On the use of genuine-impostor statistical information for score fusion in multimodal biometrics/sur l’usage de l’information statistioue client-imposteur pour la fusion des scores en biométrie multimodale

Matching score level fusion techniques in multimodal person verification conventionally use global score statistics in the normalization and fusion stages. In this paper, novel normalization and fusion methods are presented to take advantage of the separate statistics of the monomodal scores in order to reduce the genuine and impostor pdf lobe overlapping and improve the verification rate. Joint mean normalization is an affine transformation that normalizes the mean of the monomodal biometrics scores separately for the genuine and impostor individuals. Histogram equalization is used to align the statistical distribution of the monomodal scores and make the whole separate statistics comparable. The presented weighting fusion methods have been designed to minimize the variances of the separate multimodal statistics and reduce the multimodal pdf lobe overlapping. The results obtained in speech and face scores fusion upon polycost and xm2vts databases show that the proposed techniques provide better results than the conventional methods.     

In situ high temperature neutron powder diffraction study of La2Ni0.6Cu0.4O4+δ in air: Correlation with the electrical behaviour

The knowledge of the thermal evolution of the crystal structure of a cathode material across the usual working conditions in solid oxide fuel cells is essential to understand not only its transport properties but also its chemical and mechanical stability in the working environment. In this regard, high-resolution neutron powder diffraction (NPD) measurements have been performed in air from 25 to 900 °C on O₂-treated (350 °C/200 bar) La₂Ni_0.6Cu_0.4O_4+δ. The crystal structure was Rietveld-refined in the tetragonal F4/mmm space group along all the temperature range. The structural data have been correlated with the transport properties of this layered perovskite. The electrical conductivity of O₂-treated La₂Ni_0.6Cu_0.4O_4+δ exhibits a metal (high T)-to-semiconductor (low T) transition as a function of temperature, displaying a maximum value of 110 S cm⁻¹ at around 450 °C. The largest conductivity corresponds, microscopically, to the shortest axial Ni–O2 distance (2.29(1) Å), revealing a major anisotropic component for the electronic transport. We have also performed a durability test at 750 °C for 560 h obtaining a very stable value for the electrical conductivity of 87 S cm⁻¹. The thermal expansion coefficient was 12.8 × 10⁻⁶ K⁻¹ very close to that of the usual SOFC electrolytes. These results exhibit La₂Ni_0.6Cu_0.4O_4+δ as a possible alternative cathode for IT-SOFC.     

Neutron diffraction and magnetic study of the low-temperature transitions in SrMo1−xFexO3−δ

SrMo_1?xFe_xO_3?δ (x = 0, 0.1, 0.2 and 0.3) perovskites have recently been described as performing anode materials in solid-oxide fuel cells. In this work, we describe the structural phase transitions they undergo below room-temperature (RT), studied “in-situ” from neutron powder diffraction data and DSC measurements. At RT all the studied compositions are cubic, space group Pm-3m, with unit-cell parameters that decrease with Fe doping. Upon cooling the samples, two structural phase transitions are identified: one to a tetragonal structure with I4/mcm space group (around T₁ = 240 K), and the second one to an orthorhombic Imma phase below T₂ = 100 K. The magnetic properties have also been evaluated; the Fe substitution drives an evolution from a Pauli-paramagnetic state (x = 0) to a weak ferromagnetic state combined with antiferromagnetic interactions; the susceptibility and the saturation magnetization increases monotonically with increasing the Fe-doping content.     

SrCo1−xSbxO3−δ perovskite oxides as cathode materials in solid oxide fuel cells

The SrCo_1−xSb_xO_3−δ (x = 0.05, 0.1, 0.15 and 0.2) system was tested as possible cathode for solid oxide fuel cells (SOFCs). X-ray diffraction results show the stabilization of a tetragonal P4/mmm structure with Sb contents between x = 0.05 and x = 0.15. At x = 0.2 a phase transition takes place and the material is defined in the cubic Pm-3m space group. In comparison with the undoped hexagonal SrCoO₃ phase, the obtained compounds present high thermal stability without abrupt changes in the expansion coefficient. In addition, a great enhancement of the electrical conductivity was observed at low and intermediate temperatures (T ≤ 800 °C). The sample with x = 0.05 displays the highest conductivity value that reaches 500 S cm⁻¹ at 400 °C and is over 160 S cm⁻¹ in the usual working conditions of a cathode in SOFC (650-900 °C). Moreover, the impedance spectra of the SrCo_1−xSb_xO_3−δ/Ce_0.8Nd_0.2O_2−δ/SrCo_1−xSb_xO_3−δ (x ≥ 0.05) symmetrical cells reveal polarization resistances below 0.09 Ω cm² at 750 °C which are much smaller than that displayed by the pristine SrCoO_3−δ sample. The composition with x = 0.05 shows the lowest ASR values ranging from 0.009 to 0.23 Ω cm² in the 900-600 °C temperature interval with an activation energy of 0.82 eV.     

Materials development for intermediate-temperature solid oxide electrochemical devices

One of the major challenges in developing electrochemical devices for energy generation has been the identification and development of materials with outstanding performance at reduced (intermediate) temperatures (500–700 °C), increasing the durability and lowering the cost of the device. A solid-state electrochemical cell is in outline a simple device consisting of three components: anode, electrolyte and cathode. The function of each component is critical to cell performance, and as interest in fuel cells and electrolysers has gathered pace, many materials have been evaluated as functional components of these cells. Typically, the requirement for new materials development has been the drive to lower operation temperature, overcoming sluggish reaction kinetics in existing materials. Novel materials for the functional components of both electrolysers and fuel cells are introduced, with emphasis placed on the air electrode and electrolyte, with the potential of new classes of materials discussed, including layered materials, defect fluorites and tetrahedrally coordinated phases. Furthermore, the opportunity presented by thin film deposition to characterize anisotropic transport in materials and develop devices based on thin films is discussed.     

A 0.6 V and 0.395 pJ/bit nonius TDC for a passive RFID pressure sensor tag

This work presents a nonius time to digital converter (TDC) adapted to a passive RF identification (RFID) pressure sensor tag. The proposed converter exploits the characteristics of time-based sensor interfaces and allows reducing voltage supply and power consumption while maintaining resolution and conversion efficiency. The nonius TDC has been designed and fabricated using the TSMC 90 nm standard CMOS technology. The main blocks of the converter are described and both the resolution adjustment and measurement processes are explained in detail. Measurement results show 10.49 bits of effective resolution for an input time range from 28.19 to 42.93 μs. With a sampling rate of 19 KS/s the converter has a conversion efficiency of 0.395 pJ/bit with a voltage supply of only 0.6 V. This characteristics in the proposed nonius TDC enables an increased reading range of the passive RFID pressure sensor tag.     

Effect of H12MDI isomer composition on mechanical and physico-chemical properties of polyurethanes based on amorphous and semicrystalline soft segments

Two series of segmented thermoplastic polyurethanes were synthesized having 33 wt % hard segment based on 4,4′-dicyclohexyl methane diisocyanate with different trans–trans isomer contents and 1,3-propanediol chain extender. The soft segments were based on poly(hexamethylene–pentamethylene carbonate)diol and poly(butylene sebacate)diol, amorphous and semicrystalline polyol, respectively. 4,4′-Dicyclohexyl methane diisocyanate with different trans–trans isomer contents were obtained by fractional crystallization of commercial diisocyanate and were characterized by differential scanning calorimetry and nuclear magnetic resonance spectroscopy. 4,4′-Dicyclohexyl methane diisocyanate trans–trans isomer lead to some interesting properties in the synthesized polyurethanes, due to the more ordered hard domains formed by packing of trans–trans 4,4′-dicyclohexyl methane diisocyanate. Thereby, as 4,4′-dicyclohexyl methane diisocyanate trans–trans isomer content increased, a better phase separated structure was observed.