Efficient Linear Programming Decoding of HDPC Codes

We propose several improvements for Linear Programming (LP) decoding algorithms for High Density Parity Check (HDPC) codes. First, we use the automorphism groups of a code to create parity check matrix diversity and to generate valid cuts from redundant parity checks. Second, we propose an efficient mixed integer decoder utilizing the branch and bound method. We further enhance the proposed decoders by removing inactive constraints and by adapting the parity check matrix prior to decoding according to the channel observations. Based on simulation results the proposed decoders achieve near-ML performance with reasonable complexity.Comment: Submitted to the IEEE Transactions on Communications, November 200

In situ laser irradiation setup for a Bruker three-circle goniometer

A new design of a setup for in situ laser irradiation of single crystals during an X-ray diffraction experiment is presented. The system is designed for use with a Bruker three-circle goniometer in combination with a Helix ultra-low-temperature cryostat and consists of a laser mount and a set of three adjustable mirrors. The main advantages of the presented system include a stationary laser mount, the ability to irradiate a sample inside the Be nozzle and no impediments to the goniometer movements

Validation of a physically-based solid oxide fuel cell anode model combining 3D tomography and impedance spectroscopy

This study presents a physically-based model for the simulation of impedance spectra in solid oxide fuel cell (SOFC) composite anodes. The model takes into account the charge transport and the charge-transfer reaction at the three-phase boundary distributed along the anode thickness, as well as the phenomena at the electrode/electrolyte interface and the multicomponent gas diffusion in the test rig. The model is calibrated with experimental impedance spectra of cermet anodes made of nickel and scandia-stabilized zirconia and satisfactorily validated in electrodes with different microstructural properties, quantified through focused ion beam SEM tomography. Besides providing the material-specific kinetic parameters of the electrochemical hydrogen oxidation, this study shows that the correlation between electrode microstructure and electrochemical performance can be successfully addressed by combining physically-based modelling, impedance spectroscopy and 3D tomography. This approach overcomes the limits of phenomenological equivalent circuits and is suitable for the interpretation of experimental data and for the optimisation of the electrode microstructure

New method for the deposition of nickel oxide in porous scaffolds for electrodes in solid oxide fuel cells and electrolyzers

A simple chemical bath deposition is used to coat a complex porous ceramic scaffold with a conformal nickel layer. The resulting composite is used as a Solid Oxide Fuel Cell electrode and its electrochemical response is measured in humidified hydrogen. X-Ray tomography is used to determine microstructural parameters of the uncoated and Ni-coated porous structure, among other, the surface area to total volume, the radial pore size and size of the necks between pores

Operando visualisation and multi-scale tomography studies of dendrite formation and dissolution in zinc batteries

Alternative battery technologies are required to meet growing energy demands and address the limitations of present technologies. As such, it is necessary to look beyond lithium-ion batteries. Zinc batteries enable high power density while being sourced from ubiquitous and cost-effective materials. This paper presents, for the first time known to the authors, multi-length scale tomography studies of failure mechanisms in zinc batteries with and without commercial microporous separators. In both cases, dendrites were grown, dissolved, and regrown, critically resulting in different morphology of dendritic layer formed on both the electrode and the separator. The growth of dendrites and their volume-specific areas were quantified using tomography and radiography data in unprecedented resolution. High-resolution ex situ analysis was employed to characterize single dendrites and dendritic deposits inside the separator. The findings provide unique insights into mechanisms of metal-battery failure effected by growing dendrites

Platinum(IV) Complexes with Tridentate, NNC-Coordinating Ligands: Synthesis, Structures, and Luminescence

Platinum(II) complexes of NNC-cyclometalating ligands based on 6-phenyl-2,2′-bipyridine (HL1) have been widely investigated for their luminescence properties. We describe how PtL1Cl and five analogues with differently substituted aryl rings, PtL2–6Cl, can be oxidized with chlorine and/or iodobenzene dichloride to generate Pt(IV) compounds of the form Pt(NNC-Ln)Cl3 (n = 1–6). The molecular structures of several of them have been determined by X-ray diffraction. These PtLnCl3 compounds react with 2-arylpyridines to give a new class of Pt(IV) complex of the form [Pt(NNC)(NC)Cl]+. Elevated temperatures are required, and the reaction is accompanied by competitive reduction processes and generation of side-products; however, four examples of such complexes have been isolated and their molecular structures determined. Reaction of PtL1Cl3 with HL1 similarly generates [Pt(NNC-L1)2]2+, which we believe to be the first example of a bis-tridentate Pt(IV) complex. The lowest-energy bands in the UV–vis absorption spectra of all the PtLnCl3 compounds are displaced to higher energy relative to the Pt(II) precursors, but they red-shift with the electron richness of the aryl ring, consistent with predominantly 1[πAr → π*NN] character to the pertinent excited state. A similar trend is observed for the [Pt(NNC)(NC)Cl]+ complexes. They display phosphorescence in solution at room temperature, centered around 500 nm for [PtL1(ppy)Cl]+ and [Pt(L1)2]2+, and 550 nm for methoxy-substituted derivatives. The lifetimes are in the microsecond range, rising to hundreds of microseconds at 77 K, consistent with triplet excited states of primarily 3[πAr → π*NN] character with relatively little participation of the metal

Mechanistic Studies of Liquid Metal Anode SOFCs: I. Oxidation of Hydrogen in Chemical - Electrochemical Mode

Liquid metal anode (LMA) solid oxide fuel cells (SOFCs) are a promising type of high temperature fuel cell suitable for the direct oxidation of gaseous or solid fuel. Depending upon the operating conditions they can be run in four different modes. In this first of a series of studies concerning the mechanism of reaction and species transport in LMA SOFCs, the oxidation of hydrogen fuel in a liquid tin anode has been investigated. An electrochemical model is developed based upon fast dissolution of hydrogen in a molten tin anode, slow, rate-determining homogeneous reaction of hydrogen with oxygen dissolved in the liquid tin, followed by anodic oxygen injection under diffusion control to replace the oxygen removed by reaction (so-called Chemical - Electrochemical mode or CE mode). Experimentally-generated data are used to validate the model. The model has introduced a new key parameter, z¯, which takes a value between zero and unity; its value is determined by geometric and convective factors in the cell as well as the partial pressure of the supplied hydrogen fuel. Current output of the cell is proportional to the value of z¯

Luminescent bis-tridentate iridium(III) complexes: Overcoming the undesirable reactivity of trans-disposed metallated rings using –N^N^N–coordinating bis(1,2,4-triazolyl)pyridine ligands

Nine new iridium(III) complexes featuring two tridentate ligands have been synthesised of the form Ir(N^C^N)(–N^N^N–), where N^C^N represents a cyclometallating ligand based on 1,3-di(2-pyridyl)benzene and –N^N^N– is a doubly deprotonated bis(1,2,4-triazolyl)pyridine. Three examples of each ligand have been used, with different substituents in the central aryl ring of the former and para-substituted aryl groups in the 5-positions of the triazole rings of the latter. Two of the complexes have been structurally characterised in the solid-state by X-ray diffraction, confirming the mutually orthogonal arrangement of the two ligands. Unlike related tris-cyclometallated complexes of the type Ir(N^C^N)(C^N^C), which are unstable with respect to photoactivated cleavage of the trans-disposed Ir–C bonds, the new complexes show no evidence of instability. They are phosphorescent in the green region of the spectrum with lifetimes around 200 ns and quantum yields up to 3%, apparently limited by non-radiative decay processes in particular. Although there is some variation in performance with substitution pattern, the only discernible trend is that complexes of the 4-methoxy-substituted N^C^N ligand are the better emitters. Three examples of related complexes of the form Ir(N^C^N)(N^N–)Cl – incorporating a bidentate 1,2,4-triazolylpyridine – have also been prepared. They show no room-temperature emission but the properties at 77 K are similar to those of the bis-tridentate systems