• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.10
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• pp.47-53
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• 2012

Time-reversal (TR) precoding focuses the energy of the effective channel in time and improves receive performance of a single tap receiver. Frequency-domain equal-gain-combining (FD-EGC) TR scheme, which works in linear block precoding fashion, has better temporal focusing performance than the traditional TR. Also, the FD-EGC improves receive performance of minimum mean square error receiver with distributed antenna systems (DAS). The detailed receive performance of the FD-EGC was analyzed in our previous work. In this paper, we focused on capacity analysis of the FD-EGC in DAS. We derived a scaling law which shows how the use of multiple antenna can increase the capacity of the FD-EGC precoding compared with that of no precoding. In addition, we analyze the secrecy rate of the FD-EGC which shows how high-rate messages can be transmitted towards an intended user without being decoded by the other users from the view point of information theoretic security.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.4
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• pp.320-327
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• 1996

This paper presents that the lossy or amplification property of the Finite Difference-Time Domain(FD-TD) method based on the leap-frog scheme is theoretically verified by using a plane wave analysis. The basic algorithm of the FD-TD method is introduced in order to help understanding the analysis procedure. Since our analysis is formulated by the Von Neumann's approach, the stability inequality is also produced as an another outcome.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.80.2-80.2
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• 2011

The sudden decrease of galactic cosmic ray (GCR) intensity observed by ground neutron monitor (NM) is called a Forbush decrease (FD) event. The intensity time profile of FD event looks like the geomagnetic storm visualized by geomagnetic storm index Dst. Oh et al. [2008] and Oh and Yi [2009] classified the FD events into two kinds by criteria of the overlapping simultaneity of main phase in universal time (UT). The FD event is defined simultaneous if the main phase parts observed by the stations distributed evenly around the Earth are overlapped in UT and non-simultaneous if ones are overlapped in each station's local time (LT). They suggested the occurrence mechanisms of two kind FD events related to the interplanetary magnetic structures such as the interplanetary shock (IP shock) and magnetic cloud. According to their model, the simultaneity of FD depends on the strength and propagation direction of interactive magnetic structures overtaking the Earth. Now the STEREO mission can visualize the emergence and propagation direction of the coronal mass ejection (CME) in 3-dimension in the heliosphere. Thus, it is possible to test the suggested mechanisms causing two different types of FD events. One simultaneous FD observed on February 17, 2011 may be caused by a CME heading directly toward the Earth observed on February 15, 2011 by the STEREO mission. The simultaneity of FD event is proved to be a useful analysis tool in figuring out the geo-effectiveness of solar events such as interplanetary CMEs and IP shocks.

• Journal of Astronomy and Space Sciences
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• v.32 no.1
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• pp.33-38
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• 2015

Forbush Decreases (FD) are transient, sudden reductions of cosmic ray (CR) intensity lasting a few days, to a week. Such events are observed globally using ground neutron monitors (NMs). Most studies of FD events indicate that an FD event is observed simultaneously at NM stations located all over the Earth. However, using statistical analysis, previous researchers verified that while FD events could occur simultaneously, in some cases, FD events could occur non-simultaneously. Previous studies confirmed the statistical reality of non-simultaneous FD events and the mechanism by which they occur, using data from high-latitude and middle-latitude NM stations. In this study, we used long-term data (1971-2006) from middle-latitude NM stations (Irkutsk, Climax, and Jungfraujoch) to enhance statistical reliability. According to the results from this analysis, the variation of cosmic ray intensity during the main phase, is larger (statistically significant) for simultaneous FD events, than for non-simultaneous ones. Moreover, the distribution of main-phase-onset time shows differences that are statistically significant. While the onset times for the simultaneous FDs are distributed evenly over 24-hour intervals (day and night), those of non-simultaneous FDs are mostly distributed over 12-hour intervals, in daytime. Thus, the existence of the two kinds of FD events, according to differences in their statistical properties, were verified based on data from middle-latitude NM stations.

• Asia pacific journal of information systems
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• v.5 no.2
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• pp.101-129
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• 1995

This paper proposes a form-based distributed database design methodology ($FD^3$). The methodology consists of five design phases such as (i) form requirement analysis (ii) schema integration (iii) distribution analysis (iv) distribution design, and (v) local logical/physical design. In the $FD^3$, all the important design information for each phase is obtained by using an organizations forms, Users requirements are analyzed by using forms that contain logical and quantitative information for distribution design. $FD^3$ resolves naming conflicts by employing SQLs based on the form field data in the schema integration phase. Furthermore, $FD^3$ enhances the quality of distributed database design by incorporating communication costs into the design model. A real-life case is illustrated to demonstrate the usefulness of the $FD^3$.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.6
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• pp.45-56
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• 2006

The finite element method is a practical tool to compute the response of the irregularly layered soil deposit to the base-rock motions. The method is useful not only in estimating the interaction between the structure and the surrounding soil as a whole and the local behavior of the contacting area in detail, but also in predicting the resulting behavior of the superstructure affected by such soil-structure interactions. However, the computation of finite element analysis is marched in the time domain (TD), while the site response analysis has been carried out mostly in the frequency domain (FD) with equivalent linear analysis. This study is intended to compare the results of the TD and FD analysis with focus on the peak response accelerations and the predominant frequencies, and thus to evaluate the applicability and the validity of the finite element analysis in the site response analysis. The comparison shows that one can obtain the results very close to that of FD analysis, from the finite element analysis by including sufficiently large width of foundation in the model and further by applying partial mode superposition. The finite element analysis turned out to be well agreeing with FD analysis in their computed results of the peak acceleration and the acceleration response spectra, especially at the surface layer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.9A
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• pp.754-762
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• 2003

The coupled and propagated property of the composite side-polished fiber and infinite planar waveguide with conductor cladding (PWGCC) is presented by using the 3-D finite difference beam propagating method (FD-BPM) in according to the variety of refractive indexes between the fiber and the infinite planar waveguide. It is also introduced for the technique to be applied at and consisted of the analysis domain of 3-D FD-BPM for the coupling between the side-polished fiber and PWG. It is also compared the properties of coupling between the side-polished fiber and PWGCC with them of the general symmetric and asymmetric PWG without perfect conductor (PEC), which has been investigated by many researcher.

• Imaging Science in Dentistry
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• v.52 no.1
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• pp.53-60
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• 2022

Purpose: The aim of this study was to compare the fractal dimension (FD) measured at 2 bone sites (second cervical vertebra and mandible) on cone-beam computed tomography (CBCT). The research question was whether FD could serve as an accessory tool to refer postmenopausal women for densitometric analysis. Therefore, the reliability and accuracy of FD were evaluated. Materials and Methods: In total, 103 postmenopausal women were evaluated, of whom 52 had normal bone mineral density and 51 had osteoporosis, according to dual X-ray absorptiometry of the lumbar spine and hip. On the CBCT scans, 2 regions of interest were selected for FD analysis: 1 at the second cervical vertebra and 1 located at the mandible. The correlations between both measurements, intra- and inter-observer agreement, and the accuracy of the measurements were calculated. A P value less than 0.05 was considered to indicate statistical significance for all tests. Results: The mean FD values were significantly lower at the mandibular region of interest in osteoporotic patients than in individuals with normal bone mineral density. The areas under the curve were 0.644 (P=0.008) and 0.531 (P=0.720) for the mandibular and vertebral sites, respectively. Conclusion: FD at the vertebral site could not be used as an adjuvant tool to refer women for osteoporosis investigation. Although FD differed between women with normal BMD and osteoporosis at the mandibular site, it demonstrated low accuracy and reliability.

• Structural Engineering and Mechanics
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• v.39 no.5
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• pp.717-732
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• 2011

Nonlinear dynamic analysis and evaluation of eccentric braced steel frames (EBF) equipped with friction damper (FD) is studied in this research. Previous studies about assessment of seismic performance of steel braced frame with FD have been generally limited to installing this device in confluence of cross in concentrically braced frame such chevron and x-bracing. Investigation is carried out with three types of steel frames namely 5, 10 and 15 storeys, representing the short, medium and high structures respectively in series of nonlinear dynamic analysis and 10 slip force values subjected to three different earthquake records. The proper place of FD, rather than providing them at all level is also studied in 15 storey frame. Four dimensionless indices namely roof displacement, base shear, dissipated energy and relative performance index (RPI) are determined in about 100 nonlinear dynamic analyses. Then average values of maximum roof displacement, base shear, energy dissipated and storey drift under three records for both EBF and EBF equipped with friction damper are obtained. The result indicates that FD reduces the response compared to EBF and is more efficient than EBF for taller storey frames.

• The Journal of Internal Korean Medicine
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• v.40 no.3
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• pp.390-408
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• 2019

Objectives: Several pattern diagnosis questionnaires have been developed to objectify the process of pattern diagnosis in Korean medicine. In this context, this study aimed to develop a food retention questionnaire for functional dyspepsia (FRQ-FD) by modifying the previously developed food retention questionnaire (FRQ) and to verify its reliability and validity. Furthermore, this study aimed to identify the optimal cut-off value of the FRQ-FD for standardization and use in clinical situations. Methods: To develop the FRQ-FD, we extracted the major symptoms of food retention pattern for functional dyspepsia from Chinese/Korean medicine textbooks and requested an importance survey from experts using the Delphi method. The first draft of the FRQ-FD was composed of 25 questions comprising 8 questions from the textbooks and the Delphi method and 17 questions from the FRQ already developed in 2013. To analyze its reliability, validity, and optimal cut-off value, 60 subjects were enrolled in this study from June 25 to August 13, 2018. Thirty patients were diagnosed as both functional dyspepsia and food retention pattern, and 30 healthy participants were not. All participants were requested to fill up the FRQ-FD, Stomach Qi Deficiency Questionnaire (SQDQ), Scale for Stomach Qi Deficiency pattern (SSQD), visual analog scale (VAS) for dyspepsia, Nepean Dyspepsia Index-Korean version (NDI-K), and functional dyspepsia-related quality of life (FD-QoL). Results: No statistically significant differences were found in sex distribution, age, and body mass index between the patient group and the control group. As five questions affected the reliability negatively and three questions affected the clinical validity negatively, we decided to exclude the eight questions upon further investigation. The Cronbach's ${\alpha}$ coefficient of the revised FRQ-FD (17 items) was 0.899, and its clinical validity was verified. Construct validity was analyzed by factor analysis and produced five factors. Statistically significant positive correlations were found between the revised FRQ-FD and the other dyspepsia scales, namely, SQDQ, SSQD, VAS, NDI-K, and FD-QoL. VAS and NDI-K especially had strong positive correlations with FRQ-FD. Conclusions: The FRQ-FD developed in this study can provide fundamental reliability and validity for a pattern diagnosis questionnaire. FRQ-FD can help to diagnose food retention pattern in functional dyspepsia patients. Further studies are required to inspect several statistical factors.