• Journal of IKEEE
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• v.3 no.2 s.5
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• pp.305-313
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• 1999

To demodulate the received OFDM signal, symbol timing detection which finds symbol start in the received sample stream is required in the system initialization. In this paper, we analyze the effect of symbol timing offset and propose a new symbol timing detection algorithm, which is using the guard interval. The proposed algorithm requires low computational process and small memory size, and dose not be affected by frequency offset and phase offset. In addition, We apply this algorithm to European digital TV broadcasting model based on OFDM to evaluate the performance in AWGN and multipath fading channel by the computer simulation.

• Journal of computational fluids engineering
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• v.20 no.4
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• pp.109-115
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• 2015

In this study, the Stokes flow in the microchannel is analysed where the semicircular protuberances with constant spacing are attached on the upper and lower walls with staggered arrangement. For the low Reynolds number flow in microchannel, Stokes approximation is used and the periodicity and symmetry of the flow are considered to determine the stream function and pressure distribution in the flow field by using the method of least squared error. As results, the streamline patterns and pressure distributions in the flow field are shown for some specific values of the size and spacing of the protuberances, and shear stress distributions on the surface of semicircular protuberances are plotted. Especially, for an important physical property, the average pressure gradient along the microchannel is obtained and compared with that for the case of in-phase arrangement of the upper and lower protuberances. And, for the small clearance between the protuberances of upper and lower walls or between the protuberances and the opposite wall, the average pressure gradient is derived from the lubrication theory and compared with that of the present study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1376-1384
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• 1996

Measuring the velocity of fluid flow, semiconductor flow sensors are widely used in the various fields of engineering and science such as the semiconductor manufacturing processes and electronic control engines for automobiles. In the near future, this type of sensors will replace present hot wire type sensors or other type flow sensor due to its low price, easy handling and small size. To develop the advanced semiconductor flow sensor, it is necessary to obtain characteristics of the flow and the heat transfer around the sensor in advance. In the present study, the theoretical analysis including mathematical modeling and numerical calculation to predict the characteristics of heat transfer and flow field around the sensor was carried out. The main parameters for optimum design of the flow sensor are the free stream velocity, the heat generation rate of silicon arm and the distance between arms. Effects of these parameters on flow and heat transfer around the sensor and the temperature difference between arms are examined.

• Journal of the Korean Society of Visualization
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• v.8 no.4
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• pp.60-65
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• 2010

A focus is given to the breakup behavior of spray droplets issuing from a nonimpinging-type injector. The analysis has been carried out experimentally by means of the dual-mode phase Doppler anemometry (DPDA). Spray characteristic parameters in terms of axial velocity, mean diameter, velocity fluctuation, and span (width of the size distribution) of droplets are measured down the geometric axis of a nozzle orifice and on the plane normal to the spray stream with the injection pressure variations. As the injection pressure increases, the velocity and its fluctuation become higher, whereas the droplet sizes get smaller. It is also shown that the magnitudes of those parameters are smoothed out by dispersion when the droplets move downstream as well as outwardly. The atomization process is significantly influenced by the injection pressure rather than the traveling distance in the experimental condition presented.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.38-47
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• 2009

Scour means the erosion of bed material by flow change when a bridge is constructed in a stream. Scour is one of the critical factors of a bridge failure. There are several methods for the monitoring of scour near bridge foundations; Sounding rods, Magnetic sliding collar System, Sonar system, underwater camera system and so on. In general, Sonar system is preferred due to its convenience and good accuracy. In this study, the new scour monitoring system was developed using profiling sonar sensor. The new system can measure a line profile of a seabed and has small size due to the effectively designed data logger. The performance of the new scour monitoring system was evaluated at a bridge pier in tidal environment. The measured local scour depths were discussed with the result of the empirical formulas; CSU, Froehlich, Laursen and Neill.

• Journal of the Korean Institute of Rural Architecture
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• v.8 no.3
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• pp.83-90
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• 2006

1) Lee-Su village is located in a riverside of an upper Tu-men river. Since an upper stream of Tu-men river is narrow and easy to pilot a boat, early in the past, it facilitated the form of the village near to the North Korean. 2) The form of the village is parabolic from the founding period. That is, increasing the number of houses in the time of the Cultural Revilution Campaign, and the Japanese colony, the village has transformed into the bigger size about 72 families from the small town. After the cultural revolution, due to private asset allowed in accordance with the Chinese Reform and Open Policy, the number of families in the town and the population have been decreased. As a result, 28 families live in the village currently. 3) The town which was well-ordered in the Japanese colonial period has been changed to a very disordered and agricultural town, owing to the decrease of the families A road system has been also ruined naturally in accordance with the decline of the number of the families.

• Journal of The Geomorphological Association of Korea
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• v.26 no.3
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• pp.1-17
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• 2019

Naeseongcheon is Korea's representative sand stream, and it is one of the regions where the dynamic changes of various river topography developed in the sand bed can be observed. Most of drainage area near of the river channel are formed with Daebo granite, and the granite weathering zone is developed at the surface of hill. Due to the massive input of sediment flux, braided channel reaches are found some of the area. However, the results of the study shows that the alluvial layer is very thin in some reaches. In addition, bedrock or weathered materials, including the Tors are exposed at the channel beds. On the other hand, during the flood, a considerable amount of sediment was introduced, causing the massive sediment to be close to 1m thick. In addition, despite the short distance, large changes in the particle size and sorting of the sediment were observed. Vegetation, on the other hand, has been shown to have a significant effect on the development of the overall channel bed topography, as reported in previous studies. In small floods or low water levels, vegetation's protection role of the surface is predominates, but in large flood conditions, herbaceous loss at the surface of the point bars, accelerating the erosion of surface.

• Korean Journal of Environment and Ecology
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• v.33 no.3
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• pp.266-279
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• 2019

We investigated the characteristics of fish communities and habitat status of endangered species Rhodeus pseudosericeus in Heuk Stream, a tributary of the Han River, from April to October 2018. During this period, we collected 47 species of 14 families from 10 survey stations using kick nets, cast nets, and long bag set nets. The dominant and subdominant species were Zacco platypus (37.6%) and Z. koreanus (13.8%), respectively. The next most abundant species were Squalidus gracilis majimae (11.1%), Pungtungia herzi (7.7%), Rhodeus pseudosericeus (5.0%), Microphysogobio yaluensis (4.3%), and Hemibarbus longirostris (3.0%). Among the fish collected, 19 species (40.4%) were Korean endemic species. Endangered species were R. pseudosericeus and Acheilognathus signifer while exotic species were Micropterus salmoides and Oncorhynchus mykiss, and land-locked species were Plecoglossus altivelis and Rhinogobius brunneus. The community analysis showed that the dominance and evenness indexes were mostly low and that the diversity and richness indexes were high. Moreover, the river health (index of biological integrity) was mostly excllent (1 site is good, 9 sites are very good). R. pseudosericeus inhabited widely from St. 3 to St. 9 in Heuk Stream, and its population size was large. Age groups for R. pseudosericeus estimated by the frequency distribution of total length in spawning season (April) indicated the 32~45 mm group as 1-year old, the 46~59 mm group as 2-years old, 60~69 mm group as 3-years old, and the 70~89 mm group as 4-years or older. Total length range of male and female was similar, and the sex ratio of female (426) to male (394) was 1 : 0.95. A. signifer, which had been released in Heuk Stream, inhabited from St. 4 to St. 5, but its population size was small. Lastly, this paper discusses a conservation plan for fish in Heuk Stream.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.3
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• pp.98-109
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• 2002

Bluetooth technology is a publicly available specification proposed for Radio Frequency (RF) communication for short-range :1nd point-to-multipoint voice and data transfer. It operates in the 2.4㎓ ISM(Industrial, Scientific and Medical) band and offers the potential for low-cost, broadband wireless access for various mobile and portable devices at range of about 10 meters. In this paper, we describe the structure and the test results of the bluetooth baseband module with direct memory access method we have developed. This module consists of three blocks; link controller, UART interface, and audio CODEC. This module has a bus interface for data communication between this module and main processor and a RF interface for the transmission of bit-stream between this module and RF module. The bus interface includes DMA interface. Compared with the link controller with FIFOs, The module with DMA has a wide difference in size of module and speed of data processing. The small size module supplies lorr cost and various applications. In addition, this supports a firmware upgrade capability through UART. An FPGA and an ASIC implementation of this module, designed as soft If, are tested for file and bit-stream transfers between PCs.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.11
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• pp.589-598
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• 2007

In the group communication which has multiple data streams and various access privileges, it is necessary to provide group access control. The group members having the same access privilege are classified into one class, and the classes form a hierarchy based on the access relations. Then each class is assigned to a secret key. In the previous schemes, a single logical key graph is constructed from the hierarchy and each member always holds all secret keys of the classes he can access in the proactive manner. Thus, higher-privileged members hold more keys then lower-privileged members. However, if the hierarchy is large, each member manages too many keys and the size of multicast message in rekeying increases in proportion to the size of the hierarchy. Moreover, most of the members access a small portion of multiple data streams simultaneously. Therefore, it is redundant to receive rekeying message and update the keys in which he is not currently interested. In this paper, we present a new key management scheme that takes a reactive approach in which each member obtains the key of a data stream only when he wants to access the stream. Each member holds and updates only the key of the class he belongs. If he wants to get the key of other class, he derives it from his key and the public parameter. Proposed scheme considerable reduces the costs for rekeying, especially in the group where access relations are very complex and the hierarchy is large. Moreover, the scheme has another advantage that it easily reflects the change of access relations.