Theoretical Efficiency Research Articles

Efficiency of the averaged rank-based estimator for first order Sobol index inference

Among the many estimators of first order Sobol indices that have been proposed in the literature, the so-called rank-based estimator is arguably the simplest to implement. This estimator can be viewed as the empirical auto-correlation of the response variable sample obtained upon re-ordering the data by increasing values of the inputs. This simple idea can be extended to higher lags of auto-correlation, thus providing several competing estimators of the same parameter. We show that these estimators can be combined in a simple manner to achieve the theoretical variance efficiency bound asymptotically

Triethanolamine-modified layered double oxide for efficient CO2 capture with low regeneration energy

Various adsorbents for CO2 capture have been developed to mitigate the greenhouse effect. In this work, a novel CO2 adsorbent was fabricated by depositing triethanolamine (TEOA) onto the surface of nickel-cobalt-aluminum layered double oxide (NiCoAl-LDO) via the impregnation method. The CO2 capacity of the TEOA-LDO composite reached 1.27 mmol/g at 0 °C and 100 kPa, which was twice that of unmodified NiCoAl-LDO. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that the hydroxyl groups (–OH) on the surface of NiCoAl-LDO played a significant role in facilitating CO2 adsorption, similar to CO2 adsorption in the presence of H2O, where CO2 is not converted to carbamates but to bicarbonates through base-catalyzed hydration. This bicarbonate pathway doubles the theoretical amine efficiency, increases the CO2 capacity, and reduces the energy consumption during CO2 desorption. The work provides valuable insights into the development of CO2 adsorbents with high capacity, excellent cycling stability, and low regeneration energy.

Efficiency or Fairness? Research on the Allocation of Energy Consumption and Carbon Emission Rights among Chinese Provinces

Abstract Using a dynamic ZSG-SBM model under the common frontier, this paper allocates provincial energy consumption and carbon emission rights in China and conducts theoretical analysis and efficiency analysis from the perspective of balancing efficiency and fairness. The research results show that, under the allocation method that prioritizes efficiency, fossil energy consumption and carbon emission rights are significantly adjusted from the central and western regions to the economically developed eastern regions. Under the allocation model that considers fairness indicators, the net inflow of energy consumption and carbon emission rights from the eastern region is significantly reduced, with a greater focus on regional coordinated development, and a tendency to allocate more indicators to the relatively underdeveloped central and western regions in terms of energy consumption and carbon emissions. In addition, there is a significant regional difference in the initial technical efficiency gap between different regions, with the efficiency value in the eastern region significantly higher than that in the central and western regions. The allocation method that prioritizes efficiency can significantly improve energy consumption and carbon emission efficiency nationwide, but the allocation method that balances efficiency and fairness will cause some efficiency losses. Improving the national technical efficiency is the key to achieving the national “dual-carbon” and “dual-control” goals.

Vecchia Likelihood Approximation for Accurate and Fast Inference with Intractable Spatial Max-Stable Models

Max-stable processes are the most popular models for high-impact spatial extreme events, as they arise as the only possible limits of spatially-indexed block maxima. However, likelihood inference for such models suffers severely from the curse of dimensionality, since the likelihood function involves a combinatorially exploding number of terms. In this article, we propose using the Vecchia approximation, which conveniently decomposes the full joint density into a linear number of low-dimensional conditional density terms based on well-chosen conditioning sets designed to improve and accelerate inference in high dimensions. Theoretical asymptotic relative efficiencies in the Gaussian setting and simulation experiments in the max-stable setting show significant efficiency gains and computational savings using the Vecchia likelihood approximation method compared to traditional composite likelihoods. Our application to extreme sea surface temperature data at more than a thousand sites across the entire Red Sea further demonstrates the superiority of the Vecchia likelihood approximation for fitting complex models with intractable likelihoods, delivering significantly better results than traditional composite likelihoods, and accurately capturing the extremal dependence structure at lower computational cost. Supplementary materials for this article are available online.

Oxysulfide-Based Photocatalyst Sheet Modified with Silica Layer for Z-Scheme Overall Water Splitting at Atmospheric Pressure

Photocatalytic water splitting using particulate photocatalysts is considered as an ideal route to produce economically cheap renewable, and transportable H2 utilizing sunlight [1]. Photocatalyst sheets are directly scalable and have recently gained interest because a benchmark STH conversion efficiency of 1.0% was achieved at near ambient pressure using the one composed of Rh, La-codoped SrTiO3 and Mo-doped BiVO4 (BVO:Mo) as the H2- and O2- evolution photocatalysts (HEP and OEP), respectively. However, such systems absorb only a little portion of the sunlight due to the weak visible light absorption of the doped SrTiO3 [2]. To utilize longer wavelength visible light, our group has recently studied photocatalyst sheets composed of Ga-doped La5Ti2Cu0.9Ag0.1O7S5 (LTCA:Ga) (HEP) and BVO:Mo (OEP) with Au as conducting layer. The combination of LTCA:Ga/Au/BVO:Mo modified with Rh/Cr2O3 and CoO x as reduction and oxidation cocatalysts, respectively, achieved an STH efficiency of 0.4% under reduced pressure, but this was far lower than the oxide-based sheet system and the activity was decreased sharply against background pressure [3]. Considering intense visible light absorption of LTCA (λabs ~ 700 nm) and the associated maximum theoretical energy conversion efficiency for this combination, improvements in the net STH efficiency and activation under atmospheric pressure is highly indispensable.In this study, LTCA photocatalysts with different dopants were applied to the sheet system in combination with hydrothermally synthesized BVO:Mo and the resulting sheets were modified with CoO x /Cr2O3/Rh cocatalysts in an attempt to upgrade the water splitting activity. Moreover, surface modification onto LTCA-based photocatalyst sheets with a thin amorphous TiO2 and SiO2 layer were evaluated at elevated pressure and high temperature.Doped LTCA were synthesized by a conventional solid-state reaction in sealed evacuated quartz tubes similar to previous studies [3]. Precursors were blended inside a glove box. BVO:Mo (Mo 0.1 mol%) was synthesized by a hydrothermal method [4]. Photocatalyst sheet was fabricated by the particle transfer method [3]. SiO2 and TiO2 layers functioning as molecular sieves were deposited onto the cocatalyst-modified sheet from titanium tetraisopropoxide (TTIP) or tetraethyl orthosilicate (TEOS) by photo-decomposition and hydrolysis method, respectively, to prevent backward reactions at elevated pressure [5]. Photocatalytic water splitting reaction was carried out at different temperatures and pressures using a closed gas circulation system.Rh cocatalyst was first adsorbed and photo-deposited onto the doped LTCA/Au/BVO:Mo(h) sheet [3]. Gas evolution rates were significantly enhanced upon deposition of Cr2O3 layer as the oxygen reduction reaction (ORR), a backward reaction, was majorly suppressed promoted by uncovered Rh surface under the measured condition. Photocatalyst sheet composed of doped LTCA/Au/BVO:Mo(h) with optimal dopant amounts and cocatalysts loadings showed the H2 and O2 evolution rates of 110 and 54 µmol/h, respectively, under visible light irradiation and yielded an STH of 0.67% at 4 kPa and temperature 301 K [6]. The water splitting activity was improved by 1.6 times under reduced pressure compared to the previously studied LTCAGa/Au/BVO:Mo. However, this activity was highly sensitive against background pressure as nearly 90% reduced upon increasing pressure from 2 to 90 kPa owing to the predominating ORR occurring on LTCA and exposed Au surface. To suppress this backward reaction, TiO2 layer was coated to suppress ORR but the sheet failed to work at a temperature higher than 318 K due to the condensation of such layer. However, SiO2 layer coated sheet effectively suppressed ORR backward reaction and stably work under hot water and elevated pressure [6]. Consequently, under optimized condition SiO2 deposited sheet achieved an STH of 0.4% at 90 kPa at temperature 333 K.Doped LTCA materials were applied to the photocatalyst sheet systems as HEP along with BVO:Mo and Au layer as OEP and conductive layer, respectively, for Z-scheme pure water splitting under visible light. This combination achieved an STH of 0.67% at reduced pressure. This STH is considered as one of the highest values recorded for OWS systems involving non-oxide photocatalysts. The activity of the photocatalyst sheet was found negatively dependent onto background pressure due to the ORR on LTCA and Au layer. Surface modifications with SiO2 layer activated the sheet under atmospheric pressure. These findings will contribute to the improvement in the STH for other systems under realistic condition where OWS is likely to be conducted at an ambient pressure. References Nandy et al. Chem. Sci. 2021, 12, 9866-9884.Wang et al. Nat. Mater. 2016, 15, 611-615.Chen et al. ACS Catal. 2023, 13, 3285-3294.Li et al. Energy Environ. Sci., 2014, 7, 1369-1376.Pan et al. Angew. Chem. Int. Ed. 2015, 54, 2955-2959.Nandy et al. Joule, 2023, under revision.

Fabrication of a large computer-generated hologram with high diffraction efficiency and high accuracy by scanning homogenization etching.

The diffraction efficiency, defined as the ratio of diffracted power to incident power, is one of the key working indicators for a computer-generated hologram (CGH). The CGH with high diffraction efficiency could suppress stray light and eliminate ghost images, thus improving interferometric performance in aspherical testing of low-reflectivity or large off-axis distance surfaces. However, the high-efficiency CGH is hard to precisely fabricate by traditional reactive ion etching and focusing ion beam, because it requires high etching depth with a high uniformity and sub-nanometric roughness in the glass, especially in the fabrication of a large CGH with an aperture of up to 300 mm. In this study, fabrication of the above-mentioned CGH was demonstrated via what we believe to be a new method called scanning homogenization etching (SHE), in which the ion source with a Gaussian energy distribution accurately scans the glass surface to realize homogenization etching. Different from controlling dwell time at each etching point, this paper proposes to control the scanning rate to achieve not only uniform but also quantitative depth removal in a single scan. Moreover, the depth errors in deep etching across the whole glass surface can be remarkably reduced due to homogenization effects introduced by multiple scanning etching. Finally, the target etching depth of 692.3 nm with an etching uniformity of 2.2% in the etching of a 300 mm CGH was achieved. The roughness of the etched and unetched area both have Ra values of 0.3 nm. The diffraction efficiency of working order is 39.998%, achieving 98.6% of the theoretical diffraction efficiency. In addition, the SHE is not limited by the aperture of the ion source, so it can achieve even larger diffractive optical elements with high diffraction efficiency and high accuracy.

Green hydrogen production by intermediate‐temperature protonic solid oxide electrolysis cells: Advances, challenges, and perspectives

AbstractProtonic solid oxide electrolysis cells (P‐SOECs) operating at intermediate temperatures, which have low costs, low environmental impact, and high theoretical electrolysis efficiency, are considered promising next‐generation energy conversion devices for green hydrogen production. However, the developments and applications of P‐SOECs are restricted by numerous material‐ and interface‐related issues, including carrier mismatch between the anode and electrolyte, current leakage in the electrolyte, poor interfacial contact, and chemical stability. Over the past few decades, considerable attempts have been made to address these issues by improving the properties of P‐SOECs. This review comprehensively explores the recent advances in the mechanisms governing steam electrolysis in P‐SOECs, optimization strategies, specially designed components, electrochemical performance, and durability. In particular, given that the lack of suitable anode materials has significantly impeded P‐SOEC development, the relationships between the transferred carriers and the cell performance, reaction models, and surface decoration approaches are meticulously probed. Finally, the challenges hindering P‐SOEC development are discussed and recommendations for future research directions, including theoretical calculations and simulations, structural modification approaches, and large‐scale single‐cell fabrication, are proposed to stimulate research on P‐SOECs and thereby realize efficient electricity‐to‐hydrogen conversion.image

Reducing Perovskite/C60 Interface Losses via Sequential Interface Engineering for Efficient Perovskite/Silicon Tandem Solar Cell.

Wide-bandgap (WBG) perovskite solar cells hold tremendous potential for realizing efficient tandem solar cells. However, nonradiative recombination and carrier transport losses occurring at the perovskite/electron-selective contact (e.g. C60 ) interface present significant obstacles in approaching their theoretical efficiency limit. To address this, a sequential interface engineering (SIE) strategy that involves the deposition of ethylenediamine diiodide (EDAI2 ) followed by sequential deposition of 4-Fluoro-Phenethylammonium chloride (4F-PEACl) is implemented. The SIE technique synergistically narrows the conduction band offset and reduces recombination velocity at the perovskite/C60 interface. The best-performing WBG perovskite solar cell (1.67eV) delivers a power conversion efficiency (PCE) of 21.8% and an impressive open-circuit voltage of 1.262V. Moreover, through integration with double-textured silicon featuring submicrometer pyramid structures, a stabilized PCE of 29.6% is attained for a 1cm2 monolithic perovskite/silicon tandem cell (certified PCE of 29.0%).

Chalcogenide Perovskite, An Emerging Photovoltaic Material: Current Status and Future Perspectives

AbstractChalcogenide perovskite materials came into the picture of photovoltaic technology since 2015. Their admirable structural, electronic and optical properties make them highly promising for solar energy conversion. They have immense potential to solve the stability and toxicity issues of conventional perovskite solar cells. The maximum theoretical power conversion efficiency reported for them is about 30 % which is similar to CH3NH3PbI3 perovskite material. However their application in photovoltaics is limited by several challenges. In this review, we tried to provide an overview of the structural features of the chalcogenide perovskite materials and critically highlighted computational and synthetic accomplishments in this area. Various techniques developed for synthesizing these materials so far, have also been summarized. Along with that, the challenges associated in designing these materials for improved optoelectronic properties are also addressed. Serious research efforts are urgently needed for the realization of the dream of chalcogenide perovskite material based solar cells in terms of optimization of optoelectronic properties, synthetic cost, processing of thin films and application in tandem solar cell devices. This review may facilitate further progress in chalcogenide perovskite material based thin film solar cell in the future.

Process modelling and assessment of thermochemical sulfur-iodine cycle for hydrogen production considering Bunsen reaction kinetics

Thermochemical sulfur-iodine (SI) cycle is one of the large-scale, clean, and efficient hydrogen production routes. The Bunsen reaction process is always simulated by a stoichiometric reaction, without considering the realistic Bunsen reaction kinetic process. Herein, a user-defined Fortran module concerning Bunsen reaction kinetics was developed and embedded into a continuous stirred tank reactor (RCSTR), and then a SI flowsheet with 100 L/h hydrogen production was modeled. The key parameter optimization, mass and energy balance were analyzed, the internal heat exchange network was created using the pinch point temperature difference analysis and the principle of energy cascade utilization, along with thermal efficiency evaluation. Bunsen reaction process reaches equilibrium after a period, which is consistent with experiments. The increase of H2SO4 decomposition ratio is beneficial to reduce the energy consumption of system. Increase in temperature has less effect on increasing the equilibrium decomposition ratio of HI. The theoretical thermal efficiency of system reaches 14.0–57.4 % considering the recovery of exothermic heat. This work provides a theoretical basis for the optimization of SI cycle.

Elucidating the corrosion inhibition mechanisms: A computational and statistical exploration of the molecular structure-efficiency relationship for phenolic Schiff bases in acidic medium on the mild steel surface

This study investigated mild steel corrosion inhibition using four Schiff bases in a theoretical framework. The study used statistical analysis to relate the experimental inhibitor's efficacy to theoretical data, revealing the corrosion inhibition process. Density functional theory (DFT) was used to assess the global reactivity of the four inhibitors' neutral, protonated, and complex forms. Where, Fukui functions were used for local reactivity study of the four inhibitors in neutral and protonated forms. To study system dynamics at the inhibitor-steel contact, a Monte Carlo simulation was performed. The experimental and quantum results are strongly correlated when the global quantum features of the neutral and protonated forms, such as the dipole moment μ, EHOMO, and ELUMO, are examined. The PA and pKa protonation parameters demonstrate that the protonation of the compounds strongly influences the inhibition efficiency. According to Fukui functions, the amine function (N) is the highest nucleophilic reactivity, making it highly sensitive to electrophilic attack, for all four inhibitors. The stability and predominance of complex forms in the medium were interpreted using thermodynamic characteristics of PSBi-FeCl2 complexes. Monte Carlo simulation yielded the most stable adsorption configurations, which were geometrically and energetically examined to explain experimental data. QSAR shows a significant linearity between theoretical parameters and experimental inhibitory efficiency.

High‐Efficiency Infrared Sulfide Lead Quantum Dot Solar Cells via Mixed Halide Ions Ligand Engineering

Tandem solar cells are regarded as an effective way to break through the theoretical efficiency of the Shockley–Queisser limit, and large‐size lead sulfide quantum dots (PbS QDs) are considered ideal infrared (IR) photovoltaic materials for absorbing low‐energy IR photons in the bottom subcells of tandem solar cells due to their tunable bandgaps and multiexciton generation effects. However, the exposed (100) surface of large‐size PbS QDs leads to poor passivation during the ligand‐exchange process, resulting in degraded device performance. Herein, a mixed halide ions ligand passivation strategy is developed to synergistically passivate the (111) and (100) facets of large‐size QDs. Particularly, a gradual dropwise addition of lead chloride salts dissolved in dimethyl sulfoxide for achieving precisely proportional surface passivation of Cl ions in the ligand exchange is proposed, which enhances the quality of the QD solids and obtains excellent control of the surface trap states. Additionally, optical and electrical characterization results show that the passivated IR PbS QD solids have higher carrier mobility, longer carrier lifetime, and lower defect density, which increases the IR efficiency of IR PbS QD solar cells to 1.25%.

Optical–electrical simulation and optimization of an efficient lead-free 2T all perovskite tandem solar cell

The characteristics of a lead-free all perovskite tandem solar cell (P-TSC) are studied in this study. All P-TSCs were developed with the goal of breaking through the theoretical power conversion efficiency (PCE) limit for single-junction (SJ) perovskite solar cells (PSCs) established by Shockley and Queisser. Solving the toxicity problem in lead-containing sub-cells is essential for the continued growth of all P-TSCs. Here, we first present a coupled three-dimensional (3D) optical–electrical simulation of two lead-free SJ MAGeI3(Eg=1.9eV) and MASnI3(Eg=1.3eV) PSCs. The results showed that the PCE of the SJ-wide bandgap (WBG) and SJ-narrow bandgap (NBG) PSCs is 19.59% and 15.57%, respectively. Next, a two-terminal (2T) eco-friendly all P-TSC with combines these two solar cells has been designed, where the MAGeI3-PSC serves as the top sub-cell and the MASnI3-PSC serves as the bottom sub-cell. By establishing the current matching condition between two sub-cells in the 2T structure, the matched short-circuit current density (Jsc) and PCE are obtained 12.30mA/cm2 and 28.46%, respectively. Herein, a 299 nm-thick NBG-absorber layer and a 200 nm-thick WBG-absorber layer are required. In order to increase the matched Jsc and PCE and decrease the required NBG-absorber layer thickness, the parasitic absorption and reflection losses are minimized by selecting the best materials for the transparent conductive oxide (TCO) front contact and interconnecting (IC) layers, as well as the addition of an anti-reflection (AR) layer at the air/device interface as light management strategies. The results indicate that, under the current matching condition, improving the structure would lead to in a 76 nm reduction in the NBG-absorber layer’s required thickness and a 16.44% increase in PCE. Finally, we suggested the optimized 2T non-Pb all P-TSC with a high PCE of 33.14% that is environmentally safe.

Constant fed-batch cultivation with glucose and propionate as co-substrate: A strategy to fine-tune polyhydroxyalkanoates monomeric composition in Pseudomonas spp.

Pseudomonas sp. LFM693 is a 2-methylisocitrate lyase (prpB) disrupted mutant. This enzyme catalyzes a step in the 2-methylcitrate cycle, the only known and described pathway for propionate oxidation in this organism. The affected mutants can efficiently produce PHA containing even and odd-chain length hydroxyalkanoates (HAeven/odd) in the presence of propionate and glucose. In this study, a constant fed-batch configuration was utilized to control the composition of PHA and decrease the toxicity of propionate. The incorporation of HAodd into the copolymer was linear, ranging from 7 to approximately 30 %, and correlated directly with the propionate/glucose molar ratio in the feeding solution. This allowed for the molecular composition of the mclPHA to be fine-tuned with minimum process monitoring and control. The average PHA content was 52 % cell dry weight with a molar composition that favored 3-hydroxyalkanoates containing C8, C9, and C10. The conversion factor of propionate to HAodd varied between 0.36 and 0.53 mol·mol−1 (YHAodd/prop.), which are significantly lower than the theoretical maximum efficiency (1.0 mol·mol−1). These results along with the lack of 2-methylisocitrate as a byproduct provides further support for the evidence that the mutant prpB− is still capable of oxidizing propionate.

Lattice Distortion and Low-Frequency Anharmonic Phonons Suppress Charge Recombination in Lead Halide Perovskites upon Pseudohalide Doping: Time-Domain Ab Initio Analysis.

Perovskite solar cells have witnessed a surge in interest as a promising technology for low-cost, high-efficiency photovoltaics with certified power conversion efficiencies beyond 25%. However, their commercial development is hindered by poor stability and nonradiative losses that restrict their approach to the theoretical efficiency limit. Using ab initio nonadiabatic molecular dynamics, we demonstrate that nonradiative charge recombination is suppressed when the iodide in formamidinium lead iodide (FAPbI3) is partially replaced with pseudohalide anions (SCN-, BF4-, and PF6-). The replacement breaks the symmetry of the system and creates local structural distortion and dynamic disorder, decreasing electron-hole overlap and nonadiabatic electron-vibrational coupling. The charge carrier lifetime is found to increase with increased structural distortion and is the longest for PF6-. This work is fundamentally relevant to the design of high-performance perovskite materials for optoelectronic applications.

Evaluation of design approaches of desilting basins for hydroelectric projects in Himalayan region

ABSTRACT The present paper aims to evaluate the empirical as well as analytical approaches normally adopted for the computation of desilting efficiency of pressure type desilting basin used in hydroelectric project (H.E.P) constructed in Himalayan regions. Due to limited availability of space and steep topography, pressure type desilting basins are mostly preferred. Four significant projects in the Himalayan region are chosen for the performance analysis of desilting chamber: Kholongchhu H.E.P, Mangdechhu H.E.P, Teesta Stage-IV H.E.P, and Punatsangchhu Stage-II. Theoretical efficiency (function of shear velocity (µ*) and mixing coefficient (ℇ)) of all the four projects were computed by existing as well as modified formulae as suggested by Camp-Dobbin (1946) and Sinha and Singh (2019), respectively. It is concluded that particle removal efficiency obtained from model studies for these four hydropower projects and that computed by Camp-Dobbin’s approach (1946) are in close agreement. The outcome of this paper suggests that out of six commonly used approaches, the approach recommended by Camp-Dobbin (1946) is most suitable methodology to design the desilting basin in Himalayan region. It is envisaged that the present study will enable the designer to select a most appropriate approach to design an efficient and suitable desilting basin for construction in Himalayan region.

Experimental study of a linear Fresnel reflection solar concentrating system

Introduction: In the field of solar energy utilization, the construction of low cost and easy to process large concentrated photothermal system is a scientific problem to be solved. A linear Fresnel reflection solar concentrator is proposed in this paper.Methods: The position, tilt angle and width of the glass mirrors placed in the same plane are different to ensure that all the reflected light falls on the flat focal plane or cylindrical focal surface. According to the focusing principle of the concentrator, two experimental system platforms ware built. When a flat focal plane is used to receive radiation from the sun, the intensity distribution of focal plane light spot is uniform in theory.Results: The CCD measurement method is used to analyze the concentrated light spot under experimental conditions, and it is proved that the energy flux density on the focal plane is uniform. Placing monocrystalline silicon cells on the focal plane, the experimental results of p-v power generation voltammetry show that the power generation efficiency of monocrystalline silicon cell does not decrease due to the uniform solar energy density, which can reach 17.1%. The photothermal experiment is carried out by using one-dimensional tracking mode of sunlight. The concentrator reflects the sun’s rays onto the vacuum collector tubes, heating the heat conduction oil flow in. The thermocouple measures the temperature of the heat conduction oil at the inlet and outlet of the vacuum collector tubes. The experimental photothermal conversion efficiency of this concentrator was analyzed and calculated through multiple groups of photothermal experiments, and compared with the theoretical concentrator efficiency. With two collector tubes in series, the theoretical photothermal conversion efficiency reaches 0.8 and the experimental photothermal conversion efficiency reaches about 0.74.Discussion: Because of its good concentrating performance and low cost, this type concentrator can be widely used in photothermal and photovoltaic applications.

Numerical Investigations and Artificial Neural Network-Based Performance Prediction of a Centrifugal Fan Having Innovative Hub Geometry Designs

It is a well-known fact that air approaches the eye region of the rotating impeller of a centrifugal fan with shock-less entry conditions in an ideal scenario. The flow in this region is associated with induced swirl losses, leading to cumulative performance losses. Proper flow guidance in the vicinity of the eye region is essential to minimize possible flow losses. The flow guiding structure may be in the form of a projection or extrusion connected to the rotating impeller of the turbo machines and is generally named a hub. These attachments enhance the overall flow augmentation of the turbo machines in terms of static pressure improvement by reducing a significant amount of inlet turning losses. This article attempts to highlight the efficacy of hubs of various shapes and sizes on the pressure rise of the centrifugal fan using Computational Fluid Dynamics (CFD). Simulation results revealed that the optimized hub configuration yields about an 8.4% higher head coefficient and 8.6% higher relative theoretical efficiency than that obtained for the hub-less base configuration. This improvement in these paraments therefore also commemorates the global progress in energy efficiency as per the UN’s Sustainable Development Goals, SDG 7 in particular. Simultaneously, in the Artificial Neural Network (ANN), a Multi-Layer Perceptron (MLP) model is used to forecast the performance of a centrifugal fan with an optimized hub design. The results predicted by the ANN model are found to be in close agreement with the optimized hub shape’s numerical results.

Multimode Luminescent Properties from Tb3+-Yb3+ Codoped CaMoO4 for Solar Cell Spectral Conversion

NIR and visible emitting CaMoO4:Tb3+/Tb3+-Yb3+ phosphors were synthesized to harness the energy losses attribute to wavelength mismatch between response spectrum of incident solar photons and solar cells. The X-ray diffraction (XRD), field emission scanning microscopy (FE-SEM), fourier transform infrared spectroscopy (FTIR), UV–vis diffuse reflectance spectroscopy, photoluminescence (PL), up-conversion and life time measurements were used to characterized the prepared phosphors. XRD study followed by Rietveld refinement confirms the tetragonal crystal structure with space group I41a(88). The phosphors exhibit strong green emission (5D4→7F4) in visible region after an excitation wavelengths 378 nm and 980 nm, respectively through down-shifting (DS) and up-conversion (UC) processes. The UV photons (378 nm) are also split it into two NIR photons (2F7/2→2F5/2) through down-conversion process. Fluorescence quenching was observed by increasing concentration of Tb3+ and Yb3+ ions. Lifetime measurements clearly illustrates the energy transfer from Tb3+ to Yb3+ ions and mechanism involved is co-operative energy transfer. The estimated values of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are achieved as 69% and 169% respectively.

Class-E Synchronous RF Rectifier: Circuit Formulation, Geodesic Trajectory, Time-Domain Simulation, and Prototype Experiment

This paper formulates a class-E synchronous RF rectifier from a new viewpoint. The key point is to introduce a matrix and convolute the DC terms into RF matrices. The explicit expression of input impedance is demonstrated in plane geometry. We find out their input impedance exhibits a geodesic arc in hyperbolic geometry under ZVS operation, where the theoretical RF-DC conversion efficiency results in 100%. We verify the developed theory both numerically (circuit simulation) and experimentally (6.78 MHz, 100 W). We confirm that the input impedance becomes a geodesic arc for a wide range of DC load resistance. The presented theory is quite elegant since it is based on a matrix-based formulation and plane-geometrical expression.