Fair Service for High-Concurrent Requests

This thesis presents a new approach to ensuring fair service for highly concurrent requests. Our design uses the advantages of staged event-driven architecture (SEDA) to support high-concurrent loadings and makes use of control theory to manage the system performance. In order to guarantee the quality of service is fairly made to each request, based on SEDA, the control system for fairness is developed as a combination of a global control framework and a set of local self-tune stags. The global control framework is used to control the performance of the whole staged network at the top-level, aimed at coordinating the performance of the stages in the network. On the other hand, each self-tune stage under the control framework is built on the thread pool model, and will use automatic control theory to adjust its performance locally in order to meet the overall target performance. The automatic control system in each stage consists of an automatic modeling mechanism and a feedback module, which optimizes the controller parameters in the system automatically and guarantees the quality of performance (service rate here) for the stage at runtime. Based on mathematical proof and simulation results, our designs are implemented in a SEDA-based web server running in a dynamic loading environment. Results demonstrate that the performance of the new system in the real world is almost the same as the theoretical results. It demonstrates that the design is able to adaptively ensure the quality of service to the high-concurrent requests fairly. Compared to the original SEDA design, our design is an effective and handy approach to significantly enhancing the performance of SEDA in a variety of aspects, including fairer service, faster convergent speed, better robustness, higher accuracy and ease of deployment in various practical applications

Formation of hot subdwarf B stars with neutron star components

Binary population synthesis predicts the existence of subdwarf B stars (sdBs) with neutron star (NS) or black hole (BH) companions. We systematically investigate the formation of sdB+NS binaries from binary evolution and aim to obtain some clues for a search for such systems. We started from a series of MS+NS systems and determined the parameter spaces for producing sdB+NS binaries from the stable Roche-lobe overflow (RLOF) channel and from the common envelope (CE) ejection channel. Various NS accretion efficiencies and NS masses were examined to investigate the effects they have. We show the characteristics of the produced sdB+NS systems, such as the mass of components, orbital period, the semi-amplitude of the radial velocity (K), and the spin of the NS component. In the stable RLOF channel, the orbital period of sdB+NS binaries produced in this way ranges from several days to more than 1000 days and moves toward the short-period (~ hr) side with increasing initial MS mass. the sdB+NS systems that result from CE ejection have very short orbital periods and then high values of K (up to 800km s^-1). Such systems are born in very young populations (younger than 0.3 Gyr) and are potential gravitational wave sources that might be resolved by the Laser Interferometer Space Antenna (LISA) in the future. Gravitational wave radiation may again bring them into contact on a timescale of only ~Myr. As a consequence, they are rare and hard to discover. The pulsar signal is likely a feature of sdB+NS systems caused by stable RLOF, and some NS components in sdB binaries may be millisecond pulsars.Comment: 12 pages, 6 figures, 4 tables. Accepted for publication in A&

Fair Service for High-Concurrent Requests

This thesis presents a new approach to ensuring fair service for highly concurrent requests. Our design uses the advantages of staged event-driven architecture (SEDA) to support high-concurrent loadings and makes use of control theory to manage the system performance. In order to guarantee the quality of service is fairly made to each request, based on SEDA, the control system for fairness is developed as a combination of a global control framework and a set of local self-tune stags. The global control framework is used to control the performance of the whole staged network at the top-level, aimed at coordinating the performance of the stages in the network. On the other hand, each self-tune stage under the control framework is built on the thread pool model, and will use automatic control theory to adjust its performance locally in order to meet the overall target performance. The automatic control system in each stage consists of an automatic modeling mechanism and a feedback module, which optimizes the controller parameters in the system automatically and guarantees the quality of performance (service rate here) for the stage at runtime. Based on mathematical proof and simulation results, our designs are implemented in a SEDA-based web server running in a dynamic loading environment. Results demonstrate that the performance of the new system in the real world is almost the same as the theoretical results. It demonstrates that the design is able to adaptively ensure the quality of service to the high-concurrent requests fairly. Compared to the original SEDA design, our design is an effective and handy approach to significantly enhancing the performance of SEDA in a variety of aspects, including fairer service, faster convergent speed, better robustness, higher accuracy and ease of deployment in various practical applications