The shape of (nano)islands is among significant factors of the catalytic activity of supported catalysts. A lattice model of the reshaping under reaction conditions is suggested and studied by means ...of kinetic Monte Carlo simulations. It is rooted in experimental findings and is simplified as far as possible to still demonstrate reversible compact—ramified shape transitions. This simple model with complex behavior demonstrates several reshaping regimes and is considered as a possible sub-network of more realistic networks of heterogeneous catalytic reactions.
We investigate the Diophantine equation of the form
, with
where
and
are odd and
is even, and
is a sufficiently small natural number. We obtain a complete description of the set of solutions to such ...an equation.
The results of experimental studies of propagation of elastic bending waves in a metamaterial element are presented; the element is a wedge whose thickness varies by the parabolic law. The specimen ...is prepared by 3D printing from ABS polymer. The experimental setup for generation and recording of elastic bending waves in the fabricated wedge specimen is described. Elastic waves in the wedge are recorded and imaged by a laser scanning vibrometer. The peculiarities of bending wave propagation parallel and perpendicular to the edge of the fabricated wedge specimen are experimentally investigated. The experimental results are analyzed. The performed studies show that the wedge prepared in this study is a waveguide concentrating the acoustic wave energy, which is important in developing acoustic metamaterials and absorbing devices working under the principle of an acoustic black hole.
The article presents the results of experimental studies of the elastic properties of the polymer polylactide (PLA), which is widely used in 3D printing technology. The dependences of the mechanical ...stress on the static deformation magnitude are measured, and the dependence of the hysteresis is found. The values of the Young’s modulus in the linear sections of loading and unloading of the sample are estimated. It is established that the periodic loading and unloading of the sample lead to its strengthening in the region of elastic deformations. An equation that relates the change in the velocity of acoustic waves in a thin rod with the value of its static deformation is obtained, which is suitable for describing the PLA sample under study. A linear dependence of the relative change in the elastic wave velocity in the sample on the magnitude of its static deformation is found. Based on the measurement results, the third-order elastic coefficients are determined and the nonlinear acoustic parameter in the PLA polymer is calculated.
A Monte Carlo generator to simulate events of single-photon annihilation to hadrons at center-of-mass energies below 2 GeV is described. The generator is based on existing data on cross sections of ...various exclusive channels of e+e− annihilation obtained in scan and ISR experiments. It is extensively used in the software packages for analysis of experiments at the Novosibirsk e+e− colliders VEPP-2000 and VEPP-4M aimed at high-precision measurements of hadronic cross sections with different applications, e.g. to calculations of the hadronic vacuum polarization for the muon anomalous magnetic moment.
The article presents the results of experimental studies of how 3D printing with 100% filling influences the elastic properties of PLA filament polymer samples. The static and Thurston–Brugger ...methods simultaneously measure the dependence of strain and the relative change in the velocity of elastic waves on the applied mechanical stress (up to failure) for the initial and 3D-printed samples of the PLA polymer. Based on the measurement results, the linear and nonlinear Young’s moduli and second-order acoustic nonlinear parameter are calculated. It has been established that 3D printing leads to a deterioration in the strength and plastic characteristics of PLA. A different behavior of the nonlinear parameters of the initial and 3D-printed PLA samples in the loading and unloading region was revealed, associated with a change in the internal structure of the sample caused by 3D printing.
This article discusses the quality of astronomical images under conditions of moderate small-scale turbulence and varying meso-scale airflows above the Baikal Astrophysical Observatory (BAO). We ...applied a Weather Research and Forecasting (WRF) Model, as well as statistical estimations of the Fried parameter from the differential motion of the solar images. The simulations were performed with a fairly high horizontal resolution within a large area of 1600 × 1600 km. A high horizontal resolution provides representative estimations of atmospheric characteristics and correct accounting of large-scale air advection. We considered the influence of atmospheric motions over the cold water area of Lake Baikal, as well as meso-scale vortex structures over rough terrain on solar image quality. A better understanding of structured turbulent small-scale motions and optical turbulence over rough terrain may help to develop advanced methods for diagnostics and prediction of image quality. For the first time, we have shown that the BAO is located at the periphery of a meso-scale atmospheric vortex structure with an anticyclonic direction of airflows in the daytime. An increase in image quality was associated with weakening airflows over Lake Baikal and a decrease in the intensity of wind speed fluctuations. Calculated spectra of atmospheric turbulence in the daytime were close to the classical form. At night and in the morning, the spectra had a steeper slope on small scales. Deformations of the spectra were due to the suppression of turbulence under stable stratification of the atmosphere. The characteristic horizontal scales of the transition from “−5/3” to ∼“−3” spectral slope were 2–2.5 km. The results obtained using the WRF model and analysis of optical turbulence strength (namely, the Fried parameter) indicated that the parameterization schemes used in the WRF model were accurate.
The shear elastic properties of YBa
2
Cu
3
O
7 –
x
high-temperature superconducting (HTSC) ceramics are studied near the superconducting transition at a temperature of 91.3 K and room temperature of ...293 K. For the first time, a local increase in shear nonlinear acoustic parameter
N
in the region of the phase transition temperature was detected. Experimental studies of the linear and nonlinear elastic properties of YBa
2
Cu
3
O
7 –
x
HTSC ceramics in the region of the superconducting transition showed that the electronic phase transition has a significant effect on its elastic properties. Based on experimental measurements, linear and nonlinear elastic parameters are determined both at room temperature and in the region of the phase transition.
A laser scanning vibrometer was used to measure the amplitudes and phases of the vibrational velocity of shear waves excited by a one-dimensional source in the form of a narrow rectangular bar in a ...gel-like medium. The vibrations of 26 plates reflecting the laser beam and located inside an optically transparent phantom along a segment with a length of 84.5 mm at a distance of 20 mm from the source were measured. The angular distributions of the amplitude and phase of shear waves at discrete frequencies from 59 to 500 Hz were measured in continuous mode. In pulsed mode, the vibrator excited a pulse in the medium with a duration of 1.5 periods of the 300 Hz frequency. The amplitudes and phases of shear waves were calculated by fast Fourier transform of the time profile of the vibration velocity of the plates with a duration of 50 ms. The angular amplitude distributions measured in the pulsed and continuous modes are qualitatively the same. At all frequencies, the distributions are symmetrical with respect to the vertical axis. The maximum oscillation amplitude is observed at angles close to ±45°. The velocity of shear waves, calculated from the measured phase distributions, increases from 2 to 2.5 m/s with a change in frequency from 50 to 500 Hz. It is shown that this velocity behavior is well described by a relaxation model of the medium with one relaxation time equal to 0.3 ms. Shear wave attenuation depends on frequency and exceeds 1 cm
–1
for waves with frequencies above 250 Hz. The maximum attenuation per wavelength is observed near the relaxation frequency of the medium in the 300–400 Hz range. The results can be used to optimize devices for measuring the elasticity of soft tissues.
PDF
