驻波与声悬浮

<正>1886年,德国科学家孔特(Kundt)发现,谐振管中的声波能够让灰尘颗粒悬浮起来,这一发现引发了悬浮技术的大革命,而今,声悬浮的威力已     

热声热机声场的格子气分析

从格子气自动机演化方程恢复了宏观热声方程,采用D2Q9热格子气模型模拟热声热机系统的压力场、温度场和速度场,获得压力驻波的传播和反射过程。模拟结果显示,在所给模拟条件下压力波具有非线性的特征,变截面附近的流场区域会产生引起非线性耗散的涡流。本文也分析了谐振管几何尺寸及格子气粒子密度对系统频率和压力的影响,验证了热声热机格子气模型的有效性。     

新型热声谐振机构的理论分析和实验验证

谐振管作为热声发动机的重要组成部分,其长度占整个系统轴向长度的大部分。本文提出了一种利用液体和弹性膜组成谐振系统的方法,并使用这种谐振系统取代谐振管,使系统轴向尺寸减少为原来的1/5。文中利用线性热声理论对该谐振系统的谐振频率进行了计算,并对不同阻尼系数对系统的耗散做出了分析。实验结果表明,在利用驻波热声发动机驱动的情况下,谐振系统自激起振,谐振频率为360 Hz,实际谐振频率与计算值误差在5%以内。     

Polar Mixing Optical Phonon Spectra in Wurtzite GaN Cylindrical Quantum Dots： Quantum Size and Dielectric Effects

The interface-optical-propagating （IO-PR） mixing phonon modes of a quasi-zero-dimensional （QOD） wurtzite cylindrical quantum dot （QD） structure are derived and studied by employing the macroscopic dielectric continuum model. The analytical phonon states of IO-PR mixing modes are given. It is found that there are two types of IO-PR mixing phonon modes, i.e. p-IO//z-PR mixing modes and the z-IO//p-PR mixing modes existing in QOD wurtzite QDs. And each IO-PR mixing modes also have symmetrical and antisymmetrieal forms. Via a standard procedure of field quantization, the Frohlich Hamiltonians of electron-（IO-PR） mixing phonons interaction are obtained. Numerical calculations on a wurtzite GaN cylindrical QD are performed. The results reveal that both the radial-direction size and the axial-direction size as well as the dielectric matrix have great influence on the dispersive frequencies of the IO-PR mixing phonon modes. The limiting features of dispersive curves of these phonon modes are discussed in depth. The phonon modes ＂reducing＂ behavior of wurtzite quantum confined systems has been observed obviously in the structures. Moreover, the degenerating behaviors of the IO-PR mixing phonon modes in wurtzite QOD QDs to the IO modes and PR modes in wurtzite Q2D QW and QID QWR systems are analyzed deeply from both of the viewpoints of physics and mathematics.     

A fast luminosity monitor for BEPCⅡ

The fast luminosity monitor counting the γ photons above a given energy threshold emitted from radiative Bhabha scattering has been operated in the BEPC Ⅱ to measure the relative luminosity bunch by bunch for the first time and used successfully in beam tuning of BEPC Ⅱ. In the relative mode the monitor is able to deliver the relative luminosities with an accuracy of 0.8 %. By steering the electron beam while observing the counting rate changes of the monitor the horizontal and vertical sizes of the bunch spots can be estimated as： Sxe＋ =Sxe =0.356 mm, Sye＋ =Sye- =0.011 mm.     

Systematic studies on α-decay half-lives for super heavy nuclei

Radioactive decay of super heavy nuclei via the emission of α-particles has been studied theoretically in the preformed cluster model （PCM）. The nucleus-nucleus （NN） potential is obtained by double folding the density distributions of the α-particle and the daughter nucleus with a realistic effective interaction. The M3Y effective interaction, supplemented by a zero-range pseudo-potential for exchange term, is used to calculate the NN potential. The α decay half-lives for 317 nuclei at Z=102 120 are performed in the PCM framework with the theoretical Q values extracted from the MSller-Nix-Kratz and Liran-Marinov-Zeldes mass tables and are compared with the experimental data. The calculated results are also compared with those obtained by using Q values from the Muntian-Hofmann-Patyk-Sobiczewski and Myers-Swiatecki mass estimates.     

A New Approach to Measurement of Heating Rate of Trapped Ions

We propose a new scheme to estimate the heating rate of trapped ions in thermal states. By applying a controlled-U gate between the internal and the motional states of one of the trapped ions, we could obtain the mean phonon number from the population of the internal state of the ion. The imperfection due to fluctuations of the relevant parameters in real experiments is considered and we anaiyze the experimental feasibility of our scheme with sophisticated ion trap techniques.     

Study of absorption and re-emission processes in a ternary liquid scintillation system

Liquid scintillators are widely used as the neutrino target in neutrino experiments.The absorption and emission of different components of a ternary liquid scintillator （Linear Alkyl Benzene （LAB） as the solvent,2,5-diphenyloxazole （PPO） as the fluor and p-bis-（o-methylstyryl）-benzene （bis-MSB） as wavelength shifter） are studied.It is shown that the absorption of this liquid scintillator is dominant by LAB and PPO at wavelengths less than 349 nm,and the absorption by bis-MSB becomes prevalent at the wavelength larger than 349 nm.The fluorescence quantum yields,which are the key parameters to model the absorption and re-emission processes in large liquid scintillation detectors,are measured.     

Study of lower emittance dedicated synchrotron radiation mode for the BEPCⅡ

In this paper,a dedicated synchrotron radiation （SR） mode for the BEPCⅡ with an emittance of 85 nm has been designed,including the linear lattice,chromaticity correction and dynamic aperture optimization.The emittance of the new mode is about 60% of the previous mode used for routine operation of the BEPCⅡ .The effect of wigglers on the linear lattice was compensated and the total dynamic aperture including the wigglers’ nonlinear effect was estimated.The preliminary commissioning at the end of 2008 and the formal operation with the new mode confirmed its merits.