Conventional Series Research Articles

A hybrid model for metro passengers flow prediction

In this paper, a novel ensemble learning model named EWT-EnsemLSTM-SSA, which assembles long short-term memory (LSTM), support vector regression (SVR), and sparrow search algorithm (SSA), is a proposed to deal with long term metro passenger flow volume prediction, which is an essential content of traffic flow prediction problems. Firstly, the empirical wavelet transform (EWT) method is introduced to decompose the original dataset into five wavelet time-sequence data for further prediction. Then, a cluster of LSTMs with diverse hidden layers and neuron counts are employed to explore and exploit the implicit information of the EWT-decomposed signals. Next, the output of LSTMs is aggregated into a nonlinear regression method SVR. Lastly, SSA is utilized to optimize the SVR automatically. The proposed EWT-EnsemLSTM-SSA model is applied in three case studies, using the data collected from the passengers’ amount in the Minneapolis, America metro, divided into one hour in one day. Experiment results, which compare the proposed EnsemLSTM-SSA model with five conventional time series forecasting models, show that the proposed model can achieve a better performance than the traditional prediction algorithms.

Time series and regression methods for univariate environmental forecasting: An empirical evaluation

One of the most common and valuable applications of science to the environment is to forecast the future, as it affects human lives in many aspects. However, it is not yet clear which methods –conventional time series or regression– deliver the highest performance in univariate time series forecasting. This study attempts to answer that question with a large-scale comparative evaluation that includes 68 environmental variables over three frequencies (hourly, daily, monthly), forecasted in one to twelve steps into the future, and evaluated over six statistical time series and fourteen regression methods. Results suggest that the strongest representatives of the time series methods (ARIMA, Theta) exhibit high accuracies, but certain regression methods (Huber, Extra Trees, Random Forest, Light Gradient Boosting Machines, Gradient Boosting Machines, Ridge, Bayesian Ridge) deliver even more promising results for all forecasting horizons. Finally, depending on the specific use case, the suitable method should be employed, as certain methods are more appropriate for different frequencies and some have an advantageous trade-off between computational time and performance.

A Foreground Mismatch and Memory Harmonic Distortion Calibration Algorithm for TIADC

This paper proposes a foreground digital calibration algorithm that estimates and corrects the offset, gain, and time-skew mismatches for time-interleaved analog-to-digital converters (TIADCs) furthermore our algorithm is designed to correct for harmonic distortion introduced by the presence of a nonlinear front-end. We propose a novel simplified non-linear model in place of the more complex conventional Volterra series based structure. The mismatch estimation technique based on the Fast Fourier Transform (FFT) is proposed to estimate the various time-interleaving mismatches simultaneously. A Taylor-based technique is applied to compensate for these mismatches. We also consider the choice of an appropriate time reference for the time-skew correction algorithm by theoretical analysis. The nonlinear distortion correction technique is based on estimating and inverting an assumed <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3^{\text {rd}}$ </tex-math></inline-formula> order nonlinearity with a fractional delay. To do this, we design a customized filter in an offline process. Our algorithms are designed to operate in any Nyquist zone. The proposed techniques are verified by a Xilinx Zynq UltraScale+ RFSoC ZCU111 evaluation kit containing a 12-bit, 4.096 GHz TI-ADC with 8 sub-ADCs operating in the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2^{\text {nd}}$ </tex-math></inline-formula> Nyquist zone. Accordingly, we observed an improvement in SFDR of 14 dB for mismatch calibration alone and up to another 12 dB with nonlinear correction enabled.

A MACHINE LEARNING APPROACH TO GDP NOWCASTING:AN EMERGING MARKET EXPERIENCE

The growth rate of real Gross Domestic Product (GDP), as measured by the National Statistical Office of India, is an important metric for monetary policy making. Because GDP is released with a significant lag, particularly for the emerging market economies, this article presents various methodologies for nowcasting and forecasting GDP, using both traditional time series and machine learning methods. Further, considering the importance of forward-looking information, our nowcasting model incorporates financial market data and an economic uncertainty index, in addition to high-frequency traditional macroeconomic indicators. Our findings suggest an improvement in the performance of nowcasting using a hybrid of machine learning and conventional time series methods.

Analyzing the Flexural Performance of Cold-Formed Steel Sigma Section Using ABAQUS Software

Cold-formed steel structures are a type of steel fabrication that is commonly employed in building construction. Before manufacture, they are designed precisely to the appropriate dimensions using the ABAQUS software. Both the strength of the cross-section and distortional buckling determine the load-carrying capability of the section. It was found that thin walls in some cold-formed sections suffered distortional buckling under light loads, and that these elements continued to be strong even after the members buckled. To prevent local buckling, stiffness is offered by the web part. There are several methods for determining the modes and elastic buckling stress. They are finite element analysis, finite strip analysis, and conventional Fourier series solutions. The thickness of the specimen and types of stiffener selection which influence the ultimate strength and deflection should be the issue in the design of the appropriate sigma section. The non-linear numerical analysis of the web-stiffened triangular section was performed using ABAQUS v6.4. It has been demonstrated that sections with height-to-thickness (h/t) ratios have load-bearing capacities. When compared to the lower h/t ratio sections, they demonstrated an improvement in load-carrying capability from 35.13% to 37.2%.

An unrestricted MIDAS ordered logit model with applications to credit ratings

AbstractThe ordered logit (OLogit) model is a regression model for an ordinal dependent variable. For a conventional time series OLogit model, both the dependent variable and the independent variables are required to be observed at the same frequency. However, this requirement is violated under the circumstance of mixed frequency data. To this end, we introduce the unrestricted MIDAS (U‐MIDAS) method into the OLogit model and develop a novel U‐MIDAS‐OLogit model, in which high‐frequency covariates are used to predict a low‐frequency outcome with ordinal categories. The U‐MIDAS‐OLogit model enlarges the application of OLogit and enables to produce timely forecast. To verify its effectiveness, we conduct extensive Monte Carlo simulations. The numerical results show that the U‐MIDAS‐OLogit model is superior to several typical OLogit models in terms of prediction performance. We then apply the U‐MIDAS‐OLogit model to predict credit ratings of listed companies in China and the US, respectively. The empirical results also confirm its promising in practical applications.

Diagnosis of an Acute Anterior Wall Infarction in Dual-Energy CT

Due to its high morbidity and mortality, myocardial infarction is the leading cause of death worldwide. Against this background, rapid diagnosis is of immense importance. Especially in case of an atypical course, the correct diagnosis may be delayed and thus lead to increased mortality rates. In this report, we present a complex case of acute coronary syndrome. A triple-rule-out CT examination was performed in dual-energy CT (DECT) mode. While pulmonary artery embolism and aortic dissection could be ruled out with conventional CT series, the presence of anterior wall infarction was only detectable on DECT reconstructions. Subsequently, adequate and rapid therapy was then initiated leading to survival of the patient.

Bayesian Modeling of Labor Earnings in Construction

Labor costs constitute a significant portion of construction costs. Reliable forecasts provide insight into the movements of labor costs and are critical to the success of projects. Past studies have primarily focused on forecasting construction cost indexes or material costs. Only a few studies have concentrated on forecasting construction labor costs. This study presents a multivariate Bayesian structural time series (MBSTS) model to characterize the future values of construction labor’s average hourly earnings (AHE) using a set of candidate predictors. The methodologies commonly used by past studies do not adequately address the uncertainties associated with the modeling process. In contrast, MBSTS recognizes the uncertainty in its modeling process, which enables practitioners to quantify and account for future labor cost risks in decisions. Furthermore, the MBSTS method results in a transparent model, helping analysts investigate the rationality of the parameters. This article trains MBSTS models under four different data subset lengths (i.e., 150, 144, 138, and 132 months) to study the consistency of the explanatory variables and their corresponding coefficients. The analysis results indicate that the gross domestic product (GDP), housing starts (HS), number of building permits (BP), Construction Cost Index (CCI), Dow Jones Industrial Average (DJI), and Standard and Poor’s 500 index (SPI) are the most frequently used predictors in the regression component of the MBSTS models. The results indicate an inverse relationship between AHE from one side and HS and BP from the other. Likewise, a direct relationship exists between AHE and GDP, CCI, DJI, and SPI. The MBSTS model performed well on the validation subset in the midrange prediction intervals (i.e., 12- and 18-month periods). However, it was outperformed by conventional time series models [i.e., seasonal autoregressive integrated moving average (SARIMA)] when used for short-term forecasting. The proposed framework can be applied to facilitate monetary resource allocation in projects.

A Novel Bidirectional Wider Range of Boost-Buck Three-Level LCC Resonant Converter as an Energy Link

In order to maintain different voltage levels between the front and rear dc terminal bus derived from new energy industry, a novel bidirectional wider range of boost-buck three-level LCC resonant converter as an energy link is proposed by combining the LCC resonant tank module with a particular three-level coupling cascaded neutral point clamping active bridges, which is composed of two three-level neutral point clamping bridge arms. Furthermore, the converter can, respectively, establish forward LCC and backward SRC working modes to maintain unified wider bidirectional voltage gain range between the input and output by asymmetric structure of LCC resonant tank module that boost-voltage is enabled by equivalent principle of conventional LCC resonant converter and buck-voltage is enabled by equivalent principle of conventional series resonant converter, while, a unified bidirectional boost-buck voltage gain matching control strategy is designed with an optimization about parameters of LCC resonant tank module under realizing of zero voltage switching-on and reducing of reactive power losses. Finally, according to the simulation platform and experimental prototype, it can be shown that the practical voltage gain is closed to the theoretical designed gain and converter has good dynamic performances after realizing of soft-switching in each mode.

Novel Design Method in Wireless Charger for SS Topology with Current/Voltage Self-Limitation Function

This study proposes a novel wireless power transfer (WPT) resonance compensation design method based on the SS topology with a self-limitation function that achieves fault tolerance without additional components when the secondary circuit is in a short and open state. Conventionally, WPT compensation topologies have constant current (CC) or constant voltage (CV) output characteristics. The CC and CV characteristics can lead to overvoltage and overcurrent, respectively. Several control systems have been proposed to counter this issue; however, they tend to increase the cost and weight of the system. The proposed topology has a self-limitation function that limits the voltage–ampere output. Here, the wireless charging system was designed after the parameters were obtained using the proposed analysis. The performance of the proposed design was verified by configuring a 400 W experimental prototype and comparing it with the conventional series–series (SS) topology. Experimental results indicated that the system could effectively limit the output voltage and current resulting from open-or short-circuit states.

Vibration analysis of functionally graded material (FGM) double layered floating raft structure by the spectro-geometric method

This paper aims to analyze the vibration characteristics of functionally graded material (FGM) double layered floating raft structures under various boundary conditions. The artificial virtual spring technique is introduced to simulate the boundary conditions and coupling effect between the FGM plates by adjusting the spring stiffness. The spectro-geometric method is used to describe the displacement admissible function, which overcomes the discontinuity or jump phenomenon at the boundary for the conventional Fourier series. Based on the unified Rayleigh-Ritz energy framework, the dynamic equations of the FGM double layered floating raft structure are derived, and the corresponding vibration characteristics are obtained. The correctness of the presented method is verified by some numerical examples of comparisons with the calculation results obtained from the finite element method. After that, parametric analysis is carried out to investigate the effects of material parameters, geometric parameters, coupling spring stiffness, and coupling damping on the steady-state response of the FGM double layered floating raft with various boundary conditions.

Nested Magnetic Field Compensation With Regulated Coefficients for Bio-Magnetic Field Measurement

For a spin-exchange relaxation free (SERF) optically pumped magnetometer (OPM) that obtains its best performance in a zero magnetic field, an operation environment with approximately zero magnetic field is desired. This article proposes a nested magnetic field compensation system for a magnetic shielding room (MSR) to suppress the magnetic field. Two sets of coils, one set located outside of the MSR and the other one placed inside of the MSR, are combined in the system. The magnetic fields outside of the MSR are measured by tunneling magnetoresistance (TMR) sensors, while the fields inside the MSR are monitored by SERF OPMs. The two kinds of sensors complement each other in terms of measurement range and sensitivity. A nested two-stage proportional-integral (PI) closed-loop control strategy is employed to compensate for the magnetic field inside the MSR. The control parameters are regulated by the magnitude of the magnetic field to take advantage of the two kinds of sensors. The effect of the proposed system is experimentally tested. The three-axis field fluctuations are reduced by 97.52%, 98%, and 98.64% by the proposed method, respectively. The proposed method is compared with a conventional two-stage series PI control system. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x$ </tex-math></inline-formula> -axis magnetic field fluctuations of the conventional PI control system and the proposed system are 75.81 and 11.71 pT, respectively. The magnetic fluctuation of the proposed system is about 15.5% of the fluctuation of the conventional PI system. To validate the feasibility of the proposed magnetic field compensation system for ultra-weak bio-magnetic field measurement, magnetocardiography (MCG) and magnetoencephalography (MEG) signals are measured.

Harmonics Mitigation Using MMC Based UPFC and Particle Swarm Optimization

The application of non-linear loads in the power electronic device causes serious harmonic issues in the power system since it has the intrinsic property of retrieving harmonic current and reactive power from Alternating Current (AC) supply that leads to voltage instability. To maintain a reliable power flow in the power system, an innovative Unified Power Flow Converter (UPFC) is utilized in this proposed approach. The conventional series converter is replaced with the Modular Multilevel Converter (MMC) that improves the power handling capability and achieves higher modular level with minimized distortions. The shunt compensator assists in minimizing the voltage fluctuations and maximizing the voltage stability under different load constraints. The Direct Quadrature (DQ) theory is utilized in this study to separate the harmonic components by generating reference frame current. The Proportional Integral (PI) controller aids in maintaining the direct current potential difference in the constant mode whereas the Pulse Width Modulation (PWM) generator helps in delivering optimized output to the MMC. The gain parameters of PI controller are optimized with the aid of employing Particle Swarm Optimization (PSO). The entire work is validated using MATLAB simulink and the obtained outcomes proves that this new UPFC is highly beneficial in minimizing the distortions with reduced Total Harmonic Distortion (THD) of 2.21%.

Organic system vs. conventional – a Bayesian analysis of Polish potato post-registration trials

AbstractInterest in organic agriculture worldwide is growing and is mainly supported by a strong consumer interest. In the literature, a lot of attention has been paid to comparing organic and conventional systems, on studying the yield gap between the two systems and, how to reduce it. In the present work, based on the results from Polish organic and conventional series of field trials carried out in 2019–2021, organic and conventional systems were compared in terms of potato tuber yield. Moreover, we propose a Bayesian approach to the variety × environment × system data set and describe Bayesian counterparts of two stability measures. Using this methodology, we identify the most stable and highest tuber yielding varieties in the Polish potato organic and conventional series of field trials. It is shown that the tuber yield in the organic system was approx. 44% lower than the tuber yield in the conventional system. Moreover, varieties Tajfun and Otolia were the most stable and highest yielding varieties in the organic system, whereas in the conventional system, the variety Jurek was the most stable and highest yielding variety among the tested varieties. In the present work, the use of the Bayesian approach allowed us to calculate the probability that the mean of a given variety in given system exceeds the mean of control varieties in that system.

An Active-Neutral-Point-Clamped Switched-Capacitor Multilevel Inverter With Quasi-Resonant Capacitor Charging

Switched-capacitor (SC) multilevel inverters (MLIs) offer various advantages over conventional series MLIs owing to the operation from a single dc source, self-balanced capacitor voltages, and inherent voltage gain. However, these advantages come at the cost of high current stress on the capacitors, associated semiconductors, and the dc source. This inrush current has limited the practical application of SC-MLIs to a fractional kilowatt rating. This article proposes a practical solution by introducing a unity gain nine-level active-neutral-point-clamped SC-MLI with an alleviated capacitor charging current. Switching loss in the SC circuit semiconductors is reduced by using a modified switching sequence that allows the charging current to flow with a minimum interruption till it is turned off at zero-current crossing. The structure also integrates protection against the detrimental effects of voltage transients across the charging inductor. The inverter exhibits a maximum efficiency of 98.03% at 583.91 W output power. Compared with similar SC-MLIs with hard-charging, the proposed inverter significantly reduces the losses and improves efficiency. Experimental results from a 2 kVA laboratory prototype validate the theoretical analysis and show the capacitor voltages stable under varying load impedance and modulation index.

Damping Subsynchronous Oscillations Using a High Voltage Direct Current-Based Multi-Modal Damping Controller

Conventional series capacitors in transmission lines are of paramount importance for enhancing power transfer capability. However, the major drawback of series capacitors is the induced subsynchronous resonance phenomenon in power systems. This phenomenon affects nearby turbogenerator shafts and severely limits their reliability. Also, the controls of High Voltage Direct Current links are considered as a potential source of subsynchronous oscillations. This paper investigates the performance of a multimodal damping controller to stabilize unstable torsional modes in combination with a Power System Stabilizer for inertial mode damping. This research uses time-domain simulation-based multimodal damping controller design methods, namely the test signal and phase correction methods. These two methods involve injecting a test signal at a frequency of interest into the rectifier current control loop and measuring its phase difference with the electromagnetic torque, thus providing corresponding compensators to minimize the resulting angle. This work uses Power System Computer-Aided Design for time-domain simulation and Fast Fourier Transforms Analysis to conduct the phase correction method and verify controller performance.

An improved full Fourier series method approaching the stitched catenary in high-speed railway

ABSTRACT The railway catenary is the typical tensioned beam structure arranged along the railway lines, supplying power to the moving high-speed trains. The accurate static form-finding and dynamic behaviour prediction of the structure are the fundamental problems. An improved full Fourier series (IFFS) method is proposed to describe the mechanical behaviour of the stitched catenary. Different from the conventional Fourier series method, both the sin and cos series are adopted, and the proportional and constant terms are added. The initialization process and the static characteristics of the stitched catenary are given and compared to the finite element method (FEM). The effects of the expanding orders are discussed, considering the calculation efficiency and accuracy. The differences caused by the stitch wire are analysed, consisting of the static state and the dynamic performance in pantograph–catenary interaction, supporting the structural design of the high-speed railway catenary.

Proxy-based torque control of motor-driven exoskeletons for safe and compliant human-exoskeleton interaction

Exoskeletons are considered as promising devices for motion assistance of mobility impaired patients and motor ability augmentation of healthy people. Considering the interactive action between exoskeletons and human body, a safe and comfortable human-exoskeleton interaction is essential to achieve effective exoskeleton operation for human motion assistance. In this paper, a proxy-based torque controller (PTC) is designed for safe and performant interaction torque control of motor-driven exoskeletons under different scenarios. Firstly, the dynamics of commonly applied motor-based conventional stiff actuator (CSA) and series elastic actuator (SEA) for exoskeletons are modelled and analyzed. Then, the PTC with specified compensation is designed based on proxy-based sliding mode control (PSMC) strategy and the stability is theoretically proved for the closed-loop system of the two types of actuators. Meanwhile, an adaptive law is designed for online adjustment of the PTC parameter to produce an overdamped system response for the two actuators under unexpected interruptions. Following the adaptive law, the PTC robustly realizes a compliant torque control while keeping accurate torque tracking under normal operation. Experiments are conducted for two back-support exoskeletons with CSA and SEA, verifying the effectiveness of the proposed controller for safe human-exoskeleton interaction assurance under different scenarios.

Diagnostic Performance of Whole-Body Ultra-Low-Dose CT for Detection of Mechanical Ventriculoperitoneal Shunt Complications: A Retrospective Analysis.

Radiographic shunt series are still the imaging technique of choice for radiologic evaluation of VP-shunt complications. Radiographic shunt series are associated with high radiation exposure and have a low diagnostic performance. Our aim was to investigate the diagnostic performance of whole-body ultra-low-dose CT for detecting mechanical ventriculoperitoneal shunt complications. This retrospective study included 186 patients (mean age, 54.8 years) who underwent whole-body ultra-low-dose CT (100 kV[peak]; reference, 10 mAs). Two radiologists reviewed the images for the presence of ventriculoperitoneal shunt complications, image quality, and diagnostic confidence. On a 5-point Likert scale, readers scored image quality and diagnostic confidence (1 = very low, 5 = very high). Sensitivity, specificity, positive predictive value, and negative predictive value were calculated. Radiation dose estimation of whole-body ultra-low-dose CT was calculated and compared with the radiation dose of a radiographic shunt series. 34 patients positive for VP-shunt complications were correctly identified on whole-body ultra-low-dose CT by both readers. No false-positive or -negative cases were recorded by any of the readers, yielding a sensitivity of 100% (95% CI, 87.3%-100%), a specificity of 100% (95% CI, 96.9%-100%), and perfect agreement (κ = 1). Positive and negative predictive values were high at 100%. Shunt-specific image quality and diagnostic confidence were very high (median score, 5; range, 5-5). Interobserver agreement was substantial for image quality (κ = 0.73) and diagnostic confidence (κ = 0.78). The mean radiation dose of whole-body ultra-low-dose CT was significantly lower than the radiation dose of a conventional radiographic shunt series (0.67 [SD, 0.4] mSv versus 1.57 [SD, 0.6] mSv; 95% CI, 0.79-1.0 mSv; P < .001). Whole-body ultra-low-dose CT allows detection of ventriculoperitoneal shunt complications with excellent diagnostic accuracy and diagnostic confidence. With concomitant radiation dose reduction on contemporary CT scanners, whole-body ultra-low-dose CT should be considered an alternative to the radiographic shunt series.

Low-profile bandwidth and E-plane radiation pattern reconfigurable patch antenna for sub-6 GHz 5G applications

In this work, a low-profile bandwidth and E-plane radiation pattern reconfigurable microstrip antenna is presented for the fifth generation (5G) sub-6 GHz, 3.3 to 4.2 GHz band. The proposed antenna is miniaturized using a partial ground plane technique. The bandwidth and the pattern reconfigurability are realized using a reconfigurable second element feed line and an additional λ/8 connecting stub of a 2-element circular patch array. The additional λ/8 connecting stub transforms a conventional series RLC into a parallel RLC combination leading to larger bandwidth. The working principle and the design process of each iteration have been detailed. The working principle is validated using the surface current distributions in different modes and developing and testing a prototype. The proposed antenna structure has two operating modes covering from 3.28 to 4.34 GHz band; (I) measured 19.4% fractional bandwidth, unidirectional E-plane pattern and (II) 27.4% fractional bandwidth, bidirectional E-plane pattern. The measured centre frequency of both operating modes is 3.5 GHz, and 3.79 GHz with continuous coverage of the 5G band. The measured H-plane radiation pattern of the antenna is identical in both operating modes.