Journal articles on the topic 'Joint stationarity'
To see the other types of publications on this topic, follow the link: Joint stationarity.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Joint stationarity.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Fearnhead, Paul. "Haplotypes: the joint distribution of alleles at linked loci." Journal of Applied Probability 40, no. 2 (June 2003): 505–12. http://dx.doi.org/10.1239/jap/1053003559.
Full textAbstract:
We prove a result concerning the joint distribution of alleles at linked loci on a chromosome drawn from the population at stationarity. For a neutral locus, the allele is a draw from the stationary distribution of the mutation process. Furthermore, this allele is independent of the alleles at different loci on any chromosomes in the population.
2
Fearnhead, Paul. "Haplotypes: the joint distribution of alleles at linked loci." Journal of Applied Probability 40, no. 02 (June 2003): 505–12. http://dx.doi.org/10.1017/s0021900200019458.
Full textAbstract:
We prove a result concerning the joint distribution of alleles at linked loci on a chromosome drawn from the population at stationarity. For a neutral locus, the allele is a draw from the stationary distribution of the mutation process. Furthermore, this allele is independent of the alleles at different loci on any chromosomes in the population.
3
Baldan, Damiano, Elisa Coraci, Franco Crosato, Maurizio Ferla, Andrea Bonometto, and Sara Morucci. "Importance of non-stationary analysis for assessing extreme sea levels under sea level rise." Natural Hazards and Earth System Sciences 22, no. 11 (November 14, 2022): 3663–77. http://dx.doi.org/10.5194/nhess-22-3663-2022.
Full textAbstract:
Abstract. Increased coastal flooding caused by extreme sea levels (ESLs) is one of the major hazards related to sea level rise. Estimates of return levels obtained under the framework provided by extreme-event theory might be biased under climatic non-stationarity. Additional uncertainty is related to the choice of the model. In this work, we fit several extreme-value models to two long-term sea level records from Venice (96 years) and Marseille (65 years): a generalized extreme-value (GEV) distribution, a generalized Pareto distribution (GPD), a point process (PP), the joint probability method (JPM), and the revised joint probability method (RJPM) under different detrending strategies. We model non-stationarity with a linear dependence of the model's parameters on the mean sea level. Our results show that non-stationary GEV and PP models fit the data better than stationary models. The non-stationary PP model is also able to reproduce the rate of extremes occurrence fairly well. Estimates of the return levels for non-stationary and detrended models are consistently more conservative than estimates from stationary, non-detrended models. Different models were selected as being more conservative or having lower uncertainties for the two datasets. Even though the best model is case-specific, we show that non-stationary extremes analyses can provide more robust estimates of return levels to be used in coastal protection planning.
4
Stadje, Wolfgang. "Stationarity of a stochastic population flow model." Journal of Applied Probability 36, no. 1 (March 1999): 291–94. http://dx.doi.org/10.1239/jap/1032374251.
Full textAbstract:
We consider a classical population flow model in which individuals pass through n strata with certain state-dependent probabilities and at every time t = 0,1,2,…, there is a stochastic inflow of new individuals to every stratum. For a stationary inflow process we prove the convergence of the joint distribution of group sizes and derive the limiting Laplace transform.
5
Stadje, Wolfgang. "Stationarity of a stochastic population flow model." Journal of Applied Probability 36, no. 01 (March 1999): 291–94. http://dx.doi.org/10.1017/s002190020001706x.
Full textAbstract:
We consider a classical population flow model in which individuals pass through n strata with certain state-dependent probabilities and at every time t = 0,1,2,…, there is a stochastic inflow of new individuals to every stratum. For a stationary inflow process we prove the convergence of the joint distribution of group sizes and derive the limiting Laplace transform.
6
Zhang, Lei, Fucai Wang, Zenghui Gao, Shuangshuang Gao, and Chenghang Li. "Research on the Stationarity of Hexapod Robot Posture Adjustment." Sensors 20, no. 10 (May 18, 2020): 2859. http://dx.doi.org/10.3390/s20102859.
Full textAbstract:
This paper proposes a smooth adjustment method for the instability problem that occurs during the start and stop of a multi-footed robot during attitude change. First, kinematics analysis is used to establish the mapping relationship between the joint angles of the robot support legs and the body posture. The leg joint angle is a known quantity that can be measured accurately and in real time. Therefore, when the position of the foot end of the support leg is unchanged, a unique set of joint angles can be obtained with the change of body posture at a certain moment. Based on the designed mapping model, the smooth adjustment of the posture can be achieved by the smooth adjustment of the support legs. Second, a constraint index that satisfies the requirements of the robot’s steady adjustment of the robot is given. The S-curve acceleration/deceleration method is used to plan the body’s attitude angle transformation curve, and then the mapping control relationship is used to obtain the control trajectory requirements of the joint to achieve smooth adjustment. In addition, this paper also gives a simple choice and motion control method for the redundancy problem caused by the number of support legs of a multi-footed robot when the attitude is changed. The simulation and prototype experiments verify and analyze the proposed method. The results of comparative experiments show that the posture adjustment method proposed in this paper has continuous acceleration without breakpoints, the speed changes gently during the start and stop phases of the attitude transformation, and there is no sudden change in the entire process, which improves the consistency of the actual values of the attitude planning curve with the target values. The physical prototype experiment shows that the maximum deviation between the actual value of the attitude angular velocity and the target value changes from 62.5% to 5.5%, and the degree of fit increases by 57.0%. Therefore, this study solves the problem of the instability of the fuselage when the robot changes its attitude, and it provides an important reference for the multi-footed robot to improve the terrain adaptability.
7
Li, Xinning, Qin Yang, Hu Wu, Shuai Tan, Qun He, Neng Wang, and Xianhai Yang. "Joints Trajectory Planning of Robot Based on Slime Mould Whale Optimization Algorithm." Algorithms 15, no. 10 (September 29, 2022): 363. http://dx.doi.org/10.3390/a15100363.
Full textAbstract:
The joints running trajectory of a robot directly affects it’s working efficiency, stationarity and working quality. To solve the problems of slow convergence speed and weak global search ability in the current commonly used joint trajectory optimization algorithms, a joint trajectory planning method based on slime mould whale optimization algorithm (SMWOA) was researched, which could obtain the joint trajectory within a short time and with low energy consumption. On the basis of analyses of the whale optimization algorithm (WOA) and slime mould algorithm (SMA) in detail, the SMWOA was proposed by combining the two methods. By adjusting dynamic parameters and introducing dynamic weights, the proposed SMWOA increased the probability of obtaining the global optimal solution. The optimized results of 15 benchmark functions verified that the optimization accuracy of the SMWOA is clearly better than that of other classical algorithms. An experiment was carried out in which this algorithm was applied to joint trajectory optimization. Taking 6-DOF UR5 manipulator as an example, the results show that the optimized running time of the joints is reduced by 37.674% compared with that before optimization. The efficiency of robot joint motion was improved. This study provides a theoretical basis for the optimization of other engineering fields.
8
Requena, Ana I., Ilaria Prosdocimi, Thomas R. Kjeldsen, and Luis Mediero. "A bivariate trend analysis to investigate the effect of increasing urbanisation on flood characteristics." Hydrology Research 48, no. 3 (July 1, 2016): 802–21. http://dx.doi.org/10.2166/nh.2016.105.
Full textAbstract:
Flood frequency analyses are usually based on the assumption of stationarity, which might be unrealistic if changes in climate, land uses or urbanisation impact the study catchment. Moreover, most non-stationarity studies only focus on peak flows, ignoring other flood characteristics. In this study, the potential effect of increasing urbanisation on the bivariate relationship of peak flows and volumes is investigated in a case study in the northwest of England, consisting of an increasingly urbanised catchment and a nearby hydrologically and climatologically similar unchanged rural (control) catchment. The study is performed via Kendall's tau and copulas. Temporal trends are studied visually and by formal tests, considering variables individually and jointly. Bivariate joint return period curves associated with consecutive time periods are compared to understand the joint implications of such bivariate trends. Although no significant bivariate trends were detected, hydrologically relevant trends were found in the urbanised catchment.
9
Liu, Jian, and Ed Susko. "On strict stationarity and ergodicity of a non-linear ARMA model." Journal of Applied Probability 29, no. 2 (June 1992): 363–73. http://dx.doi.org/10.2307/3214573.
Full textAbstract:
Two recent papers by Petruccelli and Woolford (1984) and Chan et al. (1985) showed that the key element governing ergodicity of a threshold AR(1) model is the joint behavior of the two linear AR(1) pieces falling in the two boundary threshold regimes. They used essentially the necessary and sufficient conditions for ergodicity of a general Markov chain of Tweedie (1974), (1975) in a rather clever manner. However, it is difficult to extend the results to the more general threshold ARMA models. Besides, irreducibility is also required to apply Tweedie's results. In this paper, instead of pursuing the ideas in Tweedie's results, we shall develop a criterion similar in spirit to the technique used by Beneš (1967) in the context of continuous-time Markov chains. Consequently, we derive a necessary and sufficient condition for existence of a strictly stationary solution of a general non-linear ARMA model to be introduced in Section 2 of this paper. This condition is then applied to the threshold ARMA(1, q) model to yield a sufficient condition for strict stationarity which is identical to the condition given by Petruccelli and Woolford (1984) for the threshold AR(1). Hence, the conjecture that the moving average component does not affect stationarity is partially verified. Furthermore, under an additional irreducibility assumption, ergodicity of a non-linear ARMA model is established. The paper then concludes with a necessary condition for stationarity of the threshold ARMA(1, q) model.
10
Liu, Jian, and Ed Susko. "On strict stationarity and ergodicity of a non-linear ARMA model." Journal of Applied Probability 29, no. 02 (June 1992): 363–73. http://dx.doi.org/10.1017/s0021900200043114.
Full textAbstract:
Two recent papers by Petruccelli and Woolford (1984) and Chan et al. (1985) showed that the key element governing ergodicity of a threshold AR(1) model is the joint behavior of the two linear AR(1) pieces falling in the two boundary threshold regimes. They used essentially the necessary and sufficient conditions for ergodicity of a general Markov chain of Tweedie (1974), (1975) in a rather clever manner. However, it is difficult to extend the results to the more general threshold ARMA models. Besides, irreducibility is also required to apply Tweedie's results. In this paper, instead of pursuing the ideas in Tweedie's results, we shall develop a criterion similar in spirit to the technique used by Beneš (1967) in the context of continuous-time Markov chains. Consequently, we derive a necessary and sufficient condition for existence of a strictly stationary solution of a general non-linear ARMA model to be introduced in Section 2 of this paper. This condition is then applied to the threshold ARMA(1, q) model to yield a sufficient condition for strict stationarity which is identical to the condition given by Petruccelli and Woolford (1984) for the threshold AR(1). Hence, the conjecture that the moving average component does not affect stationarity is partially verified. Furthermore, under an additional irreducibility assumption, ergodicity of a non-linear ARMA model is established. The paper then concludes with a necessary condition for stationarity of the threshold ARMA(1, q) model.
11
Boabang, Francis. "Stationarity of the Market Model: Joint Tests of Process and Parameter Nonstationarity." Canadian Journal of Administrative Sciences / Revue Canadienne des Sciences de l'Administration 9, no. 3 (April 8, 2009): 192–202. http://dx.doi.org/10.1111/j.1936-4490.1992.tb00594.x.
Full text
12
Li, Yingchun, Shengyue Sun, and Hongwei Yang. "Scale Dependence of Waviness and Unevenness of Natural Rock Joints through Fractal Analysis." Geofluids 2020 (August 25, 2020): 1–18. http://dx.doi.org/10.1155/2020/8818815.
Full textAbstract:
The scale dependence of surface roughness is critical in characterising the hydromechanical properties of field-scale rock joints but is still not well understood, particularly when different orders of roughness are considered. We experimentally reveal the scale dependence of two-order roughness, i.e., waviness and unevenness through fractal parameters using the triangular prism surface area method (TPM). The surfaces of three natural joints of granite with the same dimension of 1000 mm×1000 mm are digitised using a 3D laser scanner at three different measurement resolutions. Waviness and unevenness are quantitatively separated by considering the area variation of joint surface as grid size changes. The corresponding fractal dimensions of waviness and unevenness in sampling window sizes ranging from 100 mm×100 mm to 1000 mm×1000 mm at an interval of 100 mm×100 mm are determined. We find that both the fractal dimensions of waviness and unevenness vary as the window size increases. No obvious stationarity threshold has been found for the three rock joint samples, indicating the surface roughness of natural rock joints should be quantified at the scale of the rock mass in the field.
13
Zheng, Jia Chun, Wen Xu, Jianwei Guo, and Wei Dong Xie. "Joint Estimation with Time Delay and Doppler Frequency Shift in the Multi-Carrier Acoustic Communication." Applied Mechanics and Materials 263-266 (December 2012): 994–99. http://dx.doi.org/10.4028/www.scientific.net/amm.263-266.994.
Full textAbstract:
Timing synchronization is very important in the multi-carrier acoustic communication system. With regard to the transmitted signal of the baseband OFDM in the acoustic communication system, which is in the complex environment over the acoustic channel gauss noisy and SαS impulse noisy interference,this paper proposes a joint time delay and Doppler frequency shift estimation algorithm based on the fractional lower order cyclic cross ambiguity function with multi-cycle frequency(FCCAF). This method combines the fractional lower order moment with the feature of cycle stationary, and can detect the signal characteristic of cyclo-stationarity under the SaS impulse noisy. The algorithm takes full advantage of the cycle frequency information of the signal, and can be equipped with the capacity of suppression interference. The simulation results show that the algorithm proposed in this paper can work very well in the presence of the impulse noise and interference, the superior to that algorithm based on the second order cycle fuzzy function, and is a robust joint estimation algorithm with time delay and Doppler shift.
14
Ning, Jing, Mingkuan Fang, Wei Ran, Chunjun Chen, and Yanping Li. "Rapid Multi-Sensor Feature Fusion Based on Non-Stationary Kernel JADE for the Small-Amplitude Hunting Monitoring of High-Speed Trains." Sensors 20, no. 12 (June 18, 2020): 3457. http://dx.doi.org/10.3390/s20123457.
Full textAbstract:
Joint Approximate Diagonalization of Eigen-matrices (JADE) cannot deal with non-stationary data. Therefore, in this paper, a method called Non-stationary Kernel JADE (NKJADE) is proposed, which can extract non-stationary features and fuse multi-sensor features precisely and rapidly. In this method, the non-stationarity of the data is considered and the data from multi-sensor are used to fuse the features efficiently. The method is compared with EEMD-SVD-LTSA and EEMD-JADE using the bearing fault data of CWRU, and the validity of the method is verified. Considering that the vibration signals of high-speed trains are typically non-stationary, it is necessary to utilize a rapid feature fusion method to identify the evolutionary trends of hunting motions quickly before the phenomenon is fully manifested. In this paper, the proposed method is applied to identify the evolutionary trend of hunting motions quickly and accurately. Results verify that the accuracy of this method is much higher than that of the EEMD-JADE and EEMD-SVD-LTSA methods. This method can also be used to fuse multi-sensor features of non-stationary data rapidly.
15
Cebrián, Ana C., Jorge Castillo-Mateo, and Jesús Asín. "Record tests to detect non-stationarity in the tails with an application to climate change." Stochastic Environmental Research and Risk Assessment 36, no. 2 (November 5, 2021): 313–30. http://dx.doi.org/10.1007/s00477-021-02122-w.
Full textAbstract:
AbstractThe analysis of trends and other non-stationary behaviours at the extremes of a series is an important problem in global warming. This work proposes and compares several statistical tools to analyse that behaviour, using the properties of the occurrence of records in i.i.d. series. The main difficulty of this problem is the scarcity of information in the tails, so it is important to obtain all the possible evidence from the available data. First, different statistics based on upper records are proposed, and the most powerful is selected. Then, using that statistic, several approaches to join the information of four types of records, upper and lower records of forward and backward series, are suggested. It is found that these joint tests are clearly more powerful. The suggested tests are specifically useful in analysing the effect of global warming in the extremes, for example, of daily temperature. They have a high power to detect weak trends and can be widely applied since they are non-parametric. The proposed statistics join the information of M independent series, which is useful given the necessary split of the series to arrange the data. This arrangement solves the usual problems of climate series (seasonality and serial correlation) and provides more series to find evidence. These tools are used to analyse the effect of global warming on the extremes of daily temperature in Madrid.
16
Zhang, Sen, Jin Song Tang, and He Ping Zhong. "A Height Estimation Method Based on Joint Time Delay and Phase Estimation for Wideband InSAR or InSAS." Advanced Materials Research 605-607 (December 2012): 1105–9. http://dx.doi.org/10.4028/www.scientific.net/amr.605-607.1105.
Full textAbstract:
In this paper, a new height estimation method based on joint time delay and phase estimation is proposed, which can solve the contradiction between the dimensions of the observing space and the hypothesis of spatial stationarity. It can improve the performance and robustness of time delay estimation by utilizing the neighboring pixels’ common information though spatial processing. The simulated data varifies the perfermance of the proposed method. The result is that its performance is better than the cross correlation estimation method.
17
Zhang, Yunyue, Zhiyi Sun, Qianlai Sun, Yin Wang, Xiaosong Li, and Jiangtao Yang. "Time-jerk optimal trajectory planning of hydraulic robotic excavator." Advances in Mechanical Engineering 13, no. 7 (July 2021): 168781402110346. http://dx.doi.org/10.1177/16878140211034611.
Full textAbstract:
Due to the fact that intelligent algorithms such as Particle Swarm Optimization (PSO) and Differential Evolution (DE) are susceptible to local optima and the efficiency of solving an optimal solution is low when solving the optimal trajectory, this paper uses the Sequential Quadratic Programming (SQP) algorithm for the optimal trajectory planning of a hydraulic robotic excavator. To achieve high efficiency and stationarity during the operation of the hydraulic robotic excavator, the trade-off between the time and jerk is considered. Cubic splines were used to interpolate in joint space, and the optimal time-jerk trajectory was obtained using the SQP with joint angular velocity, angular acceleration, and jerk as constraints. The optimal angle curves of each joint were obtained, and the optimal time-jerk trajectory planning of the excavator was realized. Experimental results show that the SQP method under the same weight is more efficient in solving the optimal solution and the optimal excavating trajectory is smoother, and each joint can reach the target point with smaller angular velocity, and acceleration change, which avoids the impact of each joint during operation and conserves working time. Finally, the excavator autonomous operation becomes more stable and efficient.
18
F.O., Enya, and Ezeali B.O. "Public Investment in Infrastructure and Economic Growth in Nigeria (1980-2020)." African Journal of Economics and Sustainable Development 4, no. 3 (September 5, 2021): 1–22. http://dx.doi.org/10.52589/ajesd-0jm1vber.
Full textAbstract:
The paper examined Public Investment in Infrastructure and the Economic Growth of Nigeria.The study adopted Econometric analysis using E-View.The stationarity test carried out in the study showed that all the variables were all stationary at first difference,1(1) and because of this the reserachers proceeded to determine evidence of co-integration among the variables,hence the result of the co-integration test shows that there is an evidence of 2 co-integration equations which shows that there is a long run relationship among the variables.The ECM test was well signed having -0.019307 with a good Adjusted Coeffiient of determination of 92.78% with a joint statistical probabibility of 0.00000.The study had it that Public Investment in Technology,Educational infrastruture and Power all have positive relationship with the Economy wheras Transport has negative relationship with the Economy.The study went further to conclude that Public Investment plays important roles in stimulation the Nigerian Economy especially in this era of democracy.
19
Yong, Rui, Shaonan Tan, Jun Ye, and Shigui Du. "Neutrosophic Function for Assessing the Scale Effect of the Rock Joint Surface Roughness." Mathematical Problems in Engineering 2021 (July 3, 2021): 1–11. http://dx.doi.org/10.1155/2021/6611627.
Full textAbstract:
A new investigation method is proposed for recording large-sized joint profiles and making statistical analyses of the joint roughness coefficient (JRC) values of the 10–300 cm sized profiles. The mechanical hand profilograph is used for joint roughness measurement due to its advantage of easy operation and high accuracy in recording joint traces. Based on the proposed method, it provides sufficient samples from various positions on the large joint profile, which allows the statistical evaluation of JRC values. A neutrosophic number (NN) is employed for revealing determinate and/or indeterminate information as it consists of determinate and indeterminate parts. Due to the uncertainty of JRC in the real world, NN is chosen to represent the JRC value, which is not only random but also a fuzzy indefinite parameter. The neutrosophic function is used to analyze and express the scale effect of joint surface roughness, and its derivative is used to describe the changing trend of the scale effect. The results show that the JRC value of the joint profile is related to the scale and has a negative effect on the surface roughness of the rock joint. The indeterminate information about the scale effect on joint roughness is described by the neutrosophic functions, and the derivative indicated that the JRC values of small samples are more sensitive than those of large-sized examples. When the length of the sample exceeds the stationarity limit of 80 cm, the roughness appears to be almost scale independent.
20
Robin, Yoann, Mathieu Vrac, Philippe Naveau, and Pascal Yiou. "Multivariate stochastic bias corrections with optimal transport." Hydrology and Earth System Sciences 23, no. 2 (February 12, 2019): 773–86. http://dx.doi.org/10.5194/hess-23-773-2019.
Full textAbstract:
Abstract. Bias correction methods are used to calibrate climate model outputs with respect to observational records. The goal is to ensure that statistical features (such as means and variances) of climate simulations are coherent with observations. In this article, a multivariate stochastic bias correction method is developed based on optimal transport. Bias correction methods are usually defined as transfer functions between random variables. We show that such transfer functions induce a joint probability distribution between the biased random variable and its correction. The optimal transport theory allows us to construct a joint distribution that minimizes an energy spent in bias correction. This extends the classical univariate quantile mapping techniques in the multivariate case. We also propose a definition of non-stationary bias correction as a transfer of the model to the observational world, and we extend our method in this context. Those methodologies are first tested on an idealized chaotic system with three variables. In those controlled experiments, the correlations between variables appear almost perfectly corrected by our method, as opposed to a univariate correction. Our methodology is also tested on daily precipitation and temperatures over 12 locations in southern France. The correction of the inter-variable and inter-site structures of temperatures and precipitation appears in agreement with the multi-dimensional evolution of the model, hence satisfying our suggested definition of non-stationarity.
21
Kang, Ling, Shangwen Jiang, Xiaoyong Hu, and Changwen Li. "Evaluation of Return Period and Risk in Bivariate Non-Stationary Flood Frequency Analysis." Water 11, no. 1 (January 4, 2019): 79. http://dx.doi.org/10.3390/w11010079.
Full textAbstract:
The concept of a traditional return period has long been questioned in non-stationary studies, and the risk of failure was recommended to evaluate the design events in flood modeling. However, few studies have been done in terms of multivariate cases. To investigate the impact of non-stationarity on the streamflow series, the Yichang station in the Yangtze River was taken as a case study. A time varying copula model was constructed for bivariate modeling of flood peak and 7-day flood volume, and the non-stationary return period and risk of failure were applied to compare the results between stationary and non-stationary models. The results demonstrated that the streamflow series at the Yichang station showed significant non-stationary properties. The flood peak and volume series presented decreasing trends in their location parameters and the dependence structure between them also weakened over time. The conclusions of the bivariate non-stationary return period and risk of failure were different depending on the design flood event. In the event that both flood peak and volume are exceeding, the flood risk is smaller with the non-stationary model, which is a joint effect of the time varying marginal distribution and copula function. While in the event that either flood peak or volume exceed, the effect of non-stationary properties is almost negligible. As for the design values, the non-stationary model is characterized by a higher flood peak and lower flood volume. These conclusions may be helpful in long-term decision making in the Yangtze River basin under non-stationary conditions.
22
Yang, Zhiqing, Jianjiang Tang, Hao Zhou, Xinjun Xu, Yingwei Tian, and Biyang Wen. "Joint Ship Detection Based on Time-Frequency Domain and CFAR Methods with HF Radar." Remote Sensing 13, no. 8 (April 16, 2021): 1548. http://dx.doi.org/10.3390/rs13081548.
Full textAbstract:
Compact high-frequency surface wave radar (HFSWR) plays a critical role in ship surveillance. Due to the wide antenna beam-width and low spatial gain, traditional constant false alarm rate (CFAR) detectors often induce a low detection probability. To solve this problem, a joint detection algorithm based on time-frequency (TF) analysis and the CFAR method is proposed in this paper. After the TF ridge extraction, CFAR detection is performed to test each sample of the ridges, and a binary integration is run to determine whether the entire TF ridge is of a ship. To verify the effectiveness of the proposed algorithm, experimental data collected by the Ocean State Monitoring and Analyzing Radar, type SD (OSMAR-SD) were used, with the ship records from an automatic identification system (AIS) used as ground truth data. The processing results showed that the joint TF-CFAR method outperformed CFAR in detecting non-stationary and weak signals and those within the first-order sea clutters, whereas CFAR outperformed TF-CFAR in identifying multiple signals with similar frequencies. Notably, the intersection of the matched detection sets by TF-CFAR and CFAR alone was not immense, which takes up approximately 68% of the matched number by CFAR and 25% of that by TF-CFAR; however, the number in the union detection sets was much (>30%) greater than the result of either method. Therefore, joint detection with TF-CFAR and CFAR can further increase the detection probability and greatly improve detection performance under complicated situations, such as non-stationarity, low signal-to-noise ratio (SNR), and within the first-order sea clutters.
23
Chakrabhavi, Niranjan, and Varadhan SKM. "Wrist Posture Does Not Influence Finger Interdependence." Journal of Applied Biomechanics 35, no. 6 (December 1, 2019): 410–17. http://dx.doi.org/10.1123/jab.2019-0010.
Full textAbstract:
A task involving an instructed finger movement causes involuntary movements in the noninstructed fingers of the hand, also known as finger interdependence. It is associated with both mechanical and neural mechanisms. The current experiment investigated the effect of finger interdependence due to systematic changes of the wrist posture, close to neutral. Eight right-handed healthy human participants performed submaximal cyclic flexion and extension at the metacarpophalangeal joint at 0° neutral, 30° extension, and 30° flexion wrist postures, respectively. The experiment comprised of an instruction to move one of the 4 fingers—index, middle, ring, and little. Movements of the instructed and noninstructed fingers were recorded. Finger interdependence was quantified using enslavement matrix, individuation index, and stationarity index, and it was compared across wrist postures. The authors found that the finger interdependence does not change with changes in wrist posture. Further analysis showed that individuation and stationarity indices were mostly equivalent across wrist postures, and their effects were much smaller than the average differences present among the fingers. The authors conclude that at wrist postures close to neutral, the finger interdependence is not affected by wrist posture.
24
Kulatilake, Pinnaduwa H. S. W., Shi-Gui Du, Mawuko Luke Yaw Ankah, Rui Yong, Desmond Talamwin Sunkpal, Xiaokang Zhao, Guang-Jian Liu, and Rui Wu. "Non-stationarity, heterogeneity, scale effects, and anisotropy investigations on natural rock joint roughness using the variogram method." Bulletin of Engineering Geology and the Environment 80, no. 8 (June 14, 2021): 6121–43. http://dx.doi.org/10.1007/s10064-021-02321-3.
Full text
25
Leiva-Yamaguchi, Valeria, and Danilo Alvares. "A Two-Stage Approach for Bayesian Joint Models of Longitudinal and Survival Data: Correcting Bias with Informative Prior." Entropy 23, no. 1 (December 31, 2020): 50. http://dx.doi.org/10.3390/e23010050.
Full textAbstract:
Joint models of longitudinal and survival outcomes have gained much popularity in recent years, both in applications and in methodological development. This type of modelling is usually characterised by two submodels, one longitudinal (e.g., mixed-effects model) and one survival (e.g., Cox model), which are connected by some common term. Naturally, sharing information makes the inferential process highly time-consuming. In particular, the Bayesian framework requires even more time for Markov chains to reach stationarity. Hence, in order to reduce the modelling complexity while maintaining the accuracy of the estimates, we propose a two-stage strategy that first fits the longitudinal submodel and then plug the shared information into the survival submodel. Unlike a standard two-stage approach, we apply a correction by incorporating an individual and multiplicative fixed-effect with informative prior into the survival submodel. Based on simulation studies and sensitivity analyses, we empirically compare our proposal with joint specification and standard two-stage approaches. The results show that our methodology is very promising, since it reduces the estimation bias compared to the other two-stage method and requires less processing time than the joint specification approach.
26
Yu, Jisoo, Tae-Woong Kim, and Dong-Hyeok Park. "Future Hydrological Drought Risk Assessment Based on Nonstationary Joint Drought Management Index." Water 11, no. 3 (March 14, 2019): 532. http://dx.doi.org/10.3390/w11030532.
Full textAbstract:
As the environment changes, the stationarity assumption in hydrological analysis has become questionable. If nonstationarity of an observed time series is not fully considered when handling climate change scenarios, the outcomes of statistical analyses would be invalid in practice. This study established bivariate time-varying copula models for risk analysis based on the generalized additive models in location, scale, and shape (GAMLSS) theory to develop the nonstationary joint drought management index (JDMI). Two kinds of daily streamflow data from the Soyang River basin were used; one is that observed during 1976–2005, and the other is that simulated for the period 2011–2099 from 26 climate change scenarios. The JDMI quantified the multi-index of reliability and vulnerability of hydrological drought, both of which cause damage to the hydrosystem. Hydrological drought was defined as the low-flow events that occur when streamflow is equal to or less than Q80 calculated from observed data, allowing future drought risk to be assessed and compared with the past. Then, reliability and vulnerability were estimated based on the duration and magnitude of the events, respectively. As a result, the JDMI provided the expected duration and magnitude quantities of drought or water deficit.
27
Vu, Vincent Q., Bin Yu, and Robert E. Kass. "Information in the Nonstationary Case." Neural Computation 21, no. 3 (March 2009): 688–703. http://dx.doi.org/10.1162/neco.2008.01-08-700.
Full textAbstract:
Information estimates such as the direct method of Strong, Koberle, de Ruyter van Steveninck, and Bialek (1998) sidestep the difficult problem of estimating the joint distribution of response and stimulus by instead estimating the difference between the marginal and conditional entropies of the response. While this is an effective estimation strategy, it tempts the practitioner to ignore the role of the stimulus and the meaning of mutual information. We show here that as the number of trials increases indefinitely, the direct (or plug-in) estimate of marginal entropy converges (with probability 1) to the entropy of the time-averaged conditional distribution of the response, and the direct estimate of the conditional entropy converges to the time-averaged entropy of the conditional distribution of the response. Under joint stationarity and ergodicity of the response and stimulus, the difference of these quantities converges to the mutual information. When the stimulus is deterministic or nonstationary the direct estimate of information no longer estimates mutual information, which is no longer meaningful, but it remains a measure of variability of the response distribution across time.
28
Wang, Xin, Daniel M. Keenan, Steven M. Pincus, Peter Y. Liu, and Johannes D. Veldhuis. "Oscillations in joint synchrony of reproductive hormones in healthy men." American Journal of Physiology-Endocrinology and Metabolism 301, no. 6 (December 2011): E1163—E1173. http://dx.doi.org/10.1152/ajpendo.00138.2011.
Full textAbstract:
Negative-feedback (inhibitory) and positive-feedforward (stimulatory) processes regulate physiological systems. Whether such processes are themselves rhythmic is not known. Here, we apply cross-approximate entropy (cross-ApEn), a noninvasive measurement of joint (pairwise) signal synchrony, to inferentially assess hypothesized circadian and ultradian variations in feedback coupling. The data comprised simultaneous measurements of three pituitary and one peripheral hormone (LH, FSH, prolactin, and testosterone) in 12 healthy men each sampled every 10 min for 4 days (5,760 min). Ergodicity, due to the time series stationarity of the measurements over the 4 days, allows for effective estimation of parameters based upon the 12 subjects. Cross-ApEn changes were quantified via moving-window estimates applied to 4-day time series pairs. The resultant ordered windowed cross-ApEn series (in time) were subjected to power spectrum analysis. Rhythmicity was assessed against the null hypothesis of randomness using 1,000 simulated periodograms derived by shuffling the interpulse-interval hormone-concentration segments and redoing cross-ApEn windows and spectral analysis. By forward cross-ApEn analysis, paired LH-testosterone, LH-prolactin, and LH-FSH synchrony maintained dominant rhythms with periodicities of 18–22.5, 18, and 22.5 h, respectively (each P < 0.001). By reverse (feedback) cross-ApEn analysis, testosterone-LH, testosterone-prolactin, and testosterone-FSH synchrony cycles were 30, 18, and 30–45 h, respectively (each P ≤ 0.001). Significant 8- or 24-h rhythms were also detected in most linkages, and maximal bihormonal synchrony occurred consistently at ∼0400–0500. Collectively, these analyses demonstrate significant ultradian (<24 h), circadian (∼24 h), and infradian (>24 h) oscillations in pituitary-testis synchrony, wherein maximal biglandular coordination is strongly constrained to the early morning hours.
29
Stiber, B., and S. Sato. "Visualization of EEG Using Time-Frequency Distributions." Methods of Information in Medicine 36, no. 04/05 (October 1997): 298–301. http://dx.doi.org/10.1055/s-0038-1636881.
Full textAbstract:
Abstract:The EEG is a time-varying or nonstationary signal. Frequency and amplitude are two of its significant characteristics, and are valuable clues to different states of brain activity. Detection of these temporal features is important in understanding EEGs. Commonly, spectrograms and AR models are used for EEG analysis. However, their accuracy is limited by their inherent assumption of stationarity and their trade-off between time and frequency resolution. We investigate EEG signal processing using existing compound kernel time-frequency distributions (TFDs). By providing a joint distribution of signal intensity at any frequency along time, TFDs preserve details of the temporal structure of the EEG waveform, and can extract its time-varying frequency and amplitude features. We expect that this will have significant implications for EEG analysis and medical diagnosis.
30
Monthus, Cécile. "Inhomogeneous asymmetric exclusion processes between two reservoirs: large deviations for the local empirical observables in the mean-field approximation." Journal of Statistical Mechanics: Theory and Experiment 2021, no. 12 (December 1, 2021): 123205. http://dx.doi.org/10.1088/1742-5468/ac4044.
Full textAbstract:
Abstract For a given inhomogeneous exclusion processes on N sites between two reservoirs, the trajectories probabilities allow to identify the relevant local empirical observables and to obtain the corresponding rate function at level 2.5. In order to close the hierarchy of the empirical dynamics that appear in the stationarity constraints, we consider the simplest approximation, namely the mean-field approximation for the empirical density of two consecutive sites, in direct correspondence with the previously studied mean-field approximation for the steady state. For a given inhomogeneous totally asymmetric model, this mean-field approximation yields the large deviations for the joint distribution of the empirical density profile and of the empirical current around the mean-field steady state; the further explicit contraction over the current allows to obtain the large deviations of the empirical density profile alone. For a given inhomogeneous asymmetric model, the local empirical observables also involve the empirical activities of the links and of the reservoirs; the further explicit contraction over these activities yields the large deviations for the joint distribution of the empirical density profile and of the empirical current. The consequences for the large deviations properties of time-additive space-local observables are also discussed in both cases.
31
Zhao, Chen. "Pseudo‐Bayesian updating." Theoretical Economics 17, no. 1 (2022): 253–89. http://dx.doi.org/10.3982/te4535.
Full textAbstract:
I propose an axiomatic framework for belief revision when new information is qualitative, of the form “event A is at least as likely as event B.” My decision maker need not have beliefs about the joint distribution of the signal she will receive and the payoff‐relevant states. I propose three axioms, Exchangeability, Stationarity, and Reduction, to characterize the class of pseudo‐Bayesian updating rules. The key axiom, Exchangeability, requires that the order in which the information arrives does not matter if the different pieces of information neither reinforce nor contradict each other. I show that adding one more axiom, Conservatism, which requires that the decision maker adjust her beliefs just enough to embrace new information, yields Kullback–Leibler minimization: The decision maker selects the posterior closest to her prior in terms of Kullback–Leibler divergence from the probability measures consistent with newly received information. I show that pseudo‐Bayesian agents are susceptible to recency bias, which may be mitigated by repetitive learning.
32
Shi, Wei, and Jun Xia. "Combined risk assessment of nonstationary monthly water quality based on Markov chain and time-varying copula." Water Science and Technology 75, no. 3 (November 30, 2016): 693–704. http://dx.doi.org/10.2166/wst.2016.553.
Full textAbstract:
Water quality risk management is a global hot research linkage with the sustainable water resource development. Ammonium nitrogen (NH3-N) and permanganate index (CODMn) as the focus indicators in Huai River Basin, are selected to reveal their joint transition laws based on Markov theory. The time-varying moments model with either time or land cover index as explanatory variables is applied to build the time-varying marginal distributions of water quality time series. Time-varying copula model, which takes the non-stationarity in the marginal distribution and/or the time variation in dependence structure between water quality series into consideration, is constructed to describe a bivariate frequency analysis for NH3-N and CODMn series at the same monitoring gauge. The larger first-order Markov joint transition probability indicates water quality state Class Vw, Class IV and Class III will occur easily in the water body of Bengbu Sluice. Both marginal distribution and copula models are nonstationary, and the explanatory variable time yields better performance than land cover index in describing the non-stationarities in the marginal distributions. In modelling the dependence structure changes, time-varying copula has a better fitting performance than the copula with the constant or the time-trend dependence parameter. The largest synchronous encounter risk probability of NH3-N and CODMn simultaneously reaching Class V is 50.61%, while the asynchronous encounter risk probability is largest when NH3-N and CODMn is inferior to class V and class IV water quality standards, respectively.
33
Chen, Yu, Huaying Li, Xiaoyu Wang, Hua Ding, and Fenghe Zhang. "A Comparative Investigation on Conventional and Stationary Shoulder Friction Stir Welding of Al-7075 Butt-Lap Structure." Metals 9, no. 12 (November 26, 2019): 1264. http://dx.doi.org/10.3390/met9121264.
Full textAbstract:
Both conventional friction stir welding (C-FSW) and stationary shoulder friction stir welding (S-FSW) were employed to join the Al-7075 butt-lap structure, then the microstructural evolution and mechanical characterization of all FSW joints were systematically studied. The C-FSW joint exhibited a rough surface with flashes and arc corrugations, while the surface of the S-FSW joint became smooth. Moreover, for the S-FSW joint, the shoulder-affected zone got eliminated and the material flow mode during FSW was changed owning to the application of stationary shoulder. Furthermore, in comparison to C-FSW, the lower welding heat input of S-FSW decreased the average grain size in the nugget zone and inhibited the coarsening of strengthening precipitates in the heat-affected zone, elevating the overall hardness for the S-FSW joint. In addition, the tensile strength of the S-FSW joint became higher compared to the C-FSW joint, and all the FSW joints failed inside the nugget zone attributing to the existence of hook defect. The sharp-angled hook defect deteriorated the plasticity of the C-FSW joint further, which was only 70% that of the S-FSW joint.
34
Pitombeira-Neto, Anselmo, Carlos Loureiro, and Luis Carvalho. "Bayesian Inference on Dynamic Linear Models of Day-to-Day Origin-Destination Flows in Transportation Networks." Urban Science 2, no. 4 (December 10, 2018): 117. http://dx.doi.org/10.3390/urbansci2040117.
Full textAbstract:
Estimation of origin–destination (OD) demand plays a key role in successful transportation studies. In this paper, we consider the estimation of time-varying day-to-day OD flows given data on traffic volumes in a transportation network for a sequence of days. We propose a dynamic linear model (DLM) in order to represent the stochastic evolution of OD flows over time. DLMs are Bayesian state-space models which can capture non-stationarity. We take into account the hierarchical relationships between the distribution of OD flows among routes and the assignment of traffic volumes on links. Route choice probabilities are obtained through a utility model based on past route costs. We propose a Markov chain Monte Carlo algorithm, which integrates Gibbs sampling and a forward filtering backward sampling technique, in order to approximate the joint posterior distribution of mean OD flows and parameters of the route choice model. Our approach can be applied to congested networks and in the case when data are available on only a subset of links. We illustrate the application of our approach through simulated experiments on a test network from the literature.
35
Sekunmade, J. O. "FDI, ECONOMIC FREEDOM AND ECONOMIC GROWTH OF NIGERIA." Open Journal of Management Science (ISSN: 2734-2107) 2, no. 2 (August 3, 2021): 01–16. http://dx.doi.org/10.52417/ojms.v2i2.231.
Full textAbstract:
This paper investigates Foreign Direct Investment, Economic Freedom and Economic Growth of Nigeria between 1995 and 2018. Specifically, the data on: Foreign Direct Investment (FDI) inflows, Economic Freedom (Aggregate index) and the data on real gross domestic product (RGDP) were used during the analysis. Time-series data were tested for stationarity using the Augmented Dickey-Fuller Unit Root test method. Vector Autoregressive (VAR) estimation method was adopted to examine the effect of FDI, Economic Freedom on Economic growth. The interactive effect of FDI and Economic Freedom on Economic growth was determined using regression analysis while Granger Causality test method was adopted for determining the causality relationship among the variables. The result of the Vector Autoregressive (VAR) suggests that both FDI and Economic freedom do not have a significant effect on economic growth in Nigeria. The result of regression analysis shows that the joint coefficient of both FDI and EF is negative and not significant. The result of Granger Causality revealed that there is a uni-directional relationship between RGDP and FDI and between EF and FDI respectively. The research recommends that the federal government of Nigeria should adopt appropriate foreign trade strategies to enhance the impact of FDI on economic growth in Nigeria.
36
Ben Bouallègue, Zied, Tobias Heppelmann, Susanne E. Theis, and Pierre Pinson. "Generation of Scenarios from Calibrated Ensemble Forecasts with a Dual-Ensemble Copula-Coupling Approach." Monthly Weather Review 144, no. 12 (November 21, 2016): 4737–50. http://dx.doi.org/10.1175/mwr-d-15-0403.1.
Full textAbstract:
Abstract Probabilistic forecasts in the form of ensembles of scenarios are required for complex decision-making processes. Ensemble forecasting systems provide such products but the spatiotemporal structures of the forecast uncertainty is lost when statistical calibration of the ensemble forecasts is applied for each lead time and location independently. Nonparametric approaches allow the reconstruction of spatiotemporal joint probability distributions at a small computational cost. For example, the ensemble copula coupling (ECC) method rebuilds the multivariate aspect of the forecast from the original ensemble forecasts. Based on the assumption of error stationarity, parametric methods aim to fully describe the forecast dependence structures. In this study, the concept of ECC is combined with past data statistics in order to account for the autocorrelation of the forecast error. The new approach, called d-ECC, is applied to wind forecasts from the high-resolution Consortium for Small-Scale Modeling (COSMO) ensemble prediction system (EPS) run operationally at the German Weather Service (COSMO-DE-EPS). Scenarios generated by ECC and d-ECC are compared and assessed in the form of time series by means of multivariate verification tools and within a product-oriented framework. Verification results over a 3-month period show that the innovative method d-ECC performs as well as or even outperforms ECC in all investigated aspects.
37
Xi, Chenbo, Guangyou Yang, Lang Liu, Hongyuan Jiang, and Xuehai Chen. "A Refined Composite Multivariate Multiscale Fluctuation Dispersion Entropy and Its Application to Multivariate Signal of Rotating Machinery." Entropy 23, no. 1 (January 19, 2021): 128. http://dx.doi.org/10.3390/e23010128.
Full textAbstract:
In the fault monitoring of rotating machinery, the vibration signal of the bearing and gear in a complex operating environment has poor stationarity and high noise. How to accurately and efficiently identify various fault categories is a major challenge in rotary fault diagnosis. Most of the existing methods only analyze the single channel vibration signal and do not comprehensively consider the multi-channel vibration signal. Therefore, this paper presents Refined Composite Multivariate Multiscale Fluctuation Dispersion Entropy (RCMMFDE), a method which extracts the recognition information of multi-channel signals with different scale factors, and the refined composite analysis ensures the recognition stability. The simulation results show that this method has the characteristics of low sensitivity to signal length and strong anti-noise ability. At the same time, combined with Joint Mutual Information Maximisation (JMIM) and support vector machine (SVM), RCMMFDE-JMIM-SVM fault diagnosis method has been proposed. This method uses RCMMFDE to extract the state characteristics of the multiple vibration signals of the rotary machine, and then uses the JMIM method to extract the sensitive characteristics. Finally, different states of the rotary machine are classified by SVM. The validity of the method is verified by the composite gear fault data set and bearing fault data set. The diagnostic accuracy of the method is 99.25% and 100.00%. The experimental results show that RCMMFDE-JMIM-SVM can effectively recognize multiple signals.
38
Johansson, Anna-Maria, Helena Grip, Louise Rönnqvist, Jonas Selling, Carl-Johan Boraxbekk, Andrew Strong, and Charlotte K. Häger. "Influence of visual feedback, hand dominance and sex on individuated finger movements." Experimental Brain Research 239, no. 6 (April 19, 2021): 1911–28. http://dx.doi.org/10.1007/s00221-021-06100-0.
Full textAbstract:
AbstractThe ability to perform individual finger movements, highly important in daily activities, involves visual monitoring and proprioception. We investigated the influence of vision on the spatial and temporal control of independent finger movements, for the dominant and non-dominant hand and in relation to sex. Twenty-six healthy middle-aged to old adults (M age = 61 years; range 46–79 years; females n = 13) participated. Participants performed cyclic flexion–extension movements at the metacarpophalangeal joint of one finger at a time while keeping the other fingers as still as possible. Movements were recorded using 3D optoelectronic motion technique (120 Hz). The movement trajectory distance; speed peaks (movement smoothness); Individuation Index (II; the degree a finger can move in isolation from the other fingers) and Stationarity Index (SI; how still a finger remains while the other fingers move) were extracted. The main findings were: (1) vision only improved the II and SI marginally; (2) longer trajectories were evident in the no-vision condition for the fingers of the dominant hand in the female group; (3) longer trajectories were specifically evident for the middle and ring fingers within the female group; (4) females had marginally higher II and SI compared with males; and (5) females had fewer speed peaks than males, particularly for the ring finger. Our results suggest that visual monitoring of finger movements marginally improves performance of our non-manipulative finger movement task. A consistent finding was that females showed greater independent finger control compared with males.
39
Kryvonosov, Valery, and Serhii Vasylenko. "MATHEMATICAL MODELS FOR DIAGNOSTICS OF A BOLTED CONDUCTIVE JOINT UNDER CONDITIONS OF CHANGING MODE PARAMETERS." Bulletin of the National Technical University "KhPI". Series: Energy: Reliability and Energy Efficiency, no. 1 (2) (July 2, 2021): 45–51. http://dx.doi.org/10.20998/2224-0349.2021.01.07.
Full textAbstract:
The reliability of the transmission and distribution of electricity in ports, ships and energy enterprises depends on the condition of the bolted conductive joints. Operational practice shows that 2 % of cases of emergency shutdowns of technological lines and fires on electrical equipment occur due to the weakening of bolted conductive joints. The main reasons for the bolted joint weakening are dynamic changes in operating current loads and changes in climatic parameters. It is possible to increase the reliability of bolted conductive joints using modern diagnostic methods that allow identifying the appearance of bolted joint weakening. The existing methods for diagnosing the state of bolted joints, which are based on monitoring the temperature of the bolted joint, are analysed. It has been established that the use of such methods to identify the initial moment of the joint weakening is impractical, since they react to the emergency state of the bolted joint, that is, to the critical temperature value. To identify the initial moment of the bolted joint weakening, it is proposed to simultaneously monitor the values of the load current and the parameters of the ambient air, which makes it possible to increase the reliability of detecting pre-emergency situations. To diagnose the initial moment of the bolted joint weakening, it is proposed to use the estimated Boolean functions. Arguments of Boolean variables are obtained for a stationary and continuous process of changing current and ambient temperatures, a stationary and deterministic process as well as a random and deterministic process. The minimized Boolean functions are given for the normal operation of the bolted joint, when the initial moment of weakening appears and when the emergency mode occurs.
40
Wu, Baosheng, Jinglin Liu, Qi Song, Zan Lv, and Wei Bai. "Controllability of joint integrity and mechanical properties of friction stir welded 6061-T6 aluminum and AZ31B magnesium alloys based on stationary shoulder." High Temperature Materials and Processes 38, no. 2019 (February 25, 2019): 557–66. http://dx.doi.org/10.1515/htmp-2019-0001.
Full textAbstract:
AbstractIn order to improve joint integrity and reduce the amount of intermetallic compounds (IMCs), 6061-T6 Al and AZ31B Mg alloys were successfully joined by stationary shoulder friction stir welding (SSFSW). The stationary shoulder effectively enhanced the joint surface integrity and reduced the thickness reduction of the Al/Mg joint. The elimination of pin adhesion was beneficial to increasing material transfer and then improving interfacial joining length of Al/Mg joint. Extremely thin IMCs layer could be achieved because of the heat sink induced by the stationary shoulder. The maximum tensile strength of the Al/ Mg joint reached 137 MPa at a welding speed of 60 mm/min, rotating velocity of 1000 rpm and offset to Mg sheet of 0.3 mm, which was 130% higher than that of conventional joint. SSFSW is feasible and has the potential to join dissimilar materials with the formation of IMCs, such as Al/Mg alloys, Al/copper alloys, Al/titanium alloys and so on.
41
Shur, E. A., V. M. Fedin, A. I. Borts, Yu V. Ronzhina, and A. I. Fimkin. "Methods of elimination of rails increased damage in the area of weld joints." Vestnik of the Railway Research Institute 78, no. 4 (November 25, 2019): 210–17. http://dx.doi.org/10.21780/2223-9731-2019-78-4-210-217.
Full textAbstract:
Rail weld joints from electric-contact welding in stationary and fi eld conditions, as well as those from aluminothermic welding are weak points on tracks that are easily damaged compared with rails outside the weld joints. Currently, these weak points are the defects connected with lack of penetration in the welding area, burns at the points of poor contact of the rail foot with the current-carrying contact tips, or with defects of the weld joint machining after welding, as well as the local hardness reduction in areas affected by heat after welding, and local heat treatment after welding. Elimination of wide areas of reduced hardness at the weld joint points producing saddles, cracks, and chipping, and promoting rails damage next to such joints is a major challenge for increasing the serviceability of weld joints. This study introduces three avenues for elimination of increased damage of rails at weld joints including:• Improvement of technology and equipment for electriccontact welding and local heat treatment after welding in the stationary and fi eld conditions.• Development of technology and equipment for induction welding in the stationary and fi eld conditions.• Development of technology and equipment for differentiated induction tempering of rails preliminary welded in strings 800 m long.
42
Okorontah, Chikeziem Fortunatus, and Onyedikachi Ogba John. "The Nigerian Capital Market and Selected Macroeconomic Variables: An Econometric Analysis." INTERNATIONAL JOURNAL OF SOCIAL SCIENCES AND MANAGEMENT RESEARCH 8, no. 2 (August 11, 2022): 26–37. http://dx.doi.org/10.56201/ijssmr.v8.no2.2022.pg26.37.
Full textAbstract:
Capital market is the major components of a modern market-based economic system as they serve as the channel for the flow of long-term financial resources from the savers of capital to the borrowers of capital. Efficient capital markets are hence essential for economic growth and prosperity. Hence this study using econometric analysis investigated the effects of some key macroeconomic variables on the Nigerian Capital Market. Secondary data sourced from Central Bank of Nigerian (CBN) Statistical Bulletin from 1981 – 2019 were employed. The data was checked for stationarity using the Unit Root Test and OLS regression analysis (through E-view package) was carried out to achieve the objective of the study. All the variables were integrated of order 1(1) except Inflation rate (INFR) that was integrated of order 1(0), therefore we ran the regression following the order of integration. The regression result depicted that, all the variables were rightly signed. However, only Money supply (MNSY) had significant relationship with market capitalization (MKCN) – proxy of Capital Market. The result is acceptable though the joint effect of the explanatory variables (R2 Adjusted = 0.48) on capital market is not so high but from the Durbin-watson statistic there is no existence of autocorrelation in the model. The study concluded that, the relationship between the selected key macroeconomic variables and the Capital Market was not strong by the time of this study, but could be improved through appropriate policies of the Government. We therefore recommend among other things that government promote policies that will encourage industrial production as this may improve the performance of some macroeconomic variables that affect the growth of the Capital Market
43
Kim, Wangdo, Antonio P. Veloso, Veronica E. Vleck, Carlos Andrade, and Sean S. Kohles. "The Stationary Configuration of the Knee." Journal of the American Podiatric Medical Association 103, no. 2 (March 1, 2013): 126–35. http://dx.doi.org/10.7547/1030126.
Full textAbstract:
Background: Ligaments and cartilage contact contribute to the mechanical constraints in the knee joints. However, the precise influence of these structural components on joint movement, especially when the joint constraints are computed using inverse dynamics solutions, is not clear. Methods: We present a mechanical characterization of the connections between the infinitesimal twist of the tibia and the femur due to restraining forces in the specific tissue components that are engaged and responsible for such motion. These components include the anterior cruciate, posterior cruciate, medial collateral, and lateral collateral ligaments and cartilage contact surfaces in the medial and lateral compartments. Their influence on the bony rotation about the instantaneous screw axis is governed by restraining forces along the constraints explored using the principle of reciprocity. Results: Published kinetic and kinematic joint data (American Society of Mechanical Engineers Grand Challenge Competition to Predict In Vivo Knee Loads) are applied to define knee joint function for verification using an available instrumented knee data set. We found that the line of the ground reaction force (GRF) vector is very close to the axis of the knee joint. It aligns the knee joint with the GRF such that the reaction torques are eliminated. The reaction to the GRF will then be carried by the structural components of the knee instead. Conclusions: The use of this reciprocal system introduces a new dimension of foot loading to the knee axis alignment. This insight shows that locating knee functional axes is equivalent to the static alignment measurement. This method can be used for the optimal design of braces and orthoses for conservative treatment of knee osteoarthritis. (J Am Podiatr Med Assoc 103(2): 126–135, 2013)
44
Ilyin, Yu P., and N. А. Berlinsky. "Balance model of dissolved nitrogen and phosphorus transportation and metabolism in the Dniester estuary system." Ukrainian hydrometeorological journal, no. 29 (July 21, 2022): 59–67. http://dx.doi.org/10.31481/uhmj.29.2022.05.
Full textAbstract:
In order to obtain quantitative estimates of water and nutrient fluxes into the Dniester estuary system, the biogeochemical modeling approach recommended by the international program LOICZ was used. The integral (reservoir) model of the system consists of balance equations for water, salinity and dissolved forms of nitrogen and phosphorus. The research involves the information of the annual cycle (from November 2003 to October 2004) of hydrochemical studies at the mouth of the Dniester River and at the exit of the estuary to the Black Sea carried out within the framework of the international project GEF/BSERP, as well as the data of hydrometeorological observations at Belgorod-Dniestrovsky hydrometeorological station, Tzargorod Gyrlo hydrometeorological post and Odesa State Environmental University training base.
The water balance equation takes into account the flows of river runoff, precipitation and evaporation. Uncertainty associated with the failure of taking into account the underground runoff still remained. The use of an independent empirical assessment of the advective water flow through the Tzargorod Strait made it possible to estimate the degree of non-stationarity of the model equations on the scale of variability from a month to a year. The flow of turbulent exchange between the estuary and the adjacent sea is estimated by means of the salt balance equation and is determined by the difference between the estuary and marine water salinity.
By calculating the monthly and yearly values it was established that, for the Dniester estuary and similar systems, the water balance equation can be considered as stationary while the precipitation and evaporation flows can be neglected: compared to the river runoff, advective and turbulent water exchange flows they are several orders of magnitude lower, that is, below the limit of errors of horizontal water flows.
The joint action of the advective and diffusion flows ensured the overall removal of nutrients from the estuary ecosystem. During the annual cycle of 2003-2004 observations 73% of total dissolved phosphorus and 92% of total dissolved nitrogen entered the sea from the estuary compared to the amount reaching the estuary with the Dniester River runoff.
Stoichiometric analysis of biogeochemical residuals showed that, for most of the year, the ecosystem of the Dniester estuary produced organic matter and consumed dissolved phosphorus, while the nitrogen fixation in the ecosystem outweighed the denitrification process.
45
Kazimierska, Agnieszka, Michał M. Placek, Agnieszka Uryga, Paweł Wachel, Małgorzata Burzyńska, and Magdalena Kasprowicz. "Assessment of Baroreflex Sensitivity Using Time-Frequency Analysis during Postural Change and Hypercapnia." Computational and Mathematical Methods in Medicine 2019 (February 3, 2019): 1–17. http://dx.doi.org/10.1155/2019/4875231.
Full textAbstract:
Baroreflex is a mechanism of short-term neural control responsible for maintaining stable levels of arterial blood pressure (ABP) in an ABP-heart rate negative feedback loop. Its function is assessed by baroreflex sensitivity (BRS)—a parameter which quantifies the relationship between changes in ABP and corresponding changes in heart rate (HR). The effect of postural change as well as the effect of changes in blood O2 and CO2 have been the focus of multiple previous studies on BRS. However, little is known about the influence of the combination of these two factors on dynamic baroreflex response. Furthermore, classical methods used for BRS assessment are based on the assumption of stationarity that may lead to unreliable results in the case of mostly nonstationary cardiovascular signals. Therefore, we aimed to investigate BRS during repeated transitions between squatting and standing in normal end-tidal CO2 (EtCO2) conditions (normocapnia) and conditions of progressively increasing EtCO2 with a decreasing level of O2 (hypercapnia with hypoxia) using joint time and frequency domain (TF) approach to BRS estimation that overcomes the limitation of classical methods. Noninvasive continuous measurements of ABP and EtCO2 were conducted in a group of 40 healthy young volunteers. The time course of BRS was estimated from TF representations of pulse interval variability and systolic pressure variability, their coherence, and phase spectra. The relationship between time-variant BRS and indices of ABP and HR was analyzed during postural change in normocapnia and hypercapnia with hypoxia. In normocapnia, observed trends in all measures were in accordance with previous studies, supporting the validity of presented TF method. Similar but slightly attenuated response to postural change was observed in hypercapnia with hypoxia. Our results show the merits of the nonstationary methods as a tool to study the cardiovascular system during short-term hemodynamic changes.
46
Li, Jianshu, Mo Bi, and Guoen Wei. "Investigating the Impacts of Urbanization on Vegetation Net Primary Productivity: A Case Study of Chengdu–Chongqing Urban Agglomeration from the Perspective of Townships." Land 11, no. 11 (November 18, 2022): 2077. http://dx.doi.org/10.3390/land11112077.
Full textAbstract:
As an emerging national strategic urban agglomeration in China, the changing trend of vegetation net primary productivity (NPP) and the impact of the urbanization level (UL) on carbon cycle functions in the Chengdu–Chongqing urban agglomeration (CUA) have received increasing attention. Previous studies have largely overlooked externalities and the heterogeneity of urbanization effects, and urbanization has also been analyzed in isolation (with focus being on land and population urbanization). In this study, the spatial evolution of NPP was evaluated from 2000 to 2020 at the township level (3859) using multivariate remote sensing data and a comprehensive index (UL) that included population urbanization, land urbanization, and economic urbanization. Bivariate spatial autocorrelation, spatial Durbin models, and geographically weighted regression models were used to analyze the spatial externalities of urbanization impacts and assess the global and local effects. The results show that the region’s mean NPP increased by 177.25 g*c/m2 (annual growth of 1.59%), exhibiting a distribution of “low in the middle and high in the periphery” and low-value clustering along major traffic arteries and rivers. Low-value-NPP areas were mainly located in urban centers, while the high-level areas were in the mountainous region (in the southwest and southeast) and significantly expanded over time. Negative correlation clusters were the main clustering types between the UL and NPP; the “High-Low” negative correlation clusters accelerated outward from the urban centers of Chengdu and Chongqing. Overall, urbanization had negative direct and spillover effects on NPP, exhibiting spatial non-stationarity of the negative driving effect within the urban agglomeration. The results indicate the need to strengthen regional ecological joint governance and adopt more place-based urbanization optimization strategies. This study offers new insights to help to reduce the constraining effects of urbanization on vegetation productivity and ecological functions from the perspectives of population agglomeration, land expansion, and industrial construction.
47
Demarie, Giacomo V., Donato Sabia, and Rosario Ceravolo. "Non-Linear Identification of a RC Element Using Time-Frequency Instantaneous Estimators." Key Engineering Materials 413-414 (June 2009): 531–38. http://dx.doi.org/10.4028/www.scientific.net/kem.413-414.531.
Full textAbstract:
The identification of non-linear systems is an important topic in structural health monitoring of structures undergoing non-stationary behavior. In general, a non-linear or hysteretic response is typical for buildings, bridges, dampers and structural elements not only as a consequence of strong excitations (i. e. earthquake), but also for low to medium loading levels, due to the constitutive behavior of structural elements or joints. This paper focuses on the non-linear identification of a RC beam-column joint, modeled as a SDoF system, subjected to non-stationary loading: the technique used entails the definition of proper instantaneous estimators of the system dynamic properties by using a linear time-varying approximation of the actual system dynamics and representing the structural response in the joint time-frequency domain.
48
Zhao, Zhanfeng, Walter A. Illman, Yuanyuan Zha, Tian-Chyi Jim Yeh, Chin Man Bill Mok, Steven J. Berg, and Dongmei Han. "Transient Hydraulic Tomography Analysis of Fourteen Pumping Tests at a Highly Heterogeneous Multiple Aquifer–Aquitard System." Water 11, no. 9 (September 8, 2019): 1864. http://dx.doi.org/10.3390/w11091864.
Full textAbstract:
Hydraulic tomography based on geostatistics has proven to be robust in characterizing subsurface heterogeneity in hydraulic conductivity (K) and specific storage (Ss) through the joint inversion of drawdown records from multiple pumping tests. However, the spatially variable estimates can be smooth or even erroneous for areas where pumping/observation data densities are not high. Previous hydraulic tomography surveys conducted at the North Campus Research Site (NCRS) on the University of Waterloo campus in Waterloo, Canada, revealed that the estimated hydraulic parameters were smooth and the known aquitard was erroneously identified as a high K zone. This was likely the consequence of the site being highly heterogeneous, while only utilizing four pumping tests and not having measurable drawdowns in the low K aquitard for inverse modeling. Here, we investigate whether improved K and Ss estimates could be obtained through the inclusion of additional pumping test data by stressing both aquifer and aquitard zones for a sufficiently long period. Specifically, six additional pumping/injection tests were conducted at the site, and a transient hydraulic tomography analysis with 14 tests was completed. Results reveal that there is a significant improvement to the K and Ss tomograms in terms of the visual correspondence with various geologic units, including its connectivity. More importantly, with the availability of additional data, we found that the inverse model now can better capture the high and low K features for nine boreholes when compared with K values obtained from permeameter tests. The estimated K and Ss tomograms are then used for the forward simulation of one additional pumping test not used for model calibration, revealing reasonable predictions. While encouraging results are obtained by including a large number of pumping tests to the transient hydraulic tomography analysis, stratigraphic boundaries are still smoothed, which is a direct consequence of utilizing a geostatistics-based inversion approach that assumes stationarity in statistical properties. To capture such sharp boundaries, incorporation of additional data types, such as geological and geophysical information, may be necessary when data densities are not sufficiently high.
49
Humbatova, Sugra. "The Impact of Oil Prices on State Budget Income and Expenses: Case of Azerbaijan." International Journal of Energy Economics and Policy 13, no. 1 (January 22, 2023): 189–212. http://dx.doi.org/10.32479/ijeep.13691.
Full textAbstract:
Since Azerbaijan is one of the oil exporting countries, its macroeconomic indicators, especially the exchange rate, the state budget are highly dependent on the oil factor. This study assessed the role of oil in the economy and the impact of the oil factor on the revenues and expenditures of the state budget of Azerbaijan in manat and dollar terms. The study covers the period 2005m03 − 2022m05. Unit root (Augmented Dickey−Fuller (ADF), Phillips−Perron (PP) and Kwiatkowski−Phillips−Schmidt−Shin (KPSS)) tests were applied to check the stationarity of variables (time series). ARDL was applied as a research method. In terms of the reliability of the obtained results, the error correction model (ECM) was used, standard tests were carried out, and the joint integration methods of FMOLS, DOLS and CCR were also applied in the evaluation. Engel−Granger and Phillips−Ouliaris tests have been used to test for cointegration interactions between variables. Short−term, long−term, and strong associations between variables were also calculated. The results of the study showed that the state budget depends on the oil and gas sector, and fluctuations in world oil prices functionally and along the chain affect oil revenues and the state budget. A different impact of oil prices (oil revenues) on the state budget in terms of manat and dollar was the devaluation of the manat, which was carried out to reduce the impact of the global financial and economic crisis on Azerbaijan. The general conclusion of the study was a recommendation to further accelerate work on the diversification of the economy and the development of the non−oil sector. The results of the conducted research can serve as a scientific basis for the economic policy of the state aimed at reducing the impact of external oil price shocks on the economy of Azerbaijan and other similar oil−exporting countries, including on the state budget, and diversifying the economy. The functional dependencies of the income and expenses of the state budget in terms of manat and dollar on world oil prices are given below.
50
Lukashevich, A. A. "Calculation-experimental method for determination of spectrum components of non-stationary loading of carbon steel welded joint." Paton Welding Journal 2016, no. 3 (March 28, 2016): 24–27. http://dx.doi.org/10.15407/tpwj2016.03.04.
Full text