Earticle

There has been increasingly large demand for next generation high speed transport system to compliment air travel and for aerospace vehicle launchers for uses such as low orbit space transports. In this study, characteristics of two pulsed power accelerator designs commonly referred as Rail Gun and Gauss Gun were tested with the custom designed experimental set up. Velocity and various side effects during the operation of the accelerator, such as “suck-back” effect and rail erosion were noted and were used to achieve minimum set of controls defined as controlled acceleration, deceleration and deflection respectively. The experimental system with four sets of acceleration motors were able to achieve acceleration with measured energy efficiency peaking at 3 percent. It was concluded that the concept of transport system utilizing electromagnetic pulsed power system can be viable with relatively simple requirements while allowing unique designs without its form factor limited to conventional strictly linear path.

최근 액셀러레이터가 새로운 스타트업 육성 기관으로 주목받고 있다. 본 연구는 스타트업이 액셀러레이팅 프로 그램을 이용하고자 액셀러레이터를 선택할 때 의사결정요인의 상대적 중요도와 우선순위를 AHP 기법을 이용해 실증 분석하였다. 그 결과 스타트업 창업자는 의사결정요인의 중요도를 자금지원 요인, 프로그램 요인, 액셀러레이터 특성 요인 순으로 인식하고 있었고, 세부 요인 간 상대적 중요도는 스타트업 창업자와 액셀러레이터 종사자 간, 사업장 소재 지 및 매출실적 유무에 따라 인식의 차이가 있는 것으로 나타났다. 이는 액셀러레이터의 자금지원 역량 강화와 스타트 업의 니즈에 부합하는 맞춤형 서비스 향상의 필요성이 있음을 시사한다. 본 연구가 스타트업이 액셀러레이터를 선택할 때 의사결정기준으로 활용되고 액셀러레이팅 프로그램에 관한 추가 연구의 기초자료로 활용될 수 있을 것이다.

Recently, accelerators are attracting attention as a new startup incubator. This study empirically analyzed the relative importance and priority of decision-making factors when a startup selects an accelerator using the AHP technique. As a result, startup founders recognized the importance of decision-making factors in the order of funding factors, program factors, and accelerator characteristic factors. there was a difference in the relative importance of detailed factors between startup founders and accelerator workers, depending on the location of the business site and the presence or absence of sales performance. This suggests that accelerators need to strengthen the financial support capabilities and improve customized services to meet the needs of startups. This study can be used as a decision-making criterion when a startup selects an accelerator, and can be used as basic data for additional research on the accelerator program.

Recently, cable conductors composed of numerous coated conductors have been developed to transport huge current for largescale applications, for example accelerators and fusion reactors. Various cable conductors such as CORC (Conductor on round core), Roebel Cable, and TSTC (Twisted stacked tape cable) have been designed and tested to apply for large-scale applications. But, these cable conductors cannot improve the engineering critical current density (Je) because they are made by simple stacking of coated conductors. In this study, multi-HTS (High temperature superconductor) layers on one substrate (MHOS) wire was fabricated to increase the engineering critical current density by using the exfoliation of superconducting layer from substrate and silver diffusion bonding method. By the repetition of these processes, the 10 m long 6-layer MHOS conductor was successfully fabricated without any intermediate layers like buffer or solder. 6-layer MHOS conductor exhibited a high critical current of 2,460A/12mm-w. and high engineering critical current density of 1,367A/mm2 at liquid nitrogen temperature.

Background: Industrial X-ray CT system is normally applied to non-destructive testing (NDT) for industrial product made from metal. Furthermore there are some special CT systems, which have an ability to inspect nuclear fuel assemblies or rocket motors, using high power and high energy (more than 6 MeV) pulsed X-ray source. In these case, pulsed X-ray are produced by the electron linear accelerator, and a huge number of photons with a wide energy spectrum are produced within a very short period. Consequently, it is difficult to measure the X-ray energy spectrum for such accelerator-based X-ray sources using simple spectrometry. Due to this difficulty, unexpected images and artifacts which lead to incorrect density information and dimensions of specimens cannot be avoided in CT images. For getting highly precise CT images, it is important to know the precise energy spectrum of emitted X-rays. Materials and Methods: In order to realize it we investigated a new approach utilizing the Bayesian estimation method combined with an attenuation curve measurement using step shaped attenuation material. This method was validated by precise measurement of energy spectrum from a 1 MeV electron accelerator. In this study, to extend the applicable X-ray energy range we tried to measure energy spectra of X-ray sources from 6 and 9 MeV linear accelerators by using the recently developed method. Results and Discussion: In this study, an attenuation curves are measured by using a step-shaped attenuation materials of aluminum and steel individually, and the each X-ray spectrum is reconstructed from the measured attenuation curve by the spectrum type Bayesian estimation method. Conclusion: The obtained result shows good agreement with simulated spectra, and the presently developed technique is adaptable for high energy X-ray source more than 6 MeV.

User authentication is a key element of security systems, requiring technologies that enhance efficiency and reliability. Although traditional fingerprint recognition is highly reliable, it requires user participation for authentication, which reduces its efficiency. To address this issue, non-intrusive and highly reliable biometric technologies, such as iris recognition, are gaining attention. In this paper, we propose a wristwatchtype biometric authentication system that utilizes electromyogram (EMG) signals, which are easy to implement in wearable systems, along with artificial intelligence (AI) hardware accelerator technology. To achieve this, a fieldprogrammable gate array (FPGA)-based hardware accelerator was utilized, with the Python on Zynq (PYNQ) platform specifically employed to maximize parallel processing capabilities and enhance the performance of the user authentication system. EMG signals were acquired through a wristwatch-type EMG sensor with two channels, and signal processing was conducted using the empirical mode decomposition (EMD) method. The artificial intelligence network employed a convolutional neural network (CNN)-long short-term memory (LSTM) architecture. This approach achieved 98.7% accuracy and a 0.5 ms response time for user authentication across four users.

2011년부터 국내 최초로 중이온가속기(RAON) 프로젝트가 런칭 되어 현재 개발 중에 있다. RAON 가속기는 초전도 가속관으로 구성된 선형가속기로 수소부터 우라늄까지의 다양한 이온을 가속할 수 있도록 디자인 되었다. RAON 가속 기 주변장치로 이온빔생성이나, 선형가속기를 통해 가속되어진 이온빔들을 연구하는 7개의 실험장치가 함께 개발되어 설치가 완료되었으며, 이와 함께 희귀 동위원소를 생산할 수 있는 ISOL (Isotope Separation On-Line) 과 IF (In-flight Fragmentation) 장치도 함께 개발되어 설치를 완료했다. 2022년도에 RAON 선형가속기 중 저에너지구간 을 성공적으로 설치하여 1단계 개발을 마무리하고 2024년부터 국내 유저들에게 빔 서비스를 운영하고 있다. 현재는 고에너지구간 구축을 위한 2단계 사업을 추진 중에 있으며 향후 고에너지구간이 완료가 되면 ISOL, 사이클로트론을 이용해 생성된 다양한 동위원소/희귀동위원소 빔을 가속하여 우주항공/신소재/방사선치료 등의 국내뿐 아니라 국제적 으로 과학기술 개발 연구에 큰 기여를 할 것으로 기대된다.

Heavy ion Linear Accelerator(LINAC), named RAON, is being constructed since 2011. Seven experimental systems for studying rare isotope science have been built. RAON linac is a superconducting linac and designed to accelerate various kinds of ions (stable ions and rare isotope ions) with a wide range of beam energy and beam current. RAON linac is composed of two sections – low energy linac and high energy linac in terms of beam energy. Low energy linac section was successfully constructed in 2022 and is now in operation for low energy required field. Rare isotopes produced from the ISOL (Isotope Separation On-Line) can be used for medical imaging. High energy linac has been being studied since 2022 for the construction. Construction of high energy section will complete entire RAON linac thus, it is expected that various experiments dealing with rare isotope science can be realized in Korea.

Binarized neural network (BNN) is one of the most efficient neural network for low-cost convolution operations. In BNN, binarized data is utilized to reduce memory size and complexity of convolution operations. A content addressable memory (CAM) based BNN accelerator can perform convolution operations efficiently by taking an advantage of fully parallel search operations in CAM. However, one of the critical issue of CAM based BNN hardware is that the operation reliability is severely degraded by the process variation during ML sensing operation. Therefore, we propose new CAM array design which can reduce hardware error probability. The proposed CAM based accelerator achieves 62% reduction in XNOR-popcount operations, and the classification accuracy drop of Fashion MNIST data set reduces from 2.33% to 1.26%.

Stereo vision is actively researched as a solution for distance measurement in autonomous driving. This technique involves triangulation-based distance calculation using left and right images acquired from two image sensors. A kernel window is employed to determine the disparity between these left and right images. To achieve optimal disparity in various environments, it is essential to support different kernel sizes. Moreover, there is a need for research to integrate high-throughput memory, such as high bandwidth memory (HBM), for processing real-time highresolution stereo vision images from sensors. In this paper, we propose a stereo vision accelerator structure utilizing HBM, which supports various kernel sizes.

Background: For an accelerator-based BNCT, we have fabricated a new detector consisting of quartz optical fibers that have excellent radiation-resistant characteristics. Materials and Methods: The developed detectors were irradiated at Kyoto University Research Reactor. Results and Discussion: The experimental results showed that the new detector had good output linearity for the neutron intensity, and the response of the new detector did not decrease during the irradiation. Conclusion: The new detector consisting of quartz optical fibers can be applied to measurement of neutron field of an accelerator-based BNCT.

The goal of this study was to evaluate the effect of spent coffee grounds (SCG) biofiller on the morphological, thermal, mechanical and hydrolytic degradation characteristics of poly(lactic acid) (PLA) based biocomposites. The PLA-based biocomposite films were fabricated by using a high-viscosity kneading and hot-pressing machine. The PLA/SCG biocomposites were analyzed with SEM, DSC, TGA, UTM and hydrolytic degradation test. Aggregation in the PLA matrix is a result of increasing SCG concentrations. In the thermal properties, it was described that the cold crystallization temperature (Tcc) decreased as SCG was added to PLA. When SCG was incorporated to PLA, the degradation onset temperature (Tonset) revealed a diminish. The elastic modulus increased while tensile strength of PLA diminished as SCG was applied. Through hydrolysis analysis, the decomposition of PLA was accelerated with the addition of SCG. This research confirmed the possibility of devloping an eco-friendly packaging material with high degradability as SCG hasten the breakdown of PLA.

An in-flight fragment separator, which aims to produce and study rare isotopes, consists of superferric quadrupole triplets and 30° dipole magnets to focus and bend the beams for achromatic focusing and momentum dispersion, respectively. The separator is divided into pre and main stages, and we plan to use superconducting magnets employing high-Tc superconductor (HTS) coils in the pre-separator area, where radiation heating is high. The HTS coils will be cooled by cold He gas in 20- 50 K, and in the other area, superferric magnets using low-temperature superconductor (LTS) will be used at 4 K. A few LTS coils were wound and successfully tested in a LHe dewar, and the design of cryostat has been optimized. Development of the HTS coils is ongoing in collaboration with a group at KERI. An HTS coil of racetrack shape was wound and tested in a LN2 bath and in a dewar with cryocooler. No degradation on critical current due to coil winding was found.

In recent years, high-temperature superconductor (HTS) Quadruple Triplets are being developed for heavy ion accelerators, because the HTS magnets are suitable to withstand radiation and high heat loads in the hot cell of accelerators. Generally, an iron yoke, which costs a mass of material, was employed to enhance the magnetic field when a quadrupole magnet was designed. The type of the magnet is called iron-dominated magnet, because the total magnetic field was mainly induced by the iron. However, in the HTS superconductor iron-dominated magnets, the coil-induced field also can have a certain proportion. Therefore, the air-core HTS quadrupole magnets can be considered instead of the iron-core HTS quadrupole magnet to be employed to save the iron material. This study presents the design of an air-core HTS quadruple triplet which consists three by air-core HTS quadruple magnet and compare the design result with that of an iron-core HTS quadruple triplet. First, the characteristics of an air-core HTS quadrupole magnet were analyzed to select the magnet system for the magnetic field uniformity impairment. Then, the field uniformity was improved(< 0.1%) exactly using evolution strategy (ES) method for each iron-core HTS quadrupole magnet and the air-core HTS quadruple triplet was established. Finally, the designed air- core triplet was compared with the iron-core HTS quadruple triplet, and the results of beam trajectories were presented with both the HTS quadruple triplet systems to show that the air-core triplet can be employed instead of the iron-core HTS triplet. The design of the air-core quadruple triplet was suggested for a heavy ion accelerator.