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W-Doped Cs<sub>2</sub>SnCl<sub>6</sub> for Near-Infrared Emission
No full text0D perovskite derivatives such as Cs2WCl6 and Cs2WOxCl6-x have been recently shown to emit near-infrared (NIR) radiation. The d-d electronic transition of W4+/W5+ yields an NIR emission. However, the close proximity of those ions can quench the photoluminescence via concentration quenching. To address this issue, here we dilute the emission centers by doping a small amount of W into the Cs2SnCl6 0D perovskite. The results suggest that the dopant centers are [WOCl5]2- replacing [SnCl6]2- octahedra in the host lattice. The optimal 3.3% W-doped Cs2SnCl6 exhibits NIR (965 nm) emission with over 52 times higher intensity compared to that of Cs2WOxCl6-x. The suppression of concentration quenching in W-doped Cs2SnCl6 also significantly alters its temperature-dependent (7–300 K) photoluminescence compared to that of Cs2WOxCl6-x. Finally, we demonstrated NIR phosphor-converted light-emitting diodes of W-doped Cs2SnCl6 showing an output power of 10.3 mW at 400 mA. This is the first report of W doping in 0D perovskites showing its potential as an NIR phosphor
Conformer‐Mediated Helical Chirality in 2D Layered Hybrid Perovskites
No full textTwo-dimensional (2D) chiral hybrid perovskites A2PbI4 (A: chiral organic ion) enable chirality controlled optoelectronic and spin-based properties. A+ organic sublattice induces chirality into the semiconducting [PbI4]2- inorganic sublattice through non-covalent interactions at organic–inorganic interface. Often, the A+ cations in the lattice have different orientations, leading to asymmetry in the non-covalent interactions. In a novel approach, we use different conformers of A+ cations to create asymmetry in the non-covalent interactions, thereby, achieving chiral perovskites with rare helical enantiomorphic structures. We prepared (R-IdPA)2PbI4 and (S-IdPA)2PbI4 (IdPA: 1-iodopropan-2-ammonium) which crystallize in the helical enantiomorphic space groups P43212 and P41212, respectively. The gauche- and anti-conformers of IdPA+ are arranged alternatively in the hybrid structure. Importantly, the anti-conformer of IdPA+ ion have significantly stronger electrostatic, N−H⋅⋅⋅I hydrogen bonding, and I⋅⋅⋅I halogen bonding interactions with the [PbI4]2- sublattice, compared to the gauche-conformer. This periodic asymmetry in non-covalent interactions caused by the alternative arrangement of gauche- and anti-conformers induces chirality in the inorganic sublattice with four-fold screw axes (43 and 41). The enantiomers (R-/S-IdPA)2PbI4 show mirror-image like circular dichroism from excitonic absorption of the inorganic sublattice. This conformer-based design of chiral hybrid perovskites in helical space groups broadens material choices for advanced optoelectronic applications
Graphical representation of global water models
No full textNumerical models are simplified representations of the real world at a finite level of complexity. Global water models are used to simulate the terrestrial part of the global water cycle, and their outputs contribute to the evaluation of important natural and societal issues, including water availability, flood risk, and ecological functioning. Whilst global water modeling is an area of science that has developed over several decades, and individual model-specific descriptions exist for some models, there has to date been no attempt to visualize the ways that several models work, using a standardized visualization framework. Here, we address this gap by presenting a community-driven process that developed a framework to visualize several global water models. The models considered participate in the Inter-Sectoral Impact Model Intercomparison Project phase 2b (ISIMIP2b). The diagrams were co-produced between a graphics designer and 16 modeling teams, based on extensive discussions and pragmatic decision-making that balanced the need for accuracy and detail against the need for effective visualization. The model diagrams are based on a standardized ISIMIP2b-complete global water model that represents what is theoretically possible to represent in the current generation of state-of-the-art global water models participating in ISIMIP2b. Model-specific diagrams are then copies of the ISIMIP2b-complete model, with individual processes either included or grayed out. An open-source tool has been developed and published jointly with the diagrams, which allows someone to generate a diagram for their own global water model by adapting the diagrams presented here. As well as serving an educational purpose, we envisage that the diagrams will help researchers in and outside of the global water model community to select suitable model(s) for specific applications, stimulate a community learning process, and identify missing components to help direct future model developments
Investigation of fair weather atmospheric electric field variations from the Eastern Himalaya Syntaxis in North-East region of India
No full textWe examine here variations of fair weather atmospheric electric field (AEF) referred to as potential gradient (PG), recorded at Namsai (27.69°N, 95.85°E) in the Eastern Himalaya Syntaxis. The work is based on data collected over 99 fair weather days spanning from November 2017 to April 2019. We aim to assess the general characteristics of PG over Namsai and further explore the possibility of deciphering seismic-associated signatures in PG. Our analysis indicates that the mean diurnal variation of fair weather PG peaks at ∼14:00 UT. Seasonal analysis shows that PG values maximized during the winter, followed by the equinox and summer. These characteristics of PG are explained in terms of variations in meteorological parameters, air pollution level, and geographical location of Namsai, i.e., the Brahmaputra river nearby and the deep forest surrounding it. We further report a significant variation in PG before the Mw 6.4 earthquake on November 17, 2017, which occurred in a blind fault near the Main Central Thrust. PG showed a bay-shaped negative anomaly lasting ∼2 h, observed ∼7 h before the event. The anomaly exceeded the 2σ limit of mean fair weather PG. The earthquake day was devoid of any significant meteorological changes. It is suggested that the PG anomaly was associated with earthquake rather than local weather changes. This study not only provides better insights into the general variability of fair weather PG over this region but also highlights the importance of AEF measurements as a potential indicator of seismic events, sensing as precursory signals several hours ahead
The Gridded Geomagnetic Field of India with MATLAB GUI
No full textA unique two-dimensional gridded geomagnetic map of India is constructed using the geomagnetic field observations from 11 observatories of India, operated by the Indian Institute of Geomagnetism. In order to create the spatial grid, 11 spatial techniques are compared with observed magnetic field during 2011–2020. Out of the 11 known techniques of spatial interpolation, the Modified Shepard’s Method is selected as the best suitable method for interpolation. The spatial gird provides the hourly values of absolute and variations in horizontal (H) and vertical (Z) magnetic field over India. The spatial grid can be applied to higher temporal resolution of data sets as well. This map can be used to get the regional changes in the magnetic field during quiet and disturbed conditions. A user-friendly MATLAB based GUI is created for obtaining the spatial gri
Community perceptions of climate change in Manipur, India
No full textClimate change poses a significant threat to the lives and livelihoods of local communities in the Himalayan regions. These regions do not have an extensive network of meteorological stations due to poor infrastructure for climate change studies. Understanding how the local community perceives climate change provides an important insight into specific features of climate change in the data-scarce regions. This study aimed to understand how local communities of Manipur in northeast India have perceived climate change, including its causes and impacts, its influences on their life and their responses. In this study, a survey was conducted in the valley and hill regions of Manipur on local community perceptions of climate change. The survey sample comprised of 193 randomly selected local inhabitants in both the regions. Through this survey, we aimed to determine how local communities respond to the effects of climate change in the study area based on their personal experiences. The results indicated that the local community has fairly strong perceptions of climate change with more than 80% of respondents reporting a change in the cultivation patterns and agricultural productivity have been changing over the years. Another 98% of the respondents acknowledged a change in “summer temperature” over the past 15–20 years as a result of climate change. Further, the majority of respondents (> 97%) are concerned that climate change may increase the frequency of natural disasters in the state. The consistency of this local’s perception with meteorological data was also evaluated. The annual mean temperature had increased at a rate of 0.027 and 0.024 °C/year in the valley and hill, respectively, while the annual precipitation declined at a rate of 0.08 and 0.12 mm/year in the valley and hill, respectively, in the past 44 years (1979–2022). The results reveal an overall consistency between local community perceptions of climate change and the scientific observations of these changes. A better understanding of how communities perceive climate change would enable decision-makers to devise local adaptation measures and formulate an effective mitigation strategy that efficiently tackles the negative impact of climate change impacts
Enhanced Electro‐Optic Properties of Blue Phase Liquid Crystals Using Slippery Polymer Stabilization
No full textBlue-phase liquid crystals (BPLCs) are promising for next-generation fast-switching displays due to their unique nanoscale self-assembly and soft-crystalline properties. However, conventional stabilization methods using high glass-transition temperature (Tg) polymers, such as acrylates or thiols, often result in high operating voltages due to strong surface anchoring at the LC-polymer interface, limiting practical applications. This study proposes using poly(hexyl methacrylate) (PHMA), a low-Tg polymer (∼−5 °C), to create a slippery polymer network that reduces operating and threshold voltages. Additionally, this sliding interface promotes the BP-III phase, further decreasing the operating voltage to 38% with minimal hysteresis and increasing the relative Kerr constant by ninefold. The biphasic interaction between BPLCs and PHMA is quantitatively analyzed, offering insights into the sliding surface mechanism and optimized the Kerr and response time equations. These findings highlight significant potential for advancing next-generation electro-optic and tunable photonic systems
Standard protocols for performance evaluation of typhoid fever in-vitro diagnostic assays in laboratory and field settings
No full textntroduction
Typhoid fever is a leading public health problem in India and other South East Asian countries. Its diagnosis traditionally relies on culture methods with poor sensitivity, and serological methods with limited role in endemic areas. Incorrect diagnosis results in antibiotic misuse, disease complications, emergence and spread of multidrug-resistant strains. There is a need to develop quality diagnostic tests for effective and early diagnosis of typhoid fever. This will help in early patient management, disease burden estimation, and assessing the impact of public health interventions including vaccines.
Aim
This paper describes standard protocols for conducting pre-licensure (analytical) and field (clinical) performance evaluation of in-vitro diagnostic tests that detect S. Typhi antigens or antibodies or gene segments in blood/serum/plasma samples.
Material and methods
The analytical performance evaluation protocol describes diagnostic accuracy studies for three different IVD formats using well-characterized clinical samples, and the field validation protocol describes the methodology for conducting a cross-sectional study for assessing IVD performance in acute undifferentiated febrile illness. The latter may also be used to establish a typhoid sample biobank. Both the protocols use statistically significant sample size and describe a detailed sample panel (including cross reactive specimens).
Discussion
These protocols will help in robust evaluation of IVDs for typhoid, especially in endemic areas and in absence of a predicate device. To the best of our knowledge, this is the first such comprehensive guidance document of their kind, which may be adapted across similar settings
Intra‐Configurational Spin‐Flip <i>d</i> → <i>d</i> Transition of Mo (III) Doped Perovskite for Ultra‐Narrow Near Infrared‐II Emission in Ambient Conditions
No full textSharp near-infrared-II (NIR-II) emissions are typically achieved through f → f electronic transitions of rare-earth ions, while d → d transitions in transition metal ions are broad due to electron–ligand interactions. An exception is the intra-configurational spin-flip (ICSF) d → d transition like t2g3 → t2g3 of Mo3+ emitting sharp NIR-II emission, but only at cryogenic temperatures under vacuum. The high oxophilicity of Mo3+ created defects during the synthesis, quenching the emission at room temperature. Herein, we overcome this issue by synthesizing Mo3+− doped Cs2NaInCl6 double perovskites in a reducing H3PO2 environment. [MoCl6]3− octahedra are formed, exhibiting ultra-narrow ICSF d → d (2T1g/2Eg → 4A2g) NIR-II emission at 1095 nm in ambient conditions. In addition, a second ICSF 2T2g → 4A2g emission is observed at 700 nm, violating the Kasha's rule. The intensity of ICSF emissions increase with increasing temperature (7–350 K) due to vibronic coupling relaxing the Laporte selection rule. The samples are stable for more than 6 months in ambient conditions, allowing for a detailed study of fundamental photophysics and fabrications of phosphor-converted light emitting diodes. This is the first Mo3+–based NIR-II optoelectronic device, opening opportunities for applications like optical fibers and lasing
Extreme Indian summer monsoon states stifled Bay of Bengal productivity across the last deglaciation
No full textIndian summer monsoon (ISM) hydrology fuels biogeochemical cycling across South Asia and the Indian Ocean, exerting a first-order control on food security in Earth’s most densely populated areas. Although the ISM is projected to intensify under continued greenhouse forcing, substantial uncertainty surrounds anticipating its impacts on future Indian Ocean stratification and primary production—processes key to the health of already-declining fisheries in the region. Here we present century-scale records of ISM runoff variability and marine biogeochemical impacts in the Bay of Bengal (BoB) since the Last Glacial Maximum (∼21 thousand years ago (ka)). These records reveal extreme monsoon states relative to modern strength, with weakest ISM intensity during Heinrich Stadial 1 (∼17.5–15.5 ka) and strongest during the early Holocene (∼10.5–9.5 ka). Counterintuitively, we find that BoB productivity collapsed during both extreme states of peak monsoon excess and deficits—both due to upper-ocean stratification. Our findings point to the possibility of future declines in BoB primary productivity under a strengthening and more variable ISM regime