Thermal diffusivity of homogeneous SBR MOX fuel with a burn-up of 35 MWd/kgHM

The effect of burn-up on the thermal conductivity of homogeneous SBR MOX fuel is investigated and compared with standard UO₂ LWR fuel. New thermal diffusivity results obtained on SBR MOX fuel with a pellet burn-up of 35 MWd/kgHM are reported. The thermal diffusivity measurements were carried out at three radial positions using a shielded “laser-flash” device and show that the thermal diffusivity increases from the pellet periphery to the centre. The fuel thermal conductivity was found to be in the same range as for UO₂ of similar burn-up. The annealing behaviour was characterized in order to identify the degradation due to the out-of-pile auto-irradiation.     

Space diversity in presence of discrete multipath fading channel

Most analytical studies of the performance of space diversity systems on fading channels assume a very rich multipath environment. In certain wireless applications, however, the number of significant multipath components can be small. In this letter, we consider a multipath channel in which the signal propagates from the transmitter to the receiver via L discrete paths which are uniformly distributed about the transmitter and receiver. For this channel, we study the effects of the number of multipath components and antenna array size on the error probability and outage capacity of space diversity systems. We observe that performance is significantly influenced by the presence of a channel with few multipath components.     

Synthesis and thermal characterization of new dumbbell shaped POSS/PS nanocomposites: Influence of the symmetrical structure of the nanoparticles on the dispersion/aggregation in the polymer matrix

A series of three novel dumbbell shaped polyhedral oligomeric silsesquioxanes (POSS)/ polystyrene (PS) nanocomposites, at different POSS contents (3%, 5% and 10% w/w), was synthesized and characterized in order to investigate the effects of this new bridged structure on the filler‐polymer interaction and then on the thermal behavior of the obtained polymer nanostructured materials (PNMs). Nanocomposites were synthesized by in situ polymerization of styrene and the actual POSS concentration in the obtained PNMs was checked by ¹H NMR spectroscopy. Scanning electron microscopy (SEM) and FTIR spectroscopy evidenced, at the same time, the presence of filler‐polymer interactions and auto‐aggregation phenomena. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates in both inert and oxidative atmospheres. The characteristic parameters of thermal stability, namely temperature at 5% mass loss and the apparent activation energy of degradation, for the various nanocomposites were determined and an increase in the initial decomposition temperatures of PNMs with increasing the POSS contents was observed. The results are discussed and interpreted. POLYM. COMPOS., 36:1394–1400, 2015. © 2014 Society of Plastics Engineers     

Joint channel estimation and data detection in space-time communications

The paper considers joint channel estimation and data sequence detection for multipath radio channels with multiple antennas at the transmitter and/or receiver. An iterative space-time receiver based on the expectation-maximization algorithm is proposed. We examine the performance of this receiver for transmit diversity and space-time coding methods over Rayleigh fading channels. Simulation results show that the receiver can often achieve near-coherent performance with modest complexity and using very few pilot symbols.     

An adaptive receiver for space-time trellis codes based on per-survivor processing

An adaptive receiver based on per-survivor processing is proposed for detecting space-time trellis codes transmitted over time-selective flat-fading channels, and its performance is examined through simulations. Results suggest that the new receiver can outperform iterative approaches based on Kalman filtering and the expectation-maximization algorithm, at the cost of increased receiver complexity.     

Thermal conductivity of homogeneous and heterogeneous MOX fuel with up to 44 MWd/kgHM burn-up

New thermal diffusivity data for homogeneous SBR and heterogeneous MIMAS and OCOM MOX fuels are reported. No significant difference between the thermal diffusivity of the homogeneous and heterogeneous fuels was found at the burn-up up to 44 MWd/kgHM. These measurements, combined with previously published results or correlation functions for irradiated UO₂ and MOX were compared and it was found that separate correlations for these two fuels are not justified. A correlation for the thermal conductivity of irradiated UO₂ and MOX as a function of burn-up and irradiation temperature is proposed.     

Anisotropic thermal expansion characteristics of lead metaniobate ceramics used in the low-liquid level sensors for fuel tanks of space launch vehicles

Low-liquid level sensors are used to monitor the fuel level in fuel tanks of space launch vehicles. These sensors, which are usually bonded to the bottom surface of the tank, are currently made of lead metaniobate ceramic. Lead metaniobate (PbNb₂O₆) is used because it has very stable piezoelectric behavior and a relatively low dielectric constant (<500). Very limited thermal expansion data, especially in the operating temperature range of the space launch vehicles, exist in the literature. This paper provides thermal expansion data for PbNb₂O₆ ceramic in both the radial (in-plane) and the thickness (out-of-plane) directions. These results clearly indicate an anisotropic thermal expansion behavior for this ceramic.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.     

Rake Reception With Channel Estimation Error

Several digital cellular systems employ coherent RAKE reception, wherein channel estimates are used to combine despread values. In this paper, a maximum likelihood (ML) approach to RAKE combining that accounts for channel estimation error, including error correlation across despread values, is examined. Fading and noise correlation are also considered. The performance of the ML approach is compared to traditional RAKE combining as well as approximate ML-based approaches. Results show that when the channel estimation error and noise are of the same order, ML-based approaches can provide gains on the order of 1 dB over traditional RAKE reception