The Influence of Machining Conditions on the Orientation of Nanocrystallites and Anisotropy of Physical and Mechanical Properties of Flexible Graphite Foils.

The physical and mechanical properties and structural condition of flexible graphite foils produced by processing natural graphite with nitric acid, hydrolysis, thermal expansion of graphite and subsequent rolling were studied. The processes of obtaining materials and changing their characteristics has been thoroughly described and demonstrated. The structural transformations of graphite in the manufacture of foils were studied by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). A decrease in the average size of the coherent scattering regions (CSR) of nanocrystallites was revealed during the transition from natural graphite to thermally expanded graphite from 57.3 nm to 20.5 nm at a temperature of 900 °C. The rolling pressure ranged from 0.05 MPa to 72.5 MPa. The thickness of the flexible graphite foils varied from 0.11 mm to 0.75 mm, the density-from 0.70 to 1.75 g/cm3. It was shown that with an increase in density within these limits, the compressibility of the graphite foil decreased from 65% to 9%, the recoverability increased from 5% to 60%, and the resiliency decreased from 10% to 6%, which is explained by the structural features of nanocrystallites. The properties' anisotropy of graphite foils was studied. The tensile strength increased with increasing density from 3.0 MPa (ρ = 0.7 g/cm3) to 14.0 MPa (ρ = 1.75 g/cm3) both in the rolling direction L and across T. At the same time, the anisotropy of physical and mechanical properties increased with an increase in density along L and T to 12% with absolute values of 14.0 MPa against 12.5 MPa at a thickness of 200 µm. Expressed anisotropy was observed along L and T when studying the misorientation angles of nanocrystallites: at ρ = 0.7 g/cm3, it was from 13.4° to 14.4° (up to 5% at the same thickness); at ρ = 1.3 g/cm3-from 11.0° to 12.8° (up to 7%); at ρ = 1.75 g/cm3-from 10.9° to 12.4° (up to 11%). It was found that in graphite foils, there was an increase in the coherent scattering regions in nanocrystallites with an increase in density from 24.8 nm to 49.6 nm. The observed effect can be explained by the coagulation of nanocrystallites by enhancing the Van der Waals interaction between the surface planes of coaxial nanocrystallites, which is accompanied by an increase in microstrains. The results obtained can help discover the mechanism of deformation of porous graphite foils. The obtained results can help discover the deformation mechanism of porous graphite foils. We assume that this will help predict the material behavior under industrial operating conditions of products based flexible graphite foils.

Evaluation of Age-Dependent Changes in the Coloration of Male Killifish Nothobranchius Guentheri Using New Photoprocessing Methods.

Fish as model objects have found wide applications in biology and fundamental medicine and allow studies of behavioral and physiological responses to various environmental factors. Representatives of the genus Nothobranchius are one of the most convenient objects for such studies. Male fish belonging to the family Nothobranchiidae are characterized by extremely diverse coloration, which constantly changes, depending on the age of the fish, environmental factors, and social hierarchical status. These fish species are characterized by a short life cycle, which allows changes in coloration, an indicator of the ontogenesis stage, to be estimated. Existing methods of fish color assessments do not allow the intensity of coloration of particular body zones to be clearly differentiated. In the present study, we suggest a method of two-factor assessment of specific fish body zones using modified methods of photofixation and image processing software. We describe the protocol of the method and the results of its application to different-aged groups of male Nothobranchius guentheri. The coloration of selected areas (i.e., red spot on the gill cover (RSGC), black border on the caudal fin (BBCF), and white border on the dorsal fin (WBDF)) differed significantly according to the size and age of the fish (p < 0.05). The data obtained suggest that N. guentheri can be a model for studying aging by the intensity of body coloration in males.

Some Aspects of Development and Histological Structure of the Visual System of Nothobranchius Guentheri.

In this, work some aspects of the development of the visual system of Nothobranchius guentheri at the main stages of ontogenesis were described for the first time. It was possible to establish that the formation of the visual system occurs similarly to other representatives of the order Cyprinodontiformes, but significantly differs in terms of the individual stages of embryogenesis due to the presence of diapause. In the postembryonic period, there is a further increase in the size of the fish's eyes and head, to the proportions characteristic of adult fish. The histological structure of the eye in adult N. guentheri practically does not differ from most teleost fish living in the same environmental conditions. The study of the structure of the retina showed the heterogeneity of the thickness of the temporal and nasal areas, which indicates the predominant role of peripheral vision. Morphoanatomical measurements of the body and eyes of N. guentheri showed that their correlation was conservative. This indicates an important role of the visual system for the survival of fish in natural conditions, both for the young and adults. In individuals of the older age group, a decrease in the amount of sodium (Na) and an increase in magnesium (Mg) and calcium (Ca) were found in the eye lens. Such changes in the elemental composition of the lens can be a sign of the initial stage of cataractogenesis and disturbances in the metabolism of lens fibers as a result of aging. This allows us to propose N. guentheri as a model for studying the structure, formation, and aging of the visual and nervous systems.

Hair Lead, Aluminum, and Other Toxic Metals in Normal-Weight and Obese Patients with Coronary Heart Disease.

The objective of the present study was to evaluate hair toxic metal levels in patients with obesity and/or coronary heart disease (CHD). Following a 2 × 2 factorial design, subjects without CHD were grouped into normal weight control (n = 123) and obese groups (n = 140). Patients suffering from CHD were divided into normal weight (n = 180) and obese CHD subjects (n = 240). Hair Al, As, Cd, Hg, Ni, and Pb levels were evaluated using inductively-coupled plasma mass-spectrometry. The data demonstrate that hair Al and Hg levels were higher in obese subjects as compared to normal weight controls. Normal weight CHD patients were characterized by significantly higher hair Al, As, Cd, and Pb levels when compared to healthy subjects. The highest hair Al, As, and Pb levels were observed in obese CHD patients, significantly exceeding the respective values in other groups. Factorial analysis revealed significant influence of factorial interaction (CHD*obesity) only for hair Pb content. Given the role of obesity as a risk factor for CHD, it is proposed that increased toxic metal accumulation in obesity may promote further development of cardiovascular diseases.

Variation of the photoluminescence spectrum of InAs/GaAs heterostructures grown by ion-beam deposition.

This work reports on an experimental investigation of the influence of vertical stacking of quantum dots, the thickness of GaAs potential barriers, and their isovalent doping with bismuth on the photoluminescence properties of InAs/GaAs heterostructures. The experimental samples were grown by ion-beam deposition. We showed that using three vertically stacked layers of InAs quantum dots separated by thin GaAs barrier layers was accompanied by a red-shift of the photoluminescence peak of InAs/GaAs heterostructures. An increase in the thickness of the GaAs barrier layers was accompanied by a blue shift of the photoluminescence peak. The effect of isovalent Bi doping of the GaAs barrier layers on the structural and optical properties of the InAs/GaAs heterostructures was investigated. It was found that the Bi content up to 4.96 atom % in GaAs decreases the density of InAs quantum dots from 1.53 × 1010 to 0.93 × 1010 cm-2. In addition, the average lateral size of the InAs quantum dots increased from 14 to 20 nm, due to an increase in the surface diffusion of In. It is shown that isovalent doping of GaAs potential barriers by bismuth was accompanied by a red-shift of the photoluminescence peak of InAs quantum dots of 121 meV.

Obtaining and doping of InAs-QD/GaAs(001) nanostructures by ion beam sputtering.

The features of InAs quantum dots obtained on GaAs(001) single-crystal substrates by ion-beam sputtering were investigated. It has been shown that in the range of ion energies of 150 to 200 eV at a temperature of 500 °C and a beam current of 120 µA InAs quantum dots with average dimensions below 15 nm and a surface density of 1011 cm-2 are formed. The technique of controlled doping of InAs/GaAs nanostructures using a SnTe solid-state source was proposed. It has been established that a maximum donor concentration of 8.7·1018 cm-3 in the GaAs spacer layer is reached at an evaporation temperature of 415 °Ð¡. At the same time, impurity accumulation in the growth direction was observed. We have shown that increasing the impurity doping of the GaAs barrier layer increases the intensity of photoluminescence peaks of the ground state and the first excited state of the InAs quantum dots.