Interferometric key readable security holograms with secrete-codes

A new method is described to create secrete-codes in the security holograms for enhancing their anti-counterfeiting characteristics. To imitate these codes is difficult as pure phase objects having complex phase distribution function are used to modulate the object beam that is recorded in conjunction with an encoded interferometric reference beam derived from a key hologram. Lloyd’s folding mirror interferometer is used to convert phase variations of the reconstructed wave-front into an intensity pattern for hologram authenticity verification. Creating the secrete-codes through an interferometric reference beam from the key hologram facilitates a multi-stage authenticity verification as well as easy repositioning of the security hologram through a specific Moiré pattern generated during the verification process.      

ZnSe sintered films: Growth and characterization

The II-VI compound semiconductor, ZnSe having wide band gap between 2.58 and 2.82 eV is a promising material for use in photovoltaic devices, blue light emitting diodes and laser diodes. Several methods have been used to prepare ZnSe thin films. We have deposited ZnSe films on ultra-clean glass substrate by sintering technique. The optical, structural and electrical properties of ZnSe thin films have been examined. The optical band gap of these films is studied using reflection spectra in wavelength range 325-600 nm and structure of these films is studied using XRD. The DC conductivity of the films was measured in vacuum by two-probe technique.Sintering is a very simple and viable method compared to other intensive methods. The results of the present investigation will be useful in characterizing the material ZnSe for its applications in photovoltaics.     

Direct visualization of Young’s boundary diffraction wave

Experimental investigations on Young’s boundary diffraction wave are presented where a wavefront division interferometric scheme is used on diffracted wavefront to generate two-beam interference fringes in the geometrically shadow region. These fringes have good visibility and are observable in the whole space, strongly advocating the physical existence of Young’s boundary diffraction wave as a separate entity. Analysis of these fringes may provide vital information about the structure and nature of boundary diffraction wave e.g. existence in whole space, dependence of amplitude on obliquity factor etc.     

Nonlinear dynamics of planetary gears using analytical and finite element models

Vibration-induced gear noise and dynamic loads remain key concerns in many transmission applications that use planetary gears. Tooth separations at large vibrations introduce nonlinearity in geared systems. The present work examines the complex, nonlinear dynamic behavior of spur planetary gears using two models: (i) a lumped-parameter model, and (ii) a finite element model. The two-dimensional (2D) lumped-parameter model represents the gears as lumped inertias, the gear meshes as nonlinear springs with tooth contact loss and periodically varying stiffness due to changing tooth contact conditions, and the supports as linear springs. The 2D finite element model is developed from a unique finite element-contact analysis solver specialized for gear dynamics. Mesh stiffness variation excitation, corner contact, and gear tooth contact loss are all intrinsically considered in the finite element analysis. The dynamics of planetary gears show a rich spectrum of nonlinear phenomena. Nonlinear jumps, chaotic motions, and period-doubling bifurcations occur when the mesh frequency or any of its higher harmonics are near a natural frequency of the system. Responses from the dynamic analysis using analytical and finite element models are successfully compared qualitatively and quantitatively. These comparisons validate the effectiveness of the lumped-parameter model to simulate the dynamics of planetary gears. Mesh phasing rules to suppress rotational and translational vibrations in planetary gears are valid even when nonlinearity from tooth contact loss occurs. These mesh phasing rules, however, are not valid in the chaotic and period-doubling regions.     

10 Gbps optical soliton transmission link using in-line SOA on standard SMF at 1.3 μm

In this paper, 10 Gbps optical soliton transmission link using in-line semiconductor optical amplifiers (SOAs) for already installed standard single mode fibers (SMF) at 1.3 μm wavelength has been reported. The pattern effect and the impact of chirp on pulse propagation after amplification have been investigated. The observations are based on modeling and simulation optical soliton transmission link. Optical soliton pulse transmission over distances of the order of several hundreds of kilometers has been shown with and without initial chirp.     

Steady-state self-focusing of Gaussian electromagnetic beams in an inhomogeneous nonlinear medium: Effect of absorption and initial curvature of the beam

The authors have investigated the effect of linear absorption and initial curvature of an electromagnetic Gaussian beam on focusing/defocusing in an inhomogeneous nonlinear medium. Numerical computations have been made for linear inhomogeneity and saturating nonlinearity, characteristic of dielectrics and collisional plasmas. The maximum and minimum of the beam width keep decreasing with increase in distance of propagation (or absorption), till the beam becomes very weak and diverges steeply; penetration in an overdense medium also decreases with increasing absorption. Converging beams initially converge and then go in: (i) the oscillatory divergence (ii) self-focusing or (iii) steady divergence mode, depending upon the initial values of beam width and axial irradiance. The maximum penetration in an overdense medium has the highest values for −0.7<(df/dξ)_ξ=0<0.4 and falls sharply, outside these limits.     

Photoluminescence properties of SHI induced F2 and F3 color centers in nano-granular LiF thin films

Photoluminescence (PL) properties of swift heavy ions-induced F₂ and F₃⁺ color centers in nano-granular lithium fluoride (LiF) thin film were studied. LiF films were deposited on glass and silica substrates and irradiated with various ion species (Ag, Ni and Au) at different irradiation temperatures. The role of ion species, their fluence and the irradiation temperature on the PL intensity of color centers induced in LiF thin films is discussed.     

Autoignition of methanol: Experiments and computations

An experimental and computational investigation into the autoignition of methanol under high‐pressure and low‐to‐intermediate temperature conditions is conducted. The ignition delay results have been obtained using a heated rapid compression machine, over a pressure range of 7–30 bar, a temperature range of 850–1100 K, and an equivalence ratio range of 0.25–2.0. Using kinetic schemes recently reported in the literature for the combustion of methanol, the experimental results are compared to computationally obtained values. The kinetic schemes studied are found to significantly underpredict ignition delays for the conditions investigated. A sensitivity analysis of the computed results to reaction rate constants is also conducted. It is shown that the reaction of methanol with HO₂ radical is critical to the predicted values of ignition delays under the current experimental conditions. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 175–184, 2011     

Evaluation of Generic Gradients, Sample Pooling and MS Detection as Chiral Resolution Screening Strategies on Diverse Chiral Stationary Phases

Increased throughput in medicinal chemistry has substantially increased the production of new chiral chemical entities with diverse structural features, requiring fast chiral screening strategies. In an effort to explore screening methods we have developed and evaluated gradients in polar organic and normal phase modes on three popular chiral stationary phases using a sample set of 19 racemic compounds. When compared, gradients performed on par with the isocratic methods besides proving to be advantageous in terms of speed of analysis and elution capacity. MS detection was successfully applied to the analysis of a pooled sample consisting 19 compounds to speed-up the screening process.