157 research outputs found
Erratum and Errata
ERRATUM in On properties of seawater defined by temperature, salinity, and pressure, by George Veronis; Journal of Marine Research 30(2): 227â255. ERRATA in On the estimation of surface gravity-wave fields in the vicinity of an array of wave recorders, by R. L. Snyder and Linda Smith; Journal of Marine Research 31(1): 51â60
Solving dielectric and plasmonic waveguide dispersion relations with a pocket calculator
We present a robust iterative technique for solving complex transcendental
dispersion equations routinely encountered in integrated optics. Our method
especially befits the multilayer dielectric and plasmonic waveguides forming
the basis structures for a host of contemporary nanophotonic devices. The
solution algorithm ports seamlessly from the real to the complex domain--i.e.,
no extra complexity results when dealing with leaky structures or those with
material/metal loss. Unlike several existing numerical approaches, our
algorithm exhibits markedly-reduced sensitivity to the initial guess and allows
for straightforward implementation on a pocket calculator.Comment: 18 pages, 11 Figures, 5 Tables, added references, Submitted to Optics
Expres
Modal Analysis and Coupling in Metal-Insulator-Metal Waveguides
This paper shows how to analyze plasmonic metal-insulator-metal waveguides
using the full modal structure of these guides. The analysis applies to all
frequencies, particularly including the near infrared and visible spectrum, and
to a wide range of sizes, including nanometallic structures. We use the
approach here specifically to analyze waveguide junctions. We show that the
full modal structure of the metal-insulator-metal (MIM) waveguides--which
consists of real and complex discrete eigenvalue spectra, as well as the
continuous spectrum--forms a complete basis set. We provide the derivation of
these modes using the techniques developed for Sturm-Liouville and generalized
eigenvalue equations. We demonstrate the need to include all parts of the
spectrum to have a complete set of basis vectors to describe scattering within
MIM waveguides with the mode-matching technique. We numerically compare the
mode-matching formulation with finite-difference frequency-domain analysis and
find very good agreement between the two for modal scattering at symmetric MIM
waveguide junctions. We touch upon the similarities between the underlying
mathematical structure of the MIM waveguide and the PT symmetric quantum
mechanical pseudo-Hermitian Hamiltonians. The rich set of modes that the MIM
waveguide supports forms a canonical example against which other more
complicated geometries can be compared. Our work here encompasses the microwave
results, but extends also to waveguides with real metals even at infrared and
optical frequencies.Comment: 17 pages, 13 figures, 2 tables, references expanded, typos fixed,
figures slightly modifie
Instability of small-amplitude convective flows in a rotating layer with stress-free boundaries
We consider stability of steady convective flows in a horizontal layer with
stress-free boundaries, heated below and rotating about the vertical axis, in
the Boussinesq approximation (the Rayleigh-Benard convection). The flows under
consideration are convective rolls or square cells, the latter being
asymptotically equal to the sum of two orthogonal rolls of the same wave number
k. We assume, that the Rayleigh number R is close to the critical one, R_c(k),
for the onset of convective flows of this wave number: R=R_c(k)+epsilon^2; the
amplitude of the flows is of the order of epsilon. We show that the flows are
always unstable to perturbations, which are a sum of a large-scale mode not
involving small scales, and two large-scale modes, modulated by the original
rolls rotated by equal small angles in the opposite directions. The maximal
growth rate of the instability is of the order of max(epsilon^{8/5},(k-k_c)^2),
where k_c is the critical wave number for the onset of convection.Comment: Latex, 12 pp., 15 refs. An improved version of the manuscript
submitted to "Mechanics of fluid and gas", 2006 (in Russian; English
translation "Fluid Dynamics"
Statistical mechanics of Fofonoff flows in an oceanic basin
We study the minimization of potential enstrophy at fixed circulation and
energy in an oceanic basin with arbitrary topography. For illustration, we
consider a rectangular basin and a linear topography h=by which represents
either a real bottom topography or the beta-effect appropriate to oceanic
situations. Our minimum enstrophy principle is motivated by different arguments
of statistical mechanics reviewed in the article. It leads to steady states of
the quasigeostrophic (QG) equations characterized by a linear relationship
between potential vorticity q and stream function psi. For low values of the
energy, we recover Fofonoff flows [J. Mar. Res. 13, 254 (1954)] that display a
strong westward jet. For large values of the energy, we obtain geometry induced
phase transitions between monopoles and dipoles similar to those found by
Chavanis and Sommeria [J. Fluid Mech. 314, 267 (1996)] in the absence of
topography. In the presence of topography, we recover and confirm the results
obtained by Venaille and Bouchet [Phys. Rev. Lett. 102, 104501 (2009)] using a
different formalism. In addition, we introduce relaxation equations towards
minimum potential enstrophy states and perform numerical simulations to
illustrate the phase transitions in a rectangular oceanic basin with linear
topography (or beta-effect).Comment: 26 pages, 28 figure
Quasiperiodic waves at the onset of zero Prandtl number convection with rotation
We show the possibility of quasiperiodic waves at the onset of thermal
convection in a thin horizontal layer of slowly rotating zero-Prandtl number
Boussinesq fluid confined between stress-free conducting boundaries. Two
independent frequencies emerge due to an interaction between a stationary
instability and a self-tuned wavy instability in presence of coriolis force, if
Taylor number is raised above a critical value. Constructing a dynamical system
for the hydrodynamical problem, the competition between the interacting
instabilities is analyzed. The forward bifurcation from the conductive state is
self-tuned.Comment: 9 pages of text (LaTex), 5 figures (Jpeg format
Thermohaline structure in the California Current System : observations and modeling of spice variance
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C02008, doi:10.1029/2011JC007589.Upper ocean thermohaline structure in the California Current System is investigated using sustained observations from autonomous underwater gliders and a numerical state estimate. Both observations and the state estimate show layers distinguished by the temperature and salinity variability along isopycnals (i.e., spice variance). Mesoscale and submesoscale spice variance is largest in the remnant mixed layer, decreases to a minimum below the pycnocline near 26.3 kg mâ3, and then increases again near 26.6 kg mâ3. Layers of high (low) meso- and submesoscale spice variance are found on isopycnals where large-scale spice gradients are large (small), consistent with stirring of large-scale gradients to produce smaller scale thermohaline structure. Passive tracer adjoint calculations in the state estimate are used to investigate possible mechanisms for the formation of the layers of spice variance. Layers of high spice variance are found to have distinct origins and to be associated with named water masses; high spice variance water in the remnant mixed layer has northerly origin and is identified as Pacific Subarctic water, while the water in the deeper high spice variance layer has southerly origin and is identified as Equatorial Pacific water. The layer of low spice variance near 26.3 kg mâ3 lies between the named water masses and does not have a clear origin. Both effective horizontal diffusivity, Îșh, and effective diapycnal diffusivity, Îșv, are elevated relative to the diffusion coefficients set in the numerical simulation, but changes in Îșh and Îșv with depth are not sufficient to explain the observed layering of thermohaline structure.We gratefully acknowledge funding from the Gordon
and Betty Moore Foundation, the Coastal Ocean Currents Monitoring
Project (COCMP), and NOAA. R. E. Todd was partially supported by the Postdoctoral
Scholar Program at the Woods Hole Oceanographic Institution,
with funding provided by the Cooperative Institute for the North Atlantic
Region.2012-08-0
CS22964-161: A Double-Lined Carbon- and s-Process-Enhanced Metal-Poor Binary Star
A detailed high-resolution spectroscopic analysis is presented for the
carbon-rich low metallicity Galactic halo object CS 22964-161. We have
discovered that CS 22964-161 is a double-lined spectroscopic binary, and have
derived accurate orbital components for the system. From a model atmosphere
analysis we show that both components are near the metal-poor main-sequence
turnoff. Both stars are very enriched in carbon and in neutron-capture elements
that can be created in the s-process, including lead. The primary star also
possesses an abundance of lithium close to the value of the ``Spite-Plateau''.
The simplest interpretation is that the binary members seen today were the
recipients of these anomalous abundances from a third star that was losing mass
as part of its AGB evolution. We compare the observed CS 22964-161 abundance
set with nucleosynthesis predictions of AGB stars, and discuss issues of
envelope stability in the observed stars under mass transfer conditions, and
consider the dynamical stability of the alleged original triple star. Finally,
we consider the circumstances that permit survival of lithium, whatever its
origin, in the spectrum of this extraordinary system.Comment: manuscript, 7 tables, 13 figures. ApJ, in pres
The spatial distribution and annual cycle of upper ocean thermohaline structure
Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C02027, doi:10.1029/2011JC007033.Observations of the spatial distribution and persistence of thermohaline structure are presented, and show how advection and diffusion affect a passive tracer. More than two years of underwater glider observations in the central subtropical North Pacific showed thermohaline variability over horizontal scales from 5 to 1300 km. Thermohaline fluctuations along isopycnals (spice fluctuations) were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions. Fluctuations were uncorrelated between the layers but stirred by the same velocity field. Spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses. Spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated. Horizontal wave number spectra of spice had slopes of â2 everywhere in the upper 1000 m. Submesoscale spice fluctuations had slopes in physical space near the ratio of the Coriolis parameter to the buoyancy frequency (f/N), consistent with predictions of quasi-geostrophic theory. In the mixed layer, thermohaline structure had a significant annual cycle with smaller interannual differences. Thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals. Horizontal diffusivity estimates in the remnant mixed layer were 0.4 m2 sâ1 at 15â28 km wavelengths and 0.9 m2 sâ1 at 35â45 km wavelengths.We gratefully acknowledge the National
Science Foundation for funding this work under grant number OCE0452574.2012-08-1
- âŠ