arXiv subjects

Bing Li

Publications and source records attributed to Bing Li.

At least 433 records · Page 24Linked to original sources

arXiv2019

Insight-HXMT observations of Swift J0243.6+6124 during its 2017-2018 outburst

The recently discovered neutron star transient Swift J0243.6+6124 has been monitored by {\it the Hard X-ray Modulation Telescope} ({\it Insight-\rm HXMT). Based on the obtained data, we investigate the broadband spectrum of the source throughout the outburst. We estimate the broadband flux of the source and search for possible cyclotron line in the broadband spectrum. No evidence of line-like features is, however, found up to $\rm 150~keV$. In the absence of any cyclotron line in its energy spectrum, we estimate the magnetic field of the source based on the observed spin evolution of the neutron star by applying two accretion torque models. In both cases, we get consistent results with $B\rm \sim 10^{13}~G$, $D\rm \sim 6~kpc$ and peak luminosity of $\rm >10^{39}~erg~s^{-1}$ which makes the source the first Galactic ultraluminous X-ray source hosting a neutron star.

astro-ph.HE↗

arXiv2019

RED: A ReRAM-based Deconvolution Accelerator

Deconvolution has been widespread in neural networks. For example, it is essential for performing unsupervised learning in generative adversarial networks or constructing fully convolutional networks for semantic segmentation. Resistive RAM (ReRAM)-based processing-in-memory architecture has been widely explored in accelerating convolutional computation and demonstrates good performance. Performing deconvolution on existing ReRAM-based accelerator designs, however, suffers from long latency and high energy consumption because deconvolutional computation includes not only convolution but also extra add-on operations. To realize the more efficient execution for deconvolution, we analyze its computation requirement and propose a ReRAM-based accelerator design, namely, RED. More specific, RED integrates two orthogonal methods, the pixel-wise mapping scheme for reducing redundancy caused by zero-inserting operations and the zero-skipping data flow for increasing the computation parallelism and therefore improving performance. Experimental evaluations show that compared to the state-of-the-art ReRAM-based accelerator, RED can speed up operation 3.69x~1.15x and reduce 8%~88.36% energy consumption.

cs.ET↗

arXiv2019

An Overview of In-memory Processing with Emerging Non-volatile Memory for Data-intensive Applications

The conventional von Neumann architecture has been revealed as a major performance and energy bottleneck for rising data-intensive applications. %, due to the intensive data movements. The decade-old idea of leveraging in-memory processing to eliminate substantial data movements has returned and led extensive research activities. The effectiveness of in-memory processing heavily relies on memory scalability, which cannot be satisfied by traditional memory technologies. Emerging non-volatile memories (eNVMs) that pose appealing qualities such as excellent scaling and low energy consumption, on the other hand, have been heavily investigated and explored for realizing in-memory processing architecture. In this paper, we summarize the recent research progress in eNVM-based in-memory processing from various aspects, including the adopted memory technologies, locations of the in-memory processing in the system, supported arithmetics, as well as applied applications.

cs.AR↗

arXiv2019

Thread Batching for High-performance Energy-efficient GPU Memory Design

Massive multi-threading in GPU imposes tremendous pressure on memory subsystems. Due to rapid growth in thread-level parallelism of GPU and slowly improved peak memory bandwidth, the memory becomes a bottleneck of GPU's performance and energy efficiency. In this work, we propose an integrated architectural scheme to optimize the memory accesses and therefore boost the performance and energy efficiency of GPU. Firstly, we propose a thread batch enabled memory partitioning (TEMP) to improve GPU memory access parallelism. In particular, TEMP groups multiple thread blocks that share the same set of pages into a thread batch and applies a page coloring mechanism to bound each stream multiprocessor (SM) to the dedicated memory banks. After that, TEMP dispatches the thread batch to an SM to ensure high-parallel memory-access streaming from the different thread blocks. Secondly, a thread batch-aware scheduling (TBAS) scheme is introduced to improve the GPU memory access locality and to reduce the contention on memory controllers and interconnection networks. Experimental results show that the integration of TEMP and TBAS can achieve up to 10.3% performance improvement and 11.3% DRAM energy reduction across diverse GPU applications. We also evaluate the performance interference of the mixed CPU+GPU workloads when they are run on a heterogeneous system that employs our proposed schemes. Our results show that a simple solution can effectively ensure the efficient execution of both GPU and CPU applications.

cs.AR↗

arXiv2019

Late-Time Afterglow from Double-Sided Structured Jets: Application to GRB 170817A

The broadband afterglow of GW170817/GRB 170817A is believed to be from an off-axis structured jet. The central engine of a gamma-ray burst usually launches a pair of outflows that move oppositely, it is reasonable to consider the emission from a double-sided structured jets, with a near-jet moving toward us and a counter-jet moving away from us. Assuming that the two branches of the jet have the same physical parameters, we have calculated their radio emission. It is found that the counter-jet component will emerge in the radio light curves $\sim$ 2500 days post-merger.It typically leads to a plateau in the light curve, thus could be hopefully revealed by high accuracy radio observations. We have also considered the possibilities that both branches have different parameters, and found that if some of the physical parameters of the counter-jet are evaluated more favorably than those of the near-jet, then the counter-jet emission will be enhanced and will clearly show up as an obvious plateau or even a rebrightening. For example, when the circum-burst medium encountered by the counter-jet is assumed to be 100 times denser than that of the near-jet, a remarkable radio plateau will appear at $\sim$ 600 days. However, in X-ray bands, the counter-jet component is generally too faint to be discerned. It is argued that the late radio observations of GW170817/GRB 170817A can help determine the key parameters and diagnose the environment of the event.

astro-ph.HE↗

arXiv2019

Multimodal Semantic Attention Network for Video Captioning

Inspired by the fact that different modalities in videos carry complementary information, we propose a Multimodal Semantic Attention Network(MSAN), which is a new encoder-decoder framework incorporating multimodal semantic attributes for video captioning. In the encoding phase, we detect and generate multimodal semantic attributes by formulating it as a multi-label classification problem. Moreover, we add auxiliary classification loss to our model that can obtain more effective visual features and high-level multimodal semantic attribute distributions for sufficient video encoding. In the decoding phase, we extend each weight matrix of the conventional LSTM to an ensemble of attribute-dependent weight matrices, and employ attention mechanism to pay attention to different attributes at each time of the captioning process. We evaluate algorithm on two popular public benchmarks: MSVD and MSR-VTT, achieving competitive results with current state-of-the-art across six evaluation metrics.

cs.CV↗

arXiv2019

Production of the exotic neutron-deficient isotopes near N, Z = 50 in multinucleon transfer reactions

The multinucleon transfer reaction in the collisions of $^{40}$Ca+$^{124}$Sn at $E_{\textrm{c.m.}}=128.5$ MeV is investigated by using the improved quantum molecular dynamics model. The measured angular distributions and isotopic distributions of the products are reproduced reasonably well by the calculations. The multinucleon transfer reactions of $^{40}$Ca+$^{112}$Sn, $^{58}$Ni+$^{112}$Sn, $^{106}$Cd+$^{112}$Sn, and $^{48}$Ca+$^{112}$Sn are also studied. It shows that the combinations of neutron-deficient projectile and target are advantageous to produce the exotic neutron-deficient nuclei near $N, Z$ = 50. The charged particles emission plays an important role at small impact parameters in the deexcitation processes of the system. The production cross sections of the exotic neutron-deficient nuclei in multinucleon transfer reactions are much larger than those measured in the fragmentation and fusion-evaporation reactions. Several new neutron-deficient nuclei can be produced in $^{106}$Cd+$^{112}$Sn reaction. The corresponding production cross sections for the new neutron-deficient nuclei, $^{101,102}$Sb, $^{103}$Te, and $^{106,107}$I, are 2.0 nb, 4.1 nb, 6.5 nb, 0.4 $μ$b and 1.0 $μ$b, respectively.

nucl-th↗

arXiv2019

Crystal growth, microstructure and physical properties of SrMnSb$_2$

We report on the crystal and magnetic structures, magnetic, and transport properties of SrMnSb$_2$ single crystals grown by the self-flux method. Magnetic susceptibility measurements reveal an antiferromagnetic (AFM) transition at $T_{\rm N} = 295(3)$ K. Above $T_{\rm N}$, the susceptibility slightly increases and forms a broad peak at $T \sim 420$ K, which is a typical feature of two-dimensional magnetic systems. Neutron diffraction measurements on single crystals confirm the previously reported C-type AFM structure below $T_{\rm N}$. Both de Haas-van Alphen (dHvA) and Shubnikov-de Haas (SdH) effects are observed in SrMnSb$_2$ single crystals. Analysis of the oscillatory component by a Fourier transform shows that the prominent frequencies obtained by the two different techniques are practically the same within error regardless of sample size or saturated magnetic moment. Transmission electron microscopy (TEM) reveals the existence of stacking faults in the crystals, which result from a horizontal shift of Sb atomic layers suggesting possible ordering of Sb vacancies in the crystals. Increase of temperature in susceptibility measurements leads to the formation of a strong peak at $T \sim {570}$ K that upon cooling under magnetic field the susceptibility shows a ferromagnetic transition at $T_{\rm C} \sim 580$ K. Neutron powder diffraction on crushed single-crystals does not support an FM phase above $T_{\rm N}$. Furthermore, X-ray magnetic circular dichroism (XMCD) measurements of a single crystal at the $L_{2,3}$ edge of Mn shows a signal due to induced canting of AFM moments by the applied magnetic field. All evidence strongly suggests that a chemical transformation at the surface of single crystals occurs above 500 K concurrently producing a minute amount of ferromagnetic impurity phase.

cond-mat.mtrl-sci↗

arXiv2019

Statistical properties of the repeating fast radio burst source FRB 121102

Currently, FRB 121102 is the only fast radio burst source that was observed to give out bursts repeatedly. It shows a high repeating rate, with more than one hundred bursts being spotted, but with no obvious periodicity in the activities. Thanks to its repetition, the source was well localized with a subarcsecond accuracy, leading to a redshift measurement of about 0.2. FRB 121102 is a unique source that can help us understand the enigmatic nature of fast radio bursts. In this study, we analyze the characteristics of the waiting times between bursts from FRB 121102. It is found that there is a clear bimodal distribution for the waiting times. While most waiting times cluster at several hundred seconds, a small portion of the waiting times are strikingly in the range of 2--40 millisecond. More interestingly, it is found that the waiting time does not correlate with the burst intensity, either for the preceding burst or for the subsequent burst. It strongly indicates that the repeating bursts should be generated by some external mechanisms, but not internal mechanisms. As a result, the models involving collisions between small bodies and neutron stars could be competitive mechanisms for this interesting source.

astro-ph.HE↗

arXiv2018

Production of new neutron-rich heavy nuclei with $Z=56-80$ in the multinucleon transfer reactions of $^{136}$Xe+$^{198}$Pt

The multinucleon transfer reactions in collisions of $^{136}$Xe+$^{198}$Pt at incident energies $E_{\textrm{lab}}=$5.25, 6.20, 7.98, 10.0, and 15.0 MeV/nucleon are investigated by using the improved quantum molecular dynamics model. It is found that 6.20 MeV/nucleon is the optimal incident energy for producing the neutron-rich heavy nuclei. About 80 unknown neutron-rich nuclei might be produced in this reaction with cross sections from 10$^{-6}$ to 10$^{-2}$ mb. The angular distributions of the neutron-rich isotopes are predicted.

nucl-th↗

arXiv2018

A fallback accretion model for the unusual type II-P supernova iPTF14hls

The Intermediate Palomar Transient Factory reported the discovery of an unusual type II-P supernova iPTF14hls. Instead of a ~100-day plateau as observed for ordinary type II-P supernovae, the light curve of iPTF14hls has at least five distinct peaks, followed by a steep decline at ~1000 days since discovery. Until 500 days since discovery, the effective temperature of iPTF14hls is roughly constant at 5000-6000K . In this paper we propose that iPTF14hls is likely powered by intermittent fallback accretion. It is found that the light curve of iPTF14hls can be well fit by the usual t^{-5/3} accretion law until ~1000 days post discovery when the light curve transitions to a steep decline. To account for this steep decline, we suggest a power-law density profile for the late accreted material, rather than the constant profile as appropriated for the t^{-5/3} accretion law. Detailed modeling indicates that the total fallback mass is ~0.2M_{sun}, with an ejecta mass M_{ej}~21M_{sun}. We find the third peak of the light curve cannot be well fit by the fallback model, indicating that there could be some extra rapid energy injection. We suggest that this extra energy injection may be a result of a magnetic outburst if the central object is a neutron star. These results indicate that the progenitor of iPTF14hls could be a massive red supergiant.

astro-ph.HE↗

arXiv2018

Isospin equilibration in multinucleon transfer reaction at near-barrier energies

The isospin equilibration process in multinucleon transfer reaction is investigated by using the improved quantum molecular dynamics model. The collision processes of $^{124}$Xe+$^{208}$Pb at near-barrier energy are studied with different symmetry energy coefficients. We find that neutrons transfer happens earlier than protons. The large symmetry energy promote the transfer of neutrons. The neutron flow from the target to projectile is along the low-density path of neck. The isospin equilibration process in $^{58}$Ni+$^{208}$Pb reaction is also investigated and compared with available experimental data. It shows that $N/Z$ values of the projectile-like products increase rapidly with increasing mass transfer. The complete isospin equilibration events are located in the region of $120<A<150$ which are produced in symmetric fission-type reactions.

nucl-th↗

arXiv2018

Colossal barocaloric effects in plastic crystals

Solid-state refrigeration technology based on caloric effects are promising to replace the currently used vapor compression cycles. However, their application is restricted due to limited performances of caloric materials. Here, we have identified colossal barocaloric effects (CBCEs) in a class of disordered solids called plastic crystals. The obtained entropy changes are about 380 J kg-1 K-1 in the representative neopentylglycol around room temperature. Inelastic neutron scattering reveals that the CBCEs in plastic crystals are attributed to the combination of the vast molecular orientational disorder, giant compressibility, and high anharmonic lattice dynamics. Our study establishes the microscopic scenario for CBCEs in plastic crystals and paves a new route to the next-generation solid-state refrigeration technology.

cond-mat.mtrl-sci↗

arXiv2018

Interaction-aware Spatio-temporal Pyramid Attention Networks for Action Classification

Local features at neighboring spatial positions in feature maps have high correlation since their receptive fields are often overlapped. Self-attention usually uses the weighted sum (or other functions) with internal elements of each local feature to obtain its weight score, which ignores interactions among local features. To address this, we propose an effective interaction-aware self-attention model inspired by PCA to learn attention maps. Furthermore, since different layers in a deep network capture feature maps of different scales, we use these feature maps to construct a spatial pyramid and then utilize multi-scale information to obtain more accurate attention scores, which are used to weight the local features in all spatial positions of feature maps to calculate attention maps. Moreover, our spatial pyramid attention is unrestricted to the number of its input feature maps so it is easily extended to a spatio-temporal version. Finally, our model is embedded in general CNNs to form end-to-end attention networks for action classification. Experimental results show that our method achieves the state-of-the-art results on the UCF101, HMDB51 and untrimmed Charades.

cs.CV↗

arXiv2018

Antiferromagnetic order in CaK(Fe[1-x]Ni[x])4As4 and its interplay with superconductivity

The magnetic order in CaK(Fe[1-x]Ni[x])4As4 (1144) single crystals (x = 0.051 and 0.033) has been studied by neutron diffraction. We observe magnetic Bragg peaks associated to the same propagation vectors as found for the collinear stripe antiferromagnetic (AFM) order in the related BaFe2As2 (122) compound. The AFM state in 1144 preserves tetragonal symmetry and only a commensurate, non-collinear structure with a hedgehog spin-vortex crystal (SVC) arrangement in the Fe plane and simple AFM stacking along the c direction is consistent with our observations. The SVC order is promoted by the reduced symmetry in the FeAs layer in the 1144 structure. The long-range SVC order coexists with superconductivity, however, similar to the doped 122 compounds, the ordered magnetic moment is gradually suppressed with the developing superconducting order parameter. This supports the notion that both collinear and non-collinear magnetism and superconductivity are competing for the same electrons coupled by Fermi surface nesting in iron arsenide superconductors.

cond-mat.supr-con↗

arXiv2018

A Model of Fast Radio Bursts: Collisions Between Episodic Magnetic Blobs

Fast radio bursts (FRBs) are bright radio pulses from the sky with millisecond durations and Jansky-level flux densities. Their origins are still largely uncertain. Here we suggest a new model for FRBs. We argue that the collision of a white dwarf with a black hole can give birth to a transient accretion disk, from which powerful episodic magnetic blobs will be launched. The collision between two consecutive magnetic blobs can result in a catastrophic magnetic reconnection, which releases a large amount of free magnetic energy and forms a forward shock. The shock propagates through the cold magnetized plasma within the blob in the collision region, radiating through synchrotron maser mechanism, which is responsible for a non-repeating FRB signal. Our calculations show that the theoretical energetics, radiation frequency, duration timescale, and event rate can be well consistent with the observational characteristic of FRBs.

astro-ph.HE↗

arXiv2018

Automatic Detection of Public Development Projects in Large Open Source Ecosystems: An Exploratory Study on GitHub

Hosting over 10 million of software projects, GitHub is one of the most important data sources to study behavior of developers and software projects. However, with the increase of the size of open source datasets, the potential threats to mining these datasets have also grown. As the dataset grows, it becomes gradually unrealistic for human to confirm quality of all samples. Some studies have investigated this problem and provided solutions to avoid threats in sample selection, but some of these solutions (e.g., finding development projects) require human intervention. When the amount of data to be processed increases, these semi-automatic solutions become less useful since the effort in need for human intervention is far beyond affordable. To solve this problem, we investigated the GHTorrent dataset and proposed a method to detect public development projects. The results show that our method can effectively improve the sample selection process in two ways: (1) We provide a simple model to automatically select samples (with 0.827 precision and 0.947 recall); (2) We also offer a complex model to help researchers carefully screen samples (with 63.2% less effort than manually confirming all samples, and can achieve 0.926 precision and 0.959 recall).

cs.SE↗

arXiv2018

Continued Brightening of the Afterglow of GW170817/GRB 170817A as due to a Delayed Energy Injection

The brightness of the multi-wavelength afterglow of GRB 170817A is increasing unexpectedly even $\sim$ 160 days after the associated gravitational burst. Here we suggest that the brightening can be caused by a late-time energy injection process. We use an empirical expression to mimic the evolution of the injection luminosity, which is consisted of a power-law rising phase and a power-law decreasing phase. It is found that the power-law indices of the two phases are $0.92$ and $-2.8$, respectively, with the peak time of the injection being $\sim 110$ days. The energy injection could be due to some kind of accretion, with the total accreted mass being $\sim 0.006 M_\odot$. However, normal fall-back accretion, which usually lasts for a much shorter period, cannot provide a natural explanation. Our best-fit decaying index of $-2.8$ is also at odds with the expected value of $-5/3$ for normal fall-back accretion. Noting that the expansion velocities of the kilonova components associated with GW170817 is $0.1-0.3\,c$, we argue that there should also be some ejecta with correspondingly lower velocities during the coalescence of the double neutron star system. They are bound by the gravitational well of the remnant central compact object and might be accreted at a timescale of about 100 days, providing a reasonable explanation for the energy injection. Detailed studies on the long-lasting brightening of GRB 170817A thus may provide useful information on the matter ejection during the merger process of binary neutron stars.

astro-ph.HE↗