Circular Phase Research Articles

Circular phase shift migration based photoacoustic computational tomography

Abstract In the recent several decades, photoacoustic technique has proved to be capable of noninvasive biomedical imaging with scalable spatial resolution and high penetration depth. To achieve faithful image reconstruction, various method has been proposed, such as back projection, phase shift migration, model-based method, etc. These methods have simple implementations in homogeneous media, whereas in the cases of heterogeneous media (e.g., layered media), complicated modifications with respect to wave propagation at layer interface are always necessary. Here, we propose a frequency domain algorithm extension of phase shift migration in polar coordinates, which is obtained by making second order approximation to the optoacoustic point spread function in cylindrical coordinates and thereafter step by step wavenumber-frequency domain wave field extrapolation along the axial direction. Theoretical simulation and phantom experimental results demonstrate that the proposed circular phase shift migration method can well solve the layered heterogeneous reconstructive problem without modifying the wave propagation model. The acoustic diffraction limited acoustic resolution (up to 225 μm) and high imaging SNR (at least 16 dB) are obtained.

Mathematical and Physical Characteristics of the Phase Spectrum of Earthquake Ground Motions

This study presents a rigorous investigation into the mathematical and physical properties inherent in the Fourier phase spectrum of earthquake ground motions. This exploration includes a detailed examination of the probability distribution of phase angles and differences, elucidated through two novel numerical experiments utilizing the reduction ad absurdum approach. Moreover, the study scrutinizes the physical attributes of earthquake ground motion’s phase spectrum, employing the circular frequency-dependent phase derivative as a key analytical factor. In a novel approach, the research delves into the relationship between circular frequency-dependent phase derivatives and Fourier amplitudes, shedding light on essential connections within earthquake phenomena, particularly addressing non-stationarity. Expanding the scope, the study comprehensively examines the influence of source, propagation path, and site on both the phase spectrum and accelerogram. Employing the control variate technique facilitates this analysis, providing valuable insights into the underlying physical mechanisms governing earthquake wave behavior. The findings highlight the temporal properties of the phase spectrum, attributing its complexity to the temporal heterogeneity in energy release during the fault rupture and dispersion of earthquake waves. This novel approach not only enhances the understanding of earthquake dynamics, but also underscores the significance of considering temporal variations in earthquake events.

Generation of auto-focusing vortex beam via segment vortex phase for imaging edge-enhancement

The auto-focusing beam based on the circular Airy beam and segmented vortex phase, termed circular Airy segmented vortex beam (CASVB), was generated. During propagation, the focusing properties of the CASVB can be flexibly tunable for multiple degrees of freedom. The results show that the segmentation type of the vortex phase are determined by the number and position of phase jumps, which results in the beam split. Moreover, the number and position of the CASVB gaps coincide with the number and position of the phase jumps. In addition, the edge images can be enhanced by combining the phase of the beam with the phase of the lens. Due to its adjustable number and position of gaps, the CASVB will likely give rise to potential applications in manipulating particles along different segmented intensity trajectories.

Adjustable damping properties of the AlCrFe2Nix medium entropy alloys by tuning phase constituent

The effects of Ni content on the phase constituent, mechanical properties and damping capacity of the AlCrFe2Nix (x = 1.0, 1.5, 1.7, 2.1, 2.2 and 2.3) medium entropy alloys (MEAs) were studied. When x = 2.1, the microstructure of the MEA consists of BCC phase as the matrix and FCC phase as the second phase with the corresponding volume fractions of 87.7, 12.3 vol%, respectively. The combination of hard BCC matrix and soft FCC secondary phase, especially, the BCC phase is isolated by the circular FCC phase, results in a very high damping capacity up to 0.06936 for the AlCrFe2Ni2.1 MEA at the corresponding strain amplitude of 2.55 × 10−4. Both the BCC matrix and the peculiar microstructure play a key role in increasing the damping capacity of the AlCrFe2Ni2.1 MEA. Excellent damping performance and comprehensive tensile properties of AlCrFe2Ni2.1 MEA indicate that it has potential applications as the candidate of damping materials.

Characterization of XUV+IR ionization using the circular dichroic phase

A strong helicity dependence of reconstruction of attosecond bursts by beating of two-photon transitions (RABBITT) with circularly polarized XUV and IR pulses was reported by Han [ and ]. They attributed a circular dichroic phase in RABBITT to the helical structure of the photoelectron wave packets in the final state. We exploit this effect to determine the magnitude and phase of two-photon XUV+IR ionization amplitudes. In s-electron targets (H, He, Li), such a determination is fully and requires no further approximations. In heavier noble gases like Ar, characterization of two-photon ionization amplitudes can be made from the circular dichroic phase with minimal and very realistic assumptions. Published by the American Physical Society 2024

Topological circular dichroism for asymmetric converging light beams

Light beams possess three types of angular momentum. They are the spin angular momentum, the extrinsic orbital angular momentum, and the intrinsic orbital angular momentum. Interaction of these momenta due to translational or cylindrical symmetry breaking leads to effects of the spin-orbit interaction of light, including topological effects. Topological optical activity or topological circular phase anisotropy, known as Rytov-Vladimirsky-Berry-Chao-Tomita plane polarization rotation, is the result of the extrinsic orbital angular momentum influence on the spin angular momentum. The effect manifests under linear polarized light propagation along a curved trajectory when the translational symmetry is breaking. We predict a new topological effect under the cylindrical symmetry breaking. This effect is the result of the extrinsic orbital angular momentum influence on the spin angular momentum in the converging asymmetrical light beam. It manifests as the transformation of linear polarized light into elliptically polarized one when an asymmetrical in the vertical direction beam passes through the left or right half of the focal plane. We have estimated the value of the ellipticity and proposed an experimental setup. We successfully observed the ellipticity change of 10(−3) using our method of small ellipticity determination. We have considered this transformation as the topological circular dichroism (topological circular amplitude anisotropy). We have demonstrated the connection of the ellipticity change with the value of the topological circular amplitude anisotropy R. The measured value of the topological circular amplitude anisotropy R turned out to be R=±(0.60±0.08)×10−3. This new effect of the spin-orbit interaction of light contributes to our understanding of the nature of light. It can be used to develop new sensors in optics, including nano and quantum optics.

The Circular Rebound Tool: A tool to move companies towards more sustainable circular business models

Companies design circular business models through experimentation. However, most companies do not consider the environmental impact of their new business model ideas during experimentation, an iterative phase of high uncertainty. Previous research shows that companies typically use ‘rules of thumb’ to estimate environmental impact in this stage due to limited time and reliable information to guide decision-making. This might prevent innovators from detecting unintended rebound effects that offset positive environmental gains of new business models. To mitigate this and let innovators think more profoundly about rebound effects during the circular business model experimentation phase, we propose an evidence-based business model ideation tool, the Circular Rebound Tool, designed around lifecycle thinking, the zero-waste hierarchy, and increased rebound effects awareness. The tool's development follows the design science research method, undergoing continuous improvement through 15 workshops. Our tool can help business innovators gain insights into the environmental impact of their early-stage business ideas.

A metasurface featuring multiple polarization conversions

This paper proposes a novel bow-tie metasurface that integrates various types of polarization conversions by optimizing traditional unit structures. The metasurface achieves wide-angle linear polarization conversion over the X-band (8–12 GHz) and has a linear polarization conversion efficiency of over 94% under normal incidence. In the Ku-band (12.4–15.6 GHz), the ellipticity value (e-value) and axial ratio calculations show that the linearly polarized waves incident along the Y axis will be effectively converted to left-handed circularly polarized waves. Additionally, in the X-band (8.9–10.5 GHz), the circular polarization and its co-polarization conversion efficiency can be maintained at 99.5%, allowing for an effective circular polarization phase shift using the Pancharatnam–Berry principle in this frequency range.

Wavelength-tunable infrared chiral metasurfaces with phase-change materials.

Optical phase-change materials exhibit tunable permittivity and switching properties during phase transition, which offers the possibility of dynamic control of optical devices. Here, a wavelength-tunable infrared chiral metasurface integrated with phase-change material GST-225 is demonstrated with the designed unit cell of parallelogram-shaped resonator. By varying the baking time at a temperature above the phase transition temperature of GST-225, the resonance wavelength of the chiral metasurface is tuned in the wavelength range of 2.33 µm to 2.58 µm, while the circular dichroism in absorption is maintained around 0.44. The chiroptical response of the designed metasurface is revealed by analyzing the electromagnetic field and displacement current distributions under left- and right-handed circularly polarized (LCP and RCP) light illumination. Moreover, the photothermal effect is simulated to investigate the large temperature difference in the chiral metasurface under LCP and RCP illumination, which allows for the possibility of circular polarization-controlled phase transition. The presented chiral metasurfaces with phase-change materials offer the potential to facilitate promising applications in the infrared regime, such as chiral thermal switching, infrared imaging, and tunable chiral photonics.

Structural and electronic properties of collapsed armchair single-walled [formula omitted]-graphyne nanotubes

The properties of radially collapsed armchair single-walled α-graphyne nanotubes (α-SWGNTs) are investigated using density functional theory with van der Waals (vdW) corrections. Here, our main goal is to study the structural properties of stable collapsed SWGNT forms and how the corresponding electronic structure are modified in comparison to the circular counterparts. The presence of carbon atoms with sp and sp2 hybridization makes the SWGNTs to present an intriguing geometry for their cross section in the collapsed form and, as a result, the electronic structure of these system is sensitivity to the stacking mode between layers. We find a threshold diameter (26 Å) for which the collapsed structure is more stable than the circular phase, indicating that the natural form of large SWGNTs is radially collapsed. Furthermore, we identified that the collapsed structure is semiconductor when the diameter of the circular phase is greater than 19 Å, with band gap values adjusted by the type of stacking between layers. We believe these results can open up possibilities of using such structures in the setups of nanoelectronic device, and provide a basis for future experimental and theoretical research about collapsed graphyne nanotubes.

Characteristics of a Gaussian focus embedded within spiral patterns in common-path interferometry with phase apertures

A phase-only method is proposed to transform an optical vortex field into desired spiral diffraction–interference patterns. Double-ring phase apertures are designed to produce a concentric high-order vortex beam and a zeroth-order vortex beam, and the diffracted intensity ratio of two beams is adjustable between 0 and 1. The coherent superposition of the two diffracted beams generates a brighter Airy spot (or Poisson spot) in the middle of the spiral pattern, where the singularity for typical vortex beam is located. Experiments employing circular, triangular, and rectangular phase apertures with topological charges from 3 to 16 demonstrate a stable, compact, and flexible apparatus for vortex beam conversion. By adjusting the parameters of the phase aperture, the proposed method can realize the optical Gaussian tweezer function and the optical vortex tweezer function simultaneously along the same axis or switch the experimental setup between the two functions. It also has potential applications in light communication through turbulent air by transmitting an orbital angular momentum-coded signal with a concentric beacon laser.

Circular economy supply network transition phases management dynamics

AbstractThis paper discusses transitions towards circular economy, developing a circular economy supply network transition phases management dynamics framework. We studied seven circular supply networks in Brazil through process analysis and system dynamics modeling. Primary data were collected through 35 manager's interviews and companies' plant and their suppliers' visits. We suggest that transition phases management are pre‐development, learning, expansion, leadership, stabilization and self‐renew with cooperative and competitive challenges, characterized by specific circular factors over time. The simulation and transition phases models provide strategic tools to make decision on which circular factor, project team should focus applying multi‐tier supply chain management and hybrid leadership to stimulate internal and integrate external stakeholders to adopt circularity, unveiling challenges and average time to achieve each phase. We also enrich circular economy supply network management theoretical background defining it in three dimensions: behavioral as supply ecosystem, structural as supply network and contextual as complex adaptive system.

Coprecipitation Synthesis of Large-Pore-Volume γ-Alumina Nanofibers by Two Serial Membrane Dispersion Microreactors with a Circulating Continuous Phase

A coprecipitation method was developed for the synthesis of fibrous γ-alumina using serial membrane dispersion microreactors with a circulating continuous phase and high concentrations of NaAlO2 and Al2(SO4)3 as reactants. Owing to the ultra-high mixing intensity and reduction of supersaturation due to the large circular phase ratio, a large pore volume and specific surface area and an extremely narrow pore diameter distribution were realized using the high-concentration and high-viscosity precipitation system. The influence of the phase ratio, dispersion order of reactants, Al2(SO4)3 residence time, and the precipitation reaction pH and time were investigated, and the nanofiber formation mechanism was explored employing theoretical calculations. By controlling the Al2(SO4)3 residence time of 3 s, phase ratio of 16, and pH of 8.0, γ-Al2O3 nanofibers with a pore volume of 1.36 cm3/g, a specific surface area of 376 m2/g, and a length/diameter ratio in the range of 30–54 were obtained without any organic reagents. This study provides an economical and readily scalable method for the synthesis of fibrous γ-Al2O3 with excellent pore properties and a large specific surface area, which can potentially be applied as an excellent catalyst support for diesel and bio-oil hydrogenation.

From Surviving to Living (on): A Grounded Theory Study on Coping in People with Pancreatic Cancer.

Little research has been conducted on the experience of pancreatic cancer from a patient's perspective. Several factors suggest that trajectory models of chronic illness or other cancers cannot be applied to pancreatic cancer. Within this grounded theory study, 26 problem-centred interviews were conducted with people with pancreatic cancer from Germany. A cancer-specific trajectory model was developed, depicting both curative and palliative courses. Two successive phases form the core: Immediately after diagnosis, there is an acute phase in which patients focus on mere survival, attempt to overcome the short-term consequences of pancreatic cancer and search for information. This initial phase is followed by a circular phase of living on with pancreatic cancer, characterized by adaptation to the long-term consequences of the disease and a repeated experience of fear of recurrence or progression and threat in the context of follow-up examinations. Understanding disease trajectories from a patient's perspective enables health professionals better to understand patients' needs, concerns, and fears and better support them in coping. Trial registration: German Clinical Trials Register, DRKS00020251, 13.01.2020.

Fourier-Domain Phase Retardation Vortex Measurement

Optical vortices have found a wide range of applications thanks to their helical phase topology allowing to carry the orbital angular momentum. In this work, self-interfering vortex beams are utilized in a new single-shot holographic method for the circular phase retardation measurement. The vortices carrying information about the phase retardation introduced between two orthogonal circular polarization modes are generated by the spin to orbital angular momentum conversion. The phase retardation is stored in off-axis holographic records acquired in a common-path setup using a geometric-phase grating. In the proposed method, the circular phase retardation is reconstructed in the Fourier domain, surpassing the measurement precision provided by methods restoring the retardation from the rotation of a Double-Helix Point Spread Function (DH PSF). The developed method can be adapted for application to polarimetry, orientation imaging and diagnostics of nano-emitters.

Probabilistic inversion of circular phase spectra: application to two-station phase-velocity dispersion estimation in western Canada

SUMMARY Periodic directional and temporal measurements are common in seismology, and necessitate specific statistical analyses that are appropriate for circular quantities. In this work, we explore the use of a von Mises distribution as a representation of errors on circular seismological observations. Specifically, we automate the estimation of surface-wave phase-velocity dispersion for the teleseismic two-station method, which generally suffers from a 2π phase ambiguity. The use of Bayesian inverse techniques, which aim to rigorously quantify model parameter uncertainty, have become widespread throughout seismology over the last decade. Here, we apply Bayesian inversion to measurements of surface-wave phase spectra in order to estimate 1-D, path-averaged Earth structure between station pairs. The dispersion curve and associated uncertainties are additional results of the inversion, which can then be used as input for subsequent analyses (e.g. tomography). We demonstrate this technique through application to surface-wave recordings from long-running seismic stations throughout western Canada. Our results for over 10 000 station pairs reveal first-order tectonic features consistent with previous studies, which provides confidence in our approach as well as an initial step towards resolving a full 3-D seismic velocity model for the region. This work also presents a foundation for the inversion of surface-wave phase spectra to estimate 3-D Earth structure directly. Finally, the ideas presented in this work are not limited to the inversion of surface-wave phase spectra, but can also be considered for Bayesian geophysical inversion of any circular quantities.

Hybrid nanofluid convection and phase change process in an expanded channel under the combined effects of double rotating cylinders and magnetic field

Convective heat transfer and phase changing process are analyzed for flow over facing step in a channel equipped with double rotating circular cylinders and phase change- packed bed (PCM-PB) under magnetic field. The favorable and opposing effects of using magnetic field with rotations on phase change and thermal performance for separated flow in PCM-PB installed system are numerically explored by using the finite element method. Base fluid with hybrid particle loading of 2% solid volume fraction is used. The analysis is performed for various values of rotational Reynolds number (Rew: −1000 and 1000), cylinder sizes (R:0.01 and 0.3), size ratio (SR:0.5 and 2) and Hartmann number (Ha: 0 and 20). When rotations are active, phase change becomes inefficient due to the establishment of the vortices near the PCM-PB zone. Complete phase transition time (tC) depends upon the rotational direction of the cylinders and fluid type. As compared to case at Rew = 0, tC rises up to 175% at Rew = 1000 by using pure fluid while using nanofluid reduces the tC value. The size and size ratio of the cylinders are highly influential on the vortex size behind the step which affects the phase transition dynamics. There are 185% and 172% variations in the tC values are observed when size and size rations are varied. The case with the PCM + nanofluid gives the highest Nusselt number (Nu) while lowest Nu is obtained when pure fluid without PCM is used. The average Nu rises with larger cylinders for counter clockwise rotations at the highest speed. Magnetic field suppresses the vortices and contributes positively to the phase change process and thermal performance while reduction of tC is up to 74% is obtained at Rew=-1000 by using magnetic field at the highest strength. Proper orthogonal decomposition (POD) is used for fluid and solid temperature reconstruction in the whole computational domain. The model captures the dynamic behavior of phase change and heat transfer under combined effects of double rotations and magnetic field with PCM-PB embedded channel with area expansion.

Autofocusing and Self-Healing Optical Vortices Realized via Circular Cubic Phase Modulation

Optical vortices have drawn extensive research interests due to their widespread applications in various fields. Therefore, it is of great significance to modulate optical vortices to endow them with more properties. Herein, the autofocusing and self-healing properties are introduced to optical vortices via implementing circular cubic phase modulation. The propagation dynamics of the modulated optical vortex is analyzed, and the experimental results match well with the simulations. Moreover, the autodefocusing optical vortices can also be generated, and the flexible switching between the autofocusing state and autodefocusing state can be easily realized by adjusting the helicity of the incident circular polarization. Besides, the topological charges of the two states are also experimentally verified. Our study provides a novel way to modulate optical vortices, which may enrich their applications in optics and photonics.

Enhanced Dual Filter for Floating Wind Lidar Motion Correction: The Impact of Wind and Initial Scan Phase Models

An enhanced filter for floating Doppler wind lidar motion correction is presented. The filter relies on an unscented Kalman filter prototype for floating-lidar motion correction without access to the internal line-of-sight measurements of the lidar. In the present work, we implement a new architecture based on two cooperative estimation filters and study the impact of different wind and initial scan phase models on the filter performance in the coastal environment of Barcelona. Two model combinations are considered: (i) a basic random walk model for both the wind turbulence and the initial scan phase and (ii) an auto-regressive model for wind turbulence along with a uniform circular motion model for the scan phase. The filter motion-correction performance using each of the above models was evaluated with reference to a fixed lidar in different wind and motion scenarios (low- and high-frequency turbulence cases) recorded during a 25-day campaign at “Pont del Petroli”, Barcelona, by clustered statistical analysis. The auto-regressive wind model and the uniform circular motion phase model permitted the filter to overcome divergence in all wind and motion scenarios. The statistical indicators comparing both instruments showed overall improvement. The mean deviation increased from 1.62% (without motion correction) to −0.07% (with motion correction), while the root-mean-square error decreased from 1.87% to 0.58%, and the determination coefficient (R2) improved from 0.90 to 0.96.

Single-Pixel Compressive Digital Holographic Encryption System Based on Circular Harmonic Key and Parallel Phase Shifting Digital Holography

An encryption system that combines compressive sensing (CS) and two-step parallel phase shifting digital holography (PPSDH) using double random phase encoding (DRPE) is presented in this paper. The two-step PPSDH is a linear inline holographic scheme and is much suitable for encrypting the 2D/3D information in a single exposure. The distribution of random phase mask (RPM) in the DRPE is implemented using circular harmonic key which increases the security of the encryption process. In this system, the keys used to encrypt are spatial positions of the planes, wavelength, and rotation of the circular harmonics in RPMs, and CS acts as an additional key that makes the system more secure than the conventional optical encryption methods. At the transmission end, two-step PPSDH is applied to encrypt the object information in single hologram. The digital mirror device (DMD) is placed between the object and a single-pixel detector for acquiring fewer hologram measurements. At the receiver end, the single digital hologram is numerically recovered by using a CS optimization problem. The original complex object field is decrypted from the CS recovered holograms by the inversion of two-step PPSDH process with the help of the correct keys. The numerical simulations are presented for complex 2D and 3D objects to test the feasibility of the proposed encryption and decryption system. The proposed method carried out intensity and phase reconstruction of the original object field using single-pixel compressive imaging. The computer simulation results demonstrated that the encrypted information is highly secured with the rotation of the circular harmonic key. The sensitivity of the decrypted intensity and phase images is also studied with variations of the encrypted keys. The obtained results show that the proposed encryption scheme is feasible and has better security performance and robustness.