Exact dynamic and static stiffness matrices of shear deformable thin-walled beam-columns

Total potential energy of non-symmetric thin-walled beam-columns in the general form is presented by introducing the displacement field based on semitangential rotations and deriving transformation equations between displacement and force parameters defined at the arbitrary axis and the centroid-shear center axis, respectively. Next, governing equations and force-deformation relations are derived from the total potential energy for a shear-deformable, uniform beam element and a system of linear eigenproblem with non-symmetric matrices is constructed based on 14 displacement parameters. And then explicit expressions for displacement parameters are derived and exact dynamic stiffness matrices are determined using force-deformatin relationships. In addition, the modified numerical method to eliminate multiple zero eigenvalues and to evaluate the exact static stiffness matrix is developed for spatial stability analysis. Finally, in order to demonstrate the validity and the accuracy of this study, the spatially coupled natural frequencies and buckling loads are evaluated and compared with analytical solutions or results analyzed by thin-walled beam elements and ABAQUS's shell elements.     

Investigation of a wake decay behind a circular disk in a hydro channel at high Reynolds numbers

LDA and PIV techniques were used to study the decay of an axisymmetrical turbulent wake originated downstream an immobile disk in a water flume for Reynolds numbers Re = 1.5?2.4?10⁵. Data were compared with experiments performed with a set of thermo-anemometers behind a disk in a wind tunnel at lower Reynolds numbers (Re = 1.3?2.6?10⁴). Observations for a new range of Reynolds number confirmed that the velocity distribution in the disk wake keeps self-similarity. The decay of a wake by the power law ?2/3 in the presented experiments remains until the maximum deficit of velocity becomes comparable with the turbulent pulsation level in the free-stream (less than 2 %).     

An aperiodic set of 13 Wang tiles

A new aperiodic tile set containing only 13 tiles over 5 colors is presented. Its construction is based on a recent technique developed by Kari. The tilings simulate the behavior of sequential machines that multiply real numbers in balanced representations by real constants.     

Erratum to: Several Articles in JETP Letters Published Online First

JETP Letters - An Erratum to this paper has been published: https://doi.org/10.1134/S0021364022330013     

Electrical Resistivity Training Effect in the Exchange-Biased GdBaCo2O5.5 Cobaltite

Journal of Experimental and Theoretical Physics - The nature of the training effect in exchange-biased compounds is studied. This effect consists in a decrease in the exchange bias field (HEB)...     

Observation of solar-magnetospheric and geophysical effects on the electron and proton fluxes detected by the satellite-borne ARINA instrument

New results are presented on the observations of bursts and variations in high-energy charged-particle fluxes in the near-Earth space by the ARINA instrument operated onboard the Resurs-DK1 satellite since 2006.     

Phase separation and anisotropy in the electrical properties of weakly doped lanthanum manganites

Variations in the thermopower, electrical resistivity, magnetoresistance, thermal expansion coefficients, and their anisotropy with temperature were detected near room temperature in single crystals of weakly doped lanthanum manganites La_1?xA_xMnO₃ (A = Ca, Sr; x = 0.07–0.125) with orthorhombic structure. The results obtained are discussed in terms of a model of phase separation related to polaron anisotropy. Due to a gain in exchange and elastic energies in the lattice, small-radius magnetic polarons can merge to form polarons of a larger size, which would contain now not one but rather a few electrons (equal in number to the polarons in the cluster). As a result, short-range order in a cluster and phase separation set in at a temperature T_ps ≈ 250–300 K, which is approximately equal to the Curie temperature T_C of conducting manganites with x ≈ 0.2–0.3.     

Contribution of carriers to optical conductivity spectra of lanthanum manganites

To study the band structure and carriers in lanthanum manganites, measurements have been made of the reflectance spectra of single crystals and polycrystals in the 0.04–1.6-eV range and of the optical conductivity σ _opt calculated by the Kramers-Kronig method as functions of the concentration and species of divalent ions in the paramagnetic (PM) and ferromagnetic (FM) regions. The optical gap for single-crystal La_0.9Sr_0.1MnO₃ is ∼0.17 eV, and the polaronband energy is 0.12 eV. In the PM region, σ _opt spectra do not indicate a band-carrier contribution, and conduction is dominated by polaron hopping and activation to the mobility edge. In the FM region, the variation in the σ _opt and absorption spectra of La_0.7Sr_0.3MnO₃ epitaxial films indicate the appearance of band carriers and a red shift of the absorption edge. The two band-carrier contributions, with weak and strong dependences on photon energy, are related to conduction in the antiferromagnetic matrix and the ferromagnetic regions. Fiz. Tverd. Tela (St. Petersburg) 41, 475–482 (March 1999)     

One-dimensional coherent four-wave mixing as a way to image the spatial distribution of atoms in a laser-produced plasma

An experimental technique based on coherent one-dimensional hyper-Raman-resonant four-wave mixing in broad cylindrically focused light beams has been developed for line-by-line imaging of spatial distribution of excited atoms in a low-temperature plasma of optical breakdown. The technique was applied to map excited lead atoms in a low-temperature laser-produced plasma.