Influence of interface roughness in quantum cascade lasers

We use a numerical model based on non-equilibrium Green's functions to investigate the influence of interface roughness (IFR) scattering in terahertz quantum cascade lasers. We confirm that IFR is an important phenomenon that affects both current and gain. The simulations indicate that IFR causes a leakage current that transfers electrons from the upper to the lower laser state. In certain cases, this current can greatly reduce gain. In addition, individual interfaces and their impact on the renormalized single particle energies are studied and shown to give both blue-and red-shifts of the gain spectrum. (C) 2015 AIP Publishing LLC

A photometric and kinematic study of the stars and interstellar medium in the central two kpc of NGC 3379

HST images of NGC 3379 show that the V and I luminosity profiles in the inner 13 arcsec of this E1 galaxy are represented by two different components: a stellar bulge following a Sersic Law with exponent n = 2.36, and a central core (r < 0.7 arcsec) with a characteristic "cuspy" profile. Subtraction of the underlying stellar component represented by the fitted Sersic profile revealed the presence of a small (r ~ 105 pc) dust disk of about 150 solar masses, oriented at PA = 125 degrees and inclined ~ 77 degrees with respect to the line of sight. The same absorption structure is detected in the color-index (V-I) image. The stellar rotation in the inner 20 arcsec is well represented by a parametric planar disk model, inclined ~ 26 degrees relative to the plane of the sky, and apparent major axis along PA ~ 67 degrees. The gas velocity curves in the inner 5 arcsec show a steep gradient, indicating that the gas rotates much faster than the stars, although in the same direction. The velocity field of the gaseous system, however, is not consistent with the simple model of Keplerian rotation sustained by the large (7 x 10E9 solar masses within a radius of ~ 90 pc) central mass implied by the maximum velocity observed, but the available data precludes a more detailed analysis.Comment: 23 pages, LaTeX(aaspp4.sty), 9 figures included. Figs. 1 and 5 are colour plates. Accepted for publication in The Astrophysical Journal (part 1

Cinemática del gas ionizado y perfiles de luminosidad de las Galaxias Porotos Verdes

Presentamos aquí los resultados espectroscópicos preliminares sobre una muestra de galaxias porotos verdes (GBG), conocidas por presentar regiones de líneas angostas ultra-luminosas y extendidas a toda escala en la galaxia huésped. Se tomaron espectros en Gemini con GMOS-S,N para obtener cocientes de líneas de emisión, cinemática del gas ionizado y perfiles de luminosidad en distintas bandas de continuo. Reportamos aquí nuevos resultados que confirman que para toda esta muestra de 12 GBG la emisión del [OIII]λ5008 tiene una extensión de 5 a 17 kpc, similar, y en algunos casos superior, a la del continuo estelar. En el caso extremo de J145533.6+044643 la emisión del [OIII] se extiende hasta un diámetro de 17.5±1.6 kpc. Determinamos que los perfiles de emisión de continuo tienen radios de escala de 3 a 7 kpc y son más extensos para longitudes de onda más cortas, lo que es consistente con los radios de escala de galaxias espirales gigantes o sistemas en fusión. Los perfiles de color que determinamos indican la presencia de extinción y posible formación estelar.We present preliminary spectroscopic results of a sample of green bean galaxies (GBG), known to show ultra-luminous, galaxy-wide, narrow-line regions. We analyze Gemini GMOS-S,N spectra of a sample of 12 GBG in order to obtain emission line ratios, gas kinematics and luminosity profiles in some continuous bands. We report here new results that confirm that the [OIII]λ5008 emission extends from 5 to 17 kpc, in all cases scales similar or larger than the stellar continuums at the spectra. In the extreme case of J145533.6+044643 the [OIII] emission reaches a diameter of 17.5±1.6 kpc. We find that the continuum half light radii extend from 3 to 7 kpc, the largest scale radius at shortest wavelengths, which is consistent with the scale lengths of large spiral galaxies or merging systems. Another new result is that the spatial variation of the continuum color profiles indicate the presence of extinction and possibly star formation.Fil: Diaz, Ruben Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Agüero, Maria Paz. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Schirmer, M.. Observatorio Gemini; Estados Unidos. Universitaet Bonn; AlemaniaFil: Holheim, K.. Observatorio Gemini; Estados UnidosFil: Levenson, N.. Observatorio Gemini; Estados UnidosFil: Winge, C.. Observatorio Gemini; Estados Unido

Reverberation Mapping and the Physics of Active Galactic Nuclei

Reverberation-mapping campaigns have revolutionized our understanding of AGN. They have allowed the direct determination of the broad-line region size, enabled mapping of the gas distribution around the central black hole, and are starting to resolve the continuum source structure. This review describes the recent and successful campaigns of the International AGN Watch consortium, outlines the theoretical background of reverberation mapping and the calculation of transfer functions, and addresses the fundamental difficulties of such experiments. It shows that such large-scale experiments have resulted in a ``new BLR'' which is considerably different from the one we knew just ten years ago. We discuss in some detail the more important new results, including the luminosity-size-mass relationship for AGN, and suggest ways to proceed in the near future.Comment: Review article to appear in Astronomical Time Series, Proceedings of the Wise Observatory 25th Ann. Symposium. 24 pages including 7 figure

Primary structure and spectroscopic studies of Neurospora copper metallothionein.

When Neurospora crassa is grown in the presence of Cu(II) ions, it accumulates the metal with the concomitant synthesis of a low molecular weight copper-binding protein. The molecule binds 6 g-atom of copper per mole protein (Mr = 2200) and shows a striking sequence homology to the zinc- and cadmium-binding vertebrate metallothioneins. Absorption, circular dichroism, and electron paramagnetic resonance spectroscopy of Neurospora metallothionein indicate the copper to be bound to cysteinyl residues as a Cu(I)-thiolate complex of the polymeric mu-thiolate structure [Cu(I)6RS7]-. This metal-binding mode is also in agreement with the unusual luminescence of the protein. Spectral perturbation studies with HgCl2 and p-(chloromercuri)benzoate suggest that the 6 Cu(I)ions are coordinated to the seven cysteinyl residues in the form of a single metal cluster. Neurospora apometallothionein is also capable of binding in vivo group IIB metal ions [Zn(II), Cd(II), and Hg(II)] as well as paramagnetic Co(II) ions with an overall metal-to-protein stoichiometry of 3. The spectroscopic properties of the fully substituted forms are indicative of a distorted tetrahedral coordination. However, metal titration of the apoprotein shows the third metal ion to be differently coordinated than the other two metal ions. This difference can be explained by the presence of only seven cysteine residues in Neurospora metallothionein as opposed to nine cysteine residues in the three-metal cluster of the mammalian metallothioneins

The origin of the Narrow Line Region of Mrk 3: an overpressured jet cocoon

We have obtained HST FOC long-slit optical spectroscopy of the Narrow Line Region of the Seyfert 2 galaxy Mrk 3. In the region cospatial with the radio-jet the velocity field is highly perturbed and shows two velocity systems separated by as much as 1700 km/s. We interpret this to be the consequence of the rapid expansion of a cocoon of hot gas, shocked and heated by the radio-emitting outflow, which compresses and accelerates the ambient gas. The NLR itself is essentially a cylindrical shell expanding supersonically. From the size and velocity of the expanding region, we derive an upper limit to the radio-source age, ~ 2 E42 erg/s required to inflate the cocoon and estimate that the jet minimum advance speed is 3 E-3 pc per year. The total kinetic energy of the high velocity NLR gas can be estimated as ~6 E54 erg, comparable to the total energy carried by the jet over its lifetime and this quantitatively supports the idea that the NLR gas is accelerated by the jet. If the advance speed of Mrk 3 is representative of the Seyfert population then these sources must also be short lived and probably recurrent. The jet kinetic luminosity of Mrk 3 is between 2 and 3 orders of magnitude smaller than that derived for radio-loud AGNs with similar emission-line luminosity. On the other hand, the fraction of jet power dissipated in radio-emission is similar. We speculate that the main distinction between radio-quiet and radio-loud AGN is ascribed to a difference in jet power rather than to a different efficiency in synchrotron emission production.Comment: 13 pages, 8 figures, Astrophysical Journal in pres

Specifications for an inductively coupled plasma simultaneous multielement analysis system

Specifications are presented for those items of hardware, software, and overall system performance which are of known importance in atomic emission spectroscopy--simultaneous multielement analyses (ICP-SMA) instrument systems. Particular attention is directed to the specified data reporting and quality assurance features which are required for improving the validity and interpretability of the analytical results, and the specified background correction procedures which are necessary for accurate quantitative determinations near the limit of detection. The specification package was prepared to specify and purchase an ICP-SMA system which will provide maximum value and utility for the simultaneous determination of major, minor and trace quantities of the elements in a wide variety of sample materials. Modifications of the analytical line array specified here may be appropriate for other, more specific, analytical tasks. Budgetary realities may necessitate additional, appropriate modifications. It is anticipated, however, that the specification package presented here will have general utility as a guide in the preparation of ICP-SMA procurement packages for other laboratories and other analytical applications