Search

The conjugate heat transfer from combustion in furnace to supercritical fluid in tube has been numerically investigated in this study. The mathematic model of the conjugate process has been constructed. The effects of the combustion status in furnace on the conjugate heat transfer process were analysed. The results demonstrate that the heat transfer deterioration of supercritical fluid in the tube will only occur in high heat flux regions such as the high temperature recirculation zone. The swirling air can suppress the high temperature recirculation zone near the furnace wall, which is beneficial to inhibit the heat transfer deterioration of supercritical fluid in the tube. [ABSTRACT FROM AUTHOR]

In the batch processing, the updated data in a database system sometimes occur with a large amount in a short time. We propose to make independent backup schedules, which copies the batch-processed data for safety, for the full backup schemes. We apply the cumulative damage process to model database backup schedule, by replacing shock by time for data update and damage by the amount of updated data. When the total rewritten data has exceeded a level K, a full backup is performed. However, the overhead for such a full backup sometimes becomes very large in a mass database system. To lessen the overhead, we make an independent backup to copy the batch-processed data. The overhead for independent backups increases in proportion to the total amount of updated data. We obtain optimum full backup intervals with independent backups to minimize the expected cost rates analytically. Numerical examples are given for the illustrations. [ABSTRACT FROM AUTHOR]

A new type of water mist fire extinguisher was proposed to be used in the manned spacecraft. The goal of prototype is that it can extinguish class 8B fires on the ground and its mass is less than 2.5 kg. The prototype employed only water as suppression agents. In the extinguisher, a piston separated the water from nitrogen artificially, which dispels the influence of the gravity on discharging. It possesses some advantages, such as high reliability, easy refilling of water and nitrogen, long life span, and convenient maintenance. A pressure-swirl nozzle was employed to produce water mist. There was no part to keep the pressure constant at the nozzle’s entrance; the service pressure of nozzle was determined in the range from 6 to 15 MPa. In that scope, the variation of droplet size with pressure did not have a significant impact on suppression performance, and the suppression time increment due to velocity reduction was in the acceptable level. A series of tests were conducted to verify its performance. The vibration test presented that there was no nitrogen leakage and no obvious resonance happened, which meant it possessed high reliability. The fire suppression tests indicated that it can suppress different fire types of a certain scale. The simulation results showed that the spray performance is improved in the microgravity. Conclusion can be drawn that the prototype is feasible in the microgravity and it reached the requirements of the design. [ABSTRACT FROM PUBLISHER]

The main purpose of this paper is to propose optimization problems in which how many number N of web servers should be provided for net jobs with random process times. We consider the first case when a single job with random time S is processed and take up the second case when number n of jobs with successive times are processed. The number n may not be a constant value that could be predefined from the practical point, so that we modify the model in the second case by supposing n to be a random variable. Next, we introduce shortage and excess costs into models to consider both costs suffered before and after failures of server system. We obtain the total expected costs for each model and optimize them analytically. When physical server failure time and job process time are exponentially distributed, optimal numbers that minimize the expected costs are computed numerically. [ABSTRACT FROM AUTHOR]

This paper proposes two modified replacement policies which combine random replacement with standard age and periodic policies, where units undergo replacement at the first completion of some random working time over a planned time T, which are called replacement overtime. The expected cost rates of age and periodic replacement overtime polices are obtained, and optimal policies which minimize them are discussed analytically. Comparisons between such two overtime policies and standard age and periodic replacements are made in detail. When two costs for replacement overtime and standard age or periodic policies are the same, it is shown as estimated previously that the standard replacements are better than their overtime policies. Furthermore, two modified replacement overtime costs are discussed and computed numerically when such new policies would be better than the standard age and periodic replacements. [ABSTRACT FROM AUTHOR]

A new preventive software rejuvenation policy is proposed in this paper. This technique is implemented when additive consumption of physical memory has reached some level. Using the theory of cumulative damage process, two models are given for two kinds of bugs. For the first model, aging-related bug is considered only and consumption of physical memory could be known by tests made at periodic times, optimal preventive rejuvenation policy is analytically derived and numerical example is given. As an extended preventive software rejuvenation policy, Heisenbug and aging-related bug are considered meanwhile in the second model. [ABSTRACT FROM AUTHOR]