Loop Methods Research Articles

GNSS/INS integrated navigation algorithm framework based on cascade vector tracking algorithm for USV

The safety of Unmanned Surface Vehicle during the autonomous phase of navigation relies heavily on the onboard navigation equipment. However, in the face of changing and diverse navigation environments, global satellite navigation systems utilizing radio communication often face signal occlusions. This significantly reduces the positioning accuracy of navigation systems. To ensure the navigation accuracy of vehicles in various harsh environments, a Global Navigation Satellite Systems and Inertial Navigation System (GNSS/INS) integrated navigation system structure based on cascaded vector-tracking loop is proposed in this paper. The integrated navigation scheme not only improved the positioning accuracy of the navigation system but also effectively improved the robustness of the system. Compared with the traditional scalar-tracking loop and vector-tracking loop methods, it exhibits better performance. The experimental results show that the proposed method can reduce the horizontal position positioning error by 73.7% compared with the traditional vector-tracking loop method in the case of signal occlusion. Simultaneously, it can continuously output reliable and high-precision positioning information in the case of serious signal occlusion. The integrated navigation scheme proposed in this paper can be used as a research direction for the development of Unmanned Surface Vehicle navigation applications and provides solutions for the development of related navigation systems.

DSP implementation and discretization of phase locked loop methods in presence of grid imperfections

DSP implementation and discretization of phase locked loop methods in presence of grid imperfections

Chern, dipole, and quadrupole topological phases of a simple magneto-optical photonic crystal with a square lattice and an unconventional unit cell

For the study of topological phases in photonics, while quantum-Hall-type first-order chiral edge states are routinely realized in magneto-optical photonic crystals, higher-order topological states are mostly explored in all-dielectric photonic crystals. In this work, we study both first- and second-order topological photonic states in magneto-optical photonic crystals. In specific, we revisit a simple magneto-optical photonic crystal in a square lattice with one gyromagnetic cylinder in each unit cell. However, rather than investigating the conventional unit cell where the cylinder is at the center of the square unit cell as previous works have done, we consider a configuration where the cylinders are located at the four corners of the square unit cell and show that this configuration hosts rich topological phases, such as dual-band Chern, dipole, and quadrupole topological phases. Our detailed characterizations of these topological states are based on the Wannier bands and their polarizations via the Wilson loop and nested Wilson loop methods. We study in detail both the edge and corner states of the different topological phases and show that they exhibit a special feature of “spectrum robustness.” For example, though the edge and corner states of the dipole phases living in a band gap could be pushed into the bulk bands by tuning the boundary conditions, they can pass through the bulk bands and reappear within a different band gap. For dual-band quadrupole phases, we can find a regime where both band gaps host a set of corner states simultaneously and, intriguingly, the filling anomaly of one set of corner states can leave their signatures in the filling anomaly of the other set of corner states though they are separated by an extensive number of bulk states. The rich topological physics revealed in a simple magneto-optical photonic crystal not only provides new insights on higher-order topological phases in time-reversal symmetry-broken photonic systems, the results may also find promising applications by harnessing the potentials of both edge and corner states. Published by the American Physical Society 2024

A Real-Time Measurement System for Atmospheric Turbulence Intensity and Distribution Based on the GLAO System

Measuring the intensity and distribution of atmospheric optical turbulence at large-aperture astronomical telescope sites is crucial to optimizing turbulence correction for different layers. A real-time measurement of turbulence distribution in large-aperture telescopes would be valuable for the parameter optimization of adaptive optics (AO) systems, especially for large field-of-view AO systems such as multi-conjugate adaptive optics (MCAO) and ground-layer adaptive optics (GLAO). Based on the GLAO system of NVST at FSO, a real-time measurement system was deployed to assess the site’s atmospheric turbulence intensity and distribution. This system is, to our knowledge, the first real-time turbulence parameter measurement system in the world with an AO system. We adopt pseudo-open loop methods to restore the turbulence information from the close-loop data of GLAO and measure the turbulence strength and distribution. Multiple subaperture pairs are used instead of a pair of subapertures for fitting calculation to increase the measurement accuracy. Two conventional measurement algorithms, SLODAR and S-DIMM+, are compared with the data from the open-source simulator SOAPY, to cross-verify the correctness of our calculation based on the data process of pseudo-open loop data and multiple subaperture pairs. The simulation results show that for two layers’ turbulence input, approximately 93% of the turbulence is correctly detected with the SLODAR method and the given parameters of wavefront sensors and correctors, while the S-DIMM+ is 87%. Real-time measurements of atmospheric turbulence at the NVST site were carried out on 28 May 2023. The observation results indicated that approximately 80% of the turbulence was located below an altitude of 2000 m; only a few appear in the upper height.

Relevance gradient descent for parameter optimization of image enhancement

Machine learning plays a pivotal role in constructing learning models and leveraging abundant image data for feature extraction, which is essential for achieving accurate and efficient image enhancement through optimization algorithms. Traditional gradient descent methods are confined to optimizing independent parameters, while recent algorithms neglect the interdependence among parameters, resulting in prolonged iteration times for each method. To address this issue, we propose a novel Correlation-Based Gradient Descent (RGD) algorithm tailored for enhancing low-light images. RGD leverages inter-iteration results for mutual parameter transmission and optimization, employing convergence or oscillation criteria to select the final enhanced image and find the optimal parameter combination for image enhancement, thereby enhancing parameter optimization efficiency. Specifically, each iteration is divided into multiple operations, with each operation adopting different enhancement schemes. During each iteration, the results of different operation parameters are shared, which facilitates the discovery of optimal parameters for low-light image enhancement. Subsequently, corresponding enhancement operations are performed based on this parameter combination to optimize standard indicators. Our experiments on medical and natural low-light scenarios demonstrate that our RGD method achieves a significant reduction in iteration time, with at least a 17% decrease compared to exhaustive loop methods.

Effect of waste binder material usage rate on thixotropic behaviour of cementitious systems

In order to investigate the feasibility of using waste as an alternative binder in cement-based materials, the effects of using recycled concrete powder (RCP), glass powder (GP), marble powder (MP), and limestone powder (LP) in place of portland cement on the rheological and fresh characteristics of cementitious systems were determined. In this regard, the influence of the utilization of waste materials and the substitution ratio (25% and 35%) on the parameters of the cement paste mixtures that change over time, such as setting time, Marsh-funnel flow time, mini-slump value, viscosity, and dynamic yield stress (DYS), were determined. The effect of 4 different type waste powder materials on the rheology and thixotropy of cementitious systems was investigated using two different methods (loop and constant shear strain rate methods). In order to reduce cement consumption, the effect of the use of waste powder materials on the time-dependent behavior of cementitious systems has been examined, and important results have been obtained for cases (such as producing 3D concrete or self compacting concrete) where time-dependent consistency change is important. It was determined that replacing RCP and GP enhanced the DYS values while replacing MP and LP decreased them. In this context, it was understood that regardless of time, MP and LP promote flowability, whereas RCP and GP diminish flowability. RCP35 had the greatest Ithix_shr and Ithix_vis values at the 20th minute, whereas MP and LP-containing mixtures had the lowest values. The mixtures with the highest and lowest thixotropic degrees were RCP35 and LP35, respectively.

The generalized residual cutting method and its convergence characteristics

AbstractIterative methods and especially Krylov subspace methods (KSM) are a very useful numerical tool in solving for large and sparse linear systems problems arising in science and engineering modeling. More recently, the nested loop KSM have been proposed that improve the convergence of the traditional KSM. In this article, we review the residual cutting (RC) and the generalized residual cutting (GRC) that are nested loop methods for large and sparse linear systems problems. We also show that GRC is a KSM that is equivalent to Orthomin with a variable preconditioning. We use the modified Gram–Schmidt method to derive a stable GRC algorithm. We show that GRC presents a general framework for constructing a class of “hybrid” (nested) KSM based on inner loop method selection. We conduct numerical experiments using nonsymmetric indefinite matrices from a widely used library of sparse matrices that validate the efficiency and the robustness of the proposed methods.

Comparison of pipe loop and pipe section reactor methods for estimating chloramine decay in harvested distribution system pipes

To assess chloramine decay, this study compared the use of pipe loops, which incorporate continuously flowing water, to static pipe section reactors (PSRs). Unlined cast iron (UCI) and cement-lined ductile iron (CLDI) were harvested from distribution systems. These were directly compared to virgin polyvinyl chloride (PVC) pipe at low (0.03 m/s) and high (0.09 m/s) water velocities as well as hydraulic residence times (HRT) of 6 and 24 h. Pipe material was observed to exert the greatest impact on chloramine decay, followed by flow velocity. First-order decay coefficients obtained using pipe loops were statistically similar to those for PSR trials when considering UCI and CLDI pipe, irrespective of pipe velocity or water age. Overall results suggest that the use of PSRs may serve as a viable and cost-effective alternative to pipe loops for assessing the impact of operational variables on disinfectant decay.

Modern multiloop calculations

Loop integrals and methods of their evaluations are vital for perturbative calculations in any quantum field theory. As the order of perturbation theory increases the complexity of the relevant multiloop integrals explodes rapidly. In the present contribution I review methods of modern multiloop calculations with the emphasis on the method based on the IBP reduction and differential equations.

Investigation of physical aspects of energy dissipation in materials under static and dynamic loading

The research is carried out to determine the qualitative and quantitative picture of changes in energy scattering in specific materials and environments under different laws of their loading, processing and creation of new mixtures and materials. It was found that different methods are used to determine the dissipative characteristics, the assessment of which makes it difficult to assess the reliability of the results, as different assumptions and assumptions are accepted. The study of the physical aspects of energy scattering in materials and media is carried out according to linear and nonlinear load laws based on the use of hysteresis loop methods in transient and constant load regimes. It is found that the shape of the hysteresis loop depends to some extent on the law of change of load per cycle. The method of attenuating oscillations of energy absorption estimation by determining the logarithmic decrement of oscillations is used. According to the results of processing the measurement results, it is found that in the studies performed, the energy absorption coefficient varies in the range of 0.04-0.20, depending on the amplitude of relative deformation. which has elastically viscous properties and is under the action of force load. In physical terms, this formula determines the energy consumption per unit volume of material, takes into account the asymmetry of the load and can serve as an energy criterion for energy dissipation in materials under load.

Comparative Study of Surgical Outcome of Linear Stapled Versus Manual Anastomosis Technique During Reversal of Loop Ileostomies

Objective: To compare the surgical outcomes of linear stapler versus manual anastomosis for the reversal of loop ileostomies Subjects and methods: This randomized control trial was conducted in the department of General Surgery at Liaquat University Hospital Jamshoro, from June 2018 to May 2019. All the patients with an age of 14 to 45 years of either gender, having typhoid perforation, and having undergone ileostomy in an emergency after 6–12 weeks of previous surgery were included. All patients were divided into two groups. Patients in group A were reversed with a linear stapler (LS), and the others were reversed through manual suturing (MS). Patients were followed for two weeks during Hospital stay and were discharged on clinically stable condition with normal bowel movements and no complication. Outcome was measured in terms of operative time, hospital stays, and postoperative complications in both groups. All the data was recorded in the predesigned proforma and analyzed by SPSS version 26. Results: A total of 218 patients were studied; the most common age group was 15–30 years in both groups, and males were in the majority in both groups. Anastomosis leakage occurred in 3.7% of patients in group A, while none was found in group B. The infection rate was significantly lower at 13.8% in group A compared to group B at 34.9% (p-0.001). Intestinal obstruction was observed in 1.8% of patients in group A compared to 8.3% in group B (p-0.002). Prolonged Hospital stay was significantly higher in group B (8.7%) (p- 0.001). Conclusion: It was concluded that stapler anastomosis is the safe, most reliable, and adaptable surgical tool for ileostomy reversal. It consumed very less operative time with very lower rate of complications and less time for follow-up as compared to manual suturing. Keywords: Reversal loop ileostomies, linear stapler, manual anastomosis

An Effective Solution to Eliminate DC-Offset for Extracting the Phase and Frequency of Grid Voltage

Recently, several approaches with the ability to reject the DC-offset in phase locked loop (PLL) methods have been developed. These approaches include different filtering structures which can be classified into two categories: prefiltering before the PLL input and in-loop filtering in the PLL control loop. As highlighted in the literature, the DC-offset rejection methods based on in-loop filtering have received less attention due to their slow dynamic performance. Therefore, this paper proposes an alternative DC-offset rejection technique as in-loop filtering of the PLL. The effectiveness of the proposed PLL is confirmed by simulation and experimental results.

Comparison of Cantilever, Heart Loop and Circular Bending Test Methods in Determining the Bending Behaviours of Sewn Woven Polyester Fabrics

Fabrics are cut and sewn to form 3-dimensional end-products. Bending rigidity is one of the properties that should be interpreted for sewn fabrics as it can affect drape, appearance and sensorial comfort of a garment. In the literature, there are several methods to measure the bending behaviours of fabrics. Parallelly, a variety of tests were employed for bending rigidity of sewn samples but their comparability for sewn samples are not known. In this study, 3 simple and standard test methods were used to compare the bending behaviours of fabrics with plied edge seams. Statistical analysis showed that, circular bend method had no or low correlation with cantilever and heart loop methods. Also any difference between the different types of sewn samples could not be detected by this method. In contrast, results of cantilever and heart loop methods showed low to moderate positive correlations for the bending lentghs and bending rigidities of samples.

Rheological behavior of oil well cement pastes containing various types of dispersants at different hydration temperatures

This research discusses the effects of different types of oil well dispersants and hydration temperatures on the rheological properties of cement pastes through rheometer. A polycondensate dispersant, AFS and three polycarboxylate dispersants, APC, PCES and MHS, were used at dosages ranging from 0.1% to 0.3% by weight of cement, and three hydration temperatures of 30, 45 and 60 ℃ were selected. The yield stress was calculated by modelling the flow curve through Herschel-Bulkley and Modified Bingham models. Furthermore, the thixotropy of the cement paste involving different dispersants and hydration temperatures was analyzed by hysteresis loop methods. Besides, the small amplitude oscillatory shear (SAOS) test was applied to evaluate rigidification rate of cementitious material, offering useful information for structuration process of cement paste. The results show that the influences of dispersants on rheological behavior are closely related to the molecular structure and the dosage of dispersant, as well as the temperature of hydration. Increasing the dosage of dispersant decreases the yield stress and apparent viscosity, but increases the hysteresis loop area, especially at the lower hydration temperature of 30 ℃. During SAOS measurement, the critical strain of cement paste with dispersants is higher than without dispersant. The storage modulus (G’) continuously increases with hydration time and temperature.

Predicting hardness profile of steel specimens subjected to Jominy test using an artificial neural network and electromagnetic nondestructive techniques

ABSTRACT Based on relationships between electromagnetic properties and microstructural changes in steel, the current paper describes the development of an electromagnetic technique to determine steel hardenability, non-destructively. Performing Jominy end-quench test, magnetic hysteresis loop and eddy current methods have been applied to SAE 4140 standard steel samples to explore applicability of the non-destructive techniques for determining hardenability. Different hysteresis loop parameters (maximum magnetic flux density, coercivity, hysteresis loss and maximum differential permeability) as well as eddy current outputs (induced voltage, normalised impedance and phase angle) as a function of distance from the end-quenched surface were investigated and the results show a clear agreement with data obtained by traditional hardness testing. In addition, taking advantage of a generalised regression neural network, magnetic data obtained from hysteresis loop and eddy current methods could be used to accurately estimate results in the hardness profile of a given sample, using a few training data points. This paper shows that coupling the proposed non-destructive methods to Jominy end-quench test facilitates accurate non-destructive hardenability determination of steel samples while reducing time and cost of the test process.

Sensor-based and Sensorless Vector Control of Permanent Magnet Synchronous Motor Drives: A Comparative Study

Background: Speed and rotor position estimation is mandatory for vector control scheme of Permanent Magnet Synchronous Motor (PMSM). Methods: The estimation accuracy of Non-adaptive (Open loop) methods degrades as mechanical speed reduces. The system becomes more robust against parameter mismatch and signal noises by employing adaptive observers for estimation of speed and position. Sensorless scheme adopted for estimating the PMSM rotor position based on its performance which eliminates the need for speed sensors which are usually required in such control applications. Results: To achieve this goal, a Space Vector Pulse Width Modulation (SVPWM) control scheme is applied to work in conjunction with a vector control PMSM drive using Simulink. The PI controller uses from estimated speed feedback for the speed sensorless control of PMSM. Conclusion: In this paper, a comprehensive analysis of sensor-based and sensorless based on Sliding Mode Observer (SMO) techniques for vector control of PMSM is presented with regards to the steadystate and dynamic performance robustness against parameter sensitivity, stability and computational complexity. The control scheme is simulated in the MATLAB/Simulink software environment.

A fast hybrid PLL with an adaptive all-pass filter under abnormal grid conditions

Recently, various phase locked loop (PLL) methods have been improved for a reliable and robust synchronization under non-ideal grid conditions. One of the PLLs is a hybrid PLL (HPLL) which is an improved structure of the quasi-type-1 PLL (QT1-PLL) method. In this paper, an enhanced HPLL that offers both fast transient response and increased disturbance rejection capability for dominant harmonics is proposed. The proposed PLL includes adaptive all-pass-filters (APFs) in pre-filtering stage to eliminate fundamental frequency negative sequence (FFNS) component. Thus, window-width of the moving average filter (MAF) is reduced by three times compared with the HPLL by means of removing the FFNS component. So, the proposed PLL, which is called fast-hybrid PLL (FH-PLL), considerably ensures a fast transient response. Also, in case of grid faults (for example, type-B, type-C, type-D, and etc.), at the same time frequency change occurs, the FH-PLL completely blocks the FFNS component by means of using adaptive DAPF. In this study, it is experimentally implemented HPLL, QT1-PLL, and the proposed FH-PLL methods. The effectiveness of the FH-PLL is verified owing to experimental results and comparison with the QT1-PLL and HPLL.

Quantitative Evaluation of Deformation Induced Martensite in Austenitic Stainless Steel Using Magnetic NDE Techniques

The goal of the present study is to examine the applicability of non-destructive magnetic hysteresis loop technique and Hall effect sensor to characterize the strain induced α′-martensite in an austenitic stainless steel. For this purpose, eight different levels of tensile deformation, from 0.05 to 0.44 true stain values, were applied and corresponding induced martensite fractions were determined, using X-ray diffraction method. Finally, magnetic hysteresis loop and Hall effect methods were applied. Results show that major outputs of hysteresis loop (maximum flux density, retentivity and coercivity) and Hall effect (real part, imaginary part, modulus and phase angle for the 3rd harmonic) are significantly affected by variations in the induced martensite fraction. Besides, a new parameter, amplitude and shape of raw received signal, was used in this study. The established relationships with high correlation coefficients between electromagnetic outputs and martensite fraction indicate the potential of the proposed methods to be used for detecting the microstructural changes in AISI 304 stainless steel subjected to different strains.

Insight into the topological phase and elastic properties of halide perovskites CsSnX3 (X = l, Br, Cl) under hydrostatic pressures

Topological materials are considered as a novel quantum state of matter, which can be characterized by symmetry-protected Dirac interfacial states, and exhibit an exotic phenomenon when combined with the other phases. The topological phase in the perovskite structures is important since it can provide various heterostructure interfaces with multifunctional properties. Alpha-(α-) phase cesium-based halide perovskites CsSnX3 (X = I, Br, Cl) can be considered as a promising candidate for topological semiconductors under hydrostatic pressures. The narrow bandgap of these compounds (≤1.83 eV) has made them interesting materials for the electronic, optoelectronic, and photovoltaic applications. In the current research, we systematically carry out first-principles density functional theory (DFT) to study the effects of hydrostatic pressure on the electronic structure of CsSnX3 (X = I, Br, Cl) compounds. The topological phase of these compositions is investigated using the Fu–Kane and Wilson loop methods in order to identify the Z2 topological invariants for each structure. The topological surface states (TSSs) of the (001) plane of these compounds are investigated using the semi-infinite Green's function. These TSSs guarantee the nontrivial nature of CsSnX3 compounds under pressure. With respect to the engineering applications, three important mechanical properties of these compounds including elastic anisotropy, ductility, and hardness are also investigated.

Cross‐comparison of convergence algorithms to solve trip‐based dynamic traffic assignment problems

AbstractSolving a dynamic traffic assignment problem in a transportation network is a computational challenge. This study first reviews the different algorithms in the literature used to numerically calculate the user equilibrium (UE) related to dynamic network loading. Most of them are based on iterative methods to solve a fixed‐point problem. Two elements must be computed: the path set and the optimal path flow distribution between all origin–destination pairs. In a generic framework, these two steps are referred to as the outer and the inner loops, respectively. The goal of this study is to assess the computational performance of the inner loop methods that calculate the path flow distribution for different network settings (mainly network size and demand levels). Several improvements are also proposed to speed up convergence: four new swapping algorithms and two new methods for the step size initialization used in each descent iteration. All these extensions significantly reduce the number of iterations to obtain a good convergence rate and drastically speed up the overall simulations. The results show that the performance of different components of the solution algorithm is sensitive to the network size and saturation. Finally, the best algorithms and settings are identified for all network sizes with particular attention being given to the largest scale.