• International Journal of High-Rise Buildings
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• v.6 no.4
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• pp.327-332
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• 2017

This paper discusses several topics associated with the densification caused by supertall buildings and their impact on city systems. The paper covers five key areas where a supertall tower creates a concentration of needs and effects. First, the paper comments on population shifts towards the city and how they affect carbon footprint, utilities infrastructure and transport. The effect of single- and mixed-use towers is discussed in the context of population density. The second section brings the issues of transit, accessibility and master planning into focus. The use and criticality of public transport, cycling and walking is described. Servicing and deliveries using freight consolidation and shared systems is also discussed along with their contribution to the culture of sustainable travel. In the third section the paper reflects on supertall buildings' below-ground utilities and drainage provision, particularly the challenges faced in established city infrastructures. The utilities issues associated with supertall concentration (in land-use terms) compared to equivalent low-rise distribution is also commented on in the context of surface water runoff. In the fourth section, the topic of supertall sustainability is discussed and how city systems need to respond to create desirable and affordable space for occupiers. The changing need for vertical communities, 'stacked neighbourhoods' and the notion of a micro-city is described. Finally, the paper considers the energy consumption and resilience of supertall buildings in the context of basic geometry, façade design, climate and mixed-use benefits as they impact city systems.

• Korean Journal of Materials Research
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• v.31 no.5
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• pp.264-271
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• 2021

Porous carbons have been widely used as electrode material for supercapacitors. However, commercial porous carbons, such as activated carbons, have low electrochemical performance. Nitrogen-doping is one of the most promising strategies to improve electrochemical performance of porous carbons. In this study, nitrogen self-doped porous carbon (NPC) is prepared from melamine foam by carbonization to improve the supercapacitive performance. The prepared NPC is characterized in terms of the chemical structures and elements, morphology, pore structures, and electrochemical performance. The results of the N₂ physisorption measurement, X-ray diffraction, and Raman analyses reveal that the prepared NPC has bimodal pore structures and pseudo-graphite structures with nitrogen functionality. The NPC-based electrode exhibits a gravimetric capacitance of 153 F g^-1 at 1 A g^-1, a rate capability of 73.2 % at 10 A g^-1, and an outstanding cycling ability of 97.85 % after 10,000 cycles at 10 A g^-1. Thus, the NPC prepared in this study can be applied as electrode material for high-performance supercapacitors.

• Environmental and Resource Economics Review
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• v.19 no.3
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• pp.597-632
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• 2010

There is general agreement that global warming is occurring and that the main contributor to this probably is the buildup of green house gasses, GHG, in the atmosphere. Two main contributors are the utilization of fossil fuels and the deforestation of many regions of the world. The burning of fossil fuels increases atmospheric carbon while the burning of fuel-wood reducing fossil fuel consumption along with its forest source maintain an atmospheric carbon level. The standing timber in the forests is a carbon sink, as are wood buildings and structures, and fossil fuel in the ground. This paper is designed to examine a number of current issues related to mitigating the global warming problem through forestry. For this purpose, we develop a modeling approach by integrating timber market, fossil fuel market and carbon cycling model. We use discrete time optimal control theory to identify optimal time paths, the laws of motion, and stationary stats solutions of endogenous variables in the model. On the basis of these results, we identify the optimal amounts of subsidies to be provided or taxes to be imposed by the regulatory agency to mitigate atmospheric carbon accumulation. We also present a numerical example to help illustrate the characteristics of variables in the model when the social cost for atmospheric carbon incrementally shifts upward. A surprising result is that the social cost function for atmospheric carbon has a very smaller impact on the optimal rotation period than previous literature suggested.

• Journal of Korean Society of Forest Science
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• v.113 no.1
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• pp.97-106
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• 2024

Evaluating carbon (C) and nitrogen (N) inputs from litterfall is important for soil nutrient management to enhance forest productivity and to understand the mechanisms of nutrient cycling in forest ecosystems. This study was conducted to compare C and N inputs from litterfall components of Cryptomeria japonica D. Don an d Chamaecyparis obtusa Endlicher planted in adjacent sites in the Jinju Research and Experimental Forests in Gyeongsangnam-do, South Korea. Litterfall into litter traps was collected at three-month intervals between December 2020 and December 2021, and the C and N concentrations of the litterfall components were measured. Litterfall amounts were not significantly different between the plantations, except for reproductive litterfall components. Litterfall accumulation peaked between December and March. The litterfall C concentration in the needle and seed litterfall was significantly higher for C. obtusa than for C. japonica. By contrast, the C concentrations in needle and flower litterfall differed seasonally. The mean N concentration of needle litterfall was significantly higher in C. japonica (0.96%) and C. obtusa collected between June and September (1.01%) than in the other seasons (C. japonica: 0.43%; C. obtusa: 0.53%). Carbon and N inputs in both plantations were highest in needle litterfall collected from December to March and lowest in needle litterfall collected from June to September. Annual C input by litterfall was similar between the plantations (C. japonica: 3,054 kg C ha^-1 yr^-1; C. obtusa: 3,129 kg C ha^-1 yr^-1), whereas total N input was higher for C. japonica (46.93 kg N ha^-1 yr^-1) than for C. obtusa (25.17 kg N ha^-1 yr^-1). The higher N input in the C. japonica plantation than in the C. obtusa plantation was associated with the input of reproductive components. These results could be applied to improve stand-scale models of C and N cycling by litterfall components in C. japonica an d C. obtusa plantations.

• Analytical Science and Technology
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• v.11 no.5
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• pp.347-352
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• 1998

A study was carried out on the elelctrochemical characteristics of chemically modified electrodes (CMEs) by cyclic voltammetry. Fabrication of CMEs was made by coating with mixed valence (mv) inorganic-metal polymeric films on the glassy carbon electrode surface by potential cycling. Anodic oxidation behavior of methanol and L-ascorbic acid was studied by using CMEs working electrode. Deposition of films such as mv ruthenium oxo/ruthenium cyanide film (mv Ru-O/CN-Ru), mv ruthenium oxo/ferrocyanide film (mv Ru-O/$Fe(CN)_6$), and mv ruthenium oxo/ruthenium cyanide/Rhodium film (mv Ru-O/CN-Ru/Rh) was obtained to coat by scan rate of 50 mV/sec within the specified potential range (-0.5V ~ +1.2V). Film thickness was controlled by the repeat of the potential cycling. Anodic oxidation behavior of methanol was as follow. Calibration graph by using mv Ru-O/CN-Ru film showed linearly from 10 mM to 80 mM MeOH with slope factor of $-7.552{\mu}A/cm^2$. Although slope factor by using mv Ru-O/$Fe(CN)_6$ film was $-5.13{\mu}A/cm^2$, yet linear range of calibration graph could be extended from 10 mM to 100 mM MeOH. Anodic oxidation behavior of L-ascorbic acid was studied by mv Ru-O/CN-Ru film on the glassy carbon electrode and the glassy carbon electrode with Rh film, Glassy carbon electrode modified with Ru polymeric film was showed better sensitivity than the Rh-glassy carbon modified electrode (mv Ru-O/CN-Ru/Rh). Calibration graph was linear from 0.1 mM to 5 mM L-ascorbic acid by using glassy carbon electrode modified with Ru polymeric film. Solpe factor and relative coefficient are $-84.78{\mu}A/mM$ and 0.998, respectively.

• Journal of the Korean Institute of Gas
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• v.17 no.6
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• pp.46-51
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• 2013

Composite cylinder is used by hydrogen fuel cell vehicles and natural gas vehicles because of high specific modulus, specific strength and fatigue resistance. composite cylinder has a seamless integrated liner and it is fully overwrapped with structural fibers of high strength carbon fibers in an epoxy matrix. In this study, filament winding pattern and autofrettage pressure design technique are presented considering structural weakness of knuckle and compressive residual stress. Presented methodology is verified by pressure cycling test of composite cylinders.

• Journal of Ecology and Environment
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• v.34 no.4
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• pp.333-345
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• 2011

Aquatic macrophytes, often also called hydrophytes, are key components of aquatic and wetland ecosystems. This review is to briefly summarizes various macrophyte classifications, and covers numerous aspects of macrophytes' role in wetland ecosystems, namely in nutrient cycling. The most widely accepted macrophyte classification differentiates between freely floating macrophytes and those attached to the substrate, with the attached, or rooted macrophytes further divided into three categories: floating-leaved, submerged and emergent. Biogeochemical processes in the water column and sediments are to a large extent influenced by the type of macrophytes. Macrophytes vary in their biomass production, capability to recycle nutrients, and impacts on the rhizosphere by release of oxygen and organic carbon, as well as their capability to serve as a conduit for methane. With increasing eutrophication, the species diversity of wetland macrophytes generally declines, and the speciose communities are being replaced by monoculture-forming strong competitors. A similar situation often happens with invasive species. The roles of macrophytes and sediment microorganisms in wetland ecosystems are closely connected and should be studied simultaneously rather than in isolation.

• Journal of the Korean Applied Science and Technology
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• v.28 no.3
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• pp.329-334
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• 2011

The electrochemical performances of an asymmetric hybrid capacitor were investigated using $LiFePO_4$ as the positive electrode and active carbon fibers(ACF) as the negative electrode. The electrochemical behaviors of a nonaqueous hybrid capacitor were characterized by constant current charge/discharge test. The specific capacitance using $LiFePO_4$/ACF electrode turned out to be $0.87F/cm^2$ and the unit cell showed excellent cycling performance. This hybrid capacitor was able to deliver a specific energy as high as 178 Wh/kg at a specific power of 1,068 W/kg.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.05b
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• pp.5-9
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• 2005

$LiFePO_4$ is a potential candidate for the cathode material of the lithium polymer batteries. $LiFePO_4$ cathode active materials were synthesized by coating on the $LiFePO_4$ was tried using $TiO_2$ and corbon in oreder to increase cyclic performance and electronic conductivity. Highly dispersed on the particles enhances the electronic conductivity and increases the capacity. For lithium polymer battery applications, $LiFePO_4$/SPE/Li and $LiFePO_4$-$TiO_2$/SPE/Li 'cells were characterized electrochemically by cyclic volatammetry and charge/discharge cycling. The $LiFePO_4$-carbon-$TiO_2$ cathode in PVDF-PC-EC-$LiCIO_4$ electrolyte showed high capacity at high current density.

• Corrosion Science and Technology
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• v.4 no.1
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• pp.23-28
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• 2005

Several plasma-sprayed ceramic coatings with two- and three-layers were characterized and tested for the application of cooling tube coatings of oxygen convert gas recovery system (OG cooling system) in the steel making plant. Thermal cycling tests using a torch heating with compressed air cooling were carried out and characterized before and after the tests. The effects of metallic bond coat as well as ceramic top coat were also studied. Possible failure mechanisms with low carbon steel substrate were assessed in term of microstructure, porosity, bond strength, thermal expansion coefficient, and the phase transformation. Finally, the results of field tests at the OG cooling system are presented and discussed their microstructural degradation. Test results have shown that three-layered coatings perform better than two-layered coatings.