Phase Variation Research Articles

Numerical investigation on circular interference photoelectron momentum distributions induced by spatiotemporal optical vortex pulse

Using the strong field approximation theory, we conducted a detailed numerical investigation on the photoelectron momentum distributions (PMDs) arising from the ionization of hydrogen atoms by a circularly polarized spatiotemporal optical vortex (STOV) pulse. STOV pulses have a unique spatial structure and peculiar phase properties. Our simulations reveal that PMDs exhibit a complex interference structure characterized by circular momentum bands intertwined with intricate interference fringes. A thorough examination of the multi-photon process provides a comprehensive explanation for the circular momentum band formation. We develop an expression to elucidate their center momentum positions within the PMDs. Furthermore, we perform a detailed analysis of the fine interference fringes, attributing their origin to the singular phase of the STOV pulse. Despite their distinct manifestations, we infer that the circular momentum bands and fine interference fringes stem from the simultaneous dependence upon the space and time variables of the STOV phase.

Solar shape variations across cycles 24 and 25: Observations from 2010 to 2023

The longest continuous time-series of solar oblateness measurements, initiated in 2010 and still ongoing, has been obtained from data collected by the Helioseismic Magnetic Imager (HMI) aboard NASA's Solar Dynamics Observatory (SDO). Based on HMI data, we developed two methods for determining the solar oblateness at 617.33\,nm in the continuum . The first method involves determining solar oblateness using HMI solar disk images and limb observations from twenty-three SDO satellite roll calibration maneuvers between 2010 and 2023 . Through meticulous analysis of these observation sequences, we obtained a precise measurement of solar oblateness using this technique, yielding a value of 9.02 (pm 0.72)times 10$^ $ (6.28pm 0.50\,kilometers), unaffected by brightness contamination from sunspots and magnetically induced excess emission. We also verified the polarization independence of light, showing consistent HMI solar oblateness measurements across Stokes states. Interestingly, our solar oblateness time-series, based on HMI solar disk images and limb observations, seems to be in anti-phase with solar activity. The second method we used relies on determining solar oblateness from HMI helioseismic inference of internal rotation. With this approach, we obtained a solar oblateness of 8.40 (pm 0.02)times 10$^ $ (5.85pm 0.01 kilometers) with a variation in phase with solar activity (0.05times 10$^ $ (0.04\,kilometers at 1\,sigma ) over an 11--year sunspot cycle). This outcome is troubling as it conflicts with our results obtained from the HMI solar limb observations

Correlation between spin-dependent recombination centers and long-lived polarons generated in organic photovoltaic devices revealed by successive ESR and EDMR measurements

Using a successive detection technique with electron spin resonance (ESR) and electrically detected magnetic resonance (EDMR), this study clarifies the quantitative correlation between photoinduced spin amounts and spin-dependent recombination (SDR) currents in organic photovoltaic devices (OPVs). Using this unique method of sequentially switching between ESR and EDMR measurements under light irradiation, we find that the intensities of light-induced ESR and EDMR spectra increase along with the light irradiation power. Although positive correlation exists between the number of photo-generated radicals and the SDR currents, the relation is not proportional, which demonstrates that most of the photo-generated radicals are residual accumulated charges. Additionally, phases of the EDMR spectra under light irradiation were found to be changed because of a delay of modulated EDMR signals. The phase variation is probably caused by recombination centers: positive polarons that have arrived at the interface between an aluminum electrode and an active layer by charge drifting after charge separation. Because positive polarons are expected to transport positive charges to the opposite-side electrode of the aluminum as a negative charge collector, this leakage current can be a factor of disturbing an optimal charge collection. This combined technique of ESR and EDMR is useful to explore the different roles of polarons in the photovoltaic conversion processes, thereby providing important information for improving the fill factors and open-circuit voltages of the OPVs, which generate long-lived polarons.

Speed gradient control over qubit states

We discuss the model of a quantum bit driven by an external classical field without decay in the rotating wave approximation. In such a model, the whole evolution of the qubit states takes place on the Bloch sphere. We reformulate the model as a unitless set of real ordinary differential equations and use the normalized external field as a feedback control parameter. The closed-loop algorithm is designed in the form of the speed gradient, driving the dynamical system towards minimizing a given nonnegative goal function expressed via the qubit variables. We investigate the achievability of the control goal, and focus on the most important features of the speed gradient algorithm applied to a quantum system in comparison with classical systems. Our approach is valid for the control over the ground and excited population levels, and over the qubit phase variables. The paper was presented at PhysCon2024.

Ungated, plug-and-play preclinical cardiac CEST-MRI using radial FLASH with segmented saturation.

Electrocardiography (ECG) and respiratory-gated preclinical cardiac CEST-MRI acquisitions are difficult because of variable saturation recovery with T1, RF interference in the ECG signal, and offset-to-offset variation in Z-magnetization and cardiac phase introduced by changes in cardiac frequency and trigger delays. The proposed method consists of segmented saturation modules with radial FLASH readouts and golden angle progression. The segmented saturation blocks drive the system to steady-state, and because center k-space is sampled repeatedly, steady-state saturation dominates contrast during gridding and reconstruction. Ten complete Z-spectra were acquired in healthy mice using both ECG and respiratory-gated and ungated methods. Z-spectra were also acquired at multiple saturation B1 values to optimize for amide and Cr contrasts. There was no significant difference between CEST contrasts (amide, Cr, magnetization transfer) calculated from images acquired using ECG and respiratory-gated and ungated methods (p = 0.27, 0.11, 0.47). A saturation power of 1.8μT provides optimal contrast amplitudes for both amide and total Cr contrast without significantly complicating CEST contrast quantification because of water direct saturation, magnetization transfer, and RF spillover between amide and Cr pools. Further, variability in CEST contrast measurements was significantly reduced using the ungated radial FLASH acquisition (p = 0.002, 0.006 for amide and Cr, respectively). This method enables CEST mapping in the murine myocardium without the need for cardiac or respiratory gating. Quantitative CEST contrasts are consistent with those obtained using gated sequences, and per-contrast variance is significantly reduced. This approach makes preclinical cardiac CEST-MRI easily accessible, even for investigators without prior experience in cardiac imaging.

Flatness constraints in the estimation of GNSS satellite antenna phase center offsets and variations

Accurate information on satellite antenna phase center offsets (PCOs) and phase variations (PVs) is indispensable for high-precision geodetic applications. In the absence of consistent pre-flight calibrations, satellite antenna PCOs and PVs of global navigation satellite systems are commonly estimated based on observations from a global network, constraining the scale to a given reference frame. As part of this estimation, flatness and zero-mean conditions need to be applied to unambiguously separate PCOs, PVs, and constant phase ambiguities. Within this study, we analytically investigate the impact of different boresight-angle-dependent weighting functions for PV minimization, and we compare antenna models generated with different observation-based weighting schemes with those based on uniform weighting. For the case of the GPS IIR/-M and III satellites, systematic differences of 10 mm in the PVs and 65 cm in the corresponding PCOs are identified. In addition, new antenna models for the different blocks of BeiDou-3 satellites in medium Earth orbit are derived using different processing schemes. As a drawback of traditional approaches estimating PCOs and PVs consecutively in distinct steps, it is shown that different, albeit self-consistent, PCO/PV pairs may result depending on whether PCOs or PVs are estimated first. This apparent discrepancy can be attributed to potentially inconsistent weighting functions in the individual processing steps. Use of a single-step process is therefore proposed, in which a dedicated constraint for PCO-PV separation is applied in the solution of the normal equations. Finally, the impact of neglecting phase patterns in precise point positioning applications is investigated. In addition to an overall increase of the position scatter, the occurrence of systematic height biases is illustrated. While observation-based weighting in the pattern estimation can help to avoid such biases, the possible benefit depends critically on the specific elevation-dependent weighting applied in the user’s positioning model. As such, the practical advantage of such antenna models would remain limited, and uniform weighting is recommended as a lean and transparent approach for the pattern estimation of satellite antenna models from observations.

Nonlocality and strength of interatomic interactions inducing the topological phonon phase transition

Understanding phonon behavior in semiconductors from a topological physics perspective offers opportunities to uncover extraordinary phenomena related to phonon transport and electron–phonon interactions. While various types of topological phonons have been reported in different crystalline solids, their microscopic origins remain quantitatively unexplored. In this study, analytical interatomic force constant (IFC) models are employed for wurtzite GaN and AlN to establish relationships between phonon topology and real-space IFCs. The results demonstrate that variations in the strength and nonlocality of IFCs can induce phonon phase transitions in GaN and AlN through band reversal, leading to the emergence of new Weyl phonons at the boundaries and within the Brillouin zones. Among the observed Weyl points, some remain identical in both materials under simple IFC modeling, while others exhibit variability depending on the specific case. Compared to the strength of the IFCs, nonlocal interactions have a significantly larger impact on inducing topological phonon phase transitions, particularly in scenarios modeled by the IFC model and the SW potential. The greater number of the third nearest neighbor atoms in wurtzite AlN provides more room for variations in the topological phonon phase than in GaN, resulting in more substantial changes in AlN.

Comparison of heart rate variability, hemodynamic, metabolic and inflammatory parameters in various phases of decompansatory hemorrhagic shock of normal and vagotomized conscious male rats

BackgroundHeart rate variability (HRV) analysis has shown promise as a valuable complementary tool for clinical assessment in trauma cases. This study aims to evaluate the utility of HRV in monitoring different severities of hemorrhagic shock (HS) and its correlation with traditional hemodynamic and metabolic parameters.MethodsMale Sprague–Dawley rats were divided into different experimental groups, including those with and without vagotomy, and were exposed to different classes of decompensatory HS. To induce varying severities of HS, volume resuscitation was delayed by gradually returning 0%, 20%, or 50% of the shed blood volume at the end of the compensation phase, referred to as 0% DFR, 20% DFR, and 50% DFR class, respectively. Hemodynamic parameters were monitored, and HRV was calculated. Levels of TNF-α and IL-10 were determined in lung tissue at the end of the experiments. Correlations between HRV, hemodynamic parameters, inflammatory gene expression and arterial blood gas variables were evaluated.ResultsHRV showed increased power of the low-frequency (LF) and respiratory sinus arrhythmia (RSA) in all groups during the hypotension phase of HS (Nadir 1). Subdiaphragmatic vagotomy blunted the increase in the LF component in the Nadir 1. After volume resuscitation, systolic blood pressure (SBP), RSA and LF returned to baseline in the 0% DFR and 20% DFR classes. However, animals in 50% DFR class exhibited a reduced SBP and LF and lower pH. Notably, strong correlations were found between LF and SBP as well as tissue hypoperfusion markers. The expression of TNF-α in the lung was increased in all HS groups, while this gene expression was significantly higher in the vagotomized animals.ConclusionThe alterations in HRV components were found to be significantly correlated with the hemodynamic and metabolic status of the animals, while showing no association with inflammatory responses. Additionally, the intervention of subdiaphragmatic vagotomy significantly impacted both HRV components and inflammatory responses. Collectively, these findings suggest the potential of HRV components for the assessment of the presence and severity of HS.

Phase and thermal diffusivity variation of saline water diagnosed by visual and temperature method during freezing process

Freezing step is a fundamental physical phenomenon of cooling a liquid formulation for guaranteeing product quality. In this study, freezing process of saline water under various concentrations was monitored through the visual and temperature methods. The formation of the ice crystal nuclei at the supercooling stage, and the increase of ice and ice/water layers were observed. The formation of the ice crystal nuclei and ice layer was affected by the location of vials placed on a shelf and the concentration of saline water. A saline water solution at a higher concentration had a lower ice layer height under the same freezing settings. The location of vial on the shelf affects the stability and efficiency of thermal transmission. Moreover, the concentration of saline water has the relationship with the thermal diffusivity, and ice layer is an indicator of variation of temperature and thermal diffusivity for saline water during freezing process. This study was able to replicate and observe the physical phenomena of the formation of ice crystal nuclei and the ice layer during the freezing process under laboratory conditions; as well as show how the specific concentration of the saline water solution affected the developmental speed of the ice layer.

A comparative study of pump-probe photothermal spectroscopy using mach-zehnder interferometer and in-fiber mode interferometer

We report a comparative study of mid-infrared photothermal spectroscopy using a Mach-Zehnder interferometer and an in-fiber mode interferometer using a tellurite hollow-core antiresonant fiber (HC-ARF). A quantum cascade laser (QCL) at 5.26 µm serves as the pump laser and is coupled into the HC-ARF to detect nitric oxide (NO). In both interferometric setups, a 1.55 µm probe laser is used to measure the phase variation induced by absorption. The Mach-Zehnder interferometer uses a servo-loop feedback control to achieve quadrature point operation, while the mode interferometer uses passive stabilization based on common mode rejection. With a fiber length of 35 cm, we achieve a noise equivalent concentration of 60 ppb with the Mach-Zehnder interferometer and 0.8 ppb with the mode interferometer. In addition, the response of the sensor to modulation parameters, gas concentration, pump power and long-term stability is also discussed in this study.

Auxiliary relaxation method to derive thermodynamically consistent phase field models with constraints and structure preserving numerical approximations

In this paper, we introduce a novel approach for formulating phase field models with constraints. The main idea is to introduce auxiliary variables that regularize and gradually dissipate constraint deviations of the phase variables, which we name the auxiliary relaxation method. It integrates seamlessly with the energy variational framework to ensure thermodynamic consistency in the resulting phase field models. Unlike traditional penalty methods, which introduce high stiffness due to large penalty parameters to enforce constraints in phase field models, our approach reduces system stiffness, allowing larger time step sizes when solving phase field models with constraints numerically, thus improving numerical accuracy and efficiency. We demonstrate the effectiveness and robustness of the proposed auxiliary relaxation method by applying it across several scenarios to derive thermodynamically consistent phase field models with constraints. Furthermore, we introduce a general second-order implicit-explicit Crank-Nicolson scheme, combining the relaxed scalar auxiliary variable method with a stabilization technique to solve these models. Through extensive numerical tests, we validate the capability of our modeling and numerical framework to reliably simulate complex dynamics governed by phase field equations with constraints.

Analysis of Depth Spatial Variations of Accelerograms Recorded from the Center for Engineering Strong Motion Data: Numerical Simulation for Multipoint Ground Motions

Studies on depth spatial variations are rare because of the limited number of measured recordings of the subsurface along the depth direction from the ground surface. However, these depth variations can directly influence the seismic dynamic response of underground structures or the foundations of space structures through multi-support excitation. In this study, depth spatial variations, including phase and amplitude, are analyzed to describe ground motions along different depths based on surface-earthquake time histories. The observed recordings from the Center for Engineering Strong Motion Data are used to investigate the spatial variation characteristics of the phase and amplitude in the depth direction, represented by the lagged coherence and Fourier amplitude spectrum ratio, respectively. A corresponding model is established under various site conditions to simulate multipoint correlated ground motions along the depth from the surface. Finally, a numerical simulation of multipoint ground motions is conducted to verify the application of the established models. This study provides an effective tool for describing spatial variations in both phase and amplitude, which are crucial for simulating ground motions at various depths.

Finite strain continuum phenomenological model describing the shape-memory effects in multi-phase semi-crystalline networks

Thermally-driven semi-crystalline polymer networks are capable to achieve both the one-way shape-memory effect and two-way shape-memory effect under stress and stress-free conditions, therefore representing an appealing class of polymers for applications requiring autonomous reversible actuation and shape changes. In these materials, the shape-memory effects are achieved by leveraging the synergistic interaction between one or more crystalline phases and the surrounding amorphous ones that are present within the network itself. The present paper introduces a general framework for the finite strain continuum phenomenological modeling of the thermo-mechanical and shape-memory behavior of multi-phase semi-crystalline polymer networks. Model formulation, including the definition of phase and control variables, kinematic assumptions, and constitutive specifications, is introduced and thoroughly discussed. Theoretical derivations are general and easily adaptable to all cross-linked systems which include two or more crystalline domains or a single crystalline phase with a wide melting range and manifest macroscopically the one-way shape-memory effect and the two-way shape-memory effect under stress and stress-free conditions. Model capabilities are validated against experimental data for copolymer networks with two different crystalline phases characterized by well-separated melting and crystallization transitions. Results demonstrate the accuracy of the proposed model in predicting all the phenomena involved and in furnishing a useful support for future material and application design purposes.

Romer-EPTI: Rotating-view motion-robust super-resolution EPTI for SNR-efficient distortion-free in-vivo mesoscale diffusion MRI and microstructure imaging.

To overcome the major challenges in diffusion MRI (dMRI) acquisition, including limited SNR, distortion/blurring, and susceptibility to motion artifacts. A novel Romer-EPTI technique is developed to achieve SNR-efficient acquisition while providing distortion-free imaging, minimal spatial blurring, high motion robustness, and simultaneous multi-TE imaging. It introduces a ROtating-view Motion-robust supEr-Resolution technique (Romer) combined with a distortion/blurring-free Echo Planar Time-resolved Imaging (EPTI) readout. Romer enhances SNR through simultaneous multi-thick-slice acquisition with rotating-view encoding, while providing high motion-robustness via a high-fidelity, motion-aware super-resolution reconstruction. Instead of EPI, the in-plane encoding is performed using EPTI readout to prevent geometric distortion, T2/T2*-blurring, and importantly, dynamic distortions that could introduce additional blurring/artifacts after super-resolution reconstruction due to combining volumes with inconsistent geometries. This further improves effective spatial resolution and motion robustness. Additional developments include strategies to address slab-boundary artifacts, achieve minimized TE and optimized readout for additional SNR gain, and increase robustness to strong phase variations at high b-values. Using Romer-EPTI, we demonstrated distortion-free whole-brain mesoscale in-vivo dMRI at both 3T (500-μm isotropic [iso] resolution) and 7T (485-μm iso resolution) for the first time. Motion experiments demonstrated the technique's motion robustness and its ability to obtain high-resolution diffusion images in the presence of subject motion. Romer-EPTI also demonstrated high SNR gain and robustness in high b-value (b = 5000 s/mm2) and time-dependent dMRI. The high SNR efficiency, improved image quality, and motion robustness of Romer-EPTI make it a highly efficient acquisition for high-resolution dMRI and microstructure imaging.

Human Daily Breathing Monitoring via Analysis of CSI Ratio Trajectories for WiFi Link Pairs on the I/Q Plane.

The measurement of human breathing is crucial for assessing the condition of the body. It opens up possibilities for various intelligent applications, like advanced medical monitoring and sleep analysis. Conventional approaches relying on wearable devices tend to be expensive and inconvenient for users. Recent research has shown that inexpensive WiFi devices commonly available in the market can be utilized effectively for non-contact breathing monitoring. WiFi-based breathing monitoring is highly sensitive to motion during the breathing process. This sensitivity arises because current methods primarily rely on extracting breathing signals from the amplitude and phase variations of WiFi Channel State Information (CSI) during breathing. However, these variations can be masked by body movements, leading to inaccurate counting of breathing cycles. To address this issue, we propose a method for extracting breathing signals based on the trajectories of two-chain CSI ratios on the I/Q plane. This method accurately monitors breathing by tracking and identifying the inflection points of the CSI ratio samples' trajectories on the I/Q plane throughout the breathing cycle. We propose a dispersion model to label and filter out CSI ratio samples representing significant motion interference, thereby enhancing the robustness of the breathing monitoring system. Furthermore, to obtain accurate breathing waveforms, we propose a method for fitting the trajectory curve of the CSI ratio samples. Based on the fitted curve, a breathing segment extraction algorithm is introduced, enabling precise breathing monitoring. Our experimental results demonstrate that this approach achieves minimal error and significantly enhances the accuracy of WiFi-based breathing monitoring.

The effect of time-varying characteristics of shallow-sea waveguides on low-frequency acoustic signal transmission

The time-varying characteristic of shallow sea channel plays one of the most important role in the exploration of ocean. However, there is still lack of estimation model to describe the time-varying characteristics of shallow water low-frequency acoustic channels. This paper proposes a low-frequency channel model based on wave equation and ray theory to estimate the time-varying characteristics of shallow sea. Firstly, for the actual characteristics of shallow sea, suitable boundary conditions are designed to solve the wave equation. Secondly, the constraint conditions of shallow sea wave equation are optimized by combining ray theory. Then, based on the physical characteristics of shallow sea, time-delay variation and phase variation are solved by shallow wave equation. Combining bellhop propagation model with ocean disturbance model, the simulation is designed to verify the time-varying characteristic model of low-frequency shallow sea in this paper. Finally, with different propagation distance measurement experiment of sea, estimation value of time-delay variation and phase variation are confirmed, which is significant to shallow sea channel.

A catalog of binary stars from phase modulation in the first four years of TESS Mission photometry

Abstract We present a catalog of binary companions to δ Scuti stars, detected through phase modulations of their pulsations in TESS data. Pulsation timing has provided orbits for hundreds of pulsating stars in binaries from space-based photometry. We have applied this technique to δ Sct stars observed in the first four years of TESS Mission photometry. We searched the 2-min cadence light curves of 1161 short-period instability strip pulsators for variations in pulsation phase caused by the dynamical influence of an unseen companion. We discovered 53 new binaries and we present orbital parameters and mass functions for the 24 systems with solvable orbits. For the brightest star in our sample α Pictoris, we perform a joint fit of the pulsation timing and Hipparcos astrometry. We present the first orbit for the α Pictoris system, obtaining an orbital period of 1316±2 days and a mass for α Pic B of 1.05±0.05 M⊙. We revisit pulsation timing binaries from Kepler with Gaia kinematics, finding four systems that are members of the Galatic thick disk or halo. This suggests that they have been rejuvenated by mass transfer, and their companions are now white dwarfs. Further follow up of these systems may yield valuable constraints of the galactic blue straggler population.

Design of optimum spacecraft reorientation control with a combined criteria of quality based on the quaternions

Specifical original problem of attitude controlling for spacecraft was proposed in this paper. Problem of optimal rotation from a known initial state in a prescribed spatial orientation was studied in detail (turnaround time is not fixed). Design of optimal program of reorientation is based on new indicator of quality that combines energy costs including the contribution of controlling torques and integral of rotary energy (in a known proportion) and reorientation time; presence of duration factor bounds time of rotation finish. To construct an optimal control of angular momentum changing, quaternionic method and the maximum principle were applied. Differential equation that relates spacecraft angular momentum and quaternion of spacecraft orientation is a base to obtain analytic solution to a problem. We reveal the properties of optimum control program analytically, and study key features of optimum motion in details. Also, we write the formalized equations, mathematical formulas to design optimal law for change of spacecraft’s angular momentum. Analytic relations and equations are given for finding the optimal solution. Control law (in as explicit dependence between phase variables and con-trolling variables has been formulated. Main relations determining optimum values of parameters for rotation control algorithm were given. The closed-form law for rotation was obtained for dynamically symmetric solids. Numerical example as well as results of mathematical modeling of spacecraft motion that formed using optimum control are presented. This data as addition to the made theoretic descriptions shows reorientation process (in virtual form) and demonstrates practical feasibility of the developed control method. A designed algorithm for optimal control of rotation improves an efficiency of attitude system, and originates more economical performing of space vehicle during its flight along orbit.

Design of optimum spacecraft reorientation control with a combined criteria of quality based on the quaternions

Specifical original problem of attitude controlling for spacecraft was proposed in this paper. Problem of optimal rotation from a known initial state in a prescribed spatial orientation was studied in detail (turnaround time is not fixed). Design of optimal program of reorientation is based on new indicator of quality that combines energy costs including the contribution of controlling torques and integral of rotary energy (in a known proportion) and reorientation time; presence of duration factor bounds time of rotation finish. To construct an optimal control of angular momentum changing, quaternionic method and the maximum principle were applied. Differential equation that relates spacecraft angular momentum and quaternion of spacecraft orientation is a base to obtain analytic solution to a problem. We reveal the properties of optimum control program analytically, and study key features of optimum motion in details. Also, we write the formalized equations, mathematical formulas to design optimal law for change of spacecraft’s angular momentum. Analytic relations and equations are given for finding the optimal solution. Control law (in as explicit dependence between phase variables and con-trolling variables has been formulated. Main relations determining optimum values of parameters for rotation control algorithm were given. The closed-form law for rotation was obtained for dynamically symmetric solids. Numerical example as well as results of mathematical modeling of spacecraft motion that formed using optimum control are presented. This data as addition to the made theoretic descriptions shows reorientation process (in virtual form) and demonstrates practical feasibility of the developed control method. A designed algorithm for optimal control of rotation improves an efficiency of attitude system, and originates more economical performing of space vehicle during its flight along orbit.

Enhancing power quality in distributed generation systems using three-phase shunt active power filter

The current paper presents a new reference current generation algorithm for shunt active power filter (SAPF) combined with distributed generation systems using the instantaneous power theory (IPT) which is organized in two main blocks. The first is the synchronization technique; we propose a new quasi open loop technique that combines a Decoupled double self-tuning filter (DDSTF) and a single-phase frequency locked loop (FLL). The DDSTF is a new technique that extracts and separates the positive and negative sequence voltage under highly unbalanced and distorted conditions with no need to the symmetrical component and/or signals delay. The FLL achieve the grid frequency adaptation. Unlike the existing frequency estimators, this technique is motivated by its simplicity and the immunity to the voltage signal amplitude and phase variation or disturbance, which is a great advantage. The second is an ADALINE in power space to separate the fundamental harmonic from the distortion harmonics of the measured currents. The effectiveness of the proposed OLS technique in their application to the SAPF is validated by simulation.