Increase in the Reduction Potential of Uranyl upon Interaction with Graphene Oxide Surfaces

Coordination of uranyl (U(VI)) with carboxylate groups on functionalized graphene oxide (GO) surfaces has been shown to alter the reduction potential of the sorbed uranium ion. A quantitative measure of the reduction potential and qualitative estimation of sorption/desorption processes were conducted using cyclic voltammetry, and the proposed coordination environment was determined using the surface sensitive attenuated total reflection mode of infrared spectroscopy (ATR-FTIR). GO is a nanostructured material possessing a large amount of oxygen-containing functional groups both on basal planes and at the edges, which can form strong surface complexes with radionuclides. The presence of these functional groups on the surface of GO allows efficient immobilization of uranium due to sorption of uranyl (UO22+) to carboxylate, hydroxide, or sulfonate functional groups and the potential for enhanced reduction of U(VI) to more strongly sorbing and insoluble U(IV). Herein, binding of U(VI) to carboxylate groups on the GO surface is proposed as the primary sorption mechanism based on the FTIR study. Furthermore, the coordination of uranium with the surface increases the reduction potential of the U(VI)/U(IV) redox couple as compared to the case of the aqueous U(VI)/U(IV) species. This is consistent with the alteration of the electronic structure of the sorbed ion, which can be determined in our case due to the use of a GO-coated working electrode. Thus, GO-coated glassy carbon electrodes and other semi-conducting electrodes with high ion sorption capacities may provide a means of examining the oxidation/reduction potentials of sorbed ions

PREDICTING THE LIFETIME OF HIGH-POWER LASER DIODES FROM THE CURRENT DEPENDENCE OF THEIR SPECTRAL CHARACTERISTICS

The high power laser diodes lifetime prediction method which is based on current de-pendence line form analysis skirting laser radiation spectrum after 200 hours of service is offered

Структура и электрические свойства легированных железом керамик на основе оксида цинка

The structure and electrical properties of (FexOy)10 (ZnO)90 ceramics (0 ≤ x ≤ 3; 1 ≤ y ≤ 4) synthesized in air by one− and two−stage method were studied. To dope ZnO, powders of FeO, α−Fe2O3, and Fe3O4 or a mixture (α−Fe2O3 + FeO) were used. On the basis of X−ray diffraction analysis, gamma−resonance spectroscopy and Raman spectroscopy, it was established that at fixed average iron concentrations of 1—3 at.% in ceramic samples, at least three phases are formed: solid solution Zn1−δFeδO with wurtzite structure and residual iron oxides FexOy, used as doping agents. Scanning electron microscopy and energy−dispersive X−ray analysis have shown that, in the studied ceramics, the grain sizes of the wurtzite phase decreased from several tens of micrometers using one−step synthesis to the submicron level for the case of two−step synthesis. It was found that the incorporation of iron into ZnO leads to a contraction of the crystal lattice in the wurtzite phase and the stronger, the higher the proportion of oxygen in the doping iron oxides FexOy. The study of the temperature dependences of the electrical resistivity have shown that deep donor centers with an activation energy of about 0.35 eV are formed in the wurtzite phase Zn1−δFeδO. The temperature dependences of the electrical resistivity in the undoped ZnO in the temperature range of 6—300 K and in the doped ceramics (FexOy)10(ZnO)90, obtained by the one−step synthesis method, at temperatures below 50 K, are characterized by a variable activation energy, which indicates a strong disordering of their structure.В настоящее время особое внимание уделяется поиску экономичных технологий производства, а также исследованию структуры и свойств новых керамических композиционных материалов на основе оксида цинка. Такие керамики имеют ряд преимуществ по сравнению с материалами, полученными по более дорогим технологиям, поскольку дают возможность изготавливать изделия различных форм и размеров, в том числе с варьированием их морфологии и структурно−фазового состояния. Это позволяет контролировать их функциональные свойства путем изменения размеров частиц в исходной шихте; температур, длительности и атмосферы синтеза и термообработок, а также типа легирующих агентов в керамиках. Исследована структура и электрические свойства керамик (FexOy)10(ZnO)90 (0 ≤ x ≤ 3; 1 ≤ y ≤ 4), синтезированных на воздухе методом одно− и двухэтапного снтеза. Для легирования ZnO использовали порошки соединений FeO, α−Fe2O3 и Fe3O4 или смесь (α−Fe2O3 + FeO). На основе экспериментальных результатов, полученных методами рентгеновского дифракционного анализа, гамма−резонансной спектроскопии и рамановской спектроскопии установлено, что при фиксируемых средних концентрациях железа 1—3 % (ат.) в керамических образцах формируется не менее трех фаз: твердый раствор Zn1−δFeδO со структурой вюрцита, феррит ZnFe2O4 со структурой шпинели, а также остаточные оксиды железа FexOy, использованные в качестве легирующих агентов. Методами сканирующей электронной микроскопии и энерго−дисперсионного рентгеновского анализа показано, что в исследованных керамиках размеры зерен вюрцитной фазы уменьшаются от нескольких десятков микрометров при использовании одноэтапного синтеза до субмикронного уровня для случая двухэтапного синтеза.Обнаружено, что введение железа в ZnO приводит к сжатию кристаллической решетки вюрцитной фазы, тем более сильному, чем выше доля кислорода в легирующих оксидах железа FexOy. Изучение температурных зависимостей удельного электросопротивления показало, что в вюрцитной фазе Zn1−δFeδO формируются глубокие донорных центры с энергией активации порядка 0,37 эВ. Температурные зависимости электросопротивления электронов в нелегированном ZnO в диапазоне температур 6—300 К и в легированной керамике (FeO)10(ZnO)90, полученной методом одноэтапного синтеза, при температурах ниже 50 К характеризуются переменной энергией активации. Это указывает на сильное разупорядочение их структуры

Catalytic residues in hydrolases: analysis of methods designed for ligand-binding site prediction

The comparison of eight tools applicable to ligand-binding site prediction is presented. The methods examined cover three types of approaches: the geometrical (CASTp, PASS, Pocket-Finder), the physicochemical (Q-SiteFinder, FOD) and the knowledge-based (ConSurf, SuMo, WebFEATURE). The accuracy of predictions was measured in reference to the catalytic residues documented in the Catalytic Site Atlas. The test was performed on a set comprising selected chains of hydrolases. The results were analysed with regard to size, polarity, secondary structure, accessible solvent area of predicted sites as well as parameters commonly used in machine learning (F-measure, MCC). The relative accuracies of predictions are presented in the ROC space, allowing determination of the optimal methods by means of the ROC convex hull. Additionally the minimum expected cost analysis was performed. Both advantages and disadvantages of the eight methods are presented. Characterization of protein chains in respect to the level of difficulty in the active site prediction is introduced. The main reasons for failures are discussed. Overall, the best performance offers SuMo followed by FOD, while Pocket-Finder is the best method among the geometrical approaches

Maze Solving Using Fatty Acid Chemistry

This study demonstrates that the Marangoni flow in a channel network can solve maze problems such as exploring and visualizing the shortest path and finding all possible solutions in a parallel fashion. The Marangoni flow is generated by the pH gradient in a maze filled with an alkaline solution of a fatty acid by introducing a hydrogel block soaked with an acid at the exit. The pH gradient changes the protonation rate of fatty acid molecules, which translates into the surface tension gradient at the liquid–air interface through the maze. Fluid flow maintained by the surface tension gradient (Marangoni flow) can drag water-soluble dye particles toward low pH (exit) at the liquid–air interface. Dye particles placed at the entrance of the maze dissolve during this motion, thus exhibiting and finding the shortest path and all possible paths in a maze

Basic properties of the fields excited by HMD located in a dielectric substrate backed by a perfectly-conducting ground plane

Fundamental antenna effects are studied of a dielectric substrate backed by a perfectly-conducting ground plane and excited by elementary dipole. The effect of the surface waves and the radiation efficiency as a function of substrate thickness and permittivity are analysed

Method of regularization in numerical simulation of axially symmetric dielectric patch antenna excited by ved

In the design of microstrip monolithic integrated circuits and millimeter-wave printed antennas, accurate numerical modeling becomes important as the operating frequency becomes higher. Besides of metallic patches, dielectric antennas are actively studied as alternative radiating elements. Our solution of the scattering by a circular dielectric patch is based on the Method of Regularization combined with the Galerkin's Method. This method has a controlled accuracy in the resonant range, and a much smaller matrix size in comparison to solutions obtained by direct applications of the Method of Moments