Symmetry breaking and manipulation of nonlinear optical modes in an asymmetric double-channel waveguide

We study light-beam propagation in a nonlinear coupler with an asymmetric double-channel waveguide and derive various analytical forms of optical modes. The results show that the symmetry-preserving modes in a symmetric double-channel waveguide are deformed due to the asymmetry of the two-channel waveguide, yet such a coupler supports the symmetry-breaking modes. The dispersion relations reveal that the system with self-focusing nonlinear response supports the degenerate modes, while for self-defocusingmedium the degenerate modes do not exist. Furthermore, nonlinear manipulation is investigated by launching optical modes supported in double-channel waveguide into a nonlinear uniform medium.Comment: 10 page

Stable isotope values in modern bryozoan carbonate from New Zealand and implications for paleoenvironmental interpretation

Bryozoan carbonate contains useful geochemical evidence of temperate shelf paleoenvironments. Stable isotope values were determined for 103 modern marine bryozoan skeletons representing 30 species from New Zealand. δ18O values range from -1.4 to 2.8 VPDB, while δ13C range from -4.5 to 2.8 VPDB (values uncorrected for mineralogical variation). These values are distinct from those of both tropical marine skeletons and New Zealand Tertiary fossils. Most bryozoans secrete carbonate in or near isotopic equilibrium with sea water, except for Celleporina and Steginoporella. The complex and variable mineralogies of the bryozoans reported here make correction for mineralogical effects problematic. Nevertheless, mainly aragonitic forms display higher isotope values, as anticipated. Both temperature and salinity constrain δ18O and δ13C values, and vary with latitude and water depth. Ten samples from a single branch of Cinctipora elegans from the Otago shelf cover a narrow range, although the striking difference in carbon isotope values between the endozone and exozone probably reflects different mineralisation histories. Our stable isotope results from three different laboratories on a single population from a single location are encouragingly consistent. Monomineralic bryozoans, when carefully chosen to avoid species suspected of vital fractionation, have considerable potential as geochemical paleoenvironmental indicators, particularly in temperate marine environments where bryozoans are dominant sediment producers

The disappearing act: a dusty wind eclipsing RW Aur

The authors acknowledge support from the Science and Technology Facilities Council through grants no. ST/K502339/1 and ST/M001296/1, and the Science Foundation Ireland through grant no. 10/RFP/AST2780.RW Aur is a young binary star that experienced a deep dimming in 2010-11in component A and a second even deeper dimming from summer 2014 to summer 2016. We present new unresolved multi-band photometry during the 2014-16 eclipse, new emission line spectroscopy before and during th dimming, archive infrared photometry between 2014-15, as well as an overview of literature data. Spectral observations were carried out witht he Fibre-fed RObotic Dual-beam Optical Spectrograph on the Liverpool Telescope. Photometric monitoring was done with the Las Cumbres Observatory Global Telescope Network and James Gregory Telescope. Ourphotometry shows that RW Aur dropped in brightness to R = 12.5 in March 2016. In addition to the long-term dimming trend, RW Aur is variable on time-scales as short as hours. The short-term variation is most likely due to an unstable accretion flow. This, combined with the presence of accretion-related emission lines in the spectra suggest that accretion flows in the binary system are at least partially visible during the eclipse. The equivalent width of [O I] increases by a factor of ten in 2014, coinciding with the dimming event, confirming previous reports.The blueshifted part of the Hα profile is suppressed during the eclipse. In combination with the increase in mid-infrared brightness during the eclipse reported in the literature and seen in WISE archival data, and constraints on the geometry of the disk around RW Aur A we arrive at the conclusion that the obscuring screen is part of a wind emanating from the inner disc.Publisher PDFPeer reviewe

Nonlinear Localization in Metamaterials

Metamaterials, i.e., artificially structured ("synthetic") media comprising weakly coupled discrete elements, exhibit extraordinary properties and they hold a great promise for novel applications including super-resolution imaging, cloaking, hyperlensing, and optical transformation. Nonlinearity adds a new degree of freedom for metamaterial design that allows for tuneability and multistability, properties that may offer altogether new functionalities and electromagnetic characteristics. The combination of discreteness and nonlinearity may lead to intrinsic localization of the type of discrete breather in metallic, SQUID-based, and ${\cal PT}-$symmetric metamaterials. We review recent results demonstrating the generic appearance of breather excitations in these systems resulting from power-balance between intrinsic losses and input power, either by proper initialization or by purely dynamical procedures. Breather properties peculiar to each particular system are identified and discussed. Recent progress in the fabrication of low-loss, active and superconducting metamaterials, makes the experimental observation of breathers in principle possible with the proposed dynamical procedures.Comment: 19 pages, 14 figures, Invited (Review) Chapte

How well do local relations predict gas-phase metallicity gradients? Results from SDSS-IV MaNGA

Funding: J.B-B thanks IA-100420 (DGAPA-PAPIIT, UNAM) and CONA-CYT grant CF19-39578 support. RR thanks Conselho Nacional de Desenvolvimento Científico e Tecnológico ( CNPq, Proj. 311223/2020-6, 304927/2017-1 and 400352/2016-8), Fundação de amparo ’a pesquisa do Rio Grande do Sul (FAPERGS, Proj. 16/2551-0000251-7 and 19/1750-2), Coordena¸cão de Aperfei¸coamento de Pessoal de Nível Superior (CAPES, Proj. 0001). RAR acknowledges financial support from Conselho Nacional de Desenvolvimento Científico e Tecnológico (302280/2019-7).Gas-phase metallicity gradients in galaxies provide important clues to those galaxies’ formation histories. Using SDSS-IV MaNGA data, we previously demonstrated that gas metallicity gradients vary systematically and significantly across the galaxy mass–size plane: at stellar masses beyond approximately 1010 M⊙, more extended galaxies display steeper gradients (in units of dex/Re) at a given stellar mass. Here, we set out to develop a physical interpretation of these findings by examining the ability of local ∼kpc-scale relations to predict the gradient behaviour along the mass–size plane. We find that local stellar mass surface density, when combined with total stellar mass, is sufficient to reproduce the overall mass–size trend in a qualitative sense. We further find that we can improve the predictions by correcting for residual trends relating to the recent star formation histories of star-forming regions. However, we find as well that the most extended galaxies display steeper average gradients than predicted, even after correcting for residual metallicity trends with other local parameters. From these results, we argue that gas-phase metallicity gradients can largely be understood in terms of known local relations, but we also discuss some possible physical causes of discrepant gradients.PostprintPeer reviewe

The low dark matter content of the lenticular galaxy NGC 3998

We observed the lenticular galaxy NGC 3998 with the Mitchell Integral-Field Spectrograph and extracted line-of-sight velocity distributions out to three half-light radii. We constructed collisionless orbit models in order to constrain NGC 3998's dark and visible structure, using kinematics from both the Mitchell and SAURON instruments. We find NGC 3998 to be almost axisymmetric, seen nearly face-on with a flattened intrinsic shape – i.e. a face-on fast rotator. We find an I-band mass-to-light ratio of 4.7 +0.32/−0.45 in good agreement with previous spectral fitting results for this galaxy. Our best-fitting orbit model shows a both a bulge and a disc component, with a non-negligible counter-rotating component also evident. We find that relatively little dark matter is needed to model this galaxy, with an inferred dark mass fraction of just 7.1 +8.1/−7.1 percent within one half-light radius.Publisher PDFPeer reviewe

Nonlinearity and disorder: Classification and stability of nonlinear impurity modes

We study the effects produced by competition of two physical mechanisms of energy localization in inhomogeneous nonlinear systems. As an example, we analyze spatially localized modes supported by a nonlinear impurity in the generalized nonlinear Schr\"odinger equation and describe three types of nonlinear impurity modes --- one- and two-hump symmetric localized modes and asymmetric localized modes --- for both focusing and defocusing nonlinearity and two different (attractive or repulsive) types of impurity. We obtain an analytical stability criterion for the nonlinear localized modes and consider the case of a power-law nonlinearity in detail. We discuss several scenarios of the instability-induced dynamics of the nonlinear impurity modes, including the mode decay or switching to a new stable state, and collapse at the impurity site.Comment: 18 pages, 22 figure

Refractive-index sensing with ultra-thin plasmonic nanotubes

We study the refractive-index sensing properties of plasmonic nanotubes with a dielectric core and ultra-thin metal shell. The few-nm thin metal shell is described by both the usual Drude model and the nonlocal hydrodynamic model to investigate the effects of nonlocality. We derive an analytical expression for the extinction cross section and show how sensing of the refractive index of the surrounding medium and the figure-of-merit are affected by the shape and size of the nanotubes. Comparison with other localized surface plasmon resonance sensors reveals that the nanotube exhibits superior sensitivity and comparable figure-of-merit

A Molecular Platinum Cluster Junction: A Single-Molecule Switch

We present a theoretical study of the electronic transport through single-molecule junctions incorporating a Pt6 metal cluster bound within an organic framework. We show that the insertion of this molecule between a pair of electrodes leads to a fully atomically engineered nano-metallic device with high conductance at the Fermi level and two sequential high on/off switching states. The origin of this property can be traced back to the existence of a HOMO which consists of two degenerate and asymmetric orbitals, lying close in energy to the Fermi level of the metallic leads. Their degeneracy is broken when the molecule is contacted to the leads, giving rise to two resonances which become pinned close to the Fermi level and display destructive interference.Comment: 4 pages, 4 figures. Reprinted (adapted) with permission from J. Am. Chem. Soc., 2013, 135 (6), 2052. Copyright 2013 American Chemical Societ