The explosion of a spherical drop under the action of laser radiation

The existence of an explosive cycle is proposed for the action of laser radiation on a water droplet, when the droplet during the time of action of the pulse is converted to supercritical steam with unchanged density. A calculation is carried out of the gas-dynamic parameters of the expanding explosion products. An estimate is made of the change of optical attenuation cross section of the expanding steam.     

The dynamic response of an inhomogeneous plasma diode to an appliedpotential drop

Recent measurements of the response to an applied step voltage in collisionless plasmas have demonstrated the importance of the initial ion density distribution for the resulting time evolution and the formation of electric double layers. The dynamic response of a plasma diode to an applied step voltage is studied by particle-in-cell simulations and an analytical model. It is shown that an ion-density cavity (a local ion-density minimum with a width of many Debye lengths) can support large potential drops for several electron transit times. The potential drop extends over a distance related to the cavity width. When the applied potential drop exceeds a certain critical value, which depends on the cavity depth, the drop instead concentrates in a cathode sheath, which also is the response obtained for homogeneous initial plasma. The existence regions for the two different response in the appropriate parameter plane are found from the simulations and shown to agree with the regions predicted analytically. The analytical potential profiles agree with those simulated     

一种气体/液滴混合流动模型与数值计算

研究均匀液滴单态氧发生器(TUDOG)的工作机理,为Cl₂/He混合气体横向流过垂直下落的BHP(按重量25%KOH,25%H₂O₂,及50%H₂O)液滴场的化学反应流动建立模型,并对模型方程做数值求解.模型方程中考虑液滴与气体间的质量、动量交换.混合流动的二维模型方程用SIMPLEC方法求解.模拟结果与相关文献提供的实测结果对比较好.结果发现:氯气利用率、单态氧产率随入流气体速度增大而减小,随液滴速度增大而增大;在含液滴区域的上游氯气的吸收利用较显著,对TUDOG的工程设计有参考价值.     

Liquid jet response to internal modulated ultrasonic radiation pressure and stimulated drop production

Experimental evidence shows that a liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. Ultrasound applied to the jet supply liquid can propagate within the jet when the acoustic frequency is near to or above the cutoff frequency. Modulated radiation pressure is used to stimulate large amplitude deformations and the breakup of the jet into drops. The jet response to the modulated internal ultrasonic radiation pressure was monitored along the jet using (a) an optical extinction method and (b) images captured by a video camera. The jet profile oscillates at the frequency of the radiation pressure modulation and where the response is small, the amplitude was found to increase in proportion to the square of the acoustic pressure amplitude as previously demonstrated for oscillating drops [P.L. Marston and R.E. Apfel, J. Acoust. Soc. Am. 67, 27-37 (1980)]. Small amplitude deformations initially grow approximately exponentially with axial distance along the jet. Though aspects of the perturbation growth can be approximated from Rayleigh's analysis of the capillary instability, some detailed features of the observed jet response to modulated ultrasound are unexplained neglecting the effects of gravity.     

A stochastic method to determine the shape of a drop on a wall

We present results of a stochastic simulation which determines the shape of a liquid drop, subject to gravity, on a wall. The system is modeled using an Ising model in a field gradient, with Kawasaki dynamics governing the time dependence. We can locate a phase transition between a hanging and a sliding phase with high precision and determine its critical exponents.     

Nodal patterns in the seismic response of sedimentary valleys

Sedimentary basins, where many large cities in the world are built, have very soft terrains. When an intense seism of long duration hits the sedimentary basin, a nodal pattern, in which regions of high seismic wave amplitudes alternate with regions where these amplitudes are very small and even null, is formed. This nodal pattern, which leads to the so called “pockets of damage”, is always observed, for example, in Mexico City. In this paper the PR mode, in which P-waves in the soft terrain are coupled to the Rayleigh wave produced in the interface with the harder subsoil underneath it, is discussed. It is proposed that this coupled mode is the culprit of the enormous damage observed in sedimentary basins due to their peculiar seismic response.     

Instability of a charged spherical drop moving relative to a medium

It is shown that the critical self-charge for the onset of instability of a charged drop in a flow of an ideal fluid decreases as the flow velocity of the fluid past the drop increases, i.e., a complex instability arises which is a superposition of the instabilities of the free surface of the drop with respect to the tangential discontinuity of the velocity field at the free surface of the drop and with respect to the self-charge. Zh. Tekh. Fiz. 69, 7–14 (May 1999)     

Electromagnetic radiation due to nonlinear oscillations of a charged drop

The nonlinear oscillations of a spherical charged drop are asymptotically analyzed under the conditions of a multimode initial deformation of its equilibrium shape. It is found that if the spectrum of initially excited modes contains two adjacent modes, the translation mode of oscillations is excited among others. In this case, the center of the drop’s charge oscillates about the equilibrium position, generating a dipole electromagnetic radiation. It is shown that the intensity of this radiation is many orders of magnitude higher than the intensity of the drop’s radiation, which arises in calculations of the first order of smallness and is related to the drop’s charged surface oscillations.     

A kinetic approach to the calculation of surface tension of a spherical drop

In literature, surface tension has been investigated mainly from a Thermodynamics standpoint, more rarely with kinetic methods. In the present work, surface tension of drops is studied in the framework of kinetic theory, starting from the Sutherland approximation to Van Der Waals interaction between molecules. Surface tension is calculated as a function of drop radius: it is found that it approaches swiftly an asymptotic value, for radii of several times the distance of minimum approach D of the Sutherland potential. This theoretical asymptotic value is compared to experimental values of surface tension in plane surfaces of a few liquids, and is found in reasonable agreement.     

Instability of a charged spherical viscous drop moving relative to a medium

It is shown that, as the velocity of the flow around a charged drop of viscous liquid increases the drop charge value critical for the occurrence of drop instability rapidly decreases. It is found that, for some domains of values of the charge, the ratio of densities of the media, and the ambient velocity, the even and odd modes of the drop capillary oscillations pairwise couple with each other, which represents drop vibrational instability against the tangential discontinuity of the velocity field at the drop surface. At medium velocities larger than those associated with such domains, the instability growth rates for odd modes exceed the increments of even modes with smaller orders, which corresponds to the parachute-like deformation of the drop in the flow.     

Equivalent linear stochastic seismic response of isolated bridges

Stochastic response of bridges seismically isolated by lead-rubber bearings (LRB) is investigated. The earthquake excitation is modeled as a non-stationary random process (i.e. uniformly modulated broad-band excitation). The stochastic response of isolated bridge is obtained using the time-dependent equivalent linearization technique as the force-deformation behavior of the LRB is highly nonlinear. The non-stationary response of isolated bridge is compared with the corresponding stationary response in order to study the effects of non-stationary characteristics of the earthquake input motion. For a given isolated bridge system and excitation, it was observed that there exists an optimum value of the yield strength of LRB for which the root mean square (rms) absolute acceleration of bridge deck attains the minimum value. The optimum yield strength of LRB is investigated under important parametric variations such as isolation period and damping ratio of the LRB and the frequency content and intensity of earthquake excitation. It is shown that the above parameters have significant effects on the optimum yield strength of LRB. Finally, closed-form expressions for the optimum yield strength of LRB and corresponding response of the isolated bridge system are proposed. These expressions were derived based on the model of bridge with rigid deck and pier condition subjected to stationary white-noise excitation. It was observed that there is a very good comparison between the proposed closed-form expressions and actual optimum parameters and response of the isolated bridge system. These expressions can be used for initial optimal design of seismic isolation system for the bridges.     

ITERң�����䳵�����ṹ���������

阐述了ITER遥控运输车初步结构和工作状况,运用有限元方法对其进行模态分析并在地震载荷作用下进行加速度反应谱分析,验证了遥控运输车在地震情况下的安全性并给下一步的优化设计和实验提供了参考数据。     

Acoustic radiation from a drop due to its nonlinear vibrations

It is shown that the intensity of acoustic radiation from a vibrating drop depends mainly on the monopole and dipole components appearing only in the second order of smallness in vibration amplitude. The intensity of the quadrupole acoustic radiation generated by the vibration fundamental mode in the first order of smallness in amplitude turns out to be much weaker. This is associated with the fact that, if the acoustic wavelength is much larger than the drop characteristic size, their ratio becomes a governing small parameter, being lesser than the ratio of the drop vibration amplitude to the drop linear size. Analytical estimates of the amplitudes of monopole, dipole, and quadrupole components of the velocity field associated with the acoustic field of the drop.     

Nonlinear vibrations of a charged drop due to the initial excitation of neighboring modes

The asymptotic analysis of the nonlinear vibrations of a charged drop that are induced by a multi-mode initial deformation of its equilibrium shape is performed. It is shown that when two, three, or several neighboring modes are present in the initial deformation spectrum, the mode with the number one (translational mode) appears in the second-order mode spectrum. The excitation of the translational mode follows from the requirement of center-of-mass immobility and causes the dipole components (which are absent in the linear analysis) to appear in the spectra of the acoustic and electromagnetic radiation of the charged drop.     

Tailoring the spectral response of add/drop single and multiple resonators in silicon-on-insulator

Channel dropping waveguide filters based on single and technology are of great interest due to their compactness multiple resonators in silicon-on-insulator （SOI） and high wavelength selectivity, which is a desirable feature for photonic modulators, detectors, and other optically integrated components in telecommu- nication systems, in particular for wavelength division multiplexing （WDM） systems. Particular advantage of these filters is that they are capable of producing relatively large free spectral range （FSR） as well as narrow 3-dB bandwidth of the filter resonances. Herein we sibility of designing mono-mode and （nearly） polarization with the FSR in excess of 30 nm. report experimental results and discuss the posindependent SOI ring and racetrack resonators