Spectral Shift Originating from Non-linear Ultrasonic Wave Propagation and Its Effect on Imaging Resolution.

An amplitude-dependent downshift in the fundamental wave spectrum of a propagating ultrasonic pulse caused by non-linear wave propagation is described. The effects of non-linearity and the associated downshift on spatial resolution are also studied. The amounts of downshift and spatial resolution are extracted from the numerically simulated beam profile based on the KZK equation. Results for a 25-MHz transducer reveal that non-linear effects can lead to 58% additional downshift in the centre frequency of a pulse compared with a linear case with downshift caused only by attenuation. This additional downshift causes about 50% degradation in axial resolution. However, as the beam becomes narrower from the non-linear effects, the overall effect of non-linearity still leads to improved lateral resolution (≤26%). Therefore, as non-linearity increases with wave pressure, it is concluded that the increase in source pressure improves lateral resolution and degrades axial resolution.

Determination of the Ultrasonic Non-linearity Parameter B/A versus Frequency for Water.

For tissue characterization, it is desirable to determine B/A using high-frequency transducers. Moreover, an accurate estimate of B/A at elevated frequencies (or at least the assumption of frequency independence of B/A) is required to evaluate the safety of high-frequency systems. However, common finite-amplitude approaches become increasingly inaccurate at high frequencies. In this article, a practical variation of the finite-amplitude method is proposed which combines experiments with numerical simulations of the Khokhlov-Zabolotskaya-Kuznetsov equation and can be used at elevated frequencies. The results at low frequencies show that the proposed approach is accurate with lower uncertainties compared with the finite-amplitude method because it avoids assumptions and approximations. The measured values of B/A versus frequency for water at 2.25-20 MHz show that there is no statistically significant variation in B/A values with frequency, and therefore the assumption of frequency independence of B/A is realistic.

Study on removal of cadmium by hybrid liquid membrane process.

Removal of cadmium as a hazardous heavy metal is studied by applying a new design of hybrid cell for liquid membrane process. Tri-iso-octyl amine (TIOA) is used as the carrier in the organic phase. The concentration of cadmium in the samples is measured by atomic absorption spectroscopy. The effect of various parameters including type of supporting membrane, pH of feed and stripping phases, initial concentration of cadmium, carrier concentration, solvent nature, and also organic film resistance on mass transfer rate and removal efficiency are studied. The effect of temperature on mass transfer flux is studied by proposing a prediction model. The optimum carrier concentration is found to be about 0.05 M. The appropriate values of pH for feed and stripping phases are about 3 and 13, respectively.

Study on removal of cadmium from wastewater by emulsion liquid membrane.

Removal of cadmium from wastewater using emulsion liquid membrane (ELM) is studied in the present study. A polyamine-type surfactant was used for stabilizing the emulsion phase. Tri-iso-octyl amine (TIOA) has been used as a carrier for transferring of cadmium through the membrane. The results show good performance in the separation process. To determine the optimum operation conditions, the effect of several parameters such as surfactant concentration, carrier concentration, pH of external and internal phases, oil to internal phase volume ratio, emulsion to external phase volume ratio, solvent type, solute concentration, presence of iodide and chloride in external phase, and mixing conditions have been investigated.

Study on a new surfactant for removal of phenol from wastewater by emulsion liquid membrane.

Removal of phenol from wastewater using emulsion liquid membrane (ELM) is studied in present study. A new polyamine-type surfactant was synthesized and used for stabilizing of the emulsion phase. The results for the emulsion made by the synthesized surfactant showed much better stability and performance in the separation process compared to that by conventionally used Span 80. To determine the optimum operation conditions, the effect of several parameters such as emulsifier concentration, concentration of NaOH in the internal phase, oil to internal phase volume ratio, mixing intensity, temperature, solvent type, and stabilizer concentration have been investigated. It was found that under the optimum conditions, more than 98% of phenol can be removed in a single-stage process. The removal efficiency can be increased to 99.8% in a two-stage process.