arXiv subjects

X. Zhang

Publications and source records attributed to X. Zhang.

At least 19 recordsLinked to original sources

arXiv2026

Electrochemical functionalization of graphene rationalized by Hammett and Swain-Lupton parameters

Graphene's sp^{2}-bonded carbon lattice makes it exceptionally resistant to covalent functionalization, with existing approaches relying on chemically specific and often harsh methods, fragmenting our understanding of its reactivity. Here we show that electric fields of approximately 1 V nm^{-1} in non-aqueous electrolytes enable the electrochemical functionalization of monolayer graphene with a broad range of substituents, leading to two-order-of-magnitude conductance modulation stable over 5,000 cycles and semi-reversible electronic conductor-insulator transitions. Analysis of the oxidation potentials across substituents reveals trends governed by classical descriptors. Species forming localised σ bonds display increasing oxidation potentials with the meta-Hammett constant (σ_m), whereas substituents interacting via delocalised π orbitals follow an inverse dependence on the modified Swain-Lupton resonance parameter (R). These relationships indicate that graphene's oxidation potential increases with the electron-withdrawing strength of the substituent. Our results provide new insights into the electrochemical activity of inert materials under strong electric fields.

physics.chem-ph↗

arXiv2026

Rare Blue-core BCGs as Optical Signatures of ICM Cooling

Blue cores in brightest cluster galaxies (BCGs) trace recent central activity associated with cooling cluster atmospheres. We search for blue cores at $z<0.6$ in five eROSITA all-sky surveys using X-ray data, optical imaging, and optical spectroscopy. We identify 379 blue-core BCGs among 11352 systems (3.3%), although contamination increases toward higher redshift. Of these, 98 (0.86%) are X-ray bright. Their defining signature is a central $g-r$ color at least 0.2 mag bluer than the reference population within $a=20$ kpc before returning to the normal BCG envelope. Ha emission equivalent width correlates strongly with the blue continuum excess, consistent with young stellar components comprising ~0.1-1% of pre-existing stellar mass. Line ratios indicate widespread LINER-like excitation, with a larger star-forming contribution in blue Ha emitters but substantial non-stellar excitation. This activity is closely linked to the thermodynamics of the host-cluster gas. At $0.1R_{500}$, cooling times decrease from BCGs without significant Ha emission to red and then blue Ha emitters. Blue BCGs preferentially occur in clusters with $L_{\rm X,300}>10^{44}$ erg s$^{-1}$; red Ha emitters also favor higher X-ray luminosities. The blue-core fraction rises with optical richness. For systems with $t_{\rm cool}(0.1R_{500})<20$ Gyr, doubling richness increases the odds of hosting a blue-core BCG by $2.45\pm0.39$. This indicates that cluster scale carries information beyond cooling time, plausibly through the amount of gas available for cooling and condensation. The scarcity of blue BCGs without significant Ha emission disfavors isolated short bursts followed by long Ha-quiet fading phases. It can instead be explained by sustained or closely recurrent star formation over timescales much longer than 100 Myr, or by Ha persisting through additional excitation mechanisms as the young stellar component fades.

astro-ph.GA↗

arXiv2026

Investigating a TeV-Halo Candidate around PSR J1928+1746 with HAWC

We present an updated High-Altitude Water Cherenkov (HAWC) analysis of the crowded Galactic-plane area near PSR J1928+1746, which was previously linked to the extended source 3HWC J1928+178. With 2904 days of HAWC data, improved event reconstruction, and a multicomponent likelihood model that includes six TeV source components and Galactic diffuse emission, we describe the region using six components and find a distinct, moderately extended source close to PSR J1928+1746. This source, HAWC J1928+1750, is detected from about 2 TeV to above 100 TeV and is well-described by a log-parabola spectrum with normalization $K = 5.0 \times 10^{-15}$ TeV$^{-1}$ cm$^{-2}$ s$^{-1}$ at 12 TeV, index $α= 2.09$, curvature $β= 0.35$, and Gaussian extension $σ= 0.19^\circ$. Interpreting the emission using diffusion-halo templates under the assumption $B = 8 μ\mathrm{G}$ yields the diffusion coefficient D(100 TeV) = $2.1 \times 10^{27}$ cm$^2$ s$^{-1}$, which is about 500 times smaller than typical interstellar diffusion values at similar energies. This suggests that particle transport around PSR J1928+1746 is strongly suppressed under the TeV-halo interpretation. The TeV spectrum is consistent with leptonic inverse-Compton emission originating from pulsar-injected electrons and positrons, which requires less than approximately 1% of the pulsar's characteristic spin-down energy. However, a hadronic contribution from the surrounding environment cannot be excluded.

astro-ph.HE↗

arXiv2026

International atomic clock comparison achieving $5\times 10^{-18}$ uncertainty

Two single-ion optical clocks, located in the United Kingdom and in Germany, are compared remotely via a 2220\,km long optical fiber link. Both clocks are based on the ${}^2S_{1/2} (F=0)\leftrightarrow {}^2F_{7/2} (F=3)$ electric octupole (E3) transition in $^{171}\text{Yb}^+$. Using more than $10^6$ seconds of measurement data, we determine a fractional frequency difference of $1.0(4.8)\times 10^{-18}$, demonstrating agreement of the independently developed systems. To our knowledge, this constitutes the first international clock comparison reaching a fractional uncertainty below $5\times 10^{-18}$, an important milestone towards an anticipated optical redefinition of the SI second. The measurement uncertainty is dominated by that of the relativistic redshift correction between the two sites, which includes time-varying gravity potential differences. We exploit the large baseline between the two clocks to search for violations of Lorentz invariance. In the absence of statistically significant modulations, we improve constraints on the Robertson-Mansouri-Sexl parameter $α$ by approximately a factor of five in the uncertainty, and provide limits on corresponding parameters within the Standard-Model Extension framework.

physics.atom-ph↗

arXiv2026

Controllable localization and manipulation of optical hollow traps by means of optical-vortex diffraction

An optical vortex (OV) is coupled with the local intensity zero and is thus a field configuration suitable for "hollow" optical traps and optical tweezers. When an incident circular OV beam experiences diffraction at a rectilinear screen edge (SE), and the conditions of weak diffraction perturbation (the SE is far enough from the beam axis) are fulfilled, the main consequence is the OV-core displacement from its initial (axial) position. Based on the model of incident Laguerre-Gaussian (LG) beam, we investigate analytically and numerically the ways of controlling the OV-core position in the diffracted-field cross section by means of changing the SE position with respect to the incident-beam axis. The results show that regulating the SE position with ~1 mcm accuracy (which is available for existing mechanical tools), controllable OV-core motion with a sub-nanometer accuracy can be realized. Possible modifications of this motion depending on the incident beam topological charge, wavefront curvature, SE properties (semitransparent screen, phase-step screen) and the distance between the diffraction plane and the observation plane are analyzed. The conditions most favorable for the micro-object trapping and manipulation are specified and discussed.

physics.optics↗

arXiv2026

The 3He(α,γ)7Be γ-ray angular distribution: measured, and calculated by effective field theory

The 3He(alpha,gamma)7Be reaction takes place in several distinct astrophysical scenarios. First, in solar hydrogen burning, 3He(alpha,gamma)7Be controls the competition between the pp-I chain, on the one hand, and the pp-II and -III chains, on the other hand. Its rate directly affects the solar model predictions for the well-measured 7Be and 8B solar neutrino fluxes, which can in principle be used as solar thermometer. Second, in Big Bang nucleosynthesis, 3He(alpha,gamma)7Be is the main production channel for primordial 7Li, the decay product of 7Be. Finally, the reaction is believed to produce radioactive 7Be in astrophysical novae. The cross section of this reaction has been studied previously using different methods, namely 7Be activation, 7Be recoil detection, and in-beam γ-ray detection. The latter studies have in many cases been performed with just one detector in close geometry. Here, for the first time a comprehensive measurement of the 3He(α,γ)7Be γ-ray angular distribution is reported. Altogether 22 high-purity germanium detectors were used, arranged at 27-145 degrees angle with respect to the beam direction. Data were taken at 442-1213 keV center-of-mass energy. In addition, one data point for the astrophysical S-factor was obtained with the activation method. The angular data are compared with the predictions from a hybrid theoretical approach, where the E1 transitions are modeled using a cluster-based effective field theory (EFT) while the M1 and E2 transitions within an EFT-inspired framework. Good agreement is found, if the interference among these multipolarities is taken into account in the theory.

nucl-ex↗

arXiv2026

TeV Gamma-Ray Emission in the DA 495 Region from HAWC Observations of J1952+2924, J1954+2837, and J1958+2848

Previous observations of the DA 495 region, which contains the pulsar wind nebula (PWN) DA 495 and other very-high-energy (VHE; $>100~\textrm{GeV}$) gamma-ray emitters, showed inconsistent results across different VHE experiments, including differences in the measured flux of DA 495 and in the number of reported sources. Our new dedicated analysis using 3071 days of HAWC data resolves these discrepancies. We identify three extended sources, HAWC J1952+2924 (DA 495), HAWC J1954+2837, and HAWC J1958+2848, all with curved spectra, and find a hint of a fourth source. For DA 495, a multi-wavelength analysis, including our results, radio, X-ray, and other gamma-ray data, reveals that its extended emission is best described by leptonic interactions with an inferred magnetic field of $B\sim10~μ\textrm{G}$ and that hadronic components are not required. On the other hand, we interpret the other two sources, which have no confirmed counterparts, as TeV halos associated with nearby pulsars, PSR J1954+2836 and PSR J1958+2846, respectively. These results reinforce the interpretation of DA 495 as a leptonic-dominated PWN and add two candidates to the growing population of TeV halos.

astro-ph.HE↗

arXiv2026

Sensitivity of fission barrier heights to nuclear matter properties

We systematically investigate the correlations between nuclear fission properties and the surface energy coefficient $a_{\rm surf}$ extracted from semi-infinite nuclear matter. To this end, we employ the covariant density functional theory based on a point-coupling energy density functional (EDF). Taking $^{240}$Pu and $^{236}$U as representative examples, we employ Gaussian-process emulators to construct the joint posterior distributions of $a_{\rm surf}$ and selected fission observables, constrained by the ground state properties of the two nuclei. The results reveal a strong correlation between $a_{\rm surf}$ and the fission barrier heights. A sensitivity analysis further shows that the height of the outer fission barrier is governed predominantly by the isoscalar-vector derivative coupling constant $δ_V$ in the point-coupling EDF, whereas that of the inner barrier is by the combined effects of $δ_V$ and several mutually correlated coupling constants.

nucl-th↗

arXiv2026

The SRG/eROSITA all-sky survey: X-ray scaling relations of galaxy groups and clusters in the western Galactic hemisphere

The soft X-ray telescope on board the SRG mission, eROSITA, has produced the largest sample to date of galaxy groups and clusters detected via their intracluster and intragroup medium emission. Scaling relations between the intrinsic properties of these systems provide valuable insight into their formation and evolution. In this work, we investigated the scaling relations between key physical properties, such as soft band X-ray luminosity, temperature, gas mass, and the low-scatter mass proxy $Y_{\rm X}$, for the galaxy groups and clusters detected in the first eROSITA All-Sky Survey (eRASS1). Our analysis fully accounts for selection effects and the redshift evolution of the observable distributions. We constructed a high-purity sample of $3061$ galaxy groups and clusters spanning the redshift range of $0.05 3$~keV, our inferred $L_{\rm X}-T$ relation is consistent with simulation models that include strong or stronger AGN feedback.

astro-ph.CO↗

arXiv2026

The SRG/eROSITA All-Sky Survey: Early dark energy and Hubble constant from the cluster mass function

The evolution of the mass function of massive galaxy clusters is a well-established probe of cosmology. Using the eROSITA X-ray instrument on board the Spectrum Roentgen Gamma (SRG) mission, the western Galactic hemisphere of eROSITA's first All-Sky Survey (eRASS1) delivers a uniformly selected and securely confirmed sample of 5259 galaxy clusters spanning $0.1 < z < 0.8$. When combined with overlapping weak lensing data from DES Year 3, KiDS, and HSC for mass calibration, this dataset enables precise tests of the standard $Λ$CDM framework and beyond. In this work, we use the $0.1 < z < 0.45$ subsample of the eRASS1 cluster catalog to place constraints on an axion-like Early Dark Energy (EDE) scenario. Such models have been proposed as a possible mechanism to alleviate the tension between early- and late-Universe measurements of the Hubble constant. In this framework, a scalar field temporarily enhances the cosmic expansion rate around the epoch of recombination before rapidly diluting at later times, leaving distinct imprints on structure growth. We leverage these signatures to present the first constraints on EDE derived from galaxy cluster number counts. Using eRASS1 number counts alone, we obtain an upper limit on the maximum EDE fraction of $f_{\rm EDE} < 0.3$, consistent with primary CMB analyses. Combining our cluster analysis with primary CMB measurements, baryon acoustic oscillations, and CMB lensing, while notably excluding distance-ladder calibration data, yields results consistent with a nonzero EDE contribution and $H_0$ values compatible with late-Universe measurements. The most significant detection, at $\sim 3.2σ$, arises from the joint analysis of the eRASS1 sample with the full set of external datasets, yielding $f_{\rm EDE} = 0.10^{+0.04}_{-0.03}$ and $H_0 = 71.4 \pm 1.4$ km/s/Mpc. [ABRIDGED]

astro-ph.CO↗

arXiv2026

Electrostatic control of Li+ density and transport rate in double-gated van der Waals devices

Ion transport in crystalline hosts is controlled by an applied potential that simultaneously sets ionic distribution and transport rate, restricting operation to a one-dimensional control space. Here we show that the transport rate of Li+ ions in double-gated van der Waals devices can be modulated while the system occupies fixed ionic-density states. We measure the ionic current along the van der Waals interfaces between hexagonal boron nitride and graphene or MoS2 while simultaneously monitoring the in-plane electronic response. The ionic current exhibits pronounced hysteresis, with plateaus marking discrete ionic-density states balanced by electronic charge, while an independently tuneable electrochemical-potential drop controls the ionic transport rate. The devices sustain over 1,000 switching cycles and function as hybrid ionic-electronic transistors capable of logic operations and memory retention, with ON/OFF ratios exceeding two orders of magnitude. This work demonstrates a two-dimensional control space for ions intercalated in layered materials.

cond-mat.mes-hall↗

arXiv2026

Apodex 1.1: Scaling Agentic Intelligence for Complex Work

General-purpose language models can reason and synthesize knowledge, but complex work also requires sustained interaction with files, information sources, and executable code, together with state maintenance, failure recovery, and verifiable delivery. We call this \emph{working capability}: sustained, verifiable progress toward a real-world objective. Apodex 1.1 develops this capability along two complementary dimensions. \emph{Environment Scaling} expands the diversity and verifiability of executable file, search, and code environments, while \emph{Agentic Coordination Scaling} trains agents to decompose long-horizon tasks, delegate parallel work, integrate asynchronous results, and replan. A shared execution harness and AgentOS maintain task state and provenance across tools and agents, and training turns environment trajectories and coordination traces into reliable behavior. Across complex professional work, finance, scientific research, mathematics, coding, and search, Apodex 1.1 reaches the leading performance band despite using a substantially smaller model than many frontier systems. The 35B-parameter Apodex 1.1 Mini further retains strong working capability in a locally deployable form. These results ground agentic intelligence in useful, verifiable work completed over time and advance our goal of building a \emph{Heavy-Duty Solver} for ambitious, long-running tasks.

cs.AI↗

arXiv2026

HAWC Study on the Ultra-High-Energy Gamma-Ray Emissions from the Pulsar Wind Nebula G32.64+0.53

Multi-TeV gamma-ray emission around eHWC J1850+001 (a source from the first HAWC catalog of gamma-ray sources emitting above 56 TeV) is spatially coincident with the pulsar wind nebula (PWN) G32.64+0.53, powered by PSR J1849-0001. The absence of counterparts in radio, optical, and GeV energy ranges, contrasted with clear detections in X-rays and very-high-energy (VHE) gamma-rays, is indicative of a non-thermal leptonic origin for the nebula. We apply a systematic analysis pipeline, including a sophisticated model for the Galactic diffuse emission, to 2860 days of data from the HAWC Observatory. Our detailed analysis confirms that the ultra-high-energy (UHE) emission originates from G32.64+0.53, and we measure its spectrum up to 270 TeV with significant emission well beyond 100 TeV. We fit the multi-wavelength observations with a time-dependent leptonic model powered by the pulsar's rotational energy, and the results establish the nebula as a leptonic PeV accelerator, capable of accelerating electrons to a maximum energy of $E_{\mathrm{cut}}\geq2.9~\mathrm{PeV}$ (95\% one-sided lower bound). The model also constrains the nebular magnetic field to $4.28 ~\mathrm{μG}$, supporting a leptonic PWN origin for the observed UHE emission.

astro-ph.HE↗

arXiv2026

Thermal or Non-thermal? Diffuse emission in the infall region of stacked galaxy groups

The faint infall regions surrounding the virial radius of galaxy groups remain largely unexplored due to their low X-ray surface brightness. Using the large statistical power of SRG/eROSITA survey observations, we present the first spectroscopic measurement of the intragroup medium (IGrM) in the infall regions of a large sample of low-mass galaxy groups ($M_{\rm tot}<1\times10^{14}\,M_{sun}$), extending to $\sim2\,R_{200m}$ (2.2 Mpc). Through spectral stacking of 827 nearby groups from the first eROSITA All-Sky Survey catalog, we detect diffuse emission and measure the thermodynamic properties of gas at densities previously inaccessible to X-ray observations. The stacked spectra are well described by a Gaussian differential emission measure model, yielding a temperature distribution with a mean temperature of $0.96_{-0.04}^{+0.05}$ keV and width of $0.28_{-0.10}^{+0.10}$ keV, and a metal abundance of $0.21_{-0.04}^{+0.06}$ A$_{sun}$, consistent with expectations for group outskirts. The inferred electron densities decrease from $(4.8\pm1.3)\times10^{-5}$cm$^{-3}$ at $(0.7-2)\,R_{500c}$ to $(5.5\pm2.0)\times10^{-6}$ cm$^{-3}$ at $(2-4)\,R_{500c}$, demonstrating eROSITA's ability to probe the low-density outskirts of galaxy groups. Residual emission in the spectra suggests the presence of an additional spectral component. While a secondary thermal interpretation requires an unexpectedly hot, metal-poor plasma, a non-thermal inverse Compton model provides an equally plausible explanation, contributing $\sim30\%$ of the thermal flux. Assuming that the additional component is produced by inverse Compton emission from a common population of relativistic electrons, the inferred magnetic field strength would be in the sub-$μ$G regime.

astro-ph.HE↗

arXiv2026

Langmuir probe and infrared thermography measurements of wide and narrow heat flux profiles in the ST40 tokamak

Very narrow heat flux profiles have been observed on ST40 with decay lengths in the near scrape-off-layer (SOL) of $λ_{q,near}<$~1~mm in H-mode plasmas. Measurements from divertor Langmuir probes are compared with an infrared (IR) thermography system for upper-single null diverted plasmas in L-mode and ELM-free H-mode. SOL current to the grounded divertor targets is measured from the Langmuir probes with profiles exhibiting a similar exponential decay to $λ_{q,near}$ suggesting the near SOL heat flux is related to enhanced electron current to the divertor. Inclusion of electron current contributions to the heat flux transmission coefficient is crucial in capturing similar narrow profiles to those from the IR thermography system. Ongoing upgrades to ST40 will enable more investigations on SOL power decay lengths on inboard and outboard targets in double and single null configurations.

physics.plasm-ph↗

arXiv2026

Sustainable Air-Ground Integrated Coverage Networks: ISCC Architecture, Technologies, and Testbed

The rapid emergence of sixth-generation (6G) networks and the low-altitude economy has accelerated the evolution of wireless infrastructures toward air-ground integrated coverage networks (AGICNs), which seamlessly fuse terrestrial and aerial communication resources. However, existing AGICN studies primarily focus on coverage enhancement, while ignoring sustainability. Pursuing sustainable AGICNs introduces new challenges due to the multidimensional resource coupling across heterogeneous air-ground segments. In view of this, this paper presents a comprehensive survey and tutorial on sustainable AGICNs, aiming to balance coverage capacity with carbon efficiency in low-altitude economies. An integrated sensing, communication, and computation (ISCC)-driven architecture, which enables dynamic resource orchestration through closed-loop control, is proposed. We thus introduce a multi-dimensional sustainability metric system, which covers operational efficiency, task-oriented performance, and full lifecycle carbon emissions, to quantify energy and carbon footprints. We review enabling technologies, including artificial intelligence, hybrid precoding, integrated sensing and communication, and simultaneous wireless information and power transfer, and discuss their integration into the ISCC framework to minimize energy consumption while maintaining robust coverage. Experimental results on a real-world testbed demonstrate a 20% reduction in power consumption while achieving over 90% coverage probability, highlighting the feasibility of sustainable AGICNs for future green networks.

cs.IT↗

arXiv2026

Gamma Backgrounds for Experiments at the High Flux Isotope Reactor

This article describes the deployment of a germanium detector at Oak Ridge National Lab's High Flux Isotope Reactor (HFIR) for the purpose of understanding the energy and spatial distribution of the gamma field in the experiment hall where the Precision Reactor Oscillation and Spectrum Experiment (PROSPECT) took data and future neutrino experiments could be located. The sources from both the reactor and the neutron beamlines are described in detail, along with their temporal variations due to reactor power and their spatial variations due to the geometry of the beamlines and building materials in the vicinity. Additionally, a shielding study was performed to assess the amount that backgrounds in tens of keV range can be mitigated. This work helps inform backgrounds for future experiments at reactors such as IBD-based neutrino measurements and CEvNS measurements.

hep-ex↗

arXiv2026

Simulation-Based Inference for Cluster Cosmology with Set-Based Neural Network Architectures

The unprecedented statistical power of galaxy cluster catalogs from the SRG (Spectrum Roentgen Gamma)/eROSITA All-Sky Survey provides a unique opportunity to place stringent constraints on cosmological models through measurements of structure growth. Fully exploiting the potential of these large X-ray-selected cluster samples, however, requires robust statistical frameworks that accurately connect observable quantities to the underlying cosmological parameters. We develop and implement a simulation-based inference (SBI) framework for cosmological parameter estimation using a realistic mock-generation pipeline calibrated on eRASS1 simulations. Synthetic galaxy cluster catalogs are propagated through the survey selection function to produce mock eRASS1 observations that reproduce the data's statistical properties. At the core of the method lies a set-based neural network (GNN on sets) that encodes information from individual clusters and is coupled to a masked autoregressive flow for flexible posterior density estimation. This approach enables the use of the full cluster-level information content without compressing the observables into binned summary statistics. Our framework recovers the input cosmologies within the inferred uncertainties, and passes calibration tests, demonstrating robustness in the presence of realistic survey effects. We obtain mock constraints of 11.5% on $Ω_m$ and 4.4% on $σ_8$ averaged over a suite of simulated cluster catalogs matching the effective sample size of the data set (3,259 clusters). We achieve a precision comparable to that obtained with traditional MCMC analyses based on substantially larger cluster samples. The framework is readily extensible to more complex forward models and additional observables. This work highlights the potential of SBI methods for next-generation large-scale structure analyses with forthcoming X-ray cluster surveys.

astro-ph.CO↗