Improvement of new logistic model for bacterial growth

Recently Fujikawa et al. [J. Food Hyg. Soc. Japan, 44, 155-160 (2003)] developed a new logistic model for bacterial growth. In the present study, an adjustment factor in the model was improved. The improved model could successfully describe growth curves of Escherichia coli and Salmonella in liquid media. In particular, the model could describe the linear growth at the early logarithmic phase more accurately than the previous model, being similar in this respect to the Baranyi model. However, the improved model more accurately predicted the rate constant of growth and the duration of the lag time as compared with the Baranyi model. These results showed that the improved model has the potential to successfully predict microbial growth.     

Estimation of bacterial concentrations in commercial foods by measuring ATP changes during incubation

Recently we have developed new kinetic methods of bacterial cell estimation in food products by measurement of the increase in bacterial adenosine-triphosphate (ATP) content during incubation using a conventional firefly luminometer [Fujikawa and Morozumi: Jpn. J. Food Hyg. (2002)]. The methods were the end point method and the delay method. We, in this study, evaluated these methods for bacterial concentration estimation in commercial foods. The methods were successfully applied to food products inoculated with Escherichia coli or Staphylococcus aureus. The methods were then used to estimate bacterial concentrations in commercial foods. For estimation, the kinetic parameter values were determined first from the data of bacterial strains studied previously. The bacterial concentrations estimated with these parameter values were slightly smaller than the measured concentrations for most of the food samples. The parameter values obtained with the least-squares method gave better estimations in both methods. The delay method predicted the bacterial concentrations in food products better than the end point method. This study showed that with appropriate parameter values, these methods could be useful tools for bacterial concentration estimation of commercial foods.     

Novel method for estimating viable Salmonella cell counts using real-time PCR

A novel method for estimating viable Salmonella Enteritidis cell counts with 5'-nuclease real-time PCR was developed in this study. Our method was based on the increase kinetics of the target DNA region (invA) of the microorganism growing in a food/clinical sample in a culture medium during incubation. The index of increase in the target DNA region studied here was threshold cycle, CT. A test Salmonella strain was grown in buffered peptone water at the optimal temperature (39 degrees C). As Salmonella cells were grown, the value of CT decreased with time, generating a downward sigmoidal curve. The slope of the curve was constant at various initial cell concentrations. With higher initial cell concentration, the CT value evaluated from the slope at a given time was lower. With this relationship, a novel method for estimating the initial viable cell concentration of a sample was developed. Dead Salmonella cells or bacteria other than the target cell caused deviation in the CT curve. Incubation in a selective media suppressed the deviation caused by other bacterial cells. We think that this method could be applied to many other microorganisms cultivable in a suitable medium.     

Diode-pumped Nd:YAG laser producing 122-W CW power at 1.319 μm

A high-power diode-pumped Nd:YAG laser oscillating at a wavelength of 1.319 μm is reported. A 122-W CW laser beam with an M2 factor of 35 has been achieved with an optical efficiency of 19.6%. The lasing characteristics, including thermal lensing, at 1.319 μm are compared with those at 1.06 μm. Under lasing conditions, the focal length of thermal lensing at 1.319 μm decreases by 25% and increases by 15% at 1.06 μm with respect to the nonlasing conditions. Based on the experimental results, the heat dissipation in an Nd:YAG rod is discussed with reference to nonradiative transitions from the upper laser level     

A control scheme for a three‐phase current source inverter in utility interactive photovoltaic system

A novel PWM control scheme for a three‐phase current source inverter of a photovoltaic (PV) generation system connected to a utility is proposed. The PV‐array output power can be adjusted by controlling the modulation factor in the proposed PWM pattern. The harmonic components of the output currents can be decreased sufficiently to satisfy the requirements of the Interactive Guidelines. Furthermore, a new Maximum Power Point Tracking control is proposed. The inverter output current should be detected, and the modulation factor may be controlled so as to obtain the maximum effective current. The inverter output power can be maintained at the maximum power point despite fluctuations of panel temperatures, insolation levels, and system voltages. © 2001 Scripta Technica, Electr Eng Jpn, 135(1): 43–55, 2001     

Copper‐Catalyzed Aromatic Trifluoromethylation via Group Transfer from Fluoral Derivatives

Starting from a readily available fluoral derivative, catalytic aromatic trifluoromethylation has been successfully achieved. A small amount of copper(I) iodide‐phenanthroline complex catalyzed the cross‐coupling reactions of aryl/heteroaryl iodides with the O‐silylated hemiaminal of fluoral (trifluoroacetaldehyde) to provide trifluoromethylated arenes in moderate to high yields.