Laser-induced photodetachment of negative oxygen ions in the spatial afterglow of an atmospheric pressure plasma jet

Negative ions are an important constituent of the spatial afterglow of atmospheric pressure plasmas, where the fundamental plasma-substrate interactions take place that are vital for applications such as biomedicine, material synthesis, and ambient air treatment. In this work, we use laser-induced photodetachment to liberate electrons from negative ions in the afterglow region of an atmospheric pressure plasma jet interacting with an argon-oxygen mixture, and microwave cavity resonance spectroscopy (MCRS) to detect the photodetached electrons. This diagnostic technique allows for the determination of the electron density and the effective collision frequency before, during and after the laser pulse was shot through the measurement volume with nanosecond time resolution. From a laser saturation study, it is concluded that O− is the dominant negative ion in the afterglow. Moreover, the decay of the photodetached electron density is found to be dominantly driven by the (re)formation of O− by dissociative attachment of electrons with O2. As a consequence, we identified the species and process responsible for the formation of negative ions in the spatial afterglow in our experiment.

Melting Point of Carbon Particles behind the Gas Detonation Front

A mathematical model of gas detonation of fuel-enriched mixtures of hydrocarbons with oxygen has been formulated, which makes it possible to numerically study the equilibrium flows of detonation products in the presence of free carbon condensation. Reference data for graphite were used to describe the thermodynamic properties of carbon condensate. The calculations are compared with the known results of experimental studies in which, when detonating an acetylene-oxygen mixture in a pipe closed at one end, it is possible to obtain nanoscale particles from a carbon material with special properties. It is assumed that the melting point of such a material is lower than that of graphite and is about 3100 K. Only with such an adjustment of the melting temperature, the best agreement (with an accuracy of about 3 %) was obtained between the calculated and experimental dependence of the detonation front velocity on the molar fraction of acetylene in the mixture.

Comparison of different infiltration amounts of CeO2 inside Ni-YSZ anodes to improve stability and efficiency of Single-Chamber SOFCs operating in methane

Electrochemically active oxide-based anodes capable of working in Single-Chamber Solid Oxide Fuel Cells (SC-SOFCs) were developed. Their performance is related to the selectivity of the electrodes. Tests are carried out on lab-scale devices with YSZ pellets as solid electrolytes in electrolyte supported cells. Selecting methane as a fuel, a gas mixture in the ratio CH4/O2 = 2 was chosen. The Ni-YSZ (NiO:YSZ=60:40) anode was optimized through CeO2 nanocatalysts infiltration to enhance the anode catalytic activity and make its reduction easier. Several infiltration amounts were compared, from null to 15% of the electrode weight. Both symmetric and complete cells (with LSCF-based cathodes) were tested in H2 and CH4/O2. For increasing amounts of infiltrated CeO2, symmetric cells tests describe an area specific resistance (ASR) reduction from 40 Ω cm2 to 1.7 Ω cm2 in hydrogen and from 11 Ω cm2 to 3.9 Ω cm2 in the methane/oxygen mixture. While complete cells tests displayed an ASR drop from 30 Ω cm2 to 2.9 Ω cm2 in H2, and from 8.7 Ω cm2 to 4.3 Ω cm2 in the methane/oxygen mixture, while OCP and power grew from 478 mV and 3.7 mW cm-2 to 766 mV and 13 mW cm-2.

IMPROVEMENT OF THE ALGORITHM FOR DIFFERENTIAL DIAGNOSIS OF INTRACYSTIC BREAST CANCER AND CYSTIC MASTOPATHY

Breast cancer is one of the most important problems of modern oncology. Intracystic cancer in the structure of malignant breast neoplasms belongs to one of the most rare forms and is a variant of intraductal papillary cancer. The issues of early diagnosis of this pathology remain controversial today. The aim of this work was to improve the algorithm of differential diagnosis of intracystic breast cancer and cystic mastopathy. Within the framework of this study, we examined 153 female patients of the prospective group with suspected breast cyst cancer and analyzed the results of examinations carried out for 59 patients of the retrospective group who were examined and treated for intracystic breast cancer in the period from 2010 to 2015 on the basis of Smolensk Regional Oncological Clinical Dispensary. The standard algorithm for examining the patients with suspected intracystic breast cancer in the framework of this study included multiparametric ultrasound (ultrasound in B-mode, ultrasonic Doppler examination, strain elastography, shear wave elastography) and fine needle aspiration puncture biopsy according to our improved technique with subsequent evaluation of the new algorithm's effectiveness. We drew conclusions on low sensitivity and specificity of the traditional algorithm for examining patients with suspected intracystic breast cancer, about a greater effectiveness of the improved algorithm for this diagnosis and advisability to use fine needle aspiration puncture biopsy using the ozone-oxygen mixture to improve the diagnosis of intracystic cancer at the preoperative stage.

Preparation and Characterization of NiCr/NiCr-Al2O3/Al2O3 Multilayer Gradient Coatings by Gas Detonation Spraying

This paper investigates the influence of the technological parameters of detonation spraying on the phase composition of NiCr- and Al2O3-based coatings. It was determined that the phase composition of Al2O3 coatings during detonation spraying strongly depends on the barrel filling volume with the gas mixture. The acetylene–oxygen mixture, which is the most frequently used fuel in the detonation spraying of powder materials, was used as a fuel gas. To obtain a ceramic layer based on Al2O3, spraying was performed at an acetylene–oxygen O2/C2H2 mixture ratio of 1.856; the volume of filling of the detonation gun barrel with an explosive gas mixture was 63%. To obtain a NiCr-based metallic layer, spraying was performed at the O2/C2H2 ratio of 1.063; the volume of filling of the detonation gun barrel with an explosive gas mixture was 54%. Based on a study of the effect of the detonation spraying mode on the phase composition of NiCr and Al2O3 coatings, NiCr/NiCr-Al2O3/Al2O3-based multilayer coatings were obtained. Mixtures of NiCr/Al2O3 powders with different component ratios were used to obtain multilayer gradient coatings. The structural-phase composition, mechanical and tribological properties of multilayer gradient metal–ceramic coatings in which the content of the ceramic phase changes smoothly along the depth were experimentally investigated. Three-, five- and six-layer gradient coatings were obtained by alternating metallic (NiCr) and ceramic (Al2O3) layers. The phase composition of all coatings was found to correspond to the removal of information from a depth of 20–30 μm. It was determined that the five-layer gradient coating, consisting of the lower metal layer (NiCr), the upper ceramic layer (Al2O3) and the transition layer of the mechanical mixture of metal and ceramics, is characterized by significantly higher hardness (15.9 GPa), wear resistance and adhesion strength.

Comparison of laser beam, oxygen and plasma arc cutting methods in terms of their advantages and disadvantages in cutting structural steels

The laser beam, plasma arc, and oxygen cutting methods are widely used in metal cutting processes. These methods are quite different from each other in terms of initial setup cost and cutting success. A powered laser beam is used in laser beam cutting, plasma is used in plasma arc cutting, flammable gas - oxygen mixture is used in the oxygen cutting method. In this study, the cutting success of these methods was investigated on tensile specimens. Microstructure, hardness (HV 0.1), surface roughness, and strengths were investigated after the cutting process. The tensile test implemented with tensile samples cut from the same material by these three methods, it was observed that the strength values of the samples changed by about 8% in tensile strength depending on the cutting process. The hardness of the cut surfaces in plasma arc cutting increased from 150 HV to 230 HV for S235JR material. For this reason, it is difficult to perform machining operations after plasma cutting. The hardness value reached after laser beam cutting is 185 HV. Plasma arc cutting is more cost-effective than laser beam cutting. 1-3° vertical inclination (conicity) occurs on the cut surface in plasma arc cutting, while this inclination almost does not occur in laser cutting. In plasma cutting benches, cutting is done with oxygen, and in cutting with oxygen, the taper is seen in a small amount.