Explore the vast range of titles available.

We present the 1D subsoil structure and local site effects at KUMA strong ground motion station in Kumamoto City, Japan. We analyze data from a field campaign conducted in the framework of the Blind Prediction BP1 test of the 6th IASPEI/IAEE International Symposium: Effects of Surface Geology on Seismic Motion. In parallel with other participants of the BP1 test, we process data from passive and active source measurements aiming to determine the shear-wave velocity, Vs, structure and the site response at KUMA station. Passive measurements are associated to five microtremor arrays. In each array, seven seismometers have been deployed in a common-center triangle shape, recording microtremors simultaneously for 1 to 2 h. The vertical component of microtremors was analyzed using the spatial autocorrelation (SPAC) method. Cross-correlation coefficients were computed for all station pairs available for each array. By fitting the average SPAC’s coefficients to the first-kind zero-order Bessel function, J0, and assuming that microtremors primarily comprise fundamental mode Rayleigh waves, phase velocity dispersion curves were determined. Phase velocity values for frequencies > 15 Hz were obtained from data of a close-by active source geophone profile. We integrated the data with those of the passive measurements and obtained an experimental phase velocity dispersion curve. The resulting curve shows low velocity variation, from 150 to 200 m/s, in the surface layers, whereas significant dispersion appears in frequencies below 2.5 Hz. By inverting this curve, we achieved to determine the 1D shear-wave velocity structure at KUMA station. Site response characteristics were determined by applying the Horizontal-to-Vertical-Spectral-Ratios method. Significantly amplified peaks in the frequency range between 0.3 to 1.5 Hz dominate HVSR spectral ratios. These peaks correspond to resonant frequencies of soils and originate from different impedance contrasts within the substratum of the site.

Reflection and transmission (R/T) responses characterize the propagation and energy distribution of incident and reflected waves on both sides of an interface which is crucial for imaging, amplitude variation with offset (AVO), and seismic inversion techniques. Subsurface media are typically characterized by anisotropy which can have a significant impact on the R/T response, even at small incident angles. Currently, anisotropic media problems including reflection, transmission, and inversion are generally discussed under a weak anisotropy assumption. However, this assumption is no longer valid in cases of large angles where anisotropy enhancement exacerbates the error of the conventional R/T coefficient approximation. An R/T coefficient approximation method for strong VTI media was proposed based on the assumption of weak-contrast of the media. In contrast to the conventional approach, which simplifies the phase velocity and polarization in an anisotropic background, the phase velocity and polarization at the weak-contrast interface of the elasticity and anisotropy parameters were approximated using a combination of the anisotropic background and perturbation terms. Specifically, a first-order approximation of the R/T coefficients for the VTI media characterized by elastic and anisotropic parameters was derived using Cramer’s law to invert the anisotropic background matrix, avoiding the assumption of weak anisotropy. Subsequently, the exact solution of the Zoeppritz equations was used to correct the isotropic part, improving the accuracy of the R/T coefficients at interfaces with high-velocity contrast. Modeling tests on four classes of typical interfaces showed that the derived equations can be degraded to the Aki approximation in isotropic media, while exhibiting high accuracy in strong VTI media. Uncertainty analyses showed that a linear approximation that facilitates seismic inversion can be obtained by taking the S- to P-velocity ratio and anisotropy parameters in the coefficient terms a priori.

The growing interest in high-power amplifiers for the terahertz (THz) radar system leads to significant performance improvements of THz wave traveling-wave tubes (TWT). This article presents a detailed development of a G-band pulsed wave TWT with 120 W output power. Three approaches have been combined to improve the tube’s output power including proposing the modified folded waveguide (MFWG) slow wave structure (SWS), using large beam current, and adopting phase velocity tapering (PVT). Firstly, the MFWG SWS circuit has an additional degree of freedom that can be used to achieve approximately 36% higher interaction impedance than that in the conventional folded waveguide (CFWG). Subsequently, the electron beam current was increased to approximately 100 mA to boost the DC power of the electron beam. Finally, the PVT technology dramatically enhanced the output power from 98 W to 143 W, concomitant with a notable increase in electronic efficiency from 4.75% to 7.03%. Hot experimental results show that the measured output power can be over 100 W at 20% duty cycle within a bandwidth of 5 GHz when the operation voltage and the current are 22.48 kV and 103.5 mA, respectively. In addition, the maximum power is 121 W with the corresponding electronic efficiency of 5.1%. The proposed G-band 100 W TWT will have broad applications in far-distance high-resolution imaging.

The malfunctioning of semicircular canals (SCCs) in the vestibular system results in diseases that disrupt the individual’s daily life. Vestibular diseases can be treated more effectively if the functioning of the SCCs is better understood. However, the SCC is difficult to dissect, because it is a complex structure buried deep in the inner ear. To thoroughly understand the function of SCCs and provide better treatment plans for vestibular diseases, we constructed a numerical model of human SCCs and validated it experimentally. Based on the principle of the vestibulo-ocular reflex, the cupula deformation deflects embedded sensory hair cell bundles, transmitting signals to the brain and inducing a slow compensatory eye movement. The slow-phase velocity (SPV) is the characteristic of the slow compensatory eye movement. We investigated the cupula deformation in the numerical model and the SPV under different conditions. The relationship between the cupula deformation and the SPV was quantified for three volunteers. It was observed that the maximal cupula deformation is proportional to the angular acceleration, while the SPV is changing nonlinearly with the angular acceleration. For three volunteers, the relationship between the cupula deformation and the SPV can be expressed by same type function of which the parameters are dependent on individual differences. These results validate the reliability of the numerical model.

A novel method based on periodic change of two-phase velocity for the droplet coalescence in microchannels is proposed. The feasibility of the method is justified by investigating the droplet coalescence in several combinations of the velocity pairs. Once the droplet pairs have been generated, the frequency of the droplet coalescence can be divided into a liquid slug of continuous phase dominated region and a real velocity ratio dominated region. Since the liquid slug between the droplet pairs and the real velocity ratio of the droplet pairs are determined by the flow rate ratios, the critical value of the flow rate ratio is determined to distinguish whether the frequency of the droplet coalescence is liquid slug dominated or real velocity ratio dominated. Compared with the traditional passive method, the droplet pairs are alternatively generated by the periodic change of the two-phase velocity. The velocity gradient of the droplet pairs can be generated spontaneously which avoids the introduction of an expansion structure. The mixing performance inside the coalesced droplet is improved due to the reorganized inner circulation when the droplets is coalesced. The quantitative mixing of the reagents can be achieved to satisfy special application needs by a precise control of the volume of the droplet pairs.

The North China Craton (NCC) has experienced strong tectonic deformation and lithospheric thinning since the Cenozoic. To better constrain the geodynamic processes and mechanisms of the lithospheric deformation, we used a linear damped least squares method to invert simultaneously Rayleigh wave phase velocity and azimuthal anisotropy at periods of 10–80 s with teleseismic data recorded by 388 permanent stations in the NCC and its adjacent areas. The results reveal that the anomalies of Rayleigh wave phase velocity and azimuthal anisotropy are in good agreement with the tectonic domains in the study area. Low-phase velocities appear in the rift grabens and sedimentary basins at short periods. A rotation pattern of the fast axis direction of the Rayleigh wave together with a distinct low-velocity anomaly occurs around the Datong volcano. A NW–SE trending azimuthal anisotropy and a low-velocity anomaly at periods of 60–80 s are observed subparallel to the Zhangbo fault zone. The whole lithosphere domain of the Ordos block shows a high-phase velocity and counterclockwise rotated fast axis. The northeastern margin of the Tibetan plateau is dominated by a low-velocity and coherent NW–SE fast axis direction. We infer that the subduction of the Paleo-Pacific plate and eastward material escape of the Tibetan plateau mainly contribute to the deformation of the crust and upper mantle in the NCC.

The possibilities of an effective method of two adjacent signals are investigated for the evaluation of Lamb waves phase velocity dispersion in objects of different types, namely polyvinyl chloride (PVC) film and wind turbine blade (WTB). A new algorithm based on peaks of spectrum magnitude is presented and used for the comparison of the results. To use the presented method, the wavelength-dependent parameter is proposed to determine the optimal distance range, which is necessary in selecting two signals for analysis. It is determined that, in the range of 0.17–0.5 wavelength where δcph is not higher than 5%, it is appropriate to use in the case of an A0 mode in PVC film sample. The smallest error of 1.2%, in the distance greater than 1.5 wavelengths, is obtained in the case of the S0 mode. Using the method of two signals analysis for PVC sample, the phase velocity dispersion curve of the A0 mode is reconstructed using selected distances x1 = 70 mm and x2 = 70.5 mm between two spatial positions of a receiving transducer with a mean relative error δcph=2.8%, and for S0 mode, x1 = 61 mm and x2 = 79.7 mm with δcph=0.99%. In the case of the WTB sample, the range of 0.1–0.39 wavelength, where δcph is not higher than 3%, is determined as the optimal distance range between two adjacent signals. The phase velocity dispersion curve of the A0 mode is reconstructed in two frequency ranges: first, using selected distances x1 = 225 mm and x2 = 231 mm with mean relative error δcph=0.3%; and second, x1 = 225 mm and x2 = 237 mm with δcph=1.3%.

The direction-of-arrival (DOA) estimation of an underwater bottom-mounted horizontal linear array (HLA) based on weighted phase velocity has been proposed in this paper. The directional response is mainly affected by differences in the modal phase velocities and the sound speed of the water column. Based on the mode theory, the acoustic intensity distribution characteristics and beam deviation were analyzed. The beamforming result obtained provides a distinguishing feature of bearing deviation when the measured sound speed was used. By applying the modal weighted phase velocity instead, source bearing can be well estimated. Particularly, in the presence of a thermocline, the propagating modes can be selected on the basis of the mode trapping theory. Both surface and submerged sources were taken into account based on the experimental data, and the deviation was well explained and reduced. For a source near the end-fire direction, the bearing estimation error was reduced from several degrees to tenths of degrees.

Surface waves are essential for resolving Earth's structure on both regional and global scales, and surface wave data are mostly exploited with velocity dispersion. However, dispersion is mostly sensitive to the integral feature of velocity structure, resulting in ambiguities of the model interpretation. Recently, it has been demonstrated that the ZH amplitude ratio of a Rayleigh wave is an effective approach for providing extra constraints to reduce ambiguity in surface wave inversion. In this paper, we studied the sensitivities of the Rayleigh wave phase velocity dispersion and the ZH ratio with layered crustal structure via forward modeling. The forward modeling experiments indicate that the Rayleigh wave ZH ratio shows different sensitivity as compared to Rayleigh wave phase velocity dispersion. The ZH ratio is more sensitive to the shallower structure compared to phase velocity dispersion of the same period, and the ZH ratio provides independent constraints on the structure. Thus, the combination of these two datasets should help to better constrain the velocity model. A joint inversion tool is developed to jointly invert for the Rayleigh wave phase velocity and the ZH ratio observations. The inversion is based on a Fast Simulated Annealing algorithm, which generates models randomly and can achieve a global minimum without requiring a sensitivity kernel. Joint inversions based on synthetic datasets confirmed that the ZH ratio together with a phase velocity dispersion curve can reduce the non-uniqueness in crustal structure inversion.

Spatiotemporal (ST) wave packets constitute a broad class of optical pulses whose spatial and temporal degrees of freedom cannot be treated independently. Such space-time non-separability can induce exotic physical effects such as non-diffraction, non-transverse waves, and sub or superluminal propagation. Here, a higher-order generalised family of ST modes is presented, where modal orders are proposed to enrich their ST structural complexity, analogous to spatial higher-order Gaussian modes. This framework also incorporates spatial eigenmodes and typical ST pulses (e.g., toroidal light pulses) as elementary members. The modal orders are strongly coupled to the Gouy phase, which can unveil anomalous ST Gouy-phase dynamics, including ultrafast cycle-switching evolution, ST self-healing, and sub/super-luminal propagation. We further introduce a stretch parameter that stretches the temporal envelope while keeping the Gouy-phase coefficient unchanged. This stretch invariance decouples pulse duration from modal order, allowing us to tune the few-cycle width without shifting temporal-revival positions or altering the phase/group-velocity laws. Moreover, an approach to analysing the phase velocity and group velocity of the higher-order ST modes is proposed to quantitatively characterise the sub/super-luminal effects. The method is universal for a larger group of complex structured pulses, laying the basis for both fundamental physics and advanced applications in ultrafast optics and structured light.