The gastrointestinal (GI) tract of an animal consists of a very complex and dynamic microbial ecosystem that is very important from a nutritional, physiological and pathological point of view. A wide ...range of microbes derived from the surrounding aquatic environment, soil/sediment and feed are found to colonize in the GI tract of fish. Among the microbial groups, bacteria (aerobic, facultative anaerobic and obligate aneraobic forms) are the principal colonizers in the GI tract of fish, and in some fish, yeasts are also reported. The common bacterial colonizers in the GI tract of freshwater and marine fish include Vibrio, Aeromonas, Flavobacterium, Plesiomonas, Pseudomonas, Enterobacteriaceae, Micrococcus, Acinetobacter, Clostridium, Fusarium and Bacteroides, which may vary from species to species as well as environmental conditions. Besides, several unknown bacteria belonging to Mycoplasma, Arthrobacter, Brochothrix, Jeotgailbacillus, Ochrobactrum, Psychrobacter and Sejongia species in the GI tract of different fish species have now been identified successfully using culture-independent techniques. Gnotobiotic and conventional studies indicate the involvement of GI microbiota in fish nutrition, epithelial development, immunity as well as disease outbreak. This review also highlights the need for manipulating the gut microbiota with useful beneficial microbes through probiotic, prebiotic and synbiotic concepts for better fish health management.
Understanding the spatial spreading patterns of plant-available sulphur (S) (AS) and plant-available micronutrients (available zinc (AZn), available iron (AFe), available copper (ACu), available ...manganese (AMn) and available boron (AB)) in soils, especially in coastal agricultural soils subjected to various natural and anthropogenic activities, is vital for sustainable crop production by adopting site-specific nutrient management (SSNM) strategies. We studied the spatial distribution patterns of AS, AZn, AFe, ACu, AMn, and AB in cultivated soils of coastal districts of India using geostatistical approaches. Altogether 39,097 soil samples from surface (0 to 15 cm depth) layers were gathered from farm lands of 68 coastal districts. The analysis of soil samples was carried out for soil pH, electrical conductivity (EC), soil organic carbon (SOC) and AS, AZn, AFe, ACu, AMn, and AB. Soil pH, EC and SOC varied from 3.70 to 9.90, 0.01 to 7.45 dS m.sup.-1 and 0.02 to 3.74%, respectively. The concentrations of AS, AZn, AFe, ACu, AMn, and AB varied widely in the study area with their corresponding mean values were 37.4±29.4, 1.50±1.53, 27.9±35.1, 2.14±1.74, 16.9±18.4 and 1.34±1.52 mg kg.sup.-1, respectively. The coefficient of variation values of analyzed soil parameters varied from 14.6 to 126%. The concentrations of AS, AZn, AFe, ACu, AMn, and AB were negatively and significantly correlated with soil pH and positively and significantly correlated with SOC. The geostatistical analysis indicated stable, Gaussian and exponential best-fit semivariogram models with moderate to strong spatial dependence for available nutrients. The generated spatial spreading maps revealed different distribution patterns for AS, AZn, AFe, ACu, AMn, and AB. There were variations in spatial spreading patterns of AS, AZn, AFe, ACu, AMn, and AB in east- and west-coastal area. About 62, 35, 12, 0.4, 23 and 45% of the study area had deficiency of AS, AZn, AFe, ACu, AMn, and AB, respectively. The spatial spreading maps will be highly useful for SSNM in the cultivated coastal soils of the country. This study could also be used as a base for assessing spatial spreading patterns of soil parameters in cultivated coastal areas of other parts of the world.
The development of transparent p‐type oxide semiconductors with good performance may be a true enabler for a variety of applications where transparency, power efficiency, and greater circuit ...complexity are needed. Such applications include transparent electronics, displays, sensors, photovoltaics, memristors, and electrochromics. Hence, here, recent developments in materials and devices based on p‐type oxide semiconductors are reviewed, including ternary Cu‐bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. The crystal and electronic structures of these materials are discussed, along with approaches to enhance valence‐band dispersion to reduce effective mass and increase mobility. Strategies to reduce interfacial defects, off‐state current, and material instability are suggested. Furthermore, it is shown that promising progress has been made in the performance of various types of devices based on p‐type oxides. Several innovative approaches exist to fabricate transparent complementary metal oxide semiconductor (CMOS) devices, including novel device fabrication schemes and utilization of surface chemistry effects, resulting in good inverter gains. However, despite recent developments, p‐type oxides still lag in performance behind their n‐type counterparts, which have entered volume production in the display market. Recent successes along with the hurdles that stand in the way of commercial success of p‐type oxide semiconductors are presented.
Recent progress in hole‐transporting (p‐type) oxide materials and devices is reviewed. Material design strategies to improve the transport properties of five classes of oxides are discussed, including ternary Cu‐bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. In addition, the performance of semiconductor electronic devices based on p‐type oxides is reviewed, including thin‐film transistors, CMOS inverters, p–n‐junction diodes, memory devices, gas sensors, and electrochromics. The recent successes and the hurdles that stand in the way of commercial adoption of p‐type semiconductors are discussed.
Graphene holds great promise for post-silicon electronics; however, it faces two main challenges: opening up a band gap and finding a suitable substrate material. In principle, graphene on hexagonal ...boron nitride (hBN) substrate provides a potential system to overcome these challenges. Recent theoretical and experimental studies have provided conflicting results: while theoretical studies suggested a possibility of a finite band gap of graphene on hBN, recent experimental studies find no band gap. Using the first-principles density functional method and the many-body perturbation theory, we have studied graphene on hBN substrate. A Bernal stacked graphene on hBN has a band gap on the order of 0.1 eV, which disappears when graphene is misaligned with respect to hBN. The latter is the likely scenario in realistic devices. In contrast, if graphene supported on hBN is hydrogenated, the resulting system (graphone) exhibits band gaps larger than 2.5 eV. While the band gap opening in graphene/hBN is due to symmetry breaking and is vulnerable to slight perturbation such as misalignment, the graphone band gap is due to chemical functionalization and is robust in the presence of misalignment. The band gap of graphone reduces by about 1 eV when it is supported on hBN due to the polarization effects at the graphone/hBN interface. The band offsets at graphone/hBN interface indicate that hBN can be used not only as a substrate but also as a dielectric in the field effect devices employing graphone as a channel material. Our study could open up new way of band gap engineering in graphene based nanostructures.
Lead halide perovskites are materials with excellent optoelectronic and photovoltaic properties. However, some hurdles remain prior to commercialization of these materials, such as chemical ...stability, phase stability, sensitivity to moisture, and potential issues due to the toxicity of lead. Here, we report a new type of lead-free perovskite related compound, Cs2PdBr6. This compound is solution processable, exhibits long-lived photoluminescence, and an optical band gap of 1.6 eV. Density functional theory calculations indicate that this compound has dispersive electronic bands, with electron and hole effective masses of 0.53 and 0.85 me, respectively. In addition, Cs2PdBr6 is resistant to water, in contrast to lead-halide perovskites, indicating excellent prospects for long-term stability. These combined properties demonstrate that Cs2PdBr6 is a promising novel compound for optoelectronic applications.
Magnetic skyrmions are topologically stable, vortex-like objects surrounded by chiral boundaries that separate a region of reversed magnetization from the surrounding magnetized material. They are ...closely related to nanoscopic chiral magnetic domain walls, which could be used as memory and logic elements for conventional and neuromorphic computing applications that go beyond Moore's law. Of particular interest is 'racetrack memory', which is composed of vertical magnetic nanowires, each accommodating of the order of 100 domain walls, and that shows promise as a solid state, non-volatile memory with exceptional capacity and performance. Its performance is derived from the very high speeds (up to one kilometre per second) at which chiral domain walls can be moved with nanosecond current pulses in synthetic antiferromagnet racetracks. Because skyrmions are essentially composed of a pair of chiral domain walls closed in on themselves, but are, in principle, more stable to perturbations than the component domain walls themselves, they are attractive for use in spintronic applications, notably racetrack memory. Stabilization of skyrmions has generally been achieved in systems with broken inversion symmetry, in which the asymmetric Dzyaloshinskii-Moriya interaction modifies the uniform magnetic state to a swirling state. Depending on the crystal symmetry, two distinct types of skyrmions have been observed experimentally, namely, Bloch and Néel skyrmions. Here we present the experimental manifestation of another type of skyrmion-the magnetic antiskyrmion-in acentric tetragonal Heusler compounds with D
crystal symmetry. Antiskyrmions are characterized by boundary walls that have alternating Bloch and Néel type as one traces around the boundary. A spiral magnetic ground-state, which propagates in the tetragonal basal plane, is transformed into an antiskyrmion lattice state under magnetic fields applied along the tetragonal axis over a wide range of temperatures. Direct imaging by Lorentz transmission electron microscopy shows field-stabilized antiskyrmion lattices and isolated antiskyrmions from 100 kelvin to well beyond room temperature, and zero-field metastable antiskyrmions at low temperatures. These results enlarge the family of magnetic skyrmions and pave the way to the engineering of complex bespoke designed skyrmionic structures.
Optoelectronic devices based on hybrid halide perovskites have shown remarkable progress to high performance. However, despite their apparent success, there remain many open questions about their ...intrinsic properties. Single crystals are often seen as the ideal platform for understanding the limits of crystalline materials, and recent reports of rapid, high-temperature crystallization of single crystals should enable a variety of studies. Here we explore the mechanism of this crystallization and find that it is due to reversible changes in the solution where breaking up of colloids, and a change in the solvent strength, leads to supersaturation and subsequent crystallization. We use this knowledge to demonstrate a broader range of processing parameters and show that these can lead to improved crystal quality. Our findings are therefore of central importance to enable the continued advancement of perovskite optoelectronics and to the improved reproducibility through a better understanding of factors influencing and controlling crystallization.
Abstract
Discovery and characterization of black holes (BHs), neutron stars (NSs), and white dwarfs (WDs) with detached luminous companions (LCs) in wide orbits are exciting because they are ...important test beds for dark remnant (DR) formation physics as well as binary stellar evolution models. Recently, 187 candidates have been identified from Gaia’s non-single star catalog as wide orbit (
P
orb
/day > 45), detached binaries hosting DRs. We identify UV counterparts for 49 of these sources in the archival GALEX data. Modeling the observed spectral energy distribution (SED) spanning from the FUV-NUV to IR for these sources and stellar evolution models, we constrain the LC properties including mass, bolometric luminosity, and effective temperature for these 49 sources. Using the LC masses, and the astrometric mass function constrained by Gaia, we constrain the DR masses for these sources. We find that nine have masses clearly in the NS or BH mass range. Fifteen sources exhibit significant NUV excess and four show excess both in the FUV and NUV. The simplest explanation for these excess UV fluxes is that the DRs in these sources are WDs. Using SED modeling we constrain the effective temperature and bolometric luminosity for these 15 sources. Our estimated DR masses for all of these 15 sources are lower than the Chandrasekhar mass limit for WDs. Interestingly, five of these sources had been wrongly identified as NSs in the literature.
The remarkable advances over the past few years in performance of photovoltaic cells, including the advent of new absorber materials, call for an update to the previous assessment of prospects for ...future progress. The same simple criteria with some refinements, based on cell and module performance data, serve to evaluate and compare most types of solar cells. Apart from Si and InP, for all types the “best cells” have improved in conversion performances (and crystalline Si modules have made major strides in cost reduction). New cell types, such as “perovskite”, sustainable chalcogenide, and quantum dot cells, are included. CdTe results bring those cells in line with other well‐developed ones, lending some credence to the idea that the criteria provide the reader with knowledge, useful for gauging possible future technological developments. Additionally, the developments of the past few years show that, while the advent of more new cell types cannot be predicted, it can be aided and stimulated by innovative, daring, and creative new materials research.
The 2011–2013 period has seen amazing progress of nearly all solar‐cell types that have possible or actual practical potential, including significant cost decreases of commercial cells. A concise update of the current status and future prospects of solar‐cell research is given.
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