECD/NRC BWR full-size fine-mesh bundle test (BFBT) benchmark offers a good opportunity to assess the accuracy of thermal hydraulic codes in predicting, among other parameters, single and two phase bundle pressure drop, cross-sectional averaged void fraction distributions and critical powers under a wide range of system conditions. The BFBT is based on a multi-rod assembly integral test facility which is able to simulate the high pressure, high temperature fluid conditions found in BWRs through electrically heated rod bundles. Since code accuracy is unavoidably affected by models and experimental uncertainties, an uncertainty analysis is fundamental in order to have a complete validation study. In this paper, statistical uncertainty and sensitivity analyses are used to validate the thermal hydraulic features of the POLCA-T code, based on a one dimensional model of the following macroscopic BFBT exercises: (1) single and two phase bundle pressure drop, (2) steady-state cross-sectional averaged void fraction, (3) transient cross-sectional averaged void fraction and (4) steady-state critical power tests. The Latin hypercube sampling (LHS) strategy was chosen since it densely stratifies across the range of each uncertain input probability distribution, allowing a much better coverage of the input uncertainties than simple random sampling (SRS). The results show that POLCA-T predictions on pressure drop and void fractions under a wide range of conditions are within the validation limits imposed by the uncertainty analysis, while the accuracy of critical power predictions depends much on the boundary and input conditions. (C) 2011 Elsevier B.V. A

关键词： BOILING water reactors NUCLEAR reactors -- Safety measures PREDICTION theory SENSITIVITY analysis coding theory UNCERTAINTY (Information theory)

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Multiplicative Gain Modulation Arises Through Unsupervised Learning in a Predictive coding Model of Cortical Function

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NEURAL COMPUTATION 2011年第6期23卷 1536-1567页

作者： De Meyer, Kris Spratling, Michael W. Kings Coll London Dept Informat London WC2R 2LS England Kings Coll London Div Engn London WC2R 2LS England

The combination of two or more population-coded signals in a neural model of predictive coding can give rise to multiplicative gain modulation in the response properties of individual neurons. Synaptic weights generating these multiplicative response properties can be learned using an unsupervised, Hebbian learning rule. The behavior of the model is compared to empirical data on gaze-dependent gain modulation of cortical cells and found to be in good agreement with a range of physiological observations. Furthermore, it is demonstrated that the model can learn to represent a set of basis functions. This letter thus connects an often-observed neurophysiological phenomenon and important neurocomputational principle (gain modulation) with an influential theory of brain operation (predictive coding).

关键词： NEURAL transmission coding theory NEUROPHYSIOLOGY NEURONS PREDICTION theory HIGHER nervous activity NEURAL circuitry

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Detection of Hidden Structures in Nonstationary Spike Trains

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NEURAL COMPUTATION 2011年第5期23卷 1205-1233页

作者： Takiyama, Ken Okada, Masato Univ Tokyo Kashiwa Chiba 2778561 Japan RIKEN Wako Saitama 3510198 Japan

We propose an algorithm for simultaneously estimating state transitions among neural states and nonstationary firing rates using a switching state-space model (SSSM). This algorithm enables us to detect state transitions on the basis of not only discontinuous changes in mean firing rates but also discontinuous changes in the temporal profiles of firing rates (e.g., temporal correlation). We construct estimation and learning algorithms for a nongaussian SSSM, whose nongaussian property is caused by binary spike events. Local variational methods can transform the binary observation process into a quadratic form. The transformed observation process enables us to construct a variational Bayes algorithm that can determine the number of neural states based on automatic relevance determination. Additionally, our algorithm can estimate model parameters from single-trial data using a priori knowledge about state transitions and firing rates. Synthetic data analysis reveals that our algorithm has higher performance for estimating nonstationary firing rates than previous methods. The analysis also confirms that our algorithm can detect state transitions on the basis of discontinuous changes in temporal correlation, which are transitions that previous hidden Markov models could riot detect. We also analyze neural data recorded from the medial temporal area. The statistically detected neural states probably coincide with transient and sustained states that have been detected heuristically. Estimated parameters suggest that our algorithm detects the state transitions on the basis of discontinuous changes in the temporal correlation of firing rates. These results suggest that our algorithm is advantageous in real-data analysis.

关键词： coding theory NEURAL networks (Computer science) ALGORITHMS STATE-space methods DISCONTINUOUS functions CORRELATION (Statistics) VARIATIONAL principles QUADRATIC forms BAYESIAN analysis

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Severe accident management strategy verification for VVER-1000 (V320) reactor

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NUCLEAR ENGINEERING AND DESIGN 2011年第9期241卷 3977-3984页

作者： Chatterjee, B. Mukhopadhyay, D. Lele, H. G. Atanasova, B. Groudev, Pavlin Bhabha Atom Res Ctr Reactor Safety Div Bombay 400085 Maharashtra India Bulgarian Acad Sci Inst Nucl Res & Nucl Energy Sofia Bulgaria

Severe accident analysis of a reactor is an important aspect in evaluation of source term. This in turn helps in emergency planning and Severe Accident Management (SAM). The use of the Severe Accident Management Guideline (SAMG) is required for accident situation which is not handled adequately through the use of Emergency Operating Procedures (EOP), thus leading to a partial or a total core melt. Actions recommended in the SAMG aim at limiting the risk of radiologically significant radioactive releases in the short- and mid-term (a few hours to a few days). Initiation of SAMG for VVER-1000 is considered at two core exit temperatures viz. 650 degrees C as a desirable entry temperature and 980 degrees C as a backup action. Analyses have been carried out for VVER-1000 (V320) for verification of some of the strategies namely water injection in primary and secondary circuit. These strategies are analysed for a high and low pressure primary circuit transients. Station Black Out (SBO) is one such high pressure transient for which core heat can be removed by natural circulation of the primary circuit inventory by maintaining the secondary side inventory. This strategy has been verified where the feed water injection to secondary side of SG is considered from external power sources (e.g. mobile DG sets) as suggested in SAM guidelines. The second transient, a low pressure event is analysed for verification of the SG flooding and core flooding strategies. The analysis shows that SG flooding is not adequate to arrest the degradation of the core. In case of core flooding strategy, the analyses show that core flooding is not adequate to arrest the degradation of the core for the large break LOCA where as for small break LOCA the injections through available safety systems are adequate. The assessments are carried out with integral severe accident computer code ASTEC V1.3. (C) 2011 Elsevier B.V. All rights reserved.

关键词： NUCLEAR reactor accidents EMERGENCY management RADIOACTIVE substances TEMPERATURE effect coding theory PRESSURE

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Characterization of Minimum Error Linear coding with Sensory and Neural Noise

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NEURAL COMPUTATION 2011年第10期23卷 2498-2510页

作者： Doi, Eizaburo Lewicki, Michael S. NYU Ctr Neural Sci New York NY 10003 USA Case Western Reserve Univ Dept Elect Engn & Comp Sci Cleveland OH 44106 USA

Robust coding has been proposed as a solution to the problem of minimizing decoding error in the presence of neural noise. Many real-world problems, however, have degradation in the input signal, not just in neural representations. This generalized problem is more relevant to biological sensory coding where internal noise arises from limited neural precision and external noise from distortion of sensory signal such as blurring and phototransduction noise. In this note, we show that the optimal linear encoder for this problem can be decomposed exactly into two serial processes that can be optimized separately. One is Wiener filtering, which optimally compensates for input degradation. The other is robust coding, which best uses the available representational capacity for signal transmission with a noisy population of linear neurons. We also present spectral analysis of the decomposition that characterizes how the reconstruction error is minimized under different input signal spectra, types and amounts of degradation, degrees of neural precision, and neural population sizes.

关键词： NEURAL networks (Computer science) ELECTRONIC noise coding theory DECOMPOSITION (Mathematics) SIGNAL processing ERROR analysis (Mathematics) PROBLEM solving

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Dependency Reduction with Divisive Normalization: Justification and Effectiveness

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NEURAL COMPUTATION 2011年第11期23卷 2942-2973页

作者： Lyu, Siwei SUNY Albany Dept Comp Sci Albany NY 12222 USA

Efficient coding transforms that reduce or remove statistical dependencies in natural sensory signals are important for both biology and engineering. In recent years, divisive normalization (DN) has been advocated as a simple and effective nonlinear efficient coding transform. In this work, we first elaborate on the theoretical justification for DN as an efficient coding transform. Specifically, we use the multivariate t model to represent several important statistical properties of natural sensory signals and show that DN approximates the optimal transforms that eliminate statistical dependencies in the multivariate t model. Second, we show that several forms of DN used in the literature are equivalent in their effects as efficient coding transforms. Third, we provide a quantitative evaluation of the overall dependency reduction performance of DN for both the multivariate t models and natural sensory signals. Finally, we find that statistical dependencies in the multivariate t model and natural sensory signals are increased by the DN transform with low-input dimensions. This implies that for DN to be an effective efficient coding transform, it has to pool over a sufficiently large number of inputs.

关键词： BIOENGINEERING coding theory NONLINEAR theories MULTIVARIATE analysis STATISTICS MATHEMATICAL models

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Coupled neutronic thermo-hydraulic analysis of full PWR core with Monte-Carlo based BGCore system

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NUCLEAR ENGINEERING AND DESIGN 2011年第9期241卷 3777-3786页

作者： Kotlyar, D. Shaposhnik, Y. Fridman, E. Shwageraus, E. Ben Gurion Univ Negev Dept Nucl Engn IL-84105 Beer Sheva Israel Helmholtz Zentrum Dresden Rossendorf Inst Safety Res D-01314 Dresden Germany

BGCore reactor analysis system was recently developed at Ben-Gurion University for calculating in-core fuel composition and spent fuel emissions following discharge. It couples the Monte Carlo transport code MCNP with an independently developed burnup and decay module SARAF. Most of the existing MCNP based depletion codes (e.g. MOCUP, Monteburns, MCODE) tally directly the one-group fluxes and reaction rates in order to prepare one-group cross sections necessary for the fuel depletion analysis. BGCore, on the other hand, uses a multi-group (MG) approach for generation of one group cross-sections. This coupling approach significantly reduces the code execution time without compromising the accuracy of the results. Substantial reduction in the BGCore code execution time allows consideration of problems with much higher degree of complexity, such as introduction of thermal hydraulic (TH) feedback into the calculation scheme. Recently, a simplified TH feedback module, THERMO, was developed and integrated into the BGCore system. To demonstrate the capabilities of the upgraded BGCore system, a coupled neutronic TH analysis of a full PWR core was performed. The BGCore results were compared with those of the state of the art 3D deterministic nodal diffusion code DYN3D (Grundmann et al., 2000). Very good agreement in major core operational parameters including k-eff eigenvalue, axial and radial power profiles, and temperature distributions between the BGCore and DYN3D results was observed. This agreement confirms the consistency of the implementation of the TH feedback module. Although the upgraded BGCore system is capable of performing both, depletion and TH analyses, the calculations in this study were performed for the beginning of cycle state with pre-generated fuel compositions. (C) 2011 Elsevier B.V. All rights reserved.

关键词： PRESSURIZED water reactors -- Cores MONTE Carlo method NUMERICAL calculations coding theory NUCLEAR reactions TEMPERATURE

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Closing the Loop between Neuroscience and Information Technology: A Possible Mission?

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NETWORK-COMPUTATION IN NEURAL SYSTEMS 2011年第1-4期22卷 1-3页

作者： Leibold, Christian Ludwig Maximilians Univ Munchen LMU Bioctr D-82152 Planegg Germany

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关键词： INFORMATION theory COMPUTATIONAL neuroscience COMPUTATIONAL neuroscientists COMPUTER scientists coding theory INFORMATION technology

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DNA NANOTECHNOLOGY Geometrical self-assembly

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NATURE CHEMISTRY 2011年第8期3卷 580-581页

作者： Turberfield, Andrew J. Univ Oxford Clarendon Lab Dept Phys Oxford OX1 3PU England

DNA origami tiles with complementary shapes have been designed and assembled into large nanostructures through the geometrically controlled stacking of their helices.

关键词： DNA MOLECULAR structure coding theory NANOSTRUCTURED materials MOLECULAR self-assembly PRODUCTION engineering NANOTECHNOLOGY GEOMETRIC modeling NANOELECTROMECHANICAL systems

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