Investigation of solid oxide fuel cell short stacks for mobile applications by electrochemical impedance spectroscopy

Solid oxide fuel cells (SOFC) for mobile applications are developed and investigated at the German Aerospace Center (DLR) in Stuttgart. Therefore a light-weight stack design was developed in cooperation with the automotive industry (BMW/Munich, Elring-Klinger/Dettingen, ThyssenKrupp/Essen) and the Research Center Jülich (FZJ). This concept is based on the application of stamped metal sheet bipolar plates, into which the SOFC cells are integrated by brazing technology. For the development and the investigation of the SOFC cells and short stacks, the electrochemical impedance spectroscopy (EIS) is an important and useful characterization method. The paper concentrates on the investigation and on the electrochemical testing of the SOFC short stacks with sintered anode-supported cells (ASC). The short stacks were electrochemically characterized mainly by electrochemical impedance spectroscopy, by current-voltage measurements and by long-term measurements. The cells and stacks were operated at different temperatures, varying fuel gas compositions, different fuel gas flow rates and at different electrical current loads. The influence of these operating conditions on the electrochemical performance of the short stacks is outlined. The nature of losses, e.g. ohmic and the polarization resistances of the electrodes were examined and determined by fitting of the impedance spectra to an equivalent circuit.     

Modeling and estimation of signal-dependent noise in hyperspectral imagery

The majority of hyperspectral data exploitation algorithms are developed using statistical models for the data that include sensor noise. Hyperspectral data collected using charge-coupled devices or other photon detectors have sensor noise that is directly dependent on the amplitude of the signal collected. However, this signal dependence is often ignored. Additionally, the statistics of the noise can vary spatially and spectrally as a result of camera characteristics and the calibration process applied to the data. Here, we examine the expected noise characteristics of both raw and calibrated visible/near-infrared hyperspectral data and provide a method for estimating the noise statistics using calibration data or directly from the imagery if calibration data is unavailable.     

Application of the stochastic mixing model to hyperspectral resolution enhancement

A maximum a posteriori (MAP) estimation method is described for enhancing the spatial resolution of a hyperspectral image using a higher resolution coincident panchromatic image. The approach makes use of a stochastic mixing model (SMM) of the underlying spectral scene content to develop a cost function that simultaneously optimizes the estimated hyperspectral scene relative to the observed hyperspectral and panchromatic imagery, as well as the local statistics of the spectral mixing model. The incorporation of the stochastic mixing model is found to be the key ingredient for reconstructing subpixel spectral information in that it provides the necessary constraints that lead to a well-conditioned linear system of equations for the high-resolution hyperspectral image estimate. Here, the mathematical formulation of the proposed MAP method is described. Also, enhancement results using various hyperspectral image datasets are provided. In general, it is found that the MAP/SMM method is able to reconstruct subpixel information in several principal components of the high-resolution hyperspectral image estimate, while the enhancement for conventional methods, like those based on least squares estimation, is limited primarily to the first principal component (i.e., the intensity component).     

MAP estimation for hyperspectral image resolution enhancement using an auxiliary sensor

This paper presents a novel maximum a posteriori estimator for enhancing the spatial resolution of an image using co-registered high spatial-resolution imagery from an auxiliary sensor. Here, we focus on the use of high-resolution panchomatic data to enhance hyperspectral imagery. However, the estimation framework developed allows for any number of spectral bands in the primary and auxiliary image. The proposed technique is suitable for applications where some correlation, either localized or global, exists between the auxiliary image and the image being enhanced. To exploit localized correlations, a spatially varying statistical model, based on vector quantization, is used. Another important aspect of the proposed algorithm is that it allows for the use of an accurate observation model relating the "true" scene with the low-resolutions observations. Experimental results with hyperspectral data derived from the airborne visible-infrared imaging spectrometer are presented to demonstrate the efficacy of the proposed estimator.     

Stochastic spectral unmixing with enhanced endmember class separation

Improvements to an algorithm for performing spectral unmixing of hyperspectral imagery based on the stochastic mixing model (SMM) are presented. The SMM provides a method for characterizing both subpixel mixing of the pure image constituents, or endmembers, and statistical variation in the endmember spectra that is due, for example, to sensor noise and natural variability of the pure constituents. Modifications of the iterative, expectation maximization approach to deriving the SMM parameter estimates are proposed, and their effects on unmixing performance are characterized. These modifications specifically concern algorithm initialization, random class assignment, and mixture constraints. The results show that the enhanced stochastic mixing model provides a better statistical representation of hyperspectral imagery from the perspective of achieving greater endmember class separation.     

Balancing phosphine in manure fermentation

The evolution of phosphine gas during the anaerobic batch fermentation of fresh swine manure was detected and correlated to the production of methane and hydrogen sulphide. A close temporal relationship between phosphine liberation and methane formation was found. However, the gaseous phosphine released from manure during fermentation only represents a tiny fraction of the overall phosphine balance. The majority of phosphine is captured in solid manure constituents. This matrix-bound phosphine is eliminated by more than 50% during anaerobic batch-fermentation. Seasonally determined phosphine concentrations in biogas and manure from two large-scale manure treatment plants also revealed net losses of phosphine in fermentation. Consequently, manure has to be considered more as a sink of phosphine rather than a phosphine-generating medium. Furthermore, a close relationship between phosphine in the feed of swine and manure of these swine was observed, implying that phosphine residues in the feed (possibly as a result of grain fumigation) represent an important source of phosphine in manure technologies that is relevant before the faecals of swine enter manure treatment plants.     

Comparison of localized proton NMR signals of skeletal muscle and fat tissue in vivo: two lipid compartments in muscle tissue

In vivo 1H NMR spectra of small volumes-of-interest (VOI) were localized in human soleus muscle (8 ml) and compared with volume selective spectra of subcutaneous fat tissue and femoral yellow bone marrow (2 ml). All examinations were performed by the double spin echo (PRESS) localization technique. To provide comparability, spectra of different tissues were recorded using identical sequence timing. Clearly improved resolution of the lipid signals of muscle tissue was obtained using long echo times TE > 200 ms. The spectra of muscle tissue exhibit lipid signals that stem from two compartments with a difference of their resonance frequencies of about 0.2 ppm (Larmor frequency difference 12-13 Hz at 1.5 T). The existence of two fatty acid compartments is supported by measurements of the relaxation times and line shape analysis. Both compartments contain fatty acids or triglycerides with similar composition. Probably one compartment corresponds to fat cells within muscle tissue, the other compartment with lower Larmor frequency is located within muscle cells.     

Comparing Two Multi-Criteria Methods for Prioritizing Wetland Restoration and Creation Sites Based on Ecological,Biophysical and Socio-Economic Factors

Wetland restoration has been recognized as a useful tool for improving water quality. Many studies have focused on developing strategies and models to optimize wetland performance. However, some important wetland placement characteristics have not been taken into account. In this research and unlike other studies, we included the social aspect (availability of public lands) as a fundamental factor to locate wetlands. Thus, environmental, biophysical and socio-economic factors were integrated through the comparison of two multi-criteria methods (a suitability model and a greedy algorithm). With nitrate removal as the main goal, the suitability model was applied considering the “terrain slope”, “proximity to watercourses” and “soil permeability”. The greedy algorithm was executed based on the “availability of public lands” and the “wetland restoration project costs”. These factors were chosen based on the Eu Life-CREAMAgua Flumen River project, which was carried out previously in the study area. Both the suitability model and the greedy algorithm provided critical information for siting a wetland and demonstrated the effectiveness of both approaches. By means of this study, we present highly applicable results as they are based on a real project (Eu Life-CREAMAgua Flumen River project), besides proposing and using the social factor as an innovative approach for the wetlands siting. This research and its possible adaptations can be used by decision makers to improve water quality using social and economic criteria, resulting in the efficient implementation of ecological-restoration projects.     

Molecular determinants of a Ca2+-binding site in the pore of cyclic nucleotide-gated channels: S5/S6 segments control affinity of intrapore glutamates

Cyclic nucleotide-gated (CNG) channels play an important role in Ca2+ signaling in many cells. CNG channels from various tissues differ profoundly in their Ca2+ permeation properties. Using the voltage-dependent Ca2+ blockage of monovalent current in wild-type channels, chimeric constructs and point mutants, we have identified structural elements that determine the distinctively different interaction of Ca2+ with CNG channels from rod and cone photoreceptors and olfactory neurons. Segments S5 and S6 and the extracellular linkers flanking the pore region are the only structural elements that account for the differences between channels. Ca2+ blockage is strongly modulated by external pH. The different pH dependence of blockage suggests that the pKa of intrapore glutamates and their protonation pattern differ among channels. The results support the hypothesis that the S5-pore-S6 module, by providing a characteristic electrostatic environment, determines the protonation state of pore glutamates and thereby controls Ca2+ affinity and permeation in each channel type.     

Novel Zinc(II) Complexes [Zn(atc-Et)2] and [Zn(atc-Ph)2]: In Vitro and in Vivo Antiproliferative Studies

Cisplatin and its derivatives are the main metallodrugs used in cancer therapy. However, low selectivity, toxicity and drug resistance are associated with their use. The zinc(II) (Zn^II) thiosemicarbazone complexes [Zn(atc-Et)₂] (1) and [Zn(atc-Ph)₂] (2) (atc-R: monovalent anion of 2-acetylpyridine N4-R-thiosemicarbazone) were synthesized and fully characterized in the solid state and in solution via elemental analysis, Fourier transform infrared (FTIR), ultraviolet-visible (UV-Vis) and proton nuclear magnetic resonance (¹H NMR) spectroscopy, conductometry and single-crystal X-ray diffraction. The cytotoxicity of these complexes was evaluated in the HepG2, HeLa, MDA-MB-231, K-562, DU 145 and MRC-5 cancer cell lines. The strongest antiproliferative results were observed in MDA-MB-231 and HepG2 cells, in which these complexes displayed significant selective toxicity (3.1 and 3.6, respectively) compared with their effects on normal MRC-5 cells. In vivo studies were performed using an alternative model (Artemia salina L.) to assure the safety of these complexes, and the results were confirmed using a conventional model (BALB/c mice). Finally, tests of oral bioavailability showed maximum plasma concentrations of 3029.50 µg/L and 1191.95 µg/L for complexes 1 and 2, respectively. According to all obtained results, both compounds could be considered as prospective antiproliferative agents that warrant further research.