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- 저자 : Ashoke Das (검색결과 33 건)
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Das, Ashok Kumar,Kim, Nam Hoon,Pradhan, Debabrata,Hui, David,Lee, Joong Hee Elsevier 2018 Composites Part B, Engineering Vol.144 No.-
<P><B>Abstract</B></P> <P>Synthesis of palladium (Pd) nanostructures with unique shapes is crucial due to their shape dependent electrochemical activity. In the current investigation, we demonstrate the electrochemical synthesis of rod-like Pd nanostructures with the assistance of nicotinamide adenine dinucleotide (NAD<SUP>+</SUP>). As-synthesized Pd nanorods were used as electrocatalysts for electrochemical oxidation of methanol and the development of highly sensitive platform for hydrazine detection. Additive NAD<SUP>+</SUP> played an important role in the morphology tuning of Pd nanostructures. Results of morphological study demonstrated the growth of Pd nanorods with an average size of 150 nm. The as-synthesized Pd nanorods had excellent electrocatalytic activity toward oxidation of methanol in alkaline pH and hydrazine oxidation in neutral pH. These Pd nanorods catalyzed the electrooxidation of methanol at −0.17 V with much better tolerance, excellent stability, and oxidation of hydrazine at −0.075 V. The Pd nanorod-based sensing platform delivered a low detection limit of 5 nM, sensitivity of 0.78 ± 0.02 μA mM<SUP>−1</SUP>cm<SUP>−2</SUP>, and stable response toward hydrazine sensing without any interference from potential interferents such as Na<SUP>+</SUP>, K<SUP>+</SUP>, NO<SUB>2</SUB> <SUP>−</SUP>, BrO<SUB>3</SUB> <SUP>−</SUP>, or Pb<SUP>2+</SUP> ion. Their electrochemical performances were found to be highly dependent on the morphology of Pd nanostructures.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Rod-like Pd nanostructure was prepared by simple electrodeposition method. </LI> <LI> The additive NAD<SUP>+</SUP> plays a significant role on the electrochemical growth of Pd nanorods. </LI> <LI> The as-synthesized Pd nanorods efficiently catalyzed the electrooxidation of methanol and hydrazine. </LI> <LI> The current synthetic approach could be applied for the synthesis of other metal nanostructures. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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A Numerical Study on the Effect of Aggregate Gradation on Mechanical Response of Asphalt Mix
Ashok Singh,Animesh Das,Sumit Basu 대한토목학회 2012 KSCE Journal of Civil Engineering Vol.16 No.4
Various aggregate gradations are recommended in various guidelines/specifications for different types of asphalt mixes. These aggregate gradations have primarily evolved through experimental studies and experience on their field performances. Given a size range of aggregates, numerous aggregate gradations (and thereby numerous asphalt mixes) are possible. It is essentially a cumbersome and time consuming task to study the laboratory or field performances for all such possible asphalt mixes. The objective of the present work is to perform a micromechanical analyses on various asphalt mixes generated from computer simulated aggregate gradations. A hierarchical modeling scheme is used in the present work, where the asphalt mix is modeled as elastic-visco-plastic matrix with aggregates as rigid particulate intrusions with large volume fraction. In this process, a large number mixes can be simulated for their mechanical responses and some of them can be chosen for further laboratory verification. It is expected that such a process would save a considerable time and effort while finalizing a suitable gradation for the mix design.
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Das, Ashok Kumar,Kim, Nam Hoon,Lee, Seung Hee,Sohn, Youngku,Lee, Joong Hee Elsevier 2018 Composites. Part B, Engineering Vol.150 No.-
<P><B>Abstract</B></P> <P>Shape tailoring of active materials could alter the performance of supercapacitors. Herein, we report the ethylenediaminetetraacetic acid (EDTA) assisted hydrothermal approach for the synthesis of single crystalline CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons and their application in a supercapacitor. Morphology and BET surface area analysis demonstrates the formation of CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons with a surface area of 61.97 m<SUP>2</SUP> g<SUP>−1</SUP>. As an active material, the CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons exhibited a high specific capacity of 989 C g<SUP>-1</SUP> at 5 mV s<SUP>−1</SUP>. In addition, a long-term cyclic stability with 87% of its initial specific capacity retention was achieved after 5000 cycles at 10 A g<SUP>−1</SUP>. This outstanding performance could be ascribed to its unique octahedron morphology. The electrochemical results demonstrate that CuCo<SUB>2</SUB>O<SUB>4</SUB> with such a unique octahedron architecture could be a potential active material for the development of a high performance supercapacitor.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons were synthesized by EDTA assisted hydrothermal method. </LI> <LI> The CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons have 61.97 m<SUP>2</SUP> g<SUP>−1</SUP> surface area. </LI> <LI> As an active material CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons delivered 989 C g<SUP>−1</SUP> a specific capacity at 5 mV s<SUP>−1</SUP> scan rate. </LI> <LI> It has a long-term cyclic stability with 87% specific capacity retention after 5000 cycles at 10 A g<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Synthesis of CuCo<SUB>2</SUB>O<SUB>4</SUB> octahedrons and their supercapacitive performance has been demonstrated.</P> <P>[DISPLAY OMISSION]</P>
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Das, Ashok Kumar,Layek, Rama K.,Kim, Nam Hoon,Jung, Daeseung,Lee, Joong Hee The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.18
<P>The design and development of cheap, highly active, and durable non-platinum (Pt)-based electrocatalysts for methanol electrooxidation is highly desirable, but is a challenging task. In this paper, we demonstrate the application of a hydrothermally synthesized NiCo2O4-reduced graphene oxide (RGO) composite as an electrocatalyst for the electrochemical oxidation of methanol in alkaline pH. The physicochemical properties of the NiCo2O4-RGO composite were investigated via Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The physical characterization methods confirm the deposition of NiCo2O4 nanoparticles on the RGO surface. The TEM image shows that the NiCo2O4 nanoparticles with an average size of 10 nm are distributed over the RGO surface. Compared to RGO and NiCo2O4 nanoparticles, the NiCo2O4-RGO-based electrode shows excellent electrocatalytic activity for the oxidation of methanol in alkaline pH. On the NiCo2O4-RGO-based electrode, the oxidation of methanol occurs at 0.6 V with a higher catalytic current density, and the response is highly stable. The excellent electrocatalytic activity of the NiCo2O4-RGO composite is attributed to the synergistic effects between the NiCo2O4 nanoparticles and RGO. Since the NiCo2O4-RGO composite shows a highly stable response during methanol oxidation reaction, it is a very promising material to be used as an electrocatalyst in the development of high performance non-Pt based alkaline fuel cells.</P>
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Das, Ashok Kumar,Kim, Nam Hoon,Lee, Seung Hee,Sohn, Youngku,Lee, Joong Hee Elsevier 2018 Composites. Part B, Engineering Vol.150 No.-
<P><B>Abstract</B></P> <P>The synthesis of metal oxide composites with porous structures for supercapacitor application has drawn much attention owing to their high surface area and easy access of the electrolyte ions to the electrode surface through the pores of the active materials. A facile hydrothermal approach is suggested for the synthesis of porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheets and their application as an active electrode material for supercapacitor application. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) measurements show the formation of porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheets. BET surface area measurements show that the porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheet has 69.44 m<SUP>2</SUP> g<SUP>−1</SUP> surface area, which is 4.7 times higher than quasi-spherical CuCo<SUB>2</SUB>O<SUB>4</SUB> nanoparticles. The porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheet delivered 1037 C g<SUP>−1</SUP> specific capacity at 5 mV s<SUP>−1</SUP>. Additionally, the porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheet retained 94% of its initial specific capacity after 5000 charge-discharge cycles at 10 A g<SUP>−1</SUP> indicating an excellent cyclic stability. This excellent supercapacitive performance is attributed to the high surface area and enhanced ion transport through the pores of the CuCo<SUB>2</SUB>O<SUB>4</SUB> sheets. This high specific capacity and excellent cyclic stability of the porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheets prove to be a promising candidate for supercapacitor application.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheets were prepared by hydrothermal and annealing approach. </LI> <LI> They delivered a specific capacity of 1037 C g<SUP>−1</SUP> at 5 mV s<SUP>−1</SUP> scan rate. </LI> <LI> They accelerated the interaction between the electrolyte and material showing high performance. </LI> <LI> The sample retained 94% of the initial capacity after 5000 cycles, indicating excellent stability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>We describe a facile approach for the synthesis of porous CuCo<SUB>2</SUB>O<SUB>4</SUB> composite sheets for high performance supercapacitor application.</P> <P>[DISPLAY OMISSION]</P>
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Prasenjit Das,Gaurav PS Gahlot,Alka Singh,Vandana Baloda,Ramakant Rawat,Anil K Verma,Gaurav Khanna,Maitrayee Roy,Archana George,Ashok Singh,Aasma Nalwa,Prashant Ramteke,Rajni Yadav,Vineet Ahuja,Vishnu 대한장연구학회 2019 Intestinal Research Vol.17 No.3
Background/Aims: The existing histological classifications for the interpretation of small intestinal biopsies are based on qualitative parameters with high intraobserver and interobserver variations. We have developed and propose a quantitative histological classification system for the assessment of intestinal mucosal biopsies. Methods: We performed a computer-assisted quantitative histological assessment of digital images of duodenal biopsies from 137 controls and 124 patients with celiac disease (CeD) (derivation cohort). From the receiver-operating curve analysis, followed by multivariate and logistic regression analyses, we identified parameters for differentiating control biopsies from those of the patients with CeD. We repeated the quantitative histological analysis in a validation cohort (105 controls and 120 patients with CeD). On the basis of the results, we propose a quantitative histological classification system. The new classification was compared with the existing histological classifications for interobserver and intraobserver agreements by a group of qualified pathologists. Results: Among the histological parameters, intraepithelial lymphocyte count of ≥25/100 epithelial cells, adjusted villous height fold change of ≤0.7, and crypt depth-to-villous height ratio of ≥0.5 showed good discriminative power between the mucosal biopsies from the patients with CeD and those from the controls, with 90.3% sensitivity, 93.5% specificity, and 96.2% area under the curve. Among the existing histological classifications, our quantitative histological classification showed the highest intraobserver (69.7%–85.03%) and interobserver (24.6%–71.5%) agreements. Conclusions: Quantitative assessment increases the reliability of the histological assessment of mucosal biopsies in patients with CeD. Such a classification system may be used for clinical trials in patients with CeD.
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A sandpaper-inspired flexible and stretchable resistive sensor for pressure and strain measurement
Chhetry, Ashok,Das, Partha Sarati,Yoon, Hyosang,Park, Jae Yeong Elsevier 2018 Organic Electronics Vol.62 No.-
<P><B>Abstract</B></P> <P>We report very small shape-factored microstructures developed via a simple and cost-effective approach, enabling a high degree of sensitivity in a low-pressure regime (<2.67 kPa). The surface intertexture on the counter electrode and irregular microstructures with a high surface area developed on the base electrode help reduce the shape factor, allowing the device to deform more easily under pressure. Moreover, the irregular patterns with higher unloaded surface area strengthen the tunneling current sufficiently at low pressure. Furthermore, the fabricated features enable the device to perform as a flexible and stretchable sensing mechanism; the outstanding performance was achieved through a novel and feasible fabrication from a low-surface-energy template without surfactant coating. An ultra-low hysteresis of 3.17%, a high sensitivity of 0.3954 kPa<SUP>−1</SUP>, a fast response time of 0.49 s and stability over 6000 cycles were achieved. Finally, the sensing capability was examined by gentle finger tapping and arbitrary movement of the sensor placed on the forefinger. The current platform can be a key component for diverse applications such as muscle movement, speech detection, and health monitoring systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Flexible and stretchable resistive sensor for pressure and strain sensing capability. </LI> <LI> Very small shape-factored microstructures were generated from sandpaper template. </LI> <LI> An ultra-low hysteresis of 3.17%, a high sensitivity of 0.3954 kPa<SUP>−1</SUP> and stability over 6000 cycles were achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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