• Journal of Communications and Networks
• /
• 제16권4호
• /
• pp.371-377
• /
• 2014

Localized topology control is attractive for obtaining reduced network graphs with desirable features such as sparser connectivity and reduced transmit powers. In this paper, we focus on studying how to prolong network lifetime in the context of localized topology control for wireless multi-hop networks. For this purpose, we propose an energy efficient localized topology control algorithm. In our algorithm, each node is required to maintain its one-hop neighborhood topology. In order to achieve long network lifetime, we introduce a new metric for characterizing the energy criticality status of each link in the network. Each node independently builds a local energy-efficient spanning tree for finding a reduced neighbor set while maximally avoiding using energy-critical links in its neighborhood for the local spanning tree construction. We present the detailed design description of our algorithm. The computational complexity of the proposed algorithm is deduced to be O(mlog n), where m and n represent the number of links and nodes in a node's one-hop neighborhood, respectively. Simulation results show that our algorithm significantly outperforms existing work in terms of network lifetime.

• 한국정보통신학회논문지
• /
• 제15권4호
• /
• pp.897-904
• /
• 2011

본 논문에서는 CMOS 능동 인덕터를 이용하여 1.8GHz PCS 대역과 2.4GHz WLAN 대역에서 동조가 가능한 저잡음 증폭기의 새로운 회로구조를 제안하였다. CMOS 능동 인덕터 부하를 이용하는 저잡음 증폭기의 높은 잡음지수를 줄이기 위한 회로구조와 잡음지수를 더욱 감소시키기 위한 잡음상쇄기법을 적용하고 해석하였다. 이 동조가능 저잡음 증폭기를 $0.18{\mu}m$ CMOS 공정기술로 시뮬레이션을 수행한 결과는 잡음성능이 약 3.4dB 향상된 것을 보여주며, 이는 주로 제안된 새로운 회로구조에 기인한다.

• Smart Structures and Systems
• /
• 제11권3호
• /
• pp.241-259
• /
• 2013

This paper presents the optimum load-speed diagram evaluation for a linear micromotor, including multitude cantilever piezoelectric bimorphs, briefly. Each microbeam in the mechanism can be actuated in both axial and flexural modes simultaneously. For this design, we consider quasi-static and linear conditions, and a relatively new numerical method called the smoothed finite element method (S-FEM) is introduced here. For this purpose, after finding an optimum volume fraction for piezoelectric layers through a standard numerical method such as quadratic finite element method, the relevant load-speed curves of the optimized micromotor are examined and compared by deterministic topology optimization (DTO) design. In this regard, to avoid the overly stiff behavior in FEM modeling, a numerical method known as the cell-based smoothed finite element method (CS-FEM, as a branch of S-FEM) is applied for our DTO problem. The topology optimization procedure to find the optimal design is implemented using a solid isotropic material with a penalization (SIMP) approximation and a method of moving asymptotes (MMA) optimizer. Because of the higher efficiency and accuracy of S-FEMs with respect to standard FEMs, the main micromotor characteristics of our final DTO design using a softer CS-FEM are substantially improved.

• Journal of Power Electronics
• /
• 제14권6호
• /
• pp.1166-1177
• /
• 2014

A new type of topology with medium-frequency-transformer (MFT) isolation for medium voltage wind power generation systems is proposed in this paper. This type of converter is a high density power conversion system, with high performance features suitable for next generation wind power systems in either on-shore or off-shore applications. The proposed topology employs single-phase cascaded multi-level AC-AC converters on the grid side and three phase matrix converters on the generator side, which are interfaced by medium frequency transformers. This avoids DC-Link electrolytic capacitors and/or resonant L-C components in the power flow path thereby improving the power density and system reliability. Several configurations are given to fit different applications. The modulation and control strategy has been detailed. As two important part of the whole system, a novel single phase AC-AC converter topology with its reliable six-step switching technique and a novel symmetrical 11-segment modulation strategy for two stage matrix converter (TSMC) is proposed at the special situation of medium frequency chopping. The validity of the proposed concept has been verified by simulation results and experiment waveforms from a scaled down laboratory prototype.

• Kyungpook Mathematical Journal
• /
• 제7권2호
• /
• pp.41-43
• /
• 1967

• ETRI Journal
• /
• 제27권5호
• /
• pp.579-584
• /
• 2005

A CMOS direct-conversion mixer with a single transistor-level topology is proposed in this paper. Since the single transistor-level topology needs smaller supply voltage than the conventional Gilbert-cell topology, the proposed mixer structure is suitable for a low power and highly integrated RF system-on-a-chip (SoC). The proposed direct-conversion mixer is designed for the multi-band ultra-wideband (UWB) system covering from 3 to 7 GHz. The conversion gain and input P1dB of the mixer are about 3 dB and -10 dBm, respectively, with multi-band RF signals. The mixer consumes 4.3 mA under a 1.8 V supply voltage.

• Journal of Electrical Engineering and Technology
• /
• 제8권5호
• /
• pp.1078-1085
• /
• 2013

This paper presents a novel topology for cascaded transformer sub-multilevel converter. Eachsub-multilevel converter consists of two DC voltage sources with six switches to achieve five-level voltage. The proposed topology results in reduction of DC voltage sources and switches number. Single phase low frequency transformers are used in proposed topology and voltage transformation and galvanic isolation between load and sources are given by transformers. This topology can operate as symmetric or asymmetric converter but in this paper we have focused on symmetric state. The operation and performance of the suggested multilevel converter has been verified by the simulation results of a single-phase nine-level multilevel converter using MATLAB/SIMULINK.

• Wind and Structures
• /
• 제18권5호
• /
• pp.497-510
• /
• 2014

Seismic and wind load performances of buildings are commonly improved by using bracing systems. In practice, standard bracing systems, such as X, Y, V, and K types are used. To determine the appropriate bracing type, the designer uses trial & error method among the standard bracings to obtain better results. However, using topology optimization yields more efficient bracing systems or new bracing can be developed depending on building and loading types. Determination of optimum bracing type for minimum deformation on a building under the effect of wind load is given in this study. A new bracing system is developed by using topology optimization. Element removal method is used to determine and remove the comparatively inefficient materials. Optimized bracing is compared with proposed bracing types available in the related literature. Maximum deformation value of building is used as performance indicator to compare effectiveness of different bracings to resist wind loads. The proposed bracing, yielded 99%, deformation reduction compared to the unbraced building.

• 대한수학회보
• /
• 제61권1호
• /
• pp.83-92
• /
• 2024

Let R be a commutative ring with nonzero identity and M be an R-module. In this paper, we first introduce the concept of S-idempotent element of R. Then we give a relation between S-idempotents of R and clopen sets of S-Zariski topology. After that we define S-pure ideal which is a generalization of the notion of pure ideal. In fact, every pure ideal is S-pure but the converse may not be true. Afterwards, we show that there is a relation between S-pure ideals of R and closed sets of S-Zariski topology that are stable under generalization.

• Korean Journal of Mathematics
• /
• 제6권2호
• /
• pp.323-329
• /
• 1998

In this paper, we introduce a new class of sets, called $m$-sets, and the notion of $m$-continuity. In particular, $m$-sets and $m$-continuity are used to extend known results for ${\alpha}$-continuity and semi-continuity and precontinuity.