Search

Advanced satellite-based frequency transfers by two-way carrier-phase (TWCP) and integer precise point positioning have been performed between the National Institute of Information and Communications Technology and Korea Research Institute of Standards and Science. We confirm that the disagreement between them is less than $1\times 10^{-16}$ at an averaging time of several days. In addition, an overseas frequency ratio measurement of Sr and Yb optical lattice clocks was directly performed by TWCP. We achieved an uncertainty at the mid-10−16 level after a total measurement time of 12 h. The frequency ratio was consistent with the recently reported values within the uncertainty.

Advanced satellite-based frequency transfers by two-way carrier-phase (TWCP) and integer precise point positioning have been performed between the National Institute of Information and Communications Technology and Korea Research Institute of Standards and Science. We confirm that the disagreement between them is less than at an averaging time of several days. In addition, an overseas frequency ratio measurement of Sr and Yb optical lattice clocks was directly performed by TWCP. We achieved an uncertainty at the mid-10

Two-Way Satellite Time and Frequency Transfer (TWSTFT or TW for short) is one of the primary techniques for the realization of Coordinated Universal Time (UTC), which is computed by the International Bureau of Weights and Measures (BIPM). TWSTFT is carried out continuously by about 20 timing laboratories around the world. One limiting factor of the TWSTFT performance is the daily pattern (diurnals) in the TWSTFT data. Their peak-to-peak variations were observed as up to 2 ns in some extreme cases. They must be attributed to the equipment on ground or the satellite transponder, but no clear understanding has been achieved for some years. In 2014 and 2015, it was demonstrated inlinks between Asian stations that the use of Software-Defined Radio (SDR) receivers for TWSTFT could considerably reduce the diurnals and also the TWSTFT measurement noise. In 2016, BIPM and the Consultative Committee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilot study on the application of SDR receivers in the Asia to Asia, Asia to Europe, Europe to Europe and Europe to USA TWSTFT networks. The very first results of the pilot study have been reported to the PTTI 2017. The results show, 1) for continental (short) links: SDR TWSTFT demonstrates a significant gain in reducing the diurnals by a factor of two to three; 2) for inter-continental (very-long) links: SDR TWSTFT displays a small gain of measurement noise at short averaging times; 3) SDR receivers show superior or at least similar performance compared with SATRE† measurements for all links. The CCTF WG on TWSTFT prepared a recommendation “On Improving the uncertainty of Two-Way Satellite Time and Frequency Transfer (TWSTFT) in UTC Generation” for the 21st CCTF meeting. One of the recommended items is to introduce the use of SDR TWSTFT in UTC generation. The recommendation was approved by CCTF during the meeting in June 2017. In the current setups, a SDR receiver and the collocated SATRE modem receive the signals transmitted by remote SATRE modems, and the two devices independently determine the arrival time of the received signal. Thus, a few setup changes are necessary to implement SDR receivers into operational TWSTFT ground stations. On the other hand, the data computation, e.g. for calibrated time transfer, needs some caution in the data processing and provision, which are not trivial. Thus, an Ad hoc Group has been established to work out a procedure for the use of the SDR TWSTFT in UTC computation. This paper reports on the progress of the work for using SDR TWSTFT in UTC computation. Section 1 introduces SDR TWSTFT and the pilot study. Section 2 presents the considerations for using SDR TWSTFT in UTC generation. Section 3 and 4 show the methods for analysing SDR TWSTFT and the analysis results. Sections 5 and 6 discusses the further improvement of SDR TWSTFT and summarizes the work towards using SDR TWSTFT in UTC generation.

Two-way satellite time and frequency transfer (TWSTFT) is a primary technique for the generation of coordinated universal time (UTC). About 20 timing laboratories around the world continuously operate TWSTFT using satellite time and ranging equipment (SATRE19) modems for remote time and frequency comparisons in this context. The precision of the SATRE TWSTFT as observed today is limited by an apparent daily variation pattern (diurnal) in the TWSTFT results. The observed peak-to-peak variation have been found as high as 2 ns in some cases. Investigations into the origins of the diurnals have so far provided no complete understanding about the cause of the diurnals. One major contributor to the diurnals, however, could be related to properties of the receive part in the modem. In 2014 and 2015, it was demonstrated that bypassing the receive part and the use of software-defined radio (SDR) receivers in TWSTFT ground stations (SDR TWSTFT) instead could considerably reduce both the diurnals and the measurement noise.In 2016, the International Bureau of Weights and Measures (BIPM) and the Consultative Committee for Time and Frequency (CCTF) working group (WG) on TWSTFT launched a pilot study on the application of SDR receivers in the TWSTFT network for UTC computation.The first results of the pilot study were reported to the CCTF WG on TWSTFT annual meeting in May 2017, demonstrating that SDR TWSTFT shows superior performance compared to that of SATRE TWSTFT for practically all links between participating stations. In particular, for continental TWSTFT links, in which the strongest diurnals appear, the use of SDR TWSTFT results in a significant suppression of the diurnals by a factor of between two and three. For the very long inter-continental links, e.g. the Europe-to-USA links where the diurnals are less pronounced, SDR TWSTFT achieved a smaller but still significant gain of 30%. These findings are supported by an evaluation of some of the links with an alternate technique based on GPS signals (GPS IPPP) as reported in this paper.Stimulated by these results, the WG on TWSTFT prepared a recommendation for the 21st CCTF meeting, which proposed the introduction of SDR TWSTFT in UTC generation. With CCTF approval of the recommendation, a roadmap was developed for the implementation of SDR TWSTFT in UTC generation. In accordance with the roadmap, most of the stations that participated in the pilot study have updated the SDR TWSTFT settings to facilitate the use of SDR TWSTFT data in UTC generation. In addition, the BIPM conducted a final evaluation to validate the long-term stability of SDR TWSTFT links, made test runs using the BIPM standard software for the calculation of UTC, now including SDR TWSTFT data, and started to calculate SDR TWSTFT time links as backup from October 2017. The use of SDR TWSTFT in UTC generation will begin in 2018.

This paper shows the analysis results of time offsets using P1, P2 and P3 code in GPS time transfer. The r2cggtts program has been used in GNSS Time Transfer and use the P3 ionosphere free combination of P1 and P2 code measurements. We modified the r2cggtts program in order to calculate and write all kinds of time offsets P3 as well as P1 and P2. The result of the modified r2cggtts program shows that time offsets using P1 and P2 are of wide distribution comparing to time offsets using P3. In order to Figure out the error factors for wide distributions of P1 and P2, we analyze and present the relation between the elevation angle and time offsets in this paper.

In this paper, we described the simulation results of the phase offset performance of a clock in holdover mode which was normally operated in GPS Disciplined Oscillator (GPSDO). In the TIE model, we included the time error term caused by environmental temperature variation because one of the most important parameters of clock phase error is the frequency offset and drift caused by the variation of temperature. For the simulation, we employed Maximum Time Interval Error (MTIE) for the performance evaluation when the frequency offset and drift are estimated by using an Unbiased Finite Impulse Response (UFIR) filter with ladder algorithm. We assumed that the noise in the GPS measurement is white Gaussian with zero mean and 1 ns standard deviation, and temperature linearly varies with a slope of per hour. From the simulation results, the followings were observed. First, with the estimation error of temperature of less than 3 % and the temperature compensation period of less than 900 seconds, the requirement of CDMA2000 phase synchronization under 10 us could be achieved for more than 40,000 seconds holdover time if we employ an OCXO (Oven Controlled Crystal Oscillator) clock. Second, in order to achieve the requirement of LTE-TDD under 1.5 us for more than 10,000 seconds holdover time, below 3 % estimation error and 500 seconds should be retained if a Rubidium clock is adopted.

Power grid techniques are distributed over general power systems ranging from power stations to power transmission, power distribution, and users. To monitor and control the elements and performance of a power system in real time in the extensive area of power generation, power transmission, wide-area monitoring (WAM) and control techniques are required (Sattinger et al. 2007). Also, to efficiently operate a power grid, integrated techniques of information and communication technology are required for the application of communication network and relevant equipment, computing, and system control software. WAM should make a precise power grid measurement of more than once per cycle by time synchronization using GPS. By collecting the measurement values of a power grid from substations located at faraway regions through remote communication, the current status of the entire power grid system can be examined. However, for GPS that is used in general national industries, unexpected dangerous situations have occurred due to its deterioration and jamming. Currently, the power grid is based on a synchronization system using GPS. Thus, interruption of the time synchronization system of the power system due to the failure or abnormal condition of GPS would have enormous effects on each field such as economy, security, and the lives of the public due to the destruction of the synchronization system of the national power grid. Developed countries have an emergency substitute system in preparation for this abnormal situation of GPS. Therefore, in Korea, a system that is used to prepare for the interruption of GPS reception should also be established on a long-term basis; but prior to this, it is required that an evaluation technique for the time synchronization performance of a GPS receiver using an atomic clock within the power grid. In this study, a monitoring system of time synchronization based on GPS at a power grid was implemented, and the results were presented.

In this paper, we described the Cramer-Rao Lower Bound (CLRB) performances of Time Difference of Arrival (TDOA) and Frequency Difference of Arrival (FDOA) methods when there are multiple emitters. The TDOA and FDOA values between two receivers can be simultaneously estimated by using the so-called Complex Ambiguity Function (CAF). In the case of multiple emitters, there exist Inter Symbol Interferences (ISIs) in the measurement data. Therefore, it is required to reduce the effect of ISI and provide a performance evaluation method of TDOA and FDOA estimations. In order to eliminate the ISIs, using of a filter bank before calculating CAF is proposed when the carrier frequencies of the emitters are different to one another. Angle of Arrival (AOA) or Received Signal Strength (RSS) methods before calculating CAF were proposed to reduce the ISIs when the carrier frequencies are the same. In order to evaluate the CRLB of TDOA and FDOA estimations, we employed the conditional probability distribution method and described the numerical comparison results.

Construction post-evaluation (CPE) boosts the efficiency of public construction projects by assessing the performance results of public construction projects and using the results to pursue similar projects. This evaluation comprehensively analyzes and assesses the planning of construction work, the estimated and actual construction costs, the construction period, the demand for construction projects, and the effects of construction projects after the construction work to ensure efficiency. The data was used to prevent lax project execution and enhance the quality and efficiency of similar construction projects. On the other hand, CPE results information must be managed systematically to refer to and use CPE data in similar construction projects. Therefore, in this study, the CPE system was developed as a measure of the systematic and comprehensive management and use of the CPE results information of individual ordering agencies. Therefore, the groundwork was laid for the assurance of quality enhancement and efficient project execution in public construction projects. This system is expected to serve as a useful tool for comprehensively analyzing and assessing construction works.

BIPM(International Bureau of Weights and Measures) uses GPS Time Transfer technique for UTC(Universal Time Coordinated). Recently, since GLONASS constellation started the service, studies on GLONASS time transfer and combination of GPS and GLONASS time transfer have been conducted. This paper introduces GNSS time, UTC and leap seconds and proposes the time offset results for applicability of leap seconds in GLONASS time transfer.

65 V1)$ # W* $3 3 $3*V $V 0 X $%+"'% 2#Y V W5 66Q1#$ $ M $ Z$ P 0 X $%+"![' 2#Y V W5 요 약 3K $9\*]^_`abcdef^_`ghi K $jklmnoop_q 3K $i K $=rmst=re\*]GFuHvFwxyz{j|}=r_q _~3K $GFuH€(U\-j‚ %MFwxmvƒ„u u†‡q ?:;‚ˆ}ef,,%L‰Šn‚‹ŠŒImIy_Ž3K $‘Fu’q “”{ uC{•e3K $=8uŒ–—7˜ cp‚™šdj›Ž†I=yœ† žŸ‚™š3K $‘Fm iƒu¢£’q b¤97˜cp3K $=8m¥/\‘F^_`¦œj›m_Ž§†I=¥/\‘F^_`m¨©€ma«^_`}¬&%%$ (­c®a ,M-_¯e”šd‡°ˆ_3K $‘F^_`e_Ž§m\*]‘F±uGF² K $m€‚ˆmvFwxy³ ´†‡q 핵심용어 ef  € 3ef µšFwx E¶x·j¸Abstract ¥1 1 $ V M2 $ $ W K $ 3K $ 3 M 2 W\*] $3 1 K $3 V1 $$ V# P 3K $ M2 $ $ VV# VP T1 V1 1 V V1$ P W K $ P M ¥1 ¹# M $ WU\o Y # VV# VP 1 $ %M V $Y W 3 3K $M # M $ $3 1 V V $ )$ 1 #3P 3K $M # M $ # $ 1 1 $ K $"Q(,,%L- $ $ T V $3#V 3 N $ O P » Y 1 3 3K $ W $V $ U M L $ M $ /WW V W $ $ 3 T 1 $ 1 O P » M 3 1 WW V $ W 1 3K $Y T $ 1 W $V (U M L $ M $ /WW V - $3 (U #$ 1T $Y V1-YPM # $ ¥/\ » W 3 1 1 ¥/\3 M # 3 1 T $ T 1 1 PV 3 ¥1 M2 3 WW $V $ 1 3 Y T $ 1 3K $ W $V $ $3 T Y # &%%$ 2 3 P T1 V1 ¹# $ $ $ W,M ¥1 # 1 T 1 K $V $M 1 ¹# M $ W %M 2 $ VV# VPW M M U\YPV V $ 1 \*] 1 # o V Key words K $ U\ 3K $ 2 $ VV# VP ¥/\6C7¼§ :< VY ½R R %' - [ "+&'%6:< XR ½R R %' - [ "+&' 6:< PR R ½R R %' - [ "++[,66:< T¾1T $ ½V$# V R %' - +",,&66:< X ½V$# V R %' - &"[+ Q 2 $3 $ # 1 :< 1P $ ½R R %' - [ "+&'!

In this study, to improve an existing ground-wave based time broadcasting system, a study that predicts the field distribution and field strength of the transmitted signal of a new ground-wave based time broadcasting system was performed. The prediction area was assumed to be the Korean peninsula; and to reflect the mountainous terrain of the Korean peninsula in the prediction of the variations of field distribution and field strength, a new prediction method based on the Monteath model was proposed and utilized. As field distribution changes depending on the position of a transmitter station, potential sites for the transmitter station were selected considering the geographical characteristics. In this regard, the ground conductivity information of North Korea cannot be obtained, and thus, the ground conductivity of the North Korean region was reflected considering the geological characteristics of South Korea and North Korea. Based on this, the variations of field distribution and field strength were predicted by setting the Korean peninsula as the prediction area, and the prediction results depending on the position of the transmitter station were discussed.

In this paper, we described the investigated theoretical time synchronization performances and experiment results obtained by commercially provided PTP (Precise Time Protocol) modules when the time of a slave clock is synchronized to the master clock. In the case of the theoretical performance analysis, we investigated 3 types of clock levels such as Crystal Oscillator (XO), TCXO (Temperature Compensated XO) and OCXO (Oven Controlled XO). From the analysis, it was observed that the synchronization performance is greatly influenced by the synchronization period and the required performance under 1 us can be achieved by using XO level clocks when the synchronization period is less than 2 seconds and the uncertainty of the propagation delay is under 100 ns. For the experiments using commercial PTP modules, the synchronization performance was investigated for direct, through 1 hub and through 2 hubs connections between the master clock and the slave clock. From the experiment results, we observed that time synchronization under 90 ns with 1,000 seconds observation interval can be achieved in the case of direct connection.

The Ministry of Land, Infrastructure and Transport was developed the Construction CALS system for improvement of the construction economy. Construction CALS system is consist by Construction Portal System, Construction Management System, Construction Authorization and Permission System, Compensation Management System, Facility Maintenance Management System and has utilized at construction site of more than 900. Ministry of Land, Infrastructure and Transport and related researcher was proposed method of various function improvements for usability of the system. However, the proposed method was expanded the problems like increase of system management cost and development cost with decrease of data process rate. The problem was increases because has added of only service function without modify of software structure to the system on each different platform base. One of the methods for solving problems is to apply the e-Government framework and then integrated the different platform. The purpose of this paper is analyse of the applicability and efficiency of e-Government framework to the construction CALS system. For that was analyzed the e-Government standard framework and the developments case. And then was verified about the adaption possibility and efficiency by use the Function Point tool.

Entry speed of the vehicle and lateral acceleration acting on the vehicle, roll-angle associated with the overthrow, and then the structure of the road, the friction of road surface are important factors in turning on the curved road. In this study, we analyzed the state change of the vehicle causing entry speed of the vehicle and superelevation of the road, the friction coefficient by using a PC-crash Program for traffic accident reconstruction. As a result, when vehicle is turning the curved road, we could ascertain that the structure of the road and state of the road surface are a major factor about the set up of limited speed. Key Words : Entry Speed, Lateral Acceleration, Roll-Angle, Friction Coefficient, Superelevation * 정회원, 가천대학교 기계· 자동차공학과 ** 정회원, 가천대학교 기계· 자동차공학과접수일자 2012년 8월 20일, 수정완료 2013년 2월 2일게재확정일자 2013년 4월 12일Received: 20 August 2012 / Revised: 2 February 2013 /Accepted: 12 April 2013 ** Corresponding Author: jkyoon@gachon.ac.krDept. of Mechanical and Automotive Engineering, Gachon University, Korea

This article presents the design of long range navigation (LORAN)-disciplined oscillator (LDO), employing the timing information of the LORAN system, which was developed as a backup system that corrects the vulnerability of the global positioning system (GPS)-based timing information utilization. The LDO designed on the basis of hardware generates a timing source synchronized with reference to the timing information of the LORAN-C receiver. As for the LDO-based timing information measurement, the Kalman filter was applied to estimate the measurement of which variance was minimized so that the stability performance could be improved. The oven-controlled crystal oscillator (OCXO) was employed as the local oscillator of the LDO. The controller was operated by digital proportional-integral-derivative (PID) controlling method. The LDO performance evaluation environment that takes into account the additional secondary factor (ASF) of the LORAN signals allows for the relative ASF observation and data collection using the coordinated universal time (UTC). The collected observation data are used to analyze the effect of ASF on propagation delay. The LDO stability performance was presented by the results of the LDO frequency measurements from which the ASF was excluded.

In the eLoran navigation system, the dominant deterioration factors of navigation accuracy are the TOA measurement errors on user receiver and the GDOP between the receiver and the transmitters. But if the ASF data measured at dLoran reference station are provided for users through the Loran data channel, it will be possible to correct the TOA measurement errors. The position accuracy can be determined by the DOP depending on the geometry of receiver-transmitters, and their optimal placement improves the navigation accuracy. In this study we determined the geometric placement in case of up to six stations, and evaluated the performance of position accuracy for the receiver-transmitter geometry set of eLoran stations. The proposed geometry of eLoran stations can be referred for the construction of eLoran infrastructure meeting the capability of HEA for maritime, and time/frequency users in Korea.

The precision of two-way satellite time and frequency transfer (TWSTFT) is currently limited due to unstable measurement of the signal arrival time. To improve the TWSTFT precision without interrupting the main system, we introduce the software-defined receiver (SDR) to measure the arrival time of the code signal. The SDRs have been successfully installed among TL, NICT and KRISS, and time-difference results for more than 20 days were obtained and compared. From the results, the SDR has better precision and less diurnal, even when an earth station suffered from a bad condition.

The precision of two-way satellite time and frequency transfer (TWSTFT) is currently limited due to instabilities of signal arrival time. We use a software-defined receiver to measure the arrival time of code signal transmitted by SATRE modem. The SDR systems have been successfully installed and performed at TL, NICT and KRISS. The SDR results show excellent suppression on the diurnals. For data of the KRISS-TL link, the TDEV of the SATRE modem shows a peak of 135 ps at 8 hours; where the TDEV of SDR is only 38 ps.

이 논문에서는 발신자가 송출한 신호를 이용하여 TDOA(Time Difference of Arrival) 방식으로 발신자의 3 차원 위치를 추정할 때, BLUE(Best Linear Unbiased Estimator) 추정기를 닫힌 해 형태로 구하였다 . 4 개의 기준국 또는 센서를 사용하여 3차원의 발신자 위치를 추정할 때, BLUE 추정기를 구하기 위해서 발신자의 위치에 대한 기준 위치를 설정한 후 이를 1 차 Taylor 급수로부터 유도된 근사화된 TDOA 쌍곡선 방정식을 사용하였다. 이 논문에서 근사화를 통해 구해진 유도식은 각 기준국 또는 센서에서의 TOA(Time of Arrival) 측정 잡음이 서로 상관관계가 없고 독립적이라는 가정하에서, 백색 가우시안 잡음에 대해서뿐만 아니라 평균이 제로인 모든 잡음에 대해서 적용할 수 있다.Key Words : TDOA, location estimator, 3 dimension, BLUE, CEP, 도착시간차, 위치추정기, 3차원, 최적선형비편향추정기, 원형공산오차ABSTRACT

In order to establish eLoran (enhanced Long Range Navigation) system, it needs the advancement of receiver, transmitter, data channel addition for Loran information, differential Loran sites for compensating Loran-c signal and ASFs (Additional Secondary Factors) database, etc. In addition, the precise synchronization of transmitting station to the UTC (Coordinated Universal Time) is essential if Loran delivers the high absolute accuracy of navigation demanded for maritime harbor entrance. For better timing synchronization to the UTC among transmitting stations, it is necessary to measure and monitor the transmission delay of the station, and the correction information of the transmitting station should be provided to the user's receivers. In this paper we presented the measurement method of absolute delay of Pohang Loran transmitting station and developed a time delay measurement system and a phase monitoring system for Loran station. We achieved -2.23 us as a result of the absolute phase delay of Pohang station and the drift of Loran pulse of the station was measured about 0.3 us for a month period. Therefore it is necessary to measure the delay offset of transmitting station and to compensate the drift of the Loran signal for the high accuracy application of PNT (Positioning, Navigation and Timing).

The a-SiGe:H TFT photosensor for embedded touch screen panel (TSP) was characterized compared with a-Si:H TFT. The photo sensitivity of a-SiGe:H sensor at 850 nm IR light was ∼15 times higher than that of a-Si:H, indicating that a-SiGe:H is a strong candidate material to an IR sensor. In order to increase the signal to noise ratio, the incoming of visible layer was blocked by visible cutting layer. A 40-inch panel in which a-SiGe:H IR sensor was embedded was successfully demonstrated, showing the excellent multi-touch property without ambient light interferences. This technology can be applied to broad use in the multi-functional TSPs without ambient light limitation.

In this paper, we derived a closed-form equation of a Best Linear Unbiased Estimator (BLUE) and its Crammer-Rao Lower Bound (CRLB) for the estimation of the position of the emitter based on the Time Difference of Arrival (TDOA) teclmique. The BLUE and CRLB were derived for the case of estimating 2 dimensional position of the emitter with 3 base stations or sensors, and for this purpose, we nsed an approximated equation of the TDOA hyperbola equation obtained from the first order Taylor-series after setting the reference points of the position. The derived equation can be used for any kind of noises which are uncorrelated in each other in the TOA measurement noises and for a white Gaussian noise also.

*,**,***,† Korea Research Institute of Standards and Science, Daejeon 305-340, Republic of Korea****,***** Chungnam National University, Daejeon 305-764, Republic of Korea요 약 :Loran(LOang RAnge Navigation) 신호를 이용한 측위 시에 정확도에 가장 큰 영향을 미치는 오차요소는 TOA(Time of Arrival) 측정에서의 ASF(Additional Secondary Factor)이다. 따라서 공항접근이나 항만 접안 등의 측위 정확도를 만족시키려면 먼저 정확한 ASF측정이 선행되어야 하는데, 본 연구에서는 해상에서 ASF를 측정하는 기법을 연구하였다. 그 측정방법으로 포항 Loran-C 주국(9930M)에서 송신하는 로란 신호와 로란 수신기의 기준신호를 세슘원자시계를 기준으로 측정함으로써 해상에서의 ASF를 측정하였고 영일만 해상의 12 곳의 측정지점을 3 km 간격으로 설정하여 측정하였다. 해상측정에서 정확도를 높이기 위해서 전기장 안테나와 자기장 안테나를 동시에 사용하였으며 정확한 위치측정을 위해서 DGPS(Differential GPS)수신기를 이용하였다. 이런 방법을 이용하여 해상에서 ASF를 측정함으로써 ASF 예측값과 비교한 결과를 얻었다.핵심용어 : 로란, ASF, 전파지연, 정확도, 해상측정Abstract : A significant factor limiting the ranging accuracy of Loran (Long Range Navigation) signal is the additional secondary factor (ASF) in the time of arrival (TOA) measurements. Precise ASF values are essential if Loran deliver the high absolute accuracies demanded for aircraft approach, maritime harbour entrance. We measured the absolute propagation delay between Pohang Loran signal and Loran receiver output signal by comparing with Cesium atomic clock. In this study we measured ASFs between Pohang 9930M station and the 12 measurement points in the Yeongil Bay by using the measurement technique of absolute time delay. The measurement points were spaced at interval of 3 km by 3 km. An E-field antenna and an H-field antenna were used to improve the accuracy of ASF measurements and a DGPS (Differential GPS) receiver was used for accurate positions. We have gotten the result that the measured ASFs were compared with the predicted ASFs through this measurement technique.Key words :Loran, ASF, propagation delay, accuracy, maritime measurement * 대표저자: 연회원, cblee@kriss.re.kr 042) 868-5140 ** 연회원, jklee@kriss.re.kr 042)868-5148 *** 연회원, racoon_z@naver.com 042)868-5232 **** 연회원, zcgizer@gmail.com 042)825-3991***** 연회원, eesjl@cnu.ac.kr 042)821-6582 †교신저자: 연회원, shyang@kriss.re.kr 042) 868-5147

In this paper, we describe a performance improvement method of the long-range navigation (LORAN) system in the field of the accurate timing applications by compensating diurnal variations. The diurnal variations in the received LORAN-C timing data can be effectively reduced by using the correlation between the LORAN-C and the temperature with/without humidity data. For achieving the timing accuracy improvement, we estimated the correlation values, and by using the estimated values, we compensated the diurnal variations. It is observed that more than 30% performance improvement in the aspect of RMS values can be achieved when the smoothing intervals are more than 30 min.

Limited information is available on the degradation of volatile hydrocarbons determined via the use of plate-inserted photocatalytic reactors. This has led to the evaluation of surface areas of cylindrical continuous-flow photocatalytic reactors for the degradation of three selected aromatic hydrocarbons. Three types of reactors were prepared: a double cylinder-type, a single cylindrical-type without plates and a single cylindrical-type with inserted glass tubes. According to diffuse reflectance, FTIR and X-ray diffraction (XRD) spec troscopy, the surface characteristics of a coated photocatalyst were very similar to those of raw TiO 2 , thereby suggesting that the coated photocatalyst exhibited the same photocatalytic activity as the raw TiO2. The photocatalytic degradation efficiencies were significantly or slightly higher for the single cylinder-type reactor than for the double cylinder-type reactor which had a greater catalytic surface area. However, for all target compounds, the degradation efficiencies increased gradually when the number of plates was increased. Accord ingly, it was suggested that the surface area being enhanced for the plate-inserted reactor would elevate the photocatalytic degradation efficiency effectively. In addition, this study confirmed that both initial concentrations of target compounds and flow rates were impor tant parameters for the photocatalytic removal mechanism of these plate-inserted photocatalytic reactors.

The LORAN system had been used widely and it was an essential navigation aid for ships in the ocean until the GPS is adopted actively. In particular, it was essential functionality for the ships to sail the oceans. According to the advancement of industry, however, the current accuracy of traditional Loran is insufficient for the utilization of harbour approach, land navigation, and the field of survey and timing. Therefore it is necessary that the study on the improvement of the positioning accuracy of Loran. The one of the improving methods is to measure and compensate the propagation time delay between the transmitter and user`s receiver, which is called as additional secondary factor (ASF). In this study, we measured the ASF between the Pohang master transmitting station (9930M) and four points where locate within 33 km apart from the transmitting station, using the measuring technique of the absolute time delay without a time of coincidence (TOC) table. As the result of measurement, the ranging error caused by the propagation delay was about 210 m at 33 km, however it can be reduced up to 40 m with ASF compensation.

The users who use a combined GPS/Galileo receiver will benefit from an improved availability of the combined system and a reduced dependence on one particular positioning system. However, these users must solve the problem of an offset between the time scales of GPS and Galileo (GGTO). GGTO must be analyzed for not only a navigation system but also a timing system requesting precise time service. This paper analyzes the interoperability problem in a combined GPS/Galileo timing receiver and estimates the timing performance under various assumptions. The GPS real measurements were collected by using the commercial timing receiver from Ashtech Ltd. and the Galileo measurements were generated by a simulation software. A suitable test scenario set-up and the performance in a point of timing stability was evaluated.

The improved structural and electrical properties of tin-oxide films produced by using ultralow-pressure sputtering (ULPS) method are reported. The Hall mobility of the film (~ 13 cm2/V s) deposited using ULPS was about 1.5 times higher than that of the film (~ 8 cm2/V s) sputtered using a pressure of 4.0 × 10− 1 Pa. As the sputtering pressure was decreased, the film was transformed from an amorphous structure to a nano-crystalline one and gained a stoichiometric SnO2 composition. These changes in the film structure sufficiently decreased the carrier concentration to facilitate application to thin film transistors.

We report on Korea's first optically pumped primary frequency standard (KRISS-1) developed at the Korea Research Institute of Standards and Science. Although a relatively small microwave cavity (the cavity drift region is about 36?cm in length) has been employed in this experiment, we achieved our desired frequency accuracy by applying the regularized inverse on the Ramsey spectrum analysis and compensating the effect of the evanescent field inside the cavity. KRISS-1 typically performs at a short term stability of with a combined uncertainty of 1.0 ? 10?14.

UTC (Coordinated Universal Time) has been made by the comparison results and the statistical analysis of primary clocks maintained by national standard institutes. Some kinds of technique have been used for international time transfer; since 1980s the study on methods and development of time transfer has conducted with activation of GPS application. And the more accurate and easier method made it use the official time transfer method for the generation of UTC. But recently TWSTFT (Two-Way Satellite Time and Frequency Transfers) as well as GPS time transfer are increasing in number because the TWSTFT is able to improve the accuracy and precision of time comparison owing to the elimination of the ionospheric and tropospheric delay errors thanks to the reciprocal propagation path. In this paper, we introduce the TWSTFT results by a multi-channel modem comparing with GPS P3-code.

The performance of carrier-phase based GPS precision time transfer was investigated by conducting a 7-month campaign of time transfer among four national timing laboratories. The Common-View and the All-in-View techniques, which are two typical techniques for the GPS carrier-phase time transfer, are examined in terms of time transfer and frequency transfer together with other independent time transfer systems such as TWSTFT. Comparison of clock estimates with BIPM Circular-T was performed and the modified Allan deviation of clock estimates was calculated to assess the relative frequency instability as a measure of frequency transfer performance. Also an issue of baseline limitation for the carrier-phase Common-View methods has been investigated by conducting a 1-month GPS time transfer to a set of IGS stations with different baselines. Finally, the potential of the GPS carrier-phase time transfer as a real-time synchronization method was assessed by carrying out the GPS time transfer with the IGS Ultra-rapid orbits.

The objectives of this study were to investigate the clinicopathological features of branch intraductal papillary mucinous neoplasm (IPMN) and to determine safe criteria for its observation. Most clinicians agree that surgical resection is required to treat main duct-type IPMN because of its high malignancy rate. However, no definite treatment guideline (with respect to surgery or observation) has been issued on the management of branch duct type IPMN.We retrospectively reviewed the clinicopathological data of 138 patients who underwent operations for IPMN between 1993 and 2006 at five institutes in Korea.Of 138 patients (mean age, 60.6 years; 87 men, 51 women), 76 underwent pancreatoduodenectomy, 39 distal pancreatectomy, 4 total pancreatectomy, and 20 limited pancreatic resection. There were 112 benign cases: 47 adenoma, 63 borderline cases, and 26 malignant cases, with 9 of these being noninvasive and 17 invasive. By univariate analysis, tumor size and the presence of a mural nodule were identified as meaningful predictors of malignancy. By receiver operating characteristic curve analysis, a tumor size of2 cm was found to be the most valuable predictor of malignancy. When cases were classified according to tumor size and the presence of a mural nodule, the malignancy rate for a tumor/=2 cm without a mural nodule was 9.2%, for a tumor of/=2 cm plus a mural nodule was 25%, and for other conditions such as tumor2 cm,25%.Many branch duct IPMNs are malignant. Surgical treatment is recommended, except in cases that are strongly suspected to be benign or cases that present a high operative risk. Observation is only recommended in patients with a tumor size of/=2 cm without a mural nodule.

By use of GPS carrier phase (CP) and two-way satellite time and frequency transfer (TWSTFT) measurements, a set of time comparison experiments has been conducted between the Korea Research Institute of Standards and Science and other time laboratories in East Asia. The TWSTFT results using a multichannel modem were compared with those of the GPS CP measurements using a geodetic receiver. In this paper, the authors present the time comparison results obtained with those two time-transfer methods, as well as those obtained from the GPS P3 data analysis. From the results, it was observed that the time comparison performances obtained from the GPS CP were comparable to that of the TWSTFT, and it appeared that the associated Allan deviations were slightly different depending on the type of atomic clock (hydrogen maser and cesium) used in the comparison

Summary There is no agreement regarding the treatment of early allograft rejection (EAR) in adult living donor liver transplantation (LDLT). A protocol biopsy was performed in 62 adult LDLT recipients. Twenty-one patients (33.9%) had histological evidence of EAR. Of these, 14 patients had biochemical abnormalities and seven patients had no associated biochemical abnormalities. None of the seven patients with subclinical EAR (11.3% of the entire study population) were treated, and no subsequent rejection was observed. Gender mismatch (female-to-male) was the single independent risk factor for histological EAR [odds ratio (OR) = 13.458; 95% confidence interval (CI), 1.836–98.649] and the cumulative probability for a subsequent rejection was higher in patients with EAR (OR = 11.085; 95% CI, 1.221–100.654). However, the actuarial 1 year patient and graft survival rate in patients with EAR (81.0% and 85.5%) were similar to those without EAR (92.7% and 97.25%; P = 0.127 and 0.302, respectively). The presence of an initial biochemical abnormality was an independent risk factor for both a decreased patient survival (OR = 5.827; 95% CI, 1.095–31.017; P = 0.039) and graft loss (OR = 20.646; 95% CI, 2.044–208.524; P = 0.010). Subsequent rejection developed more frequently in patients with EAR. However, the survival is not determined by the presence of EAR but by the presence of a biochemical abnormality.

This paper analyzes 14,578 cases of construction industry accidents based on big data for the improvement of the construction work accident information service contents of the Construction Project Management System ("CPMS"). The data were gathered from South Korea's major portal site that provides the accident causes, workers' behavior, injury areas, and injury factors. The data were surveyed in the following order. Factors (words) were extracted and classified into various categories, factors with predicates and adverbs were re-extracted, the target data were verified, factors were standardized and classified, and the rate and correlational rate by factor were analyzed. The analysis revealed that crash accidents involving high-place work accounted for 47% of all the accidents, arm and leg injuries, 29% and 26%, respectively, and bone fractures, 47%. For the injury causes by injury factor, crashes from ladders and roofs occurred most frequently, and for the injury areas by injury factor, leg injuries associated with materials, reinforcing bars, and excavators occurred most frequently.