• Title/Summary/Keyword: defense performance

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A Study on the ISAR Image Reconstruction Algorithm Using Compressive Sensing Theory under Incomplete RCS Data (데이터 손실이 있는 RCS 데이터에서 압축 센싱 이론을 적용한 ISAR 영상 복원 알고리즘 연구)

  • Bae, Ji-Hoon;Kang, Byung-Soo;Kim, Kyung-Tae;Yang, Eun-Jung
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.25 no.9
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    • pp.952-958
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    • 2014
  • In this paper, we propose a parametric sparse recovery algorithm(SRA) applied to a radar signal model, based on the compressive sensing(CS), for the ISAR(Inverse Synthetic Aperture Radar) image reconstruction from an incomplete radar-cross-section(RCS) data and for the estimation of rotation rate of a target. As the SRA, the iteratively-reweighted-least-square(IRLS) is combined with the radar signal model including chirp components with unknown chirp rate in the cross-range direction. In addition, the particle swarm optimization(PSO) technique is considered for searching correct parameters related to the rotation rate. Therefore, the parametric SRA based on the IRLS can reconstruct ISAR image and estimate the rotation rate of a target efficiently, although there exists missing data in observed RCS data samples. The performance of the proposed method in terms of image entropy is also compared with that of the traditional interpolation methods for the incomplete RCS data.

Design of Control System for Organic Flight Array based on Back-stepping Controller (Backstepping 기법을 이용한 유기적 비행 어레이의 제어시스템 설계)

  • Oh, Bokyoung;Jeong, Junho;Kim, Seungkeun;Suk, Jinyoung
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.45 no.9
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    • pp.711-723
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    • 2017
  • This paper proposes a flight control system for an organic flight array(OFA) which has a new configuration to consist of multi modularized ducted-fan unmanned aerial vehicles (UAVs). The OFA is able to apply to various missions such as indoor reconnaissance, communication relay, and radar jamming by using capability of hover flight. The OFA has a distinguished advantage due to reconfigurable structure to assemble or separate with respect to its missions or operational conditions. A dynamic modelling of the OFA is derived based on equations of motion of the single ducted-fan modules. In order to apply nonlinear control method, an affine system of attitude dynamics is derived. Moreover, the control system is composed of a back-stepping controller for attitude control and a PID controller for position control. Then the performance of the proposed controller is verified via a numerical simulation under wind disturbance.

Case Studies on Applications of Conformal Cooling Channel Based On DMT Technology (DMT기술을 활용한 형상적응형 냉각채널 적용 사례 연구)

  • Kim, Woo-Sung;Hong, Myung-Pyo;Park, Jun-Seok;Lee, Yun-Soon;Cha, Kyoung Je;Sung, Ji-Hyun;Jung, Min-Wha;Lee, Ye-Hwan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.14 no.3
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    • pp.9-14
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    • 2015
  • The Direct Metal Tooling (DMT) process is a kind of additive manufacturing processes, which is developed using various commercial steel powders, such as P20, P21, SUS420, and other non-ferrous metal powders. The DMT process is a versatile process that can be applied to various fields, such as the molding industry, the medical industry, and the defense industry. Among them, the application of the DMT process to the molding industry is one of its most attractive and practical applications, since the conformal cooling channel cores of injection molds can be fabricated at a slightly expensive cost by using the hybrid fabrication method of DMT technology compared with parts fabricated with machining technology. The main objectives of this study are to provide various characteristics of the parts made using the DMT process compared with the same parts machined from bulk materials and evaluate the performance of the injection mold equipped with a conformal cooling channel core fabricated using the hybrid method of the DMT process.

Theoretical Analysis of Heat Pipe Thermal Performance According to Nanofluid Properties (나노유체 특성에 따른 히트파이프 성능해석)

  • Lim, Seung Min
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.7
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    • pp.599-607
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    • 2015
  • In this study, we theoretically investigate the thermal performances of heat pipes that have different nano-fluid properties. Two different types of nano-particles have been used: $Al_2O_3$ and CuO. The thermal performances of the heat pipes are observed for varying nano-particle aggregations and volume fractions. Both the viscosity and the conductivity increase as the volume fraction and the aggregation increase, respectively. Increasing the volume fraction helps increase the capillary limit in the well-dispersed condition. Whereas, the capillary limit is decreased under the aggregate condition, when the volume fraction increases. The dependence of the heat pipe thermal resistance on the volume fraction, aggregation, and conductivity of the nano-particles is analyzed. The maximum thermal transfer of the heat pipe is highly dependent on the volume fraction because of the high permeability of the heat pipe. For the proposed heat pipe, the optimum volume fraction of the nano-particle can be seen through 3D graphics.

An Experimental Study on the Material Characteristics of Mechanical Filters for Eliminating High-Frequency Noise in Accelerometer Measurements (가속도 측정에 있어 고주파 잡음 제거를 위한 기계적 필터의 재료 특성에 관한 실험적 연구)

  • Choi, Won-Yeong;Yoo, Seong-Yeol;Cha, Ki-Up;Kim, Sung-Soo;Noh, Myoung-Gyu
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.7
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    • pp.773-778
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    • 2011
  • Accelerometers are widely used to measure the lateral vibrations of pipe-like structures such as a gun tube under impulse loads. Stress waves that precede the lateral vibrations due to the explosion within a gun contribute little to the vibrations, but saturate the accelerometer input. A mechanical filter eliminates this high-frequency stress wave and only transmits the signal corresponding to the lateral vibrations. The mechanical filter consists of a mechanical structure for mounting the accelerometers and a damping material. The low-pass filter characteristics are determined from the equivalent damping and stiffness property of this damping material. In this paper, we tested nine commercially available damping materials for their vibration characteristics by using a test rig. We also observed the change in the vibration characteristics while compressing the material. We designed and manufactured a mechanical filter and verified its filtering performance.

A study on stress in Children (소아(小兒) stress에 관한 문헌적(文獻的) 고찰(考察))

  • Kim, Ki-Bong;Kim, Jang-Hyun
    • The Journal of Pediatrics of Korean Medicine
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    • v.16 no.1
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    • pp.105-124
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    • 2002
  • With the progress of civilization, the disorders due to the stress, which derived from the social-structural complexity and diversity, are on an increasing trend in our times. Accordingly, the accurate diagnosis and appropriate treatment for them are required. Especially in the current years, children's disorders delivered by the emotional problems keep increasing. In this research, the researcher tried to figure out the cause of the children's stress and its treatment, studied the theories of the stress in the modem medicine and the sever emotions in oriental medicine, and came to the conclusion as follows: 1. The stress can be defined as the combination of the reaction to noxious stimuli and its defense mechanism of the body, In oriental medicine, it is considered as pathological notions which includes seven emotions as the internal factor, six evils as the external factor and other foods, expectoration, ecchymoma as the non-internal/external factors. 2. Children usually get stressed by various reasons in a growth process such as schooling, relationship with friends, the opposite sex of family, or change of surroundings, and these can cause the various disorders. 3. In the study of the children's stress symptoms, it is found that the silent reaction is uncommon. It usually appeared in both reactions: firs, physical reactions such as stomachache, vomiting, headache, neural frequent urination, bronchial asthma or excessive respiration and/or, second, behavioral reactions such as a decline of performance, alimentary disorder, e.g. anorexia nervosa or bulimia, sleep disorder, e.g. nightmare or panic in sleep, anthrophobia, refusal to a school attendance or hyperactiveness. Besides, the peculiar mental disorder such as paroxysm of anger, tic, autism, nocturnal enuresis, lack of attentiveness, impediment in linguistic development, learning difficulty, intellectual decline, etc. can be appeared, and the heavy stress during the babyhood can cause the regression of behavior or the immaturity of formation of character. 4. The appropriate treatments for the children's stress are Osteopathy, Manpulation, Aroma Therapy, Alexander Technique, Autonomic Never Control Treatment, Biofeedback, Chiropractic, Dance Therapy, Feldenkrasis Technique, Gravity Therapy, Homepathy, Aquatherapy, Hypnotherapy, Naturopathy and Meditation.

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RSNT-cFastICA for Complex-Valued Noncircular Signals in Wireless Sensor Networks

  • Deng, Changliang;Wei, Yimin;Shen, Yuehong;Zhao, Wei;Li, Hongjun
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • v.12 no.10
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    • pp.4814-4834
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    • 2018
  • This paper presents an architecture for wireless sensor networks (WSNs) with blind source separation (BSS) applied to retrieve the received mixing signals of the sink nodes first. The little-to-no need of prior knowledge about the source signals of the sink nodes in the BSS method is obviously advantageous for WSNs. The optimization problem of the BSS of multiple independent source signals with complex and noncircular distributions from observed sensor nodes is considered and addressed. This paper applies Castella's reference-based scheme to Novey's negentropy-based algorithms, and then proposes a novel fast fixed-point (FastICA) algorithm, defined as the reference-signal negentropy complex FastICA (RSNT-cFastICA) for complex-valued noncircular-distribution source signals. The proposed method for the sink nodes is substantially more efficient than Novey's quasi-Newton algorithm in terms of computational speed under large numbers of samples, can effectively improve the power consumption effeciency of the sink nodes, and is significantly beneficial for WSNs and wireless communication networks (WCNs). The effectiveness and performance of the proposed method are validated and compared with three related BSS algorithms through theoretical analysis and simulations.

The Nonlinear Combustion Instability Prediction of Solid Rocket Motors (고체로켓모터의 비선형 연소 불안정성 예측 기법)

  • Hong, Ji-Seok;Moon, Hee-Jang;Sung, Hong-Gye;Um, Won-Seok;Seo, Seonghyeon;Lee, Do-hyung
    • Journal of the Korean Society of Propulsion Engineers
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    • v.20 no.1
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    • pp.20-27
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    • 2016
  • The prediction of combustion instability is important to avoid an obvious threat to the structural safety and the motor performance because it affects the apparent response function of the propellant, the burning rate, and a mean flow Mach number at the local surface. The combustion instability occurs in case acoustic waves were coupled with the combustion/flow dynamic frequency. In this paper, an acoustic instability model is derived from the nonlinear wave equation for analysing acoustic dynamics in solid rocket motors. The chamber pressure and burning rate effects on combustion instability have been investigated.

Prognostic Significance of Altered Blood and Tissue Glutathione Levels in Head and Neck Squamous Cell Carcinoma Cases

  • Khan, Sami Ullah;Mahjabeen, Ishrat;Malik, Faraz Arshad;Kayani, Mahmood Akhtar
    • Asian Pacific Journal of Cancer Prevention
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    • v.15 no.18
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    • pp.7603-7609
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    • 2014
  • Glutathione is a thiol compound that plays an important role in the antioxidant defense system of the cell and its deficiency leads to an increased susceptibility to oxidative stress and, thus, progression of many disease states including head and neck cancer. In the present study, alterations of glutathione levels were investigated in study cohort of 500 samples (cohort 1 containing 200 head and neck cancer blood samples along with 200 healthy controls and cohort II with 50 head and neck squamous cell carcinoma tissue samples along with 50 control tissues) by high performance liquid chromatography. The results indicated that mean blood glutathione levels were significantly reduced in head and neck cancer patients (p<0.001) compared to respective controls. In contrast, the levels of glutathione total (p<0.05) and glutathione reduced (p<0.05) were significantly elevated in head and neck squamous cell carcinoma tissues compared to the adjacent cancer-free control tissues. In addition to this, pearson correlation performed to correlate different tissue glutathione levels (GSH) with clinical/pathological parameters demonstrated a significant negative correlation between pT-stage and GSH level ($r=-0.263^{**}$; p<0.01), C-stage and GSH level ($r=-0.335^{**}$; p<0.01), grade and GSH ($r=-0.329^{**}$; p<0.01) and grade versus redox index ($r=-0.213^{**}$; p<0.01) in HNSCC tissues. Our study suggests that dysregulation of glutathione levels in head and neck cancer has the potential to predict metastasis, and may serve as a prognostic marker.

Analysis on Infrared Stealth Performance with Emissivity Controlled Aircraft Surface Structure at Various Background (항공기 적외선 스텔스 기술 적용을 위한 다양한 배경조건에서의 방사율 제어구조 성능 분석)

  • Bae, Munjang;Kim, Taehwan;Kim, Taeil;Jung, Daeyoon;Cho, Hyung Hee
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.29 no.5
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    • pp.455-461
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    • 2016
  • Survivability of an aircraft has been greatly threatened by the development of a weapon system using infrared. Therefore, the infrared stealth technology is a very important technique to improve the survivability of an aircraft. In this study, the infrared signal of an aircraft was analyzed which corresponding to the aircraft surface temperature and environmental conditions with various surface conditions(especially emissivity changed). Based on the analyzed infrared signal, the optimized surface emissivity was suggested to reduce the average contrast radiance and contrast radiant intensity(CRI). In addition, we confirmed that the infrared contrast radiant intensity between the aircraft and the background can be minimized through an appropriately controlled surface emissivity of the aircraft at specific background.