Assessment of Salinity-Induced Antioxidative Defense System of Diazotrophic Cyanobacterium Nostoc muscorum

( Srivastava ),( Ashish Kumar ) 한국미생물 · 생명공학회 2010 Journal of microbiology and biotechnology Vol.20 No.11

The present study examined the salinity-induced oxidative damage and differential response of enzymatic and nonenzymatic antioxidants of Nostoc muscorum. As compared with carotenoid content that showed induction, the chlorophyll and phycocyanin contents were inhibited after salt stress. Acceleration of lipid peroxidation and peroxide production suggested the onset of oxidative damage. The activities of all studied enzymatic antioxidants were significantly increased by salt stress, with maximum induction occuring with superoxide dismutase (154.8% at 200 mM NaCl treatment). Interestingly, under severe stress condition (250 mM NaCl), ascorbate peroxidase seemed to be more crucial than catalase for peroxide scavenging. Among the studied nonenzymatic antioxidants, α-tocopherol was induced maximally (56.0%); however, ascorbate and reduced glutathione were increased by only 8.9% after 250 mM NaCl treatment as compared with control cells. Therefore, salinity was found to induce the antioxidative defense system of N. muscorum.

Physiological Mechanism and Nutrient Management Strategies for Flood Tolerance in Rice Grown in Lowland Flood Prone Ecosystem

Sharad Kumar Dwivedi,Santosh Kumar,Narayan Bhakta,Ashish Kumar Srivastava,Janki Sharan Mishra,Virendar Kumar,B H Kumara,Bhagwati Prasad Bhatt,Sudhanshu Singh 한국작물학회 2018 Journal of crop science and biotechnology Vol.21 No.4

In flood-prone areas, rice must have flood tolerance characteristics either through genotypic selections or by nutrient application management strategies. The current study was conducted at ICAR Research Complex for Eastern Region, Patna during the wet season to investigate the effect of post-flood nutrient application methods on submerged rice survival and productivity. Our study showed that the 3-d submergence duration had no effect on the survival (100%) of 21-day-old seedlings but survival percentage decreased to 97 and 65% at 7-d and 11-d submergence, respectively. Total chlorophyll, total soluble sugar, and starch concentrations also exhibited a similar pattern of decline. The activity of anti-oxidative defense enzymes (CAT, POX, SOD, and APX), recorded just after de-submergence was found to be 1.5-10-foldhigher than before submergence, increasing with the increase in the severity of stress. Additional post-flood application of K2O and N at 5-6 days after de-submergence led to the improvement in photosynthetic rate, yield attributes, and grain yield. An additional 10 kg each of N and K2O produced maximum 1000-grain weight and higher grain yield and harvest index. After submergence, the meta-analysis exhibited a significant reduction in total chlorophyll concentration due to increasing submergence duration, whereas the significantly higher activity of antioxidants was recorded irrespective of submergence duration. In association with the better anti-oxidative defense mechanism of Sub1 varieties, the additional doses of N and K2O at 5-d after de-submergence significantly enhanced the survival, post-flood recovery, and the rate of photosynthesis after de-submergence. These nutrient management options can provide an opportunity to explore the productivity potential of the SUB1-introgressed variety under natural flash-flood conditions, helping to cope with the existing problems in flood-prone areas. The findings of the study suggest that a proper time and method of N application with basal P can significantly contribute to higher rice yield in flash-flood prone areas.

Elastic properties of CNT- and graphene-reinforced nanocomposites using RVE

Dinesh Kumar,Ashish Srivastava 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.5

The present paper is aimed to evaluate and compare the effective elastic properties of CNT- and graphene-based nanocomposites using 3-D nanoscale representative volume element (RVE) based on continuum mechanics using finite element method (FEM). Different periodic displacement boundary conditions are applied to the FEM model of the RVE to evaluate various elastic constants. The effects of the matrix material, the volume fraction and the length of reinforcements on the elastic properties are also studied. Results predicted are validated with the analytical and/or semiempirical results and the available results in the literature. Although all elastic stiffness properties of CNT- and graphene-based nanocomposites are found to be improved compared to the matrix material, but out-of-plane and in-plane stiffness properties are better improved in CNT- and graphene-based nanocomposites, respectively. It is also concluded that long nanofillers (graphene as well as CNT) are more effective in increasing the normal elastic moduli of the resulting nanocomposites as compared to the short length, but the values of shear moduli, except G23 of CNT nanocomposite, of nanocomposites are slightly improved in the case of short length nanofillers (i.e., CNT and graphene).

Liquid Phase Exfoliation and Characterization of Few Layer MoS2 and WS2 Nanosheets as Channel Material in Field Effect Transistor

Rohit Sharma,Ashish Kumar,Anit Dawar,Sunil Ojha,Ambuj Mishra,Anshu Goyal,Radhapiyari Laishram,V. G. Sathe,RITU SRIVASTAVA,Om Prakash Sinha 한국전기전자재료학회 2023 Transactions on Electrical and Electronic Material Vol.24 No.2

Field effect transistors (FETs) are considered as the backbone of electronic industry. In this study, we adopted a simple drop cast method for the fabrication of MoS2 and WS2 channel based FET on commercially available pre-patterned OFET devices. The synthesis of few-layers thick MoS2 and WS2 nanosheets (NSs) has been done by solvent-assisted exfoliation method. FESEM and TEM study reveals that NSs have lateral dimensions in micron and have polycrystalline nature. From XPS, it is observed that MoS2 NSs has 2H phase whereas WS2 have hybrid 1T and 2H phase. The frequency difference in Raman vibrational mode for MoS2 and WS2 NSs is 24.08 cm-1 and 63.84 cm-1 respectively, confirms that number of layers is reduced after sonication. UV-visible spectroscopy reveals that the bandgap is 1.7 eV and 1.8 eV for MoS2 and WS2 NSs respectively. Later, these nanosheets have been drop-casted as the channel material on pre-patterned FETs devices and their output and transfer characteristics have been studied. It found that the current On/Off ratio is 10 4 and 10 3 for MoS 2 and WS2-FET device respectively. This facile fabrication of FET devices may provide a new stage for researchers who do not have access of lithography facilities for FET fabrication.

Utilization of Chrome Containing Leather Waste in Development of Aluminium Based Green Composite Material

Shashi Prakash Dwivedi,Ashish Kumar Srivastava 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.3

Leather industries are produced lots of hazardous waste in the town areas. Due to which level of soil and air pollutants are increasing day by day. These wastes also harm human health especially children and old age peoples. Among these leather wastes, chrome containing leather waste can be utilized to produce composite materials eff ectively. In the present work, an attempt is made to excerpt the chromium (Cr) based collagen powder from leather waste and utilize in the synthesis of MMCs. In this work, aluminium is used as base material whereas collagen powder is used as reinforcement along with Al 2 O 3 ceramic particles as a primary reinforcement material. Results reveal the homogeneous distribution of Al 2 O 3 particles and collagen powder in matrix material during the microstructural examination. Proper wettability and good interfacial reaction layer were observed between Collagen powder and Aluminium matrix material. Tensile strength was improved about 14.32% by adding simultaneously 5 wt. % Al 2 O 3 and 1.25 wt. % collagen powder in the aluminium matrix material. However, the hardness was improved about 35.29% by adding 6.25 wt. % Al 2 O 3 in aluminium. It has been also observed that impact strength signifi cantly improved (27.77%) by adding 2.5 wt. % Al 2 O 3 and 3.75 wt. % collagen powder simultaneously in aluminium. Minimum corrosion loss and thermal expansion have been observed for Al/1.25% Al 2 O 3 /5% collagen powder composite and Al/0% Al 2 O 3 /6.25% collagen powder composite respectively. X-ray diff raction analysis was also performed to validate the presence of Al 2 O 3 and Cr in Al/Al 2 O 3 /Collagen powder metal matrix composite material. Mechanical properties were improved signifi cantly by adding Al 2 O 3 and Collagen powder simultaneously in Aluminium. Corrosion behaviour and thermal expansion of composite material were also identifi ed to observe the Al 2 O 3 and Collagen powder addition in Aluminium.

Investigation on Bonding Strength and Tribological Performances of Ceramic Laminated AA6063 Composite Developed by Friction Stir Additive Manufacturing

Ravi Prajapati,Suryank Dwivedi,Deepak Kumar,Ashish Kumar Srivastava,Amit Rai Dixit 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.11 No.1

The demand for novel laminated sheets encouraged using newer technologies to produce tailored materials for multipurpose applications. An inventive solid-state joining method: friction stir additive manufacturing, which offers several advantages over traditional lamination processes. In this study, the Al2O3 powder is used as reinforcement during AA6063/Al2O3/AA6063 composites fabrication. The fabricated specimen was characterized by bonding features such as thickness reduction, metallography, mechanical properties, and tribological performances and compared with sheet lamination and base metal. The optical microscope and scanning electron microscopic images showed that the Al2O3 powder is distributed within the composites. The structural analysis at the interface of the fabricated composite was conducted through X-ray diffraction, confirming the compounds like Mg2SiO4, Mg2Al4, and Al2O3 in the crystallographic planes. The microstructural and morphological results of the laminated composite showed the refined and equiaxed grains and also depicted the dispersion of the Al2O3 powder near the stir zone. The microhardness properties were enhanced and obtained as 91.2 HV and 77.5 HV with and without reinforcement, respectively. Further, the ultimate tensile strength with and without reinforcement is improved by 36.9% and 24.7% compared to the base metal. Furthermore, the tribological analysis was performed at variable process parameters. Taguchi's L9 orthogonal array and variance analysis (ANOVA) were done to analyze the effect of individual parameters and their significance. The obtained results showed that load and frequency are significant parameters during the tribology test. The laminated composite's specific wear rate, wear depth, and COF values are less than the sheet lamination and align with ANOVA test results. Furthermore, the wear mechanism was observed, and it was found that sheet lamination has high wear at increased load when compared to laminated composite parts. Therefore, the obtained results dictate that the addition of Al2O3 powder can significantly enhance the bonding strength, mechanical and tribological properties of the fabricated composites.