Impact of the Volatile Cr-species' Attack on the Conductivity of La(Ni,Fe)O3

This study demonstrates the detrimental impact of Cr on the electronic conductivity of a $LaNi_{0.6}Fe_{0.4}O_3$ (LNF) porous cathode layer at 800 ºC. Vapor transport of Cr-species, originating from a porous metallic foam, and subsequent reaction with LNF results in a decrease of the electronic conductivity of the LNF-layer. Cr has been detected throughout the whole cross-section of the LNF-layer. Transmission electron microscopy revealed that Cr is gradually incorporated into the LNF-grains, while Ni is proportionally expelled. The progressing Cr deposition and penetration into the LNF-grains most likely explains the electronic conductivity drop. The Cr-poisoning impact on the electronic conductivity of the LNF porous layer is considerably smaller at 600ºC than at 800ºC. A tentative mechanism for the Cr attack and its influence on the electronic conductivity of the LNF layer will be presented

Structural analysis of flavinylation in vanillyl-alcohol oxidase

Vanillyl-alcohol oxidase (VAO) is member of a newly recognized flavoprotein family of structurally related oxidoreductases. The enzyme contains a covalently linked FAD cofactor. To study the mechanism of flavinylation we have created a design point mutation (His-61 --> Thr). In the mutant enzyme the covalent His-C8 alpha -flavin linkage is not formed, while the enzyme is still able to bind FAD and perform catalysis. The H61T mutant displays a similar affinity for FAD and ADP (K-d = 1.8 and 2.1 muM, respectively) but does not interact with FMN. H61T is about 10-fold less active with 4-(methoxymethyl)phenol) (k(cat) = 0.24 s(-1), K-m = 40 muM) than the wild-type enzyme. The crystal structures of both the hole and apo form of H61T are highly similar to the structure of wild-type VAO, indicating that binding of FAD to the apoprotein does not require major structural rearrangements. These results show that covalent flavinylation is an autocatalytical process in which His-BI plays a crucial role by activating His-422. Furthermore, our studies clearly demonstrate that in VAO, the FAD binds via a typical lock-and-key approach to a preorganized binding site

Covalent flavinylation is essential for efficient redox catalysis in vanillyl-alcohol oxidase

By mutating the target residue of covalent flavinylation in vanillyl-alcohol oxidase, the functional role of the histidyl-FAD bond was studied. Three His(422) mutants (H422A, H422T, and H422C) were purified, which all contained tightly but noncovalently bound FAD. Steady state kinetics revealed that the mutants have retained enzyme activity, although the turnover rates have decreased by 1 order of magnitude. Stopped-flow analysis showed that the H422A mutant is still able to form a stable binary complex of reduced enzyme and a quinone methide product intermediate, a crucial step during vanillyl-alcohol oxidase-mediated catalysis, The only significant change in the catalytic cycle of the H422A mutant is a marked decrease in reduction rate. Redox potentials of both wild type and H422A vanillyl-alcohol oxidase have been determined. During reduction of H422A, a large portion of the neutral flavin semiquinone is observed. Using suitable reference dyes, the redox potentials for the two one-electron couples have been determined: -17 and -113 mV. Reduction of wild type enzyme did not result in any formation of flavin semiquinone and revealed a remarkably high redox potential of +55 mV, The marked decrease in redox potential caused by the missing covalent histidyl-FAD bond is reflected in the reduced rate of substrate-mediated flavin reduction limiting the turnover rate. Elucidation of the crystal structure of the H422A mutant established that deletion of the histidyl-FAD bond did not result in any significant structural changes. These results clearly indicate that covalent interaction of the isoalloxazine ring with the protein moiety can markedly increase the redox potential of the flavin cofactor, thereby facilitating redox catalysis, Thus, formation of a histidyl-EAD bond in specific flavoenzymes might have evolved as a way to contribute to the enhancement of their oxidative power

Super nucleation and orientation of poly (butylene terephthalate) crystals in nanocomposites containing highly reduced graphene oxide

The ring opening polymerization of cyclic butylene terephthalate into poly (butylene terephthalate) (pCBT) in the presence of reduced graphene oxide (RGO) is an effective method for the preparation of polymer nanocomposites. The inclusion of RGO nanoflakes dramatically affects the crystallization of pCBT, shifting crystallization peak temperature to higher temperatures and, overall, increasing the crystallization rate. This was due to a super nucleating effect caused by RGO, which is maximized by highly reduced graphene oxide. Furthermore, combined analyses by differential scanning calorimetry (DSC) experiments and wide angle X-ray diffraction (WAXS) showed the formation of a thick {\alpha}-crystalline form pCBT lamellae with a melting point of ~250 {\deg}C, close to the equilibrium melting temperature of pCBT. WAXS also demonstrated the pair orientation of pCBT crystals with RGO nanoflakes, indicating a strong interfacial interaction between the aromatic rings of pCBT and RGO planes, especially with highly reduced graphene oxide. Such surface self-organization of the polymer onto the RGO nanoflakes may be exploited for the enhancement of interfacial properties in their polymer nanocomposites

Ion-ion proton transfer reactions of bio-ions involving noncovalent interactions: Holomyoglobin

Multiply protonated horse skeletal muscle holomyoglobin and apomyoglobin have been subjected to ion-ion proton transfer reactions with anions derived from perfluoro-1,3dimethylcyclohexane in a quadrupole ion trap operated with helium as a bath gas at 1 mtorr. Neither the apomyoglobin nor holomyoglobin ions show any sign of fragmentation associated with charge state reduction to the 1 + charge state. This is particularly noteworthy for the holomyoglobin ions, which retain the noncovalently bound heme group. For example, no sign of heme loss is associated with charge state reduction from the 9 + charge state of holomyoglobin to the 1 + charge state despite the eight consecutive highly exothermic proton transfer reactions required to bring about this charge change. This result is consistent with calculations that show the combination of long ion lifetime and the high ion-helium collision rate relative to the ion-ion collision rate makes fragmentation unlikely for high mass ions in the ion trap environment even for noncovalently bound complexes of moderate binding strength. The ion-ion proton transfer rates for holo- and apomyoglobin ions of the same charge state also were observed to be indistinguishable, which supports the expectation that ion-ion proton transfer rates are insensitive to ion structure and are determined primarily by the attractive Coulomb field

Designing Visual Markers for Continuous Artificial Intelligence Support

Colonoscopy, the visual inspection of the large bowel using an endoscope, offers protection against colorectal cancer by allowing for the detection and removal of pre-cancerous polyps. The literature on polyp detection shows widely varying miss rates among clinicians, with averages ranging around 22%--27%. While recent work has considered the use of AI support systems for polyp detection, how to visualise and integrate these systems into clinical practice is an open question. In this work, we explore the design of visual markers as used in an AI support system for colonoscopy. Supported by the gastroenterologists in our team, we designed seven unique visual markers and rendered them on real-life patient video footage. Through an online survey targeting relevant clinical staff (N = 36), we evaluated these designs and obtained initial insights and understanding into the way in which clinical staff envision AI to integrate in their daily work-environment. Our results provide concrete recommendations for the future deployment of AI support systems in continuous, adaptive scenarios

La(Ni,Fe)O3 Stability in the Presence of Chromia—A Solid-State Reactivity Study

The perovskite $La(Ni_{0.6}Fe_{0.4})O_3$ (LNF) is a candidate material for the electrochemically active cathode layer, the cathode current collecting layer, and/or the interconnect protective coating in intermediate temperature solid oxide fuel cells (IT-SOFCs) operated at . Since these operating temperatures enable the use of relatively cheap interconnect materials such as chromia-forming ferritic stainless steel, investigation of the chemical stability of LNF in the presence of chromium species is of importance. This study demonstrates that LNF is chemically unstable at when it is in direct contact with $Cr_2O_3$. It has been observed that Cr enters the perovskite phase, replacing first Ni and then Fe, already after 200h. At 600°C, however, only minor reaction products were detected after 1000h exposure to $Cr_2O_3$. Although this is a promising result, long-term testing under fuel cell operating conditions at 600°C is needed to prove that LNF is a viable IT-SOFC material

Automating Agential Reasoning: Proof-Calculi and Syntactic Decidability for STIT Logics

This work provides proof-search algorithms and automated counter-model extraction for a class of STIT logics. With this, we answer an open problem concerning syntactic decision procedures and cut-free calculi for STIT logics. A new class of cut-free complete labelled sequent calculi G3LdmL^m_n, for multi-agent STIT with at most n-many choices, is introduced. We refine the calculi G3LdmL^m_n through the use of propagation rules and demonstrate the admissibility of their structural rules, resulting in auxiliary calculi Ldm^m_nL. In the single-agent case, we show that the refined calculi Ldm^m_nL derive theorems within a restricted class of (forestlike) sequents, allowing us to provide proof-search algorithms that decide single-agent STIT logics. We prove that the proof-search algorithms are correct and terminate

Impact of Cr-poisoning on the conductivity of different LaNi0.6Fe0.4O3 cathode microstructures

The microstructure of porous LaNi0.6Fe0.4O3 (LNF) layers has a significant influence on the degree of the Cr-poisoning impact. The increase in the in-plane resistance and Cr accumulation in poisoned LNF-layers has been correlated with microstructural features. The Cr-poisoning impact is more severe in the case of a microstructure characterized by finer particles, higher porosity and larger particle surface area