arXiv subjects

Pei Wang

Publications and source records attributed to Pei Wang.

At least 127 records · Page 7Linked to original sources

arXiv2024

A discovery of Two Slow Pulsars with FAST: "Ronin" from the Globular Cluster M15

Globular clusters harbor numerous millisecond pulsars, but long-period pulsars ($P \gtrsim 100$ ms) are rarely found. In this study, we employed a fast folding algorithm to analyze observational data from multiple globular clusters obtained by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), aiming to detect the existence of long-period pulsars. We estimated the impact of the median filtering algorithm in eliminating red noise on the minimum detectable flux density ($S_{\rm min}$) of pulsars. Subsequently, we successfully discovered two isolated long-period pulsars in M15 with periods approximately equal to 1.928451 seconds and 3.960716 seconds, respectively. On the $P-\dot{P}$ diagram, both pulsars are positioned below the spin-up line, suggesting a possible history of partial recycling in X-ray binary systems disrupted by dynamical encounters later on. According to timing results, these two pulsars exhibit remarkably strong magnetic fields. If the magnetic fields were weakened during the accretion process, then a short duration of accretion might explain the strong magnetic fields of these pulsars.

astro-ph.HE↗

arXiv2024

Magnetic-field induced spiral order in the electric polarization

We present a phenomenological model for magnetoelectricity in multiferroic materials. The distinctive feature of the model is a two-component complex order parameter that encodes the electric polarization, along with a direct coupling between the polarization and magnetic field. Our model effectively elucidates that a sufficiently strong magnetic field can destroy electric polarization. Furthermore, the transition field strength diminishes with rising temperature, following a power-law relation with the exponent being precisely worked out. At lower field strength, the electric polarization takes a spiral order in the magnetic field, with the spiral wavelength inversely proportional to the magnetic field strength. We anticipate these predictions can be experimentally tested in future studies on multiferroic materials.

cond-mat.mtrl-sci↗

arXiv2024

A born ultramassive white dwarf-hot subdwarf super-Chandrasekhar candidate

Although supernovae is a well-known endpoint of an accreting white dwarf, alternative theoretical possibilities has been discussing broadly, such as the accretion-induced collapse (AIC) event as the endpoint of oxygen-neon (ONe) white dwarfs, either accreting up to or merging to excess the Chandrasekhar limit (the maximum mass of a stable white dwarf). AIC is an important channel to form neutron stars, especially for those unusual systems, which are hardly produced by core-collapse supernovae. However, the observational evidences for this theoretical predicted event and its progenitor are all very limited. In all of the known progenitors, white dwarfs increase in mass by accretion. Here, we report the discovery of an intriguing binary system Lan 11, consisted of a stripped core-helium-burning hot subdwarf and an unseen compact object of 1.08 to 1.35 $M_{\odot}$. Our binary population synthesis calculations, along with the absence of detection from the deep radio observations of the Five-hundred-meter Aperture Spherical Radio Telescope, strongly suggest that the latter is an ONe white dwarf. The total mass of this binary is 1.67 to 1.92 $M_{\odot}$}, significantly excessing the Chandrasekhar limit. The reproduction of its evolutionary history indicates that the unique system has undergone two phases of common envelope ejections, implying a born nature of this massive ONe white dwarf rather than an accretion growth from its companion. These results, together with short orbital period of this binary (3.65 hours), suggest that this system will merge in 500-540 Myr, largely triggering an AIC event, although the possibility of type Ia supernova cannot be fully ruled out. This finding greatly provides valuable constraints on our understanding of stellar endpoints, whatever leading to an AIC or a supernova.

astro-ph.SR↗

arXiv2024

Mixed-Query Transformer: A Unified Image Segmentation Architecture

Existing unified image segmentation models either employ a unified architecture across multiple tasks but use separate weights tailored to each dataset, or apply a single set of weights to multiple datasets but are limited to a single task. In this paper, we introduce the Mixed-Query Transformer (MQ-Former), a unified architecture for multi-task and multi-dataset image segmentation using a single set of weights. To enable this, we propose a mixed query strategy, which can effectively and dynamically accommodate different types of objects without heuristic designs. In addition, the unified architecture allows us to use data augmentation with synthetic masks and captions to further improve model generalization. Experiments demonstrate that MQ-Former can not only effectively handle multiple segmentation datasets and tasks compared to specialized state-of-the-art models with competitive performance, but also generalize better to open-set segmentation tasks, evidenced by over 7 points higher performance than the prior art on the open-vocabulary SeginW benchmark.

cs.CV↗

arXiv2024

Periodicity of sub-pulses in a radio pulsar

Pulsars are known to manifest complex phenomena, such as nulling, sub-pulse drifting, and periodicity. Within the purview of this investigation, we have harnessed the wavelet analysis technique to scrutinize the multifaceted periodicities and sub-pulse drifting characteristics exhibited by PSR J1926-0652, discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Our analysis draws upon the rich dataset acquired from the FAST ultra-wide-bandwidth receiver (UWB), meticulously examining pulse attributes encompassing an entire pulse. It is notable that the pulse apex recurrently manifests approximately every 17.11 times the pulsar's period P, individual sub-pulses exhibit a drifting phenomenon, with a phase decrement of approximately $1.04^\circ$ over each P. Intriguingly, the central phase of each sub-pulse track gradually increments over temporal evolution. Furthermore, the relative offset distribution between successive sub-pulse tracks emanating from the trailing and leading components remains comparatively stable, with a central tendency of approximately $\sim$6.87$\pm$2.56 P. Most notably, derived from the outcomes of wavelet analysis, we ascertain a negative correlation of -0.98 between the periods of sub-pulses and their drifting rates, alongside the intrinsic period of sub-pulses identified at 28.14 seconds.

astro-ph.HE↗

arXiv2024

Beyond the Known: Investigating LLMs Performance on Out-of-Domain Intent Detection

Out-of-domain (OOD) intent detection aims to examine whether the user's query falls outside the predefined domain of the system, which is crucial for the proper functioning of task-oriented dialogue (TOD) systems. Previous methods address it by fine-tuning discriminative models. Recently, some studies have been exploring the application of large language models (LLMs) represented by ChatGPT to various downstream tasks, but it is still unclear for their ability on OOD detection task.This paper conducts a comprehensive evaluation of LLMs under various experimental settings, and then outline the strengths and weaknesses of LLMs. We find that LLMs exhibit strong zero-shot and few-shot capabilities, but is still at a disadvantage compared to models fine-tuned with full resource. More deeply, through a series of additional analysis experiments, we discuss and summarize the challenges faced by LLMs and provide guidance for future work including injecting domain knowledge, strengthening knowledge transfer from IND(In-domain) to OOD, and understanding long instructions.

cs.CL↗

arXiv2024

The arrival time and energy of FRBs traverse the time-energy bivariate space like a Brownian motion

The origin of fast radio bursts (FRBs), the brightest cosmic explosion in radio bands, remains unknown. We introduce here a novel method for a comprehensive analysis of active FRBs' behaviors in the time-energy domain. Using ``Pincus Index'' and ``Maximum Lyapunov Exponent'', we were able to quantify the randomness and chaoticity, respectively, of the bursting events and put FRBs in the context of common transient physical phenomena, such as pulsar, earthquakes, and solar flares. In the bivariate time-energy domain, repeated FRB bursts' behaviors deviate significantly (more random, less chaotic) from pulsars, earthquakes, and solar flares. The waiting times between FRB bursts and the corresponding energy changes exhibit no correlation and remain unpredictable, suggesting that the emission of FRBs does not exhibit the time and energy clustering observed in seismic events. The pronounced stochasticity may arise from a singular source with high entropy or the combination of diverse emission mechanisms/sites. Consequently, our methodology serves as a pragmatic tool for illustrating the congruities and distinctions among diverse physical processes.

astro-ph.HE↗

arXiv2024

Multi-Perspective Consistency Enhances Confidence Estimation in Large Language Models

In the deployment of large language models (LLMs), accurate confidence estimation is critical for assessing the credibility of model predictions. However, existing methods often fail to overcome the issue of overconfidence on incorrect answers. In this work, we focus on improving the confidence estimation of large language models. Considering the fragility of self-awareness in language models, we introduce a Multi-Perspective Consistency (MPC) method. We leverage complementary insights from different perspectives within models (MPC-Internal) and across different models (MPC-Across) to mitigate the issue of overconfidence arising from a singular viewpoint. The experimental results on eight publicly available datasets show that our MPC achieves state-of-the-art performance. Further analyses indicate that MPC can mitigate the problem of overconfidence and is effectively scalable to other models.

cs.CL↗

arXiv2024

DolphCoder: Echo-Locating Code Large Language Models with Diverse and Multi-Objective Instruction Tuning

Code Large Language Models (Code LLMs) have demonstrated outstanding performance in code-related tasks. Several instruction tuning approaches have been proposed to boost the code generation performance of pre-trained Code LLMs. In this paper, we introduce a diverse instruction model (DolphCoder) with self-evaluating for code generation. It learns diverse instruction targets and combines a code evaluation objective to enhance its code generation ability. Our model achieves superior performance on the HumanEval and MBPP benchmarks, demonstrating new insights for future code instruction tuning work. Our key findings are: (1) Augmenting more diverse responses with distinct reasoning paths increases the code capability of LLMs. (2) Improving one's ability to evaluate the correctness of code solutions also enhances their ability to create it.

cs.CL↗

arXiv2024

Upper limits on the radio pulses from magnetars and a central compact object with FAST

Magnetars and central compact objects (CCOs) are subgroups of neutron stars that show a number of properties distinguished from canonical radio pulsars. We performed radio observations of three magnetars SGR 0418+5729, 1E 2259+586, 4U 0142+61, and a CCO PSR J1852+0040 with the Fivehundred-meter Aperture Spherical radio Telescope (FAST) at 1.25 GHz, aiming to search for radio pulsations in their quiescent states. During two observation epochs, no radio pulses have been detected towards any target above a significance of signal-to-noise ratio (S/N) = 7 from either the direct folding or blind search. We provided the most stringent upper limit of radio flux (<~ 2 -- 4 $μ$Jy) for the magnetars and the CCO. For the magnetars with long periods, the real upper limits are likely an order of magnitude larger due to the red noise. The deep radio observations suggest that these magnetars and the CCO are indeed radio-quiet sources or unfavorably beamed.

astro-ph.HE↗

arXiv2024

Discovery and timing of pulsar J2016$+$3711 in supernova remnant CTB 87 with FAST

We report on our discovery of the radio pulsar, PSR J2016$+$3711, in supernova remnant (SNR) CTB 87, with a $\sim10.8σ$ significance of pulses, which confirms the compact nature of the X-ray point source in CTB 87. It is the first pulsar discovered in SNRs using Five-hundred-meter Aperture Spherical radio Telescope (FAST). Its integrated radio pulse profile can be well described by a single component, with a width at 50% of the peak flux density of about 28.1$^\circ$ and an effective width of about 32.2$^\circ$. The mean flux density at 1.25 GHz is estimated to be about 15.5$μ$Jy. Combined with the non-detection of the radio pulse at lower frequencies, the radio spectral index of the pulsar is constrained to be $\lesssim 2.3$. We also present the timing solution based on 28 follow-up FAST observations. Our results reveal a period of 50.81 ms, period derivative of $7.2\times 10^{-14}$ s s$^{-1}$, and dispersion measure of 428 pc cm$^{-3}$. The strength of the equatorial surface magnetic dipole magnetic field is inferred to be about $1.9\times10^{12}$ G. Using the ephemeris obtained from the radio observations, we searched Fermi-LAT data for gamma-ray pulsations but detected no pulsed signal. We also searched for radio pulses with FAST toward the X-ray counterpart of the gamma-ray binary HESS J1832$-$093 proximate to SNR G22.7$-$00.2 but found no signal.

astro-ph.HE↗

arXiv2024

Plasma lensing interpretation of FRB 20201124A bursts at the end of September 2021

When the radio photons propagate through a non-uniform electron density volume, the plasma lensing effect can induce an extreme magnification to the observed flux at certain frequencies. Because the plasma lens acts as a diverging lens, it can extremely suppress the observed flux when aligned with source. These two properties can theoretically cause a highly magnified Fast Radio Burst (FRB) to faint or even disappear for a period of time. In this paper, we interpret that the significant increase in burst counts followed by a sudden quenching in FRB 20201124A in September 2021 can be attributed to plasma lensing. Based on the one-dimensional Gaussian lens model, we search for double main-peak structures in spectra just before its extinction on September 29, 2021. After the de-dispersion and de-scintillation procedures, we find eight bursts with double main-peaks at stable positions. There are three parameters in our modelling, the height and width of the one-dimension Gaussian lens and its distance to the source. We reformulate them as a combined parameter $\mathrm{P}_0 \propto \left ( \frac{a}{\mathrm{AU}}\right )\sqrt{\frac{\mathrm{kpc}}{D_{\mathrm{LS}}} \frac{\mathrm{pc}\;\mathrm{cm}^{-3}}{N_0} }$. The frequency spectra can give an accurate estimation of $\mathrm{P}_0$ corresponding to $\left ( \frac{a}{\mathrm{AU}}\right )\sqrt{\frac{\mathrm{kpc}}{D_{\mathrm{LS}}} \frac{\mathrm{pc}\;\mathrm{cm}^{-3}}{N_0} } \approx 28.118$, while the time of arrival only give a relatively loose constraint on $a^2/D_{\mathrm{LS}}$. Comparing with the observation dynamic spectra, we suggest that for a plasma lens in host galaxy, e.g., $D_{\mathrm{LS}}\approx 1\mathrm{kpc}$, the width of lens can not be larger than $40\mathrm{AU}$. At last, we estimate the relative transverse motion velocity between the lens and source, $v\approx98\left(\frac{a}{\mathrm{AU}}\right)\mathrm{km/s}$.

astro-ph.HE↗

arXiv2023

Scintillation Arc from FRB 20220912A

We present the interstellar scintillation analysis of fast radio burst (FRB) 20220912A during its extremely active episode in 2022 using data from the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). We detect a scintillation arc in the FRB's secondary spectrum, which describes the power in terms of the scattered FRB signals' time delay and Doppler shift. The arc indicates that the scintillation is caused by a highly localized region of the ionized interstellar medium (IISM). Our analysis favors a Milky Way origin for the localized scattering medium but cannot rule out a host galaxy origin. We present our method for detecting the scintillation arc, which can be applied generally to sources with irregularly spaced bursts or pulses. These methods could help shed light on the complex interstellar environment surrounding the FRBs and in our Galaxy.

astro-ph.HE↗

arXiv2023

Discovery and Timing of Millisecond Pulsars in the Globular Cluster M5 (NGC 5904) with FAST and Arecibo

We report on a comprehensive multi-wavelength study of the pulsars in the globular cluster (GC) M5, including the discovery of M5G, a new compact non-eclipsing "black widow" pulsar. Thanks to the analysis of 34 years of radio data taken with the FAST and Arecibo telescopes, we obtained new phase-connected timing solutions for four pulsars in the clusters and improved those of the other three known pulsars. These have resulted in, among other things: a) much improved proper motions for five pulsars, with transverse velocities that are smaller than their respective escape velocities; b) 3-sigma and 1.5-sigma detections of Shapiro delays in M5F and M5D, respectively; c) greatly improved measurement of the periastron advance in M5B, whose value of 0.01361(6) implies that M5B is still likely to be a heavy neutron star. The binary pulsars M5D, E and F are confirmed to be in low-eccentricity binary systems, the low-mass companions of which are newly identified to be He white dwarfs using Hubble Space Telescope data. Four pulsars are also found to be associated with X-ray sources. Similarly to the eclipsing pulsar M5C, M5G shows little or no non-thermal X-ray emission, indicative of weak synchrotron radiation produced by intra-binary shocks. All the seven pulsars known in M5 have short spin periods and five are in binary systems with low orbital eccentricities. These characteristics differ from the overall GC pulsar population, but confirm the expectations for the pulsar population in a cluster with a small rate of stellar encounters per binary system.

astro-ph.HE↗

arXiv2023

The Nearest Neutron Star Candidate in a Binary Revealed by Optical Time-domain Surveys

The near-Earth (within $\sim 100$ pc) supernova explosions in the past several million years can cause the global deposition of radioactive elements (e.g., $^{60}$Fe) on Earth. The remnants of such supernovae are too old to be easily identified. It is therefore of great interest to search for million-year-old near-Earth neutron stars or black holes, the products of supernovae. However, neutron stars and black holes are challenging to find even in our Solar neighbourhood if they are not radio pulsars or X-ray/$γ$-ray emitters. Here we report the discovery of one of the nearest ($127.7 \pm 0.3$ pc) neutron star candidates in a detached single-lined spectroscopic binary LAMOST J235456.73+335625.9 (hereafter J2354). Utilizing the time-resolved ground-based spectroscopy and space photometry, we find that J2354 hosts an unseen compact object with $M_{\mathrm{inv}}$ being $1.4 \sim 1.6\ M_{\odot}$. The follow-up Swift ultraviolet (UV) and X-ray observations suggest that the UV and X-ray emission is produced by the visible star rather than the compact object. Hence, J2354 probably harbours a neutron star rather than a hot ultramassive white dwarf. Two-hour exceptionally sensitive radio follow-up observations with Five-hundred-meter Aperture Spherical radio Telescope fail to reveal any pulsating radio signals at the $6σ$ flux upper limit of $12.5\ μ\mathrm{Jy}$. Therefore, the neutron star candidate in J2354 can only be revealed via our time-resolved observations. Interestingly, the distance between J2354 and our Earth can be as close as $\sim 50$ pc around $2.5$ Myrs ago, as revealed by the Gaia kinematics. Our discovery demonstrates a promising way to unveil the hidden near-Earth neutron stars in binaries by exploring the optical time domain, thereby facilitating understanding of the metal-enrichment history in our Solar neighbourhood.

astro-ph.HE↗

arXiv2023

Applying hybrid clustering in pulsar candidate sifting with multi-modality for FAST survey

Pulsar search is always the basis of pulsar navigation, gravitational wave detection and other research topics. Currently, the volume of pulsar candidates collected by Five-hundred-meter Aperture Spherical radio Telescope (FAST) shows an explosive growth rate that has brought challenges for its pulsar candidate filtering System. Particularly, the multi-view heterogeneous data and class imbalance between true pulsars and non-pulsar candidates have negative effects on traditional single-modal supervised classification methods. In this study, a multi-modal and semi-supervised learning based pulsar candidate sifting algorithm is presented, which adopts a hybrid ensemble clustering scheme of density-based and partition-based methods combined with a feature-level fusion strategy for input data and a data partition strategy for parallelization. Experiments on both HTRU (The High Time Resolution Universe Survey) 2 and FAST actual observation data demonstrate that the proposed algorithm could excellently identify the pulsars: On HTRU2, the precision and recall rates of its parallel mode reach 0.981 and 0.988. On FAST data, those of its parallel mode reach 0.891 and 0.961, meanwhile, the running time also significantly decrease with the increment of parallel nodes within limits. So, we can get the conclusion that our algorithm could be a feasible idea for large scale pulsar candidate sifting of FAST drift scan observation.

astro-ph.IM↗

arXiv2023

APP: Adaptive Prototypical Pseudo-Labeling for Few-shot OOD Detection

Detecting out-of-domain (OOD) intents from user queries is essential for a task-oriented dialogue system. Previous OOD detection studies generally work on the assumption that plenty of labeled IND intents exist. In this paper, we focus on a more practical few-shot OOD setting where there are only a few labeled IND data and massive unlabeled mixed data that may belong to IND or OOD. The new scenario carries two key challenges: learning discriminative representations using limited IND data and leveraging unlabeled mixed data. Therefore, we propose an adaptive prototypical pseudo-labeling (APP) method for few-shot OOD detection, including a prototypical OOD detection framework (ProtoOOD) to facilitate low-resource OOD detection using limited IND data, and an adaptive pseudo-labeling method to produce high-quality pseudo OOD\&IND labels. Extensive experiments and analysis demonstrate the effectiveness of our method for few-shot OOD detection.

cs.CL↗

arXiv2023

Large Language Models Meet Open-World Intent Discovery and Recognition: An Evaluation of ChatGPT

The tasks of out-of-domain (OOD) intent discovery and generalized intent discovery (GID) aim to extend a closed intent classifier to open-world intent sets, which is crucial to task-oriented dialogue (TOD) systems. Previous methods address them by fine-tuning discriminative models. Recently, although some studies have been exploring the application of large language models (LLMs) represented by ChatGPT to various downstream tasks, it is still unclear for the ability of ChatGPT to discover and incrementally extent OOD intents. In this paper, we comprehensively evaluate ChatGPT on OOD intent discovery and GID, and then outline the strengths and weaknesses of ChatGPT. Overall, ChatGPT exhibits consistent advantages under zero-shot settings, but is still at a disadvantage compared to fine-tuned models. More deeply, through a series of analytical experiments, we summarize and discuss the challenges faced by LLMs including clustering, domain-specific understanding, and cross-domain in-context learning scenarios. Finally, we provide empirical guidance for future directions to address these challenges.

cs.CL↗