arXiv subjects

H. Xie

Publications and source records attributed to H. Xie.

At least 19 recordsLinked to original sources

arXiv2026

SKINOPATHY AI: Smartphone-Based Ophthalmic Screening and Longitudinal Tracking Using Lightweight Computer Vision

Early ophthalmic screening in low-resource and remote settings is constrained by access to specialized equipment and trained practitioners. We present SKINOPATHY AI, a smartphone-first web application that delivers five complementary, explainable screening modules entirely through commodity mobile hardware: (1) redness quantification via LAB a* color-space normalization; (2) blink-rate estimation using MediaPipe FaceMesh Eye Aspect Ratio (EAR) with adaptive thresholding; (3) pupil light reflex characterization through Pupil-to-Iris Ratio (PIR) time-series analysis; (4) scleral color indexing foricterus and anemia proxies via LAB/HSV statistics; and (5) iris-landmark-calibrated lesion encroachment measurement with millimeter-scale estimates and longitudinal trend tracking. The system is implemented as a React/FastAPI stack with OpenCV and MediaPipe, MongoDB-backed session persistence, and PDF report generation. All algorithms are fully deterministic, privacy-preserving, and designed for non-diagnostic consumer triage. We detail system architecture, algorithm design, evaluation methodology, clinical context, and ethical boundaries of the platform. SKINOPATHY AI demonstrates that multi-signal ophthalmic screening is feasible on unmodified smartphones without cloud-based AI inference, providing a foundation for future clinically validated mobile ophthalmoscopy tools.

cs.CV↗

arXiv2026

AI-Driven Three-Dimensional Reconstruction and Quantitative Analysis for Burn Injury Assessment

Accurate, reproducible burn assessment is critical for treatment planning, healing monitoring, and medico-legal documentation, yet conventional visual inspection and 2D photography are subjective and limited for longitudinal comparison. This paper presents an AI-enabled burn assessment and management platform that integrates multi-view photogrammetry, 3D surface reconstruction, and deep learning-based segmentation within a structured clinical workflow. Using standard multi-angle images from consumer-grade cameras, the system reconstructs patient-specific 3D burn surfaces and maps burn regions onto anatomy to compute objective metrics in real-world units, including surface area, TBSA, depth-related geometric proxies, and volumetric change. Successive reconstructions are spatially aligned to quantify healing progression over time, enabling objective tracking of wound contraction and depth reduction. The platform also supports structured patient intake, guided image capture, 3D analysis and visualization, treatment recommendations, and automated report generation. Simulation-based evaluation demonstrates stable reconstructions, consistent metric computation, and clinically plausible longitudinal trends, supporting a scalable, non-invasive approach to objective, geometry-aware burn assessment and decision support in acute and outpatient care.

cs.CV↗

arXiv2025

Solar Cycle Variation of Sustained Gamma-ray Emission Events from the Sun and Related Energetic Events

The sustained gamma ray emission (SGRE) from the Sun is one of the fascinating high energy phenomena closely related to the acceleration of protons to energies >300 MeV. Here we report on the solar cycle variation of SGRE events based on observations from Fermi's Large Area Telescope (LAT). This report covers solar cycles (SCs) 24 and 25 during which Fermi has been operating. Since SGRE events are closely related to solar energetic particle (SEP) events and interplanetary type II radio bursts caused by fast and wide coronal mass ejections (CMEs), we consider these phenomena as well. Many studies have shown that SC 25 is similar or slightly stronger than SC 24. The number of SEP events, GLE events, IP type II bursts, and fast and wide CMEs confirm this conclusion. However, the number of SGRE events observed by Fermi LAT has diminished significantly in SC 25 relative to SC 24. One of the issues has been the reduced coverage of the Sun since 2018 due to a mechanical problem with a solar array of the Fermi mission. By identifying the Fermi LAT gaps and the number of energetic events (fast and wide CMEs, interplanetary type II bursts) we conclude that about three times more SGRE events must have occurred than the 15 events observed by Fermi.

astro-ph.HE↗

arXiv2024

High Performance Operation of a Direct-Current and Superconducting Radio-Frequency Combined Photocathode Gun

Superconducting radio-frequency (SRF) guns are promising candidates to deliver high brightness continuous-wave (CW) electron beams for new generations of coherent linac light sources, ultrafast electron diffractions, MeV pulsed beam applications, etc. To solve the compatibility problem of semiconductor photocathodes, a hybrid gun combining a direct-current gap and an SRF cavity has been developed. The gun, employing K2CsSb photocathodes driven by a green laser, has been brought into stable CW operation with a dark current below 100 pA, delivering electron beams at an energy gain of 2.4 MeV, an electron bunch charge of 100 pC, and a repetition rate of 1 MHz. A normalized beam emittance of 0.54 mm-mrad has been achieved at the bunch charge of 100 pC and peak current of about 6 A. CW operation at 81.25 MHz repetition rate has also been tested with the maximum average beam current reaching 3 mA.

physics.acc-ph↗

arXiv2024

Intense Geomagnetic Storms during Solar Cycles 23-25

Intense geomagnetic storms are characterized by a minimum value of the Dst index at or below -100 nT. It is well known that these storms are caused by the southward magnetic fields in coronal mass ejections (CMEs) and corotating interaction regions (CIRs). While CIR storms are confined to Dst values at or above -150 nT, CME storms can reach Dst -500 nT or lower. In this report, we illustrate the need to understand the storm evolution based on solar source and solar wind parameters using a recent storm (2023 April 24) by way of providing the motivation to catalog such events for a better understanding of the main phase time structure of geomagnetic storms

astro-ph.SR↗

arXiv2023

Implementation of Multiple-Step Quantized STDP Based on Novel Memristive Synapses

Memristors have been widely studied as artificial synapses in neuromorphic circuits, due to their functional similarity with biological synapses, low operating power, and high integration density. In this work, a memristive synapse, composed of four memristors and two resistors, for SNN is designed and utilized for a neuron circuit implementing the robust spike-timing dependent plasticity learning. The synapse can be either excitatory or inhibitory by rationally arranging the resistors in the circuit. This is the first of its kind, enabling Hebbian and anti-Hebbian training without requiring additional processing of neural signals. Then, a neuron circuit is designed based on the proposed synapses. The robustness and compatibility of this neuron circuit are greatly enhanced by employing the clock-based square-wave pulsed to transmit spikes and modulate the synaptic weight. To study the performance of proposed synapses and circuit, simulations based on behavior models are carried out in the MATLAB Simulink and Simscape. Specially, a memristor model with balanced flexibility, efficiency, convergence, and emulation performance, is developed through including the nonlinear Joule effect. Using this memristor model in pattern learning, the influence of weak signal-induced weight variation on circuit performance can be rigorously assessed. This proposed circuit could give some inspiration for combining the analog memristive synapse and leaky integrate-and-fire neuron with digital control units, prompting their development as edge computing devices.

cs.ET↗

arXiv2023

Solar Energetic Particle-Associated Coronal Mass Ejections Observed by the Mauna Loa Solar Observatory Mk3 and Mk4 Coronameters

We report on the first comprehensive study of the coronal mass ejections (CMEs) associated with $\sim$25 MeV solar energetic proton (SEP) events in 1980-2013 observed in the low/inner corona by the Mauna Loa Solar Observatory (MLSO) Mk3 and Mk4 coronameters. Where possible, these observations are combined with spacebased observations from the Solar Maximum Mission C/P, P78-1 SOLWIND or SOHO/LASCO coronagraphs. The aim of the study is to understand directly-measured (rather than inferred from proxies) CME motions in the low to middle corona and their association with SEP acceleration, and hence attempt to identify early signatures that are characteristic of SEP acceleration in ground-based CME observations that may be used to warn of impending SEP events. Although we find that SEP events are associated with CMEs that are on average faster and wider than typical CMEs observed by MLSO, a major challenge turns out to be determining reliable estimates of the CME dynamics in the low corona from the 3-minute cadence Mk3/4 observations since different analysis techniques can produce inconsistent results. This complicates the assessment of what early information on a possible SEP event is available from these low coronal observations

astro-ph.SR↗

arXiv2023

Speed and Acceleration of CMEs Associated with Sustained Gamma-Ray Emission Events Observed by Fermi/LAT

The sustained gamma-ray emission (SGRE) from the Sun is a prolonged enhancement of >100 MeV gamma-ray emission that extends beyond the flare impulsive phase.The origin of the >300 MeV protons resulting in SGRE is debated, both flares and shocks driven by coronal mass ejections (CMEs) being the suggested sites of proton acceleration. We compared the near-Sun acceleration and space speed of CMEs with 'Prompt' and 'Delayed' (SGRE) gamma-ray components (Ajello et al. 2021). We found that 'Delayed'-component-associated CMEs have higher initial acceleration and space speed than 'Prompt-only'-component-associated CMEs. We selected halo CMEs (HCMEs) associated with type II radio bursts (shock-driving HCMEs) and compared the average acceleration and space speed between HCME populations with or without SGRE events, major solar energetic particle (SEP) events, metric, or decameter-hectometric (DH) type II radio bursts. We found that the SGRE-producing HCMEs associated with a DH type II radio burst and/or a major SEP event have higher space speeds and especially initial accelerations than those without an SGRE event. We estimated the radial distance and speed of the CME-driven shocks at the end time of the 2012 January 23 and March 07 SGRE events using white-light images of STEREO Heliospheric Imagers and radio dynamic spectra of Wind WAVES. The shocks were at the radial distances of 0.6-0.8 au and their speeds were high enough (~975 km s$^{-1}$ and ~750 km s$^{-1}$, respectively) for high-energy particle acceleration. Therefore, we conclude that our findings support the CME-driven shock as the source of >300 MeV protons.

astro-ph.HE↗

arXiv2023

Nanoscale Sn off-centering behind low thermal conductivity in SnSe thermoelectric

The local atomic structure of SnSe was characterized across its orthorhmbic-to-orthorhombic structural phase transition using x-ray pair distribution function analysis. Substantial Sn off-centering distortions persist in the high symmetry high temperature phase, with symmetry different from that of ordered distortions below the transition. The analysis implies that the transition is neither order-disorder nor displacive, but rather a complex crossover where the character of coupling changes from 3D-like at low temperature to 2D-like at high temperature. Robust ferro-coupled SnSe intra-layer distortions suggest a ferroelectric-like instability as the driving force. Complex local Sn off-centering is integral to the ultra-low lattice thermal conductivity mechanism in SnSe.

cond-mat.mtrl-sci↗

arXiv2022

What is Unusual about the Third Largest Geomagnetic Storm of Solar Cycle 24?

We report on the solar and interplanetary (IP) causes of the third largest geomagnetic storm (2018 August 26) in solar cycle 24. The underlying coronal mass ejection (CME) originating from a quiescent filament region becomes a 440 km/s magnetic cloud (MC) at 1 au after ~5 days. The prolonged CME acceleration (for about 24 hrs) coincides with the time profiles of the post-eruption arcade intensity and reconnected flux. Chen et al. (2019) obtain lower speed since they assumed that the CME does not accelerate after about 12 hrs. The presence of multiple coronal holes near the filament channel and the high-speed wind from them seem to have the combined effect of producing complex rotation in the corona and IP medium resulting in a high-inclination MC. The Dst time profile in the main phase steepens significantly (rapid increase in storm intensity) coincident with the density increase (prominence material) in the second half of the MC. Simulations using the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model shows that a higher ring current energy results from larger dynamic pressure in MCs. Furthermore, the Dst index is highly correlated with the main-phase time integral of the ring current injection that includes density, consistent with the simulations. A complex temporal structure develops in the storm main phase if the underlying MC has a complex density structure during intervals of southward interplanetary magnetic field. We conclude that the high intensity of the storm results from the prolonged CME acceleration, complex rotation, and the high density in the 1-au MC.

astro-ph.SR↗

arXiv2022

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

The Common Origin of High-energy Protons in Solar Energetic Particle Events and Sustained Gamma-ray Emission from the Sun

We report that the number of > 500 MeV protons (Ng) inferred from sustained gamma ray emission (SGRE) from the Sun is significantly correlated with that of protons propagating into space (NSEP) as solar energetic particles (SEPs). Under the shock paradigm for SGRE, shocks driven by coronal mass ejections (CMEs) accelerate high-energy protons sending them toward the Sun to produce SGRE by interacting with the atmospheric particles. Particles also escape into the space away from the Sun to be detected as SEP events. Therefore, the significant NSEP vs. Ng correlation (correlation coefficient 0.77) is consistent with the common shock origin for the two proton populations. Furthermore, the underlying CMEs have properties akin to those involved in ground level enhancement (GLE) events indicating the presence of high-energy (up to GeV) particles required for SGRE. We show that the observed gamma-ray flux is an underestimate in limb events (central meridian distance > 60 degrees) because SGRE sources are partially occulted when the emission is spatially extended. With the assumption that the SEP spectrum at the shock nose is hard and that the 100 MeV particles are accelerated throughout the shock surface (half width in the range 60 to 120 degrees) we find that the latitudinal widths of SEP distributions are energy dependent with the smallest width at the highest energies. Not using the energy-dependent width results in an underestimate of NSEP in SGRE events occurring at relatively higher latitudes. Taking these two effects into account removes the apparent lack of NSEP - Ng correlation reported in previous studies.

astro-ph.SR↗

arXiv2020

Connection between Bandgap Evolution and Strains of Octahedron in non-Perovskite \b{eta}-MnO2 under pressure: A First Principle Study

Lattice distortion due to octahedral rotation and distortion are high focussed, and it produces profound effect on a material's properties, such as its bandgap, magnetism and optical properties etc. Rutile-type \b{eta}-MnO2 is a wide used non-Perovskite magnetic material with octahedrons. We systematically studied its stability, electronic structures, magnetic structures, and optical properties within 0-100 GPa with density-functional theory (DFT). We find that the competition between bondlength and bonding angle leads its bandgap enlarging or shrinking within in the Pnnm phase with increasing pressure, because of the interaction of Mn-d and O-p states. We also find same pressure indused bandgap evolutions in the Pnnm phases of SiO2, GeO2, SnO2 and PbO2. The different ways of octahedral connection in Pnnm phase and Pa-3 phase leads to an interesting pressure-induced bandgap enlarging. And in the Pa-3 phase, the band gap can be tuned to 1.34 eV by pressure to meet the Shockley-Queisser limit. Moreover the two high pressure phases can be quenched to ambient pressure. Together with its mechanical, optical and antiferromagnetic properties, it ensures MnO2's application as a photovoltaic material for all working condition with multi-purpose. This study extends MnO2's application and give some new mechanism of pressure induced bandgap enlargement.

cond-mat.mtrl-sci↗

arXiv2020

The Coronal Mass Ejection Visibility Function of Modern Coronagraphs

We analyze the detection capability of Coronal Mass Ejections (CMEs) for all currently operating coronagraphs in space. We define as CMEs events that propagate beyond 10 solar radii with morphologies broadly consistent with a magnetic flux rope presence. We take advantage of multi-viewpoint observations over five month-long intervals, corresponding to special orbital configurations of the coronagraphs aboard the STEREO and SOHO missions. This allows us to sort out CMEs from other outward-propagating features (e.g. waves or outflows), and thus to identify the total number of unique CMEs ejected during those periods. We determine the CME visibility functions of the STEREO COR2-A/B and LASCO C2/C3 coronagraphs directly as the ratio of observed to unique CMEs. The visibility functions range from 0.71 to 0.92 for a 95% confidence interval. By comparing detections between coronagraphs on the same spacecraft and from multiple spacecraft, we assess the influence of field of view, instrument performance, and projection effects on the CME detection ability without resorting to proxies, such as flares or radio bursts. We find that no major CMEs are missed by any of the coronagraphs, that a few slow halo-like events may be missed in synoptic cadence movies and, that narrow field of view coronagraphs have difficulties discriminating between CMEs and other ejections leading to false detection rates. We conclude that CME detection can only be validated with multi-viewpoint imaging-- two coronagraphs in quadrature offer adequate detection capability. Finally, we apply the visibility functions to observed CME rates resulting in upward corrections of 40%.

astro-ph.SR↗

arXiv2020

Effect of the Weakened Heliosphere in Solar Cycle 24 on the Properties of Coronal Mass Ejections

Solar cycle (SC) 24 has come to an end by the end of 2019, providing information on two full cycles to understand the manifestations of SC 24, the smallest cycle in the Space Age that has resulted in a weak heliospheric state indicated by the reduced pressure. The backreaction of the heliospheric state is to make the coronal mass ejections (CMEs) appear physically bigger than in SC 23, but their magnetic content has been diluted resulting in a lower geoeffectiveness. The heliospheric magnetic field is also lower in SC 24, leading to the dearth of high-energy solar energetic particle (SEP) events. These space weather events closely follow fast and wide (FW) CMEs. All but FW CMEs are higher in number in SC 24. The CME rate vs. sunspot number (SSN) correlation is high in both cycles but the rate increases faster in SC 24. We revisit the study of limb CMEs (those with source regions within 30 degrees from the limb) previously studied over partial cycles. We find that limb CMEs are slower in SC 24 as in the general population but wider. Limb halo CMEs follow the same trend of slower SC-24 CMEs. However, the SC-24 CMEs become halos at a shorter distance from the Sun. Thus, slower CMEs becoming halos sooner is a clear indication of the backreaction of the weaker heliospheric state on CMEs. We can further pin down the heliospheric state as the reason for the altered CME properties because the associated flares have similar distributions in the two cycles, unaffected by the heliospheric state.

astro-ph.SR↗

arXiv2020

Source of Energetic Protons in the 2014 September 1 Sustained Gamma-ray Emission Event

We report on the source of greater than 300 MeV protons during the SOL2014-09-01 sustained gamma-ray emission (SGRE) event based on multi-wavelength data from a wide array of space- and ground-based instruments. Based on the eruption geometry we provide concrete explanation for the spatially and temporally extended γ-ray emission from the eruption. We show that the associated flux rope is of low inclination (roughly oriented in the east-west direction), which enables the associated shock to extend to the frontside. We compare the centroid of the SGRE source with the location of the flux rope leg to infer that the high-energy protons must be precipitating between the flux rope leg and the shock front. The durations of the SOL2014-09-01 SGRE event and the type II radio burst agree with the linear relationship between these parameters obtained for other SGRE events with duration exceeding 3 hrs. The fluence spectrum of the SEP event is very hard, indicating the presence of high-energy (GeV) particles in this event. This is further confirmed by the presence of an energetic coronal mass ejection (CME) with a speed more than 2000 km/s, similar to those in ground level enhancement (GLE) events. The type II radio burst had emission components from metric to kilometric wavelengths as in events associated with GLE events. All these factors indicate that the high-energy particles from the shock were in sufficient numbers needed for the production of γ-rays via neutral pion decay.

astro-ph.SR↗

arXiv2019

On the Shock Source of Sustained Gamma-Ray Emission from the Sun

It has recently been shown that the spatially and temporally extended gamma-ray emission in solar eruptions are caused by greater than 300 MeV protons precipitating on the Sun from shocks driven by coronal mass ejections (CMEs). The gamma-rays result from the decay of neutral pions produced in the proton-proton interaction when the greater than 300 MeV protons collide with those in the chromosphere. The evidence comes from the close correlation between the durations of the sustained gamma-ray emission (SGRE) and the associated interplanetary (IP) type II radio bursts. In this paper, we provide further evidence that support the idea that protons accelerated in IP shocks driven by CMEs propagate toward the Sun, precipitate in the chromosphere to produce the observed SGRE. We present the statistical properties of the SGRE events and the associated CMEs, flares, and type II radio bursts. It is found that the SGRE CMEs are similar to those associated with ground level enhancement events. The CME speed is well correlated with the SGRE fluence. High CME speed is an important requirement for the occurrence of SGRE, while the flare size is not. Based on these results, we present a schematic model illustrating the spatially and temporally extended nature of SGRE related to the CME flux rope-shock structure.

astro-ph.SR↗

arXiv2018

Fermi, Wind, and SOHO Observations of Sustained Gamma-Ray Emission from the Sun

We report on the linear relationship between the durations of two types of electromagnetic emissions associated with shocks driven by coronal mass ejections: sustained gamma-ray emission (SGRE) and interplanetary type II radio bursts. The relationship implies that shocks accelerate about 10 keV electrons (for type II bursts) and greater than 300 MeV protons (for SGRE) roughly over the same duration. The SGRE events are from the Large Area Telescope (LAT) on board the Fermi satellite, while the type II bursts are from the Radio and Plasma Wave Experiment (WAVES) on board the Wind spacecraft. Here we consider five SGRE events that were not included in a previous study of events with longer duration (greater than 5 hours). The five events are selected by relaxing the minimum duration to 3 hours. We found that some SGRE events had a tail that seems to last until the end of the associated type II burst. We pay special attention to the 2011 June 2 SGRE event that did not have a large solar energetic particle event at Earth or at the STEREO spacecraft that was well connected to the eruption. We suggest that the preceding CME acted as a magnetic barrier that mirrored protons back to Sun.

astro-ph.SR↗