Fabrication of microwave assisted biogenic magnetite-biochar nanocomposite: A green adsorbent from jackfruit peel for removal and recovery of nutrients in water sample

A. Nayak,Brij Bhushan,Vartika Gupta,Shreya Kotnala 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.100 No.-

Presence of nutrients in municipal sewage water in high concentrations has raised awareness of theirreuse as a vital limiting resource. With an aim to recover the nutrients in a form that can be used as a soilamendment, a novel biocompatible nanocomposite (BC-P@MNP) was fabricated using green methods. Polysaccharide induced biogenic magnetite nanoparticles (P@MNP) were immobilized onto the biocharof jackfruit peel (BC) to fabricate BC-P@MNP. Microwave irradiation employed during the fabrication ofBC-P@MNP involved less energy consumption, high yields and better adsorption performance ascompared to BC and other reported biochar-composites. Structural features like mesoporosity,crystallinity, magnetism, functionality and nano-sized dimension was demonstrated in BC-P@MNP. Under optimized conditions, batch studies revealed a maximum adsorption efficiency of 7.94 mg/g and5.26 mg/g for phosphates and nitrates respectively. Thermodynamics revealed the feasibility andexothermicity of the system. The high selectivity in the presence of competing co-anions, highregeneration capacity and better separability enable BC-P@MNP to be used as advanced, economicaladsorbent for wastewater applications. High nutrient recovery and biocompatibility ensured thepotential of the spent adsorbent to be used as a soil amendment. Breakthrough curves obtained fromfixed-bed column tests conducted on agricultural wastewater demonstrated the use of higher bed depthsand lowerflow rates for achieving higher phosphate removal as well as for ensuring lower unusedcolumn bed. The study demonstrated the technological advancement of a biogenic nanocompositefabricated from green methods over other reported adsorbents for removal and recovery of nutrientsfrom water. © 2021 The Korean

Managing a Prolonged Station Blackout Condition in AHWR by Passive Means

Mukesh Kumar,A. K. Nayak,V. Jain,P. K. Vijayan,K.K. Vaze 한국원자력학회 2013 Nuclear Engineering and Technology Vol.45 No.5

Removal of decay heat from an operating reactor during a prolonged station blackout condition is a big concern for reactor designers, especially after the recent Fukushima accident. In the case of a prolonged station blackout condition, heat removal is possible only by passive means since no pumps or active systems are available. Keeping this in mind, the AHWR has been designed with many passive safety features. One of them is a passive means of removing decay heat with the help of Isolation Condensers (ICs) which are submerged in a big water pool called the Gravity Driven Water Pool (GDWP). The ICs have many tubes in which the steam, generated by the reactor core due to the decay heat, flows and condenses by rejecting the heat into the water pool. After condensation, the condensate falls back into the steam drum of the reactor. The GDWP tank holds a large amount of water, about 8000 m3, which is located at a higher elevation than the steam drum of the reactor in order to promote natural circulation. Due to the recent Fukushima type accidents, it has been a concern to understand and evaluate the capability of the ICs to remove decay heat for a prolonged period without escalating fuel sheath temperature. In view of this, an analysis has been performed for decay heat removal characteristics over several days of an AHWR by ICs. The computer code RELAP5/MOD3.2 was used for this purpose. Results indicate that the ICs can remove the decay heat for more than 10 days without causing any bulk boiling in the GDWP. After that, decay heat can be removed for more than 40days by boiling off the pool inventory. The pressure inside the containment does not exceed the design pressure even after 10days by condensation of steam generated from the GDWP on the walls of containment and on the Passive Containment Cooling System (PCCS) tubes. If venting is carried out after this period, the decay heat can be removed for more than 50 days without exceeding the design limits.

MANAGING A PROLONGED STATION BLACKOUT CONDITION IN AHWR BY PASSIVE MEANS

Kumar, Mukesh,Nayak, A.K.,Jain, V,Vijayan, P.K.,Vaze, K.K. Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.5

Removal of decay heat from an operating reactor during a prolonged station blackout condition is a big concern for reactor designers, especially after the recent Fukushima accident. In the case of a prolonged station blackout condition, heat removal is possible only by passive means since no pumps or active systems are available. Keeping this in mind, the AHWR has been designed with many passive safety features. One of them is a passive means of removing decay heat with the help of Isolation Condensers (ICs) which are submerged in a big water pool called the Gravity Driven Water Pool (GDWP). The ICs have many tubes in which the steam, generated by the reactor core due to the decay heat, flows and condenses by rejecting the heat into the water pool. After condensation, the condensate falls back into the steam drum of the reactor. The GDWP tank holds a large amount of water, about 8000 $m^3$, which is located at a higher elevation than the steam drum of the reactor in order to promote natural circulation. Due to the recent Fukushima type accidents, it has been a concern to understand and evaluate the capability of the ICs to remove decay heat for a prolonged period without escalating fuel sheath temperature. In view of this, an analysis has been performed for decay heat removal characteristics over several days of an AHWR by ICs. The computer code RELAP5/MOD3.2 was used for this purpose. Results indicate that the ICs can remove the decay heat for more than 10 days without causing any bulk boiling in the GDWP. After that, decay heat can be removed for more than 40 days by boiling off the pool inventory. The pressure inside the containment does not exceed the design pressure even after 10 days by condensation of steam generated from the GDWP on the walls of containment and on the Passive Containment Cooling System (PCCS) tubes. If venting is carried out after this period, the decay heat can be removed for more than 50 days without exceeding the design limits.

A V2O5 nanorod decorated graphene/polypyrrole hybrid electrode: a potential candidate for supercapacitors

DeAdhikari, A.,Oraon, R.,Tiwari, S.,Lee, J.,Kim, N.,Nayak, G. Royal Society of Chemistry 2017 NEW JOURNAL OF CHEMISTRY Vol.41 No.4

<P>Vanadium pentoxide (V2O5) nanorod decorated graphene polypyrrole nanocomposites have been synthesized successfully by a facile hydrothermal process for supercapacitor (SC) applications. The morphological study revealed the successful decoration of V2O5 nanorods and polypyrrole (PPy) within the intergallery of graphitic materials due to their high degree of propensity for intercalation which leads to the formation of mesoporous 3D nanostructures. These mesoporous structures can efficiently allow fast diffusion and ion transport at the electrode-electrolyte interface towards high electrochemical utilization and superior performance. Here, decoration of V2O5 within a polymer matrix along with a graphitic material renders different electrical profiles by virtue of their electron hopping within nanocomposites. Galvanostatic charging discharging revealed that VGP was found to be superior with a maximum specific capacitance of 787 F g(-1) at a current density of 1 A g(-1) using KCl as an electrolyte. These observations were also confirmed by electrochemical measurements through CV and EIS studies. Furthermore, cyclic stability performed for 5000 consecutive cycles also substantiate their high durability and high power delivery uptake. Thus, considering all such key features, V2O5 based nanocomposites can be suitable for SC applications.</P>

THERMAL AND STRUCTURAL ANALYSIS OF CALANDRIA VESSEL OF A PHWR DURING A SEVERE ACCIDENT

Kulkarni, P.P.,Prasad, S.V.,Nayak, A.K.,Vijayan, P.K. Korean Nuclear Society 2013 Nuclear Engineering and Technology Vol.45 No.4

In a postulated severe core damage accident in a PHWR, multiple failures of core cooling systems may lead to the collapse of pressure tubes and calandria tubes, which may ultimately relocate inside the calandria vessel forming a terminal debris bed. The debris bed, which may reach high temperatures due to the decay heat, is cooled by the moderator in the calandria. With time, the moderator is evaporated and after some time, a hot dry debris bed is formed. The debris bed transfers heat to the calandria vault water which acts as the ultimate heat sink. However, the questions remain: how long would the vault water be an ultimate heat sink, and what would be the failure mode of the calandria vessel if the heat sink capability of the reactor vault water is lost? In the present study, a numerical analysis is performed to evaluate the thermal loads and the stresses in the calandria vessel following the above accident scenario. The heat transfer from the molten corium pool to the surrounding is assumed to be by a combination of radiation, conduction, and convection from the calandria vessel wall to the vault water. From the temperature distribution in the vessel wall, the transient thermal loads have been evaluated. The strain rate and the vessel failure have been evaluated for the above scenario.

Thermal and Structural Analysis of Calandria Vessel of a PHWR during a Severe Accident

P.P. KULKARNI,S. V. Prasad,A. K. Nayak,P. K. Vijayan 한국원자력학회 2013 Nuclear Engineering and Technology Vol.45 No.4

In a postulated severe core damage accident in a PHWR, multiple failures of core cooling systems may lead to the collapse of pressure tubes and calandria tubes, which may ultimately relocate inside the calandria vessel forming a terminal debris bed. The debris bed, which may reach high temperatures due to the decay heat, is cooled by the moderator in the calandria. With time, the moderator is evaporated and after some time, a hot dry debris bed is formed. The debris bed transfers heat to the calandria vault water which acts as the ultimate heat sink. However, the questions remain: how long would the vault water be an ultimate heat sink, and what would be the failure mode of the calandria vessel if the heat sink capability of the reactor vault water is lost?In the present study, a numerical analysis is performed to evaluate the thermal loads and the stresses in the calandria vessel following the above accident scenario. The heat transfer from the molten corium pool to the surrounding is assumed to be by a combination of radiation, conduction, and convection from the calandria vessel wall to the vault water. From the temperature distribution in the vessel wall, the transient thermal loads have been evaluated. The strain rate and the vessel failure have been evaluated for the above scenario.

Time-Dependant Microstructural Evolution and Tribological Behaviour of a 26 wt% Cr White Cast Iron Subjected to a Destabilization Heat Treatment

U. Pranav Nayak,Frank Mücklich,María Agustina Guitar 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.4

By employing destabilization heat treatments (HT), it is possible to create microstructures possessing different fractionsof carbides, martensite, and austenite, which lead to varying tribological responses in abrasion-resistant high-chromiumwhite cast irons. In the current work, the destabilization temperature was kept constant at 980 °C, whereas the time wasvaried from 0 to 90 min. As a result, the microstructure of the 26 wt% Cr white cast iron had a mixture of M23C6secondarycarbides (SC), martensite, and a decrease in the amount of retained austenite (RA) with increasing destabilization holdingtime. The microstructures as well as their tribological characteristics were evaluated by combining confocal laser scanningmicroscopy, SEM, XRD, and EBSD, together with dry-sliding linear reciprocating wear tests. Results show that the volumefraction of SC were statistically comparable in samples destabilized for 0 and 90 min, although the average size was almosttwo-fold in the latter. This had direct implications on the wear properties where a decrease of up to 50% in the wear rate ofdestabilized samples compared to the non-treated material was observed. Furthermore, the sample with the lowest increase inthe matrix hardness (~ 20% higher than non-treated), showed the highest wear resistance. This was attributed to a favourabledistribution of the RA (~ 10%) and SC volume fraction (~ 5%), in combination with the harder martensitic matrix. Finally,the results obtained from this study shed light on the ability to alter the HT parameters to tune the microstructure dependingupon the application prerequisite.

Intersection-Based Geographical Routing Protocol for VANETs: A Proposal and Analysis

Saleet, H.,Langar, R.,Naik, K.,Boutaba, R.,Nayak, A.,Goel, N. IEEE 2011 IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY Vol.60 No.9

<P>This paper presents a class of routing protocols for vehicular ad hoc networks (VANETs) called the Intersection-based Geographical Routing Protocol (IGRP), which outperforms existing routing schemes in city environments. IGRP is based on an effective selection of road intersections through which a packet must pass to reach the gateway to the Internet. The selection is made in a way that guarantees, with high probability, network connectivity among the road intersections while satisfying quality-of-service (QoS) constraints on tolerable delay, bandwidth usage, and error rate. Geographical forwarding is used to transfer packets between any two intersections on the path, reducing the path's sensitivity to individual node movements. To achieve this, we mathematically formulate the QoS routing problem as a constrained optimization problem. Specifically, analytical expressions for the connectivity probability, end-to-end delay, hop count, and bit error rate (BER) of a route in a two-way road scenario are derived. Then, we propose a genetic algorithm to solve the optimization problem. Numerical and simulation results show that the proposed approach gives optimal or near-optimal solutions and significantly improves VANET performance when compared with several prominent routing protocols, such as greedy perimeter stateless routing (GPSR), greedy perimeter coordinator routing (GPCR), and optimized link-state routing (OLSR).</P>

Structure–Activity Relationships of Neplanocin A Analogues as <i>S</i>-Adenosylhomocysteine Hydrolase Inhibitors and Their Antiviral and Antitumor Activities

Chandra, Girish,Moon, Yang Won,Lee, Yoonji,Jang, Ji Yong,Song, Jayoung,Nayak, Akshata,Oh, Kawon,Mulamoottil, Varughese A.,Sahu, Pramod K.,Kim, Gyudong,Chang, Tong-Shin,Noh, Minsoo,Lee, Sang Kook,Choi, American Chemical Society 2015 Journal of medicinal chemistry Vol.58 No.12

<P>On the basis of the potent inhibitory activity of neplanocin A (1) against S-adenosylhomocysteine (AdoHcy) hydrolase, we analyzed the comprehensive structure-activity relationships by modifying the adenine and carbasugar moiety of 1 to find the pharmacophore in the active site of the enzyme. The introduction of 7-deazaadenine instead of adenine eliminated the inhibitory activity against the AdoHcy hydrolase, while 3-deazaadenine maintained the inhibitory activity of the enzyme, indicating that N-7 is essential for its role as a hydrogen bonding acceptor. The substitution of hydrogen at the 6'-position with fluorine increased the inhibitory activity Of the enzyme. The one-carbon homologation at the 5'-position generally decreased the inhibitory activity of the enzyme, indicating that steric repulsion exists. A molecular docking study also supported these experimental data. In this study, 6'-fluoroneplanocin A (2) was the most potent inhibitor of AdoHcy hydrolase (IC50 = 0.24 mu M). It showed a potent anti-VSV activity (EC50 = 0.43 mu M) and potent anticancer activity in all the human tumor cell lines tested.</P>

Probing Evolution of Twist-Angle-Dependent Interlayer Excitons in MoSe₂/WSe₂ van der Waals Heterostructures

Nayak, Pramoda K.,Horbatenko, Yevhen,Ahn, Seongjoon,Kim, Gwangwoo,Lee, Jae-Ung,Ma, Kyung Yeol,Jang, A-Rang,Lim, Hyunseob,Kim, Dogyeong,Ryu, Sunmin,Cheong, Hyeonsik,Park, Noejung,Shin, Hyeon Suk American Chemical Society 2017 ACS NANO Vol.11 No.4

<P>Interlayer excitons were observed at the heterojunctions in van der Waals heterostructures (vdW HSs). However, it is not known how the excitonic phenomena are affected by the stacking order. Here, we report twist-angle-dependent interlayer excitons in MoSe2/WSe2 vdW HSs based on photoluminescence (PL) and vdW-corrected density functional theory calculations. The PL intensity of the interlayer excitons depends primarily on the twist angle: It is enhanced at coherently stacked angles of 0 degrees and 60 degrees (owing to strong interlayer coupling) but disappears at incoherent intermediate angles. The calculations confirm twist-angle-dependent interlayer coupling: The states at the edges of the valence band exhibit a long tail that stretches over the other layer for coherently stacked angles; however, the states are largely confined in the respective layers for intermediate angles. This interlayer hybridization of the band edge states also correlates with the interlayer separation between MoSe2 and WSe2 layers. Furthermore, the interlayer coupling becomes insignificant, irrespective of twist angles, by the incorporation of a hexagonal boron nitride monolayer between MoSe2 and WSe2.</P>