Soojeon Lee

Thermostable D-hydantoinase from thermophilic Bacillus stearothermophilus SD-1 : characteristics of purified enzyme

One thousand thermophiles isolated from soils were screened for hydantoinase and its thermostability. One thermophilic bacterium that showed the highest thermostability and activity of hydantoinase was identified to be Bacillus stearothermophilus SD-1 according to morphological and physiological characteristics. The hydantoinase of B. stearothermophilus SD-1 was purified to homogeneity via ammonium sulfate fractionation, anion-exchange chromatography, heat treatment, hydrophobic-interaction chromatography, and preparative gel electrophoresis. The relative molecular mass of the hydantoinase was determined to be 126 kDa by gel-filtration chromatography, and a value of 54 kDa was obtained as a molecular mass of the subunit on analytical sodiumdodecylsulfate/polyacrylamide gel electrophoresis. The hydantoinase was strictly d-specific and metal-dependent. The optimal pH and temperature were about 8.0 and 65°C respectively, and the half-life of the d-hydantoinase was estimated to be 30 min at 80°C, indicating the most thermostable enzyme so far.

TCPRand: Randomizing TCP payload size for TCP fairness in data center networks

As many-to-one traffic patterns prevail in data center networks, TCP flows often suffer from severe unfairness in sharing bottleneck bandwidth, which is known as the TCP outcast problem. The cause of the TCP outcast problem is the bursty packet losses by a drop-tail queue that triggers TCP timeouts and leads to decreasing the congestion window. This paper proposes TCPRand, a transport layer solution to TCP outcast. The main idea of TCPRand is the randomization of TCP payload size, which breaks synchronized packet arrivals between flows from different input ports. We investigate how TCPRand reduces consecutive packet drops and demonstrate various benefits of TCPRand with extensive experiments and ns-3 simulation. Our evaluation results show that TCPRand guarantees the superior enhancement of TCP fairness with negligible overheads in all of our test cases.

Preliminary design for satellite mission operation from mission request to command planning

Communication, ocean, and meteorological satellite (COMS) is a geostationary satellite system which performs multi-mission such as communications services, ocean data acquisition, and meteorological data acquisition. Each mission is operated by different users, but it is the COMS satellite ground control system (SGCS) that practically controls all missions at an end. Therefore, all requests for performing the COMS mission have to be collected into COMS SGCS, and then the gathered mission requests shall be converted into the command to be transmitted to satellite after scheduling the requested mission in an optimal schedule. This paper introduces mission planning system and process which gathers mission requests, performs interactive mission scheduling, and generates command plan in order to carry out the various satellite missions of the COMS. First of all, we will see the system configuration and developing environment for mission planning. This paper will describe the main functions such as mission request gathering, mission scheduling, mission timeline reporting, and command planning. It deals with the role and design of each function in detail, and finally represents the operation concept to have the operator perform the mission planning efficiently when the COMS will be on orbit later on

Randomizing TCP payload size for TCP fairness in data center networks

Abstract As many-to-one traffic patterns prevail in data center networks, TCP flows often suffer from severe unfairness in sharing bottleneck bandwidth, which is known as the TCP outcast problem. The cause of the TCP outcast problem is the bursty packet losses by a drop-tail queue that triggers TCP timeouts and leads to decreasing the congestion window. This paper proposes TCPRand, a transport layer solution to TCP outcast. The main idea of TCPRand is the randomization of TCP payload size, which breaks synchronized packet arrivals between flows from different input ports. Based on the current congestion window size and the CUBIC’s congestion window growth function, TCPRand adaptively determines the proper level of randomness. With extensive ns-3 simulations and experiments, we show that TCPRand guarantees the superior enhancement of TCP fairness by reducing the TCP timeout period noticeably even in an environment where serious TCP outcast happens. TCPRand also minimizes the total goodput loss since its adaptive mechanism avoids unnecessary payload size randomization. Compared with DCTCP, TCPRand performs fairly well and only requires modification at the transport layer of the sender which makes its deployment relatively easier.

CFTUE: "Construct First-finished Task avoiding Unconditional Exclusion" Algorithm for Single-Resource Satellite Mission Scheduling

In this paper, we propose an Construct First-finished Task avoiding Unconditional Exclusion (CFTUE) Algorithm for Single-Resource Satellite Mission Scheduling. At each step of the algorithm, the task which is able to be finished first is considered earlier to be scheduled based on a greedy approach. By selecting the task, however, another task might be discarded even though both of them may coexist. In this case, we schedule the discarded one instead of the former one. This principle does not follow the conventional wisdom that the current partial schedule should be compressed as much as possible so that more tasks are to be inserted later. However, performance evaluation shows that CFTUE algorithm contains more tasks than Construct First-finished Task (CFT) algorithm.

Development of the Satellite Ground Control System for Multi-mission Geostationary Satellite COMS

A multi-mission GEO satellite, COMS has three payloads including Ka-band communications, GOCI, and MI. COMS SGCS is the only system for monitor and control of the satellite in orbit. In order to fulfill the mission operations of the three payloads and spacecraft bus, COMS SGCS performs the following functions such as reception and processing of telemetry data via S-band link, planning and transmission of telecommand, tracking and ranging of the satellite, control and monitoring of SGCS equipment, analysis and simulation of the satellite, processing and analysis of flight dynamics data, and mission scheduling and reporting. By the proper functional allocations, COMS SGCS is divided into five subsystems such as TTC, ROS, MPS, FDS, and CSS. COMS SGCS is linked with MSC, KOSC, and IDACS for satellite related data exchange. The software in the COMS SGCS is designed using the object-oriented methodology and implemented using Microsoft C# .NET environment on Intel microprocessor based computers. The hardware in the COMS SGCS includes 13-m S-band mono-pulse Cassegrain antenna and RF/BB equipment. In this paper, development of the COMS SGCS is described with respect to system functional allocations, software and hardware design, system implementation, and system test.

A Multiple-Forwarder based File Distribution Scheme using Join Time Interval over A Tree-based Overlay Multicast

In this paper, we suggest a efficient multiple-forwarder based file distribution scheme working over a tree-based overlay multicast. The proposed scheme takes advantage of a fact that each member joins the session with time interval. In a tree, the set of data delivered from a parent to each member since a member has joined until the next member joins is not overlapped. By using this property, in the proposed scheme, each forwarder distributes data to its succeeding members regardless of the underlying tree. The effectiveness of the proposed scheme is measured using numerical analysis and the performance evaluation on planet-lab shows that the proposed scheme enhances the throughput while maintaining data duplication ratio and control overhead significantly less compared to an existing scheme, Bullet.

OMFVS: overlay multicast for file distribution using virtual sources

There have been many research efforts to enhance the throughput of file distribution using overlay multicast. The tree-based approach has limitations in enhancing throughput due to its single forwarder architecture. Recent approaches introduce multiple packet forwarders other than the parent in the delivery tree for throughput enhancement. However, the overhead of control packet exchanges is required to appoint proper forwarders and to avoid duplicate packet delivery. In this paper, we suggest a throughput enhancement scheme for a tree-based overlay multicast scheme with multiple forwarders. It exploits a forward error correction scheme and the fact that the members join the session with time interval. Thus, each set of packets that are delivered from a parent to a member after the member joins and before a succeeding member joins is not overlapped. By deploying a dedicated sender to manage the membership information and packet reception state, the overhead of control packet exchanges is alleviated significantly. The performance evaluation shows that the proposed scheme reduces file delivery time with low control overheads and small packet duplication ratio, compared with existing scheme, Bullet.