Target strength of an oily deep-water fish, orange roughy (Hoplostethus atlanticus). II. Modeling

Orange roughy consist of approximately 18% lipids by weight, mostly as wax esters, and the lipids must be taken into account when modeling target strength. A deformed cylinder model incorporating the effect of temperature and pressure on sound speed through wax ester was used to scale experimental measurements of target strength to the temperatures and pressures where orange roughy live (approximately 6 degrees C, depths approximately 800-1300 m). The effect of decreasing temperature and increasing pressure is to increase the sound speed in orange roughy lipids. Modeling shows that the net effect of this is to reduce tilt-averaged target strength, 'TS', by approximately 2 dB. Adjusting experimental results to compensate for temperature and pressure effects gives a predicted 'TS' for a 35-cm orange roughy of -48.3 dB. Adjusting in situ estimates of orange roughy 'TS' for avoidance behavior [McClatchie et al., J. Acoust. Soc. Am. 106, 131-142 (1999)] suggests the correct 'TS' is approximately -47.5 dB, rather than -50 dB as previously reported [Kloser et al., ICES J. Mar. Sci. 54, 60-71 (1997)]. We conclude that experimental and in situ estimates now converge at a 'TS' of approximately -48 dB for a 35-cm fish.     

Enhancement and inhibition of acoustic radiation in spherical cavities

Acoustic radiation from a source located inside layered cavities is studied using the transfer matrix method. It is shown that the radiation can be either enhanced or inhibited, depending on the characteristics and the material composition of the cavities. The analysis predicts well-defined spectral peaks and nodes in some cavities. It is found that significant enhancement and inhibition are possible by varying acoustic parameters. The results also show that the strength of the radiating source can be significantly modified due to the presence of layered structures. The link to the similar phenomena in the optical cavities is discussed.     

Real three-dimensional microstructures fabricated by photopolymerization of resins through two-photon absorption

Effective energy windows for two-photon absorption (TPA) photopolymerization of resins were investigated and, with a properly selected laser pulse energy, exquisite three-dimensional (3D) microstructures with submicrometer spatial resolution were achieved. The results show the inherent utility of TPA in the fabrication of real 3D patterns. In particular, we propose and utilize a resin pre-exposure technique by which freely movable components affixed to an axle are built, demonstrating a new application of TPA in laser microfabrication.     

Spin-locking mechanism of spin I = 3/2 quadrupolar nuclei undergo magic angle spinning

The spin-locking mechanism of the spin I=3/2 quadrupolar nuclei under magic angle spinning (MAS) has been theoretically and experimentally investigated, and the criterion of adiabatic passage around zero-crossings of the quadrupole splitting was inferred from the time-dependent Shrödinger equation in this article. The theory, numerical simulations, and experiments conducted in this work all indicated that second-order quadrupole interaction and off-resonance play important roles in the spin-locking of the quadrupolar nuclei, and they were responsible for the great loss of the spin-locking signals. The spin-locking for a spin I=3/2 nucleus might be achieved by minimizing the effect of the second-order quadrupole interaction by using a radio frequency (RF) offset. This offset was realized by setting the RF to the opposite position of the isotropic second-order quadrupolar shift of single quantum coherences.     

Direct link between microwave and optical frequencies with a 300 THz femtosecond laser comb

We demonstrate a great simplification in the long-standing problem of measuring optical frequencies in terms of the cesium primary standard. An air-silica microstructure optical fiber broadens the frequency comb of a femtosecond laser to span the optical octave from 1064 to 532 nm, enabling us to measure the 282 THz frequency of an iodine-stabilized Nd:YAG laser directly in terms of the microwave frequency that controls the comb spacing. Additional measurements of established optical frequencies at 633 and 778 nm using the same femtosecond comb confirm the accepted uncertainties for these standards.     

超导储能系统用斩波器的原理及设计

超级储能系统(SMES)的特点是,储能密度大,超导电阻为零,并且容易控制.这使得超导储能不仅能在微秒、毫秒放电领域与电容器竞争,在秒级放电领域与旋转储能装置和电池组竞争,而且使它能在其他许多领域大显身手.本文介绍了超导储能系统(SMES)用斩波器的原理和特点.根据超导储能磁体的要求,提出了一种适用于超导储能用斩波器的电路拓扑结构,并分析了斩波器的工作原理和特点.通过计算机仿真验证了峰值电流控制方式的正确性.     

北京谱仪Ⅲ飞行时间计数器系统刻度中的关联分析

利用电子对事例对北京谱仪Ⅲ飞行时间的测量误差, 以及不同测量之间的关联因子随击中位置的变化进行了仔细的研究. 加权的飞行时间由不同的测量值及其相关的误差矩阵计算而得. 蒙特卡罗研究表明. 为北京谱仪Ⅲ开发的关联分析算法 可以正确地处理包含公有误差项的多个实验测量结果的合并, 并且能够为粒子鉴别提供可靠的飞行时间信息.     

激光金属汽化汽离混合区状态参量的稳定性及其影响因素分析

在汽离混合区激光强度时空修正的基础上,近似求解了流体力学模型下的状态参数,找出了稳定状态参数的共同自洽参量,分析了自洽参量的取值方法,研究了相关参数对自洽参量的影响机制,结果发现:(1)汽离混合区内,状态参量的稳定性可用自洽参量的稳定性来表征;(2)当入射激光强度小于108W.cm-2时,自洽参量随入射激光强度变化相对较快,稳定性差;当激光强度大于108W.cm-2时,自洽参量随入射激光强度变化相对较慢,稳定性高;(3)汽离混合区各处的约化自洽参量随辐照激光的波长成变周期增加的变化,波长越长,约化自洽参量越大;(4)要使自洽参量稳定,纹波较小,宜采取短波激光辐照;(5)当蒸汽压强小于2.7×106Pa时,自洽参量随蒸汽压强成指数递减规律变化;当蒸汽压大于2.7×106Pa时,自洽参量与蒸汽压强之间没有对应关系.     

Deposition of silver nanoparticles on silica spheres via ultrasound irradiation

Silver-decorated silica spheres of submicrometer-sized silica spheres with a core-shell structure were obtained based on a seed-mediated growth process, where silver nanoparticles were firstly formed from reducing Ag⁺ to Ag⁰ in N,N-dimethylformamide (DMF) in the presence of poly(vinylpyrrolidone) (PVP) as protective agent under ultrasound irradiation, followed by the growth of silver shell served silver nanoparticles as nucleation sites and formaldehyde as reducer. The results revealed that the terms of PVP addition and ultrasonic surroundings had great influence on the fabrication of silver seeds.     

Generation of a four-atom entangled cluster state in cavity QED

We propose a method of generating a four-atom entangled cluster state by considering two kinds of the atoms–cavity field interaction in cavity QED. During the preparation the cavity is only virtually excited no quantum information will be transferred from the atoms to the cavity and thus the scheme is insensitive to the cavity field states and cavity decay. The scheme can also be used to generate the cluster state for the trapped ions.