Plastic slip distribution in two-phase laminate microstructures: Dislocation-based versus generalized-continuum approaches

The size-dependent mechanical response of a simple model microstructure is investigated using continuum dislocation-based, Cosserat and strain-gradient models of crystal plasticity. The governing equations and closed-form analytical solutions for plastic slip and lattice rotation are directly compared. The microstructure consists of a periodic succession of hard (elastic) and soft (elastoplastic single-crystal) layers, subjected to single glide perpendicular to the layers. In the dislocation-based approach, inhomogeneous plastic deformation and lattice rotation are shown to develop in the soft channels, either because of bowing of dislocations or owing to pile-up formation. The generalized continuum non-local models are found to be able to reproduce the plastic slip and lattice rotation distribution. In particular, a correspondence was found between the generalized-continuum results and line tension effects; the additional or higher- order balance equations introduced in the non-local models turn out to be the counterparts of the equilibrium equation for bowed dislocations. The relevance and possible physical interpretation of additional or higher-order interface conditions responsible for the inhomogeneous distribution of plastic slip and lattice rotations are discussed.     

Simultaneous excitation of long and short range surface plasmons in an asymmetric structure

An asymmetric multilayer structure allowing nearly 100% simultaneous excitation of both symmetric and antisymmetric surface plasmons is proposed. It is shown that the two surface plasmons can be excited at a fixed angle of incidence with polychromatic light or with monochromatic light at different angles of incidence, depending on the design. The structure can be of interest in high-performance surface plasmon resonance sensing and in all-optical signal processing.     

Coupling to circularly asymmetric modes via long-period gratings made in a standard straight fiber

We demonstrate long-period fiber gratings made in a straight standard optical fiber via a CO₂ laser side irradiation that couples light between modes of different azimuthal symmetry. We show that such coupling can be even stronger than that to the azimuthally symmetric modes, provided the photoinduced asymmetry in the refractive index change across the fiber cross-section is high enough. This suggests that some previously-observed phenomena with CO₂-written LPGs not observed with other types of LPGs may be attributed to LPG resonances that couple light into the cladding modes with higher azimuthal symmetry. We show it on an example of bend-induced LPG resonance position tuning with the resonance depth maintained constant.     

Dislocation-based modeling of size effects in microscale plasticity

A continuum dislocation-based model for the size-dependent plastic deformation at the microscale is presented. An outlook to its application to the single-slip bending of a thin strip is given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

High-resolution microwave frequency transfer over an 86-km-long optical fiber network using a mode-locked laser

We demonstrate the transfer of an ultrastable microwave frequency by transmitting a 30-nm-wide optical frequency comb from a mode-locked laser over 86?km of installed optical fiber. The pulse train is returned to the transmitter via the same fiber for compensation of environmentally induced optical path length changes. The fractional transfer stability measured at the remote end reaches 4×10(-17) after 1600?s, corresponding to a timing jitter of 64?fs.     

Xenon(II) Polyfluoridotitanates(IV): Synthesis and Structural Characterization of [Xe2F3]+ and [XeF]+ Salts

Thermal reaction between XeF₂ and excess TiF₄ resulted in the unexpected formation of a highly ionized Xe^II species. The products [Xe₂F₃][Ti₈F₃₃] and [XeF]₂[Ti₉F₃₈] represent the first examples of [Xe₂F₃]⁺ and [XeF]⁺ compounds, which differ from known Xe^II salts containing discrete fluoride anions with pentavalent metalloid/metal centers. A new structural type of 2D polyanion [Ti₈F₃₃]^? and the formation and structure of the novel 1D [Ti₉F₃₈]^2? are discussed. Both products were characterized by single‐crystal X‐ray analysis and Raman spectroscopy.     

Energy driven crack propagation at finite strains based on the embedded strong discontinuity approach

New advances in three-dimensional finite element modeling of crack propagation at finite strains are presented. The proposed numerical model is based on the Enhanced Assumed Strain concept. The enhanced part of the deformation gradient is associated with a displacement discontinuity. In contrast to previous works, a new, energy based criterion for crack propagation is presented. The necessity for a tracking algorithm for the crack path is avoided by using more than one discontinuity within each finite element. This leads to a strictly local formulation, i.e., no information about the neighboring elements are required. Further advantages of such a formulation are a symmetric tangent stiffness matrix and the reduction of locking effects. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Design of terahertz-bandwidth arbitrary-order temporal differentiators based on long-period fiber gratings

We show that long-period fiber grating (LPG) incorporating N-1pi-phase shifts can serve as an Nth order temporal differentiator that operates in transmission. Due to the inherent large bandwidth provided by LPGs, subpicosecond (terahertz-bandwidth) optical signals may be processed with centimeters-length devices. Design parameters for up to fifth-order differentiators are given.