arXiv subjects

Tao Wang

Publications and source records attributed to Tao Wang.

At least 811 records · Page 45Linked to original sources

arXiv2018

The morphological evolution, AGN fractions, dust content, environments, and downsizing of massive green valley galaxies at 0.5<z<2.5 in 3D-HST/CANDELS

To explore the evolutionary connection among red, green, and blue galaxy populations, based on a sample of massive ($M_* > 10^{10} M_{\odot} $) galaxies at 0.5 2. A significant environmental difference is found between green and red galaxies at z<1.5. Green and blue galaxies at z>0.5 seem to have similar local density distributions, suggesting that environment quenching is not the major mechanism to cease star formation at z>0.5. The fractions of three populations as functions of mass support a "downsizing" quenching picture that the bulk of star formation in more massive galaxies is completed earlier than that of lower mass galaxies.

astro-ph.GA↗

arXiv2018

Global Spherical Symmetric Flows for a Viscous Radiative and Reactive Gas in an Exterior Domain with Large Initial Data

In this paper, we study the global existence, uniqueness and large-time behavior of spherically symmetric solution of a viscous radiative and reactive gas in an unbounded domain exterior to the unit sphere in $\mathbb{R}^{n}$ for $n\geq 2$. The key point in the analysis is to deduce certain uniform estimates on the solutions, especially on the uniform positive lower and upper bounds on the specific volume and the temperature.

math.AP↗

arXiv2018

Recognizing number of communities and detecting community structures in complex networks

Recognizing number of communities and detecting community structures of complex network are discussed in this paper. As a visual and feasible algorithm, block model has been successfully applied to detect community structures in complex network. In order to measure the quality of the block model, we first define an objective function WQ value. For obtaining block model B of a network, GSA algorithm is applied to optimize WQ with the help of random keys. After executing processes AO (Adding Ones) and RO (Removing Ones) on block model B, the number of communities of a network can be recognized distinctly. Furthermore, based on the advantage of block model that its sort order of nodes is in correspondence with sort order of communities, so a new fuzzy boundary algorithm for detecting community structures is proposed and successfully applied to some representative networks. Finally, experimental results demonstrate the feasibility of the proposed algorithm.

physics.soc-ph↗

arXiv2018

Onset of lasing in small devices: the identification of the first threshold

We present a simple and flexible technique for identifying the onset of coherent emission in lasers, from the mesoscale to the nanoscale, which makes use of photon counting and a small amplitude modulation added to the pump. The optimal modulation frequency is obtained from the radiofrequency power spectrum of the unperturbed laser emission. The identification of the lasing onset rests on the appearence of a resonance in the response of the zero-order autocorrelation function ($g^{(2)}(0)$) plotted as a function of the pump rate. The intrinsic simplicity of this technique and its use of photon counting make it an excellent tool for certifying the onset of laser emission in nanoscale sources.

physics.optics↗

arXiv2018

Mössbauer spectroscopy study of magnetic fluctuations in superconducting RbGd$_2$Fe$_4$As$_4$O$_2$

$^{57}$Fe Mössbauer spectra were measured at different temperatures between 5.9 K and 300 K on the recently discovered self-doped superconducting RbGd$_2$Fe$_4$As$_4$O$_2$ with T$_c$ as high as 35 K. Singlet pattern was observed down to the lowest temperature measured in this work, indicating the absence of static magnetic order on the Fe site. The intermediate isomer shift in comparison with that of the samples RbFe$_2$As$_2$ and GdFeAsO confirms the self doping induced local electronic structure change. Surprisingly, we observe two magnetic fluctuation induced spectral broadenings below $\sim$15 K and $\sim$100 K which are believed to be originated from the transferred magnetic fluctuations of the Gd$^{3+}$ moments and that of the magnetic fluctuations of the Fe atoms, respectively.

cond-mat.supr-con↗

arXiv2018

Optimizing Precision for Open-World Website Fingerprinting

Traffic analysis attacks to identify which web page a client is browsing, using only her packet metadata --- known as website fingerprinting --- has been proven effective in closed-world experiments against privacy technologies like Tor. However, due to the base rate fallacy, these attacks have failed in large open-world settings against clients that visit sensitive pages with a low base rate. We find that this is because they have poor precision as they were designed to maximize recall. In this work, we argue that precision is more important than recall for open-world website fingerprinting. For this reason, we develop three classes of {\em precision optimizers}, based on confidence, distance, and ensemble learning, that can be applied to any classifier to increase precision. We test them on known website fingerprinting attacks and show significant improvements in precision. Against a difficult scenario, where the attacker wants to monitor and distinguish 100 sensitive pages each with a low mean base rate of 0.00001, our best optimized classifier can achieve a precision of 0.78; the highest precision of any known attack before optimization was 0.014. We use precise classifiers to tackle realistic objectives in website fingerprinting, including selection, identification, and defeating website fingerprinting defenses.

cs.CR↗

arXiv2018

"Super-deblended" Dust Emission in Galaxies: I. The GOODS-North Catalog and the Cosmic Star Formation Rate Density out to Redshift 6

We present a new technique to measure multi-wavelength "Super-deblended" photometry from highly confused images, which we apply to Herschel and ground-based far-infrared (FIR) and (sub-)millimeter (mm) data in the northern field of the Great Observatories Origins Deep Survey (GOODS). There are two key novelties. First, starting with a large database of deep Spitzer 24μm and VLA 20cm detections that are used to define prior positions for fitting the FIR/submm data, we perform an active selection of useful priors independently at each frequency band, moving from less to more confused bands. Exploiting knowledge of redshift and all available photometry, we identify hopelessly faint priors that we remove from the fitting pool. This approach significantly reduces blending degeneracies and allows reliable photometry to be obtained for galaxies in FIR+mm bands. Second, we obtain well-behaved, nearly Gaussian flux density uncertainties, individually tailored to all fitted priors in each band. This is done by exploiting extensive simulations that allow us to calibrate the conversion of formal fitting uncertainties to realistic uncertainties depending on quantities directly measurable. We achieve deeper detection limits with high fidelity measurements and uncertainties at FIR+mm bands. As an illustration of the utility of these measurements, we identify 70 galaxies with z>3 and reliable FIR+mm detections. We present new constraints on the cosmic star formation rate density at 3 3 dusty galaxies that are missed by optical-to-near-infrared color selection. Photometric measurements for 3306 priors, including over 1000 FIR+mm detections are released publicly with our catalog.

astro-ph.GA↗

arXiv2018

Approaching perfect absorption of monolayer molybdenum disulfide at visible wavelengths using critical coupling

A simple perfect absorption structure is proposed to achieve the high efficiency light absorption of monolayer molybdenum disulfide (MoS 2 ) by the critical coupling mechanism of guided resonances. The results of numerical simulation and theoretical analysis show that the light absorption in this atomically thin layer can be as high as 98 . 3% at the visible wavelengths, which is over 12 times more than that of a bare monolayer MoS 2 . In addition, the operating wavelength can be tuned flexibly by adjusting the radius of the air hole and the thickness of the dielectric layers, which is of great practical significance to improve the efficiency and selectivity of the absorption in monolayer MoS 2 . The novel idea of using critical coupling to enhance the light-MoS 2 interaction can be also adopted in other atomically thin materials. And the meaningful improvement and tunability of the absorption in monolayer MoS 2 provide a good prospect for the realization of high-performance MoS 2 -based optoelectronic applications, such as photodetection and photoluminescence.

physics.optics↗

arXiv2018

UAV Offloading: Spectrum Trading Contract Design for UAV Assisted 5G Networks

Unmanned Aerial Vehicle (UAV) has been recognized as a promising way to assist future wireless communications due to its high flexibility of deployment and scheduling. In this paper, we focus on temporarily deployed UAVs that provide downlink data offloading in some regions under a macro base station (MBS). Since the manager of the MBS and the operators of the UAVs could be of different interest groups, we formulate the corresponding spectrum trading problem by means of contract theory, where the manager of the MBS has to design an optimal contract to maximize its own revenue. Such contract comprises a set of bandwidth options and corresponding prices, and each UAV operator only chooses the most profitable one from all the options in the whole contract. We analytically derive the optimal pricing strategy based on fixed bandwidth assignment, and then propose a dynamic programming algorithm to calculate the optimal bandwidth assignment in polynomial time. By simulations, we compare the outcome of the MBS optimal contract with that of a social optimal one, and find that a selfish MBS manager sells less bandwidth to the UAV operators.

eess.SP↗

arXiv2017

Leveraging extreme laser-driven magnetic fields for gamma-ray generation and pair production

The ability of an intense laser pulse to propagate in a classically over-critical plasma through the phenomenon of relativistic transparency is shown to facilitate the generation of strong plasma magnetic fields. Particle-in-cell simulations demonstrate that these fields significantly enhance the radiation rates of the laser-irradiated electrons, and furthermore they collimate the emission so that a directed and dense beam of multi-MeV gamma-rays is achievable. This capability can be exploited for electron-positron pair production via the linear Breit-Wheeler process by colliding two such dense beams. Presented simulations show that more than $10^3$ pairs can be produced in such a setup, and the directionality of the positrons can be controlled by the angle of incidence between the beams.

physics.plasm-ph↗

arXiv2017

Effective reduction of the coercivity for Co$_{72}$Pt$_{28}$ thin film by exchange coupled Co$_{81}$Ir$_{19}$ soft layer with negative magnetocrystalline anisotropy

We report on the investigation of coercivity changes of the Co$_{72}$Pt$_{28}$/Co$_{81}$Ir$_{19}$ exchange-coupled composite (ECC) media with negative soft-layer (SL) magnetocrystalline anisotropy (MA) . Our results show that the hard-layer (HL) of our sample exhibits a columnar type microstructure with well isolated grains and the SL with hcp-structure grows on top of the HL with the same texture. Therefore, strong coupling of the two layers have been realized as evidenced by the magnetic characterization. Importantly, we observe a more effective reduction of the coercivity of the ECC media by using SLs with negative MA when compared to the use of SLs with positive or negligible MA. The experimental results are corroborated by theoretical calculations.

physics.app-ph↗

arXiv2017

Phonon transport unveils the prevalent point defects in GaN

Determining the types and concentrations of vacancies present in intentionally doped GaN is a notoriously difficult and long-debated problem. Here we use an unconventional approach, based on thermal transport modeling, to determine the prevalence of vacancies in previous measurements. This allows us to provide conclusive evidence of the recent hypothesis that gallium vacancies in ammonothermally grown samples can be complexed with hydrogen. Our calculations for O-doped and Mg-O co-doped samples yield a consistent picture interlinking dopant and vacancy concentration, carrier density, and thermal conductivity, in excellent agreement with experimental measurements. These results also highlight the predictive power of ab initio phonon transport modeling, and its value for understanding and quantifying defects in semiconductors.

cond-mat.mtrl-sci↗

arXiv2017

Jekyll & Hyde: quiescence and extreme obscuration in a pair of massive galaxies 1.5 Gyr after the Big Bang

We obtained ALMA spectroscopy and imaging to investigate the origin of the unexpected sub-mm emission toward the most distant quiescent galaxy known to date, ZF-COSMOS-20115 at z=3.717. We show here that this sub-mm emission is produced by another massive, compact and extremely obscured galaxy, located only 3.1 kpc away from the quiescent galaxy. We dub the quiescent and dusty galaxies Jekyll and Hyde, respectively. No dust emission is detected at the location of Jekyll, implying SFR < 13 Msun/yr, which is the most stringent upper limit ever obtained for a quiescent galaxy at these redshifts. The two sources are confirmed to lie at the same redshift thanks to the detection of [CII]158 in Hyde, which provides one the few robust redshifts for an "H-dropout" galaxy. The line has a rotating-disk velocity profile blueshifted from Jekyll by 549+/-60 km/s, demonstrating that it is produced by another galaxy. Careful de-blending of the Spitzer imaging confirms the existence of Hyde, and its non-detection with Hubble requires extreme attenuation by dust. Modeling the photometry of both galaxies shows that Jekyll has fully quenched >200 Myr prior to observation and still presents a challenge for models, while Hyde only harbors moderate star-formation (SFR<120 Msun/yr) and is located at least a factor 1.4 below the z~4 main sequence. Hyde could also have stopped forming stars <200 Myr before being observed, which would be consistent with its hight compactness similar to z~4 quiescent galaxies and its low [CII]/FIR ratio, but significant SF cannot be ruled out. Finally, we show that Hyde hosts a dense reservoir of gas comparable to that of extreme starbursts, suggesting that its SFR was reduced without expelling the gas outside of the galaxy. We argue that Jekyll and Hyde can be seen as two stages of quenching, and provide a unique laboratory to study this poorly understood phenomenon. [abridged]

astro-ph.GA↗

arXiv2017

Star 5-edge-colorings of subcubic multigraphs

The star chromatic index of a multigraph $G$, denoted $χ'_{s}(G)$, is the minimum number of colors needed to properly color the edges of $G$ such that no path or cycle of length four is bi-colored. A multigraph $G$ is star $k$-edge-colorable if $χ'_{s}(G)\le k$. Dvořák, Mohar and Šámal [Star chromatic index, J Graph Theory 72 (2013), 313--326] proved that every subcubic multigraph is star $7$-edge-colorable, and conjectured that every subcubic multigraph should be star $6$-edge-colorable. Kerdjoudj, Kostochka and Raspaud considered the list version of this problem for simple graphs and proved that every subcubic graph with maximum average degree less than $7/3$ is star list-$5$-edge-colorable. It is known that a graph with maximum average degree $14/5$ is not necessarily star $5$-edge-colorable. In this paper, we prove that every subcubic multigraph with maximum average degree less than $12/5$ is star $5$-edge-colorable.

math.CO↗

arXiv2017

Odd graph and its applications to the strong edge coloring

A strong edge coloring of a graph is a proper edge coloring in which every color class is an induced matching. The strong chromatic index $χ_s'(G)$ of a graph $G$ is the minimum number of colors in a strong edge coloring of $G$. Let $Δ\geq 4$ be an integer. In this note, we study the odd graphs and show the existence of some special walks. By using these results and Chang's ideas in [Discuss. Math. Graph Theory 34 (4) (2014) 723--733], we show that every planar graph with maximum degree at most $Δ$ and girth at least $10 Δ- 4$ has a strong edge coloring with $2Δ- 1$ colors. In addition, we prove that if $G$ is a graph with girth at least $2Δ- 1$ and mad$(G) < 2 + \frac{1}{3Δ- 2}$, where $Δ$ is the maximum degree and $Δ\geq 4$, then $χ_s'(G) \leq 2Δ- 1$, if $G$ is a subcubic graph with girth at least $8$ and mad$(G) < 2 + \frac{2}{23}$, then $χ_s'(G) \leq 5$.

math.CO↗

arXiv2017

Dust temperature and mid-to-total infrared color distributions for star-forming galaxies at 0<z<4

We present a new, publicly available library of dust spectral energy distributions (SEDs). These SEDs are characterized by only three parameters: the dust mass (Mdust), the dust temperature (Tdust), and the mid-to-total infrared color (IR8=LIR/L8). The latter measures the relative contribution of PAH molecules to the LIR. We used this library to model star-forming galaxies at 0.5 1, 3.2, 3.8, and 5.7, respectively. Starburst galaxies above the MS have LIR significantly underestimated and Mdust overestimated. These results can be used immediately to interpret more accurately the large amount of archival data from Spitzer, Herschel and ALMA. [abridged]

astro-ph.GA↗

arXiv2017

The Cosmic Axion Spin Precession Experiment (CASPEr): a dark-matter search with nuclear magnetic resonance

The Cosmic Axion Spin Precession Experiment (CASPEr) is a nuclear magnetic resonance experiment (NMR) seeking to detect axion and axion-like particles which could make up the dark matter present in the universe. We review the predicted couplings of axions and axion-like particles with baryonic matter that enable their detection via NMR. We then describe two measurement schemes being implemented in CASPEr. The first method, presented in the original CASPEr proposal, consists of a resonant search via continuous-wave NMR spectroscopy. This method offers the highest sensitivity for frequencies ranging from a few Hz to hundreds of MHz, corresponding to masses $ m_{\rm a} \sim 10^{-14}$--$10^{-6}$ eV. Sub-Hz frequencies are typically difficult to probe with NMR due to the diminishing sensitivity of magnetometers in this region. To circumvent this limitation, we suggest new detection and data processing modalities. We describe a non-resonant frequency-modulation detection scheme, enabling searches from mHz to Hz frequencies ($m_{\rm a} \sim 10^{-17}$--$10^{-14} $ eV), extending the detection bandwidth by three decades.

physics.ins-det↗

arXiv2017

Prediction analysis for microbiome sequencing data

One primary goal of human microbiome studies is to predict host traits based on human microbiota. However, microbial community sequencing data present significant challenges to the development of statistical methods. In particular, the samples have different library sizes, the data contain many zeros and are often over-dispersed. To address these challenges, we introduce a new statistical framework, called predictive analysis in metagenomics via inverse regression (PAMIR). An inverse regression model is developed for over-dispersed microbiota counts given the trait, and then a prediction rule is constructed by taking advantage of the dimension-reduction structure in the model. An efficient Monte Carlo expectation-maximization algorithm is designed for carrying out maximum likelihood estimation. We demonstrate the advantages of PAMIR through simulations and a real data example.

stat.ME↗