arXiv subjects

T. Wang

Publications and source records attributed to T. Wang.

At least 37 records · Page 2Linked to original sources

arXiv2025

The FAST Galactic Plane Pulsar Snapshot survey: VIII. 116 binary pulsars

Finding pulsars in binaries are important for measurements of the masses of neutron stars, for tests of gravity theories, and for studies of star evolution. We are carrying out the Galactic Plane Pulsar Snapshot survey (GPPS) by using the the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here we present the Keplerian parameters for 116 newly discovered pulsars in the FAST GPPS survey, and obtain timing solutions for 29 pulsars. Companions of these pulsars are He white dwarfs, CO/ONe white dwarfs, neutron stars, main sequence stars and ultra light objects or even planets. Our observations uncover eclipses of 8 binary systems. The optical counterpart for the companion of PSR J1908+1036 is identified. The Post-Keplerian parameter $\dotω$ for the double neutron star systems PSR J0528+3529 and J1844-0128 have been measured, with which the total masses of the binary systems are determined.

astro-ph.HE↗

arXiv2025

Design and Commissioning of Readout Electronics for a $K_L^0$ and $μ$ Detector at the Belle II Experiment

The K-long and muon detector (KLM) constitutes the outer-most volume of the Belle II spectrometer at the interaction region of the SuperKEKB collider in Tsukuba, Japan. The KLM detector was partially upgraded since the Belle experiment by replacing many of its resistive-plate chambers with scintillators containing wavelength-shifting fibers and instrumenting it with silicon photomultipliers. We describe the readout electronics, firmware, and software created to control and acquire data from the scintillators and resistive-plate chambers.

hep-ex↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot Survey: VII. Six millisecond pulsars in compact orbits with massive white dwarf companions

Binary millisecond pulsars with a massive white dwarf (WD) companion are intermediate-mass binary pulsars (IMBPs). They are formed via the Case BB Roche-lobe overflow evolution channel if they are in compact orbits with an orbital period of less than 1 day. They are fairly rare in the known pulsar population; only five such IMBPs have been discovered before, and one of them is in a globular cluster. Here we report six IMBPs in compact orbits: PSRs J0416+5201, J0520+3722, J1919+1341, J1943+2210, J1947+2304 and J2023+2853, discovered during the Galactic Plane Pulsar Snapshot survey by using the Five-hundred-meter Aperture Spherical radio Telescope, doubling the number of such IMBPs due to the high survey sensitivity in the short survey time of 5 minutes. Follow-up timing observations show that they all have either a CO WD or an ONeMg WD companion with a mass greater than about 0.8~$M_\odot$ in a very circular orbit with an eccentricity in the order of $\lesssim10^{-5}$. PSR J0416+5201 should be an ONeMg WD companion with a remarkable minimum mass of 1.28 $M_\odot$. These massive WD companions lead to a detectable Shapiro delay for PSRs J0416+5201, J0520+3722, J1943+2210, and J2023 +2853, indicating that their orbits are highly inclined. From the measurement of the Shapiro delay, the pulsar mass of J1943+2210 was constrained to be 1.84$^{\,+0.11}_{-0.09}$~$M_\odot$, and that of PSR J2023+2853 to be 1.28$^{\,+0.06}_{-0.05}$~$M_\odot$.

astro-ph.HE↗

arXiv2025

The FAST Galactic Plane Pulsar Snapshot survey: VI. The discovery of 473 new pulsars

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive telescope at the $L$-band (1.0-1.5 GHz) and has been used to carry out the FAST Galactic Plane Pulsar Snapshot (GPPS) survey in the last 5 yr. Up to now, the survey has covered one-fourth of the planned areas within $\pm10^{\circ}$ from the Galactic plane visible by FAST, and discovered 751 pulsars. After the first publication of the discovery of 201 pulsars and one rotating radio transient (RRAT) in 2021 and 76 RRATs in 2023, here we report the discovery of 473 new pulsars from the FAST GPPS survey, including 137 new millisecond pulsars and 30 new RRATs. We find 34 millisecond pulsars discovered by the GPPS survey which can be timed with a precision better than 3 $μ$s by using FAST 15 minute observations and can be used for pulsar timing arrays. The GPPS survey has discovered eight pulsars with periods greater than 10 s including one with 29.77 s. The integrated profiles of pulsars and individual pulses of RRATs are presented. During the FAST GPPS survey, we also detected previously known pulsars and updated parameters for 52 pulsars. In addition, we discovered two fast radio bursts plus one probable case with high dispersion measures indicating their extragalactic origin.

astro-ph.HE↗

arXiv2024

Enabling low threshold laser through an asymmetric tetramer metasurface harnessing polarization-independent quasi-BICs

We propose and numerically demonstrate a novel strategy to achieve dual-band symmetry-protected bound states in the continuum (BICs) based on a nanodisk tetramer metasurface for lasing generation. The method involves breaking the in-plane symmetry along the diagonal of the metasurface unit cell by introducing air holes in the tetramers. Through our simulations, we show that this flexible approach enables the support of dual-band BICs in the telecom-band range, with these modes evolving into quasi-BICs with remarkably high quality factors by breaking the symmetry of the system. Furthermore, the ultracompact device exhibits the unique characteristic of being polarization-independent across all viewing angles. Finally, the optically pumped gain medium provides sufficient optical gain to compensate the quasi-BIC mode losses, enabling two mode lasing with ultra-low pump threshold and very narrow optical linewidth in the telecom-band range. Our adaptable device paves the way for polarization-insensitive metasurfaces with multiple lasing resonances. This innovation holds the potential to transform areas like low-threshold lasing and biosensing by delivering improved performance and broader capabilities.

physics.optics↗

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

DeepSeek-V2: A Strong, Economical, and Efficient Mixture-of-Experts Language Model

We present DeepSeek-V2, a strong Mixture-of-Experts (MoE) language model characterized by economical training and efficient inference. It comprises 236B total parameters, of which 21B are activated for each token, and supports a context length of 128K tokens. DeepSeek-V2 adopts innovative architectures including Multi-head Latent Attention (MLA) and DeepSeekMoE. MLA guarantees efficient inference through significantly compressing the Key-Value (KV) cache into a latent vector, while DeepSeekMoE enables training strong models at an economical cost through sparse computation. Compared with DeepSeek 67B, DeepSeek-V2 achieves significantly stronger performance, and meanwhile saves 42.5% of training costs, reduces the KV cache by 93.3%, and boosts the maximum generation throughput to 5.76 times. We pretrain DeepSeek-V2 on a high-quality and multi-source corpus consisting of 8.1T tokens, and further perform Supervised Fine-Tuning (SFT) and Reinforcement Learning (RL) to fully unlock its potential. Evaluation results show that, even with only 21B activated parameters, DeepSeek-V2 and its chat versions still achieve top-tier performance among open-source models.

cs.CL↗

arXiv2024

AI-Assisted Detector Design for the EIC (AID(2)E)

Artificial Intelligence is poised to transform the design of complex, large-scale detectors like the ePIC at the future Electron Ion Collider. Featuring a central detector with additional detecting systems in the far forward and far backward regions, the ePIC experiment incorporates numerous design parameters and objectives, including performance, physics reach, and cost, constrained by mechanical and geometric limits. This project aims to develop a scalable, distributed AI-assisted detector design for the EIC (AID(2)E), employing state-of-the-art multiobjective optimization to tackle complex designs. Supported by the ePIC software stack and using Geant4 simulations, our approach benefits from transparent parameterization and advanced AI features. The workflow leverages the PanDA and iDDS systems, used in major experiments such as ATLAS at CERN LHC, the Rubin Observatory, and sPHENIX at RHIC, to manage the compute intensive demands of ePIC detector simulations. Tailored enhancements to the PanDA system focus on usability, scalability, automation, and monitoring. Ultimately, this project aims to establish a robust design capability, apply a distributed AI-assisted workflow to the ePIC detector, and extend its applications to the design of the second detector (Detector-2) in the EIC, as well as to calibration and alignment tasks. Additionally, we are developing advanced data science tools to efficiently navigate the complex, multidimensional trade-offs identified through this optimization process.

physics.ins-det↗

arXiv2024

The FAST Galactic Plane Pulsar Snapshot Survey -- V. PSR J1901+0658 in a double neutron star system

Double neutron star (DNS) systems offer excellent opportunities to test gravity theories. We report the timing results of PSR J1901+0658, the first pulsar discovered in the FAST Galactic Plane Pulsar Snapshot (GPPS) Survey. Based on timing observations by FAST over 5 yr, we obtain the phase-coherent timing solutions and derive the precise measurements of its position, spin parameters, orbital parameters, and dispersion measure. It has a period of 75.7 ms, a period derivative of 2.169(6)$\times 10^{-19}$ s s$^{-1}$, and a characteristic age of 5.5 Gyr. This pulsar is in an orbit with a period of 14.45 d and an eccentricity of 0.366. One post-Keplerian parameter, periastron advance, has been well-measured as being 0.00531(9) deg yr$^{-1}$, from which the total mass of this system is derived to be 2.79(7) M$_{\odot}$. The pulsar has the mass upper limit of 1.68 M$_{\odot}$, so the lower limit for the companion mass is 1.11 M$_{\odot}$. Because PSR J1901+0658 is a partially recycled pulsar in an eccentric binary orbit with such a large companion mass, it should be in a DNS system according to the evolution history of the binary system.

astro-ph.HE↗

arXiv2024

Dwarf pulses of 10 pulsars detected by FAST

How pulsars radiate is a long-standing problem. Detailed polarization measurements of individual pulses shed light on currently unknown emission processes. Recently, based on supersensitive observations, dwarf pulses have been recognized as weak narrow pulses often appearing during the nulling state. In this study, we report the detection of dwarf pulses from ten pulsars, PSRs B0525+21, B1237+25, J1538+2345, J1824$-$0127, J1851$-$0053, B1901+10, J1939+10, B1944+17, B2000+40 and J2112+4058, based on observations conducted with the Five-hundred-meter Aperture Spherical radio Telescope. Dwarf pulses of five pulsars are clearly discernible in the two-dimensional distribution of pulse intensity and pulse width. For the other five pulsars, PSRs J1538+2345, J1824$-$0127, J1939+10, B2000+40, and J2112+4058, only a few dwarf pulses are detected from pulse stacks. The dwarf pulses can emerge in both cone and core emission components for PSR B1237+25, and the polarization angles of these dwarf pulses are mostly in the orthogonal polarization mode of normal pulses for PSR B1944+17. In general, pulsars with detected dwarf pulses tend to be located within the "death valley" region of the distribution of pulsar periods and period derivatives.

astro-ph.HE↗

arXiv2023

Densifying MIMO: Channel Modeling, Physical Constraints, and Performance Evaluation for Holographic Communications

As the backbone of the fifth-generation (5G) cellular network, massive multiple-input multiple-output (MIMO) encounters a significant challenge in practical applications: how to deploy a large number of antenna elements within limited spaces. Recently, holographic communication has emerged as a potential solution to this issue. It employs dense antenna arrays and provides a tractable model. Nevertheless, some challenges must be addressed to actualize this innovative concept. One is the mutual coupling among antenna elements within an array. When the element spacing is small, near-field coupling becomes the dominant factor that strongly restricts the array performance. Another is the polarization of electromagnetic waves. As an intrinsic property, it was not fully considered in the previous channel modeling of holographic communication. The third is the lack of real-world experiments to show the potential and possible defects of a holographic communication system. In this paper, we propose an electromagnetic channel model based on the characteristics of electromagnetic waves. This model encompasses the impact of mutual coupling in the transceiver sides and the depolarization in the propagation environment. Furthermore, by approximating an infinite array, the performance restrictions of large-scale dense antenna arrays are also studied theoretically to exploit the potential of the proposed channel. In addition, numerical simulations and a channel measurement experiment are conducted. The findings reveal that within limited spaces, the coupling effect, particularly for element spacing smaller than half of the wavelength, is the primary factor leading to the inflection point for the performance of holographic communications.

cs.IT↗

arXiv2023

Characterization, Simulation and Test Beam Data Analysis of Stitched Passive CMOS Strip Sensors

In the passive CMOS Strips Project, strip sensors were designed at the University of Bonn and produced by LFoundry in 150 nm technology, with an additional backside processing from IZM Berlin. Up to five individual reticules were connected by stitching at the foundry in order to obtain the typical strip lengths required for the LHC Phase-II upgrade of ATLAS or CMS trackers. After dicing, sensors were tested in a probe station and characterised with a Sr90-source as well as laser-based edge- and top-TCT systems. Sensors were also simulated using Sentaurus TCAD. At last, detector modules were constructed from several sensors and thoroughly studied in two beam campaigns at DESY. All of these measurements were performed before and after irradiation. This contribution provides an overview of simulation results, summarises the laboratory measurements and in particular presents first test beam results for irradiated and unirradiated passive CMOS strip sensors. We are demonstrating that large area sensors with sufficient radiation hardness can be obtained by stitching during the CMOS process, and presenting our plans for the next submission in the framework of this project.

physics.ins-det↗

arXiv2023

The FAST Galactic Plane Pulsar Snapshot survey: IV. Discovery of five fast radio bursts

We report five new fast radio bursts (FRBs) discovered from the Galactic Plane Pulsar Snapshot (GPPS) survey by the Five-hundred-meter Aperture Spherical radio Telescope (FAST): FRB\,20210126, FRB\,20210208, FRB\,20210705, FRB\,20211005 and FRB\,20220306. To date, no repeating bursts from these FRB sources have been detected in the follow-up monitoring observations, leading to their classification as potential one-off events. We obtain the basic parameters for these bursts, including position, dispersion measure (DM), pulse width, spectral index, scattering time-scale, etc. The fluences and flux densities are generally lower in comparison to the values observed in one-off bursts discovered by other telescopes. Among the observed bursts, polarization data for 4 bursts were recorded during observations. Consequently, we obtain polarization profiles and Faraday rotation measures (RMs) for these bursts.

astro-ph.HE↗

arXiv2023

Strong and weak pulsar radio emission due to thunderstorms and raindrops of particles in the magnetosphere

Pulsars radiate radio signals when they rotate. However, some old pulsars often stop radiating for some periods. The underlying mechanism remains unknown, while the magnetosphere during nulling phases is hard to probe due to the absence of emission measurement. Here we report the detection and accurate polarization measurements of sporadic weak narrow dwarf pulses detected in the ordinary nulling state of pulsar B2111+46 via the Five-Hundred-Meter Aperture Spherical radio Telescope (FAST). Further analysis shows that their polarization angles follow the average polarization angle curve of normal pulses, suggesting no change of magnetic field structure in the emission region in the two emission states. Whereas radio emission of normal individual pulses is radiated by a thunderstorm of particles produced by copious discharges in regularly formed gaps, dwarf pulses are produced by one or a few raindrops of particles generated by pair production in a fragile gap of this near-death pulsar.

astro-ph.HE↗

arXiv2023

Extreme events generated in microcavity lasers and their predictions by reservoir computing

Extreme events generated by complex systems have been intensively studied in many fields due to their great impact on scientific research and our daily lives. However, their prediction is still a challenge in spite of the tremendous progress that model-free machine learning has brought to the field. We experimentally generate, and theoretically model, extreme events in a current-modulated, single-mode microcavity laser operating on orthogonal polarizations, where their strongly differing thresholds -- due to cavity birefringence -- give rise to giant light pulses initiated by spontaneous emission. Applying reservoir-computing techniques, we identify in advance the emergence of an extreme event from a time series, in spite of coarse sampling and limited sample length. Performance is optimized through new hybrid configurations that we introduce in this paper. Advance warning times can reach 5ns, i.e. approximately ten times the rise time of the individual extreme event.

physics.optics↗

arXiv2023

FAST pulsar database: I. Polarization profiles of 682 pulsars

Pulsar polarization profiles are very basic database for understanding the emission processes in pulsar magnetosphere. After careful polarization calibration of the 19-beam L-band receiver and verification of beam-offset observation results, we obtain polarization profiles of 682 pulsars from observations by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during the survey tests for the Galactic Plan Pulsar Snapshot (GPPS) survey and other normal FAST projects. Among them, polarization profiles of about 460 pulsars are observed for the first time. The profiles exhibit diverse features. Some pulsars have a polarization position angle curve with a good S-shaped swing, and some with orthogonal modes; some have components with highly linearly components or strong circularly polarized components; some have a very wide profile, coming from an aligned rotator, and some have an interpulse from a perpendicular rotator; some wide profiles are caused by interstellar scattering. We derive geometry parameters for 190 pulsars from the S-shaped position angle curves or with orthogonal modes. We find that the linear and circular polarization or the widths of pulse profiles have various frequency dependencies. Pulsars with large fraction of linear polarization are more likely to have a large Edot.

astro-ph.HE↗

arXiv2023

Reservoir computing and task performing through using high-$β$ lasers with delayed optical feedback

Nonlinear photonic sources including semiconductor lasers have recently been utilized as ideal computation elements for information processing. They supply energy-efficient way and rich dynamics for classification and recognition tasks. In this work, we propose and numerically study the dynamics of complex photonic systems including high-$β$ laser element with delayed feedback and functional current modulation, and employ nonlinear laser dynamics of near-threshold region for the application in time-delayed reservoir computing. The results indicate a perfect (100$\%$) recognition accuracy for the pattern recognition task, and an accuracy of about 98$\%$ for the Mackey-Glass chaotic sequences prediction. Therefore, the system shows an improvement of performance with low-power consumption, in particular, the error rate is an order of magnitude smaller in comparison with previous works. Furthermore, by changing the DC pump, we are able to modify the amount of spontaneous emission photons of the system, this then allow us to explore how the laser noise impact the performance of the reservoir computing system. Through manipulating these variables, we show a deeper understanding on the proposed system, which is helpful for the practical applications of reservoir computing.

physics.optics↗

arXiv2023

Unbiased surveys of dust-enshrouded galaxies using ALMA

The ALMA lensing cluster survey (ALCS) is a 96-hr large program dedicated to uncovering and characterizing intrinsically faint continuum sources and line emitters with the assistance of gravitational lensing. All 33 cluster fields were selected from HST/Spitzer treasury programs including CLASH, Hubble Frontier Fields, and RELICS, which also have Herschel and Chandra coverages. The total sky area surveyed reaches $\sim$133 arcmin$^2$ down to a depth of $\sim$60 $μ$Jy beam$^{-1}$ (1$σ$) at 1.2 mm, yielding 141 secure blind detections of continuum sources and additional 39 sources aided by priors. We present scientific motivation, survey design, the status of spectroscopy follow-up observations, and number counts down to $\sim$7 $μ$Jy. Synergies with JWST are also discussed.

astro-ph.GA↗