Non-uniform Density Distribution Research Articles

Study of the importance of non-uniform mass density in numerical simulations of fire spread over MDF panels in a corner configuration

The distribution of mass density through the thickness of Medium Density Fiberboard (MDF) panels is known to be non-uniform. A few studies have previously investigated the influence of this non-uniform through-thickness density distribution on the thermal behavior of MDF panels in small-scale tests. This study assesses the significance of this material property on flame spread simulations in a medium-scale set-up, namely that of Single Burning Item (SBI) corner fire tests. Simulations are performed using FireFOAM 2.2.x, considering both uniform and non-uniform MDF material density profiles, using model-effective material properties determined from bench-scale pyrolysis tests conducted in a Fire Propagation Apparatus (FPA). The heat transfer from the gas phase is modeled by means of empirical expressions with adjusted parameters. The simulations are assessed against the results of several SBI experiments with MDF panels and a test with Calcium Silicate (CS) panels. When the non-uniform nature of the through-thickness density is taken into account, the fire growth prediction in terms of the total Heat Release Rate (HRR) is considerably different (20% higher peak HRR), mainly due to the characteristic high peak mass loss rate at the initiation of pyrolysis of MDF material, resulting from the higher mass density near the surface of the panels. Furthermore, total heat fluxes on the panels, lateral flame spread, surface pyrolysis and through-thickness char formation visibly depend on the non-uniform distribution of mass density, particularly in regions further away from the corner where the influence of thermal attack from the burner is less dominant. A new diagnostic is proposed for determining the pyrolysis front location and spread on the surface of the charring panels.

Inversion of the density structure of the lithosphere in the North China Craton from GOCE satellite gravity gradient data

Lithospheric thinning in the North China Craton (NCC), one of the oldest cratons on Earth, has been a focus of geoscientists across the globe for a long time. In this study, seismic tomographic P-wave velocity variations are converted to density perturbations as the initial constraint values, and the four components of the GOCE Level-2 gravity gradient product are subjected to topographic effect correction, relief correction on the Moho and sedimentary layer boundary, and long-wavelength correction. In addition, the anomalous gravity gradient effect resulting from the uncertainty of the Moho and sedimentary layer depth is considered. Considering the effects of temperature variations in the lithosphere, which leads to the non-uniform density distribution, the anomalous gravity gradient effect resulting from the temperature variations is corrected at the first time in this area. Inverse computation is performed based on the preconditioned conjugate gradient algorithm. Because the Lagrange empirical parameter in the algorithm exhibits uncertainty in data inversion, the regularization parameter, which is typically an empirical parameter, is replaced with the value of the inflection point of the L-curve. The results show the followings. The non-uniform density distribution in the lithosphere is related not only to the composition but also to the internal temperature variations in the lithosphere. The density of the lithosphere in the NCC is significantly non-uniform in both the horizontal and vertical directions and exhibits a notable segment-wise spatial distribution pattern. Two tectonic units, namely the Taihangshan tectonic zone and the Linfen–Weihe graben, constitute a central gravity gradient transition zone. There is a significant difference in the density distribution on the two sides of this central transition zone.

Design and analysis of a high quality factor multipath spiral inductor

Recently high quality factor and small-occupying-area inductors are prerequisite for wireless communication products such as mobile phones and wireless network, low cost and high performance on chip radio-frequency devices and microwave integrated circuit applications. In high frequencies, non-uniform current density distribution in the edge of the coil due to skin effect and proximity effect increases effective resistance of inductor and reduces the quality factor. This paper presented a multipath circular spiral inductor. The multipath technique reduces the skin and proximity effects, therefore increases the quality factor of the inductors. Simulation has been taken using COMSOL Multiphysics software. The results show maximum quality factor of proposed inductor have been achieved about 79 at 230 MHz that have been improved around 73% compared with conventional one. The dimension of the inductor is 2300 µm × 2300 µm. The small size proposed structure with high Q-factor is sufficient for the wireless applications.

A Modified Boundary Condition of Velocity for Continuity Equation with Non-uniform Density Distribution at Outlet Boundary Plane

Boundary conditions in computational fluid dynamics significantly affect the prediction of flow field. However, the outlet boundary conditions for the continuity equation have been rarely investigated. In addition, the velocities at the outlet boundary might not be accurately predicted with the conventional outlet boundary conditions when a flow that has non-uniform density distribution on the outlet boundary is simulated. In the present study, we modified a boundary condition for the continuity equation in consideration of the non-uniform density distribution on the outlet boundary plane, comparing the numerical results of combustion between the conventional and modified boundary conditions. As a result, the proposed boundary condition can resist the generation of an unrealistic temperature field better than the conventional methods.

Electronic structure of isomeric graphene nanoflakes

A comparative theoretical study of graphene nanoflakes (NFs) and isomeric NFs based on two different graphene allotropes has been carried out using hybrid density functional theory and complete active space calculations. Two graphene allotropes H1 and H2 consisted of fused azulene rings were found to be less stable compared to isomeric graphene NFs at all theoretical levels. H1 and H2 have closed shell singlet ground state independently on their size and strong bond length alternation. For all types of NFs, the evolution of the ionization potential (IP), electron affinity (EA) and band gap (Eg) with size is similar. IP and Eg drop and EA increases with NF size. H1 and H2 show lower IPs and Egs and higher EAs compared to the corresponding graphene NF of the same size. However, IPs, Egs and EAs converge with size for all three types of the NF becoming nearly identical for the largest representatives of H1, H2 and graphene NF. H1 and H2 types of NF have a non-uniform distribution of the electron density across the NF, unlike graphene systems, which makes them promising candidates for regioselective chemical modification.

Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow

Context. In the inner regions of asymptotic giant branch (AGB) outflows, several molecules have been detected with abundances much higher than those predicted from thermodynamic equilibrium chemical models. The presence of the majority of these species can be explained by shock-induced non-equilibrium chemical models, where shocks caused by the pulsating star take the chemistry out of equilibrium in the inner region. Moreover, a non-uniform density structure has been detected in several AGB outflows. Both large-scale structures, such as spirals and disks, and small-scale density inhomogeneities or clumps have been observed. These structures may also have a considerable impact on the circumstellar chemistry. A detailed parameter study on the quantitative effects of a non-homogeneous outflow has so far not been performed. Aims. We examine the effects of a non-uniform density distribution within an AGB outflow on its chemistry by considering a stochastic, clumpy density structure. Methods. We implement a porosity formalism for treating the increased leakage of light associated with radiation transport through a clumpy, porous medium. We then use this method to examine the effects from the altered UV radiation field penetration on the chemistry, accounting also for the increased reaction rates of two-body processes in the overdense clumps. The specific clumpiness is determined by three parameters: the characteristic length scale of the clumps at the stellar surface, the clump volume filling factor, and the inter-clump density contrast. In this paper, the clumps are assumed to have a spatially constant volume filling factor, which implies that they expand as they move outward in the wind. Results. We present a parameter study of the effect of clumping and porosity on the chemistry throughout the outflow. Both the higher density within the clumps and the increased UV radiation field penetration have an important impact on the chemistry, as they both alter the chemical pathways throughout the outflow. The increased amount of UV radiation in the inner region leads to photodissociation of parent species, releasing the otherwise deficient elements. We find an increased abundance in the inner region of all species not expected to be present assuming thermodynamic equilibrium chemistry, such as HCN in O-rich outflows, H2O in C-rich outflows, and NH3 in both. Conclusions. A non-uniform density distribution directly influences the chemistry throughout the AGB outflow, both through the density structure itself and through its effect on the UV radiation field. Species not expected to be present in the inner region of the outflow assuming thermodynamic equilibrium chemistry are now formed in this region, including species that are not formed in greater abundance by shock-induced non-equilibrium chemistry models. Outflows whose clumps have a large overdensity and that are very porous to the interstellar UV radiation field yield abundances comparable to those observed in O-rich and C-rich outflows for most of the unexpected species investigated. The inner wind abundances of H2O in C-rich outflows and of NH3 in O-rich and C-rich outflows are however underpredicted.

Radiobiological parameters in a tumour control probability model for prostate cancer LDR brachytherapy

To provide recommendations for the selection of radiobiological parameters for prostate cancer treatment planning. Recommendations were based on validation of the previously published values, parameter estimation and a consideration of their sensitivity within a tumour control probability (TCP) model using clinical outcomes data from low-dose-rate (LDR) brachytherapy.The proposed TCP model incorporated radiosensitivity (α) heterogeneity and a non-uniform distribution of clonogens. The clinical outcomes data included 849 prostate cancer patients treated with LDR brachytherapy at four Australian centres between 1995 and 2012. Phoenix definition of biochemical failure was used. Validation of the published values from four selected literature and parameter estimation was performed with a maximum likelihood estimation method. Each parameter was varied to evaluate the change in calculated TCP to quantify the sensitivity of the model to its radiobiological parameters.Using a previously published parameter set and a total clonogen number of 196 000 provided TCP estimates that best described the patient cohort. Fitting of all parameters with a maximum likelihood estimation was not possible. Variations in prostate TCP ranged from 0.004% to 0.67% per 1% change in each parameter. The largest variation was caused by the log-normal distribution parameters for α (mean, , and standard deviation, σα).Based on the results using the clinical cohort data, we recommend a previously published dataset is used for future application of the TCP model with inclusion of a patient-specific, non-uniform clonogen density distribution which could be derived from multiparametric imaging. The reduction in uncertainties in these parameters will improve the confidence in using biological models for clinical radiotherapy planning.

Combination of shape and X-ray inspection for apple internal quality control: in silico analysis of the methodology based on X-ray computed tomography

Multisensor inspection allows for inline detection of internal defects of products with variable shapes, such as fruit and vegetables, by combining X-ray radiography with 3D shape recognition and modelling. For products with a complex internal structure such as apple fruit, inspection must also account for the corresponding internal density gradients that can affect X-ray radiographic images. Apple fruit consist of different tissues with spatially varying differences and gradients in porosity, resulting in corresponding density gradients. Development of internal browning disorders during storage of apples result in damage to tissue structure and associated changes of density distribution. In this paper, a method is developed and evaluated to account for density gradients in apple to improve detection success of defected apples. Experiments were conducted with 26 ‘Braeburn’ apples that were subjected to storage conditions in which internal browning develops. X-ray CT images of each apple were taken at 5 time points over a period of 9 months to obtain a reference dataset of 130 apples with varying levels of defects that could be accurately characterized. The fruit were additionally subjected to multisensory inspection. Using the images of healthy fruit, an internal density distribution model was created and used in the image processing pipeline of the proposed technique to correct for internal gradients. Accounting for a non-uniform internal density distribution increased the R2adj value from 0.73 to 0.86 for prediction of the degree of browning in a fruit. A receiver operator characteristic analysis found that accounting for non-uniform samples reduced the number of false positives from 14 to 5% at a true positive rate of 90%. It was demonstrated that the multisensor inspection approach requires relatively simple hardware of combined with prior knowledge in the form of a statistical shape model and associated density distribution. It is also flexible, since no specific segmentation and detection methods have to be developed for different types of defects.

Diagnostic of semiconductor device structures by spin-labeled electrons

The influence of non-uniform distribution of spin density in the temperature range from 5 to 80 K under the conditions of optical orientation of electrons in semiconductors is analyzed. Possibility to determine the kinetic parameters of carriers by depolarization of recombination radiation in a magnetic field is shown. Electron diffusion length and mobility is defined for materials with a hole conductivity. An estimated value of the rate of recombination on a free surface and its influence on the distribution of the concentration of non-equilibrium electrons from the excitation surface into the bulk is presented.

Computational thermofluid-dynamic analysis of DEMO divertor cassette body cooling circuit

Within the framework of the Work Package Divertor, Subproject: Cassette Design and Integration (WPDIV-Cassette) of the EUROfusion action, a research campaign has been jointly carried out by ENEA and University of Palermo to investigate the thermal-hydraulic performances of the DEMO divertor cassette cooling system.The research activity has been carried out following a theoretical-computational approach based on the finite volume method and adopting a qualified Computational Fluid-Dynamic (CFD) code.Fully-coupled fluid-structure CFD analyses have been carried out for the recently-revised cassette body cooling circuit under nominal steady state conditions, imposing a non-uniform spatial distribution of nuclear-deposited heat power volumetric density drawn from the most recent neutron transport analysis. The pertaining thermal-hydraulic performances have been assessed in terms of coolant flow velocity and total pressure distributions as well as of coolant and structure temperature distributions to check whether they comply with the corresponding prescribed limits. Results obtained are reported and critically discussed.

Design and analysis of a novel MEMS spiral inductor with high quality factor

In this paper a novel spiral inductor with high quality (Q)-factor is presented. Non-uniform current density distribution, especially in inner turn, increases the effective metal resistance due to skin and proximity effect. In order to overcome this problem, an improved inductor layout with non-uniform metal width and non-uniform spacing is proposed to increase the quality factor. For this inductor layout, from outer coil to inner coil, the metal widths are reduced but spacing between strips are increased. Mainly due to the decrease of eddy current loss by weakening the current crowding effect in the center of the spiral inductor. By reducing the current crowding effect, the effective resistance is minimized, thereby increase the quality factor. Simulation has been taken using COMSOL Multiphysics software. The results indicate that maximum value of quality factor and self-inductance of the novel inductor have been obtained about 80.34 and 324 nH, respectively. Which Q-factor improves 27% more than conventional inductors with uniform width. The dimension of the inductor is 1700 × 1660 μm.

Counting challenging crowds robustly using a multi-column multi-task convolutional neural network

Counting challenging crowds from still images has a wide range of applications, such as surveillance event detection, public safety control, traffic monitoring, and urban planning. Early studies on crowd counting focused on extracting hand-crafted features and building effective regression models. However, previous approaches may encounter many challenges, such as partial occlusion, non-uniform density distribution, and variations in scale and perspective. A multi-column multi-task convolutional neural network (MMCNN) is proposed for robust crowd counting, which is achieved through summing up the density map estimated by the proposed network. A novel approach is used to generate the ground truth of density map that focuses on location and detailed information. A multi-column CNN is designed to address drastic scale variation exists in crowds. Per-scale loss is minimized to make the features of different scales highly discriminative. Meanwhile, a multi-task strategy is utilized to simultaneously estimate the density map, crowd density level, and background/foreground mask. Contrastive evaluations in benchmarking datasets are implemented with several state-of-the-art CNN-based crowd counting approaches. Results reveal the accuracy and robustness of our approach in counting challenging crowds. The proposed approach achieves the state-of-the-art performance in terms of mean absolute error and mean squared error. The counting approach can be also extended to other related tasks, such as anomaly detection.

Observation of non-symmetric side-scattering during high-intensity laser-plasma interactions

Non-symmetric side-scattering has been observed during the interaction between a high-intensity laser pulse and under-dense argon plasma. The angle between the laser’s forward direction and the scattered radiation is found to decrease for increasing electron densities ranging from 0.01 to 0.25nc, where nc is the critical density for the laser wavelength. We show that the observed features of the scattering cannot be described by Raman side-scattering but can be explained to be a consequence of the non-uniform density distribution of the plasma with the scattering angle being oriented along the direction of the resulting electron density gradient.

Turbulent stagnation in a Z-pinch plasma.

The ion kinetic energy in a stagnating plasma was previously determined by Kroupp etal. [Phys. Rev. Lett. 107, 105001 (2011)PRLTAO0031-900710.1103/PhysRevLett.107.105001] from Doppler-dominated line shapes augmented by measurements of plasma properties and assuming a uniform-plasma model. Notably, the energy was found to be dominantly stored in hydrodynamic flow. Here we advance a new description of this stagnation as supersonically turbulent. Such turbulence implies a nonuniform density distribution. We demonstrate how to reanalyze the spectroscopic data consistent with the turbulent picture and show that this leads to better concordance of the overconstrained spectroscopic measurements, while also substantially lowering the inferred mean density.

Optimization of the Hot Forging Processing Parameters for Powder Metallurgy Fe-Cu-C Connecting Rods Based on Finite Element Simulation

Powder forged connecting rods have the problem of non-uniform density distributions because of their complex geometric shape. The densification behaviors of powder metallurgy (PM) connecting rod preforms during hot forging processes play a significant role in optimizing the connecting rod quality. The deformation behaviors of a connecting rod preform, a Fe-3Cu-0.5C (wt pct) alloy compacted and sintered by the powder metallurgy route (PM Fe-Cu-C), were investigated using the finite element method, while damage and friction behaviors of the material were considered in the complicated forging process. The calculated results agree well with the experimental results. The relationship between the processing parameters of hot forging and the relative density of the connecting rod was revealed. The results showed that the relative density of the hot forged connecting rod at the central shank changed significantly compared with the relative density at the big end and at the small end. Moreover, the relative density of the connecting rod was sensitive to the processing parameters such as the forging velocity and the initial density of the preform. The optimum forging processing parameters were determined and presented by using an orthogonal design method. This work suggests that the processing parameters can be optimized to prepare a connecting rod with uniform density distribution and can help to better meet the requirements of the connecting rod industry.

Non-uniform effect on the thermal/aging performance of Lithium-ion pouch battery

Non-uniform distribution of current density and temperature is inevitable especially in high C-rate and it can lead to bad performance of battery. Therefore, the non-uniform effect (non-uniform temperature, current density and aging) on the pouch battery performance is studied with experiment and simulation. A new method, which measures the direct current resistance (DCR) based on the discharge curve, is proposed to get more detail of resistance variation. The measurement shows that the resistance of Lithium-ion pouch battery with non-uniform temperature is similar to that of average temperature. Then, effect of non-uniform aging is simulated based on the electro-thermal coupled model. It is found that battery suffering non-uniform aging has smaller discharging capacity relatively. The main cause for the discharge capacity reduction between the uniform and non-uniform aging battery is the big difference of local stoichiometry of cathode electrode θLiFePO4. The capacity reduction in 1C rate occupies about 6% of the permissible capacity loss. Finally, tabs of battery are changed in order to acquire uniform temperature distribution. Battery whose tabs are put on the middle of the top side and the bottom side has a better performance in the opinion of thermal analysis.

Repetitive nanosecond electron accelerators type URT-1 for radiation technology

The electron accelerator URT-1М-300 for mobile installation was created for radiation disinfecting to correct drawbacks that were found the URT-1M electron accelerator operation (the accelerating voltage up to 1 МV, repetition rate up to 300 pps, electron beam size 400 × 100mm, the pulse width about 100ns). Accelerator configuration was changed that allowed to reduce significantly by 20% tank volume with oil where is placed the system of formation high-voltage pulses, thus the average power of the accelerator is increased by 6 times at the expense of increase in pulses repetition rate. Was created the system of the computerized monitoring parameters (output parameters and thermal mode) and remote control of the accelerator (charge voltage, pulse repetition rate), its elements and auxiliary systems (heat of the thyratron, vacuum system), the remote control panel is connected to the installation by the fiber-optical channel, what lightens the work for service personnel. For generating an electron beam up to 400mm wide there are used metal- ceramic] and metal-dielectric cold cathodes of several emission elements (plates) with a non-uniform distribution of the electron beam current density on the output foil ± 15%. It was found that emission drop of both type of cathodes, during the operation at the high repetition rate (100pps) is substantial at the beginning of the process, and then proceeds rather slowly that allows for continuous operation up to 40h. Experiments showed that linear dependence of the voltage and a signal from the pin-diode remains within the range of the charge voltage 45–65kV. Thus, voltage increases from 690 to 950kV, and the signal from the pin-diode – from (2,8–4,6)*104Gy/s. It allows to select electron energy quite precisely with consideration of the radiation technology requirements.

Measurements of trap dynamics of cold OH molecules using resonance-enhanced multiphoton ionization

Trapping cold, chemically important molecules with electromagnetic fields is a useful technique to study small molecules and their interactions. Traps provide long interaction times that are needed to precisely examine these low density molecular samples. However, the trapping fields lead to non-uniform molecular density distributions in these systems. Therefore, it is important to be able to experimentally characterize the spatial density distribution in the trap. Ionizing molecules in different locations in the trap using resonance enhanced multiphoton ionization (REMPI) and detecting the resulting ions can be used to probe the density distribution even with the low density present in these experiments because of the extremely high efficiency of detection. Until recently, one of the most chemically important molecules, OH, did not have a convenient REMPI scheme. Here, we use a newly developed 1 + 1' REMPI scheme to detect trapped cold OH molecules. We use this capability to measure trap dynamics of the central density of the cloud and the density distribution. These types of measurements can be used to optimize loading of molecules into traps, as well as to help characterize the energy distribution, which is critical knowledge for interpreting molecular collision experiments.

High performance planar micro-transformer using novel crossover connection

In this paper a novel planar micro-transformer with high performance is presented. Non-uniform current density distribution, especially in inner turn, increases the effective metal resistance due to skin and proximity effect. In order to overcome this problem, a novel crossover connection between turns has been used to make equal current paths in the turns and uniform the current distribution. By reducing the current crowding effects, the effective resistance is minimized, thereby the transformer performance characteristics can be increased. Simulation has been taken using ADS Momentum and HFSS software. The results show that the quality factor, self-inductance, mutual inductance and coupling factor are about 42.6, 4.9, 3.3 nH, 0.747 respectively, at 3.5 GHz frequency. The footprint of proposed structure is 860 μm × 860 μm. Compare with conventional micro-transformer, 17% in quality factor, 5% in coupling coefficient and more than 20% in self and mutual inductance improvement has been achieved.

Dynamics of a charged gas suspension with an initial spatially nonuniform distribution of the average dispersed phase density during the transition to the equilibrium state

Results of calculations are presented for the transition of a charged gas suspension from the initial nonequilibrium state with a spatially nonuniform distribution of the average density to a state with a uniform distribution of the average density and charge in a bounded volume. A numerical solution is obtained for the system of equations describing the motion of a polydisperse multirate and multitemperature gas suspension, the particles of which carry an electric discharge and create a self-consistent electric field.