2,802 research outputs found
Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves
The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a \blue{dissipative} plasmonic material. Correspondingly, the ESWs transmute from Dyakonov--Tamm surface waves into surface--plasmon--polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results
Polarization--universal rejection filtering by ambichiral structures made of indefinite dielectric--magnetic materials
An ambichiral structure comprising sheets of an anisotropic dielectric
material rejects normally incident plane waves of one circular polarization
(CP) state but not of the other CP state, in its fundamental Bragg regime.
However, if the same structure is made of an dielectric--magnetic material with
indefinite permittivity and permeability dyadics, it may function as a
polarization--universal rejection filter because two of the four planewave
components of the electromagnetic field phasors in each sheet are of the
positive--phase--velocity type and two are of the negative--phase--velocity
type.Comment: Cleaned citations in the tex
Predicted FeII Emission-Line Strengths from Active Galactic Nuclei
We present theoretical FeII emission line strengths for physical conditions
typical of Active Galactic Nuclei with Broad-Line Regions. The FeII line
strengths were computed with a precise treatment of radiative transfer using
extensive and accurate atomic data from the Iron Project. Excitation mechanisms
for the FeII emission included continuum fluorescence, collisional excitation,
self-fluorescence amoung the FeII transitions, and fluorescent excitation by
Lyman-alpha and Lyman-beta. A large FeII atomic model consisting of 827 fine
structure levels (including states to E ~ 15 eV) was used to predict fluxes for
approximately 23,000 FeII transitions, covering most of the UV, optical, and IR
wavelengths of astrophysical interest. Spectral synthesis for wavelengths from
1600 Angstroms to 1.2 microns is presented. Applications of present theoretical
templates to the analysis of observations are described. In particular, we
discuss recent observations of near-IR FeII lines in the 8500 Angstrom -- 1
micron region which are predicted by the Lyman-alpha fluorescence mechanism. We
also compare our UV spectral synthesis with an empirical iron template for the
prototypical, narrow-line Seyfert galaxy I Zw 1. The theoretical FeII template
presented in this work should also applicable to a variety of objects with FeII
spectra formed under similar excitation conditions, such as supernovae and
symbiotic stars.Comment: 33 pages, 15 postscript figure
Hybrid-Entanglement in Continuous Variable Systems
Entanglement is one of the most fascinating features arising from
quantum-mechanics and of great importance for quantum information science. Of
particular interest are so-called hybrid-entangled states which have the
intriguing property that they contain entanglement between different degrees of
freedom (DOFs). However, most of the current continuous variable systems only
exploit one DOF and therefore do not involve such highly complex states. We
break this barrier and demonstrate that one can exploit squeezed cylindrically
polarized optical modes to generate continuous variable states exhibiting
entanglement between the spatial and polarization DOF. We show an experimental
realization of these novel kind of states by quantum squeezing an azimuthally
polarized mode with the help of a specially tailored photonic crystal fiber
Mise en place d’outils d’aide à la prescription des antibiotiques dans les établissements de santé (ES) des Pays de la Loire : création d’un thésaurus régional de protocoles d’antibiothérapie
Date du colloque : 2008</p
The Origin of Fe II Emission in AGN
We used a very large set of models of broad emission line (BEL) clouds in AGN
to investigate the formation of the observed Fe II emission lines. We show that
photoionized BEL clouds cannot produce both the observed shape and observed
equivalent width of the 2200-2800A Fe II UV bump unless there is considerable
velocity structure corresponding to a microturbulent velocity parameter v_turb
> 100 km/s for the LOC models used here. This could be either microturbulence
in gas that is confined by some phenomenon such as MHD waves, or a velocity
shear such as in the various models of winds flowing off the surfaces of
accretion disks. The alternative way that we can find to simultaneously match
both the observed shape and equivalent width of the Fe II UV bump is for the Fe
II emission to be the result of collisional excitation in a warm, dense gas.
Such gas would emit very few lines other than Fe II. However, since the
collisionally excited gas would constitute yet another component in an already
complicated picture of the BELR, we prefer the model involving turbulence. In
either model, the strength of Fe II emission relative to the emission lines of
other ions such as Mg II depends as much on other parameters (either v_turb or
the surface area of the collisionally excited gas) as it does on the iron
abundance. Therefore, the measurement of the iron abundance from the FeII
emission in quasars becomes a more difficult problem.Comment: 23 pages. Accepted by Ap
Benefits and barriers in the design of harmonized access agreements for international data sharing
In the past decade, there has been a surge in the number of sensitive human genomic and health datasets available to researchers via Data Access Agreements (DAAs) and managed by Data Access Committees (DACs). As this form of sharing increases, so do the challenges of achieving a reasonable level of data protection, particularly in the context of international data sharing. Here, we consider how excessive variation across DAAs can hinder these goals, and suggest a core set of clauses that could prove useful in future attempts to harmonize data governance
Curvature tensors on distorted Killing horizons and their algebraic classification
We consider generic static spacetimes with Killing horizons and study
properties of curvature tensors in the horizon limit. It is determined that the
Weyl, Ricci, Riemann and Einstein tensors are algebraically special and
mutually aligned on the horizon. It is also pointed out that results obtained
in the tetrad adjusted to a static observer in general differ from those
obtained in a free-falling frame. This is connected to the fact that a static
observer becomes null on the horizon.
It is also shown that finiteness of the Kretschmann scalar on the horizon is
compatible with the divergence of the Weyl component or
in the freely falling frame. Furthermore finiteness of is compatible
with divergence of curvature invariants constructed from second derivatives of
the Riemann tensor.
We call the objects with finite Krestschmann scalar but infinite
``truly naked black holes''. In the (ultra)extremal versions of these objects
the structure of the Einstein tensor on the horizon changes due to extra terms
as compared to the usual horizons, the null energy condition being violated at
some portions of the horizon surface. The demand to rule out such divergencies
leads to the constancy of the factor that governs the leading term in the
asymptotics of the lapse function and in this sense represents a formal analog
of the zeroth law of mechanics of non-extremal black holes. In doing so, all
extra terms in the Einstein tensor automatically vanish.Comment: 21 pages, To appear in Class. Quant. Gra
The Intrinsically X-ray Weak Quasar PHL 1811. II. Optical and UV Spectra and Analysis
This is the second of two papers reporting observations and analysis of the
unusually bright (m_b=14.4), luminous (M_B=-25.5), nearby (z=0.192) narrow-line
quasar PHL 1811. The first paper reported that PHL 1811 is intrinsically X-ray
weak, and presented a spectral energy distribution (SED). Here we present HST
STIS optical and UV spectra, and ground-based optical spectra. The optical and
UV line emission is very unusual. There is no evidence for forbidden or
semiforbidden lines. The near-UV spectrum is dominated by very strong FeII and
FeIII, and unusual low-ionization lines such as NaID and CaII H&K are observed.
High-ionization lines are very weak; CIV has an equivalent width of 6.6A, a
factor of ~5 smaller than measured from quasar composite spectra. An unusual
feature near 1200A can be deblended in terms of Ly\alpha, NV, SiII, and CIII*
using the blueshifted CIV profile as a template. Photoionization modeling shows
that the unusual line emission can be explained qualitatively by the unusually
soft SED. Principally, a low gas temperature results in inefficient emission of
collisionally excited lines, including the semiforbidden lines generally used
as density diagnostics. The emission resembles that of high-density gas; in
both cases this is a consequence of inefficient cooling. PHL 1811 is very
unusual, but we note that quasar surveys are generally biased against finding
similar objects.Comment: Accepted for publication in ApJS. Full resolution figures available
here: http://www.nhn.ou.edu/~leighly/phl1811_paper1.pd
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