arXiv subjects

Chao Wang

Publications and source records attributed to Chao Wang.

At least 739 records · Page 41Linked to original sources

arXiv2016

Non-Markov property of afterpulsing effect in single-photon avalanche detector

Single-photon avalanche photodiode(SPAD) has been widely used in researching of quantum optics. Afterpulsing effect, which is an intrinsic character of SPAD, affects the system performance in most of the experiments and needs to be carefully handled. For a long time, afterpulsing has been presumed to be determined by the pre-ignition avalanche. We studied the afterpulsing effect of a commercial InGaAs/InP SPAD (APD: Princeton Lightwave PGA-300) and demonstrated that its afterpulsing is non-Markov, which has memory effect of the avalanching history. Theoretical analysis and the experimental results clearly indicate that the embodiment of this memory effect is the afterpulsing probability, which increases as the number of ignition-avalanche pulses increase. The conclusion makes the principle of afterpulsing effect clearer and is instructive to the manufacturing processes and afterpulsing evaluation of high-count-rate SPADs. It can also be regarded as an fundamental premise to handle the afterpulsing signals in many applications, such as quantum communication and quantum random number generator.

physics.ins-det↗

arXiv2016

A novel and automatic pectoral muscle identification algorithm for mediolateral oblique (MLO) view mammograms using ImageJ

Pectoral muscle identification is often required for breast cancer risk analysis, such as estimating breast density. Traditional methods are overwhelmingly based on manual visual assessment or straight line fitting for the pectoral muscle boundary, which are inefficient and inaccurate since pectoral muscle in mammograms can have curved boundaries. This paper proposes a novel and automatic pectoral muscle identification algorithm for MLO view mammograms. It is suitable for both scanned film and full field digital mammograms. This algorithm is demonstrated using a public domain software ImageJ. A validation of this algorithm has been performed using real-world data and it shows promising result.

cs.CV↗

arXiv2016

Opportunistic Jamming for Enhancing Security: Stochastic Geometry Modeling and Analysis

This correspondence studies the secrecy communication of the single-input single-output multi-eavesdropper (SISOME) channel with multiple single-antenna jammers, where the jammers and eavesdroppers are distributed according to the independent two-dimensional homogeneous Poisson point process (PPP). For enhancing the physical layer security, we propose an opportunistic multiple jammer selection scheme, where the jammers whose channel gains to the legitimate receiver less than a threshold, are selected to transmit independent and identically distributed (\emph{i.i.d.}) Gaussian jamming signals to confound the eavesdroppers. We characterize the secrecy throughput achieved by our proposed jammer selection scheme, and show that the secrecy throughput is a quasi-concave function of the selection threshold.

cs.IT↗

arXiv2015

Localized direct CP violation in $B^\pm\rightarrow ρ^0 (ω)π^\pm\rightarrow π^+ π^-π^\pm$

We study the localized direct CP violation in the hadronic decays $B^\pm\rightarrow ρ^0 (ω)π^\pm\rightarrowπ^+ π^-π^\pm$, including the effect caused by an interesting mechanism involving the charge symmetry violating mixing between $ρ^0$ and $ω$. We calculate the localized integrated direct CP violation when the low invariant mass of $π^+π^-$ [$m(π^+π^-)_{low}$] is near $ρ^0(770)$. For five models of form factors investigated, we find that the localized integrated direct CP violation varies from -0.0170 to -0.0860 in the ranges of parameters in our model when $0.750<m(π^+π^-)_{low}<0.800$\,GeV. This result, especially the sign, agrees with the experimental data and is independent of form factor models. The new experimental data shows that the signs of the localized integrated CP asymmetries in the regions $0.470<m(π^+π^-)_{low}<0.770$\,GeV and $0.770<m(π^+π^-)_{low}<0.920$\,GeV are positive and negative, respectively. We find that $ρ$-$ω$ mixing makes the localized integrated CP asymmetry move towards the negative direction, and therefore contributes to the sign change in those two regions. This behavior is also model independent. We also calculate the localized integrated direct CP violating asymmetries in the regions $0.470<m(π^+π^-)_{low}<0.770$\,GeV and $0.770<m(π^+π^-)_{low}<0.920$\,GeV and find that they agree with the experimental data in some models of form factors.

hep-ph↗

arXiv2015

The Cauchy problem on large time for surface waves type Boussinesq systems II

This paper is a continuation of a previous work by two of the Authors on long time existence for Boussinesq systems modeling the propagation of long, weakly nonlinear water waves. We provide proofs on examples not considered previously in particular we prove a long time well-posedness result for a delicate "strongly dispersive" Boussinesq system.

math.AP↗

arXiv2015

Optimization of the Block-level Bit Allocation in Perceptual Video Coding based on MINMAX

In video coding, it is expected that the encoder could adaptively select the encoding parameters (e.g., quantization parameter) to optimize the bit allocation to different sources under the given constraint. However, in hybrid video coding, the dependency between sources brings high complexity for the bit allocation optimization, especially in the block-level, and existing optimization methods mostly focus on frame-level bit allocation. In this paper, we propose a macroblock (MB) level bit allocation method based on the minimum maximum (MINMAX) criterion, which has acceptable encoding complexity for offline applications. An iterative-based algorithm, namely maximum distortion descend (MDD), is developed to reduce quality fluctuation among MBs within a frame, where the Structure SIMilarity (SSIM) index is used to measure the perceptual distortion of MBs. Our extensive experimental results on benchmark video sequences show that the proposed method can greatly enhance the encoding performance in terms of both bits saving and perceptual quality improvement.

cs.MM↗

arXiv2015

Possible large $CP$ violation in three body decays of heavy baryon

We propose a new mechanism which can introduce large $CP$ asymmetries in the phase spaces of three-body decays of heavy baryons. In this mechanism, a large $CP$ asymmetry is induced by the interference of two intermediate resonances, which subsequently decay into two different combinations of final particles. We apply this mechanism to the decay channel $Λ_b^0 \to p π^0π^-$, and find that the differential $CP$ asymmetry can reach as large as $50\%$, while the regional $CP$ asymmetry can reach as large as $16\%$ in the interference region of the phase space.

hep-ph↗

arXiv2015

Edge-Mediated Skyrmion Chain and Its Collective Dynamics in a Confined Geometry

The emergence of a topologically nontrivial vortex-like magnetic structure, the magnetic skyrmion, has launched new concepts for memory devices. There, extensive studies have theoretically demonstrated the ability to encode information bits by using a chain of skyrmions in one-dimensional nanostripes. Here, we report the first experimental observation of the skyrmion chain in FeGe nanostripes by using high resolution Lorentz transmission electron microscopy. Under an applied field normal to the nanostripes plane, we observe that the helical ground states with distorted edge spins would evolves into individual skyrmions, which assemble in the form of chain at low field and move collectively into the center of nanostripes at elevated field. Such skyrmion chain survives even as the width of nanostripe is much larger than the single skyrmion size. These discovery demonstrates new way of skyrmion formation through the edge effect, and might, in the long term, shed light on the applications.

cond-mat.mes-hall↗

arXiv2015

Gate-tunable quantum oscillations in ambipolar Cd3As2 thin films

Electrostatic doping in materials can lead to various exciting electronic properties, such as metal-insulator transition and superconductivity, by altering the Fermi level position or introducing exotic phases. Cd3As2, a three-dimensional (3D) analog of graphene with extraordinary carrier mobility, was predicted to be a 3D Dirac semimetal, a feature confirmed by recent experiments. However, most research so far has been focused on metallic bulk materials that are known to possess ultra-high mobility and giant magnetoresistance but limited carrier transport tunability. Here, we report on the first observation of a gate-induced transition from band conduction to hopping conduction in single-crystalline Cd3As2 thin films via electrostatic doping by solid electrolyte gating. The extreme charge doping enables the unexpected observation of p-type conductivity in a 50 nm-thick Cd3As2 thin film grown by molecular beam epitaxy. More importantly, the gate-tunable Shubnikov-de Haas (SdH) oscillations and the temperature-dependent resistance reveal a unique band structure and bandgap opening when the dimensionality of Cd3As2 is reduced. This is also confirmed by our first-principles calculations. The present results offer new insights towards nanoelectronic and optoelectronic applications of Dirac semimetals in general, and provide new routes in the search for the intriguing quantum spin Hall effect in low-dimension Dirac semimetals, an effect that is theoretically predicted but not yet experimentally realized.

cond-mat.mtrl-sci↗

arXiv2015

Maximum Orders of Cyclic and Abelian Extendable Actions on Surfaces

Let $Σ_g (g>1)$ be a closed surface embedded in $S^3$. If a group $G$ can acts on the pair $(S^3, Σ_g)$, then we call such a group action on $Σ_g$ extendable over $S^3$. In this paper we show that the maximum order of extendable cyclic group actions is $4g+4$ when $g$ is even and $4g-4$ when $g$ is odd; the maximum order of extendable abelian group actions is $4g+4$. We also give results of similar questions about extendable group actions over handlebodies.

math.GT↗

arXiv2015

Improving protein threading accuracy via combining local and global potential using TreeCRF model

Protein structure prediction remains to be an open problem in bioinformatics. There are two main categories of methods for protein structure prediction: Free Modeling (FM) and Template Based Modeling (TBM). Protein threading, belonging to the category of template based modeling, identifies the most likely fold with the target by making a sequence-structure alignment between target protein and template protein. Though protein threading has been shown to more be successful for protein structure prediction, it performs poorly for remote homology detection.

q-bio.BM↗

arXiv2015

The Enhanced Performance of C2H2 Gas Sensor based on Carbon-decorated SnO2 Nanoparticles via CVD method

As a flammable and explosive industrial gas, C2H2 gas detection is necessary and significant. Herein, highly sensitive C2H2 gas sensor was initially fabricated by carbon-decorated SnO2 nanoparticles, which was prepared using CVD method with C2H2 Gas as raw material. The effects of preparation conditions on sensor response were studied and the response to 1000 ppm C2H2 at working temperature of 370 C reached a value of 106.3, which is much higher than that of other materials reported. In addition, the carbon-decorated SnO2 sensor showed very good stability and C2H2 selectivity against other gases. Raman spectroscopy reveals that the response of sensors is affected by carbon-loading and degree of graphitization, which depend on the CVD temperature. It is speculated that the sensor response is enhanced by electron penetration effect from internal SnO2 nanoparticles to the external carbon layer, due to Schottky Barrier formed between SnO2 nanoparticle and carbon layer.

cond-mat.mtrl-sci↗

arXiv2015

A Strategy for Improving the Interfacial Crystallinity and Carrier Mobility of SnO2 Porous Nanosolids

SnO2 porous nanosolid (PNS) was prepared by a solvothermal hot-press method, and a new strategy was developed to improve its interfacial crystallinity and carrier mobility. It was found that the carrier mobility of SnO2 PNS was improved after being calcined at 500 °C in high-pressure oxygen. Furthermore, the mobility was greatly increased by calcining SnO2 PNS at 350 °C for 12 h in high-pressure oxygen, and the highest mobility reached 35 cm2/Vs. On the other hand, the complex impedance spectra of the samples revealed that the annihilation of oxygen vacancies mainly happens within the interfacial region among SnO2 nanoparticles during the calcinations process in high-pressure oxygen. As a result, the interfacial crystallinity was improved and carrier mobility was increased. Based on the analysis of experimental data, a simple model was proposed to explain the above phenomena. And the simple model may find applications in improving the carrier mobility of other oxide semiconductors used in photovoltaic cells.

cond-mat.mtrl-sci↗

arXiv2015

TOPO: Improving remote homologue recognition via identifying common protein structure framework

Protein structure prediction remains a challenge in the field of computational biology. Traditional protein structure prediction approaches include template-based modelling (say, homology modelling, and threading), and ab initio. A threading algorithm takes a query protein sequence as input, recognizes the most likely fold, and finally reports the alignments of the query sequence to structure-known templates as output. The existing threading approaches mainly utilizes the information of protein sequence profile, solvent accessibility, contact probability, etc., and correctly recognize folds for some proteins. However, the existing threading approaches show poorly performance for remote homology proteins. How to improve the fold recognition for remote homology proteins remains to be a difficult task for protein structure prediction.

q-bio.OT↗

arXiv2015

Local well-posedness and break-down criterion of the incompressible Euler equations with free boundary

In this paper, we prove the local well-posedness of the free boundary problem for the incompressible Euler equations in low regularity Sobolev spaces, in which the velocity is a Lipschtiz function and the free surface belongs to $C^{\f32+\varepsilon}$. Moreover, we also present a Beale-Kato-Majda type break-down criterion of smooth solution in terms of the mean curvature of the free surface, the gradient of the velocity and Taylor sign condition.

math.AP↗

arXiv2015

Robust quantum random number generator based on avalanche photodiodes

We propose and demonstrate a scheme to realize a high-efficiency truly quantum random number generator (RNG) at room temperature (RT). Using an effective extractor with simple time bin encoding method, the avalanche pulses of avalanche photodiode (APD) are converted into high-quality random numbers (RNs) that are robust to slow varying noise such as fluctuations of pulse intensity and temperature. A light source is compatible but not necessary in this scheme. Therefor the robustness of the system is effective enhanced. The random bits generation rate of this proof-of-principle system is 0.69 Mbps with double APDs and 0.34 Mbps with single APD. The results indicate that a high-speed RNG chip based on the scheme is potentially available with an integrable APD array.

quant-ph↗

arXiv2015

Spectral imaging with dual compressed sensing

We experimentally demonstrated a spectral imaging scheme with dual compressed sensing. With the dimensions of spectral and spatial information both compressed, the spectral image of a colored object can be obtained with only a single point detector. The effect of spatial and spectral modulation numbers on the imaging quality is also analyzed. Our scheme provides a stable, highly consistent approach of spectral imaging.

physics.optics↗

arXiv2015

Alternating Heegaard diagrams and Williams solenoid attractors in 3--manifolds

We find all Heegaard diagrams with the property "alternating" or "weakly alternating" on a genus two orientable closed surface. Using these diagrams we give infinitely many genus two 3--manifolds, each admits an automorphism whose non-wondering set consists of two Williams solenoids, one attractor and one repeller. These manifolds contain half of Prism manifolds, Poincaré's homology 3--sphere and many other Seifert manifolds, all integer Dehn surgeries on the figure eight knot, also many connected sums. The result shows that many kinds of 3--manifolds admit a kind of "translation" with certain stability.

math.GT↗