The validation of thermal hydraulic system codes like TRACE is a demanding and highly needed task for the nuclear engineering community. In the present paper the validation of TRACE is focused on the heat transfer enh...
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The validation of thermal hydraulic system codes like TRACE is a demanding and highly needed task for the nuclear engineering community. In the present paper the validation of TRACE is focused on the heat transfer enhancement models for spacer grids. Several test sections are selected for that purpose whereas several coolants, different rod arrangements and dimensions, and various thermal hydraulic boundary conditions are considered. The systematic evaluation by means of post-test calculations shows that the present TRACE model is well able to represent the magnitude of the heat transfer enhancement directly at the spacer grid. Nevertheless, improvements of the model were necessary in order to catch the enhancement downstream of the spacer grid. With the present model, the exponential decay of the enhancement is over estimated. The comparison with experimental data suggests a faster establishment of the fully developed flow. Adjustments to the model are done in order to represent the data correctly in terms of magnitude and duration. (C) 2013 Elsevier B.V. All rights reserved.
Some results of a numerical analysis of the serious unanticipated accident at the Fukishima-1 NPP are presented. The analysis was performed in March 2011 as part of the support given by Rosatom, including in making de...
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Some results of a numerical analysis of the serious unanticipated accident at the Fukishima-1 NPP are presented. The analysis was performed in March 2011 as part of the support given by Rosatom, including in making decisions about possible protection of the population in the Far East region of Russia. On the basis of calculations performed with the SOKRAT code, the state of the core during the first week and the possible reasons of the explosions in the first three power units were evaluated: the core of all three reactors melted and in course of its degradation from 950 to 1100 kg of hydrogen could have been formed followed by the formation of a burning mixture. The computational data on hydrogen emission due to oxidation of the melt by steam agree with experiments performed with the QUENCH and PARAMETR facilities. It can be asserted 1.5 years after the accident that post-accident studies confirm the main results of the real-time calculations.
Cooperative communication has been shown to be an effective technique enabling single-antenna users to share their antennas to create a virtual MIMO system, thus providing extra spatial diversity in wireless networks....
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Cooperative communication has been shown to be an effective technique enabling single-antenna users to share their antennas to create a virtual MIMO system, thus providing extra spatial diversity in wireless networks. Distributed coding is a type of channel coding strategy developed for cooperative wireless networks. As opposed to conventional channel coding schemes, distributed coding constructs the whole codeword in a distributed manner among the cooperative users. Properly designed distributed coding can effectively approach the capacity of cooperative wireless networks. The aim of this article is to present an overview of recent development in distributed coding design in cooperative wireless networks.
In this paper, we study a MIMO system with a transmitter using a linear dispersion code (LDC) and a linear minimum mean square-error (MMSE) detector at the receiver in a Ricean flat-fading environment. We assume that ...
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In this paper, we study a MIMO system with a transmitter using a linear dispersion code (LDC) and a linear minimum mean square-error (MMSE) detector at the receiver in a Ricean flat-fading environment. We assume that the receiver has perfect channel state information and the transmitter knows only the mean channel matrix either by feedback or channel estimation. The focus of our work is the analysis of the optimal transmit strategy using different types of LDC. On the one hand, we consider spatial multiplexing schemes that achieve high data rates, but sacrifice diversity. On the other hand, we have schemes that achieve full diversity like quasi-orthogonal space-time block codes or orthogonal space-time block code. Depending on the LDC in use, the optimization problem is either convex or nonconvex. For both of these classes of LDC, we first derive the properties of the average normalized MSE and then analyze the impact of the mean component on the MSE, the optimal transmit strategy and the optimal power allocation. Finally, we derive some bounds on the error rate performance for different scenarios with the MMSE receiver.
An explicit construction for nonbinary quantum Goppa codes exceeding the quantum Gilbert-Varshamov bound is given. First, we introduce a weighted symplectic inner product and show a method how to transform weighted co...
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An explicit construction for nonbinary quantum Goppa codes exceeding the quantum Gilbert-Varshamov bound is given. First, we introduce a weighted symplectic inner product and show a method how to transform weighted codes into quantum codes with respect to the standard symplectic inner product. Then an algorithm to construct a quantum code out of any hyperelliptic curve is presented and implemented in Magma. Finally, we apply a generalization of this algorithm to a tower of function fields by Stichtenoth and show that these codes lie above the quantum Gilbert-Varshamov bound.
Resolution of displacement measurements based on ultrasound pulse-echo techniques is limited by the center frequency of the transmitted wave, echo sampling rate, quantization errors, and electronic noises in the measu...
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Resolution of displacement measurements based on ultrasound pulse-echo techniques is limited by the center frequency of the transmitted wave, echo sampling rate, quantization errors, and electronic noises in the measurement system. We developed a new method utilizing the clutter signal in coded excitations to determine the displacement of an object or a desired region of an object with much improved resolution. The method includes transmitting a pair of Golay complementary sequences, receiving echoes from the object or a region of the object, compressing the pulse, eliminating the main lobe, and determining the object displacement between the two transmissions from the residual clutter signal around the main lobe of the compressed pulse. Results of computer simulations showed that the new method improved the resolution by several orders of magnitude and was more robust to noise than traditional pulse-echo methods. The new method was also evaluated using an experimental ultrasound system (10 MHz center frequency, 100 MHz sampling rate, and 8-bit sampling precision). A high precision in the displacement measurement was achieved with a measurement error of -5.76 nm +/- 36.27 nm (mean +/- standard deviation). The method has the potential to be applied in biomedical and industrial measurements of distance, displacement, and thickness.
A new and simple rate-adaptive transmission scheme for indoor unguided optical links is proposed. This scheme is based on the use of variable silence periods and on-off keying (OOK) formats with memory. These variable...
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A new and simple rate-adaptive transmission scheme for indoor unguided optical links is proposed. This scheme is based on the use of variable silence periods and on-off keying (OOK) formats with memory. These variable silence times are used for modifying the statistics of the amplitude sequence regarding the statistics of the message sequence, giving an increase in the peak-to-average optical power ratio. This is a favourable characteristic in intensity modulation and direct detection infrared links. In this fashion, OOK formats with Gaussian pulses modifying their position within the symbol period are adopted, obtaining a good trade-off between performance and required complexity. This is applied to links operating at a high initial bit rate, providing a signalling rate with a wide dynamic range and a relevant improvement in performance with gradual complexity in implementation, compared with the scheme proposed and specified in the Advanced Infrared (AIr) standard by the Infrared Data Association (IrDA), which is based on repetition coding and pulse-position modulation.
In this paper, we study the codes C-k(n, q) arising from the incidence of points and k-spaces in PG(n, q) over the field F-p, with q = p(h), p prime. We classify all codewords of minimum weight of the dual code C-k (n...
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In this paper, we study the codes C-k(n, q) arising from the incidence of points and k-spaces in PG(n, q) over the field F-p, with q = p(h), p prime. We classify all codewords of minimum weight of the dual code C-k (n, q)(perpendicular to) in case q is an element of {4, 8}. This is equivalent to classifying the smallest sets of even type in PG(n, q) for q is an element of{4, 8}. We also provide shorter proofs for some already known results, namely, of the best known lower bound on the minimum weight of C-k(n, q)(perpendicular to) for general values of q, and of the classification of all codewords of Cn-1(n, q) of weight up to 2(qn-1).
The global minimum of the potential energy of a molecule corresponds to its most stable conformation and it dictates most of its properties. Due to the extensive search space and the massive number of local minima tha...
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The global minimum of the potential energy of a molecule corresponds to its most stable conformation and it dictates most of its properties. Due to the extensive search space and the massive number of local minima that propagate exponentially with molecular size, determining the global minimum of a potential energy function could prove to be significantly challenging. This study demonstrates the application of newly designed real-coded genetic algorithm (RCGA) called RX-STPM, which incorporates the use of Rayleigh crossover (RX) and scale-truncated Pareto mutator (STPM) as defined earlier for minimizing molecular potential energy functions. Computational results for problems with up to 100 degrees of freedom are compared with five other existing methods from the literature. The numerical results indicate the underlying reliability (robustness) and efficiency of the proposed approach compared to other existing algorithms with low computational costs.
We develop a new transmission scheme for additive white Gaussian noisy (AWGN) channels based on Fuchsian groups from rational quaternion algebras. The structure of the proposed Fuchsian codes is nonlinear and nonunifo...
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We develop a new transmission scheme for additive white Gaussian noisy (AWGN) channels based on Fuchsian groups from rational quaternion algebras. The structure of the proposed Fuchsian codes is nonlinear and nonuniform, hence conventional decoding methods based on linearity and symmetry do not apply. Previously, only brute force decoding methods with complexity that is linear in the code size exist for general nonuniform codes. However, the properly discontinuous character of the action of the Fuchsian groups on the complex upper half-plane translates into decoding complexity that is logarithmic in the code size via a recently introduced point reduction algorithm. (C) 2014 The Franklin Institute. Published by Elsevier Ltd. All rights reserved.
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