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X. H. Li

Publications and source records attributed to X. H. Li.

16 recordsLinked to original sources
arXiv2025

Synthetic gauge field enabled realization of bulk- and edge-transported states in an aperiodic acoustic structure

Topologically protected edge states with immunity against various disorders have been implemented in a variety of topological insulators. In this Letter, we reveal that Landau levels in aperiodic acoustic structures can be achieved under different pseudomagnetic fields (PMFs). The produced zero order Landau modes (ZOLMs) could transmit along the channels at the interior or exterior of the inhomogeneous array, which are separately termed as "bulk-transported states" (BTSs) and "edge-transported states" (ETSs). Distinct from conventional valley edge states, the ZOLMs show intriguing self-collimation feature. If a pseudoelectric field (PEF) is further included, the combination of a PMF and PEF can result in the formation of bulk or edge Landau rainbow, where Landau zero modes are distributed at various positions of the bulk or boundary of the sample at different frequencies. The synthetic-gauge-field-controlled topological states can enable fully control of robust transmission, and using the entire footprint of a topological lattice. Our findings not only profoundly advance the current understanding of topological phase matter but also offer new avenues for constructing topological acoustic devices.

cond-mat.mes-hall↗
arXiv2023

Stochastic p-Bits Based on Spin-Orbit Torque Magnetic Tunnel Junctions

Stochastic p-Bit devices play a pivotal role in solving NP-hard problems, neural network computing, and hardware accelerators for algorithms such as the simulated annealing. In this work, we focus on Stochastic p-Bits based on high-barrier magnetic tunnel junctions (HB-MTJs) with identical stack structure and cell geometry, but employing different spin-orbit torque (SOT) switching schemes. We conducted a comparative study of their switching probability as a function of pulse amplitude and width of the applied voltage. Through experimental and theoretical investigations, we have observed that the Y-type SOT-MTJs exhibit the gentlest dependence of the switching probability on the external voltage. This characteristic indicates superior tunability in randomness and enhanced robustness against external disturbances when Y-type SOT-MTJs are employed as stochastic p-Bits. Furthermore, the random numbers generated by these Y-type SOT-MTJs, following XOR pretreatment, have successfully passed the National Institute of Standards and Technology (NIST) SP800-22 test. This comprehensive study demonstrates the high performance and immense potential of Y-type SOT-MTJs for the implementation of stochastic p-Bits.

cond-mat.mes-hall↗
arXiv2022

New continuum and polarization observations of the Cygnus Loop with FAST II. Images and analyses

We present total-intensity and polarized-intensity images of the Cygnus Loop supernova remnant (SNR) observed by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The high angular-resolution and high-sensitivity images enable us to thoroughly compare the properties of the northern part with the southern part of the SNR. The central filament in the northern part and the southern part have a similar foreground rotation measure, meaning their distances are likely similar. The polarization analysis indicates that the random magnetic field is larger than the regular field in the northern part, but negligible in the southern part. The total-intensity image is decomposed into components of various angular scales, and the brightness-temperature spectral index of the shell structures in the northern part is similar to that in the southern part in the component images. All these evidence suggest that the northern and southern part of the Cygnus Loop are situated and thus evolved in different environments of interstellar medium, while belonging to the same SNR.

astro-ph.GA↗
arXiv2022

Realization of ultra-broadband IR up-conversion imaging

Ultra-broadband imaging devices with high performance are in great demand for a variety of technological applications, including imaging, remote sensing, and communications. An ultra-broadband up-converter is realized based on a p-GaAs homojunction interfacial workfunction internal photoemission (HIWIP) detector-light emitting diode (LED) device. The device demonstrates an ultra-broad response ranging from visible to terahertz (THz) with good reproducibility. The peak responsivity in the mid-infrared (MIR) region is 140 mA/W at 10.5 microns. The HIWIP-LED shows enormous potential for ultra-broadband up-conversion covering all infrared atmospheric windows, as well as the THz region, and the pixel-less imaging of the MIR spot from the CO2 laser is further demonstrated. In addition, the proposed up-converter also performs as a near-infrared and visible detector under zero bias by using a bi-functional LED. Thanks to its ultra-wide response, the HIWIP-LED up-converter has great promise for stable, high-performance ultra-broadband pixel-less imaging and multi-functional analysis systems.

physics.optics↗
arXiv2021

Systematic study of two-proton radioactivity with a screened electrostatic barrier

In this study, a phenomenological model is proposed based on Wentzel-Kramers-Brillouin (WKB) theory and applied to investigate the two-proton ($2p$) radioactive half-lives of nuclei near or beyond the proton drip line. The total diproton-daughter nucleus interaction potential is composed of the Hulthen-type electrostatic term and the centrifugal term. The calculated $2p$ radioactive half-lives can accurately reproduce the existing 10 experimental datasets of five true $2p$ radioactive nuclei with $σ$ = 0.736. In addition, we extend this model to predict the half-lives of possible $2p$ radioactive nuclei whose $2p$ radioactivity is energetically allowed or observed but not yet quantified in NUBASE2016. The predicted results are in agreement with those obtained using the Gamow-like model, generalized liquid drop model, Sreeja formula, and Liu formula.

nucl-th↗
arXiv2020

Measurement of $^{58}$Ni($p$, $p$)$^{58}$Ni elastic scattering at low momentum transfer by using the HIRFL-CSR heavy-ion storage ring

The very first in-ring reaction experiment at the HIRFL-CSR heavy-ion storage ring, namely proton elastic scattering on stable $^{58}$Ni nuclei, is presented. The circulating $^{58}$Ni$^{19+}$ ions with an energy of 95 MeV/u were interacting repeatedly with an internal hydrogen gas target in the CSRe experimental ring. Low energy proton recoils from the elastic collisions were measured with an ultra-high vacuum compatible silicon-strip detector. Deduced differential cross sections were normalized by measuring K-shell X-rays from $^{58}$Ni$^{19+}$ projectiles due to the $^{58}$Ni$^{19+}$-H$_2$ ionization collisions. Compared to the experimental cross sections, a good agreement has been achieved with the theoretical predictions in the measured region, which were obtained by using the global phenomenological optical model potentials. Our results enable new research opportunities for optical model potential studies on exotic nuclides by using the in-ring reaction setup at the HIRFL-CSR facility.

nucl-ex↗
arXiv2020

Sunspot penumbral filaments intruding into a light bridge and the resultant reconnection jets

Penumbral filaments and light bridges are prominent structures inside sunspots and are important for understanding the nature of sunspot magnetic fields and magneto-convection underneath. We investigate an interesting event where several penumbral filaments intruded into a sunspot light bridge for more insights into magnetic fields of the sunspot penumbral filament and light bridge, as well as their interaction. The emission, kinematic, and magnetic topology characteristics of the penumbral filaments intruding into the light bridge and the resultant jets are studied. At the west part of the light bridge, the intruding penumbral filaments penetrated into the umbrae on both sides of the light bridge, and two groups of jets were also detected. The jets shared the same projected morphology with the intruding filaments and were accompanied by intermittent footpoint brightenings. Simultaneous spectral imaging observations provide convincing evidences for the presences of magnetic reconnection related heating and bidirectional flows near the jet bases and contribute to measuring vector velocities of the jets. Additionally, nonlinear force-free field extrapolation results reveal strong and highly inclined magnetic fields along the intruding penumbral filaments, consistent well with the results deduced from the vector velocities of the jets. Therefore, we propose that the jets could be caused by magnetic reconnections between emerging fields within the light bridge and the nearly horizontal fields of intruding filaments. They were then ejected outward along the stronger filaments fields. Our study indicates that magnetic reconnection could occur between the penumbral filament fields and emerging fields within light bridge and produce jets along the stronger filament fields. These results further complement the study of magnetic reconnection and dynamic activities within the sunspot.

astro-ph.SR↗
arXiv2020

Predictions of $α$ decay half-lives for even-even superheavy nuclei with $104 \leqslant Z \leqslant 128$ based on two-potential approach within cluster-formation model

In present work, we systematically study the $α$ decay half-lives of 170 even-even nuclei with $60 \leqslant Z \leqslant 118$ within the two-potential approach while the $α$ decay preformation factor $P_α$ is obtained by the cluster-formation model. The calculated results can well reproduce the experimental data. In addition, we extend this model to predict the $α$ decay half-lives of 64 even-even nuclei with $104 \leqslant Z \leqslant 128$ whose $α$ decay is energetically allowed or observed but not yet quantified. For comparing, the two famous models i.e. SemFIS proposed by D. Poenaru ${et\ al.}$ [\href {https://doi.org/10.1209/0295-5075/77/62001}{Europhys. Lett. \textbf{77} (2007) 62001}] and UDL proposed by C. Qi ${et\ al.}$ [\href {https://doi.org/10.1103/PhysRevLett.103.072501}{Phys. Rev. Lett. \textbf{103} (2009) 072501}] are used. The predicted results of these models are basically consistent. At the same time, through analyzing the changing trend of $α$ decay energy $Q_α$ of \emph{Z} = 118, 120, 122, 124, 126 and 128 isotopes nuclei with the increasing of neutron number \emph{N} and that of $α$ decay preformation factor $P_α$ of those isotopes even-even nuclei with the increasing of neutron number \emph{N}, \emph{N} = 178 may be a new neutron magic number.

nucl-th↗
arXiv2018

Eruption of a multi-flux-rope system in solar active region 12673 leading to the two largest flares in Solar Cycle 24

Solar active region (AR) 12673 in 2017 September produced two largest flares in Solar Cycle 24: the X9.3 flare on September 06 and the X8.2 flare on September 10. We attempt to investigate the evolutions of the two great flares and their associated complex magnetic system in detail. Aided by the NLFFF modeling, we identify a double-decker flux rope configuration above the polarity inversion line (PIL) in the AR core region. The north ends of these two flux ropes were rooted in a negative- polarity magnetic patch, which began to move along the PIL and rotate anticlockwise before the X9.3 flare on September 06. The strong shearing motion and rotation contributed to the destabilization of the two magnetic flux ropes, of which the upper one subsequently erupted upward due to the kink-instability. Then another two sets of twisted loop bundles beside these ropes were disturbed and successively erupted within 5 minutes like a chain reaction. Similarly, multiple ejecta components were detected to consecutively erupt during the X8.2 flare occurring in the same AR on September 10. We examine the evolution of the AR magnetic fields from September 03 to 06 and find that five dipoles emerged successively at the east of the main sunspot. The interactions between these dipoles took place continuously, accompanied by magnetic flux cancellations and strong shearing motions. In AR 12673, significant flux emergence and successive interactions between the different emerging dipoles resulted in a complex magnetic system, accompanied by the formations of multiple flux ropes and twisted loop bundles. We propose that the eruptions of a multi-flux-rope system resulted in the two largest flares in Solar Cycle 24.

astro-ph.SR↗
arXiv2006

Born-Infeld Type Phantom Model in the $ω-ω'$ Plane

In this paper, we investigate the dynamics of Born-Infeld(B-I) phantom model in the $ω-ω'$ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to $N$(the logarithm of the scale factor $a$). We find the scalar field equation of motion in $ω-ω'$ plane, and show mathematically the property of attractor solutions which correspond to $ω_ϕ\sim-1$, $Ω_ϕ=1$, which avoid the "Big rip" problem and meets the current observations well.

hep-th↗
arXiv2005

X-ray spectroscopy of PSR B1951+32 and its pulsar wind nebula

We present spatially resolved X-ray spectroscopy of PSR B1951+32 and its pulsar wind nebula (PWN) in supernova remnant (SNR) CTB 80 using a {\sl Chandra} observation. The {\sl Chandra} X-ray map reveals clearly various components of a ram-pressure confined PWN embedded in the SNR ejecta: a point source representing the pulsar, X-ray emission from the bow shock, a luminous X-ray tail, a 30$\arcsec$ diameter plateau whose northwestern part is absent, and the outside more diffuse X-ray emission. The plateau is just surrounded by the radio, [O III], [S II], and [N II] shells, and the outside diffuse emission is mostly within the H$α$ shells. While the spectra of all the features are well fitted with power law models, a power law plus blackbody model can fit the spectrum of the pulsar significantly better than using a power law model alone. Generally the spectra of these components obey the trend of steepening from the inside to the outside. However, the edge of the plateau probably has a harder spectrum than that of the central region of the plateau. The cause of the apparent hard spectrum of the plateau edge is unclear, and we speculate that it might be due to a shock between the PWN and the SNR ejecta. The possible blackbody radiation component from the pulsar has a temperature of 0.13$\pm0.02$ keV and an equivalent emitting radius of 2.2$^{+1.4}_{-0.8}$ (d/2 kpc) km, and is thus probably from the hot spots on the pulsar. We also show in this paper that the blackbody temperature of the entire surface of PSR B1951+32 is much lower than those predicted by the standard neutron star cooling models.

astro-ph↗
arXiv2003

Comparing Geometrical and Delay Radio Emission Heights in Pulsars

We use a set of carefully selected published average multifrequency polarimetric observations for six bright cone dominated pulsars and devise a method to combine the multifrequency polarization position angle (PPA) sweep traverses. We demonstrate that the PPA traverse is in excellent agreement with the rotating vector model over this broad frequency range confirming that radio emission emanates from perfectly dipolar field lines. For pulsars with central core emission in our sample, we find the peak of central core component to lag the steepest gradient of the PPA traverse at several frequencies. Also significant frequency evolution of the core width is observed over this frequency range. The above facts strongly suggest: (a) the peak core emission does not lie on the fiducial plane containing the dipole magnetic axis and the rotation axis, and (b) the core emission does not originate from the polar cap surface.

astro-ph↗
arXiv2003

The Effect of Scattering on Pulsar Polarization Angle

The low-frequency profiles of some pulsars manifest temporal broadening due to scattering, usually accompanied by flat polarization position angle (PA) curves. Assuming that the scattering works on the 4 Stokes parameters in the same way, we have simulated the effect of scattering on polarization profiles and find that the scattering can indeed flatten the PA curves. Since the higher-frequency profiles suffer less from scattering, they are convolved with scattering models to fit the observed low-frequency profiles. The calculated flat PA curves exactly reproduce the corresponding observations.

astro-ph↗
arXiv2001

Pulsars in FIRST Observations

We identified 16 pulsars from the Faint Images of the Radio Sky at Twenty-cm (FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from the FIRST catalog. Comparing the source positions with those in the PSRcatalog, we obtained better determined positions of PSRs J1022+1001, J1518+4904, J1652+2651, and proper motion upper limits of another three pulsars PSRs J0751+1807, J1012+5307, J1640+2224. Proper motions of the other 10 pulsars are consistent with the values in the catalog.

astro-ph↗
arXiv2000

Ratio of Hadronic Decay Rates of Jψand ψ(2S) and the ρπPuzzle

The so-called ρπpuzzle of Jψand ψ(2S) decays is examined using the experimental data available to date. Two different approaches were taken to estimate the ratio of Jψand ψ(2S) hadronic decay rates. While one of the estimates could not yield the exact ratio of ψ(2S) to Jψinclusive hadronic decay rates, the other, based on a computation of the inclusive ggg decay rate for ψ(2S) (Jψ) by subtracting other decay rates from the total decay rate, differs by two standard deviations from the naive prediction of perturbative QCD, even though its central value is nearly twice as large as what was naively expected. A comparison between this ratio, upon making corrections for specific exclusive two-body decay modes, and the corresponding experimental data confirms the puzzles in Jψand ψ(2S) decays. We find from our analysis that the exclusively reconstructed hadronic decays of the ψ(2S) account for only a small fraction of its total decays, and a ratio exceeding the above estimate should be expected to occur for a considerable number of the remaining decay channels. We also show that the recent new results from the BES experiment provide crucial tests of various theoretical models proposed to explain the puzzle.

hep-ph↗