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Song Wang

Publications and source records attributed to Song Wang.

At least 469 records · Page 26Linked to original sources
arXiv2014

Measuring the superconducting coherence length in thin films using a two-coil experiment

We present measurements of the superconducting coherence length ξ in thin (d < 100 Å) films of MoGe alloy and Nb using a combination of linear and nonlinear mutual inductance techniques. As the alternating current in the drive coil is increased at fixed temperature, we see a crossover from linear to nonlinear coupling to the pickup coil, consistent with the unbinding of vortex-antivortex pairs as the peak pair momentum nears \hbar\/ξ and the unbinding barrier vanishes. We compare measurements of ξ made by this mutual inductance technique to values determined from the films' upper critical fields, thereby confirming the applicability of a recent calculation of the upper limit on a vortex-free state in our experiment.

cond-mat.supr-con↗
arXiv2014

Grunwald- Wang Theorem, an Effective Version

The main purpose of this note is to establish an effective version of the Grunwald--Wang Theorem, which asserts that given a family of local characters $χ^{v}$ of $K_{v}^{*}$ of exponent $m$ where $v \in S$ for a finite set $S$ of primes of $K$, there exists a global character $χ$ of the idele class group $C_{K}$ of exponent $m$ (unless some special case occurs, when it is $2 m$) whose component at $v$ is $χ^{v}$. The effectiveness problem for this theorem is to bound the norm $N (χ)$ of the conductor of $χ$ in terms of $K$, $m$, $S$ and $N (χ^{v})$. The Kummer case (when $K$ contains $μ_{m}$) is easy since it is almost an application of the Chinese Remainder Theorem. In this note, we solve this problem completely in general case, and give three versions of bound, one is with \GRH, and the other two are unconditional bounds. These effective results have some interesting applications in concrete situations. To give a simple example, if we fix $p$ and $l$, one gets a good least upper bound for $N$ such that $p$ is not an $l$--th power mod $N$. One also gets the least upper bound for $N$ such that $l^{r} \mid ϕ(N)$ and $p$ is not an $l$--th power mod $N$. Some part of this note is adopted (with some revision) from my unpublished thesis (2001) (\cite{Wang2001}).

math.NT↗
arXiv2013

Lie bialgebras of generalized loop Virasoro algebras

The first cohomology group of a generalized loop Virasoro algebra with coefficients in the tensor product of its adjoint module is shown to be trivial. The result is applied to prove that Lie bialgebra structures on generalized loop Virasoro algebras are coboundary triangular. We then generalize the results to generalized map Virasoro algebras.

math.QA↗
arXiv2013

Structural parameters for globular clusters in M31

In this paper, we present surface brightness profiles for 79 globular clusters in M31, using images observed with {\it Hubble Space Telescope}, some of which are from new observations. The structural and dynamical parameters are derived from fitting the profiles to several different models for the first time. The results show that in the majority of cases, King models fit the M31 clusters as well as Wilson models, and better than Sérsic models. However, there are 11 clusters best fitted by Sérsic models with the Sérsic index $n>2$, meaning that they have cuspy central density profiles. These clusters may be the well-known core-collapsed candidates. There is a bimodality in the size distribution of M31 clusters at large radii, which is different from their Galactic counterparts. In general, the properties of clusters in M31 and the Milky Way fall in the same regions of parameter spaces. The tight correlations of cluster properties indicate a "fundamental plane" for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation.

astro-ph.CO↗
arXiv2012

On Local and Global Conjugacy

In this note we discuss and classify LFMO-spcial representations, for which under certain functoriality, it gives the instance of failure of multiplicity one.

math.RT↗
arXiv2012

Metal Abundance and Kinematical Properties of M81 Globular Cluster System

In this paper, we presented metal abundance properties of 144 M81 globular clusters. These globulars consist of the largest globular cluster sample in M81 till now. Our main results are: the distribution of metallicities are bimodal, with metallicity peaks at [Fe/H]\sim-1.51 and -0.58, and the metal-poor globular clusters tend to be less spatially concentrated than the metal-rich ones; the metal-rich globular clusters in M81 do not demonstrate a centrally concentrated spatial distribution as the metal-rich ones in M31 do; like our Galaxy and M31, the globular clusters in M81 have a small radial metallicity gradient. These results are consistent with those obtained based on a small sample of M81 globular clusters. In addition, this paper showed that there is evidence that a strong rotation of the M81 globular cluster system around the minor axis exists, and that rotation is present in the metal-rich globular cluster subsample, while the metal-poor globular cluster subsample shows no evidence for rotation. The most significant difference between the rotation of the metal-rich and metal-poor globular clusters occurs at intermediate projected galactocentric radii. The results of this paper confirm the conclusion of Schroder et al. that M81's metal-rich globular clusters at intermediate projected radii were associated with a thick disk of M81.

astro-ph.CO↗
arXiv2012

Age and mass studies for young star clusters in M31 from SEDs-fit

In this paper, we present photometry for young star clusters in M31, which are selected from Caldwell et al. These star clusters have been observed as part of the Beijing--Arizona--Taiwan--Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2008 March. The BATC images including these star clusters are taken with 15 intermediate-band filters covering 3000--10000 Å. Combined with photometry in the {\sl GALEX} far- and near-ultraviolet, broad-band $UBVRI$, SDSS $ugriz$, and infrared $JHK_{\rm s}$ of Two Micron All Sky Survey, we obtain their accurate spectral energy distributions (SEDs) from 1538-20000 Å. We derive these star clusters' ages and masses by comparing their SEDs with stellar population synthesis models. Our results are in good agreement with previous determinations. The mean value of age and mass of young clusters ($<2$ Gyr) is about 385 Myr and $2\times 10^4 {M_\odot}$, respectively. There are two distinct peaks in the age distribution, a highest peak at age $\sim$ 60 Myr and a secondary peak around 250 Myr, while the mass distribution shows a single peak around $10^4 {M_\odot}$. A few young star clusters have two-body relaxation times greater than their ages, indicating that those clusters have not been well dynamically relaxed and therefore have not established the thermal equilibrium. There are several regions showing aggregations of young star clusters around the 10 kpc ring and the outer ring, indicating that the distribution of the young star clusters is well correlated with M31's star-forming regions. The young massive star clusters (age $\leq 100$ Myr and mass $\geq 10^4 {M_\odot}$) show apparent concentration around the ring splitting region, suggesting a recent passage of a satellite galaxy (M32) through M31 disk.

astro-ph.CO↗
arXiv2012

Large-Scale Automatic Labeling of Video Events with Verbs Based on Event-Participant Interaction

We present an approach to labeling short video clips with English verbs as event descriptions. A key distinguishing aspect of this work is that it labels videos with verbs that describe the spatiotemporal interaction between event participants, humans and objects interacting with each other, abstracting away all object-class information and fine-grained image characteristics, and relying solely on the coarse-grained motion of the event participants. We apply our approach to a large set of 22 distinct verb classes and a corpus of 2,584 videos, yielding two surprising outcomes. First, a classification accuracy of greater than 70% on a 1-out-of-22 labeling task and greater than 85% on a variety of 1-out-of-10 subsets of this labeling task is independent of the choice of which of two different time-series classifiers we employ. Second, we achieve this level of accuracy using a highly impoverished intermediate representation consisting solely of the bounding boxes of one or two event participants as a function of time. This indicates that successful event recognition depends more on the choice of appropriate features that characterize the linguistic invariants of the event classes than on the particular classifier algorithms.

cs.CV↗
arXiv2012

Video In Sentences Out

We present a system that produces sentential descriptions of video: who did what to whom, and where and how they did it. Action class is rendered as a verb, participant objects as noun phrases, properties of those objects as adjectival modifiers in those noun phrases,spatial relations between those participants as prepositional phrases, and characteristics of the event as prepositional-phrase adjuncts and adverbial modifiers. Extracting the information needed to render these linguistic entities requires an approach to event recognition that recovers object tracks, the track-to-role assignments, and changing body posture.

cs.CV↗
arXiv2012

Structural Parameters for Globular Clusters in the Outer Halo of M31

In this paper, we present internal surface brightness profiles, using images in the F606W and F814W filter bands observed with the Advanced Camera for Surveys on the {\it Hubble Space Telescope}, for ten globular clusters (GCs) in the outer halo of M31. Standard King models are fitted to the profiles to derive their structural and dynamical parameters. The results show that, in general, the properties of clusters in M31 and the Milky Way fall in the same regions of parameter spaces. The outer halo GCs of M31 have larger ellipticities than most of GCs in M31 and the Milky Way. Their large ellipticities may be due to galaxy tides coming from satellite dwarf galaxies of M31 or may be related to the apparently more vigorous accretion or merger history that M31 has experienced. The tight correlation of cluster binding energy $E_b$ with mass $M_{\rm mod}$ indicates that, the "fundamental plane" does exist for clusters, regardless of their host environments, which is consistent with previous studies.

astro-ph.CO↗
arXiv2011

Age and structure parameters of a remote M31 globular cluster B514 based on HST, 2MASS, GALEX and BATC observations

B514 is a remote M31 globular cluster which locating at a projected distance of R_p~55 kpc. Deep observations with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) are used to provide the accurate integrated light and star counts of B514. By coupling analysis of the distribution of the integrated light with star counts, we are able to reliably follow the profile of the cluster out to ~40". Based on the combined profile, we study in detail its surface brightness distribution in F606W and F814W filters, and determine its structural parameters by fitting a single-mass isotropic King model. The results showed that, the surface brightness distribution departs from the best-fit King model for r>10". B514 is quite flatted in the inner region, and has a larger half-light radius than majority of normal globular clusters of the same luminosity. It is interesting that, in the M_V versus log R_h plane, B514 lies nearly on the threshold for ordinary globular clusters as defined by Mackey & van den Bergh. In addition, B514 was observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey, using 13 intermediate-band filters covering a wavelength range of 3000--8500 Å. Based on aperture photometry, we obtain its SEDs as defined by the 13 BATC filters. We determine the cluster's age and mass by comparing its SEDs (from 2267 to 20000Å, comprising photometric data in the near-ultraviolet of GALEX, 5 SDSS bands, 13 BATC intermediate-band, and 2MASS near-infrared JHKs} filters) with theoretical stellar population synthesis models, resulting in age of $11.5\pm3.5$ Gyr. This age confirms the previous suggestion that B514 is an old GC in M31. B514 has a mass of $0.96-1.08 \times 10^6 \rm M_sun$, and is a medium-mass globular cluster in M31.

astro-ph.CO↗
arXiv2011

Extension of vertex operator algebra $V_{\hat{H}_{4}}(\ell,0)$

We classify the irreducible restricted modules for the affine Nappi-Witten Lie algebra $\hat{H}_{4}$ with some natural conditions. It turns out the representation theory of $\hat{H}_{4}$ is quite different from the theory of representations of Heisenberg algebras. We also study the extension of the vertex operator algebra $V_{\hat{H}_{4}}(\ell,0)$ by the even lattice $L$. We give the structure of the extension $V_{\hat{H}_{4}}(\ell,0)\otimes \C[L]$ and its irreducible modules via irreducible representations of $V_{\hat{H}_{4}}(\ell,0)$ viewed as a vertex algebra.

math.QA↗
arXiv2011

Age and mass constraints for a young massive cluster in M31 based on spectral-energy-distribution fitting

VDB0-B195D is a massive, blue star cluster in M31. It was observed as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey using 15 intermediate-band filters covering a wavelength range of 3000--10,000 Å. Based on aperture photometry, we obtain its spectral-energy distribution (SED) as defined by the 15 BATC filters. We apply previously established relations between the BATC intermediate-band and the Johnson-Cousins $UBVRI$ broad-band systems to convert our BATC photometry to the standard system. A detailed comparison shows that our newly derived $VRI$ magnitudes are fully consistent with previous results, while our new $B$ magnitude agrees to within $2σ$. In addition, we determine the cluster's age and mass by comparing its SED (from 3000 to 20,000Å, comprising photometric data in the 15 BATC intermediate bands, optical broad-band $BVRI$, and 2MASS near-infrared $JHK_{\rm s}$ data) with theoretical stellar population synthesis models, resulting in age and mass determinations of $60.0\pm 8.0$~Myr and $(1.1-1.6) \times 10^5 M_\odot$, respectively. This age and mass confirms previous suggestions that VDB0-B195D is a young massive cluster in M31.

astro-ph.CO↗
arXiv2010

Determination of fundamental properties of an M31 globular cluster from main-sequence photometry

M31 globular cluster B379 is the first extragalactic cluster, the age of which was determined by main-sequence photometry. In this method, the age of a cluster is obtained by fitting its CMD with stellar evolutionary models. However, different stellar evolutionary models use different parameters of stellar evolution, such as range of stellar masses, different opacities and equations of state, and different recipes, and so on. So, it is interesting to check whether different stellar evolutionary models can give consistent results for the same cluster. Brown et al. (2004a) constrained the age of B379 by comparing its CMD with isochrones of the 2006 VandenBerg models. Using SSP models of BC03 and its multi-photometry, Ma et al. (2007) independently determined the age of B379, which is in good agreement with the determination of Brown et al. (2004a). The BC03 models are calculated based on the Padova evolutionary tracks. It is necessary to check whether the age of B379 which, being determined based on the Padova evolutionary tracks, is in agreement with the determination of Brown et al. (2004a). So, in this paper, we re-determine its age using isochrones of the Padova stellar evolutionary models. In addition, the metal abundance, the distance modulus, and the reddening value for B379 are also determined in this paper. The results obtained in this paper are consistent with the previous determinations, which including the age obtained by Brown et al. (2004a). So, this paper confirms the consistence of the age scale of B379 between the Padova isochrones and the 2006 VandenBerg isochrones, i.e. the results' comparison between Brown et al. (2004a) and Ma et al. (2007) is meaningful. The results obtained in this paper are: the metallicity [M/H]=-0.325, the age $τ=11.0\pm1.5$ Gyr, the reddening value E(B-V)=0.08, and the distance modulus $(m-M)_{0}=24.44\pm0.10$.

astro-ph.CO↗
arXiv2010

Spectral energy distributions and age estimates of 104 M31 globular clusters

We present photometry of 104 M31 globular clusters (GCs) and GC candidates in 15 intermediate-band filters of the Beijing-Arizona-Taiwan-Connecticut (BATC) photometric system. The GCs and GC candidates were selected from the Revised Bologna Catalog (v.3.5). We obtain the cluster ages by comparing the photometric data with up-to-date theoretical synthesis models. The photometric data used are {\sl GALEX} far- and near-ultraviolet and 2MASS near-infrared $JHK_{\rm s}$ magnitudes, combined with optical photometry. The ages of our sample clusters cover a large range, although most clusters are younger than 10 Gyr. Combined with the ages obtained in our series of previous papers focusing on the M31 GC system, we present the full M31 GC age distribution. The M31 GC system contains populations of young and intermediate-age GCs, as well as the `usual' complement of well-known old GCs, i.e., GCs of similar age as the majority of the Galactic GCs. In addition, young GCs (and GC candidates) are distributed nearly uniformly in radial distance from the center of M31, while most old GCs (and GC candidates) are more strongly concentrated.

astro-ph.CO↗
arXiv2007

Dimension Data, Local and Global Conjugacy in Reductive Groups

Let G be a connected reductive group (over $\mathbb{C}$) and H a connected semisimple subgroup. The dimension data of H (realative to its given embedding in G) is the collection of the numbers $\{{\rm dim} V^{H}\}$, where V runs over all the finite dimensional representations of G. By a Theorem of Larsen-Pink ([L-P90]), the dimension data determines H up to isomorphism, and if G = GL (n) even up to conjugacy. Professor Langlands raised the question as to whether the strong (conjugacy) result holds for arbitrary G. In this paper We provided the following (negative) answer: If H is simple of type A_{4 n}, $B_{2 n} (n \geq 2)$, $C_{2 n} (n \geq 2)$, E_{6}, E_{8}, F_{4} and G_{2}, then there exist (for suitable $N$) pairs of embeddings i and i' of H into $G = SO (2 N)$ such that there image i (H) and i' (H) have the same dimension data but are not conjugate. In fact we have shown that i (H) and i' (H) are \emph{locally conjugate}, i.e., that i (h) and i' (h) are conjugate in G for all semisimple $h \in H$. If one assumes functoriality, this result will furnish the failure of multiplicity one for automorphic forms on such G over global fields. Such things are known in the disconnected cases, especially when H is finite, as in the works of Blasius [Blasius94] for $SL (n) (n \geq 3)$ and Gan-Gurevich-Jiang2002 ([Gan]) for G_{2}.

math.RT↗