• Progress in Superconductivity
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• 제9권1호
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• pp.40-44
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• 2007

We investigated signal-to-noise ratios (SNRs) of magnetocardiography (MCG) signals using the first-order and the second-order gradiometers of different baselines. The MCG signals were recorded using a measurement system with 61 magnetometers which measured the normal magnetic component to the chest surface. The distance between the chest surface and the bottom of the dewar was changed from 0 cm to 15 cm, and the MCGs were measured for each distance. By subtracting the other signals (distance = 1 to 15 cm) from the reference signal (distance =0 cm), we could simulate the first-order and the second-order gradiometer signals with various baselines. In addition, to evaluate the reproducibility of the simulation, we fabricated the wire wound first-order and second-order gradiometers which measured a normal magnetic component to the chest surface. The baselines of the first-order gradiometers were, respectively, 50 mm, 70 mm and 100 mm and the baseline of the second-order gradiometer was 50 mm. Using these gradiometers, we recorded the MCG signal and compared the SNR between the simulation and the measurement.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1802-1819
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• 2017

Correlation-enhanced collision attack has been proposed by Moradi et al. for several years. However, in practical operations, this method costs lots of time on trace acquisition, storage and averaging due to its bytewise collision detection. In this paper, we propose a bitwise collision attack based on second-order distance model. In this method, only 9 average traces are enough to finish a collision attack. Furthermore, two candidate models are given in this study to distinguish collisions, and the corresponding practical experiments are also performed. The experimental results indicate that the operation time of our attack is only 8% of that of correlation-enhanced collision attack, when the two success rates are both above 0.9.

• ETRI Journal
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• 제26권3호
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• pp.277-280
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• 2004

The distributions of electric field and induced second-order nonlinearity are analyzed in the periodic poling of optical fibers. A quasi-phase matching efficiency for the induced nonlinearity is calculated in terms of both the electrode separation distance between the applied voltage and generalized electrode width for the periodic poling. Our analysis of the quasi-phase matching efficiency implies that the conversion efficiency can be enhanced through adjusting the separation distance, and the electrode width can be maximized if the electrode width is optimized.

• Journal of Positioning, Navigation, and Timing
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• 제4권2호
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• pp.79-85
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• 2015

Existing Differential GPS (DGPS) pseudorange correction (PRC) generation techniques based on a virtual reference station cannot effectively assign a weighting factor if the baseline distance between a user and a reference station is not long enough. In this study, a virtual reference station DGPS PRC generation technique was developed based on an enhanced inverse distance weighting method using an exponential function that can maximize a small baseline distance difference due to the dense arrangement of DGPS reference stations in South Korea, and its positioning performance was validated. For the performance verification, the performance of the model developed in this study (EIDW) was compared with those of typical inverse distance weighting (IDW), first- and second-order multiple linear regression analyses (Planar 1 and 2), the model of Abousalem (1996) (Ab_EXP), and the model of Kim (2013) (Kim_EXP). The model developed in the present study had a horizontal accuracy of 53 cm, and the positioning based on the second-order multiple linear regression analysis that showed the highest positioning accuracy among the existing models had a horizontal accuracy of 51 cm, indicating that they have similar levels of performance. Also, when positioning was performed using five reference stations, the horizontal accuracy of the developed model improved by 8 ~ 42% compared to those of the existing models. In particular, the bias was improved by up to 27 cm.

• 대한안전경영과학회지
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• 제15권4호
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• pp.123-129
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• 2013

Among various manual materials handling tasks, pushing/pulling was known to be one of the risk factors for the low back and shoulder musculoskeletal disorders (MSDs). This study was conducted to find out an optimal solution set of the handle height and distance for 4-wheel cart with two vertical handles. Ten male college students participated in the pushing force measurement experiment. The face-centered cube design, one of the central composite designs, was applied for the experiment, and the isometric voluntary pushing force was measured in 9 treatment conditions. The second order response surface model was predicted by using the pushing strength as a response variable, and the handle height and distance as independent factors. According to the 2nd order response model, the handle height and distance showed nonlinear relationship with the isometric pushing strength. To maximize the 2nd order response model (pushing force), the handle height and distance were optimized. The optimal handle height was 'xyphoid process height - stature', and the optimal handle distance was '$1.25{\times}shoulder$ width'. When calculated using the anthropometric data of the subjects of this study, the optimal handle height was $115.4{\pm}3.4$ cm, slightly higher than the elbow height, and the handle distance was $52.9{\pm}2.3$ cm.

• Restorative Dentistry and Endodontics
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• 제41권3호
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• pp.182-188
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• 2016

Objectives: The purpose of this study was to evaluate the proximity of the mandibular molar apex to the buccal bone surface in order to provide anatomic information for apical surgery. Materials and Methods: Cone-beam computed tomography (CBCT) images of 127 mandibular first molars and 153 mandibular second molars were analyzed from 160 patients' records. The distance was measured from the buccal bone surface to the root apex and the apical 3.0 mm on the cross-sectional view of CBCT. Results: The second molar apex and apical 3 mm were located significantly deeper relative to the buccal bone surface compared with the first molar (p < 0.01). For the mandibular second molars, the distance from the buccal bone surface to the root apex was significantly shorter in patients over 70 years of age (p < 0.05). Furthermore, this distance was significantly shorter when the first molar was missing compared to nonmissing cases (p < 0.05). For the mandibular first molars, the distance to the distal root apex of one distal-rooted tooth was significantly greater than the distance to the disto-buccal root apex (p < 0.01). In mandibular second molar, the distance to the apex of C-shaped roots was significantly greater than the distance to the mesial root apex of non-C-shaped roots (p < 0.01). Conclusions: For apical surgery in mandibular molars, the distance from the buccal bone surface to the apex and apical 3 mm is significantly affected by the location, patient age, an adjacent missing anterior tooth, and root configuration.

• Journal of Electrical Engineering and Technology
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• 제8권3호
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• pp.499-506
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• 2013

The accurate estimation of a fault location is desired in distance protection schemes for transmission lines in order to selectively deactivate a faulted line. However, a typical method to estimate a fault location by calculating impedances with voltages and currents at relaying points may have errors due to various factors such as the mutual impedances of lines, fault impedances, or effects of parallel circuits. The proposed algorithm in this paper begins by extracting the fundamental phasor of the positive sequence currents from the three phase currents. The second-order difference of the phasor is then calculated based on the fundamental phasor of positive sequence currents. The traveling times of the waves generated by a fault are derived from the second-order difference of the phasor. Finally, the distance from the relaying point to the fault is estimated using the traveling times. To analyze the performance of the algorithm, a power system with EHV(Extra High Voltage) untransposed double-circuit transmission lines is modeled and simulated under various fault conditions, such as several fault types, fault locations, and fault inception angles. The results of the simulations show that the proposed algorithm has the capability to estimate the fault locations with high speed and accuracy.

• 한국정보과학회논문지:데이타베이스
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• 제28권3호
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• pp.373-383
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• 2001

거리조인은 두 공간 데이터 집합 사이의 데이터쌍을 거리 상 가까운 순으로 검색하는 공간조인이다. 본 논문에서는 [1]에서 제시한 적응식 다단계 거리 조인 기법을 최적화하기 위한 기법들을 제안한다. 첫째, 평면 스위핑 축 선택을 위해 사용되는 스위핑 인덱스 공식을 최적화한다. 둘째, 노드쌍을 관리하는데 사용한 메인큐의 성능 향상을 위하여 노드쌍의 최대 거리값을 큐의 2차 우선 순위로 적용하는 기법을 제안한다. 또한, 균등 분포 및 비균등 분포 가정하의 한계 거리값 예측 기법의 장단점을 비교한다. 실험 결과는 제안하는 기법들을 통하여 알고리즘의 성능이 CPU 비용과 I/O 비용 면에서 크게 향상되었음을 보여준다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.569-572
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• 2005

Technological feasibility of using recently-available femtosecond ultra short pulse lasers for advanced precision length metrology is investigated with emphasis on absolute distance measurements with $10{\mu}m$ ??resolution over extensive ranges. The idea of using femtosecond lasers for the measurement of absolute distances is based on the fact that a short pulse train is a mode-locked combination of discrete monochromatic light components spanning a wide spectral bandwidth. The synthetic wavelength is created from the repetition frequency, $f_r$ of the femtosecond laser and for more precise resolution, higher-order harmonics of the repetition frequency may be selected as the synthetic wavelength by using appropriate electronic filters.

• 한국정밀공학회지
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• 제15권11호
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• pp.130-136
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• 1998

This paper develops an efficient algorithm for the minimum distance calculation between two general polyhedra(convex and/or concave) in three-dimensional space. The polyhedra approximate objects using flat polygons which composed of more than three vertices. The algorithm developed in this paper basically computes minimum distance between two polygons(one polygon per object) and finds a set of two polygons which makes a global minimum distance. The advantage of the algorithm is that the global minimum distance can be computed in any cases. But the big disadvantage is that the minimum distance computing time is rapidly increased with the number of polygons which used to approximate an object. This paper develops a method to eliminate sets of two polygons which have no possibility of minimum distance occurrence, and an efficient algorithm to compute a minimum distance between two polygons in order to compensate the inherent disadvantage of the algorithm. The correctness of the algorithm is verified not only comparing analytically calculated exact minimum distance with one calculated using the developed algorithm but also watching a line which connects two points making a global minimum distance of a convex object and/or a concave object. The algorithm efficiently finds minimum distance between two convex objects made of 224 polygons respectively with a computation time of about 0.1 second.