arXiv subjects

Chunyu Zhang

Publications and source records attributed to Chunyu Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Axion Generation in a Three-Dimensional Optical Trap

The axion is a theoretical particle that could resolve multiple fundamental problems, most notably the strong Charge-conjugation-parity-symmetry (CP) problem in quantum chromodynamics and the nature of dark matter.To date, however, the axion has never been detected in any free-space experiment. In this work, we designed and constructed a laser-based system that generates a three-dimensional, closed trapping potential field with a null central region. Owing to its spindle-like geometry, we term this configuration an optical spindle trap (OST). Along the propagation axis, the photon population evolves in a distinct manner from the left to the right terminus of the trap: it first diminishes and then recovers to its baseline value.This behavior is analogous to the photon axion photon conversion process sought in light shining through wall experiments(LSW)1-3, in which a measured photon deficit would constitute evidence for axion conversion. The photon population was monitored with a single-photon counter (SPC) operated well below its saturation threshold, and the observed behavior was corroborated by charge-coupled device (CCD) imaging at extremely low optical powers, thereby excluding detector artefacts as the origin of the photon deficit.Under the constraint of energy conservation, the missing photons are attributed to conversion into axions that remain undetectable by both the SPC and the CCD. The underlying conversion mechanism is ascribed to spin-coupled axion photon interactions. This tens-of-millimeter-scale optical spindle trap thus provides a viable free-space axion source, generated by a table-top laser, for the study of the strong CP problem and axion-like dark matter candidates.

physics.optics↗

arXiv2026

Microparticles manipulation with a three-dimensional closed optical trap

Gaussian optical tweezers have strong phototoxicity to bioactive substances and it is difficult to achieve capture and manipulation of multiple particles. Moreover, vortex optical tweezers face several challenges, such as weak axial confinement and dependence on complex optical elements like a spatial light modulator (SLM). Therefore, we design and construct a novel three-dimensional (3D) "optical spindle trap" (OST) system that does not require a SLM. By employing intracavity mode modulation and a simple extra-cavity lens modulation, we generate a fully enclosed 3D dark potential well with zero central intensity. Experimental results demonstrate that the system achieves stable trapping of single or multiple micrometer-sized particles with excellent 3D confinement and enables the trapping of mouse hepatocytes under low-power conditions. The system exhibits high physical stability. Its closed dark-field structure can also reduce phototoxic damage to biological samples. Furthermore, the dimensions of the optical trap can be flexibly tuned to suit various application scenarios. This study provides a novel, highly efficient, gentle, and low-cost optical trap platform for biomedicine and micro/nanoscale manipulation.

physics.optics↗

arXiv2025

Analytical sensitivity curves of the second-generation time-delay interferometry

Forthcoming space-based gravitational-wave (GW) detectors will employ second-generation time-delay interferometry (TDI) to suppress laser frequency noise and achieve the sensitivity required for GW detection. We introduce an inverse light-path operator $\mathcal{P}_{i_{1}i_{2}i_{3}\ldots i_{n-1}i_{n}}$, which enables simple representation of second-generation TDI combinations and a concise description of light propagation. Under the instantaneous equal-arm, equilateral triangular-constellation approximation, analytical expressions and high-accuracy approximate formulas are derived for the sky- and polarization-averaged response functions, noise power spectral densities (PSDs), and sensitivity curves of TDI Michelson, Sagnac-type ($\alpha,\beta,\gamma$), Monitor, Beacon, Relay, and fully symmetric Sagnac ($\zeta$) combinations, as well as their orthogonal $A, E, T$ channels. The validity of the analytical results is confirmed via Monte Carlo integration with $10^{4}$ randomly sampled sky locations and polarization angles. Our results show that: (i) second-generation TDIs have the same sensitivities as their first-generation counterparts; (ii) the $A, E, T$ sensitivities and the optimal sensitivity are independent of the TDI generation and specific combination; (iii) the $A$ and $E$ channels have equal averaged responses, noise PSDs, and sensitivities, while the $T$ channel has much weaker response and sensitivity at low frequencies; (iv) except for the $(\alpha,\beta,\gamma)$ and $\zeta$ combinations and the $T$ channel, all sensitivity curves exhibit a flat section; (v) the averaged response, noise PSD, and sensitivity of $\zeta$ scale with those of the $T$ channel. These analytical and approximate formulations provide useful equal-arm benchmarks for instrument optimization and data-analysis preparatory studies for future space-based GW detectors.

gr-qc↗

arXiv2025

Constraint on gravitational-wave polarizations for space-based detectors with time-delay interferometry

Probing extra polarizations in gravitational waves (GWs) with space-based detectors is the most direct method for testing theories of gravity. In this paper, by employing the second-generation time-delay interferometry (TDI) to cancel out the laser frequency noise in a rotating and flexing configuration with arm lengths varying linearly in time, we study the detectors' constraint ability on extra polarizations, and explore the impacts of TDI on the constraint of polarizations. Working in the parametrized post-Einstein (ppE) waveform framework, we find that the constraints on extra polarizations are significantly weaker than those for the tensor mode. For the tensor mode, the constraint ability for the detectors scales with signal-to-noise ratio (SNR). At low frequency, due to signal cancellation effects, the SNR registered is lower for the detectors with TDI method than that with the simplified equal-arm Michelson interferometer method. Therefore, tensor-mode constraints are degraded when TDI is applied. Although the direct detection of extra polarizations remains challenging, the constraint ability of the space-based detectors on the vector mode is better than the scalar modes. Besides, the detectability on extra polarizations will be enhanced with TDI, and the improvement of the constraint on the vector mode is less than scalar modes due to the inclination-dependent waveforms.

gr-qc↗

arXiv2024

Rotating galactic black holes

The galactic black hole is a supermassive black hole located at the center of a galaxy surrounded by a dark matter halo. For the first time, we establish a generic, fully-relativistic formalism to calculate solutions of Einstein's gravity minimally coupled to an anisotropic fluid modeled by the Einstein cluster in axisymmetric, non-vacuum spacetimes, which are extensions of spherically-symmetric cases. These asymptotically flat spacetimes with regular horizons can describe the geometry of galaxies harboring supermassive black holes and are useful to constrain the environment surrounding astrophysical black holes. Our findings provide a solid groundwork for future studies on the shadows, quasi-normal modes, and other phenomena associated with rotating galactic black holes.

gr-qc↗

arXiv2023

TIA: A Teaching Intonation Assessment Dataset in Real Teaching Situations

Intonation is one of the important factors affecting the teaching language arts, so it is an urgent problem to be addressed by evaluating the teachers' intonation through artificial intelligence technology. However, the lack of an intonation assessment dataset has hindered the development of the field. To this end, this paper constructs a Teaching Intonation Assessment (TIA) dataset for the first time in real teaching situations. This dataset covers 9 disciplines, 396 teachers, total of 11,444 utterance samples with a length of 15 seconds. In order to test the validity of the dataset, this paper proposes a teaching intonation assessment model (TIAM) based on low-level and deep-level features of speech. The experimental results show that TIAM based on the dataset constructed in this paper is basically consistent with the results of manual evaluation, and the results are better than the baseline models, which proves the effectiveness of the evaluation model.

cs.SD↗

arXiv2023

Testing alternative theories of gravity with space-based gravitational wave detectors

We use gravitational waves (GWs) from binary black holes (BBHs) and neutron stars inspiraling into intermediate-mass black holes to evaluate how accurately the future space-based GW detectors such as LISA, Taiji and TianQin and their combined networks can determine source parameters and constrain alternative theories of gravity. We find that, compared with single detector, the detector network can greatly improve the estimation errors of source parameters, especially the sky localization, but the improvement of the constraint on the graviton mass $m_g$ and the Brans-Dicke coupling constant $ω_{BD}$ is small. We also consider possible scalar modes existed in alternative theories of gravity and we find the inclusion of the scalar mode has little effect on the constraints on source parameters, $m_g$, and $ω_{BD}$ and the parametrized amplitude $A_B$ of scalar modes are small. For the constraint on the graviton mass, we consider both the effects in the GW phase and the transfer function due to the mass of graviton. With the network of LISA, Taiji and TianQin, we get the lower bound on the graviton Compton wavelength $λ_g\gtrsim 1.24 \times 10^{20}$ m for BBHs with masses $(10^6+10^7)M_\odot$, and $A_B< 5.7\times 10^{-4}$ for BBHs with masses $(1+2)\times 10^5M_\odot$; $ω_{BD}>6.11\times10^{6}$ for neutron star-black hole binary with masses $(1.4+400)M_{\odot}$.

gr-qc↗

arXiv2023

Probing the equation of state of neutron stars with captured primordial black holes

Gravitational waves (GWs) from primordial black holes (PBHs) inspiraling within neutron stars (NSs) -- should they exist -- are detectable by ground-based detectors and offer a unique insight into the internal structure of NSs. To provide accurate templates for GW searches, we solve Einstein's equations within NSs and calculate the orbital motion of the captured PBH by considering dynamical friction, accretion, and gravitational radiation. Equipped with precise GW waveforms for PBHs inspiraling inside NSs, we find that the Einstein Telescope can differentiate between various equations of state for NSs. As PBHs inspiral deeper into NSs, the GW frequency rises near the surface, then decreases to a constant value deeper within NSs. The distinctive characteristics of GW frequency serve as the smoking gun for GW signals emitted by PBHs inspiraling inside NSs and can be used to probe the nuclear matter in the crust and core of NSs.

gr-qc↗

arXiv2023

Estimating Continuous Muscle Fatigue For Multi-Muscle Coordinated Exercise: A Pilot Study on Walking

Assessing the progression of muscle fatigue for daily exercises provides vital indicators for precise rehabilitation, personalized training dose, especially under the context of Metaverse. Assessing fatigue of multi-muscle coordination-involved daily exercises requires the neuromuscular features that represent the fatigue-induced characteristics of spatiotemporal adaptions of multiple muscles and the estimator that captures the time-evolving progression of fatigue. In this paper, we propose to depict fatigue by the features of muscle compensation and spinal module activation changes and estimate continuous fatigue by a physiological rationale model. First, we extract muscle synergy fractionation and the variance of spinal module spikings as features inspired by the prior of fatigue-induced neuromuscular adaptations. Second, we treat the features as observations and develop a Bayesian Gaussian process to capture the time-evolving progression. Third, we solve the issue of lacking supervision information by mathematically formulating the time-evolving characteristics of fatigue as the loss function. Finally, we adapt the metrics that follow the physiological principles of fatigue to quantitatively evaluate the performance. Our extensive experiments present a 0.99 similarity between days, a over 0.7 similarity with other views of fatigue and a nearly 1 weak monotonicity, which outperform other methods. This study would aim the objective assessment of muscle fatigue.

cs.HC↗

arXiv2022

R-matrix electron-impact excitation data for the H- and He-like ions with Z=6-30

Plasma models built on extensive atomic data are essential to interpreting the observed cosmic spectra. H-like Lyman series and He-like triplets observable in the X-ray band are powerful diagnostic lines to measure the physical properties of various types of astrophysical plasmas. Electron-impact excitation is a fundamental atomic process for the formation of H-like and He-like key diagnostic lines. Electron-impact excitation data adopted by the widely used plasma codes (AtomDB, CHIANTI, and SPEX) do not necessarily agree with each other. Here we present a systematic calculation of electron-impact excitation data of H-like and He-like ions with the atomic number Z=6-30 (i.e., C to Zn). Radiation damped R-matrix intermediate coupling frame transformation calculation was performed for each ion with configurations up to $n=6$. We compare the present work with the above three plasma codes and literature to assess the quality of the new data, which are relevant for current and future high-resolution X-ray spectrometers.

physics.atom-ph↗

arXiv2022

A Review of Machine Learning-based Failure Management in Optical Networks

Failure management plays a significant role in optical networks. It ensures secure operation, mitigates potential risks, and executes proactive protection. Machine learning (ML) is considered to be an extremely powerful technique for performing comprehensive data analysis and complex network management and is widely utilized for failure management in optical networks to revolutionize the conventional manual methods. In this study, the background of failure management is introduced, where typical failure tasks, physical objects, ML algorithms, data source, and extracted information are illustrated in detail. An overview of the applications of ML in failure management is provided in terms of alarm analysis, failure prediction, failure detection, failure localization, and failure identification. Finally, the future directions on ML for failure management are discussed from the perspective of data, model, task, and emerging techniques.

cs.NI↗

arXiv2022

Source localizations with the network of space-based gravitational wave detectors

The sky localization of the gravitational wave (GW) source is an important scientific objective for GW observations. A network of space-based GW detectors dramatically improves the sky localization accuracy compared with an individual detector not only in the inspiral stage but also in the ringdown stage. It is interesting to explore what plays an important role in the improvement. We find that the angle between the detector planes dominates the improvement, and the time delay is the next important factor. A detector network can dramatically improve the source localization for short signals and long signals with most contributions to the signal-to-noise ratio (SNR) coming from a small part of the signal in a short time, and the more SNR contributed by smaller parts, the better improvement by the network. We also find the effects of the arm length in the transfer function and higher harmonics are negligible for source localization with the detector network.

gr-qc↗

arXiv2022

Detection of gravitational wave mixed polarization with single space-based detectors

General Relativity predicts only two tensor polarization modes for gravitational waves while at most six possible polarization modes are allowed in general metric theory of gravity. The number of polarization modes is determined by the specific modified theory of gravity. Therefore, the determination of polarization modes can be used to test gravitational theory. We introduce a concrete data analysis pipeline for a space-based detector such as LISA to detect the polarization modes of gravitational waves. This method can be used for monochromatic gravitational waves emitted from any compact binary system with known sky position and frequency to detect mixtures of tensor and extra polarization modes. We use the source J0806.3+1527 with one-year simulation data as an example to show that this approach is capable of probing pure and mixed polarizations without knowing the exact polarization modes. We also find that the ability of detection of extra polarization depends on the gravitational wave source location and the amplitude of non-tensorial components.

gr-qc↗

arXiv2021

Parameter estimation for space-based gravitational wave detectors with ringdown signals

Unlike ground-based gravitational wave detectors, space-based gravitational wave detectors can detect the ringdown signals from massive black hole mergers with large signal-to-noise ratios, help to localize sources and extract their parameters. To reduce the computation time in the Fisher information matrix analysis, we derive the analytical formulas of frequency-domain ringdown signals for both heliocentric and geocentric detectors by considering the effects of the harmonic phases, the rotation period of the geocentric detector, and the detector's arm length. We explore median errors of the parameter estimation and source localization with ringdown signals from binaries with different masses and different redshifts. Using a binary source with the total mass $M=10^7\ M_\odot$ at the redshift $z=1$, we analyze the dependence of these errors on the sky position. We find that the network of space-based gravitational wave detectors can significantly improve the source localization at the ringdown stage. The results of the Fisher matrix approximation are also checked by Bayesian inference method.

gr-qc↗

arXiv2021

Sky localization of space-based gravitational wave detectors

Localizing the sky position of the gravitational wave source is a key scientific goal for gravitational wave observations. Employing the Fisher information matrix approximation, we compute the angular resolutions of LISA and TianQin, two planned space-based gravitational wave detectors and examine how detectors' configuration properties, such as the orientation change of the detector plane, heliocentric or geocentric motion and the arm length etc. affect the accuracy of source localization. We find that the amplitude modulation due to the annual changing orientation of the detector plane helps LISA get better accuracy in the sky localization and better sky coverage at frequencies below several mHz, and its effect on TianQin is negligible although the orientation of TianQin's detector plane is fixed. At frequencies above roughly 30mHz, TianQin's ability in the sky localization is better than LISA. Further we explore potential space detector networks for fast and accurate localization of the gravitational wave sources. The LISA-TianQin network has better ability in sky localization for sources with frequencies in the range 1-100 mHz and the network has larger sky coverage for the angular resolution than the individual detector.

astro-ph.IM↗

arXiv2021

Accuracy of estimation of parameters with space-borne gravitational wave observatory

Employing the Fisher information matrix analysis, we estimate parameter errors of TianQin and LISA for monochromatic gravitational waves. With the long-wavelength approximation we derive analytical formulas for the parameter estimation errors. We separately analyze the effects of the amplitude modulation due to the changing orientation of the detector plane and the Doppler modulation due to the translational motion of the center of the detector around the Sun. We disclose that in the low frequency regime there exist different patterns in angular resolutions and estimation errors of sources' parameters between LISA and TianQin, the angular resolution falls off as $S_n(f)/f^2$ for TianQin but $S_n(f)$ for LISA, and the estimation errors of the other parameters fall off as $\sqrt{S_n(f)}/f$ for TianQin but $\sqrt{S_n(f)}$ for LISA. In the medium frequency regime we observe the same pattern where the angular resolution falls off as $S_n(f)/f^2$ and the estimation errors of the other parameters fall off as $\sqrt{S_n(f)}$ for both TianQin and LISA. In the high frequency regime, the long-wavelength approximation fails, we numerically calculate the parameter estimation errors for LISA and TianQin and find that the parameter estimation errors measured by TianQin are smaller than those by LISA.

gr-qc↗

arXiv2020

Role of Digital Twin in Optical Communication: Fault Management, Hardware Configuration, and Transmission Simulation

Optical communication is developing rapidly in the directions of hardware resource diversification, transmission system flexibility, and network function virtualization. Its proliferation poses a significant challenge to traditional optical communication management and control systems. Digital twin (DT), a technology that utilizes data, models, and algorithms and integrates multiple disciplines, acts as a bridge between the real and virtual worlds for comprehensive connectivity. In the digital space, virtual models are stablished dynamically to simulate and describe the states, behaviors, and rules of physical objects in the physical space. DT has been significantly developed and widely applied in industrial and military fields. This study introduces the DT technology to optical communication through interdisciplinary crossing and proposes a DT framework suitable for optical communication. The intelligent fault management model, flexible hardware configuration model, and dynamic transmission simulation model are established in the digital space with the help of deep learning algorithms to ensure the highreliability operation and high-efficiency management of optical communication systems and networks.

cs.NI↗

arXiv2020

Full analytical formulas for frequency response of space-based gravitational wave detectors

The discovery of gravitational waves, which are ripples of space-time itself, opened a new window to test general relativity, because it predicts that there are only plus and cross polarizations for gravitational waves. For alternative theories of gravity, there may be up to six polarizations. The measurement of the polarization is one of the major scientific goals for future gravitational wave detectors. To evaluate the capability of the detector, we need to use the frequency dependent response functions averaged over the source direction and polarization angle. We derive the full analytical formulas of the averaged response functions for all six possible polarizations and present their asymptotic behaviors based on these analytical formulas. Compared with the numerical simulation, the full analytical formulas are more efficient and valid for any equal-arm interferometric gravitational wave detector without optical cavities in the arms and for a time-delay-interferometry Michelson combination.

gr-qc↗