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Empirical Model of Equatorial ElectroJet (EEJ) Using Long‐Term Observations From the Indian Sector
No full textThe Equatorial Electrojet (EEJ) is one of the important near-earth space weather phenomena which exhibits significant diurnal, seasonal and solar activity variations. This paper investigates the EEJ variations at diurnal, seasonal and solar cycle time scales from the Indian sector and portrays a new empirical EEJ field model developed using the observations spanning over nearly two solar cycles. The Method of Naturally Orthogonal Components (MNOC), also known as Principal Component Analysis (PCA), was employed to extract the dominant patterns of principal diurnal, semi-diurnal, and ter-diurnal components contributing to the EEJ variation. The amplitudes of these diurnal, semi-diurnal, and ter-diurnal components in EEJ are found to vary significantly with the season and solar activity. The seasonal and solar activity dependencies of these principal components are modeled using suitable bimodal distribution functions. Finally, the empirical model for EEJ field was built by combining the principal components with their corresponding modeled amplitudes. This model accurately reproduces the diurnal, seasonal and solar activity variations of EEJ. The modeled monthly mean variations of EEJ field at ground exhibit excellent correlation of 0.96 with the observations with the root mean square error <5 nT. It also successfully captures the seasonal and solar activity variations of Counter Electrojet (CEJ). Finally, this model named “Indian Equatorial Electrojet (IEEJ) Model” is made publicly available for interested scientific users (https://iigm.res.in/system/files/IEEJ_model.html)
A clinical mutation in uvrA , a DNA repair gene, confers survival advantage to Mycobacterium tuberculosis in the host
No full textDNA repair pathways play an essential role in maintaining the genomic integrity of bacteria, and a perturbation in their biological activity helps bacteria survive under duress. In drug-resistant clinical strains, we identified a Q135K mutation in the uvrA gene, a DNA repair pathway gene. To delineate the role of uvrA and the Q135K mutation, we generated the gene replacement mutant of UvrA (RvΔuvrA) in Mycobacterium tuberculosis H37Rv (Mtb-Rv). While the lack of UvrA function in RvΔuvrA could be restored upon complementation with uvrA, the uvrA-Q135K mutant identified in clinical drug-resistant strains failed to do so. This was reflected in higher mutation rates in RvΔuvrA and RvΔuvrA::uvrAQ135A, compared with wild-type Rv or RvΔuvrA::uvrA complemented strains in the presence and absence of oxidative stress. Killing kinetics experiments with anti-TB drugs showed increased survival of RvΔuvrA and RvΔuvrA::uvrAQ135K, strains compared with Rv or RvΔuvrA::uvrA. Importantly, RvΔuvrA and RvΔuvrA::uvrAQ135K showed enhanced survival in peritoneal macrophages and murine infection model of infection. Together, data suggests that acquiring Q135K mutation benefits the pathogen, which helps enhance the host's survival adaptability
Mixed-valent cobalt phosphate/borophene nanohybrids for efficient electrocatalytic oxygen evolution reaction
No full textDeveloping efficient, low-cost, non-precious and stable electrocatalyst is necessary for sustainable electrocatalytic water splitting. Recently, borophene has emerged as a novel two-dimensional material with exciting properties. Although several researchers have theoretically predicted its applicability towards effective electrocatalytic water splitting, studies on its practical applications are still limited. In this regard, a mixed-valent cobalt phosphate/borophene nanohybrid (BCoPi) was synthesized using hydrothermal method, and its activity towards oxygen evolution reaction (OER) was systematically studied. The electron-deficient nature of borophene enables activation of catalytic sites and facilitates electron transport owing to its highly conductive nature. It can act as a proton acceptor along with phosphate groups, as well as provide multiple secondary active sites in addition to Co, breaking the scaling relation of OER. For BCoPi, achieving a current density of 50 mA cm-2, 100 mA cm-2 and 500 mA cm-2 requires an overpotential of 337 mV, 357 mV and 401 mV, respectively, in an alkaline medium, that are superior to pristine cobalt phosphate (CoPi). It also exhibits low Tafel slope of 61.81 mV dec-1, suggesting faster OER kinetics and excellent long-term stability. This study will extend the development and application of borophene-based heterostructures for highly active and stable electrocatalysts for various applications
Operando investigation of the origin of C─C coupling in electrochemical CO<sub>2</sub> reduction upon releasing bonding strength, structural ordering in Pd─Cu catalyst
No full textIt is widely established that the electroreduction of carbon dioxide on a copper surface yields a spectrum of alcohols and hydrocarbons. But the selectivity of Cu toward a certain product is extremely poor as it forms a variety of reduced products concurrently. Controlling selectivity and overall performance depends on the modification of the Cu site and local environment. This study depicts how the product selectivity can be switched from C1 to C2 and multicarbon products by systematic incorporation of secondary metal (Pd) into the Cu lattice. Upon releasing the structural ordering from intermetallic to alloy and then to bimetallic, a systematic enhancement on the formation of C2 products from CO2 has been observed. Real-time in situ X-ray absorption spectroscopy (XAS) study showed the potential dependent evolution of Pd─Cu and Cu─Cu bonds in different Pd-Cu-based catalysts. The detailed analysis of in situ IR and Raman also determined the adsorbed intermediate species and helped to identify the mechanism. Computational studies show the feasibility of multicarbon product formation on bimetallic catalysts compared to alloy and intermetallic catalysts. The current density and the activity of the CO2 electroreduction have been enhanced by the utilization of the flow cell in the gas diffusion electrode configuration
Emerging collective quantum phenomena of excitons in metal-halide perovskites
No full textMetal-halide perovskites (MHPs) with unique electronic and optical properties have emerged as promising materials with a broad spectrum of applications in photovoltaics, optoelectronic, and photonic devices. The distinct properties and tremendous potential of MHPs are intricately defined by excitons and collective quantum states. This article reviews the excitonic states and coordinated interplay of charge, spin, and lattice. We discuss the recent experimental and theoretical discoveries of excitonic phenomena, as well as correlated states involving condensation and cooperative emission. Additionally, our exploration extends to the structural properties of MHPs that facilitate the emergence of robust quantum states, even at room temperatures. Finally, an overview of the remaining challenges and potential applications of MHPs in quantum optics, coherent light sources, electrically driven amplified spontaneous emission, and superfluorescent lasing is provided
Land and Atmospheric Drivers of the 2023 Flood in India
No full textFloods in India are recurring natural disasters resulting from extreme precipitation during the summer monsoon season (June–September). The recent flood in North India in July 2023 caused substantial damage to lives, agriculture, and infrastructure. However, what led to the 2023 North India flood and the role of atmospheric and land drivers still need to be examined. Using in situ observations, satellite data, and ERA5 reanalysis combined with hydrological and hydrodynamical modeling, we examine the role of land and atmospheric drivers in flood occurrence and its impacts. Extreme precipitation in a large region during 7–10 July 2023 created favorable conditions for the flood in the hilly terrains and plains of north India. More than 300 mm of precipitation fell in just 4 days, which was eight times higher than the long-term average (2001–2022). Anomalously high moisture transport over northern India was recorded on 7 July 2023, making atmospheric conditions favorable for intense landfall. Increased column water vapor and specific humidity at different pressure levels confirmed the continuous moisture presence before the extreme rainfall that caused floods in northern India from 7 to 12 July 2023. Atmospheric and land (high antecedent soil moisture) conditions contributed to a more than 200% rise in streamflow at several gauge stations. Satellite-based flood extent shows a considerable flood inundation that caused damage in the Sutlej and Yamuna River basins. Our findings highlight the crucial role of the favorable land and atmospheric conditions that caused floods and flash floods in north India in July 2023
Impact of geomagnetic activity on stratosphere and upper troposphere
No full textDuring active geomagnetic conditions, a large amount of energy is deposited in the polar atmosphere in the form of particle precipitation that leads to Joule heating creating circulation of intense currents in the auroral region. It can affect the existing background pressure fluctuations in the stratospheric and tropospheric heights, leading to anomalous changes in the vertical temperature (T), zonal (u) and meridional (v) wind. In this study, we demonstrate the effect of active geomagnetic conditions on these atmospheric variables in different longitudinal regions. The investigation involves daily, monthly and seasonal variation of active geomagnetic conditions. Active geomagnetic conditions are selected using geomagnetic activity indices like auroral activity index |AL|>1000 nT, Disturbed Storm time index Dst < -150 and polar cap index PC > 5. Events are identified during November to March for 1990 to 2020 period. Among them 99 active geomagnetic conditions occurred in the month of March which are considered for further investigation. Composite analysis of T, u and v reflects that the temperature shows an increase in the entire atmospheric column; the anomalies in u (u′) and v (v′) show a regional dependence and strengthen in their amplitudes. It is seen from the monthly investigation of March that the Western Pacific, Canadian and East Pacific sectors respond to the active geomagnetic conditions at upper atmospheric pressure levels (approximately 40–70 km altitude) in the polar region. This is indicative of a vertical translation of energy to lower atmosphere during active geomagnetic conditions
Policy Framework to Combat the Challenges of Climate Change in the Upper Indus Basin
No full textThe Indus River Basin (IRB), one of the major river basins in the Hindu Kush Himalaya, is primarily sustained by meltwater from the cryosphere. It caters to diverse sectors, including intense irrigation-supported agriculture, energy production, tourism and biodiversity. The cryosphere of the Upper Indus Basin (UIB) is mainly influenced by the western disturbances with subordinate contribution from the Indian Summer Monsoon. Increase in ambient temperature, shrinking cryospheric reserves, fluctuating surface runoff and enhanced frequency of extreme weather events are some of the noticeable indicators of climate change in the UIB. These changes will most likely adversely affect the water-dependent sectors in the upstream and downstream of IRB, posing serious threat to food security and livelihoods. Although the region has gained significant attention in recent years, there remains a noticeable knowledge gap pertaining to certain key issues with serious implications for the natural environment and the people. A national workshop was organized for stimulated deliberations to identify the major knowledge gaps and suggest a policy framework for climate change mitigation in the UIB. The workshop underscores the urgent need of multi-institutional, multidisciplinary , comprehensive, coordinated and time-bound collaboration to study the interplay of complex drivers on water resources of the UIB
Magnetic fabrics of west coast dyke swarm from Deccan volcanic province, Maharashtra, India and their relationship with magma flow direction
No full textDykes are one of the primary subvolcanic bodies that transport magma from the shallow magma chamber or from the deep-seated magma reservoir. The mechanism of magma transport and emplacement in dyke swarms can contribute precious details on source and how magma has associated with crustal rocks. Here we are presenting the results obtained from the Anisotropy of magnetic susceptibility (AMS) on their mode of emplacement and to understand magma flow direction. AMS and rock magnetic studies were performed on 33 dykes located on the West coast of Maharashtra, (India) to determine the magma flow direction using magnetic fabric. Thermomagnetic curves and hysteresis loop measurement indicates that titanomagnetite of associated pseudo-single-domain/multi-domain grain sizes are responsible for the magnetic fabrics. Based on the clustering of the principal AMS axes, three types of AMS fabrics were recognized, (i) Normal fabric, interpreted as due to magma flow characterised by clustering of K 1–K 2 axes on the dyke plane and K3 axes are nearly perpendicular to it, (ii) Inverse fabric with K 2–K 3 plane parallel to the dyke plane and K 3 is perpendicular to it and (iii) Intermediate fabric, with K 1–K 3 axes clustering close to dyke plane. The inclination of the K 1 axis (IK 1) of Normal fabric is the most important to determine the flow of magma for the studied dyke swarm. The IK1 of the studied dykes were fed dominantly by horizontal (IK 1 > 30°), inclined (30° > IK 1 > 60°) up to vertical fluxes (IK 1 > 60°). These results suggest that the dykes may be closer to the magma source and horizontal magma flow inferred from the dykes reveals source is located further away. The present AMS study along with geophysical, geochemical and petrological study supports the evidence of feeder fed mechanism
Maneuvering superparamagnetic particles in a nematic liquid crystal by transverse electric and in-plane rotating magnetic fields
No full textThe transport of microparticles in fluids is of current interest and controlling their trajectories at will is of paramount importance for fundamental research and applications. Here, we demonstrate the effect of an ac electric field and a dc magnetic field on the orientation and electrophoretic propulsion of superparamagnetic microparticles in a nematic liquid crystal. The magnetic field changes the orientation of the elastic dipoles in the plane, and the competing effect of the elastic and magnetic torques is used to measure the induced magnetic moment of a single particle. In the absence of the magnetic field, the particles propel along the far-field director under the application of a low-frequency transverse electric field. The rotating magnetic field changes the direction of motion, facilitating remote control of the particle trajectories. Our study demonstrates the potentialities of orthogonal electric and magnetic fields for maneuvering microparticle trajectories, which are important for practical applications, ranging from targeted delivery and microfluidics to microrobotics