arXiv subjects

Bo Zhang

Publications and source records attributed to Bo Zhang.

At least 883 records · Page 49Linked to original sources

arXiv2010

Investigation for the enrichment pattern of the element abundances in r+s star HE 0338-3945: a special r-II star?

The very metal-poor star HE 0338-3945 shows a double-enhanced pattern of the neutron-capture elements. The study to this sample could make people gain a better understanding of s- and r-process nucleosynthesis at low metallicity. Using a parametric model,we find that the abundance pattern of the neutron-capture elements could be best explained by a binary system formed in a molecular cloud, which had been polluted by r-process material. The observed abundance pattern of C and N can be explained by an AGB model(Karakas & Lattanzio 2007), . Combing with the parameters obtained from Cui & Zhang (2006), we suggest that the initial mass of the AGB companion is most likely to be about 2.5Msun, which excludes the possibility of forming a type-1.5 supernova. By comparing with the observational abundance pattern of CS 22892-052, we find that the dominating production of O should accompany with the production of the heavy r-process elements of r+s stars. Similar to r-II stars, the heavy r-process elements are not produced in conjunction with all the light elements from Na to Fe group. The abundance pattern of the light and r-process elements for HE 0338-3945 is very close to the pattern of the r-II star CS 22892-052. So, we suggest that this star HE 0338-3945 should be a special r-II star.

astro-ph.SR↗

arXiv2010

An inverse electromagnetic scattering problem for a bi-periodic inhomogeneous layer on a perfectly conducting plate

This paper is concerned with uniqueness for reconstructing a periodic inhomogeneous medium covered on a perfectly conducting plate. We deal with the problem in the frame of time-harmonic Maxwell systems without TE or TM polarization. An orthogonal relation for two refractive indices is obtained, and then inspired by Kirsch's idea, the refractive index can be identified by utilizing the eigenvalues and eigenfunctions of a quasi-periodic Sturm-Liouville eigenvalue problem.

math.AP↗

arXiv2010

The linear sampling method for the inverse electromagnetic scattering by a partially coated bi-periodic structure

In this paper, we consider the inverse problem of recovering a doubly periodic Lipschitz structure through the measurement of the scattered field above the structure produced by point sources lying above the structure. The medium above the structure is assumed to be homogenous and lossless with a positive dielectric coefficient. Below the structure is a perfect conductor partially coated with a dielectric. A periodic version of the linear sampling method is developed to reconstruct the doubly periodic structure using the near field data. In this case, the far field equation defined on the unit ball of R^3 is replaced by the near field equation which is a linear integral equation of the first kind defined on a plane above the periodic surface.

math.AP↗

arXiv2010

Magnetic Field Control of the Quantum Chaotic Dynamics of Hydrogen Analogues in an Anisotropic Crystal Field

We report magnetic field control of the quantum chaotic dynamics of hydrogen analogues in an anisotropic solid state environment. The chaoticity of the system dynamics was quantified by means of energy level statistics. We analyzed the magnetic field dependence of the statistical distribution of the impurity energy levels and found a smooth transition between the Poisson limit and the Wigner limit, i.e. transition between regular Poisson and fully chaotic Wigner dynamics. Effect of the crystal field anisotropy on the quantum chaotic dynamics, which manifests itself in characteristic transitions between regularity and chaos for different field orientations, was demonstrated.

nlin.CD↗

arXiv2010

Intrinsic dimension estimation of data by principal component analysis

Estimating intrinsic dimensionality of data is a classic problem in pattern recognition and statistics. Principal Component Analysis (PCA) is a powerful tool in discovering dimensionality of data sets with a linear structure; it, however, becomes ineffective when data have a nonlinear structure. In this paper, we propose a new PCA-based method to estimate intrinsic dimension of data with nonlinear structures. Our method works by first finding a minimal cover of the data set, then performing PCA locally on each subset in the cover and finally giving the estimation result by checking up the data variance on all small neighborhood regions. The proposed method utilizes the whole data set to estimate its intrinsic dimension and is convenient for incremental learning. In addition, our new PCA procedure can filter out noise in data and converge to a stable estimation with the neighborhood region size increasing. Experiments on synthetic and real world data sets show effectiveness of the proposed method.

cs.CV↗

arXiv2010

The inverse electromagnetic scattering problem in a piecewise homogeneous medium

This paper is concerned with the problem of scattering of time-harmonic electromagnetic waves from an impenetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is established, employing the integral equation method. Inspired by a novel idea developed by Hahner [11], we prove that the penetrable interface between layers can be uniquely determined from a knowledge of the electric far field pattern for incident plane waves. Then, using the idea developed by Liu and Zhang [21], a new mixed reciprocity relation is obtained and used to show that the impenetrable obstacle with its physical property can also be recovered. Note that the wave numbers in the corresponding medium may be different and therefore this work can be considered as a generalization of the uniqueness result of [20].

math.AP↗

arXiv2010

An Explicit Nonlinear Mapping for Manifold Learning

Manifold learning is a hot research topic in the field of computer science and has many applications in the real world. A main drawback of manifold learning methods is, however, that there is no explicit mappings from the input data manifold to the output embedding. This prohibits the application of manifold learning methods in many practical problems such as classification and target detection. Previously, in order to provide explicit mappings for manifold learning methods, many methods have been proposed to get an approximate explicit representation mapping with the assumption that there exists a linear projection between the high-dimensional data samples and their low-dimensional embedding. However, this linearity assumption may be too restrictive. In this paper, an explicit nonlinear mapping is proposed for manifold learning, based on the assumption that there exists a polynomial mapping between the high-dimensional data samples and their low-dimensional representations. As far as we know, this is the first time that an explicit nonlinear mapping for manifold learning is given. In particular, we apply this to the method of Locally Linear Embedding (LLE) and derive an explicit nonlinear manifold learning algorithm, named Neighborhood Preserving Polynomial Embedding (NPPE). Experimental results on both synthetic and real-world data show that the proposed mapping is much more effective in preserving the local neighborhood information and the nonlinear geometry of the high-dimensional data samples than previous work.

cs.CV↗

arXiv2009

The Vortex Structure of SU(2) Calorons

We reveal the center vortex content of SU(2) calorons and ensembles of them. We use Laplacian Center Gauge as well as Maximal Center Gauges to show that the vortex in a single caloron consists of two parts. The first one connects the constituent dyons of the caloron (which are monopoles in Laplacian Abelian Gauge) and extends in time. The second part is predominantly spatial, encloses one of the dyons and can be related to the twist in the caloron gauge field. This part depends strongly on the caloron holonomy and degenerates to a plane when the holonomy is maximally nontrivial, i.e. when the asymptotic Polyakov loop is traceless. Correspondingly, we find the spatial vortices in caloron ensembles to percolate in this case. This finding fits perfectly in the confinement scenario of vortices and shows that calorons are suitable to facilitate the vortex confinement mechanism.

hep-th↗

arXiv2009

Inverse scattering by an inhomogeneous penetrable obstacle in a piecewise homogeneous medium

This paper is concerned with the inverse problem of scattering of time-harmonic acoustic waves by an inhomogeneous penetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is first established by using the integral equation method. We then proceed to establish two tools that play an important role for the inverse problem: one is a mixed reciprocity relation and the other is a priori estimates of the solution on some part of the interfaces between the layered media. For the inverse problem, we prove in this paper that both the penetrable interfaces and the possible inside inhomogeneity can be uniquely determined from a knowledge of the far field pattern for incident plane waves.

math.AP↗

arXiv2009

Heating rate and spin flip lifetime due to near field noise in layered superconducting atom chips

We theoretically investigate the heating rate and spin flip lifetimes due to near field noise for atoms trapped close to layered superconducting structures. In particular, we compare the case of a gold layer deposited above a superconductor with the case of a bare superconductor. We study a niobium-based and a YBCO-based chip. For both niobium and YBCO chips at a temperature of 4.2 K, we find that the deposition of the gold layer can have a significant impact on the heating rate and spin flip lifetime, as a result of the increase of the near field noise. At a chip temperature of 77 K, this effect is less pronounced for the YBCO chip.

physics.atom-ph↗

arXiv2009

Direct and inverse obstacle scattering problems in a piecewise homogeneous medium

This paper is concerned with the problem of scattering of time-harmonic acoustic waves from an impenetrable obstacle in a piecewise homogeneous medium. The well-posedness of the direct problem is established, employing the integral equation method and then used, in conjunction with the representation in a combination of layer potentials of the solution, to prove a priori estimates of solutions on some part of the interface between the layered media. The inverse problem is also considered in this paper. An uniqueness result is obtained for the first time in determining both the penetrable interface and the impenetrable obstacle with its physical property from a knowledge of the far field pattern for incident plane waves. In doing so, an important role is played by the a priori estimates of the solution for the direct problem.

math.AP↗

arXiv2009

Isometric Multi-Manifolds Learning

Isometric feature mapping (Isomap) is a promising manifold learning method. However, Isomap fails to work on data which distribute on clusters in a single manifold or manifolds. Many works have been done on extending Isomap to multi-manifolds learning. In this paper, we first proposed a new multi-manifolds learning algorithm (M-Isomap) with help of a general procedure. The new algorithm preserves intra-manifold geodesics and multiple inter-manifolds edges precisely. Compared with previous methods, this algorithm can isometrically learn data distributed on several manifolds. Secondly, the original multi-cluster manifold learning algorithm first proposed in \cite{DCIsomap} and called D-C Isomap has been revised so that the revised D-C Isomap can learn multi-manifolds data. Finally, the features and effectiveness of the proposed multi-manifolds learning algorithms are demonstrated and compared through experiments.

cs.LG↗

arXiv2009

Vortex Content of SU(2) Calorons and Multi-Calorons

We use Laplacian Center Gauge to reveal the vortex content of single SU(2) calorons and multi-caloron systems at different holonomies. The vortex surfaces in a single SU(2) caloron consist of two parts that are induced by the constituent dyon charges and by the twist between the dyons, respectively. The latter part percolates in a caloron ensemble at maximal nontrivial holonomy. This finding fits perfectly in the confinement scenario of vortices and shows that calorons are suitable to facilitate the vortex confinement mechanism.

hep-lat↗

arXiv2009

The puzzle of excessive non-$D\bar D$ component of the inclusive $ψ(3770)$ decay and the long-distant contribution

In this letter we suggest that the obvious discrepancy between theoretical prediction on the $\mathrm{non}-D\bar D$ decays of $ψ(3770)$ and data is to be alleviated by taking final state interaction (FSI) into account. By assuming that $ψ(3770)$ overwhelmingly dissociates into $D\bar D$, then the final state interaction induces a secondary process, we calculate the branching ratios of $ψ(3770)\to D\bar D\to J/ψη, ρπ, ωη, K^*K$. Our results show that the branching ratio of $ψ(3770)\to \mathrm{non}-D\bar{D}$ can reach up to $\mathcal{B}_{\mathrm{non}-D\bar{D}}^{FSI}=(0.2\sim1.1)%$ while typical parameters $I=0.4$ GeV$^{-2}$ and $α=0.8\sim 1.3$ are adopted. This indicates that the FSI is obviously non-negligible.

hep-ph↗

arXiv2008

Superconducting atom chips: advantages and challenges

Superconductors are considered in view of applications to atom chip devices. The main features of magnetic traps based on superconducting wires in the Meissner and mixed states are discussed. The former state may mainly be interesting for improved atom optics, while in the latter, cold atoms may provide a probe of superconductor phenomena. The properties of a magnetic side guide based on a single superconducting strip wire placed in an external magnetic field are calculated analytically and numerically. In the mixed state of type II superconductors, inhomogeneous trapped magnetic flux, relaxation processes and noise caused by vortex motion are posing specific challenges for atom trapping.

quant-ph↗

arXiv2008

The two-body open charm decays of $Z^+(4430)$

The two-body open charm decays $Z^+(4430)\to D^{+}\bar{D}^{*0}, D^{*+}\bar{D}^{0}, D^{*+}\bar{D}^{*0}$ occur through the re-scattering mechanism and their branching ratios are strongly suppressed if $Z^+(4430)$ is a $D_1\bar D^*$ molecular state. In contrast, $Z^+(4430)$ falls apart into these modes easily with large phase space and they become the main decay modes if $Z^+(4430)$ is a tetraquark state. Experimental search of these two-body open charm modes and the hidden charm mode $χ_{cJ}ρ$ will help distinguish different theoretical schemes.

hep-ph↗

arXiv2008

Fast Poisson Noise Removal by Biorthogonal Haar Domain Hypothesis Testing

Methods based on hypothesis tests (HTs) in the Haar domain are widely used to denoise Poisson count data. Facing large datasets or real-time applications, Haar-based denoisers have to use the decimated transform to meet limited-memory or computation-time constraints. Unfortunately, for regular underlying intensities, decimation yields discontinuous estimates and strong "staircase" artifacts. In this paper, we propose to combine the HT framework with the decimated biorthogonal Haar (Bi-Haar) transform instead of the classical Haar. The Bi-Haar filter bank is normalized such that the p-values of Bi-Haar coefficients (pBH) provide good approximation to those of Haar (pH) for high-intensity settings or large scales; for low-intensity settings and small scales, we show that pBH are essentially upper-bounded by pH. Thus, we may apply the Haar-based HTs to Bi-Haar coefficients to control a prefixed false positive rate. By doing so, we benefit from the regular Bi-Haar filter bank to gain a smooth estimate while always maintaining a low computational complexity. A Fisher-approximation-based threshold imple- menting the HTs is also established. The efficiency of this method is illustrated on an example of hyperspectral-source-flux estimation.

math.ST↗

arXiv2007

What can we learn from the decay of $ N_X(1625)$ in molecule picture?

Considering two molecular state assumptions, i.e. S-wave $\barΛ-K^-$ and S-wave $\barΣ^0-K^-$ molecular states, we study the possible decays of $\bar N_X(1625)$ that include $\bar N_X(1625)\to K^{-}\barΛ, π^{0}\bar{p}, η\bar{p}, π^{-}\bar{n}$. Our results indicate: (1) if $\bar N_{X}(1625)$ is $\barΛ-K^-$ molecular state, $K^{-}\barΛ$ is the main decay modes of $\bar N_{X}(1625)$, and the branching ratios of the rest decay modes are tiny; (2) if $\bar N_{X}(1625)$ is $\barΣ^0-K^-$ molecular state, the branching ratio of $\bar N_{X}(1625)\to K^{-}\barΛ$ is one or two order smaller than that of $\bar N_{X}(1625)\to π^{0}\bar{p}, η\bar{p}, π^{-}\bar{n}$. Thus the search for $\bar N_X(1625)\to π^{0}\bar{p}, η\bar{p}, π^{-}\bar{n}$ will be helpful to shed light on the nature of $\bar N_X(1625)$.

hep-ph↗