10,775 research outputs found
Efficient analysis and design of low-loss whispering-gallery-mode coupled resonator optical waveguide bends
Waveguides composed of electromagnetically-coupled optical microcavities
(coupled resonator optical waveguides or CROWs) can be used for light guiding,
slowing and storage. In this paper, we present a two-dimensional analysis of
finite-size straight and curved CROW sections based on a rigorous Muller
boundary integral equations method. We study mechanisms of the coupling of
whispering gallery (WG) modes and guiding light around bends in CROWs composed
of both identical and size-mismatched microdisk resonators. Our accurate
analysis reveals differences in WG modes coupling in the vicinity of bends in
CROWs composed of optically-large and wavelength-scale microcavities. We
propose and discuss possible ways to design low-loss CROW bends and to reduce
bend losses. These include selecting specific bend angles depending on the
azimuthal order of the WG mode and tuning the radius of the microdisk
positioned at the CROW bend.Comment: 8 pages with 10 figures (to appear in IEEE/OSA J. Lightwave
Technology, 2007
QCD Flux Tubes as Sigma Model Relics
We describe flux tubes and their interactions in a low energy sigma model
induced by SU(\NF) \goto SO(\NF) flavor symmetry breaking in QCD.
Gauge confinement manifests itself in the low energy theory through flux tube
interactions with unscreened sources. The flux tubes which mediate confinement
also illustrate an interesting ambiguity in defining global Alice strings.Comment: 12 pages (REVTEX) plus one figur
Methods development for total organic carbon accountability
This report describes the efforts completed during the contract period beginning November 1, 1990 and ending April 30, 1991. Samples of product hygiene and potable water from WRT 3A were supplied by NASA/MSFC prior to contract award on July 24, 1990. Humidity condensate samples were supplied on August 3, 1990. During the course of this contract chemical analyses were performed on these samples to qualitatively determine specific components comprising, the measured organic carbon concentration. In addition, these samples and known standard solutions were used to identify and develop methodology useful to future comprehensive characterization of similar samples. Standard analyses including pH, conductivity, and total organic carbon (TOC) were conducted. Colorimetric and enzyme linked assays for total protein, bile acid, B-hydroxybutyric acid, methylene blue active substances (MBAS), urea nitrogen, ammonia, and glucose were also performed. Gas chromatographic procedures for non-volatile fatty acids and EPA priority pollutants were also performed. Liquid chromatography was used to screen for non-volatile, water soluble compounds not amenable to GC techniques. Methods development efforts were initiated to separate and quantitate certain chemical classes not classically analyzed in water and wastewater samples. These included carbohydrates, organic acids, and amino acids. Finally, efforts were initiated to identify useful concentration techniques to enhance detection limits and recovery of non-volatile, water soluble compounds
Spreading Disinformation on Facebook: Do Trust in Message Source, Risk Propensity, or Personality Affect the Organic Reach of “Fake News”?
There is considerable concern about the propagation of disinformation through social media, particularly for political purposes. 'Organic reach' has been found to be important in the propagation of disinformation on social networks. This is the phenomenon whereby social media users extend the audience for a piece of information: interacting with it, or sharing it with their wider networks, greatly increases the number of people the information reaches. This project evaluated the extent to which characteristics of the message source (how trustworthy they were) and the recipient (risk propensity and personality) influenced the organic reach of a potentially false message. In an online study, 357 Facebook users completed personality and risk propensity scales, and rated their likelihood of interacting in various ways with a message posted by either a trustworthy or untrustworthy source. Message source impacted on overall organic reach, with messages from trusted sources being more likely to be propagated. Risk propensity did not influence reach. However, low scores on trait agreeableness predicted greater likelihood of interacting with a message. Findings provide preliminary evidence that both message source and recipient characteristics can potentially influence the spread of disinformation
Q-factor and emission pattern control of the WG modes in notched microdisk resonators
Two-dimensional (2-D) boundary integral equation analysis of a notched
circular microdisk resonator is presented. Results obtained provide accurate
description of optical modes, free from the staircasing and discretization
errors of other numerical techniques. Splitting of the double degenerate
Whispering-Gallery (WG) modes and directional light output is demonstrated. The
effect of the notch depth and width on the resonance wavelengths, Q-factors,
and emission patterns is studied. Further improvement of the directionality is
demonstrated in an elliptical notched microdisk. Applications of the notched
resonators to the design of microdisk lasers, oscillators, and biosensors are
discussed.Comment: 7 pages with 11 figures; to appear in IEEE J. Select. Topics Quantum.
Electron., Jan/Feb 200
Spectral shift and Q-change of circular and square-shaped optical microcavity modes due to periodic sidewall surface roughness
Radiation loss and resonant frequency shift due to sidewall surface roughness
of circular and square high-contrast microcavities are estimated and compared
by using a boundary integral equations method. An effect of various harmonic
components of the contour perturbation on the Whispering-Gallery (WG) modes in
the circular microdisk and WG-like modes in the square microcavity is
demonstrated. In both cases, contour deformations that are matched to the mode
field pattern cause the most significant frequency detuning and Q-factor
change. Favorably mode-matched deformations have been found, enabling one to
manipulate the Q-factors of the microcavity modes.Comment: 5 pages with 6 figure
Who provided maize to Chaco Canyon after the mid-12th-century drought?
Between A.D. 1181 and 1200, in the early part of a climatically wet period, corn was imported to Chaco Canyon from a region outside the Chaco Halo (defined in this paper as the region between the base of the Chuska Mountains and RatonWells). Strontium-isotope (87Sr/86Sr) analyses of 12 corn cobs dating to this period match 87Sr/86Sr ratios from five potential source areas, including: the Zuni region, the Mesa Verde-McElmo Dome area, the Totah, the Defiance Plateau, and Lobo Mesa. The latter two areas were eliminated from consideration as possible sources of corn in that they appear to have been unpopulated during the time period of interest. Therefore, it appears that the corn cobs were imported from the Zuni region, the Mesa Verde-McElmo Dome area, or the Totah area during a time when the climate was relatively wet and when a surplus of corn was produced in regions outside Chaco Canyon. Based on proximity to and cultural affiliation with Chaco Canyon, it is hypothesized that the corn probably was imported from the Totah
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