arXiv subjects

Ming Zhao

Publications and source records attributed to Ming Zhao.

At least 145 records · Page 8Linked to original sources

arXiv2011

First visual orbit for the prototypical colliding-wind binary WR 140

Wolf-Rayet stars represent one of the final stages of massive stellar evolution. Relatively little is known about this short-lived phase and we currently lack reliable mass, distance, and binarity determinations for a representative sample. Here we report the first visual orbit for WR 140(=HD193793), a WC7+O5 binary system known for its periodic dust production episodes triggered by intense colliding winds near periastron passage. The IOTA and CHARA interferometers resolved the pair of stars in each year from 2003--2009, covering most of the highly-eccentric, 7.9 year orbit. Combining our results with the recent improved double-line spectroscopic orbit of Fahed et al. (2011), we find the WR 140 system is located at a distance of 1.67 +/- 0.03 kpc, composed of a WR star with M_WR = 14.9 +/- 0.5 Msun and an O star with M_O = 35.9 +/- 1.3 Msun. Our precision orbit yields key parameters with uncertainties times 6 smaller than previous work and paves the way for detailed modeling of the system. Our newly measured flux ratios at the near-infrared H and Ks bands allow an SED decomposition and analysis of the component evolutionary states.

astro-ph.SR↗

arXiv2011

Ground-based detections of thermal emission from CoRoT-1b and WASP-12b

We report a new detection of the H-band thermal emission of CoRoT-1b and two confirmation detections of the Ks-band thermal emission of WASP-12b at secondary eclipses. The H-band measurement of CoRoT-1b shows an eclipse depth of 0.145%\pm0.049% with a 3-σ percentile between 0.033% - 0.235%. This depth is consistent with the previous conclusions that the planet has an isother- mal region with inefficient heat transport from dayside to nightside, and has a dayside thermal inversion layer at high altitude. The two Ks band detections of WASP-12b show a joint eclipse depth of 0.299%\pm0.065%. This result agrees with the measurement of Croll & collaborators, providing independent confirmation of their measurement. The repeatability of the WASP-12b measurements also validates our data analysis method. Our measurements, in addition to a number of previous results made with other telescopes, demonstrate that ground-based observations are becoming widely available for characterization of atmospheres of hot Jupiters.

astro-ph.EP↗

arXiv2011

Optimal Power Allocation for OFDM-Based Wire-Tap Channels with Arbitrarily Distributed Inputs

In this paper, we investigate power allocation that maximizes the secrecy rate of orthogonal frequency division multiplexing (OFDM) systems under arbitrarily distributed inputs. Considering commonly assumed Gaussian inputs are unrealistic, we focus on secrecy systems with more practical discrete distributed inputs, such as PSK, QAM, etc. While the secrecy rate achieved by Gaussian distributed inputs is concave with respect to the transmit power, we have found and rigorously proved that the secrecy rate is non-concave under any discrete inputs. Hence, traditional convex optimization methods are not applicable any more. To address this non-concave power allocation problem, we propose an efficient algorithm. Its gap from optimality vanishes asymptotically at the rate of $O(1/\sqrt{N})$, and its complexity grows in the order of O(N), where $N$ is the number of sub-carriers. Numerical results are provided to illustrate the efficacy of the proposed algorithm.

cs.IT↗

arXiv2011

Competition between Intra-community and Inter-community Synchronization

In this paper the effects of external links on the synchronization performance of community networks, especially on the competition between individual community and the whole network, are studied in detail. The study is organized from two aspects: the number or portion of external links and the connecting strategy of external links between different communities. It is found that increasing the number of external links will enhance the global synchronizability but degrade the ynchronization performance of individual community before some critical point. After that the individual community will synchronize better and better as part of the whole network because the community structure is not so prominent. Among various connection strategies, connecting nodes belonging to different communities randomly rather than connecting nodes with larger degrees is the most efficient way to enhance global synchronization of the network. However, a preferential connection scheme linking most of the hubs from the communities will allow rather efficient global synchronization while maintaining strong dynamical clustering of the communities. Interestingly, the observations are found to be relevant in a realistic network of cat cortex. The synchronization state is just at the critical point, which shows a reasonable combination of segregated function in individual communities and coordination among them. Our work sheds light on principles underlying the emergence of modular architectures in real network systems and provides guidance for the manipulation of synchronization in community networks.

physics.soc-ph↗

arXiv2010

Establishing Alpha Oph as a Prototype Rotator: Improved Astrometric Orbit

The nearby star Alpha Oph (Ras Alhague) is a rapidly rotating A5IV star spinning at ~89% of its breakup velocity. This system has been imaged extensively by interferometric techniques, giving a precise geometric model of the star's oblateness and the resulting temperature variation on the stellar surface. Fortuitously, Alpha Oph has a previously known stellar companion, and characterization of the orbit provides an independent, dynamically-based check of both the host star and the companion mass. Such measurements are crucial to constrain models of such rapidly rotating stars. In this study, we combine eight years of Adaptive Optics imaging data from the Palomar, AEOS, and CFHT telescopes to derive an improved, astrometric characterization of the companion orbit. We also use photometry from these observations to derive a model-based estimate of the companion mass. A fit was performed on the photocenter motion of this system to extract a component mass ratio. We find masses of 2.40^{0.23}_{0.37} solar masses and 0.85^{0.06}_{0.04} solar masses for Alpha Oph A and Alpha Oph B, respectively. Previous orbital studies of this system found a mass too high for this system, inconsistent with stellar evolutionary calculations. Our measurements of the host star mass are more consistent with these evolutionary calculations, but with slightly higher uncertainties. In addition to the dynamically-derived masses, we use IJHK photometry to derive a model-based mass for Alpha Oph B, of 0.77 +/- 0.05 solar masses marginally consistent with the dynamical masses derived from our orbit. Our model fits predict a periastron passage on 2012 April 19, with the two components having a ~50 milliarcsec separation from March to May 2012. A modest amount of interferometric and radial velocity data during this period could provide a mass determination of this star at the few percent level.

astro-ph.SR↗

arXiv2010

In the Shadow of the Transiting Disk: Imaging epsilon Aurigae in Eclipse

Eclipses of the single-line spectroscopic binary star, epsilon Aurigae, provide an opportunity to study the poorly-defined companion. We used the MIRC beam combiner on the CHARA array to create interferometric images during eclipse ingress. Our results demonstrate that the eclipsing body is a dark disk that is opaque and tilted, and therefore exclude alternative models for the system. These data constrain the geometry and masses of the components, providing evidence that the F-star is not a massive supergiant star.

astro-ph.SR↗

arXiv2009

Synchronization on Effective Networks

The study of network synchronization has attracted increasing attention recently. In this paper, we strictly define a class of networks, namely effective networks, which are synchronizable and orientable networks. We can prove that all the effective networks with the same size have the same spectra, and are of the best synchronizability according to the master stability analysis. However, it is found that the synchronization time for different effective networks can be quite different. Further analysis show that the key ingredient affecting the synchronization time is the maximal depth of an effective network: the larger depth results in a longer synchronization time. The secondary factor is the number of links. The more links connecting the nodes in the same layer (horizontal links) will lead to longer synchronization time, while the increasing number of links connecting nodes in neighboring layers (vertical links) will accelerate the synchronization. Our findings provide insights into the roles of horizontal and vertical links in synchronizing process, and suggest that the spectral analysis is helpful yet insufficient for the understanding of network synchronization.

cond-mat.stat-mech↗

arXiv2009

Mass-sensing BioCD Protein Array towards Clinical Application: Prostate Specific Antigen Detection in Patient Sera

Mass-sensing biosensor arrays for protein detection require no fluorophores or enzyme labels. However, few mass biosensor protein arrays have demonstrated successful application in high background samples, such as serum. In this paper, we test the BioCD as a mass biosensor based on optical interferometry of antibodies covalently attached through Schiff-base reduction. We use the BioCD to detect prostate specific antigen (PSA, a biomarker of prostate cancer) in patient sera in a 96-well anti-PSA microarray. We have attained a 4 ng/ml detection limit in full serum and have measured PSA concentrations in three patient sera.

physics.bio-ph↗

arXiv2009

Reducing the Heterogeneity of Payoffs: an Effective Way to Promote Cooperation in Prisoner's Dilemma Game

In this paper, the total payoff of each agent is regulated to reduce the heterogeneity of the distribution of the total payoffs. It is found there is an optimal regulation strength where the fraction of cooperation is prominently promoted, too weak or too strong of the strength will have little effects or result in the disappearance of the cooperators. It is also found that most of the cooperators are not distributed in isolation but form the cooperator clusters, and to promote the cooperation the only way is to enlarge the size of the cooperator clusters. Finally, we try to explain the emergence of larger clusters and prove the existence of the optimal regulation strength. Our works provide insight into the understanding of the relations between the distribution of payoffs and the cooperative behaviors.

physics.soc-ph↗

arXiv2009

Optical Trajectory of the Insulator-to-metal Transition of Ultra-thin Gold Films

We apply interferometric picometrology to measure the complex refractive index and dielectric properties of ultra-thin gold films as a continuous function of thickness from 0.2 nm to 10 nm deposited on thermal oxide on silicon. Three distinct regimes are found for the dielectric constant trajectory in the complex plane. The first regime shows a circular trajectory predicted by the Drude equation tracing the gold bulk-to-thin film transition. The second and third regimes are manifested as metal clusters range from large to small size and sparse coverage. The entire atom-to-bulk transition of gold is revealed from the optical perspective.

cond-mat.mtrl-sci↗

arXiv2009

Quantifying Stellar Mass Loss with High Angular Resolution Imaging

Mass is constantly being recycled in the universe. One of the most powerful recycling paths is via stellar mass-loss. All stars exhibit mass loss with rates ranging from ~10(-14) to 10(-4) M(sun) yr-1, depending on spectral type, luminosity class, rotation rate, companion proximity, and evolutionary stage. The first generation of stars consisted mostly of hydrogen and helium. These shed material - via massive winds, planetary nebulae and supernova explosions - seeding the interstellar medium with heavier elements. Subsequent generations of stars incorporated this material, changing how stars burn and providing material for planet formation. An understanding of mass loss is critical for modeling individual stars as well as answering larger astrophysical questions. Understanding mass loss is essential for following the evolution of single stars, binaries, star clusters, and galaxies. Mass loss is one of our weakest areas in the modeling of fundamental stellar processes. In large part this is owing to lack of confrontation with detailed observations of stellar photospheres and the mass-loss process. High resolution optical imagery with telescope arrays is beginning to provide these data and, combined with spectroscopy and broad infrared and sub-mm coverage, supporting more sophisticated models on fast computers and promising a new era in mass-loss studies.

astro-ph.SR↗

arXiv2007

Synchronization on complex networks with different sorts of communities

In this paper, inspired by the idea that many real networks are composed by different sorts of communities, we investigate the synchronization property of oscillators on such networks. We identify the communities by the intrinsic frequencies probability density $g(ω)$ of Kuramoto oscillators. That is to say, communities in different sorts are functional different. For a network containing two sorts of communities, when the community strength is strong, only the oscillators in the same community synchronize. With the weakening of the community strength, an interesting phenomenon, \emph{Community Grouping}, appears: although the global synchronization is not achieved, oscillators in the same sort of communities will synchronize. Global synchronization will appear with the further reducing of the community strength, and the oscillators will rotate around the average frequency.

physics.data-an↗

arXiv2007

Enhance synchronizability via age-based coupling

In this brief report, we study the synchronization of growing scale-free networks. An asymmetrical age-based coupling method is proposed with only one free parameter $α$. Although the coupling matrix is asymmetric, our coupling method could guarantee that all the eigenvalues are non-negative reals. The eigneratio R will approach to 1 in the large limit of $α$.

cond-mat.dis-nn↗

arXiv2006

Better synchronizability predicted by a new coupling method

In this paper, inspired by the idea that the hub nodes of a highly heterogeneous network are not only the bottlenecks, but also effective controllers in the network synchronizing process, we bring forward an asymmetrical coupling method where the coupling strength of each node depends on its neighbors' degrees. Compared with the uniform coupled method and the recently proposed Motter-Zhou-Kurth method, the synchronizability of scale-free networks can be remarkably enhanced by using the present coupled method.

cond-mat.stat-mech↗

arXiv2006

Phase Synchronization of non-Abelian Oscillators on Small-World Networks

In this paper, by extending the concept of Kuramoto oscillator to the left-invariant flow on general Lie group, we investigate the generalized phase synchronization on networks. The analyses and simulations of some typical dynamical systems on Watts-Strogatz networks are given, including the $n$-dimensional torus, the identity component of 3-dimensional general linear group, the special unitary group, and the special orthogonal group. In all cases, the greater disorder of networks will predict better synchronizability, and the small-world effect ensures the global synchronization for sufficiently large coupling strength. The collective synchronized behaviors of many dynamical systems, such as the integrable systems, the two-state quantum systems and the top systems, can be described by the present phase synchronization frame. In addition, it is intuitive that the low-dimensional systems are more easily to synchronize, however, to our surprise, we found that the high-dimensional systems display obviously synchronized behaviors in regular networks, while these phenomena can not be observed in low-dimensional systems.

cond-mat.stat-mech↗

arXiv2006

Synchronization on community networks

In this Letter, we propose a growing network model that can generate scale-free networks with a tunable community strength. The community strength, $C$, is directly measured by the ratio of the number of external edges to internal ones; a smaller $C$ corresponds to a stronger community structure. According to the criterion obtained based on the master stability function, we show that the synchronizability of a community network is significantly weaker than that of the original Barabási-Albert network. Interestingly, we found an unreported linear relationship between the smallest nonzero eigenvalue and the community strength, which can be analytically obtained by using the combinatorial matrix theory. Furthermore, we investigated the Kuramoto model and found an abnormal region ($C\leq 0.002$), in which the network has even worse synchronizability than the uncoupled case (C=0). On the other hand, the community effect will vanish when $C$ exceeds 0.1. Between these two extreme regions, a strong community structure will hinder global synchronization.

cond-mat.dis-nn↗

arXiv2006

Relations between Average Distance, Heterogeneity and Network Synchronizability

By using the random interchanging algorithm, we investigate the relations between average distance, standard deviation of degree distribution and synchronizability of complex networks. We find that both increasing the average distance and magnifying the degree deviation will make the network synchronize harder. Only the combination of short average distance and small standard deviation of degree distribution that ensures strong synchronizability. Some previous studies assert that the maximal betweenness is a right quantity to estimate network synchronizability: the larger the maximal betweenness, the poorer the network synchronizability. Here we address an interesting case, which strongly suggests that the single quantity, maximal betweenness, may not give a comprehensive description of network synchronizability.

cond-mat.stat-mech↗

arXiv2006

Growing Scale-free Small-world Networks with Tunable Assortative Coefficient

In this paper, we propose a simple rule that generates scale-free small-world networks with tunable assortative coefficient. These networks are constructed by two-stage adding process for each new node. The model can reproduce scale-free degree distributions and small-world effect. The simulation results are consistent with the theoretical predictions approximately. Interestingly, we obtain the nontrivial clustering coefficient $C$ and tunable degree assortativity $r$ by adjusting the parameter: the preferential exponent $β$. The model can unify the characterization of both assortative and disassortative networks.

physics.soc-ph↗