Pump power calculation for parametric diodes with variable series resistance

Relations are given for the pump power lost in a parametric diode with voltage-dependent series resistance. It is shown that in the case of voltage pumping, unlike current pumping, the effective resistance for the pump power calculation is different from the average value.     

Extraction of singular stress fields using the axisymmetric single-fiber micromechanics model

The stress distributions near the points of singularity in a single-fiber micromechanics model as obtained by local asymptotic methods and global (numerical solutions to full-field boundary value problem) methods are described. While the numerical/analytical solutions (without special treatment of the singularity) can capture higher order terms and are sufficiently accurate away from points of singularity, the solutions are approximate in the neighborhood of the singularity due to the inherent assumptions (single-valued at the point of singularity) about the nature of the stress fields. The study focuses on a methodology for accurate determination of generalized stress intensity factors from the approximate methods of stress analysis with relatively coarse discretizations and without any special modeling of the singularity. The approach adopted entails the comparison of the angular distribution of the stress components at varying radial distances near the point of singularity and identifying a region in which the numerical/analytical solutions have the best ability to determine the stress intensity factor. Determination of the generalized stress intensity factors is illustrated for a penny-shaped crack in a homogeneous medium and for a crack in fiber terminating at the fiber-matrix interface (fiber-break problem).*Author for correspondence (E-mail: kpochira@stevens.edu)     

DYNAMIC MODELS FOR THE TRANSIENT ANALYSIS OF INDUCTION MACHINES WITH ASYMMETRICAL WINDING CONNECTIONS

ABSTRACT

Dynamic analytical models have been developed for the transient analysis of induction machines with asymmetrical winding connections using the instantaneous symmetrical components (i.s.c.) and the associated operational equivalent circuits. The i.s.c. theory has been shown to be a very powerful tool for developing models for both symmetrical and any type of asymmetrical winding connections. Different practical situations have been considered and the model equations developed for analysis. It is shown that these models are very convenient for direct digital simulation. The equations are dervied in terms of the measurable resistance and reactance parameters of the equivalent circuit.     

STORAGE QUALITY OF PASTEURIZED AND UV TREATED APPLE CIDER

Two studies were conducted to assess the effect of hot-fill pasteurization at 63C and UV irradiation at 14 mJ/cm² on the quality and shelf-life of apple cider packaged under controlled conditions with minimal packaging contamination, and under pilot plant conditions resembling commercial operations. The processed cider was stored at 7C for up to 14 weeks in the first study and 4 weeks in the second. Microbiological, chemical and sensory tests were conducted weekly on cider samples. There were no significant differences among the fresh processed ciders with regard to taste and preference. All treatments achieved a reasonable reduction in microbial counts, although hot-fill pasteurization provided longer shelf-life. There were significant changes in pH, titratable acidity, soluble solids and turbidity of samples during storage. Hot-fill at 63C is a comparable alternative to flash pasteurization at 71C for 6 s for the production of safe quality cider at small cider mills.     

A Method for Thermal Process Evaluation of Conduction Heated Foods in Retortable Pouches

A mathematical model was developed to evaluate thermal processing of conduction heated foods in retortable pouches. This model uses any given finite value of surface thermal conductance (h) which is encountered in commercial sterilization of retortable pouches using hot water as the heating medium. The model is capable of determining process time, mass average sterilizing value and nutrient retention for a prefixed critical point sterilizing value using any retort temperature profile. Results of thiamin assay in pea puree processed in retortable pouches indicated good agreement between experimental and model predicted values of thiamin retention.     

Evaluation of Thermal Processing of Retortable Pouches Filled with Conduction Heated Foods Considering their Actual Shapes

A computer model was developed to evaluate thermal processing of a retortable pouch containing a conduction heated food. In this model, a transient 2-dimensional heat conduction equation was solved using a modified finite difference technique for a food-filled retortable pouch considering its actual shape. The model was used to determine process time, mass average sterilizing value and nutrient retention to achieve a prefixed level of lethality in the pouched product for a given temperature profile of the heating medium. Temperature distributions and sterilizing values predicted by the developed model were compared with similar values obtained by applying a finite element technique with the aid of a package program (ANSYS). Close agreements were found between the developed model and the finite element technique.