• Applied Chemistry for Engineering
• /
• v.9 no.1
• /
• pp.20-27
• /
• 1998

The characteristics of the bubble adsorptive separation of CTAB(cetyltrimethylammonium bromide) and CuS precipitates was investigated. The Langmuir adsorption equation was adequate at very low concentration of CTAB, and the adsorption heat was determined from the batch analysis considering the bulk liquid accompanied between bubbles. The adsorption mechanism was explained with the collision adsorption between bubbles and precipitate particles. The optimum concentration ratio of (CTAB) to (CuS) for adsorptive separation was 0.1 and coincided with the ratio for the coagulation of particles. The collection efficiency was depended on pH and CTAB concentration but independent of the air flow rate, and the maximum efficiency was 0.0002. The selective separation of ZnS from the mixture of Cu-Cd-Zn sulfides was obtained by the bubble adsorption with CTAB.

• Journal of Advanced Navigation Technology
• /
• v.13 no.4
• /
• pp.551-558
• /
• 2009

Most of clustering schemes focusing on the energy efficiency have only a cluster head in each cluster, thus the energy consumption of cluster head in a cluster can rapidly increase. To reduce the energy consumption, recently, the dual-layered clustering which is separated a cluster ranges into two parts, i.e., data aggregation layer and data transmission layer, based on a sensor equipped with geographical positioning system (GPS), was proposed. However, the logical regions existing within the dual-layered clustering range can not distinguish efficiently. This scheme leads to many messages collision and transmission delay among member nodes. In this paper, to solve these problems, we propose a separated dual-layered routing scheme using the position information and the cluster radius. Proposed scheme clearly distinguish the dual-layered clustering range and gets the balanced number of member nodes in each cluster. Therefore, the proposed routing scheme could prolong the overall network life time about 10% compared to the previous two layered clustering scheme and LEACH.

• Journal of Communications and Networks
• /
• v.13 no.6
• /
• pp.664-677
• /
• 2011

In order to control interference and improve spectrum efficiency in the femtocell and macrocell overlaid system (FMOS), we propose a joint frequency bandwidth dynamic division, clustering and power control algorithm (JFCPA) for orthogonal-frequency-division-multiple access-based downlink FMOS. The overall system bandwidth is divided into three bands, and the macro-cellular coverage is divided into two areas according to the intensity of the interference from the macro base station to the femtocells, which are dynamically determined by using the JFCPA. A cluster is taken as the unit for frequency reuse among femtocells. We map the problem of clustering to the MAX k-CUT problem with the aim of eliminating the inter-femtocell collision interference, which is solved by a graph-based heuristic algorithm. Frequency bandwidth sharing or splitting between the femtocell tier and the macrocell tier is determined by a step-migration-algorithm-based power control. Simulations conducted to demonstrate the effectiveness of our proposed algorithm showed the frequency-reuse probability of the FMOS reuse band above 97.6% and at least 70% of the frequency bandwidth available for the macrocell tier, which means that the co-tier and the cross-tier interference were effectively controlled. Thus, high spectrum efficiency was achieved. The simulation results also clarified that the planning of frequency resource allocation in FMOS should take into account both the spatial density of femtocells and the interference suffered by them. Statistical results from our simulations also provide guidelines for actual FMOS planning.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.10B
• /
• pp.955-963
• /
• 2009

In this paper, we propose a medium access control(MAC) protocol for reducing the energy efficiency and for improving the transmission efficiency in underwater acoustic sensor networks. In underwater environment, the transmission delay is longer and bandwidth is smaller than terrestrial environment. Considering these points, we propose a new MAC protocol to enhance throughput and to manage efficiently the energy of nodes. The proposed protocol operates as a channel reservation scheme to decrease data collisions, and uses a mechanism to control the hidden node problem and the exposed node problem occurred in ad hoc networks. The proposed protocol consists of the slotted based transmission frame and reduces data collisions between nodes by putting separately the reservation period in the transmission frame. In addition, it is able to solve the hidden node problem and the exposed node problem by reservation information between nodes. We carry out the simulation to evaluate the proposed protocol in terms of the average energy consumption, the ratio of collision, throughput, and the average transmission delay, and compare the proposed protocol to a traditional MAC protocol in the underwater environment. The simulation results show that the proposed protocol outperforms the traditional protocol under a various of network parameters.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.10
• /
• pp.1958-1968
• /
• 2015

Things intelligence communication (M2M or IoT) service activation and global company of OneM2M-related business on aggressive investing and has led to the acceleration of change in the ICT market. But a variety of hacking security technology because of the possibility of secure communication (data exposure, theft, modification, deletion, etc.) has been issued as an important requirement. In this paper, we propose a mutual authentication protocol for secure communications chameleon hash based on the M2M environment. The results of performance analysis efficiency is encryption and decryption an average of 0.7%, calculated rate showed good results as compared to the target algorithm, equivalent to a 3%(Average 0.003 seconds) difference, mutual authentication and encryption region by using the key update advantage of ECC(Elliptic Curve Cryptography)based Chameleon hash function is signed of the operational efficiency, using a collision message verifiable properties demonstrated strong security of the communication section.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.35 no.1B
• /
• pp.144-153
• /
• 2010

Flooding based routing protocols are usually used to disseminate information in wireless sensor networks. Those approaches, however, require message retransmissions to all nodes and induce huge collision rate and high energy consumption. In this paper, HoGoP (Hop based Gossiping Protocol) in which all nodes consider the number of hops from sink node to them, and decide own gossiping probabilities, is introduced. A node can decide its gossiping probability according to the required average reception percentage and the number of parent nodes which is counted with the difference between its hop and neighbors' ones. Therefore the decision of gossiping probability for network topology is adaptive and this approach achieves higher message reception percentage with low message retransmission than the flooding scheme. Through simulation, we compare the proposed protocol with some previous ones and evaluate its performance in terms of average reception percentage, average forwarding percentage, and forwarding efficiency. In addition, average reception percentage is analyzed according to the application requirement.

• Journal of the Korea Convergence Society
• /
• v.11 no.5
• /
• pp.175-182
• /
• 2020

The calculation of the optimal trajectory of the stepped top-down robot was made using a genetic algorithm and a computational torque controller. First, the total energy efficiency was minimized using the Red-Cold Generic Algorithm (RCGA) consisting of reproductive, cross, and mutation. The reproducibility condition related to the position assembly of the start and end of the stride and the joints, angles, and angular velocities are linear constraints. Next, the unequal constraint accompanies the condition for preventing the collision of the swing leg at the corner with the outer surface of the stairs, the condition of the knee joint for preventing kinematic peculiarity, and the condition of no moment in safety in the traveling direction. Finally, the angular trajectory of each joint is defined by fourth-order polynomial whose coefficient is to approximate chromosomes. This is to approximate walking. In this study, the energy efficiency of the optimal trajectory was analyzed by computer simulation through a biped robot with seven degrees of freedom composed of seven links.

• Journal of the Korea Society of Computer and Information
• /
• v.26 no.10
• /
• pp.45-51
• /
• 2021

In this paper, we propose a 3D design method of the vacuum forming method of the front part to improve the lightness and production efficiency of agricultural electric vehicles. For agricultural electric vehicles, lightness and production efficiency are more important than the strength of materials for collision protection. In this paper, we propose a vacuum forming design method that can replace complex machining processes such as laser machining, bending, and painting. The main purpose of this research is to improve product stability, productivity and convenience through 3D design of the front part and development of vacuum forming mold technology. Research procedure follows the 3D modeling of the front part using CATIA, finite element analysis for the structural stability using ABAQUS, manufacturing prototype for the investigation of the dimensions using 3D scanner and actual driving test under agricultural electric vehicle usage environment. The results verifies the proposed 3D design method of the vacuum forming method and are expected to be widely used by agricultural workers through the simplification of the production process of agricultural electric vehicles.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.32 no.5
• /
• pp.205-211
• /
• 2022

The Granule Spray in Vacuum (GSV) process is a method of forming a dense nanostructured ceramic coating film by spraying ceramic granules on a substrate at room temperature in a vacuum. In the Granule Spray, the granules made by agglomerating particles with the size from submicrometer to micrometer can be sprayed into the substrate. Once the granules were squashed upon collision with the substrate, they become several dozens of nanometer-sized crystals in vacuum process. The zirconia of the monoclinic phase transform into tetragonal phase at 1150℃. At this time, its volume is changed by about 6.5 %. For this reason, it is widely held that it is difficult to acquire a compact of monoclinic zirconia sinter. In this study, the effect of particle treatment temperature and standoff distance on the substrate of zirconia granules were investigated in GSV. Also, particle treatment temperature, standoff distance, coating efficiency, and microstructure of the film were considered in forming the monoclinic zirconia coating film in GSV without any heating process. The deposited films exhibited monoclinic zirconia phase without any other detectable phase by X-ray diffractometer (XRD).

• Journal of Advanced Navigation Technology
• /
• v.27 no.4
• /
• pp.365-373
• /
• 2023

Unmanned aerial vehicles are widely used in various fields, and real-time path replanning is a critical factor in enhancing the safety and efficiency of these devices. In this paper, we propose a real-time path replanning technique based on RRT* and LOSPO. The proposed technique first generates an initial path using the RRT* algorithm and then optimizes the path using LOSPO. Additionally, the optimized path can be converted into a trajectory that considers actual time and the dynamic limits of the aircraft. In this process, environmental changes and collision risks are detected in real-time, and the path is replanned as needed to maintain safe operation. This method has been verified through simulation-based experiments. The results of this paper make a significant contribution to the research on real-time path replanning for UAVs, and by applying this technique to various situations, the safety and efficiency of UAVs can be improved.