Browsing by Author "Gupta, Rashmi"

Now showing 1 - 6 of 6
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    A review of Antarctic ice sheet fluctuations records during Cenozoic and its cause and effect relation with the climatic conditions
    (Elsevier B.V., 2021) Pandey, Mayuri; Pant, Naresh Chandra; Arora, Devsamridhi; Gupta, Rashmi
    Antarctic cryosphere has significant impact on the global climate system by influencing the ocean currents, the atmosphere, and the sea level for long term durations. Antarctic Ice Sheet (AIS) has evolved from temporary to permanent ice sheet during Oligocene (~32 Ma). Throughout its evolution, it witnessed severe climatic conditions leading to several phases of retreat and advancements. Major climatic events were directly associated with the evolution of AIS. Paleocene Eocene Thermal Maximum (PETM), Early Eocene Climatic Optimum (EECO, ~44.9 Ma), Eocene Oligocene Boundary (Oi1 event, ~34 Ma), Oligocene-Miocene Boundary (Mi1 event ~25Ma), Mid Miocene Climatic Optimum (MMCO; ~15Ma), Miocene-Pliocene Boundary (~3Ma) and Mid-late Pleistocene Transition (MPT, after ~1.25 Ma) are the major reported global climatic events. This work summarises these events and critically reviews the role of various factors in the advancement and retreat of AIS and its coupled response to the global climate change including future global challenges. Existing knowledge gaps and challenges are outlined for each of the climatic events and priorities for future research are suggested. � 2021
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    Design and development of a multiwalled carbon nanotubes-based copper (II) Schiff base complex for the facile non-enzymatic electrochemical sensing of glucose
    (Springer, 2023) Gupta, Rashmi; Yadav, Mamta; Singh, Smita; Ganesan, Vellaichamy; Singh, Bachcha
    A new bifunctional nanomaterial, [SBCu(II)Hyd]-MWCNTs, exhibiting exotic electrical and magnetic properties has been synthesized via chemical modification of MWCNT-COOH. Double probe DC electrical conductivity, CV and EIS studies show better conductivity of the material than that of MWCNT-COOH. With higher saturation and remanent magnetization, as well as coercivity, [SBCu(II)Hyd]-MWCNTs showed better ferromagnetic characteristics. Mott�Schottky electrochemical analysis was carried out to explore capacitive and dielectric properties. The enhancement in electrical conductivity of [SBCu(II)Hyd]-MWCNTs is also confirmed by optical and electrochemical band gaps studies. Subsequently, this material has been utilized to fabricate an electrochemical sensor by coating it over glassy carbon electrode for the determination of glucose. The corresponding sensitivity and limit of detection values are calculated to be 1.1 �A �M?1�cm?2 and 0.09��M, respectively. Graphical Abstract: [Figure not available: see fulltext.] � 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Evidence of Paleoproterozoic metamorphism in Vestfold Hills, East Antarctica: Insights from phase equilibria modelling and monazite CHIME dating
    (Elsevier B.V., 2023) Naik, Aditya; Arora, Devsamridhi; Pandey, Mayuri; Pant, Naresh Chandra; Gupta, Rashmi
    The Vestfold Hills sector on the coastal fringe of the Princess Elizabeth Land forms part of an Archean to Paleoproterozoic aged cratonic nucleus of the East Antarctic Shield. A charnockite-granite association from the Mossel Gneiss Group in the northern region of the Vestfold Hills is investigated in this work to characterise the metamorphic-magmatic evolution of the area. Conventional thermometry and phase equilibria modelling indicate that the charnockite formed as a result of ultra-high temperature metamorphism at low-intermediate pressure (?4 kbar). Phase equilibria modelling, reveals that the melt-integrated charnockite composition is a restitic product of a protolith of quartz diorite composition which underwent isobaric heating (peak temperature up to 960 �C) at 4 kbar pressure followed by anatexis. The anatexis of the quartz diorite protolith also resulted in the formation of the associated granitic melt. U�Th-PbTotal ages obtained from monazites of the granite integrated with CHIME ages extracted using the isochron method indicate an emplacement age of ?2200 Ma and two younger events are recorded at ?2000 Ma and ?1700 Ma. The younger ages are ascribed to the resetting during the emplacement of younger basalt dykes that cross cut the charnockite-granite sequence. Vestfold Hills� geological correlations with Indian and Australian cratons are discussed considering this new data. � 2023 Elsevier B.V. and NIPR
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    Evincing the presence of a trans-Gondwanian mobile belt in the interior of the Princess Elizabeth Land, East Antarctica: insights from offshore detrital sediments, rock fragments, and monazite geochronology
    (John Wiley and Sons Ltd, 2022) Gupta, Rashmi; Pandey, Mayuri; Arora, Devsamridhi; Pant, Naresh Chandra; Rao, N. V. Chalapathi
    East Gondwana was assembled through the stitching of the Indo-Antarctica and Australo-Antarctica domains which also represents the key Gondwana-forming regions in present-day East Antarctica. However, the Indo-Antarctica and Australo-Antarctica boundaries remain speculative and contentious, as the thick Antarctic Ice sheet precludes direct geological characterization of these terranes. In addition, the exact role of the Gamburtsev Subglacial Mountains, present in the interior of Princess Elizabeth Land (PEL), during the amalgamation of Gondwana, has not been well understood. We present new mineralogical data of offshore sediments from Prydz Bay to infer the geology of the interior of the PEL terrain, East Antarctica. Coast marginal outcrops dominantly expose igneous and granulite facies metamorphic rocks. Heavy minerals characterization of the rock fragments followed by consideration of the outcrop geology indicate a possible contribution of sediments from the far interior of PEL terrain. Total U�Pb chemical geochronology of detrital monazites dominantly shows a bimodal age distribution ascribable to Stenian to Tonian (~1,100 Ma, 900 Ma) event ages and a younger Pan-African event (~500 Ma). Besides these, Tonian-Cryogenian (~700 Ma) ages from texturally constrained monazites of a low-grade schist rock fragment is reported for the first time from this sector. Consideration of glacial flow directions and the nature of rock fragments indicate their sourcing from the distal hinterland. The possible provenance is inferred to be from the Gamburtsev Subglacial Mountains. � 2022 John Wiley & Sons Ltd.
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    Role of tannic acid in desiging of electrically active and magnetic gold nanoparticles and enhanced photovoltaic performance of gold@titania photoanode in DSSC
    (Elsevier Ltd, 2022) Gupta, Rashmi; Singh, Shalini; Srivastava, Pankaj; Singh, Bachcha
    We describe here in significance of tannic acid in obtaining size dependent electrochemically active and magnetic gold nanoparticles (GNPs). In this account, two types of GNPs (SCGNPs and SC-TAGNPs) were synthesized by using sodium citrate and sodium citrate-tannic acid as reducing agents, respectively. Highly monodispersed, uniformly distributed and small size GNPs were produced when tannic acid was used together with sodium citrate. SC-TAGNPs exhibited room temperature ferromagnetism while SCGNPs revealed diamagnetism. With higher anodic peak current and lower charge transfer resistance, the SC-TAGNPs exhibited better conductivity and electron transfer ability than SCGNPs. Mott-Schottky analysis revealed n-type semiconducting behavior of GC/SCGNPs & GC/SC-TAGNPs and showed positive shift in flat-band potential of GC/SC-TAGNPs compared to GC/SCGNPs suggesting better conductivity of SC-TAGNPs. Subsequently, SCGNPs and SC-TAGNPs were added to TiO2 nanoparticles to fabricate modified titania photoanodes (SCGNPs@TiO2 and SC-TAGNPs@TiO2) for dye-sensitized solar cells (DSSCs) application. With the use of TiO2, SCGNPs@TiO2 and SC-TAGNPs@TiO2 photoanodes, the short-circuit current density (JSC) was observed to be 2.18, 4.50 and 6.68 mA/cm2, while energy conversion efficiency (?) was found to be 0.75, 1.74 and 2.50%, respectively. The TiO2 photoanode employing SC-TAGNPs exhibited remarkably increased JSC and ? by ?48 and ?44%, respectively, then SCGNPs modified photoanode. � 2021 Elsevier B.V.
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    Unravelling the complex sub-ice geology of the Wilkes Subglacial Basin region of East Antarctica from marine sediment provenance analyses
    (Cambridge University Press, 2023) Pandey, Mayuri; Pant, Naresh Chandra; Arora, Devsamridhi; Ferraccioli, Fausto; Gupta, Rashmi; Joshi, Sonalika
    Deciphering the sub-ice geology in the Wilkes Subglacial Basin region is important for understanding solid earth-ice sheet evolution and for assessing geological ties between East Antarctica and formerly contiguous Australia. We analyse marine sediment samples derived from drill site U1359 of Integrated Oceanic Drilling Program Expedition 318. Our study reports for the first time that the inland sediment source area comprises a complex mafic igneous terrain and a metamorphosed Precambrian subglacial basement. Pyroxene geochemical analyses confirm the presence of tholeiitic to calc-alkaline basalts. The high-grade part of the subglacial terrain contains upper amphibolite to granulite facies rocks that are comparable to Archaean to Palaeoproterozoic rocks exposed in the Terre Ad�lie Craton and the formerly adjacent Gawler Craton in Australia. Chemical Th-U-total Pb isochron method (CHIME) ages extracted from a subhedral monazite grain associated with the low-grade biotite-muscovite schist rock fragment provide a unimodal age of 799 � 13 Ma. Rare occurrences of 800 Ma age in the Terre Ad�lie Craton and/or George V Coast provide evidence for the presence of at least one late Neoproterozoic magmato-metamorphic event in the interior of Wilkes Land. The affinity of the unexposed geological domains of Wilkes Land, East Antarctica, with their Australian counterparts is discussed in the context of the Rodinia supercontinent. Copyright � The Author(s), 2023. Published by Cambridge University Press on behalf of Antarctic Science Ltd.