The tin sulfide solar cell has acquired prominence in recent years. We present the characteristics of two polymorphs of SnS and their perspectives in thin‐film solar cells. Thin‐film SnS with cubic ...crystalline structure (SnS‐CUB) was obtained via two chemical routes. This semiconductor is distinct from the more common SnS thin films of orthorhombic crystalline structure (SnS‐ORT), also obtained by chemical routes. The SnS‐CUB reported here with a lattice constant a of 11.587 Å replaces the zinc blende structure previously reported for this material with a of 5.783 Å. Thin films of SnS‐CUB have an optical bandgap (Eg) of 1.66–1.72 eV and electrical conductivity (σ) of 10−6 Ω−1 cm−1. These characteristics distinguish them from SnS‐ORT presented here with an Eg of 1.1 eV and σ typically higher by two orders of magnitude. We discuss the uncertainties that have prevailed in the assignment of crystalline structure for SnS‐CUB and SnS‐ORT. The optical and electrical properties of these two polymorphs of SnS are contrasted in the context of light‐generated current density in solar cells. We conclude that the two SnS polymorphs when considered together as optical absorbers offer wider prospects for tin sulfide thin‐film solar cells.
Given the recognized role of agroforestry systems (AFS) in climate change mitigation through carbon sequestration, it is important to have rigorous and consistent procedures to measure the extent of ...C sequestration. The methods used currently vary widely and the estimations entail several assumptions, some of which are erroneous. Large-scale global models that are based on such measurements and estimations are thus likely to result in serious under- or overestimations. These methodological problems, though common to most land-use systems, are of a higher order of magnitude in AFS compared with agricultural systems because of the integrated nature of AFS and the lack of rigorous data on the area under the practice. While there are no easy, fast, and pragmatic solution to these complex issues in the short term, agroforestry researchers could, at the very minimum, include accurate description of the methods and procedures they use, such as sampling scheme, analytical details, and computational methods, while reporting results. That will help other researchers to examine the datasets and incorporate them in larger databases and help agroforestry earn its deserving place in mainstream efforts. Missing the opportunity to capitalize on the environmental services of agroforestry for the lack of rigorous and consistent procedures for data collection and reporting will be a serious setback to the development of agroforestry.
The entanglement entropy (EE) of gauge theories in three spacetime dimensions is analyzed using manifestly gauge-invariant variables defined directly in the continuum. Specifically, we focus on the ...Maxwell, Maxwell-Chern-Simons (MCS), and non-Abelian Yang-Mills theories. Special attention is paid to the analysis of edge modes and their contribution to EE. The contact term is derived without invoking the replica method and its physical origin is traced to the phase space volume measure for the edge modes. The topological contribution to the EE for the MCS case is calculated. For all the Abelian cases, the EE presented in this paper agrees with known results in the literature. The EE for the non-Abelian theory is computed in a gauge-invariant Gaussian approximation, which incorporates the dynamically generated mass gap. A formulation of the contact term for the non-Abelian case is also presented.
Nickel has emerged as a desirable substitute for palladium in Sonogashira coupling reactions due to its abundance, less toxicity and high catalytic activity. Ni complexes have been developed to ...catalyse C(sp)-C(sp
) and C(sp)-C(sp
) Sonogashira couplings that find applications in the synthesis and modifications of biologically relevant molecules. This review focuses on the catalytic potential and mechanistic details of various Ni complexes employed in the Sonogashira coupling. These include homogeneous catalytic systems with Ni-phosphorus and Ni-nitrogen catalysts, ligand-free catalysts, and carbonylative coupling strategies. Various heterogeneous catalytic systems using supported Ni complexes, Ni nanoparticles and Pd-Ni bimetallic catalysts have also been discussed. This is the first review reported so far dealing exclusively with Ni-catalysed Sonogashira coupling reactions. This review illustrates the current strategies and potential of Ni-catalysed Sonogashira coupling reactions in both homogeneous and heterogeneous systems, and covers the literature up to 2020.
We calculate the pair production rates for spin-1 or vector particles on spaces of the form M×R1,1, with M corresponding to R2 (flat), S2 (positive curvature), and H2 (negative curvature), with and ...without a background (chromo)magnetic field on M. Beyond highlighting the effects of curvature and background magnetic field, this is particularly interesting since vector particles are known to suffer from the Nielsen-Olesen instability, which can dramatically increase pair production rates. The form of this instability for S2 and H2 is obtained. We also give a brief discussion of how our results relate to ideas about confinement in non-Abelian theories.
Changes in rainfall affect drinking water, river and surface runoff, soil moisture, groundwater reserve, electricity generation, agriculture production and ultimately the economy of a country. Trends ...in rainfall, therefore, are important for examining the impact of climate change on water resources for its planning and management. Here, as analysed from 119 years of rainfall measurements at 16 different rain gauge stations across northeast India, a significant change in the rainfall pattern is evident after the year 1973, with a decreasing trend in rainfall of about 0.42 ± 0.024 mm dec−1. The wettest place of the world has shifted from Cherrapunji (CHE) to Mawsynram (MAW) (separated by 15 km) in recent decades, consistent with long-term rainfall changes in the region. The annual mean accumulated rainfall was about 12 550 mm at MAW and 11 963 mm at CHE for the period 1989-2010, as deduced from the available measurements at MAW. The changes in the Indian Ocean temperature have a profound effect on the rainfall in the region, and the contribution from the Arabian Sea temperature and moisture is remarkable in this respect, as analysed with a multivariate regression procedure for the period 1973-2019. The changes in land cover are another important aspect of this shift in rainfall pattern, as we find a noticeable reduction in vegetation area in northeast India in the past two decades, implying the human influence on recent climate change.
Shaded perennial agroforestry systems contain relatively high quantities of soil carbon (C) resulting from continuous deposition of plant residues; however, the extent to which the C is sequestered ...in soil will depend on the extent of physical protection of soil organic C (SOC). The main objective of this study was to characterize SOC storage in relation to soil fraction-size classes in cacao (Theobroma cacao L.) agroforestry systems (AFSs). Two shaded cacao systems and an adjacent natural forest in reddish-yellow Oxisols in Bahia, Brazil were selected. Soil samples were collected from four depth classes to 1 m depth and separated by wet-sieving into three fraction-size classes (>250 μm, 250-53 μm, and <53 μm)--corresponding to macroaggregate, microaggregate, and silt-and-clay size fractions--and analyzed for C content. The total SOC stock did not vary among systems (mean: 302 Mg/ha). On average, 72% of SOC was in macroaggregate-size, 20% in microaggregate-size, and 8% in silt-and-clay size fractions in soil. Sonication of aggregates showed that occlusion of C in soil aggregates could be a major mechanism of C protection in these soils. Considering the low level of soil disturbances in cacao AFSs, the C contained in the macroaggregate fraction might become stabilized in the soil. The study shows the role of cacao AFSs in mitigating greenhouse gas (GHG) emission through accumulation and retention of high amounts of organic C in the soils and suggests the potential benefit of this environmental service to the nearly 6 million cacao farmers worldwide.
Silvopastoral systems that integrate trees in pasture production systems are likely to enhance soil carbon (C) storage in lower soil layers due to the presence of deep tree roots. To quantify the ...relative soil C contribution from trees (C3 plants) and warm season grasses (C4 plants) in silvopastoral systems, soil samples were collected and analyzed from silvopastures of slash pine (Pinus elliottii)+bahiagrass (Paspalum notatum), and adjacent open pasture (OP), at six depths down to 125 cm, at four sites representing two major soil orders (Spodosols and Ultisols) of Florida. The plant sources of C in whole (nonfractionated) and three soil fraction sizes (250-2000, 53-250, and <53 μm) were traced using stable C isotope signatures. The silvopasture sites contained higher amounts of C3-derived soil organic carbon (SOC) compared with OP sites, at all soil depths. Slash pine trees (C3 plants) seemed to have contributed more C in the silt+clay-sized (<53 μm) fractions than bahiagrass (C4 plants), particularly deeper in the soil profile. Spodosols sites contained more C in the <53 μm fraction at and below the spodic horizon (occurring between 15 and 50 cm) in silvopasture compared with OP. The results indicate that most of SOC in deeper soil profiles and the relatively stable <53 μm C fraction were derived from tree components (C3 plants) in all the sites, suggesting that the tree-based pasture system has greater potential to store more stable C in the soil compared with the treeless system.
Heavy metals are an important group of chemical contaminants and food is the major vehicle for entry into the system. Fish constitute a major source of heavy metals in food. Concentration of heavy ...metals in commercially important species of fish, shellfish and fish products from fish markets in and around the Cochin area was evaluated using an atomic absorption spectrometer. The concentration ranges of Cd, Pb, Hg, Cr, As, Zn, Cu, Co, Mn, Ni, and Se in the samples were <0.07–1, <0.07–1.32, <0.05–2.31, <0.05 to 3.65, <0.1–4.14, 0.6 to 165, 0.15 to 24, <0.02 to 0.85, <0.08 to 9.2, <0.032–1.38 and; <0.03–1.35
mg/kg, respectively. The present study showed that different metals were present in the samples at different levels but within the maximum residual levels prescribed by the EU and USFDA and the fish and shellfish from these areas, in general, are safe for human consumption.
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