Horizontally polarized waves in inhomogeneous media--Energy conservation and reciprocity relationships

Full wave solutions for the electromagnetic fields of a horizontally polarized wave propagating through an inhomogeneous ionized medium are derived using a generalized WKB method. Both the electron density and the collision frequency of the horizontally stratified media are assumed to vary and special attention is given to permittivity profiles with critical coupling regions. The reflection and transmission coefficients and the characteristic surface impedance for an inhomogeneous layer of finite thickness are computed as functions of the transverse wave number for various permittivity profiles. Excitation of both propagating and evanescent waves are considered. For some special permittivity profiles considered, closed form analytical solutions for the electromagnetic fields are known. Computations derived from these solutions are in good agreement with those obtained using the generalized WKB method. The results are also shown to satisfy energy conservation and reciprocity relationships in electromagnetic theory.     

A hybrid technique for wire antennas in a cavity

Two numerical techniques for solving the current distribution on wire antennas, namely point matching and reaction matching, have been combined in a particular fashion to yield a new technique termed the "hybrid method." The hybrid method is well suited for a wire antenna mounted in a cavity. Over the antenna, piecewise sinusoidal basis functions with reaction matching are used, and on the support structure, point matching is used with pulse basis functions. The hybrid method has been applied to calculate the input impedance and the radiation efficiency of the three-turn loop antenna in an open circular cavity. Calculated input resistance of the antenna is found to agree quite well with measured data. Effects of varying the extent of recession of the antenna and varying the radius and the material of the antenna wire on the bandwidth, the efficiency, the antiresonance frequencies, and the general input reactance level of the antenna have been examined for a specific antenna geometry. The results are considered to be indicative of the general characteristics of a multiturn loop antenna with nearby support structure. The computer program that has been developed may be applied to a systematic parametric study of this type of antenna in order to optimize it for a particular application.     

Hexagonal dislocation networks in titanium

Hexagonal dislocation networks which occurred in as-annealed commercial Ti-A 50 rod and following partial extrusion under hydrostatic pressure at room temperature were studied using transmission electron microscopy. For the as-annealed condition networks were observed on the prism, basal and {2•1•1x} planes, while for the extrusion networks were only observed on the basal plane. The various stages in the development of the networks are presented and mechanisms by which they form are proposed. The self energies of the dislocation hexagons constituting the various networks are calculated using the equations proposed by de Wit and Ruff. They increase in the order: a) networks on the basal plane in the as-annealed condition, b) networks on the prism plane in the asannealed condition and c) networks on the basal plane in the partially extruded condition. This paper is based on Doctoral Thesis presented in October 1973 by S. P. AGRAWAL to the Department of Metallurgical Engineering and Materials Science at the University of Kentucky.     

Synthesis, characterization, thermolysis and performance evaluation of mercuric-5-nitrotetrazole (MNT)

Mercuric-5-nitrotetrazole (MNT) was synthesized on using a reported method. The product having bulk density of 1.5 g/cm3, was obtained during this work using mercuric nitrate doped with additives such as cephol/dextrin in the process. Synthesized MNT was characterized by metal content analysis, IR and ESCA. The DTA profile indicated the thermal stability of MNT up to 200 degrees C. It revealed its higher thermally sensitive [thermal sensitive figure (S) approximately 0.8] in comparison to that of service lead azide (SLA) [S approximately 0.4]. Percussion sensitivity data also showed higher sensitivity of MNT. However, it was found less friction sensitive than SLA. The chemical stability of MNT in a carbon dioxide environment was evaluated in comparison to SLA by determining mercury (gravimetrically) and lead azide (volumetrically) contents respectively. Results obtained indicated that no discernable changes occurred in MNT, even after storage for 90 days while in case of SLA, drastic change in lead azide content was observed. IR spectra of MNT sample stored in a closed aluminum dish for 5-10 years could be superimposed on that of the freshly prepared MNT sample. The performance of MNT filled detonator no. 27 assessed in terms of extent of damage on a witness plate was found equivalent to that of the standard ASA (azide, styphynate and aluminium) composition filled detonator.     

Synthesis and characterisation of 4-picrylamino-2,6-dinitrotoluene (PADNT): a new insensitive explosive

A chemoselective reductive method has been achieved for the preparation of 4-picrylamino-2,6-dinitrotoluene (PADNT), a new insensitive energetic material which has been characterised by spectral data and elemental analysis. Some explosive properties of the compound have also been determined and the results indicate that PANDT is quite safe to impact and friction.     

Strengthening of alumina by cerium-zirconate (Ce2Zr2O7)

Composite powders of Al₂O₃ and 0 to 30 vol% Ce₂Zr₂O₇ are prepared by a hybrid sol-gel method using Al₂O₃ powders and a sol formed from Zr-alkoxide and cerium nitrate. All the Zr from the sol goes to form the cerium zirconate phase when the powders are calcined in N₂. Pressureless sintering in air at 1500°C yields composites with high density (98%). Maximum values of fracture toughness and strength, 6.5 MPa and 620 MPa respectively, (e.g. 3.5 MPa and 350 MPa for pure Al₂O₃) are obtained in 10 vol% Ce₂Zr₂O₇ composite sintered in air. The dominant mechanism for enhancement in K _IC is believed to be crack bridging. Crack bridging activity in the 10 vol% composite is found to be maximum and extends upto 190 m from the crack tip.     

Study of Molten Salt Corrosion of High Velocity Oxy-Fuel Sprayed Cermet and Nickel-Based Coatings at 900 °C

Absract Samples of Cr₃C₂-NiCr cermet and NiCrBSi coatings formed by the high velocity oxy-fuel (HVOF) process on Superni 718 superalloy have been corroded in the Na₂SO₄-V₂O₅ molten salt environment at 900 °C under cyclic conditions. The hot corrosion behavior of the coatings has been investigated by means of thermogravimetric analysis, X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy, and electron probe microanalyzer techniques. Efforts have been made to formulate the mode of corrosion attack. Both the coatings protected the substrate superalloy Superni 718 completely. While protecting the superalloy, the Cr₃C₂-NiCr cermet coating partially oxidized along the splat boundaries up to the coating substrate interface, whereas only the upper part of the coating, to about 100 μm from the surface, oxidized in the case of the NiCrBSi coating. The hot corrosion resistance of both the coatings has been attributed to the formation of protective oxides of chromium/silicon at the surface and at the splat boundaries of the coatings.     

Fast computation of spatial selections and joins using graphics hardware

Spatial database operations are typically performed in two steps. In the filtering step, indexes and the minimum bounding rectangles (MBRs) of the objects are used to quickly determine a set of candidate objects. In the refinement step, the actual geometries of the objects are retrieved and compared to the query geometry or each other. Because of the complexity of the computational geometry algorithms involved, the CPU cost of the refinement step is usually the dominant cost of the operation for complex geometries such as polygons. Although many run-time and pre-processing-based heuristics have been proposed to alleviate this problem, the CPU cost still remains the bottleneck. In this paper, we propose a novel approach to address this problem using the efficient rendering and searching capabilities of modern graphics hardware. This approach does not require expensive pre-processing of the data or changes to existing storage and index structures, and is applicable to both intersection and distance predicates. We evaluate this approach by comparing the performance with leading software solutions. The results show that by combining hardware and software methods, the overall computational cost can be reduced substantially for both spatial selections and joins. We integrated this hardware/software co-processing technique into a popular database to evaluate its performance in the presence of indexes, pre-processing and other proprietary optimizations. Extensive experimentation with real-world data sets show that the hardware-accelerated technique not only outperforms the run-time software solutions but also performs as well if not better than pre-processing-assisted techniques.     

Optimal Design of Level 1 Redundant Water Distribution Networks Considering Nodal Storage

A water distribution network (WDN) is designed to meet time-varying demands with sufficient pressure, taking into consideration an appropriate demand during peak hours. Therefore, a network has inherent redundancy in the sense that under abnormal conditions such as those arising due to pipe breaks or pump failures, deficiency in supply during peak hours can be met through additional supply during off-peak periods. However, this necessitates a storage facility at the consumer end of the network, which is normally available in the form of a sump or an overhead tank in developing countries. Such a storage enables the consumer to store water during the off-peak period and then use it during the peak period. Reliability of a WDN is assessed herein considering nodal storage, and an iterative method is proposed for the optimal design of Level 1 redundant WDNs, i.e., networks that can sustain a single pipe failure without affecting consumer services either in part or in full. The method is illustrated through an example and the designs of a network with and without storage are compared. Provision of a nodal storage is found to reduce the total cost of the network.