• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.1
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• pp.23-28
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• 2011

This paper outlines extraction potential of tidal stream resources from the simplified channel in which flow is driven by a head difference between inlet and outlet. Energy extraction alters the flow within a simple channel, and extraction of 10% energy flux in a natural channel would give rise to a flow speed reduction of about 5.7%. If 20% of the undisturbed energy flux is extracted, the flow speed is reduced by 11.3%. The simple channel also suggests that extractable energy might be higher if flow speed reductions are considered acceptable.

• Journal of Electrical Engineering and Technology
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• v.3 no.4
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• pp.566-570
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• 2008

Vertical nanowire SGFETs(Surrounding Gate Field Effect Transistors) provide full gate control over the channel to eliminate short channel effects. This paper presents design and characterization of a differential pair amplifier using NMOS and PMOS SGFETs with a 10nm channel length and a 2nm channel radius. The amplifier dissipates $5{\mu}W$ power and provides 5THz bandwidth with a voltage gain of 16, a linear output voltage swing of 0.5V, and a distortion better than 3% from a 1.8V power supply and a 20aF capacitive load. The 2nd and 3rd order harmonic distortions of the amplifier are -40dBm and -52dBm, respectively, and the 3rd order intermodulation is -24dBm for a two-tone input signal with 10mV amplitude and 10GHz frequency spacing. All these parameters indicate that vertical nanowire surrounding gate transistors are promising candidates for the next generation high speed analog and VLSI technologies.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.5
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• pp.1654-1675
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• 2014

In practical wireless systems, the erroneous channel state information (CSI) sometimes deteriorates the performance drastically. This paper focuses on robust design of coordinated set planning of coordinated multi-point (CoMP) transmission, with respect to the feedback delay and link error. The non-ideal channel models involving various uncertainty conditions are given. After defining a penalty factor, the robust net ergodic capacity optimization problem is derived, whose variables to be optimized are the number of coordinated base stations (BSs) and the divided area's radius. By the maximum minimum criterion, upper and lower bounds of the robust capacity are investigated. A practical scheme is proposed to determine the optimal number of cooperative BSs. The simulation results indicate that the robust design based on maxmin principle is better than other precoding schemes. The gap between two bounds gets smaller as transmission power increases. Besides, as the large scale fading is higher or the channel is less reliable, the number of the cooperated BSs shall be greater.

• Bulletin of the Korean Chemical Society
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• v.24 no.9
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• pp.1339-1344
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• 2003

Flow field-flow fractionation (FlFFF) is a technology to separate the molecules by size in an open channel. Molecules with different size have different diffusivities and are located vertically in different positions when passing through an open channel. In this study, hollow fiber membranes instead of conventional rectangular channels have been used as materials for the open channel and this change would decrease the cost of manufacturing. FlFFF is a useful technique to characterize the biopolymeric materials. Retention time, diffusion coefficients and Stokes radius of analysis can be calculated from the related simple equations. Hollow-fiber flow field-flow fractionation (HF-FlFFF) has been used for the characterization and separation of protein mixture in a phosphate buffer solution and has demonstrated the potential to be developed into a disposable FlFFF channel. The important indexes for the analytical separation are selectivity, resolution and plate height. The optimized separation condition for protein mixture of Ovalbumin, Alcohol dehydrogenase, Apoferritin and Thyroglobulin is ${\dot V}_{out}/{\dot V}_{rad}=0.65/0.85\;mL/min$.

• Journal of Korea Water Resources Association
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• v.39 no.12 s.173
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• pp.1023-1030
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• 2006

The characteristics of the longitudinal velocity in a $180^{\circ}$ constant-radius, recirculating laboratory channel were investigated. Three-dimensional velocity fields were measured using a side-looking ADV. The shortcomings of existing equations for longitudinal velocity are discussed. An eddy viscosity model is adopted in the downstream momentum equation. A mathematical equation was developed to describe the vertical distribution of longitudinal velocity. The comparisons of the longitudinal velocity show generally good agreement. It is found that the curvature change in the curved channel affects the vertical location of maximum velocity and the vertical profile of longitudinal velocity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.9
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• pp.1957-1967
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• 1997

Adaptive channel equlization accomplished without resorting to a training sequence is known as blind equalization. In this paper, in order to reduce the speed of the convergence and the steady-state mean squared error simultaneously, we propose the multi-stage RD(radius-directed) algorithm derived from the combination of the constant modulus algorithm and the radius-directed algorithm. In the starting stage, multi-stage RD algorithm are identical to the constant modulus algorithm which guarantees the convergence of the equalizer. As the blind identical to the constant modulus algorithm which guarantees the convergence of the equalizer. As the blind equalizer converges, the number of the level of the quantizers is increased gradually, so that the proposed algorithm operate identical to the radius-directed algorithm which leads to the low error power after the covnergence. Therefore, the multi-stage RD algorithm obtains fast convergence rage and low steady stage mean square error.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.10 s.241
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• pp.1083-1091
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• 2005

Turbulent flow around a rotating circular cylinder is investigated by Direct Numerical Simulation. The calculation is performed at three cases of low Reynolds number, Re=161, 348 and 623, based on the cylinder radius and friction velocity. Statistically strong similarities with fully developed channel flow are observed. Instantaneous flow visualization reveals that the turbulence length scale typically decreases as Reynolds number increases. Some insight into the spacial characteristics in conjunction with wave number is provided by wavelet analysis. The budget of dissipation rate as well as turbulent kinetic energy is computed and particular attention is given to the comparison with plane channel flow.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.461-466
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• 2000

Direct numerical simulations (DNS) is carried out to study fully-developed turbulent concentric annular pipe flow with two radius ratios at $Re_{Dh}\;=\;8900$. In case of $R_1/R_2\;=\;0.5$, the present result for the mean flow is in good agreement with the previous experimental data. Because of the transverse curvature effects, the distributions of mean flow and turbulent intensities are asymmetric in contrast to those of other fully-developed flows (channel and pipe flow). From the distributions of skewness of radial velocity fluctuations, it co be identified that all of the characteristics of channel, pipe and turbulent flow on a cylinder in axial flow can be appeared in concentric annular pipe flow.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1560-1565
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• 2007

In this study, Chiu's velocity distribution equation recently developed from the probability and entropy concepts is used to establish a linkage between the mean velocity obtained from the Manning's equation and the corresponding velocity distribution in a channel cross section. The linkage to be established enables computing the velocity distribution along with the mean velocity, from simple hydraulic data such as Manning's n, hydraulic radius and channel slope irrespective of including sediment or not.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.370-373
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• 2008

It is known that the temperatures of die, punch, holder and punch pad need to be kept different to get better formability in Mg sheet forming processes. Heating and cooling channels are usually equipped in each tool to assign different temperature. This study focused on the optimal design of the heating and cooling channels for a cross-shaped deep drawing die set. While the die and blankholder were heated to and kept at $250^{\circ}C$ by using heat cartridges, the punch and punch pad were kept at much lower temperature than that of the die and blankholder by water circulating through cooling channels. All the approaches were done by numerical analyses, aiming to maximize the cup height and to minimize the punch corner radius without any failure.