中国近海悬浮颗粒物海水声波衰减

在对颗粒物声吸收机理分析的基础上,根据已有的南黄海和莱州湾海洋调查数据,对中国近海实际海域悬浮颗粒物海水在声呐工作频段内的声波衰减进行了计算分析。结果表明,在悬浮颗粒物浓度高的海水区域内,悬浮颗粒物粘滞性声吸收所造成的声波衰减与不计及颗粒物存在的海水声吸收相比不可忽略。计算分析同时表明,在声呐工作频段内,颗粒物的散射声吸收可以忽略不计。取可使粘滞衰减为较大值的粒径为5μm的悬浮颗粒物海水进行计算,在低于几十千赫兹的频率范围内,当泥沙类悬浮颗粒物浓度高于0.1kg/m³、有机类悬浮颗粒物浓度高于1kg/m³,颗粒物粘滞衰减系数将大于清澈海水的衰减系数。泥沙类悬浮颗粒物海水浓度高于0.1kg/m³、有机类悬浮颗粒物海水浓度高于1kg/m³,可以作为是否需要计及颗粒物声吸收的比较保守的估计判据,或是作为悬浮颗粒物海水达到声学混浊的估计判据。     

Capillary force on colloidal particles in a freely suspended liquid thin film

The dynamic behavior of micron-sized polystyrene latex particles confined in a free-standing liquid film is experimentally studied. When the thickness of the film is less than the particle diameter and varies depending on position, the particles are accelerated toward the thicker region. Using a simple geometrical model and hydrodynamic theory, we calculate the capillary force on the particle. The drag coefficient of the particle is found to depend on the thickness of the film from the value of near zero to the Stokes' drag coefficient.     

Thermal response of superparamagnetic particles suspended in liquid and solid media

The purpose of this study was to explore the properties of coated superparamagnetic nanoparticles (SPNs) specifically for their use in thermal-responsive drug delivery systems. Coated, magnetite SPNs were prepared and dispersed in cyclohexane or cetyl alcohol, a solid lipid at the physiological temperatures of 37 °C. The induced temperature change as a function of SPN concentration and external magnetic field and frequency was consistent with theoretical predictions. SPNs dispersed in a solid lipid matrix underwent heating and the associated melting occurred at a temperature suitable for a thermal-responsive drug delivery system.     

Sound attenuation in forests

Many measurements of sound attenuation rates in forests have been made but there is little in common in the measuring procedures used or the results obtained. Consequently there is a considerable divergence of opinion on the effectiveness of vegetation as a noise control measure. In this paper the factors controlling the transmission of sound through vegetation are examined and the attenuation rates achieved in pine plantations are presented.     

Variation of chaotic motion of silicon particles suspended in liquid under field

A decrease in the characteristic correlation time of light scattered by silicon particles in transformer oil and an increase in their effective diffusion coefficient when the particle suspension in oil is exposed to a dc electric field were experimentally shown. The current in the suspension did not exceed 100 nA and its temperature was unchanged. It was also shown that the shape of the correlation function of light scattered by particles changes, i.e., a Gaussian factor appears in it. The dependences of the exponential and Gaussian components on the electrode voltage are presented.     

Sound wave attenuation in foam

Experimental measurements are presented for sound wave attenuation in foam without additives (standing wave method) and in foam with added particles (pulse method). A setup is developed that makes it possible to obtain a standing sound wave in stable foam and estimate the attenuation coefficient. A comparison is made of the coefficients of sound attenuation in foam in the sonic and ultrasonic frequency ranges, which have been published in a number of works. It is shown that the introduction of particles into foam leads to an increase in sound wave attenuation and may be the result of the viscous mechanism of sound wave energy loss.     

Features of the motion of particles suspended in liquid under an applied field

It is experimentally shown that a tenfold-hundredfold increase in the effective diffusion coefficient along the direction perpendicular to an applied electric field takes place in various emulsions and suspensions. It is caused by electrophoretic motion of particles. In inverse emulsions and many suspensions, only a certain fraction of dispersed material is contained in particles whose average radius is determined by the dynamic light scattering method. It is shown that the average coherence time of light scattered by silicon particle suspensions at a constant laser power depends on the beamdiameter. This means that semiconductor particles are characterized by strong nonlinearity.     

Sound attenuation in doped displacive ferroelectrics

An expression is obtained for the sound attenuation constant in a doped displacive ferroelectrics in the presence of an external electric field, using double-time temperature-dependent Green’s function technique. The mass and force constant changes due to impurity atoms, are taken into account along with higher order anharmonic and electric dipole moment terms, in the Silverman-Joseph Hamiltonian. The attenuation constant increases with an external electric field. The soft mode is responsible for the anomalously increasing behaviour of the attenuation constant in the vicinity of the Curie temperature. The results agree with those attained by Tani and Tsuda and Heuter and Neuhaus.     

High-frequency electric-field trap for micron and submicron particles

Summary Four e-beam-processed, planar electrodes with gaps between 0.5 and 4 μm were used to create quadrupole electric-field trap. The electrodes were immersed in an aqueous particle suspension and driven by kHz to MHz signals of several volts amplitude. Micron and submicron particles could be stably trapped by negative dielectrophoresis. Latex beads of 1000, 600, 100 and 14 nm diameter could be concentrated between the electrodes (positive dielectrophoresis) or levitated as condensed cloud (negative dielectrophoresis). The results are surprising since polarisation forces depend on the volume of the particle and, up to now, it was expected that thermal forces would dominate the behaviour of particles with diameters <100 nm. However, micron-scaled electrode configurations allow the application of extremely strong fields (up to 20 MV/m) and open up new perspectives for microparticle handling and macromolecule trapping.     

Sound absorption in a colloidal solution of interacting particles

The absorption of sound in a colloidal solution is studied with allowance for interaction between microparticles or nanoparticles. It is shown that electrostatic repulsion, which is typical of charged colloids used in science and engineering, leads to an increase in absorption, all other factors being the same. This is related to the fact that the effective correlation length characterizing the motion of particles increases when the interparticle interaction becomes stronger.     

Sound attenuation of a periodic array of micro-perforated tube mufflers

The wave propagation in a periodic array of micro-perforated tube mufflers is investigated theoretically, numerically and experimentally. Because of the high acoustic resistance and low mass reactance due to the sub-millimeter perforation, the micro-perforated muffler can provide considerable sound attenuation of duct noise. Multiple mufflers are often used to enhance attenuation performance. When mufflers are distributed periodically in a duct, the periodic structure produces special dispersion characteristics in the overall sound transmission loss. The Bloch wave theory and the transfer matrix method are used to study the wave propagation in periodic micro-perforated tube mufflers and the dispersion characteristics of periodic micro-perforated mufflers are examined. The results predicted by the theory are compared with finite element method simulation and experimental results. The results indicate that the periodic structure can influence the performance of micro-perforated mufflers. With different periodic distances, the combination of the periodic structure and the micro-perforated tube muffler can contribute to the control of lower frequency noise with a broader frequency range or improvement of the peak transmission loss around the resonant frequency.     

Massive particles in five dimensions

We consider a five-dimensional model of the universe with a dynamical extra dimension. Calculations of the ratio of the number density of Kolb and Slansky type pyrgons to that photons show the model to be uncacceptable. However by inserting N matter fields into the original action, it becomes possible to reduce the ratio below the observational bound.     

Flows with suspended and floating particles

The evolution of the configuration of a set of particles dispersed in a flowing liquid is crucial in many applications such as sedimentation, slurry transport, rheology and structured arrays of micro- and nano-particles. Direct simulation based on what is called fictitious domain method coupled with finite element method has been used to study particulate flows and sedimentation process. Here we extend the previously proposed formulations to naturally include buoyancy force and the capillary driven attraction or repulsion of particles located at fluid interfaces. The set of differential equations is discretized using a fully implicit-fully coupled fictitious domain/finite element approach, avoiding numerical instabilities that may arise from explicit integration. The proposed formulation and implementation are validated by comparing the predictions of simple 2D flows to available numerical or analytical solutions. The method is then used to analyze the flotation of 2D particles and capillary driven aggregation at fluid interfaces.     

Electrochemical synthesis of metallic micro-rose having petals in nanometer dimensions

Nature plays a big role through chemico-physical phenomenon in defining the morphological features of any object existing in this universe at the micro and macrolevels. In the present paper, we report on the synthesis of micro-sized three-dimensional metallic (copper) floral formation resembling natural flowers and botanical specimen using track-etch membranes via the technique of template synthesis. Scanning Electron Microscopy was used to study the surface morphology of the microflowers.     

Sound attenuation of TDH-39 earphones in a diffuse field of narrow-band noise

The sound attenuation characteristics of the audiometric earphone Telephonics TDH-39 with cushion MX-41/AR have been tested, using the hearing threshold method according to the International Standard ISO 4869-1981 ("Acoustics--Measurement of sound attenuation of hearing protectors--Subjective method"). This method specifies 1/3-oct bands of noise as test signals and a diffuse sound field. This is in contrast to the use of pure tones in a frontally incident free sound field, by means of which most earlier attenuation data have been obtained. The mean sound attenuation values obtained from a group of 20 normal-hearing subjects were up to 3-5 dB lower than those previously reported for pure tones in a free field.     

Sound attenuation in one-dimensional magnetic systems at finite temperatures

Sound attenuattion constants are calculated for the one-dimensional ferro- and antiferromagnetic systems at finite temperatures. Their frequency dependences, in both cases, turn out to be $\text{ω}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}_{\mathrm{<mtext>k</mtext>}}\text{if}\text{ω}{}_{\mathrm{<mtext>k</mtext>}}\text{? ω}{}_{\mathrm{c}}\text{and}\text{ω}{}^2{}_{\mathrm{<mtext>k</mtext>}}\text{if}\text{ω}{}_{\mathrm{<mtext>k</mtext>}}\text{?ω}{}_{\mathrm{c}}$, where ω_c is a “cut-off” frequency related to the three-dimensional anisotropic interactions.