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Defects tune the acidic strength of amorphous aluminosilicates
No full textCrystalline zeolites have high acidity but limited utility due to microporosity, whereas mesoporous amorphous aluminosilicates offer better porosity but lack sufficient acidity. In this work, we investigated defect engineering to fine-tune the acidity of amorphous acidic aluminosilicates (AAS). Here we introduced oxygen vacancies in AAS to synthesize defective acidic aluminosilicates (D-AAS). 1H, 27Al, and 17O solid-state nuclear magnetic resonance (NMR) studies indicated that defects induced localized structural changes around the acidic sites, thereby modifying their acidity. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy studies substantiated that oxygen vacancies alter the chemical environment of Brønsted acidic sites of AAS. The effect of defect creation in AAS on its acidity and catalytic behavior was demonstrated using four different acid-catalyzed reactions namely, styrene oxide ring opening, vesidryl synthesis, Friedel-Crafts alkylation, and jasminaldehyde synthesis. The defects played a role in activating reactants during AAS-catalyzed reactions, enhancing the overall catalytic process. This was supported by in-situ FTIR, which provided insights into the molecular-level reaction mechanism and the role of defects in reactant activation. This study demonstrates defect engineering as a promising approach to fine-tune acidity in amorphous aluminosilicates, bridging the porosity and acidity gaps between mesoporous amorphous aluminosilicates and crystalline zeolites
Pt-doped Ru nanoparticles loaded on 'black gold' plasmonic nanoreactors as air stable reduction catalysts
No full textThis study introduces a plasmonic reduction catalyst, stable only in the presence of air, achieved by integrating Pt-doped Ru nanoparticles on black gold. This innovative black gold/RuPt catalyst showcases good efficiency in acetylene semi-hydrogenation, attaining over 90% selectivity with an ethene production rate of 320 mmol g−1 h−1. Its stability, evident in 100 h of operation with continuous air flow, is attributed to the synergy of co-existing metal oxide and metal phases. The catalyst’s stability is further enhanced by plasmon-mediated concurrent reduction and oxidation of the active sites. Finite-difference time-domain simulations reveal a five-fold electric field intensification near the RuPt nanoparticles, crucial for activating acetylene and hydrogen. Kinetic isotope effect analysis indicates the contribution from the plasmonic non-thermal effects along with the photothermal. Spectroscopic and in-situ Fourier transform infrared studies, combined with quantum chemical calculations, elucidate the molecular reaction mechanism, emphasizing the cooperative interaction between Ru and Pt in optimizing ethene production and selectivity
Spatiotemporal Variability of Extreme Precipitation Events and Associated Atmospheric Processes Over Dronning Maud Land, East Antarctica
No full textWe investigate the spatial and temporal variability of extreme precipitation events (EPEs) in the Dronning Maud Land (DML) sector of Antarctica using high-resolution ECMWF ERA5 reanalysis data. This study examines the spatial occurrence of EPEs across DML, focusing particularly on six locations spanning the coastal and interior parts of the area. The largest snowfall amounts are usually found on eastward-facing slopes in the coastal zone. EPEs occur predominantly in north-easterly to easterly flows, leading to enhanced precipitation on the windward side of the orographic features with a steep gradient. Wind during EPEs was found to be more directionally consistent in the coastal area than in the interior. An east-west couplet of a mid-tropospheric ridge and low-pressure center is essential for steering warm moist maritime airmasses into the DML region before EPEs. Approximately 40% of EPEs result from atmospheric rivers (ARs), narrow bands of moist air originating at subtropical latitudes, which provide the greatest daily precipitation amounts. From 1979 to 2018, much of the DML experienced a statistically significant (p < 0.05) increase in the number of EPEs per year, along with increased precipitation from the EPEs. These trends were associated with significant changes in moisture availability and poleward meridional winds in the Atlantic sector of the Southern Ocean. The inter-annual variability in the number of EPEs is primarily dictated by regional atmospheric variability, while the influence of the Southern Oscillation Index and Southern Annular Mode is limited
Manipulating crack formation in air-dried clay suspensions with tunable elasticity
No full textClay, the major ingredient of natural soils, is used as a rheological modifier while formulating paints and coatings. When subjected to desiccation, colloidal clay suspensions and clayey soils crack due to the accumulation of drying-induced stresses. Even when desiccation is suppressed, aqueous clay suspensions exhibit physical aging, with their elastic and viscous moduli increasing over time as the clay particles self-assemble into gel-like networks due to time-dependent inter-particle screened electrostatic interactions. The rate of evolution of the suspension structures and therefore of the mechanical moduli can be controlled by changing clay concentration or by incorporating additives. Since physical aging and desiccation should both contribute to the consolidation of drying clay suspensions, we manipulate the desiccation process via alterations of clay and additive concentrations. For a desiccating sample with an accelerated rate of aging, we observe faster consolidation into a semi-solid state and earlier onset of cracks. We estimate the crack onset time, tc, in direct visualization experiments and the elasticity of the drying sample layer, E, using microindentation in an atomic force microscope. We demonstrate that tc∝√Gc/E, where Gc, the fracture energy, is estimated by fitting our experimental data to a linear poroelastic model that incorporates the Griffith's criterion for crack formation. Our work demonstrates that early crack onset is associated with lower sample ductility. The correlation between crack onset in a sample and its mechanical properties as uncovered here is potentially useful in preparing crack-resistant coatings and diverse clay structures
Interfacial instabilities in confined displacements involving non-Newtonian fluids
No full textThe growth of interfacial instabilities during fluid displacements can be driven by gradients in pressure, viscosity and surface tension, and by applying external fields. Since displacements of non-Newtonian fluids such as polymer solutions, colloidal and granular slurries are ubiquitous in natural and industrial processes, understanding the growth mechanisms and fully developed morphologies of interfacial patterns involving non-Newtonian fluids is extremely important. In this perspective, we focus on displacement experiments, wherein competitions between capillary, viscous, elastic and frictional forces drive the onset and growth of primarily viscous fingering instabilities in confined geometries. We conclude by highlighting several exciting open problems in this research area
Nondestructive evaluation of mechanical heart valve disc thickness degradation due to accelerated durability test using THz-TDS measurements
No full textQuality assurance and control during the mechanical heart valve components’ production process is paramount to mitigate most of the valve-related complications arising from valve replacement. Nondestructive evaluation of heart valve implants with complex profiles during production is challenging due to the biocompatibility requirements and clean room assembly conditions. This study first tested the UHMWPE disc of TTK Chitra mechanical heart valve models TC1 and TC2 using Terahertz imaging in reflection mode. The UHMWPE discs were raster scanned in X-Y directions to obtain a Terahertz-C scan to locate the macro defects due to wear out, and to distinguish between the true positive and true negative samples. The results were verified with digital microscope studies. Second, this study investigates a unique relationship between Terahertz imaging in reflection mode and heart valve disc degradation due to accelerated durability study. Third, the variation of disc surface roughness due to accelerated durability test was studied by Gaussian curve fitting analysis of fast Fourier transform of the Terahertz reflections. Finally, a comparison between the TC1 and TC2 heart valve model’s wear-out foot print was carried out using Terahertz C-scan. Our results imply that Terahertz time-domain spectroscopy has promising applications in NDE measurements of biocompatible implants
Biodiversity responses to climate change – a sustainable development perspective from India
No full textThe papers presented in this special issue cover a wide range of topics including the impact of climate change on Indian biodiversity through modelling approaches, the resilience of ecosystems to climate-induced shifts, and the role of remote sensing in monitoring forest dynamics. This body of research focuses on various ecological systems, highlighting the consequences of climate change and providing actionable insights for conservation policy and practice. By addressing data gaps, enhancing model precision, and integrating technological advancements like GIS and Earth Observation systems, this research supports the ongoing efforts to conserve biodiversity in fragile ecosystems, such as the Himalaya. Furthermore, studies synthesising and collecting data on India’s biodiversity help in understanding patterns of biodiversity and their biotic and abiotic drivers in the country’s varied landscapes, which offer valuable perspectives on conservation and sustainable development strategies. By highlighting these diverse research efforts, this special issue seeks to advance our understanding of climate change impacts on biodiversity and foster the development of resilient ecosystems in alignment with the UN Sustainable Development Goals, particularly Goal 13 (Climate Action) and Goal 15 (Life on Land)
Mitochondrial topoisomerase 1 targeted anticancer therapy using irinotecan encapsulated mesoporous MIL-101(Fe) synthesized <i>via</i> a vapour assisted method
No full textMitochondrial topisomerase 1 (Top1mt) is critical for mtDNA replication, transcription, and energy production. Here, we investigate the carrier-mediated targeted delivery of the anticancer drug irinotecan into the mitochondria to selectively trap Top1mt covalent complexes (Top1mtcc) and its role in anticancer therapeutics. We have designed a biocompatible mesoporous metal–organic framework (MOF) material, namely MIL-101(Fe), as the drug delivery carrier that selectively localizes inside mitochondria. In contrast to the traditional way of synthesising MOFs, here we have employed a vapour-assisted solvothermal method for the synthesis of MIL-101(Fe) using terephthalic acid as the organic linker and Fe(III) as the metal source. The advantage of this method is that it recycles the excess solvent (DMF) and reduces the amount of washing solvent. We demonstrate that MIL-101(Fe)-encapsulated irinotecan (MIL-Iri) was selectively targeted towards the mitochondria to poison Top1mtcc in a dose-dependent manner and was achieved at a low nanomolar drug concentration. We provide evidence that Top1mtcc generated by MIL-Iri leads to mtDNA damage in human colon and breast cancer cells and plays a significant role in cellular toxicity. Altogether, this study provides evidence for a new and effective strategy in anticancer chemotherapy
Super‐Intense Geomagnetic Storm on 10–11 May 2024: Possible Mechanisms and Impacts
No full textOne of the most intense geomagnetic storms of recent times occurred on 10–11 May 2024. With a peak negative excursion of Sym-H below −500 nT, this storm is the second largest of the space era. Solar wind energy transferred through radiation and mass coupling affected the entire Geospace. Our study revealed that the dayside magnetopause was compressed below the geostationary orbit (6.6 RE) for continuously ∼6 hr due to strong Solar Wind Dynamic Pressure (SWDP). Tremendous compression pushed the bow-shock also to below the geostationary orbit for a few minutes. Magnetohydrodynamic models suggest that the magnetopause location could be as low as 3.3RE. We show that a unique combination of high SWDP (≥15 nPa) with an intense eastward interplanetary electric field (IEFY ≥ 2.5 mV/m) within a super-dense Interplanetary Coronal Mass Ejection lasted for 409 min–is the key factor that led to the strong ring current at much closer to the Earth causing such an intense storm. Severe electrodynamic disturbances led to a strong positive ionospheric storm with more than 100% increase in dayside ionospheric Total Electron Content (TEC), affecting GPS positioning/navigation. Further, an HF radio blackout was found to occur in the 2–12 MHz frequency band due to strong D- and E-region ionization resulting from a solar flare prior to this storm
Statistics of Higher Harmonics SRS at Low Latitude Station, Shillong
No full textThis is the first statistical ground investigation of unique low latitude Spectral Resonance Structures (SRS) that increase beyond , 5Hz crossing the fundamental Schumann resonance at few occurrences. The study is carried out using high resolution magnetic field variation data obtained from induction coil magnetometer (ICM) installed at very low latitude Indian station, Shillong (25.56°N geographic latitude, 91.86°E geographic longitude, dipoleL=1.08) for the duration 2013–2018. This study focuses on the characteristics of SRS whose harmonic frequencies reach 5Hz and above. The study reveals that the occurrence of SRS events above 5Hz is higher in winter as compared to summer, also the occurrence is higher during low solar activity period as compared to period of solar maximum. It is seen that both the cavities, viz. Ionospheric Alfven Resonator (IAR) and Magnetospheric Alfven Resonator (MAR) support such SRS and have their respective quality factor (Q-factor). The seasonal variability of the Q-factor of these cavities also shows a trend similar to the occurrence, with higher values of Q-factor during winter as compared to summer. Dependence of SRS events on parameters such as height of the IAR cavity, ion mass density, conductivities, which affects the Q-factor reveals that IAR above 5Hz is supported by a larger height of the cavity with very low ion densities. On the other hand, the MAR cavity efficiency is higher when the Alfven wave conductance is much larger than the Pedersen conductivity