Wet-etch optimization of free-standing terahertz frequency-selective structures

Free-standing frequency-selective surfaces consisting of approximately 10-microm-thick copper films with cross-aperture arrays are found to be tunable toward lower frequencies by means of wet chemical etching. Center frequencies were tuned from 1.57 to 1.53 THz while maintaining high transmittance. Wet etching also adjusts bandwidth, peak transmittance, and sidelobe transmittance. The advantage of the wet-etch technique is demonstrated by employment of these devices as bandpass filters for difluoromethane-based terahertz lasers. Adjustment in aperture dimensions because of etching results in suppression of a competing laser line (133.93 microm) by 15 dB while maintaining high transmittance at the operating wavelength of 192.06 microm.     

Kink band propagation in layered structures

Confined layered structures in layer-parallel compression exhibit kink band deformation that has an associated severe initial instability. However, once the first kink band forms the system restabilizes and the bands then propagate in two mechanisms: band broadening and band progression. Previous work on triggering the initial instability and band broadening is now extended to include band progression. A new model for this propagation mechanism that successfully accounts for the modulating restabilizing response is presented and quantitative comparisons with the physical experiments yield excellent results.     

Parallel folding in multilayered structures

A recent two-layer nonlinear model for parallel folding is extended to a full multilayer formulation for n identical layers. The general behaviour of the multilayer is characterized using a sinusoidal Galerkin approximation substituted into the linearized potential energy function and equations for the wavelength and critical load are found. Comparisons with experiments conducted on layers of paper constrained between two sheets of foam rubber show that the trend of the load-amplitude plots is in good agreement with that predicted. Excellent correlation is also achieved between the wavelengths calculated by the linearized buckling analysis and those seen experimentally.     

Cellular Buckling in Long Structures

A long structural system with an unstable (subcritical)post-buckling response that subsequently restabilizes typically deformsin a cellular manner, with localized buckles first forming and thenlocking up in sequence. As buckling continues over a growing number ofcells, the response can be described by a set of lengthening homoclinicconnections from the fundamental equilibrium state to itself. In thelimit, this leads to a heteroclinic connection from the fundamentalunbuckled state to a post-buckled state that is periodic. Under suchprogressive displacement the load tends to oscillate between twodistinct values.The paper is both a review and a pointer tofuture research. The response is described via a typical system, asimple but ubiquitous model of a strut on a foundation which includesinitially-destabilizing and finally-restabilizing nonlinear terms. Anumber of different structural forms, including the axially-compressedcylindrical shell, a typical sandwich structure, a model of geologicalfolding and a simple link model are shown to display such behaviour. Amathematical variational argument is outlined for determining the globalminimum postbuckling state under controlled end displacement (rigidloading). Finally, the paper stresses the practical significance of aMaxwell-load instability criterion for such systems. This criterion,defined under dead loading to be where the pre-buckled and post-buckledstate have the same energy, is shown to have significance in the presentsetting under rigid loading also. Specifically, the Maxwell load isargued to be the limit of minimum energy localized solutions asend-shortening tends to infinity.     

Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber

Saturated absorption spectroscopy is performed on the acetylene nu(1) + nu(3) band near 1532 nm inside photonic bandgap fibers of small (approximately 10 microm) and large (approximately 20 microm) core diameters. The observed linewidths are narrower in the 20 microm fiber and vary from 20 to 40 MHz depending on pressure and power. Variations in the background light transmission, attributed by others to surface modes, are significantly reduced in the 20 microm fiber. The optimum signal for use as a frequency reference in a 0.8 m long, 20 microm diameter fiber is found to occur at about 0.5 torr for 30 mW of pump power. The saturation power is found by modeling the propagation and attenuation of light inside the fiber.     

Effects of orthotropy and variation of Poisson's ratio on the behaviour of tubes in pure flexure

The behaviour of tubes under conditions of pure bending is investigated for the cases where the material of which they are constructed is either orthotropic or of various Poisson's ratios. Large deflections and moderate nonlinear strains are considered and the modelling incorporates Timoshenko beam theory thereby allowing non-zero shear strains to develop. This in turn makes axially inhomogeneous deformation of the cross-section possible and, in particular, the compressed side can develop wrinkling. Numerical solutions are presented for various material types and tube dimensions and some interesting phenomena, such as mode interaction and jumping, are demonstrated.     

Computational analysis of entropy generation in mixed convection flow past a vertical wavy cone

Journal of Thermal Analysis and Calorimetry - The problem of entropy generation in mixed convection flow of incompressible viscous fluid along an isothermal vertical wavy cone is investigated...     

Lie group analysis of viscoelastic MHD aligned flow and heat transfer

Exact solutions for an incompressible, viscoelastic, electrically conducting MHD aligned fluid are obtained for velocity components and temperature profiles. Lie Group method is applied to obtain the solution and the symmetries used are of translational type.The English text was polished by Keren Wang and Yunming Chen.     

Applications of thin-layer chromatography and thin-layer electrophoresis in the analysis of inorganic anions: a review

JPC – Journal of Planar Chromatography – Modern TLC - This review is intended to highlight various applications of thin-layer chromatography (TLC) and thin-layer electrophoresis (TLE)...     

Development and applications of deep eutectic solvents in different chromatographic techniques

JPC – Journal of Planar Chromatography – Modern TLC - Deep eutectic solvents (DESs) being inexpensive, easy to prepare, biocompatible, biodegradable and environmentally benign have...