Influence of a Liquid on the Deformation Behavior of Porous Nickel and Titanium under Compression

The deformation behavior of capillary porous (CP) Ni and CP Ti is examined under uniaxial compression in air, water, and ethanol. CP metals contained inert liquids such as H20 and C2H5OH are used as the heat pipes' active elements in space applications. The samples for mechanical testing were isostatic compacting and vacuum annealing (porosity of 60%). Uniaxial compression tests were carried out in the air, water, and ethanol in Shimadzu AG-50K XD (traverse rate 0.1 mm/min). It was shown that CP Ni and CP Ti exhibit the ductile deformation behavior in all cases, which is inherent to Ni and Ti. The ethanol environment induces the increase of the compression strength and the total deformation in both materials compared to deformation behavior in air and water. Therefore, a heat pipe's failure containing CP Ni and CP Ti matrixes and ethanol as the working body is caused rather by manufacturing defects, but not the structural materials' intrinsic properties. © Published under licence by IOP Publishing Ltd.The Russian Foundation for Basic research (№ 20-48-660017)

On Malleability of Rhenium at Room Temperature

The problem of the malleability of rhenium at room temperature is discussed. It has shown that rhenium manufactured by the mean of the electron beam melting is able to the mechanical treatment by rolling at room temperature. The primary condition for mechanical treatment is the minor share of the tensile stress in the processing scheme. It suppresses the grain boundary sliding in a coarse-grained workpiece of this refractory HCP-metal. © Published under licence by IOP Publishing Ltd.The Russian Science Foundation supports this work (№ 18-19-00217)

Mechanical Behavior of Polycrystalline Rhenium under 3-Points Bending at a Low Homological Temperature

Mechanical behaviour of polycrystalline rhenium under 3-points bending at such low homological temperature as room is discussed. Two metallurgical technologies (electron beam melting and powder metallurgy) were used for the samples preparation. Fine-grained samples (PM metal) exhibit some plasticity prior the failure, while coarse-grained ones (EBM metal) behave like a brittle solid. The intergranular fracture is the fracture mode of rhenium in both cases. Basal slip and prismatic slip of dislocations are not active in rhenium at low homological temperature, but the grain boundary sliding occurs under these conditions. Therefore, polycrystalline rhenium cannot be machined at room temperature despite the growth of grain boundary cracks are braked in the samples due to grain boundary sliding. © Published under licence by IOP Publishing Ltd.Russian Science Foundation, RSF: 18-19-00217This work is supported by the Russian Science Foundation (#18-19-00217)

Electronic structure and magnetic properties of fete, bifeo3, srfe12o19 and srcotife10o19 compounds

The electronic energy structures and magnetic properties of iron-based compounds with group VI elements (FeTe, BiFeO3, SrFe12O19 and SrCoTiFe10O19) are studied using the density functional theory (DFT) methods. Manifestations of different types of chemical bonds in magnetism of these compounds are studied theoretically. Calculations of electronic structures of these systems are performed, by using the generalized gradient approximation (GGA) for the description of the exchange and correlation effects within DFT. For SrFe12O19 and SrCoTiFe10O19 hexaferrites, the GGA + U method is also employed to deal with strongly correlated 3d-electrons. The calculations have revealed distinctive features of the electronic structure of the investigated iron-based compounds with strongly correlated 3d-electrons, which can be responsible for their peculiar structural and magnetic properties

Electronic structure and magnetic properties of RT4Al8 (R = Sc, Y, La, Lu; T = Fe, Mn, Cr) compounds. Hydrostatic pressure effects

We present results of theoretical and experimental studies of the electronic structure and magnetic properties of RFe4Al8, RMn4Al8, and RCr4Al8 compounds with nonmagnetic elements R = Sc, Y, La, and Lu. The electron spectrum and field induced magnetic moment, as well as their dependences on the unit cell volume, are calculated for the paramagnetic phase of the RT4Al8 systems. The calculations are supplemented by measurements of the magnetic susceptibility of representative RT4Al8 compounds as a function of temperature and hydrostatic pressure

Pressure effect on magnetic susceptibility of LaCoO3_3

The effect of pressure on magnetic properties of LaCoO$_3$ is studied experimentally and theoretically. The pressure dependence of magnetic susceptibility $\chi$ of LaCoO$_3$ is obtained by precise measurements of $\chi$ as a function of the hydrostatic pressure $P$ up to 2 kbar in the temperature range from 78 K to 300 K. A pronounced magnitude of the pressure effect is found to be negative in sign and strongly temperature dependent. The obtained experimental data are analysed by using a two-level model and DFT+U calculations of the electronic structure of LaCoO$_3$. In particular, the fixed spin moment method was employed to obtain a volume dependence of the total energy difference $\Delta$ between the low spin and the intermediate spin states of LaCoO$_3$. Analysis of the obtained experimental $\chi(P)$ dependence within the two-level model, as well as our DFT+U calculations, have revealed the anomalous large decrease in the energy difference $\Delta$ with increasing of the unit cell volume. This effect, taking into account a thermal expansion, can be responsible for the temperatures dependence of $\Delta$, predicting its vanishing near room temperature.Comment: 7 pages, 9 figure

Influence of magnetic field on paramagnetic-ferromagnetic transition in La1−x_{1-x}Cax_{x}MnO3_{3} (x≈0.25x\approx 0.25) crystal: ultrasonic and transport studies

The ultrasonic properties of La$_{1-x}$Ca$_{x}$MnO$_{3}$ ($x\approx 0.25$) with the Curie temperature $T_C$ about 200 K are studied. Temperature dependences of longitudinal and transverse sound velocities were measured in zero magnetic field and for different constant magnetic fields as well. The ultrasonic study is supported by magnetic, resistive, magnetoresistive, structural and other measurements of the sample that facilitate interpretation of the results obtained. The magnetic field influence on sound properties found in this study presents some new features of the interplay between the elastic and magnetic properties of these compounds. It is shown that the paramagnetic-ferromagnetic transition in the sample studied is first order, but can become second order under the influence of applied magnetic field.Comment: submitted to Phys. Rev.

Dynamics of lattice spins as a model of arrhythmia

We consider evolution of initial disturbances in spatially extended systems with autonomous rhythmic activity, such as the heart. We consider the case when the activity is stable with respect to very smooth (changing little across the medium) disturbances and construct lattice models for description of not-so-smooth disturbances, in particular, topological defects; these models are modifications of the diffusive XY model. We find that when the activity on each lattice site is very rigid in maintaining its form, the topological defects - vortices or spirals - nucleate a transition to a disordered, turbulent state.Comment: 17 pages, revtex, 3 figure