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Topological properties of bound states in the continuum in geometries with broken anisotropy symmetry
摘要： Waveguiding structures made of anisotropic media support bound states in the continuum (BICs) that arise when the radiation channel of otherwise semileaky modes is suppressed. Hitherto, only structures with optical axes aligned in symmetric orientations inside the waveguide plane, where BICs appear as lines in the momentum-frequency dispersion diagram, have been considered. Here we address settings where such symmetry is broken and unveil a number of fundamental different features. Weak and strong symmetry-breaking regimes are identified, corresponding to azimuthal and polar optical axes orientation asymmetries, respectively. The azimuthal symmetry breaking is found to still preserve the existence loci of BICs in the momentum-frequency dispersion diagram as lines. However, all possible BICs become interferometric, while the polarization separable states that occur in symmetric settings cease to exist. The polar symmetry breaking has stronger effects and transforms the BICs’ existence loci from lines to points, which correspond to full-vector states that exist at discrete values of the optical axis orientation for a given wavelength. Such transformation results in fundamental changes in the topological properties of the radiated field around the BICs.
关键词： anisotropic media,bound states in the continuum,topological properties,symmetry breaking,waveguiding structures
更新于2025-09-04 15:30:14
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PT symmetry protected non-Hermitian topological systems
摘要： We study PT symmetry protected topological phase in non-Hermitian 1D and 2D systems. We show that topological phase exist in non-Hermitian PT symmetric systems for both gapped and gapless systems and discuss appearance of exceptional points. We apply our formalism to a complex extension of the SSH model, topological semimetals and nodal superconductors.
关键词： SSH model,nodal superconductors,non-Hermitian systems,topological semimetals,PT symmetry,topological phase
更新于2025-09-04 15:30:14
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Threshold effect on particle tracking algorithms
摘要： Automated particle tracking algorithms are widely used by soft matter physicists as a research tool to detect and construct the trajectories of micron-sized particles in ?uids. Analyzing these trajectories will uncover the physics of the investigated particles mainly on the type of motion they undergo making them suitable for potential applications. A plethora of methods has been proposed and used for detection and tracking. In this work, we examine the performance of two commonly used tracking algorithms in terms of threshold dependencies in digital video images. One of them is the centroid method (CM), a well-known and used algorithm and the other is radial symmetry method (RSM) which is recently proposed. Here, we generate the synthetic digital video images consisting of randomly placed multiple particles and compare the absolute errors on the particle detection by varying threshold values. Our results suggest that both algorithms show dependence on the threshold value and on comparison RSM algorithm performs better than the CM algorithm when the noise level is zero. Moreover, the measured absolute errors show a strong dependence on threshold values when noise levels are increased (up to 20) especially for the RSM algorithm.
关键词： centroid method,radial symmetry method,particle tracking algorithms,threshold dependencies,digital video images
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Dispersion Analysis of Polar Glide Symmetry with Coaxial Rings
摘要： In this article, the dispersion properties of a coaxial transmission line with polar glide-symmetric rings are analyzed. This symmetry is obtained by introducing periodic polar rings on either the inner or outer conductor of a coaxial guide. By modifying the relative radii of both rings, we demonstrate that a zero bandgap with non-zero group velocity at the Brillouin zone boundary can be achieved. Such quasi-linear dispersion is analyzed by applying both a circuit-based method and full-wave simulations. A good agreement is achieved between the methods.
关键词： glide symmetry,coaxial guide,dispersion analysis,equivalent circuit
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Engineering Modes of PT Symmetric Photonic Crystals
摘要： This work explores the effects of parity-time (PT) symmetry on the modes of photonic crystal defect waveguides. Two designs are considered. In the ?rst, the defect modes are protected from PT transitions, but edge modes in the complex conjugate frequency regime appear. In the second design, the defect modes exhibit thresholdless PT transitions.
关键词： photonic crystals,optical waveguides,parity-time symmetry,photonic integrated circuits,semiconductor waveguides
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Time-modulated Periodic Systems with PT Symmetry
摘要： This work explores the effects of parity-time (PT) symmetry in time-modulated periodic systems. Mechanisms for dynamic tunability of exceptional points are presented. We show that synthetic linear momentum imparted by time-modulation leads to uni-directional exceptional points. Such structures could see application in uni-directional lasers with tunable directionality.
关键词： semiconductor lasers,photonic crystals,distributed feedback lasers,time-varying circuits,parity-time symmetry,time-varying systems,optical modulation
更新于2025-09-04 15:30:14
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Machine Learning for Organic Cage Property Prediction
摘要： We use machine learning to predict shape persistence and cavity size in porous organic cages. The majority of hypothetical organic cages suffer from a lack of shape persistence and as a result lack intrinsic porosity, rendering them unsuitable for many applications. We have created the largest computational database of these molecules to date, numbering 63,472 cages, formed through a range of reaction chemistries and in multiple topologies. We study our database and identify features which lead to the formation of shape persistent cages. We find that the imine condensation of trialdehydes and diamines in a [4+6] reaction is the most likely to result in shape persistent cages, whereas thiol reactions are most likely to give collapsed cages. Using this database, we develop machine learning models capable of predicting shape persistence with an accuracy of up to 93%, reducing the time taken to predict this property to milliseconds, and removing the need for specialist software. In addition, we develop machine learning models for two other key properties of these molecules, cavity size and symmetry. We provide open-source implementations of our models, together with the accompanying data sets, and an online tool giving users access to our models to easily obtain predictions for a hypothetical cage prior to a synthesis attempt.
关键词： shape persistence,machine learning,symmetry,cavity size,organic cages
更新于2025-09-04 15:30:14
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Análise da expans?o térmica volumétrica e das características estruturais de solu??es sólidas de (Pb, Ca)TiO3 entre 150 e 570 K
摘要： Ceramic samples of lead modified calcium titanate (Pb1-xCaxTiO3) with calcium concentration between 0.24≤x≤0.55 were prepared and analyzed in order to determine the structural origin of the negative thermal expansion observed in this ferroelectric system. The Rietveld structural refinement method was used to assess the thermal evolution of the structural parameters using powder X-ray diffraction data collected between 150 and 570 K. Since the Pb1-xCaxTiO3 phase diagram and space groups are still unknown for the temperature range investigated, the structural analyses were based on adjustments of the refinement protocol. The results revealed the existence of a correlation between symmetry transitions and anomalies in the thermal expansion of the unit cell, being such transitions not necessarily of the ferroelectric-paraelectric nature.
关键词： Rietveld refinement method,symmetry transitions,structural analyses,unit cell thermal expansion,ferroelectric ceramics
更新于2025-09-04 15:30:14
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[IEEE 2018 Iranian Conference on Electrical Engineering (ICEE) - Mashhad (2018.5.8-2018.5.10)] Electrical Engineering (ICEE), Iranian Conference on - Tunable Filter by Using Parity Time (PT) Symmetric Periodic Array Electronic
摘要： A circuit model of a periodic array of PT-symmetric (gain/loss coupled) waveguides is reported for the design of a novel tunable filter. This model consists of a pair of coupled circuits, one with amplification resistance and the other with an equivalent attenuation. By varying the value of the gain/loss, one can control the size of bandgap and hence the allowed frequencies propagating within the structure. For a critical value of gain/loss, the eigenvalues merge and the gap disappears. As a result, all frequencies can pass the structure i.e, an all pass filter. The Q-factor of reflected frequency can be varied such that, tunable Q from 20 to greatest has been successfully realized in the central frequency of 0.283 MHz. The remarkable feature of this design lies with its tunability, high speed, and relative simplicity.
关键词： RLC Circuit Model,Parity-Time (PT) Symmetry,Grating Waveguides,Optical Waveguides,Band Stop Filter (BSF)
更新于2025-09-04 15:30:14
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Study of Optical Soliton Perturbation with Quadratic-Cubic Nonlinearity by Lie Symmetry and Group Invariance
摘要： Here, optical soliton perturbation with quadratic-cubic nonlinearity has been discussed by applying Lie symmetry and group invariants. The perturbation terms include third and fourth order dispersions in addition to self-steepening, intermodal dispersion and higher order dispersion effects. Using presented algorithms, Bright and dark soliton solutions are revealed.
关键词： group invariants,higher order dispersion effects,third and fourth order dispersions,optical soliton perturbation,Lie symmetry,quadratic-cubic nonlinearity,Bright and dark soliton solutions,self-steepening,intermodal dispersion
更新于2025-09-04 15:30:14