• Atmosphere
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• v.25 no.2
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• pp.193-203
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• 2015

A large aperture scintillometer (LAS) was deployed with an optical path length of 2.1 km to estimate turbulent sensible heat flux (${\mathcal{Q}}_H$) over a highly heterogeneous urban area. Scintillation measurements were conducted during cold season in November and December 2013, and the daytime data of 14 days were used in the analysis after quality control processes. The LAS-derived ${\mathcal{Q}}_H$ show reasonable temporal variation ranging $20{\sim}160W\;m^{-2}$ in unstable atmospheric conditions, and well compare with the measured net radiation. The LAS footprint analysis suggests that ${\mathcal{Q}}_H$ can be relatively high when the newly built-up urban area has high source contribution of the turbulent flux in the study area ('northwesterly winds'). Sensitivity tests show that the LAS-derived ${\mathcal{Q}}_H$ are highly sensitive to non-dimensional similarity function for temperature structure function parameter, but relatively less sensitive to surface aerodynamic parameters and meteorological variables (temperature and wind speed). A lower Bowen ratio also has a significant influence on the flux estimation. Overall uncertainty of the estimated daytime ${\mathcal{Q}}_H$ is expected within about 20% at an upper limit for the analysis data. It is also found that stable atmospheric conditions can be poorly determined when the scintillometry technique is applied over the highly heterogeneous urban area.

• Structural Engineering and Mechanics
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• v.72 no.6
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• pp.713-722
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• 2019

Micromechanics is a technique for the analysis of composites or heterogeneous materials which focuses on the components of the intended structure. Each one of the components can exhibit isotropic behavior, but the microstructure characteristics of the heterogeneous material result in the anisotropic behavior of the structure. In this research, the general mechanical properties of a 3D anisotropic and heterogeneous Representative Volume Element (RVE), have been determined by applying periodic boundary conditions (PBCs), using the Asymptotic Homogenization Theory (AHT) and strain energy. In order to use the homogenization theory and apply the periodic boundary conditions, the ABAQUS scripting interface (ASI) has been used along with the Python programming language. The results have been compared with those of the Homogeneous Boundary Conditions method, which leads to an overestimation of the effective mechanical properties. According to the results, applying homogenous boundary conditions results in a 33% and 13% increase in the shear moduli G₂₃ and G₁₂, respectively. In polymeric composites, the fibers have linear and brittle behavior, while the resin exhibits a non-linear behavior. Therefore, the nonlinear effects of resin on the mechanical properties of the composite material is studied using a user-defined subroutine in Fortran (USDFLD). The non-linear shear stress-strain behavior of unidirectional composite laminates has been obtained. Results indicate that at arbitrary constant stress as 80 MPa in-plane shear modulus, G₁₂, experienced a 47%, 41% and 31% reduction at the fiber volume fraction of 30%, 50% and 70%, compared to the linear assumption. The results of this study are in good agreement with the analytical and experimental results available in the literature.

• The Journal of Korea Robotics Society
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• v.3 no.3
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• pp.226-236
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• 2008

In this paper, control software architecture is designed to enable a heterogeneous multiple humanoid robot demonstration executing tasks cooperating with each other. In the heterogeneous humanoid robot team, one large humanoid robot and two small humanoid robots are included. For the efficient and reliable information sharing between many software components for humanoid control, sensing and planning, CORBA based software framework is applied. The humanoid tasks are given in terms of finite state diagram based human-robot interface, which is interpreted into the XML based languages defining the details of the humanoid mission. A state transition is triggered based on the event which is described in terms of conditions on the sensor measurements such as robot locations and the external vision system. In the demonstration of the heterogeneous humanoid team, the task of multiple humanoid cleaning the table is given to the humanoid robots and successfully executed based on the given state diagram.

• Nuclear Engineering and Technology
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• v.53 no.11
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• pp.3517-3527
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• 2021

New 80-MW (electric) ultra-long-life sodium cooled fast reactor core having inherent safety characteristics is designed with heterogeneous fuel assemblies comprised of driver and blanket fuel rods. Several options using upper sodium plenum and SSFZ (Special Sodium Flowing Zone) for reducing sodium void reactivity are neutronically analyzed in this core concept in order to improve the inherent safety of the core. The SSFZ allowing the coolant flow from the peripheral fuel assemblies increases the neutron leakage under coolant expansion or voiding. The Monte Carlo calculations were used to design the cores and analyze their physics characteristics with heterogeneous models. The results of the design and analyses show that the final core design option has a small burnup reactivity swing of 618 pcm over ~54 EFPYs cycle length and a very small sodium void worth of ~35pcm at EOC (End of Cycle), which leads to the satisfaction of all the conditions for inherent safety with large margin based on the quasi-static reactivity balance analysis under ATWS (Anticipated Transient Without Scram).

• Korean Chemical Engineering Research
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• v.56 no.2
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• pp.275-280
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• 2018

Methyl ester derived from coconut oil is very interesting to study since it contains free-fatty acid with chemical structure of medium carbon chain ($C_{12}-C_{14}$), so the methyl ester obtained from its part can be a biodiesel and another partially into biokerosene. The use of heterogeneous catalysts in the production of methyl ester requires severe conditions (high pressure and high temperature), while at low temperature and atmospheric conditions, yield of methyl ester is relatively very low. By using microwave irradiation trans-esterification reaction with heterogeneous catalysts, it is expected to be much faster and can give higher yields. Therefore, we studied the production of methyl ester from coconut oil using CaO catalyst assisted by microwave. Our aim was to find a kinetic model of methyl ester production through a transesterification process from coconut oil assisted by microwave using heterogeneous CaO catalyst. The experimental apparatus consisted of a batch reactor placed in a microwave oven equipped with a condenser, stirrer and temperature controllers. Batch process was conducted at atmospheric pressure with a variation of CaO catalyst concentration (0.5; 1.0; 1.5; 2.0, 2.5%) and microwave power (100, 264 and 400 W). In general, the production process of methyl esters by heterogeneous catalyst will obtain three layers, wherein the first layer is the product of methyl ester, the second layer is glycerol and the third layer is the catalyst. The experimental results show that the yield of methyl ester increases along with the increase of microwave power, catalyst concentration and reaction time. Kinetic model of methyl ester production can be represented by the following equation: $-r_{TG}=1.7{\cdot}10^6{_e}{\frac{-43.86}{RT}}C_{TG}$.

• Bulletin of the Korean Chemical Society
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• v.23 no.11
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• pp.1683-1684
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• 2002

• The Journal of Information Technology
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• v.8 no.3
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• pp.131-142
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• 2005

The principles on which the Internet was designed and has evolved were first laid out in an explicit way 20 years age. The basic principle is that in layered communications network such as the Internet, functions should always be implemented at the end systems whenever the option exists. This applies to all functions that can be implemented either in the network or at the end systems. End-to-end arguments have recently been reexamined as the Internet and its uses have evolved, and a new set of requirements has begun to emerge. In addition to these, it add a new, and perhaps more important, requirement to this list in the case of heterogeneous networks: the proliferation of unpredictable wireless networks. Wireless networks must cope with dynamic link conditions not present in wired infrastructures, which place a heavy burden on quality of service management solutions. Managing QoS in the face of constantly changing operating conditions demands dynamic management approaches that span multiple layers in the protocol stack. Such as cross-layer design approaches have recently received attention in the context of cellular and mobile special networks. This article introduce the notion of network predictability and describe its relationship to achievable QoS. This relationship is used to propose a framework for cross layer design that can be used to guide development efforts and direct investment decisions for future networks.

• Journal of Korean Society on Water Environment
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• v.35 no.2
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• pp.115-122
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• 2019

The objective of this study was to investigate the sonophysical and sonochemical effects induced by acoustic cavitation in heterogeneous systemin a 28 kHz double-bath reactor using calorimetry, the aluminiumfoil erosion test, and the luminol test. With no glass beads, calorimetric power in the inner vessel increased as much as the outer sonoreactor lost and total calorimetric power was maintained for various liquid height conditions (0.5 ~ 7 cm) in the vessel. Higher calorimetric energy was obtained at higher liquid height conditions. Similar results were obtained when glass beads were placed with various beads heights (0.5 ~ 2.0 cm) and relatively high calorimetric energy was obtained in spite of large attenuation in the glass beads layer. An aluminium foil placed between the bottom of the inner vessel and the glass beads layer was damaged, indicating significant sonophysical effects. Much less damage was detected when the foil was placed above the beads layer due to large attenuation of ultrasound. Sonochemical effects, visualized by sonochemiluminescence (SCL), also decreased significantly when the beads were placed in the vessel. It was established that the optimization of the liquid height above the solid-material layer could enhance the sonophysical and sonochemical effects in the double-bath sonoreactors.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06a
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• pp.350-351
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• 2011

In this paper we study the impact of heterogeneous round trip times on multipath TCP (MPTCP) performance via analysis the fluid model and simulation. Using parameter 'a' in MPTCP can alleviate poor performance due to divergent RTTs between paths. Moreover, divergent RTIs in MPTCP can affect response to changes in the network conditions.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1388-1390
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• 2009