83 research outputs found

    О деформированном состоянии в зоне резания

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    Нагрев и пределы частотного регулирования асинхронного двигателя, работающего с наименьшими годовыми приведенными затратами

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    Исследуется тепловой режим асинхронного двигателя, оптимизированного по минимуму годовых приведенных затрат при переменной частоте питающего напряжения. Определены пределы регулирования скорости. Показана целесообразность оптимизации двигателя по экономическому критерию

    Probing atom-surface interactions by diffraction of Bose-Einstein condensates

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    In this article we analyze the Casimir-Polder interaction of atoms with a solid grating and an additional repulsive interaction between the atoms and the grating in the presence of an external laser source. The combined potential landscape above the solid body is probed locally by diffraction of Bose-Einstein condensates. Measured diffraction efficiencies reveal information about the shape of the Casimir-Polder interaction and allow us to discern between models based on a pairwise-summation (Hamaker) approach and Lifshitz theory.Comment: 5 pages, 4 figure

    Implementation of Vibration Signals Receiving Unit on Raspberry Single-Board Computers

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    The paper dedicated to vibration measurement system development on the Raspberry Pi basis. Main features of the solution are low-cost, easy access to components and functionality and flexibility provided by Raspberry Pi usage. Circuit solution and configuring procedures are presented and described. In particular, block diagram of the vibration measurement system with piezo-electric sensors. Two variants of the vibration measurement system, on the Raspberry Pi B+ and Raspberry Pi 3B correspondingly, were implemented and tested as well. In addition, two variants of impedance-matching device were implemented. Conducted and described experiments confirm performance both separate components and the whole solution. Presented results are applicable for correlation leak detectors new algorithmic solutions and in educational process

    Structural and enzymatic analysis of TarM from <i>Staphylococcus aureus</i> reveals an oligomeric protein specific for the glycosylation of wall teichoic acid.

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    Anionic glycopolymers known as wall teichoic acids (WTAs) functionalize the peptidoglycan layers of many Gram-positive bacteria. WTAs play central roles in many fundamental aspects of bacterial physiology, and they are important determinants of pathogenesis and antibiotic resistance. A number of enzymes that glycosylate WTA in Staphylococcus aureus have recently been identified. Among these is the glycosyltransferase TarM, a component of the WTA de novo biosynthesis pathway. TarM performs the synthesis of α-O-N-acetylglycosylated poly-5′-phosphoribitol in the WTA structure. We have solved the crystal structure of TarM at 2.4 Å resolution, and we have also determined a structure of the enzyme in complex with its substrate UDP-GlcNAc at 2.8 Å resolution. The protein assembles into a propeller-like homotrimer in which each blade contains a GT-B-type glycosyltransferase domain with a typical Rossmann fold. The enzymatic reaction retains the stereochemistry of the anomeric center of the transferred GlcNAc-moiety on the polyribitol backbone. TarM assembles into a trimer using a novel trimerization domain, here termed the HUB domain. Structure-guided mutagenesis experiments of TarM identify residues critical for enzyme activity, assign a putative role for the HUB in TarM function, and allow us to propose a likely reaction mechanism

    Hard X‐ray Nanotomography for 3D Analysis of Coking in Nickel‐based Catalysts

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    Understanding catalyst deactivation by coking is crucial for knowledge-based catalyst and process design in reactions with carbonaceous species. Post-mortem analysis of catalyst coking is often performed by bulk characterization methods. Here, hard X-ray ptychographic computed tomography (PXCT) was used to study Ni/Al2_{2}O3_{3} catalysts for CO2_{2} methanation and CH4_{4} dry reforming after artificial coking treatment. PXCT generated quantitative 3D maps of local electron density at ca. 80 nm resolution, allowing to visualize and evaluate the severity of coking in entire catalyst particles of ca. 40 μm diameter. Coking was primarily revealed in the nanoporous solid, which was not detectable in resolved macropores. Coke formation was independently confirmed by operando Raman spectroscopy. PXCT is highlighted as an emerging characterization tool for nanoscale identification, co-localization, and potentially quantification of deactivation phenomena in 3D space within entire catalyst particles

    Hard X-Ray Nanotomography for 3D Analysis of Coking in Nickel-Based Catalysts

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    Understanding catalyst deactivation by coking is crucial for knowledge-based catalyst and process design in reactions with carbonaceous species. Post-mortem analysis of catalyst coking is often performed by bulk characterization methods. Here, hard X-ray ptychographic computed tomography (PXCT) was used to study Ni/Al2O3 catalysts for CO2 methanation and CH4 dry reforming after artificial coking treatment. PXCT generated quantitative 3D maps of local electron density at ca. 80 nm resolution, allowing to visualize and evaluate the severity of coking in entire catalyst particles of ca. 40 μm diameter. Coking was primarily revealed in the nanoporous solid, which was not detectable in resolved macropores. Coke formation was independently confirmed by operando Raman spectroscopy. PXCT is highlighted as an emerging characterization tool for nanoscale identification, co-localization, and potentially quantification of deactivation phenomena in 3D space within entire catalyst particles

    Complementary operando insights into the activation of multicomponent selective propylene oxidation catalysts

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    Two Bi–Mo–Co–Fe–O catalysts were synthesized by flame spray pyrolysis and tested for their catalytic performance in selective oxidation of propylene to acrolein. Pronounced structural changes during temperature–programmed oxidation and reaction were observed by operando X–ray absorption spectroscopy, X–ray diffraction, Raman spectroscopy, and thermogravimetric analysis. During oxidative treatment, mainly binary oxide phases (α–Bi2^{2}Mo3^{3}O12^{12}, β–CoMoO4^{4}, Fe2^{2} (MoO4^{4})3^{3}) were observed, but single (MoO3^{3}) or ternary (Bi3^{3} (FeO4^{4})(MoO4^{4})2^{2}) oxides also formed depending on the relative elemental catalyst composition. During propylene oxidation, the reduction of Fe3+^{3+} to Fe2+^{2+} led to a strong rise in activity and induced further phase transformations. MoO3^{3} was found to be unselective towards acrolein but was essential in binding other single oxides. The formation of β–Co0.7^{0.7}Fe0.3^{0.3}MoO4^{4} and Bi3^{3} (FeO4^{4})(MoO4^{4})2^{2} as well as their synergistic interplay with α–Bi2^{2}Mo3^{3}O12^{12} are key factors for high performance. The combination of complementary operando methods was crucial to reveal new structure–activity/selectivity correlations, therefore bridging the knowledge gap between simplified model systems and complex applied catalysts

    Harte Röntgen‐Nanotomographie zur 3D‐Analyse der Verkokung in Nickel‐basierten Katalysatoren

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    Das Verständnis der Katalysatordesaktivierung durch Verkokung ist entscheidend für ein wissensbasiertes Katalysator- und Prozessdesign bei Reaktionen mit Kohlenstoffverbindungen. Die Katalysatorverkokung wird dabei typischerweise durch Post-Mortem-Analyse untersucht. In der vorliegenden Arbeit wird ptychographische Röntgentomographie (PXCT) zur Analyse von künstlich verkokten Ni/Al2O3-Katalysatoren für die CO2-Methansierung und CH4-Trockenreformierung verwendet. PXCT liefert dabei 3D-Informationen der lokalen Elektronendichte mit ca. 80 nm Auflösung und ermöglicht somit die Visualisierung und Untersuchung der Ausprägung der Verkokung in Katalysatorpartikeln mit einem Durchmesser von ca. 40 μm. Die Verkokung wurde hauptsächlich im nanoporösen Festkörper identifiziert und konnte nicht in den aufgelösten Makroporen gefunden werden. Die Kohlenstoffbildung wurde unabhängig dazu mittels operando Raman-Spektroskopie bestätigt. PXCT wird als aufkommende Charakterisierungstechnik hervorgehoben, die eine nanoskalige Identifizierung, Lokalisierung und möglicherweise Quantifizierung von verschiedenen Desaktivierungsphänomenen mit 3D-Auflösung in kompletten Katalysatorpartikeln ermöglicht

    Исследование влияния параметров нефтяного шлама на характеристики шнекового дозатора

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    Работа посвящена определению конструктивных особенностей шнекового дозатора при различных параметрах и свойствах нефтяного шлама при его подаче на установку по переработке нефтяных отходов производительностью 1000 кг/ч.The work is devoted to determining the design features of a screw dispenser with various parameters and properties of oil sludge when it is fed to an oil waste processing plant with a capacity of 1000 kg/hr
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