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Athanasia: A User-Transparent and Fault-Tolerant System for Parallel Applications
Hyungsoo Jung,Hyuck Han,Yeom, H. Y.,Sooyong Kang IEEE 2011 IEEE transactions on parallel and distributed syst Vol.22 No.10
<P>This article presents Athanasia, a user-transparent and fault-tolerant system, for parallel applications running on large-scale cluster systems. Cluster systems have been regarded as a de facto standard to achieve multitera-flop computing power. These cluster systems, as we know, have an inherent failure factor that can cause computation failure. The reliability issue in parallel computing systems, therefore, has been studied for a relatively long time in the literature, and we have seen many theoretical promises arise from the extensive research. However, despite the rigorous studies, practical and easily deployable fault-tolerant systems have not been successfully adopted commercially. Athanasia is a user-transparent checkpointing system for a fault-tolerant Message Passing Interface (MPI) implementation that is primarily based on the sync-and-stop protocol. Athanasia supports three critical functionalities that are necessary for fault tolerance: a light-weight failure detection mechanism, dynamic process management that includes process migration, and a consistent checkpoint and recovery mechanism. The main features of Athanasia are that it does not require any modifications to the application code and that it preserves many of the high performance characteristics of high-speed networks. Experimental results show that Athanasia can be a good candidate for practically deployable fault-tolerant systems in very-large and high-performance clusters and that its protocol can be applied to a variety of parallel communication libraries easily.</P>
Hyungsoo Shin,Kihyun Kim,Namjin Jung 국제물리치료연구학회 2020 Journal of International Academy of Physical Ther Vol.11 No.1
Background: The alignment of the neck and shoulder is important in people with forward head posture. However, previous studies have mainly conducted fragmentary studies on the neck and shoulders, and studies on the combined movement of the neck and shoulders are incomplete. Objective: To investigate the effects of 6 week dynamic exercise program using Thera-band on craniovertebral angle (CVA) in adults with forward head posture. Design: Quasi-experimental study. Methods: The study was conducted on 24 adults with forward head posture and experimented with neck and shoulder exercises and divided them into groups of neck exercises, shoulder exercises, and neck and shoulder exercises to measure CVA values before and after the experiment. The neck exercise program included flexion and extension muscles of the neck and shoulder exercises included dynamic exercise of the upper extremities such as the trapezius muscles and serratus anterior muscle. The CVA results were measured using PA200. Results: Following the interventions, neck exercise group showed significant improvement in CVA (P<.05), but shoulder exercise group and combined exercise group did not show any significant results (P>.05). However, both groups showed some positive results. Significant differences were seen in the comparisons between the three groups (P<.05), and the results of the posthoc test showed significant differences in neck exercise group and shoulder exercise, neck exercise and combine exercise group. Conclusion: This study suggested that the Thera-band neck exercise is beneficial for foward head posture patients and is expected to be used in clinical trials.
Hyungsoo Jung,한혁,염헌영,강수용 한국통신학회 2010 Journal of communications and networks Vol.12 No.3
The efficient network resource management is one of the important topics in a real-time system. In this paper, we present a practical network resource management framework, controltheoretic packet scheduler (CPS) system. Using our framework, an operating system can schedule both input and output streams accurately and efficiently. Our framework adopts very portable feedback control theory for efficiency and accuracy. The CPS system is able to operate independent of the internal network protocol state,and it is designed to schedule packet streams in fine-grained time intervals to meet the resource requirement. This approach simplifies the design of the CPS system, and leads us to obtain the intended output bandwidth. We implemented our prototype system in Linux, and measured the performance of the network resource management system under various network QoS constraints. The distinctive features of our principles are as follows: It is robust and accurate, and its operation is independent of internal network protocols.
Influence of Segregation on Microstructure and Hot Workability of Grade 250 Maraging Steel
Hyungsoo Lee,Hi Won Jeong,Seong Moon Seo,Dae Won Yun,Kyungmi Park,Kwang Hyuk Yim,Young Soo Yoo 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.4
The optimal process parameters of grade 250 maraging steel for hot forging were investigated with a process map and microstructureanalysis. To generate the process map, hot compression tests were performed at 800–1200 °C and strain rates of0.01–5 s−1. The flow stress–strain curves were calibrated by Bayesian artificial neural network (ANN) modeling to compensatethe heat generated by dynamic deformation. The Ni and Mo segregation during the solidification of the ingot causedalternating layers of Ni- and Mo-rich and -lean bands, which affected the recrystallization behavior during hot compression. According to the calculated process map, 1100–1200 °C × 0.01–0.7 s−1 and 1000–1200 °C × 0.01–0.2 s−1 are favorableprocess conditions that ensure wide process windows in terms of strain rate and temperature, respectively. The commonfeatures of the microstructure deformed under both conditions were relatively coarse martensite blocks and low values in theelectron backscattered diffraction (EBSD) kernel average misorientation (KAM) results (i.e., low residual stresses), whichwere attributed to a low fraction of fine martensite block region.
TCP-GT: A New Approach to Congestion Control Based on Goodput and Throughput
Hyungsoo Jung,Shin-Gyu Kim,염헌영,강수용 한국통신학회 2010 Journal of communications and networks Vol.12 No.5
A plethora of transmission control protocol (TCP) congestion control algorithms have been devoted to achieving the ultimate goal of high link utilization and fair bandwidth sharing in high bandwidth-delay product (HBDP) networks. We present a new insight into the TCP congestion control problem; in particular an end-to-end delay-based approach for an HBDP network. Our main focus is to design an end-to-end mechanism that can achieve the goal without the assistance of any network feedback. Without a router’s aid in notifying the network load factor of a bottleneck link, we utilize goodput and throughput values in order to estimate the load factor. The obtained load factor affects the congestion window adjustment. The new protocol, which is called TCP-goodput and throughput (GT), adopts the carefully designed inversely-proportional increase multiplicative decrease window control policy. Our protocol is stable and efficient regardless of the link capacity, the number of flows, and the round-trip delay. Simulation results show that TCP-GT achieves high utilization,good fairness, small standing queue size, and no packet loss in an HBDP environment.