On the time-varying characteristic of the 6-year oscillation signal in length-of-day

<p>A significant 6-year oscillation (SYO) signal existing in the length-of-day (LOD) variations may reflect the fast dynamics of the Earth cores. The time-varying characteristic (TVC) of this signal may reveal the relevant details on the geophysical excitation process. However, it is still debate about the TVC of the SYO. Our previous works indicated that the SYO signal was showing an obviously decaying trend during 1962~2012 based on the normal Morlet wavelet transform (NMWT) method, while other works did not show the similar decaying result based on the other methods (e.g., the least square fitting- LSF). Here, in order to solve this controversial issue, we revisit the SYO and its TVC. Through a lot of numerical simulation tests, NMWT method is further confirmed to be a good approach to quantitatively recover the target damped harmonic signals from the complex background noises, but the classical LSF method can destroy the original harmonic signal. This work indicates that the unattenuated SYO result obtained by the LSF method is not reliable. In addition, this work further analyzes the LOD data during a longer span (i.e., 1840~2018) and extracts the SYO result in the time domain, the result of which &#160;shows: 1) the amplitude modulation phenomenon of the SYO itself on the longer time span, revealing the relevant excitation information within the Earth system; 2) a decreasing trend of the SYO signal in its amplitude after 1960s, which further supports the current SYO decaying result during 1962~2019. This recovered SYO result during a longer time-span obtained by this work is significant to understand the nature of the SYO change and its excitation process.</p>

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Quasi-1500-Year-Cycle Signal in Length-of-Day Change

Artificial Satellites ◽

10.2478/arsa-2021-0002 ◽

2021 ◽

Vol 56 (2) ◽

pp. 10-17

Author(s):

Lihua MA

Keyword(s):

Rotation Rate ◽

Time Span ◽

Historical Documents ◽

Data Series ◽

Earth’S Rotation ◽

Time Varying ◽

Length Of Day ◽

The Past ◽

Continuous Sequence

Abstract Length-of-day (LOD) change, i.e., variations in Earth’s rotation rate, includes the long-term slowdown trend, as well as periodic and irregular fluctuations. The current continuous sequence of the LOD change covers a time span of <400 years. Using astronomical records in ancient historical documents, combined with a modern astronomical ephemeris, it is possible to obtain ancient LOD change. Some scholars have given a discontinuous LOD data series for the past 4000 years. In this paper, the author uses the Lomb–Scargle periodogram to study the LOD series and finds a significant quasi-1500-year-cycle signal. Furthermore, with weighted wavelet Z-transform, time-varying characteristics of the cycle in the LOD change are obtained.

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Rotation of the Rigid Earth

International Astronomical Union Colloquium ◽

10.1017/s0252921100046704 ◽

1997 ◽

Vol 165 ◽

pp. 295-300

Author(s):

P. Bretagnon

Keyword(s):

Time Domain ◽

Time Span ◽

Euler Angles ◽

The Sun ◽

The Moon ◽

The Earth ◽

Rigid Earth ◽

The Time Domain ◽

Tesseral Harmonics ◽

External Forces

AbstractWe present the results of a solution of the Earth’s rotation built with analytical solutions of the planets and of the Moon’s motion. We take into account the influence of the Moon, the Sun and all the planets on the potential of the Earth for the zonal harmonics Cj,0 for j from 2 to 5, and also for the tesseral harmonics C2,2, S2,2C3,k, S3,k for k from 1 to 3 and C4,1, S4,1. We determine three Euler angles ψ, ω, and φ by calculating the components of the torque of the external forces with respect to the geocenter in the case of the rigid Earth. The analytical solution of the precession-nutation has been compared to a numerical integration over the time span 1900–2050. The differences do not exceed 16 μas for ψ and 8 μas for ω whereas the contribution of the tesseral harmonics reaches 150 μas in the time domain.

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On the ~ 7 year periodic signal in length of day from a frequency domain stepwise regression method

Journal of Geodesy ◽

10.1007/s00190-021-01503-x ◽

2021 ◽

Vol 95 (5) ◽

Author(s):

Can-Can Hsu ◽

Peng-Shuo Duan ◽

Xue-Qing Xu ◽

Yong-Hong Zhou ◽

Cheng-Li Huang

Keyword(s):

Frequency Domain ◽

Stepwise Regression ◽

Regression Method ◽

Periodic Signal ◽

Time Varying ◽

Length Of Day ◽

Retrieval Model ◽

Harmonic Retrieval ◽

The Time Domain ◽

Periodic Components

AbstractThe intradecadal variations in length-of-day (LOD) and their time-varying characteristics still need to be further studied. Given that the corresponding signal periods on the intradecadal scales are quite close to each other and the span of currently observed ΔLOD data (i.e., 1962–2019, only 57 years) is not long enough, accurate detection of these signals depends on using effective mathematical method. On the basis of the traditional harmonic retrieval model, this work proposes a frequency domain stepwise regression method, which can well identify the periodic components with close periods and recognize the weaker signals to estimate the relevant harmonic parameters (i.e., amplitude, frequency and phase). Furthermore, we apply this method to detection of the actual LOD intradecadal variations, the result of which shows that there are three components (i.e., the ~ 5.9 years, ~ 8.3 years and ~ 7.3 years) existing in LOD intradecadal variations. Here, we firstly give the time-domain harmonic expression of the ~ 7.3 years signal, i.e., $$y\left(t\right)=A\mathrm{cos}\left(\frac{2\pi }{T}\left(t-1962+\psi \right)\right)$$ y t = A cos 2 π T t - 1962 + ψ , where the period $$T=7.33$$ T = 7.33 years, amplitude $$A=0.0413(\pm 0.0099)$$ A = 0.0413 ( ± 0.0099 ) ms, phase $$\psi =-1.58(\pm 0.30)$$ ψ = - 1.58 ( ± 0.30 ) years. The mechanism of this ~ 7.3 years signal needs to be further studied.

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Optimal Hedge Ratio and Hedging Effectiveness in Stock Futures Market: Evidence from National Stock Exchange, India

Restaurant Business ◽

10.26643/rb.v118i3.7637 ◽

2019 ◽

Vol 118 (3) ◽

pp. 137-152

Author(s):

A. Shanthi ◽

R. Thamilselvan

Keyword(s):

Banking Sector ◽

Stock Exchange ◽

Research Work ◽

Futures Market ◽

Least Square ◽

Time Varying ◽

Hedge Ratio ◽

Hedging Effectiveness ◽

Out Of Sample ◽

Optimal Hedge

The major objective of the study is to examine the performance of optimal hedge ratio and hedging effectiveness in stock futures market in National Stock Exchange, India by estimating the following econometric models like Ordinary Least Square (OLS), Vector Error Correction Model (VECM) and time varying Multivariate Generalized Autoregressive Conditional Heteroscedasticity (MGARCH) model by evaluating in sample observation and out of sample observations for the period spanning from 1st January 2011 till 31st March 2018 by accommodating sixteen stock futures retrieved through www.nseindia.com by considering banking sector of Indian economy. The findings of the study indicate both the in sample and out of sample hedging performances suggest the various strategies obtained through the time varying optimal hedge ratio, which minimizes the conditional variance performs better than the employed alterative models for most of the underlying stock futures contracts in select banking sectors in India. Moreover, the study also envisage about the model selection criteria is most important for appropriate hedge ratio through risk averse investors. Finally, the research work is also in line with the previous attempts Myers (1991), Baillie and Myers (1991) and Park and Switzer (1995a, 1995b) made in the US markets

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Experimental Identification Technique of Nonlinear Beams in Time Domain

Volume 1C: 16th Biennial Conference on Mechanical Vibration and Noise ◽

10.1115/detc97/vib-4114 ◽

1997 ◽

Author(s):

Kimihio Yasuda ◽

Keisuke Kamiya

Keyword(s):

Time Domain ◽

Harmonic Balance ◽

Least Square Method ◽

Least Square ◽

Governing Equations ◽

Experimental Identification ◽

Initial Values ◽

Nonlinear Beams ◽

Identification Technique ◽

The Time Domain

Abstract In previous papers the authors proposed a new experimental identification technique applicable to elastic structures. The proposed technique is based on the principle of harmonic balance, and can be classified as the frequency domain technique. The technique requires the excitation force to be periodic. This is in some cases a restriction. So another technique free from this restriction is of use. In this paper, as a first step for developing such techniques, a technique applicable to beams is proposed. The proposed technique can be classified as the time domain one. Two variations of the technique are proposed, depending on what methods are used for estimating the parameters of the governing equations. The first method is based on the usual least square method. The second is based on solving a minimization problem with constraints. The latter usually yields better results. But in this method, an iteration procedure is used, which requires initial values for the parameters. To determine the initial values, the first method can be used. So both methods are useful. Finally the applicability of the proposed technique is confirmed by numerical simulation and experiments.

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Impacto das exportações de alta tecnologia no crescimento econômico: evidências empíricas do Paquistão

Journal on Innovation and Sustainability RISUS ISSN 2179-3565 ◽

10.24212/2179-3565.2017v8i1p91-105 ◽

2017 ◽

Vol 8 (1) ◽

pp. 91 ◽

Cited By ~ 1

Author(s):

Muhammad Usman

Keyword(s):

Economic Growth ◽

World Bank ◽

Time Span ◽

Least Square ◽

High Tech ◽

Ordinary Least Square ◽

Robust Standard Error ◽

Long Run ◽

Data Source ◽

The Impact

The goal of this study is to explore the impact of high tech exports on economic growth of Pakistan. To examine this relationship, data are collected from World Bank database, State Bank of Pakistan data source and Statistical Bureau of Pakistan. Time span of study is consisting of 20 years from 1995 to 2014. By using ordinary least square (OLS) with robust standard error, results confirm that there is a positive and statistically significant impact of high tech exports on economic growth. Although Pakistan is an agriculture country and its economic growth is largely depend upon farming, but for long run economic growth, Pakistan has to increase its high tech exports.

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Numerical Study on Hydrodynamic Responses of a Two-Body System in Side-by-Side Operation

Volume 7: Ocean Engineering ◽

10.1115/omae2016-54625 ◽

2016 ◽

Author(s):

Shaowu Ou ◽

Shixiao Fu ◽

Wei Wei ◽

Tao Peng ◽

Xuefeng Wang

Keyword(s):

Numerical Study ◽

Low Frequency ◽

Optimal Operation ◽

Hydrodynamic Interactions ◽

Irregular Waves ◽

Mooring System ◽

Time Varying ◽

Body System ◽

The Time Domain ◽

Two Bodies

Typically, in some side-by-side offshore operations, the speed of vessels is very low or even 0 and the headings are manually maneuvered. In this paper, the hydrodynamic responses of a two-body system in such operations under irregular seas are investigated. The numerical model includes two identical PSVs (Platform Supply Vessel) as well as the fenders and connection lines between them. A horizontal mooring system constraining the low frequency motions is set on one of the ships to simulate maneuver system. Accounting for the hydrodynamic interactions between two bodies, 3D potential theory is applied for the analysis of their hydrodynamic coefficients. With wind and current effects included, these coefficients are further applied in the time domain simulations in irregular waves. The relevant coefficients are estimated by experiential formulas. Time-varying loads on fenders and connection lines are analyzed. Meanwhile, the relative motions as well as the effects of the hydrodynamic interactions between ships are further discussed, and finally an optimal operation scheme in which operation can be safely performed is summarized.

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Identification of Methamphetamine Abstainers by Resting-State Functional Magnetic Resonance Imaging

Frontiers in Psychology ◽

10.3389/fpsyg.2021.717519 ◽

2021 ◽

Vol 12 ◽

Author(s):

Tingting Dong ◽

Qiuping Huang ◽

Shucai Huang ◽

Jiang Xin ◽

Qiaolan Jia ◽

...

Keyword(s):

Magnetic Resonance Imaging ◽

Magnetic Resonance ◽

Functional Magnetic Resonance Imaging ◽

Time Domain ◽

Resting State ◽

Time Varying ◽

Functional Magnetic Resonance ◽

Resonance Imaging ◽

Normal People ◽

The Time Domain

Methamphetamine (MA) can cause brain structural and functional impairment, but there are few studies on whether this difference will sustain on MA abstainers. The purpose of this study is to investigate the correlation of brain networks in MA abstainers. In this study, 47 people detoxified for at least 14 months and 44 normal people took a resting-state functional magnetic resonance imaging (RS-fMRI) scan. A dynamic (i.e., time-varying) functional connectivity (FC) is obtained by applying sliding windows in the time courses on the independent components (ICs). The windowed correlation data for each IC were then clustered by k-means. The number of subjects in each cluster was used as a new feature for individual identification. The results show that the classifier achieved satisfactory performance (82.3% accuracy, 77.7% specificity, and 85.7% sensitivity). We find that there are significant differences in the brain networks of MA abstainers and normal people in the time domain, but the spatial differences are not obvious. Most of the altered functional connections (time-varying) are identified to be located at dorsal default mode network. These results have shown that changes in the correlation of the time domain may play an important role in identifying MA abstainers. Therefore, our findings provide valuable insights in the identification of MA and elucidate the pathological mechanism of MA from a resting-state functional integration point of view.

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