• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.351-366
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• 2016

Macroperforations improve the sound absorption performance of porous materials in acoustic cavities and in waveguides. In an acoustic cavity, enhanced noise reduction is achieved using porous materials having macroperforations. Double porosity materials are obtained by filling these macroperforations with different poroelastic materials having distinct physical properties. The locations of macroperforations in porous layers can be chosen based on cavity mode shapes. In this paper, the effect of variation of macroporosity and double porosity in porous materials on noise reduction in an acoustic cavity is presented. This analysis is done keeping each perforation size constant. Macroporosity of a porous material is the fraction of area covered by macro holes over the entire porous layer. The number of macroperforations decides macroporosity value. The system under investigation is an acoustic cavity having a layer of poroelastic material rigidly attached on one side and excited by an internal point source. The overall sound pressure level (SPL) inside the cavity coupled with porous layer is calculated using mixed displacement-pressure finite element formulation based on Biot-Allard theory. A 32 node, cubic polynomial brick element is used for discretization of both the cavity and the porous layer. The overall SPL in the cavity lined with porous layer is calculated for various macroporosities ranging from 0.05 to 0.4. The results show that variation in macroporosity of the porous layer affects the overall SPL inside the cavity. This variation in macroporosity is based on the cavity mode shapes. The optimum range of macroporosities in poroelastic layer is determined from this analysis. Next, SPL is calculated considering periodic and nodal line based optimum macroporosity. The corresponding results show that locations of macroperforations based on mode shapes of the acoustic cavity yield better noise reduction compared to those based on nodal lines or periodic macroperforations in poroelastic material layer. Finally, the effectiveness of double porosity materials in terms of overall sound pressure level, compared to equivolume double layer poroelastic materials is investigated; for this the double porosity material is obtained by filling the macroperforations based on mode shapes of the acoustic cavity.

• Smart Structures and Systems
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• 제19권1호
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• pp.1-10
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• 2017

The operation of subway trains induces secondary structure-borne vibrations in the nearby underground spaces. The vibration, along with the associated noise, can cause annoyance and adverse physical, physiological, and psychological effects on humans in dense urban environments. Traditional tethered instruments restrict the rapid measurement and assessment on such vibration effect. This paper presents a novel approach for Wireless Smart Sensor (WSS)-based autonomous evaluation system for the subway train-induced vibrations. The system was implemented on a MEMSIC's Imote2 platform, using a SHM-H high-sensitivity accelerometer board stacked on top. A new embedded application VibrationLevelCalculation, which determines the International Organization for Standardization defined weighted acceleration level, was added into the Illinois Structural Health Monitoring Project Service Toolsuite. The system was verified in a large underground space, where a nearby subway station is a good source of ground excitation caused by the running subway trains. Using an on-board processor, each sensor calculated the distribution of vibration levels within the testing zone, and sent the distribution of vibration level by radio to display it on the central server. Also, the raw time-histories and frequency spectrum were retrieved from the WSS leaf nodes. Subsequently, spectral vibration levels in the one-third octave band, characterizing the vibrating influence of different frequency components on human bodies, was also calculated from each sensor node. Experimental validation demonstrates that the proposed system is efficient for autonomously evaluating the subway train-induced ambient vibration of underground spaces, and the system holds the potential of greatly reducing the laboring of dynamic field testing.

• 한국음향학회지
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• 제37권6호
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• pp.422-427
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• 2018

본 연구에서는 소형 물체가 음파 정상파의 압력 마디 부근에 소형 물체가 부양하는 정상파 음파 공중부양(standing wave acoustic levitation) 현상에 대해 베르누이 원리를 이용하여 부양의 원인이 되는 음향 방사힘(acoustic radiation force)의 근원과 개형을 기존에 알려진 진동자에서 떨어진 거리에 따른 음향 방사힘의 그래프와 비교함을 통해 개념적으로 설명했다. 이러한 설명을 뒷받침하는 일련의 실험들을 BLT(Bolt-clamped Langevin Type) 초음파 진동자를 이용해서 수행하여, 물체들이 공기의 압력 마디 부근에 부양하고 있음을 확인했고, 물체가 부양하고 있는 상태에서 정상파가 형성되는 조건임을 확인했다. 더불어, 정상파 음파 공중부양 현상에서 부양하는 물체들이 수직하게 일렬로 정렬하는 현상 역시 설명할 수 있었다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.711-732
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• 2019

Many unmanned aerial vehicle (UAV) applications have been employed for performing data collection in facilitating tasks such as surveillance and monitoring objectives in remote and dangerous environments. In light of the fact that most of the existing UAV relaying applications operate in conventional half-duplex (HD) mode, a full-duplex (FD) based UAV relay aided wireless network is investigated, in which the UAV relay helps forwarding information from the source (S) node to the destination (D). Since the activated UAV relays are always floating and flying in the air, its channel state information (CSI) as well as channel capacity is a time-variant parameter. Considering decode-and-forward (DF) relaying protocol in UAV relays, the cooperative relaying channel capacity is constrained by the relatively weaker one (i.e. in terms of signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR)) between S-to-relay and relay-to-D links. The channel capacity can be optimized by adaptively optimizing the transmit power of S and/or UAV relay. Furthermore, a hybrid HD/FD mode is enabled in the proposed UAV relays for adaptively optimizing the channel utilization subject to the instantaneous CSI and/or remaining self-interference (SI) levels. Numerical results show that the channel capacity of the proposed UAV relay aided wireless networks can be maximized by adaptively responding to the influence of various real-time factors.

• 화훼연구
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• 제26권4호
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• pp.166-178
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• 2018

In this study, the principal objective was to investigate the effect of light quality and vessel ventilation on the growth and development, physiology, activities of antioxidant enzymes, and contents of mineral nutrients of carnation (Dianthus caryophyllus L.) 'Marble Beauty'. Single node cuttings stuck into the plant growth regulator (PGR)-free MS medium in containers covered with caps with or without a ventilation filter were cultured first four weeks under white and then additional four weeks under either white (control), blue, red, or red + blue light emitting diodes (LEDs) for 56 days. Interestingly, a ventilated culture condition not only reduced the percentage of the hyperhydricity, but also increased the total chlorophyll content (Chl a + Chl b) of the plantlets as compared to the non-ventilated condition. In addition, blue LEDs produced plantlets with the greatest number of shoots and red LEDs produced plantlets with the greatest shoot length. The quality of plantlets was improved under a ventilation condition. Besides, under a ventilated condition, red + blue LEDs raised APX activity, and blue LEDs not only raised the activity of the CAT, but also increased tissue contents of such elements as K, Ca, Mg, Zn, Mn and Fe. The red LEDs increased contents of B and Si under a ventilated condition, and Na accumulation under a non-ventilated condition. Thus, including blue or red LEDs as the light source in a ventilated culture condition will produce plantlets of carnation 'Marble Beauty' in vitro with improved quality.

• 융합신호처리학회논문지
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• 제22권2호
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• pp.64-70
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• 2021

최근 무선 네트워크 기반 실시간 원격제어에 대한 관심이 크게 증가하고 있다. 무선 네트워크를 통하여 실시간 원격 제어를 구현하는데 있어서, 중요한 요소들 중 하나가 실시간 제어메시지의 지연시간 성능이다. 특히, 주기적으로 송신되는 실시간 제어메시지의 안정적인 수신을 위해 지연시간 지터를 줄이는 기술이 필요하다. 본 논문에서는 실시간 제어메시지를 무선 네트워크에서 운용 하는데 있어서 지연시간 지터를 감소시키는 동기화 전송을 제안한다. 제안된 동기화 전송은 송신노드와 무선통신기 간의 동기화를 바탕으로 적절한 전송시점을 제어하여 실시간 제어메시지가 항상 정해진 시간에 무선 네트워크를 통하여 전송 되도록 한다. 군용무인차량 시스템을 이용한 실험 결과에 따르면, 제안된 동기화 전송은 지연시간 지터를 일반 전송 방식의 지연시간 지터의 32% 수준으로 감소시켰다.

• International Journal of Computer Science & Network Security
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• 제22권7호
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• pp.91-102
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• 2022

With the evolution of wireless sensor network (WSN) technology, the routing policy has foremost importance in the Internet of Things (IoT). A systematic routing policy is one of the primary mechanics to make certain the precise and robust transmission of wireless sensor networks in an energy-efficient manner. In an IoT environment, WSN is utilized for controlling services concerning data like, data gathering, sensing and transmission. With the advantages of IoT potentialities, the traditional routing in a WSN are augmented with decision-making in an energy efficient manner to concur finer optimization. In this paper, we study how to combine IoT-based deep learning classifier with routing called, Kriging Regressive Deep Belief Neural Learning (KR-DBNL) to propose an efficient data packet routing to cope with scalability issues and therefore ensure robust data packet transmission. The KR-DBNL method includes four layers, namely input layer, two hidden layers and one output layer for performing data transmission between source and destination sensor node. Initially, the KR-DBNL method acquires the patient data from different location. Followed by which, the input layer transmits sensor nodes to first hidden layer where analysis of energy consumption, bandwidth consumption and light intensity are made using kriging regression function to perform classification. According to classified results, sensor nodes are classified into higher performance and lower performance sensor nodes. The higher performance sensor nodes are then transmitted to second hidden layer. Here high performance sensor nodes neighbouring sensor with higher signal strength and frequency are selected and sent to the output layer where the actual data packet transmission is performed. Experimental evaluation is carried out on factors such as energy consumption, packet delivery ratio, packet loss rate and end-to-end delay with respect to number of patient data packets and sensor nodes.

• 한국전기전자재료학회논문지
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• 제35권5호
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• pp.459-465
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• 2022

This paper reports a method to use a wireless sensor network deployed in the field to real-time monitor soil moisture, warning when the moisture level reaches a specific value, and wirelessly controlling an additional device (LED or water supply system, etc.). In addition, we report all processes related to wireless irrigation system, including field deployment of sensors, real-time monitoring using a smartphone, data calibration, and control of additional devices deployed in the field by smartphone. A commercially available open-source Internet of Things (IoT) platform, NodeMCU, was used, which was combined with a 9V battery, LED and soil humidity sensor to be integrated into a portable prototype. The IoT-based soil humidity sensor prototype deployed in the field was installed next to a tree for on-site demonstration for the measurement of soil humidity in real-time for about 30 hours, and the measured data was successfully transmitted to a smartphone via Wifi. The measurement data were automatically transmitted via e-mail in the form of a text file, stored on the web, followed by analyses and calibrations. The user can check the humidity of the soil real-time through a personal smartphone. When the humidity of a soil reached a specific value, an additional device, an LED device, placed in the field was successfully controlled through the smartphone. This LED can be easily replaced by other electronic devices such as water supplies, which can also be controlled by smartphones. These results show that farmers can not only monitor the condition of the field real-time through a sensor monitoring system manufactured simply at a low cost but also control additional devices such as irrigation facilities from a distance, thereby reducing unnecessary energy consumption and helping improve agricultural productivity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권4호
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• pp.1224-1248
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• 2022

In various sensor network applications, such as climate observation organizations, sensor nodes need to collect information from time to time and pass it on to the recipient of information through multiple bounces. According to field tests, this information corresponds to most of the energy use of the sensor hub. Decreasing the measurement of information transmission in sensor networks becomes an important issue.Compression sensing (CS) can reduce the amount of information delivered to the network and reduce traffic load. However, the total number of classification of information delivered using pure CS is still enormous. The hybrid technique for utilizing CS was proposed to diminish the quantity of transmissions in sensor networks.Further the energy productivity is a test task for the sensor nodes. However, in previous studies, a clustering approach using hybrid CS for a sensor network and an explanatory model was used to investigate the relationship between beam size and number of transmissions of hybrid CS technology. It uses efficient data integration techniques for large networks, but leads to clone attacks or attacks. Here, a new algorithm called SBEA (Snowball Endurance Algorithm) was proposed and tested with a bow. Thus, you can extend the battery life of your WSN by running effective copy detection. Often, multiple nodes, called observers, are selected to verify the reliability of the nodes within the network. Personal data from the source centre (e.g. personality and geographical data) is provided to the observer at the optional witness stage. The trust and reputation system is used to find the reliability of data aggregation across the cluster head and cluster nodes. It is also possible to obtain a mechanism to perform sleep and standby procedures to improve the life of the sensor node. The sniffers have been implemented to monitor the energy of the sensor nodes periodically in the sink. The proposed algorithm SBEA (Snowball Endurance Algorithm) is a combination of ERCD protocol and a combined mobility and routing algorithm that can identify the cluster head and adjacent cluster head nodes.This algorithm is used to yield the network life time and the performance of the sensor nodes can be increased.

• 한국시뮬레이션학회논문지
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• 제19권1호
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• pp.161-171
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• 2010

많은 센서 네트워크 응용분야에서 센서 노드는 개방된 환경에 놓이게 된다. 공격자는 개방된 환경에 놓인 센서 노드를 물리적으로 획득할 수 있으며, 포획한 노드를 이용하여 허위보고서를 센서네트워크에 삽입 시킬 수 있다. 삽입된 허위보고서는 제한된 센서노드 에너지를 고갈 시키며, 허위 경보를 일으켜 심각한 문제를 야기 시킬 수도 있다. 이러한 공격을 막기 위해 Ye 등은 통계적 여과 기법(Statistical En-route Filtering) 방법을 제안하였다. 통계적 여과기법은 CoS(Center of Stimulus)로부터 생성된 이벤트 보고서가 베이스 스테이션으로 전송되는 동안 중간의 모든 노드들이 검증을 하게 된다. 본 논문은 통계적 여과 기법에 확률 검증 기법을 적용하여 에너지 효율적인 정적 확률 통계적 여과 기법을 제안하고자 한다. 베이스 스테이션과 이벤트 발생 지역까지의 거리가 멀어질수록 에너지 절약 효과가 극대화 될 것으로 기대된다.