共查询到20条相似文献,搜索用时 218 毫秒
1.
Chen W Chen X Lu M Miao G Wei R 《The Journal of the Acoustical Society of America》2002,111(6):2632-2637
The dependence of the single bubble sonoluminescence (SBSL) on the waveforms of the driving ultrasound has been investigated by both experiment and numerical calculation. Three types of non-simple-harmonic waves, the rectangular, triangular and as well as the sinusoidal wave with a pulse, are used to drive the SBSL in our research. The triangular wave is the most effective, while the rectangular wave is the worst and the sinusoidal wave in the middle. However, the rectangular wave drives the brightest SBSL among those waves if the sound pressure amplitude keeps constant. When we use a simple-harmonic wave with a pulse as the driving sound, stable and periodic SBSL flashes have been observed. An increase in the flash intensity can be observed as the pulse is put at a suitable phase related to the sinusoidal wave. All of the observations are investigated numerically. Well qualitative agreements between the numerical simulations and the experimental measurements have been achieved. 相似文献
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Entropy generation minimization approach is a very good method allowing to analyze the engineering systems to exclude technical failure. The present study deals with computational analysis of triple diffusive flow, energy transference and entropy production in different porous cavities from square to triangular through trapezoidal shape. The formulated boundary-value problem has been worked out using the finite element technique and non-primitive variables. The developed computational code has been verified using numerical results of other researchers. Analysis of entropy production due to energy and mass transport, motion friction, and porous material has been performed for different chamber's shapes. Entropy generation analysis in chambers of various geometries under the triple-diffusive flow is a novelty of the present research, where different entropy production mechanisms have been scrutinized for one complex problem. It has been ascertained that average total entropy generation strength raises with buoyancy ratios, Lewis and Rayleigh numbers, but it has the minimum value for the square chamber in comparison with triangular and trapezoidal shapes. Moreover, obtained results characterize a neglecting influence of motion friction on the total entropy generation. 相似文献
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研究了电吸收调制器(EAM)的衰减随外加反向电压增加而指数增加的情形下,短脉冲光源的脉冲输出和解复用器的开关窗口对EAM的消光效率、反向DC偏置电压以及正弦RF驱动信号的幅度等参量的依赖关系.在基于EAM的短脉冲光源中,输出脉冲的消光比等于EAM消光效率η与正弦驱动电压峰峰值Vpp的乘积,输出光脉冲的消光比和脉宽均与EAM的反向偏置电压无关,但输出脉冲的峰值功率与η、Vpp和Vb都有关系.在基于EAM的解复用器中,为了使解复用器的开关窗口近似为矩形,可利用EAM的削波效应,使Vpp/2>Vb.在EAM的消光效率η已知时,通过仔细设计反向DC偏置电压Vb和正弦驱动电压的峰峰值Vpp,达到OTDM解复用器所需要的开关窗口形状、宽度和消光比. 相似文献
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Analysis and design of grating couplers 总被引:5,自引:0,他引:5
Based on an accurate perturbation analysis of the guiding properties of dielectric gratings, simple design criteria are developed
for grating couplers which transfer the energy of a beam into or out of an optical waveguide. Gratings having arbitrary groove
shapes are considered and explicit formulae are given for the leakage parameters of gratings with symmetric profiles. The
results cover TEv and TMv modes and they apply to both shallow and deep grating grooves. The variation of the leakage parameter α in rectangular gratings
is examined in detail; these rectangular gratings are then used as basic configurations for predicting the characteristics
of other grating profiles. Particular attention is given to trapezoidal and triangular profiles and gratings with asymmetric
profiles are also discussed. 相似文献
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Forced axisymmetric response of circular plates is considered on the basis of an improved theory which takes into account the effect of rotatory inertia and shear deformation. Explicit solutions are obtained for distributed, ring and concentrated impulsive loadings with half-sine, triangular, blast and rectangular pulse shapes. Natural frequencies are presented for the first 20 modes of four plate models with clamped and supported edges. Numerical results are presented to illustrate the differences between the improved and classical theories, and the effects of edge conditions, loading conditions, pulse shapes and pulse durations. 相似文献
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Yu-Soo Lee Hyun-Ju Chung Jong-Han Joung Eung-Jo Kim Hee-Je Kim 《Optics & Laser Technology》2004,36(1):461-61
We describe the pulse forming of pulsed CO2 laser using multi-pulse superposition technique. Various pulse shapes, high duty cycle pulse forming network (PFN) are constructed by time sequence. This study shows a technology that makes it possible to make various long pulse shapes by activating SCRs of three PFN modules consecutively at a desirable delay time with the aid of a PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a high voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage by driving the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence.We investigated various long pulse shapes as different trigger time intervals of SCRs among three PFN modules. As a result, we could obtain laser beam with various pulse shapes and durations from about 250 to 1000 μs. 相似文献
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Microplasma array devices with coplanar electrodes have been fabricated and operated in neon at pressures up to 684 Torr. The microcavity of the device is composed of a couple of electrodes instead of dielectric or single cathode. The experiment results for the line array with 12 microcavities driven by AC sinusoidal voltage show that the power loading of each microcavity reaches approximately several kW cm−3 and the luminance reaches 2500 cd m−2. The discharge delay time for the devices excited by AC pulse voltage is about 1-3 μs. The lighting patterns of the devices with address electrode validate the addressing ability of the proposed devices. 相似文献
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设计了一种基于Marx电路的方波脉冲电源,该电源采用磁环隔离驱动方案与全桥Marx电路相结合,实现了正极性、负极性和双极性高压方波脉冲的输出,解决了常规脉冲电源只能输出特定极性脉冲的限制。对电路的运行模式经行了理论分析,并搭建了16级实验样机。实验结果表明:在空载条件下,实现了频率1 kHz,幅值10 kV的正极性、负极性及双极性高压方波脉冲输出。其最小脉宽1μs,极性可调。该脉冲电源结构紧凑,可以实现输出电压、脉宽、脉冲极性可调。最后使用该方波脉冲电源驱动平行板介质阻挡放电反应器。结果表明:该方波脉冲电源可以作为介质阻挡放电驱动源。 相似文献
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为定量研究电磁波与微带线的耦合终端响应问题,提出一种基于BLT方程的电磁波与微带线耦合分析方法,相比传统方法计算效率高、占用内存少。将PCB板上微带线等效为有耗传输线模型,对辐照平面波进行矢量分析并求解等效激励源,运用BLT方程研究不同入射方式、脉冲波形对微带线终端的影响,并对入射波与终端响应进行了时域、频域分析。研究表明:当入射波频率与微带线长度满足一定关系式时对微带线的耦合最强,耦合电压峰值达2.4 mV;电场平行微带线入射比垂直PCB入射时的终端电压峰值大一倍;且同幅同脉宽的矩形脉冲较高斯脉冲和三角脉冲对微带线的耦合峰值电压大;不同波形的脉冲通过调节脉宽都可对微带线耦合终端电压达到mV量级。 相似文献
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In the present study, the effect of triangular, rectangular and trapezoidal ribs on the laminar heat transfer of water-Ag nanofluid in a ribbed triangular channel under a constant heat flux was numerically studied using finite volume method. Height and width of ribs have been assumed to be fixed in order to study the effect of different rib forms. Modeling were performed for laminar flow (Re=1, 50 and 100) and nanofluid volume fractions of 0, 2% and 4%. The results indicated that an increase in volume fraction of solid nanoparticle leads to convectional heat transfer coefficient enhancement of the cooling fluid, whereas increasing the Nusselt number results in a loss of friction coefficient and pressure. Also, along with the fluid velocity increment, there will be an optimal proportion between heat and hydrodynamic transfer behavior which optimizes performance evaluation criteria (PEC) behavior. Among all of the investigated rib forms, the rectangular one made the most changes in the streamlines and the triangular form has the best thermal performance evaluation criteria values. For all studied Reynold numbers, heat transfer values are least for rectangular rib from. Therefore, trapezoidal ribs are recommended in high Reynold numbers. 相似文献
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A study is made of the effect of pulse repetition rate (0.1−103 s−1) and average discharge current (0–1 A) on the breakdown delay time and burning voltage of low-pressure glow discharges (p<0.1 Pa) in an electrode system of the reverse magnetron type with a large cathode surface area (≈103 cm2). It is shown that increasing the repetition rate leads to a many-fold reduction in the statistical spread in the delay time
and in the discharge formation time, while the average discharge current has a significant effect on the burning voltage.
The mechanism for the observed phenomena is interpreted qualitatively in terms of the presence of thin dielectric films on
the cathode surface.
Zh. Tekh. Fiz. 69, 20–24 (May 1999) 相似文献
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研究了电吸收调制器(EAM) 的衰减随外加反向电压增加而指数增加的情形下,短脉冲光源的脉冲输出和解复用器的开关窗口对EAM 的消光效率、反向DC 偏置电压以及正弦RF 驱动信号的幅度等参量的依赖关系- 在基于EAM 的短脉冲光源中,输出脉冲的消光比等于EAM 消光效率η与正弦驱动电压峰峰值Vpp 的乘积,输出光脉冲的消光比和脉宽均与EAM 的反向偏置电压无关,但输出脉冲的峰值功率与η、Vpp 和Vb 都有关系- 在基于EAM的解复用器中,为了使解复用器的开关窗口近似为矩形,可利用EAM 的削波效应,使Vpp/2> Vb- 在EAM 的消光效率η已知时,通过仔细设计反向DC 偏置电压Vb 和正弦驱动电压的峰峰值Vpp ,达到OTDM 解复用器所需要的开关窗口形状、宽度和消光比- 相似文献
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The average and instantaneous luminances of a thin-film electroluminescent device (TFELD) are determined as functions of the
voltage rise time by solving kinetic equations for the concentration of excited emission centers in the electroluminescent
layer of the device. It is shown theoretically and experimentally that the dependences of the average and peak luminances,
the external and internal quantum yield, the energy yield, and the luminous efficacy as functions of the voltage rise time
all have a maximum, and the position of that maximum depends on the frequency of the driving voltage. The calculated and experimental
dependences make it possible to determine the main parameters of the electroluminescence process: the collisional excitation
cross section for the emission centers, the concentration of emission centers, and the transition probability of the emission
centers to an excited state, as well as the radiative and nonradiative recombination probabilities of these and other centers.
Zh. Tekh. Fiz. 69, 58–63 (February 1999) 相似文献
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使用矩形截面磁芯研制了一台磁开关作为脉冲驱动源的主开关,并利用电容器放电法对磁芯不同位置处的磁滞回线进行了测量。结果表明,短边和长边测量得到的磁滞回线均能够适应磁开关需求,不同的励磁位置对磁滞回线形状的影响有限。设计了基于该磁芯的磁开关,使用PSpice软件进行了数值模拟,结果与理论分析相一致。结合卷绕型带状脉冲形成线,对磁开关作为脉冲驱动源主开关进行了实验研究。结果表明研制的磁开关实现了主开关功能,在1.1 的低阻抗负载上获得了峰值电压9 V、上升沿80 ns、脉冲半高宽230 ns的准方波脉冲输出。 相似文献
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文中采用ANSYS热分析软件对矩形槽、梯形槽、三角形槽三种微槽平板热管进行了模拟仿真。通过比较加热功率分别为30W、40W、50W三种情况下热管下表面中心点温度值,得出了梯形槽平板热管具有更优良的传热性能的结论。 相似文献
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在诸如粒子加速器等应用中,要求高压脉冲的电压、电流顶降尽可能低。减小顶降的常用方法是增加储能电容器的容量,但代价是系统的能效较低、体积较大、功率较高。另一种方法是插入一些特殊级来补偿电压顶降。在固态Marx发生器中,当谐振电感和补偿开关串联起来与普通级中的主电容并联时,就得到了补偿级。本文在16级单极性固态Marx发生器中加入了四个基于谐振电路的补偿级,以补偿不同负载、不同脉宽下的电压顶降。在放电过程中,将正弦电压的近线性部分加到负载上作为补偿,实现了几乎无电压顶降的矩形脉冲。不同的补偿级数可以对电压顶降进行不同程度的补偿,补偿效果也是可调的。此外,只要关断谐振管,这些补偿级也可以作为固态Marx发生器中的普通级工作,从而加以利用。由于谐振补偿级中的电容也与Marx电路中的电容并联充电,因此不需要辅助电源充电。实验结果表明,在400 Ω和5 kΩ阻性负载上,2.5 kV和10.5 kV脉冲的电压顶降分别都能得到理想的补偿。为了获得更好的补偿效果,脉冲宽度应小于正弦电压的近线性部分的长度。 相似文献