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Analysis of Imperfect Acoustic Cloaking Resonances

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Chinese Physics Letters 2012年第12期29卷 119-122页

作者： kim Seungil Department of Mathematics and Research Institute for Basic Sciences Kyung Hee UniversitySeoul 130-701Korea

We study the resonance phenomenon arising from imperfect acoustic cloaking in 2D based on a small perturbation of the transformation *** is shown that the resonant frequencies of imperfect cloaking appearing in the total scattering cross section converge to Dirichlet eigenvalues of the concealed region as a perturbation parameter approaches *** theory enables us to predict the location of the resonant frequencies of imperfect cloaking and to identify the corresponding resonance modes.

关键词： perturbation imperfect resonant

Effective Denoising Architecture for Handling Multiple Noises

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Computer Systems Science & Engineering 2023年第3期44卷 2667-2682页

作者： Na Hyoun kim Namgyu kim The Graduate School of Business IT of Kookmin University Seoul02707Korea

Object detection,one of the core research topics in computer vision,is extensively used in various industrial *** there have been many studies of daytime images where objects can be easily detected,there is relatively little research on nighttime *** the case of nighttime,various types of noises,such as darkness,haze,and light blur,deteriorate image ***,an appropriate process for removing noise must precede to improve object detection *** there are many studies on removing individual noise,only a few studies handle multiple noises *** this paper,we pro-pose a convolutional denoising autoencoder(CDAE)-based architecture trained on various types of *** also present various composing modules for each noise to improve object detection performance for night *** the exclusively dark(ExDark)Image dataset,experimental results show that the Sequentialfiltering architecture showed superior mean average precision(mAP)compared to other architectures.

关键词： Object detection computer vision nighttime multiple noises convolutional denoising autoencoder

Identities for degenerate Bernoulli polynomials and Korobov polynomials of the first kind

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Science China Mathematics 2019年第5期62卷 999-1028页

作者： Taekyun kim Dae San kim Department of Mathematics Kwangwoon University Department of Mathematics Sogang University

In this paper, we derive five basic identities for Sheffer polynomials by using generalized Pascal functional and Wronskian matrices. Then we apply twelve basic identities for Sheffer polynomials, seven from previous results, to degenerate Bernoulli polynomials and Korobov polynomials of the first kind and get some new identities. In addition, letting λ→ 0 in such identities gives us those for Bernoulli polynomials and Bernoulli polynomials of the second kind.

关键词： generalized Pascal functional matrix Wronskian matrix degenerate Bernoulli polynomial Krobov polynomial of the first kind

Adaptive Data Transmission Method According to Wireless State in Long Range Wide Area Networks

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Computers, Materials & Continua 2020年第7期64卷 1-15页

作者： Seokhoon kim Dae-Young kim Department of Computer Software Engineering Soonchunhyang UniversityAsan-si31538Korea School of Computer Software Daegu Catholic UniversityGyeongsan-si38430Korea

The Internet of Things(IoT)has enabled various intelligent services,and IoT service range has been steadily extended through long range wide area communication technologies,which enable very long distance wireless data ***-nodes are connected to a gateway with a single *** consume very low-power,using very low data rate to deliver *** long transmission time is consequently needed for each data packet transmission in long range wide area networks,data transmission should be efficiently ***,this paper proposes a multicast uplink data transmission mechanism particularly for bad network *** delay will be increased if only retransmissions are used under bad network ***,employing multicast techniques in bad network conditions can significantly increase packet delivery ***,retransmission can be reduced and hence transmission efficiency ***,the proposed method adopts multicast uplink after network condition *** predict network conditions,the proposed method uses a deep neural network *** proposed method performance was verified by comparison with uplink unicast transmission only,confirming significantly improved performance.

关键词： IoT wide area communication machine learning uplink transmission.

Anomaly Detection in Imbalanced Encrypted Traffic with Few Packet Metadata-Based Feature Extraction

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Computer Modeling in Engineering & Sciences 2024年第10期141卷 585-607页

作者： Min-Gyu kim Hwankuk kim Department of Financial Information Security Kookmin UniversitySeoul02707Republic of Korea Department of Information Security Cryptography Mathematics Kookmin UniversitySeoul02707Republic of Korea

In the IoT(Internet of Things)domain,the increased use of encryption protocols such as SSL/TLS,VPN(Virtual Private Network),and Tor has led to a rise in attacks leveraging encrypted *** research on anomaly detection using AI(Artificial Intelligence)is actively progressing,the encrypted nature of the data poses challenges for labeling,resulting in data imbalance and biased feature extraction toward specific *** study proposes a reconstruction error-based anomaly detection method using an autoencoder(AE)that utilizes packet metadata excluding specific node *** proposed method omits biased packet metadata such as IP and Port and trains the detection model using only normal data,leveraging a small amount of packet *** makes it well-suited for direct application in IoT environments due to its low resource *** experiments comparing feature extraction methods for AE-based anomaly detection,we found that using flowbased features significantly improves accuracy,precision,F1 score,and AUC(Area Under the Receiver Operating Characteristic Curve)score compared to packet-based ***,for flow-based features,the proposed method showed a 30.17%increase in F1 score and improved false positive rates compared to Isolation Forest and ***,the proposedmethod demonstrated a 32.43%higherAUCwhen using packet features and a 111.39%higher AUC when using flow features,compared to previously proposed oversampling *** study highlights the impact of feature extraction methods on attack detection in imbalanced,encrypted traffic environments and emphasizes that the one-class method using AE is more effective for attack detection and reducing false positives compared to traditional oversampling methods.

关键词： One-class anomaly detection feature extraction auto-encoder encrypted traffic CICIoT2023

Ag-GST/HfO_(x)-based unidirectional threshold switching selector with low leakage current and threshold voltage distribution for high-density cross-point arrays

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Rare Metals 2024年第1期43卷 280-288页

作者： Kyoung-Joung Yoo Dae-Yun Kang Nahyun kim Ho-Jin Lee Ta-Hyeong kim Taeho kim Tae Geun kim School of Electrical Engineering Korea UniversitySeoul 02841Republic of Korea

The use of electrochemical-metallization-based volatile threshold switching selectors in cross-point arrays has been widely explored owing to their high on-off ratios and simple ***,these devices are unsuitable for cross-point architectures because of the difficulty in controlling the random filament formation that results in large fluctuations in the threshold voltage during *** this study,we investigated the unidirectional threshold transition characteristics associated with an Ag/GST/HfO_(x)/Pt-based bilayer selector and demonstrated the occurrence of a low leakage current(<1×10^(-11) A) and low distribution of the threshold voltage(Δ0.11 V).The bilayer structure could control the filament formation in the intermediate state through the insertion of an HfO_(x) tunneling *** stacking a bilayer selector with NiO_(x)based resistive random-access memory,the leakage and programming currents of the device could be significantly *** the crossbar array configuration,we performed equivalent circuit analysis of a one-selector oneresistor(1S1R) devices and estimated the optimal array size to demonstrate the applicability of the proposed *** maximum acceptable crossbar array size of the 1S1R device with the Ag/GST/HfO_(x)/Pt/Ti/NiO_(x)/Pt structure was 5.29×10^(14)(N^(2),N=2.3×10^(7)).

关键词： Selector device Tunneling barrier Threshold switching Sputtering 1S1R Cross-point array

EFFECT OF SPECIMEN ASPECT RATIO ON FATIGUE LIFE OF CLOSED CELL Al-Si-Ca ALLOY FOAM

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Acta Mechanica Solida Sinica 2008年第4期21卷 354-358页

作者： Amkee kim Ilhyun kim Division of Mechanical and Automotive Engineering Kongju National University275Budae-dongCheonanChungnam 330-717Korea

Quasi-static and compressive fatigue tests on the closed cell Al-Si-Ca alloy foam specimens with three different aspect ratios were performed. It turned out that the onset of cyclic shortening of foam with a lower aspect ratio took place earlier and the fatigue strength was lower compared with the specimen with a higher aspect ratio, although all the dimensions of specimen satisfied the seven times the cell size criterion, while the quasi-static stress-strain curves were almost same having same Young＇s modulus, yield stress and plateau stress. Therefore, the seven times the cell size criterion for the quasi-static compression behavior was not applicable to the fatigue analysis of Al-Si-Ca alloy foam.

关键词： aluminum foam aspect ratio fatigue behavior compressive strength

Phase-pure Na3V2(PO4)2F3 embedded in carbon matrix through a facile polyol synthesis as a potential cathode for high performance sodium-ion batteries

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Nano Research 2019年第4期12卷 911-917页

作者： Sohyun Park Jinju Song Seyeon kim Balaji Sambandam Vinod Mathew Sungjin kim Jeonggeun Jo Seokhun kim Jaekook kim Department of Materials Science and Engineering Chonnam National University 300 Ybngbong-dong Buk-gu Gwangju 500-757 Republic of Korea Gwangju Bio/Energy R&D Center Korea Institute of Energy Research (KIER) 270-25 Samso-ro Buk-gu Gwangju 61003 Republic of Korea

In this study,a pseudo-layered Na super-ionic conductor of Na3V2(PO4)2F3 (NVPF)/C cathode for sodium-ion batteries is prepared successfully using a facile polyol refluxing process without any impurity *** X-ray diffraction and Rietveld refinement results confirm that NVPF possesses tetragonal NASICON-type lattice with a space group of P42/*** this preparative method,polyol is utilized as a solvent as well as a carbon *** presence of nanosized NVPF particles in the carbon network is confirmed by field-emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM).The existence of carbon is analyzed by Raman scattering and elemental *** applied as a Na-storage material in a potential window of 2.0-4.3 V,the electrode exhibits two flat voltage plateaus at 3.7 and 4.2 V with an electrochemically active V^3+/V^4+ redox *** addition,Na3V2(PO4)2F3/C composite achieved a retention capacity of ~ 88% even after 1,500 cycles at 15 ***,at high current densities of 30 and 50 C,Na3V2(PO4)2F3/C cathode retains the specific discharge capacities of 108.4 and 105.9 mAh·g-1,respectively,revealing the structural stability of the material prepared through a facile polyol refluxing method.

关键词： fluorophosphate Na3V2(PO4)2F3 polyol process sodium ion batteries long life stability

The Effect of Diffuser Angle on the Discharge Coefficient of a Miniature Critical Nozzle

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Journal of Thermal Science 2010年第3期19卷 222-227页

作者： Jae Hyung kim Heuy Dong kim Toshiaki Setoguchi School of Mechanical Engineering Andong National UniversityAndong760-749Korea Department of Mechanical Engineering Saga University1HonjoSagaJapan

Many researches on critical nozzles have been performed to accurately measure the mass flow rate of gas flow,and to standardize the performance as a flow ***,much interest is being paid on the measurement of very small mass flow rate in industry fields such as MEMS ***,the design and performance data of the critical nozzles obtained so far have been applied mainly to the critical nozzles with comparatively large diameters,and the works available on miniature critical nozzles are *** the present study,a computational fluid dynamics method has been applied to investigate the influence of the diffuser angle on discharge coefficient of the miniature critical *** computations,the throat diameter of critical nozzle is varied from 0.2 mm to 5.0 mm and the diffuser angle is changed from 2 deg to 8 *** computational results are validated with some experimental data *** results show that the present computational results predict appropriately the discharge coefficient of the gas flows through miniature critical *** is known that the discharge coefficient is considerably influenced by the diffuser angle,as the throat diameter of nozzle becomes small below a certain *** implies that the miniature critical nozzles should be carefully designed.

关键词： Compressible Flow Critical Nozzle Compressible Flow Discharge Coefficient Diffuser Configuration Reynolds Number