• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.4
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• pp.1368-1389
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• 2014

Three-dimensional multiple-input multiple-output (3D MIMO) and large-scale MIMO are two promising technologies for upcoming high data rate wireless communications, since the inter-user interference can be reduced by exploiting antenna vertical gain and degree of freedom, respectively. In this paper, we derive the achievable sum rate of 3D MIMO systems employing zero-forcing (ZF) receivers, accounting for log-normal shadowing fading, path-loss and antenna gain. In particular, we consider the prevalent log-normal model and propose a novel closed-form lower bound on the achievable sum rate exploiting elevation features. Using the lower bound as a starting point, we pursue the "large-system" analysis and derive a closed-form expression when the number of antennas grows large for fixed average transmit power and fixed total transmit power schemes. We further model a high-building with several floors. Due to the floor height, different floors correspond to different elevation angles. Therefore, the asymptotic achievable sum rate performances for each floor and the whole building considering the elevation features are analyzed and the effects of tilt angle and user distribution for both horizontal and vertical dimensions are discussed. Finally, the relationship between the achievable sum rate and the number of users is investigated and the optimal number of users to maximize the sum rate performance is determined.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.1
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• pp.15-21
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• 2013

The safety and stability of 5MW class offshore wind turbine Jack-up platform was investigated through ocean basin experiment. For simulating the environmental condition of yellow sea in the South Korea, diverse waves, winds and currents were performed based on Froude's number. Regular wave and irregular wave based on Froude's number were applied to the wind turbine structure. In experiments, the height and period of regular wave type were scaled down as the 1:50 ratio of real wave condition. Irregular wave type was simulated with TMA(Texel Storm, Marsen and Arsloe)spectrum. The vertical reaction force, resonance period and wave pressure applied to multi-supporters of wind offshore structure were measured experimentally. Finally, the results showed that the capsizing situation of the offshore structure was generated by the severe environmental condition.

• International Journal of High-Rise Buildings
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• v.2 no.2
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• pp.153-169
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• 2013

The past decade has witnessed an unprecedented boom in tall and supertall building construction worldwide (Wood, 2011). Because of their massive bulk and soaring height, tall buildings often create serious placemaking problems. Employing extensive photographs and sketches, this paper examines architectural and urban design strategies that improve placemaking with tall buildings. The paper embraces a comprehensive approach that considers the relationship of tall buildings to their surroundings at the macro and micro scales. It also considers non-physical factors that tall buildings need to address, such as the social life the building creates. It is hoped that the placemaking factors discussed in this article will provide the required groundwork for future research that explores regulations and codes that foster placemaking with tall buildings.

• Proceedings of the Korea Concrete Institute Conference
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• 1991.10a
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• pp.68-73
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• 1991

Results of an experimental investigation of low-rise reinforced concrete shear walls with barbell cross section under cyclic loads are discussed and evaluated. Four halr scale models of test specimens with height to length ratio of 0.75 were experimented. The dimension of all walls is 1500mm wide $\times$ 950 mm high $\times$ 100 mm thick and the section of all boundary column at both ends is 200 mm $\times$ 200mm. Main variables are : design concept, vertical flexural reinflrcement ratios and reinforcement details(including crossed diagonal shear reinforcement in SW7 specimen). In SW7 specimen, maximum strength and consequently dissipating energy index were 1.45 and 1.28 times greater than those of SW6 specimen, respectively.

• Proceedings of the Korea Institute of Fire Science and Engineering Conference
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• 1997.11a
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• pp.361-368
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• 1997

Summary of experiments for the investigation of a fire which caused an upward fire spread for over 12 floors through balconies in a high-rise apartment complex is reported. The experiments include indoor tests to obtain fire properties of vertical PMMA fences and outdoor ones with a full scale model of the balcony. The test results suggest significance of the increase of total flame height by the merging of flames and a cooperative effect of the burning of the PMMA fence and combustibles on the balconies for the generation of a tall flame enough to cause ignition on the upper floors.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.121-126
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• 2001

In this study, reduced-scale experiments were conducted to understand smoke movements in tunnel fires with the natural ventilation. The 1/20 scale experiments were conducted under the Froude scaling since the smoke movement in tunnels is governed by buoyancy force. Six cases of experiments(pool diameter is 6.5cm, 7.3cm, 8.3cm, 10cm, l2.5cm and l5.4cm), in which vertical vents positioned 1m from the fire source symmetrically, were conducted in order to evaluate the effect of the vent on smoke movement. In case of heat release rate under 2MW, smoke front reached to the tunnel exit about 20 see delayed with ventilation and the smoke velocity was proportional to the power of the heat release rate. Temperature after the vent was lower than without vent. In case of l5.4cm pool, the temperature difference was about $50^{\circ}C$. It was confirmed that the thickness of smoke layer was maintained uniformly under the 35% height of tunnel through the visualized smoke flow by a laser sheet and the digital camcoder.

• Wind and Structures
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• v.30 no.6
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• pp.575-595
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• 2020

The characteristics of winds associated with tropical cyclones are of great significance in many engineering fields. This paper presents an investigation of wind characteristics over a coastal urban terrain based on field measurements collected from multiple cup anemometers and ultrasonic anemometers equipped at 13 height levels on a 356-m-high meteorological tower in Shenzhen during severe Typhoon Hato. Several wind quantities, including wind spectrum, gust factor, turbulence intensity and length scale as well as wind profile, are presented and discussed. Specifically, the probability distributions of fluctuating wind speeds are analyzed in connection with the normal distribution and the generalized extreme value distribution. The von Karman spectral model is found to be suitable to depict the energy distributions of three-dimensionally fluctuating winds. Gust factors, turbulence intensity and length scale are determined and discussed. Moreover, this paper presents the wind profiles measured during the typhoon, and a comparative study of the vertical distribution of wind speeds from the field measurements and existing empirical models is performed. The influences of the topography features and wind speeds on the wind profiles were investigated based on the field-measured wind records. In general, the empirical models can provide reasonable predictions for the measured wind speed profiles over a typical coastal urban area during a severe typhoon.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.231-253
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• 1992

A model for the distribution of stars in the disk and the spheroid of our Galaxy is reexamined from an edge-on view of the Galaxy obtained by selecting infrared sources from the IRAS Point Source Catalog. The sources are counted as a function of galactic latitude. longitude and $12{\mu}m$ apparent magnitude. The source counts are reasonably separated into the disk component and the spheroid component contributions and each of the contributions is further interpreted as a convolution of a spatial density distribution and a luminosity function based on the least-square fit method. The spatial density of the disk component has an exponential radial scale length of $h_R{\sim}2.6\;kpc$ and the vertical distribution follows a canonical $sech^2$ law with a scale height $h_z{\sim}240\;pc$. The distribution of the spheroid component can be represented by an oblate spheriod with an axis ratio $k{\sim}0.61$ and a de Vaucouleurs' $r^{1/4}$ law with an effective radius of $R_e{\sim}120\;pc$. The steep density gradient of the spheroid component is consistent with that of late M giants in the central bulge. The luminosity functions of the disk and the spheroid component stars resemble respectively those of the K luminosity function of disk M giants (Garwood and Jones 1986) and the bolometric luminosity function of M giants in bulge fields (Frogel et al, 1990).

• Earthquakes and Structures
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• v.18 no.2
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• pp.163-170
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• 2020

Floor acceleration plays a major role in the seismic design of nonstructural components and equipment supported by structures. Large floor acceleration may cause structural damage to or even collapse of buildings. For precision instruments in high-tech factories, even small floor accelerations can cause considerable damage in this study. Six P-wave parameters, namely the peak measurement of acceleration, peak measurement of velocity, peak measurement of displacement, effective predominant period, integral of squared velocity, and cumulative absolute velocity, were estimated from the first 3 s of a vertical ground acceleration time history. Subsequently, a new predictive algorithm was developed, which utilizes the aforementioned parameters with the floor height and fundamental period of the structure as the new inputs of a support vector regression model. Representative earthquakes, which were recorded by the Structure Strong Earthquake Monitoring System of the Central Weather Bureau in Taiwan from 1992 to 2016, were used to construct the support vector regression model for predicting the peak floor acceleration (PFA) of each floor. The results indicated that the accuracy of the predicted PFA, which was defined as a PFA within a one-level difference from the measured PFA on Taiwan's seismic intensity scale, was 96.96%. The proposed system can be integrated into the existing earthquake early warning system to provide complete protection to life and the economy.

• The Journal of the Acoustical Society of Korea
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• v.21 no.7
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• pp.624-631
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• 2002

The insertion loss of the noise barriers with several top shape is measured in an anechoic room by using a reduced scale model test. The insertion loss differences between a straight vertical barrier having 0.3 m height and several barriers with simple top shaped are compared. The results show that the latter is more effective than the former and absorptive barrier is more effective than the reflective one. Among the barrier types of 'T', 'Y', and '(equation omitted)', type 'Y' is the best one and the rest have similar effect. This result is well agree with Alfredson (PIOC. Inter-Noise 95, p. 381, 1995)'s but contradict to May (J. Sound Vb. 71, p. 73, 1980)'s. Therefore, it is difficult to determine which type is the best. In order to find out this discrepancy, boundary element method is adopted and the result shows one can have different result because each supposed different experimental conditions like height of noise barrier, positions of sound source and receiver, etc.