Magnesia–doped alumina and yttria–doped zirconia nano-powders were synthesized using sucrose as a chelating agent and template material from the aqueous solutions of aluminium nitrate, magnesium nitrate, ytrrium nitrate and zirconyl nitrate, respectively. Synthesis parameters were optimized with varying sucrose to metal ion ratio, calcinations time, and temperature to produce these nano-powders. As-synthesized powders were characterized by room temperature X-ray diffraction, BET surface area analyzer and transmission electron microscopy. Y2O3–ZrO2 nano-powders had particle size in the range of 80–200 nm with specific average surface area of 119 m2/g and for MgO–Al2O3 powders, particle sizes were 30–200 nm with the specific average surface area of 250 m2/g. Our results indicate that this synthesis method is a versatile one and can be applied to a variety of oxide-based materials to form nano-powders. Nano-powders were compacted uniaxially and densified in a muffle furnace. Sintered discs were used for hardness testing and density measurements, as well as for microstructural characterization. 相似文献
2D triaxially braided carbon fiber composites were subjected to off-axis compression under static and low velocity impact loading. Three types of specimens with axial fiber tows at angles of 30°, 60°, and 75° to the direction of loading were studied under uniaxial compression loading using a modified compression loading fixture that has anti-buckling guides. Static tests were carried out using a hydraulically activated MTS loading frame, while, low velocity impact tests were conducted using a drop tower facility. A three parameter homogenized orthotropic plasticity model was used to characterize the inelastic response and the constants associated with this characterization were determined uniquely. Results from this characterization were subsequently used to analyze the rate dependent interfacial effects in these materials. Two types of composites made from two different resins, but with the same textile architecture were used for this study. The effect of the resin properties on the unusual rate effects exhibited by the composite is seen to be captured well with the three parameter orthotropic plasticity model adopted. 相似文献
This paper presents an adaptive multiuser channel estimator using the reduced-Kalman least-mean-square (RK-LMS) algorithm.
The frequency-selective fading channel is modeled as a tapped-delay-line filter with smoothly time-varying Rayleigh distributed
tap coefficients. The multiuser channel estimator based on minimum-mean-square-error (MMSE) criterion is used to predict the
filter coefficients. We also present its convergence characteristics and tracking performance using the RK-LMS algorithm.
Unlike the previously available Kalman filtering algorithm based approach (Chen, Chen IEEE Trans Signal Process 49(7): 1523–1532, 2001) the incorporation of RK-LMS algorithm reduces the computational complexity of multiuser channel estimator
used in the code division multiple access wireless systems. The computer simulation results are presented to demonstrate the
substantial improvement in its tracking performance under the smoothly time-varying environment.
Coal is heterogeneous in nature,and thus the characterization of coal is essential before its use for a specific purpose.Thus,the current study aims to develop ... 相似文献
We present an iterative algorithm for robustly estimating the ego-motion and refining and updating a coarse depth map using parametric surface parallax models and brightness derivatives extracted from an image pair. Given a coarse depth map acquired by a range-finder or extracted from a digital elevation map (DEM), ego-motion is estimated by combining a global ego-motion constraint and a local brightness constancy constraint. Using the estimated camera motion and the available depth estimate, motion of the three-dimensional (3-D) points is compensated. We utilize the fact that the resulting surface parallax field is an epipolar field, and knowing its direction from the previous motion estimates, estimate its magnitude and use it to refine the depth map estimate. The parallax magnitude is estimated using a constant parallax model (CPM) which assumes a smooth parallax field and a depth based parallax model (DBPM), which models the parallax magnitude using the given depth map. We obtain confidence measures for determining the accuracy of the estimated depth values which are used to remove regions with potentially incorrect depth estimates for robustly estimating ego-motion in subsequent iterations. Experimental results using both synthetic and real data (both indoor and outdoor sequences) illustrate the effectiveness of the proposed algorithm. 相似文献
The vehicular delay-tolerant network is the real-life application based area of Delay tolerant network where communication takes place using vehicular nodes and roadside units. The topology used in vehicular networks is highly dynamic by architecture due to the use of moving vehicular nodes. It operates in such a scenario where a direct path between source and destination remains absent on the most piece of the time. In case of non-existence of connected path vehicular delay-tolerant network works opportunistically and uses the same store, carry, and forward paradigm as Delay Tolerant Network. However, the routing protocols designed for vehicular delay-tolerant network faces crucial challenges like inadequate relay node, incomplete data transfer, a large number of packet drop, and uncertain delivery time. In this research paper,
we propose a novel routing strategy for the vehicular delay-tolerant network. The proposed routing strategy selects efficient vehicular relay node for complete packet transfer and intelligently reduces the packet drop for timely packet delivery. We implement the proposed routing strategy in the ONE simulator; the ONE simulator provides an opportunistic environment for nodes. We analyze the performance of the proposed strategy under various simulations results using different parameters. The results show that the proposed strategy outperforms standard routing protocols in terms of considered parameters and provide an efficient solution for the problem of disconnection.
A novel method for preparation of nano-crystalline gadolinium aluminate (GdAlO3) powder, based on combustion synthesis, is reported. It was observed that aluminium nitrate and gadolinium nitrate exhibit different combustion characteristics with respect to urea, glycine and β-alanine. While urea was proven to be a suitable fuel for direct formation of crystalline α-Al2O3 from its nitrate, glycine and β-alanine are suitable fuels for gadolinium nitrate for preparation of its oxide after combustion reaction. Based on the observed chemical characteristics of gadolinium and aluminium nitrates with respect to above mentioned fuels for the combustion reaction, the fuel mixture composition could be predicted that could lead to phase pure perovskite GdAlO3 directly after the combustion reaction without any subsequent calcination step. The use of single fuel, on the other hand, leads to formation of amorphous precursor powders that call for subsequent calcination for the formation of crystalline GdAlO3. The powders produced directly after combustion reactions using fuel mixtures were found to be highly sinterable. The sintering of the powders at 1550 °C for 4 h resulted in GdAlO3 with sintered density of more than 95%. T.D. 相似文献
This first generation investigation evaluates the in vitro tribological performance of laser-processed Ta coatings on Ti for load-bearing implant applications. Linear reciprocating wear tests in simulated body fluid showed one order of magnitude less wear rate, of the order of 10(-4)mm(3)(N.m)(-1), for Ta coatings compared to Ti. Our results demonstrate that Ta coatings can potentially minimize the early-stage bone-implant interface micro-motion induced wear debris generation due to their excellent bioactivity comparable to that of hydroxyapatite (HA), high wear resistance and toughness compared to popular HA coatings. 相似文献