Fiber torsion sensor demodulated by a high-birefringence fiber Bragg grating

A new high-birefringence (Hi-Bi) fiber torsion sensor demodulated by a Hi-Bi fiber Bragg grating (FBG) is proposed in this study. The twisted Hi-Bi fiber sensor characteristics are analyzed using the Jones matrix. The intensity ratio from two reflected Bragg wavelengths is associated with the twist angle of the measured Hi-Bi fiber. It is found that the twist angle resolution is estimated at around 0.3° under ±0.1 dB readout from an optical spectrum analyzer if the polarization state of the light source is stable. The advantages of this new torsion sensor are: (1) insensitivity to intensity variations from the light source, (2) insensitivity to the torsion gauge length, and (3) absolute measurement in the twist angle. However, the polarization state of light in the proposed method needs to be controlled, and any birefringence change in the twisted Hi-Bi fiber needs to be prevented.     

X-Ray Structure and Proton NMR Study of a Hexacoordinated Lithium Complex

The structure of the lithium complex with1,3,5-tris[oxymethylene(N,N-dicyclohexyl)carboxyamido]cyclohexanehas been determined by the X-ray method.The compound is triclinic, space group P¯1,a = 15.623(3), b = 19.279(4),c = 19.295(4)Å = 102.32(3), = 92.45(3), = 105.67(3)0, V = 5436(2)Å3, Z = 4. Itscomposition is represented by the formulaC48H82N3O6LiI 0.5H2O. The lithium cationis encapsulated in a polar pseudo-cavity of six oxygen atoms of the ligandmolecule and displays a distorted trigonal prism coordination. The conformationof the ligand in the solid state complex has been compared with the conformationof the complex in solution determined by 1H-NMR measurements.Supplementary data relevant to this publication have been deposited with the British Library, No. SUP 82224 (21 pages).     

High‐efficiency polymer solar cells based on phenylenevinylene copolymer with BF2‐azopyrrole complex and CN‐PC70BM with solvent additive

Power conversion efficiency (PCE) of phenylenevinylene‐based copolymer with BF₂ azopyrrole complex (PB)/modified PC₇₀BM, that is, CN‐PC₇₀BM bulk heterojunction solar cells improves from 2.16 to 4.90% using a processing additive and drying condition. The results demonstrate that a processing additive and drying condition provides an effective means to control both the surface roughness and finer interpenetrating networks to enhance the exciton dissociation into free charge carriers, charge transportation, and collection. Taking into the account of simple device fabrication process without thermal annealing, the PCE of the polymer solar cell can further improved by chloronapthalene (CN) additive under the fast drying condition. The average carrier lifetimes extracted from the impedance spectra and found to correlate with measured PCEs. At short circuit conditions and illumination, the average charge carrier lifetime was found vary from 16.8 to 32 μs with power conversion efficiencies ranging from 3.0 to 4.9%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Stability and integrity of mechanical joints in flight vehicles: Local and global energy density

A methodology is presented for analyzing the inlfuence of mechanical joint failure on the global instability of flight vehicles. Considered are the ways with which loading, geometry and material of the vehicle can affect the structure instability and/or integrity. The peaks and valleys of the volume energy density function are assumed to coincide with failure by fracture and/or yielding while the distance between their local and global stationary values govern the structure instability. A single length parameter l can thus be applied to provide a measure of stability. The simultaneous occurrence of high energy density and large l at the same location should be avoided as it may have undesirable consequences.A flight vehicle consisting of four cylindrical shell-like structures connected by three tongue-and-groove joints is analyzed. The time-dependent load can be axisymmetric or non-axisymmetric. A semi-analytical finite element program is developed and used to solve for the transient stress and strain distribution from which contours of the volume energy density in the structure are obtained as a function of time. The magnitudes and locations of their local and global stationary values are then calculated and discussed in connection with potential failure by fracture. Stability behavior does not alter appreciably for axisymmetric flight. Considerable fluctuations in the energy density and the dynamic stability length parameter are found when non-axisymmetric loads are considered.     

Experimental results on neutrino-electron scattering

A determination of sin² θ _w based on measurements of elastic scattering of muon-neutrinos and muon-anti-neutrinos on atomic electrons is described. These purely leptonic processes were studied using the CHARM calorimeter exposed to neutrino and antineutrino wide-band beams at the CERN super proton synchrotron. A total of 83±16 neutrino-electron and 112±21 antineutrino-electron events have been detected. From the measurement of the ratio of muon-neutrino and muon-antineutrino cross-sections a value of sin² θ _w =0.211±0.037 was obtained.     

Truncation rules for modelling discontinuities with Galerkin method in electromagnetic theory

It is well known that apparently similar discretization schemes of Maxwell's equations in Fourier series may provide very different convergence performances because of truncation. We argue that this work performed in grating theory can be applied to other electromagnetic theories relying on expansions over series different from Fourier series. This generalization is supported by an intuitive argument and by a simple numerical example with Hermite–Gauss functions.     

Failure initiation sites and instability of structural components with localized energy density

When the surface or interior of a solid undergoes curvature and/or material change, there results localized fluctuation of the energy density field depending on the type of loading. These fluctuations are related to changes in the distortion and dilatation of material elements that could lead to failure by yielding and/or fracture should their magnitude become sufficiently large. According to the strain energy density criterion, failure is assumed to initiate at site of local maximum of minimum strain energy density denoted by [(dW/dV)_min^max]_L and tends toward the global maximum of [(dW/dV)_min^max]_G. The distance l between these two stationary values of dW/dV at L and G provides an indication of failure instability. That is, large l corresponds to more wide spread failure while the opposite holds for small l.Specimens with three different geometries are analyzed; they consist of round shoulder, hole and edge notch. The loads are either bending or tension. As the severity of notch or hole curvature is varied, predicted failure path also altered from boundary to boundary or an interior point of the specimen. The narrowest section turns out to be most vulnerable. If the hole is filled with a material of higher modulus, it acts as a reinforcer such that failure site would be shifted away from the interface. In general, there prevails a trade off between l and [(dW/dV)_min^max]_L. The undesirable combination would be for l and [(dW/dV)_min^max]_L to increase simultaneously. Failure initiation and global instability would then likely occur in tandem. This corresponds to the bending of a specimen with round shoulders. A variety of other conditions are analyzed with results displayed graphically so that the ways with which load, geometry and material inhomogeneity affect the failure behavior of structural components with notches and holes could be better understood.     

Stress singularities near the apex of a cylindrically polarized piezoelectric wedge

Summary In this paper, the stress singularities for a cylindrically polarized piezoelectric wedge are investigated. The characteristic equations are derived analytically by using the extended Lekhnitskii formulation. The piezoelectric material (PZT-4) is polarized in the radial, circular or axial direction, respectively. Similar to the rectilinearly polarized piezoelectric problem, the inplane and antiplane stress fields are uncoupled. The results show the variations of the singularity orders with the changes of the wedge angle, material constants, polarized direction, and the boundary conditions.     

Transport with a Very Low Density Contrast in Hele–Shaw Cell and Porous Medium: Evolution of the Mixing Zone

The optimal concentration of a blue dye solution with 'tracer' properties, enabling a pollutant to be marked was determined by the use of numerical, theoretical and experimental approaches. Experimental investigations were performed on a transparent Hele–Shaw cell and the concentration distribution was analyzed using an optical technique based on dye light absorption properties. The injected optimal concentration was established thanks to a theoretical and experimental study carried out on the output signal dynamics. Using the same experimental conditions, numerical simulations were performed. The very good agreement between the data (experimental and numerical) clarified that: (i) the choice of the blue dye optimal concentration was valid and (ii) the concentration-dependent density should not be neglected in flow and transport equations even if it concerns a so-called 'tracer'. Following this remark, a theoretical aspect was developed in order to determine the analogous conditions between a Hele–Shaw cell and a porous medium for the variable density transport phenomenon. The structure of the concentration-dependent dispersion tensor used in the numerical code was obtained by homogenizing the Stokes flow of a bi-component mixture. The numerical results show that, as long as the tracer density does not exceed a certain value, it is not necessary to take into account a density contrast in terms of the dispersion tensor. The classical form of the Taylor dispersion tensor can be used successfully.