Influence of dimethyl dicarbonate on the resistance of Escherichia coli to a combined UV-Heat treatment in apple juice

Commercial apple juice inoculated with Escherichia coli was treated with UV-C, heat (55°C) and dimethyl dicarbonate – DMDC (25, 50, and 75 mg/L)-, applied separately and in combination, in order to investigate the possibility of synergistic lethal effects. The inactivation levels resulting from each treatment applied individually for a maximum treatment time of 3.58 min were limited, reaching 1.2, 2.9, and 0.06 log10 reductions for UV, heat, and DMDC (75 mg/L), respectively. However, all the investigated combinations resulted in a synergistic lethal effect, reducing the total treatment time and UV dose, with the synergistic lethal effect being higher when larger concentrations of DMDC were added to the apple juice. The addition of 75 mg/L of DMDC prior to the combined UV-C light treatment at 55°C resulted in 5 log10 reductions after only 1.8 min, reducing the treatment time and UV dose of the combined UV-Heat treatment by 44

MODELING OF POWER SEMICONDUCTOR DEVICES

One of the requirements for choosing a proper power electronic device for a converter is that it must possess a low specific on-resistance. The specific on-resistance of a bipolar device is related to the base width and doping concentration of the lightly doped drift region. This means that the doping concentration and the width of the low-doped base region in a bipolar device must be carefully considered to achieve a desired avalanche breakdown voltage and on-resistance. In order to determine the technological parameters of a semiconductor device, a one dimensional analysis is used to calculate the minimum depletion layer width, Wmin, for a given breakdown voltage, VBD, in Si, SiC and GaN p+n-n+structures. Further investigation is done to determine the optimum width of associated depletion layers for different blocking voltages to achieve a minimal forward conduction voltage drop. The complete one-dimensional model for calculation of the minimum depletion layer width, Wmin, for a given breakdown voltage, VBD, of a p+n–n+ structure is developed and used to calculate the optimum width of the depletion layer for different blocking voltages to achieve a minimal forward drop. The results show that the calculations of the lightly doped drift region thicknesses, and associated breakdown voltages and forward voltage drops, lead to incorrect solutions when applied to high voltage p+n–n+ structures using the simplified model equations for a p+n structure. These results also indicate a minimal impurity doping concentration for p+n–n+ structures, below which little improvement in breakdown capability can be had. The analysis shows for example that optimization of the doping concentration to minimize VF in a 5 kV Si diode could result in more than a 12% decrease in the forward drop, while for SiC and GaN this decrease is insignificant; typically less than 1%. Therefore, an optimization of the forward voltage drop by using the optimal doping concentration for corresponding breakdown voltages is necessary for proper design of a Si diode, while for wide band gap material devices this optimization is not necessary. The second part of the dissertation presents a physics-based model of a SiC BJT and verification of its validity through experimental testing. The Fourier series solution is used to solve the ambipolar diffusion equation (ADE) in the transistor collector region. The model is realized using MATLAB® and Simulink®. The experimental results of static operation and also the simulated and experimental results of switching waveforms are given. From the experimental and simulated results it is concluded that the model represents the static and switching characteristics of the SiC BJT quite well. From the experimental measurement results are calculated the switching losses of the BJT. The differences between simulated and measured switching losses during the turn-on and turn-off are 6.28% and 3.52%, respectively. Adviser: Jerry L. Hudgin

Ultraviolet and Pulsed Electric Field Treatments Have Additive Effect on Inactivation of \u3ci\u3eE. coli\u3c/i\u3e in Apple Juice

Apple juice inoculated with Escherichia coli ATCC 23472 was processed continuously using either ultraviolet (UV), high-voltage pulsed electric field (PEF), or a combination of the PEF and UV treatment systems. Apple juice was pumped through either of the systems at 3 flow rates (8, 14, and 20 mL/min). E. coli was reduced by 3.46 log CFU/mL when exposed in a 50 cm length of UV treatment chamber at 8 mL/min (2.94 s treatment time with a product temperature increase of 13 °C). E. coli inactivation of 4.87 log CFU/mL was achieved with a peak electric field strength of 60 kV/cm and 11.3 pulses (average pulse width of 3.5 μs, product temperature increased to 52 °C). E. coli reductions resulting from a combination treatment of UV and PEF applied sequentially were evaluated. A maximum E. coli reduction of 5.35 log CFU/mL was achieved using PEF (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) and UV treatments (length of 50 cm, treatment time of 2.94 s, and flow rate of 8 mL/min). An additive effect was observed for the combination treatments (PEF and UV), regardless of the order of treatment (P \u3e 0.05). E. coli reductions of 5.35 and 5.30 log CFU/mL with PEF treatment (electrical field strength of 60 kV/cm, specific energy of 162 J/mL, and 11.3 pulses) followed by UV (length of 30 cm, treatment time of 1.8 s, and flow rate of 8 mL/min) and UV treatment followed by PEF (same treatment conditions), respectively. No synergistic effect was observed

Monitoring IGBT’s Health Condition via Junction Temperature Variations

Insulated gate bipolar transistor (IGBT) failures are a major issue in modern power electronics applications. Two most dominated failure mechanisms of IGBTs are solder fatigue and bond wire wear-out. This paper proposes a new method to online monitor an IGBT’s health condition by using the instantaneous junction temperature variation between present and the first operating cycles of the IGBT with the same operating current. In this work, the instantaneous junction temperature of an IGBT is estimated from a thermal network model. The proposed method is validated by experimental results obtained from accelerated aging tests for IGBTs

Enhanced Anthocyanin Extraction from Red Cabbage Using Pulsed Electric Field Processing

This study was conducted to evaluate the effect of pulsed electric field (PEF) treatment on anthocyanin extraction from red cabbage using water as a solvent. Mashed cabbage was placed in a batch treatment chamber and subjected to PEF (2.5 kV/cm electric field strength; 15 μs pulse width and 50 pulses, specific energy 15.63 J/g). Extracted anthocyanin concentrations (16 to 889 μg/mL) were determined using HPLC. Heat and light stabilities of the control and PEF-treated samples, having approximately the same initial concentrations, were studied. PEF treatments enhanced total anthocyanin extraction in water from red cabbage by 2.15 times with a higher proportion of nonacylated forms than the control (P \u3c 0.05). The heat and light stabilities of the PEF-treated samples and control samples were not significantly different (P \u3e 0.05). Practical Application: An innovative pretreatment technology, pulsed electric field processing, enhanced total anthocyanin extraction in water from red cabbage by 2.15 times. Manufacturers of natural colors can use this technology to extract anthocyanins from red cabbage efficiently

Modeling, Simulation, and Validation of a Power SiC BJT

This paper presents a physics-based model of a silicon carbide bipolar junction transistor and verification of its validity through experimental testing. The Fourier series solution is used to solve the ambipolar diffusion equation in the transistor collector region. The model is realized using MATLAB and Simulink. The experimental results of static operation and also the simulated and experimental results of switching waveforms are given

Modeling bipolar power semiconductor devices gachovska

This book presents physics-based models of bipolar power semiconductor devices and their implementation in MATLAB and Simulink. The devices are subdivided into different regions, and the operation in each region, along with the interactions at the interfaces which are analyzed using basic semiconductor physics equations that govern their behavior. The Fourier series solution is used to solve the ambipolar diffusion equation in the lightly doped drift region of the devices. In addition to the external electrical characteristics, internal physical and electrical information, such as the junction voltages and the carrier distribution in different regions of the device, can be obtained using the models. Table of Contents: Introduction to Power Semiconductor Device Modeling/Physics of Power Semiconductor Devices/Modeling of a Power Diode and IGBT/IGBT Under an Inductive Load-Switching Condition in Simulink/Parameter Extraction. © 2013 by Morgan & Claypool