• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.4
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• pp.573-582
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• 2020

Fuzzing is a method of testing software by randomly generating test cases. Since its introduction, a variety of fuzzing techniques have been studied. Among them, mutation-based fuzzing is an efficient method that finds real-world bugs even though it uses a simple approach such as probabilistic bit-flipping and character substitution. However, the interpreter fuzzing has difficulty in applying general mutation techniques because the interpreter requires grammar and semantic correctness input values. In this paper, we present a novel mutation-based fuzzing on JavaScript interpreters with a dynamic data flow analysis. To this end, we implement JMFuzzer that can generate various types of mutated test cases that operate normally without runtime errors in JavaScript interpreter considering syntax and semantics. As a result, we found numerous unknown vulnerabilities in the latest JavaScript interpreters. We reported all of them to the vendors.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.6
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• pp.485-496
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• 2015

The present study presents experimental results on the characteristics of emission spectra of kerosene/air swirl flames. The aviation fuel Jet A-1, which is used for the liquid rocket engines of the Korea Space Launch Vehicle, is used with three different swirlers to investigate the swirl strength effects. The emission spectra from the flames are measured with a spectrometer as the swirl strength and combustion air temperature are varied. Chemiluminescence intensities of $OH^*$, $CH^*$ and $C_2{^*}$ are identified from the spectra. The chemiluminescence intensities from the kerosene flames show sensitivity to the swirl strength and are affected by changes in the combustion air temperature. Among the three radicals of interest, $C_2{^*}$ show the most significant changes in chemiluminescence intensity with the swirl strength and equivalence ratio. The intensity ratios $I_{OH^*}/I_{CH^*}$ and $I_{C_2{^*}}/I_{CH^*}$ are adequate for indicating changes in the equivalence ratio with the air and fuel mass flow rates, respectively.

• Journal of Korean Society of Transportation
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• v.22 no.2 s.73
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• pp.43-54
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• 2004

This study analyzes characteristics and applicability of genetic algorithms and genetic operators to optimize highway alignments. Genetic algorithms, one of artificial intelligence techniques, are fast and efficient search algorithms for generating, evaluation and finding optimal highway alignment alternatives. The performance of genetic algorithms as an optimal search tool highly depends on genetic operators that are designed as a problem-specific. This study adopts low mutation operators(uniform mutation operator, straight mutation operator, non-uniform mutation operator whole non-uniform mutation operator) to explore whole search spaces, and four crossover operators(simple crossover operator, two-point crossover operator, arithmetic crossover operator, heuristic crossover operator) to exploit food characteristics of the best chromosome in previous generations. A case study and a sensitivity analysis have shown that the eight problem-specific operators developed for optimizing highway alignments enhance the search performance of genetic algorithms, and find good solutions(highway alignment alternatives). It has been also found that a mixed and well-combined use of mutation and crossover operators is very important to balance between pre-matured solutions when employing more crossover operators and more computation time when adopting more mutation operators.

• The Journal of the Korea Contents Association
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• v.17 no.7
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• pp.93-100
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• 2017

Recently, demands for high-performance flash-based storage devices (i.e., flash SSD) have rapidly grown in social network services, cloud computing, super-computing, and enterprise storage systems. The industry and academic communities made the NVMe specification for high-performance storage devices, and NVMe-based flash SSDs can be now obtained in the market. In this article, we evaluate performance of NoSQL databases that social network services and cloud computing services heavily adopt by using NVMe-based flash SSDs. To this end, we use NVMe SSD that Samsung Electronics recently developed, and the SSD used in this study has performance up to 3.5GB/s for sequential read/write operations. We use WiredTiger for NoSQL databases, and it is a default storage engine for MongoDB. Our experimental results show that log processing in NoSQL databases is a major overhead when high-performance NVMe-based flash SSDs are used. Furthermore, we optimize components of log processing and optimized WiredTiger show up to 15 times better performance than original WiredTiger.

• Journal of Biosystems Engineering
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• v.31 no.1 s.114
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• pp.1-8
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• 2006

This study was conducted to identify the characteristics of PTO rattle noise of a direct engine-PTO driveline for agricultural tractors. In order to reduce production costs of agricultural tractors, a direct engine-PTO driveline was recently introduced to the tractors produced in Korea. This simplified drive line reduced a number of gears and counter shafts in previous one. However, it caused a severe rattle noise under an idle condition, which was perceived as intolerable by many tractor operators. PTO rattle noise was measured at two locations: one 3 em apart radially from the centerline of the PTO shaft and another 100 em apart backward from the PTO end and 160 em high from the ground. Characteristics of the rattle was analyzed using the data measured near the PTO shaft. It was found that the period of rattle noise was same as the explosion stroke of engine and its peak level was about 123 dB (A) with PTO engaged at an idle engine speed of 880 rpm. As the engine speed increased, the rattle noise decreased. The frequency band of the rattle was 0.5-2.0 kHz and the frequency of peak sound pressure was 1.4 kHz. When compared the rattle noise between the locally produced and imported tractors of the same type of PTO driveline, the former generated louder rattle noise than the imported one by 7 dB (A). It was suggested that the rattle noise of local tractors must be reduced at least by 7 dB (A) to meet the international level.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.72-78
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• 2003

In the present paper, computational studies on the hydrodynamic behavior of the inducer for the rocket-engine turbopump are presented including the effect of the mass flow rate. As the mass flow rate is increased, the inducer showed better performance with weak back flows which may have deleterious effects upon the anti-cavitation ability. But the adopted inducer showed low head rise with high volume flow rates, which may be caused by the small passage area near the trailing edge. The static pressure distributions at the shroud surface are compared with experimental results showing very good agreements except near the leading edge where strong back flows are present. The overall performance of the inducer such as, efficiency, head rise is also compared with experiments. The computational results are generally in good agreements with experimental ones near the design point, but two results show discrepancy at the high flow rate.

• Journal of KIISE:Computer Systems and Theory
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• v.35 no.5
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• pp.231-236
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• 2008

This paper proposes a cost-efficient and flexible FPGA-based logic circuit emulation platform. By improving the performance and adding more features, this new platform is an enhanced version of our LAPG. It consists of an FPGA-based hardware engine and software element to drive the emulation and monitor the results. It also provides an interactive verification environment which uses an efficient communication protocol through a bi-directional serial link between the host and the FPGA board. The experimental results show that this new approach saves $55%{\sim}99%$ of communication overhead compared with other methods. According to the test results, the new LAPG is more area efficient in complex circuits with many I/O ports.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.3
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• pp.967-976
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• 2012

This study presents a model to minimize vibration and noise of powertrain mount on a compact car which has the application of Stop & Go performance, in order to reduce CO2 and achieve better fuel-efficiency in accordance with the environmental regulations in automotive industries. In the first step, we analyze the powertrain mount system of the automobile "A" and present variables about rubber stiffness applied on powertrain mount using the Taguchi method. In the next step, we verify the optimization of vibration and noise which meet Stop & Go performance using the AHP(Analytic Hierarchy Process) method on the proto products for each variable. Using this validation system on the initial stage of the powertrain mount design, it is expected that we can grasp vibration and noise problems caused by engine movements and control them effectively without engineering know-how about powertrain mount rubber stiffness.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.103-120
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• 2010

A development history of the thrusters used for space-vehicle orbit maneuver/attitude control is reviewed with their performance characteristics. Especially, a scrutiny is made for the current and practical application of TVC/Gimbal/Thrusters to the roll/pitch/yaw-axis control of each stage of launch vehicles. It is well perceived that a precise 3-axis attitude control system (ACS) must be equipped on the final stage of space launch vehicles (SLV) for an attainment of orbit-insertion accuracy. Under the superior reliability as well as moderate performance features, the monopropellant hydrazine thrusters occupy most of the SLV's 3-axis ACS currently operated. Domestic development status of the medium-thrust-level thruster is shortly introduced, finally.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.6
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• pp.1220-1228
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• 2009

Ontologies, which are the core of the Semantic Web, are usually limited by specific domains or created by defining meanings and relationships that depend on the heuristic. However, the creation of an ontology is not only very difficult but also very time-consuming. In contrast with ontologies that are used in specific fields, an ontology for the Web entails an unlimited scope of knowledge and expression of information. Hence, it is hard to express information in the same way that is used to create ontologies in specific fields. Therefore, the automatic generation of an ontology takes very important role in the Semantic Web. In this paper, to make ontologies automatically, we suggest the methods to create and renew ontologies by expanding keywords related to the index-terms which are extracted from the search keywords which users input in the search engines by analyzing the morphemes.