Peter J. Lesniewski

Signal recovery in imaging photoplethysmography

Imaging photoplethysmography is an emerging technique for the extraction of biometric information from people using video recordings. The focus is on extracting the cardiac heart rate of the subject by analysing the luminance of the colour video signal and identifying periodic components. Advanced signal processing is needed to recover the information required. In this paper, independent component analysis (ICA), principal component analysis, auto- and cross-correlation are investigated and compared with respect to their effectiveness in extracting the relevant information from video recordings. Results obtained are compared with those recorded by a modern commercial finger pulse oximeter. It is found that ICA produces the most consistent results.

Application of high frequency ultrasound in the destruction of DDT in contaminated sand and water

High frequency ultrasound, as an alternative to high cost incineration, has been investigated to remediate DDT from sand and soil slurries. In this study, low power high frequency ultrasound (1.6 MHz; 150 W/L), with operating costs much lower than low frequency ultrasound, has been used to remediate DDT in liquid solution and in sand slurries. At 1.6 MHz, the wavelength, cycle time, bubble size and bubble life time are much smaller and the number of bubbles per litre is much larger than at frequencies below 50 kHz. These large differences affect the effective mass transfer to the bubbles and subsequent energy release, hydrolysis of water and degradation mechanism. Based on DDT measurement, using high frequency ultrasound, 90% of 8 mg/L of DDT from liquid solution was destroyed in 90 min. Removal efficiency from 32.6 mg/L of DDT in a 40 wt.% sand slurry was 22% in 90 min. Other slurry and DDT combinations are reported. Incremental chloride measurements indicated that combination of ultrasound and iron powder helps to increase the remediation rate of DDT from sand slurry, e.g. 46% cf. 32% for a 20 wt.% slurry. The results show that high frequency ultrasound is effective in degrading the non-polar pollutant DDT dispersed in water and in sand slurry. In practice, due to intensity limitations in currently available equipment and higher attenuation of energy, high frequency ultrasound has a low volume coverage and would require circulation of the slurry past the sonotrode, multiple sonotrodes, larger sonotrode area and lower slurry densities may still be required.

Performance limits of ICA-based heart rate identification techniques in imaging photoplethysmography

Imaging photoplethysmography is a relatively new technique for extracting biometric information from video images of faces. This is useful in non-invasive monitoring of patients including neonates or the aged, with respect to sudden infant death syndrome, sleep apnoea, pulmonary disease, physical or mental stress and other cardio-vascular conditions. In this paper, we investigate the limits of detection of the heart rate (HR) while reducing the video quality. We compare the performance of three independent component analysis (ICA) methods (JADE, FastICA, RADICAL), autocorrelation with signal conditioning techniques and identify the most robust approach. We discuss sources of increasing error and other limiting conditions in three situations of reduced signal-to-noise ratio: one where the area of the analyzed face is decreased from 100 to 5%, another where the face area is progressively re-sampled down to a single RGB pixel and one where the HR signal is severely reduced with respect to the boundary noise. In most cases, the cardiac pulse rate can be reliably and accurately detected from videos containing only 5% facial area or from a face occupying just 4 pixels or containing only 5% of the facial HR modulation.

Application of neural networks with novel independent component analysis methodologies to a Prussian blue modified glassy carbon electrode array

Sodium potassium absorption ratio (SPAR) is an important measure of agricultural water quality, wherein four exchangeable cations (K(+), Na(+), Ca(2+) and Mg(2+)) should be simultaneously determined. An ISE-array is suitable for this application because its simplicity, rapid response characteristics and lower cost. However, cross-interferences caused by the poor selectivity of ISEs need to be overcome using multivariate chemometric methods. In this paper, a solid contact ISE array, based on a Prussian blue modified glassy carbon electrode (PB-GCE), was applied with a novel chemometric strategy. One of the most popular independent component analysis (ICA) methods, the fast fixed-point algorithm for ICA (fastICA), was implemented by the genetic algorithm (geneticICA) to avoid the local maxima problem commonly observed with fastICA. This geneticICA can be implemented as a data preprocessing method to improve the prediction accuracy of the Back-propagation neural network (BPNN). The ISE array system was validated using 20 real irrigation water samples from South Australia, and acceptable prediction accuracies were obtained.

Application of neural networks with novel independent component analysis methodologies for the simultaneous determination of cadmium, copper, and lead using an ISE array

The paper introduces a novel chemometric strategy based on independent component analysis (ICA) coupled with a back‐propagation neural network. In this approach, one of the most popular ICA methods, the fast fixed‐point algorithm for ICA (fastICA), was implemented by the genetic algorithm (geneticICA) to avoid the local maxima problem commonly observed with fastICA. As a case study, an ion‐selective electrode (ISE) array, consisting of three working electrodes and one reference electrode, was used for the simultaneous determination of three heavy metals (cadmium, copper, and lead) in aqueous solutions, which are normally prone to severe interferences. The robustness and appropriateness of the approach were assessed using the average mean of relative error (MRE) of triplicated external validation. After configuration and optimization, the average MRE for Cu was <5%. For the determination of Cd and Pb, whose ISEs normally cannot tolerate Cu ions even at the microgram per liter levels, the MREs were 8%. This article demonstrated that this approach can be applied to the detection of heavy metal contamination in industrial wastewater with prediction accuracies comparable with other popular quantitative chemometric neural network methods. Copyright

Discrete component equivalent circuit for Webster's horns

Abstract A general equivalent circuit for the family of common acoustic horns has been presented. Using simple matrix manipulation, the ‘irregular’ constituting equations of the hyperbolic horn theory have been reduced to a simpler form for which a discrete equivalent circuit could have been derived. The advantage of the equivalent circuit is its simplicity and suitability for use in a quick analysis or synthesis using existing CAD packages dedicated to electrical circuit simulation.

Fast template tracking in video sequences.

Tracking of poorly defined, rotating and/or distorted objects in a video sequence poses significant problems especially in medical diagnostics including ultrasound (sonographic) video used for examination and diagnosis of internal movement of tissue or muscle and nerve action. Cross-correlation techniques have been successful in retrieving dynamic information directly from ultrasound video data. We outline a fast implementation of tracking based on normalized cross-correlation using an adaptive template and present results from our application, developed in MATLAB™, which successfully tracks arbitrarily selected objects in deformed or severely compromised images. Common ultrasound image evaluation is qualitative but there is need to retrieve quantitative dynamic information such as the trajectory or velocity of selected areas. Our approach uses normalized two-dimensional cross-correlation to find the position of an initially selected template enclosing the feature of interest and map its trajectory frame-by-frame to produce displacement and velocity plots. We illustrate operation of the application using routine ultrasound data and demonstrate its performance using test video of objects rotating full circle and rolling down a ramp. We analyse errors associated with sampling to compare performance of our implementation with a more rigorous but tedious and computationally expensive correlation of a resampled, rotated, and shifted template.

Universal Laboratory Networking System (ULabNet)

The Laser Light Scattering and Materials Science Group (LLSMS) at the University of South Australia (www.unisa.edu.au/laser) has developed sophisticated instrumentation which has been widely used by many researchers from outside the laboratory. To increase convenience and utilization, it is desirable remote users could gain access to the instruments. Here we outline the development and testing of a remote instrumentation solution (ULabNet) which provides a free generic tool to create a remote control capability for laboratory instrumentation systems over a variety of Microsoft Windows platforms

Sonochemical destruction of chloroform by using low frequency ultrasound in batch and flow cell

Ultrasound assisted environmental remediation is emerging as a viable technology to remove organic pollutants. In this study, the potential of low frequency ultrasound (20 kHz) to remediate chloroform contaminated waters (demineralised water and groundwater) in batch and flow cell treatment was evaluated. The results show that approx. 8 mg/L of chloroform was completely mineralized within 60 min in batch as well as flow cell treatments in both waters. However, flow cell treatment was superior to the batch mode for demineralised water in contrast to the groundwater for which there was no appreciable difference between batch and flow cell modes during initial 30 min. The presence of dissolved organic carbon, higher total dissolved solid content and any other co-contaminants might have contributed to the slower rate of chloroform destruction in the groundwater compared to the demineralised water. This study demonstrates the potential of low frequency ultrasound for remediation of chloroform contaminated waters.

Linear time domain model of the acoustic potential field

A new time domain formulation of the acoustic wave is developed to avoid approximating assumptions of the linearized scalar wave equation that limit its validity to low Mach particle velocity modeling or to a smooth potential field in a stationary medium. The proposed model offers precision of the moving frame while retaining the form of the widely used linearized scalar wave equation although with respect to modified coordinates. It is applicable to field calculations involving transient waves with unlimited particle velocity, propagating in inhomogenous fluids or in those with time varying density. The model is based on the exact flux continuity equation and the equation of motion, both using the moving reference frame. The resulting closed-form free space scalar wave equation employing total derivatives is converted back to the partial differential form by using modified independent variables. The modified variables are related to the common coordinates of space and time following integral expressions involving transient particle velocity representing wave radiated by each point of a stationary source. Consequently, transient field produced by complex surface velocity sources can be calculated following existing surface integrals of the radiation theory although using modified coordinates. The use of the proposed model is presented in a numerical simulation of a transient velocity source vibrating at selected magnitudes, leading to the determination of the propagating pressure and velocity wave at any point.