• 한국멀티미디어학회논문지
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• 제11권12호
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• pp.1697-1705
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• 2008

Several studies made for wireless mesh networks aim to optimize the capacity for wireless networks. Aside from protocol improvements, researches were also done on the physical layer particularly on modulation techniques and antenna efficiency schemes. This paper is concerned with the capacity improvements derived from using spatial diversity with smart adaptive array antennas. The use of spatial diversity, which has been widely proposed for use in cellular networks in order to lessen frequency re-use, can be used in mesh networks both to minimize co-channel interference (CCI) and enable multiple transmissions. This paper aims to study the capacity region and bounds in using smart antennas for single-channel multi-radio systems in relation to the number of spatial diversity or sectors as defined by the beam angle $\beta$.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집 특별세미나,특별/일반세션
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• pp.615-619
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• 2009

There are many increasing demands for efficient high power density of auxiliary power unit(APU) for high speed traction application. Many techniques have been proposed to measure the voltage flicker on the traditional pulse width modulation(PWM) inverter. This paper proposes a novel functionality of the static inverter on the APU to mitigate the voltage flicker and regulate the output voltage. A new control algorithm for the inverter based on the Hilbert transform(HT) is presented. The HT is employed as an effective technique for tracking the voltage flicker levels in APU systems. Simulation results are provided to verify the tracking capabilities of the HT and to evaluate the performance of the proposed DG interface for multi-function operation.

• 한국산업융합학회 논문집
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• 제25권1호
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• pp.47-53
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• 2022

This paper proposes a method for selecting the capacitance of DC-link capacitors of inverters. In general, the DC-link capacitance of the inverter system must be considered for DC-link voltage, ripple current, switching frequency, ripple voltage, and pulse-width modulation techniques. Therefore, the appropriate capacitance can be determined by finding the rms and peak values of the ripple current of the capacitor. In this paper, the process of extracting the ripple current of DC-link capacitor is described in detail. In addition, the simple method for finding DC-link capacitor capacitance using the result value is presented through the simulations.

• 전력전자학회논문지
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• 제27권2호
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• pp.118-125
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• 2022

With the aim to maximize the use of a given voltage source in the field of railway and electric vehicles, this study applies a technique for controlling the overmodulation region between the linear and the six-step regions. High linearity overmodulation techniques that do not use look-up table (LUT) to digital signal processor (DSP) using carrier based pulse width modulation (PWM) are proposed. Such technique requires the phase of the voltage vector at the point where the circular trajectory of the voltage command vector and hexagonal cross each other. Therefore, a method is proposed to obtain a phase of a voltage vector that is derived through an equation and applied to a carrier-based PWM. Validity of the proposed implementation method is confirmed through simulation and experiment.

• 전자통신동향분석
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• 제37권3호
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• pp.33-40
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• 2022

Communication technologies are evolving to meet the ever-increasing demand for fast transmission speeds and large capacity. However, the introduction of new mobile networks, such as 5G, should be accompanied by changes in corresponding frequency and modulation techniques to enable the commercialization of its services. Hence, investigating the human health effects of electromagnetic exposures used in these new communication systems is crucial. Since in vitro electromagnetic experiments can provide essential information on important mechanisms of exposure effects, this article presents in vitro exposure systems necessary for reliable experiments. Moreover, the fundamental requirements for system implementation and the features of various systems are discussed.

• Smart Structures and Systems
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• 제32권2호
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• pp.111-121
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• 2023

This study proposes an automated assembly performance evaluation method for prefabricated steel structures (PSSs) using machine learning methods. Assembly component images were segmented using a modified version of the receptive field pyramid. By factorizing channel modulation and the receptive field exploration layers of the convolution pyramid, highly accurate segmentation results were obtained. After completing segmentation, the positions of the bolt holes were calculated using various image processing techniques, such as fuzzy-based edge detection, Hough's line detection, and image perspective transformation. By calculating the distance ratio between bolt holes, the assembly performance of the PSS was estimated using the k-nearest neighbors (kNN) algorithm. The effectiveness of the proposed framework was validated using a 3D PSS printing model and a field test. The results indicated that this approach could recognize assembly components with an intersection over union (IoU) of 95% and evaluate assembly performance with an error of less than 5%.

• Current Optics and Photonics
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• 제8권2호
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• pp.156-161
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• 2024

Recently, a new kind of optical multiplexing called optical-receiver-mode (ORM)-division multiplexing (ORMDM) has been proposed, in which an optical channel is a linear sum of ORM subchannels modulated independently. Using coherent-optical (CO) techniques, it has been reported that COORMDM communication systems can have very high spectral efficiencies (SEs). To estimate the SEs of CO-ORMDM communication systems, we introduce a new method of crosstalk analysis. Using this method, we can allocate quadrature-amplitude-modulation (QAM) codes and QAM step sizes unevenly over ORM subchannels to obtain higher SEs. With 50 Gaussian ORMs, we obtain a SE of up to 15.29 bit s^-1 Hz^-1.

• Clinical and Experimental Reproductive Medicine
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• 제50권4호
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• pp.213-222
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• 2023

Cryopreservation is an option for the preservation of pre- or post-pubertal female or male fertility. This technique not only is beneficial for human clinical applications, but also plays a crucial role in the breeding of livestock and endangered species. Unfortunately, frozen germ cells, including oocytes, sperm, embryos, and spermatogonial stem cells, are subject to cryoinjury. As a result, various cryoprotective agents and freezing techniques have been developed to mitigate this damage. Despite extensive research aimed at reducing apoptotic cell death during freezing, a low survival rate and impaired cell function are still observed after freeze-thawing. In recent decades, several cell death pathways other than apoptosis have been identified. However, the relationship between these pathways and cryoinjury is not yet fully understood, although necroptosis and autophagy appear to be linked to cryoinjury. Therefore, gaining a deeper understanding of the molecular mechanisms of cryoinjury could aid in the development of new strategies to enhance the effectiveness of the freezing of reproductive tissues. In this review, we focus on the pathways through which cryoinjury leads to cell death and propose novel approaches to enhance freezing efficacy based on signaling molecules.

• Journal of Ginseng Research
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• 제27권3호
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• pp.120-128
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• 2003

Alternative medicines such as herbal products are increasingly being used for preventive and therapeutic purposes. Ginseng is the best known and most popular herbal medicine used worldwide. In spite of some beneficial effects of ginseng on the nervous system, little scientific evidence shows at the cellular level. In the present study, I have examined the direct modulation of ginseng total saponins and individual ginsenosides on the activation of $Ca^{2+}$ channels and NMDA-gated channels in cultured rat dorsal root ganglion (DRG) and hippocampal neurons, respectively. In DRG neurons, application of ginseng total saponins suppressed high-voltage-activated $Ca^{2+}$ channel currents and ginsenoside Rg$_3$, among the 11 ginsenosides tested, produced the strongest inhibition on $Ca^{2+}$ channel currents. Occlusion experiments using selective $Ca^{2+}$ channel blockers revealed that ginsenoside Rg$_3$ could modulate L-, N-, and P/Q-type currents. In addition, ginsenoside Rg$_3$ also proved to be an active component of ginseng actions on NMDA receptors in cultured hippocampal neurons. Application of ginsenoside Rg$_3$ suppressed NMDA-induced [Ca$^{2+}$]$_{i}$ increase and -gated channels using fura-2-based digital imaging and patch-clamp techniques, respectively. These results suggest that the modulation of $Ca^{2+}$ channels and NMDA receptors by ginsenoside Rg$_3$ could be part of the pharmacological basis of ginseng actions in the peripheral and central nervous systems.ous systems.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.319-320
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• 2012

Large aperture optical modulator called optical shutter is a key component to realize time-of-flight (TOF) based three dimensional (3D) imaging systems [1-2]. The transmission type electro-absorption modulator (EAM) is a prime candidate for 3D imaging systems due to its advantages such as small size, high modulation performance [3], and ease of forming two dimensional (2D) array over large area [4]. In order to use the EAM for 3D imaging systems, it is crucial to remove GaAs substrate over large area so as to obtain high uniformity modulation performance at 850 nm. In this study, we propose and experimentally demonstrate techniques for backside etching of GaAs substrate over a large area having high uniformity. Various methods such as lapping and polishing, dry etching for anisotropic etching, and wet etching ([20%] C6H8O7 : H2O2 = 5:1) for high selectivity backside etching [5] are employed. A high transmittance of 80% over the large aperture area ($5{\times}5mm^2$) can be obtained with good uniformity through optimized backside etching method. These results reveal that the proposed methods for backside etching can etch the substrate over a large area with high uniformity, and the EAM fabricated by using backside etching method is an excellent candidate as optical shutter for 3D imaging systems.