RETORTABILITY of THIN-WALLED ALUMINUM CONTAINERS PRESSURIZED WITH ADDED LIQUID NITROGEN (LN2)

Studies were conducted to investigate the effect of initial container pressure on heat penetration parameters using flexible aluminum containers. A pilot scale liquid nitrogen dispenser, regulated to discharge a fine stream of liquid nitrogen (LN₂), provided approximately 10 to 15 psi pressure within the container prior to end‐over‐end processing in a computer‐controlled retort using water immersion with 32 psi over pressure. Thermal process parameters including the heating rate index (f_h), lag factor (j_h), the cumulative lethality (F_o), cook‐value (C_o) and the overall heat transfer coefficient (U_o) were examined in relation to retort temperature (241–261F), rpm (0–15 rpm) and product initial temperature (54–121F) using 5% w/w bentonite suspension with or without liquid nitrogen. Generally, containers with added liquid nitrogen had no impact on evaluated data compared to their counterparts without LN₂ under similar experimental conditions. Estimated overall heat transfer coefficient (U_o) compared favorably with published data, while the C_o/F_o ratio decreased with increasing temperatures as expected. Product cold spot location migrated in either upward or downward direction depending on the mode of heat transfer. Although added LN₂ generally had no limiting effect on both heat transfer and heat penetration data, processing aluminum containers with high initial pressure at high retort temperatures could create excessively high internal pressure that could compromise container seam integrity.     

THE EFFECT OF THERMOCOUPLE AND RECEPTACLE TYPE ON OBSERVED HEATING CHARACTERISTICS OF CONDUCTION-HEATING FOODS PACKAGED IN SMALL METAL CONTAINERS

Three different types of thermocouples and receptacles were studied to determine the effect on the observed heat penetration rate of a conduction‐heating food packaged in 202 × 204 and 211 × 300 cans. The studies were conducted at two product initial temperatures (70 and 140F) and three retort temperatures (240, 250 and 260F) using an Allpax R&D retort. The results indicated that the Ecklund stainless steel receptacles and needle type thermocouples in 202 × 204 cans increased the apparent heat penetration rates significantly, which resulted in underestimated Ball Formula process times (≈5%) and overestimated process lethalities (≈27%). However, in the 211 × 300 cans only minimal effects were seen on the apparent heat penetration rates, Ball process times and resulting lethalities. The use of plastic Delrin receptacles and thermocouples in 202 × 204 and 211 × 300 cans produced results in close agreement with those obtained from thin‐gauge flexible thermocouples having minimum conduction error.     

LETHALITY CONTRIBUTION FROM THE TUBULAR HEAT EXCHANGER DURING HIGH-TEMPERATURE SHORT-TIME PROCESSING OF A MODEL LIQUID FOOD

Experiments were conducted using Bacillus stearothermophilus spores in 0.5% w/w carboxymethylcellulose suspension to evaluate come‐up contributions from the tubular heat exchanger. A lab‐scale UHT/HTST simulator that allowed samples to be collected at the exit of the heat exchanger and holding tube was used with operating temperatures up to 270F. The bulk mean residence time in the heat exchanger ranged from 30 to 89 sec, while that in the holding tube ranged from 4 to 14 sec. It was observed that between 40% and 51% of the cumulative lethality ( ) at the exit of the holding tube, was contributed by come‐up in the tubular heat exchanger. This come‐up contribution was determined on the basis of having an of 8.5 min in the holding tube alone. It was evident that come‐up lethality will depend on product initial temperature, residence time and temperature history in the heat exchanger, with higher temperatures obviously contributing more lethality. Therefore, the entire aseptic system becomes even more complex since several critical parameters need to be monitored, controlled and documented. Experimental data compared favorably with computer‐simulated data using the AseptiCAL? software, with the software package giving more conservative results. Ultimately, come‐up credit (CUC) should be tested on a pilot scale or industrial setup by way of reduced residence time (i.e. increased fluid flow rate), reduced holding tube length or temperature in order to determine if CUC can be applied towards the lethality required for the product. Monitoring and control devices become critical to ensure consistency and reproducibility in product residence time and time–temperature history, in the tubular heat exchanger.     

基于模糊逻辑的自主移动机器人实时滚动路径规划及控制

针对动态不确定环境下自主移动机器人路径规划和运动控制这一工程实际问题,提出一种简化的实验参考系统结构模型。在此基础上,借鉴预测控制的基本原理,运用模糊逻辑推理方法解决了自主移动机器人导航和避障问题,实现了自主移动机器人实时滚动路径规划和控制,仿真结果表明了算法的有效性。     

Regulatory Pricing Rules to Neutralize Network Dominance

This paper evaluates the effectiveness of several pricing rulesintended to promote entry into a network industry dominatedby an incumbent carrier. Drawing on the work of Cournot andHotelling, we develop a model of competition between two interconnectednetworks. In a symmetric equilibrium, the price of cross-networkcalls exceeds the price of internal calls. This ‘callingcircle discount’ tends to ‘tip’ the industryto a monopoly equilibrium as would a network externality. Byequalizing charges for terminating calls, reciprocity eliminatesdifferences between internal and cross-network prices and makesmonopoly less likely. Imputation counteracts an incentive bythe dominant network to ‘price squeeze’ a rivalby eliminating differences in the wholesale price of terminationand the implicit price for internal use. By increasing profitsof rival networks and increasing their subscribers‘ surplus,imputation supports additional entry. Finally, an unbundlingrule reduces termination fees charged by a dominant networkthat was engaging in pure bundling. Again, entry will be facilitatedas rival networks offer potential subscribers a more attractiverate schedule.