arXiv subjects

Bo Peng

Publications and source records attributed to Bo Peng.

At least 397 records · Page 22Linked to original sources

arXiv2018

A Blended Deep Learning Approach for Predicting User Intended Actions

User intended actions are widely seen in many areas. Forecasting these actions and taking proactive measures to optimize business outcome is a crucial step towards sustaining the steady business growth. In this work, we focus on pre- dicting attrition, which is one of typical user intended actions. Conventional attrition predictive modeling strategies suffer a few inherent drawbacks. To overcome these limitations, we propose a novel end-to-end learning scheme to keep track of the evolution of attrition patterns for the predictive modeling. It integrates user activity logs, dynamic and static user profiles based on multi-path learning. It exploits historical user records by establishing a decaying multi-snapshot technique. And finally it employs the precedent user intentions via guiding them to the subsequent learning procedure. As a result, it addresses all disadvantages of conventional methods. We evaluate our methodology on two public data repositories and one private user usage dataset provided by Adobe Creative Cloud. The extensive experiments demonstrate that it can offer the appealing performance in comparison with several existing approaches as rated by different popular metrics. Furthermore, we introduce an advanced interpretation and visualization strategy to effectively characterize the periodicity of user activity logs. It can help to pinpoint important factors that are critical to user attrition and retention and thus suggests actionable improvement targets for business practice. Our work will provide useful insights into the prediction and elucidation of other user intended actions as well.

cs.LG↗

arXiv2018

Accretion in Common Envelope Evolution

Common envelope evolution (CEE) occurs in some binary systems involving asymptotic giant branch (AGB) or red giant branch (RGB) stars, and understanding this process is crucial for understanding the origins of various transient phenomena. CEE has been shown to be highly asymmetrical and global 3D simulations are needed to help understand the dynamics. We perform and analyze hydrodynamic CEE simulations with the adaptive mesh refinement (AMR) code AstroBEAR, and focus on the role of accretion onto the companion star. We bracket the range of accretion rates by comparing a model that removes mass and pressure using a subgrid accretion prescription with one that does not. Provided a pressure-release valve, such as a bipolar jet, is available, super-Eddington accretion could be common. Finally, we summarize new results pertaining to the energy budget, and discuss the overall implications relating to the feasibility of unbinding the envelope in CEE simulations.

astro-ph.SR↗

arXiv2018

Person Re-Identification by Semantic Region Representation and Topology Constraint

Person re-identification is a popular research topic which aims at matching the specific person in a multi-camera network automatically. Feature representation and metric learning are two important issues for person re-identification. In this paper, we propose a novel person re-identification method, which consists of a reliable representation called Semantic Region Representation (SRR), and an effective metric learning with Mapping Space Topology Constraint (MSTC). The SRR integrates semantic representations to achieve effective similarity comparison between the corresponding regions via parsing the body into multiple parts, which focuses on the foreground context against the background interference. To learn a discriminant metric, the MSTC is proposed to take into account the topological relationship among all samples in the feature space. It considers two-fold constraints: the distribution of positive pairs should be more compact than the average distribution of negative pairs with regard to the same probe, while the average distance between different classes should be larger than that between same classes. These two aspects cooperate to maintain the compactness of the intra-class as well as the sparsity of the inter-class. Extensive experiments conducted on five challenging person re-identification datasets, VIPeR, SYSU-sReID, QUML GRID, CUHK03, and Market-1501, show that the proposed method achieves competitive performance with the state-of-the-art approaches.

cs.CV↗

arXiv2018

Extreme Network Compression via Filter Group Approximation

In this paper we propose a novel decomposition method based on filter group approximation, which can significantly reduce the redundancy of deep convolutional neural networks (CNNs) while maintaining the majority of feature representation. Unlike other low-rank decomposition algorithms which operate on spatial or channel dimension of filters, our proposed method mainly focuses on exploiting the filter group structure for each layer. For several commonly used CNN models, including VGG and ResNet, our method can reduce over 80% floating-point operations (FLOPs) with less accuracy drop than state-of-the-art methods on various image classification datasets. Besides, experiments demonstrate that our method is conducive to alleviating degeneracy of the compressed network, which hurts the convergence and performance of the network.

cs.CV↗

arXiv2018

Theoretical investigation of novel electronic, optical, mechanical and thermal properties of metallic hydrogen at 495 GPa

Atomic metallic hydrogen has been produced in the laboratory at high pressure and low temperature, prompting further investigations of its different properties. However, purely experimental approaches are infeasible because of the extreme requirements in producing and preserving the metastable phase. Here we perform a systematic investigation of the electronic, optical, mechanical and thermal properties of $I4_1/amd$ hydrogen at 495 GPa using first-principles calculations. We calculate the electronic structure and dielectric function to verify the metallic behaviour of $I4_1/amd$ hydrogen. The calculated total plasma frequency from both intraband and interband transitions, 33.40 eV, agrees well with the experimental result. The mechanical properties including elastic stability and sound velocity are also investigated. The mechanical stability of $I4_1/amd$ hydrogen is limited by shear modulus other than bulk modulus, and the high Young's modulus indicates that $I4_1/amd$ hydrogen is a stiff material. After investigating the lattice vibrational properties, we study the thermodynamical properties and lattice anharmonicity to understand thermal behaviours in metallic hydrogen. Finally, the lattice thermal conductivity of $I4_1/amd$ hydrogen is calculated to be 194.72 W/mK and 172.96 W/mK along the $x$ and $z$ directions, respectively. Using metallic hydrogen as an example, we demonstrate that first-principles calculations can be a game-changing solution to understand a variety of material properties in extreme conditions.

cond-mat.mtrl-sci↗

arXiv2018

Accretion in common envelope evolution

Common envelope evolution (CEE) is presently a poorly understood, yet critical, process in binary stellar evolution. Characterizing the full 3D dynamics of CEE is difficult in part because simulating CEE is so computationally demanding. Numerical studies have yet to conclusively determine how the envelope ejects and a tight binary results, if only the binary potential energy is used to propel the envelope. Additional power sources might be necessary and accretion onto the inspiraling companion is one such source. Accretion is likely common in post-asymptotic giant branch (AGB) binary interactions but how it operates and how its consequences depend on binary separation remain open questions. Here we use high resolution global 3D hydrodynamic simulations of CEE with the adaptive mesh refinement (AMR) code AstroBEAR, to bracket the range of CEE companion accretion rates by comparing runs that remove mass and pressure via a subgrid accretion model with those that do not. The results show that if a pressure release valve is available, super-Eddington accretion may be common. Jets are a plausible release valve in these environments, and they could also help unbind and shape the envelopes.

astro-ph.SR↗

arXiv2018

High-Performance Massive Subgraph Counting using Pipelined Adaptive-Group Communication

Subgraph counting aims to count the number of occurrences of a subgraph T (aka as a template) in a given graph G. The basic problem has found applications in diverse domains. The problem is known to be computationally challenging - the complexity grows both as a function of T and G. Recent applications have motivated solving such problems on massive networks with billions of vertices. In this chapter, we study the subgraph counting problem from a parallel computing perspective. We discuss efficient parallel algorithms for approximately resolving subgraph counting problems by using the color-coding technique. We then present several system-level strategies to substantially improve the overall performance of the algorithm in massive subgraph counting problems. We propose: 1) a novel pipelined Adaptive-Group communication pattern to improve inter-node scalability, 2) a fine-grained pipeline design to effectively reduce the memory space of intermediate results, 3) partitioning neighbor lists of subgraph vertices to achieve better thread concurrency and workload balance. Experimentation on an Intel Xeon E5 cluster shows that our implementation achieves 5x speedup of performance compared to the state-of-the-art work while reduces the peak memory utilization by a factor of 2 on large templates of 12 to 15 vertices and input graphs of 2 to 5 billions of edges.

cs.DC↗

arXiv2018

Room Temperature Continuous-wave Excited Biexciton Emission in CsPbBr3 Nanocrystals

Biexcitons are a manifestation of many-body excitonic interactions crucial for quantum information and quantum computation in the construction of coherent combinations of quantum states. However, due to their small binding energy and low transition efficiency, most biexcitons in conventional semiconductors exist either at cryogenic temperature or under femtosecond pulse laser excitation. Here we demonstrate room temperature, continuous wave driven biexciton states in CsPbBr3 perovskite nanocrystals through coupling with a plasmonic nanogap. The room temperature CsPbBr3 biexciton excitation fluence (~100 mW/cm2) is reduced by ~10^13 times in the Ag nanowire-film nanogaps. The giant enhancement of biexciton emission is driven by coherent biexciton-plasmon Fano interference. These results provide new pathways to develop high efficiency non-blinking single photon sources, entangled light sources and lasers based on biexciton states.

cond-mat.mes-hall↗

arXiv2018

Electronic, optical and transport properties of van der Waals Transition-metal Dichalcogenides Heterostructures: A First-principle Study

Two-dimensional (2D) transition-metal dichalcogenide (TMD) MX$_2$ (M = Mo, W; X= S, Se, Te) possess unique properties and novel applications. In this work, we perform first-principles calculations on the van der Waals (vdW) stacked MX$_2$ heterostructures to investigate their electronic, optical and transport properties systematically. We perform the so-called Anderson's rule to classify the heterostructures by providing the scheme of the construction of energy band diagrams for the heterostructure consisting of two semiconductor materials. For most of the MX$_2$ heterostructures, the conduction band maximum (CBM) and valence band minimum (VBM) reside in two separate semiconductors, forming type II band structure, thus the electron-holes pairs are spatially separated. We also find strong interlayer coupling at $Γ$ point after forming MX$_2$ heterostructures, even leading to the indirect band gap. While the band structure near $K$ point remain as the independent monolayer. The carrier mobilities of MX$_2$ heterostructures depend on three decisive factors, elastic modulus, effective mass and deformation potential constant, which are discussed and contrasted with those of monolayer MX$_2$, respectively.

cond-mat.mtrl-sci↗

arXiv2017

Mid-infrared variability of changing-look AGN

It is known that some active galactic nuclei (AGNs) transited from type 1 to type 2 or vice versa. There are two explanations for the so-called changing look AGNs: one is the dramatic change of the obscuration along the line-of-sight, the other is the variation of accretion rate. In this paper, we report the detection of large amplitude variations in the mid-infrared luminosity during the transitions in 10 changing look AGNs using WISE and newly released NEOWISE-R data. The mid-infrared light curves of 10 objects echoes the variability in the optical band with a time lag expected for dust reprocessing. The large variability amplitude is inconsistent with the scenario of varying obscuration, rather supports the scheme of dramatic change in the accretion rate.

astro-ph.GA↗

arXiv2017

Discovery of a Mid-infrared Echo from the TDE candidate in the nucleus of ULIRG F01004-2237

We present the mid-infrared (MIR) light curves (LCs) of a tidal disruption event (TDE) candidate in the center of a nearby ultraluminous infrared galaxy (ULIRG) F01004-2237 using archival {\it WISE} and {\it NEOWISE} data from 2010 to 2016. At the peak of the optical flare, F01004-2237 was IR quiescent. About three years later, its MIR fluxes have shown a steady increase, rising by 1.34 and 1.04 mag in $3.4$ and $4.6μ$m up to the end of 2016. The host-subtracted MIR peak luminosity is $2-3\times10^{44}$\,erg\,s$^{-1}$. We interpret the MIR LCs as an infrared echo, i.e. dust reprocessed emission of the optical flare. Fitting the MIR LCs using our dust model, we infer a dust torus of the size of a few parsecs at some inclined angle. The derived dust temperatures range from $590-850$\,K, and the warm dust mass is $\sim7\,M_{\odot}$. Such a large mass implies that the dust cannot be newly formed. We also derive the UV luminosity of $4-11\times10^{44}$\,erg\,s$^{-1}$. The inferred total IR energy is $1-2\times10^{52}$\,erg, suggesting a large dust covering factor. Finally, our dust model suggests that the long tail of the optical flare could be due to dust scattering.

astro-ph.HE↗

arXiv2017

Electronic, transport and optical properties of monolayer $α$ and $β-$GeSe: A first-principles study

The extraordinary properties and the novel applications of black phosphorene induce the research interest on the monolayer group-IV monochalcogenides. Here using the first-principles calculations, we systematically investigate the electronic, transport and optical properties of monolayer $α-$ and $β-$GeSe, the latter of which was recently experimentally realized. We found that, monolayer $α-$GeSe is a semiconductor with direct band gap of 1.6 eV, and $β-$GeSe displays indirect semiconductor with the gap of 2.47 eV, respectively. For monolayer $β-$GeSe, the electronic/hole transport is anisotropic with an extremely high electron mobility of 7.84 $\times10^4$$cm^2/V\cdot {s}$ along the zigzag direction, comparable to that of black phosphorene. Furthermore, for $β-$GeSe, robust band gaps nearly disregarding the applied tensile strain along the zigzag direction is observed. Both monolayer $α-$ and $β-$GeSe exhibit anisotropic optical absorption in the visible spectrum.

cond-mat.mtrl-sci↗

arXiv2017

Atomically sharp 1D SbSeI, SbSI and SbSBr with high stability and novel properties for microelectronic, optoelectronic, and thermoelectric applications

In scaling of transistor dimensions with low source-to-drain currents, 1D semiconductors with certain electronic properties are highly desired. We discover three new 1D materials, SbSeI, SbSI and SbSBr with high stability and novel electronic properties based on first principles calculations. Both dynamical and thermal stability of these 1D materials are examined. The bulk-to-1D transition results in dramatic changes in band gap, effective mass and static dielectric constant due to quantum confinement, making 1D SbSeI a highly promising channel material for transistors with gate length shorter than 1 nm. Under small uniaxial strain, these materials are transformed from indirect into direct band gap semiconductors, paving the way for optoelectronic devices and mechanical sensors. Moreover, the thermoelectric performance of these materials is significantly improved over their bulk counterparts. Finally, we demonstrate the experimental feasibility of synthesizing such atomically sharp V-VI-VII compounds. These highly desirable properties render SbSeI, SbSI and SbSBr promising 1D materials for applications in future microelectronics, optoelectronics, mechanical sensors, and thermoelectrics.

cond-mat.mtrl-sci↗

arXiv2017

The anisotropic ultrahigh hole mobility in strain-engineering two-dimensional penta-SiC$_2$

Using the first-principles calculations based on density functional theory, we systematically investigate the strain-engineering (tensile and compressive strain) electronic, mechanical and transport properties of monolayer penta-SiC$_2$. By applying an in-plane tensile or compressive strain, it is easy to modulate the electronic band structure of monolayer penta-SiC$_2$, which subsequently changes the effective mass of carriers. Furthermore, the obtained electronic properties are predicted to change from indirectly semiconducting to metallic. More interestingly, at room temperature, uniaxial strain can enhance the hole mobility of penta-SiC$_2$ along a particular direction by almost three order in magnitude, $i.e.$ from 2.59 $\times10^3 cm^2/V s$ to 1.14 $\times10^6 cm^2/V s$ (larger than the carrier mobility of graphene, 3.5 $\times10^5 cm^2/V s$), with little influence on the electron mobility. The high carrier mobility of monolayer penta-SiC$_2$ may lead to many potential applications in high-performance electronic and optoelectronic devices

cond-mat.mtrl-sci↗

arXiv2016

Unexpected phonon-transport properties of stanene among 2D group-IV materials from \textit{ab initio}

It has been argued that stanene has lowest lattice thermal conductivity among 2D group-IV materials because of largest atomic mass, weakest interatomic bonding, and enhanced ZA phonon scattering due to the breaking of an out-of-plane symmetry selection rule. However, we show that although the lattice thermal conductivity $κ$ for graphene, silicene and germanene decreases monotonically with decreasing Debye temperature, unexpected higher $κ$ is observed in stanene. By enforcing all the invariance conditions in 2D materials and including Ge $3d$ and Sn $4d$ electrons as valence electrons for germanene and stanene respectively, the lattice dynamics in these materials are accurately described. A large acoustic-optical gap and the bunching of the acoustic phonon branches significantly reduce phonon scattering in stanene, leading to higher thermal conductivity than germanene. The vibrational origin of the acoustic-optical gap can be attributed to the buckled structure. Interestingly, a buckled system has two competing influences on phonon transport: the breaking of the symmetry selection rule leads to reduced thermal conductivity, and the enlarging of the acoustic-optical gap results in enhanced thermal conductivity. The size dependence of thermal conductivity is investigated as well. In nanoribbons, the $κ$ of silicene, germanene and stanene is much less sensitive to size effect due to their short intrinsic phonon mean free paths. This work sheds light on the nature of phonon transport in buckled 2D materials.

cond-mat.mes-hall↗

arXiv2016

Stability and Strength of Atomically Thin Borophene from First Principles Calculations

A new two-dimensional (2D) material, borophene (2D boron sheet), has been grown successfully recently on single crystal Ag substrates by two parallel experiments [Mannix \textit{et al., Science}, 2015, \textbf{350}, 1513] [Feng \textit{et al., Nature Chemistry}, 2016, \textbf{advance online publication}]. Three main structures have been proposed ($β_{12}$, $χ_3$ and striped borophene). However, the stability of three structures is still in debate. Using first principles calculations, we examine the dynamical, thermodynamical and mechanical stability of $β_{12}$, $χ_3$ and striped borophene. Free-standing $β_{12}$ and $χ_3$ borophene is dynamically, thermodynamically, and mechanically stable, while striped borophene is dynamically and thermodynamically unstable due to high stiffness along $a$ direction. The origin of high stiffness and high instability in striped borophene along $a$ direction can both be attributed to strong directional bonding. This work provides a benchmark for examining the relative stability of different structures of borophene.

cond-mat.mtrl-sci↗

arXiv2016

First-principle calculations of phononic, electronic and optical properties of monolayer arsenene and antimonene allotropes

Recently a stable monolayer of antimony in buckled honeycomb structure called antimonene was successfully grown on 3D topological insulator Bi$_2$Te$_3$ and Sb$_2$Te$_3$, which displays semiconducting properties. By first principle calculations, we systematically investigate the phononic, electronic and optical properties of $α-$ and $β-$ allotropes of monolayer arsenene/antimonene. We investigate the dynamical stabilities of these four materials by considering the phonon dispersions. The obtained electronic structures reveal the direct band gap of monolayer $α-$As/Sb and indirect band gap of $β-$As/Sb. Significant absorption is observed in $α-$Sb, which can be used as a broad saturable absorber.

cond-mat.mtrl-sci↗

arXiv2016

Electronic, optical, and thermodynamic properties of borophene from first-principle calculations

Borophene (two-dimensional boron sheet) is a new type of two-dimensional material, which was recently grown successfully on single crystal Ag substrates. In this paper, we investigate the electronic structure and bonding characteristics of borophene by first-principle calculations. The band structure of borophene shows highly anisotropic metallic behaviour. The obtained optical properties of borophene exhibit strong anisotropy as well. The combination of high optical transparency and high electrical conductivity in borophene makes it a promising candidate for future design of transparent conductors used in photovoltaics. Finally, the thermodynamic properties are investigated based on the phonon properties.

cond-mat.mes-hall↗