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排序方式: 共有591条查询结果,搜索用时 31 毫秒
41.
N. Balasubramanian R.S. Mishra K. Krishnamurthy 《Journal of Materials Processing Technology》2009,209(8):3696-3704
Commercially available compact heat exchangers are currently fabricated in several steps by joining multiple tubes, or by independently fabricating and joining fluid channels. Friction stir channeling (FSC) is a simple and innovative technique of manufacturing heat exchangers in a single step by creating continuous, integral channels in a monolithic plate in a single pass. FSC relies on the frictional heat generated between the tool material and the metal workpiece to soften and deform the material to facilitate the creation of a continuous channel. The channel shape, size, and integrity depend on the processing parameters and the tool design. In this paper the structural characteristics and the relationship between the channel features and the processing parameters are discussed. FSC is being developed as a technique for manufacturing heat exchangers. The channel is characterized by roughness features on the inside, which can be analyzed using optical microscopy techniques. 相似文献
42.
C. V. R. Reddy T. S. Krishnamurthy S. Haranath T. N. Suresh 《Mechanism and Machine Theory》1989,24(6):481-492
This paper deals with theoretical and experimental investigations on the free vibration characteristics of representative large flexible solar array appendages used in spacecrafts under vacuum environmental conditions prevailing in space. Eight different configurations of solar panels with varied flexibility and surface area have been studied. The theoretical results, namely the modal parameters, have been correlated with results from experiments. These are performed on solar arrays of different configurations under varied parameters of panel flexibility, vacuum and amplitudes of vibration. 相似文献
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Pukar Malla Hasnain Lakdawala Ravi Naiknaware Krishnamurthy Soumyanath Kevin Kornegay 《Analog Integrated Circuits and Signal Processing》2010,65(2):197-208
Modern multi-standard receivers in deep-submicron technologies pose significant design challenges on the analog baseband.
Moving this analog filtering to the digital domain simplifies the design, yielding a process-scalable implementation. However,
analog-to-digital converter (ADC) specifications now become more stringent and must be obtained by comprehending the standard
and the system. Assuming a receiver NF of 5.96 dB and SNR degradation of 0.36 dB by the ADC, the proposed dual-mode WiFi/WiMAX
receiver attains an input sensitivity of −74 dBm (20 MHz channel bandwidth). To accommodate the high dynamic range and the
anti-alias rejection needed for the system, a Delta-Sigma (ΔΣ) ADC is proposed. Single-loop and Multi-Stage Noise-Shaping
(MASH) architectures that achieve a SNR of 69 dB at a low oversampling ratio (OSR) of 8 for a conversion bandwidth of 40 MHz
(108 Mbps, OFDM) are investigated at system level. Based on thermal noise, harmonic distortion, and power tradeoffs, a ΔΣ
ADC design that meets the design specifications is presented. 相似文献
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Determination of the elastic moduli of polymer matrix based structural composite materials is necessary to characterize their strength after fabrication and while in service. This paper reports a modification to goniometry based ultrasonic through transmission data collection by using wide aperture low cost polyvinylidene fluoride (PVDF) based receiver. The use of PVDF based receiver more than satisfies the plane-wave conditions required from measurement. The use of a hybrid inversion technique which combines genetic algorithm based evolutionary approach, critical angle information and the use of stiffness invariants is implemented for determination of stiffness values from experimental transmission spectra measurements. Results for unidirectional and a multi-layered composite laminate are presented. 相似文献
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Stochastic gradient algorithms for design of minimum error-rate linear dispersion codes in MIMO wireless systems 总被引:1,自引:0,他引:1
Xiaodong Wang Krishnamurthy V. Jibing Wang 《Signal Processing, IEEE Transactions on》2006,54(4):1242-1255
Linear dispersion (LD) codes are a good candidate for high-data-rate multiple-input multiple-ouput (MIMO) signaling. Traditionally LD codes were designed by maximizing the average mutual information, which cannot guarantee good error performance. This paper presents a new design scheme for LD codes that directly minimizes the block error rate (BLER) in MIMO channels with arbitrary fading statistics and various detection algorithms. For MIMO systems employing LD codes, the error rate does not admit an explicit form. Therefore, we cannot use deterministic optimization methods to design the minimum-error-rate LD codes. In this paper, we propose a simulation-based optimization methodology for the design of LD codes through stochastic approximation and simulation-based gradient estimation. The gradient estimation is done using the score function method originally developed in the discrete-event-system community. The proposed method can be applied to design the minimum-error-rate LD codes for a variety of detector structures including the maximum-likelihood (ML) detector and several suboptimal detectors. It can also design optimal codes under arbitrary fading channel statistics; in particular, it can take into account the knowledge of spatial fading correlation at the transmitter and receiver ends. Simulation results show that codes generated by the proposed new design paradigm generally outperform the codes designed based on algebraic number theory. 相似文献
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