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Battery loss prediction using various loss models: A case study for a residential building
Get PDFThis work compares and quantifies the annual losses for three battery system loss representations in a case study for a residential building with solar photovoltaic (PV). Two loss representations consider the varying operating conditions and use the measured performance of battery power electronic converters (PECs) but differ in using either a constant or current-dependent internal battery cell resistance. The third representation is load-independent and uses a (fixed) round trip efficiency. The work uses sub-hourly measurements of the load and PV profiles and includes the results from varying PV and battery size combinations. The results reveal an inadequacy of using a constant battery internal resistance and quantify the annual loss discrepancy to −38.6%, compared to a case with current-dependent internal resistance. The results also show the flaw of modelling the battery system\u27s efficiency with a fixed round trip efficiency, with loss discrepancy variation between −5 to 17% depending on the scenario. Furthermore, the necessity of accounting for the cell\u27s loss is highlighted, and its dependence on converter loading is quantified
Determinants of electricity consumption from decentralized solar PV mini-grids in rural East Africa: An econometric analysis
Get PDFThe use of decentralized solar photovoltaic (PV) mini-grids for rural electrification is increasing in developing countries, but little is known about the determinants of electricity consumption of communities electrified through these technologies. This paper examines the factors influencing the electricity consumption of rural households and small businesses electrified by off-grid PV mini-grids based on actual metered load data and a survey of 218 customers in two isolated small towns (Omorate and Tum) in Ethiopia. Empirical analyses were performed using Censored Tobit models. Results showed that the load curves of the two towns have different characteristics and patterns. While the load curve at Omorate is regularly interrupted for 13 h a day due to load-shedding, the mini-grid at Tum generates enough electricity to meet demand. Empirical results showed that electricity consumption of households is significantly associated with household size, income, dwelling type, number of rooms, cooling fans, cooking with electricity and load-shedding. In contrast, the electricity consumption of businesses is strongly linked with income, electricity price, number of rooms, number of cooling fans, refrigerators, number of other (productive use) appliances, and load-shedding/location. The findings suggest three key points. First, electricity demand of rural households and businesses is influenced by separate but interconnected sets of factors. Second, supply-side factors, appliance factors, type of end-use of electricity and location -specific factors influence demand more than income and price factors. Third, mini-grid policy making and dimensioning in rural East Africa must take into account the differing electricity demands and determinants across customer groups and locations
On Viscosity and Density Affecting Aeroelasticity of ONERA M6 Wing from Subsonic to Transonic Regimes
No full textThe effects of fluid viscosity and density on the aeroelasticity of the ONERA M6 wing over a wide range of free-stream Mach numbers, spanning --, based on viscous and inviscid flow assumptions are studied. Both static and dynamic responses of the wing are examined. We employ a hybrid Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES) method for the viscous flow, namely Delayed Detached-Eddy Simulation (DDES) with the Spalart-Allmaras (SA) turbulence model. The inviscid flow solver uses the Euler equations. A few selected cases are also analysed using Unsteady RANS (URANS). The flow solvers are strongly coupled to a structural analysis software, which uses a modal formulation. The structural responses are analysed using a constant free-stream density for all Mach numbers. In addition, higher densities are used for all Mach numbers in order to find the critical dynamic pressure where flutter is obtained. A substantial difference in the aeroelastic responses is found for Mach numbers ranging --, when comparing viscous and inviscid flow simulations. Furthermore, it is shown that viscosity is of minor importance at subsonic and supersonic speeds. At Mach number it is shown that DDES provides close to identical structural responses as URANS. The largest difference of the predicted flutter boundaries is found in the transonic region. The flutter boundary for viscous flow stands out at Mach where it is higher than the flutter boundary predicted by inviscid flow. Simulations with URANS showed that it would predict a lower flutter boundary at Mach , compared to DDES
Comparison of Electrodeposited and Sputtered Tungsten Trioxide Films for Inorganic Electrochromic Nanostructures
No full textHierarchical spatio-temporal change-point detection
Get PDFDetecting change-points in multivariate settings is usually carried out by analyzing all marginals either independently, via univariate methods, or jointly, through multivariate approaches. The former discards any inherent dependencies between different marginals and the latter may suffer from domination/masking among different change-points of distinct marginals. As a remedy, we propose an approach which groups marginals with similar temporal behaviors, and then performs group-wise multivariate change-point detection. Our approach groups marginals based on hierarchical clustering using distances which adjust for inherent dependencies. Through a simulation study we show that our approach, by preventing domination/masking, significantly enhances the general performance of the employed multivariate change-point detection method. Finally, we apply our approach to two datasets: (i) Land Surface Temperature in Spain, during the years 2000–2021, and (ii) The WikiLeaks Afghan War Diary data
The impact of fusion-born alpha particles on runaway electron dynamics in ITER disruptions
Get PDFIn the event of a tokamak disruption in a D-T plasma, fusion-born alpha particles take several milliseconds longer to thermalise than the background. As the damping rates drop drastically following the several orders of magnitudes drop of temperature, Toroidal Alfv\ue9n Eigenmodes (TAEs) can be driven by alpha particles in the collapsing plasma before the onset of the current quench. We employ kinetic simulations of the alpha particle distribution and show that the TAEs can reach sufficiently strong saturation amplitudes to cause significant core runaway electron (RE) transport in unmitigated ITER disruptions. As the eigenmodes do not extend to the plasma edge, this effect leads to an increase of the RE plateau current. Mitigation via massive material injection however changes the Alfv\ue9n frequency and can lead to mode suppression. A combination of the TAE-caused core RE transport with other perturbation sources could lead to a drop of runaway current in unmitigated disruptions
Ultrafast hot electron-hole plasma photoluminescence in two-dimensional semiconductors
No full textThe transition metal dichalcogenide family of semiconducting two-dimensional materials has recently shown a prominent potential to be an ideal platform to study the exciton Mott transition into electron-hole plasma and liquid phases due to their strong Coulomb interactions. Here, we show that pulsed laser excitation at high pump fluences can induce this exciton Mott transition to an electron-hole plasma in mono and few-layer transition metal dichalcogenides at room temperature. The formation of an electron-hole plasma leads to a broadband light emission spanning from the near infrared to the visible region. In agreement with our theoretical calculations, the photoluminescence emission at high energies displays an exponential decay that directly reflects the electronic temperature - a characteristic fingerprint of unbound electron-hole pair recombination. Furthermore, two-pulse excitation correlation measurements were performed to study the dynamics of electronic cooling, which shows two decay time components, one of less than 100 fs and a slower component of few ps associated with the electron-phonon and phonon-lattice bath thermalizations, respectively. Our work may shed light on further studies of the exciton Mott transition into other two-dimensional materials and their heterostructures and its applications in nanolasers and other optoelectronic devices
Directed evolution of a wax ester synthase for production of fatty acid ethyl esters in Saccharomyces cerevisiae
No full textAbstract: Wax ester synthases (WSs) utilize a fatty alcohol and a fatty acyl-coenzyme A (activated fatty acid) to synthesize the corresponding wax ester. There is much interest in developing novel cell factories that can produce shorter esters, e.g., fatty acid ethyl esters (FAEEs), with properties similar to biodiesel in order to use these as transportation fuels. However, ethanol is a poor substrate for WSs, and this may limit the biosynthesis of FAEEs. Here, we implemented a random mutagenesis approach to enhance the catalytic efficiency of a WS from Marinobacter hydrocarbonoclasticus (MhWS2, encoded by the ws2 gene). Our selection system was based on FAEE formation serving as a detoxification mechanism for excessive oleate, where high WS activity was essential for a storage-lipid free yeast to survive. A random mutagenesis library of ws2 was used to transform the storage-lipid free yeast, and mutants could be selected by plating the transformants on oleate containing plates. The variants encoding WS with improved activity were sequenced, and an identified point mutation translated into the residue substitution at position A344 was discovered to substantially increase the selectivity of MhWS2 toward ethanol and other shorter alcohols. Structural modeling indicated that an A344T substitution might affect the alcohol selectivity due to change of both steric effects and polarity changes near the active site. This work not only provides a new WS variant with altered selectivity to shorter alcohols but also presents a new high-throughput selection system to isolate WSs with a desired selectivity. Key Points: • The work provides WS variants with altered substrate preference for shorter alcohols • A novel method was developed for directed evolution of WS of desired selectivity
Weak solutions to gamma-driven stochastic differential equations
Get PDFWe study a stochastic differential equation driven by a gamma process, for which we give results on the existence of weak solutions under conditions on the volatility function. To that end we provide results on the density process between the laws of solutions with different volatility functions
Rail and wheel health management
Get PDFRail and wheel health management is investigated with focus on deterioration phenomena in the wheel/rail contact interface – plastic deformation, wear, and rolling contact fatigue (RCF). How operational conditions affect deterioration, and how they can be included in wheel/rail health predictions is linked to a more in-depth description of deterioration mechanisms. Here means of measuring, quantifying, and predicting deterioration is in focus. This discussion provides the basis for the outline of a rail and wheel health management framework. As discussed in the paper, the proposed framework is well in line with the requirements in the ISO 55000 standard for asset management