Uniform Source Research Articles

Characterization of shape factor with multi slip and inclined magnetized radiative Casson hybrid nanofluid transport in an expanding/contracting convective sheet

The current study explores the behavior of particle shape on the radiative flow of Casson hybrid nanofluid towards an expanding/contracting convective sheet. The nanofluid under onsideration is a water-based hybrid comprising carbon nanotubes (CNTs) with particle shapes. The particle shape factor is employed to determine its significance on the flow characteristic. The standard equations for the flow and thermal transportation are derived based on the conservation laws, including the simultaneous effects of viscous dissipation, thermal radiation, along with uniform heat source. The Casson based model is employed to pronounce the rheological characteristic of the nanofluid, taking into account the non-Newtonian nature of the fluid. To further explore the system, the influence of multiple slip effects and an inclined magnetic field is considered. Multiple slip effects occur due to the simultaneous presence of velocity, thermal, and concentration slips at the solid-fluid interface. The inclined magnetic field is introduced to investigate the magnetohydrodynamic (MHD) effects on the flow characteristics. Numerical simulations are performed using appropriate numerical techniques to solve the resulting system of equations. The effects of various parameters, such as particle shape, slip parameters, magnetic field inclination, and thermal radiation, are thoroughly analyzed. The main findings of this works are; the interaction of CNTs that enhances the thermal conductivity of the nanofluid boost up the heat transfer rate further, and the particle concentrations enhance the fluid temperature significantly. The observation indicates that the increasing slip enhances both the velocity and temperature distribution.

Effect of air layer location and depth on redistribution of convective heat transfer induced by energy source in a sandwiched porous-air-porous enclosure free from temperature difference at external boundaries

The study deals with nonlinear convection in a three-layered porous-air-porous enclosure with zero temperature difference at the external impermeable thermally conductive boundaries. The upper and lower porous matrices are internally heated with a uniform energy source. To describe redistribution of heat energy between the top and bottom surfaces of the enclosure, we introduce a relative heat transfer coefficient qr that has the conduction and convection parts. The former part tends to unity in the fully filled porous domain. The symmetry of heat transfer from the inner area towards the outer surfaces breaks down if one adds an intermediate air layer with low thermal conductivity. Two sandwiched systems which have equal depth ratio d but distinct air layer location are considered. In system 1, the air layer is located in the upper unstably stratified half of the enclosure. In system 2, this layer is in the lower stably stratified half. The total value of qr always increases due to penetrative convection. At d = 0.1, local convection in system 1 is easily initiated in contrast to the hard-to-generate large-scale convection in system 2 due to a strong destabilization. The latter most effectively enhances heat transport though the top surface with increasing the supercriticality.

Effect of Arrhenius activation energy on two-phase nanofluid flow and heat transport inside a circular segment with convective boundary conditions: Optimization and sensitivity analysis

This paper analyzes the heat transport phenomena of two-phase nanofluid within a permeable circular segment with an interaction of Arrhenius activation energy and, examines the interaction of convective boundary conditions affecting the flow characteristics. The pre-exponential factor of the Arrhenius equation deals with the collision between molecules, and it has significant applications for getting the rate of a chemical reaction and is used to estimate material properties with changes in temperature and energy. To a greater extent, the external uniform heat source encourages thermal properties on account of the behavior of Brownian and thermophoresis parameters. The transformation of the standard nondimensional form of the governing equations is obtained for the assumption of appropriate similarity variables and stream function. The set of these transformed equations is tackled numerically with the shooting technique. The characteristics of physical parameters on the flow phenomena are presented graphically and the validation with earlier research displays a strong correlation for the specific case. The special attraction of the present investigation is the regression analysis for the simulated results of heat and solutal transfer rates using Response Surface Methodology considering various characterizing parameters like heat source, thermal radiation, curvature, activation energy, thermal and solutal Biot numbers within certain range.

Origin and mineralization processes of REE during magmatic-hydrothermal evolution: Insights from in-situ geochemistry of calcite from the Weishan REE deposit, eastern North China Craton

The Weishan REE deposit, hosting more than one million tons of light REE oxides (LREE2O3), is one of the largest LREE deposits in China. It has been considered to be a carbonatite-related REE deposit, but whether carbonatites occurred or not is still controversial, leading to the confusions of how the LREE originated and mineralized. Here, we conducted in-situ elemental and Sr-Nd isotopic analyses on different stages of calcite from the Weishan REE deposit, combined with petrographic and bulk C-O isotopic studies, with the aim to unravel the origin and mineralization processes of REE. Four stages of calcite (Cal-1, Cal-2, Cal-3 and Cal-4) were identified, of which the Cal-1 typically coexists with K-feldspar and quartz while the Cal-2 and Cal-3 coexist with sulfates and REE minerals (e.g., bastnäsite and parisite), respectively. The Cal-4 occurs in the post-ore veinlets and coexists with sulfides. The Cal-1 is characterized by exsolution of carbocernaite along its cleavage planes with highest Na, K, Sr, Ba and LREE contents. The other stages of calcite show continuous decrease of the above elements. Combined with petrographic features and elemental discrimination diagrams, it is concluded that the Cal-1 is magmatic while the others are hydrothermal. These calcites thus indicate a continuous magmatic-hydrothermal evolution. The four stages of calcite show similar isotopic compositions, which are consistent with those of the alkaline silicate rocks in the ore district, suggesting an uniform source or magma chamber for their derivation. Considering the magmatic features of Cal-1, it is inferred that carbonate melts coupled with abundant alkaline fluids were exsolved from the alkaline magmas. Alkalis (e. g., K and Na) were enriched in the magmatic-hydrothermal system with potassic metasomatism being more prevalent, which might play an important role in REE exsolution and transportation. Focused REE deposition occurred shortly after massive deposition of sulfates, indicating that REE-sulfate complexes might be the dominant transporting ligands of REE. The deposition of REE was mainly induced by fluid boiling, as indicated by the boiling/unmixing features of fluid inclusions. The Sr-Nd isotopic compositions of ores and associated alkaline rocks show affinities to the enriched lithospheric mantle (EM) beneath the study region, but are more depleted. Because subduction of the Paleo-Pacific oceanic plate beneath the eastern Asian occurred since the Jurassic, it is inferred that CO2- and REE-rich melts/fluids released from the subducted oceanic slab metasomatized the EM, leading to a REE-rich carbonated mantle. Rollback of the subducted slab occurred during the early Cretaceous, resulting in partial melting of the EM and thus generating the CO2- and REE-rich alkaline magmas. This deposit shows significant hydrothermal features with poorly-developed carbonatites, distinct from the typical carbonatite-related REE deposits in the other places. The REE mineralization is thus considered to be basically controlled by the alkaline magmas rather than the carbonatites.

Numerical solution of non-linear advection-dispersion equation in a finite porous domain

This study presents a numerical simulation of the one-dimensional concentration-dependent convection-dispersion equation in a finite heterogeneous porous formation. The solution of the convection-diffusion equation with variable coefficients is obtained with the help of MATLAB pdepe solver. The groundwater flow velocity depends on the pollutant concentration, and the dispersion coefficient is proportional to the groundwater flow velocity. The effects of the zero-order production term and the first-order decay are also considered. The aquifer is assumed to be heterogeneous and finite, with sources concentrated in the flow direction. It is assumed that the porous media and the pollutant are chemically non-reactive. Initially porous domain is considered not solute free. The model assumes a uniform continuous input point source and a variable input point source released from the left end of the aquifer domain. The obtained results graphically describe the importance of the dispersion coefficient and other relevant parameters for solute transport in porous media. The developed numerical solution is verified with an analytical solution, and it is found that they are in good agreement.

Fast Ewald summation for Stokes flow with arbitrary periodicity

A fast and spectrally accurate Ewald summation method for the evaluation of stokeslet, stresslet and rotlet potentials of three-dimensional Stokes flow is presented. This work extends the previously developed Spectral Ewald method for Stokes flow to periodic boundary conditions in any number (three, two, one, or none) of the spatial directions, in a unified framework. The periodic potential is split into a short-range and a long-range part, where the latter is treated in Fourier space using the fast Fourier transform. A crucial component of the method is the modified kernels used to treat singular integration. We derive new modified kernels, and new improved truncation error estimates for the stokeslet and stresslet. An automated procedure for selecting parameters based on a given error tolerance is designed and tested. Analytical formulas for validation in the doubly and singly periodic cases are presented. We show that the computational time of the method scales like O(Nlog⁡N) for N sources and targets, and investigate how the time depends on the error tolerance and window function, i.e. the function used to smoothly spread irregular point data to a uniform grid. The method is fastest in the fully periodic case, while the run time in the free-space case is around three times as large. Furthermore, the highest efficiency is reached when applying the method to a uniform source distribution in a primary cell with low aspect ratio. The work presented in this paper enables efficient and accurate simulations of three-dimensional Stokes flow with arbitrary periodicity using e.g. boundary integral and potential methods.

Optical ray-tracing simulation method for the investigation of radiance non-uniformity of an integrating sphere

The paper deals with possibilities and limits of optical simulations of extended uniform light sources. Optical simulations of ideal and real light sources are performed using optical ray-tracing software which is capable to simulate non-imaging systems such as Lambertian disc and integrating spheres. The simulation methodology is validated by comparing the developed simulation model with a real experiment previously performed in optical laboratory. The comparison is made on the radiance uniformity measurement and simulation results of a general purpose integrating sphere rather than on less convenient and more frequent irradiance uniformity measurements. The aim is to develop a reliable simulation method for the investigation of radiance non-uniformity of any real extended uniform light source.

Mechanism of heat transfer in Falkner–Skan flow of buoyancy-driven dissipative hybrid nanofluid over a vertical permeable wedge with varying wall temperature

Heat transport issues of wedge-shaped flow on hybrid nanofluids are of special significance by reason of their importance in manufacturing uses including heat exchangers solar panels, electronic equipment cooling, drying processes, and air heaters. Consequently, the current investigation investigates the behavior of dissipative Single-walled Carbone nanotubes (SWCNT) — Multi-walled Carbon nanotubes (MWCNT) hybrid nanofluid in the buoyant flow towards a radiative vertical permeable wedge subjected to variable wall temperature considering heat source/sink. By selecting appropriate similarity conversions, the resultant flow regulating nonlinear boundary layer PDEs are subsequently transformed into coupled nonlinear ODEs. After that, the boundary layer Boussinesq approximations are numerically resolved. The significant outcome of the current investigation is the heat transport which is higher for linear radiation, volume fraction, and uniform heat source parameters. The momentum is controlled with wedge angle and volume fraction of nanotube particles. The momentum boundary layer is upsurged with mixed convection parameters for an assisting flow. Changes to the Nusselt number and fluid flow rate are measured for flow-controlling parameters. Furthermore, the results are compared and effectively validated with previously reported literature results.

The influence of global and domestic uncertainty on electricity supply: A study of Swedish power sources

Developing sustainable energy systems through system integration and sector coupling may involve permeating previous isolated and idiosyncratic reactions through the whole system. This study examines supply side dynamics of how uncertainty and spot prices influence electric power supply in an internationally connected electricity system. By applying quantile methods, the study reveals highly nonlinear and asymmetric responses in supplied electricity given a change in uncertainty or system spot prices. The findings show that while the total supply of electricity is largely unaffected by uncertainty and spot price, both supply level and changes in power supply for specific dispatchable power sources are influenced differently depending on the type of uncertainty (domestic or global). The findings also show that the response structure induced by uncertainty and spot price seems to be largely uniform and power source specific. This has implications for creating, amongst other things, integrated systems, and sector coupling, where there is a need for inexpensive excess power supply.

Thermal analysis of ultrasonic vibration-assisted grinding with moment-triangle heat sources

AISI 9310 steel has garnered increasing attention for its superior mechanical properties in the manufacturing of transmission gears for helicopters and accessory transmission systems in aero-engines. The ultrasonic vibration-assisted grinding (UVAG) technique is a new potential method to machine tooth surface given the periodically changing trajectory between abrasive grains and the workpiece, contributing to enhancing heat transfer and thus solving sudden burns. The accurate prediction of grinding heat and the proposal of the associated control strategy are desired to ensure the machining quality. Combined with the separation coefficient model and the chip volume distribution of UVAG processes, a new moment-triangle (MT) heat source model was established. Subsequently, comparative analyses on grinding temperature with conventional grinding and UVAG process were performed using the conditional triangular heat source model and the proposed MT heat source model. Results show that the MT heat source model has a lower prediction error with an average error of 7.13%, which is improved by 7.33% compared with that of the triangular heat source model. The prediction accuracy for the maximum grinding temperature can be raised by 13.39% when the MT heat source model is applied in place of the other one under UVAG processes. In addition, the heat source model transits from triangular into uniform heat source gradually as the ultrasonic amplitude increases, and the transition rate is positively correlated with the ultrasonic amplitude. On this basis, the desired controlling strategy is proposed to enhance the machining performance of ultrasonic grinding processes and effectively reduce heat generations during grinding by increasing the ultrasonic amplitude, reducing the depth of cut and decreasing the workpiece speed.

Healthcare professionals’ views on shared decision-making in plastic surgery in the Netherlands

In shared decision-making (SDM), patients and healthcare professionals (HCPs) reach a joint clinical decision based on the best available evidence and the patient's preferences. SDM seems particularly valuable in plastic surgery, as often multiple treatment options are available. This cross-sectional online survey study aimed to assess HCPs' views and knowledge about SDM, identify facilitators and barriers of SDM, and determine specific requirements for SDM within plastic surgery. Participants were HCPs working in plastic surgery in the Netherlands. Participant characteristics, SDM knowledge, perceived facilitators and barriers, and requirements were assessed using a custom-made online survey. Two researchers thematically analyzed qualitative data. We received 124 responses (with a response rate of 23%). Most respondents were attending plastic surgeons (79%), and 60% had more than 10 years of experience. Almost all respondents considered SDM important (91%), and most (78%) indicated that they applied SDM during consultations. However, only 15% of the HCPs showed a comprehensive understanding of the principle of SDM. Sufficient time, available sources of information (on treatment options and SDM), and decision support tools were identified as important requirements for SDM. Despite the positive attitudes toward SDM, there is a clear need for SDM training of HCPs, uniform sources of information and guidelines, and improved awareness and availability of decision support tools. National plastic surgery societies can play a crucial role in improving SDM-related knowledge, the availability of information and decision support tools, and the implementation of SDM in the field of plastic surgery.

A Study on the Applicability of Aromatic Parameters in the Maturity Evaluation of Lacustrine Source Rocks and Oils Based on Pyrolysis Simulation Experiments.

Aromatic maturity parameters were evaluated via closed-system pyrolysis experiments using a Mesozoic lacustrine source rock from the Yingen-Ejinaqi Basin, thereby ensuring a uniform source. Pulverized rock aliquots (200 mg) were reacted with water at temperatures ranging from 250 to 550 °C at 5 °C/min, and the aromatic fractions of expelled oil and extracts of the solid residue were analyzed by GC-MS. The experiments showed that the relative abundance of aromatic hydrocarbons in the oil and extractable organic matter (EOM) of source rock had different evolutionary characteristics. With the increase in the thermal evolution degree, the relative abundance of aromatic hydrocarbons in the EOM showed the characteristics of ″increased early (Ro < 0.80), unchanged middle (Ro = 0.80-2.00%), decreased lately (Ro > 2.00%)″. While the relative abundance of aromatic hydrocarbons in the expelled oils continuously increased, as the Ro values increased from 0.62 to 2.39%, the relative abundance of aromatic hydrocarbons gradually increased from 8 to 46%. With increased maturity, the relative abundance of 1-3-ring aromatic hydrocarbons continuously decreased, as observed in the phenanthrene homologs. Meanwhile, the relative abundance of 4+-ring aromatic hydrocarbons continuously increased, as seen in chrysene homologs. It was suggested that the effects of maturity on the composition of aromatic hydrocarbons might not be sufficiently obvious. The effective application range of the alkylnaphthalene-related maturity parameters (2-/1-methylnaphthalenes, (2,6- + 2,7-)/1,5-dimethylnaphthalenes, 2,3,6-/(1,4,6- + 1,3,5-) trimethylnaphthalenes, and (2,3,6- + 1,3,7-)/(1,4,6- + 1,3,5- + 1,3,6-) trimethylnaphthalenes) and the alkyldibenzothiophene maturity parameters (4-/1-methyldibenzothiophenes, 4,6-/(1,4- + 1,6-) dimethyldibenzothiophenes, and (2,6- + 3,6-)/(1,4- + 1,6-) dimethyldibenzothiophenes) was 0.84-2.06% Ro. The alkylphenanthrene-related maturity parameters had a wide application range for lacustrine source rocks with an Ro < 2.06%. These parameters included 1.5 × (2- + 3-)/(phenanthrene +1- + 9-) methylphenanthrenes, 3 × 2-/(phenanthrene + 1- + 9-) methylphenanthrenes, (2- + 3-)/(1- + 9-) methylphenanthrenes, 2-/1-methylphenanthrenes, (3- + 2-)/(1- + 2- + 3- + 9-) methylphenanthrenes, 2-/(1- + 2- + 3- + 9-) methylphenanthrenes, and 2,7-/1,8-dimethylphenanthrenes. In addition, the effective applicable range of the methylnaphthalene-related maturity parameter 3-/1-methylchrysenes was an Ro value less than 1.79%. The results clarified the validity scope of some aromatics' maturity parameters and provided a theoretical basis for the scientific application of these parameters.

Evaluating the influence of radial power heterogeneity of fuel rod on its temperature in an accelerator driven subcritical system

Abstract The radial non-uniformity of an ADS fuel rod power density on the peak plane is as high as 10.46 %, which is derived from the reactor physics calculations. In order to investigate the influence of the above-mentioned radial power inhomogeneity on the fuel temperature distribution, this paper constructs a set of two-dimensional comparison examples, where one example uses a uniform heat source and another uses a non-uniform heat source distribution, with taking the fuel segment and its corresponding cladding segment in the region where the peak plane is located as the research object. The finite element software COMSOL is used to conduct the heat transfer analysis. The results of the study show that the fuel temperature under radial non-uniform power distribution is almost the same as that under uniform power. Therefore, this radial non-uniformity can be completely ignored when the research object of temperature is considered. The quantitative calculation carried out in this research can provide certain data support for the engineering research of accelerator driven subcritical system, and can also provide certain guidance for the performance analysis of such fuel elements.

Entropy and exergy analysis of coupled radiative heat transfer and heat conduction: A new thermodynamics approach

This study presents a new approach for evaluating the thermodynamic efficiency of a coupled radiative and conductive heat transfer process with an internal heat source. In this approach, the exergy balance equation is derived, and the exergy augmentation rate due to the internal heat source is found to be the sum of the exergy of the system output to the environment surroundings, the exergy stored in the system, and the exergy consumption rate due to the irreversibility of heat transfer in the system. The exergetic efficiency of the coupled heat transfer process is then obtained according to the radiative exergy balance equation. Based on the above theoretical derivation, we carry out a thermodynamic analysis of an example including five coupled heat conduction-radiation transfer systems with a uniform internal heat source and different boundary conditions. The variations in the numerical results are discussed according to the exergy balance principle, and the behaviours of the exergy components over time under transient conditions are analysed. Our numerical results show that increasing the area of the adiabatic boundary and reducing the heat loss of the system should be considered when designing heat-transfer systems (as the exergetic efficiency increases from 0.515 to 0.617). The larger the area of the adiabatic boundary of the system, the stronger the effect of increasing this area on the overall optimisation. When a system has two adiabatic boundaries, a symmetrical arrangement of the adiabatic boundaries is suggested, although this is much less effective than increasing the number of adiabatic boundaries.

Influence of magnetic boundary conditions on the quantitative modelling of magnetorheological elastomers

The complex magneto-mechanical coupling that governs the material response of magnetorheological elastomers (MREs) requires computational tools to assist the design process. Computational models are usually based on finite element frameworks that often simplify and idealise the magnetic source and the associated magnetic boundary conditions (BCs). However, these simplifications may lead to important disagreement between the actual material behaviour and the modelled one, even at the qualitative level. In this work, we provide a comprehensive study on the influence of magnetic BCs and demonstrate the importance of considering them in the overall material-structure modelling strategy. To this end, we implement a magneto-mechanical framework to model the response of soft- and hard-magnetic MREs under magnetic fields generated by an idealised far-field uniform magnetic source, a permanent magnet, a coil system, and an electromagnet with two iron poles. The results unveil remarkable heterogeneities in computed local magnetostriction and magnetic fields depending on the magnetic setup used. A detailed discussion based on material and structural contributions provides a robust, rigorous, and necessary modelling route for future works.

Experimental and numerical investigation on the uniformity of nanosecond pulsed dielectric barrier discharge influenced by pulse parameters

Nanosecond (ns) pulsed dielectric barrier discharge (DBD) is considered as a promising method to produce controllable large-volume and high activity low-temperature plasma at atmospheric pressure, which makes it suitable for wide applications. In this work, the ns pulse power supply is used to excite Ar DBD and the influences of the pulse parameters (voltage amplitude, pulse width, pulse rise and fall times) on the DBD uniformity are investigated. The gas gap voltage (U g) and conduct current (I g) are separated from the measured voltage and current waveforms to analyze the influence of electrical parameters. The spectral line intensity ratio of two Ar excited species is used as an indicator of the electron temperature (T e). The time resolved discharge processes are recorded by an intensified charge-coupled device camera and a one-dimensional fluid model is employed to simulate the spatial and temporal distributions of electrons, ions, metastable argon atoms and T e. Combining the experimental and numerical results, the mechanism of the pulse parameters influencing on the discharge uniformity is discussed. It is shown that the space electric field intensity and the space particles’ densities are mainly responsible for the variation of discharge uniformity. With the increase of voltage and pulse width, the electric field intensity and the density of space particles increased, which results in the discharge mode transition from non-uniform to uniform, and then non-uniform. Furthermore, the extension of pulse rise and fall times leads to the discharge transition from uniform to non-uniform. The results are helpful to reveal the mechanism of ns pulsed DBD mode transition and to realize controllable and uniform plasma sources at atmospheric pressure.

In situ measurement of dynamic surface charge on dielectrics interacted with plasma jet arrays

As a flexible tool to generate large-scale non-thermal plasma in ambient air, plasma jet arrays have attracted academic attention from multiple fields of biomedicine and material surface sciences. Optimization of plasma processing that heavily relies on trial-and-error experiments requires quantitative in situ diagnostics of plasma–surface interaction. This study focuses on the fundamental surface charge evolution in quartz dielectric deposited by plasma jet arrays. The thin quartz plate is attached to an electro-optic BSO crystal that is conductive and grounded in the back. These jet arrays are driven by a positive microsecond pulsed voltage with kHz frequency. Special attention is paid to the properties and mechanisms of the intriguing convergence of multiple adjacent surface charge patterns. The measured 1D and 2D jet arrays verify the trend of homopolar charge fusion at the plasma–surface interface, which was initially thought to be repulsive under electrostatic forces. The fusion of surface charges is considerably enhanced when more charges are transported onto targeted dielectrics, as well as at smaller separations. The simulation results reveal the mechanism of charge fusion that occurs when surface ionization waves (IWs) are in close proximity, and the high electric field between their heads provides a cluster of high-energy electrons that forces two IWs to merge until they connect. In the case of extremely small separations, the close-in IWs directly merge in bulk before touching the target. Quantitative in situ measurements of surface charges and the corresponding simulations provide fresh insight into the electrical interaction in large-scale atmospheric-pressure plasma jets. The properties of charge fusion can help with manufacturing and optimizing large-area uniform plasma jet sources for various dielectric materials.

High-sensitivity cardiac SPECT system design with collimator-less interspaced mosaic-patterned scintillators.

Single-photon emission computed tomography (SPECT) is an important tool for myocardial perfusion imaging (MPI). Mechanical collimators cause the resolution-sensitivity trade-off in the existing cardiac SPECT systems, which hinders fast cardiac scan capability. In this work, we propose a novel collimator-less cardiac SPECT system with interspaced mosaic-patterned scintillators, aiming to significantly improve sensitivity and reduce scan time without trading-off image resolution. We propose to assemble a collimator-less cardiac SPECT with 7 mosaic-patterned detector modules forming a half-ring geometry. The detector module consists of 10 blocks, each of which is assembled with 768 sparsely distributed scintillators with a size of 1.68 mm × 1.68 mm × 20 mm, forming a mosaic pattern in the trans-axial direction. Each scintillator bar contains 5 GAGG(Ce) scintillators and 5 optical-guide elements, forming a mosaic pattern in the axial direction. In the Monte Carlo simulations, the in-plane resolution and axial resolution are evaluated using a hot-rod phantom and 5 disk phantoms, respectively. We simulate a cardiac phantom that is placed in a water-filled cylinder and evaluate the image performance with different data acquisition time. We perform image reconstruction with the expectation-maximization algorithm using system matrices derived from the simulation of a uniform cylindrical source filling the field-of-view (FOV). Besides, a 2-D prototype system is designed to demonstrate the feasibility of the collimator-less imaging concept. In the simulation system, the sensitivity is 16.31% ± 8.85% in a 180 mm (Φ) × 100 mm (L) FOV. The 6-mm rods in the hot rod phantom and the 5-mm disks in the disk phantom are clearly separable. Satisfactory MPI image quality is achieved in the cardiac phantom study with an acquisition time of 30 s. In prototype experiments, the point sources with an 8 mm center-to-center distance are clearly separable at different positions across the FOV. The study reveals a promising approach to high-sensitivity SPECT imaging without a heavy-metal collimator. In cardiac imaging, this approach opens the way to a very fast cardiac scan with good resolution. Further works are ongoing to build a practical 3-D imaging system based on the existing design.

A Lattice-Boltzmann-based modelling chain for traffic-related atmospheric pollutant dispersion at the local urban scale

Urban traffic-related air pollution is a major source of environmental and health damage and is difficult to quantify due to its inherent physical complexity. We construct a CFD-based simulation framework coupling an efficient numerical method for turbulent fluid flows with a microscopic traffic model and an emissions model to simulate road transport pollutant dispersion at the urban microscale. We improve the open-source Lattice-Boltzmann based CFD software OpenLB to overcome its original stability deficiencies for high Reynolds number flows. A stable recursive regularization procedure with a double distribution function approach is proposed to solve an advection diffusion equation for passive scalar transport at high Reynolds number. The code is successfully validated on three reference cases of increasing complexity and the traffic model SUMO along with a physical engine emissions model are coupled with OpenLB to simulate traffic-induced pollution from a road network in a realistic complex geometry. Transient flow features are analysed and the time-averaged concentration levels in different neighbourhoods of the considered geometry are evaluated: high concentration levels are observed close to the streets but also inside specific building infrastructures due to complex wind dynamics. Analyses of altitudinal concentration variations show that flow recirculations located close to traffic lights can drive pollutant over the buildings and increase concentration levels inside inner courtyards. Time-averaged concentration maps are constructed using both spatially uniform and non-uniform line sources and it is shown that using uniform sources leads to up to 20% local concentration overestimations inside the urban canopy.

Exploring and enhancing the volumetric behaviour in solar receivers through specular reflectivity and simplified design

One of the remaining challenges of point focusing concentrating solar power systems is the realization of a true volumetric receiver, one whose entire volume is utilized for the absorption of irradiance. Commercial state-of-the-art receivers (e.g., HiTRec-II and SolAir-200) have not demonstrated the volumetric effect, because of low radiation penetration within the absorber. Then, literature state-of-the-art receivers were able to demonstrate a volumetric behaviour (toward achieving the volumetric effect) through axially varied macro-scale porosity (void fraction), but at the cost of design complexity and manufacturability. This study presents the conceptual design and computational assessment of an improved volumetric receiver by employing varied reflectivity on the irradiated surfaces, thereby enhancing radiation penetration. This approach maintains the simplicity, manufacturability, and commercial viability of structured receivers. Three reflectivity distributions were initially investigated using a 3D heat transfer mathematical model, verified with literature experimental data, which incorporated a source term ascertained through Monte-Carlo Ray Tracing (MCRT). The findings from these three design cases revealed that while diffuse reflectivity distributions could improve thermal efficiency, they were unable to enhance radiation penetration. Consequently, an improved volumetric solar receiver was realized by integrating specular reflectivity, leading to a more uniform source term distribution and achieving a thermal efficiency of 96%, as opposed to the 85% thermal efficiency of the commercial state-of-the-art HiTRec-II receiver. The discovery of the specular receiver as a true volumetric receiver facilitated an exploration of quantitative definitions of the volumetric effect. The exploration concluded that volumetric effect metrics would only target designs that maximizing thermal efficiency when the receiver is exhibits a truly volumetric nature, characterized by a uniform source term distribution.