Scattering of surface plasmons by one-dimensional periodic nanoindented surfaces

In this work, the scattering of surface plasmons by a finite periodic array of one-dimensional grooves is theoretically analyzed by means of a modal expansion technique. We have found that the geometrical parameters of the array can be properly tuned to achieve optimal performance of the structure either as a Bragg reflector or as a converter of surface plasmons into light. In this last case, the emitted light is collimated within a few degrees cone. Importantly, we also show that a small number of indentations in the array are sufficient to fully achieve its functional capabilities.Comment: 5 pages, 5 figures; changed sign convention in some definition

Deep into the Water Fountains: The case of IRAS 18043-2116

(Abridged) The formation of large-scale (hundreds to few thousands of AU) bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic Giant Branch (post-AGB) stars is poorly understood. The shape of these structures, traced by emission from fast molecular outflows, suggests that the dynamics at the innermost regions of these CSEs does not depend only on the energy of the radiation field of the central star. Deep into the Water Fountains is an observational project based on the results of programs carried out with three telescope facilities: The Karl G. Jansky Very Large Array (JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large Telescope (SINFONI-VLT). Here we report the results of the observations towards the WF nebula IRAS 18043$-$2116: Detection of radio continuum emission in the frequency range 1.5GHz - 8.0GHz; H$_{2}$O maser spectral features and radio continuum emission detected at 22GHz, and H$_{2}$ ro-vibrational emission lines detected at the near infrared. The high-velocity H$_{2}$O maser spectral features, and the shock-excited H$_{2}$ emission detected could be produced in molecular layers which are swept up as a consequence of the propagation of a jet-driven wind. Using the derived H$_{2}$ column density, we estimated a molecular mass-loss rate of the order of $10^{-9}$M$_{\odot}$yr$^{-1}$. On the other hand, if the radio continuum flux detected is generated as a consequence of the propagation of a thermal radio jet, the mass-loss rate associated to the outflowing ionized material is of the order of 10$^{-5}$M$_{\odot}$yr$^{-1}$. The presence of a rotating disk could be a plausible explanation for the mass-loss rates estimated.Comment: 10 pages, 5 figures. Accepted for publication in A&

Effect of a magnetic flux on the critical behavior of a system with long range hopping

We study the effect of a magnetic flux in a 1D disordered wire with long range hopping. It is shown that this model is at the metal-insulator transition (MIT) for all disorder values and the spectral correlations are given by critical statistics. In the weak disorder regime a smooth transition between orthogonal and unitary symmetry is observed as the flux strength increases. By contrast, in the strong disorder regime the spectral correlations are almost flux independent. It is also conjectured that the two level correlation function for arbitrary flux is given by the dynamical density-density correlations of the Calogero-Sutherland (CS) model at finite temperature. Finally we describe the classical dynamics of the model and its relevance to quantum chaos.Comment: 5 pages, 4 figure

Geometrically constrained magnetic wall

The structure and properties of a geometrically constrained magnetic wall in a constriction separating two wider regions are investigated theoretically. They are shown to differconsiderably from those of an unconstrained wall, so that the geometrically constrained magnetic wall truly constitutes a new kind of magnetic wall, besides the well known Bloch and Neel walls. In particular, the width of a constrained wall cann become very small if the characteristic length of the constriction is small, as is actually the case in an atomic point contact. This provides a simple, natural explanation for the large magnetoresistance observed in ferromagnetic atomic point contacts.Comment: RevTeX, 4 pages, 4 eps figures; v2: revised version; v3: ref. adde

Integral Field Spectroscopy based H\alpha\ sizes of local Luminous and Ultraluminous Infrared Galaxies. A Direct Comparison with high-z Massive Star Forming Galaxies

Aims. We study the analogy between local U/LIRGs and high-z massive SFGs by comparing basic H{\alpha} structural characteristics, such as size, and luminosity (and SFR) surface density, in an homogeneous way (i.e. same tracer and size definition, similar physical scales). Methods. We use Integral Field Spectroscopy based H{\alpha} emission maps for a representative sample of 54 local U/LIRGs (66 galaxies). From this initial sample we select 26 objects with H{\alpha} luminosities (L(H{\alpha})) similar to those of massive (i.e. M\ast \sim 10^10 M\odot or larger) SFGs at z \sim 2, and observed on similar physical scales. Results. The sizes of the H{\alpha} emitting region in the sample of local U/LIRGs span a large range, with r1/2(H{\alpha}) from 0.2 to 7 kpc. However, about 2/3 of local U/LIRGs with Lir > 10^11.4 L\odot have compact H{\alpha} emission (i.e. r1/2 < 2 kpc). The comparison sample of local U/LIRGs also shows a higher fraction (59%) of objects with compact H{\alpha} emission than the high-z sample (25%). This gives further support to the idea that for this luminosity range the size of the star forming region is a distinctive factor between local and distant galaxies of similar SF rates. However, when using H{\alpha} as a tracer for both local and high-z samples, the differences are smaller than the ones recently reported using a variety of other tracers. Despite of the higher fraction of galaxies with compact H{\alpha} emission, a sizable group (\sim 1/3) of local U/LIRGs are large (i.e. r1/2 > 2 kpc). These are systems showing pre-coalescence merger activity and they are indistinguishable from the massive high-z SFGs galaxies in terms of their H{\alpha} sizes, and luminosity and SFR surface densities.Comment: Accepted for publication in A&A. (!5 pages, 7 figures, 2 tables

Heisenberg-limited eavesdropping on the continuous-variable quantum cryptographic protocol with no basis switching is impossible

The Gaussian quantum key distribution protocol based on coherent states and heterodyne detection [Phys. Rev. Lett. 93, 170504 (2004)] has the advantage that no active random basis switching is needed on the receiver's side. Its security is, however, not very satisfyingly understood today because the bounds on the secret key rate that have been derived from Heisenberg relations are not attained by any known scheme. Here, we address the problem of the optimal Gaussian individual attack against this protocol, and derive tight upper bounds on the information accessible to an eavesdropper. The optical scheme achieving this bound is also exhibited, which concludes the security analysis of this protocol.Comment: 10 pages, 6 figure

Terahertz surface plasmon polariton propagation and focusing on periodically corrugated metal wires

In this letter we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. In this way, highly localized SPPs can be sustained in the terahertz region of the electromagnetic spectrum. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.Comment: accepted at PRL, submitted 29th May 200

An infrared study of galactic OH/IR stars. I. An optical/near-IR atlas of the Arecibo sample

In this paper we present optical and near-infrared finding charts, accurate astrometry (~1") and single-epoch near-infrared photometry for 371 IRAS sources, 96% of those included in the so-called Arecibo sample of OH/IR stars (Eder et al. 1988; Lewis et al. 1990a; Chengalur et al. 1993). The main photometric properties of the stars in the sample are presented and discussed as well as the problems found during the process of identification of the optical/near-infrared counterparts. In addition, we also identify suitable reference stars in each field to be used for differential photometry purposes in the future. We find that 39% of the sources (144 in number) have no optical counterpart, 8 of them being invisible even at near infrared wavelengths. The relative distribution of sources with and without optical counterpart in the IRAS two-colour diagram and their characteristic near infrared colours are interpreted as the consequence of the increasing thickness of their circumstellar shells. Among the objects not detected at near infrared wavelengths four non-variable sources are proposed to be heavily obscured post-AGB stars which have just very recently left the AGB. Eight additional objects with unusually bright and/or blue near-infrared colours are identified as candidate post-AGB stars and/or proto-planetary nebulae.Comment: 28 pages, 9 figures, for associated finding charts see: http://www.edpsciences.org/articles/aa/full/2005/08/aa1709/FINDING_CHARTS/are cibo_index.htm

A test for asymptotic giant branch evolution theories: Planetary Nebulae in the Large Magellanic Cloud

We used a new generation of asymptotic giant branch (AGB) stellar models that include dust formation in the stellar winds to find the links between evolutionary models and the observed properties of a homogeneous sample of Large Magellanic Cloud (LMC) planetary nebulae (PNe). Comparison between the evolutionary yields of elements such as CNO and the corresponding observed chemical abundances is a powerful tool to shed light on evolutionary processes such as hot bottom burning (HBB) and third dredge-up (TDU). We found that the occurrence of HBB is needed to interpret the nitrogen-enriched (log(N/H)+12>8) PNe. In particular, N-rich PNe with the lowest carbon content are nicely reproduced by AGB models of mass M >=6 Mo, whose surface chemistry reflects the pure effects of HBB. PNe with log(N/H)+12<7.5 correspond to ejecta of stars that have not experienced HBB, with initial mass below about 3 Mo. Some of these stars show very large carbon abundances, owing to the many TDU episodes experienced. We found from our LMC PN sample that there is a threshold to the amount of carbon accumulated at AGB surfaces, log(C/H)+12<9. Confirmation of this constraint would indicate that, after the C-star stage is reached,AGBs experience only a few thermal pulses, which suggests a rapid loss of the external mantle, probably owing to the effects of radiation pressure on carbonaceous dust particles present in the circumstellar envelope. The implications of these findings for AGB evolution theories and the need to extend the PN sample currently available are discussed.Comment: 12 pages, 4 figures, 1 table, accepted for publication in MNRAS (2015 July 13; in original form 2015 June 9