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111.
112.
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. 相似文献
113.
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. 相似文献
114.
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. 相似文献
115.
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. 相似文献
116.
Magan Lal Agrawal Rajesh Gupta Pramod R. Bhave 《Canadian Metallurgical Quarterly》2007,133(3):319-330
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. 相似文献
117.
MaryGail Perkins Steven W. Effler Feng Peng Donald Pierson David G. Smith Yogesh C. Agrawal 《Canadian Metallurgical Quarterly》2007,133(8):800-808
Characterization of the particle population for a location in a water supply reservoir, Kensico Reservoir, N.Y., is documented for a high turbidity event, from its onset, through alum treatment and its waning. Supporting in situ measurements included the beam attenuation coefficient at 670?nm (c670) and 660?nm (c660) [surrogates of turbidity (Tn)], particle concentrations (N) and size distributions (PSDs), and size class specific settling velocities (SVs). Laboratory measurements included chemical and morphometric analyses of individual particles, and routine measurements of Tn. The turbidity is shown to be primarily derived from clay minerals, mostly in the size range of 1.5–6?μm. An initial high c670 level (40?m?1;Tn ~ 100?NTU) decreased sevenfold in less than 1?week in response to alum treatment that largely eliminated the particle size classes responsible for the elevated turbidity. Successful SV experiments, made using a laser in situ scattering and transmissometry (LISST) instrument, for seven particle size classes in the range of 1.25–129?μm yielded SV values of 0.17–69.4?m?day?1. Size classes larger than ~ 5?μm settled much slower than Stokes law predictions, before alum treatment, indicating that these classes existed as porous flocs or aggregates. Decreases in SVs following treatment suggest changes in floc character consistent with increased porosity. In situ measurements of c670, N, PSDs, and SVs can contribute to the development and testing of a multiple particle size class model to simulate fate, transport, and impacts of suspended particles. 相似文献
118.
Pankaj Agrawal Silvia I. Oliveira E. M. Araújo Tomas J. A. Melo 《Journal of Materials Science》2007,42(13):5007-5012
In this work, the rheological, mechanical and morphological properties of nylon 6/polypropylene compatibilized blends were
investigated. Two types of polypropylene were used. One with MFI of 40 g/10 min (PP H103) and the other with MFI of 3.5 g/10 min
(PP H503). The compatibilizers used were polypropylene grafted with 6% of acrylic acid (PPgAA) and polypropylene grafted with
1% of maleic anhydride (PPgMA). The blends composition was 80/20 (wt%) for the PA6/PP binary blends and 80/10/10(wt%) for
the nylon 6/PPgAA/polypropylene and nylon 6/PPgMA/polypropylene ternary blends. Torque rheometry analysis showed that when
PPgAA and PPgMA were added to nylon 6/polypropylene blends, there was an increase in the torque, indicating that reactive
compatibilization has occurred. There is no influence of the polypropylene MFI on the mechanical properties of the uncompatibilized
and compatibilized blends. The impact strength of the blends containing PPgMA were greater than those of the blends containing
PPgAA. The blends containing PPgAA are unstable. SEM analysis showed that PPgMA improves considerably the adhesion between
PA6/PP phases, leading to good mechanical properties. 相似文献
119.
Badri Narayan Subudhi Susmita Ghosh Ashish Ghosh 《Machine Vision and Applications》2013,24(4):795-809
Although background subtraction techniques have been used for several years in vision systems for moving object detection, many of them fail to provide good results in presence of noise, illumination variation, non-static background, etc. A basic requirement of background subtraction scheme is the construction of a stable background model and then comparing each incoming image frame with it so as to detect moving objects. The novelty of the proposed scheme is to construct a stable background model from a given video sequence dynamically. The constructed background model is compared with different image frames of the same sequence to detect moving objects. In the proposed scheme the background model is constructed by analyzing a sequence of linearly dependent past image frames in Wronskian framework. The Wronskian based change detection model is further used to detect the changes between the constructed background scene and the considered target frame. The proposed scheme is an integration of Gaussian averaging and Wronskian change detection model. Gaussian averaging uses different modes which arise over time to capture the underlying richness of background, and it is an approach for background building by considering temporal modes. Similarly, Wronskian change detection model uses a spatial region of support in this regard. The proposed scheme relies on spatio-temporal modes arising over time to build the appropriate background model by considering both spatial and temporal modes. The results obtained by the proposed model is found to provide accurate shape of moving objects. The effectiveness of the proposed scheme is verified by comparing the results with those of some of the existing state of the art background subtraction techniques on public benchmark databases. We found that the average F-measure is significantly improved by the proposed scheme from that of the state-of-the-art techniques. 相似文献
120.
This paper proposes a new hybrid fuzzy multi-objective evolutionary algorithm (HFMOEA) based approach for solving complex multi-objective, mixed integer nonlinear problems such as optimal reactive power dispatch considering voltage stability (ORPD-VS). In HFMOEA based optimization approach, the two parameters like crossover probability (PC) and mutation probability (PM) are varied dynamically through the output of a fuzzy logic controller. The fuzzy logic controller is designed on the basis of expert knowledge to enhance the overall stochastic search capability for generating better pareto-optimal solution. Two detailed case studies are presented: Firstly, the performance of HFMOEA is tested on five benchmark test problems such as ZDT1, ZDT2, ZDT3, ZDT4 and ZDT6 as suggested by Zitzler, Deb and Thiele; Secondly, HFMOEA is applied to multi-objective ORPD-VS problem. In both the case studies, the optimization results obtained from HFMOEA are analysed and compared with the same obtained from two versions of elitist non-dominated sorting genetic algorithms such as NSGA-II and MNSGA-II in terms of various performance metrics. The simulation results are promising and confirm the ability of HFMOEA for generating better pareto-optimal fronts with superior convergence and diversity. 相似文献