arXiv subjects

Qian Wang

Publications and source records attributed to Qian Wang.

At least 559 records · Page 31Linked to original sources

arXiv2017

Exotic candidates with heavy quark(s)

In the last decades, the number of exotic candidates which are beyond the conventional quark model has grown dramatically. At the same time, numerous theoretical interpretations, such as tetraquark, hybrid, hadroquarkonium and hadronic molecule, have been proposed to understand their nature. In principle, all the configurations with the same quantum numbers can mix with each other. Thus at present we aim at identifying the prominent component. As an extended object, a hadronic molecule has some distinguishable features from other more compact configurations. In the end, the two $Z_b$ states are used to illustrate some features of the molecular scenario.

hep-ph↗

arXiv2017

Double heavy tri-hadron bound state via delocalized $π$ bond

The number of exotic candidates which are beyond the conventional quark model has grown dramatically during the last decades. Some of them could be viewed as analogues of the deuteron. Similarly, the existence of the triton indicates that bound states formed by three hadrons could also exist. To illustrate this possibility, we study the $DD^*K$ and $BB^*\bar{K}$ systems by using the Born-Oppenheimer Approximation. To leading order, only one-pion exchange potentials are considered, which means that the three constitutes share one virtual pion. That is similar to the role of the delocalized $π$ bond for the formation of Benzene in chemistry. After solving the Schrödinger equation, we find two three-body $DD^*K$ and $BB^*\bar{K}$ bound states with masses $4317.92_{-4.32}^{+3.66}~\mathrm{MeV}$ and $11013.65_{-8.84}^{+8.49}~\mathrm{MeV}$, respectively. The masses of their $D\bar{D}^*K$ and $B\bar{B}^*\bar{K}$ analogues are $4317.92_{-6.55}^{+6.13}~\mathrm{MeV}$ and $11013.65_{-9.02}^{+8.68}~\mathrm{MeV}$. From the experimental side, the $D\bar{D}^*K$ bound state could be found by analyzing the current world data of the $B\to J/ψππK$ process by focusing on the $J/ψπK$ channel. Its confirmation could also help to understand the formation of kaonic nuclei in nuclear physics.

hep-ph↗

arXiv2017

Deep Embedding Convolutional Neural Network for Synthesizing CT Image from T1-Weighted MR Image

Recently, more and more attention is drawn to the field of medical image synthesis across modalities. Among them, the synthesis of computed tomography (CT) image from T1-weighted magnetic resonance (MR) image is of great importance, although the mapping between them is highly complex due to large gaps of appearances of the two modalities. In this work, we aim to tackle this MR-to-CT synthesis by a novel deep embedding convolutional neural network (DECNN). Specifically, we generate the feature maps from MR images, and then transform these feature maps forward through convolutional layers in the network. We can further compute a tentative CT synthesis from the midway of the flow of feature maps, and then embed this tentative CT synthesis back to the feature maps. This embedding operation results in better feature maps, which are further transformed forward in DECNN. After repeat-ing this embedding procedure for several times in the network, we can eventually synthesize a final CT image in the end of the DECNN. We have validated our proposed method on both brain and prostate datasets, by also compar-ing with the state-of-the-art methods. Experimental results suggest that our DECNN (with repeated embedding op-erations) demonstrates its superior performances, in terms of both the perceptive quality of the synthesized CT image and the run-time cost for synthesizing a CT image.

cs.CV↗

arXiv2017

Real-time Traffic Accident Risk Prediction based on Frequent Pattern Tree

Traffic accident data are usually noisy, contain missing values, and heterogeneous. How to select the most important variables to improve real-time traffic accident risk prediction has become a concern of many recent studies. This paper proposes a novel variable selection method based on the Frequent Pattern tree (FP tree) algorithm. First, all the frequent patterns in the traffic accident dataset are discovered. Then for each frequent pattern, a new criterion, called the Relative Object Purity Ratio (ROPR) which we proposed, is calculated. This ROPR is added to the importance score of the variables that differentiate one frequent pattern from the others. To test the proposed method, a dataset was compiled from the traffic accidents records detected by only one detector on interstate highway I-64 in Virginia in 2005. This dataset was then linked to other variables such as real-time traffic information and weather conditions. Both the proposed method based on the FP tree algorithm, as well as the widely utilized, random forest method, were then used to identify the important variables or the Virginia dataset. The results indicate that there are some differences between the variables deemed important by the FP tree and those selected by the random forest method. Following this, two baseline models (i.e. a nearest neighbor (k-NN) method and a Bayesian network) were developed to predict accident risk based on the variables identified by both the FP tree method and the random forest method. The results show that the models based on the variable selection using the FP tree performed better than those based on the random forest method for several versions of the k-NN and Bayesian network models.The best results were derived from a Bayesian network model using variables from FP tree. That model could predict 61.11% of accidents accurately while having a false alarm rate of 38.16%.

stat.AP↗

arXiv2017

Isospin analysis of $B\to D^*\bar{D}K$ and the absence of the $Z_c(3900)$ in $B$ decays

We study the isospin amplitudes in the exclusive $B$ to $D^*\bar{D}K$ decay process and fit the available $D^{*0}\bar{D}^0$ invariant mass distributions near threshold. The analysis demonstrates that the production of the isospin triplet $D^*\bar{D}$ state is highly suppressed compared to the isospin singlet one. That explains why the $Z_c(3900)$ has not been found in $B$ decays. In addition, the production of the negative charge-parity state might be further suppressed in the heavy quark limit. These two reasons which are based on the molecular assumption offer the first explanation why the $Z_c(3900)$ is absent in $B$ decays. Further studies of the absence from both the experimental and the theoretical side is extremely important for understanding the nature of the $X(3872)$ and the $Z_c(3900)$.

hep-ph↗

arXiv2017

Data-Driven Robust Taxi Dispatch under Demand Uncertainties

In modern taxi networks, large amounts of taxi occupancy status and location data are collected from networked in-vehicle sensors in real-time. They provide knowledge of system models on passenger demand and mobility patterns for efficient taxi dispatch and coordination strategies. Such approaches face new challenges: how to deal with uncertainties of predicted customer demand while fulfilling the system's performance requirements, including minimizing taxis' total idle mileage and maintaining service fairness across the whole city; how to formulate a computationally tractable problem. To address this problem, we develop a data-driven robust taxi dispatch framework to consider spatial-temporally correlated demand uncertainties. The robust vehicle dispatch problem we formulate is concave in the uncertain demand and convex in the decision variables. Uncertainty sets of random demand vectors are constructed from data based on theories in hypothesis testing, and provide a desired probabilistic guarantee level for the performance of robust taxi dispatch solutions. We prove equivalent computationally tractable forms of the robust dispatch problem using the minimax theorem and strong duality. Evaluations on four years of taxi trip data for New York City show that by selecting a probabilistic guarantee level at 75%, the average demand-supply ratio error is reduced by 31.7%, and the average total idle driving distance is reduced by 10.13% or about 20 million miles annually, compared with non-robust dispatch solutions.

eess.SY↗

arXiv2017

C-field smoothing by trajectory dynamically tracing compensation in rubidium fountain clock

We present a trajectory dynamically tracing compensation method to smooth the spatial fluctuation of the static magnetic field (C-field) that provides a quantization axis in the fountain clock. The C-field coil current is point-to-point adjusted in accordance to the atoms experienced magnetic field along the flight trajectory. A homogeneous field with a 0.2 nT uncertainty is realized compared to 5 nT under the static magnetic field with constant current during the Ramsey interrogation. The corresponding uncertainty associated with the second-order Zeeman shift that we calculate is improved by one order of magnitude. The technique provides an alternative method to improve the magnetic field uniformity particularly for large-scale equipment that is difficult to machine with magnetic shielding. Our method is simple, robust, and essentially important in frequency evaluations concerning the dominant uncertainty contribution due to the quadratic Zeeman shift.

physics.atom-ph↗

arXiv2017

Probing the excited-state quantum phase transition through statistics of Loschmidt echo and quantum work

By analyzing the probability distributions of the Loschmidt echo (LE) and quantum work, we examine the nonequilibrium effects of a quantum many-body system, which exhibits an excited-state quantum phase transition (ESQPT). We find that depending on the value of the controlling parameter the distribution of the LE displays different patterns. At the critical point of the ESQPT, both the averaged LE and the averaged work show a cusplike shape. Furthermore, by employing the finite-size scaling analysis of the averaged work, we obtain the critical exponent of the ESQPT. Finally, we show that at the critical point of ESQPT the eigenstate is a highly localized state, further highlighting the influence of the ESQPT on the properties of the many-body system.

quant-ph↗

arXiv2017

The merging galaxy cluster A520 --- a broken-up cool core, a dark subcluster, and an X-ray channel

We present results from a deep Chandra X-ray observation of a merging galaxy cluster A520. A high-resolution gas temperature map, after the subtraction of the cluster-scale emission, reveals a long trail of dense, cool clumps --- apparently the fragments of a cool core that has been completely stripped from the infalling subcluster by ram pressure. In this scenario, we can assume that the clumps are still connected by the magnetic field lines. The observed temperature variations imply that thermal conductivity is suppressed by a factor >100 across the presumed direction of the magnetic field (as found in other clusters), and is also suppressed -along- the field lines by a factor of several. Two massive clumps in the periphery of A520, visible in the weak lensing mass map and the X-ray image, have apparently been completely stripped of gas during the merger, but then re-accreted the surrounding high-entropy gas upon exit from the cluster. An X-ray hydrostatic mass estimate for one of the clumps (that has simple geometry) agrees with the lensing mass. Its current gas mass to total mass ratio is very low, 1.5-3%, which makes it a "dark subcluster". We also found a curious low X-ray brightness channel (likely a low-density sheet in projection) going across the cluster along the direction of an apparent secondary merger. The channel may be caused by plasma depletion in a region of an amplified magnetic field (with plasma $β\sim 10-20$). The shock in A520 will be studied in a separate paper.

astro-ph.CO↗

arXiv2017

Alternative Semantic Representations for Zero-Shot Human Action Recognition

A proper semantic representation for encoding side information is key to the success of zero-shot learning. In this paper, we explore two alternative semantic representations especially for zero-shot human action recognition: textual descriptions of human actions and deep features extracted from still images relevant to human actions. Such side information are accessible on Web with little cost, which paves a new way in gaining side information for large-scale zero-shot human action recognition. We investigate different encoding methods to generate semantic representations for human actions from such side information. Based on our zero-shot visual recognition method, we conducted experiments on UCF101 and HMDB51 to evaluate two proposed semantic representations . The results suggest that our proposed text- and image-based semantic representations outperform traditional attributes and word vectors considerably for zero-shot human action recognition. In particular, the image-based semantic representations yield the favourable performance even though the representation is extracted from a small number of images per class.

cs.CV↗

arXiv2017

Zero-Shot Visual Recognition via Bidirectional Latent Embedding

Zero-shot learning for visual recognition, e.g., object and action recognition, has recently attracted a lot of attention. However, it still remains challenging in bridging the semantic gap between visual features and their underlying semantics and transferring knowledge to semantic categories unseen during learning. Unlike most of the existing zero-shot visual recognition methods, we propose a stagewise bidirectional latent embedding framework to two subsequent learning stages for zero-shot visual recognition. In the bottom-up stage, a latent embedding space is first created by exploring the topological and labeling information underlying training data of known classes via a proper supervised subspace learning algorithm and the latent embedding of training data are used to form landmarks that guide embedding semantics underlying unseen classes into this learned latent space. In the top-down stage, semantic representations of unseen-class labels in a given label vocabulary are then embedded to the same latent space to preserve the semantic relatedness between all different classes via our proposed semi-supervised Sammon mapping with the guidance of landmarks. Thus, the resultant latent embedding space allows for predicting the label of a test instance with a simple nearest-neighbor rule. To evaluate the effectiveness of the proposed framework, we have conducted extensive experiments on four benchmark datasets in object and action recognition, i.e., AwA, CUB-200-2011, UCF101 and HMDB51. The experimental results under comparative studies demonstrate that our proposed approach yields the state-of-the-art performance under inductive and transductive settings.

cs.CV↗

arXiv2017

A geometric perspective on the method of descent

We derive a representation formula for the tensorial wave equation $\Box_\bg ϕ^I=F^I$ in globally hyperbolic Lorentzian spacetimes $(\M^{2+1}, \bg)$ by giving a geometric formulation of the method of descent which is applicable for any dimension.

math.AP↗

arXiv2017

Understanding quantum work in a quantum many-body system

Based on previous studies in a single particle system in both the integrable [Jarzynski, Quan, and Rahav, Phys.~Rev.~X {\bf 5}, 031038 (2015)] and the chaotic systems [Zhu, Gong, Wu, and Quan, Phys.~Rev.~E {\bf 93}, 062108 (2016)], we study the the correspondence principle between quantum and classical work distributions in a quantum many-body system. Even though the interaction and the indistinguishability of identical particles increase the complexity of the system, we find that for a quantum many-body system the cumulative quantum work distribution still converges to its classical counterpart in the semiclassical limit. Our results imply that there exists a correspondence principle between quantum and classical work distributions in an interacting quantum many-body system, especially in the large particle number limit, and further justify the definition of quantum work via two point energy measurements in quantum many-body systems.

quant-ph↗

arXiv2017

The bunch current measurement using high-speed photodetector at HLS II

This contribution presents a novel bunch current measurement system based on an ultra-fast photodetector and a high-speed digitizer at Hefei Light Source II (HLS II). In order to achieve bunch-by-bunch resolution, the sampling rate of the system is nearly 225 GS/s via a dedicated equivalent sampling algorithm. According to preliminary tests of daily operation mode and single-bunch mode, the root-mean-square (rms) of current relative error distribution is 1.03%, which illustrates the new system satisfies requirements for high-precision bunch current measurement. In addition, experiment results of "HLS" Morse code fill pattern mode demonstrate this system also could be a convenient and robust tool for beam top-up mode in the future.

physics.acc-ph↗

arXiv2017

Where does the X(5568) structure come from?

We study the semi-exclusive production of $π^\pm B_s^0$ pairs in hadron colliders which is associated with the $X(5568)$ structure observed by the D0 Collaboration in 2016, but that was not confirmed by LHCb and CMS later. The reason of its appearance in the D0 and absence in LHCb and CMS is discussed in this letter. In a semi-exclusive process, one might miss the third particle which is produced together with the $π^\pm B_s^0$ simultaneously. In the three-body Dalitz plot, once the remaining region is narrow enough after the kinematic cuts, its reflection to another invariant mass distribution will accumulate a large number of events within a specific energy region. If there is an enhancement in the remaining region, it will make the reflection structure more pronounced. The precise line shape of the reflection will depend on the specific interaction form. A combined study of different cone cuts and the low-energy dynamics, e.g. the Landau singularity, demonstrates that the $X(5568)$ structure could come from this kinematic reflection. This conclusion can be checked by both searching for the enhancement in another invariant mass distribution, such as $B_s^0\bar{B}^0$, and the cone cut dependence of the $X(5568)$ mass. Such a combined study can be used to distinguish the effects of the triangle singularity from a genuine state. We also propose how to avoid this kinematic reflection in future experimental analysis.

hep-ph↗

arXiv2017

Local Linear Constraint based Optimization Model for Dual Spectral CT

Dual spectral computed tomography (DSCT) can achieve energy- and material-selective images, and has a superior distinguishability of some materials than conventional single spectral computed tomography (SSCT). However, the decomposition process is illposed, which is sensitive with noise, thus the quality of decomposed images are usually degraded, especially the signal-to-noise ratio (SNR) is much lower than single spectra based directly reconstructions. In this work, we first establish a local linear relationship between dual spectra based decomposed results and single spectra based directly reconstructed images. Then, based on this constraint, we propose an optimization model for DSCT and develop a guided image filtering based iterative solution method. Both simulated and real experiments are provided to validate the effectiveness of the proposed approach.

math.OC↗

arXiv2016

$P$-wave coupled channel effects in electron-positron annihilation

$P$-wave coupled channel effects arising from the $D\bar{D}$, $D\bar{D}^*+c.c.$, and $D^*\bar{D}^*$ thresholds in $e^+e^-$ annihilations are systematically studied. We provide an exploratory study by solving the Lippmann-Schwinger equation with short-ranged contact potentials obtained in the heavy quark limit. These contact potentials can be extracted from the $P$-wave interactions in the $e^+e^-$ annihilations, and then be employed to investigate possible isosinglet $P$-wave hadronic molecules. In particular, such an investigation may provide information about exotic candidates with quantum numbers $J^{PC}=1^{-+}$. In the mass region of the $D\bar{D}$, $D\bar{D}^*+c.c.$, and $D^*\bar{D}^*$ thresholds, there are two quark model bare states, i.e. the $ψ(3770)$ and $ψ(4040)$, which are assigned as $(1^3D_1)$ and $(3^1S_1)$ states, respectively. By an overall fit of the cross sections of $e^+e^-\to D\bar{D}$, $D\bar{D}^*+c.c.$, $D^*\bar{D}^*$, we determine the physical coupling constants to each channel and extract the pole positions of the $ψ(3770)$ and $ψ(4040)$. The deviation of the ratios from that in the heavy quark spin symmetry (HQSS) limit reflects the HQSS breaking effect due to the mass splitting between the $D$ and the $D^*$. Besides the two poles, we also find a pole a few MeV above the $D\bar{D}^*+c.c.$ threshold which can be related to the so-called $G(3900)$ observed earlier by BABAR and Belle. This scenario can be further scrutinized by measuring the angular distribution in the $D^*\bar{D}^*$ channel with high luminosity experiments.

hep-ph↗

arXiv2016

Private and Truthful Aggregative Game for Large-Scale Spectrum Sharing

Thanks to the rapid development of information technology, the size of the wireless network becomes larger and larger, which makes spectrum resources more precious than ever before. To improve the efficiency of spectrum utilization, game theory has been applied to study the spectrum sharing in wireless networks for a long time. However, the scale of wireless network in existing studies is relatively small. In this paper, we introduce a novel game and model the spectrum sharing problem as an aggregative game for large-scale, heterogeneous, and dynamic networks. The massive usage of spectrum also leads to easier privacy divulgence of spectrum users' actions, which calls for privacy and truthfulness guarantees in wireless network. In a large decentralized scenario, each user has no priori about other users' decisions, which forms an incomplete information game. A "weak mediator", e.g., the base station or licensed spectrum regulator, is introduced and turns this game into a complete one, which is essential to reach a Nash equilibrium (NE). By utilizing past experience on the channel access, we propose an online learning algorithm to improve the utility of each user, achieving NE over time. Our learning algorithm also provides no regret guarantee to each user. Our mechanism admits an approximate ex-post NE. We also prove that it satisfies the joint differential privacy and is incentive-compatible. Efficiency of the approximate NE is evaluated, and the innovative scaling law results are disclosed. Finally, we provide simulation results to verify our analysis.

cs.GT↗