Electrochemical Reducing of Terbium and Holmium Ions in the Sodium and Potassium Chlorides Melt with Equimolar Composition

Interest to rare-earth metals (REM) and their alloys is due to the possibility of using them for the creation of new materials need for modern technology. For instance, REM as alloying components allows for preparation of material with special magnetic properties. A promising method for forming such coating is the surface treatment of metals. This process has an electrochemical character as such for the organization of technology the knowledge of kinetics and mechanism of these processes is important. Despite significant interest in rare-earth metals, these issues are not well described in the literature. In order to choose an adequate mathematical model for calculation of kinetic primers, preliminary experiments that allow evaluating the reversibility of the electrode process have been conducted. Based on that, it was concluded that cathodic reduction of terbium and holmium ions in equimolar NaCl-KCl melt is irreversible. By means of voltammetric analysis, kinetic parameters (transfer coefficients, heterogeneous constants of charge transfer rate) of terbium and holmium electroreduction in equimolar NaCl-KCl melt were determined. The experiment was conducted in a three-electrode cell under a purified argon atmosphere. A dependency of kinetic parameters on the concentration of terbium and holmium chlorides wt (%): 1, 3, 5, 7, 10, was determined. The experiment was conducted in 1073–1173K temperature range. Values of kinetic parameters increase with temperature but decrease with the increase of REM chloride. Based on obtained data, it was found that electroreduction of chloride complexes LnCl63– (Ln–Tb, Ho) in equimolar NaCl-KCl melt is irreversible in the studied range of temperatures and REM concentrations. In summary of experimental data, in range of temperature and rare-earth chloride concentration, and assumption was made that reduction of terbium and holmium ions occurs in two stages. The process includes the preceding stage of complex dissociation. A mechanism of LnCl63– complex reduction in the mentioned melt is proposed. The obtained results are in agreement with literate data for analogues systems

Determination Of Formation Regimes For Bilayer Cobalt Dysprosium Intermetalic Surface Alloy

High tech industrial fields on modern development stage are in need of construction materials with an optimal ratio of volume and surface properties, along with low cost of material itself. As evidenced by studies, in order to give a set complex of properties to a workpiece that operates under specific conditions, it is often sufficient to only modify its surface area. Over the course of studies, by means of gravimetric, influence of technological parameters (temperature and time samples are kept in the melt) on specific mass change of cobalt samples, that act as substrate, during electroless diffusive saturation with dysprosium in eutectic melt of lithium and potassium chlorides have been studied. A mathematical dependency was established for specific mass change of cobalt samples on time spent in melt for temperature range of 873–973 K. Composition of intermetallic coats obtained on surface of cobalt samples was studied means of EDX and SEM analyses. It was discovered, that for chosen temperature range, diffusion layers formed on surface of cobalt samples consists of two structural zones that correspond to Co-Dy and Cp2Dy phases

Quasi free-standing one-dimensional nanocrystals of PbTe grown in 1.4 nm SWNTs

Here, we show successful filling of 1.4 nm single-walled carbon nanotubes (SWNT) with PbTe nanocrystals. The structure of one-dimensional PbTe in SWNT was determined using high-resolution transmission electron microscopy (HRTEM). The electronic structure of composites was studied by optical absorbance and Raman spectroscopies indicating no noticeable interaction of encapsulated PbTe with SWNT wall. Experimental data are supported by ab-initio calculations, showing non-zero density of states at the Fermi level of PbTe@SWNT(10,10) provided by both SWNT and PbTe states and thus metallic conductivity of the composite

Acute ischemic stroke lesion segmentation in non-contrast CT images using 3D convolutional neural networks

In this paper, an automatic algorithm aimed at volumetric segmentation of acute ischemic stroke lesion in non-contrast computed tomography brain 3D images is proposed. Our deep-learning approach is based on the popular 3D U-Net convolutional neural network architecture, which was modified by adding the squeeze-and-excitation blocks and residual connections. Robust pre-processing methods were implemented to improve the segmentation accuracy. Moreover, a specific patches sampling strategy was used to address the large size of medical images, to smooth out the effect of the class imbalance problem and to stabilize neural network training. All experiments were performed using five-fold cross-validation on the dataset containing non-contrast computed tomography volumetric brain scans of 81 patients diagnosed with acute ischemic stroke. Two radiology experts manually segmented images independently and then verified the labeling results for inconsistencies. The quantitative results of the proposed algorithm and obtained segmentation were measured by the Dice similarity coefficient, sensitivity, specificity and precision metrics. Our proposed model achieves an average Dice of $0.628\pm0.033$, sensitivity of $0.699\pm0.039$, specificity of $0.9965\pm0.0016$ and precision of $0.619\pm0.036$, showing promising segmentation results.Comment: 18 pages, 4 figures, 2 table

Controlled thermodynamics for tunable electron doping of graphene on Ir(111)

The electronic properties and surface structures of K-doped graphene supported on Ir(111) are characterized as a function of temperature and coverage by combining low-energy electron diffraction, angle-resolved photoemission spectroscopy, and density functional theory (DFT) calculations. Deposition of K on graphene at room temperature (RT) yields a stable (√3 × √3) R30° surface structure having an intrinsic electron doping that shifts the graphene Dirac point by ED = 1.30 eV below the Fermi level. Keeping the graphene substrate at 80 K during deposition generates instead a (2 × 2) phase, which is stable until full monolayer coverage. Further deposition of K followed by RT annealing develops a double-layer K-doped graphene that effectively doubles the K coverage and the related charge transfer, as well as maximizing the doping level (ED = 1.61 eV). The measured electron doping and the surface reconstructions are rationalized by DFT calculations. These indicate a large thermodynamic driving force for K intercalation below the graphene layer. The electron doping and Dirac point shifts calculated for the different structures are in agreement with the experimental measurements. In particular, the K4s bands are shown to be sensitive to both the K intercalation and periodicity and are therefore suggested as a fingerprint for the location and ordering of the K dopants

Synthesis, X-ray crystal structure and antimycobacterial activity of enantiomerically pure 1-ethyl-2,3-dicyano-5-(het)aryl-6-hetaryl-1,6- dihydropyrazines

The Petasis reaction of 6-alkoxy adducts of 1-alkyl-2,3-dicyano-5- arylpyrazinium salts with aromatic boronic acids, such as 2-thienylboronic, 2-furanylboronic and 3-thienylboronic acids, or their benzo analogs in dichloromethane proceeds smoothly at room temperature with the formation of the corresponding 5-aryl-6-hetaryl substituted 1,6-dihydropyrazine derivatives. All dihydropyrazines were separated as pure enantiomers by chiral HPLC, and their absolute configurations for each pair of enantiomers have been determined by X-ray analysis. Individual enantiomers were screened in vitro for their antimycobacterial activities against Mycobacterium tuberculosis H37Rv, avium, terrae and extensively drug-resistant and multi-drug-resistant strains isolated from tuberculosis patients in Ural region (Russia). It has been shown that several compounds exhibit a good level of antituberculosis activity compared to the reference drugs. © ARKAT-USA, Inc

Observation of a universal donor-dependent vibrational mode in graphene

Electron-phonon coupling and the emergence of superconductivity in intercalated graphite have been studied extensively. Yet, phonon-mediated superconductivity has never been observed in the 2D equivalent of these materials, doped monolayer graphene. Here we perform angle-resolved photoemission spectroscopy to try to find an electron donor for graphene that is capable of inducing strong electron-phonon coupling and superconductivity. We examine the electron donor species Cs, Rb, K, Na, Li, Ca and for each we determine the full electronic band structure, the Eliashberg function and the superconducting critical temperature Tc from the spectral function. An unexpected low-energy peak appears for all dopants with an energy and intensity that depend on the dopant atom. We show that this peak is the result of a dopant-related vibration. The low energy and high intensity of this peak are crucially important for achieving superconductivity, with Ca being the most promising candidate for realizing superconductivity in graphene

ФЛУОРЕСЦЕНТНОЕ ОПРЕДЕЛЕНИЕ ПАРОВ НИТРОБЕНЗОЛА С ИСПОЛЬЗОВАНИЕМ ДОПИРОВАННОГО ФЛУОРОФОРАМИ ПОЛИСТИРОЛА

Integration of fluorescent substances into polymeric matrices can improve their sensory properties and photostability. In this work, fluorescent materials based on fluorophore-doped polystyrene were obtained and characterized as sensors towards the ecotoxicant nitrobenzene in gas phase. Melamine-formaldehyde foam has been proposed as a permeable substrate for the sensor material deposition applicable for gas-phase measurements. The effect on sensor properties of the porous material surface obtained via Breath Figure pore generation technique was investigated. Limits of detection and calibration relationships of obtained materials towards nitrobenzene were evaluated by materials exposure to low concentrations of nitrobenzene vapors. The sorption properties of polystyrene allow the retention of the quencher near the fluorophore, leading to improved detection limits compared with pure fluorophores. Obtaining a porous surface of the polymer material by the Breath Figure technique increases the scale of its fluorescence quenching by vapors. Detection limits (down to 0.45 ppm) and detectable concentration ranges (0.5 - 371.6 ppm) have been experimentally established. The relative standard deviations of the fluorescent signal of polymer materials do not exceed 13.3 % for a number of concentrations in the detectable range. The applicability of the calibration linear relationship of the logarithm of the fluorescent signal on the logarithm of the nitrobenzene vapor concentration is shown. Fluorescence signal measurements were performed using the original sensor element and the luminescence detector employing an array of fluorescent materials. The developed device is simple in application, portable, automated, and in combination with the used polymeric materials allows detection of nitrobenzene vapors in concentrations 2.5 times lower than the maximum permissible level.  Keywords: Fluorescence, nitrobenzene, polystyrene, melamine, doping, breath figure, fluorescence readerИнтеграцией флуоресцентных веществ в полимерные матрицы можно улучшить их сенсорные свойства и фотостабильность. В работе получены и исследованы флуоресцентные материалы на основе допированного флуорофорами полистирола в качестве сенсоров на экотоксикант нитробензол в газовой фазе. Меламин-формальдегидная пена предложена в качестве проницаемого субстрата для нанесения сенсорных составов. Исследовано влияние техники создания пористой поверхности материала Breath Figure на сенсорные свойства. Пределы обнаружения нитробензола в газовой фазе с использованием полученных материалов были оценены экспозицией малым концентрациям паров нитробензола. Измерения флуоресцентного сигнала были выполнены с помощью оригинальных сенсорного элемента и регистратора люминесценции, применяющих комбинацию флуоресцентных материалов. Разработанное техническое решение регистратора люминесценции является простым в применении, портативным, автоматизированным и позволяет с использованием полученных полимерных материалов обнаружение паров нитробензола в концентрациях ниже предельно допустимой по гигиеническим нормативам