• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.72-78
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• 2008

The speed variation of SRM is fulfilled throughout a transition from chopping control to single pulse operation. (i,e., low speed to high speed operation). It is unsatisfied with performance at all operational regimes. In this paper, the operational performance of SRM can be improved by using current hysteresis control method. This method maintains a generally flat current waveform. At the high speed, the current chopping capability is lost due to the development of the back-EMF. Therefore SRM operates in single pulse mode. By using zero-current switching and zero-voltage switching technique, the stress of power switches can be reduce in chopping mode. When the commutation from one phase winding to another phase winding, the current can be zero as fast as possible in this period because several times negative voltage of DC-source voltage produce in phase winding. This paper is compared to performance based on conventional C-dump converter topology and the proposed resonant C-dump converter topology. Simulation and experimental results are presented to verify the effectiveness of the proposed circuit.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.1
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• pp.71-77
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• 2001

A flow visualization study using the oil film method and the smoke-laser light sheet arrangement is carried out to investigate the three-dimensional flow pattern around the free end surface region of a finite circular cylinder (aspect ratios of 1.25 and 4.25) mounted on a flat plate. The experiment is performed for the cases of two Reynolds numbers: 5.92${\times}$10$^3$and 1.48${\times}$10(sup)5. Various kinds of singular points on the free-end surface are disclosed from the oil surface flow visualization. The smoke-laser light sheet visualization, to aid in understanding the oil streak-line patterns, clearly demonstrates that a pair of tornado-like vortices marched along the downstream together with a pair of side tip vortices. A topological sketch to characterize the surface flow and the four vortices emanating from the top surface is included.

• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.210-212
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• 2018

A new switching mode has been proposed to obtain high power factor and low THD in single stage AC-DC converter. The conventional voltage mode control in critical conduction mode distorts input current shape with poor THD in flyback topology. Once TRIAC dimmer is connected, visible flicker in the LED lamp is easily detected due to a lack of TRAIC holding current near the input voltage zero cross. The newly proposed method can shape the input current by providing a desired reference voltage so that low THD is obtained by ideal sinusoidal input current in case of no dimmer connection and flat input current performs good TRIAC dimmer compatibility in phase-cut dimming condition. To confirm the validity of the proposed method, theoretical analysis and experimental result from 8W dimmable LED lighting system are presented.

• Journal of Communications and Networks
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• v.13 no.6
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• pp.602-611
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• 2011

The inter-domain routing scalability issue is a major challenge facing the Internet. Recent wide deployments of multihoming and traffic engineering urge for solutions to this issue. So far, tunnel-based proposals and compact routing schemes have been suggested. An implicit assumption in the routing community is that structured address labels are crucial for routing scalability. This paper first systematically examines the properties of identifiers and address labels and their functional differences. It develops a simple Internet routing model and shows that a binary relation T defined on the address label set A determines the cardinality of the compact label set L. Furthermore, it is shown that routing schemes based on flat address labels are not scalable. This implies that routing scalability and routing stability are inherently related and must be considered together when a routing scheme is evaluated. Furthermore, a metric is defined to measure the efficiency of the address label coding. Simulations show that given a 3000-autonomous system (AS) topology, the required length of address labels in compact routing schemes is only 9.12 bits while the required length is 10.64 bits for the Internet protocol (IP) upper bound case. Simulations also show that the ${\alpha}$ values of the compact routing and IP routing schemes are 0.80 and 0.95, respectively, for a 3000-AS topology. This indicates that a compact routing scheme with necessary routing stability is desirable. It is also seen that using provider allocated IP addresses in multihomed stub ASs does not significantly reduce the global routing size of an IP routing system.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.10 no.1
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• pp.65-72
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• 2016

In this study, a fully active transfemoral prothesis with a knee joint is designed considering stair walking conditions. Since the torque at the knee joint required for stair walking condition is relative high compared with the one in normal walking condition, the proposed design has high torque generating mechanism. Moreover, the transfemoral prothesis is designed in compact size to reduce its weight, which is related to comfortable fit and fatigue of patients. Flat type BLDC motor is used for simple and compact structure and various components are used to generate required torque with target working angle and speed. The weight reduction of structure is carried out using optimization method after the initial design process is complete. The optimization is conducted under the load conditions of stair walking. The optimized design is validated via finite element analysis and experiments. As a result, the weight is reduced using topology and shape optimization but maintaining the safety of structure. Also the space efficiency is improved due to its compact size.

• Journal of Power Electronics
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• v.7 no.4
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• pp.278-285
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• 2007

Recently, plasma display panels (PDP) have become the most promising candidate in the market for large screen size flat panel displays. PDPs have many merits such as a fast display response time and wide viewing angle. However, there are still concerns about high cost because they require complex driving circuits composed of high power switching devices to generate various voltage waveforms for three operational modes of reset, scan, and sustain. Conventional PDP driving circuits use path switches for voltage separation and a scan switch to offer a scan voltage for reset and scan operations, respectively. In addition, there exist reset switches to initialize PDPs by regulating the wall charge conditions with ramp shaped pulses, which means the necessity of specific power devices for the reset operation. Because power for the plasma discharge accompanied by a large current is transferred to a panel via path switches, high power rating switches are used for path switches. Therefore, this paper proposes a novel low-cost PDP driving scheme achieved by not only eliminating path switches but also merging the function of reset switches into other switches used for sustain or scan operations. The simulated voltage waveforms of the proposed topology and experimental results implemented in a 42-inch panel to demonstrate the validity of using a new gate driver that merges the functions of power switches are presented.

• Proceedings of the KIPE Conference
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• 2006.06a
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• pp.403-405
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• 2006

Over the years, plasma display panel (PDP) manufacturers have impressed the flat panel display industry with yet another new product essentially having the merits of a larger screen size. Since larger size implies higher power ratings, voltage/current ratings of the power devices used have become a rising concern. Another important concern is the brightness of PDP, one way of increasing which is by operating the PDP at higher frequencies. In order to address the above issues, a transformer coupled sustain-driver for AC-PDP is proposed During the transition time, the two windings of the transformer greatly boost up the displacement current flowing through the panel capacitance and hence enable a fast inversion of the voltage polarity with practical values of resonant inductance. In the proposed topology, the resonant inductance can be increased by a factor of $(n+1)^2$ as compared to prior approaches. Increased inductance results in lower current stresses. Moreover, high frequency operation is possible by using higher value of n (turn ratio of the transformer). The operational principle and design procedure of the proposed circuit are presented with theoretical analysis. The validity of the proposed sustain driver is established through simulation and experimental results using a 42-in PDP

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.6
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• pp.1586-1605
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• 2012

With the prevalence of multimedia applications and the potential commercial usage of Mobile Ad hoc Networks (MANETs) in group communications, Quality of Service (QoS) support became a key requirement. Recently, some researchers studied QoS multicast issues in MANETs. Most of the existing QoS multicast routing protocols are designed with flat topology and small networks in mind. In this paper, we investigate the scalability problem of these routing protocols. In particular, a Position-Based QoS Multicast Routing Protocol (PBQMRP) has been developed. PBQMRP builds a source multicast tree guided by the geographic information of the mobile nodes, which helps in achieving more efficient multicast delivery. This protocol depends on the location information of the multicast members which is obtained using a location service algorithm. A virtual backbone structure has been proposed to perform this location service with minimum overhead and this structure is utilized to provide efficient packet transmissions in a dynamic mobile Ad hoc network environment. The performance of PBQMRP is evaluated by performing both quantitative analysis and extensive simulations. The results show that the used virtual clustering is very useful in improving scalability and outperforms other clustering schemes. Compared to On-Demand Multicast Routing Protocol (ODMRP), PBQMRP achieves competing packet delivery ratio and significantly lower control overhead.

• Journal of the Korean Institute of Landscape Architecture International Edition
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• no.2
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• pp.130-139
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• 2004

Shiwha Lake is an excellent example of a body of water restored from a state of heavy pollution to a cleaner and more ecological state. This paper will explore techniques and methods available to landscape planning for the creation of new migratory birds habitats in Shiwha Lake. Because Shiwha lake is located adjacent to a new industrial site on reclaimed land, any planning effort aimed at restoring bird habitats must carefully consider the existing context. This plan had 3 goals; (1) to restore the coastal environment, (2) to create a habitat for migratory birds, and (3) to administer environmental education programs. To achieve these goals, several objectives were determined and planning criteria were proposed for topology, water environment(fresh, brackish and salt water swamps), zoning(for experts and general visitors), circulations, planting and mounding. The flora and fauna of the site was surveyed, and 5 alternatives were suggested and compared in several aspects. Planting species were carefully selected considering target birds and habitat requirements. In order to increase bio-diversity of the site, the plan proposed multi-staired mounds and extensive drainage systems. Bird watching facilities with natural materials, and the remote observing system using CCTV and the internet were some of the ecological techniques recommended by the plan. The bird watching trails are divided into two different zones for experts and general visitors.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.411-411
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• 2012

Over the recent years, surface enhanced Raman spectroscopy (SERS) has dramatically grown as a label-free detecting technique with the high level of selectivity and sensitivity. Conventional SERS-active nanostructured layers have been deposited or patterned on rigid substrates such as silicon wafers and glass slides. Such devices fabricated on a flexible platform may offer additional functionalities and potential applications. For example, flexible SERS-active substrates can be integrated into microfluidic diagnostic devices with round-shaped micro-channel, which has large surface area compared to the area of flat SERS-active substrates so that we may anticipate high sensitivity in a conformable device form. We demonstrate fabrication of flexible SERS-active nanostructured substrates based on soft-lithography for simple, low-cost processing. The SERS-active nanostructured substrates are fabricated using conventional Si fabrication process and inkjet printing methods. A Si mold is patterned by photolithography with an average height of 700 nm and an average pitch of 200 nm. Polydimethylsiloxane (PDMS), a mixture of Sylgard 184 elastomer and curing agnet (wt/wt = 10:1), is poured onto the mold that is coated with trichlorosilane for separating the PDMS easily from the mold. Then, the nano-pattern is transferred to the thin PDMS substrates. The soft lithographic methods enable the SERS-active nanostructured substrates to be repeatedly replicated. Silver layer is physically deposited on the PDMS. Then, gold nanoparticle (AuNP) inks are applied on the nanostructured PDMS using inkjet printer (Dimatix DMP 2831) to deposit AuNPs on the substrates. The characteristics of SERS-active substrates are measured; topology is provided by atomic force microscope (AFM, Park Systems XE-100) and Raman spectra are collected by Raman spectroscopy (Horiba LabRAM ARAMIS Spectrometer). We anticipate that the results may open up various possibilities of applying flexible platform to highly sensitive Raman detection.