Modelling the bacterial survival/death interface induced by high pressure processing

The survival/death interface model was developed for prediction of inactivation of Listeria monocytogenes by high pressure processing (HPP). The model was derived from data sets comprising 360 combinations of environmental factors such as pressure (200, 300 400, and 500 MPa), pressure-holding time (1, 3, 5, 10, 20, 30 min), pH (3, 4, 5, 6, 7), and inoculum level (3, 5, 7 log(10) CFU/ml). The determination of survival/death of L. monocytogenes after HPP was confirmed by the presence/absence of colony forming ability on non-selective agar plates after 30 days of incubation at 20 degrees C in broth to take into account recovery of HPP-induced injured cells. The developed linear logistic model with time logarithmically transformed gave a degree of agreement between probabilities predicted by the fitted model and all observations as 99.3% concordant. The model provided a good fit to the data as shown by performance statistics. The developed interface model in the present study provided requisite process conditions for the target effect of HPP on L. monocytogenes. In addition to using the simple linear logistic model, a polynomial logistic model was also fitted to the data where pressure-holding time was not logarithmically transformed. That model did not produce a better fit to the data and resulted in some potentially misleading predictions. Optimization of HPP could be accomplished using the model developed in this study. Furthermore, choice in processing factors allows for processing flexibility in HPP and specifies the process criteria that are incorporated into the HACCP plan.     

Study on Dip Slope Failure at Higashi Takezawa Induced by 2004 Niigata-Ken Chuetsu Earthquake

An extensive number of slopes failed in the 2004 Niigata-ken Chuetsu Earthquake. Among them, a dip slope containing a weak layer in Yamakoshi Village (currently Nagaoka City) was investigated intensively. Regarding its morphological characteristics, it is argued that the earthquake reactivated a pre-existing failure plane which then formed most of the present sliding plane. In order to reveal the strength properties of the weak layer that formed the sliding plane, including the behavior against cyclic loading, a series of triaxial compression tests and simple shear tests was performed on undisturbed specimens that were retrieved by block sampling from the site. Based on the test results, a stability analysis and the calculation of the earthquake-induced displacement were performed. By extending Newmark's sliding block analysis, while considering the effects of the irregular geometry of the sliding plane and its strain-softening properties, a reasonable simulation of the process of this slope failure could be provided.     

Influence of inherent anisotropy on the seismic behavior of liquefiable sandy level ground

Inherent anisotropy is a crucial aspect to consider for an improved understanding of the strength and deformation characteristics of granular materials. It has been the focus of intense investigation since the mid-1960s. However, inherent anisotropy’s influence on ground seismic responses, such as liquefaction, has not been extensively studied. In this paper, inherent anisotropy’s influence on ground seismic responses is examined through a series of dynamic centrifuge model tests on liquefiable level sand deposits. During the model setup, five different deposition angles (0, 30, 45, 60, and 90 degrees) were achieved using a specially designed rigid container. The models were exposed to tapered sinusoidal input accelerations and the recorded results were fully investigated. It was found that deposition angle-caused inherent anisotropy significantly influenced the excess pore pressure responses during the shaking and dissipation phases. The amount of excess pore pressure build-up and the high excess pore pressure duration increased with the deposition angle, while the dissipation rate decreased as the deposition angle increased. The inherent anisotropy also influenced liquefaction-induced ground settlement, with volumetric strain increasing along with the deposition angle. With respect to response acceleration, inherent anisotropy’s effects depended on the amount of excess pore pressure build-up (i.e., degree of liquefaction). In view of these results, it was concluded that a sandy ground, deposited at a higher angle (i.e., closer to 90 degrees), is more susceptible to liquefaction and that inherent anisotropy’s influence should be considered when evaluating the liquefaction potential and performing effective stress analyses.