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X. Yan

Publications and source records attributed to X. Yan.

At least 19 recordsLinked to original sources
arXiv2026

Dual AGN and Multiple SMBH Systems in the Era of SKAO

We present a radio-oriented review of current strategies for the detection and characterization of dual active galactic nuclei (DAGN) and supermassive black hole binaries (SMBHBs), emphasizing the crucial role of radio interferometry in advancing this field. We discuss how high-resolution radio imaging - particularly through very long baseline interferometry (VLBI) - provides a unique, dust-unbiased tool to identify multiple accreting SMBHs, disentangle AGN-related emission from star formation, and trace components from tens of kpc to sub-parsec scales. We summarize current observational limitations, such as insufficient sensitivity-resolution combination and area coverage. We then outline how the SKAO will overcome these constraints through its unprecedented combination of sensitivity, survey speed, imaging fidelity and angular resolution, enabling the discovery and characterization of dual and binary SMBHs from the nearby Universe to the epoch of reionization. Several science cases are presented, including radio follow-ups of optical/infrared-selected DAGN, direct blind radio selection of DAGN, studies of compact bound SMBHBs, and the link between SMBHB orbital evolution and low-frequency gravitational wave emission. We further emphasize the synergy between SKAO observations and modern and upcoming facilities such as the James Webb and Euclid space telescopes, Rubin Observatory, and gravitational wave detectors including the Laser Interferometer Space Antenna and pulsar timing arrays. These combined capabilities will allow SKAO to enable the first comprehensive radio census of dual and binary SMBH systems, bridge the gap between electromagnetic and gravitational wave observations, and provide a statistically significant view of SMBH pairing, accretion, and merger-driven feedback throughout cosmic history.

astro-ph.HE↗
arXiv2026

Real-Time Wiener Deconvolution for feature reconstruction in JUNO

In particle physics, experiments generate substantial amounts of data that can be difficult to process without preliminary scaling. To avoid losing potentially crucial data, experimental collaborations are studying novel techniques for real-time data processing to extract features for further physics analysis. A common approach, especially in neutrino physics, is to use FPGAs for data acquisition and pre-processing. This paper presents an advanced Real-Time Wiener deconvolution algorithm designed to leverage the processing capabilities of the FPGA integrated into the readout boards of the Jiangmen Underground Neutrino Observatory (JUNO). The goal is to enable real-time reconstruction of the signal generated by photomultiplier tubes (PMTs) when neutrino interactions are detected. By exploiting online reconstruction of the signal generated by PMTs, we expect to improve the detection of low-energy depositions, such as those produced by transient astrophysical phenomena. These depositions are usually not saved because of the significant background that affects the low end of the energy spectrum, which would result in a large trigger rate, hence a large amount of data required for storage. This paper presents the features of the algorithm, including its ability to manage high-throughput data streams with minimal latency, adaptability, and resilience in discerning the characteristics of input data. Performance is evaluated on a JUNO electronic board. This study further demonstrates the potential of FPGA-based solutions for neutrino physics.

physics.ins-det↗
arXiv2025

Graphene Electro-Absorption Modulators for Energy-Efficient and High-Speed Optical Transceivers

The increasing demand for energy-efficient hardware for artificial intelligence (AI) and data centres requires integrated photonic solutions delivering optical transceivers with Tbit/s data rates and energy consumption$<$1pJ/bit. Here, we report double single-layer graphene electro-absorption modulators on Si optimized for energy-efficient and ultra-fast operation, demonstrating 67GHz bandwidth and 80Gbit/s data rate, in both O and C bands, using a fabrication tailored for wafer-scale integration. We measure a data rate$\sim$1.6 times larger than previously reported for graphene. We scale the modulator's active area down to 22$\mu$m$^2$, achieving a dynamic power consumption$\sim$58fJ/bit, $\sim$3 times lower than previous graphene modulators and Mach-Zehnder modulators based on Si or lithium niobate. We show devices with$\sim$0.037dB/V$\mu$m modulation efficiency,$\sim$16 times better than previous demonstrations based on graphene. This paves the way to wafer-scale production of graphene modulators on Si useful for Tbit/s optical transceivers and energy-efficient AI

cond-mat.mtrl-sci↗
arXiv2024

Suppression of Edge Localized Modes in ITER Baseline Scenario in EAST using Edge Localized Magnetic Perturbations

We report the suppression of Type-I Edge Localized Modes (ELMs) in the EAST tokamak under ITER baseline conditions using $n = 4$ Resonant Magnetic Perturbations (RMPs), while maintaining energy confinement. Achieving RMP-ELM suppression requires a normalized plasma beta ($\beta_N$) exceeding 1.8 in a target plasma with $q_{95}\approx 3.1$ and tungsten divertors. Quasi-linear modeling shows high plasma beta enhances RMP-driven neoclassical toroidal viscosity torque, reducing field penetration thresholds. These findings demonstrate the feasibility and efficiency of high $n$ RMPs for ELM suppression in ITER.

physics.plasm-ph↗
arXiv2024

Emergent Topological Semimetal

A material's electronic topology, which is generally described via its Bloch states and the associated bandstructure, will be enriched by the presence of interactions. In metallic settings, the interactions are usually treated through the concept of quasiparticles. Using the genuinely quantum critical heavy fermion compound CeRu$_4$Sn$_6$, we investigate what happens if no well-defined quasiparticles are present. Surprisingly, we discover a topological semimetal phase that emerges from the material's quantum critical state and exhibits a dome structure as a function of magnetic field and pressure. To understand these results, we study a Weyl-Kondo semimetal model at a Kondo destruction quantum critical point. Indeed, it exhibits features in the spectral function that can define topological crossings beyond the quasiparticle picture. We expect our work to stimulate the search for other emergent topological phases.

cond-mat.str-el↗
arXiv2023

Ce$_3$Bi$_4$Ni$_3$ $-$ A large hybridization-gap variant of Ce$_3$Bi$_4$Pt$_3$

The family of cubic noncentrosymmetric 3-4-3 compounds has become a fertile ground for the discovery of novel correlated metallic and insulating phases. Here, we report the synthesis of a new heavy fermion compound, Ce$_3$Bi$_4$Ni$_3$. It is an isoelectronic analog of the prototypical Kondo insulator Ce$_3$Bi$_4$Pt$_3$ and of the recently discovered Weyl-Kondo semimetal Ce$_3$Bi$_4$Pd$_3$. In contrast to the volume-preserving Pt-Pd substitution, structural and chemical analyses reveal a positive chemical pressure effect in Ce$_3$Bi$_4$Ni$_3$ relative to its heavier counterparts. Based on the results of electrical resistivity, Hall effect, magnetic susceptibility, and specific heat measurements, we identify an energy gap of 65-70 meV, about eight times larger than that in Ce$_3$Bi$_4$Pt$_3$ and about 45 times larger than that of the Kondo-insulating background hosting the Weyl nodes in Ce$_3$Bi$_4$Pd$_3$. We show that this gap as well as other physical properties do not evolve monotonically with increasing atomic number, i.e., in the sequence Ce$_3$Bi$_4$Ni$_3$-Ce$_3$Bi$_4$Pd$_3$-Ce$_3$Bi$_4$Pt$_3$, but instead with increasing partial electronic density of states of the $d$ orbitals at the Fermi energy. To understand under which condition topological states form in these materials is a topic for future studies.

cond-mat.str-el↗
arXiv2022

Cascade of magnetic-field-driven quantum phase transitions in Ce3Pd20Si6

Magnetically hidden order is a hypernym for electronic ordering phenomena that are visible to macroscopic thermodynamic probes but whose microscopic symmetry cannot be revealed with conventional neutron or x-ray diffraction. In a handful of f-electron systems, the ordering of odd-rank multipoles leads to order parameters with a vanishing neutron cross-section. Among them, Ce$_3$Pd$_{20}$Si$_6$ is known for its unique phase diagram exhibiting two distinct multipolar-ordered ground states (phases II and II'), separated by a field-driven quantum phase transition associated with a putative change in the ordered quadrupolar moment from $O_2^0$ to $O_{xy}$. Using torque magnetometry at subkelvin temperatures, here we find another phase transition at higher fields above 12 T, which appears only for low-symmetry magnetic field directions $\mathbf{B} \parallel \langle11L\rangle$ with $1 < L \leq 2$. While the order parameter of this new phase II'' remains unknown, the discovery renders Ce$_3$Pd$_{20}$Si$_6$ a unique material with two field-driven phase transitions between distinct multipolar phases. They are both clearly manifested in the magnetic-field dependence of the field-induced (111) Bragg intensities measured with neutron scattering for $\mathbf{B} \parallel [112]$. We also find from inelastic neutron scattering that the number of nondegenerate collective excitations induced by the magnetic field correlates with the number of phases in the magnetic phase diagram for the same field direction. Furthermore, the magnetic excitation spectrum suggests that the new phase II'' may have a different propagation vector, revealed by the minimum in the dispersion that may represent the Goldstone mode of this hidden-order phase.

cond-mat.str-el↗
arXiv2021

GlassNet: Label Decoupling-based Three-stream Neural Network for Robust Image Glass Detection

Most of the existing object detection methods generate poor glass detection results, due to the fact that the transparent glass shares the same appearance with arbitrary objects behind it in an image. Different from traditional deep learning-based wisdoms that simply use the object boundary as auxiliary supervision, we exploit label decoupling to decompose the original labeled ground-truth (GT) map into an interior-diffusion map and a boundary-diffusion map. The GT map in collaboration with the two newly generated maps breaks the imbalanced distribution of the object boundary, leading to improved glass detection quality. We have three key contributions to solve the transparent glass detection problem: (1) We propose a three-stream neural network (call GlassNet for short) to fully absorb beneficial features in the three maps. (2) We design a multi-scale interactive dilation module to explore a wider range of contextual information. (3) We develop an attention-based boundary-aware feature Mosaic module to integrate multi-modal information. Extensive experiments on the benchmark dataset exhibit clear improvements of our method over SOTAs, in terms of both the overall glass detection accuracy and boundary clearness.

cs.CV↗
arXiv2021

Interplay of anionic quasi-atom and interstitial point defects in electrides: abnormal interstice occupation and colossal charge state of point defects in dense FCC-lithium

Electrides are an emerging class of materials with highly-localized electrons in the interstices of a crystal that behave as anions. The presence of these unusual interstitial quasi-atom (ISQ) electrons leads to interesting physical and chemical properties, and wide potential applications for this new class of materials. Crystal defects often have a crucial influence on the properties of materials. Introducing impurities has been proved to be an effective approach to improve the properties of a material and to expand its applications. However, the interactions between the anionic ISQs and the crystal defects in electrides are as yet unknown. Here, dense FCC-Li was employed as an archetype to explore the interplay between anionic ISQs and interstitial impurity atoms in this electride. This work reveals a strong coupling among the interstitial impurity atoms, the ISQs, and the matrix Li atoms near to the defects. This complex interplay and interaction mainly manifest as the unexpected tetrahedral interstitial occupation of impurity atoms and the enhancement of electron localization in the interstices. Moreover, the Be impurity occupying the octahedral interstice shows the highest negative charge state (Be8-) discovered thus far. These results demonstrate the rich chemistry and physics of this emerging material, and provide a new basis for enriching their variants for a wide range of applications.

cond-mat.mtrl-sci↗
arXiv2021

The PRad Windowless Gas Flow Target

We report on a windowless, high-density, gas flow target at Jefferson Lab that was used to measure $r_p$, the root-mean-square charge radius of the proton. To our knowledge, this is the first such system used in a fixed-target experiment at a (non-storage ring) electron accelerator. The target achieved its design goal of an areal density of 2$\times$10$^{18}$ atoms/cm$^2$, with the gas uniformly distributed over the 4 cm length of the cell and less than 1% residual gas outside the cell. This design eliminated scattering from the end caps of the target cell, a problem endemic to previous measurements of the proton charge radius in electron scattering experiments, and permitted a precise, model-independent extraction of $r_p$ by reaching unprecedentedly low values of $Q^2$, the square of the electron's transfer of four-momentum to the proton.

physics.ins-det↗
arXiv2020

First Measurement of the Asymmetry and the Gerasimov-Drell-Hearn Integrand from $\vec{{^3}He}(\vec{\gamma},p)d$ reaction at the Incident Photon Energy of 29 MeV

The first measurement of the $\vec{^3He}(\vec{\gamma},p)d$ process was performed at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility at Triangle Universities Nuclear Laboratory (TUNL) using a circularly polarized, monoenergetic $\gamma$-ray beam and a longitudinally polarized $^3$He target. The spin-dependent asymmetry and the contribution from the two-body photodisintegration to the $^3$He Gerasimov-Drell-Hearn integrand are extracted and compared with state-of-the-art three-nucleon system calculations at the incident photon energy of 29.0 MeV. The data are in general agreement with the various theoretical predictions based on the Siegert theorem or on explicit inclusion of meson-exchange currents.

nucl-ex↗
arXiv2020

Embedded Readout Electronics R&D for the Large PMTs in the JUNO Experiment

Jiangmen Underground neutrino Observatory (JUNO) is a next generation liquid scintillator neutrino experiment under construction phase in South China. Thanks to the anti-neutrinos produced by the nearby nuclear power plants, JUNO will primarily study the neutrino mass hierarchy, one of the open key questions in neutrino physics. One key ingredient for the success of the measurement is to use high speed, high resolution sampling electronics located very close to the detector signal. Linearity in the response of the electronics in another important ingredient for the success of the experiment. During the initial design phase of the electronics, a custom design, with the Front-End and Read-Out electronics located very close to the detector analog signal has been developed and successfully tested. The present paper describes the electronics structure and the first tests performed on the prototypes. The electronics prototypes have been tested and they show good linearity response, with a maximum deviation of 1.3% over the full dynamic range (1-1000 p.e.), fulfilling the JUNO experiment requirements.

physics.ins-det↗
arXiv2019

Generalizing the Sokolov-Ternov effect for radiative polarization in intense laser fields

A consistent description of the radiative polarization for relativistic electrons in intense laser fields is derived by generalizing the Sokolov-Ternov effect in general field structure. The new form together with the spin-dependent radiation-reaction force provides a complete set of dynamical equations for electron momentum and spin in strong fields. When applied to varying intense fields, e.g. the laser fields, the generalized Sokolov-Ternov effect allows electrons to gain or lose polarization in any directions other than along the magnetic field in the rest frame of the electron. The generalized theory is applied to the collision process between initially polarized/unpolarized high energy electrons with linearly polarized ultra-intense laser pulse, showing results that eliminate the dependence on specific choices of a quantization axis and spin initialization existing in spin-projection models.

physics.plasm-ph↗
arXiv2019

On Solving a Class of Linear Semi-Infinite Programs by the Trigonometric Moment

In this paper, we propose a new easily implementable method for solving a class of semi-infinite programs, where an approximate linear semidefinite program is constructed for the concerned semi-infinite program based on the duality theory of semi-infinite programs and the theory of the trigonometric moments. We obtain a lnK/K-optimal solution for the semi-infinite program, where K is the truncation factor. Moreover, we present some numerical examples to show the efficiency of the new method.

math.OC↗
arXiv2019

Nanostructured clathrates and clathrate-based nanocomposites

Intermetallic clathrates are candidate materials for thermoelectric applications above room temperature. Here we explore whether their intrinsically low lattice thermal conductivities can be further reduced by nanostructuring and whether this can further enhance their thermoelectric performance.}{As bulk nanostructuring routes we studied melt spinning and ball milling. To optimize the compaction process and/or stabilize the nanostructure we varied the process parameters, used additives, and studied clathrate-based composites. Initial results on clathate nanowires as simpler model nanostructures are also presented.

cond-mat.mtrl-sci↗
arXiv2019

Radiative deflection by spin effect in the quantum radiation-reaction regime

The colliding between ultra-relativistic electrons and an ultra-intense laser pulse is a powerful approach to testify the physics in strong-field QED regime. By considering spin-dependent radiation-reaction during laser-electron collision we find anti-symmetric deflection of electrons with different spin states. We revealed that such deflection is induced by the non-zero work done by radiation-reaction force along field polarization-direction in a half-period of phase, which is larger for spin-anti-paralleled electrons and smaller for spin-paralleled electrons. The spin-projection on the magnetic field of an electron gets inversed in adjacent half-periods due to oscillating magnetic field and therefore the deflection due to spin-dependent radiation is accumulated rather than vanishing. The new mechanism provides an extra dimension to observe quantum radiation-reaction effect in the strong-field QED regime by measuring the anti-symmetric distribution.

physics.plasm-ph↗
arXiv2018

Origin of planar Hall effect in type-II Weyl semimetal MoTe2

Besides the negative longitudinal magnetoresistance (MR), planar Hall effect (PHE) is a newly emerging experimental tool to test the chiral anomaly or nontrivial Berry curvature in Weyl semimetals (WSMs). However, the origins of PHE in various systems are not fully distinguished and understood. Here we perform a systematic study on the PHE and anisotropic MR (AMR) of Td-MoTe2, a type-II WSM. Although the PHE and AMR curves can be well fitted by the theoretical formulas, we demonstrate that the anisotropic resistivity arises from the orbital MR (OMR), instead of the negative MR as expected in the chiral anomaly effect. In contrast, the absence of negative MR indicates that the large OMR dominates over the chiral anomaly effect. This explains why it is difficult to measure negative MR in type-II WSMs. We argue that the measured PHE can be related with the chiral anomaly only when the negative MR is simultaneously observed.

cond-mat.mtrl-sci↗