508 research outputs found
Subcooled water quenching on a super-hydrophilic surface under atmospheric pressure
No full textThe goal of this work is (i) to evaluate the cooling rate on a super-hydrophilic surface as a function of the subcooled degree Delta T-sub of the liquid coolant, (ii) to analyze the contact heat transfer q ''(c) of the liquid-solid contact, and (iii) to investigate the mechanism of microbubble emission boiling (MEB). We fabricated a super-hydrophilic surface by anodic oxidation of a zirconium vertical rod, so called completely wettable surface (CWS), which had surface microstructures with super-hydrophilicity. The CWS results in a decrease of the cooling time t(cool) as compared with the Bare Zirconium surface (BZS) results under small Delta T-sub (t(cool) similar to 50% decrease for Delta T-sub = 0, 15, and 40 K, respectively). However, its surface effect is limited in the case of large Delta T-sub (t(cool) similar to within 5% for Delta T-sub = 60 and 75 K). The fast quench on the CWS under Delta T-sub, explained by the increase in minimum film-boiling temperature T-MFB and rewetting velocity U, is due to the liquid-solid contact. We evaluate the contact area A(c) and volumetric absorption rate of the liquid dV/dt by conducting liquid absorption experiments. The increase in A(c) and dV/dt contribute to an increase in q"(c), by forming the liquid film at the liquid-solid contact spot. The orders of the time scale between capillary-wicking and liquid-solid contact are comparable. Destabilization of the large vapor bubble is caused by an increase in q"(c), which is a major reason for MEB generation, and this mechanism enables the q" to be significantly high on the CWS under subcooled quenching. (C) 2017 Elsevier Ltd. All rights reserved.116sciescopu
High performance binder-free Fe-Ni hydroxides on nickel foam prepared in piranha solution for the oxygen evolution reaction
No full textNickel foam (NF) can be directly utilized as an electrochemical electrode because of its conductive, rigid and porous structure. Herein, a novel robust binder-free Fe-Ni hydroxide-loaded NF electrode is prepared by simple corrosion of NF in a home-made piranha solution with an Fe3+ precursor. The roughened NF surface observed after the sample treatment indicates the formation of active species associated with amorphous Fe-hydroxide and/or FeNi-hydroxide particles. The piranha solution-corroded NF electrode generates more hydroxide groups compared to the water-corroded NF electrode, and exhibits remarkable electrochemical oxygen evolution reaction activity in alkaline medium with a low overpotential of 245 mV at 10 mA cm(-2). It also maintains low working potential below 267 mV at 10 mA cm(-2) over 500 h operation without any sign of degradation, indicating excellent long-term stability, which can be attributed to the robust binder-free electrode and the cooperative synergistic interaction between Fe-hydroxides and Ni-hydroxides in the FeNi hybrid composite of individually incompetent OER components, generated over the NF. The role of Fe doped in Ni(OH)(2) is theoretically studied by DFT calculations, and it is found that the adsorption free energies of OH* and OOH* are significantly reduced by the addition of Fe into Ni(OH)(2), accelerating the OER compared to bare Ni(OH)(2). Furthermore, when the active electrode is equipped with a solar cell, a high current density of 23-24 mA cm(-2) is observed for 10 h under AM 1.5G 1 sun irradiation, suggesting high possibility for the production of green hydrogen from renewable solar energy.1
Efficient production of 3,6-anhydro-L-galactose from red algal neoagarobiose by whole-cell biocatalysis of recombinant Corynebacterium glutamicum
No full text3,6-Anhydro-L-galactose (AHG) is a potent food and cosmetic ingredient affecting the anticariogenic and antimelanogenic activities of red algal polysaccharides. For efficient AHG production instead of enzymatic process, whole-cell biocatalyst of recombinant Corynebacterium glutamicum CG-H4-NABH with an alpha-neoagarobiose hydrolase (NABHase) dividing red algal neoagarobiose (NAB) to AHG and D-galactose was developed. To prepare high concentration of the biocatalyst, fed-batch cultivation of CG-H4-NABH yielded 71.8 g/L dry cell mass and 58.9 U/mL NABHase activity. For efficient transport and hydrolysis of NAB and elevating AHG production, the CG-H4-NABH cells permeabilized by toluene showed 37 times higher activity than the untreated cells. After seven cycles of repeated whole-cell reaction, the permeabilized-immobilized cells exhibited a 3.6 times higher NAB-hydrolyzing rate and a 1.6-fold higher cumulative AHG concentration than the permeabilized free-cells. Conclusively, the whole-cell biocatalysis using C. glutamicum could serve as an efficient and alternative process for production of monosaccharides by disaccharide hydrolysis.
Organic Transistor-Based Chemical Sensors for Wearable Bioelectronics
No full textCONSPECTUS: Bioelectronics for healthcare that monitor the health information on users in real time have stepped into the limelight as crucial electronic devices for the future due to the increased demand for "point-of-care" testing, which is defined as medical diagnostic testing at the time and place of patient care. In contrast to traditional diagnostic testing, which is generally conducted at medical institutions with diagnostic instruments and requires a long time for specimen analysis, point-of-care testing can be accomplished personally at the bedside, and health information on users can be monitored in real time. Advances in materials science and device technology have enabled next-generation electronics, including flexible, stretchable, and biocompatible electronic devices, bringing the commercialization of personalized healthcare devices increasingly within reach, e.g., wearable bioelectronics attached to the body that monitor the health information on users in real time. Additionally, the monitoring of harmful factors in the environment surrounding the user, such as air pollutants, chemicals, and ultraviolet light, is also important for health maintenance because such factors can have short- and long-term detrimental effects on the human body. The precise detection of chemical species from both the human body and the surrounding environment is crucial for personal health care because of the abundant information that such factors can provide when determining a person's health condition. In this respect, sensor applications based on an organic-transistor platform have various advantages, including signal amplification, molecular design capability, low cost, and mechanical robustness (e.g., flexibility and stretchability). This Account covers recent progress in organic transistor-based chemical sensors that detect various chemical species in the human body or the surrounding environment, which will be the core elements of wearable electronic devices. There has been considerable effort to develop high-performance chemical sensors based on organic-transistor platforms through material design and device engineering. Various experimental approaches have been adopted to develop chemical sensors with high sensitivity, selectivity, and stability, including the synthesis of new materials, structural engineering, surface functionalization, and device engineering. In this Account, we first provide a brief introduction to the operating principles of transistor-based chemical sensors. Then we summarize the progress in the fabrication of transistor-based chemical sensors that detect chemical species from the human body (e.g., molecules in sweat, saliva, urine, tears, etc.). We then highlight examples of chemical sensors for detecting harmful chemicals in the environment surrounding the user (e.g., nitrogen oxides, sulfur dioxide, volatile organic compounds, liquid-phase organic solvents, and heavy metal ions). Finally, we conclude this Account with a perspective on the wearable bioelectronics, especially focusing on organic electronic materials and devices.11sciescopu
Minimum heat flux and minimum film-boiling temperature on a completely wettable surface: Effect of the Bond number
No full textWe investigated the effect of Bond number of sphere Bo(s) and surface super-hydrophilicity at minimum film-boiling temperature T-MFB and minimum heat flux q ''(min) using quenching experiment at atmospheric pressure and the saturation temperature of water. In particular, we focused on the vapor-releasing dynamics in film boiling and evaluated the main parameters such as vapor-bubble releasing frequency f(b) and vapor-bubble departure diameter D-b. We selected two sizes of quench sphere (sphere diameter D-s = 15 mm and 25 mm) based on critical Bond number Bo(C) to evaluate the vapor-releasing dynamics depending on the Bo(s). The super-hydrophilic surface was prepared by the anodic oxidation on zirconium (Zr-702) sphere. High speed visualization and inverse heat transfer calculation facilitate a qualitative and quantitative analysis of film boiling heat transfer. The surface super-hydrophilicity of the quench sphere increases T-MFB and q ''(min): 12% and 366% increase for D-s = 15 mm and 20% and 305% increase for D-s = 25 mm, respectively. D-b strongly depends on D-s and exhibits a relatively weak dependency to the surface super-hydrophilicity. f(b) is affected by the D-s and the surface super-hydrophilicity. The increase in T-MFB is explained by the liquid-solid contact in film boiling. The D25-CWS exhibits the large area fraction of liquid-solid contact versus total heat transfer surface compared to the D15-CWS. The increase in q ''(min), is related to minimum frequency of vapor-bubble releasing to sustain the stable liquid-vapor interface f(b,min) because the large f(b,min) indicates the fast destabilization of the liquid-vapor interface in film boiling during quenching. (C) 2017 Elsevier Ltd. All rights reserved.11Nsciescopu
The role of surface energy in heterogeneous bubble growth on ideal surface
No full textAn analytical model for heterogeneous bubble growth during nucleate boiling with variable wettability on an ideal smooth surface has been developed. We analyzed the growth of bubbles in terms of the motion of the triple line, and three stages of bubble growth were identified based on the triple line motion. The transition points between these stages were modelled using a free-energy analysis and force-balance of the bubble growth system. We considered two bubble-growth pathways: one with a constant angle between the liquid-vapor interface and the surface, and one with a constant base (i.e., constant triple line), and the two paths are linked during a bubble growth. It is hypothesized that the transition from a regime to another is linked to the less expansive energy path. To confirm this, a bubble growth was experimentally observed on various different wettability surfaces, and the results of these experiments were compared with the analytical model. In general, a larger contact angle (i.e., a more hydrophobic surface)resulted in bubble growth with a larger triple line, and hence a larger base diameter and a larger departing bubble diameter.113sciescopu
Effect of Dual Coplanar Electrodes on Mercury-Free Flat Fluorescent Lamps for Liquid Crystal Display
No full textThe effects of dual coplanar electrodes on a Hg-free flat fluorescent lamp were studied. For a dual coplanar lamp, brightness and efficacy were improved by 80% compared to a conventional coplanar lamp. The improvement is regarded as the result of reduced diffusion loss and the effective usage of the discharge volume in the dual coplanar lamps. An efficacy of 35.9 lm/w (14900 cd/m(2)) was achieved for 250 torr of a Xe(30%)/Ne(70%) gas mixture, by a 20-kHz ac pulse driving
Automatic extension of Gene Ontology with flexible identification of candidate terms
No full textThis is a pre-copy-editing, author-produced PDF of an article accepted for publication in Bioinformatics following peer review. The definitive publisher-authenticated version is available online at: http://bioinformatics.oxfordjournals.org/cgi/reprint/22/6/665Motivation: Gene Ontology (GO) has been manually developed to provide a controlled vocabulary for gene product attributes. It continues to evolve with new concepts that are compiled mostly from existing concepts in a compositional way. If we consider the relatively slow growth rate of GO in the face of the fast accumulation of the biological data, it is much desirable to provide an automatic means for predicting new concepts from the existing ones. Results: We present a novel method that predicts more detailed concepts by utilizing syntactic relations among the existing concepts. We propose a validation measure for the automatically predicted concepts by matching the concepts to biomedical articles. We also suggest how to find a suitable direction for the extension of a constantly growing ontology such as GO.This work was supported by MOST/KOSEF through AITrc
Induced liquid-solid contact via micro/nano multiscale texture on a surface and its effect on the Leidenfrost temperature
No full textA significant increase in the Leidenfrost temperature (LFT) was observed on a micro/nano rnultiscale textured surface (MTS) compared with a polished surface (PS) and a micro rough surface (MRS). MTS was fabricated by anodic oxidation and has nano-scaled needles with micro roughness. It showed improved surface wetting characteristics (0 contact angle with liquid spreading). On the other hand, MRS was fabricated by mechanical polishing and it only has micro roughness. LFT on MTS and MRS increased by approximately 150 degrees C and 30 degrees C, respectively, compared with one for PS. The textures on each surface influenced the water droplet dynamics. The relationship between LFT and the dynamics of water droplet were studied by high-speed photography. The key phenomenon determining LFT was the rebound process of the droplet during a few milliseconds. On MRS and MTS, the rebound phenomenon of the droplet was disturbed by the surface-texture-induced liquid-solid contact even when the surface was initially at a high temperature over 300 degrees C. The precursor wetting front, observed only on MTS and the capillary wicking phenomenon are likely the responsible mechanisms that significantly increased LFT on MTS. (C) 2017 Elsevier Inc. All rights reserved.1110sciescopu
Pre-Oxidation Effect of a Zirconium-silicide Sputtered Surface on Boiling Performance and Oxidation Resistance
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