Vibrational Modes and Crystallographic Structure of Cd3As2 and (Cd1-xZnx)3As2 Epilayers

Low-temperature Raman scattering is used to study the crystal structure of molecular-beam epitaxially grown layers of the Dirac semimetal Cd3As2 and its related alloy (Cd1-xZnx)3As2. The combination of narrow-linewidth spectra, multiple growth directions and full polarization analysis allows improved accuracy in identifying the irreducible representation of over 57 Raman-active vibrations. Several disagreements with previous identifications are found. Structurally, the results agree with the centrosymmetric I41/acd space group of bulk-grown Cd3As2 and are clearly distinct from the Raman spectra of nanoscale platelets and wires. 3-fold twinning is seen in (112) Cd3As2 grown on (111) zincblende substrates corresponding to the three possible tetragonal orientations. In dilute (Cd1-xZnx)3As2, phonons have a frequency and scattering amplitude dependence on Zn concentration that is continuous with Cd3As2 but at least one frequency is absent at the alloy endpoint, preventing a simple one-mode description of the alloy phonon.

High-Velocity Shear and Soft Friction at the Nanometer Scale

We study high-speed friction on soft polymer materials by measuring the amplitude dependence of cyclic lateral forces on the atomic force microscope (AFM) tip as it slides on the surface with fixed contact force. The resulting dynamic force quadrature curves separate the elastic and viscous contributions to the lateral force, revealing a transition from stick-slip to free-sliding motion as the velocity increases. We explain force quadratures and describe how they are measured, and we show results for a variety of soft materials. The results differ substantially from the measurements on hard materials, showing hysteresis in the force quadrature curves that we attribute to the finite relaxation time of viscoelastic surface deformation.

Fatigue Crack Growth Behaviour and Role of Roughness-Induced Crack Closure in CP Ti: Stress Amplitude Dependence

This paper investigated the fatigue crack propagation mechanism of CP Ti at various stress amplitudes (175, 200, 227 MPa). One single crack at 175 MPa and three main cracks via sub-crack coalescence at 227 MPa were found to be responsible for fatigue failure. Crack deflection and crack branching that cause roughness-induced crack closure (RICC) appeared at all studied stress amplitudes; hence, RICC at various stages of crack propagation (100, 300 and 500 µm) could be quantitatively calculated. Noticeably, a lower RICC at higher stress amplitudes (227 MPa) for fatigue cracks longer than 100 µm was found than for those at 175 MPa. This caused the variation in crack growth rates in the studied conditions.

Strain Amplitude Dependence of High Damping Grp/Mg97Zn1Y2 Composites Ranging from Anelastic to Microplastic

In this paper, the damping capacities and damping mechanisms of high damping, graphite-reinforced Mg97Zn1Y2 composites were investigated. Composites consisting of different graphite particle sizes (24, 11, and 3 μm) were designed and prepared using the casting method. The microstructure of the composites was examined using optical microscopy (OM) and transmission electron microscopy (TEM), which confirmed that the graphite particles were successfully planted into the Mg97Zn1Y2 matrix. Measurements made with a dynamic mechanical analyzer (DMA) showed that the Grp/Mg97Zn1Y2 composite has a high damping capacity. At the anelastic strain amplitude stage, the damping properties of the Grp/Mg97Zn1Y2 composites were found to be higher than those of the Mg97Zn1Y2 alloy. Furthermore, decreasing the graphite particle size was found to improve the damping properties of the Grp/Mg97Zn1Y2 composites. At the microplastic strain amplitude stage, the damping properties of the Mg97Zn1Y2 alloy were found to be higher than those of the Grp/Mg97Zn1Y2 composites. Moreover, the damping properties of the Grp/Mg97Zn1Y2 composites were found to decrease with increasing graphite particle size. The reason for the increased damping of the Grp/Mg97Zn1Y2 composites during the anelastic strain amplitude stage can be attributed to the increase in the number of damping sources and weak interactions among the dislocation damping mechanisms. At the microplastic strain amplitude stage, the damping properties of the composite are mainly affected by the activation volume of the slipped dislocation.

Fixed Points on Active and Passive Dynamics of Active Hydraulic Mounts with Oscillating Coil Actuator

Active hydraulic mounts with an inertia track, decoupler membrane, and oscillating coil actuator (AHM-IT-DM-OCAs) have been studied extensively due their compact structure and large damping in the low-frequency band. This paper focuses on a comprehensive analysis of the active and passive dynamics and their fixed points in mid-low-frequency bands, which will be helpful for parameter identification. A unified lumped parameter mechanical model with two degrees-of-freedom is established. The inertia and damping forces of the decoupler/actuator mover may be neglected, and a nonlinear mathematical model can be obtained for mid-low-frequency bands. Theoretical analysis of active and passive dynamics for fluid-filled state reveals the amplitude dependence and a fixed point in passive dynamic stiffness in-phase or active real-frequency characteristics. The amplitude dependence of local loss at the fluid channel entrance and outlet induces the amplitude-dependent dynamics. The amplitude-dependent dynamics constitute a precondition for fixed points. A single fixed point in passive dynamics is experimentally validated, and a pair of fixed points in active dynamics for an AHM-IT-DM-OCA is newly revealed in an experiment, which presents a new issue for further analysis.

INVESTIGATION PARAMETERS ULTRASONIC DEVICE ON PHASED ARRAYS. FOCUSING MODES FOR ULTRASONIC DEVICE TYPE OF OMNISCAN

The article is devoted to possibilities of regular focusing of Omniscan device on phased arrays. Questions are raised about evaluation of testing results when using linear and sector scan-ning with different focus parameters. The question of size near-field for phased arrays and asso-ciated choice of focus mode is discussed. The article is based on experiments conducted on samples with artificial reflectors at the same size, but different in type: a non-directional reflector (a side-drill hole) and a directional reflector (a flat-bottomed reflector), located at the same depth. The study was conducted for transducers with different frequencies. Families of curves of the signal amplitude dependence are obtained: on depth reflector, on focus depth setting, and on type reflector. The results emphasize need for precise focusing with-in the near-field of the transducer for small thicknesses or shallow depth of occurrence of discontinuities, and large variability in choice of focusing for depths in far-field. The study notes a significant difference in values of depth reflector at different focusses at a fixed position of transducer. In this article, in addition to considering possibility of focusing a flaw detector with phased arrays, the focus is on interpretation of results and reliability of testing in the analysis and comparison data. An integral part of the technological testing protocol for phased array is the depth of focus and the type of scanning. The obtained data do not depend on the frequency of transducer, which means that conclusions are applicable to general range of flaw detectors on phased arrays.

Modeling and Solution of Large Amplitude Vibration Problem of Construction Elements Made of Nanocomposites Using Shear Deformation Theory

The main purpose of the study is to investigate the vibration behaviors of carbon nanotube (CNT) patterned double-curved construction elements using the shear deformation theory (SDT). After the visual and mathematical models of CNT patterned double-curved construction elements are created, the large amplitude stress–strain relationships and basic dynamic equations are derived using the first order shear deformation theory (FSDT). Then, using the Galerkin method, the problem is reduced to the nonlinear vibration of nanocomposite continuous systems with quadratic and cubic nonlinearities. Applying the Grigolyuk method to the obtained nonlinear differential equation, large-amplitude frequency-amplitude dependence is obtained. The expressions for nonlinear frequencies of homogenous and inhomogeneous nanocomposite construction members such as plates, panels, spherical and hyperbolic-paraboloid (hypar) shells in the framework of FSDT are found in special cases. The accuracy of the results of the current study has been confirmed by comparing them with the reliable results reported in the literature. Original analyses are carried out to examine the effects of nonlinearity, CNT patterns and volume fraction changes on frequencies in the framework of shear deformation and classical shell theories.

Assessment and incidence of PV gaps as determined by HD Grid and circular mapping catheters

Funding Acknowledgements Type of funding sources: None. Background Many tools and techniques are utilized to assess pulmonary vein isolation (PVI), such as evaluation of entrance and exit block, voltage mapping, and use of drugs such as adenosine. It is unclear which tools and techniques may provide greater sensitivity in the identification and elimination of pulmonary vein (PV) gaps, leading to better long-term outcomes. The HD Grid simultaneously records orthogonal bipolar EGMs to reduce directional sensitivity. Previously published data suggest that the use of HD Grid may improve sensitivity for gap identification. Purpose To determine, in a large cohort of procedures, the rate of gap detection when using HD Grid to check for PVI as compared to circular mapping catheters (CMC). Methods Anonymized, acute procedural data was prospectively collected in de novo AF ablation procedures in which either a 10- or 20-pole CMC or HD Grid catheter was used to assess PVI. Procedural data including gap detection and PVI assessment method were analyzed using chi-squared test. Results 559 cases from over 60 institutions in 8 countries were analyzed. Of the 559 cases, 47.4% (265/599) used HD Grid, and 52.6% (294/599) used a CMC. PV gaps were found in 52.5% (139/265) of HD Grid procedures and in 36.7% (108/294) of CMC procedures (p < 0.001). The most common PVI assessment method in both HD Grid and CMC groups was entrance/exit block (90.9%, 92.5%, respectively). Mapping as a post-ablation assessment method was used in 69.1% (183/265) of HD Grid procedures whereas it was only used in 42.8% (126/294) of CMC procedures (p < 0.001). Of the 183 HD Grid procedures that utilized mapping for PV assessment, 57.9% (106/183) used both voltage and activation mapping, 41.0% (75/183) used voltage only and 1.1% (2/183) used activation mapping only. Significantly more gaps were found in the HD Grid group that used both activation and voltage mapping (83.0%, 88/106) as compared to voltage mapping only (49.3%, 37/75, p < 0.001). At the end of the procedure, 95.8% of patients in the HD Grid group were in sinus rhythm, as compared to 84.7% of the CMC group. Conclusions While this analysis does not represent a direct comparison of the sensitivity of the two different technologies, HD Grid detected significantly more PV gaps compared to CMC in AF procedures. Previous publications have attributed similar findings to HD Grid’s ability to reduce voltage amplitude dependence on wavefront directionality. The significantly larger number of HD Grid cases that utilized mapping as a method of determining PVI could be explained by the need to maneuver the HD Grid around the circumference of the vein, which may naturally lead to map collection. This data also suggests that using both voltage and activation mapping identifies significantly more gaps as compared to only voltage mapping, however, further analysis could be warranted to better understand how these maps were collected and what map settings were used.

Amplitude-dependent hysteresis of wave velocity in rocks n wide frequency range: an experimental study

This research belongs to the field of rock physics. In recent years, in solid state physics and materials science, new knowledge has emerged about microplastic strain of various materials, including rocks. These data were obtained using high-precision micro- and nanoscale strain measurements. The very fact of the existence of the poorly studied rock property in the earth sciences requires the study of the possible influence of the rock microplasticity on the propagation of seismic and acoustic waves. The studies were carried out using three alternative methods and under different observation conditions. The field measurements were carried out in the zone of low velocities in crosshole space with transmitted waves of frequency of 240–850 Hz. The laboratory measurements were carried out on sandstone samples with transmitted (6.8 kHz) and reflected (1 MHz) waves at the strain of 10−8–10−6. The manifestations of microplasticity were recorded using high-resolution recording of signals with discretization time tdiscret = 1 μs – 40 μs and 32.5 ns. The wave amplitude variation was provided in a closed cycle: discrete increasing the amplitude from minimum to maximum and return to the initial value (A1+ → A2+ → … Amax … → А2– → A1–). In this amplitude range, an amplitude hysteresis was observed, a sign of which was the inequality of wave velocities on the upward and downward amplitude courses. This effect was recorded for all three measurement methods at different frequencies. However, the amplitude hysteresis of the wave velocity was not observed only in the measurements at full water saturation of loam. The largest amplitude-dependent change in the wave velocity reached 2% (at the accuracy of 0.02%), and the change in the attenuation value amounted to 5%. The reason for this effect could be microplastic inelasticity, which manifested itself by amplitude plateaus located within the waveform. The amplitude microhysteresis forms overall picture of the amplitude dependence of the wave velocity in wide amplitude range. Proposals for the potential use of the obtained data for solving some applied problems have been presented.