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Microwave Tube Fault-Current Model for Design of Crowbar Protection
No full textMany applications that use high-energy plasma are realized using microwave tubes (MWT) that operate at peak power in the range of hundreds of MW and frequency in GHz. One failure mode of the MWT is due to the excess energy in the tube during internal arcing events. Crowbar is used to protect the MWT by diverting the energy during fault. To compute the energy released into the MWT, the dc fault current model and the MWT model are essential. An equivalent fuse wire model is utilized for the MWT for the crowbar applications. The paper proposes a model for the dc fault current, the analysis for which is based on Joules Integral energy concept. The model provides flexibility to choose a range of practically observed reactance to resistance ratio (X/R) of transformer and also allows the use of a range of dc current-limiting resistances that are utilized in the high-voltage (HV) power supply circuits in microwave applications. The nonlinearity of the system due to the multipulse diode rectifier is also considered by introducing a correction factor in the model. This paper shows that the same correction factor can be applied for both dc side parallel-and series-connected rectifier circuits. Both dc fault current and MWT models are verified experimentally. Using the model, a 10 kV, 1 kA crowbar is built to limit the energy in MWT below 10 J
Structural and electrochemical investigation of binary Na2Fe1-xZnxP2O7 (0 <= x <= 1) pyrophosphate cathodes for sodium-ion batteries
No full textTransition metal pyrophosphate material forms a robust polyanionic cathode family for sodium-ion batteries. Here, binary Na-2(Fe1-yMny)P2O7 (0 <= y <= 1) system has been recently investigated by different groups, as Na2FeP2O7 is reported as a low-cost cathode with promising electrochemical performance and thermal stability. While the isostructural Na2FeP2O7 and Na2MnP2O7 assume triclinic P1 (#2) framework, pyrophosphate system shows structural diversity/polymorphism. Considering this, we have investigated the binary Na-2(Fe1-xZnx)P2O7 (0 <= x <= 1) pyrophosphate family with anisostructural end members Na2FeP2O7 (P1, #2) and Na2ZnP2O7 (P4(2)/n, #86). The current study reports solution combustion as well as solid-state preparation of novel Na-2(Fe1-xZnx)P2O7 (0 <= x <= 1) family of materials, their structural and electrochemical characterizations. The degree of solid-solution formation and effect of Zn on Fe-redox activity in Na-2(Fe1-xZnx)P2O7 (x = 0, 0.25) cathodes has been examined using electrochemical titration techniques such as galvanostatic intermittent titration (GITT) and potentiostatic intermittent titration (PITT) mode
Synergies in Operational Oceanography: The Intrinsic Need for Sustained Ocean Observations
No full textOperational oceanography can be described as the provision of routine oceanographic information needed for decision-making purposes. It is dependent upon sustained research and development through the end-to-end framework of an operational service, from observation collection to delivery mechanisms. The core components of operational oceanographic systems are a multi-platform observation network, a data management system, a data assimilative prediction system, and a dissemination/accessibility system. These are interdependent, necessitating communication and exchange between them, and together provide the mechanism through which a clear picture of ocean conditions, in the past, present, and future, can be seen. Ocean observations play a critical role in all aspects of operational oceanography, not only for assimilation but as part of the research cycle, and for verification and validation of products. Data assimilative prediction systems are advancing at a fast pace, in tandem with improved science and the growth in computing power. To make best use of the system capability these advances would be matched by equivalent advances in operational observation coverage. This synergy between the prediction and observation systems underpins the quality of products available to stakeholders, and justifies the need for sustained ocean observations. In this white paper, the components of an operational oceanographic system are described, highlighting the critical role of ocean observations, and how the operational systems will evolve over the next decade to improve the characterization of ocean conditions, including at finer spatial and temporal scales
A review on sintering technology of proton conducting BaCeO3-BaZrO3 perovskite oxide materials for Protonic Ceramic Fuel Cells
No full textCeramic proton conductors can reduce the operating temperature of solid oxide fuel cells (SOFCs) to the intermediate temperature range, 400-600 degrees C, due to their higher ionic conductivity in comparison to oxide-ion conductors under these conditions. Nonetheless, the most promising proton conducting materials, typically yttrium-doped barium cerates and zirconates with nominal compositions: BaCe1-xYxO3-delta (BCY ), BaZr1-xYxO3-delta (BZY) and Ba(Ce,Zr)(1-y)YyO3-delta (BCZY) exhibit major challenges with respect to the production of dense electrolyte membranes. To improve the processing of these materials, liquid phase sintering (LPS) induced by the addition of transition and alkali metal oxides as sintering additives, is proposed as an effective way to promote densification, where the benefits of LPS may be further extended when this method is used in combination with solid-state reactive sintering (SSRS) to reduce the fabrication time and cost. Nonetheless, recent literature highlights that the addition of these sintering additives can have highly negative secondary impacts on bulk transport properties and overall fuel cell performance. This review summarises the recent developments and the innovative methods employed to overcome the processing difficulties in these materials, including diverse potential sintering methods, the effect of different sintering additives and their impact on densification, ionic transport and electrochemical properties
Lightweight Epoxy-Based Composites for EMI Shielding Applications
No full textThe rapid advancement in wireless technology has become both a boon and a curse for mankind. With the development of sophisticated electronics that serve to ease our day-to-day work, the emergence of electromagnetic waves from individual components interfere with each other and harm our physical as well as mental well-being. In this scenario, epoxy-based composites are emerging to be a state-of-the-art electromagnetic interference (EMI) shielding alternative to conventional materials such as metals. Their lightweight structure and improved mechanical properties render epoxy composites extremely efficient for structural applications. Reinforcements in the form of particles/fabrics are widely used in this regard. The present review deals with the various advancements in the field of modifications of epoxy composites to develop EMI shielding materials. Primary focus has been given on the development of lightweight epoxy modified composites through carbonaceous reinforcements either in the form of particles or fiber mats. Synthesis of hybrid nanoparticles in an epoxy matrix to account for both reflection and absorption losses has also been detailed in this review. Subsequently, we present an outlook on which the direction of future research work can be carried out
Anatomy of heavy gauge bosons in a left-right supersymmetric model
No full textWe perform a detailed study of the various decay channels of the heavy charged and neutral gauge bosons (W-R and Z(R), respectively) in a left-right supersymmetric framework. The decay branching ratios of the W-R and Z(R) bosons depend significantly on the particle spectrum and composition of the supersymmetric (SUSY) states. We consider several combinations of mass spectrum for the SUSY particles to facilitate the decay of theses heavy gauge bosons into various combinations of final states. Finally, we choose two benchmark points and perform detailed collider simulations for these heavy gauge bosons in the context of the high energy and high luminosity run of the Large Hadron Collider. We analyze two SUSY cascade decay channels, mono-W + E-T and mono-Z + E-T, along with the standard dilepton and dijet final states. Our results show that the existence of these heavy gauge bosons can be ascertained in the direct decay channels of dilepton and dijet, whereas the other two channels are required to establish the supersymmetric nature of this model
The Impact of Acquisition Date on the Prediction Performance of Topsoil Organic Carbon from Sentinel-2 for Croplands
No full textThe spatial assessment of soil organic carbon (SOC) is a major environmental challenge, notably for evaluating soil carbon stocks. Recent works have shown the capability of Sentinel-2 optical data to predict SOC content over temperate agroecosystems characterized by annual crops, using a single acquisition date. Considering a Sentinel-2 time series, this work intends to analyze the impact of acquisition date, and related weather and soil surface conditions on the prediction performance of topsoil SOC content (plough layer). A Sentinel-2 time-series was gathered, comprised of the dates corresponding to both the maximum of bare soil coverage and minimum of cloud coverage. Cross-validated partial least squares regression (PLSR) models were constructed between soil reflectance image spectra, and SOC content analyzed from 329 top soil samples collected over the study area. Cross-validation R-2 ranged from 0.005 to 0.58, root mean square error from 5.86 to 3.02 g.kg(-1) and residual prediction deviation values from 1.0 to 1.5 (without unit), according to date. The main factors influencing these differences were soil roughness, in conjunction with soil moisture, and the cloud and cloud shadow cover of the entire tile. The best performing dates were spring dates characterized by both lowest soil surface roughness and moisture content. Normalized difference vegetation index (NDVI) values below 0.35 did not influence prediction performance. This consolidates the previous results obtained during single date acquisitions and offers wider perspectives for the further use of Sentinel-2 into multidate mosaics for digital soil mapping
Aggregation-Induced and Polymorphism-Dependent Thermally Activated Delayed Fluorescence (TADF) Characteristics of an Oligothiophene: Applications in Time-Dependent Live Cell Multicolour Imaging
No full textTypically, molecules with a twisted donor-acceptor (D-A) architecture have been exploited for constructing thermally activated delayed fluorescence (TADF) materials. Herein, we report the first example of a thiophene-based thermally activated delayed fluorescent molecule without a D-A architecture. Compound 1 (2,5-bis(2,2-di(thiophen-2-yl)vinyl)thiophene) is conformationally flexible and shows weak fluorescence in the solution state but displays bright TADFin both condensed and solid states. Compound 1 crystallized in two different polymorphs (1 a and 1 b). Interestingly, both polymorphs show distinctly different TADF features. The broad spectral features and the TADF characteristics of 1 have been explored for the time-dependent multicolor (green, yellow and red) imaging of living cells
Microstructural Evolution and Corrosion Behavior of ZnNi-Graphene Oxide Composite Coatings
No full textThis work correlates microstructural evolution and corrosion behavior of electrodeposited ZnNi-graphene oxide composite coatings. Incorporation of GO improved the coating compactness and decreased the surface roughness. Structural characterization revealed that the pure ZnNi coating contained only intermetallic phases (gamma-NiZn3, gamma-Ni3Zn22, and gamma-Ni5Zn21), whereas ZnNi-GO coatings contained Zn phase along with the intermetallics. Addition of GO gradually increased the volume fraction of the Zn phase and reduced its crystallite size. With the addition of GO, a noticeable and systematic variation in the growth texture of the coatings was also observed. Corrosion resistance of the composite coating increased with increase in the addition of GO. Microstructural characterization revealed that the composite coating contained Zn phase along with the GO forming a Zn-GO matrix containing intermetallics. Further investigation of the GO extracted from the electrolyte bath revealed that during the electrodeposition process, Zn nucleated and grew over the GO in the electrolyte itself which led to the co-existence of Zn and GO in the coating matrix. Enhancement in the coating compactness, increase in the Zn phase which is sacrificial, and the impermeability of the GO led to the high corrosion resistance of the ZnNi-GO composite coatings when compared to the pure ZnNi coating
Black carbon physical and optical properties across northern India during pre-monsoon and monsoon seasons
No full textBlack carbon (BC) is known to have major impacts on both climate and human health and is therefore of global importance, particularly in regions close to large populations that have strong sources. The size-resolved mixing state of BC-containing particles was characterised using a single-particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain (IGP) during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons of 2016. Over the IGP, BC mass concentrations were greater (1.95 mu gm(-3)) compared to north-west India (1.50 mu gm(-3)) and north-east India (0.70 mu gm 3) during the pre-monsoon season. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter < 0 :16 mu m and coating thickness < 50 nm) and a mode of moderately coated BC (core diameter < 0 :22 mu m and coating thickness of 50-200 nm). The IGP and north-east India locations exhibited moderately coated black carbon particles with enhanced coating thicknesses, core sizes, mass absorption cross sections, and scattering enhancement values compared to much lower values present in the north-west. The coating thickness and mass absorption cross section increased with altitude (13 %) compared to those in the boundary layer. As the monsoon arrived across the region, mass concentration of BC decreased over the central IGP and north-east locations (38% and 28% respectively), whereas for the northwest location BC properties remained relatively consistent. Post-monsoon onset, the coating thickness, core size, mass absorption cross section, and scattering enhancement values were all greatest over the central IGP much like the pre-monsoon season but were considerably reduced over both north-east and north-west India. Increases in mass absorption cross section through the atmospheric column were still present during the monsoon for the north-west and central IGP locations, but less so over the north-east due to lack of long-range transport aerosol aloft. Across the Indo-Gangetic Plain and north-east India during the pre-monsoon and monsoon seasons, solid-fuel (wood burning) emissions form the greatest proportion of BC with moderately coated particles. However, as the monsoon develops in the north-east there was a switch to small uncoated BC particles indicative of traffic emissions, but the solid-fuel emissions remained in the IGP into the monsoon. For both seasons in the north-west, traffic emissions form the greatest proportion of BC particles. Our findings will prove important for greater understanding of the BC physical and optical properties, with important consequences for the atmospheric radiative forcing of BC-containing particles. The findings will also help constrain the regional aerosol models for a variety of applications such as space-based remote sensing, chemistry transport modelling, air quality, and BC source and emission inventories