• Bulletin of the Korean Chemical Society
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• v.32 no.11
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• pp.4035-4040
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• 2011

Long $TiO_2$ nanotube (NT) arrays, prepared by electrochemical anodization of Ti foils, have been utilized as dye-adsorbing electrodes in dye-sensitized solar cells (DSCs). By anodizing for 1-24 hr and subsequent annealing, highly crystallized and tightly-adhered NT arrays were tailored to 11-150 ${\mu}m$ lengths, ~90 nm innerpore diameter and ~30 nm wall thickness. I-V curves revealed that the photovoltaic conversion efficiency (${\eta}$) was proportional to the NT length up to 36 ${\mu}m$. Beyond this length, the ) was proportional to the NT length up to ${\eta}$ was still steadily increased, though at a much lower rate. For example, an ${\eta}$ of 5.05% at 36 ${\mu}m$ was increased to 6.18% at 150 ${\mu}m$. Transient photoelectron spectroscopic analyses indicated that NT array-based DSCs revealed considerably higher electron diffusion coefficient ($D_e$) and life time (${\tau}_e$) than those with $TiO_2$ nanoparticles (NP). Moreover, the electron diffusion lengths ($L_e$) of the photo-injected electrons were considerably larger than the corresponding NT lengths in all the cases, suggesting that electron transport in NT arrays is highly efficient, regardless of tube length.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.11
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• pp.1429-1436
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• 1999

데이타들에 대한 선인출 효과를 얻기 위하여 캐쉬 메모리의 캐쉬 블록은 다중 워드로 구성된다. 그러나 선인출된 데이타들이 사용되지 않을 경우 캐쉬 메모리가 낭비되고 따라서 캐쉬 실패율이 증가한다. 데이타 배열 병합 방법은 캐쉬 실패 원인의 하나인 캐쉬 충돌 실패를 감소시키기 위하여 사용되고 있다. 그러나 기존의 배열 병합 방법은 유용하지 못한 데이타들을 캐쉬 블록에 선인출하는 현상을 보인다. 본 논문에서는 이러한 현상을 개선한 스트라이드 배열 병합을 제안한다. 모의시험에서 캐쉬 블록이 다중 워드로 구성된 경우 스트라이드 배열 병합은 캐쉬 충돌 실패를 감소시킬 뿐 만 아니라 유용한 데이타 선인출을 증가 시키므로 캐쉬 성능을 향상시킴을 보여준다. 또한 이렇게 향상된 캐쉬 성능은 프로세서 증가에 따른 확장성 있는 프로그램 성능을 나타낸다.Abstract The cache memory is composed of cache lines with multiple words to achieve the effect of data prefetching. However, if the prefetched data are not used, the spaces of the cache memory are wasted and thus the cache miss rate increases. The data merging-arrays method is used for the sake of the reduction of the cache conflict misses. However, the existing merging-arrays method results in the useless data prefetching. In this paper, a stride merging-arrays method is suggested for improving this phenomenon. Simulation results show that when a cache line is composed of multiple words, the stride merging-arrays method increases the cache performance due to not only the reduction of cache conflict misses but also the useful data prefetching. This enhanced cache performance also represents the more scalable performance of parallel applications according to increasing the number of processors.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.5_6
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• pp.169-175
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• 2007

Suffix arrays, fundamental full-text index data structures, can be efficiently used where patterns are queried many times. Although many useful full-text index data structures have been proposed, their O(nlogn)-bit space consumption motivates researchers to develop more space-efficient ones. However, their space efficient versions such as the compressed suffix array and the FM-index have been developed; those can not reduce the practical working space because their constructions are based on the existing suffix array. Recently, two direct construction algorithms of compressed suffix arrays from the text without constructing the suffix array have been proposed. In this paper, we compare practical performance of these algorithms of compressed suffix arrays with that of various algorithms of suffix arrays by measuring the construction times, the peak memory usages during construction and the sizes of their final outputs.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.662-667
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• 2007

The thermal performance comparisons of the dish solar collector system are numerically investigated with mirror arrays and receiver shapes. In order to compare the performances of the dish solar collector systems, six different mirror arrays and four different receiver shapes are considered and the radiative heat flux distribution on the inside of the receiver is analyzed. A parabolic-shaped perfect mirror of which diameter is 1.5 m is considered as a reference of the mirror arrays. Five different mirror arrays of twelve identical parabolic -shaped mirror facets of which diameter are 0.4 m are proposed in this study. Their reflecting areas, which are 1.5 $m^2$, are the same. Four different receiver shapes are a dome, a conical, a cylindrical and a unicorn type. The solar irradiation reflected by mirrors is traced using the Monte-Carlo method. In addition, the radiative properties of the mirror surface can vary the thermal performance of the dish solar collector system so that the effects of the surface reflectivity and the surface absorptivity are considered. Based on the calculation, the design information of dish solar collector system for producing the electric power can be obtained. The results show that the dome type has the best performance in receiver shapes and the 2AND4INLINE has the best performance in mirror arrays except the perfect mirror.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.226-226
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• 2013

Si is a dominant solar material, which is the second most abundant element in the earth giving a benefit in the aspect in cost with low toxicity. However, the inherent limit of Si has an indirect band gap of 1.1 eV resulting in the limited optical absorption. Therefore, a critical issue has been raised to increase the utilization of the incident light into the Si absorber. The enhancement of light absorption is a crucial to improve the performances and thus relieves the cost burden of Si photovoltaics. For the optical aspect, an efficient design of a front surface, where the incident light comes in, has been intensively investigated to improve the performance of photon absorption. Lambertian light trapping can be attained when the light active surface is ideally rough to increase the optical length by about 50 compared to a planar substrate. This suggests that an efficient design may reduce thickness of the Si absorber from the conventional 100~300 ${\mu}m$ to less than 3 ${\mu}m$. Theoretically, a hole-array structure satisfies an equivalent efficiency of c-Si with only one-twelfth mass and one-sixth thickness. Various approaches have been applied to improve the incident light utilization in a Si absorber using textured structures, periodic gratings, photonic crystals, and nanorod arrays. We have designed hole and pillar structured Si absorbers. Four-different Si absorbers have been simultaneously fabricated on an identical Si wafer with hole arrays or pillar arrays at a fixed depth of 2 ${\mu}m$. We have found that the significant enhanced solar cell performances both for the hole arrayed and pillar arrayed Si absorbers compared to that of a planar Si wafer resulting from the effective improvement in the quantum efficiencies.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.9
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• pp.38-45
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• 2003

This research is concerned with the dynamic modeling of the multi-purpose satellite with deployable solar arrays equipped with strain energy hinges(SEH). To this end, we proposed the use of the equivalent torsional spring for the SEH and derived the equations of motion assuming that the satellite and solar arrays are being rigid. We also considered the effect of the support string for the ground experiment model, which has been observed as a critical factor affecting the deployment in the ground experiments. From the numerical simulation results, it is found that solar arrays are deployed in a similar pattern but the hub motions are different because of the support strings. It was concluded that the non-gravity deployment of the solar arrays can be approximately simulated by the ground experimental facility. The effects of the support string are also investigated by varying the length of the string. It was found that the current length of the string is adequate for the ground experiment. Ground experimental results will follow.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1493-1510
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• 2000

Theoretical models that can be used to predict the range of main lobe widths and the probability distribution of the peak sidelobe levels of two-dimensionally sparse arrays are presented here. The arrays are considered to comprise microphones that are randomly positioned on a segmented grid of a given size. First, approximate expressions for the expected squared magnitude of the aperture smoothing function and the variance of the squared magnitude of the aperture smoothing function about this mean are formulated for the random arrays considered in the present study. By using the variance function, the mean value and the lower end of the range i.e., the first I percent of the mainlobe distribution can be predicted with reasonable accuracy. To predict the probability distribution of the peak sidelobe levels, distributions of levels are modeled by a Weibull distribution at each peak in the sidelobe region of the expected squared magnitude of the aperture smoothing function. The two parameters of the Weibull distribution are estimated from the means and variances of the levels at the corresponding locations. Next, the probability distribution of the peak sidelobe levels are assumed to be determined by a procedure in which the peak sidelobe level is determined as the maximum among a finite number of independent random sidelobe levels. It is found that the model obtained from the above approach predicts the probability density function of the peak sidelobe level distribution reasonably well for the various combinations of two different numbers of microphones and grid sizes tested in the present study. The application of these models to the design of random, sparse arrays having specified performance levels is also discussed.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.3
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• pp.295-302
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• 1990

In this paper, a methodology for the automatic design of the optimal systolic arrays is proposed. Algorithm transformation is the main mathematical tool on which this methodology is based. Also, technique for partitioning algorithm into systolic arrays is presented. Algorithm partitioning is essential when the size of the computational problem is larger than the size of the array. This study results in (a) reduction of the design time of systolic arrays for given algorithms, (b) CRT display of the structures of systolic arrays, and (c) automatic designing of the optimal systolic array by the criteria such as the number of processing elements, bands, and communication paths. The procedure for these results was programmed using HP BASIC language on HP-9836 computer.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.444-444
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• 2011

Recently, patterned magnetic films and elements attract a wide interest due to their technological potentials in ultrahigh-density magnetic recording and spintronic devices. Among those patterned magnetic structures, magnetic anti-dot patterning induces a strong shape anisotropy in the film, which can control the magnetic properties such as coercivity, permeability, magnetization reversal process, and magneto-resistance. While majority of the previous works have been concentrated on anti-dot arrays with a single magnetic layer, there has been little work on multilayered anti-dot arrays. In this work, we report on study of the magnetic properties of bilayered anti-dot system consisting of upper perforated Co layer of 40 nm and lower continuous Ni layer of 5 nm thick, fabricated by photolithography and wet-etching processes. The magnetic hysteresis (M-H) loops were measured with a superconducting-quantum-interference-device (SQUID) magnetometer (Quantum Design: MPMS). For comparison, investigations on continuous Co thin film and single-layer Co anti-dot arrays were also performed. The magnetic-domain configuration has been measured by using a magnetic force microscope (PSIA: XE-100) equipped with magnetic tips (Nanosensors). An external electromagnet was employed while obtaining the MFM images. The MFM images revealed well-defined periodic domain networks which arise owing to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The inclusion of holes in a uniform magnetic film and the insertion of a uniform thin Ni layer, drastically affected the coercivity as compared with single Co anti-dot array, without severely affecting the saturation magnetization ($M_s$). The observed changes in the magnetic properties are closely related to the patterning that hinders the domain-wall motion as well as to the magneto-anisotropic bilayer structure.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.5
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• pp.208-217
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• 2013

When a beamforming can be processed separately in horizontal and vertical directions with the planar arrays used in sonar systems, there are several merits such as that practically reduce the required computations and volumes. However, the common planar arrays used in sonar systems are generally non-separable, so the beamforming with separable weighting results in the differences between the desired beam characteristics and the resultant beam characteristics. In this paper, we propose a new separable weighting method which can achieve the wanted beam characteristics by using the separable weights in horizontal and vertical directions for the non-separable planar arrays. In order to achieve the wanted beam characteristics, the proposed method minimizes the differences between the desired weights and the resultant weights based on the number of effective sensors in horizontal and vertical directions of the planar arrays.