Search

Introduction. Safety of navigation and development of underwater mineral deposits require the accurate detection of various underwater objects. The literature discusses the issues of tracking their motion and trajectory. Sonar methods are proposed to maintain high accuracy of underwater object positioning. High accuracy of the bearing of stereo sensors with an ultrashort base is noted. However, this equipment is sensitive to the sampling rate of the signals, which causes “sampling noise”. There are no publicly available publications dedicated to the solution to this problem. The presented study is designed to fill this gap. This work is aimed to study the possibility of obtaining data clarifying information about the bearing of underwater objects through using the phase information about echoed probing signals and an additional procedure for resampling the source data.Materials and Methods. The location of the object was determined using the experimental complex for studying hydroacoustic sensors created by V.A. Shirokov and V.N. Milich at the Udmurt Federal Research Center, the Ural Branch of the Russian Academy of Sciences. A stereo sensor with a small base (30 mm) was used compared to the distance to the object (≈800–900 mm). Digital filtering methods and mathematical apparatus of correlation analysis of return hydroacoustic signals obtained by the phase method were used for data processing.Results. The results of comparing two methods for determining the bearing on an object are presented: by the difference in the time of arrival of the pulse-leading edges and by the maximum of the cross-correlation function (CCF). The change in bearing as the object moves, is graphically shown. The use of the leading edge of the signal caused small outliers of values along the entire bearing curve (less than 0.12 rad). At the maximum CCF, emissions were recorded only in some areas, but they were quite significant (about 0.17 rad). It showed how to select points corresponding to a smoother and more valid object trajectory, and how to work with erroneous points. The presented method of error correction can be implemented programmatically. With a quasi-harmonious signal, rare measurements of the original signal are interpolated by frequent calculated values. Thanks to this virtual increase in the sampling rate (oversampling), intermediate indicators can be recorded in the digitized source data. Interpolation of the signal values by a cubic spline allowed us to obtain 20 points for 1 period of the signal instead of 5 points in the original version. In this case, the trajectory formed with the maximum CCF is more correct.Discussion and Conclusion. The direction-finding problem can be solved with the accuracy required for practical application. Taking into account the factor of smoothness and continuity of the object's trajectory makes it possible to qualitatively correct the selection of the maximum of the cross-correlation function of the stereo sensor signals. The proposed methods have great potential for the development of underwater vision systems.

The study area is located in the karst development area of Pingxiang in the west of Jiangxi Province, China. The landform of this area is complex, low in the northwest and high in the southeast. The fold action and gravitational sliding action led to the development of faults and extensional sliding nappe structures in the area, accompanied by magmatic intrusion activities, which has formed multi-phase superimposed complex structures. Atmospheric precipitation and groundwater in the upstream limestone areas constitute the main water source in the study area. Meanwhile, karst collapses may cause the formation of holes below the surface, seriously endangering people's life and property. Therefore, finding out the geological situation of the collapse area can provide a reference for the understanding of the geological characteristics and the groundwater system in this area. Microtremor is a kind of persistent weak vibration signal observed on the surface caused by industrial vibrations, traffic noises, tidal currents, atmospheric activities and other activities on the earth. Surface waves are formed by vertical waves and transverse waves interfering on the surface. They have the characteristics of low speed, low frequency and frequency dispersion, which lay a foundation for the detection of underground structure. The method of microtremor surface waves survey utilizes various types of vibrations that continuously exist in nature as signal sources. It extracts the information on seismic surface wave field from microtremor records and uses this type of information for imaging underground media. The steps include microtremor signal acquisition in the study area, data preprocessing, empirical Green function calculation, extraction of surface wave dispersion curves and inversion of velocity structure for transverse waves. Among these steps, the empirical Green function is obtained through the crosscorrelation operation of the microtremor signals recorded by two detectors, and calculating the empirical Green function is the key to obtain the surface wave information. This study detects the karst collapses in the study area by using microtremor surface waves. However, the surface wave signals are affected by uneven distribution of natural noise sources and random noises, which may cause the low signal-to-noise ratio of the Green function. Therefore, the direct use of the empirical Green function for subsequent data processing may get the dispersion energy spectrum with low resolution, which is not conducive to the subsequent extraction of high-quality dispersion curves and accurate inversion. Due to the above shortcomings, this study first optimized the window function for the cross-correlation function of microtremor signals to improve the signal-to-noise rate of microtremor data, and to enhance the resolution of energy spectrum of microtremor surface wave dispersion. Then, the extraction of dispersion curves and inversion of the virtual source surface record of each group in the study area were conducted to obtain the transverse wave velocity structure of each point along the measurement line. Finally, the distribution positions and depths of karst collapses in the study area were revealed, according to the the transverse wave velocity section below the measurement line generated by inversion as well as the geological interpretation of drilling data. The results show as follows, (1) The selection of window function in the cross-correlation function calculation will affect the resolution of the dispersion energy spectrum, and the window function should be tested in processing the microtremor data. (2) The processing and optimizing of window function for the cross-correlation function can effectively improve the signal-to-noise rate of microtremor surface wave and the resolution of the dispersion energy spectrum, widen the frequency band range of dispersion curves, and improve the accuracy of the inversion. (3) The method of microtremor surface waves survey is highly applicable to karst collapse detection, and the optimization of the window function can determine the range of underground hazards in a more accurate way [ABSTRACT FROM AUTHOR]

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, we propose a method for recommending appropriate combinations of stocks based on the waveforms of stock price changes. Many Japanese prefer to maintain stability when managing their assets. Specialized knowledge is required to invest in stocks while reducing risk. Hence, stock recommendation methods with different characteristics are required. Stock price movements can be captured as waveforms. Dynamic time warping (DTW), cross–correlation functions, and fast Fourier transforms (FFTs) are used to compare the features of the waveforms. A combination of stocks with different waveforms avoids the risk of simultaneous crashes. In the current experiment, one–year stock waveforms are used to obtain the recommended stock. The combined stocks selected using the DTW, cross–correlation functions, and FFT are shown to be suitable. [ABSTRACT FROM AUTHOR]

This paper discusses the auto-correlation functions of chaotic binary sequences obtained by a one-dimensional chaotic map and two binary functions. The two binary functions are alternately used to obtain a binary sequence from a chaotic real-valued sequence. We consider two similar methods and give the theoretical auto-correlation functions of the new binary sequences, which are expressed by the auto-/cross-correlation functions of the two chaotic binary sequences generated by a single binary function. Furthermore, some numerical experiments are performed to confirm the validity of the theoretical auto-correlation functions. [ABSTRACT FROM AUTHOR]

This paper discusses the auto-correlation functions of chaotic binary sequences obtained by a one-dimensional chaotic map and two binary functions. The two binary functions are alternately used to obtain a binary sequence from a chaotic real-valued sequence. We consider two similar methods and give the theoretical auto-correlation functions of the new binary sequences, which are expressed by the auto-/cross-correlation functions of the two chaotic binary sequences generated by a single binary function. Furthermore, some numerical experiments are performed to confirm the validity of the theoretical auto-correlation functions.

Ambient noise technology can efficiently extract surface wave signals from seismic background noise and has been extensively utilized in imaging lithospheric structures. However, retrieving crustal body wave signals, such as PmP or SmS phases, still poses a challenge. Only a limited number of reports have successfully extracted these regional-scale body wave signals from ambient noise in only a few limited study areas. It remains unclear why these signals are difficult to retrieve from ambient noise data. To investigate the mechanism of recovering body wave signals in noise cross-correlations, we calculate cross-correlation functions at four regions and observe the similarity of the recovered body waves. Through a series of synthetic simulations, we demonstrate that the appearance of body wave signals in noise cross-correlations is closely related to the distribution of noise sources. Among these signals, the post-critical SmS wave proves to be the most readily recoverable from ambient noise data, primarily stemming from distant sources. In contrast, the recovery of P -wave requires the array to be in proximity to the sources. Our experiments also reveal that the main origin of PL waves is the multiple reflections of S -waves propagating in the crust. [ABSTRACT FROM AUTHOR]

The article is mainly devoted to the analysis of the transient process during the phase change of the intra-impulse modulated signal of the system, which is composed of a pair of piezoelectric ceramic transducers. In the introductory part, this article is focused on the most accurate determination of the parameters of electrical equivalent circuit of piezoelectric ceramic transducers commonly available on the market of electrical components and less economically demanding. Based on the determination of these parameters, a system consisting of the piezoelectric ceramic transducer, transmitter - environment - piezoelectric ceramic transducer, receiver is then assembled and represented by transfer function. This system is subjected to simulation. An intra-impulse modulated signal with phase modulation is connected to the system input. The response to this signal is subsequently analyzed and compared with the real response of a real system. The goal is therefore to verify the suitability of the simulation model and, on the basis of this analysis, to determine the possibility of using specific piezoelectric ceramic transducers for application of intra-impulse modulated signal. As a method of verification, main parameter analysis of a cross-correlation function was selected. Based on this analysis it was found that this method is relevant for this purpose.

An array consisting of three sensors was used for correlation measurements of thermal acoustic radiation. For the first time, all cross-correlation functions were obtained for each pair of sensors. The measurements were carried out at two positions of the source (a heated narrow Teflon cylinder), the distance between which was equal to half the spatial period of the cross-correlation function of adjacent sensors. The measured correlation functions were in antiphase, which corresponds to the calculated correlation functions of thermal acoustic radiation. To pass from correlation functions to temperature distribution, spatial cross-correlation functions for adjacent and the outermost sensors in the array are summed. The correlation methodology makes it possible to significantly increase the spatial resolution of the method. [ABSTRACT FROM AUTHOR]

Migratory fishes of the Mekong Basin are facing challenges from human-induced stressors. Quantifying the patterns of fish's early life stages provides important information on spawning seasons, spawning and nursery habitats, reproductive strategies, migration and dispersal patterns, and stock status. However, the ecology of the Mekong larval fishes, including patterns and drivers of larval fish dispersal, is not well understood. Here, we investigate the temporal variability of drifting larval and juvenile fish assemblages in the Cambodian Mekong River and identify their environmental drivers using long-term (10 year) daily fish larval/juvenile data collections. We found that, in the Mekong main channel, the larval and juvenile assemblages were dominated by longitudinal migrants from the families Cyprinidae and Pangasiidae. Peak abundance and richness were found to occur in July and August, respectively. We detected a significant decline in larval and juvenile abundance and richness over the study period. Cross-wavelet analysis revealed that water levels always lead larval abundance, but lag richness. In addition, cross-correlation analysis observed that peak abundance and richness occurred eight weeks and one week, respectively, before the peak water level. We also discovered that species abundance and richness had a strongly positive relationship with maximum water levels. Variation in fish larval and juvenile abundance and richness was also related to total phosphorus, nitrate, alkalinity, and conductivity. Maximum water levels and the key water quality parameters (e.g., phosphorus, nitrate, alkalinity, and conductivity) significantly influence larval and juvenile fish abundance and richness patterns. Therefore, safeguarding natural seasonal flows, especially maximum flows associated with the peak flood pulse, as well as maintaining good water quality, are key to the reproductive success of many migratory fishes and effective dispersal of offspring to the lower floodplain for nursing, rearing, and growth. Clean and unregulated rivers support productive and diverse fisheries. [ABSTRACT FROM AUTHOR]

Factor models have been widely used in recent years to model high‐dimensional spatio‐temporal data. However, the validity of employing factor models in a specific application has received less attention. This article proposes test statistics for testing the symmetry in cross‐correlation matrices of a high‐dimensional stochastic process implied by exact factor models. A rejection of symmetry indicates that the use of an exact factor model is questionable. Both simulations and real examples are used to demonstrate the applications and to study the finite‐sample performance of the proposed test statistics. Empirical results show that the proposed test statistics are effective in identifying cases where exact factor models are not appropriate, providing valuable guidance for choosing factor models in a high‐dimensional setting. [ABSTRACT FROM AUTHOR]

In this study, the reverse plumb lines of the Chirkey hydropower plant dam were analyzed in association with seasonal changes in atmospheric temperature and water level in the reservoir during 2010 – 2014. The WinABD software package was used, which is designed to study time series obtained as a result of continuous long-term observations and provides a full cycle of statistical analysis of series that comprise failures, errors, and omissions. A significant relationship was established with seasonal changes in atmospheric temperature and water level in the reservoir. [ABSTRACT FROM AUTHOR]

In this paper planar STIT tessellations with weighted axis-parallel cutting directions are considered. They are known also as weighted planar Mondrian tessellations in the machine learning literature, where they are used in random forest learning and kernel methods. Various second-order properties of such random tessellations are derived, in particular, explicit formulas are obtained for suitably adapted versions of the pair- and cross-correlation functions of the length measure on the edge skeleton and the vertex point process. Also, explicit formulas and the asymptotic behaviour of variances are discussed in detail. [ABSTRACT FROM AUTHOR]

Millimeter wave is an important core technology of 5G communication,which has a broad development prospect.With the improvement of communication frequency,the influence of weather on signal transmission is increasing,especially in rainfall environment.In order to establish an accurate and effective communication channel model,a three-dimensional millimeter wave MIMO spatial channel model based on 25 GHz,30 GHz and 78 GHz is proposed for the base station mobile communication scena-rio in rainfall environment.In this paper,the geometric and physical characteristics of raindrops are introduced,and then the rain failure engineering model is briefly described.On this basis,the expression of dynamic rain attenuation is proposed.The model considers the non-stationary channel in time and space domain by the line-of-sight distance and non-line-of-sight path of base station and signal receiver,as well as the non-stationary of receiver motion and dynamic scattering cluster.Finally,the channel is theoretically analyzed by birth death process,and the effects of frequency,rainfall,pitch angle and other parameters on the cross-correlation function and channel capacity are deduced.The influence of pitch angle and other parameters on the correlation function and channel capacity is found to be highly fitting with the actual measurement results by comparing with the measured data in the previous literatures.The research has important theoretical and practical significance for the application of wireless communication system in rainfall environment,which extends the research and application of mobile wireless communication channel model.

The problem considered in this paper is assessing the quality of the time delay estimate between leak signals measured on water pipes. This is practically important, as a quantitative assessment of the accuracy of time delay estimation (TDE) results makes it possible to infer the reliability of acoustic leak localisation results in a given situation. Three quality assessment approaches are developed by considering the statistical properties of the cross-correlation function (CCF): information-criterion, processing gain, and statistical approaches. In the information-criterion approach, the Bayes factor (BF) is employed to decide the most likely probability distribution of observed CCF peak values. The processing gain approach determines the quality of the time delay estimate using indices that indicate detectability of the CCF peak, namely, the peak-to-side lobe ratio (PSR) and the peak-to-mean ratio (PMR). In the statistical approach, an index termed inconsistency score (ICS) is used to describe the quality of TDE results based on root-mean square of deviations of time delay estimates from their statistical mode. Experimental results show that the proposed approaches provide effective means of assessing the accuracy of the time delay estimate in acoustic leak detection applications. Also, the proposed indices can be employed as figures of merit for selecting best parameters for TDE, for example, filter cut-off frequencies. • Quality of time delay estimate is related to properties of cross-correlation function. • Information criterion index considers distribution of cross-correlation function peak. • Peak-to-side lobe ratio describes detectability of cross-correlation function peak. • Inconsistency score assesses root-mean square error of time delay estimates. • The quality indices are effective for selecting best time delay estimation parameters. [ABSTRACT FROM AUTHOR]

• Development of a novel long-range tracking continuously scanning laser Doppler vibrometer (LR-TCSLDV) system for modal analysis. • Demonstration of a motion theory that utilizes visual identification techniques to overcome environmental interference and effectively control the laser spot for simultaneous tracking and scanning. • Introduction of an improved natural excitation technique, incorporating cross-correlation functions, which considers the responses in the directions of pitch angle of slanted rotational blade and the tilt angle of the laser beam. • Conducting outdoor LR-TCSLDV measurements under natural excitation conditions, representing the first application of this methodology in such settings. In this study, we present the measurements of slanted rotational blades (SRBs) under natural excitation, which accurately represent the operational conditions of wind-driven generators and turbine blades. To track and scan the SRB, we develop a novel long-range tracking continuously scanning laser Doppler vibrometer (LR-TCSLDV) system. By sweeping a laser spot across the blade surface to capture real-time rotation, we apply an operational modal analysis (OMA) method, including an improved natural excitation technique (NExT), to determine the natural frequencies of SRB. The extraction of mode shapes (MSs) from SRBs employs a demodulation method for responses from broadband excitation. The estimation method of natural frequency is an improved NExT, whose derivation begins at the derivation of the measured vibration considering the tilt angle of the laser beam and the pitch angle of the SRB and ends at the cross-correlation function of the corresponding output responses. The tracking of the laser spot scanning the SRB is realized through visual identity, a LabVIEW module that utilizes grayscale recognition to define the position of the SRB. Outdoor experiments need additional precautions to minimize the influence of natural elements on visual identity, where the motion of the laser spot is controlled by a programmed path. An experimental investigation of the OMA method using the LR-TCSLDV system is conducted. Modal parameter estimation of the SRB using the OMA method is performed at different constant rotational speeds and validation is carried out by comparing the results from a stationary slanted blade. [ABSTRACT FROM AUTHOR]

This work employees the modification of the Reynolds equation for computational efficiency by analyzing rough surfaces in the hydrodynamic flow regime through the use of flow factors. This analysis is aimed towards modeling the surface interactions and pressure variations across power cylinder components of an internal combustion engine, namely the piston ring and cylinder wall. The Patir and Cheng equations are for general surfaces that accounts for the overall effect of roughness and anisotropic structure. However, rough surfaces are not fully characterized by these two parameters and therefore the aim of this paper was to provide flow-factors specific to the cross-hatched cylinder liner surfaces and piston ring interface. These interacting surfaces were measured directly through the use of a profilometer. Average flow factors are derived via full deterministic solution of the Reynolds equation over rough surfaces to model the pressure and shear variations relative to smooth surfaces. These flow factors can then be used to consider the effect of roughness in lubrication problems without deterministically modeling roughness. [ABSTRACT FROM AUTHOR]

Power inversion algorithms (PI) are widely used by ant-jamming receivers in harsh environment, but it also induces pseudo-range measurement error which is fatal to high precision receivers. In this paper, it proposes a more accurate method based on the S Curve Bias (SCB) to evaluate the pseudo-range bias which can actually affect the positioning results, as it excludes a fixed time delay contained in the directly differing method. When using this method to assess the bias, it is found that pseudo-range errors can be influenced by many factors including the type of interference. Simulation as well as experiment based on a 4-element array antenna are designed and carried out. The simulation has shown that both SOP-PI and STAP-PI will bring bias to pseudo-range measurement. Specifically, the maximum bias caused by SOP-PI is 1m while the bias caused by STAP-PI is up to 10m. Moreover, comparing to the method which directly differs the pseudo-range of output signal and the reference signal, the method proposed in this paper has better performance. Furthermore, the experimental results verify the effectiveness of the proposed evaluating method.

It is noted that during changes in the geodetic state of urban development area, as well as the technical condition of the objects located there, the noisy signals coming from the corresponding sensors contain noise correlated with the useful signal. It is shown that the characteristics of the relationship between the useful signal and the noise are informative attributes of the beginning of anomalous natural phenomena, as well as changes in the stress-strain state of objects of the urban development complex. We have developed algorithms for calculating the estimates of the relay cross-correlation functions, normalized cross-correlation functions, as well as the correlation coefficient between the useful signal and the noise. It is noted that the use of the algorithms for calculating these characteristics in control systems allows detecting nascent anomalous processes, as well as defects of building structures at the initial latent stage and to prevent the possibility of accident situations. [ABSTRACT FROM AUTHOR]

The analysis of the impact of foreign direct investment (FDI) on the rate of economic growth on the example of China and Ukraine is carried out. It is shown that foreign direct investment has a positive impact, but this is not the only factor that determines economic growth. Apart from the attracted foreign investment, the country must have developed institutions that will protect foreign capital from both the internal political and the external risks. Such an institutional environment will contribute to the growth of foreign direct investment and the effectiveness of their implementation. It is shown that at the same levels of foreign direct investment per capita – investments in China tend to grow steadily and less volatility. At the same time, foreign investment in Ukraine is unstable and highly dependent on macroeconomic factors, such as global economic crises and armed aggression of the neighboring country. To determine the impact of foreign investments on the pace of economic growth, the article used a regression and correlation apparatus. A cross-correlation function was used to assess the lagging impact of foreign investment on economic growth. The novelty of this publication is that by using correlation analysis, a significant difference in the lags of FDI impact on the GDP growth rates for the economies of Ukraine and China has been proved. It is found that Ukraine is characterized by a rapid short-term response to foreign direct investment with zero and single lag, while for the Chinese economy this response is dissolved over time. The main stagnation factors in Ukraine include the following: practical absence of the possibility of direct investment of the population into the country’s economy (underdeveloped stock market), significant political (risks of loss of property), macroeconomic and corruption risks.

The cross-correlation function (CCF) is an established technique to calculate time-of-flight for ultrasonic signals. However, the quality of the CCF depends on the shape of the input signals. In many use cases, the CCF can exhibit secondary maxima in the same order of magnitude as the main maximum, making its interpretation less robust against external disturbances. This paper describes an approach to optimize ultrasonic signals for time-of-flight measurements through coded excitation sequences. The main challenge for applying coded excitation sequences to ultrasonic signals is the influence of the piezoelectric transducer on the outgoing signal. Thus, a simulation model to describe the transfer function of an experimental setup was developed and validated with common code sequences such as pseudo noise sequences (PN), Barker codes and chirp signals. Based on this model an automated optimization of ultrasonic echoes was conducted with random generated sequences, resulting in a decrease in the secondary positive maximum of the CCF to 56.6%. Based on these results, further empiric optimization leveraging the nonlinear regime of the piezoelectric transducer resulted in an even lower secondary positive maximum of the CCF with a height of 25% of the first maximum. Experiments were conducted on different samples to show that the findings hold true for small variations in the experimental setup; however, further work is necessary to develop transfer functions and simulations able to include a wider parameter space, such as varying transducer types or part geometry.

Objectives: With the development of gravity observation technology, the typhoon tracking research by gravity network composed of gPhone with 1 Hz sampling rate can not only improve the ability of typhoon monitoring, but also distinguish the pre-earthquake anomalous signals related to earthquake hypocenters from typhoon excitation signals, thereby improving the ability of earthquake prediction.Methods: Firstly, the original gravity earth tide data are pre-processed and cross-correlated as the ambient noise cross-correlation function(NCF) matrix from the gravity network in Fujian Province and its adjacent areas. Secondly, by selecting the NCF with signal-to-noise ratio (SNR)≥25 as NCF matrix and calculating the optimal azimuth of the signal source by the normalized background energy flux (NBEF) method, the NCF matrix is sorted by the distance of gravity station pairs and the travel time of the Rayleigh wave cross-correlated signal is confirmed. Assuming that the speed of microseisms is 2.9 km/s in the ocean, and 11 km/s in the land, the normalized value in the location area is calculated by the difference of travel time from a signal source to the gravity station pairs in research region. The minimal normalized value in locating area is the typhoon center or the excited signal source. Meanwhile, the microseisms vertical displacement simulated with the Ardhuin seismic spectra model (ASSM) and the optimal path of MITAG typhoon(2019) has been used to check the reliability of the locating results. Finally, the 7 optimal azimuth estimated strategies have been used for comparison of typhoon orientation, and the influence of the high-speed cross-correlated signal has been discussed to verify the reliability of the location method. Results: When the MITAG typhoon is approaching the gravity network, the locating area can cover the location of the typhoon center. The extreme value region of the microseism vertical displacement simulated by the ASSM model is also consistent with the typhoon path during the period of approaching the gravity network. After eliminating the NCF with high-speed cross-correlated signals, the location area can also cover the typhoon trajectory during the period of turning away from the gravity network. Conclusions: By specifying SNR and distance of gravity station pairs and excluding NCFs with high-speed cross-correlated signal, the Raleigh wave cross-correlated signal travel time locating method can be used to trace the typhoon based on Fujian Province gravity network. The study can provide new data and methods for tracking typhoons by gravity network. [ABSTRACT FROM AUTHOR]

Reliable dispersion measurement between two seismic stations is an essential basis of surface wave imaging. Noise source directivity has become an inescapable obstacle and a main concern for passive seismic survey: It basically breaks the principle of Green's function retrieval in travel-time tomography; moreover, the azimuthal effect of heterogeneous ambient noise sources will inherently cause different levels of early arrival on cross-correlation functions, and the apparent velocity of surface waves can be overestimated by either multichannel slant stackings or interstation frequency–time analysis. Waveforms intrinsically contain the features of travel-time, energy and asymmetry in cross-correlation functions, and in return, they can be mapped into the causative noise sources and medium structures. Based on the theoretical framework of full waveform ambient noise inversion, we proposed a method to jointly invert noise source distributions and the corresponding unbiased surface wave velocities. The coupled dependencies of source distributions and path velocities in waveform misfit function show necessity of source–structure joint inversion. The decoupling strategy of partial derivatives is approved by the synthetic tests. Field experiments in the Hangzhou urban area further reveal the practicability of the theory. The inverted noise source models are comparable with the in situ noise distributions in urban environment, and the delineated surface wave velocities have been verified by local borehole datasets. Finally, we concluded that the developed waveform joint imaging algorithm can well relieve the dilemma of source induced velocity uncertainties. [ABSTRACT FROM AUTHOR]

Aim/purpose – Owing to the huge risk occasioned by negative contagion effects associated with financial market linkages, markets participants and academia have continued to examine the capital market cross country interdependence at different levels. In this paper, we examined the causal relationships among the U.S., China and some top African capital market indexes.

The pulse with intra-pulse modulation plays an important role in the design of radar systems. The first class of the signals type is the linear frequency modulation technique. The linear frequency modulation is used to resolve range resolution problems. This paper provides a new algorithm for detecting linear frequency modulation signals at a low signal-to-noise ratio. The core idea of the proposed method is firstly to analyse the linear frequency modulation signals via Fast Fourier Transform; and then to accumulate all energy to achieve signal detection using cross-correlation methods. The proposed algorithm showed better results in comparison with current algorithms, which are used to estimate the parameters of the linear frequency modulation signals at a low signal-to-noise ratio.

In this paper, a new method for detecting and estimating the parameters of a binary phase shift keying (BPSK) signal, based on a cross-correlation function, is proposed. The proposed method consists of two stages. The first stage is used to detect or estimate a signal carrier frequency, and the second stage is used to estimate its pulse width or symbol rate. Firstly, the proposed method is investigated by use of a simulated BPSK signal in the form of Barker Codes 7, 11, and 13 in the MATLAB environment. Based on the simulation results, the functionality of this method is verified using a real-time BPSK signal generated by an E8267C generator. This is described in the second part of this paper. The experimental test results confirm that the proposed method is able to detect and estimate the parameters of all BPSK signals with S N R ≥ − 21   dB. [ABSTRACT FROM AUTHOR]

Copyright of Radio Electronics, Computer Science, Control is the property of Zaporizhzhia National Technical University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: Large‐scale structures are subjected to environmental loads or frequent seismic motion with irremediable effect. These loads have often multidirectional actions on structures, and it couples their responses and leads to multiple‐input multiple‐output (MIMO) problem. The complexity of MIMO model and the relative time‐delays in sensing networks are among major sources of error in dynamic properties identification in large scale structures. This study proposed a parametric‐time domain method to reduce the negative effect of these problems. For this purpose, the contribution of each input in the output signals is determined using QR decomposition and converts a MIMO problem into multiple single‐input multiple‐output (SIMO) ones. In this regard, an Autoregressive Moving Average with eXogenous (ARMAX) model is implemented on decoupled signals for modal identification. Further, for time synchronization of records, a cross‐correlation function has been used to achieve more precise results. The method was employed real strong‐motion response recorded by different sensors at a high rise 64‐story concrete building. Results demonstrate the promising precision of the proposed algorithm for identifying current structural modal properties under real earthquake excitations. Hence, structures can be monitored efficiently along seismic experiences to detect any possible variations in their structural features. The comparison between the output of the proposed method and previous study indicates a considerable improvement on accuracy of the estimated model property particularly on mode shapes. [ABSTRACT FROM AUTHOR]

Bu çalışmada, TÜBİTAK Ulusal Gözlemevinde (TUG) devam etmekte olan ötegezegen araştırmasının bir parçası olarak HD 199719’un tayfsal çizgi ortaylarının (bisektör) değişimleri incelendi. Gözlemsel tayflara bir şablon tayf ile çapraz korelasyon fonksiyonları (CCF) uygulanarak, ortalama çizgi profilleri elde edildi. Bu profillerden çizgi ortayları belirlendi. Bu çizgi ortaylarını nicel olarak tanımlamak için çizgi ortay ölçütleri kullanıldı. Bu ölçütler ile çizgi profillerindeki hız alanları hesaplandı ve dikine hız ölçümleri arasındaki ilişki araştırıldı. Yıldızın doğası kaynaklı (bulgurlanma (granülasyon), zonklama (pulsasyon), manyetik etkinlik kaynaklı yüzey lekeleri ve manyetik çevrim gibi) etkileri araştırmak için çizgi ortayların yanı sıra, Hα ve H çizgilerinin eşdeğer genişlik ölçümleri de yapıldı. Yıldızın çizgi ortay hız ile dikine hız değerleri arasında bir korelasyon olmadığı görüldü. Çizgi ortay hız ölçümleri (BIS ve BVC) için yapılan dönem analizlerinde 4.88 ve 10.36 günlük dönemleri işaret eden pikler elde edildi. Hα’nın eşdeğer genişlik ölçümleri için uzun dönemli bir değişim olabileceği görülse de, benzer bir değişim H’nın eşdeğer genişlik ölçümlerinde elde edilmedi.

The problems of exploitation of technological windows of opportunity are of particular scientific and practical interest in terms of the development of Russia's national economy, and the Arctic region, which has a strong mineral and raw materials potential, is important in terms of its use for achieving the technological and national security of the Russian state. Considering this, the study of the theoretical and methodical aspects of the development of emerging technological windows of opportunity is important and relevant for the regions of the Russian Arctic zone. The purpose of this study is to assess the potential and reserves for exploitation of the emerging technological windows of opportunity during the deployment of a new technological order by mobilizing material and human capital in the Arctic regions. Methodological tools for the study of this problem included dynamic series analysis, structural analysis, comparison, description, descriptive statistics, crosscorrelation analysis, production function model and its visualization. An analytical review of scientific publications, a set of tools and methods of research, allowed to obtain the following scientific results: A significant variability in the contribution of science-intensive and high-tech industry to the formation of gross value added in the Arctic region has been revealed; meanwhile, we can note stable dynamics of the contribution of the Arctic economy to the gross domestic product (GRP) of Russia as a whole. There is a steady excess of the productivity index over the Russian average, which can be regarded as a potential for growth of high-tech components of labor in the development of the economy of the Arctic region. There is a negative statistically significant relationship between the share of the gross regional product of the Arctic in the Russian GRP and the share of gross value added (GVA) of science-intensive products in the Arctic GRP, which can be regarded as a factor preventing the exploitation of the emerging technological windows of opportunity. The construction of a model of production function of technological windows of opportunities for the Arctic zone of Russia pointed to the presence of potential in the exploitation of emerging technological windows in the Arctic zone of Russia in the development of human capital through the activation and use of high labor productivity, creating high-performance jobs. The results of the study, its findings and its proposals can be used in the development, monitoring and implementation of state federal and regional programs and projects aimed at improving the level of technology and science intensity of production in the Arctic zone, improving its competitiveness, which is highly important for the national economy. [ABSTRACT FROM AUTHOR]

The pulse with intra-pulse modulation plays an important role in the design of radar systems. The first class of the signals type is the linear frequency modulation technique. The linear frequency modulation is used to resolve range resolution problems. This paper provides a new algorithm for detecting linear frequency modulation signals at a low signal-to-noise ratio. The core idea of the proposed method is firstly to analyse the linear frequency modulation signals via Fast Fourier Transform; and then to accumulate all energy to achieve signal detection using cross-correlation methods. The proposed algorithm showed better results in comparison with current algorithms, which are used to estimate the parameters of the linear frequency modulation signals at a low signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

• Damping ratio is related to the amplitude and static levitation height. • Damping differs on both sides of the vibration equilibrium point. • Calculating system damping through the cross-correlation function. • Eddy current damping of conductive shell couples with the hysteresis damping. High-temperature superconducting (HTS) pinning maglev has achieved rapid development in recent decades. The levitation system of the HTS pinning maglev is mainly composed of Dewar with built-in HTS bulks and permanent magnet guideway (PMG). For a maglev transportation system, damping is important for vibration attenuation, and the inherent damping characteristics of the HTS pinning maglev system have not been evaluated clearly. In this paper, the damping characteristics of the HTS pinning maglev system are analyzed through experiments and simulations. Experiments are conducted to measure the dynamic responses of the system under free and forced vibrations. The logarithmic envelope method is used to evaluate the system damping under free vibration. The cross-correlation function is utilized to obtain the phase difference between the system vibration signal and excitation signal, and then calculate the system damping under forced vibration conditions. In addition, a two-dimensional finite element model including HTS bulks, PMG, and Dewar conductive shells is established to evaluate the damping force generated by each component during system vibrations. The additional eddy current damping of the conductive Dewar shell is considered and analyzed. Finally, from the perspective of system damping and thermal stability of HTS bulks, suggestions for selecting Dewar shell materials are proposed. [ABSTRACT FROM AUTHOR]

In order to study the channel transmission characteristics of three-dimensional massive multiple input multiple output (m-MIMO) antenna arrays in an air-to-ground (A2G) environment, an A2G MIMO channel model of unmanned aerial vehicle (UAV) and vehicles with spherical scatterers is proposed. Compared with the previous air ground m-MIMO models, fee influence of mutual coupling on antenna arrays is considered in the modeling process, and the non-stationay chaacteristics of m-MIMO antenna ae analyzed and modeled in the birth-death process. The cross-correlation function of the UAV and ca in different height, direction and time at any moving state and fee influence of different angle expansion on channel capacity ae derived. Simulation results ae compared with the measured data in previous literature. It is shown that fee characteristics of the channel model fit well wife the actual measurement results. By analyzing the fading channel data, increasing fee spacing and number of antennas and controlling the flight altitude and pitch angle of UAV can effectively improve fee channel capacity within limits, which lays a foundation for the design of advanced signal processing technology of antenna arrays in large-scale m-MIMO and directional antenna used in fee aviation communication link. [ABSTRACT FROM AUTHOR]

The main goal of this study was to survey a possible correlation between atmospheric parameters (air temperature, precipitation rate) and subsequent earthquakes in Iran and the surrounding Middle Eastern region. This research was carried out in response to previous work regarding atmospheric anomalies prior to major earthquake events. Area-averaged daily and monthly time-series data were compiled from global reanalyzed datasets for the study area between 1980 and 2018. The time-lagged correlation test through the cross-correlation function was examined to distinguish possible relationships between earthquake events and climatic elements within daily and monthly shifts. The results revealed that the precipitation has a strong ability to predict the earthquake series at least from 3½ months prior to the earthquakes. The estimated lagged correlation confirms a positive relationship between precipitation and subsequent earthquake events within 3 to 103 days lag-time (CCF= 0.036 to 0.046). Contrarily, no precursory relation was found between atmospheric temperature variations and subsequent earthquake events in Iran and the surrounding region. [ABSTRACT FROM AUTHOR]

One of the main challenges for structural damage detection using monitoring data is to acquire features that are sensitive to damages but insensitive to noise (e.g. sensor measurement noise) as well as environmental and operational effects (e.g. temperature effect). Inspired by the capabilities of deep learning methods in representation learning, various deep neural networks have been developed to obtain effective damage features from raw vibration data. However, most of the available deep neural networks are supervised, resulting in practical difficulties owing to the lack of damage labels. This article proposes a damage detection strategy based on an unsupervised deep neural network, referred to as deep convolutional denoising autoencoder, which accepts multi-dimensional cross-correlation functions as input. The strategy aims to extract damage features from field measurements of undamaged structures under the influence of noise and temperature uncertainties. In the proposed strategy, cross-correlation functions of vibration data are first calculated as basic features; then deep convolutional denoising autoencoder is developed to reconstruct cross-correlation functions from their noise-corrupted versions to extract desired features; exponentially weighted moving average control charts are finally established for these features to identify minor structural damages. The strategy is evaluated through a numerical simply supported beam model and an experimental continuous beam model. The mechanism of deep convolutional denoising autoencoder to extract damage features is interpreted by visualizing feature maps of convolutional layers in the encoder. It is found that these layers perform rough estimations of modal properties and preserve the damage information as the general trend of these properties in multiple extra frequency bands. The results show that the proposed strategy is competent for structural damage detection under the exposed environment and worth further exploring its capabilities in applications of real bridges. [ABSTRACT FROM AUTHOR]

The purpose of the paper is to study the effect of temperature change on the theory of inner product vector (IPV). The IPV method can be used to detect structural damage. This study evaluates the IPV method ability to detect damage of an Airbus A320 slat-track, which is in the form of a longitudinal crack. The results show that the IPV method is able to detect defects in the structure as well as its location, with close approximation. Then, the Airbus A320 slat-track was investigated for the effect of changes in temperature on the IPV method, evaluated over a temperature between –73 and 260 °C. The effect of temperature on the performance of IPV damage detection method has not been investigated so far. The results of the IPV method show a spurious defect in the structure as the temperature changes; therefore, the IPV method is temperature-sensitive. Also, this study highlighted the importance of applying simulation methods to develop vibration-based damage detection (VBDD) techniques, especially for evaluating the effect of changes in environmental temperature when the structure is complex.

Copyright of Radio Electronics, Computer Science, Control is the property of Zaporizhzhia National Technical University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the article possibility of account of phase fluctuations of signals reflected is examined from littlepitch aims location, during optimization of process of measuring of time of delay of signal. The process of optimization of measuring of distance to the aim on conditions of superrefraction is examined in supposition, that fluctuations of the signals reflected from лоцируемых aims up-diffused on a normal law, and the cross-correlation function of these fluctuations has an arbitrary kind. Within the limits of suppositions got correlation for the optimal estimation of time of delay of the reflected signals. Using the obtained ratios to determine the delay time and the variance of the group delay estimation, the target distance meter was synthesized under the radar of the target above the sea beyond the line of sight for the case when the correlation function of phase fluctuations is described by an exponential function. The proposed optimal estimation algorithm and rangefinder can be used to construct promising radar locations for low altitude targets. The use of such a meter can improve the accuracy of measuring the target range from 2 to 2,5 times.

The purposes of this study were to clarify if force fluctuations during steady multi-muscle contractions have a temporal correlation with a low-frequency component of rectified surface EMG (rEMG) in the involved muscles and collection of that component across muscles allows for the reconstruction of force fluctuations across a wide range of contraction intensities. Healthy young men (n = 15) exerted steady isometric plantarflexion force at 5–60% of maximal force. Surface EMG was recorded from the medial and lateral gastrocnemii, soleus, peroneus longus, abductor hallucis, and tibialis anterior muscles. The cross-correlation function (CCF) between plantarflexion force fluctuations and low-pass filtered rEMG in each muscle was calculated for 8 s. To reconstruct force fluctuations from rEMGs, the product of rEMG and an identified constant factor were summed across muscles with time-lag compensation for electro-mechanical delay. A distinct peak of the CCF was found between plantarflexion force fluctuations and rEMG in most cases except for the tibialis anterior. The CCF peak was greatest in the medial gastrocnemius and soleus. Reconstructed force from rEMGs was temporally correlated with measured force fluctuations across contraction intensities (average CCF peak: r = 0.65). The results indicate that individual surface rEMG has a low-frequency component that is temporally correlated with net force fluctuations during steady multi-muscle contractions and contributes to the reconstruction of force fluctuations across a wide range of contraction intensities. It suggests a potential applicability of individual surface EMGs for identifying the contributing muscles to controlling or disturbing isometric steady force in multi-muscle contractions. [ABSTRACT FROM AUTHOR]

The object of research is the structure of flows in the absorber of hydrogen chloride. One of the most problematic areas in the study of flow hydrodynamics in chemical-technological devices are both technological and technical difficulties, when the device is exposed to random disturbances and/or the supply of a standard indicator is impossible due to a violation of the technological regulations. A method for studying the hydrodynamic structure of flows in a shelf absorber of hydrogen chloride of the «Korobon-KA» type (Germany) in the normal operation of a chemical apparatus using the theory of random functions is proposed. An industrial experiment was carried out on the operating equipment to determine the input and output concentrations of the components of the gas flow. The absorber of hydrogen chloride is considered as a one-dimensional object, at the input of which a random function acts – the concentration of hydrogen chloride in the input stream, and at the output there is a random variable – the concentration of hydrogen chloride in the output stream. The method for determining hydrogen chloride and chlorine in a gas stream is based on the absorption of chlorine by a solution of potassium iodide, followed by titration of the released iodine with sodium thiosulfate. In parallel, portions of acid were sampled at the inlet and outlet, and then the density and temperature of the hydrochloric acid solutions were determined. An algorithm for calculating the impulse function estimates is developed. The obtained experimental data are smoothed. As a result of processing the experimental data, autocorrelation and cross-correlation functions were obtained, the Wiener-Hopf equation was solved, and the impulse weight function was obtained. Having calculated the moments of the obtained impulse weight function, it was proved that the structure of flows in the «Korobon-KA» absorber can be satisfactorily described by the ideal displacement model. The calculations were carried out in software environments MathCAD, Matlab. According to the results obtained, the proposed method for determining the hydrodynamic structure of flows will find application in the study of chemical-technological devices, when the object is exposed to random disturbances and the supply of a standard indicator is impossible due to violation of technological regulations. This makes it possible to find the parameters of flow hydrodynamics in the apparatus in the mode of its normal operation. [ABSTRACT FROM AUTHOR]

Copyright of Scientia Medica is the property of EDIPUCRS - Editora Universitaria da PUCRS and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the pressure on water resources, especially in agricultural sectors, evaluation of the effective strategies on decrease in water consumption has an applicable and important role in field water management. In this research, the effectiveness rate of the 7 climatic parameters on the water requirement of barley (amount of potential evapotranspiration of barley (PETB) during the growth period) using the random forest algorithm (RF), Bayesian multiple linear regression (BR) and cross-correlation function (CCF) was investigated and prioritized. The results of this research can help the managers to control effective climatic variables on PETB. In this paper, the climatic data series of 8 stations with different climate conditions (with two replicates for each climate condition) in Iran during 1968–2017 was used. The results showed the linear regression of simulated PETB using AquaCrop model and predicted PETB using the RF and BR models had no difference with perfect reliable in 0.05 significant levels (T-Statistics varies from 0.010–0.103 and 0.000–0.842 in BR and RF models, respectively, and the R-square (R2) between simulated and predicted PETB were significant in 0.01 levels at all stations (R2 varies from 0.843–0.996 and 0.930–0.999 in BR and RF models, respectively; therefore, the RF and BR models had a good accuracy to predict PETB based on the climatic parameters and the accuracy of RF was more than BR model. The results indicated that based on the all statistical methods the wind speed had the most impact on the PETB (at 62.5% of stations) and based on the RF, BR and CCF methods the average of minimum temperature, the average of sunshine and the average of precipitation had the lowest impact on the PETB, respectively. [ABSTRACT FROM AUTHOR]