Study of band structure of one-dimensional photonic crystal composed of dispersive and nonlinear dielectric materials

The analysis of band structure of one-dimensional (1-D) photonic crystal containing dispersive and non-linear dispersive materials has been presented. The band spectra for the different combination of photonic crystals have been calculated by the well-known plane wave expansion method. The effect of the dispersive and non-linear materials on the band structures has been determined. The third-order nonlinearity has been considered in the non-linear material, and Lorentz–Drude model has been taken for dispersive material. The band gaps of considered photonic crystal are affected by the nonlinearity in the presence of dispersive material like gold. We have observed that the normalized frequency difference between photonic bands decreases on increasing intensity of input beam. This work may be useful in optical switching devices.     

Finite element modelling of lamb waves propagation in 2D plates and thin sheets for damage detection

Structural health monitoring is an evolving technology applied to identify, locate and quantify severity of damages in structures before failure. Lamb waves have become a keen interest for inspection since they can be used to monitor a large area from one single location. The objective of this research is to simulate lamb wave response using finite element method and its application to crack detection and identification in thin metallic engineering structures. Two types of specimen i. e. two‐dimensional aluminium plate and thin aluminium sheets are simulated using commercially available finite element package ABAQUS. Initially phase velocity and group velocity dispersion curve are plotted for aluminium material. Thereafter simulation of individual specimens with cracks and without cracks is performed. Simulation results were compared and validated with actual results and were found to be in reasonably good agreement. This is certainly done by employing group velocity and time of flight for the distance travelled between the monitoring point and crack position. Assessment of lamb waves sensitivity to various sizes and shapes of cracks like rectangular and circular are also investigated and its effect on the structure is discussed in detail.     

Phosphate fertilization in intensive annual cropping with wheatgreen gram (or cowpea) — pearl millet

In a four year study on a wheat-green gram (or cowpea) — pearl millet intensive cropping system a total production of 9–10 tonnes of wheat equivalents per year removed 29–30kg P ha^–1. If only 26 kg P ha^–1 was used then total grain production as well as P uptake, was highest when all the P was applied to wheat. Only when amounts larger than 26 kg P ha^–1 were applied was it justified to apply P to pearl millet and green gram (or cowpea). Productivity of the cropping system increased up to 58.5 kg P ha^–1 and at this level two thirds of P was applied to wheat, while pearl millet and green gram or cowpea received the remaining one-third. A positive P balance in soil was observed only when 26 k P ha^–1 yr^–1 or more was applied.Pressure of growing population and per capita diminution or arable land has focussed attention on multiple cropping systems in many Asian countries [1, 2]. In North-Western India the cropping system changed from a single rainy (July–October) or winter (November–April) crop a year prior to the 1960's to two-crops-a-year (both a rainy season and winter crop) in the 1970.s and then in the late 1970's a third summer (May–June) crop was also included. Wheat — green gram (or cowpea) — pearl millet is such a three-crops-a-year multiple cropping system.Phosphate is the costliest major plant nutrient in India and farmers following multiple cropping systems are keen to know the way the phosphate should be apportioned to different crops in a cropping system particularly when small amounts of P are applied. Such information can come only from long-term P fertilization experiments [3, 4]. The objective of the present experiment on a wheat-green gram (or cowpea) — pearl millet multiple cropping system was to study the direct and residual effects of P applied to one crop on the other crops grown in succession and to find the best possible way in which a limited amount of P could be apportioned between the different crops in the rotation. An attempt has also been made to work out the P balance in soil.     

Influence of carding and drawing processes on orientation of fibers in slivers

The orientation of fibers is known to play a very important role in determining the quality of the carded and drawn slivers as well as the quality of the ultimate yarns produced from those slivers. Also, the orientation of fibers is considered to be a very useful parameter for evaluating the effectiveness of the carding and drawing processes in aligning the fibers. In addition, the orientation of fibers is known to determine the length utilization of the fibers in the slivers. This article reports on the influence of carding and drawing processes on the orientation of fibers in the carded and drawn slivers. A series of carded and drawn slivers were prepared by using polyester staple fibers and making various changes in the carding and drawing processes and the orientation of fibers in the slivers was evaluated based on Lindsley’s methodology in conjunction with a mathematical model of fiber orientation in slivers. It was observed that the increase in cylinder speed and the decrease in doffer speed resulted in more anisotropic fiber orientation distribution in the carded slivers and the degree of anisotropy was found to be more in the forward direction as compared to the backward direction of the carded slivers. The higher draft and doubling in the drawframe resulted in higher anisotropy in the orientation of fibers in the drawn slivers and the drawn slivers displayed more anisotropy in the backward direction as compared to the forward direction. The higher delivery speed of the drawframe resulted in higher anisotropy in fiber orientation in the drawn slivers and the drawn slivers exhibited more anisotropy in the backward direction as compared to the forward direction. The results of fiber orientation in the carded and drawn slivers obtained by using the mathematical model were compared to the fiber orientation parameters suggested by earlier researchers and a satisfactory correlation between them was observed.     

Catalytic effect of carbon nanostructures on the hydrogen storage properties of MgH2–NaAlH4 composite

The present investigation describes the hydrogen storage properties of 2:1 molar ratio of MgH₂–NaAlH₄ composite. De/rehydrogenation study reveals that MgH₂–NaAlH₄ composite offers beneficial hydrogen storage characteristics as compared to pristine NaAlH₄ and MgH₂. To investigate the effect of carbon nanostructures (CNS) on the de/rehydrogenation behavior of MgH₂–NaAlH₄ composite, we have employed 2 wt.% CNS namely, single wall carbon nanotubes (SWCNT) and graphene nano sheets (GNS). It is found that the hydrogen storage behavior of composite gets improved by the addition of 2 wt.% CNS. In particular, catalytic effect of GNS + SWCNT improves the hydrogen storage behavior and cyclability of the composite. De/rehydrogenation experiments performed up to six cycles show loss of 1.50 wt.% and 0.84 wt.% hydrogen capacity in MgH₂–NaAlH₄ catalyzed with 2 wt.% SWCNT and 2 wt.% GNS respectively. On the other hand, the loss of hydrogen capacity after six rehydrogenation cycles in GNS + SWCNT (1.5 + 0.5) wt.% catalyzed MgH₂–NaAlH₄ is diminished to 0.45 wt.%.