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1.
Wireless Personal Communications - In this paper the conventional circular patch has been reshaped by two circular arcs with the FR4 Epoxy material for substrate. This is supported by the... 相似文献
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Ramanujam J. Jinpyo Hong Kandemir M. Narayan A. Agarwal A. 《Signal Processing, IEEE Transactions on》2006,54(1):286-294
Most embedded systems have limited amount of memory. In contrast, the memory requirements of the digital signal processing (DSP) and video processing codes (in nested loops, in particular) running on embedded systems is significant. This paper addresses the problem of estimating and reducing the amount of memory needed for transfers of data in embedded systems. First, the problem of estimating the region associated with a statement or the set of elements referenced by a statement during the execution of nested loops is analyzed. For a fixed execution ordering, a quantitative analysis of the number of elements referenced is presented; exact expressions for uniformly generated references and a close upper and lower bound for nonuniformly generated references are derived. Second, in addition to presenting an algorithm that computes the total memory required, this paper also discusses the effect of transformations (that change the execution ordering) on the lifetimes of array variables, i.e., the time between the first and last accesses to a given array location. The term maximum window size is introduced, and quantitative expressions are derived to compute the maximum window size. A detailed analysis of the effect of unimodular transformations on data locality, including the calculation of the maximum window size, is presented. 相似文献
6.
Neog D.K. Pattnaik S.S. Panda D.C. Devi S. Khuntia B. Dutta M. 《Antennas and Propagation Magazine, IEEE》2005,47(3):60-65
This paper deals with the design of a multi-slot hole-coupled microstrip antenna on a substrate of 2 mm thickness that gives multi-frequency (wideband) characteristics. The Method of Moments (MoM)-based IE3D software was used to simulate the results for return loss, VSWR, the Smith chart, and the radiation patterns. A tunnel-based artificial neural network (ANN) was also developed to calculate the radiation patterns of the antenna. The radiation patterns were measured experimentally at 10.5 GHz and 12 GHz. The experimental results were in good agreement with the simulated results from IE3D and those of the artificial neural network. A new method of using a genetic algorithm (GA) in an artificial neural network is also discussed. This new method was used to calculate the resonant frequency of a single-shorting-post microstrip antenna. The resonant frequency calculated using the genetic-algorithm-coupled artificial neural network was compared with the analytical and experimental results. The results obtained were in very good agreement with the experimental results. 相似文献
7.
The reliability of a system is the probability that the system will perform its intended mission under given conditions. This
paper provides an overview of the approaches to reliability modelling and identifies their strengths and weaknesses. The models
discussed include structure models, simple stochastic models and decomposable stochastic models. Ignoring time-dependence,
structure models give reliability as a function of the topological structure of the system. Simple stochastic models make
direct use of the properties of underlying stochastic processes, while decomposable models consider more complex systems and
analyse them through subsystems. Petri nets and dataflow graphs facilitate the analysis of complex systems by providing a
convenient framework for reliability analysis. 相似文献
8.
Efficient algorithms for the fast computation of 2D and 3D discrete Hartley transforms have been proposed. It is shown that the proposed algorithms offer a significant saving in computation over the existing methods for various array sizes.<> 相似文献
9.
Thermal shock and thermal fatigue study of ceramic materials on a newly developed ascending thermal shock test equipment 总被引:1,自引:0,他引:1
P. K. Panda T. S. Kannan J. Dubois C. Olagnon G. Fantozzi 《Science and Technology of Advanced Materials》2002,3(4):44
A test equipment was designed to study thermal shock and thermal fatigue of ceramic materials subjected to fast heating (ascending). The equipment was designed to generate thermal stress in a test specimen by heating one surface of it by an oxy-hydrogen flame while cooling the opposite surface. The sample cracked when thermal stress exceeded its mechanical strength. The in situ crack formation was detected by an acoustic emission system coupled to the set up. The hot zone temperature was measured by an infra red pyrometer. The equipment was also designed to run thermal fatigue test cycles in automatic mode between two selected temperatures. The temperature and thermal stress distribution in the test specimen were modelled using finite element software. The effect of temperature distribution of the top and bottom surfaces on thermal stresses was studied. It was observed that the thermal stress is very sensitive to the temperature distribution on the top surface and maximum near the periphery of the top surface. This was in agreement with the experimental results in which the cracks were originated from the periphery of top surface. It was also observed that the failure temperature was higher for thicker samples. 相似文献
10.
The study focused on the in-situ synthesis of titanium (Ti)-titanium boride (TiB) composites with β phase in the matrix by reaction sintering of TiB2 with Ti and alloying element powders. The goal was to examine the nature of TiB whisker formation in three different kinds
of powder mixtures: (1) β-Ti alloy powders and TiB2; (2) α-Ti powder, a master alloy (Fe-Mo) powder containing the β-stabilizing elements, and TiB2; and (3) α-Ti powder, a β-stabilizing elemental powder (Mo or Nb), and TiB2. The effects of powder packing and the relative locations of powder particles on the morphological changes in TiB whisker
formation and their growth were studied at processing temperatures ranging from 1100°C to 1300°C. The morphology, size, and
distribution of whiskers were found to be influenced by the powder-packing conditions. A large particle-size ratio in bimodally
packed mixtures led to the formation of a TiB monolithic layer around β grains. With a relatively finer starting powder, smaller size ratio, and trimodal packing arrangement, the TiB whiskers were
found to be distributed more homogeneously in the matrix. The study also used the X-ray direct comparison method and the structure
factor for the β phase to determine the volume fraction of TiB phase from X-ray data. Tensile tests and fractographic investigations were
carried out on selected composites. The evolution of the composite microstructure, the influence of powder-packing variables,
and the morphology and growth of TiB whiskers and their effect on mechanical properties are discussed. 相似文献