Seismic Wave Propagation Characteristics and Their Effects on the Dynamic Response of Layered Rock Sites

To investigate the seismic response of layered rock sites, a multidomain analysis method was proposed. Three finite element models with infinite element boundaries for layered sites were analysed. The results of this multidomain analysis show that stratum properties and elevation have an impact on wave propagation characteristics and the dynamic response of layered sites. Compared with the rock mass, the overlying gravel soil has a greater dynamic amplification effect at the sites. A time domain analysis parameter PGA(IMF) was proposed to analyse the effects of different strata on the seismic magnification effect of layered sites, and its application was also discussed in comparison with PGA. According to the frequency domain analysis, the interface of the rock mass strata has a low impact on the Fourier spectrum characteristics of the sites, but gravel soil has a great magnification effect on the spectrum amplitude in the high-frequency band (≥30 Hz) of waves. Moreover, the stratum properties have a great influence on the shape and peak value of the Hilbert energy and marginal spectrum at layered sites. When waves propagate from hard rock to soft rock, the peak value of the Hilbert energy spectrum changes from single to multiple peaks; then, in gravelly soil, the Hilbert energy spectral peak, its nearby amplitude and the amplitude in the high-frequency band (28–36 Hz) are obviously amplified. The frequency components and amplitude of the marginal spectrum become more abundant and larger from rock to gravelly soil in the high-frequency band (28–35 Hz).

High frequency band limits in spectral analysis of heart rate variability in preterm infants

Objectives The current study aims to assess different high-frequency (HF) band power calculations based on different frequency bandwidth values, and compare them with the time domain the root mean square of successive RR differences (RMSSD) value in preterm infants. Methods At week 32, electrocardiogram (ECG) and breathing rate (BR) were recorded for 24 h on 30 preterm infants born between 28 and 32 weeks. The recording held in the neonatal intensive care unit without any interruption of routine. Results The median 24 h BR was 40–78 breaths per minute. The RMSSD was highly and positively correlated with frequency bands that were based on each preterms BR range, or on a constant frequency with band limits of 0.4–2 Hz. Conclusions At week 32, HF band Hz limits should be calculated based on each child’s breathing rate, generally between 0.4 and 2 Hz.

Internal Leakage Predicition of Hydraulic Spool valves Based on Acoustic Emission Technology

In order to realize the nondestructive testing (NDT) of the internal leakage fault of hydraulic spool valves, the internal leakage rate must be predicted by AE (acoustic emission) technology. An AE experimental platform of internal leakage of hydraulic spool valves is built to study the characteristics of AE signals of internal leakage and the relationship between AE signals and leakage rates. The research results show the AE signals present a wideband characteristic. The main frequencies are concentrated in 30~50 kHz and the peak frequency is around 40 kHz. When the leakage rate is large, there are significant signal characteristics appearing in the high frequency band of 75~100 kHz. The exponent of the root mean square(RMS) of AE signals is positively correlated with the exponent of the leakage rate only if the leakage rate is greater than 2~3 mL/min. This find could be used to predict the internal leakage rate of hydraulic spool valves.

Beeinflusst das Tragen einer Gangjustierhilfe in Sicherheitsschuhen die allgemeine Beanspruchung bei Produktionsarbeitern in der Spätschicht?

Zusammenfassung Hintergrund Sicherheitsschuhe sind Teil einer persönlichen Schutzausrüstung zur Minderung des Unfallrisikos am Arbeitsplatz und bei vielen Tätigkeiten in verschiedenen Berufsgruppen vorgeschrieben. Das Tragen von normierten Arbeitsschuhen kann aufgrund der besonderen Eigenschaften (Passform und Gewicht) zu einer erhöhten Beanspruchung des Arbeiters führen. Eine zusätzliche Optimierung von Arbeitsschuhen, mit dem Ziel der Symmetrisierung des Ganges und der damit einhergehenden Verminderung der Beanspruchung, unter den besonderen Bedingungen des Arbeitsschutzes ist daher anzustreben. In dieser Studie soll überprüft werden, ob das Anbringen einer Gangjustierhilfe mit dem Ziel der Symmetrisierung des Ganges einen Einfluss auf die allgemeine Beanspruchung von Schichtarbeitern hat. Methodik Dafür wurde bei 29 männlichen Probanden (Interventionsgruppe: n = 15, Kontrollgruppe: n = 14) zu 2 Messzeitpunkten während der Spätschicht die Herzfrequenzvariabilität (HRV) kontinuierlich erfasst. Ergebnisse Nach 2‑wöchigem Tragen der Gangjustierhilfe zeigt sich eine signifikante Erhöhung der zeitbezogenen HRV-Parameter bei der Interventionsgruppe. Die frequenzbezogenen Parameter Gesamtleistung (Total Power) und Leistung im High Frequency Band (Power HF Band) zeigen bei der Kontrollgruppe eine Verringerung vom 1. zum 2. Messzeitpunkt. Die Ergebnisse sprechen dafür, dass die Gangjustierhilfe durchaus positive Effekte auf die HRV hat und damit die allgemeine Beanspruchungslage am Arbeitsplatz bei dieser Stichprobe positiv beeinflussen kann. Diskussion Weitere Studien zum Überprüfen eines Effektes mit größeren Fallzahlen und unter Berücksichtigung weitere Gruppierungsmöglichkeiten (bspw. Parameter der Ganganalyse, körperliche Leistungsfähigkeit und Vorerkrankungen) sind jedoch erforderlich.

A Survey on Integrated Access and Backhaul Networks

Benefiting from the usage of the high-frequency band, utilizing part of the large available bandwidth for wireless backhauling is feasible without considerable performance sacrifice. In this context, integrated access and backhaul (IAB) has been proposed by the Third Generation Partnership Project (3GPP) to reduce the expenses related to the deployment of fiber optics for 5G and beyond networks. In this paper, first, a brief introduction of IAB based on the 3GPP release is presented. Then, the existing research on IAB networks based on 3GPP specifications and possible non-3GPP research extensions are surveyed. The research on non-3GPP extensions includes the integration of IAB networks with other advanced techniques beyond the currently defined protocol stacks, such as the integration of IAB to cache-enabled, optical communication transport, and non-terrestrial networks. Finally, the challenges and opportunities related to the development and commercialization of the IAB networks are discussed.

Research on the air–oil two-phase flow regime in an aeroengine bearing chamber based on Hilbert–Huang transform

The development of aeroengines toward a lighter and compact structure has put forward a stringent requirement on the lubrication systems, especially on the bearing chambers which contain complex air–oil two-phase fluids. Understanding the flow characteristics is of considerable significance to ensure the cooling and lubrication effect and to improve the working reliability of the aeroengine. Hilbert–Huang transform (HHT) was used to analyze the spectral characteristics of the pressure signals in the bearing chamber, in order to establish the correlation between the energy indicator k and the flow regime. The influences of the operating conditions and lubricant physical properties on the flow regime were discussed. The findings indicate that this approach can distinguish two typical flow regimes in the bearing chamber. With the increase of oil inflow and the decrease of draft speed, the flow regime changes from homogeneous flow to stratified flow, and k shifts from high-frequency band to low-frequency band. At the same lubricant mass inflow, k shifts from low-frequency band to high-frequency band with the increase of lubricant density, and the oil film on the wall becomes thinner. As the viscosity increases, the flow resistance grows and more oil accumulates on the wall. The flow regime converts from homogeneous flow to stratified flow, with k shifting from high-frequency band to low-frequency band. In addition, higher surface tension will cause more oil agglomeration, which results in less stable two-phase flow with irregular and uneven distribution of the oil on the wall.

Metamaterials and their applications: An overview

Metamaterials are man-made substances with unique spatial alternations in their constituent components. They are widely used in modifying elastic, acoustic, or electromagnetic properties of materials. Metamaterials induce low/high-frequency band gaps to control wave propagations with different wavelengths and are also frequently applied in microwave engineering, waveguides, dispersion compensation, smart antennas, and lenses. For instance, permittivity and permeability of the metamaterials can take positive or negative values. Due to smaller single-cell dimensions than their wavelength, the selective frequency of surface-based metamaterials is used for waveguiding. The need for adjustable bandgaps can also lead to a plethora of research into metamaterials’ tunability for structures that operate at different speeds. In this article, recent studies in the field of metamaterials and their applications are reviewed. The piezoelectric metamaterials and the electromagnetic metamaterials are introduced that is followed by a review of new types of chiral metamaterials. Additionally, absorber, nonlinear, terahertz, tunable, photonic, selective surface-based frequency in acoustic metamaterials are comparedand some remarks on tuning bandgaps methods in locally resonant metamaterials are provided.