Electrospun yttria-stabilized zirconia nanofibers for low-temperature solid oxide fuel cells

Koo, J.Y.,Lim, Y.,Kim, Y.B.,Byun, D.,Lee, W. Pergamon Press ; Elsevier Science Ltd 2017 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.42 No.24

<P>We report a 3.5-fold improvement in the performance of solid oxide fuel cells (SOFCs) operating at 450 degrees C with the introduction of electrospun yttria-stabilized zirconia (YSZ) nanofiber interlayers between the electrolyte and cathode. YSZ nanofibers with diameters of 150-200 nm were uniformly deposited with various thicknesses on a single-crystal YSZ substrate. Electrochemical impedance spectroscopy analyses revealed a drastically reduced polarization resistance, which was mainly attributed to the high specific surface area and high porosity of the YSZ nanofiber interlayers. Our results demonstrate the possibility of using YSZ nanofibers for the development of high-performance SOFCs at low temperature. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.</P>

Sustainable harvesting of aqueous phase fatty acids by expanded graphite and isopropyl alcohol

Do, Q.C.,Kim, M.S.,Kim, D.,Ko, S.O.,Kang, S. Pergamon Press ; Elsevier Science Ltd 2016 International journal of hydrogen energy Vol.41 No.46

<P>Fatty acids (FA) from organic wastes are environmentally friendly raw materials with high economic value ranging from fuels to oleo-chemicals for growing diversity of products. In this study, expanded graphite (EG) and isopropyl alcohol have been used to adsorb and concentrate the low content of FA in aqueous solution to replace the existing solid-phase extraction methods. The results showed that the maximum adsorption capacity of EG was more than 8.2 g-FA/g due to the inter-latticed structure of graphene sheets, and subsequent coalescence of FA droplets. The extraction efficiency of isopropyl alcohol was always higher than those of dichloromethane and ethanol for the recovery of absorbed FA due to the lower surface tension and higher miscibility with water. After 5 times of recycle, although the specific FA adsorption was decreased 42% of raw EG, extraction efficiencies by isopropyl alcohol were not changed. In conclusion, our study suggested that the EG and isopropyl alcohol could achieve the efficient and environmentally friendly harvesting of low concentration of FA in aqueous solutions during the biological conversion of organic matters in food waste. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.</P>

Weaving nanofibers by altering counter-electrode electrostatic signals

An, S.,Lee, M.W.,Jo, H.S.,Al-Deyab, S.S.,Yoon, S.S. Pergamon Press ; Elsevier Science Ltd 2016 Journal of aerosol science Vol.95 No.-

<P>Orderly aligned polymer nanofibers can facilitate the technological advancement of applications such as gas sensors, functional fabrics, biological and medical engineering, water and air purification filters, fuel cell membranes, ultra-speed fiber optics, and electronics. The electrospun nanofibers were actively controlled by rapidly altering the signals, and this enabled their orthogonal deposition. The tunable alternating signals imposed on the counter electrodes facilitate the fiber-on-demand (FOD) method as a potential intricate patterning tool. The method is simple and requires no post-processing. This proof-of concept can be extended in order to design more complex patterns through the intelligent design of the counter electrodes. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Learning to segment and unfold polyhedral mesh from failures

Xi, Z.,Kim, Y.h.,Kim, Y.J.,Lien, J.M. Pergamon Press ; Elsevier Science Ltd 2016 Computers & graphics Vol.58 No.-

<P>Folding planar sheets to make 3D shapes from is an ancient practice with many new applications, ranging from personal fabrication of customized items to design of surgical instruments for minimally invasive surgery in self-folding machines. Given a polyhedral mesh, unfolding is an operation of cutting and flattening the mesh. The flattened polyhedral nets are then cut out of planar materials and folded back to 3D. Unfolding a polyhedral mesh into planar nets usually require segmentation. Either used as a preprocessing step to simplify the mesh and provide semantics or as the result of unfolding to avoid overlapping, the segmentation and the unfolding operations are decoupled. Consequently, segmented components may not be unfoldable and unfolded nets usually provide no semantic meaning and make folding difficult. In this paper, we propose a strategy that tightly couples unfolding and segmentation. We show that the proposed method produces unfoldable segmentation that resembles carefully designed paper craft. The key idea that enables this capability is an algorithm that learns from failed unfoldings. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Analysis of the timing of phase changes in the chlorophyll concentration in the East/Japan Sea

Jo, Y.H.,Kim, H.C.,Son, S.,Kim, D. Pergamon Press ; Elsevier Science Ltd 2016 Continental shelf research Vol.127 No.-

<P>Geographically heterogeneous linear and non-linear chlorophyll-a (CHL) trends in the East Sea/Japan Sea (EJS) region were analyzed based on monthly mean Moderate Resolution Imaging Spectroradiometer (MODIS) CHL data from January 2003 to December 2012. The non-linear trends were derived from the residuals of decomposed CHL time series using ensemble empirical mode decomposition (EEMD). To understand the general spatial and temporal variability of the non-linear CHL trends, a complex empirical orthogonal function (CEOF) was employed. The first two CEOF modes indicate that an upward CHL trend occurred in 2007 with 95.6% variance, whereas a downward CHL trend occurred in 2009 with 4.1% variance. Furthermore, the specific timing of the phase changes in CHL was calculated based on upward or downward non-linear trends of CHL for six major regions of interests. To examine the dominant forces in phase changes in CHL, the Multivariate El Nino-Southern Oscillation (ENSO) Index (MEI) was used. We determined that the local turning patterns of CHL over the last ten years were closely related to changes in ENSO events, which were also associated with changes in the total amount of fish catches off the east coast of the Korean Peninsula. These results also suggest that the short-term total amount of fish catches may be predictable based on the remotely sensed non-linear CHL observations. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Brief review of removal effect of hydrogen-plasma arc melting on refining of pure titanium and titanium alloys

Oh, J.M.,Roh, K.M.,Lim, J.W. Pergamon Press ; Elsevier Science Ltd 2016 International journal of hydrogen energy Vol.41 No.48

<P>In this study, the effect of hydrogen-plasma arc melting (HPAM) on the removal of metallic and gaseous impurities from pure titanium and titanium alloys is briefly reviewed according to the previous results and a newly added experiment. The highest removal degree (RD) of metallic impurities from pure titanium by HPAM with an Ar-20 vol.% of H-2 gas is 84.8%. In the titanium alloys, the RD values of the metallic impurities of the Ti-Ni, Ti-Mo, Ti-Al, and Ti-6A1-4V alloys regarding HPAM with an Ar-20 vol.% of H-2 gas are 82.6%, 86.2%, 49.1%, and 76.6%, respectively. The total amount of gaseous impurities such as O, N, C, and H was decreased to 962 ppm from 2697 ppm, whereby a high RD value of 64.6% is shown despite the strong affinity of titanium regarding gaseous elements. It is suggested that HPAM exerts a dramatic effect on the removal of metallic impurities from pure titanium and titanium alloys, and it is appropriate for the refining of titanium alloys whereby a significant weight loss needs to be avoided. Thereby, HPAM process can be applied to industrial refining of commercial titanium and titanium alloys. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.</P>

Porous carbon based on polyvinylidene fluoride: Enhancement of CO₂ adsorption by physical activation

Hong, S.M.,Choi, S.W.,Kim, S.H.,Lee, K.B. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.99 No.-

<P>Global warming has become a crucial issue and various efforts have been made to mitigate the emission of CO2, the most dominant greenhouse gas. Adsorption is considered a promising technology for CO2 capture, and carbon materials are good candidates for CO2 adsorption. In this study, highly porous carbons were prepared from polyvinylidene fluoride by single-step physical activation under CO2 flow at temperatures of 700-950 degrees C. The effect of activation temperature on the characteristics and CO2 adsorption properties of the prepared porous carbons was studied. Additionally, the dependence of CO2 adsorption capacity on various textural properties was investigated to identify the most important factor that determines CO2 adsorption. Both surface area and pore volume increased proportionally with activation temperature because of the newly produced pores and enlarged pore size within the carbon. Additionally, CO2 adsorption is highly dependent on the volume of pores that are below 0.70 nm in size. Among the samples tested, the porous carbon prepared at 800 degrees C exhibited maximum CO2 adsorption capacities of 6.05 and 3.84 mol kg(-1) at 0 and 25 degrees C, respectively, besides showing good CO2/N-2 selectivity, excellent recyclability, easy regeneration, and rapid adsorption-desorption kinetics. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Concentration of culturable bioaerosols during winter

Uk Lee, B.,Lee, G.,Joon Heo, K. Pergamon Press ; Elsevier Science Ltd 2016 Journal of aerosol science Vol.94 No.-

<P>Concentrations of fungal and bacterial bioaerosols were measured during winter. Environmental parameters such as temperature, relative humidity, ultraviolet irradiation intensity, and the amount of snowfall precipitation were also measured with bioaerosol concentrations. Experimental results show that significant amounts of culturable fungal bioaerosols exist in the air during winter. The amount of fungal bioaerosols present in winter is comparable with that recorded in summer. In contrast, few culturable bacterial bioaerosols were detected in the air during winter. This quantitative result can be used to explain patterns of diseases that occur in winter. In addition, the effects of environmental factors on bioaerosols in winter were analyzed. (C) 2015 Elsevier Ltd. All rights reserved.</P>

Optimized double sweep Schwarz method by complete radiation boundary conditions

Kim, S.,Zhang, H. Pergamon Press ; Elsevier Science Ltd 2016 COMPUTERS & MATHEMATICS WITH APPLICATIONS - Vol.72 No.6

<P>We present an optimized double sweep nonoverlapping Schwarz method for solving the Helmholtz equation in semi-infinite waveguides. The domain is decomposed into nonover-lapped layered subdomains along the axis of the waveguide and local wave propagation problems equipped with complete radiation conditions for high-order absorbing boundary conditions are solved forward and backward sequentially. For communication between subdomains, Neumann data of local solutions in one domain are transferred to the neighboring subdomain in the forward direction and Dirichlet data are exploited in the backward direction. The complete radiation boundary conditions enable us to not only minimize reflection coefficients for most important modes in an optimal way but also find Neumann data without introducing errors that would be produced if finite difference formulas were used for computing Neumann data. The convergence of the double sweep Schwarz method is proved and numerical experiments using it as a preconditioner are presented to confirm the convergence theory. (C) 2016 Elsevier Ltd. All rights reserved.</P>

An unambiguous correlation function for generic sine-phased binary offset carrier signal tracking

Chae, K.,Lee, S.R.,Liu, H.,Yoon, S. Pergamon Press ; Elsevier Science Ltd 2016 Computers & electrical engineering Vol.49 No.-

<P>This paper proposes an unambiguous correlation function applicable to generic sine-phased binary offset carrier (BOC) signal tracking. In the proposed scheme, first, we view the BOC sub-carrier pulse as a sum of multiple rectangular pulses. Then, we obtain partial correlation functions by correlating the multiple rectangular pulses with the received signal, and subsequently, construct two symmetric correlation functions by combining the partial correlation functions in a specialized way. Finally, we generate an unambiguous correlation function by combining the two symmetric correlation functions. The proposed correlation function has a sharper main-peak, and consequently, provides a better tracking performance than those of the conventional correlation functions in terms of the tracking error standard deviation (TESD). (C) 2015 Elsevier Ltd. All rights reserved.</P>