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Yong Zhang

Publications and source records attributed to Yong Zhang.

At least 775 records · Page 43Linked to original sources
arXiv2012

CO Structure of the 21 Micron Source IRAS 22272+5435: A Sign of a Jet Launch?

We report the results of radio interferometric observations of the 21-micron source IRAS 22272+5435 in the CO J=2-1 line. 21-micron sources are carbon-rich objects in the post-AGB phase of evolution which show an unidentified emission feature at 21 micron. Since 21-micron sources usually also have circumstellar molecular envelopes, the mapping of CO emission from the envelope will be useful in tracing the nebular structure. From observations made with the Combined Array for Research in Millimeter-wave Astronomy (CARMA), we find that a torus and spherical wind model can explain only part of the CO structure. An additional axisymmetric region created by the interaction between an invisible jet and ambient material is suggested.

astro-ph.SR↗
arXiv2012

Discovery of a halo around the Helix Nebula NGC 7293 in the WISE all-sky survey

We report the discovery of an extended halo (40' in diameter) around the planetary nebula NGC7293 (the Helix Nebula) observed in 12micron band from the Wide-field Infrared Survey Explorer all-sky survey. The mid-infrared halo has an axisymmetric structure with a sharp boundary to the northeast and a more diffuse boundary to the southwest, suggesting an interaction between the stellar wind and the interstellar medium (ISM). The symmetry axis of the halo is well aligned with that of a northeast arc, suggesting that the two structures are physically associated. We have attempted to fit the observed geometry with a model of a moving steady-state stellar wind interacting with the ISM. Possible combinations of the ISM density and the stellar velocity are derived from these fittings. The discrepancies between the model and the observations suggest that the stellar mass loss has a more complicated history, including possible time and angle dependences.

astro-ph.SR↗
arXiv2012

Weak amenability of commutative Beurling algebras

For a locally compact Abelian group $G$ and a continuous weight function $ω$ on $G$ we show that the Beurling algebra $L^1(G, ω)$ is weakly amenable if and only if there is no nontrivial continuous group homomorphism $ϕ$: $G\to \mathbb{C}$ such that $\sup_{t\in G}\frac{|ϕ(t)|}{ω(t)ω(t^{-1})} < \infty$. Let $\hatω(t) = \limsup_{s\to \infty}ω(ts)/ω(s)$ ($t\in G$). Then $L^1(G, ω)$ is 2-weakly amenable if there is a constant $m> 0$ such that $\liminf_{n\to \infty}\frac{ω(t^n)\hatω(t^{-n})}{n} \leq m$ for all $t\in G$.

math.FA↗
arXiv2012

Fixed point properties for semigroups of nonlinear mappings and amenability

In this paper we study fixed point properties for semitopological semigroup of nonexpansive mappings on a bounded closed convex subset of a Banach space. We also study a Schauder fixed point property for a semitopological semigroup of continuous mappings on a compact convex subset of a separated locally convex space. Such semigroups properly include the class of extremely left amenable semitopological semigroups, the free commutative semigroup on one generator and the bicyclic semigroup $S_1 = < a, b: ab = 1 >$.

math.FA↗
arXiv2012

Solved and unsolved problems in generalized notions of amenability for Banach algebras

We survey the recent investigations on (bounded, sequential) approximate amenability/contractibility and pseudo-amenability/contractibility for Banach algebras. We will discuss the core problems concerning these notions and address the significance of any solutions to them to the development of the field. A few new results are also included.

math.FA↗
arXiv2012

$2m$-Weak amenability of group algebras

A common fixed point property for semigroups is applied to show that the group algebra $L^1(G)$ of a locally compact group $G$ is $2m$-weakly amenable for each integer $m\geq 1$.

math.FA↗
arXiv2012

Normal heat conduction in one dimensional momentum conserving lattices with asymmetric interactions

The heat conduction behavior of one dimensional momentum conserving lattice systems with asymmetric interparticle interactions is numerically investigated. It is found that with certain degree of interaction asymmetry, the heat conductivity measured in nonequilibrium stationary states converges in the thermodynamical limit, in clear contrast to the well accepted viewpoint that Fourier's law is generally violated in low dimensional momentum conserving systems. It suggests in nonequilibrium stationary states the mass gradient resulted from the asymmetric interactions may provide an additional phonon scattering mechanism other than that due to the nonlinear interactions.

cond-mat.stat-mech↗
arXiv2012

Sparse Approximation via Penalty Decomposition Methods

In this paper we consider sparse approximation problems, that is, general $l_0$ minimization problems with the $l_0$-"norm" of a vector being a part of constraints or objective function. In particular, we first study the first-order optimality conditions for these problems. We then propose penalty decomposition (PD) methods for solving them in which a sequence of penalty subproblems are solved by a block coordinate descent (BCD) method. Under some suitable assumptions, we establish that any accumulation point of the sequence generated by the PD methods satisfies the first-order optimality conditions of the problems. Furthermore, for the problems in which the $l_0$ part is the only nonconvex part, we show that such an accumulation point is a local minimizer of the problems. In addition, we show that any accumulation point of the sequence generated by the BCD method is a saddle point of the penalty subproblem. Moreover, for the problems in which the $l_0$ part is the only nonconvex part, we establish that such an accumulation point is a local minimizer of the penalty subproblem. Finally, we test the performance of our PD methods by applying them to sparse logistic regression, sparse inverse covariance selection, and compressed sensing problems. The computational results demonstrate that our methods generally outperform the existing methods in terms of solution quality and/or speed.

cs.LG↗
arXiv2012

Penalty Decomposition Methods for Rank Minimization

In this paper we consider general rank minimization problems with rank appearing in either objective function or constraint. We first establish that a class of special rank minimization problems has closed-form solutions. Using this result, we then propose penalty decomposition methods for general rank minimization problems in which each subproblem is solved by a block coordinate descend method. Under some suitable assumptions, we show that any accumulation point of the sequence generated by the penalty decomposition methods satisfies the first-order optimality conditions of a nonlinear reformulation of the problems. Finally, we test the performance of our methods by applying them to the matrix completion and nearest low-rank correlation matrix problems. The computational results demonstrate that our methods are generally comparable or superior to the existing methods in terms of solution quality.

math.OC↗
arXiv2012

Penalty Decomposition Methods for $L0$-Norm Minimization

In this paper we consider general l0-norm minimization problems, that is, the problems with l0-norm appearing in either objective function or constraint. In particular, we first reformulate the l0-norm constrained problem as an equivalent rank minimization problem and then apply the penalty decomposition (PD) method proposed in [33] to solve the latter problem. By utilizing the special structures, we then transform all matrix operations of this method to vector operations and obtain a PD method that only involves vector operations. Under some suitable assumptions, we establish that any accumulation point of the sequence generated by the PD method satisfies a first-order optimality condition that is generally stronger than one natural optimality condition. We further extend the PD method to solve the problem with the l0-norm appearing in objective function. Finally, we test the performance of our PD methods by applying them to compressed sensing, sparse logistic regression and sparse inverse covariance selection. The computational results demonstrate that our methods generally outperform the existing methods in terms of solution quality and/or speed.

math.OC↗
arXiv2012

Homotopy Transfer Theorem for Linearly Compatible Di-algebras

This paper studies the operad of linearly compatible di-algebras, denoted by $As^{2}$, which is a nonsymmetric operad encoding the algebras with two binary operations that satisfy individual and sum associativity conditions. We also prove that the operad $As^{2}$ is exactly the Koszul dual operad of the operad $^{2}As$ encoding totally compatible di-algebras. We show that the operads $As^{2}$ and $^{2}As$ are Koszul by rewriting method. We make explicit the Homotopy Transfer Theorem for $As^{2}$-algebras.

math.RA↗
arXiv2012

Research of the active reflector antenna using laser angle metrology system

Active reflector is one of the key technologies for constructing large telescopes, especially for the millimeter/sub-millimeter radio telescopes. This article introduces a new efficient laser angle metrology system for the active reflector antenna of the large radio telescopes, with a plenty of active reflector experiments mainly about the detecting precisions and the maintaining of the surface shape in real time, on the 65-meter radio telescope prototype constructed by Nanjing Institute of Astronomical Optics and Technology (NIAOT). The test results indicate that the accuracy of the surface shape segmenting and maintaining is up to micron dimension, and the time-response can be of the order of minutes. Therefore, it is proved to be workable for the sub-millimeter radio telescopes.

astro-ph.IM↗
arXiv2012

Deterministic Polynomial-Time Algorithms for Designing Short DNA Words

Designing short DNA words is a problem of constructing a set (i.e., code) of n DNA strings (i.e., words) with the minimum length such that the Hamming distance between each pair of words is at least k and the n words satisfy a set of additional constraints. This problem has applications in, e.g., DNA self-assembly and DNA arrays. Previous works include those that extended results from coding theory to obtain bounds on code and word sizes for biologically motivated constraints and those that applied heuristic local searches, genetic algorithms, and randomized algorithms. In particular, Kao, Sanghi, and Schweller (2009) developed polynomial-time randomized algorithms to construct n DNA words of length within a multiplicative constant of the smallest possible word length (e.g., 9 max{log n, k}) that satisfy various sets of constraints with high probability. In this paper, we give deterministic polynomial-time algorithms to construct DNA words based on derandomization techniques. Our algorithms can construct n DNA words of shorter length (e.g., 2.1 log n + 6.28 k) and satisfy the same sets of constraints as the words constructed by the algorithms of Kao et al. Furthermore, we extend these new algorithms to construct words that satisfy a larger set of constraints for which the algorithms of Kao et al. do not work.

cs.DS↗
arXiv2011

Integrable Quantum Computation

Integrable quantum computation is defined as quantum computing via the integrable condition, in which two-qubit gates are either nontrivial unitary solutions of the Yang--Baxter equation or the Swap gate (permutation). To make the definition clear, in this article, we explore the physics underlying the quantum circuit model, and then present a unified description on both quantum computing via the Bethe ansatz and quantum computing via the Yang--Baxter equation.

physics.gen-ph↗
arXiv2011

Planetary Nebulae Detected in the Spitzer Space Telescope GLIMPSE 3D Legacy Survey

We used the data from the Spitzer Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) to investigate the mid-infrared (MIR) properties of planetary nebulae (PNs) and PN candidates. In previous studies of GLIMPSE I& II data, we have shown that these MIR data are very useful in distinguishing PNs from other emission-line objects. In the present paper, we focus on the PNs in the field of the GLIMPSE 3D survey, which has a more extensive latitude coverage. We found a total of 90 Macquarie-AAO-Strasbourg (MASH) and MASH II PNs and 101 known PNs to have visible MIR counterparts in the GLIMPSE 3D survey area. The images and photometry of these PNs are presented. Combining the derived IRAC photometry at 3.6, 4.5, 5.8, 8.0 um with the existing photometric measurements from other infrared catalogs, we are able to construct spectral energy distributions (SEDs) of these PNs. Among the most notable objects in this survey is the PN M1-41, whose GLIMPSE 3D image reveals a large bipolar structure of more than 3 arcmin in extent.

astro-ph.SR↗
arXiv2011

$\ell_0$ Minimization for Wavelet Frame Based Image Restoration

The theory of (tight) wavelet frames has been extensively studied in the past twenty years and they are currently widely used for image restoration and other image processing and analysis problems. The success of wavelet frame based models, including balanced approach and analysis based approach, is due to their capability of sparsely approximating piecewise smooth functions like images. Motivated by the balanced approach and analysis based approach, we shall propose a wavelet frame based $\ell_0$ minimization model, where the $\ell_0$ "norm" of the frame coefficients is penalized. We adapt the penalty decomposition (PD) method to solve the proposed optimization problem. Numerical results showed that the proposed model solved by the PD method can generate images with better quality than those obtained by either analysis based approach or balanced approach in terms of restoring sharp features as well as maintaining smoothness of the recovered images. Some convergence analysis of the PD method will also be provided.

cs.CV↗