arXiv subjects

C. Xu

Publications and source records attributed to C. Xu.

At least 19 recordsLinked to original sources

arXiv2024

Single-molecule Surface-Induced Fluorescence Attenuation Based on Reduced Graphene Oxide

Single-molecule surface-induced fluorescence attenuation (smSIFA) is a precise method for studying the vertical movement of biological macromolecules using two-dimensional material acceptors. Unlike other methods, smSIFA is not influenced by the planar motion of membranes or proteins. However, the detection range and accuracy of vertical movement are dependent on the properties of these two-dimensional materials. Recently, smSIFA utilizing graphene oxide and graphene has significantly advanced the study of biomacromolecules, although the detection range is restricted by their inherent quenching distances. Modifying these distances necessitates the replacement of the medium material, which presents challenges in material selection and preparation. Consequently, there is a pressing need to develop controllable materials for smSIFA applications. In this study, we enhance the smSIFA technique using graphene oxide as the medium acceptor through thermal reduction. By adjusting the reduction temperature, we prepare reduced graphene oxides at varying degrees of reduction, thus fine-tuning the quenching distances. The adjustment of these distances is measured using fluorescently labeled DNA. This modified smSIFA approach, employing reduced graphene oxide, is then applied to observe conformational changes in the Holliday junction, demonstrating the enhanced detection capabilities of reduced graphene oxide.

physics.bio-ph↗

arXiv2024

Harmonizing Pixels and Melodies: Maestro-Guided Film Score Generation and Composition Style Transfer

We introduce a film score generation framework to harmonize visual pixels and music melodies utilizing a latent diffusion model. Our framework processes film clips as input and generates music that aligns with a general theme while offering the capability to tailor outputs to a specific composition style. Our model directly produces music from video, utilizing a streamlined and efficient tuning mechanism on ControlNet. It also integrates a film encoder adept at understanding the film's semantic depth, emotional impact, and aesthetic appeal. Additionally, we introduce a novel, effective yet straightforward evaluation metric to evaluate the originality and recognizability of music within film scores. To fill this gap for film scores, we curate a comprehensive dataset of film videos and legendary original scores, injecting domain-specific knowledge into our data-driven generation model. Our model outperforms existing methodologies in creating film scores, capable of generating music that reflects the guidance of a maestro's style, thereby redefining the benchmark for automated film scores and laying a robust groundwork for future research in this domain. The code and generated samples are available at https://anonymous.4open.science/r/HPM.

cs.MM↗

arXiv2024

Enhanced $S$-factor for the $^{14}$N$(p,\gamma)^{15}$O reaction and its impact on the solar composition problem

The solar composition problem has puzzled astrophysicists for more than 20 years. Recent measurements of carbon-nitrogen-oxygen (CNO) neutrinos by the Borexino experiment show a $\sim2\sigma$ tension with the "low-metallicity" determinations. $^{14}$N$(p,\gamma)^{15}$O, the slowest reaction in the CNO cycle, plays a crucial role in the standard solar model (SSM) calculations of CNO neutrino fluxes. Here we report a direct measurement of the $^{14}$N$(p,\gamma)^{15}$O reaction, in which $S$-factors for all transitions were simultaneously determined in the energy range of $E_p=110-260$ keV for the first time. Our results resolve previous discrepancies in the ground-state transition, yielding a zero-energy $S$-factor $S_{114}(0) = 1.92\pm0.08$ keV b which is 14% higher than the $1.68\pm0.14$ keV b recommended in Solar Fusion III (SF-III). With our $S_{114}$ values, the SSM B23-GS98, and the latest global analysis of solar neutrino measurements, the C and N photospheric abundance determined by the Borexino experiment is updated to $N_{\mathrm{CN}}=({4.45}^{+0.69}_{-0.61})\times10^{-4}$. This new $N_{\mathrm{CN}}$ value agrees well with latest "high-metallicity" composition, however, is also consistent with the "low-metallicity" determination within $\sim 1\sigma$ C.L., indicating that the solar metallicity problem remains an open question. In addition, the significant reduction in the uncertainty of $S_{114}$ paves the way for the precise determination of the CN abundance in future large-volume solar neutrino measurements.

nucl-ex↗

arXiv2024

Exploring non-Euclidean photonics: Pseudosphere microlaser

Classical and wave properties of microlasers with the shape of a truncated pseudosphere are investigated through experiments and numerical simulations. These pseudosphere microlasers are surface-like organic microlasers with constant negative curvature, which were fabricated with high optical quality by direct laser writing. It is shown that they behave, in many ways, similar to two-dimensional flat disks, regardless of their different Gaussian curvature. We derive the monodromy matrices for geodesics on the pseudosphere and demonstrate that the periodic geodesics are marginally stable. Actually, due to the rotational symmetry, the pseudosphere is an integrable system.

physics.optics↗

arXiv2024

Topological phases of the interacting Su-Schrieffer-Heeger model: An analytical study

The interacting SSH model provides an ideal ground to study the interplay between topologically insulating phases and electron-electron interactions. We study the polarization density as a topological invariant and provide an analytic treatment of its behavior in the low-energy sector of the one-dimensional interacting SSH model. By formulating the topological invariant in terms of Green's functions, we use the low-energy field theory of the Thirring model to derive the behavior of the polarization density. We show that the polarization density in the continuum theory describes the usual topological insulating phases. Still, it contains an extra factor from the fields' scaling dimensions in the low-energy quantum field theory. We interpret this as a measure of the modified charge of the new excitations in the system. We find two distinct contributions: a renormalization of the electronic charge $e$ of a Fermi liquid because of quasiparticle smearing and an additional contribution coming from the topological charge of the soliton arising in the bosonized version of the Thirring model, the sine-Gordon model.

cond-mat.str-el↗

arXiv2024

A newly developed multi-kilo-channel high-speed and precision waveform digitization system for neutrino experiments

The Jinping Neutrino Experiment(JNE), conducted within the China Jinping Underground Laboratory, aims to detect and analyze of solar neutrinos, geo-neutrinos, and supernova neutrinos. A one-ton prototype will soon be in commision with an upgrade from 30 channels to 60 channels, which will increase the data bandwidth by one to two orders of magnitude and exceed the capacity of the current CAEN DAQ system. Additionally, enhancing the performance and flexibility of JNE DAQ system is crucial. This paper presents the design of a new Tsinghua DAQ system for the JNE and its performance and stability. The new Tsinghua DAQ(THDAQ) system for JNE is based on the cPCI protocol and demonstrates powerful performance improvements: ADC ENOB of the THDAQ system approximately exceeds 9.8-bit, marking a 14% improvement over the CAEN DAQ system; The maximum clock deviation within a single chassis is 85.6 ps, satisfying sub-nanosecond synchronization criteria; Each DAQ board features two QSFP+ optical ports with 82.5Gbps transmission capability, while the PCIe board supports a transmission rate of 100.2 Gbps. In addition, comparative experiments between the two systems were also tested in detail. The analysis results of waveform and charge spectrum prove the high stability of the THDAQ system. This provides a foundation for the 60-channel and 4000-channel DAQ systems.

physics.ins-det↗

arXiv2024

Alpha-like correlations in $^{20}$Ne, comparison of quartetting wave function and THSR approaches

$^{20}$Ne can be considered as a double-magic $^{16}$O core nucleus surrounded by four nucleons, the constituents of an $\alpha$-like quartet. Similar to other nuclei ($^{212}$Po, $^{104}$Ti, etc.) with a quartet on top of a double-magic core nucleus, significant $\alpha$-like correlations are expected. Correlations in the ground state of $^{20}$Ne are investigated using different approaches. The quartetting wave function approach (QWFA) predicts a large $\alpha$-like cluster contribution near the surface of the nuclei. The Tohsaki-Horiuchi-Schuck-R\"opke (THSR) approach describes $\alpha$-like clustering in nuclear systems. The results of the QWFA in the Thomas-Fermi and shell-model approximation are compared with THSR calculations for the container model. Results for the $\alpha$ formation probability and the rms radii are shown.

nucl-th↗

arXiv2023

The FAST all sky HI survey (FASHI): The first release of catalog

The FAST All Sky HI survey (FASHI) was designed to cover the entire sky observable by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), spanning approximately 22000 square degrees of declination between -14 deg and +66 deg, and in the frequency range of 1050-1450 MHz, with the expectation of eventually detecting more than 100000 HI sources. Between August 2020 and June 2023, FASHI had covered more than 7600 square degrees, which is approximately 35% of the total sky observable by FAST. It has a median detection sensitivity of around 0.76 mJy/beam and a spectral line velocity resolution of ~6.4 km/s at a frequency of ~1.4 GHz. As of now, a total of 41741 extragalactic HI sources have been detected in the frequency range 1305.5-1419.5 MHz, corresponding to a redshift limit of z<0.09. By cross-matching FASHI sources with the Siena Galaxy Atlas (SGA) and the Sloan Digital Sky Survey (SDSS) catalogs, we found that 16972 (40.7%) sources have spectroscopic redshifts and 10975 (26.3%) sources have only photometric redshifts. Most of the remaining 13794 (33.0%) HI sources are located in the direction of the Galactic plane, making their optical counterparts difficult to identify due to high extinction or high contamination of Galactic stellar sources. Based on current survey results, the FASHI survey is an unprecedented blind extragalactic HI survey. It has higher spectral and spatial resolution and broader coverage than the Arecibo Legacy Fast ALFA Survey (ALFALFA). When completed, FASHI will provide the largest extragalactic HI catalog and an objective view of HI content and large-scale structure in the local universe.

astro-ph.GA↗

arXiv2023

Structure discovery in Atomic Force Microscopy imaging of ice

The interaction of water with surfaces is crucially important in a wide range of natural and technological settings. In particular, at low temperatures, unveiling the atomistic structure of adsorbed water clusters would provide valuable data for understanding the ice nucleation process. Using high-resolution Atomic Force Microscopy (AFM) and Scanning Tunnelling Microscopy, several studies have demonstrated the presence of water pentamers, hexamers, heptamers (and of their combinations) on a variety of metallic surfaces, as well the initial stages of 2D ice growth on an insulating surface. However, in all these cases, the observed structures were completely flat, providing a relatively straightforward path to interpretation. Here, we present high-resolution AFM measurements of several new water clusters on Au(111) and Cu(111), whose understanding presents significant challenges, due to both their highly 3D configuration and to their large size. For each of them, we use a combination of machine learning, atomistic modelling with neural network potentials and statistical sampling to propose an underlying atomic structure, finally comparing its AFM simulated images to the experimental ones. These results provide new insights into the early phases of ice formation, which is a ubiquitous phenomenon ranging from biology to astrophysics.

cond-mat.mtrl-sci↗

arXiv2023

Drift Observations and Mitigation in LCLS-II RF

The LCLS-II RF system physically spans ~700m and has strict requirements -- on the order of 20 fs -- on the phase stability of the accelerating RF fields in its SRF linac. While each LLRF rack is crudely temperature-stabilized, the weather inside the service building as a whole is usually compared to a tin shack in the California sun. A phase-averaging reference line is the primary system deployed in support of the phase stability goals. There are other, secondary subsystems (SEL phase offset, and determination of cavity detuning) that are also sensitive to RF phase drift. We present measurements of phase shifts observed in the overall RF system, and how diagnostics are able to sense and correct for them during beam operations.

physics.acc-ph↗

arXiv2023

Atomic-scale investigation of $\gamma$-Ga$_2$O$_3$ deposited on MgAl$_2$O$_4$ and its relationship with $\beta$-Ga$_2$O$_3$

Nominally phase-pure $\gamma$-$Ga_2O_3$ was deposited on (100) $MgAl_2O_4$ within a narrow temperature window centered at $\sim$470 $^{\circ}$C using metal-organic chemical vapor deposition (MOCVD). The film deposited at 440 $^{\circ}$C exhibited either poor crystallization or an amorphous structure; the film grown at 500 $^{\circ}$C contained both $\beta$-$Ga_2O_3$ and $\gamma$-$Ga_2O_3$. A nominally phase-pure $\beta$-$Ga_2O_3$ film was obtained at 530 $^{\circ}$C. Atomic-resolution scanning transmission electron microscopy (STEM) investigations of the $\gamma$-$Ga_2O_3$ film grown at 470 $^{\circ}$C revealed a high density of antiphase boundaries. A planar defect model developed for $\gamma$-$Al_2O_3$ was extended to explain the stacking sequences of the Ga sublattice observed in the STEM images of $\gamma$-$Ga_2O_3$. The presence of the 180$^{\circ}$ rotational domains and 90$^{\circ}$ rotational domains of $\beta$-$Ga_2O_3$ inclusions within the $\gamma$-$Ga_2O_3$ matrix is discussed within the context of a comprehensive investigation of the epitaxial relationship between those two phases in the as-grown film at 470 $^{\circ}$C and the same film annealed at 600 $^{\circ}$C. The results led to the hypotheses that (i) incorporation of certain dopants including Si, Ge, Sn, Mg, Al, and Sc, into $\beta$-$Ga_2O_3$, locally stabilizes the "$\gamma$-phase" and (ii) the site preference(s) for these dopants promotes the formation of the "$\gamma$-phase" and/or $\gamma$-$Ga_2O_3$ solid solutions. However, in the absence of such dopants, pure $\gamma$-$Ga_2O_3$ remains the least stable $Ga_2O_3$ polymorph, as indicated by its very narrow growth window, lower growth temperatures relative to other $Ga_2O_3$ polymorphs, and the largest calculated difference in Helmholtz free energy per formula unit between $\gamma$-$Ga_2O_3$ and $\beta$-$Ga_2O_3$ than all other polymorphs.

cond-mat.mtrl-sci↗

arXiv2023

ZrOsSi: A $Z_2$ topological metal with a superconducting ground state

The silicide superconductors (Ta, Nb, Zr)OsSi are among the best candidate materials for investigating the interplay of topological order and superconductivity. Here, we investigate in detail the normal-state topological properties of (Ta, Nb, Zr)OsSi, focusing on ZrOsSi, by employing a combination of $^{29}$Si nuclear magnetic resonance (NMR) measurements and first-principles band-structure calculations. We show that, while (Ta, Nb)OsSi behave as almost ideal metals, characterized by weak electronic correlations and a relatively low density of states, the replacement of Ta (or Nb) with Zr expands the crystal lattice and shifts ZrOsSi towards an insulator. Our ab initio calculations indicate that ZrOsSi is a $Z_2$ topological metal with clear surface Dirac cones and properties similar to a doped strong topological insulator.

cond-mat.supr-con↗

arXiv2023

Strain Dependent Spin Hall Magnetoresistance in the Multiferroic Antiferromagnet BiFeO$_3$

The spin Hall magnetoresistance (SMR) of epitaxial BiFeO$_3$ thin films is investigated. SMR consistent with ferromagnetic interfacial states for BiFeO$_3$ films fabricated on (001) SrTiO$_3$ (R' BFO) and LaAlO$_3$ (T' BFO) substrates is found, albeit with different temperature dependencies. For T' BFO, the SMR is enhanced at room temperature, and decays with reduced temperatures. By contrast, R' BFO shows a monotonic decrease in SMR response with increasing temperature, mirroring the trend of a weak ferromagnet. Density functional theory shows that this difference originates from the coupling of the applied magnetic field to oxygen octahedral rotation (R') and spin (T') degrees of freedom.

cond-mat.mtrl-sci↗

arXiv2022

An efficient numerical approach for stochastic evolution PDEs driven by random diffusion coefficients and multiplicative noise

In this paper, we investigate the stochastic evolution equations (SEEs) driven by $\log$-Whittle-Mat$\acute{{\mathrm{e}}}$rn (W-M) random diffusion coefficient field and $Q$-Wiener multiplicative force noise. First, the well-posedness of the underlying equations is established by proving the existence, uniqueness, and stability of the mild solution. A sampling approach called approximation circulant embedding with padding is proposed to sample the random coefficient field. Then a spatio-temporal discretization method based on semi-implicit Euler-Maruyama scheme and finite element method is constructed and analyzed. An estimate for the strong convergence rate is derived. Numerical experiments are finally reported to confirm the theoretical result.

math.NA↗

arXiv2021

Navigation of micro-swimmers in steady flow: the importance of symmetries

Marine microorganisms must cope with complex flow patterns and even turbulence as they navigate the ocean. To survive they must avoid predation and find efficient energy sources. A major difficulty in analysing possible survival strategies is that the time series of environmental cues in non-linear flow is complex, and that it depends on the decisions taken by the organism. One way of determining and evaluating optimal strategies is reinforcement learning. In a proof-of-principle study, Colabrese et al. [Phys. Rev. Lett. (2017)] used this method to find out how a micro-swimmer in a vortex flow can navigate towards the surface as quickly as possible, given a fixed swimming speed. The swimmer measured its instantaneous swimming direction and the local flow vorticity in the laboratory frame, and reacted to these cues by swimming either left, right, up, or down. However, usually a motile microorganism measures the local flow rather than global information, and it can only react in relation to the local flow, because in general it cannot access global information (such as up or down in the laboratory frame). Here we analyse optimal strategies with local signals and actions that do not refer to the laboratory frame. We demonstrate that symmetry-breaking is required in order to learn vertical migration in a meaningful way. Using reinforcement learning we analyse the emerging strategies for different sets of environmental cues that microorganisms are known to measure.

physics.flu-dyn↗

arXiv2020

Sample Dependence of Magnetism in the Next Generation Cathode Material LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_2$

We present a structural and magnetic study on two batches of polycrystalline LiNi$_{0.8}$Mn$_{0.1}$Co$_{0.1}$O$_2$ (commonly known as Li NMC 811), a Ni-rich Li ion battery cathode material, using elemental analysis, X-ray and neutron diffraction, magnetometry, and polarised neutron scattering measurements. We find that the samples, labelled S1 and S2, have the composition Li$_{1-x}$Ni$_{0.9+x-y}$Mn$_y$Co$_{0.1}$O$_2$, with $x = 0.025(2)$, $y = 0.120(2)$ for S1 and $x = 0.002(2)$, $y = 0.094(2)$ for S2, corresponding to different concentrations of magnetic ions and excess Ni$^{2+}$ in the Li$^+$layers. Both samples show a peak in the zero-field cooled (ZFC) dc susceptibility at 8.0(2) K but the temperature at which the ZFC and FC (field-cooled) curves deviate is substantially different: 64(2) K for S1 and 122(2) K for S2. Ac susceptibility measurements show that the transition for S1 shifts with frequency whereas no such shift is observed for S2 within the resolution of our measurements. Our results demonstrate the sample dependence of magnetic properties in Li NMC 811, consistent with previous reports on the parent material LiNiO$_2$. We further establish that a combination of experimental techniques are necessary to accurately determine the chemical composition of next generation battery materials with multiple cations.

cond-mat.mtrl-sci↗

arXiv2019

Exclusive $\pi^+$ electroproduction off the proton from low to high -t

Background: Measurements of exclusive meson production are a useful tool in the study of hadronic structure. In particular, one can discern the relevant degrees of freedom at different distance scales through these studies. Purpose: To study the transition between non-perturbative and perturbative Quantum Chromodyanmics as the square of four momentum transfer to the struck proton, -t, is increased. Method: Cross sections for the $^1$H(e,e'$\pi^+$)n reaction were measured over the -t range of 0.272 to 2.127 GeV$^2$ with limited azimuthal coverage at fixed beam energy of 4.709 GeV, Q$^2$ of 2.4 GeV$^2$ and W of 2.0 GeV at the Thomas Jefferson National Accelerator Facility (JLab) Hall C. Results: The -t dependence of the measured $\pi^+$ electroproduction cross section generally agrees with prior data from JLab Halls B and C. The data are consistent with a Regge amplitude based theoretical model, but show poor agreement with a Generalized Parton Distribution (GPD) based model. Conclusion: The agreement of cross sections with prior data implies small contribution from the interference terms, and the confirmation of the change in t-slopes between the low and high -t regions previously observed in photoproduction indicates the changing nature of the electroproduction reaction in our kinematic regime.

nucl-ex↗

arXiv2019

ATCA LLRF System for ASU Compact FEL

SLAC National Accelerator Laboratory is collaborating with Arizona State University to design a LLRF system towards the advancement of the ASU Compact X-ray Light Source (CXLS). The CXLS is a phased project to develop small brilliant x-ray sources that may produce coherent x-rays appropriate as a seed source for LCLS and LCLS II. The CXLS electron beam is produced by an x-band photoinjector and linac operating at 9.3 GHz RF frequency and 1 kHz repetition rate with up to 300 pC per bunch. The linac consists of 3 short 20-cell sections of standing wave linac. The RF gun and linac sections are powered by two 6 MW transmitters using L3 klystrons and Scandi-nova K1 modulators. The accelerator will initially operate in single-bunch mode and may be upgraded to multi-bunch operation at a later date. SLAC National Laboratory has developed a LLRF system in Advanced Telecommunication Computing Architecture (ATCA) for the ASU project. This talk will discuss the design of the LLRF for this project and discuss the ATCA implementation.

physics.acc-ph↗