A dynamic call admission scheme for VBR traffic in ATM networks

The role of call admission control (CAC) in high-speed networks is to maintain the network utilization at a high level, while ensuring that the quality of service (QoS) requirements of the individual calls are met. We use the term static CAC to describe schemes that always allocate the same bandwidth to a specific group of multiplexed calls, independent of the other traffic sharing the link. Dynamic CAC, on the other hand, denotes a scheme in which the bandwidth allocation to a group of calls sharing a queue is influenced by the traffic in other queues destined for the same outgoing link. We propose a generic dynamic call admission scheme for VBR and ABR traffic whose aim is to reduce the blocking rate for VBR calls at the expense of a higher blocking rate for ABR calls. Our scheme is generic because it builds up on a pre-existing static scheme, e.g., one based on a simple notion of effective bandwidth. Our simple approach results in a significant reduction of the blocking rate for VBR traffic (several orders of magnitude), if the bandwidth requirements of a single call are a reasonably small fraction of the link capacity. At the same time, the deterioration of service for ABR traffic can be contained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tapered, both in dimension and in index, velocity coupler: theoryand experiment

The authors consider a tapered velocity coupler (TVC) that meets the adiabatic invariance condition with sufficiently strong coupling between the fundamental modes of individual guides in the middle region of the coupler while permitting individual excitation at the input end and sorting of the modes at the output end. This approach helps reduce the device length considerably by permitting much higher taper angle. A TVC consisting of one tapered and another straight, graded index waveguide is modeled using the normal modes of the entire, composite TVC structure. The analytical results are in excellent agreement with experimental results for a TVC fabricated in Ti:LiNbO₃. It is shown that the representation of the local normal modes as the superposition of the modes of the uncoupled guides leads to erroneous results     

A variational finite-difference method for analyzing channel waveguides with arbitrary index profiles

A variational, finite-difference method for computing the normalized propagation constants and the normalized field profiles of channel waveguides with arbitrary index profiles as well as aspect ratios is presented. Mode dispersion curves and the field profiles of the fundamental mode of channel waveguides having profiles of practical interest are included.     

Ohmic Tempering of Frozen Potato Puree

Frozen potato puree samples were tempered using an ohmic heating technique. Three salt concentrations (0.50, 0.75, and 1.00 %) and three frequency levels (10, 20, and 30 kHz) were used as experimental variables, and the effects of salt concentration and frequency on ohmic tempering were investigated. Temperature, electrical current, and voltage were measured during the ohmic tempering. Electrical conductivities were evaluated based on the sample geometry and the ohmic heating principle. Increasing the salt concentration and/or frequency increased the electrical conductivity and heating rate, and hence contributed to decreasing the tempering time for the frozen potato puree samples. The tempering time was lowest with the highest salt concentration employed, and longest for the lowest salt concentration and frequency. Temperature differences within the sample during ohmic heating were found to be lowest when employing 0.50 % salt concentration and 10 kHz frequency.     

Color and Texture Change Kinetics in Ripening Bananas

Kinetics of color and texture changes in ripening bananas were investigated as a function of storage temperature (10, 16, 22, 28 °C). Color was evaluated in terms of L, a and b values as well as the total color difference (ΔE) representing the residual deviations from the ripe stage. Puncture force (PF) was used to evaluate the texture properties of banana. The results indicated that the time dependence of L, ΔE and PF values followed a logistic model, while a and b values were well described by a simple zero-order and fraction conversion models, respectively. The Arrhenius equation adequately described the temperature dependence of the reaction rate constants for both color and texture parameters, from which the activation energies and rate constant at reference temperature 15 °C were obtained. There were significant linear correlations between color parameters (L, a, b, ΔE) and texture parameter (PF).     

EFFECT OF CHILLING AND FREEZING ON SURVIVAL OF VIBRIO PARAHAEMOLYTICUS ON FISH FILLETS1

Vibrio parahaemolyticus is a foodborne pathogen isolated from coastal waters of the United States, and from seafoods including fish. No information is available on the viability of V. parahaemolyticus on raw, chilled and frozen fish. A three‐strain mixture of V. parahaemolyticus was inoculated on fish fillets (pH 6.4) to obtain a bacterial load of 10⁴ (high) or 10³ (low) CFU/fillet, and stored at 4C or 8C for 9 days or at – 18C for seven weeks. At 4C and 8C, and at both levels of inoculation, V. parahaemolyticus survived on the fillets for the entire duration of the study. However, there was a significant reduction (P < 0.01) in V. parahaemolyticus population on the fillets by 9 days of storage. In the frozen fillets, there was a sharp decline (P < 0.01) in the population of V. parahaemolyticus by day 5 of storage. Although chilling and freezing significantly (P < 0.01) inactivated high numbers of V. parahaemolyticus on fish, they cannot be relied upon as a method to reduce V. parahaemolyticus on fish, since the time and magnitude of reduction depends on the initial load of the pathogen and the storage temperature.     

Pathogenicity of three species of entomopathogenic nematodes to some major stored-product insect pests

Entomopathogenic nematodes (Nematoda: Heterorhabditidae and Steinernematidae) are commonly used biological control agents of insects in cryptic habitats, but their potential for suppressing stored-product insects in these habitats has not been explored previously. Here, we provide data from the first step in a program to evaluate entomopathogenic nematodes in the genus Steinernema as biological control agents of stored-product pests by determining their pathogenicity to some of the major stored-product pest species. When evaluated against larvae, pupae and adults of six pest species (Plodia interpunctella, Ephestia kuehniella, Oryzaephilus surinamensis, Tenebrio molitor, Tribolium castaneum, and Trogoderma variabile), and the adults of two additional pest species (Sitophilus oryzae and Rhyzopertha dominica), Steinernema riobrave was either the most pathogenic or of similar pathogenicity compared to S. carpocapsae and S. feltiae. A dose of 10 infective juveniles of S. riobrave caused 80% or higher mortality against larvae of P. interpunctella, E. kuehniella, T. castaneum, and O. surinamensis, pupae of T. castaneum and T. molitor, and adults of T. molitor and the two moth species. All stages of Trogoderma variabile exhibited 70% or higher mortality. Adults of S. oryzae and R. dominica exhibited low susceptibility with 15% and 35% mortality, respectively. On the basis of these results, S. riobrave was selected for further evaluation under more field-like conditions.     

Inactivation Kinetics of Geobacillus stearothermophilus Spores in Water Using High-pressure Processing at Elevated Temperatures

ABSTRACT: Establishment of a high-pressure sterilization process requires data on pressure and temperature-dependent inactivation kinetics of target pathogenic, spoilage, or surrogate spore-forming bacteria in the food being tested. The objective of this study was to examine the response of Geobacillus stearothermophilus ATCC10149 spores to various temperature, time, and pressure combination treatments (500 to 700 MPa; 92°C to 111°C, 0.01 to 360 s). The pressure inactivation of spores was characterized at elevated temperatures under isobaric and isothermal conditions during the holding time using a laboratory-scale high-pressure unit. The inactivation kinetics was well described by the log-linear regression model. As expected, the rate of spore inactivation increased with increasing pressure and temperature. Decimal reduction times at constant pressure ( D _T,P values) varied from 29.4 to 108.8 s at 92°C, 17.4 to 76 s at 100°C, and 6.1 to 51.3 s at 111°C within the pressure range of 500 to 700 MPa. The resistance of spores to temperature and pressure was characterized with z_T and z_P values and compared with their resistance to conventional steam heating. The conventional thermal resistance of G. stearothermophilus species did not correlate to the thermal resistance at high pressure. The study provides kinetic data on the effects of pressure and temperature on the inactivation of a heat-resistant bacterial spore species under conditions applicable to the commercial processing of low-acid foods.     

Effect of inoculum level on aflatoxin production by Aspergillus flavus under modified atmosphere packaging (MAP) conditions

The combined effect of inoculum level and other environmental factors (water activity, storage temperature and level of headspace oxygen) on the growth and aflatoxin production by Aspergillus flavus under MAP conditions on a synthetic medium was studied using a full factorial experimental design. Regression analysis of the data showed that inoculum level, water activity (a_w), storage temperature and headspace O₂ all had a significant effect on both growth of, and aflatoxin production by, A. flavus. Maximum growth (4·17 mg g^-1) occurred at an inoculum level of 10⁴ spores per plate, an a_w of 0·95, storage temperature of 20°C and headspace O₂ of 15% (balance CO₂:N₂ (60%:40%)). However, maximum aflatoxin level of 3·45 μg g^-1 (3450 ng g^-1) occurred at an inoculum level of 10³ spores per plate, an a_w of 0·96, storage temperature of 25°C and a reduced level of headspace O₂ (10%). Packing under almost completely anaerobic conditions using Ageless oxygen absorbents inhibited both growth and aflatoxin production by A. flavus, irrespective of the inoculum levels and storage temperature used.