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931.
932.
Ashish Ganvir Chamara Kumara Mohit Gupta Per Nylen 《Journal of Thermal Spray Technology》2017,26(1-2):71-82
Axial suspension plasma spraying (ASPS) can generate microstructures with higher porosity and pores in the size range from submicron to nanometer. ASPS thermal barrier coatings (TBC) have already shown a great potential to produce low thermal conductivity coatings for gas turbine applications. It is important to understand the fundamental relationships between microstructural defects in ASPS coatings such as crystallite boundaries, porosity etc. and thermal conductivity. Object-oriented finite element (OOF) analysis has been shown as an effective tool for evaluating thermal conductivity of conventional TBCs as this method is capable of incorporating the inherent microstructure in the model. The objective of this work was to analyze the thermal conductivity of ASPS TBCs using experimental techniques and also to evaluate a procedure where OOF can be used to predict and analyze the thermal conductivity for these coatings. Verification of the model was done by comparing modeling results with the experimental thermal conductivity. The results showed that the varied scaled porosity has a significant influence on the thermal conductivity. Smaller crystallites and higher overall porosity content resulted in lower thermal conductivity. It was shown that OOF could be a powerful tool to predict and rank thermal conductivity of ASPS TBCs. 相似文献
933.
A Rama Chandra Murthy Smitha Gopinath Ashish Shrivastav G. S. Palani Nagesh R. Iyer 《计算机、材料和连续体(英文)》2011,25(1):1-18
This paper presents methodologies for crack growth study and fatigue remaining life prediction of reinforced concrete structural components accounting for the corrosion effects. Stress intensity factor (SIF) has been computed by using the principle of superposition. At each incremental crack length, net SIF has been computed as the difference of SIF of plain concrete and reinforcement. The behaviour of reinforcement has been considered as elasto-plastic. Uniform corrosion rate has been assumed in the modeling. Corrosion effect has been accounted in the form of reduction in the diameter and modulus of elasticity of steel. Numerical studies have been carried out to validate the methodologies. It is observed that the predicted remaining life for RC beam without corrosion effects is significantly larger compared to plain beams. The predicted remaining life decreases with increase in percentage of corrosion. 相似文献
934.
Anwar Demsis Bhaskar Verma S.V. Prabhu Amit Agrawal 《International Journal of Thermal Sciences》2010,49(10):1994-1999
The purpose of this paper is to present heat transfer measurements of gas in a tube under rarefied condition. The measurements are made in a circular tube of inner diameter 25 mm for approximately constant wall temperature boundary conditions, with nitrogen, oxygen, argon, and helium as the working fluids. The range of Knudsen and Reynolds numbers covered in this study are 0.0022–0.032 and 0.13–14.7, respectively. Whereas the continuum values are correctly reproduced in our setup, the measured values for Nusselt numbers are very small in the slip regime. The measured values are two-five orders of magnitude smaller than the corresponding values in the continuum regime, and suggest that the Nusselt number is a strong function of Reynolds, Knudsen and Brinkmann numbers in the slip flow regime. These are among the first heat transfer measurements in the slip flow regime and the current theoretical and simulation models are inadequate to explain such low values of Nusselt number. 相似文献
935.
A systematic experimental and theoretical investigation of the elastic and failure properties of ZnO nanowires (NWs) under
different loading modes has been carried out. In situ scanning electron microscopy (SEM) tension and buckling tests on single ZnO NWs along the polar direction [0001] were conducted.
Both tensile modulus (from tension) and bending modulus (from buckling) were found to increase as the NW diameter decreased
from 80 to 20 nm. The bending modulus increased more rapidly than the tensile modulus, which demonstrates that the elasticity
size effects in ZnO NWs are mainly due to surface stiffening. Two models based on continuum mechanics were able to fit the
experimental data very well. The tension experiments showed that fracture strain and strength of ZnO NWs increased as the
NW diameter decreased. The excellent resilience of ZnO NWs is advantageous for their applications in nanoscale actuation,
sensing, and energy conversion.
相似文献
936.
This paper presents an analytical model for the response of rectangular, specially orthotropic, symmetric laminated composite plates simply supported on all four sides subjected to low-velocity impact at the midpoint of the plate. The analysis is based considering both global and local effects. The influence of through-the-thickness normal stress on the magnitudes of inplane stresses is also considered. The plate is impacted by an impactor with a hemispherical tip. Contact force at the impact point, lateral displacements and velocities of the plate and the impactor and the stress state within the plate have been determined using modal solution technique. The governing equations, which apply to small deflection elastic response of specially orthotropic laminates, include combined effects of shear deformation and rotary inertia and non-linear Hertzian contact law. Inplane and interlaminar failure functions have been determined using quadratic failure criteria. Based on failure functions, damage initiation in the form of yarn/fiber breakage has been predicted. In general, it is observed that overall failure function is lower for woven fabric composites than for crossply laminates made of unidirectional layers. 相似文献
937.
Yun Wang Xiaodong Wang Bin Xie Demin Wang Agrawal D.P. 《Mobile Computing, IEEE Transactions on》2008,7(6):698-711
Intrusion detection in Wireless Sensor Network (WSN) is of practical interest in many applications such as detecting an intruder in a battlefield. The intrusion detection is defined as a mechanism for a WSN to detect the existence of inappropriate, incorrect, or anomalous moving attackers. For this purpose, it is a fundamental issue to characterize the WSN parameters such as node density and sensing range in terms of a desirable detection probability. In this paper, we consider this issue according to two WSN models: homogeneous and heterogeneous WSN. Furthermore, we derive the detection probability by considering two sensing models: single-sensing detection and multiple-sensing detection. In addition, we discuss the network connectivity and broadcast reachability, which are necessary conditions to ensure the corresponding detection probability in a WSN. Our simulation results validate the analytical values for both homogeneous and heterogeneous WSNs. 相似文献
938.
Standardization of wireless technologies is a continuous process, and even established standards are updated and modified in response to changes in the technology and the marketplace. One such example is the successful IEEE 802.11 standard for wireless local area networks (WLANs), which was originally designed for 1 and 2 Mb/s traffic, and is now being upgraded to support 600 Mb/s in 802.11n and being considered as a high-throughput (up to 1 Gb/s) wireless interface for the nomadic scenarios of the next generation of wireless systems. Similarly, enhancements to the IEEE 802.16 standard for wireless metropolitan area networks (WMANs) are being considered to develop a mobile air interface with support for up to 100 Mb/s in high mobility scenarios. This continuous evolution of the IEEE 802.11 WLAN and 802.16 WMAN standards is made possible with new innovation and contribution from both academia and industry. Given the rapid growth of these technologies, it is important to understand what new application scenarios have triggered the recent developments within WLAN and WMAN standards, how they are evolving, the technological challenges they face, and the opportunities for both the industry and research communities. In this issue, from a large number of submissions, we have selected five key articles for inclusion, which provide the reader with ongoing developments in these standards, technology roadmaps, current research challenges, and comprehensive evolution of these technologies, as well as deployment experience and application requirements. 相似文献
939.
Ashish K Ahuja Matthew R Behrend Masako Kuroda Mark S Humayun James D Weiland 《IEEE transactions on bio-medical engineering》2008,55(6):1744-1753
Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-microm-diameter stimulating electrodes and 10-microm-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 micros) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrode-electrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 +/- 6.6 nC) compared with monopolar stimulation (13.3 +/- 1.7 nC, p < 0.02). Presynaptic stimulation of the same ganglion cell with both 200- and 10-microm-diameter electrodes yielded threshold charge densities of 12 +/- 6 and 7.66 +/- 1.30 nC/cm2, respectively, while the required charge was 12.5 +/- 6.2 and 19 +/- 3.3 nC. 相似文献
940.
With applied potential, the current distribution at the surface of a disk electrode is spatially nonuniform and time dependent. This distribution is important to control in applications that desire a uniform current density profile or minimal corrosion. We examine the current density profile of a capacitive disk electrode subjected to a voltage-step using finite element analysis software to solve the system of partial differential equations. In detailed analyses we show quantitatively that the current density shifts from peripheral enhancement to near-uniformity following 1/2 of the lumped element time constant. As charging continues, the current density is slightly enhanced in the central region. We present curves for the evolution of local "time constants" as time progresses and calculate their effective values. The model is intended to be the basis of future work to control the corrosion profile of biologically implantable electrodes of arbitrary shape. Data suggest a means to control corrosion by retarding the edges of a stimulus pulse. Additionally, smaller electrodes may be more effective in fully utilizing surface area for charge transfer due to their shorter time constants. 相似文献