Photoelastic studies of advanced lap joint concept

Photoelasticity was introduced as a quantitative tool in the experimental stress analysis of anisotropic birefringent composite model materials. The investigation was divided into three parts: (1) separation of principal stresses or strains, (2) photoelastic calibration, and (3) development of model-prototype relations

Determination of principal stress in birefringent composites by hole-drilling method

The application of transmission photoelasticity to stress analysis of composite materials is discussed.The method consists in drilling very small holes at points where the state of stress has to be determined. Experiments are described which verify the theoretical predicitons. The limitations of the method are discussed and it is concluded that valuable information concerning the state of stress in a composite model can be obtained through the suggested method

Development of the Magnetic Excitations of Charge-Stripe Ordered La(2-x)Sr(x)NiO(4) on Doping Towards Checkerboard Charge Order

The magnetic excitation spectrums of charge stripe ordered La(2-x)Sr(x)NiO(4) x = 0.45 and x = 0.4 were studied by inelastic neutron scattering. We found the magnetic excitation spectrum of x = 0.45 from the ordered Ni^2+ S = 1 spins to match that of checkerboard charge ordered La(1.5)Sr(0.5)NiO(4). The distinctive asymmetry in the magnetic excitations above 40 meV was observed for both doping levels, but an additional ferromagnetic mode was observed in x = 0.45 and not in the x = 0.4. We discuss the origin of crossover in the excitation spectrum between x = 0.45 and x = 0.4 with respect to discommensurations in the charge stripe structure.Comment: 4 Figures. To be appear in the J. Kor. Phys. Soc. as a proceedings paper from the ICM 2012 conferenc

Linear and Nonlinear Optical Properties of Mn doped Benzimidazole Thin Films

In the present work, the Mn doped benzimidazole (BMZ) thin films were prepared by simple chemical bath deposition technique. The material was directly deposited as thin film on glass substrates and the metal concentration in the solution was varied in weight percentage in order to investigate the dopant effect on the properties of thin films. Similarly, the Mn doped BMZ films were deposited in different solution temperature to study the effect of deposition temperature on the properties of thin films. The PXRD and FT-IR spectroscopy are used to study the structural and the presence of functional groups in the BMZ medium. Depending upon the solution temperature, thickness of the films varying from 0.6 to 1.2 {\mu}m and the optical transparency of the samples increases with the increasing temperature up to 50 {\deg}C. Second Harmonic Generation (SHG) efficiency of the films is measured for all the films. Third order nonlinear optical properties of the films were analyzed using Z-scan technique. The experimental results show that Mn doped BMZ films exhibits saturation absorption and negative nonlinearity.Comment: This has been presented in DAE 58th Solid State Symposium held at Thapar University, Patiala, Punjab, India. Will be published in AIP conference proceedings soo

Development of computer program NAS3D using Vector processing for geometric nonlinear analysis of structures

An algorithm for vectorized computation of stiffness matrices of an 8 noded isoparametric hexahedron element for geometric nonlinear analysis was developed. This was used in conjunction with the earlier 2-D program GAMNAS to develop the new program NAS3D for geometric nonlinear analysis. A conventional, modified Newton-Raphson process is used for the nonlinear analysis. New schemes for the computation of stiffness and strain energy release rates is presented. The organization the program is explained and some results on four sample problems are given. The study of CPU times showed that savings by a factor of 11 to 13 were achieved when vectorized computation was used for the stiffness instead of the conventional scalar one. Finally, the scheme of inputting data is explained

High temperature onset of field-induced transitions in the spin-ice compound Dy2Ti2O7

We have studied the field-dependent ac magnetic susceptibility of single crystals of Dy2Ti2O7 spin ice along the [111] direction in the temperature range 1.8 K - 7 K. Our data reflect the onset of local spin ice order in the appearance of different field regimes. In particular, we observe a prominent feature at approximately 1.0 T that is a precursor of the low-temperature metamagnetic transition out of field-induced kagome ice, below which the kinetic constraints imposed by the ice rules manifest themselves in a substantial frequency-dependence of the susceptibility. Despite the relatively high temperatures, our results are consistent with a monopole picture, and they demonstrate that such a picture can give physical insight to the spin ice systems even outside the low-temperature, low-density limit where monopole excitations are well-defined quasiparticles

Polarization memory in the nonpolar magnetic ground state of multiferroic CuFeO2

We investigate polarization memory effects in single-crystal CuFeO2, which has a magnetically-induced ferroelectric phase at low temperatures and applied B fields between 7.5 and 13 T. Following electrical poling of the ferroelectric phase, we find that the nonpolar collinear antiferromagnetic ground state at B = 0 T retains a strong memory of the polarization magnitude and direction, such that upon re-entering the ferroelectric phase a net polarization of comparable magnitude to the initial polarization is recovered in the absence of external bias. This memory effect is very robust: in pulsed-magnetic-field measurements, several pulses into the ferroelectric phase with reverse bias are required to switch the polarization direction, with significant switching only seen after the system is driven out of the ferroelectric phase and ground state either magnetically (by application of B > 13 T) or thermally. The memory effect is also largely insensitive to the magnetoelastic domain composition, since no change in the memory effect is observed for a sample driven into a single-domain state by application of stress in the [1-10] direction. On the basis of Monte Carlo simulations of the ground state spin configurations, we propose that the memory effect is due to the existence of helical domain walls within the nonpolar collinear antiferromagnetic ground state, which would retain the helicity of the polar phase for certain magnetothermal histories.Comment: 9 pages, 7 figure

Structural efficiency studies of corrugated compression panels with curved caps and beaded webs

Curved cross-sectional elements are employed in structural concepts for minimum-mass compression panels. Corrugated panel concepts with curved caps and beaded webs are optimized by using a nonlinear mathematical programming procedure and a rigorous buckling analysis. These panel geometries are shown to have superior structural efficiencies compared with known concepts published in the literature. Fabrication of these efficient corrugation concepts became possible by advances made in the art of superplastically forming of metals. Results of the mass optimization studies of the concepts are presented as structural efficiency charts for axial compression

Multisensory 3D saliency for artficial attention systems

In this paper we present proof-of-concept for a novel solution consisting of a short-term 3D memory for artificial attention systems, loosely inspired in perceptual processes believed to be implemented in the human brain. Our solution supports the implementation of multisensory perception and stimulus-driven processes of attention. For this purpose, it provides (1) knowledge persistence with temporal coherence tackling potential salient regions outside the field of view, via a panoramic, log-spherical inference grid; (2) prediction, by using estimates of local 3D velocity to anticipate the effect of scene dynamics; (3) spatial correspondence between volumetric cells potentially occupied by proto-objects and their corresponding multisensory saliency scores. Visual and auditory signals are processed to extract features that are then filtered by a proto-object segmentation module that employs colour and depth as discriminatory traits. We consider as features, apart from the commonly used colour and intensity contrast, colour bias, the presence of faces, scene dynamics and also loud auditory sources. Combining conspicuity maps derived from these features we obtain a 2D saliency map, which is then processed using the probability of occupancy in the scene to construct the final 3D saliency map as an additional layer of the Bayesian Volumetric Map (BVM) inference grid