Influence of band selection and target estimation error on the performance of the matched filter in hyperspectral imaging

The matched filter is a widely used detector in hyperspectral detection applications because of its simplicity and its efficiency in practical situations. We propose to estimate its performance with respect to the number of spectral bands. These spectral bands are selected thanks to a genetic algorithm in order to optimize the contrast between the target and the background in the detection plane. Our band selection method can be used to optimize not only the position but also the linewidth of the spectral bands. The optimized contrast always increases with the number of selected bands. However, in practical situations, the target spectral signature has to be estimated from the image. We show that in the presence of estimation error, the maximum number of bands may not always be the best choice in terms of detection performance.     

Performance predictions improve prospective memory and influence retrieval experience.

In retrospective memory, performance predictions have been found to enhance performance on subsequent memory tests. In prospective memory, the influence of metacognitive judgments on performance has not been investigated systematically. In the present study, 140 undergraduate students performed a complex short-term memory task that included a prospective memory task. Half of them gave performance predictions after the prospective memory task instructions. In addition, the specificity of the prospective memory task was manipulated by instructing participants either to perform an action when a word that belongs to the category of musical instruments was presented or to respond when the word “trumpet” was presented. The results showed that performance predictions enhanced performance, but only for the categorical task. Additional analyses of retrieval experience showed that performance predictions lead to an increase in search experiences while cue specificity was accompanied by an increase in pop up experiences. The results indicate that performance predictions can improve prospective performance and thus may be a valuable strategy for assisting prospective memory. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Design of Catalytically Active Cylindrical and Macroporous Gold Microelectrodes

Porous gold structures with a well‐defined pore size and thickness are obtained through electrochemical deposition of gold in a colloidal crystal template synthesized by the Langmuir–Blodgett (LB) technique. Cylindrical gold wires were used as substrates for the LB deposition of successive monolayers of silica particles of various sizes, and the electrodeposition of gold through this inorganic template led to a homogeneous, porous metal structure. These materials were characterized through typical electrochemical experiments and showed high surface‐to‐volume ratios with promising features for their further use in miniaturized electrocatalytic devices.     

Beta zeolite supported sol-gel TiO2 materials for gas phase photocatalytic applications

Beta zeolite supported sol-gel TiO(2) photocatalytic materials were prepared according to a sol-gel route in which high specific surface area Beta zeolite powder was incorporated into the titanium isopropoxide sol during the course of the sol-gel process. This led to an intimate contact between the zeolite surface and the TiO(2) precursors, and resulted in the anchorage of large amounts of dispersed TiO(2) nanoparticles and in the stabilization of TiO(2) in its anatase form, even for high TiO(2) wt. contents and high calcination temperatures. Taking the UV-A photocatalytic oxidation of methanol as gas phase target reaction, high methanol conversions were obtained on the Beta zeolite supported TiO(2) photocatalysts when compared to bulk sol-gel TiO(2), despite lower amounts of TiO(2) within the photoactive materials. The methanol conversion was optimum for about 40 wt.% TiO(2) loading and calcination temperatures of 500-600°C.     

Thermoforming of film-based biomedical microdevices

For roughly ten years now, a new class of polymer micromoulding processes comes more and more into the focus both of the microtechnology and the biomedical engineering community. These processes can be subsumed under the term "microthermoforming". In microthermoforming, thin polymer films are heated to a softened, but still solid state and formed to thin-walled microdevices by three-dimensional stretching. The high material coherence during forming is in contrast to common polymer microreplication processes where the material is processed in a liquid or flowing state. It enables the preservation of premodifications of the film material. In this progress report, we review the still young state of the art of microthermoforming technology as well as its first applications. So far, the applications are mainly in the biomedical field. They benefit from the fact that thermoformed microdevices have unique properties resulting from their special, unusual morphology. The focus of this paper is on the impact of the new class of micromoulding processes and the processed film materials on the characteristics of the moulded microdevices and on their applications.     

Surface properties and cell adhesion onto allylamine-plasma and amine-plasma coated glass coverslips

Surface properties of nanoparticles to be used for radioimmunotherapy need to be optimized to allow antibody conjugation while ensuring biocompatibility. We aimed to investigate cell adhesion and proliferation onto different coatings to be used for nanoparticles. C, CH _x or SiO _x coatings deposited onto glass coverslips by magnetron deposition as well as nitrogen functionalized materials synthetized using different reactive sputtering conditions and PPAA (plasma polymerized allylamine) coating, were compared. Amine functionalization did increase hydrophilicity in all the materials tested. Biocompatibility was assessed by measuring cell viability, morphology, attachment, spreading, and pro-inflammatory cytokine secretion. The results show that C and CN _x were the most biocompatible substrates while SiO _x and SiO _x N _y were the most toxic materials. PPAA coatings displayed unexpectedly an intermediate biocompatibility. A correlation could be observed between wettability and cell proliferation except for C coated surface, indicating that more complex processes than hydrophilicity alone are taking place that affect cell functions.     

Negative thermal expansion in Th2O(PO4)2

High temperature X ray diffraction performed on recently discovered orthorhombic Th₂O(PO₄)₂ shows a continuous linear thermal contraction (−1.6 × 10⁻⁶ °C⁻¹) in 20–600 °C range and a near-zero expansion at higher temperatures resulting from a dual structural deformation involving oxygen oscillations and inter-cations repulsions. Although similar mechanisms were observed in isotypic Zr₂O(PO₄)₂ (+1.5 × 10⁻⁶ °C⁻¹) and U₂O(PO₄)₂ (−1.4 × 10⁻⁶ °C⁻¹), those observed in Th₂O(PO₄)₂ are particularly intense because of the high ionic radius of tetravalent thorium.     

Influence of Cu off-stoichiometry on wide band gap CIGSe solar cells

The electric properties of solar cells based on co-evaporated Cu(In,Ga)Se₂ (CIGSe) thin film show a good tolerance regarding the absorber Cu content (y = [Cu]/([In] + [Ga])) for standard Ga concentration, i.e. x = [Ga] / ([In] + [Ga]) ~ 0.3. In the present contribution, we show that this tolerance is lost when the gallium content is increased. Wide bandgap CIGSe samples (x ~ 0.55) with a variation in y from 0.97 to 0.84 have been grown. The efficiency of the cells decreases from 12.6% to 6.5% for y = 0.97 and 0.84 respectively. For the lowest y, the efficiency is harmed because of a low short-circuit current density (J_sc), an increased voltage dependency in the current collection, which affects the fill factor (FF), and a decrease of the open-circuit voltage (V_oc). For y = 0.97 and 0.84 respectively, the decrease of the activation energy (E_a) from 1.36 to 1.24 eV indicates a shift of the area of the dominant recombination from the space charge region towards the interface. There seems to be evidence that reducing the Cu-content in the CIGSe thin film will cause a decrease in the width of the space charge region. Solar cells based on Cu-rich CIGSe (1.03 < y < 1.09) have also been fabricated and characterized. A strong deterioration of their electrical properties is observed despite the KCN etch of the segregated Cu_2 − xSe binary phases at the surface, suggesting the presence of residual Cu_2 − xSe precipitates within the layer.     

Mechanical properties of model ice ridge keels

Rubble ice presents pressure dependent yield strength and its behaviour can be described by mathematical models based on several mechanical parameters. They are investigated for HSVA model rubble ice through the analysis of three different tests: the oedometer test, the pile test and the punch test. This last test is analysed with the non-linear Eulerian finite element method. The tests were performed on 4 ice ridges with two different submersion times. A 0.5 to 1.2 kPa model scale Mohr-Coulomb cohesion (0.6 to 1.5 kPa Drucker-Prager cohesion), depending on the ridge history, was used in the simulations of the model scale punch tests. The friction angle is estimated between 30 and 45° (40 and 50° Drucker-Prager friction angle). The upper value was used in the punch test simulations. A 0.9 MPa Young modulus was derived and the hydrostatic compressive yield curve was determined. The numerical model is able to estimate the rubble action during the entire penetration of the punch test in the keel and it is shown that a cohesive softening occurs in the rubble. In order to reproduce the experimental load time series for the short submersion time ridges it was necessary to use a vertical distribution of the cohesion representing the vertical distribution of the freeze-bond strength. A sensitivity analysis of the punch test shows that the keel depth and the ice density are the main parameters governing the keel frictional resistance. A precise determination of these parameters is therefore crucial for a correct determination of the rubble mechanical properties from the numerical simulation of experimental punch tests. The punch test is not appropriate for the determination of the friction angle due to the low confinement pressure at the failure plane. The numerical analysis of the punch test allows the estimation of different assumptions used in analytical models for the rubble failure: the cohesion averaging is an under-conservative approximation, and the non-simultaneity of the cohesive and shear resistance maximum values can be considered in the peak load estimation by the computation of their quadratic mean. The comparison with full scale values shows a reasonably good scaling of the cohesion for the model ice ridges with a long submersion time.