Electromagnetic forward and inverse scattering analysis of a one‐dimensional collision system

A one‐dimensional electromagnetic scattering analysis in presence of a colliding system is presented. A detailed analysis of higher order Doppler effect, due to multiple electromagnetic field reflection upon the two moving objects is performed, invoking the center of momentum frame and taking all possible range of velocity into account. A quasi‐stationary based finite difference time domain numerical method is then performed in order to test the proposed mathematical model for forward scattering analysis. Further, a spectral‐temporal mathematical derivation is performed for the inverse scattering analysis to compute the spatial and temporal information of the target system.     

Quad notch UWB antenna using combination of slots and split‐ring resonator

A novel coplanar waveguide fed UWB antenna with quad notch band characteristics has been proposed in this work. The antenna layout is designed based on a combination of well‐known geometrical shapes: a half ellipse patch, rectangle, and triangle. The shape of the ground plane is partially tapered rectangular. The overall dimension of the antenna is 41.5 × 32 mm. The antenna uses three U‐shaped slots at the top surface to create three notched band characteristics. A split‐ring resonator is then introduced at the bottom surface of the antenna. With the integration of split‐ring resonator at the bottom surface, an additional notch band at 7.25 to 7.75 (6.7%) GHz is created in the antenna. The designed antenna has an operating impedance bandwidth (VSWR ≤2) ranges from 3.03 to 12.34 GHz except in quad frequency stop bands of 3.3 to 3.7 (11.4%), 5.15 to 5.35 (3.8%), 5.725 to 5.825 (1.7%), and 7.25 to 7.75 (6.7%) GHz. The proposed antennas are successfully designed, prototyped, and measured. The simulated and measured results are extensively studied and discussed. Correlation between the time‐domain transmitting antenna input signal and the received antenna output signal is calculated in order to ensure that the proposed antenna can be used in pulse‐communication systems. This antenna finds applications in medical imaging, military radar systems, and other common UWB applications.     

Three-dimensional heat transfer analysis of LENSTM process using finite element method

Laser-engineered net shaping, referred to as LENS^TM process, is an additive manufacturing technique for building metallic parts, layer by layer, by direct deposition of metal powders in a melt pool created by a focused laser beam. The process involves rapid melting and solidification of a controlled amount of injected metal powders as a laser beam scans over each layer building the structure from the bottom to the top. Due to its unique capability to deposit precise amounts of powder material at a desired location, the LENS^TM process finds potential application in rapid tooling, prototyping, precision repair work, and manufacture of complex, intricate components with varying compositions. The peak temperature and thermal cycle experienced by each layer influence the final mechanical properties and dimensional accuracy of the part. An understanding and quantitative knowledge of the peak temperature, melt pool dimensions, and thermal cycles experienced in the deposited layers are essential for a priori selection of the process parameters in LENS^TM technique. It is important to ensure that the deposited layers have the desired dimensions, good interlayer bonding, and requisite mechanical properties. In an attempt to understand the process parameters to be used in achieving the desired nature of deposition, a three-dimensional model is developed based on finite element method to numerically simulate heat transfer phenomenon in LENS^TM process considering deposition of SS316 powders on a substrate of the same material. The computed temperature profiles are first validated with experimental results reported in the literature. The influence of process parameters on peak temperature, thermal cycles, and melt pool dimensions are studied subsequently. The continuous movement of laser and synchronized activation of elements depicting addition of powder particles are incorporated through an externally written user subroutine and using the element deactivation and activation features in the commercial finite element software ABAQUS 6.7. A unique non-dimensional parameter specific to LENS^TM process is defined considering the combined influence of process parameters and material properties. The non-dimensional parameter is further used to serve as a guideline for the selection of appropriate process parameters that can result in a steady melt pool dimension, thereby ensuring a target layer width with good interlayer bonding.     

The Effect of Pitting on Fatigue Lives of Peak-Aged and Overaged 7075 Aluminum Alloys

Fatigue lives at high peak stresses for peak-aged (T6) and overaged (T73) 7075 aluminum alloy were compared in the uncorroded and precorroded (pitted) states. Absolute fatigue lives of T73 samples were much higher than that of T6 in the virgin as well as precorroded condition, but the normalized life of T73 was less than that of T6, indicating an intrinsic crack initiation resistance in the former, borne out by fractography, which showed that fatigue cracks almost always initiated at pits for T73 but not for T6. The various crack initiation methodologies observed and the effect of pitting on fatigue lives in the two aging conditions are discussed.     

Effect of plasma ion implantation on the hydrogen embrittlement of Cu strengthened HSLA-100 steel

The effect of low dosage plasma ion implantation on hydrogen embrittlement was studied for an HSLA steel using notched tensile samples. The plasma treatment caused an enhancement in the linear strain to failure under embrittling conditions. This was however not reflected in the fracture surfaces of the treated samples which had similar fractographic features as those of untreated samples. The plasma treatment delayed the process of embrittlement without causing any alteration in the basic mechanism of embrittlement. This was due to introduction of residual compressive stresses as well as reduction in the hydrogen permeation flux. Implantation in pure nitrogen seemed most beneficial while implantation in pure argon caused very little improvement.     

Electrochemical response of Fe65.5Cr4Mo4Ga4P12 C5B5.5 bulk amorphous alloy in different aqueous media

A bulk amorphous Fe_65.5Cr₄Mo₄Ga₄P₁₂C₅B_5.5 alloy was investigated for its electrochemical behaviour in different electrolytes. The investigations showed substantial differences in response between the rapidly quenched and cast samples of the same composition. Annealing of the cast samples improved their corrosion resistance, which was possibly due to structural relaxation processes. The alloy was found to have very good resistance to neutral and slightly acidic chloride solutions in the rapidly quenched form. The passivation observed could not be attributed to any metal/metalloid oxide and was most probably due to an adsorbed oxygen layer. No chromium or molybdenum enrichment was observed at the surface. However, a sub‐surface phosphorus enrichment was observed in rapidly quenched samples, in the as‐received state as well as after electrochemical treatments, which may be responsible for their improved corrosion resistance.     

Effect of Size Parameters of Mix Ingredients on the Porosity and Reduction Characteristics of Sinter

The paper aims to describe the effect of size parameters of the mix ingredients on the tumbler index, porosity and reduction properties of sinter. These parameters are important factors for the furnace performance when the sinter is fed as burden material Understandably, the fines generated inside the furnace in the stack zone or during reduction affect the permeability of the stack zone, which results in a decrease in driving rate and CO utilisation. Pot sintering studies were carried out using hematite ore mix from typical mines in India. The sinter basicity (CaO/SiO₂) and MgO content in the sinter were kept at 2.1 and 1.5% respectively. The effect of the size parameters of the mix ingredients, namely size of coke, size of ore fines and that of limestone, on the porosity and quality parameters of sinter was investigated. The studies have shown that reducibility of sinter was well correlated with the proportion of micro‐pores out of total pores available in the sinter. Micro‐porosity of the sinter samples and their reducibility increased with decrease in the size range of coke breeze. Sintering of ore fines with reduced size, also, increased the sinter micro‐porosity. Besides, the average pore radius and density of the sinter sample and consequently the sinter reducibility increased with decreasing ore size. When the size of flux was narrowed down to –3+0.5 mm from –3 mm, the reduction degradation index value declined from 26.8% to 25.6% with marginal decrease in sinter reducibility. Moreover, the speed of sintering increased as well.     

Compliance with Good Agricultural Practices (GAPs) by state-registered and non-registered vegetable farmers in Trinidad,West Indies

If Trinidad farmers are to meet consumers’ demands for safer food and also the requirements for export of produce then they must embrace Good Agricultural Practices (GAPs) on farms. This study assessed the extent of compliance with GAPs among smallholder vegetable farmers (n?=?196) across Trinidad, West Indies. Farmers were randomly selected and surveyed using a structured interview schedule designed to capture personal, demographic and farm related data as well as the extent of compliance with GAPs from the recommended protocols governing production and post production practices. Data were analyzed using ANOVA and categorical regression. Overall, compliance was low among all farmers; farmers registered as exporters with the state owned national marketing company had lower compliance levels than those not registered; the level of compliance with GAPs was different based on gender, education, farming experience, number of extension visits received, size of farm, land tenure status and export status (all at p?≤?0.05 of level of significance). Categorical regression results showed that the status of land tenure, number of extension visits received and the institution at which farmers were trained were the most important factors determining the extent of compliance with GAPs. Land tenure and number of extension visits were consistently the most important factors among the entire sample and subsamples (registered as exporters and non-registered with the state owned national marketing company). If Trinidad farmers are to produce vegetables of higher quality, which are safe to eat and meet all international safety protocols then urgent actions are needed i) to better educate the extension service in order to improve GAPs compliance and ii) for governmental intervention to improve farmers’ land tenancy arrangements.     

Investigations on Sound Absorption Properties of Luffa Fibrous Mats

In this study, the natural fibrous mats were developed using luffa fibrous materials and their sound absorption properties were investigated. Kapok/cotton web was used as middle layer in between two mats in order to improve the sound absorption efficiency. Four fibrous mats with different composition of layers were developed using thermal bonding. The developed mats were tested for Noise Reduction Coefficient (NRC) as per ASTM E 1050. The parameters influencing sound absorption properties of the developed mats such as addition of kapok/cotton web on the mats, thickness of mats and air gap maintained in the impedance tube during testing have been investigated. The sound absorption properties of developed mats improved due to the addition of kapok/cotton web and increased air gap. The increase in thickness of mats resulted in increase in sound absorption properties. Luffa mats having 4 layers had NRC value of 0.39 at the frequency range of 250 Hz to 2000 Hz which is comparable with commercially available glass fiber board.     

Corrosive degradation and failure of vertical furnace wall tubes of a boiler

The failures of vertical furnace wall tubes of a co-generation boiler have been investigated. The thinned section failures, often accompanied by buckling prior to failure, were found to be due to acid attack as a consequence of “hideout”. The local corrosion and consequent thick and non-protective iron-oxide deposition at the sites of attack produced hot spots, which is evident from the microstructure of those regions. Decarburization by hydrogen generated during the corrosion process also contributed to the loss in strength of the material. The possibility of “alkali attack” as opposed to acid attack was ruled out by the various findings of this investigation.