Park C.-W.,KAIST |
Lee H.-J.,Defense Agency for Technology and Quality |
IEEE Communications Letters | Year: 2012
In this paper, we propose a fair semi-distributed resource allocation scheme over relay-enhanced orthogonal frequency-division multiple access (OFDMA) cellular networks. Since the existing works based on the centralized manner require the heavy feedback overhead between a base station (BS) and relay stations (RSs), we design a resource allocation scheme in the semi-distributed manner to reduce the feedback overhead. In the proposed scheme, a frame is divided into subframes and the BS and RSs allocate the subchannel in the dedicated subframe to its associated mobile stations (MSs). In addition, the proposed scheme guarantees fairness among MSs with the throughput-optimal scheduling. Through the simulation, we show that the proposed scheme is effective to guarantee fairness among MSs while it achieves the higher average throughput than the existing opportunistic schemes. © 1997-2012 IEEE.
Lee J.,Defense Agency for Technology and Quality |
Dixon W.E.,University of Florida |
Ziegert J.C.,Clemson University
International Journal of Advanced Manufacturing Technology | Year: 2012
The quality of products from a machine tool system is largely determined by the tolerances maintained, which is a function of how well the desired contour is tracked. To mitigate contour errors in a three-axis machine tool feed drive system, the control development in this paper is based on an error system that is transformed into tangential, normal, and binormal components to the desired contour (i.e., a cross-coupling controller (CCC)). Unlike previous CCCs, the controller developed in this paper does not assume exact knowledge of the inertia and friction matrices. Specifically, an adaptive estimate is developed to compensate for uncertain friction and inertial parameters. Lyapunov-based methods are used to craft the adaptive estimate and to prove global asymptotic contour tracking. Experimental results of the proposed controller on the x-y-axes of the high speed milling machine showed improvement of the contouring accuracy compared to proportional-derivative controller and a benchmark CCC. © 2011 Springer-Verlag London Limited.
Gigalane Co. and Defense Agency For Technology And Quality | Date: 2012-07-10
Disclosed is a connector for preventing unlocking which includes a signal pin transferring a signal; a body into which the signal pin is inserted and which is electrically isolated from the signal pin; a first housing having a hollow portion into which one end of the body is inserted, a thread groove and at least one protruding portion or a plurality of fixing grooves formed at an inner circumferential surface of the other end thereof; and a second housing having a hollow portion into which the other body end is inserted and through which the second housing is moved along an outer circumferential surface of the body in an axial direction.
Defense Agency For Technology And Quality and Gigalane Co. | Date: 2014-06-11
Disclosed is a connector for preventing unlocking. The connector for preventing unlocking may includes a signal pin transferring a signal; a body into which the signal pin is inserted and which is electrically isolated from the signal pin by an insulator and transfers a ground voltage; a first housing having a hollow portion defined therein, into which one end of the body is inserted, a thread groove for screw-coupling, which is defined in an inner circumferential surface of one end thereof, and at least one protruding portion or a plurality of fixing grooves formed on or in an inner circumferential surface of the other end thereof; and a second housing having a hollow portion defined therein, into which the other end of the body is inserted and through which the second housing is moved along an outer circumferential surface of the body in an axial direction, and one of the at least one protruding portion and the plurality of fixing grooves, which is not formed at the first housing but is formed on or in an outer circumferential surface of one end thereof. When the one end of the second housing is inserted and fixed between the inner circumferential surface of the other end of the first housing and the outer circumferential surface of the body, the at least one protruding portion is coupled in the plurality of fixing grooves so as to prevent rotation of the first housing.
Han J.,Defense Agency for Technology and Quality |
Lee H.,Gwangju Institute of Science and Technology
Information Sciences | Year: 2016
Recent research has focused on extracting personal interest data from social media. Although many methods have been developed, accurately estimating users' interests is often difficult because messages on social media are short and are not classified into any predefined categories. We propose a new method to overcome this problem by incorporating heterogeneous media, such as news. In our method, we first extract explicit features and implicit topics of categories using news media, where implicit topics are determined using a refined topic model. Next, we describe social media messages using these features and topics to estimate users' interests. Compared with several other approaches, our approach provides more accurate estimations of users' interests. We also demonstrate that the accuracy of friend recommendations is increased using the users' interests estimated by our method. Thus, we expect that the proposed approach could be helpful for enhancing the personalization of social media services. © 2016 Elsevier Inc. All rights reserved.
Han H.-S.,Defense Agency for Technology and Quality
Engineering Failure Analysis | Year: 2014
The vibratory torque of a diesel engine caused by the reciprocating motion of the mass and gas pressure force of a cylinder is one of the main causes of the failure of the driving shaft of the diesel engine and the connecting shaft to the reduction gear. Because high cycle torsional fatigue can occur in the reduction gear shaft connecting the engine under vibratory torsional stress, the US Navy restricts it under the MIL G 17859D(SH) standard and suggests a procedure for evaluating the safety of the shaft for the reduction gear. In this study, the structural safety of the reduction gear input shaft in which fatigue failure occurs in typical naval vessels is investigated in accordance with the VDI 3822 RCA (root cause analysis) procedure based on the MIL G 17859D(SH) standard. When evaluating the safety factor in accordance with the MIL G 17859D(SH) standard, the alternating bending moment from the lateral vibration and the stress concentration factor under static load are considered. In addition, an improved design is suggested by CAE to satisfy the safety factor suggested by the MIL G 17859D(SH) standard. © 2014 Elsevier Ltd.
Hwang S.,Defense Agency for Technology and Quality |
Jeong J.H.,Pusan National University
International Journal of Air-Conditioning and Refrigeration | Year: 2016
Offset strip fins (OSF) have been widely used in plate-fin heat exchangers. Conventional OSFs are constructed with plain fins. Various design modifications to improve the performance of OSFs are compared here. The modifications suggested include perforations, dimples, vortex generators, and a double-layer design. The performance capabilities are evaluated using a computational fluid dynamics (CFD) analysis. The performances are compared in terms of the j-factor, f-factor, area goodness factor, and volume goodness factor. The f-factors of all modified designs appeared to be higher than that of the plain OSF, while the j-factor was found to be higher or lower than that of the plain OSF depending on the design modification used. The plain OSF has the largest area goodness factor, while OSFs with multiple perforations and dimples show a higher volume goodness factor than the plain OSF. © 2016 World Scientific Publishing Company
Kim Y.S.,Defense Agency for Technology and Quality |
Kim S.-J.,University of Seoul
Japanese Journal of Applied Physics | Year: 2011
A poled lead zirconate titanate (PZT) wafer is subjected to electric field loading of pulse type whose magnitude is increasing until polarization direction is completely reversed. Then it is subjected to the same type of electric field loading in the opposite direction to return to initial state. During the complete cycle of polarization reversal, electric displacement in thickness direction and in-plane strain are measured in both loaded and unloaded states. The same measurement is made at four different temperatures. From the measured data, permittivity and piezoelectric coefficient are evaluated and fitted as linear functions of remanent polarization and temperature. Reference remanent polarization-reference remanent in-plane strain plots are drawn and switching processes at different temperatures are compared with each other. The present observations will be helpful in constructing constitutive models for nonlinear thermo-electro-mechanical behavior of ferroelectric ceramics. © 2011 The Japan Society of Applied Physics.
Kim S.-J.,University of Seoul |
Kim Y.S.,Defense Agency for Technology and Quality
Ceramics International | Year: 2010
A PZT wafer is subjected to a temperature increase from the reference temperature 20-111 °C under no electric field. During the temperature increase, the variations of remanent polarization in thickness direction and remanent in-plane strain are measured. From the measurements, the values of pyroelectric coefficient in thickness direction and in-plane thermal expansion coefficient are estimated. The temperature experiment is repeated starting at various different values of initial remanent polarization, and the dependency of pyroelectric and thermal expansion coefficients on initial remanent polarization is obtained. In the tested range of temperature, it is found that the pyroelectric coefficient can be given as a linear function of remanent polarization and that the in-plane thermal expansion coefficient is given as a linear function of remanent in-plane strain or as a quadratic function of remanent polarization. © 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Park C.-W.,Korea Advanced Institute of Science and Technology |
Lee H.-J.,Defense Agency for Technology and Quality |
Lim J.-T.,Korea Advanced Institute of Science and Technology
IEEE Transactions on Vehicular Technology | Year: 2012
In order to reduce feedback overload, a framework of contention-based feedback was established. However, since a user is randomly chosen, it cannot maximize capacity. Moreover, if a collision occurs, a base station cannot obtain any information to schedule a user; thus, a scheduling outage happens. In this paper, we propose a two-stage opportunistic feedback scheme to maximize capacity with the limited feedback. The proposed scheme guarantees selecting the user with the highest signal-to-noise ratio (SNR) channel state and considers the scheduling outage situation using previous feedback information. In addition, we define the effective capacity to show the relation between the capacity and the feedback overload. Simulation results show that the proposed scheme achieves higher effective capacity with limited feedback than existing contention-based feedback schemes do. © 2011 IEEE.