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Fan Wang

Publications and source records attributed to Fan Wang.

At least 397 records · Page 22Linked to original sources
arXiv2017

Investigating the excited $Ω^{0}_{c}$ states through $Ξ_{c}K$ and $Ξ^{'}_{c}K$ decay channels

Inspired by the five newly observed $Ω^{0}_{c}$ states by the LHCb detector, we study the $Ω_{c}^{0}$ states as the $S-$wave molecular pentaquarks with $I=0$, $J^{P}=\frac{1}{2}^{-}$, $\frac{3}{2}^{-}$, and $\frac{5}{2}^{-}$ by solving the RGM equation in the framework of chiral quark model. Both the energies and the decay widths are obtained in this work. Our results suggest that $Ω_{c}(3119)^{0}$ can be explained as an $S-$wave resonance state of $ΞD$ with $J^{P}=\frac{1}{2}^{-}$, and the decay channels are the $S-$wave $Ξ_{c} K$ and $Ξ^{'}_{c}K$ . Other reported $Ω^{0}_{c}$ states cannot be obtained in our present calculation. Another $Ω_{c}^{0}$ state with much higher mass 3533 MeV with $J^{P}=\frac{5}{2}^{-}$ is also obtained. In addition, the calculation is extended to the $Ω_{b}^{0}$ states, similar results as that of $Ω^{0}_{c}$ are obtained.

hep-ph↗
arXiv2017

Seeds Cleansing CNMF for Spatiotemporal Neural Signals Extraction of Miniscope Imaging Data

Miniscope calcium imaging is increasingly being used to monitor large populations of neuronal activities in freely behaving animals. However, due to the high background and low signal-to-noise ratio of the single-photon based imaging used in this technique, extraction of neural signals from the large numbers of imaged cells automatically has remained challenging. Here we describe a highly accurate framework for automatically identifying activated neurons and extracting calcium signals from the miniscope imaging data, seeds cleansing Constrained Nonnegative Matrix Factorization (sc-CNMF). This sc-CNMF extends the conventional CNMF with two new modules: i) a neural enhancing module to overcome miniscope-specific limitations, and ii) a seeds cleansing module combining LSTM to rigorously select and cleanse the set of seeds for detecting regions-of-interest. Our sc-CNMF yields highly stable and superior performance in analyzing miniscope calcium imaging data compared to existing methods.

q-bio.NC↗
arXiv2017

Heavy pentaquark states and a novel color structure

Encouraged by the observation of the pentaquark states $P^+_c(4380)$ and $P^+_c(4450)$, we propose a novel color flux-tube structure, pentagonal state, for pentaquark states within the framework of color flux-tube mode involving a five-body confinement potential. Numerical results on the heavy pentaquark states indicate that the states with three color flux-tube structures, diquark, octet and pentagonal structures, have the close masses, which can therefore be called QCD isomers analogous to isomers in Chemistry. The pentagonal structure has lowest energy. The state $P^+_c(4380)$ can be described as the compact pentaquark state $uudc\bar{c}$ with the pentagonal structure and $J^P=\frac{3}{2}^-$ in the color flux-tube model. The state $P^+_c(4450)$ can not be accommodated into the color flux-tube model. The heavy pentaquark states $uudc\bar{b}$, $uudb\bar{c}$ and $uudb\bar{b}$ are predicted in the color flux-tube model. The five-body confinement potential basing on the color flux-tube picture as a collective degree of freedom is a dynamical mechanism in the formation of the compact heavy pentaquark states.

hep-ph↗
arXiv2016

Possible pentaquarks with heavy quarks

Inspired by the discovery of two pentaquarks $P_{c}(4380)$ and $P_{c}(4450)$ at the LHCb detector, we study possible hidden-charm molecular pentaquarks in the framework of quark delocalization color screening model. Our results suggest that both $Nη_{c}$ with $IJ^{P}=\frac{1}{2}\frac{1}{2}^{-}$ and $NJ/ψ$ with $IJ^{P}=\frac{1}{2}\frac{3}{2}^{-}$ are bounded by channels coupling. However, $NJ/ψ$ with $IJ^{P}=\frac{1}{2}\frac{3}{2}^{-}$ may be a resonance state in the $D-$wave $Nη_{c}$ scattering process. Moreover, $P_{c}(4380)$ can be explained as the molecular pentaquark of $Σ^{*}_{c}D$ with quantum numbers $IJ^{P}=\frac{1}{2}\frac{3}{2}^{-}$. The state $Σ^{*}_{c}D^{*}$ with $IJ^{P}=\frac{1}{2}\frac{5}{2}^{-}$ is a resonance, it may not be a good candidate of the observed $P_{c}(4450)$ because of the opposite parity of the state to $P_{c}(4380)$, although the mass of the state is not far from the experimental value. In addition, the calculation is extended to the hidden-bottom pentaquarks, the similar properties as that of hidden-charm pentaquarks system are obtained.

hep-ph↗
arXiv2016

Exciton Brightening in Monolayer Phosphorene via Dimensionality Modification

Two-dimensional (2D) monolayer phosphorene, a 2D system with quasi-one-dimensional (quasi-1D) excitons, provides a unique 2D platform for investigating the dynamics of excitons in reduced dimensions and fundamental many-body interactions. However, on the other hand, the quasi-1D excitonic nature can limit the luminescence quantum yield significantly. Here, we report exciton brightening in monolayer phosphorene achieved via the dimensionality modification of excitons from quasi-1D to zero-dimensional (0D), through the transference of monolayer phosphorene samples onto defect-rich oxide substrate deposited by plasma-enhanced chemical vapor deposition (PECVD). The resultant interfacial luminescent local states lead to exciton localization and trigger efficient photon emissions at a new wavelength of ~920 nm. The luminescence quantum yield of 0D-like localized excitons is measured to be at least 33.6 times larger than that of intrinsic quasi-1D free excitons in monolayer phosphorene. This is primarily due to the reduction of non-radiative decay rate and the possibly enhanced radiative recombination probability. Owing to the large trapping energy, this new photon emission from the localized excitons in monolayer phosphorene can be observed at elevated temperature, which contrasts markedly with defect-induced photon emission from transition metal dichalcogenide (TMD) semiconductor monolayers that can only be observed at cryogenic temperatures. Our findings introduce new avenues for the development of novel photonic devices based on monolayer phosphorene, such as near-infrared lighting devices that are operable at elevated temperature. More importantly, 2D phosphorene with quasi-1D free excitons and 0D-like localized excitons provides a unique platform to investigate the fundamental phenomena in the ideal 2D-1D-0D hybrid system.

cond-mat.mtrl-sci↗
arXiv2015

10 Observations on Google Cluster Trace + 2 Measures for Cluster Utilization Enhancement

Utilization enhancement is a key concern to cluster owners. Google's cluster manager named Borg manages its clusters at an overall utilization higher than many others' clusters. Recently, Google has disclosed the details of its powerful cluster manager Borg. Quite a few lessons are summarized from the Borg experiences. Nevertheless, we find that more can be learned if the Borg design is correlated with the trace analysis of a Google cluster managed by Borg. There is one such trace released four years ago. In this paper, we analyze the Google cluster trace and make 10 observations not found in previous analyses. We also correlates the results of our analysis and previous analyses to the Borg design, such that we find two measures that can possibly further improve cluster utilization over Borg.

cs.DC↗
arXiv2015

Further study of the $NΩ$ dibaryon within constituent quark models

Inspired by the discovery of the dibaryon $d^{*}$ and the experimental search of $NΩ$ dibaryon with the STAR data, we study the strange dibaryon $NΩ$ further in the framework of quark delocalization color screening model and chiral quark model. We have shown $NΩ$ is a narrow resonance in $ΛΞ$ D-wave scattering before. However, the $Λ$-$Ξ$ scattering data analysis is quite complicated. Here we calculate the low-energy $NΩ$ scattering phase shifts, scattering length, effective range and binding energy to provide another approach of STAR data analysis. Our results show there exists an $NΩ$ "bound" state, which can be observed by the $N$-$Ω$ correlation analysis with RHIC and LHC data, or by the new developed automatic scanning system at J-PARC. Besides, we also find that the hidden color channel-coupling is important for the $NΩ$ system to develop intermediate-range attraction.

hep-ph↗
arXiv2015

Systematic study of $Z^+_c$ family from quark model's perspective

Inspired by the present experimental status of charged charmonium-like states $Z_c^+$, the tetraquark states $[cu][\bar{c}\bar{d}]$ are systematically studied in a color flux-tube model with a multi-body confinement potential. The investigation indicates that charged charmonium-like states $Z_c^+(3900)$ or $Z_c^+(3885)$, $Z_c^+(3930)$, $Z_c^+(4020)$ or $Z_c^+(4025)$, $Z_1^+(4050)$, $Z_2^+(4250)$, and $Z_c^+(4200)$ can be uniformly described as tetraquark states $[cu][\bar{c}\bar{d}]$ with the quantum numbers $n^{2S+1}L_J$ and $J^P$ of $1^{3}S_1$ and $1^+$, $2^{3}S_1$ and $1^+$, $1^5S_2$ and $2^+$, $1^3P_1$ and $1^-$, $1^5D_1$ and $1^+$, and $1^3D_1$ and $1^+$, respectively. The predicted lowest charged tetraquark state $[cu][\bar{c}\bar{d}]$ with $0^+$ and $1^1S_0$ has a energy of $3780\pm10$ MeV in the model. The tetraquark states are compact three-dimensional spatial configurations similar to a rugby ball, the higher orbital angular momentum $L$ between the diquark $[cu]$ and antidiquark $[\bar{c}\bar{d}]$, the more prolate of the states. The multibody color flux-tube, a collective degree of freedom, plays an important role in the formation of those charge tetraquark states. However, the two heavier charged states $Z^+_c(4430)$ and $Z^+_c(4475)$ can not be explained as tetraquark states $[cu][\bar{c}\bar{d}]$ in this model approach.

hep-ph↗
arXiv2015

Configuration mixing and effective baryon-baryon interactions

The effective baryon-baryon interactions is studied in the refined quark delocalization color screening model (QDCSM), in which the different quark clusterings are fully taken into account, instead of controlling by a variational delocalization parameter $ε(s)$ between two 3-quark clusters. The symmetry bases are employed to do the calculation, all possible configurations for two quark clusters are considered. The results obtained are very similar to that of QDCSM. It is inferred that the delocalization parameter $ε(s)$ used in QDCSM is an economic and effective way to describe the mixing of quarks between baryons.

hep-ph↗
arXiv2015

Optical Tuning of Exciton and Trion Emissions in Monolayer Phosphorene

Monolayer phosphorene provides a unique two-dimensional (2D) platform to investigate the fundamental dynamics of excitons and trions (charged excitons) in reduced dimensions. However, owing to its high instability, unambiguous identification of monolayer phosphorene has been elusive. Consequently, many important fundamental properties, such as exciton dynamics, remain underexplored. We report a rapid, noninvasive, and highly accurate approach based on optical interferometry to determine the layer number of phosphorene, and confirm the results with reliable photoluminescence measurements. Furthermore, we successfully probed the dynamics of excitons and trions in monolayer phosphorene by controlling the photo-carrier injection in a relatively low excitation power range. Based on our measured optical gap and the previously measured electronic energy gap, we determined the exciton binding energy to be ~0.3 eV for the monolayer phosphorene on SiO2/Si substrate, which agrees well with theoretical predictions. A huge trion binding energy of ~100 meV was first observed in monolayer phosphorene, which is around five times higher than that in transition metal dichalcogenide (TMD) monolayer semiconductor, such as MoS2. The carrier lifetime of exciton emission in monolayer phosphorene was measured to be ~220 ps, which is comparable to those in other 2D TMD semiconductors. Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene.

cond-mat.mtrl-sci↗
arXiv2014

Theoretical study of a $d^{*}$ resonance in $^{3}G_{3}$ partial wave of nucleon-nucleon scattering

Inspired by the recent results of the WASA-at-COSY Collaboration, in which they found a resonance pole in the coupled $^{3}D_{3}$ - $^{3}G_{3}$ partial waves as expected from the $d^{*}$ resonance hypothesis, we calculated the resonance structure in the coupled $^{3}D_{3}$ - $^{3}G_{3}$ partial wave phase shifts of nucleon-nucleon scattering in the framework of two constituent quark models: the quark delocalization color screening model and the chiral quark model. Our results show that there is a resonance $^{7}S_{3}^{ΔΔ}$ in the coupled $^{3}D_{3}^{NN}$ and $^{3}G_{3}^{NN}$ partial waves in both of these two models, which is in accordance with the expectation from the $d^{*}$ resonance structure. The resonance shape in the $^{3}D_{3}^{NN}$ partial wave is remarkable, whereas in the $^{3}G_{3}^{NN}$ phase shifts there is a small rise around the resonance energy. This result is in agreement with the recent experimental observations of WASA-at-COSY Collaboration.

nucl-th↗
arXiv2014

Unambiguous identification of monolayer phosphorene by phase-shifting interferometry

Monolayer phosphorene provides a unique two-dimensional (2D) platform to investigate the fundamental many-body interactions. However, owing to its high instability, unambiguous identification of monolayer phosphorene has been elusive. Consequently, many important fundamental properties, such as exciton dynamics, remain underexplored. We report a rapid, noninvasive, and highly accurate approach based on optical interferometry to determine the layer number of phosphorene, and confirm the results with reliable photoluminescence measurements. Based on the measured optical gap and the calculated electronic energy gap, we determined the exciton binding energy to be ~0.4 eV for the monolayer phosphorene on SiO2/Si substrate, which agrees well with theoretical predictions. Our results open new avenues for exploring fundamental phenomena and novel optoelectronic applications using monolayer phosphorene.

cond-mat.mtrl-sci↗
arXiv2014

3D-Assisted Image Feature Synthesis for Novel Views of an Object

Comparing two images in a view-invariant way has been a challenging problem in computer vision for a long time, as visual features are not stable under large view point changes. In this paper, given a single input image of an object, we synthesize new features for other views of the same object. To accomplish this, we introduce an aligned set of 3D models in the same class as the input object image. Each 3D model is represented by a set of views, and we study the correlation of image patches between different views, seeking what we call surrogates --- patches in one view whose feature content predicts well the features of a patch in another view. In particular, for each patch in the novel desired view, we seek surrogates from the observed view of the given image. For a given surrogate, we predict that surrogate using linear combination of the corresponding patches of the 3D model views, learn the coefficients, and then transfer these coefficients on a per patch basis to synthesize the features of the patch in the novel view. In this way we can create feature sets for all views of the latent object, providing us a multi-view representation of the object. View-invariant object comparisons are achieved simply by computing the $L^2$ distances between the features of corresponding views. We provide theoretical and empirical analysis of the feature synthesis process, and evaluate the proposed view-agnostic distance (VAD) in fine-grained image retrieval (100 object classes) and classification tasks. Experimental results show that our synthesized features do enable view-independent comparison between images and perform significantly better than traditional image features in this respect.

cs.CV↗
arXiv2014

Atomically Thin Optical Lenses and Gratings

Two-dimensional (2D) materials have emerged as promising candidates for miniaturized optoelectronic devices, due to their strong inelastic interactions with light. On the other hand, a miniaturized optical system also requires strong elastic light-matter interactions to control the flow of light. Here, we report giant optical path length (OPL) from a single-layer molybdenum disulfide (MoS2), which is around one order of magnitude larger than that from a single-layer graphene. Using such giant OPL to engineer the phase front of optical beams, we demonstrated, to the best of our knowledge, the world's thinnest optical lens consisting of a few layers of MoS2 less than 6.3 nm thick. Moreover, we show that MoS2 has much better dielectric response than good conductor (like gold) and other dielectric materials (like Si, SiO2 or graphene). By taking advantage of the giant elastic scattering efficiency in ultra-thin high-index 2D materials, we demonstrated high-efficiency gratings based on a single- or few-layers of MoS2. The capability of manipulating the flow of light in 2D materials opens an exciting avenue towards unprecedented miniaturization of optical components and the integration of advanced optical functionalities.

cond-mat.mtrl-sci↗
arXiv2014

Extraordinarily bound quasi-one-dimensional trions in two-dimensional phosphorene atomic semiconductors

The anisotropic nature of the new two-dimensional (2D) material phosphorene, in contrast to other 2D materials such as graphene and transition metal dichalcogenide (TMD) semiconductors, allows excitons to be confined in a quasi-one-dimensional (1D) space predicted in theory, leading to remarkable phenomena arising from the reduced dimensionality and screening. Here, we report a trion (charged exciton) binding energy of 190 meV in few-layer phosphorene at room temperature, which is nearly one to two orders of magnitude larger than those in 2D TMD semiconductors (20-30 meV) and quasi-2D quantum wells (1-5 meV). Such a large binding energy has only been observed in truly 1D materials such as carbon nanotubes, whose optoelectronic applications have been severely hurdled by their intrinsically small optical cross-sections. Phosphorene offers an elegant way to overcome this hurdle by enabling quasi-1D excitonic and trionic behaviors in a large 2D area, allowing optoelectronic integration. We experimentally validated the quasi-1D nature of excitonic and trionic dynamics in phospherene by demonstrating completely linearly polarized light emission from excitons and trions. The implications of the extraordinarily large trion binding energy in a higher-than-one-dimensional material are far-reaching. It provides a room-temperature 2D platform to observe the fundamental many-body interactions in the quasi-1D region. The strong photoluminescence emission in phosphorene has been electrically tuned over a large spectral range at room temperature, which opens a new route for tunable light sources.

cond-mat.mtrl-sci↗
arXiv2014

Gauge invariance, Lorentz covariance and canonical quantization in nucleon structure studies

There are different operators of quark and gluon momenta, orbital angular momenta, and gluon spin in the nucleon structure study. The precise meaning of these operators are studied based on gauge invariance, Lorentz covariance and canonical quantization rule. The advantage and disadvantage of different definitions are analyzed. A gauge invariant canonical decomposition of the total momentum and angular momentum into quark and gluon parts is suggested based on the decomposition of the gauge potential into gauge invariant (covariant) physical part and gauge dependent pure gauge part. Challenges to this proposal are answered. \keywords{Physical and pure gauge potentials; Gauge invariant canonical quark and gluon momenta, orbital angular momenta and spins; Homogeneous and non-homogeneous Lorentz transformations; Gauge invariant decomposition and gauge invariant extension; Classical and quantum measurements.

hep-ph↗