A LysR-family transcriptional regulator is involved in the selenium-dependent transcriptional regpression of selenium-free hydrogenase gene groups in Methanococcus voltae

Methanococcus voltae besitzt zwei Coenzym F420 reduzierende und zwei Coenzym 420 nicht reduzierende Hydrogenasen. Zwei davon, Fru und Vhu, sind Selenoproteine. Eine F420 reduzierende Hydrogenase (Frc) und eine F420 nicht reduzierende Hydrogenase (Vhc) enthalten kein Selenocystein. Die Gengruppen, die für diese Enzyme codieren, sind durch eine gemeinsame intergene Region verbunden. Es wurde beschrieben, dass die Transkription der vhc-frc-Cluster durch die Anwesenheit von Selen im Wachstumsmedium inhibiert wird, obwohl die Anwesenheit von Spuren von Selen die Voraussetzung dafür ist, dass unter Laborbedingungen maximale Wachstumsraten erreicht werden. Ortsspezifische Mutagenese in der intergenen Region führte zur Identifizierung von Bindungsstellen für positiv und negativ regulatorischen Proteine geführt. In den hier beschriebenen Untersuchungen wurde das Gen für ß-Glucuronidase (uidA) benutzt, um das Transkriptionsniveau der frc- und vhc-Gengruppen in M. voltae-Stämmen (F3 und V1) in vivo indirekt zu verfolgen. Insertionsvektoren wurden konstruiert, um Zufalls-insertionen zu erzeugen. Mit diesem Ansatz wurden keine deregulierten Mutanten gefunden. Jedoch führte die Transformation mit einem Integrationsvektor, der die frc-vhc-intergene Region als Promotorregion für den Selektionsmarker trug, zur Derepression eines Hydrogenasepromotors unter gleichzeitiger Amplifikation des Vektors im Chromosom. Dies wurde als weiterer Anhaltspunkt dafür angesehen, dass es eine Bindungsstelle für den negativen Regulator in der intergenen Region gibt. Daraufhin wurde DNA-Affinitiätschromatogrphie eingesetzt, um zu versuchen, (das) negative Regulatorprotein(e) zu reinigen. An biotinmarkierter DNA, die die hypothetische Bindungsstelle für den negativen Regulator in der intergenen Region enthielt, wurde ein Protein teilweise gereinigt. Die N-terminale Sequenz des Proteins wurde bestimmt. BLAST-Analysen ergaben, dass es zur LysR-Familie prokaryotischer Regulationsproteine gehört. Nach der Erstellung der kompletten Nukelotidsequenz, wurde ein Knockout des Gens im M. voltae-Stamm V1 durchgeführt. Die Zerstörung des Gens im Stamm V1 führte zur Transkription des Reportergens und auch der Hydrogenasegene in Gegenwart von Selen. Dieser Regulator erhielt daher den Namen HrsM (selenabhängiger Repressor von Hydrogenasen in Methanococcus voltae). HrsM ist der erste beschriebene zur bakteriellen LysR-Familie gehörige Regulator in Archaea

High Frequency Gravitational Waves from Pulsar Timing Arrays

Several pulsar timing array (PTA) experiments such as NANOGrav and PPTA reported evidence of a gravitational wave background at the nano-Hz frequency band recently. This signal can originate from scalar-induced gravitational waves (SIGW) generated by the enhanced curvature perturbation. Here we perform a joint likelihood inference on PTA datasets, and our results show that if the PTA signals were indeed of SIGW origin, the curvature perturbations amplitude required will produce primordial black holes (PBHs) in $[2 \times 10^{-5}, 2 \times 10^{-2}]\ m_\odot$ mass range. Mergers of these PBHs can leave a strong gravitational wave signature in the $[10^{-3}, 10^8]$ Hz frequency range, to be detectable at upcoming interferometers such as the Einstein Telescope, DECIGO and BBO, etc. This offers a multi-frequency opportunity to further scrutinize the source of the observed PTA signal.Comment: 7 pages, 5 figure

Why Are They so Cruel ?: A Psychological Exploration of Terrorist Crime

In recent years, terrorist crime brought about great threats and enormous challenges to the stability of international communities and safety of people. From the perspective of criminal psychology, this paper combines “breeding soil for terrorist crime”, “psychological mechanism of individual evolution” and “rational mechanism of inhibitory process”, analyzes the causes of terrorist crimes. The analysis of the causes gives us some enlightenment: The root to solve terrorist crimes needs to address the problem of potential injustice so as to win over more people, and once the government wins public support, terrorist crime will inevitably reduce until go to demise

Pseudo-magnetic fields in square lattices

We have investigated the effects of strain on two-dimensional square lattices and examined the methods for inducing pseudo-magnetic fields. In both the columnar and staggered $\pi$-flux square lattices, we have found that strain only modulates Fermi velocities rather than inducing pseudo-magnetic fields. However, spatially non-uniform on-site potentials (anisotropic hoppings) can create pseudo-magnetic fields in columnar (staggered) $\pi$-flux square lattices. On the other hand, we demonstrate that strain does induce pseudo-magnetic fields in staggered zero-flux square lattices. By breaking a quarter of the bonds, we clarify that a staggered zero-flux square lattice is topologically equivalent to a honeycomb lattice and displays pseudo-vector potentials and pseudo-Landau levels at the Dirac points.Comment: 11 pages, 8 figure

NOVEL NANOSTRUCTURED HIGH-PERFORMANCE ANION EXCHANGE IONOMERS FOR ANION EXCHANGE MEMBRANE FUEL CELLS

poster abstractA novel block copolymer, styrene-ethylene/butylene-styrene (SEBS), was chosen as the starting material to prepare pendant quaternary ammonium-based ionomers with an ion-exchange-capacity (IEC) of 0.66, 1.30, and 1.54 meq g-1, denoted by QSEBS-L, QSEBS-M, and QSEBS-H, respectively. These QSEBS ionomers were demonstrated to have excellent dimensional stability against hydration without significantly sacrificing the ionic conductivity as compared to the widely studied polysulfone (PSf) based ionomers. The water uptake of the QSEBS-based ionomers depended on their functionality; a higher IEC in the ionomer resulted in more water uptake and a higher ionic conductivity. The MEAs fabricated with the QSEBS-M and QSEBS-H ionomers showed the best H2/O2 fuel cell performance with peak power densities reaching 210 mW cm-2 at 50 °C, which was significantly higher than that of the PSf-based ionomers (~30 mW cm-2). Electrochemical impedance spec-troscopy (EIS) analysis indicated that the superior fuel cell performance ob-served with the QSEBS-based ionomers can be attributed to: (1) the low in-ternal cell resistance due to good comparability of the QSEBS-based ionomers with the membranes and (2) the low mass transport and charge transport in both the anode and the cathode due to the excellent dimension-al stability and balanced conductivity-hydrophobicity originated by the unique morphology of the QSEBS-based ionomers. AFM phase imaging measurements of the QSEBS-based ionomers revealed unique nanostruc-tures containing isolated hydrophobic and continuous anion conducting hy-drophilic domains. By further optimizing the chemistry and morphology of the ionomers and the membranes, the resistance of the anode and cathode of the AEMFCs will be further reduced

Klein-bottle quadrupole insulators and Dirac semimetals

The Benalcazar-Bernevig-Hughes (BBH) quadrupole insulator model is a cornerstone model for higher-order topological phases. It requires \pi flux threading through each plaquette of the two-dimensional Su-Schrieffer-Heeger model. Recent studies show that particular \pi-flux patterns can modify the fundamental Brillouin zone from the shape of a torus to a Klein-bottle with emerging topological phases. By designing different \pi-flux patterns, we propose two types of Klein-bottle BBH models. These models show rich topological phases including Klein-bottle quadrupole insulators and Dirac semimetals. The phase with nontrivial Klein-bottle topology shows twined edge modes at open boundaries. These edge modes can further support second-order topology yielding a quadrupole insulator. Remarkably, both models are robust against flux perturbations. Moreover, we show that different \pi-flux patterns dramatically affect the phase diagram of the Klein-bottle BBH models. Going beyond the original BBH model, Dirac semimetal phases emerge in Klein-bottle BBH models featured by the coexistence of twined edge modes and bulk Dirac points.Comment: 11 pages, 11 figure

New Understandings of Ethanol Oxidation Reaction Mechanism on Pd/C and Pd2Ru/C Catalysts in Alkaline Direct Ethanol Fuel Cells

Ethanol oxidation reaction (EOR) on Pd2Ru/C and Pd/C catalysts in alkaline media is studied comprehensively by cyclic voltammetry, chronoamperometry, in situ FTIR, single fuel cell test and electrochemical impedance spectroscopy measurements. The results show that, as compared to Pd/C, Pd2Ru/C favors acetaldehyde formation and hinders its oxidation. Based on X-ray absorption data, which evidence that Ru promotes a larger electronic vacancy of the Pd 4d band, it is expected that the formation of adsorbed ethoxy is favored on Pd2Ru/C and followed by its oxidation to acetaldehyde facilitated by oxygenated species provided by Ru. In contrast, acetaldehyde oxidation is more difficult on Pd2Ru/C than on Pd/C likely because the adsorption energy of the reactive species is increased. We also show that the performance of Pd2Ru/C anode in alkaline direct ethanol fuel cell (ADEFC) is initially better but degrades much more rapidly than that with Pd/C anode under the same test conditions. The degradation is demonstrated to result from the accumulation of large amounts of acetaldehyde, which in alkaline media forms dimers by the aldol condensation reaction. The dimers tend to be responsible for blocking the active sites for further ethanol oxidation. This comprehensive study provides new understandings of the roles of Ru in Pd2Ru/C for EOR in alkaline media, unveils the causes of the performance degradation of fuel cells with Pd2Ru/C and demonstrates that initial good performances are not necessarily a valid criterion for selecting appropriate anode catalysts for ADEFC applications

Homologous Expression of a Subcomplex of Pyrococcus furiosus Hydrogenase that Interacts with Pyruvate Ferredoxin Oxidoreductase

Hydrogen gas is an attractive alternative fuel as it is carbon neutral and has higher energy content per unit mass than fossil fuels. The biological enzyme responsible for utilizing molecular hydrogen is hydrogenase, a heteromeric metalloenzyme requiring a complex maturation process to assemble its O2-sensitive dinuclear-catalytic site containing nickel and iron atoms. To facilitate their utility in applied processes, it is essential that tools are available to engineer hydrogenases to tailor catalytic activity and electron carrier specificity, and decrease oxygen sensitivity using standard molecular biology techniques. As a model system we are using hydrogen-producing Pyrococcus furiosus, which grows optimally at 100°C. We have taken advantage of a recently developed genetic system that allows markerless chromosomal integrations via homologous recombination. We have combined a new gene marker system with a highly-expressed constitutive promoter to enable high-level homologous expression of an engineered form of the cytoplasmic NADP-dependent hydrogenase (SHI) of P. furiosus. In a step towards obtaining ‘minimal’ hydrogenases, we have successfully produced the heterodimeric form of SHI that contains only two of the four subunits found in the native heterotetrameric enzyme. The heterodimeric form is highly active (150 units mg−1 in H2 production using the artificial electron donor methyl viologen) and thermostable (t1/2 ∼0.5 hour at 90°C). Moreover, the heterodimer does not use NADPH and instead can directly utilize reductant supplied by pyruvate ferredoxin oxidoreductase from P. furiosus. The SHI heterodimer and POR therefore represent a two-enzyme system that oxidizes pyruvate and produces H2 in vitro without the need for an intermediate electron carrier