• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.12
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• pp.34-41
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• 2008

In this paper, we present an asymptotical analysis of channel capacity of Bell labs layered space-time (BLAST) architectures based on a zero-forcing (ZF) criterion in the sense of signal-to-noise ratio (SNR). We begin by introducing a new relationship related to multi-input multi-output (MIMO) channel capacity. We prove that Diagonal Bell Labs Space-Time (DBLAST) attains the lower bound for MIMO channels when interference nulling is carried out based on the ZF-criterion. An exact closed-form expression for the probability density function of the channel capacity is analyzed. Based on the asymptotic behavior of the channel capacity of each layer, closed-form expressions for the asymptotic ergodic capacity are derived for BLAST. Based on the analysis presented in this paper, we gain an insight on the channel capacity behavior for a MIMO channel. Computer simulation results have verified the validity and accuracy of the proposed analysis for a wide range of antenna array sizes.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.1
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• pp.107-116
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• 2011

Purpose: The review article was written to establish an excel program that could calculate minimal Dk of contact lens without $O^2$ deficiency and actual $O^2$ concentration on cornea when contact lens were being fitted by changing lens-related factors. Methods: An excel program was formulated to calculate the thickness of post-lens lacrimal layer, Dk of contact lens and $O^2$ concentration on cornea. Results: With the excel program established, minimal $O^2$ concentration needed on cornea could be calculated when the thickness of post-lens lacrimal layer was changed by varying lens-related factors. A different route in the excel program was needed to choose based on the shape of lacrimal layer. The thickness of lacrimal layer was determined by the shape of meniscus made of tear between lens edge and cornea with flat fit. Thus, the $O^2$ concentration showing negative number in calculation decreased on peripheral cornea with flatter fitting and actual $O^2$ concentration would be zero on cornea. With tight fitting, the thickness of post-lens lacrimal layer is much thicker than lens itself thus negative number in calculation by the excel program is shown indicating zero oxygen on cornea. It can cause $O^2$ deficiency regardless of Dk of contact lens. Conclusions: The calculation of thickness of post-lens lacrimal layer and $O^2$ concentration on cornea by the established excel program is suggested to avoid $O^2$ deficiency when fitting state is varied by changing lens-related factors.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.20 no.1
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• pp.71-78
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• 1990

This research was made to investigate the change of the image layer and of the vertical and horizontal magnification on the Panelipse radiographic image by the control of profile index. Using the Panelipse, a series of 60 exposures were taken with the steel balls placed in the holes of the plastic model plate, and then evaluated by 4 observers. Two points were assigned for a reading of sharp, one for middling sharp, and zero for unsharp. Each ball image then could be given a total reader score of 0 to 8. The author analyzed the image layer as defined by a sharpness score of 6 or more. The results obtained were as follows: As the profile index was increased, the shape of the image layer was not changed, and the width of the image layer was increased, and the position of the layer shifted away from the rotation center. As the profile index was increased, the ranges of vertical and horizontal magnification was increased, especially the ranges of horizontal magnification was greater than that of vertical magnification.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.6
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• pp.102-108
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• 2001

To prevent green house effect and destruction of an ozone layer, an ozone destruction potential(OBP) must be zero and a refrigerant for low global warming potential(GWP) is needed. HFC-l34a, in which hydrogen is mixed instead of chlorine is a refrigerant used for automobile conditioners and its destruction potential is ecologically zero. However, it is not consid- ered as a perfect substitutive refrigerant as its GWP is high. It is studied refrigerant mixtures in which HFC-l52a and $CF_3 I$ in HFC-l52a with low GWP and zero ODP are mixed by experimentally and concluded as follows: 1) With the variation of speed of compressor outside temperature and flow rate, 7he heat of evaporator and compressor and coefficient of perfor- mance was varied, and influenced the air conditioner. 2) The pressure of evaporator was decreased with increasing the speed of compressor and the pressure of evaporator with the refrigerant HFC-l52a was higher 24% than that of azotrope refrigerant mixed with $CF_3 I$

• Journal of Power Electronics
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• v.4 no.3
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• pp.152-160
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• 2004

This paper presents analysis, modeling, and design of a low-harmonic, isolated, active-clamped SEPIC for future avionics applications. Simpler converter dynamics, high switching frequency, zero voltage-Transition-PWM switching, and a single-layer transformer construction result. This paper describes complete design of a digital controller for a high-frequency switching power supply. Guidelines for the minimum required resolution of the analog-to-digital converter, the pulse-width modulator, and the fixed-point computational unit is derived. A design example based on a SEPIC converter operating at the high switching frequency is presented. The controller design is based on direct digital design approach and standard root-locus techniques.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.347-351
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• 1997

A micromachined piezoelectic cantilever transducer,which works both as a microphone and as a microspeaker,has been fabricated and tested. The 2000*2000*3.mu.m .sap2. cantilever has oxide(ZnO)piezoelectric thin film on a supporting layer of low-pressure chemical-vapor-deposited(LPCVD)low-stress siliconnitride. A highlight of the fabrication process which may also be relevant for other micromachined stuctures is the technique for producing a flat,multilayer cantilever. The measured microphone sensitivity is fairly constant at 2 mV/.mu.bar in the low frequency range and rise to 20 mV/.mu.bar at the lowest resonant frequency of 890 Hz. The 2 mV/.mu.bar sensitivity is the highest report to data for a microphone with a micromachined diaphragm. When measured into a 2 cm/sap3 coupler with 4V (zero-park)drive,the microspeaker output sound pressure level(SPL) is 75 dB at 890 Hz. It increases to approximately 100dB SPL at 4.8kHz with 6V(zero-park)drive. The measured microphone frequency response agrees well with the results of an ABAQUS simulation.

• Journal of the Semiconductor & Display Technology
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• v.14 no.3
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• pp.27-31
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• 2015

It was the electrical properties of ZnS treated by the annealing in a vaccum and an atmosphere conditions to reseached the leakage current effect of semiconductor devices. Most samples were shown the non-linear with unipolar properties, but the ZnS annealed at $100^{\circ}C$ in a vaccum was only observed no leakage current in a range of -20 V< voltage < 15 V. The crystallinity of ZnS with no leakage current was improved and optical property was also improved. Because the ambipolar characteristics and low leakage currents originated from the extension effect of a depletion width by electron-hole combination in the depletion layer.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.506-511
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• 2001

This paper presents how redevelopment of the boundary layer in a backward-facing step flow is affected by boundary conditions imposed on velocity at the inlet, top and exit of the flow. A two-dimensional, laminar, incompressible flow over a backward-facing step with an open top boundary has been computed by using numerical methods of second-order time and spatial accuracy and a fractional-step method that guarantees a divergence-free velocity field at all time. The inlet velocity profile above the step is of Blasius type. Along the top boundary, shear-tree and Dirichlet conditions on the streamwise velocity were considered and at the exit fully-developed and convective boundary conditions were examined. (The vertical velocity at all boundaries were assumed to be zero explicitly or implicitly.) From the computed flow fields, the reattachment on the bottom side of shear layer separated from the tip of the step and succeeding redevelopment of the boundary layer were investigated.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.9
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• pp.31-36
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• 1999

A capacitance-type sensor using porous silicon layer is developed to measure aqueous alcohol concentration. Since alcohol, so called ethanol, is very permeable into the silicon wafer, it is often used to help chemical reaction when the silicon wafer is processed under some aqueous solution. In this work, the sensing property was measured for the alcohol concentration from zero to near 100 percent with two types of samples with porous silicon layer formed in 25 and 35% HF solution, respectively. Good reliability as well as fast response time and good linearity were shown over 10kHz and the measured capacitance was observed to be inverse to alcohol concentration due to the decrease of the whole dielectric constant in porous silicon layer.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.1071-1074
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• 2002

This paper presents Bi thin films have been fabricated by atomic layer-by-layer deposition and co-deposition at an IBS method. The growth rates of the films was set in the region from 0.17 to 0.27 nm/min. MgO(100) was used as a substrate. In order to appreciate stable existing region of Bi 2212 phase with temperature and ozone pressure, the substrate temperature was varied between 655 and $820^{\circ}C$ and the highly condensed ozone gas pressure$(PO_3)$ in vacuum chamber was varied between $2.0{\times}10^{-6}$ and $2.3{\times}10^{-5}Torr$. Bi 2212 phase appeared in the temperature range of 750 and $795^{\circ}C$: and single phase of Bi 2201 existed in the lower region than $785^{\circ}C$. Whereas, $PO_3$ dependance on structural formation was scarcely observed regardless of the pressure variation. And high quality of c-axis oriented Bi 2212 thin film with $T_c$(onset) of about 90 K and $T_c$(zero) of about 45 K is obtained. Only a small amount of CuO in some films was observed as impurity, and no impurity phase such as $CaCuO_2$ was observed in all of the obtained films.