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1.
Influence of input acoustic power on regenerator＇s performance   总被引：2，自引：0，他引：2  
Performance of a pulse tube cooler significantly depends on the efficient operation ofits regenerator. Influence of input acoustic power on regenerator＇s performance is simulated and analyzed with simple harmonic analysis method. Given regenerator＇s dimensions and pressure ratio, there is an optimal input acoustic power for achieving a highest coefficient of performance, due to a compromise between relative time-averaged total energy flux in regenerator and relative acoustic power at regenerator＇s cold end. Additionally, optimal dimensions of regenerator are also estimated and presented for different input acoustic powers. The computed optimal diameter obviously increases with increase of input acoustic power, while the optimal length decreases slightly, and as a result, a larger input acoustic power requires a smaller aspect ratio （length over diameter）.  相似文献   

2.
INTRODUCTION In the past 30 years, much progress has been achieved in thermoacoustic research (Backhaus and Swift, 1999; Garrett et al., 1993; Zhou and Matsubara,1998). However, most of them were still at laboratory scale. Aiming for industrial applications, recent re-searches began to pay attention to larger or smaller scale systems. The problem of heat dissipation from miniature high-tech products (say ICs, MEMS) at-tracts more attention due to the higher heat flux ac-companying th…  相似文献   

3.
The axisymmetric themoelastic problem of a uniformly heated, functionally graded isotropic hollow cylinder is considered. An analytical form of solution is proposed. For the case when the Young's modulus and thermal expansion coefficient have a power-law dependence on the radial coordinate, explicit exact solution is obtained. For the degenerated case, i.e. when the cylinder is homogeneous and isotropic, no stresses will occur provided it is subjected to a uniform temperature. Numerical results are finally given and some important inclusions are obtained. Project (No.10002016) supported by the National Natural Science Foundation of China (NSFC).  相似文献   

4.
This paper proposes a global stabilization method for a class of planar switched systems with input saturation constrains by using a state feedback and switching strategy. This method is proved to be effective by analyzing the characteristics of the trajectory of second-order linear systems with input saturation. Project supported by the China Postdoctoral Science Foundation (Grant No.20070420643), the National Natural Science Foundation of China (Grant No.60774059), and the Innovation Program of the Shanghai Municipal Science and Technology Commission (Grant No.08DZ2272400)  相似文献   

5.
A new PWM converter based on soft-switching is introduced.The converter uses a minimum number of devices,and requires less switching operations than conventional techniques,Switching is realized solely in a ZVS)zero voltage switching)mode,therefore the loss is reduced and EMI(electromagnetic interference)is suppressed.The paper analyzes the operation of ZVS,and discusses the methods for maintaining a unit power factor and constant DC voltage.Changing the modulation index M and the phase angle θ keeps the input current in phase with the voltage.It also keeps the current sinusoidal,and ensures a constant output voltage.  相似文献   

6.
A new kind of fuzzy control scheme, based on the identification of the signal's main frequency and the behavior of the ER damper, is proposed to control the semi-active suspension system. This method adjusts the fuzzy controller to achieve the best isolation effect by analyzing the main frequency's characters and inspecting the change of system parameters. The input of the fuzzy controller is the main frequency and the optimal damping ratio is the output. Simulation results indicated that the proposed control method is very effective in isolating the vibration. Project (No. 69974024) supported by the National Natural Science Foundation of China  相似文献   

7.
INTRODUCTION The reactive power dispatch is aimed at mini- mizing the active power loss in the transmission network by allocating the reactive power generation under several security constraints. The reactive power dispatch problem has significant influence on secure and economic operation of power systems. The reac- tive power generation affects the overall generation cost via transmission loss. A procedure which allo- cates the reactive power generation so as to minimize the transmissio…  相似文献   

8.
This paper presents a sliding mode (SM) based identifier to deal with the parameter identification problem for a class of parameter uncertain nonlinear dynamic systems with input nonlinearity. A sliding mode controller (SMC) is used to ensure the global reaching condition of the sliding mode for the nonlinear system; an identifier is designed to identify the uncertain parameter of the nonlinear system. A numerical example is studied to show the feasibility of the SM controller and the asymptotical convergence of the identifier. Project supported by the National Natural Science Foundation of China(No. 69974035) and Zhejiang Provincial Natural Science Key Foundation of China (ZD9905)  相似文献   

9.
PWM逆变器载波方式的选择   总被引：1，自引：2，他引：1  
In this paper the influence of different carrier waveforms upon the output characteristics of PWM inverter is described in detail. When a triangular carrier waveform is used in hard-switching PWM inverters, harmonics exist in the neighborhood of the output frequency of the inverter output voltage and current due to the dead time. The triangular carrier waveform used in soft-switching PWM inverter will cause difficulties in controlling resonance-trigger time, higher loss in the resonant circuit, and less utilization of the DC bus voltage. If a sawtooth carrier is used in hard-switching PWM inverter, there will be severe distortion in the current waveform. When sawtooth carriers with alternate positive and negative slopes are used in soft-switching PWM inverters, the resonancetrigger time is easy to control, and distortion in the output voltage and current caused by the dead time will not appear.  相似文献   

10.
A new photonic bandgap (PBG) cover for a patch antenna with a photonic bandgap substrate is introduced. The plane wave expansion method and the FDTD method were used to calculate such an antenna system. Numerical results for the input return loss, radiation pattern, surface wave, and the directivity of the antennas are presented. A comparison between the conventional patch antenna and the new PBG antenna is given. It is shown that the new PBG cover is very efficient for improving the radiation directivity. The physical reasons for the improvement are also given. Project supported by the National Natural Science Foundation of China (No. 90101024) and the Science and Technologies of Zhejiang Provinc (No. ZD0002)  相似文献   

11.
Reaction thrust of water jet for conical nozzles   总被引：1，自引：0，他引：1  
Clear knowledge on the reaction thrust of water jet is valuable for better design of water jet propulsion system. In
this paper, theoretical, numerical and experimental studies were carried out to investigate the effects of the nozzle geometry
as well as the inlet conditions on the reaction thrust of water jet. Comparison analyses reveal that the reaction thrust has a
direct proportional relationship with the product of the inlet pressure, the square of flow rate and two-thirds power exponent
of the input power. The results also indicate that the diameter of the cylinder column for the conical nozzle has great influence
on the reaction thrust characteristics. In addition, the best values of the half cone angle and the cylinder column length exist
to make the reaction thrust reach its maximum under the same inlet conditions．  相似文献   

12.
A first order system model is proposed for simulating the influence of stress stimulation on fracture strength during fracture healing. To validate the model, the diaphyses of bilateral tibiae in 70 New Zealand rabbits were osteotomized and fixed with rigid plates and stress-relaxation plates, respectively. Stress shielding rate and ultimate bending strength of the healing bone were measured at 2 to 48 weeks postoperatively. Ratios of stress stimulation and fracture strength of the healing bone to those of intact bone were taken as the system input and output. The assumed first order system model can approximate the experimental data on fracture strength from the input of stress stimulation over time, both for the rigid plate group and the stress-relaxation plate group, with different system parameters of time constant and gain. The fitting curve indicates that the effect of mechanical stimulus occurs mainly in late stages of healing. First order system can model the stress adaptation process of fracture healing. This approach presents a simple bio-mathematical model of the relationship between stress stimulation and fracture strength, and has the potential to optimize planning of functional exercises and conduct parametric studies. Project (No. 39470698) supported by the National Natural Science Foundation of China  相似文献   

13.
In this paper, a modified transient finite element (FE) algorithm for the performance analysis of magnetically levitated vehicles of electromagnetic type is presented. The algorithm incorporates the external power system and vehicle’s movement equations into FE model of transient magnetic field computation directly. Sliding interface between stationary and moving region is used during the transient analysis. The periodic boundaries are implemented in an easy way to reduce the computation scale. It is proved that this method can be used for both electro-motional static and dynamic cases. The test of a transformer and an EMS-Maglev system reveals that the method generates reasonable results at very low computational costs comparing with the transient FE analysis.  相似文献   

14.
Samarium and a catalytic amount of iodine were used to obtain functionalized cyclopentenes by reductive dimerization followed by intramolecular cyclization of 1,1-dicyanoalkenes under mild conditions. Preject (No. 20072033) supported by the National Natural Science Foundation of China, and Zhejiang Provincial Natural Science Foundation of China  相似文献   

15.
Implementing VLPR systems based on TMS320DM6421   总被引：2，自引：0，他引：2  
This paper gives a practical schema for using DSP boards to construct Vehicle License Plate Recognition （VLPR） modules that could be embedded in any Intelligent Transportation System （ITS）. Using DSP can avoid the heavy investment in dedicated VLPR system and improve the computational power compared to PC software environment. Low cost, high computational power, and high flexibility of DSP provide the License Plate Recognition System （LPRS） an excellent cost-effective solution to execute the major part of the recognition tasks. This paper describes a successful implementation of VLPR system based on Texas Instruments （TI）＇s TMS320DM642. The DSP board acquires video （which could be output to a monitor for surveillance） from a camera, captures images from the video, locates and recognizes the license plates in images, and then sends the recognized results and related images after compression to a host PC through the network. Finally, the overall software is optimized according to the features of DM642 chip. Experiments showed that the DSP VLPR system performs well on the local license plates, and that the processing speed and accuracy can meet the requirement of practical applications.  相似文献   

16.
The technique of real-time digital speckle pattern interferometry is proposed to study diffusion of surfactants in hydrogel. The diffusion coefficient is simply and directly determined from the interferograms. An example of diffusion coefficient measurement of surfactant in agarose gel demonstrates the usefulness of the method. The results obtained are compared with the theoretical simulating values. Project Supported by National Natural Science Foundation of China (No. 29904007), Zhejiang Provincial Natural Science Foundation of China (No. 699031), and SRF for ROCS, SEM, China  相似文献   

17.
With the use of this novel everage model for Single Stage Flyback PFC+Flyback DC/DC converter, voltage control mode, peak current control mode and average current control mode can be simulated easily by changing the model's parameters. It can be used to do various analysis not only for small signal and static behavior but also for large signal and dynamic behavior of the converter. By using this average model the simulation speed can be improved by 2 orders of magnitude above that obtained by using the conventional switched model. It can be applied to optimize the trade-off between high power factor, voltage stress, current stress and good output performance while designing this kind of single stage PFC converter. A 60W single stage power factor corrector was built to verify the proposed model. The modeling principle can be applied to other Single Stage PFC topologies. Project (No. 50077020) supponted by the National Natural Science Foundation of China.  相似文献   

18.
A new algorithm is presented that generates developable Bézier surfaces through a Bézier curve called a directrix. The algorithm is based on differential geometry theory on necessary and sufficient conditions for a surface which is developable, and on degree evaluation formula for parameter curves and linear independence for Bernstein basis. No nonlinear characteristic equations have to be solved. Moreover the vertex for a cone and the edge of regression for a tangent surface can be obtained easily. Aumann’s algorithm for developable surfaces is a special case of this paper. Project supported by the National Basic Research Program (973) of China (No. 2004CB719400), the National Natural Science Foundation of China (Nos. 60373033 and 60333010) and the National Natural Science Foundation for Innovative Research Groups (No. 60021201), China  相似文献   

19.
Plastids of nongreen tissues import carbon as a source of biosynthetic pathways and energy, and glucose 6-phosphate is the preferred hexose phosphate taken up by nongreen plastids. A cDNA clone encoding glucose 6-phosphate/phosphate translocator (GPT) was isolated from a cDNA library of immature seeds of rice and named asOsGPT. The cDNA has one uninterrupted open reading frame encoding a 42 kDa polypeptide possessing transit peptide consisting of 70 amino acid residues. TheOsGPT gene maps on chromosome 8 of rice and is linked to the quantitative trait locus for 1000-grain weight. The expression ofOsGPT is mainly restricted to heterotrophic tissues. These results suggest that glucose 6-phosphate imported viaGPT can be used for starch biosynthesis in rice nongreen plastids. Project supported by National Natural Scienc Foundation of China (No.39830250) and Natural Science Foundation of Zhejiang Province (No.2A0106), China. The nucleotide sequence data will appear in the GenBank under accession number AF375053.  相似文献   

20.
The effects of five domestic cooking methods, including steaming, microwaving, boiling, stir-frying, and stir-frying followed by boiling (stir-frying/boiling), on the nutrients and health-promoting compounds of broccoli were investigated. The results show that all cooking treatments, except steaming, caused significant losses of chlorophyll and vitamin C and significant decreases of total soluble proteins and soluble sugars. Total aliphatic and indole glucosinolates were significantly modified by all cooking treatments but not by steaming. In general, the steaming led to the lowest loss of total glucosinolates, while stir-frying and stir-frying/boiling presented the highest loss. Stir-frying and stir-frying/boiling, the two most popular methods for most homemade dishes in China, cause great losses of chlorophyll, soluble protein, soluble sugar, vitamin C, and glucosinolates, but the steaming method appears the best in retention of the nutrients in cooking broccoli. Project supported by the High-Tech R&D Program (863) of China (No. 2008AA10Z111), the National Natural Science Foundation of China (No. 30320974), the Fok Ying Tong Education Foundation of China (No. 104034), and the Program for New Century Excellent Talents in the University of China (No. NCET-05-0516)  相似文献   

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