Strain sensing of carbon fiber reinforced geopolymer concrete

Health monitoring of concrete structures is performed by assessing the structure’s state of stress. One such method involves monitoring electrical resistance variations as an indirect measure of stress variations. Carbon fibers were added to fresh geopolymer mix to enhance its electrical conductivity. AC-impedance spectroscopy analyses were performed on sample specimens to obtain their electrical resistance. Geopolymer concrete specimens entrained with carbon fibers were dynamically loaded in bending and uniaxial compression to observe changes in electrical resistance with respect to variations in their stress state. For beam specimens electrical resistance was found to follow a descending trend with increasing bending stresses. A more complex relationship was noted for cylinder specimens that were loaded axially. Overall experimental results suggest that conductive geopolymer could serve as a smart material in health monitoring applications of concrete structures.     

Modeling representative Gen‐IV molten fuel reactivity effects in the ZEPHYR ZPR ‐ LFR analysis

Studies related to severe core accidents constitute a crucial element in the safety design of Gen‐IV systems. A new experimental program, related to severe core accidents studies, is proposed for the zero‐power experimental physics reactor (ZEPHYR) future reactor. The innovative program aims at studying reactivity effects at high temperature during degradation of Gen‐IV cores by using critical facilities and surrogate models. The current study introduces the European lead‐cooled system (ELSY) as an additional Gen‐IV system into the representativity arsenal of the ZEPHYR, in addition to the sodium‐cooled fast reactors. Furthermore, this study constitutes yet another step towards the ultimate goal of studying severe core accidents on a full core scale. The representation of the various systems is enabled by optimizing the content of plutonium oxide in the ZEPHYR fuel assembly. The study focuses on representing reactivity variation from 900°C at nominal state to 3000°C at a degraded state in both ELSY and Advanced Sodium Technological Reactor for Industrial Demonstration (ASTRID) cores. The study utilizes the previously developed calculation scheme, which is based on the coupling of stochastic optimization process and Serpent 2 code for sensitivity analysis. Two covariance data are used: the ENDF 175 groups for ELSY and the Covariance Matrix Cadarache (COMAC) 33 groups for ASTRID. The effect of the energy group structure of the covariance data on the representativity process is found to be significant. The results for single degraded ELSY fuel assembly demonstrate high representativity factor (>0.95) for reactivity variation and for the criticality level. Also, it is shown that the finer energy group structure of the covariance matrices results in dramatic improvement in the representation level of reactivity variations.     

Full-scale field tests of concrete slabs subjected to blast loads

This paper describes full-scale field explosion tests on protected and unprotected concrete slabs. The experiments were performed by the Protective Technologies Research & Development Center of the Faculty of Engineering Sciences of the Ben-Gurion University of the Negev (BGU-PTR&DC) under a contract with the Israeli Ministry of Defense (MoD) and the supervision of the IDF Steering Committee for R&D of Protective Structures. The aims of the tests were to: (1) extract data on the dynamic response of an elementary concrete structure to blast loads in order to verify and validate (V&V) our corresponding computer codes; and (2) check the ability of aluminum foams to mitigate blast wave loads. Time-dependent measurements of the response of the concrete slabs to the blast wave loads were successfully recorded using a variety of measurement devices. The obtained data have been used to verify and validate our computer codes.     

Capacity and lattice strategies for canceling known interference

We consider the generalized dirty-paper channel Y=X+S+N,E{X/sup 2/}/spl les/P/sub X/, where N is not necessarily Gaussian, and the interference S is known causally or noncausally to the transmitter. We derive worst case capacity formulas and strategies for "strong" or arbitrarily varying interference. In the causal side information (SI) case, we develop a capacity formula based on minimum noise entropy strategies. We then show that strategies associated with entropy-constrained quantizers provide lower and upper bounds on the capacity. At high signal-to-noise ratio (SNR) conditions, i.e., if N is weak relative to the power constraint P/sub X/, these bounds coincide, the optimum strategies take the form of scalar lattice quantizers, and the capacity loss due to not having S at the receiver is shown to be exactly the "shaping gain" 1/2log(2/spl pi/e/12)/spl ap/ 0.254 bit. We extend the schemes to obtain achievable rates at any SNR and to noncausal SI, by incorporating minimum mean-squared error (MMSE) scaling, and by using k-dimensional lattices. For Gaussian N, the capacity loss of this scheme is upper-bounded by 1/2log2/spl pi/eG(/spl Lambda/), where G(/spl Lambda/) is the normalized second moment of the lattice. With a proper choice of lattice, the loss goes to zero as the dimension k goes to infinity, in agreement with the results of Costa. These results provide an information-theoretic framework for the study of common communication problems such as precoding for intersymbol interference (ISI) channels and broadcast channels.     

Approximate belief updating in max-2-connected Bayes networks is NP-hard

A max-2-connected Bayes network is one where there are at most 2 distinct directed paths between any two nodes. We show that even for this restricted topology, null-evidence belief updating is hard to approximate.     

Electromagnetic scattering analysis using a model of dipoleslocated in complex space

Fictitious current-models have been applied extensively in recent years to a variety of time-harmonic electromagnetic wave scattering problems. This paper is introducing an extension of the current-model technique which facilitates the solution to problems subsuming metallic scatterers whose periphery contains a variety of length-scales features. This extension is in tune with the current-model technique philosophy of using simple current sources the fields of which are analytically derivable. It amounts to letting the coordinates of part of the source centers assume complex values. Positioned in complex space, the simple current sources radiate beam-type fields which are more localized and are better approximations of the scattering by the smooth expanses of the structure. The coordinates of the other source centers can retain their conventional real values or have only a relatively small imaginary constituent. These latter current sources are used to approximate the fields in the vicinity of the more rapidly varying regions of the structure. The new approach is applied to analyze electromagnetic scattering by a perfectly conducting oblate spheroid. It is found to render the solution computationally more effective at the expense of only a slight increase in its complexity     

Nested linear/lattice codes for structured multiterminal binning

Network information theory promises high gains over simple point-to-point communication techniques, at the cost of higher complexity. However, lack of structured coding schemes limited the practical application of these concepts so far. One of the basic elements of a network code is the binning scheme. Wyner (1974, 1978) and other researchers proposed various forms of coset codes for efficient binning, yet these schemes were applicable only for lossless source (or noiseless channel) network coding. To extend the algebraic binning approach to lossy source (or noisy channel) network coding, previous work proposed the idea of nested codes, or more specifically, nested parity-check codes for the binary case and nested lattices in the continuous case. These ideas connect network information theory with the rich areas of linear codes and lattice codes, and have strong potential for practical applications. We review these developments and explore their tight relation to concepts such as combined shaping and precoding, coding for memories with defects, and digital watermarking. We also propose a few novel applications adhering to a unified approach     

Wavefront reconstruction from its gradients

Wavefronts reconstructed from measured gradients are composed of a straightforward integration of the measured data, plus a correction term that disappears when there are no measurement errors. For regions of any shape, this term is a solution of Poisson's equation with Dirichlet conditions (V = 0 on the boundaries). We show that for rectangular regions, the correct solution is not a periodic one, but one expressed with Fourier cosine series. The correct solution has a lower variance than the periodic Fourier transform solution. Similar formulas exist for a circular region with obscuration. We present a near-optimal solution that is much faster than fast-Fourier-transform methods. By use of diagonal multigrid methods, a single iteration brings the correction term to within a standard deviation of 0.08, two iterations, to within 0.0064, etc.     

Laser operation with two orthogonally polarized transverse modes

Laser resonator configurations, which enable laser operation with two orthogonally polarized transverse modes, are presented. The intensity distributions of these two modes can be chosen to be complementary, so the gain medium can be exploited more efficiently than with a single mode, leading to improved output power. Moreover, the two modes can be combined and efficiently transformed into a single high-quality beam. Basic principles and experimental results with Nd:YAG lasers are presented.