Investigation of the mechanical and thermal properties of <small>L</small>-glutathione modified graphene/epoxy composites

Chhetri, Suman,Adak, Nitai Chandra,Samanta, Pranab,Murmu, Naresh Chandra,Hui, David,Kuila, Tapas,Lee, Joong Hee Elsevier 2018 Composites Part B, Engineering Vol.143 No.-

<P><B>Abstract</B></P> <P>Nacre-like graphene nanosheets (GNS) obtained from the <SMALL>L</SMALL>-glutathione mediated reduction of graphene oxide (GO) were used to develop epoxy composites. Field emission scanning electron microscopy (FE-SEM) revealed the layer-by-layer nacre-like structure of GNS. Fourier transform infrared spectra (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, and thermogravimetric analysis (TGA) measurements confirmed the successful reduction of GO. The oxidized product of <SMALL>L</SMALL>-glutathione is expected to perform as capping agent to stabilize the GNS, and also stitches the graphene sheets through hydrogen bonding. Transmission electron microscopy was used to confirm the dispersion of GNS in the epoxy matrix. The GNS/epoxy composites showed significant improvement of ∼91% in fracture toughness (K<SUB>IC</SUB>), 46% in flexural strength, and 71% in flexural modulus at 0.25 wt% GNS loadings. The probable toughening mechanism was elucidated from fracture FE-SEM images. The improved compatibility and strong interfacial interaction were reflected in the enhanced storage modulus value. The thermal stability of the composites as investigated by TGA showed appreciable improvement in the degradation temperature.</P>

HEALTH PROMOTION IN NEPAL

Chhetri,M.K. Korean Society for Health Education and Promotion 1999 International Symposium Vol.1999 No.-

네팔의 보건부산하 보건서비스부서에서는 5개년계획을 게우고 있으며, 지방에서 기본적인 보건의료서비스제공을 위한 주요 전략으로 일차보건의료사업을 하고 있다. 그러나 자유화 정책(Liberation policy)으로 인해 도시지역의 전문화된 서비스 개발, 인간자원 개발, 경영강화와 민간 및 대외 투자 등이 활발해졌다. 그러나 네팔은 아직도 높은 출산력, 영양결핍, 전염병, 높은 사망률 등을 겪고 있는 데 이는 조기결혼, 미신적인 전통신앙과 행동, 비위생적 생활, 빈곤, 문명, 감독과 모니터링의 결핍, 높은 인구밀도, 민간 및 대외활동에 더 많이 투자해야 하고; 인력개발 및 전문화된 서비스가 관리되어야 하며; 경영기술이 강화되고 이전사업의 평가를 통해 향후 사업수행상의 오류를 피할 수 있도록 해야 한다. 이러한 것들이 개선된다면 네필주민의 건강목표는 달성될 것이다. Department of Health Services, under the Ministry of Health, Nepal has adopted the five year plan and Primary Health Care service as the main strategy to provide basic health service at the rural areas. However, development of the Specialized Services in the Urban areas, Human Resource Development, Management Strengthening and Investment of Private and External Sector are also highly entertained through its Liberalization Policy. But due to, Early Marriage, Superstitious Traditional Beliefs & behavior, Poor Sanitation of living, Poverty, Illiteracy, Lack of Supervision and Monitoring, High Density population in relation to arable land and Lack of Private and External Sector Investment, the Country is still suffering from high Fertility, Malnutrition, Infectious diseases and so high Death Rates. So Primary Health Care Services should be more emphasized than before; Community Financing, Private and External Sector should be highly involved; Manpower Development and Specialized Services should be most taken care; Management Skills be more strengthened and Evaluating the previous work and avoiding the mistake for the future program implementation should be well done. If these are improved, then the health will be definitely promoted to meet the Health Target of Nepal.

A flexible and highly sensitive capacitive pressure sensor based on conductive fibers with a microporous dielectric for wearable electronics

Chhetry, Ashok,Yoon, Hyosang,Park, Jae Yeong The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.38

<P>In this study, a flexible and highly sensitive capacitive pressure sensor has been fabricated by coating a microporous polydimethylsiloxane (PDMS) elastomeric dielectric onto conductive fibers. Conductive fibers were prepared by depositing silver nanoparticles (AgNPs) in poly(styrene-<I>block</I>-butadiene-styrene) (SBS) polymer on the surface of Twaron fibers. The configuration obtained by cross-stacking of two microporous PDMS-coated fibers imitates a capacitive sensor, which responds to compressive stress by increasing the contact area and decreasing the separation between the fiber electrodes. Moreover, the gradual closure of micropores under pressure increases the effective permittivity of the dielectric, thereby enhancing the sensitivity of the sensor. A relatively high sensitivity of 0.278 kPa<SUP>−1</SUP>for a low pressure region (<2 kPa), negligible hysteresis of 6.3%, a dynamic response time in the millisecond range (∼340 ms), a low detection limit of 38.82 Pa and an excellent repeatability of over 10 000 cycles were achieved. Finally, the practicality of the sensor was also demonstrated by loading small objects (∼9.4 mg) and gentle finger touches (<10 kPa). By virtue of its excellent sensitivity, low pressure detection and cost-effective fabrication process, our sensor is applicable for next-generation advanced touch panels with a more human-friendly interface, non-invasive health monitoring systems, and artificial robot arms.</P>

Devosia rhizoryzae sp. nov., and Devosia oryziradicis sp. nov., novel plant growth promoting members of the genus Devosia, isolated from the rhizosphere of rice plants

Chhetri Geeta,Kim Inhyup,Kang Minchung,Kim Jiyoun,So Yoonseop,Seo Taegun 한국미생물학회 2022 The journal of microbiology Vol.60 No.1

Two novel Gram-negative, aerobic, asporogenous, motile, rodshaped, orange and white pigmented, designated as LEGU1T and G19T, were isolated from the roots of rice plants, collected from Goyang, South Korea. Phylogenetic analysis based on their 16S rRNA gene sequences revealed that they belonged to the genus Devosia and formed a different lineage and clusters with different members of the genus Devosia. These strains shared common chemotaxonomic features. In particular, they had Q-10 as the sole quinone, phosphatidylglycerol, diphosphatidylglycerol as the principal polar lipids and C16:0, C18:1 ω7c 11-methyl and summed feature 8 (comprising C18:1 ω7c/ C18:1 ω6c) as the main fatty acids. The draft genome sequences of strains LEGU1T and G19T were 3,524,978 and 3,495,520 bp in size, respectively. Their average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values were 72.8–81.9% and 18.7–25.1%, respectively, with each other and type strains of related species belonging to the genus Devosia, suggesting that these two strains represent novel species. The G + C content of strains LEGU1T and G19T were 62.1 and 63.8%, respectively. Of the two strains, only LEGU1T produced carotenoid and flexirubin-type pigment. Both strains produced siderophore and indole acetic acid (IAA) in the presence of L-tryptophan. Siderophore biosynthesis genes, auxin responsive genes and tryptophan biosynthesis genes were present in their genomes. The present study aimed to determine the detailed taxonomic positions of the strains using the modern polyphasic approach. Based on the results of polyphasic analysis, these strains are suggested to be two novel bacterial species within the genus Devosia. The proposed names are D. rhizoryzae sp. nov., and Devosia oryziradicis sp. nov., respectively. The plant growth promoting effects of these strains suggest that they can be exploited to improve rice crop productivity. The type strain of D. rhizoryzae is LEGU1T (KCTC 82712T = NBRC 114485T) and D. oryziradicis is G19T (KCTC 82688T = NBRC 114842T).

Ultrasensitive Interfacial Capacitive Pressure Sensor Based on a Randomly Distributed Microstructured Iontronic Film for Wearable Applications

Chhetry, Ashok,Kim, Jiyoung,Yoon, Hyosang,Park, Jae Yeong American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.3

<P>The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (<2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with poly(vinylidene fluoride-<I>co</I>-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the solid electrolyte help the material to elastically deform under pressure. Moreover, the interfacial capacitance is improved by utilizing a highly conductive porous percolated network of silver nanowires reinforced with poly(dimethylsiloxane) as the electrodes. An ultrahigh-pressure sensitivity of 131.5 kPa<SUP>-1</SUP>, a low dynamic response time of ∼43 ms, a low limit of detection of 1.12 Pa, and a high stability for over 7000 cycles are achieved. Finally, we demonstrate the application of the sensor for international Morse code detection, artery pulse detection, and eye blinking. Owing to the ultrahigh sensitivity, the as-fabricated sensor will have great potential for wearable devices in health status monitoring, motion detection, and electronic skin.</P> [FIG OMISSION]</BR>

Efficient Plant Regeneration from Petal Segment of Standard-Type Chrysanthemum

Chhetri, Mahesh,Jeon, Su-Min,Naing, Aung Htay,Kim, Chang Kil Institute of Agricultural Science and Technology 2013 慶北大農學誌 Vol.31 No.2

An efficient plant regeneration protocol is developed for a standard-type chrysanthemum. When petal segments derived from flower buds (4 or 8cm in diameter) were used as the culture material, the highest shoot regeneration frequency (96%) was obtained on a Murashige and Skoog (MS) medium supplemented with 0.5 mg/L IAA, 2 mg/L BA, 3% sucrose, and a 0.8% agar. Pre-culturing the explants under dark conditions for 14 days produced better results for the shoot regeneration frequency than the explants cultured under a continuous 16 h photoperiod ($40{\mu}molm^{-2}s^{-1}$). The shoot regeneration frequency ranged from 19.0% for the Shinmato cultivar to 89.1% for the Baeksun cultivar. Activated charcoal (0.2%) enhanced the root formation of the regenerated shoots in a hormone-free MS medium. The rooted plantlets were acclimatized and successfully established in a greenhouse.

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>

Enhanced Mechanical Properties of Functionalized Graphene Oxide/linear Low Density Polyethylene Composites Prepared by Melt Mixing

( Suman Chhetri ),( Pranab Samanta ),( Naresh Chandra Murmu ),( Tapas Kuila ),( Joong Hee Lee ) 한국복합재료학회 2016 Composites research Vol.29 No.4

Graphene oxide (GO) was concurrently reduced and functionalized using long alkyl chain dodecyl amine (DA). The DA functionalized GO (DA-G) was assumed to disperse homogenously in linear low density polyethylene (LLDPE). Subsequently, DA-G was used to fabricate DA-G/LLDPE composites by melt mixing technique. Fourier transform infrared spectra analysis was performed to ascertain the simultaneous reduction and functionlization of GO. Field emission scanning electron microscopy analysis was performed to ensure the homogenous distribution and dispersion of DA-G in LLDPE matrix. The enhanced storage modulus value of the composites validates the homogenous dispersion of DA-G and its good interfacial interaction with LLDPE matrix. An increased in tensile strength value by ~ 64% also confirms the generation of good interface between the two constituents, through which efficient load transfer is possible. However, no significant improvement in glass transition temperature was observed. This simple technique of fabricating LLDPE composites following industrially viable melt mixing procedure could be realizable to developed mechanically strong graphene based LLDPE composites for future applications.

Efficient Plant Regeneration from Petal Segment of Standard-Type Chrysanthemum

Mahesh Chhetri,Su-Min Jeon,Aung Htay Naing,Chang Kil Kim 경북대학교 농업생명과학대학 2013 Current Research on Agriculture and Life Sciences Vol.31 No.2

An efficient plant regeneration protocol is developed for a standard-type chrysanthemum. When petal segments derived from flower buds (4 or 8cm in diameter) were used as the culture material, the highest shoot regeneration frequency (96%) was obtained on a Murashige and Skoog (MS) medium supplemented with 0.5 mg/L IAA, 2 mg/L BA, 3% sucrose, and a 0.8% agar. Pre-culturing the explants under dark conditions for 14 days produced better results for the shoot regeneration frequency than the explants cultured under a continuous 16 h photoperiod (40 μmolm-2 s -1 ). The shoot regeneration frequency ranged from 19.0% for the Shinmato cultivar to 89.1% for the Baeksun cultivar. Activated charcoal (0.2%) enhanced the root formation of the regenerated shoots in a hormone-free MS medium. The rooted plantlets were acclimatized and successfully established in a greenhouse.

In Vitro Shoot Organogenesis from Petal of Standard Type Chrysanthemum Cultivar

Mahesh Chhetri,Su Min Jeon,Aung Htay Naing,Kyung Il Park,Mi Young Chung,Chang Kil Kim 한국원예학회 2013 한국원예학회 학술발표요지 Vol.2013 No.5