Low Frequency Vector Research Articles

Carbon emissions and economic growth in China: Based on mixed frequency VAR analysis

This study endeavors to examine the association between carbon emissions and economic growth in China spanning the period from 1992 to 2018, employing a mixed frequency vector autoregressive model (MF-VAR). In contrast to the low frequency vector autoregressive model (LF-VAR), the MF-VAR model employed in this research does not involve any filtering procedure; instead, it directly employs variables with distinct frequencies for regression computation. Comparative analysis of the findings reveals that the utilization of the MF-VAR model yields bidirectional causality between carbon emissions and economic growth, a relationship that cannot be validated through employment of the LF-VAR model. Furthermore, the prediction error variance decomposition outcomes of the MF-VAR model exhibit a higher level of explicatory capacity when compared to those of the LF-VAR model. These outcomes carry significant implications for China, as well as other global economies, in the pursuit of the Sustainable Development Goals (SDGs). The analysis outcomes further underscore the necessity of effectively curbing greenhouse gas emissions in China, while simultaneously maintaining a certain level of economic development.

Oil price, green innovation and institutional pressure: A China's perspective

Oil is of dominated role in global energy market, and its price volatility would bring significant economic and environmental consequents. Given China is the largest oil importer, this paper applies the mixed frequency vector autoregression (MF-VAR) to investigate the causal relationship among oil price (OP), green innovation (GI), and institutional pressure (IP). The empirical results from MF-VAR model show that quarterly OP would stimulate GI with time-varying, which is not found in low frequency vector autoregression (LF-VAR). The new evidence mainly due to the mix frequency technique, which allows heterogeneous impacts exist between high and low frequency variables. In addition, higher IP is also discovered to promote GI. The major contribution is that a theoretical framework is initially constructed, and oil price is proven to as important booster for China's green innovation. Therefore, some policies such as innovation subsidy and green credit need to be employed to reduce the impacts from oil price fluctuations and main sustainable GI capability. Meanwhile, IP mainly from environmental protection requires government to launch stricter environmental regulations and laws, and establish reward and punishment mechanism to promote GI.

Infant Mortality and Inflation in China: Based on the Mixed Frequency VAR Analyses.

Reducing neonatal mortality is an important goal in the Sustainable Development Goals (SDGs), and with the outbreak of the new crown epidemic and severe global inflation, it is extremely important to explore the relationship between inflation and infant mortality. This paper investigates the causal relationship between inflation and infant mortality using a mixed frequency vector autoregressive model (MF-VAR) without any filtering procedure, along with impulse response analysis and forecast misspecification variance decomposition, and compares it with a low frequency vector autoregressive model (LF-VAR). We find that there is a causal relationship between inflation and infant mortality, specifically, that is inflation increases infant mortality. Moreover, the contribution of CPI to IMR is greater in the forecast error variance decomposition in the MF-VAR model compared to the LF-VAR model, indicating that CPI has stronger explanatory power for IMR in mixed-frequency data. The results of the study have important implications for China and other developing countries in reducing infant mortality and achieving the Sustainable Development Goals (SDGs). Policymakers should focus on inflation as a macroeconomic variable that reduces the potential negative impact of inflation on infant mortality. The results of the analysis further emphasize the importance of price stability in the context of global inflation caused by the outbreak of the coronavirus pandemic outbreak.

Low frequency absolute calibration of complex sensitivity of vector receivers in free-field

Three-transducers spherical wave reciprocity method in free-field is demonstrated effectively for absolute calibration of the complex sensitivity of underwater sound pressure gradient of vector receiver in the frequency range 250 Hz to 4 kHz. The regularity of underwater sound pressure gradient distribution in the spherical wave, the theory of three-transducers reciprocity calibration method and the technique of complex moving weighted average (CMWA) are studied and reviewed. The VHS90 vector receiver manufactured by Hangzhou Applied Acoustics Research Institute (HAARI) is calibrated using underwater sound pressure gradient calibration facility in a 50 m×15 m×10 m anechoic tank. To verify the results of measurements, the VHS90 vector receiver is also calibrated using low frequency vector receiver calibration facility and the underwater sound pressure calibration facility. The calibration results and the comparisons with these facilities prove the accuracy of the calibration method and facilities described in this paper. The max deviation of modulus of complex sensitivity is 0.7 dB and max deviation of phase congruency of three channels is 1.6°.

Vector field observations near the continental slope off Big Sur, California

In this work, data collected approximately 3 km off the coast of Big Sur, California, by a low frequency vector sensor system will be analyzed. Directional and temporal variations in the ambient noise field will be evaluated, and causes will be considered including flow noise due to currents, surface (wind) noise, distant shipping, and marine mammals. Bearing estimation results for shipping will be compared with AIS tracks recorded during the period of deployment. Local sound speed measurements and bathymetry in the vicinity of the deployment area will be used as inputs to a two-dimensional propagation model that properly invokes reciprocity of the acoustic vector field. Surface wave spectra collected by a nearby buoy will be used to generate rough surface realizations in order to evaluate the impact of these perturbations on low frequency vector field structure. These results will be combined with acoustic data observations in attempts to determine the impact of propagation on the structure of the field. Such an approach may allow us to infer acoustic source levels of AIS traffic off the coast.

Non-inertial low frequency vector sensor with torsional suspension

Conventional low frequency (from 10 Hz) velocity vector sensors utilize inertial approach using neutrally buoyant body with inertial sensor (accelerometer or moving coil geophone) inside. In order to achieve high sensitivity at the low frequencies these sensors must have relatively high inertia (mass). High mass leads to increased size (such as soccer ball) of the sensor in order to satisfy the condition of neutral buoyancy. The developed alternative non-inertial sensor utilizes torsional frictionless and extremely compliant suspension enabling very light and small, yet sensitive with low resonance sensor.

Tuneable, non-degenerated, nonlinear, parametrically-excited amplifier

The proposed parametric amplifier scheme can be tuned to amplify a wide range of input frequencies by altering the parametric excitation with no need to physically modify the oscillator. Parametric amplifiers had been studied extensively, although most of the work focused on amplifiers that are parametrically excited at a frequency twice the amplifier׳s natural frequency. These amplifiers are confined to amplifying predetermined frequencies. The proposed parametric amplifier׳s bandwidth is indeed tuneable to nearly any input frequency, not bound to be an integer multiple of a natural frequency. In order to tune the stiffness and induce a variable frequency parametric excitation, a digitally controlled electromechanical element must be incorporated in the realization. We introduce a novel parametric amplifier with nonlinearity, Duffing type hardening, that bounds the otherwise unlimited amplitude. Moreover, we present a multi degree of freedom system in which a utilization of the proposed method enables the projection of low frequency vector forces on any eigenvector and corresponding natural frequency of the system, and thus to transform external excitations to a frequency band where signal levels are considerably higher. Using the method of multiple scales, analytical expressions for the responses have been retrieved and verified numerically. Parametric studies of the amplifiers׳ gain, sensitivities and spatial projection of the excitation on the system eigenvectors were carried out analytically. The results demonstrate the advantage of the proposed approach over existing schemes. Practical applications envisaged for the proposed method will be outlined.

The interference structure of very low frequency vector acoustic field and its positioning application

Vector hydrophone has natural dipole beam-pattern, and can also simultaneously and colocatedly measure the scalar and vector information of ocean acoustic field, which makes it convenient to determine the direction of arrival (DOA) and represent the stable interference structure of vector acoustic field. Utilizing the DOA and interference structure information together acquired by single vector hydrophone, it is able to position the target of interest. Firstly, bearing-time course for passing-by target is obtained by using the line or continuous spectrum imbedded in the received signal of vector hydrophone. Then, CPA ratio between the CPA range and speed of target as well as CPA instant are estimated on the basis on LMS criteria. Finally, the speed of target can be determined through the theoretically predicted interference range and the real interference time interval to fulfill target positioning including DOA and range. The idea was effectively validated during the experiment that took place in October of 2010 in South China Sea nearly 100m depth. Moreover, the idea presented here can be easily extended for further application such as combining the waveguide invariant. [Work supported by the National 863 Project (No. 2011AA090502) and National Defense Foundation Project (B2420132004).]

A Low Frequency Vector Fast Multipole Algorithm with Vector Addition Theorem

A Low Frequency Vector Fast Multipole Algorithm with Vector Addition Theorem

Simulation of the vector wave field of a low-frequency sound source in the ocean: Some important features

An approach to the simulation of low frequency vector wave fields in stratified media (mainly in the ocean) is considered. The approach is characterized by an improved stability with respect to dividing the medium into many layers of arbitrary thickness. The model for the sound field of a point source is based on an integral representation of two-dimensional, cylindrically symmetric vector wave fields in inhomogeneous media, so that the contributions of all types of waves are included automatically. The model medium is subdivided into N horizontally homogeneous layers for which 4(N−1) equations are formulated to satisfy the boundary conditions between adjacent layers. The method of the generalized Schmidt matrix is used to obtain the coefficients of the equations; these coefficients are substituted into the expressions (of the Fourier-Bessel integral type) for the local parameters of the field. The latter are calculated according to the numerical procedure, and the results are used to model the distributions of the acoustic pressure and the horizontal and vertical components of the particle velocity in liquid and elastic media. The instability of the calculation procedure may result in a disagreement between the model and the exact solution. However, the disagreement is shown to occur mainly in models containing excessively thick layers. A way for improving the stability of the numerical model is suggested. The simulation results are compared with the exact analytical solution for the simplest example and with the results obtained according to the commonly used generalized matrix procedure (the benchmark problem). The examples of the practical application of the model for investigating more complex seismoacoustic wave fields in the ocean are presented.

Finite element analysis of a deformable array transducer

Deformable array transducers have previously been described to implement 2-D phase aberration correction of near-field aberrators with only a 1xN or 2xN array configuration. This transducer design combines mechanical phase correction using an actuator with electronic phase correction for a 2-D correction with significantly fewer elements than a full 2-D array. We have previously reported the fabrication and results of a 1x32 deformable array fabricated with a RAINBOW (Reduced And INternally Biased Wafer) actuator. Because of the complicated construction of deformable arrays, we propose to use finite element analysis (FEA) as a design tool for array development. In this paper, we use 2-D and 3-D FEA to model the experimental results of the deformable array as the first step toward development of a design tool. Because the deformable array combines a mechanical actuator with a medical ultrasound transducer, improvement in performance must consider both the ultrasound characterization along with the low frequency actuator characterization. For the ultrasound characterization, time domain FEA simulations of electrical vector impedance accurately predicted the measurements of single array elements. Additionally, simulations of pulse-echo sensitivity and bandwidth were also well matched to measurements. For the low frequency actuator characterization, time domain simulation of the low frequency vector impedance accurately predicted measurement and confirmed the fundamental flexure resonance of the cantilever configuration at 1.3 kHz. Frequency domain FEA included thermal processing effects and predicted actuator curvature arising during fabrication. Finally, frequency domain FEA simulations of voltage-induced displacement accurately predicted measured displacement.