Post-peak response analysis of SFRC columns including spalling and buckling

Dhakal, Rajesh P. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.22 No.3

Standard compression tests of steel fiber reinforced concrete (SFRC) cylinders are conducted to formulate compressive stress versus compressive strain relationship of SFRC. Axial pullout tests of SFRC specimens are also conducted to explore its tensile stress strain relationship. Cover concrete spalling and reinforcement buckling models developed originally for normal reinforced concrete are modified to extend their application to SFRC. Thus obtained monotonic material models of concrete and reinforcing bars in SFRC members are combined with unloading/reloading loops used in the cyclic models of concrete and reinforcing bars in normal reinforced concrete. The resulting path-dependent cyclic material models are then incorporated in a finite-element based fiber analysis program. The applicability of these models at member level is verified by simulating cyclic lateral loading tests of SFRC columns under constant axial compression. The analysis using the proposed SFRC models yield results that are much closer to the experimental results than the analytical results obtained using the normal reinforced concrete models are.

Enhanced production of nargenicin A1 and creation of a novel derivative using a synthetic biology platform

Dhakal, D.,Chaudhary, A. K.,Yi, J. S.,Pokhrel, A. R.,Shrestha, B.,Parajuli, P.,Shrestha, A.,Yamaguchi, T.,Jung, H. J.,Kim, S. Y. Springer Science + Business Media 2016 Applied microbiology and biotechnology Vol.100 No.23

<P>Nargenicin A1, an antibacterial produced by Nocardia sp. CS682 (KCTC 11297BP), demonstrates effective activity against various Gram-positive bacteria. Hence, we attempted to enhance nargenicin A1 production by utilizing the cumulative effect of synthetic biology, metabolic engineering and statistical media optimization strategies. To facilitate the modular assembly of multiple genes for genetic engineering in Nocardia sp. CS682, we constructed a set of multi-monocistronic vectors, pNV18L1 and pNV18L2 containing hybrid promoter (derived from ermE* and promoter region of neo (r) ), ribosome binding sites (RBS), and restriction sites for cloning, so that each cloned gene was under its own promoter and RBS. The multi-monocistronic vector, pNV18L2 containing transcriptional terminator showed better efficiency in reporter gene assay. Thus, multiple genes involved in the biogenesis of pyrrole moiety (ngnN2, ngnN3, ngnN4, and ngnN5 from Nocardia sp. CS682), glucose utilization (glf and glk from Zymomonas mobilis), and malonyl-CoA synthesis (accA2 and accBE from Streptomyces coelicolor A3 (2)), were cloned in pNV18L2. Further statistical optimization of specific precursors (proline and glucose) and their feeding time led to similar to 84.9 mg/L nargenicin from Nocardia sp. GAP, which is similar to 24-fold higher than Nocardia sp. CS682 (without feeding). Furthermore, pikC from Streptomyces venezuelae was expressed to generate Nocardia sp. PikC. Nargenicin A1 acid was characterized as novel derivative of nargenicin A1 produced from Nocardia sp. PikC by mass spectrometry (MS) and nuclear magnetic resonance (NMR) analyses. We also performed comparative analysis of the anticancer and antibacterial activities of nargenicin A1 and nargenicin A1 acid, which showed a reduction in antibacterial potential for nargenicin A1 acid. Thus, the development of an efficient synthetic biological platform provided new avenues for enhancing or structurally diversifying nargenicin A1 by means of pathway designing and engineering.</P>

Review of Multi-Generation Innovation Diffusion Models

DHAKAL THAKUR,Kyoung-Soon Min,Dae-Eun Lim 대한산업공학회 2019 Industrial Engineeering & Management Systems Vol.18 No.4

In recent years, innovation diffusion models and their applications are increasingly studied because of the rapid development of technology. Since the publication of Norton and Bass (1987), the models on multi-generation diffusionhave resulted in a body of articles, books, and reports. In this study, the progress of multi-generation innovation diffusion studies based on 44 research papers published from 1971 to 2018 is reviewed. Insights from different researchstreams are summarized and outlines an entry point for new researchers focusing on multi-generation innovation diffusion is provided.

Cyclic behavior of interior beam-column connections in non-seismic RC frames at different loading rates

Dhakal, Rajesh P.,Pan, Tso-Chien Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.23 No.2

This paper provides an insight into the response of non-seismic reinforced concrete (RC) building frames to excitations of different frequencies through experimental investigation. The results of cyclic loading tests of six full-scale RC beam-column sub-assemblies are presented. The tested specimens did not have any transverse reinforcement inside the joint core, and they were subjected to quasi-static and dynamic loading with frequencies as high as 20 Hz. Some important differences between the cyclic responses of non-seismic and ductile RC frames are highlighted. The effect of excitation frequency on the behavior of non-seismic joints is also discussed. In the quasi-static tests, shear deformation of the joint panel accounted for more than 50% of the applied story drift. The test results also showed that higher-frequency excitations are less detrimental than quasi-static cyclic loads, and non-seismic frames can withstand a higher load and a larger deformation when they are applied faster.

A Compact Symmetric Microstrip Filter Based on a Rectangular Meandered-Line Stepped Impedance Resonator with a Triple-Band Bandstop Response

Dhakal, Rajendra,Kim, Nam-Young Hindawi Publishing Corporation 2013 The Scientific World Journal Vol.2013 No.-

<P>This paper presents a symmetric-type microstrip triple-band bandstop filter incorporating a tri-section meandered-line stepped impedance resonator (SIR). The length of each section of the meandered line is 0.16, 0.15, and 0.83 times the guided wavelength (<I>λ</I><SUB><I>g</I></SUB>), so that the filter features three stop bands at 2.59 GHz, 6.88 GHz, and 10.67 GHz, respectively. Two symmetric SIRs are employed with a microstrip transmission line to obtain wide bandwidths of 1.12, 1.34, and 0.89 GHz at the corresponding stop bands. Furthermore, an equivalent circuit model of the proposed filter is developed, and the model matches the electromagnetic simulations well. The return losses of the fabricated filter are measured to be −29.90 dB, −28.29 dB, and −26.66 dB while the insertion losses are 0.40 dB, 0.90 dB, and 1.10 dB at the respective stop bands. A drastic reduction in the size of the filter was achieved by using a simplified architecture based on a meandered-line SIR.</P>

Heterogeneous modulation of exciton emission in triangular WS₂ monolayers by chemical treatment

Dhakal, Krishna P.,Roy, Shrawan,Yun, Seok Joon,Ghimire, Ganesh,Seo, Changwon,Kim, Jeongyong The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.27

<▼1><P>Spatially heterogeneous effects of bis(trifluoromethane)sulfonimide (TFSI) and benzyl viologen (BV) treatment on the optical properties of triangular monolayer tungsten disulfides are investigated by nanoscale spectral imaging.</P></▼1><▼2><P>Chemical treatments were recently shown to be very effective in enhancing the exciton emission of monolayer transition metal dichalcogenides (1L-TMDs) by suppressing the exciton quenching caused by structural defects. However, the effects of these chemical treatments varied greatly depending on the synthesis method and the type of 1L-TMD; therefore, the exact origin of the emission enhancement is still elusive. Here we report the spatially heterogeneous effects of bis(trifluoromethane)sulfonimide (TFSI) and benzyl viologen (BV) treatment on the optical properties of triangular 1L-WS2 grown by chemical vapor deposition (CVD). Nanoscale photoluminescence (PL) and Raman spectral maps showed that TFSI had a minimal effect on the inner region of the triangular WS2 grain, whereas the PL of the edge region was enhanced up to 25 times; further, BV reduced the PL, also more strikingly in the edge region. Systematic variation of the spectral weights among neutral excitons, trions, and bi-excitons indicated that p-doping and n-doping with TFSI and BV, respectively, occurred in both the inner and edge regions; however, the PL enhancement was attributed mainly to the reduction of structural defects caused by TFSI treatment. Our observation of the spatially heterogeneous effects of chemical treatment suggests that the inner and edge regions of CVD-grown 1L-WS2 are populated with different types of structural defects and helps in clarifying the mechanism by which chemical treatment enhances the optical properties of 1L-TMDs.</P></▼2>

Enhanced production of nargenicin A(1) and generation of novel glycosylated derivatives.

Dhakal, Dipesh,Le, Tuoi Thi,Pandey, Ramesh Prasad,Jha, Amit Kumar,Gurung, RitBahadur,Parajuli, Prakash,Pokhrel, Anaya Raj,Yoo, Jin Cheol,Sohng, Jae Kyung Humana Press 2015 Applied biochemistry and biotechnology Vol.175 No.6

<P>Nargenicin A(1), an antibacterial polyketide macrolide produced by Nocardia sp. CS682, was enhanced by increasing the pool of precursors using different sources. Furthermore, by using engineered strain Nocardia sp. ACC18 and supplementation of glucose and glycerol, enhancement was similar to 7.1 fold in comparison to Nocardia sp. CS682 without supplementation of any precursors. The overproduced compound was validated by mass spectrometry and nuclear magnetic resonance analyses. The novel glycosylated derivatives of purified nargenicin A(1) were generated by efficient one-pot reaction systems in which the syntheses of uridine diphosphate (UDP)-alpha-D-glucose and UDP-alpha-D-2-deoxyglucose were modified and combined with glycosyltransferase (GT) from Bacillus licheniformis. Nargenicin A(1) 11-O-beta- D-glucopyranoside, nargenicin A(1) 18-O-beta-D-glucopyranoside, nargenicin A(1)11 18-O-beta-D- diglucopyranoside, and nargenicin 11-O-beta-D-2-deoxyglucopyranoside were generated. Nargenicin A(1) 11-O-beta-D-glucopyranoside was structurally elucidated by ultra-high performance liquid chromatography-photodiode array (UPLC-PDA) conjugated with high-resolution quantitative time-of-flight-electrospray ionization mass spectroscopy (HR-QTOF ESI-MS/MS), supported by one- and two-dimensional nuclear magnetic resonance studies, whereas other nargenicin A(1) glycosides were characterized by UPLC-PDA and HR-QTOF ESI-MS/MS analyses. The overall conversion studies indicated that the one-pot synthesis system is a highly efficient strategy for production of glycosylated derivatives of compounds like macrolides as well. Furthermore, assessment of solubility indicated that there was enhanced solubility in the case of glycoside, although a substantial increase in activity was not observed.</P>

Screen-Printed Flexible Bandstop Filter on Polyethylene Terephthalate Substrate Based on Ag Nanoparticles

Dhakal, Rajendra,Jung, Younsu,Park, Hyejin,Cho, Gyoujin,Kim, Nam Young Hindawi Limited 2015 Journal of nanomaterials Vol.2015 No.-

<P>We present a low-power, cost-effective, highly reproducible, and disposable bandstop filter by employing high-throughput screen-printing technology. We apply large-scale printing strategies using silver-nanoparticle-based ink for the metallization of conductive wires to fabricate a bandstop filter on a polyethylene terephthalate (PET) substrate. The filter exhibits an attenuation pole at 4.35 GHz with excellent in-and-out band characteristics. These characteristics reflect a rejection depth that is better than −25 dB with a return loss of −0.75 dB at the normal orientation of the PET substrate. In addition, the filter characteristics are observed at various bending angles (0°, 10°, and 20°) of the PET substrate with an excellent relative standard deviation of less than 0.5%. These results confirm the accuracy, reproducibility, and independence of the resonance frequency. This screen-printing technology for well-defined nanostructures is more favorable than other complex photolithographic processes because it overcomes signal losses due to uneven surface distributions and thereby reveals a homogeneous distribution. Moreover, the proposed methodology enables incremental steps in the process of producing highly flexible and cost-effective printed-electronic radio devices.</P>

Stability of linolenic acid in seed oil of soybean accessions with elevated linolenic acid concentration

Dhakal, K.H.,Lee, J.-D.,Jeong, Y.-S.,Kim, H.-S.,Shannon, J.G.,Hwang, Y.-H. WFL PUBLISHER 2013 Journal of food, agriculture & environment Vol.11 No.1

Gold nanoparticle hybridized rubrene nanofibers made by electrospinning: enhancement of optical and structural properties

Dhakal, K.,Lee, H.,Lee, J.,Lee, S.,Joo, J.,Kim, J. Royal Society of Chemistry 2014 Journal of Materials Chemistry C Vol.2 No.10

We prepared gold nanoparticle (Au NP) hybridized organic rubrene nanofibers (NFs) using a convenient electrospinning method. Au NPs of size 2-3 nm were incorporated throughout the light emitting rubrene NFs, which was confirmed by high resolution transmission electron microscopy. Au NP hybridized rubrene NFs showed a distinct nanoporous surface, compared to the smooth surface of rubrene NFs. Nanoscale confocal spectroscopy was performed on a single NF level and the results showed that the photoluminescence (PL) of the hybrid NFs made with 15 wt% Au NP mixture solution was 2.5 times higher than the PL of the rubrene NFs. And the optical extinction (scattering and absorption) of hybrid NFs increased monotonically with increasing Au NP concentrations. These enhanced optical properties of hybrid NFs were attributed to localized surface plasmon resonance of the embedded Au NPs. Structural modification from the monoclinic phase to the orthorhombic phase of the rubrene structure was obtained by XRD analysis indicating a better ordering along the rubrene ab plane of the hybrid NFs.