Defence Science Journal
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Carbon Fiber Composites: A Solution for Light Weight Dynamic Components of AFVs
Get PDFChanging circumstances across the world require armored fighting vehicle (AFV) of a country to be more agile, easily manoeuverable and transportable besides other key requirements like firepower and protection. Therefore, the AFV should be as light as possible. The use of conventional materials and techniques do not fulfill the requirement of light weight AFV. The composite materials having high specific modulus, specific strength and directional properties are the alternative substitution for reducing the weight. A customized design approach with proper selection of composite material is essential to make AFV components with required properties at lower weight as compared to the traditional approach. Special properties like resistance to moisture, solvents, UV degradation etc. could be imparted to the composite components by the use of proper additives or fillers. This paper deals with the development of dynamic members like road wheel, top roller and axle arm, whose count is always more in any AFVs, using carbon-epoxy composite material. The details of composite materials used and the manufacturing processes adopted are briefly discussed. The static load test carried out to assess the structural integrity as well as non-destructive tests (NDT) performed to detect the defects are also dealt in detail. Preliminary Finite Element Analysis and Multi-body Dynamic Analysis have also been discussed. These analyses have been done mainly to understand the sustainability and performance of the components developed under the given loading conditions
An Approach to Reduce the Sample Consumption for LIBS based Identification of Explosive Materials
Get PDFAn experimental design based on spectral construction, which has potential to minimise the sample consumption, the number of laser shots and time required to collect the data from laser induced breakdown spectroscopy for identification of the explosive materials is reported in the study. This approach is an ideal solution in the field of hazardous material detection, where the availability of the sample can be a serious limiting factor. The experimental data recorded on a set of five high energy materials has been considered to test the performance of the proposed methodology. Multiple spectra are constructed by assuming a normal distribution at each wavelength of the spectrum, where random numbers are generated using the mean and standard deviations obtained from arbitrarily chosen five experimental spectra from each class. The newly generated spectra are called as synthetic spectra. The correct classification obtained from – K - nearest neighbour combined with principal component analysis and partial least square – discriminant analysis demonstrated very promising results. The correct classification rates differed by only4 per cent - 7 per cent as compared to conventional approach where experimental spectra alone are considered for the analysis. Further, when RDX is excluded, the obtained results are almost identical with conventional approach
Infrared Avalanche Photodiode Detectors
Get PDFThis study presents on the design, fabrication and characteristics of HgCdTe mid-wave infrared avalanche photodiode (MWIR APD). The gain of 800 at - 8 V bias is measured in n+-ν-p+ detector array with pitch size of 30 μm. The gain independent bandwidth of 6 MHz is achieved in the fabricated device. This paper also covers the status of HgCdTe and III-V material based IR-APD technology. These APDs having high internal gain and bandwidth are suitable for the detection of attenuated optical signals such as in the battle field conditions/long range imaging in defence and space applications. It provides a combined solution for both detection and amplification if the detector receives a very weak optical signal. HgCdTe based APDs provide high avalanche gain with low excess noise, high quantum efficiency, low dark current and fast response time
Computer Graphic and Photographic Image Classification using Local Image Descriptors
Get PDFWith the tremendous development of computer graphic rendering technology, photorealistic computer graphic images are difficult to differentiate from photo graphic images. In this article, a method is proposed based on discrete wavelet transform based binary statistical image features to distinguish computer graphic from photo graphic images using the support vector machine classifier. Textural descriptors extracted using binary statistical image features are different for computer graphic and photo graphic which are based on learning of natural image statistic filters. Input RGB image is first converted into grayscale and decomposed into sub-bands using Haar discrete wavelet transform and then binary statistical image features are extracted. Fuzzy entropy based feature subset selection is employed to choose relevant features. Experimental results using Columbia database show that the method achieves good detection accuracy
Ab Initio Studies on the Interaction Between Copper(I) and 5-Nitrotetrazolate Anion
Get PDFAb initio molecular orbital calculations on the interaction between Copper(I) and 5-nitrotetrazolate anion were done using different basis sets, at the HF, B3LYP and MP2 levels of theory. Three minima were found to 1A, 1B and IC structures of Cu(I)-5-NTz complex. At the B3LYP/LanL2DZ level, the energy difference between 1A and 1B was computed to be 8.18 kcal/mol, while that between 1A and 1C is 22.76 kcal/mol. The presence of both Cu-N and Cu-O interactions is revealed in 1A structure using both natural bond orbital and atoms-in-molecules analyses, which makes more stable than those of 1B and 1C complexes. The binding energy corrected for both ZPE and BSSE for 1A is found to be -150.59 kcal/mol at the B3LYP/LanL2DZ level. The barrier for the 1B → 1A and 1C → 1B conversion is calculated to be 7.80 kcal/mol and 9.40 kcal/mol, respectively
An Adaptive Spectrum-Sensing Algorithm for Cognitive Radio Networks based on the Sample Covariance Matrix
Get PDFA novel adaptive threshold spectrum sensing technique based on the covariance matrix of received signal samples is proposed. The adaptive threshold in terms of signal to noise ratio (SNR) and spectrum utilisation ratio of primary user is derived. It considers both the probability of detection and the probability false alarm to minimise the overall decision error probability. The energy- based spectrum sensing scheme shows high vulnerability under noise uncertainty and low SNR. The existing covariance-based spectrum sensing technique overcomes the noise uncertainty problem but its performance deteriorates under low SNR. The proposed covariance-based scheme effectively addresses the low SNR problem. The superior performance of this scheme over the existing covariance-based detection method is confirmed by the simulation results in terms of probability of detection, probability of error, and requirement of samples for reliable detection of spectrum
Tracking Control Design for Quadrotor Unmanned Aerial Vehicle
Get PDFThe model of a quadrotor unmanned aerial vehicle (UAV) is nonlinear and dynamically unstable. A flight controller design is proposed on the basis of Lyapunov stability theory which guarantees that all the states remain and reach on the sliding surfaces. The control strategy uses sliding mode with a backstepping control to perform the position and attitude tracking control. This proposed controller is simple and effectively enhance the performance of quadrotor UAV. In order to demonstrate the robustness of the proposed control method, White Gaussian Noise and aerodynamic moment disturbances are taken into account. The performance of the nonlinear control method is evaluated by comparing the performance with developed linear quadratic regulator and existing backstepping control technique and proportional-integral-derivative from the literature. The comparative performance results demonstrate the superiority and effectiveness of the proposed control strategy for the quadrotor UAV
Infrared Characterisation and Prediction of Aviation Turbine Fuel Plume
Get PDFBroad (3.7 μm - 4.8 μm) as well as narrow band (4.16 μm - 4.24 μm) mid wave infrared characterisation of plume has been reported here. Multiple angular measurements (azimuth) were carried out on a laboratory developed plume source with aviation turbine fuel (ATF) using thermal imaging systems. Correlation of IR prediction to experimental results is the key objectives of this study. As this narrow band covers the blue spike of plume, a comparison of the same with broad band plume contribution has been reported for the first time. Also, a model to simulate the IR radiation of two-dimensional parabolic jet was developed and used to predict spectral contribution from major hydrocarbon fuel combustion products (CO2 and H2O). In addition, it was found that the plume transmission characteristics extracted form imager measurements are qualitatively in agreement with prediction results.
HeW: AHash Function based on Lightweight Block Cipher FeW
Get PDFA new hash function HeW: A hash function based on light weight block cipher FeW is proposed in this paper. The compression function of HeW is based on block cipher FeW. It is believed that key expansion algorithm of block cipher slows down the performance of the overlying hash function. Thereby, block ciphers become a less favourable choice to design a compression function. As a countermeasure, we cut down the key size of FeW from 80-bit to 64-bit and provide a secure and efficient key expansion algorithm for the modified key size. FeW based compression function plays a vital role to enhance the efficiency of HeW. We test the hash output for randomness using the NIST statistical test suite and test the avalanche effect, bit variance and near collision resistance. We also give the security estimates of HeW against differential cryptanalysis, length extension attack, slide attack and rotational distinguisher.