Acoustic radiation from the submerged circular cylindrical shell treated with active constrained layer damping

Based on the transfer matrix method of exploring the circular cylindrical shell treated with active constrained layer damping(i.e., ACLD), combined with the analytical solution of the Helmholtz equation for a point source, a multi-point multipole virtual source simulation method is for the first time proposed for solving the acoustic radiation problem of a submerged ACLD shell. This approach, wherein some virtual point sources are assumed to be evenly distributed on the axial line of the cylindrical shell, and the sound pressure could be written in the form of the sum of the wave functions series with the undetermined coefficients, is demonstrated to be accurate to achieve the radiation acoustic pressure of the pulsating and oscillating spheres respectively. Meanwhile, this approach is proved to be accurate to obtain the radiation acoustic pressure for a stiffened cylindrical shell. Then, the chosen number of the virtual distributed point sources and truncated number of the wave functions series are discussed to achieve the approximate radiation acoustic pressure of an ACLD cylindrical shell. Applying this method, different radiation acoustic pressures of a submerged ACLD cylindrical shell with different boundary conditions, different thickness values of viscoelastic and piezoelectric layer, different feedback gains for the piezoelectric layer and coverage of ACLD are discussed in detail. Results show that a thicker thickness and larger velocity gain for the piezoelectric layer and larger coverage of the ACLD layer can obtain a better damping effect for the whole structure in general. Whereas, laying a thicker viscoelastic layer is not always a better treatment to achieve a better acoustic characteristic.     

Transfer reactions by heavy ions and finite-range DWBA calculations

Experimental data of one-, three- and four-nucleon transfer reactions induced by the heavy-ion projectiles ¹⁶O and ¹⁹F on the targets ¹¹B and ¹²C are analyzed within the framework of finite-range DWBA. In many-nucleon transfer reactions, the cross section is composed of the coherent sum of amplitudes corresponding to the transfer of clusters with different intrinsic states. The spectroscopic amplitudes are calculated using the results of the intermediate-coupling shell model. The calculated cross sections can reproduce the experiments fairly well in most cases. The method is compared with other approximations from the viewpoint of the selection rules for the angular-momentum transfer.     

LINE FORCE RECEPTANCE OF AN ELASTIC CYLINDRICAL SHELL WITH HEAVY EXTERIOR FLUID LOADING

A time-harmonic line force is applied to an infinite elastic cylindrical shell immersed in compressible fluid. The force may also have axial harmonic dependence. The formal solution for the shell displacement is obtained as the sum of circumferential harmonics and evaluated in the asymptotic limit of heavy exterior fluid-loading. The resulting asymptotic expressions for the elements of the receptance matrix, either at the line of application of the force, or elsewhere on the shell surface, are simple trigonometric functions of the shell and fluid parameters, and show excellent agreement with numerical evaluation of the circumferential harmonic series over a wide frequency range.     

Theoretical investigation of hydrogen atom transfer in the hydrated C–G base pair

Hydrogen atom transfer and the related electronic rearrangement in the hydrated C–G base pair have been studied in order to understand the role of the hydrogen bonds between the bases and those with the water molecules in these processes. The modification of hydrogen transfer due to the first shell and bulk hydration has been analysed. The different structures, when the hydrogen atom moves in a H-bond or in another bond, have been studied. Two naïve schemes, where the water molecules are only indirectly or directly involved in the hydrogen atom transfer, have been considered. The results support the idea that the actual mechanisms are more complex than these schemes. Hydration modifies the potential energy curves of both tautomers and zwitterionic structures, but does not generate new stable structures (minimum PES) of these types. We find a new stable structure due to both a reorganization of the two down water molecules and other global changes of the system. This new system is generated from a zwitterionic structure. The charges, during hydrogen transfer, of the hydrogen donor and of the hydrogen acceptor part of the base pair and of the hydrogen atoms between the bases have been determined and their modifications, due to the first shell and bulk hydration, have been analysed. The qualitative and quantitative behavior has been studied.     

Spectral fine structure of the atomic ground states based on full relativistic theory

We focus on the full relativistic quantum mechanical calculations from boron to fluorine atoms with electronic configuration of 1s2 2s2 2p n(n =1,2,3,4,and 5),where 1s2 2s2 is the closed shell and 2p n is the open shell.Their active electrons in the open shell occupy all the six spinors as far as possible.Therefore,we suggest a new rule called "maximum probability" for the full symmetry group relativistic theory.Furthermore,the spectral fine structure of the atomic ground states based on the full relativistic theory and their intervals of L-S splitting are all reasonable.It is impossible to calculate the L-S splitting through non-relativistic quantum mechanics.The relativistic effect of atomic mass is increased significantly by about 12 folds from boron atom to fluorine atom.     

水中分层弹性球壳高频时域回波的声学编码研究

针对水下集群目标及敌我目标识别的难题,该文提出了一种基于水中分层弹性球壳高频时域回波的声学编码原理及方法。推导了水中4层弹性球壳目标散射声压的简正级数解,并与有限元结果进行了对比验证。通过构造高频主动声呐的探测脉冲信号,与4层弹性球壳声传递函数的简正级数解做卷积运算,获得了目标的时域回波脉冲序列。研究了分层弹性球壳的厚度、各层材料属性、排布顺序等对时域回波特征的影响规律,提出了基于时域回波特征的声学编码方法。研究表明：利用水中分层弹性球壳目标高频时域回波特征能够实现声学编码,回波结构稳定,且不受限于探测方向。通过携带或安装这种分层弹性球壳结构,有望识别水下航行体/悬浮体等目标。该文的研究对水下目标的主动探测身份识别及导航等具有一定的参考价值。     

f72 neutron occupancies in the Ca isotopes

Methods of obtaining nucleon occupancies from total energy-weighted sum rules for spectroscopic factors are described and applied to $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ neutron transfer data for Ca isotopes. The $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ neutron occupancies obtained are consistent with shell model expectations and, for ⁴¹Ca and ⁴³Ca, with values previously obtained from an analysis using non-energy-weighted sum rules.     

Inclusive radiative pion capture by N = Z nuclei in the 1p shell

A study of inclusive radiative pion capture by means of sum rules is given for the case of self-conjugated nuclei in the 1p shell. The sum rules M₀ and M₁ are evaluated for the dominant Kroll-Rudermann term in the effective hamiltonian. Total branching ratios and mean photon energies are determined from the calculated sum rules. These quantities compare reasonably well with experiment.     

Stability of an encapsulated bubble shell

The stability of an encapsulated bubble filled with gas is studied where gas is allowed to diffuse out of the bubble. A mechanistic model that takes into account shell stiffness and surface tension is considered. A critical shell radius for loss of mechanical stability is derived based on a technique adapted for small radius, where surface tension effects become substantial. A new parameter is defined that determines the relative importance of surface tension forces and shell stiffness for shell stability. The developed technique allows to predict, for a given bubble population and gas saturation level of the surrounding liquid, a range of bubble sizes which may collapse in time. Surface tension effects are dominant in determining the critical radius but have a negligible effect on the minimal radius for collapse. The influence of the surface tension on the stability of the shell is illustrated for Optison, a typical ultrasound contrast agent.     

Dynamics of a thin shell in the Reissner—Nordström metric

The dynamics of a thin spherically symmetric gravitating shell around an electrically charged Reissner—Nordström black hole is considered. The energy—momentum tensor of an electrically neutral shell is modeled by an ideal fluid with a polytropic equation of state. The dynamics of a shell with a dust equation of state can be traced completely analytically. The Carter—Penrose diagrams that describe the global geometry and all possible types of motions of a gravitating shell in the case of an eternal black hole have been constructed.The conditions have been found under which stable oscillatory motions of the shell take place. These transfer it successively from one universe to the next in an infinite series of identical universes. Such stable oscillatory shell motions are shown to be possible for an arbitrary polytropic equation of state of the shell.     

关于软玻密子的结构

本文修改了Landshoff-Nachtmann的软玻密子(Pomeron P)场论模型.从强子组分夸克具有结构的观点出发,根据高能强作用软过程中的最大非微扰强作用反应假定,提出了有关软P新的结构图像.对撞强子中的一对组分夸克被分解为裸夸克和一系列非微扰胶子(和夸克对).与此相应,软P的结构是由胶子形成的一系列切割梯形图之和所代表.在系统能量s很大而动量转移|t|很小的多重雷吉(Regge)运动学区间,并在保留lns的领头阶近似下,计算了这组切割梯形图之和所对应的散射振幅和总截面.它们的表达式出现了对s的Regge型幂次因子,得出了软P轨迹的简洁表达式.简单说明了按本文提出的方案可以讨论那些相关的强作用过程.     

Twist mode in spherical alkali metal clusters

A remarkable orbital quadrupole magnetic resonance, so-called twist mode, is predicted in alkali metal clusters where it is represented by Ipi = 2(-) low-energy excitations of valence electrons with strong M2 transitions to the ground state. We treat the twist by both macroscopic and microscopic ways. In the latter case, the shell structure of clusters is fully exploited, which is crucial for the considered size region ( 8相似文献   

On a hollow superconducting sphere in a magnetic field

A system consisting of a single-domain ferromagnetic ball surrounded by a spherical superconducting shell and current-carrying wires wound on the shell is considered. The magnetic moment of the superconductor is calculated in terms of the London theory, in particular, for the case when the sum of the magnetic moments of the ball and system of currents is equal to a null vector.     

HL—1装置外垂直场代替内垂直场的改进

利用缝隙系数将钢壳内外各种电流源在壳内产生的磁场分成两部分,一部分按无壳处理,另一部分按无洞无缝的铜壶处理,因而各部分垂直场的解析计算结果与实验值符合很好,并能很好地解释HL-1装置平衡放电长达1S和外加垂直场很小的根本原因。经在装置上关闭内垂直场试验,结果表明,虽然有厚钢壳存在,外垂直场完全可以代替内垂直场。与以前相比,明显地改善了等离子体位置的平衡控制。     

Multipole moments and spin-dependent sum rules and their applications to f72 and s-d shell nuclei

Matrix elements of multipole operators, defined separately for neutrons and protons, are related to spin-dependent sums of spectroscopic factors. A clarification of their relation to the matrix elements of single-particle operators enables the overlap representation to be formally extended to a stripping form for J ≠ 0 operators. Multipole moments obtained from $\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ transfer data are found to be dominated by the quadrupole moments when the final nucleus is odd-odd.A previously found (2J + 1) rule for spectroscopic sums, which arises when the odd-J multipole moments vanish, is shown to lead to approximate sum rules which apply separately to stripping and pickup data. The sum rules are generally well satisfied for transfers leading to odd-odd nuclei in the s-d shell.     

核壳型量子点(ME)4@(ME)28(M=Cd/Zn，E=Se/S)核壳间相互作用研究

采用密度泛函理论和自然键轨道理论结合的方法对核壳型量子点团簇(ME)4@(ME)28(M=Cd/Zn,E=Se/S)的几何结构、范德华体积、分子轨道和核层与壳层间的轨道占据进行模拟,分析不同核壳团簇结构中核与壳之间的相互作用。结果显示,核层金属原子与壳层非金属间距离大于核层非金属原子与壳层金属原子间距离,相同壳层时,Zn-Se/S键长小于Cd/Zn-Se键长,孤立的核和壳体积之和大于相应核壳构型的体积;核壳间的相互作用主要源于壳层非金属原子Se的sp杂化轨道和核层金属原子Cd/Zn的s、p及少量的d轨道相互作用。研究表明,一方面,核内原子和壳上的原子之间存在很强的化学键的作用;另一方面,在核与壳之间存在着显著的边界,表明核、壳构型有差异,核壳构型中的核与壳之间存在相互作用且二者相互影响。     

水中双层弹性球壳的回声特性

研究水中双层同心弹性球壳的声散射.利用严格弹性理论和分离变量法导出了Rnyleigh简正级数解.计算并比较了单层和双层弹性球壳的反向散射形态函数.为了分析回波结构也计算了窄脉冲回波序列.结果表明,外壳很薄内壳稍厚的双层弹性球壳的回波特性主要依赖于内壳。在低ka时双层壳体的回波可以近似用内部充水的外壳和内部真空的内壳的回波叠加而成。     

ELECTROHYDRODYNAMIC ENHANCEMENT OF HEAT TRANSFER IN A SHELL-AND TUBE HEAT EXCHANGER

Enhancement of heat transfer in a heat exchanger via a DC corona discharge was studied experimentally using a single-tube shell-and-tube heat exchanger. Air was the working fluid in both the tube and shell sides. Excitation of the tube side was via a single wire electrode, while that of the shell side was via four rod electrodes oriented symmetrically at 90^° intervals. Three series of experiments were performed: (1) excitation of the tube side only, (2) excitation of the shell side only, and (3) simultaneous excitation of the tube and shell sides. Both heat transfer and pressure drop measurements were performed, with Reynolds number and electric field potential as parametric quantities in the tube and shell sides. It was found that highest enhancements take place when the tube and shell sides are excited simultaneously, yielding a 322% increase in the overall heat transfer coefficient. Study of the heat transfer enhancements per unit pumping power indicates that for the range of parameters studied, the technique is most efficient at moderate Reynolds numbers and at electrode potentials in the midrange between threshold and sparkover limits.     

Electronuclear sum rules

Generalized sum rules are derived by integrating the electromagnetic structure functions along lines of constant ratio of momentum and energy transfer. For non-relativistic systems these sum rules are related to the conventional photonuclear sum rules by a scaling transformation. The generalized sum rules are connected with the absorptive part of the forward scattering amplitude of virtual photons. The analytic structure of the scattering amplitudes and the possible existence of dispersion relations have been investigated in schematic relativistic and non-relativistic models. While for the non-relativistic case analyticity does not hold, the relativistic scattering amplitude is analytical for time-like (but not for space-like) photons and relations similar to the Gell-Mann-Goldberger-Thirring sum rule exist.