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Hong Xiao

Publications and source records attributed to Hong Xiao.

At least 19 recordsLinked to original sources

Restrict, Don't Retrain: Inference-Time VLM Guidance for Zero-Shot Aerial Segmentation

Global welfare often depends on the correct interpretation of aerial and satellite imagery. Acting on such imagery (mapping flooded ground, crop extent, or damaged infrastructure) demands pixel-level segmentation to ensure perfect class localization. Pretrained general foundation models, when applied directly, often miss important features and cannot always find all the classes belonging to a given scene, overlooking smaller objects that matter most. We use a single consumer-grade GPU running a vision-language model (VLM) to supply this missing guidance, improving segmentation while producing structured, auditable evidence that drives the result and can be inspected on its own. We fuse three approaches: the frozen foundation model that labels every pixel, and two queries to a VLM, one to choose the classes that matter, and one to locate the small objects the base model misses. Evaluating across four aerial datasets, we see consistent gains at each stage where the base model is competent.

cs.CV

Pressure Induced 18 K Superconductivity and Two Superconducting Phases in CuIr2S4

We report pressure-induced superconductivity in the spinel CuIr$_{2}$S$_{4}$ with a transition temperature ($T_{\text{c}}$) reaching \textbf{18.2 K}, establishing a new record for this class of materials and surpassing the decades-old limit of 13.7 K. Our electrical transport and synchrotron X-ray diffraction studies up to 224 GPa reveal the emergence of \textbf{two distinct superconducting phases} from a charge-ordered insulating state. The first phase (SC-I) appears around 18 GPa, and forms a dome-shaped superconducting region in which the resistivity exhibits a pronounced, field- and current-sensitive drop without reaching strict zero above our base temperature. Above 111.8 GPa, a second, lower-$T_{\text{c}}$ phase (SC-II) emerges and coexists with SC-I over a broad pressure range, and SC-II ultimately develops a true zero-resistance state above 122.2 GPa. These superconducting phases are intimately linked to a cascade of structural transitions that systematically distort the frustrated pyrochlore lattice of Ir atoms. Our results expand the potential for superconductivity in spinels and demonstrate a pathway to high-$T_{\text{c}}$ pairing directly from a correlated insulating state driven by lattice tuning.

cond-mat.supr-con

Natural Language Processing Methods for the Study of Protein-Ligand Interactions

Recent advances in Natural Language Processing (NLP) have ignited interest in developing effective methods for predicting protein-ligand interactions (PLIs) given their relevance to drug discovery and protein engineering efforts and the ever-growing volume of biochemical sequence and structural data available. The parallels between human languages and the "languages" used to represent proteins and ligands have enabled the use of NLP machine learning approaches to advance PLI studies. In this review, we explain where and how such approaches have been applied in the recent literature and discuss useful mechanisms such as long short-term memory, transformers, and attention. We conclude with a discussion of the current limitations of NLP methods for the study of PLIs as well as key challenges that need to be addressed in future work.

q-bio.QM

Generation of bright collimated vortex $\gamma$-ray via laser driven cone-fan target

We use numerical simulations to demonstrate that a source of bright collimated vortex $\gamma$-ray with large orbital angular momentum can be achieved by irradiating a circularly polarized laser with an intensity about $10^{22}\rm{W/{cm^2}}$ on a cone-fan target. In the studied setup, electron beam of energy of hundreds of MeV and vortex laser pulse are formed. And furthermore a high quality vortex $\gamma$-ray is yielded with small divergence of $5^{\circ}$ and high peak brilliance $\sim5\times10^{22}$ photons ${\rm\cdot s^{-1} \cdot mm^{-2} \cdot mrad^{-2}}$ $0.1\%\mathrm{BW}$ at $10\mathrm{MeV}$. A considerable fraction of angular momentum of laser is converted to electron beam and vortex $\gamma$-ray, which are roughly $27.8\%$ and $3\%$, respectively. And the conversion efficiency of energy from laser to electron beam and vortex $\gamma$-ray are around $41\%$ and $3.8\%$. Moreover, comparative simulations for different right radius of cone reveal that there exists an optimal size that makes the highest angular momentum of $\gamma$-ray photons to be around $2.8\times10^6\hbar$. The comparative simulations for different laser modes exhibit that it is more appropriate to choose the circularly polarized laser to generate vortex $\gamma$-ray than the Laguerre-Gaussian one.

physics.plasm-ph

Angular distributions of nonlinear Thomson scattering in combining field with a general elliptically polarized laser and a background magnetic field

Nonlinear Thomson scattering of an electron motion in a combining field constituted by an elliptically polarized laser and a background magnetic field is investigated. The dependence of the electron trajectories, the fundamental frequency, the maximum radiation power in spatial distribution and corresponding spatial angle on ellipticity are obtained. In addition, we find that the angular distributions of scattering spectra with respect to the azimuthal angle exhibits the symmetry no matter what the order of harmonics, the laser intensity, the magnetic resonance parameter and the initial axial momentum are. Meanwhile, the polar angle distribution of the spectra approaches more and more the laser propagation direction with the laser intensity, the magnetic resonance parameter and the initial axial momentum. The maximum radiated power increases and the corresponding polar angle decreases. The optimal angle for the maximum radiated power per unit of solid, the corresponding photon number and the photons brightness can be obtained, which implies that the high quality XUV or/and x-ray can be generated by the studied scheme when the suitable parameters are chosen.

physics.optics

Probing magnetic anisotropy in Kagome antiferromagnetic Mn$_3$Ge with torque magnetometry

We investigate the magnetic symmetry of the topological antiferromagnetic material Mn$_3$Ge by using torque measurements. Below the Neel temperature, detailed angle-dependent torque measurements were performed on Mn$_3$Ge single crystals in directions parallel and perpendicular to the Kagome basal plane. The out-of plane torque data exhibit $\pm\sin\theta$ and $\sin2\theta$ behaviors, of which the former results from the spontaneous ferromagnetism within the basal plane and the latter from the in- and out-of-plane susceptibility anisotropy. The reversible component of the in-plane torque exhibits $\sin6\varphi$ behavior, revealing the six-fold symmetry of the in-plane magnetic free energy. Moreover, we find that the free energy minima are pinned to the direction of spontaneous ferromagnetism, which correspond to the maxima of the irreversible component of the in-plane torque. We provide an effective spin model to describe the in-plane magnetic anisotropy. Our results demonstrate that the ground state of Mn$_3$Ge is described by the coexistence of a strong six-fold antichiral order and a weak ferromagnetic order induced by second-order spin anisotropy.

cond-mat.str-el

Observation of Two-dimensional Superconductivity in an Ultrathin Iron-Arsenic Superconductor

Two-dimensional (2D) superconductors supply important platforms for exploring new quantum physics and high-$T_c$ superconductivity. The intrinsic superconducting properties in the 2D iron-arsenic superconductors are still unknown owing to the difficulties in the preparation of ultrathin samples. Here we report the fabrication and physical investigations of the high quality single-crystalline ultrathin films of the iron-arsenic superconductor KCa$_2$Fe$_4$As$_4$F$_2$. For the sample with the thickness of 2.6$\sim$5 nm (1$\sim$2 unit cells), a sharp superconducting transition at around 30 K (onset point) is observed. Compare with the bulk material, the ultrathin sample reveals a relatively lower $T_c$, wider transition width, and broader flux liquid region under the in-plane field. Moreover, the angle dependent upper critical field follows the Tinkham model, demonstrating the two-dimensional superconductivity in ultrathin KCa$_2$Fe$_4$As$_4$F$_2$.

cond-mat.supr-con

Origin of superconductivity and giant phonon softening in TlInTe$_2$ under pressure

Analogous to 2D layered transition metal dichalcogenides, the TlSe family of 1D chain materials with Zintl-type structure exhibits exotic phenomena under high-pressure. In the present work, we have systematically investigated the high-pressure behavior of TlInTe 2 using Raman spectroscopy, synchrotron X-ray diffraction, and transport measurements, in combination with crystal structure prediction (CSP) based on the evolutionary approach and first principles calculations. We found that TlInTe$_2$ undergoes a pressure driven semiconductor to semimetal transition at 4 GPa, followed by a superconducting transition at 5.7 GPa (with Tc = 3.8 K) induced by a Lifshitz transition. The Lifshitz transition is initiated by the appearance of new electron pockets on the Fermi surface, which evolve with pressure and connect to the adjacent electron pockets forming an umbrella shaped Fermi surface at the top and bottom of the Brillouin zone. An unusual giant phonon softening (Ag mode) concomitant with a V-shaped Tc behavior appears at 10-12 GPa as a result of the interaction of optical phonons with the conduction electrons, resulting in Fano line shaped asymmetry in Ag mode. A prominent Tc anomaly concurrent with the Ag mode softening at 19-20 GPa is correlated to the semimetal to metal transition. The CSP calculations reveal that these transitions are not accompanied by any structural phase transitions up to the maximum pressure achieved, 33.5 GPa. Our findings on TlInTe$_2$ open up a new platform to study a plethora of unexplored high pressure novel phenomena in TlSe family induced by Lifshitz transition (electronic driven), phonon softening and electron-phonon coupling.

cond-mat.supr-con

Photon Reconstruction Performance at the CEPC baseline detector

The Circular Electron Positron Collider (CEPC) is a proposed Higgs/Z factory. The photon reconstruction is critical to its physics program. We study the photon reconstruction at the CEPC baseline detector, a Particle Flow oriented detector. We characterized the objective performance at both single-photon and di-photon samples. At the single-photon sample, we quantify the photon conversion rate, the differential reconstruction efficiency and energy resolution, and the identification performance. Using di-photon samples, our analysis shows that the CEPC baseline detector reaches a relative mass resolution of 1.7 - 2.2% of the Higgs boson at the $H\toγγ$ sample, and can reconstruct the $π^0$ with energy as high as 20 - 30 GeV. We also investigate the impact of geometry defects on photon energy resolution and discuss the possible corrections according to the reconstructed photon position.

physics.ins-det

An Immersed Discontinuous Galerkin Method for Compressible Navier-Stokes Equations on Unstructured Meshes

We introduce an immersed high-order discontinuous Galerkin method for solving the compressible Navier-Stokes equations on non-boundary-fitted meshes. The flow equations are discretised with a mixed discontinuous Galerkin formulation and are advanced in time with an explicit time marching scheme. The discretisation meshes may contain simplicial (triangular or tetrahedral) elements of different sizes and need not be structured. On the discretisation mesh the fluid domain boundary is represented with an implicit signed distance function. The cut-elements partially covered by the solid domain are integrated after tessellation with the marching triangle or tetrahedra algorithms. Two alternative techniques are introduced to overcome the excessive stable time step restrictions imposed by cut-elements. In the first approach the cut-basis functions are replaced with the extrapolated basis functions from the nearest largest element. In the second approach the cut-basis functions are simply scaled proportionally to the fraction of the cut-element covered by the solid. To achieve high-order accuracy additional nodes are introduced on the element faces abutting the solid boundary. Subsequently, the faces are curved by projecting the introduced nodes to the boundary. The proposed approach is verified and validated with several two- and three-dimensional subsonic and hypersonic low Reynolds number flow applications, including the flow over a cylinder, a space capsule and an aerospace vehicle.

math.NA

Two-Gap Superconductivity in CaFe_{0.88}Co_{0.12}AsF Revealed by Temperature Dependence of the Lower Critical Field H_{c1}^c(T)

Gap symmetry and structure are crucial issues in understanding the superconducting mechanism of unconventional superconductors. Here we report an in-depth investigation on the out-of-plane lower critical field $H_{c1}^{c}$ of fluorine-based 1111 system superconductor CaFe$_{0.88}$Co$_{0.12}$AsF with $T_c$ = 21 K. A pronounced two-gap feature is revealed by the kink in the temperature dependent $H_{c1}^c(T)$ curve. The magnitudes of the two gaps are determined to be $Δ_1$ = 0.86 meV and $Δ_2$ = 4.48 meV, which account for 74% and 26% of the total superfluid density respectively. Our results suggest that the local antiferromagnetic exchange pairing picture is favored compared to the Fermi surface nesting scenario.

cond-mat.supr-con

Lattice frustration in spin-orbit Mott insulator Sr3Ir2O7 at high pressure

The intertwined charge, spin, orbital, and lattice degrees of freedom could endow 5d compounds with exotic properties. Current interest is focused on electromagnetic interactions in these materials, whereas the important role of lattice geometry remains to be fully recognized. For this sake, we investigate pressure-induced phase transitions in the spin-orbit Mott insulator Sr3Ir2O7 with Raman, electrical resistance, and x-ray diffraction measurements. We reveal an interesting magnetic transition coinciding with a structural transition at 14.4 GPa, but without a concurrent insulator-metal transition. The conventional correlation between magnetic and Mott insulating states is thereby absent. The observed softening of the one-magnon mode can be explained by a reduced tetragonal distortion, while the actual magnetic transition is associated with tilting of the IrO6 octahedra. This work highlights the critical role of lattice frustration in determining the high-pressure phases of Sr3Ir2O7. The ability to control electromagnetic properties via manipulating the crystal structure with pressure promises a new way to explore new quantum states in spin-orbit Mott insulators.

cond-mat.str-el

Unravelling the mechanism of the semiconducting-like behavior and its relation to superconductivity in (CaFe$_{1-x}$Pt$_{x}$As)$_{10}$Pt$_{3}$As$_{8}$

The temperature-dependence of the in-plane optical properties of (CaFe$_{1-x}$Pt$_{x}$As)$_{10}$Pt$_{3}$As$_{8}$ have been investigated for the undoped ($x=$0) parent compound, and the optimally-doped ($x=$0.1) superconducting material ($T_{c}\simeq$ 12 K) over a wide frequency range. The optical conductivity has been described using two free-carrier (Drude) components, in combination with oscillators to describe interband transitions. At room temperature, the parent compound may be described by a strong, broad Drude term, as well as a narrow, weaker Drude component. Below the structural and magnetic transitions at $\simeq$ 96 and 83 K, respectively, strength is transferred from the free-carrier components into a bound excitation at $\simeq$ 1000 cm$^{-1}$, and the material exhibits semiconducting-like behavior. In the optimally-doped sample, at room temperature the optical properties are again described by narrow and broad Drude responses comparable to the parent compound; however, below $T^\ast \simeq$ 100 K, strength from the narrow Drude is transferred into a newly-emergent low-energy peak at $\simeq$ 120 cm$^{-1}$, which arises from a localization process, resulting in semiconducting-like behavior. Interestingly, below $T_{c}$, this peak also contributes to the superfluid weight, indicating that some localized electrons condense into Cooper pairs; this observation may provide insight into the pairing mechanism in iron-based superconductors.

cond-mat.supr-con

Diffusion-controlled Alloying of Single-phase Multi-principal Covalent Transition Metal Carbides with Enhanced Damage tolerance and Exceptional Thermal Properties

Multicomponent alloying has displayed extraordinary potential for producing exceptional structural and functional materials. However, the synthesis of single-phase, multi-principal covalent compounds remains a challenge. Here we present a diffusion-controlled alloying strategy for the successful realization of covalent multi-principal transition metal carbides (MPTMCs) with a single face-centered cubic (FCC) phase. The increased interfacial diffusion promoted by the addition of a nonstoichiometric compound leads to rapid formation of the new single phase at much lower sintering temperature. Direct atomic-level observations via scanning transmission electron microscopy demonstrate that MPTMCs are composed of a single phase with a random distribution of all cations, which holds the key to the unique combinations of improved fracture toughness, superior Vickers hardness, and extremely lower thermal diffusivity achieved in MPTMCs. The present discovery provides a promising approach toward the design and synthesis of next-generation high-performance materials.

cond-mat.mtrl-sci

A machine learning method to separate cosmic ray electrons from protons from 10 to 100 GeV using DAMPE data

DArk Matter Particle Explorer (DAMPE) is a general purpose high energy cosmic ray and gamma ray observatory, aiming to detect high energy electrons and gammas in the energy range 5 GeV to 10 TeV and hundreds of TeV for nuclei. This paper provides a method using machine learning to identify electrons and separate them from gammas,protons,helium and heavy nuclei with the DAMPE data from 2016 January 1 to 2017 June 30, in energy range from 10 to 100 GeV.

astro-ph.IM

Universal linear-temperature resistivity: possible quantum diffusion transport in strongly correlated superconductors

The strongly correlated electron fluids in high temperature cuprate superconductors demonstrate an anomalous linear temperature ($T$) dependent resistivity behavior, which persists to a wide temperature range without exhibiting saturation. As cooling down, those electron fluids lose the resistivity and condense into the superfluid. However, the origin of the linear-$T$ resistivity behavior and its relationship to the strongly correlated superconductivity remain a mystery. Here we report a universal relation $dρ/dT=(μ_0k_B/\hbar)λ^2_L$, which bridges the slope of the linear-$T$-dependent resistivity ($dρ/dT$) to the London penetration depth $λ_L$ at zero temperature among cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ and heavy fermion superconductors CeCoIn$_5$, where $μ_0$ is vacuum permeability, $k_B$ is the Boltzmann constant and $\hbar$ is the reduced Planck constant. We extend this scaling relation to different systems and found that it holds for other cuprate, pnictide and heavy fermion superconductors as well, regardless of the significant differences in the strength of electronic correlations, transport directions, and doping levels. Our analysis suggests that the scaling relation in strongly correlated superconductors could be described as a hydrodynamic diffusive transport, with the diffusion coefficient ($D$) approaching the quantum limit $D\sim\hbar/m^*$, where $m^*$ is the quasi-particle effective mass.

cond-mat.supr-con

Formation of As-As Bond and Its Effect on Absence of Superconductivity in Collapsed Tetragonal Phase of Ca0.86Pr0.14Fe2As2 : An Optical Spectroscopy Study

The temperature dependence of in plane optical conductivity has been investigated for Ca0.86Pr0.14Fe2As2 which shows a structural transition from tetragonal (T) to collapsed tetragonal(cT) phase at TcT=73 K. Upon entering the cT phase, drastic change characterized by the formation of a midinfrared peak near 3200 cm-1(0.4 eV) in the optical conductivity is observed.Analysis of the spectral weight reveals reduced electron correlation after the cT phase transition.Based on the calculated band structure and simulated optical conductivity, we attribute the new feature around 0.4 eV to the formation of interlayer As-As bond. The As-As bond strongly affects the Fe-As hybridizations, and in turn, drastically changes the Ca0.86Pr0.14Fe2As2 into a nonmagnetic Fermi liquid system without bulk superconductivity in the cT phase.

cond-mat.supr-con

On-orbit calibration of soft X-ray detector on Chang'E-2 satellite

X-ray spectrometer is one of the satellite payloads on Chang'E-2 satellite. The soft X-ray detector is one of the device on X-ray spectrometer which is designed to detect the major rock-forming elements within 0.5-10keV range on lunar surface. In this paper, energy linearity and energy resolution calibration is done using a weak Fe55 source, while temperature and time effect is considered not take big error. The total uncertainty is estimated to be within 5% after correction.

physics.ins-det