High velocity oblique impact and ricochet mainly of long rod projectiles: An overview

A review of the literature on high velocity oblique impact and the ricochet of projectiles of various shapes is given, with emphasis on long rod projectiles. Aspects of cratering and penetration in oblique impact are highlighted and the mechanics of ricochet off solid, fluid and granular media are also discussed.     

Design of efficient lightweight strategies to combat DoS attack in delay tolerant network routing

Delay tolerant networks (DTNs) are characterized by delay and intermittent connectivity. Satisfactory network functioning in a DTN relies heavily on co-ordination among participating nodes. However, in practice, such co-ordination cannot be taken for granted due to possible misbehaviour by relay nodes. Routing in a DTN is, therefore, vulnerable to various attacks, which adversely affect network performance. Several strategies have been proposed in the literature to alleviate such vulnerabilities—they vary widely in terms of throughput, detection time, overhead etc. One key challenge is to arrive at a tradeoff between detection time and overhead. We observe that the existing table-based reactive strategies to combat Denial-of-service (DoS) attacks in DTN suffer from two major drawbacks: high overhead and slow detection. In this paper, we propose three secure, light-weight and time-efficient routing algorithms for detecting DoS attacks (Blackhole and Grey-hole attacks) in the Spray & Focus routing protocol. The proposed algorithms are based on use of a small fraction of privileged (trusted) nodes. The first strategy, called TN, outperforms the existing table-based strategy with 20–30 % lesser detection time, 20–25 % higher malicious node detection and negligible overhead. The other two strategies, CTN_MI and CTN_RF explore the novel idea that trusted nodes are able to utilize each others’ information/experience using their long range connectivity as and when available. Simulations performed using an enhanced ONE simulator reveals that investing in enabling connectivity among trusted nodes (as in CTN_RF) can have significant performance benefits.     

The architecture of a knowledge-based process planning system for small scale industriee

The objective of this paper is to describe a knowledge-based system to assist engineers to generate optimum process plans. The knowledge base is defined using a PASCAL-like language and is maintained in the form of PROLOG sentences. The knowledge base may be readily modified by process planners to meet their specific requirements. An inferece engine systematically tries to apply the rules to generate basic process plans. These plans are then optimised by repeated applications of user difined rules. The system is being written in PROLOG.     

Redshifting and broadening of quantum-well infrared photodetector'sresponse via impurity-free vacancy disordering

The partial intermixing of the well and barrier materials offers unique opportunities to shift locally the bandgap of quantum-well (QW) structures. We have demonstrated redshifting and broadening of the wavelength responses of bound-to-continuum GaAs and InP based quantum-well infrared photodetectors (QWIP's) after growth via impurity-free vacancy disordering (IFVD). A comprehensive set of experiments is conducted on QWIP's fabricated from both as-grown and multiple-quantum-well (MQW) structures. Compared to the as-grown detector, the peak spectral responses of the disordered detectors were shifted to longer wavelengths. The peak absolute response of the disordered GaAs based QWIP is lower by almost a factor of four. However, the responsivity characteristics of the disordered InP based QWIP show no major degradation. In general, with the spectral broadening taken into account, the overall performance of the disordered QWIP's has not dropped significantly. Thus, the postgrowth control of the QW composition profiles by impurity-free vacancy disordering offers unique opportunities to fine tune various aspects of a photodetector's response. Theoretical calculations of the absorption coefficient spectrum are in excellent agreement with the experimental data     

A dynamic mechanical study on unidirectional carbon fiber-reinforced polypropylene composites

Fiber-reinforced polymer composites show high specific strength and stiffness. The alignment of reinforcing fibers results in anisotropy of the material. This anisotropic behavior has been studied through dynamic mechanical analysis of unidirectional carbon fiber-reinforced polypropylene (CFRPP) composites measured in both parallel and transverse directions to fiber arrangement. Several parameters such as storage modulus (E′), loss modulus (E″), loss factor or damping factor (tan δ), and complex viscosity (MU^*) have been determined over a wide range of frequencies and at a fixed temperature. Relaxation and retardation spectra have been constructed for these composites. Modulus enhancement occurs due to stiffness imparted by the fiber and efficient stress transfer at the interface. Relaxation of the polymer matrix ceases with increase in the volume fraction of the fibers. α′-relaxation is observed for the composite having a 13% volume fraction of fibers and is ascribed to relaxation in the crystalline phase where the additional crystallinity arises out of the transcrystalline growth at the fiber–matrix interface. There exists a good correlation between theroretical curves with the experimental ones. Relaxation and retardation spectra and the dynamic parameters determined for these composites show a good correlation with the volume fraction of fibers as well as the direction of the applied load. © 1994 John Wiley & Sons, Inc.     

Graft copolymerization of methyl methacrylate and natural rubber

Graft copolymerization of natural rubber and MMA was carried out in the presence of Bz₂O₂ or AIBN as thermal initiator and hydrogen peroxide or benzophenone as photosensitizer. From the overall copolymerization product, the rubber–PMMA graft copolymer fraction was isolated from unreacted rubber and free PMMA fractions and composition characterization of the separated fractions was done by determination of rubber unsaturation. The efficiency of grafting under different conditions has been calculated and compared.     

The magnitude of arsenic contamination in groundwater and its health effects to the inhabitants of the Jalangi--one of the 85 arsenic affected blocks in West Bengal, India

To better understand the magnitude of arsenic contamination in groundwater and its effects on human beings, a detailed study was carried out in Jalangi, one of the 85 arsenic affected blocks in West Bengal, India. Jalangi block is approximately 122 km2 in size and has a population of 215538. Of the 1916 water samples analyzed (about 31% of the total hand tubewells) from the Jalangi block, 77.8% were found to have arsenic above 10 microg l(-1) [the World Health Organization (WHO)-recommended level of arsenic in drinking water], 51% had arsenic above 50 microg l(-1) (the Indian standard of permissible limit of arsenic in drinking water) and 17% had arsenic at above 300 microg l(-1) (the concentration predicting overt arsenical skin lesions). From our preliminary medical screening, 1488 of the 7221 people examined in the 44 villages of Jalangi block exhibit definite arsenical skin lesions. An estimation of probable population that may suffer from arsenical skin lesions and cancer in the Jalangi block has been evaluated comparing along with international data. A total of 1600 biologic samples including hair, nail and urine have been analyzed from the affected villages of Jalangi block and on an average 88% of the biologic samples contain arsenic above the normal level. Thus, a vast population of the block may have arsenic body burden. Cases of Bowen's disease and cancer have been identified among adults who also show arsenical skin lesions and children in this block are also seriously affected. Obstetric examinations were also carried out in this block.