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1.
2.
We use field trial results obtained from a multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) wireless system with two transmitter and three receiver antennas (2/spl times/3), to first validate the properties of the transmit correlation matrix in a macro-cellular environment. We find that approximately 20% of the locations have well-defined transmit correlation matrices. Furthermore, the eigenvectors of the transmit correlation matrix vary slowly over distance with 60% of the locations having eigenvector variation of less than 1 dB over a distance of 20 m. Next, we quantify the performance of the optimal statistical linear precoding (OSLP) , and statistical one-dimensional (1-D) eigenbeamforming (SEB) based on transmit correlation matrices, and the 1-D eigenbeamforming (EB)-based on perfect channel knowledge at the transmitter. We find that the OSLP and SEB schemes obtain array gain over the Alamouti scheme at lower signal-to-noise ratio (SNR) with a median gain of 2.0 (1.5) dB at the 1.0-(3.5) km cell-radii. However, the SEB scheme (unlike the OSLP scheme) looses diversity order at higher SNR that leads to a performance loss. The EB scheme provides the best performance over the Alamouti scheme, at the expense of increased feedback requirements. 相似文献
3.
Aside from its importance as a design parameter for thermal barrier coatings, measuring thermal conductivity of thermal sprayed
coatings itself provides a unique method to critically characterize the nature, quantity, and anisotropy of the defect morphologies
in these splat-based coatings. In this paper, the authors present a systematic assessment of thermal conductivity of wide
range using the flash diffusivity technique. For the case of plasma sprayed yttria-stabilized zirconia (YSZ), coatings obtained
from wide-ranging initial powder morphologies as well as those fabricated under different particle states were characterized.
Both in-plane and through-thickness properties were obtained. Other material systems that were considered include: metallic
alloys and semiconductors of interests. Issues such as reproducibility and reliability in measurements were also considered
and assessed. Finally, work in collaboration with the Oak Ridge National Laboratory (ORNL) for alternate approaches to characterization
of thermal conductivity as well as high-temperature measurements was performed.
This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials
Park, OH, 2006. 相似文献
4.
Prahladavaradan Sampath 《Formal Aspects of Computing》2014,26(4):695-727
The primary aim of a software product-line is to maximise reuse of software components by managing the variability in component functionalities and product configurations. Feature oriented domain analysis (FODA) diagrams are a formalism for modelling the variability in a software product-line, and are used as a tool for managing a product-line and planning its evolution. This paper presents an elementary theory of variations in a product-line, leading up to a technique for extracting FODA diagrams from legacy product-lines. The theory is elementary in the sense that it is built using very simple mathematical structures, making minimal assumptions on the structure of product-lines. Examples drawn from the automotive domain are used to illustrate the theoretical developments. 相似文献
5.
T. Sampath Kumar ;S. Balasivanandha Prabu ;Geetha Manivasagam ;K.A. Padmanabhan 《北京科技大学学报(英文版)》2014,(8):796-805
Monolayer and bilayer coatings of TiAlN, AlCrN, and AlCrN/TiAlN were deposited onto tungsten carbide inserts using the plasma enhanced physical vapor deposition process. The microstructures of the coatings were characterized using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The SEM micrographs revealed that the AlrN and AlCrN/TiAlN coatings were uniform and highly dense and contained only a limited number of microvoids. The TiAIN coating was non-uniform and highly porous and contained more micro droplets. The hardness and scratch resistance of the specimens were measured using a nanoindentation tester and scratch tester, respectively. Different phases formed in the coatings were analyzed by X-ray diffraction (XRD). The AlCrN/TiAlN coating exhibited a higher hardness (32.75 GPa), a higher Young's modulus (561.97 GPa), and superior scratch resistance (LcN = 46 N) compared to conventional coatings such as TiAlN, A1CrN, and TiN. 相似文献
6.
Thermally sprayed WC-Co is widely used as a wear-resistant coating for a variety of applications. Although it is well established
that thermal spray processes significantly affect chemistry, microstructure, and the phase distribution of WC-Co coatings,
little is known about how these changes influence wear resistance. In this study, the microstructure and wear behavior of
sintered and thermally sprayed WC-Co materials are examined. Powders of WC-12 wt% Co and WC-17 wt% Co were pressed and sintered,
as well as thermally sprayed by high-velocity oxy-fuel (HVOF), air plasma spray (APS), and vacuum plasma spray (VPS) techniques.
Results indicated considerable differences in the resulting microstructures, mechanical properties, and wear resistance. The
thermally sprayed coatings showed anisotropic fracture toughness, whereas the sintered materials did not. It was also shown
that a combined mechanical property/microstructure parameter, based on considerations of indentation fracture mechanisms,
can be used in most cases to describe abrasive and erosive wear resistance of thermally sprayed WC-Co materials as follows:
Wear resistance a
whereK
ic
is the indentation fracture toughness,H is hardness, andV
Co
f
is the volume fraction of cobalt. This relationship provides a means for assessing wear resistance of WC-Co coatings intended
for industrial applications requiring abrasion and/or erosion resistance. 相似文献
7.
W. S. Sampath R. Wei P. J. Wilbur 《JOM Journal of the Minerals, Metals and Materials Society》1987,39(4):17-19
A study of several engineering alloys implanted at ultrahigh current densities has revealed that the process induces no change in the bulk microsctructure of the materials. Even though temperatures induced during processing exceed the transformation (tempering and annealing) temperatures, there is insufficient time for nucleation and growth reactions to occur during the temperature excursion associated with typical implantation dose and energy conditions. Substantially lower costs should accompany the shorter duration ultrahigh current density implantation process. Auger electron spectrographs reveal a substantially extended nitrogen range over those observed at low current densities (four-fold increase). This enhanced range appears to be due to radiation enhanced diffusion effects. Deeper penetration could lead to more durable surface layers. 相似文献
8.
Composite Materials Based on Shape‐Memory Ti2NiCu Alloy for Frontier Micro‐ and Nanomechanical Applications 下载免费PDF全文
9.
10.
E. Shankar S. Balasivanandha Prabu T. Sampath Kumar M. R. Stalin John 《Materials and Manufacturing Processes》2018,33(11):1242-1249
Burnishing avoids the need for super finishing operations after the conventional turning process, to enhance the surface quality. This paper deals with the surface modifications of Al(B4C)p Metal Matrix Composites (MMC) workpiece material after burnishing with a TiAlN coated WC roller. The burnishing speed, lubrication type, burnishing passes, and coating were the input parameters. Surface hardness and roughness after the burnishing were studied. It was found that the coating on the WC roller had enhanced the hardness in the workpiece after burnishing in the case of Al-5?wt.% (B4C)p, under all conditions. The effect of the coating on the work piece surface hardness was not significant with Al-10?wt.% (B4C)p. While burnishing Al-5?wt.% (B4C)p, the minimum surface roughness combined with maximum surface hardness was obtained, during the third pass under dry condition using uncoated rollers. The number of passes to achieve the desired surface conditions reduced, on using coated rollers with kerosene as the lubricant. 相似文献