Sheila Galt

Simulation of the temperature increase in pulsed electric field (PEF) continuous flow treatment chambers

Abstract The application of intense pulsed electric fields (PEF) in foods is intended to be a non-thermal method to inactivate microorganisms. However, it is well known that an increase in temperature is present in this process due to ohmic heating, where the pulsed electric field energy input is transformed into heat. The aim of this study was to investigate the computer modeled temperature increase in the outflow for different flow-through PEF treatment chamber designs. Given equal experimental conditions, the temperature increase is indicative of the PEF dose, and a more uniform temperature profile is thus indicative of a more homogeneous PEF treatment. The radial distribution of the temperature increase was simulated in computer models of four different chambers. The temperature increase was found to be more homogeneous in the treatment chambers making use of a decrease in the insulator diameter, i.e. a design letting the insulators and electrodes intersect at angles close to 90°. The maximum temperature increase was found close to the wall, where the flow velocity is low. Cooling of the electrodes and electric insulators is recommended to avoid too high a temperature increase. The minimum temperature increase found was 29% of the calculated average in the worst case studied here. The minimum PEF dose to which the food was subjected would thus is less than the intended dose, since the food clearly was not subjected to the intended electric field strength during the intended exposure time. This is an important result in terms of food safety in the sense that a minimum PEF treatment should be guaranteed. The microbiological inactivation was experimentally evaluated using two of the treatment chamber designs. The result is consistent with the simulations and shows a small increase in inactivation and less needed energy input giving less average temperature increase for the chamber implementing a contraction of the diameter of the insulating spacer.

Demonstration and analysis of a 40-gigasample/s interferometric analog-to-digital converter

A novel interferometric scheme for photonic analog-to-digital conversion is for the first time experimentally demonstrated at a real-time sample rate of 40 gigasamples/s. The scheme includes sampling as well as binary encoding, and the input signal in the experiment was a 1.25-GHz sinusoidal tone that was successfully digitized with a nominal resolution of 21 digital levels. Single-sample measurements yielded an effective number of bits (ENOB) of 2.6, which was limited by thermal detection noise while multisample averaged measurements resulted in an ENOB of 3.6 bits, mainly limited by phase drift. Apart from the experimental results, this paper covers an extensive theoretical analysis of the system, including calculations on the fundamental maximum bandwidth, the required optical power, the generated binary code, and its error robustness, as well as the impact of detection noise on the signal-to-noise ratio of the digitized signal. The major benefits of this interferometric scheme are that only one standard phase modulator is required and that the phase swing does not have to be larger than plusmnpi to reach the full digital value space

Interferometric analog-to-digital conversion scheme

A novel interferometric analog-to-digital converter (ADC) scheme for real-time conversion at multiple-gigahertz bandwidth is presented and theoretically analyzed. The input analog signal is applied as an optical phase modulation in one of the arms of a Mach-Zehnder interferometer and the digital output is obtained in encoded form as a set of optical intensities in the interference pattern. Particular benefits of the proposed device are its simple design which facilitates integration, the extremely high bandwidth, and the inherent 2/spl pi/-periodicity that in comparison with conventional flash ADCs relaxes the demands on the comparators and allows unwrapping of the output for higher resolution.

Cytoplasmic Ca2+ oscillations in human leukemia T-cells are reduced by 50 Hz magnetic fields.

The effect of 50 Hz magnetic fields on the cytosolic calcium oscillator in Jurkat E6.1 cells was investigated for field strengths within the range from 0 to 0.40 mT root mean square. The intracellular Ca2+ concentration data were collected for single Jurkat cells that exhibited a sustained spiking for at least 1 h while repeatedly exposing them to an alternating magnetic field in 10-min intervals interposed with nonexposure intervals of the same length. The obtained data were analysed by computing spectral densities of the Ca2+ oscillating patterns for each of these 10-min intervals. For every single-cell experiment the spectra of all exposure as well as nonexposure periods were then averaged separately. A comparison between the resulting averages showed that the total spectral power of the cytosolic Ca2+ oscillator was reduced by exposure of the cells to an alternating magnetic field and that the effect increased in an explicit dose-response manner. The same relationship was observed within the 0-10 mHz (10 x 10(-3) Hz) subinterval of the Ca2+ oscillation spectrum. For subintervals at higher frequencies, the change caused by the exposure to the magnetic field was not significant.

Diffraction-based determination of the phase modulation for general spatial light modulators

We describe a characterization method based on diffraction for obtaining the phase response of spatial light modulators (SLMs), which in general exhibit both amplitude and phase modulation. Compared with the conventional interferometer-based approach, the method is characterized by a simple setup that enables in situ measurements, allows for substantial mechanical vibration, and permits the use of a light source with a fairly low temporal coherence. The phase determination is possible even for a SLM with a full amplitude modulation depth, i.e., even if there are nulls in the amplitude transmission characteristic of the SLM. The method successfully determines phase modulation values in the full 2pi rad range with high accuracy. The experimental work includes comparisons with interferometer measurements as well as a SLM characterization with a light-emitting diode (LED).

The influence of 50-Hz magnetic fields on cytoplasmic Ca2+ oscillations in human leukemia T-cells

We have studied the effects of 50-Hz 100-microT rms magnetic fields on intracellular Ca2+ concentration in the Jurkat T lymphocyte variant E6.1 using fluorescent probes Indo-1 and Fura-2. We found, however, that the pattern of intracellular Ca2+ fluctuations also depended on the agent used for cell attachment, in our case the polypeptide poly-L-lysine. In order to isolate possible effects of magnetic field exposure from those of poly-L-lysine, the action of polypeptide on cytosolic Ca2+ was studied as well. It was found that a 10(-7)% concentration of polypeptide triggered prolonged Ca2+ spiking. Higher (10(-4)%) concentrations induced rapid increases in intracellular Ca2+ followed by high, unstable Ca2+ levels. The response of these cells to the monoclonal antibody anti-CD3 was also inhomogeneous, similar to one caused by poly-L-lysine. The effect of magnetic field exposure was studied on cells initially exhibiting (1) non-oscillating, low Ca2+ concentration and (2) prolonged Ca2+ concentration oscillations. In case (1) the result was negative. In case (2), statistically significant changes were found: the oscillation amplitude was reduced on average by 30%, and the frequency composition was shifted towards higher frequencies.

A Combined Electromagnetic and Heat Transfer Model for Heating of Foods in Microwave Combination Ovens

The objective of the present research was to establish a combined electromagnetic and heat transfer model to predict the temperature distribution in food loads during microwave and forced air heating in a microwave combination oven. The microwave process was modelled using the finite difference time domain (FDTD) method to numerically solve Maxwell’s equations in three dimensions, assuming the food properties to be constant. The power dissipated at each cell in the computational domain was subsequently calculated. Heat transfer was modelled using Fourier’s equation for heat conduction with convective boundary conditions. The conduction model was spatially discretised using finite elements. The power dissipation field was transferred to the finite element heat transfer code using interpolation modules to couple the models. Validation experiments were made for comparisons with predicted temperatures inside a model food load with brick-shaped geometry. Good qualitative agreement between predicted and measured temperature profiles was obtained.

ELF magnetic fields in a city environment

Some epidemiological studies indicate an association between extremely low frequency electromagnetic field (ELF-EMF) exposure and cancer risks. These studies have mainly taken residential and occupational exposure into consideration. Outdoor environments are often considered as low level areas, but in this paper we show that this is not true in a city environment. We have mapped the ELF magnetic flux densities along certain stretches of sidewalk in central Göteborg City, Sweden. About 50% of the investigated street length shows flux densities of the same order of magnitude (0.2 microT and above) as those associated with increased risks of cancer in epidemiological studies. We conclude that the outdoor exposures in a city environment also should be considered in exposure assessments and risk evaluations. These elevated flux densities are probably due to stray currents. We also found strong magnetic flux densities (> 1.0 microT) close to ordinary distribution pillars, power substations, shoplifting alarms, and other electrical devices.

Signal Reconstruction by Phase Retrieval and Optical Backpropagation in Phase-Diverse Photonic Time-Stretch Systems

The signal-to-noise ratio and bandwidth of photonic time-stretch (PTS) systems have previously been limited due to the nonlinear distortion caused by modulator response and dispersive propagation. In this paper, we present a novel method for the reconstruction of the input signal from two phase-diverse intensity measurements. The method consists of optical phase retrieval at the measurement point followed by simulated optical backpropagation to the modulation point. By numerical simulation of a PTS system with realistic parameters, we analyze the proposed method and compare it with the previously suggested maximum ratio combining (MRC) method. We show that the proposed optical backpropagation method, unlike the MRC method that treats the system as being linear from electrical input to output, can reconstruct the signal even at a large modulation depth and that the method is insensitive to biasing error or drift and not overly sensitive to misestimation of system parameters. Furthermore, to reduce the computational effort associated with the simulation of PTS systems, we present a numerical propagation method whereby the required number of sampling points is reduced by several orders of magnitude.

Study of effects of 50 Hz magnetic fields on chromosome aberrations and the growth-related enzyme ODC in human amniotic cells

Abstract The clastogenic effect of a 3 day exposure of human amniotic cells to a 50 Hz 30 μTrms sinusoidal magnetic field was tested. The experiment was designed to replicate that by Nordenson and coworkers in which chromosome gap and break frequencies were found to be relatively high after exposure. No increase in chromosome defects in the exposed cells was measured in our data; rather, an opposite tendency was observed. The concentration of ornithine decarboxylase (ODC) was also measured after exposure. Elevated levels of ODC would be expected if the exposure had produced a growth-stimulating effect. No significant difference was seen in the ODC concentrations in exposed cells compared with a sham-exposed sample.