Spectroscopic Properties of QSOs Selected from Ultraluminous Infrared Galaxy Samples

We performed spectroscopic observations for a large infrared QSO sample with a total of 25 objects. The sample was compiled from the QDOT redshift survey, the 1 Jy ULIRGs survey and a sample obtained by a cross-correlation study of the IRAS Point Source Catalogue with the ROSAT All Sky Survey Catalogue. Statistical analyses of the optical spectra show that the vast majority of infrared QSOs have narrow permitted emission lines (with FWHM of Hbeta less than 4000 km/s) and more than 60% of them are luminous narrow line Seyfert 1 galaxies. Two of the infrared QSOs are also classified as low ionization BAL QSOs. More than 70% of infrared QSOs are moderately or extremely strong Fe II emitters. This is the highest percentage of strong Fe II emitters in all subclasses of QSO/Seyfert 1 samples. We found that the Fe II to Hbeta, line ratio is significantly correlated with the [OIII]5007 peak and Hbeta blueshift. Soft X-ray weak infrared QSOs tend to have large blueshifts in permitted emission lines and significant Fe II48,49 (5100--5400 A) residuals relative to the Boroson & Green Fe II template. If the blueshifts in permitted lines are caused by outflows, then they appear to be common in infrared QSOs. As the infrared-selected QSO sample includes both luminous narrow line Seyfert 1 galaxies and low ionization BAL QSOs, it could be a useful laboratory to investigate the evolutionary connection among these objects.Comment: 35 pages,14 figures, 4 tables, accepted for publication in A

Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity

Magnetic fields generated by human and animal organs, such as the heart, brain and nervous system carry information useful for biological and medical purposes. These magnetic fields are most commonly detected using cryogenically-cooled superconducting magnetometers. Here we present the frst detection of action potentials from an animal nerve using an optical atomic magnetometer. Using an optimal design we are able to achieve the sensitivity dominated by the quantum shot noise of light and quantum projection noise of atomic spins. Such sensitivity allows us to measure the nerve impulse with a miniature room-temperature sensor which is a critical advantage for biomedical applications. Positioning the sensor at a distance of a few millimeters from the nerve, corresponding to the distance between the skin and nerves in biological studies, we detect the magnetic field generated by an action potential of a frog sciatic nerve. From the magnetic field measurements we determine the activity of the nerve and the temporal shape of the nerve impulse. This work opens new ways towards implementing optical magnetometers as practical devices for medical diagnostics.Comment: Main text with figures, and methods and supplementary informatio

Chandra Observations of MRK 273: Unveiling the Central AGN and the Extended Hot Gas Halo

We report X-ray observations of the field containing the ultraluminous IRAS galaxy Mrk~273 Using the ACIS-S3 instrument on board Chandra. The high resolution X-ray image, for the first time, reveals a compact hard X-ray nucleus in Mrk~273. Its X-ray energy distribution is well described by a heavily obscured power-law spectrum plus a narrow \Feka emission line at 6.4 keV. The neutral hydrogen column density is about 4\times10^{23}\cm^{-2}, implying an absorption -corrected X-ray luminosity (0.1--10 keV) for the nucleus of \Lx\approx 6.5\times 10^{43} \ergs. There are also bright soft X-ray clumps and diffuse soft X-ray emissions surrounding the central hard X-ray nucleus within the 10\arcsec of the nuclear region. Its spectrum can be fitted by a MEKAL thermal model with temperature of about 0.8 keV and high metallicity ($Z\sim 1.5Z_\odot$) plus emission lines from $\alpha$ elements and ions. Further outside the central region, the Chandra observations reveal a very extended hot gas halo with a projected diameter of about 108 \kpc\times 68 \kpc and soft X-ray luminosity of \Lx\approx 1.9\times 10^{41} \ergs. The temperature of the hot gas is about 0.62 keV with a low metallicity ($Z \sim 0.1 Z_\odot$). We discuss the nature of the AGN in Mrk~273 and the implications of our results on the origin of X-ray halos in elliptical galaxies. We also discuss the properties of Mrk~273x, a background AGN in the Mrk~273 field. The AGN has an X-ray luminosity of \Lx \approx 2.43\times 10^{44}\ergs in the 0.5-10 keV band. Its X-ray properties resemble those of Seyfert 1 galaxies while its optical properties are similar to Seyfert 2 galaxies. Such mixed classifications may be a challenge for the unification scheme of AGNs.Comment: 23 pages, 11 figures. ApJ accepted, minor revised versio

Persistent spin splitting of a two-dimensional electron gas in tilted magnetic fields

By varying the orientation of the applied magnetic field with respect to the normal of a two-dimensional electron gas, the chemical potential and the specific heat reveal persistent spin splitting in all field ranges. The corresponding shape of the thermodynamic quantities distinguishes whether the Rashba spin-orbit interaction RSOI, the Zeeman term or both dominate the splitting. The interplay of the tilting of the magnetic field and RSOI resulted to an amplified splitting in weak fields. The effects of changing the RSOI strength and the Landau level broadening are also investigated.Comment: 10 pages, 5 figure

Quantum-inspired interferometry with chirped laser pulses

We introduce and implement an interferometric technique based on chirped femtosecond laser pulses and nonlinear optics. The interference manifests as a high-visibility (> 85%) phase-insensitive dip in the intensity of an optical beam when the two interferometer arms are equal to within the coherence length of the light. This signature is unique in classical interferometry, but is a direct analogue to Hong-Ou-Mandel quantum interference. Our technique exhibits all the metrological advantages of the quantum interferometer, but with signals at least 10^7 times greater. In particular we demonstrate enhanced resolution, robustness against loss, and automatic dispersion cancellation. Our interferometer offers significant advantages over previous technologies, both quantum and classical, in precision time delay measurements and biomedical imaging.Comment: 6 pages, 4 figure

The space group classification of topological band insulators

Topological band insulators (TBIs) are bulk insulating materials which feature topologically protected metallic states on their boundary. The existing classification departs from time-reversal symmetry, but the role of the crystal lattice symmetries in the physics of these topological states remained elusive. Here we provide the classification of TBIs protected not only by time-reversal, but also by crystalline symmetries. We find three broad classes of topological states: (a) Gamma-states robust against general time-reversal invariant perturbations; (b) Translationally-active states protected from elastic scattering, but susceptible to topological crystalline disorder; (c) Valley topological insulators sensitive to the effects of non-topological and crystalline disorder. These three classes give rise to 18 different two-dimensional, and, at least 70 three-dimensional TBIs, opening up a route for the systematic search for new types of TBIs.Comment: Accepted in Nature Physic

An X-ray Luminous, Dwarf Seyfert Companion of Mrk 273

We report the discovery of the brightest X-ray source hosted by a faint (M_B=-16) dwarf galaxy in the immediate vicinity of the ultraluminous IRAS merging galaxy Mrk 273. The dwarf galaxy, 1.3 arcmin away from Mrk 273, is at the tip of a faint northeast plume of Mrk 273. Its spectrum exhibits strong [OIII], Halpha, [NII] emission lines, which establish the redshift of the dwarf galaxy, $z=0.0376$, the same as that of Mrk 273. The emission line ratios are typical of Seyfert galaxies. The X-ray emission is consistent with a point-like source coincident with the center of the dwarf galaxy. The intrinsic X-ray luminosity, 6.3x10^{41} ergs, in the 0.1--2.4 keV energy range, is about seven times larger than the B band luminosity. The X-ray spectrum of the source can be fit with a power-law. All the evidence is consistent with the source being a Seyfert galaxy. It is mysterious why out of $\sim 10$ faint objects in the same field only one is detected by ROSAT and its ratio of soft X-ray to optical luminosity is as high as those for BL Lac objects and few active galactic nuclei (AGNs). If there is a population of such dwarf AGNs hidden as companions of major merger galaxies (such as Mrk 273), they may contribute to the luminosity function of AGNs and the cosmic X-ray background at the faint end.Comment: 15 pages, 2 figures, ApJ Letters, in pres

DINE: A Framework for Deep Incomplete Network Embedding

Network representation learning (NRL) plays a vital role in a variety of tasks such as node classification and link prediction. It aims to learn low-dimensional vector representations for nodes based on network structures or node attributes. While embedding techniques on complete networks have been intensively studied, in real-world applications, it is still a challenging task to collect complete networks. To bridge the gap, in this paper, we propose a Deep Incomplete Network Embedding method, namely DINE. Specifically, we first complete the missing part including both nodes and edges in a partially observable network by using the expectation-maximization framework. To improve the embedding performance, we consider both network structures and node attributes to learn node representations. Empirically, we evaluate DINE over three networks on multi-label classification and link prediction tasks. The results demonstrate the superiority of our proposed approach compared against state-of-the-art baselines.Comment: 12 pages, 3 figure