Study of the impact of reactants utilization on the performance of PEMFC commercial stacks by impedance spectroscopy

Reactants utilization is a key stake for a PEMFC system: a too low utilization leads to a waste of reactant but a too high utilization may result in a detrimental starvation. To study these impacts, two commercial stacks were characterised by impedance spectroscopy under different hydrogen and oxygen utilizations (from nominal conditions to quasi-starvation). One was fresh while the other was operated on-field during 10,000 h. This study shows that the two capacitive loops in the lowest frequency range (1 Hz and below) correspond respectively to oxygen and hydrogen mass transfer limitations: the limiting reactant can be clearly identified from the impacted frequencies. The size of these loops was increased by up to 30% when the cell operated at high reactant utilizations. These results could therefore pave the way to the development of algorithms able to estimate the degree of starvation of some cells.     

Cyclic cold isostatic pressing and improved particle packing of coarse grained oxide ceramics for refractory applications

This study investigated the cold isostatic pressing of coarse grained alumina refractories applying either a cyclic pressure increase or a cycling at maximum pressure. Additionally the effects of the maximum pressure and the particle size distribution on physical, mechanical and thermomechanical properties were analyzed. The cyclic pressure increase resulted in a slightly higher apparent density and lower apparent porosity. A cycling at maximum pressure decreased the median pore size to some extent. Remarkably, an optimized particle size distribution resulted in a lower apparent porosity, lower median pore size and in a higher Young's modulus before and after thermal shock together with a slightly lower relative decrease of the Young's modulus. A higher pressing pressure which decreased the apparent porosity did not affect the Young's modulus. Thus, apparently the optimized particle size distribution improved the particle packing which was associated with a smaller median pore size. This smaller pore size increased the number of pores relative to the total porosity, which then acted as points of crack initiation and crack deflection limiting the length of propagating cracks in case of thermal shock. Thus, tailoring the pore size distribution is a promising starting point to improve the thermomechanical properties of refractories.     

Universitärer Forschungscluster „Sustainable Technologies in Metal Production and Processing” (STMP)

Foundation of a university research cluster — Co-operation along the value creation chain from raw materials to components — Evidence of joint performance offers — Utilization of synergies — Integration of Christian Doppler Laboratories — Flexible arrangement of co-operations and networks     

Studying sulfur functional groups in Norway spruce year rings using S L-edge total electron yield spectroscopy

Profiles of the major sulfur functional groups in mature Norway spruce wood tissue have been established for the first time. The big challenge was the development of a method suitable for sulfur speciation in samples with very low sulfur content (<100 ppm). This became possible by synchrotron X-ray absorption spectroscopy at the sulfur L-edge in total electron yield (TEY) detection mode with thin gold-coated wood slices. Functional groups were identified using sulfur compound spectra as fingerprints. Latewood of single year rings revealed metabolic plausible sulfur forms, particularly inorganic sulfide, organic disulfide, methylthiol, and highly oxidized sulfur. Form-specific profiles with Norway spruces from three different Swiss forest sites revealed high, but hitherto little-noticed, sulfur intensities attributable to natural heartwood formation and a common, but physiologically unexpected maximum around year ring 1986 with trees from the industrialized Swiss Plateau. It is hypothesized whether it may have resulted from the huge reduction in sulfur emissions after 1980 due to Swiss policy. Comparison with total S content profiles from optical emission spectroscopy underlined the more accurate and temporally better resolved TEY data with single wood year rings and it opened novel insights into the wood cell chemistry.     

Anticancer Potential of (Pentamethylcyclopentadienyl)chloridoiridium(III) Complexes Bearing κP and κP,κS‐Coordinated Ph2PCH2CH2CH2S(O)xPh (x=0–2) Ligands

Iridium(III) complexes of the type [Ir(η⁵‐C₅Me₅)Cl₂{Ph₂PCH₂CH₂CH₂S(O)_xPh‐κP}] (x=0–2; 1 – 3 ) and [Ir(η⁵‐C₅Me₅)Cl{Ph₂PCH₂CH₂CH₂S(O)_xPh‐κP,κS}][PF₆] (x=0–1; 4 and 5 ) with 3‐(diphenylphosphino)propyl phenyl sulfide, sulfoxide, and sulfone ligands Ph₂PCH₂CH₂CH₂S(O)_xPh were designed, synthesized, and characterized fully, including X‐ray diffraction analyses for complexes 3 and 4 . In vitro studies against human thyroid carcinoma (8505C), submandibular carcinoma (A253), breast adenocarcinoma (MCF‐7), colon adenocarcinoma (SW480), and melanoma (518A2) cell lines provided evidence for the high biological potential of the neutral and cationic iridium(III) complexes. Neutral iridium(III) complex 5 proved to be the most active, with IC₅₀ values up to about 0.1 μM , representing activities of up to one order of magnitude higher than cisplatin. Using 8505C cells, apoptosis was shown to be the main mechanism through which complex 5 exerts its tumoricidal action. The described iridium(III) complexes represent potential leads in the search for novel metal‐based anticancer agents.     

AstPT Catalyses both Reverse N1‐ and Regular C2 Prenylation of a Methylated Bisindolyl Benzoquinone

Prenylated bisindolyl benzoquinones exhibit interesting biological activities, such as antidiabetic or anti‐HIV activities. A number of these compounds, including asterriquinones, have been isolated from Aspergillus terreus. In this study, we identified two putative genes by genome mining, ATEG_09980 and ATEG_00702, which share high sequence similarity with the known bisindolyl benzoquinone prenyltransferase TdiB from Aspergillus nidulans. The coding sequences were cloned and overexpressed in E. coli. The overproduced recombinant proteins were purified to near homogeneity and used for enzyme assays with asterriquinone D in the presence of dimethylallyl diphosphate. HPLC analysis showed that product formation was only detected in enzyme assays with EAU29429 encoded by ATEG_09980, not in those with EAU39348 encoded by ATEG_00702. Product isolation and structure elucidation by NMR and MS analyses led to identification of N1‐reversely and C2‐regularly monoprenylated derivatives, as well as N1′,N1′′reversely, N1′‐reversely, C2′′‐regularly diprenylated derivatives. This proved that EAU29429 functions as an asterriquinone prenyltransferase (AstPT) and indicated the involvement of EAU29429 rather than EAU39348 in the biosynthesis of methylated asterriquinones. Furthermore, incubation of monoprenylated enzyme products with AstPT resulted in the formation of the diprenylated derivatives.     

边走边吃 墨西哥城玉米饼烘焙坊

<正>设计师说,玉米饼烘焙坊(El Expendio de Maíz)的故事缘于三五好友的一次公路旅行。那次,他们决定离开墨西哥城几天,离开在首都的时髦都市生活,去那些乡村僻野,那些没什么旅游者的地方,那些简朴的村庄里,享受简单的食物,体验真实而简单的墨西哥生活,就那么看着人们的日常生活。在墨西哥驱车旅行时,连续行驶七八个小时是很常见的事情。就是说,在某个     

Modeling of the Twin-Roll Casting Process: Transition from Casting to Rolling

During twin-roll casting, an alloy melt is passing the gap between two counter-rotating rolls, where cooling and solidification leads to the continuous formation of a solid strand. In order to describe this process, a two-phase Eulerian–Eulerian volume-averaging model is presented that accounts for (1) transport and growth of spherical grains within a flowing melt, (2) the formation of a coherent solid network above a specific solid fraction and (3) the viscoplastic flow of the solid network with the interstitial melt during casting and compression. For the considered case of an inoculated Al–4wt%Cu alloy, the process conditions are chosen such that two relatively thick viscoplastic semi-solid shells meet between the rolls, and thus, the material is pressed together and squeezed against the casting direction. The squeezed out material consists of segregated melt and some solid that quickly disappears after melting. It is observed during this study that macrosegregation distributions are inherently connected to the mush deformation that is enforced during the hot rolling process.     

Photohistorica gottingensis. Part Two: Daguerreotypy in Göttingen — Philipp Petri (1800–1887)

Abstract

After over 140 years it is difficult to form a complete picture of the early years of photography in Gi:ittingen. Around 1840 there existed neither a regularly appearing daily newspaper in this small university town, nor city directories which might have served as sources of information today. The first printed announcement about Göttingen photographers is found in a guide-book of 1854, which mentions ‘daguerreotypes furnished by the painters Petri and Spangenberg’¹. Spangenberg, self-appointed ‘Artist and Photographer’, offered ‘porcelain pictures, as well as the manufacture of photographs at the least expensive prices to all visitors’. Likewise, the lithographic establishment of Hermann Stromfeldt offered ‘Portraits’ and ‘Daguerreotypes’ at reasonable prices, and ‘Gerhard Steuber, Art Supplies and Stationery’, offered ‘Copper Engravings and Lithography’ as well as the ‘Production of Silhouettes of Every Sort’. To all appearances, the artist Spangenberg and the lithographer Stromfeldt dedicated themselves to this new business of photography, so ripe for exploitation, a full decade after Petri, and then worked much more intensely with the newly developed, and more popular, negativepositive process².