Impact of interstitial air holes on a wide-bandwidth rejection filter made from a photonic crystal fiber

We have investigated the spectral properties of a band rejection filter made with a long-period fiber grating written in photonic crystal fiber that has interstitial air holes. Experiments showed that only one mode was coupled strongly to the fundamental core mode over a 600 nm spectral range. The central wavelength of the filter could be tuned over that range without being appreciably affected by any other mode. By using the multipole method, we found that the interstitial air holes of the photonic crystal fiber played a critical role in limiting the number of modes that could strongly interact with the fundamental mode and in obtaining well-separated resonance peaks. Excellent agreement between theory and experiment was obtained.     

Interaction of nonlinearity and polarization mode dispersion

The derivation of the coupled nonlinear Schrödinger equation and the Manakov-PMD equation is reviewed. It is shown that the usual scalar nonlinear Schrödinger equation can be derived from the Manakov-PMD equation when polarization mode dispersion is negligible and the signal is initially in a single polarization state as a function of time. Applications of the Manakov-PMD equation to studies of the interaction of the Kerr nonlinearity with polarization mode dispersion are then discussed.     

Micron-sized atom traps made from magneto-optical thin films

We have produced magnetic patterns suitable for trapping and manipulating neutral atoms on a 1-m length scale. The required patterns are made in Co/Pt thin films on a silicon substrate, using the heat from a focused laser beam to induce controlled domain reversal. In this way we draw lines and paint shaped areas of reversed magnetisation with sub-micron resolution. These structures produce magnetic microtraps above the surface that are suitable for holding rubidium atoms with trap frequencies as high as 1 MHz. PACS 39.25.+k; 03.75.Be; 75.50.Ss; 75.70.-i     

Ideal cylindrical cloak: perfect but sensitive to tiny perturbations

A cylindrical wave expansion method is developed to obtain the scattering field for an ideal two-dimensional cylindrical invisibility cloak. A near-ideal model of the invisibility cloak is set up to solve the boundary problem at the inner boundary of the cloak shell. We confirm that a cloak with the ideal material parameters is a perfect invisibility cloak by systematically studying the change of the scattering coefficients from the near-ideal case to the ideal one. However, because of the slow convergence of the zeroth-order scattering coefficients, a tiny perturbation on the cloak would induce a noticeable field scattering and penetration.     

Crystallization of the $${\text{Mn}}^{{\text{II}}}[12{\text{-MC}}_{{\text{Mn}}^{{\text{III}}}{\text{(N)shi}}}{\text{-}}4]^{2+}$$ Mn II [ 12 -MC Mn III (N)shi - 4 ] 2 + Structure with 1,2,4-Triazolate from Methanol

Journal of Chemical Crystallography - The metallacrown (MC) dimer complex {MnII(OAc)(1,2,4-trz) $$[12{\text{-MC}}_{{\text{Mn}}^{{\text{III}}}{\text{(N)shi}}}{\text{-}}4]$$...     

Cyclotomic factors of Coxeter polynomials

In this paper we show that the cyclotomic factors of the En Coxeter polynomials depend only on the value of nmod360, and come exclusively from spherical subdiagrams.     

Stoichiometric determination of moisture in edible oils by Mid-FTIR spectroscopy

A simple and accurate method for the determination of moisture in edible oils by differential FTIR spectroscopy has been devised based on the stoichiometric reaction of the moisture in oil with toluenesulfonyl isocyanate (TSI) to produce CO₂. Calibration standards were devised by gravimetrically spiking dry dioxane with water, followed by the addition of neat TSI and examination of the differential spectra relative to the dry dioxane. In the method, CO₂ peak area changes are measured at 2335 cm⁻¹ and were shown to be related to the amount of moisture added, with any CO₂ inherent to residual moisture in the dry dioxane subtracted ratioed out. CO₂ volatility issues were determined to be minimal, with the overall SD of dioxane calibrations being ∼18 ppm over a range of 0–1000 ppm. Gravimetrically blended dry and water-saturated oils analysed in a similar manner produced linear CO₂ responses with SD's of <15 ppm on average. One set of dry–wet blends was analysed in duplicate by FTIR and by two independent laboratories using coulometric Karl Fischer (KF) procedures. All 3 methods produced highly linear moisture relationships with SD's of 7, 16 and 28 ppm, respectively over a range of 200–1500 ppm. Although the absolute moisture values obtained by each method did not exactly coincide, each tracked the expected moisture changes proportionately. The FTIR_TSI-H2O method provides a simple and accurate instrumental means of determining moisture in oils rivaling the accuracy and specificity of standard KF procedures and has the potential to be automated. It could also be applied to other hydrophobic matrices and possibly evolve into a more generalized method, if combined with polar aprotic solvent extraction.     

The Crystal and Molecular Structure of Bis(cyclopentadienyldicarbonylchromium) (CrCr)

The crystal structure of bis(cyclopentadienyldicarbonyl-chromium) has been determined by x-ray diffraction. The compound crystalizes in the triclinic system, space group P1¯(C¹_i, No. 2) with unit cell parameters: a, 7.829(3); b, 14.543(6); c, 6.588(2)Å; α, 94.67(3), β, 110.70(3); γ, 104.04°(3); V, 699.1(4)ų; z=2. There are two independent molecules per unit cell located at the inversion centers at O,O,O and O, 1/2, O. The CrCr bond distances are, respectively 2.200(3) and 2.230(3), thus supporting their formulation as triple bonds. The CpCrCr angles in the two molecules are 165.0° and 158.7°, respectively. The structural features are compared with those of Cp₂Mo₂(CO)₄, which has a linear CpMoMoCp axis; and the differences rationalized in terms of electronic interactions of the Cp-ligand with the orbitals of the M₂ unit. The differences observed in the structures of the two independent molecules are also related to the proposed bonding model and to packing considerations.