arXiv subjects

Xin Zhang

Publications and source records attributed to Xin Zhang.

At least 1,045 records · Page 58Linked to original sources

arXiv2019

Improving cosmological parameter estimation with the future gravitational-wave standard siren observation from the Einstein Telescope

Detection of gravitational waves produced by merger of binary compact objects could provide an independent way for measuring the luminosity distance to the gravitational-wave burst source, indicating that gravitational-wave observation, combined with observation of electromagnetic counterparts, can provide "standard sirens" for investigating the expansion history of the universe in cosmology. In this work, we wish to investigate how the future gravitational-wave standard siren observations would break the parameter degeneracies existing in the conventional optical observations and how they help improve the parameter estimation in cosmology. We take the third-generation ground-based gravitational-wave detector, the Einstein Telescope, as an example to make an analysis. By simulating 1000 events data in the redshift range between 0 and 5 based on the ten-year observation of the Einstein Telescope, we find that the gravitational-wave data could largely break the degeneracy between the matter density and the Hubble constant, thus significantly improving the cosmological constraints. We further show that the constraint on the equation-of-state parameter of dark energy could also be significantly improved by including the gravitational-wave data in the cosmological fit.

astro-ph.CO↗

arXiv2019

List edge coloring of outer-1-planar graphs

A graph is outer-1-planar if it can be drawn in the plane so that all vertices are on the outer face and each edge is crossed at most once. It is known that the list edge chromatic number $χ'_l(G)$ of any outer-1-planar graph $G$ with maximum degree $Δ(G)\geq 5$ is exactly its maximum degree. In this paper, we prove $χ'_l(G)=Δ(G)$ for outer-1-planar graphs $G$ with $Δ(G)=4$ and with the crossing distance being at least 3.

math.CO↗

arXiv2019

Can the $H_0$ tension be resolved in extensions to $Λ$CDM cosmology?

We wish to investigate whether there is an extension to the base $Λ$CDM cosmology that can resolve the tension between the Planck observation of the cosmic microwave background anisotropies and the local measurement of the Hubble constant. We consider various plausible extended models in this work, and we use the Planck 2015 observation, combined with the baryon acoustic oscillation data, the JLA type Ia supernovae data, and the local measurement of the Hubble constant (by Riess et al. in 2016), to make an analysis. We find that the holographic dark energy plus sterile neutrino model can reduce the tension to be at the 1.11$σ$ level, but this model is obviously not favored by the current observations. Among these extended models, the $Λ$CDM+$N_{\rm eff}$ model is most favored by the current observations, and this model can reduce the tension to be at the 1.87$σ$ level. By a careful test, we conclude that none of these extended models can convincingly resolve the $H_0$ tension.

astro-ph.CO↗

arXiv2019

The analysis of effective galaxies number count for Chinese Space Station Optical Survey(CSS-OS) by image simulation

The Chinese Space Station Optical Survey (CSS-OS) is a mission to explore the vast universe. This mission will equip a 2-meter space telescope to perform a multi-band NUV-optical large area survey (over 40% of the sky) and deep survey (~1% of the sky) for the cosmological and astronomical goals. Galaxy detection is one of the most important methods to achieve scientific goals. In this paper, we evaluate the galaxy number density for CSS-OS in i band (depth, i ~26 for large area survey and ~27 for the deep survey, point source, 5-sigma by the method of image simulation. We also compare galaxies detected by CSS-OS with that of LSST (i~27, point source, 5-sigma. In our simulation, the HUDF galaxy catalogs are used to create mock images due to long enough integration time which meets the completeness requirements of the galaxy analysis for CSS-OS and LSST. The galaxy surface profile and spectrum are produced by the morphological information, photometric redshift and SEDs from the catalogs. The instrumental features and the environmental condition are also considered to produce the mock galaxy images. The galaxies of CSS-OS and LSST are both extracted by SExtractor from the mock i band image and matched with the original catalog. Through the analysis of the extracted galaxies, we find that the effective galaxy number count is ~13 arcmin^-2, ~40 arcmin^-2 and ~42 arcmin^-2 for CSS-OS large area survey, CSS-OS deep survey and LSST, respectively. Moreover, CSS-OS shows the advantage in small galaxy detection with high spatial resolution, especially for the deep survey: about 20% of the galaxies detected by CSS-OS deep survey are not detected by LSST, and they have a small effective radius of re < 0.3".

astro-ph.IM↗

arXiv2018

An Improved Decentralized Control of Grid-Connected Cascaded Inverters with Different Power Capacities

The existing decentralized control for cascaded inverters is based on the assumption that all modules have same capacities, and a local fixed-amplitude-varied-phase voltage control is adopted for each inverter module. However, available source power capacities of cascaded inverters may be different in some practical applications. To address this issue, this letter proposes an improved decentralized control scheme, in which the voltage amplitudes are varied according to their individual available powers. Moreover, a power factor consistency control is proposed to achieve autonomous voltage phase synchronization. The steady-state analysis and synchronization mechanism of cascaded inverters are illustrated. In addition, the proposed strategy has other advantages, such as adjustable grid power factor and immune to the grid voltage fault. The effectiveness of the proposed control is tested by experiments.

eess.SP↗

arXiv2018

Secure and Efficiently Searchable IoT Communication Data Management Model: Using Blockchain as a new tool

With the rapid development of the Internet of things (IoT), more and more IoT devices are connected and communicate frequently. In this background, the traditional centralized security architecture of IoT will be limited in terms of data storage space, data reliability, scalability, operating costs and liability judgment. In this paper, we propose an new key information storage framework based on a small distributed database generated by blockchain technology and cloud storage. Specifically, all encrypted key communication data will be upload to public could server for enough storage, but the abstracts of these data (called "communication logs") will be recorded in "IoT ledger" (i.e., an distributed database) that maintained by all IoT devices according to the blockchain generation approach, which could solve the problem of data reliability, scalability and liability judgment. Besides, in order to efficiently search communication logs and not reveal any sensitive information of communication data, we design the secure search scheme for our "IoT ledger", which exploits the Asymmetric Scalar-product Preserving Encryption (ASPE) approach to guarantee the data security, and exploits the 2-layers index which is tailor-made for blockchain database to improve the search efficiency. Security analysis and experiments on synthetic dataset show that our schemes are secure and efficient.

cs.CR↗

arXiv2018

Skeleton-based Gesture Recognition Using Several Fully Connected Layers with Path Signature Features and Temporal Transformer Module

The skeleton based gesture recognition is gaining more popularity due to its wide possible applications. The key issues are how to extract discriminative features and how to design the classification model. In this paper, we first leverage a robust feature descriptor, path signature (PS), and propose three PS features to explicitly represent the spatial and temporal motion characteristics, i.e., spatial PS (S_PS), temporal PS (T_PS) and temporal spatial PS (T_S_PS). Considering the significance of fine hand movements in the gesture, we propose an "attention on hand" (AOH) principle to define joint pairs for the S_PS and select single joint for the T_PS. In addition, the dyadic method is employed to extract the T_PS and T_S_PS features that encode global and local temporal dynamics in the motion. Secondly, without the recurrent strategy, the classification model still faces challenges on temporal variation among different sequences. We propose a new temporal transformer module (TTM) that can match the sequence key frames by learning the temporal shifting parameter for each input. This is a learning-based module that can be included into standard neural network architecture. Finally, we design a multi-stream fully connected layer based network to treat spatial and temporal features separately and fused them together for the final result. We have tested our method on three benchmark gesture datasets, i.e., ChaLearn 2016, ChaLearn 2013 and MSRC-12. Experimental results demonstrate that we achieve the state-of-the-art performance on skeleton-based gesture recognition with high computational efficiency.

cs.CV↗

arXiv2018

Scanning tunneling microscopic evidence of interface enhanced high-Tc superconductivity in Pb islands grown on SrTiO3

The discovery of the interface enhanced superconductivity in the single layer film of FeSe epitaxially grown on SrTiO3 substrates has triggered a flurry of activity in the field of superconductivity. It raised the hope to find more conventional high-Tc superconductors which are purely driven by the electron-phonon interaction at ambient pressure. Here we report the experimental evidence from the measurement of scanning tunneling spectroscopy for the interface enhanced high-Tc superconductivity in the Pb thin film islands grown on SrTiO3 substrates. The superconducting energy gap of the Pb film is found to depend on both the thickness and the volume of the islands. The largest superconducting energy gap is found to be about 10 meV, which is 7 times larger than that in the bulk Pb. The corresponding superconducting transition temperature, estimated by fitting the temperature dependence of the gap values using the BCS formula, is found to be 47 K, again 7 times higher than that of the bulk Pb.

cond-mat.supr-con↗

arXiv2018

Watermark Retrieval from 3D Printed Objects via Convolutional Neural Networks

We present a method for reading digital data embedded in planar 3D printed surfaces. The data are organised in binary arrays and embedded as surface textures in a way inspired by QR codes. At the core of the retrieval method lies a Convolutional Neural Network, outputting a confidence map of the location of the surface textures encoding value 1 bits. Subsequently, the bit array is retrieved through a series of simple image processing and statistical operations applied on the confidence map. Extensive experimentation with images captured from various camera views, under various illumination conditions and from objects printed with various material colours, shows that the proposed method generalizes well and achieves the level of accuracy required in practical applications.

cs.CV↗

arXiv2018

Search for sterile neutrinos in a universe of vacuum energy interacting with cold dark matter

We investigate the cosmological constraints on sterile neutrinos in a universe in which vacuum energy interacts with cold dark matter by using latest observational data. We focus on two specific interaction models, $Q=βHρ_{\rm v}$ and $Q=βHρ_{\rm c}$. To overcome the problem of large-scale instability in the interacting dark energy scenario, we employ the parametrized post-Friedmann (PPF) approach for interacting dark energy to do the calculation of perturbation evolution. The observational data sets used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation measurements, the type-Ia supernova data, the Hubble constant direct measurement, the galaxy weak lensing data, the redshift space distortion data, and the Planck lensing data. Using the all-data combination, we obtain $N_{\rm eff}<3.522$ and $m_{ν,{\rm sterile}}^{\rm eff}<0.576$ eV for the $Q=βHρ_{\rm v}$ model, and $N_{\rm eff}=3.204^{+0.049}_{-0.135}$ and $m_{ν,{\rm sterile}}^{\rm eff}=0.410^{+0.150}_{-0.330}$ eV for the $Q=βHρ_{\rm c}$ model. The latter indicates $ΔN_{\rm eff}>0$ at the 1.17$σ$ level and a nonzero mass of sterile neutrino at the 1.24$σ$ level. In addition, for the $Q=βHρ_{\rm v}$ model, we find that $β=0$ is consistent with the current data, and for the $Q=βHρ_{\rm c}$ model, we find that $β>0$ is obtained at more than 1$σ$ level.

astro-ph.CO↗

arXiv2018

Cosmic ray $e^{+} e^{-}$ spectrum excess and peak feature observed by the DAMPE experiment from dark matter

The Chinese satellite Wukong, also known as the DArk Matter Particle Explorer (DAMPE), has released its observation data of the cosmic ray (CR) electrons and positrons. The data shows an excess in the energy spectrum up to TeV energy, and possibly a peak-like fine structure at $\sim 1.4 \TeV$. We investigate the scenario that the source of the excess comes from dark matter annihilation or decay. We find that the annihilation or decay of diffuse dark matter particles in the Galactic halo can give excellent ($W^+W^-$ channel) or at least good (double $τ^+τ^-$ channel) fits to the broad excess. However, the annihilation cross-section is $10^{-23}\cm^3s^{-1}$, larger than required for getting the correct relic abundance. We then study whether the narrow peak at $\sim 1.4\TeV$ could be explained by a nearby subhalo, which thanks to the smaller distance, could supply $e^+e^-$ within a narrow energy range. We find that in order to produce a peak width less than the energy bin width (0.2 TeV), the source must be located within $r\lsim 0.53~\kpc$. Our global fit models do not produce the peak-like feature, instead at 1.4 TeV the spectrum show either a slope or a cliff-like feature. However, if less than optimal fit is allowed, the peak-like feature could be generated. Furthermore, an excellent fit with peak could be obtained with model B if the background is rescaled. If the dark matter decay and annihilation rates are determined using the broad excess, the required subhalo mass $\sim10^{5}~M_\odot$ for decay model, or $\sim10^{4.5}\Msun$ for annihilation model and a shallower density profile slope $α=1.2$, or $\sim10^{2.5}\Msun$ for the steep density profile $α=1.7$. However, the probability for the existence of a such nearby subhalo as massive as given above is very low.

astro-ph.HE↗

arXiv2018

Iterative Marginal Maximum Likelihood DOD and DOA Estimation for MIMO Radar in the Presence of SIRP Clutter

The spherically invariant random process (SIRP) clutter model is commonly used in scenarios where the radar clutter cannot be correctly modeled as a Gaussian process. In this short communication, we devise a novel Maximum-Likelihood (ML)-based iterative estimator for direction-of-departure and direction-of-arrival estimation in the Multiple-input multiple-output (MIMO) radar context in the presence of SIRP clutter. The proposed estimator employs a stepwise numerical concentration approach w.r.t. the objective function related to the marginal likelihood of the observation data. Our estimator leads to superior performance, as our simulations show, w.r.t. to the existing likelihood based methods, namely, the conventional, the conditional and the joint likelihood based estimators, and w.r.t. the robust subspace decomposition based methods. Finally, interconnections and comparison between the Iterative Marginal ML Estimator (IMMLE), Iterative Joint ML Estimator (IJMLE) and Iterative Conditional ML Estimator (ICdMLE) are provided.

eess.SP↗

arXiv2018

Some free boundary problem for two phase inhomogeneous incompressible flow

In this paper, we establish some local and global solutions for the two phase incompressible inhomogeneous flows with moving interfaces in $L_p-L_q$ maximal regularity class. Compared with previous results obtained by V.A.Solonnikov and by Y.Shibata \& S.Shimizu, we find the local solutions in $L_p-L_q$ class in some general uniform $W^{2-1\slash r}_r$ domain in $\BBR^N$ by assuming $(p, q)\in ]2,\infty[\times ]N,\infty[$ or $(p, q)\in ]1,2[ \times ]N,\infty[$ satisfying $1 \slash p + N \slash q>3\slash 2.$ In particular, less regular initial data are allowed by assuming $p<2.$ In addition, if the density and the viscosity coefficient are piecewise constant, we can construct the long time solution from the small initial states in the case of the bounded droplet. This is due to some decay property for the corresponding linearized problem.

math.AP↗

arXiv2018

Exploring interacting holographic dark energy in a perturbed universe with parameterized post-Friedmann approach

The model of holographic dark energy in which dark energy interacts with dark matter is investigated in this paper. In particular, we consider the interacting holographic dark energy model in the context of a perturbed universe, which was never investigated in the literature. To avoid the large-scale instability problem in the interacting dark energy cosmology, we employ the generalized version of the parameterized post-Friedmann approach to treat the dark energy perturbations in the model. We use the current observational data to constrain the model. Since the cosmological perturbations are considered in the model, we can then employ the redshift-space distortions (RSD) measurements to constrain the model, in addition to the use of the measurements of expansion history, which was either never done in the literature. We find that, for both the cases with $Q=βHρ_{\rm c}$ and $Q=βH_0ρ_{\rm c}$, the interacting holographic dark energy model is more favored by the current data, compared to the holographic dark energy model without interaction. It is also found that, with the help of the RSD data, a positive coupling $β$ can be detected at the $2.95σ$ statistical significance for the case of $Q=βH_0ρ_{\rm c}$.

astro-ph.CO↗

arXiv2018

$R_{D^{(\ast)}}$, $R_{K^{(\ast)}}$ and neutrino mass in the 2HDM-III with right-handed neutrinos

Given that the two-Higgs-doublet model of type III (2HDM-III) has the potential to address the $R_{D^{(\ast)}}$ anomalies while the resolution to the $R_{K^{(\ast)}}$ deficits requires new degrees of freedom within this framework, we consider in this paper a unified scenario where the low-scale type-I seesaw mechanism is embedded into the 2HDM-III, so as to accommodate the $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies as well as the neutrino mass. We first revisit the $R_{D^{(\ast)}}$ anomalies and find that the current world-averaged results can be addressed at $2σ$ level without violating the bound from the branching ratio $\mathcal{B}(B_c^-\rightarrow τ^- \barν)\leqslant 30\%$. The scenario predicts two sub-eV neutrino masses based on a decoupled heavy Majorana neutrino and two nearly degenerate Majorana neutrinos with mass around the electroweak scale. For the $R_{K^{(\ast)}}$ anomalies, the same scenario can generate the required Wilson coefficients in the direction $ C_{9 μ}^{\rm NP}=-C_{10 μ}^{\rm NP}<0$, with $\mathcal{O}(1)$ Yukawa couplings for the muon and the top quark.

hep-ph↗

arXiv2018

Open-Loop and Closed-Loop Solvabilities for Stochastic Linear Quadratic Optimal Control Problems of Markov Regime-Switching System

This paper investigates the stochastic linear quadratic (LQ, for short) optimal control problem of Markov regime switching system. The representation of the cost functional for the stochastic LQ optimal control problem of Markov regime switching system is derived using the technique of It{ô}'s formula. For the stochastic LQ optimal control problem of Markov regime switching system, we establish the equivalence between the open-loop (closed-loop) solvability and the existence of an adapted solution to the corresponding forward-backward stochastic differential equation with constraint (the existence of a regular solution to the Riccati equation). Also, we analyze the interrelationship between the strongly regular solvability of the Riccati equation and the uniform convexity of the cost functional.

math.OC↗

arXiv2018

A note on the edge partition of graphs containing either a light edge or an alternating 2-cycle

Let $\mathcal{G}_α$ be a hereditary graph class (i.e, every subgraph of $G_α\in \mathcal{G}_α$ belongs to $\mathcal{G}_α$) such that every graph $G_α$ in $\mathcal{G}_α$ has minimum degree at most 1, or contains either an edge $uv$ such that $d_{G_α}(u)+d_{G_α}(v)\leq α$ or a 2-alternating cycle. It is proved that every graph in $\mathcal{G}_α$ ($α\geq 5$) with maximum degree $Δ$ can be edge-partitioned into two forests $F_1$, $F_2$ and a subgraph $H$ such that $Δ(F_i)\leq \max\{2,\lceil\frac{Δ-α+6}{2}\rceil\}$ for $i=1,2$ and $Δ(H)\leq α-5$.

math.CO↗

arXiv2018

Interpreting Neural Network Judgments via Minimal, Stable, and Symbolic Corrections

We present a new algorithm to generate minimal, stable, and symbolic corrections to an input that will cause a neural network with ReLU activations to change its output. We argue that such a correction is a useful way to provide feedback to a user when the network's output is different from a desired output. Our algorithm generates such a correction by solving a series of linear constraint satisfaction problems. The technique is evaluated on three neural network models: one predicting whether an applicant will pay a mortgage, one predicting whether a first-order theorem can be proved efficiently by a solver using certain heuristics, and the final one judging whether a drawing is an accurate rendition of a canonical drawing of a cat.

cs.LG↗