A methodology for the modernization of technological processes for the hot forging of aluminum alloy forgings based on computer simulation has been developed. The modernization procedure is outlined, ...including the analysis of an analogous technological process, the development of a virtual technological process structure, the creation of forging and die models in the SolidWorks program, the formulation of a computer simulation problem, the input of simulation parameters, the launch and analysis of a computer technology model, and the development of recommendations for modernizing an existing process with subsequent pilot testing of technology. An example of the methodology was the die forging technology “Rack” made of 5083 alloy, which is a single-plane complex-shaped panel with stiffeners. The analysis of the technology-analogue made it possible to formulate the problem of finding the possibility of reducing operations. Temperature, speed, and power deformation modes were introduced, which were a deformation rate of 0.3 mm/s, billet-heating temperature 450 °C, and the temperature of a die 400 °C. The output was a database of the process. At the end of the virtual experiment, the technology was tested on laboratory equipment, and a comparative analysis of the two technologies was carried out, which presented the advantages of the proposed isothermal die forging technology and developed recommendations for updating the existing technology. The transition to isothermal die forging will reduce the number of passes from three to one. All this will lead to an increase in metal utilization rate from 0.44 to 0.77.
The paper reviews history of studies and research areas on a frozen mummy of the woolly mammoth (
Mammuthus primigenius
) found in 2010 in Oyogoss Yar, about 30 km west of the Kondratyeva River ...mouth, northern Yakutia. Introduced to the scientific literature as the Yuka Mammoth, it became the first, partly preserved carcass of female woolly mammoth of adolescent age found in the world, which lived about 39 000 calendar years BP, during relatively warm period (MIS 3, Molotkovskian, or Leningrad Interstadials).The multidisciplinary study of Yuka by various approaches (anatomical-morphological, palynological, paleobotanical, microbiological, computer tomography, and radiocarbon dating methods) yielded fundamentally new data on this proboscidean species. The paper evaluates systematic studies of this unique specimen, from identification of its age and studies of skeletal morphology, ontogenetic development and environmental conditions to reporting the presence of viable bacteria in Yuka’s soft tissues. This paper also features the discovery of the preserved brain and analysis of its structure, as well as a revelation of unique morphology of the trunk, for the first time for this species. The paleobotanical data indicated predomination of open herbaceous landscapes during Yuka’s life. New features of the species morphology were revealed: delayed eruption of the permanent tusks (I) and different number of nail plates and phalanges on the forelegs. The presence of viable bacteria strains of
Bacillus
genus was recorded in Yuka’s tissues.
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This work presents the results of the mineralogical, crystallochemical, and geochronological study of globular phyllosilicates (GPS) of glauconite–illite series from the Bakeevo Formation. This ...formation is the basal member of the Vendian Asha Group in the Southern Urals. The monomineral GPS fractions representing the globules varying in size and density are composed of Al-glauconite and illite. The Rb–Sr dating of the GPS of the Bakeevo Formation in combination with the modeling of cation distribution in their structure and comparison of the model data with Mössbauer and IR spectroscopy data was performed for the first time. The Rb–Sr age of the Bakeevo glauconite is 642 ± 9 Ma. The mineralogical and geochemical characteristics in combination with model calculations show that the stratigraphic significance of this age is quite reasonable. The initial
87
Sr/
86
Sr ratio in the glauconitization environment is 0.7080 ± 0.0009 and is consistent within the experimental error with this ratio in the Vendian seawater. Thus, the lower boundary of the Vendian in the Southern Urals has an age of about 640 Ma.
We have theoretically analyzed conditions under which the screening of a flow of evaporated metal atoms by the Langmuir layer formed due to ionization of atoms in this layer can significantly ...influence the dynamics of hot plasma in contact with a metal surface. It is established that allowance for the screening of evaporated atomic flow by this Langmuir layer is necessary in many cases, in particular, in simulations of laser-plume dynamics.
In direct experiments, rate constants of photochemical (
k
P
) and non-photochemical (
k
P
+
) fluorescence quenching were determined in membrane fragments of photosystem II (PSII), in ...oxygen-evolving PSII core particles, as well as in core particles deprived of the oxygen-evolving complex. For this purpose, a new approach to the pulse fluorometry method was implemented. In the “dark” reaction center (RC) state, antenna fluorescence decay kinetics were measured under lowintensity excitation (532 nm, pulse repetition rate 1 Hz), and the emission was registered by a streak camera. To create a “closed” P680
+
Q
A
–
RC state, a high-intensity pre-excitation pulse (pump pulse, 532 nm) of the sample was used. The time advance of the pump pulse against the measuring pulse was 8 ns. In this experimental configuration, under the pump pulse, the P680
+
Q
A
–
state was formed in RC, whereupon antenna fluorescence kinetics was measured using a weak testing picosecond pulsed excitation light applied to the sample 8 ns after the pump pulse. The data were fitted by a two-exponential approximation. Efficiency of antenna fluorescence quenching by the photoactive RC pigment in its oxidized (P680
+
) state was found to be ∼1.5 times higher than that of the neutral (P680) RC state. To verify the data obtained with a streak camera, control measurements of PSII complex fluorescence decay kinetics by the single-photon counting technique were carried out. The results support the conclusions drawn from the measurements registered with the streak camera. In this case, the fitting of fluorescence kinetics was performed in three-exponential approximation, using the value of τ
1
obtained by analyzing data registered by the streak camera. An additional third component obtained by modeling the data of single photon counting describes the P680
+
Pheo
–
charge recombination. Thus, for the first time the ratio of
k
P
+
/
k
P
= 1.5 was determined in a direct experiment. The mechanisms of higher efficiency for non-photochemical antenna fluorescence quenching by RC cation radical in comparison to that of photochemical quenching are discussed.
Experimental results on the laser ablation of the highly oriented pyrolytic graphite by using light pulses of an Nd:YAG laser (pulse width 25 ns, pulse energy 220 mJ) are presented. Analysis of the ...surface profile of the carbon target shows that the target material melts in the course of the laser ablation. As a result of ablation, a coating consisting of carbon nanoparticles about 10 nm in size is formed on the substrate placed at a distance of 4 cm from the target. It is assumed that such particles are formed as a result of the electrodispersion of carbon droplets detached from the target surface and charged to an unstable state in the laser plasma plume. Raman spectra of the coatings indicate that the carbon nanoparticles being formed have an amorphous structure.
We have experimentally studied the action of high-power plasma flows on pure tungsten plates covered with multilayer films of tungsten nanoparticles formed by the method of laser electrodeposition. ...The samples were irradiated using a plasma gun producing hydrogen (helium) plasma flows with power density up to 35 GW/cm
2
. The resulting surface morphology was studied by scanning electron microscopy (SEM). SEM data showed that tungsten plates coated by nanoparticles are more resistant to the formation of microcracks than are pure tungsten plates.
Frequency and density dependencies of the effective conductivity and permittivity of carbon nanotube (CNT) and graphene nanoplatelet (GNP) based polymer composites are studied in the microwave ...(0.1-20, 26-36 GHz) and terahertz (0.2-1.0 THz) ranges. Strong frequency dependencies of the effective conductivity are associated with the screening effect occurred in individual nanoparticles and their agglomerates. Density dependencies are fitted with power-law formulas with frequency dependent exponents. Thin films comprising the CNTs or GNPs were proposed to consider as 'perfect' composites with the maximal possible electromagnetic interaction of the inclusions. Comparison between films and polymer composites has been done. The ratio of the microwave to terahertz conductivities of the composite is proposed to estimate the efficacy of GNP interaction with the electromagnetic field. Synergy effect in the enhancement of the effective microwave conductivity is demonstrated for the composite comprising a mixture of CNTs and GNPs.
Covalently linked hybrid structures of semiconductor nanocrystals (CdSe/ZnS quantum dots) as an inorganic component with a fluorescence maximum at 620 nm and photosynthetic protein allophycocyanin ...(APC) as an organic part are created. It is found out that CdSe/ZnS quantum dots form stable complexes with APC through covalent bonding in aqueous solutions. It is shown that the efficiency of electronic excitation energy transfer (EET) in such systems may be significantly enhanced under the conditions at which the monomerization of allophycocyanin trimers occurs. In this paper the EET efficiency is evaluated under differing experimental conditions (pH, temperature, and presence of NaSCN) for hybrid systems obtained by the self-assembling of components via electrostatic interactions, as well as via covalent linking. Under the most optimal conditions, there is a 20-fold increase in the APC fluorescence after the excitation of QDs due to the more efficient EET for the covalently linked components compared to the complexes obtained by the self-assemblage. The obtained covalently linked hybrid structures unfold new opportunities for their practical use as fluorescent markers, hybrid photosensors, and structural elements in photovoltaic devices.
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