Phase Variation Research Articles

Measurement of the electric field distribution in streamer discharges

Using electric field induced second harmonic generation (E-FISH), we performed direction-resolved absolute electric field measurements on single-channel streamer discharges in 70 mbar (7 kPa) air with 0.2 mm and 2 ns resolutions. In order to obtain the absolute (local) electric field, we developed a deconvolution method taking into account the phase variations of E-FISH. The acquired field distribution shows good agreement with the simulation results under the same conditions, in direction, magnitude, and shape. This is the first time that E-FISH is applied to streamers of this size (>0.5 cm radius), crossing a large gap. Achieving these high resolution electric field measurements benefits further understanding of streamer discharges and enables future use of E-FISH on cylindrically symmetric (transient) electric field distributions. Published by the American Physical Society 2025

Inter-segmental coordination variability during hopping and running on natural and synthetic turf surfaces.

An athlete's performance and musculoskeletal health hinges on their ability to adapt their movements to varying environmental constraints. However, research has yet to offer a thorough understanding of whether coordination variability is altered in response to different synthetic and natural turf surfaces. The purpose of this study was to investigate lower extremity coordination variability during hopping and running on four turf surfaces-three synthetic and one natural. Continuous relative phase (CRP) variability of six segment couplings was computed to examine coordination variability during the braking and propulsion sub-phases of running and hopping. Coordination variability in the sagittal plane pelvis-thigh coupling during the braking sub-phase of hopping was significantly affected by turf surface (χ2 (3) = 8.365, p = .039), with significantly less CRP variability observed on the firmest of the synthetic surfaces compared to the natural turf (55.3° ± 16.8° vs. 67.1° ± 17.2°, p = .032, W = .16). No other significant surface effects were observed. Our findings suggest that lower extremity inter-segmental coordination variability is largely unaffected by different turf surfaces during an acute exposure. However, the reduced variability observed between the pelvis and thigh during hopping may indicate decreased flexibility of the motor system and warrants further attention.

Cleaning WASP-33 b transits from the host star photometric variability: analysis of TESS data from two sectors

ABSTRACT Based on TESS observations of a $\delta$ Scuti variable WASP-33 obtained in 2019 and 2022, we thoroughly investigate the power spectrum of this target photometric flux and construct a statistically exhaustive model for its variability. This model contains 30 robustly justified harmonics detected in both the TESS sectors simultaneously, 13 less robust harmonics detected in a single TESS sector, a red noise, and a quasi-periodic noise term. This allowed us to greatly improve the accuracy of the exoplanet WASP-33 b transit timings, reducing the TTV residuals r.m.s. drastically, by a factor of 3.5, from 63 to 18 s. Finally, our analysis does not confirm existence of a detectable orbital phase variation claimed previously based on WASP-33 TESS photometry of 2019.

Phases Unlocked: The Crucial Role of Qubit Phases in Quantum Computing

Quantum computing applies quantum physics ideas to problems that traditional computers cannot address. The qubit, or quantum equivalent of the classical bit, is fundamental to this paradigm shift. Unlike its classical equivalent, a qubit can exist in a superposition of states, representing both 0 and 1. This superposition is defined not only by magnitudes, but also by important phase variables. These phases have a significant impact on qubit behavior and quantum computation outputs. This work conducts a thorough investigation of qubit phases, exploring their tremendous impact on the efficacy and capabilities of quantum algorithms. We investigate how constructive and destructive interference caused by phase interactions provides the foundation of quantum algorithms. Furthermore, we look into the intricate role of phases in establishing and managing entanglement, a unique quantum phenomenon that allows tremendous interactions between qubits. Our investigation includes the effects of numerous quantum operations on qubit phases. We present a thorough mathematical framework for describing how typical quantum gates, such as Hadamard, Pauli, and phase-shift gates, change the phase and thus the overall state of a qubit. We show these concepts through actual implementations of the Qiskit library. Finally, we discuss the intrinsic difficulty of managing and monitoring qubit phases, particularly the negative impacts of decoherence, which disrupts the delicate phase relationships. We describe tactics for mitigating these obstacles and investigate techniques for extracting phase information indirectly, such as quantum state tomography and interferometry. This comprehensive study seeks to provide a better understanding of the critical role phases play in quantum computing, paving the way for advances in algorithm design, quantum control, and the development of fault-tolerant quantum computers.

Uniform dipole resonance and suppressed quadrupole resonance for constant transmittivity full phase control plasmonic metasurfaces

Transmission-type plasmonic phase metasurfaces utilizing the Pancharatnam-Berry (PB) phase require constant transmittivity with complete phase variation from 0 to 2. Usually, this is achieved by rotating metallic nanoparticles in an otherwise uniform lattice arrangement. However, this rotation and the chosen lattice structure cause a significant change in the transmittivity, resulting in a lower intensity of light with certain phases and a higher intensity for other phases. Even though they are called full phase metasurfaces, their intensities can be near maximum or near minimum depending on the rotation and the lattice structure. We show that it is possible to achieve full phase constant transmittivity metasurfaces using the PB phase and the most elementary metallic anisotropic nanoparticles (elliptical) by inserting a thin metal sheet between the nanoparticles and the substrate. Without this metal sheet, while full phase control could be achieved by merely rotating the particles, the transmittivity varies by about 50% depending on the nanoparticles’ orientation. With the metal sheet, full phase control from 0-2 with a transmittivity variation of only 13%, even in a square lattice, is demonstrated with simulations and experiments. We show that this is due to the annihilation of quadrupole resonances along with broader uniform dipole resonance in the case of the nanoparticles with the metal sheet below. We also show that precise phase control is possible by generating varieties of orbital angular momentum beams and complex beams in the visible spectrum using nanofabricated metasurfaces.

Separation property and asymptotic behavior for a transmission problem of the bulk-surface coupled Cahn–Hilliard system with singular potentials and its Robin approximation

We consider a class of bulk-surface coupled Cahn–Hilliard systems in a smooth, bounded domain [Formula: see text] [Formula: see text], where the bulk phase variable is connected to the surface phase variable via a Dirichlet boundary condition or its Robin approximation. For a general class of singular potentials (including the physically relevant logarithmic potential), we establish the regularity propagation of global weak solutions to the initial boundary value problem. In particular, when the spatial dimension is two, we prove the instantaneous strict separation property, which ensures that every global weak solution remains uniformly away from the pure states [Formula: see text] after any given positive time. In the three-dimensional case, we obtain the eventual strict separation property that holds for sufficiently large time. This strict separation property allows us to prove that every global weak solution converges to a single equilibrium as time goes to infinity using the Łojasiewicz–Simon approach. Finally, we study the double obstacle limit for the problem with logarithmic potentials in the bulk and on the boundary, showing that as the absolute temperature [Formula: see text] tends to zero, the corresponding weak solutions converge (for a suitable subsequence) to a weak solution of the problem with a double obstacle potential.

Measurement of Atmospheric Coherence Length from a Shack–Hartmann Wavefront Sensor with Extended Sources

Free Space Optical Communication (FSOC) is a wireless communication method that utilizes laser beams for high speed and secure data transmission. Its performance is affected by various factors, among which atmospheric turbulence causes random fluctuations in the atmospheric refractive index, significantly impacting the reliability of communication links. The atmospheric coherence length is a key parameter describing the coherence properties of a laser signal as it propagates through the atmosphere, and accurately measuring it is crucial for assessing the quality of FSOC links. This paper proposes a novel strategy that utilizes extended sources directly as the information sources, combining the wavefront phase variance method with the extended source offset algorithm based on Shack–Hartmann wavefront sensors to directly measure atmospheric coherence length. Existing methods in extended scenarios typically rely on deploying laser beacons to aid in the calibration of atmospheric coherence length but setting up suitable beacons on horizontal communication links is challenging. Additionally, these approaches can be costly in terms of equipment and measurement expenses. Compared to traditional measurement methods, the algorithm proposed in this paper can measure directly based on extended scenarios in horizontal links, thereby effectively reducing system complexity and equipment costs. To verify the feasibility and effectiveness of this method, targeted simulations and experiments were conducted, and the results show that the coherence length measured by the algorithm is highly consistent with that measured by the Differential Image Motion Monitor (DIMM), with a deviation of less than 2% from actual values, effectively demonstrating the algorithm’s feasibility in coherence length assessment.

Effects of Radially Variable Sweep Vanes on Rotor–Stator Interaction Noise

Abstract This article presents a three-dimensional semianalytic cascade model for the prediction of rotor–stator interaction noise, which includes the effects of radially variable sweep angle and chord length to better account for the latest trends in the fan-stage stator design of turbofan aero-engines. The theoretical modeling and solution method are first introduced, with special attention paid to the singularity problem brought by the nonuniformity of the stator vanes in the radial direction. The tonal rotor–stator interaction noise for stators with a radially varying sweep angle or a radially varying chord length is then calculated and analyzed. It is discovered that the phase variation in unsteady pressure loading near the stator leading edge greatly affects the resulting tonal interaction noise, while the sweep of a stator trailing edge shows less influence on the rotor–stator interaction. The duct mode characteristic of the cut-on modes has proved to be an important factor in the design of a swept stator. In addition, the soft vane design can further reduce the tonal interaction noise on a swept stator cascade.

Experimental measurement of transverse spin dynamics in the nonparaxial focal region

Abstract The superposition of complex optical fields in three-dimension is the basis of several non-trivial wave phenomena. Significant among them are the non-uniform (inhomogeneous) polarization distribution and their topological character, leading to the emergence of transverse spin angular momenta spin-momentum locking, and their dynamics. These aspects are experimentally measured in the nonparaxial focal region of a circularly-polarized Gaussian input beam. A dielectric mirror, kept in the focal region, is axially scanned to obtain the phase and polarization variations in the retroreflected output beam using an interferometer and spatially-resolved Stokes parameter measurements. The identification of phase and polarization singularities in the beam cross-section and their behaviour as a function of the mirror position enabled us to map and study the phase-polarization variations in the nonparaxial focal region. The lemon-monstar type polarization patterns surrounding the C-point singularity in the output beam are identified and tracked to study the transverse spin dynamics and spin-momentum locking for the right- and left- circular polarization of the input beam. Direct measurement of the input beam polarization helicity-independent and helicity-dependent aspects of the transverse and longitudinal spin angular momenta in the nonparaxial focal region are the significant findings reported here. The proposed and demonstrated measurement method allows us to investigate the nonparaxial focal region in more detail and has the potential to unravel other intricate optical field effects.

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.

Selfing Shapes Fixation of a Mutant Allele Under Flux Equilibrium.

Sexual reproduction with alternative generations in a life cycle is an important feature in eukaryotic evolution. Partial selfing can regulate the efficacy of purging deleterious alleles in the gametophyte phase and the masking effect in heterozygotes in the sporophyte phase. Here, we develop a new theory to analyze how selfing shapes fixation of a mutant allele that is expressed in the gametophyte or the sporophyte phase only or in two phases. In an infinitely large population, we analyze a critical selfing rate beyond which the mutant allele tends to be fixed under equilibrium between irreversible mutation and selection effects. The critical selfing rate varies with genes expressed in alternative phases. In a finite population with partial self-fertilization, we apply Wright's method to calculate the fixation probability of the mutant allele under flux equilibrium among irreversible mutation, selection, and drift effects and compare it with the fixation probability derived from diffusion model under equilibrium between selection and drift effects. Selfing facilitates fixation of the deleterious allele expressed in the gametophyte phase only but impedes fixation of the deleterious allele expressed in the sporophyte phase only. Selfing facilitates or impedes fixation of the deleterious allele expressed in two phases, depending upon how phase variation in selection occurs in a life cycle. The overall results help to understand the adaptive strategy that sexual reproductive plant species evolve through the joint effects of partial selfing and alternative generations in a life cycle.

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.

Tracking the long-term timing accuracy of the X-Ray Telescope on board the Neil Gehrels Swift Observatory

Context. The Neil Gehrels Swift Observatory has been operational since November 2004. Its X-ray Telescope (XRT), operating in the 0.3–10.0 keV range, is designed to provide detailed position, timing, and spectroscopic information. Aims. The calibration procedure for assessing the absolute timing accuracy of XRT was described in a previous paper. Here we update the past analysis using the complete data set of the Crab pulsar observations up to October 2022 and using a new version of the data-processing software package that includes corrections to several issues that could have affected the previous results. Methods. We evaluate the accuracy of the Crab pulse period determination using the folding technique and the pulse-phase analysis and compare our results with the values derived from radio observations. We also check the absolute time reconstruction, measuring the phase position of the main peak in the Crab profile and comparing it with the value reported in the literature, which is based on Rossi X-Ray Timing Explorer (RXTE) observations. Results. We find that the accuracy in period determination for the Crab pulsar is of the order of a few picoseconds for the observations with the largest data time span. The absolute time reconstruction, measured using the position of the main pulse peak, shows that the main peak precedes the phase of the position reported in the literature for RXTE by ~263 µs on average. This corresponds to 0.982 in phase, with an observed dispersion of ±0.02 in phase values. We also find that observations very close in time (down to ~1 day separation) show a significant variation in absolute phase.

Rotation signal on the full disc of the solar chromosphere

ABSTRACT The rotation signal on the full disc of the solar chromosphere was studied by using the Ca ii K normalized intensity from 938 Carrington rotation (CR) synoptic maps (from CR827 to CR1764) obtained from the Mount Wilson Observatory during the period of 1915 August 10 to 1985 July 7. In this study, our main focus is on the distribution characteristics of the rotation signal on the full disc of the solar chromosphere and its variation with the solar cycle. We found that the chromospheric rotation signal is more pronounced in the latitudinal belt of sunspot activity and tends to extend to higher latitudes, and the trend is essentially the same for each solar cycle. The chromospheric rotation signal is also found to have phase differences in latitudes. The period of the chromospheric rotation signal varies regularly in latitudes, but its phase variation is irregular. In addition, we found that the intensity background is lowest in the latitudinal belt of sunspot drift where the chromospheric rotation signal is generated, but it increases with latitude and tends to extend to higher latitudes. We discussed the possible mechanisms of the above analysis results and thought that the chromospheric rotation signal is mainly caused by sunspots and plages.

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.

Digital Twin for a Frequency Mixer Used as a Phase Sensor.

The Portuguese Institute for Quality is responsible for the realization and dissemination of the frequency standard in Portugal. There are several techniques for frequency transfer, but we use a frequency mixer to detect phase variations between two light signals with different wavelengths, traveling along an optical fibre. In this paper, we present the development of a digital twin (DT) that replicates the use of a frequency mixer to improve the frequency transfer problem. A setup was built to train and validate the technique: a frequency mixer was used to determine the phase difference between the two signals, which are caused by temperature gradients in the fibre, together with real-time temperature data from sensors placed along the fibre and on the mixer itself. The DT was trained with two machine learning algorithms, in particular, ARIMA and LSTM networks. To estimate the accuracy of the frequency mixer working as a phasemeter, several sources of uncertainty were considered and included in the DT model, with the goal of obtaining a phase value measurement and its uncertainty in real time. The JCGM 100:2008 and JCGM 101:2008 approaches were used for the estimation of the uncertainty budget. With this work, we merge DT technology with a frequency mixer used for phase detection to provide its value and uncertainty in real time.