Cavitation activity stimulation by low frequency field pulses

The influence of a short-time action of a low-frequency ultrasound on the sonoluminescence generation by a high frequency pulsed field has been studied. This action remarkably lowers the cavitation thresholds and increases the sonoluminescence intensity. The stimulating effect of the low-frequency field action depends on its duration and on the intensities of both fields. Possible mechanisms of this effect are discussed.     

The shear modulus of the human vocal fold in a transverse direction

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3g was applied to the epithelium, and the resultant displacement logged at a rate of 1kHz. Force measurement accuracy was 20microg and position measurement accuracy was 4microm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.     

Enhancement of high-frequency acoustic cavitation effects by a low-frequency stimulation

The cavitation effects given by a high-frequency pulsed ultrasound field are studied with and without the stimulation of a low-frequency field. Sonoluminescence intensity and subharmonic one-half intensity of the high-frequency field are measured. The stimulation gives a sharp rise of both subharmonic and sonoluminescence intensities.     

Enhancement of sonoluminescence emission from a multibubble cavitation zone

Investigations have been performed on various methods of increasing cavitation activity measured by the intensity of sonoluminescence. It is shown that the effect of the combined action of (a) pulsed modulation of an acoustic field, (b) liquid degassing and cooling and (c) increasing the static pressure considerably exceeds the sum of the effects achieved by each of these methods individually. A more than 250-fold increase of the sonoluminescence intensity has been attained compared with continuous irradiation under normal conditions (room temperature, atmospheric pressure, gas-saturated liquid). An interpretation of the results obtained is proposed.     

Multibubble sonoluminescence intensity dependence on liquid temperature at different ultrasound intensities.

It is shown that the influence of liquid temperature on the sonoluminescence (SL) intensity is different depending on the ultrasound intensity. At the ultrasound intensities not much higher than the cavitation appearance threshold the SL intensity increases with the temperature. At the ultrasound intensities considerably exceeding the cavitation threshold the SL intensity decreases with an increase of the temperature. At intermediate ultrasound intensities the SL intensity temperature dependence is extreme: the cavitation activity at first increases with temperature, reaches a maximum and then decreases. Continuous and pulsed modes of irradiation at frequencies 880 and 21.9 kHz were used in experiments.     

Characterization of acoustic cavitation in water and molten aluminum alloy

High-intensive ultrasonic vibrations have been recognized as an attractive tool for refining the grain structure of metals in casting technology. However, the practical application of ultrasonics in this area remains rather limited. One of the reasons is a lack of data needed to optimize the ultrasonic treatment conditions, particularly those concerning characteristics of cavitation zone in molten aluminum.The main aim of the present study was to investigate the intensity and spectral characteristics of cavitation noise generated during radiation of ultrasonic waves into water and molten aluminum alloys, and to establish a measure for evaluating the cavitation intensity. The measurements were performed by using a high temperature cavitometer capable of measuring the level of cavitation noise within five frequency bands from 0.01 to 10 MHz. The effect of cavitation treatment was verified by applying high-intense ultrasonic vibrations to a DC caster to refine the primary silicon grains of a model Al–17Si alloy. It was found that the level of high frequency noise components is the most adequate parameter for evaluating the cavitation intensity. Based on this finding, it was concluded that implosions of cavitation bubbles play a decisive role in refinement of the alloy structure.     

Study into mechanisms of the enhancement of multibubble sonoluminescence emission in interacting fields of different frequencies

The main factor of the enhancement of sonoluminescence (SL) emission by the interaction of two fields of highly different frequencies is the generation of new cavitation nuclei upon collapse of bubbles driven by the low-frequency (LF) field. The factors connected with the direct interaction of the two fields play a significant role in the enhancement of SL emission only in the case when intensities of the fields are less or not much higher than the corresponding thresholds of SL emission. The phenomena of afteraction of the LF field on cavitation generated by the high-frequency field is explained also by the generation of new nuclei upon collapse of bubbles driven by the LF fields.     

COMPOSITION OF INDOOR AEROSOLS AT EMPEROR QIN''''S TERRA-COTTA MUSEUM, XI''''AN, CHINA, DURING SUMMER, 2004

Particle samples were collected in August 2004 both inside and outside Emperor Qin's Terra-Cotta Museum in Xi'an, China. Mass and chemical composition of total suspended particles (JSP, particles with aerodynamic diameter less than-30μm), PM2.5(particles with aerodynamic diameter <2.5μm) were determined. The average levels of indoor PM2.5 and TSP were 108.4 and 172.4 μg·m-3, respectively, with PM2.5 constituting 62.9% of the TSP mass. Sulfate ((32.4±6.2)%), organics ((27.7±8.0)%), and geological material ((12.5±3.4)%) dominated indoor PM2.5, followed by ammonium ((8.9±2.8)%), nitrate ((7.0±2.9)%), and elemental carbon (EC, (3.9±1.5)%). Particle size distribution varied with the number of tourists in the museum. The size of sulfate, organics, EC, nitrate, and ammonium was found to vary in the range of 0.43 to 3.3 μm in fraction. Ion balance indicated that the aerosol was acidic, with insufficient ammonium ions to neutralize the sulfuric and nitric acids. High concentrations of acidic aerosols will erode the Terra-cotta warriors and horses especially in the summer season with high temperature (30℃) and relative humidity (70%) and undesirable solar radiation inside the museum. More attention should be paid to protecting these precious antiques made 2000 years ago.     

An ultra-low hydrolysis sol-gel route for titanosilicate xerogels and their characterization

In this work TiO₂-SiO₂ xerogels were prepared through an ultra low hydrolysis method using titanium and silicon alkoxide. The samples were heat treated to 500°C. The xerogels were characterized using TGA/DTA, FTIR, XRD and TEM. The samples showed the formation of Si–O–Ti bridges by its characteristic vibration within 925–960 cm⁻¹ range. Si–O–Si bond angles were calculated using the central force network model. The TiO₂ in all the samples crystallized on heat treatment to 500°C. The crystallite size calculated using the Scherer formula from the XRD was verified from the Transmission Electron Micrograph. Samples heat treated to 350°C remained amorphous and hence could be used as hosts for biomaterials and organic optical materials.