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This paper studies finite sample minimax optimal randomization schemes and estimation schemes in estimating parameters including the average treatment effect, when treatment effects are heterogeneous. A randomization scheme is a distribution over a group of permutations of a given treatment assignment vector. An estimation scheme is a joint distribution over assignment vectors, linear estimators, and permutations of assignment vectors. The key element in the minimax problem is that the worst case is over a class of distributions of the data which is invariant to a group of permutations. First, I show that given any assignment vector and any estimator, the uniform distribution over the same group of permutations, namely the complete randomization scheme, is minimax optimal. Second, under further assumptions on the class of distributions and the objective function, I show the minimax optimal estimation scheme involves completely randomizing an assignment vector, while the optimal estimator is the difference-in-means under complete invariance and a weighted average of within-block differences under a block structure, and the number of treated units is determined by the Neyman allocation.

A 3D laser scanning strategy based on cascaded deep neural network is proposed for the scanning system converted from 2D Lidar with a pitching motion device. The strategy is aimed at moving target detection and monitoring. Combining the device characteristics, the strategy first proposes a cascaded deep neural network, which inputs 2D point cloud, color image and pitching angle. The outputs are target distance and speed classification. And the cross-entropy loss function of network is modified by using focal loss and uniform distribution to improve the recognition accuracy. Then a pitching range and speed model are proposed to determine pitching motion parameters. Finally, the adaptive scanning is realized by integral separate speed PID. The experimental results show that the accuracies of the improved network target detection box, distance and speed classification are 90.17%, 96.87% and 96.97%, respectively. The average speed error of the improved PID is 0.4239°/s, and the average strategy execution time is 0.1521 s. The range and speed model can effectively reduce the collection of useless information and the deformation of the target point cloud. Conclusively, the experimental of overall scanning strategy show that it can improve target point cloud integrity and density while ensuring the capture of target.

The supply of species gases and removal of liquid water in a PEM fuel cell are performed through gas flow channels. Therefore, optimising the flow channel configurations is critical for maximising performance of fuel cells. In this paper, the ANSYS PEM Fuel Cell Module is used to simulate a PEM fuel cell with an active area of 100 cm2 and four different flow channel configurations: single-channel serpentine, two-channel serpentine, three-channel serpentine, and parallel channel with headers under two set of different operating conditions. Under both sets of operating conditions, the simulation results indicated that 3-channel serpentine configuration has the best performance due to uniform distribution of species gases over the catalyst layer. It was concluded from the simulation results that the pressure-drop along the 3-channel serpentine configuration is less compared to other serpentine channel configurations, which will require less power for the blowing in of the species gases. The results obtained from simulation under more optimal operating conditions (set 2) used by Hwang’s URFC, predicted increase in the performance of all the four channel configurations compared to the set 1 operating conditions due to higher cell temperature and stichometry of inlet gases. Under set 2 operating conditions, the values of pressure drop across all the channel configurations have increased substantially due to higher flow rates of inlet gases.

We investigated the solid–liquid suspension characteristics in the tank with a liquid height/tank diameter ratio of 1.5 stirred by a novel long-short blades (LSB) impeller by the Euler granular flow model coupled with the standard k–e turbulence model. After validation of the local solid holdup by experiments, numerical predictions have been successfully used to explain the influences of impeller rotating speed, particle density, particle size, liquid viscosity and initial solid loading on the solid suspension behavior, i.e. smaller particles with lower density are more likely to be suspended evenly in the liquid with higher liquid viscosity. At a low impeller rotating speed (N), increase in N leads to an obvious improvement in the solid distribution homogeneity. Moreover, the proposed LSB impeller has obvious advantages in the uniform distribution of the solid particles compared with single Rushton turbine (RT), dual RT impellers or CBY hydrofoil impeller under the same power consumption.

For investigating whether the MARSSIM nonparametric test has sufficient statistical power when a site has a specific contamination distribution before conducting a final status survey (FSS), a novel approach was proposed to predict the release probability of the site. Five distributions were assumed: lognormal distribution, normal distribution, maximum extreme value distribution, minimum extreme value distribution, and uniform distribution. Hypothetical radioactivity populations were generated for each distribution, and Sign tests were performed to predict the release probabilities after extracting samples using Monte Carlo simulations. The designed Type I error (0.01, 0.05, and 0.1) was always satisfied for all distributions, while the designed Type II error (0.01, 0.05, and 0.1) was not always met for the uniform, maximum extreme value, and lognormal distributions. Through detailed analyses for lognormal and normal distributions which are often found for contaminants in actual environmental or soil samples, it was found that a greater statistical power was obtained from survey units with normal distribution than with lognormal distribution. This study is expected to contribute to achieving the designed decision error when the contamination distribution of a survey unit is identified, by predicting whether the survey unit passes the statistical test before undertaking the FSS according to MARSSIM.

Let B n ( m ) be a set picked uniformly at random among all m-elements subsets of { 1 , 2 , … , n } . We provide a pathwise construction of the collection ( B n ( m ) ) 1 ⩽ m ⩽ n and prove that the logarithm of the least common multiple of the integers in ( B n ( ⌊ m t ⌋ ) ) t ⩾ 0 , properly centered and normalized, converges to a Brownian motion when both m , n tend to infinity. Our approach consists of two steps. First, we show that the aforementioned result is a consequence of a multidimensional central limit theorem for the logarithm of the least common multiple of m independent random variables having uniform distribution on { 1 , 2 , … , n } . Second, we offer a novel approximation of the least common multiple of a random sample by the product of the elements of the sample with neglected multiplicities in their prime decompositions.

This paper proposes new indices of cascaded multilevel inverters (MLIs) in order to compare the conventional topology with 10-existed new topologies. Reduction in the number of power switches is the main target of these new topologies. This aim is to reduce the total cost of designed inverters, though the mentioned aim is not enough to design new inverters. Thus, in this study, four comparative indices including sources power uniform distribution index (SPUDI), switches current uniform distribution index (SCUDI), switches loss uniform distribution index (SLUDI), and switches voltage uniform distribution index (SVUDI), are proposed. In addition, it is shown that in most of the new topologies, reducing the number of switches can lead to lowered values of the proposed indices, after which non-uniform power, current, loss, and voltage pattern are obtained. The results prove that mere emphasis on the number of switches, along with the exclusion of either of the proposed indices will cause significant problems, where cost reduction may be underachieved. Based on new indices, the advantages of conventional topology over new ones are presented in this study.

In this paper, the experimental and numerical investigations of both swirling hybrid rocket motors without and with the design of regenerative cooling (RC hereafter), using 90%-wt H 2 O2 and polypropylene (PP) as the liquid oxidizer and the solid fuel, respectively, were performed and compared. We implemented a new design of regenerative cooling using the oxidizer to transfer the heat generated from combustion. A series of ground horizontal hot-fire tests, which include the catalytic-bed only and the motor without/with RC were performed to measure the propulsion performance related parameters. The resulting C* efficiency of the RC design with catalytic-bed only remained in comparison with the one without RC. With a similar initial combustion chamber geometry, the RC implementation resulted in a better engine Isp efficiency from 96.3 to 98.6 with a lower O/F ratio from 6.49 to 5.94. In addition, the topologies of the burned fuel grain surface were optically measured by a 3D laser scanner. The resulting variation of regression rates between the upstream and downstream fuel for the chamber with the RC was smaller than case without the RC. Moreover, a simplified semi-empirical computational fluid dynamics (CFD) model based on the measured regression rates was constructed for investigating the physical phenomenon inside the hybrid rocket combustion chamber. The simulations show that a higher swirling number in the later portion of the port was found for the RC case. By concerning about the different O/F ratios and port size of the burned fuel, a series of simplified numerical CFD investigation with a fixed O/F and a fixed port size varying the regression rates from upstream to downstream fuel systematically with the same average region rate was performed to complement the semi-empirical CFD simulations. The results showed that there were two distinct regions including an upstream non-classical region dominated by the gas impingement of gas and a downstream classical region caused by the swirling effect of gases. In the non-classical region, the calculated distributions of the swirling numbers of the former are essentially the same for all the cases no matter what the magnitude of the regression rate is, while in the classical region higher swirling numbers are found for the case of more uniform distribution of regression rates. Heat generated near the upstream of the fuel grain was transferred more efficiently through the design of RC, which makes the resulting fuel regression more uniform than that without RC. The resulting swirling efficiency in the RC case was higher than that without RC. The HRM with RC hence had a better engine Isp efficiency with a lower O/F ratio.

The development of ultrastrong maraging stainless steels (MSSs) is always in high demand. However, traditional high-strength MSSs generally exhibit early plastic instability with a low uniform strain since the precipitated nanoparticles are non-coherent with the body-centered-cubic (BCC) lath martensitic matrix. Here, we design a novel ultrahigh strength MSS (Fe-5.30Cr-13.47Ni-3.10Al-1.22Mo-0.50W-0.23Nb-0.03C-0.005B, wt.%) using a cluster formula approach. A fabulous microstructure consisting of a uniform distribution of high-density coherent B2-NiAl nanoprecipitates (3−5 nm) in BCC martensitic matrix was successfully obtained. This alloy has not only an exceedingly high ultimate tensile strength of 2.0 GPa, but also a decent uniform elongation of 4.2%−5.1%, which is almost triple of the value observed in existing MSSs. We present an in-depth discussion on the origins of ultrahigh strength and uniform plastic strain in the new alloy to validate our design strategy and further offer a new pathway to exploit high-performance MSSs.

We develop a formal framework to analyse a monopoly’s problem when demand is determined by a Poisson-distribution and the valuations of the buyers are draws from a common distribution. The buyers have unit demand, and the good in question is discrete. The monopoly has to make its quantity and pricing decisions before demand is realised. We determine sufficient conditions for the monopoly’s pricing decision to be unique, and we demonstrate the difference to the planner’s problem by numerical examples. We also study an economy with a fixed number of buyers assuming that the valuations are draws from the uniform distribution. When the economy grows in the limit one recovers the standard case of a monopoly with linear demand and constant marginal costs.

The aim of this paper is to propose a demountable shear wall (DSW) system for multistory precast concrete buildings. For this purpose, instead of a large wall panel, several slender walls are used by connecting to adjacent beams. To evaluate the efficiency of the DSW system, nonlinear cyclic and time history analyses are performed on eighteen 4-, 8- and 12-story models, including three conventional shear wall models and fifteen DSW models with various wall numbers. The results indicate that for DSW system, when using more walls with a smaller width, the structural deformation tends from flexural-type to almost shear-type. This result prevents the plastic strain from concentrating on the columns and walls of the first story and causes the damage to be uniformly distributed on the walls of all stories. The DSW models exhibit hysteretic behavior without significant strength degradation at high drift levels. Also, DSW models with more walls, while increasing the ductility factor (up to 30%) and creating a more uniform distribution of drifts, reveal less value of maximum floor acceleration (up to 48%) and story shear (up to 53%), compared to conventional shear wall models.

Designing a generative model to synthesize realistic tabular data is of great significance in data science. Existing tabular data generative models have difficulty in handling complicated and diverse marginal distribution types due to the gradient vanishing problem, and these models pay little attention to the correlation between attributes. We propose a method that improves the generative adversarial network (GAN) with inverse cumulative distribution function for tabular data synthesis. This method first transforms continuous columns into uniform distribution data by using the cumulative distribution function, which can alleviate the gradient vanishing problem in model training. Then the method trains GAN with the transformed data, where the discriminator with label reconstruction function is presented to model the correlation among attributes accurately by introducing an auxiliary supervised task to help the correlations extraction. After that, we train a neural network for each continuous column to perform the inverse transformation of generated data into the target distribution, thereby the synthetic data is obtained. Experiments on simulated and real-world datasets show that our method compares favorably against the state-of-the-art methods in modeling tabular data.

In this paper, important functional parameters of solid oxide fuel cells are identified by introducing a novel high-speed optimization method, namely adaptive chaotic grey wolf optimization algorithm. The suggested optimization method is obtained by combining the adaptive grey wolf optimization and chaotic grey wolf optimization algorithms. The chaotic algorithm is applied to the basic grey wolf optimization to achieve higher convergence speed, keep the population's diversity, and provide an initial population with uniform distribution. Besides, a nonlinear convergence factor is defined for balancing the global and local exploration abilities. Employing the improved convergence factor resulted in a new version of the grey wolf optimization algorithm, namely adaptive grey wolf optimization algorithm. Adaptive chaotic grey wolf optimization algorithm adopts the advantages of both chaotic grey wolf optimization and adaptive grey wolf optimization methods simultaneously. The adaptive grey wolf optimization algorithm is applied to a 5 kW dynamic tubular stack. The results of the simulation report the lowest values of mean squared error, higher accuracy, higher robustness, and high convergence speed for the adaptive grey wolf optimization algorithm compared to some well-known optimization methods. Besides, the proposed method shows a good agreement with experimental results with lower computational difficulty.

There are several algorithms for determining control forces of active devices in civil engineering structures. Uniform distribution of deformations theory is a structural concept which mainly focuses on equalizing deformations in order to promote the utilization of ductility capacity of structural elements thereby mitigating damages to a structure. In common active control algorithms, deformation uniformity and reducing damages are barely noted. In this research, a new active control algorithm regarding uniform deformation theory will be proposed. Uniform distribution of Deformation Control (UDC) algorithm consists of a massless optimized Virtual Added linear structure with Pinned connections (VAP) which is added to a desired original structure. This VAP can be treated as an added stiffness matrix. Once the parameters of the VAP were optimized in a manner that the desired responses were obtained from the new integrated structure, then, the new integrated structure is developed and analyzed in each time step. Finally, the VAP beams axial forces are extracted and applied to the original structure as control forces via active control devices such as active tendons. This proposed control algorithm is simple and effective in reducing responses especially drifts, making more uniform thereby reducing structural damages as well as decreasing the required capacity of actuators and the power consumption eventually. High potential and promising performance of the proposed UDC algorithm will be represented through numerical investigation in an office building example. The results are compared with Nonlinear Instantaneous Optimal Control (NIOC) algorithm as a very common active control algorithm for linear and nonlinear structures.

In this study, a performance-based optimisation framework is proposed for optimal cross-sectional distribution of steel moment resisting frames (MRFs) subject to earthquake excitations. For the first time, the concept of uniform distribution of damage (UDD) is adopted for the complex optimisation of moment resisting steel frames under dynamic earthquake excitations. To enhance the computational efficiency of the optimisation process, a novel adaptive algorithm is proposed, where the power functions change based on the demand to capacity ratio of the structural elements. The framework is then used for optimisation of 3, 5, 7, 10 and 15-storey steel MRFs under a set of representative earthquake records. Maximum plastic rotations and strength-based demand to capacity ratios are considered as the main performance parameters for deformation-controlled and force-controlled members, respectively. The results indicate that the proposed method is very efficient at improving the seismic performance of the designed structures in only a few steps by satisfying all the prescribed performance targets. It is shown that, for the same performance level, the optimum design frames require up to 38% less structural-weight compared to their code-based design counterparts. The average storey shear force distributions of the optimum frames under the design spectrum-compatible earthquakes are then used to obtain more efficient lateral load patterns for seismic design of steel MRFs. It is shown that by adopting the proposed load pattern in the conventional seismic design process, the frames exhibit significantly (up to 70%) less global damage compared to the similar frames designed based on code suggested load pattern.

Parabolic trough collector stands out as the most proven and widely adopted technology for concentrating solar power. A simple mathematical model based on dividing the trough’s aperture and the surface of the absorber into small segments is developed herein. The model is used to investigate the influence of the design and operational parameters on the distribution of the concentrated solar flux over. In this study, eight absorbers with different geometries are considered and the effect of the rim angle, absorber’s geometry, and operational mode on the distribution of the concentrated solar flux over their surfaces have been addressed. For all absorbers, it has been found that increasing the rim angle results in reducing the intensity of the concentrated solar flux with increase in its coverage area. The distribution of the concentrated solar flux over the surface of the parabolic shaped absorber (ABS.6) is found to be uniform over the portion of the surface located between its two rims. It has also been demonstrated that the operation under free absorber mode can help in redistributing the concentrated solar flux over the absorber surface resulting in a more uniform distribution compared to that over the surface of the fixed absorber. From the combined geometries of the investigated absorbers two optimal shapes are obtained and are found to perform much better than the circular absorber ABS.1.

LPN (learning parity with noise) problem is a good candidate for post-quantum cryptography which enjoys simplicity and suitability for weak-power devices. Dottling et al. (ASIACRYPT 2012) initiated the first secure public key encryption (PKE) under the low-noise LPN assumption. Kiltz et al. (PKC 2014) proposed a simpler and more efficient scheme using double-trapdoor technique from the same assumption. Both schemes abide the decoding failure rate (DFR) 2 − Θ ( k ) (k is the security parameter) and there exists CPA/CCA2-secure PKE with squared-exponential DFR 2 − Θ ( k 2 ) from constant-noise LPN (Yu and Zhang, CRYPTO 2016). In this work, we give a positive answer with squared-exponential DFR in the low-noise setting. More precisely, we first introduce a variant (VxLPN) of the low-noise Exact LPN (xLPN, proposed by Jain et al. at ASIACRYPT 2012 and used as building block in commitments and zero-knowledge proofs), where the coefficient matrix A follows the uniform distribution over { 0 , 1 } q × n ( n = Θ ( k 2 ) , q = Θ ( n ) ), the secret x is sampled from B μ n ( B μ is the Bernoulli distribution with noise rate μ = Θ ( 1 q ) ), and the noise e follows a column vector distribution uniform over { z ∈ { 0 , 1 } q : | z | = q μ } . A series of reductions show that VxLPN is at least as hard as the standard LPN for the same noise rate μ. We then construct from the VxLPN CPA/CCA2 secure PKE schemes with squared-exponential DFR 2 − Θ ( k 2 ) which share the common structure extrinsically with Kiltz et al. and Yu-Zhang schemes. The secret key(s) in our schemes are simply sampled from the Bernoulli distribution, and comparatively, the secret key(s) in Yu-Zhang schemes must be chosen from a tailored version of Bernoulli distribution (along with the coefficient matrix A that follows a distribution D λ n × n = U n × λ ⋅ U λ × n induced by multiplying two random matrices in the public key, λ = Θ ( log 2 ⁡ n ) ) in order to guarantee the correctness of their schemes. Consider the performance on 128-bit security level, our CCA2-secure scheme only holds 117.79 MB public keys, 67.31 MB secret keys and 10.15 KB ciphertexts, and thus is more efficient than the schemes of Dottling et al. and Kiltz et al. ((14.53 GB, 14.48 GB, 14.06 KB) and (161.78 MB, 92.45 MB, 13.60 KB) respectively).

In this paper, numerical study of flow field in the new design cyclones with five different wall temperature profiles are investigated. The new design cyclone is based on the idea of improving cyclone collection efficiency and pressure drop by increasing the vortex length. In this paper, the five wall temperature profiles are as follows: (A) cooling with uniform distribution, (B) without temperature change, (C) heating with uniform distribution, (D) incremental linear heating, (E) reduction linear heating. Results are compared in new design and conventional cyclones. The Reynolds averaged Navier–Stokes equations with Reynolds stress turbulence model (RSM) are solved. The Eulerian-Lagrangian computational procedure is used to predict particles tracking in the cyclones. The velocity fluctuations are simulated using the Discrete Random Walk (DRW). Results show that generally, heating the bottom zone of the cyclones can improve the collection efficiency and reduce the pressure drop while heating the top zone of the cyclones marginally affects the flow field. Moreover, cooling the cyclones reduces the efficiency and causes a higher pressure drop. Among five different wall temperature profiles, C and E profiles can increase the efficiency about 8% and profile C reduces the pressure drop by about 9%. The mentioned values in different conditions including particle diameter, flow rate, etc. can be different.

An alternative particle receiver using downward particle flow in a quartz tube with a conical hopper at the bottom has been evaluated to eliminate particle loss associated with directly irradiated solid particle solar receivers (SPSR). A computational particle fluid dynamic (CPFD) simulation is performed to investigate the particle flow characteristics in the packed moving bed quartz tube SPSR with embedded insert. Whether an insert is added in the tube or not, a consistent regular pattern is achieved for the time-varied average solid fractions at different packed heights in the tube. However, inconsistent distribution of axial particle velocity on the cross-sectional area is obtained, and the particle layer thickness affects the uniformity of the axial particle velocities. The thinner particle layer leads to a uniform distribution of axial particle velocities, and the average axial particle velocity is higher than that with a thick particle layer, which can enhance the operating safety and heat transfer of the solar receiver according to the previous investigations. In this study, the particle layer thickness of 5 mm is recommended according to the CPFD simulation. In addition, the radial movement in the semi-annular flow channel is negligible if sufficient particles are provided by the top particle dispenser. The conclusions in this cold state numerical study can provide the basis for the establishment of a further accurate thermal model for the solar receiver.

A novel method was developed via the continuous refinement of grains to prepare an Mg–6.5Y–1.2Er–1.6Zn (wt.%) alloy with a ductility of 35% and an ultimate tensile strength of 377 MPa. It involved the use of a 32-pass equal-channel angular pressing process. The strength and ductility of the obtained magnesium alloy after the rapid processing were improved by 188.5% and 700%, respectively, compared with an as-cast alloy. These improvements are attributed to the refined 14H-LPSO, uniform distribution of the spheroidized second phase, and a large number of dynamic recrystallized grains.

Ti64/CaP nanocomposite powder was fabricated and characterized for use in powder-bed 3D printing. The microstructure and phase composition, morphology, particle size distribution, sphericity, flow behavior and dispersion of the as-fabricated particles on the building plate of the 3D printer were investigated. The results confirmed a uniform distribution of nanostructured calcium phosphate particles on the surface of primary Ti64 ones. Calcium phosphate appears as an octa-calcium phosphate phase. The morphology of the particles was shown as spherical, and their sphericity was better than the as-received Ti64 particles. The particle size distribution of nanocomposite powder indicated a smaller amount than the as-received Ti64 particles. Additionally, the flow behavior was improved compared to the as-received Ti64 and delivered an optimal dispersion on the building platform. Ultimately, Ti64/CaP nanocomposite powder has a very homogeneous and uniform microstructure and bears a proper flow behavior for use in powder-bed additive manufacturing machines.

A stiffness-based method for the preliminary design of outrigger braced skyscrapers is proposed. The method is founded on the concept of uniform distribution of deformation. This approach originates from the minimum-compliance optimization, in which the stiffest layout for the structure is sought for a given amount of material. Design variables include: the flexural stiffness of the core structure, the outrigger-belt elevation, and the peripheral column dimensions. These parameters are specified by requiring the curvature to be kept constant, yet minimum, as long as the allowable stress and displacement constraints are imposed. The resulting procedure is presented through a simplified hand-calculation algorithmic framework, which may be used during the preliminary design stage to estimate the size of elements and to give an initial assessment of the structural behavior. In order to show the practical application of the proposed method, a structure equipped with one outrigger is designed using the proposed algorithm. The comparative analysis of the results reveals that the presented method provides a rather high degree of accuracy in practice.

Based on Fluent software, the gas−liquid two-phase flow in the horizontal stirred tank was simulated with SST k−ω turbulence model, Eulerian−Eulerian two-fluid model, and multi-reference flame method. The mixing process in the tank was calculated by tracer method. The results show that increasing the rotating speed or gas flow is conducive to a more uniform distribution of the gas phase and accelerates the mixing of the liquid phase. When the rotating speed exceeds 93 r/min, the relative power demand remains basically constant. The change in the inclination angle of the upper impeller has minimal effect on the gas phase distribution. When the inclination angle is 50°, the relative power demand reaches the maximum. An appropriate increase in the impeller distance from the bottom improves the gas holdup and gas phase distribution but increases the liquid phase mixing time.

Mixing of nanoparticle agglomerates in a fluidized bed was investigated by CFD-DEM. A parallel program was used that simultaneously uses the computational resources of GPU and CPU on a single computer. The bed expansion obtained from simulation was compared with experimental and good agreement was observed. Bed expansion in agglomerate particulate fluidization (APF) was 2 to 5 times the initial bed height and final bed expansion in agglomerate bubbling fluidization (ABF) was 1 to 2 times the initial bed height by changing the gas velocity from 2 to 4 and 4 to 8 cm/s for APF and ABF regimes respectively. Gas volume fraction distribution was investigated for both APF and ABF regimes, which showed a more uniform distribution in APF. Increasing the gas velocity led to a more homogenous in the APF bed but it did not change the homogeneity of the ABF bed. Besides, the axial and radial dispersion coefficients in ABF were greater than those in APF. Axial dispersion coefficient varied from 2 × 10−6 to 4 × 10−5 m2/s. Lacey mixing index was investigated in both APF and ABF regimes and it showed that the quality of mixing in ABF was better than APF.

To have a uniform distribution of reactants is an advantage to a fuel cell. We report results for such a distributor with tree-like flow field plates (FFP). Numerical simulations have shown that the width scaling parameters of tree-like patterns in FFPs used in polymer electrolyte membrane fuel cells (PEMFC) reduces the viscous dissipation in the channels. In this study, experimental investigations were conducted on a 2-layer FF plate possessing a tree-like FF pattern which was CNC milled on high-quality graphite. Three FF designs of different width scaling parameters were employed. I–V curves, power curves and impedance spectra were generated at 70%, 60% and 50% relative humidity (25 cm2 active area), and compared to those obtained from a conventional 1-channel serpentine FF. It was found that the FF design, with a width scaling factor of 0.917 in the inlet and 0.925 in the outlet pattern, exhibited the best peak power out of the three designs (only 11% - 0.08 W/cm2 lower than reference serpentine FF). Results showed that a reduction of the viscous dissipation in the flow pattern was not directly linked to a PEMFC performance increase. It was found that water accumulation, together with a slight increase in single PEMFC resistance, were the main reasons for the reduced power density. As further improvements, a reduction of the number of branching generation levels and width scaling factor were recommended.

Sparsest packing for irregular 3D objects is introduced. This problem is motivated by the thermal deburring – modern clean and energy saving technology of removing burrs from machine parts (objects) by detonating gas mixtures in a deburring chamber. The objects in the chamber are placed in a vertical cylindrical rack (container) divided into sub-containers by horizontal shelves rigidly fixed on a thin rod passing through the centre of the rack. To achieve a stable processing quality and the most uniform distribution of thermal and power effects, the parts have to be placed sufficiently distant one from another, as well as from the lateral cylindrical surface of the container. The objects are assigned to specific shelves and are represented by a union of basic convex 3D shapes (e.g., cylinders, prisms, cuboids, cones). The sparsest packing is aimed to place the 3D objects as distant as possible, freely sliding and rotating on the shelves subject to balancing conditions. Using the phi-function technique a corresponding nonlinear programming model is constructed. A solution algorithm is proposed and computational results are presented.

A screw feeder is mainly used in industries for conveying and elevating granular materials. Despite having a simplistic design, the mechanics of conveying the material is quite complex. The flow behavior of particles in a screw feeder is influenced by its geometric and operating parameters. In this study, the authors focus on the change in flow behavior by changing these parameters, using the discrete element method (DEM) simulations software LIGGGHTS. The mass flow rate measurement and visual examination of the particle fill level in our experimental studies served as model validation. The simulations were conducted with monosized spherical particles, and a mass-based uniform distribution of particles, with diameters between 2 and 5 mm. A mass based uniform size distribution was considered to represent multisized biomass particles, with particle properties of a representative biomass being used. The simulations quantify the screw feeder performance in terms of mass flow rate, average particle speeds (axial, radial, and swirl), and average contact forces (normal and tangential). The average particle axial and radial speed increased and swirl speed decreased with increasing rotational speed. The increase in feed rate and flight pitch ratio enhances the average radial and swirl speed of particles. The swirl and radial speeds are highest for smallest particle diameter for all three varying parameters. The average normal and tangential contact forces increased with increasing rotational speed, particle feed rate and pitch flight ratio and was found highest for biggest particle diameter.

The electrospinning process is a simple and versatile method for the fabrication of nanofibers. The low production rate of fibers in a conventional single-nozzle setup inhibits the commercialization of the process for large-scale applications. Multiple-nozzle electrospinning is a straightforward approach in the efforts of increasing fiber yield. The installation of multiple nozzles in a single setup alters the electric field in the working space, affecting the process and fiber quality. In this study, the effects of varying the distance between adjacent nozzles are investigated in terms of the jet behavior and fiber distribution, comparing between equally-spaced and unequally-spaced nozzles. The simulation of the electric field shows a more uniform electric field distribution near the nozzle tips for the unequally-spaced nozzles. The unequally-spaced setup also resulted in a more uniform distribution of fiber diameter and deposited fiber mats. Additionally, electrospinnability was also improved by using unequally-spaced nozzles.

Let α , β ∈ ( 0 , 1 ) such that at least one of them is irrational. We take a random walk on the real line such that the choice of α and β has equal probability 1/2. We prove that almost surely the αβ-orbit is uniformly distributed module one, and the exponential sums along its orbit have the square root cancellation. We also show that the exceptional set in the probability space, which does not have the property of uniform distribution modulo one, is large in the terms of topology and Hausdorff dimension.

Assessment of fiber distribution characteristics is critical in the determination of the mechanical properties of the Fiber Reinforced Concrete (FRC). In this study an experimental investigation was carried out to ascertain the Fiber distribution characteristics (Fiber dispersion coefficient and Fiber orientation factor) of the M30 grade Mono Glass FRC (MGFRC), Mono Steel FRC (MSFRC), Graded FRC (GrFRC), Hybrid FRC (HyFRC) and Hybrid Graded FRC (HyGrFRC). Two lengths of glass fibers and two lengths of steel fibers were blended into the concrete to obtain MGFRC, MSFRC, GrFRC, HyFRC, and HyGrFRC mixes. An image analysis technique using an optical microscope was used to determine the dispersion coefficient and orientation factor of all the mixes, as mentioned earlier. Effect of fiber length, fiber type and fiber grading on the fiber distribution characteristics of the FRC mixes were discussed. The fiber distribution characteristics were improved by the addition of glass and steel fibers, where glass fibers enhance the dispersion coefficient, and steel fibers enhance the orientation factor. Graded FRC specimens exhibited better fiber distribution than Mono FRC specimens. HyGrFRC specimens showed better fiber distribution characteristics when compared to HyFRC specimens, and this may be due to the more uniform distribution of fibers without clumping in HyGrFRC mixes due to the grading of fibers. From this study, it can be inferred that the blending of graded glass and graded steel fibers in a hybrid form into the concrete have shown a remarkable enhancement in the fiber distribution characteristics.

Flow field design on the cathode side, inspired by leaf shapes, leads to a high performance, as it achieves a good distribution of reactants. Furthermore, the addition of baffles to the cathode channel also increases the supply of reactants in the cathode catalyst. However, research on the addition of baffles to the cathode channel has still been limited to straight channels and conventional flow fields. Therefore, in this work, a numerical study was conducted to investigate the effect of baffles on the leaf flow field on the performance of a polymer electrolyte membrane fuel cell. The generated 3D model is composed of nine layers with a 25-cm2 active area. The beam and chevron shapes of the baffles, which were inserted into the mother channel, were compared. The simulation results revealed that the addition of beam-shaped baffles that are close to each other can increase the current and power densities by up to 18% due to the more uniform distribution of the oxygen mass fraction.

Composite materials are new generation materials used in various fields like aerospace, automobile, electronics due to their tailored properties. Most of the composites are prepared by the stir casting technique. So, a detailed study about stir casting parameter like stirrer speed, preheat temperature is needed to identify the effect of these parameters on the properties of composite materials. It has been found that the properties of Aluminium alloy MMC are affected due to the variation in the speed of stirrer and preheat temperature. After reviewing many papers, we find the range of stirrer speed is 150–1300 RPM and preheat temperature 250°C–1100°C is suitable because there is an increase in stirrer speed, uniform distribution of the reinforcement particles, and proper spreading of reinforcements in the matrix and muscular bonding between matrix were obtained. After investigating the newly developed composite by X-ray diffraction (XRD) and Scanning Electron Microscopic (SEM) microstructure method, it has been found that an increase in preheat temperature of reinforced material improves the mechanical property like toughness, wear resistance. This research paper will help the researcher select metal alloy; additive reinforces the material and their size and volume.

Fabrication of particulate composite with aluminum6061 reinforced with red-mud as reinforcement has been done by stir-casting. Uniform distribution of red-mud particles in aluminum matrix has been examined by Scanning electron microscopy. For confirmation of red-mud in the matrix, energy dispersive spectroscopy spectrum has been obtained from the surface. The results show that there has been first increase in friction force upto 12% red-mud and then decrease in friction force. Value of friction force has been found minimum at 125 µm particle size and maximum at 250 µm. Analysis reveals that friction force increases with increase in applied load and sliding distance. The effect of load and sliding speed on friction force has been reported significant by ANOVA analysis. Load has been found most effective parameter on friction force followed by sliding speed, sliding distance, particle size and aging time. Response table shows percentage reinforcement has least effect on friction force.

The static design of artificial ground freezing during the construction of mine shafts includes the strength analysis of the frozen wall (FW). The existing formulas for FW strength calculation do not take into account the non-uniform distribution of strength properties in the volume of frozen soils. The non-uniform distribution of the properties is caused, first of all, by the non-uniform temperature distribution inside the FW. This article shows the significance of this factor in analyzing the FW thickness. The elastic-plastic stress analysis was carried out under the assumption of an infinite height of the thick-walled cylinder consisting of frozen soil. An integral function was obtained to calculate the FW thickness by strength given the arbitrary radial non-uniformity of the cohesion in the frozen soil volume. Also, an approximate formula is proposed for calculating the FW thickness in the case of a piecewise linear cohesion function of the radial coordinate.

Glass wool finds its application in soundproofing materials and insulation. This paper studies the effect of high-energy shock waves on glass wool fibres using modified Reddy shock tube. Changes in composition and properties of fibres are reported through SEM analysis. With driver pressure of 6.79 bar, Mach number, maximum pressure and temperature achieved are 1.46, 4.845 atm and 482.91 K respectively. Due to diaphragm material, carbon content of 2.92% by weight is observed in shocked specimen. SEM images show curliness in fibers, increased number and uniform distribution of binder clusters and air voids resulting in enhanced strength, hardness and insulation properties of fibres.

This investigation focused to develop homogeneous self-lubricating composites of CuO/MgO/ZTA through powder metallurgy route. FESEM and XRD plots are carried out to show the uniform distribution of CuO particles inside the matrix. The result of mechanical characterisation shows a slight reduction in bulk density and hardness, due to formation of higher grain size. An improvement in fracture toughness is noticed due to the presence of CuO that act as a ductile particle, enhances the crack deflection and crack bridging phenomenon. The tribological study shows an improvement in COF due to self-lubrication phenomenon. This improvement is attributed to the formation of long elastic smooth patchy layer between siding surfaces. The effect of sliding velocity is higher due to high smearing and squeezing action takes place at higher sliding speed.

Cubic Boron Nitride (c-BN) reinforced Al2014 composites are fabricated via stir casted technique. Composites are fabricated using different weight proportion as 1, 2 & 3% of cubic boron nitride of less than 10 μm size. The fabricated composites are tested for mechanical properties like hardness, tensile strength and density. Microstructure is analysed with the help of scanning electron microscope. Strength of Al2014 increased with the addition of reinforcement up to 2%. A uniform distribution of reinforcements is obtained but at 3% porosity was higher. The analysis revealed that the incorporation of hard c-BN enhances the strength due to grain refinement and dislocation generation.

Examines the impact of the factory-supplied a pipe round cross-section on the final wall thickness distribution steeply curved pipe. The purpose of this study is to obtain a more uniform distribution of the wall thickness. Studies have shown that using the factory-supplied billets at orientation in the die cavity can be reduced by forming a level difference thickness obtained items by 17%.

Tribological behaviour of Polypropylene (PP) reinforced with carboxyl functionalized multi walled carbon nano tube (MWCNT- COOH) nanocomposites prepared by melt blending using injection moulding were studied. The experiment was conducted by taguchi technique using the L18 orthogonal array for dry sliding condition at room temperature. Sliding speed, applied load and MWCNT-COOH wt% are the testing variables, and wear rate was seen as the solution. The influence of MWCNT-COOH on the wear properties was examined. Wear resistance has been found to increase with increasing the percentage of MWCNT-COOH due to uniform distribution of MWCNT-COOH in PP.

Jet impingement technique with pulsed jet arrays has proved to be one of the most efficient heat transfer technologies for cooling applications. Detailed investigations are required to optimize the different parameters to achieve maximum heat transfer. Present study is an effort in this direction by analyzing the heat transfer from a flat heating film of dimension 60 × 60 × 0.1 mm. The chip generates a heat of 30 W which is to be carried away by means of air jets. The nozzle plate at the top generating the air jet has a set of 9 nozzles arranged in a 3x3 inline configuration. Two sides of the flow arrangement are confined and flow is only along one direction. The nozzle diameter is 5 mm and pitch length from center to center X/D and Y/D are 3. The nozzle plate, heating plate gap Z/D is 4. The Reynolds number values are in the range 3500 to 14000. The cross-flow approaches in a direction perpendicular to the jets and mixes with the jet flow. The results obtained predict a dominance of pulsed jets over steady jets, if heat transfer is considered. Among pulsed jets, those with higher amplitudes and lower frequencies showcase better heat transfer and more uniform distribution throughout the heated plate.

The performances of the cut-set distributions in the fuzzy reliability evaluation are studied based on cut-set method. Firstly, a theorem is proved to indicate the convergence defect of the model with the three commonly used cut-set distributions, including uniform distribution, linear distribution and truncated normal distribution. Secondly, a general method is proposed to construct a new family of cut-set distributions named intrinsic cut-set distributions, and three specific intrinsic cut-set distributions are obtained based on this method, including modified truncated normal distribution, truncated lognormal distribution and truncated Weibull distribution. Thirdly, numerical examples are carried out to verify the above theoretical results. It is shown that, compared with the three commonly used cut-set distributions, the proposed intrinsic cut-set distributions make the evaluation more stable and the fuzzy reliability model achieve good convergence at the boundary cases, which could effectively improve the evaluation accuracy and broaden the application of the model. Finally, some recommendations are given to show how to choose a suitable cut-set distribution in practice.

The dynamic liquid distribution and holdup in a TBR packed with porous quadrilobe catalyst were studied using advanced Gamma-ray Computed Tomography. A multi-compartment module is used to quantify the maldistribution factor which shows that there is a transition region from high maldistribution to relatively uniform distribution depending on the flowrates. The 3D maldistribution maps show that there is more dynamic liquid close to the column center at high bed height and there is no high correlation between the average dynamic liquid holdup and the bed height. If the gas flowrate increases while keeping the liquid flowrate fixed, the average dynamic liquid holdup decreases; however, if the gas flowrate is fixed, there is no dominant increasing or decreasing trend showing up. A Deep Neural Network model and a pseudo-3D model are developed showing high accuracy for predicting the local dynamic liquid holdup at different bed heights, radius, and flowrates.

A new method was developed to optimize the microwave heating thickness of the spent automobile catalyst in order to improve the uniform distribution of the temperature field. The average penetration depth and the microwave heating thickness of the spent automobile catalyst were calculated by Gauss model and numerical calculation based on dielectric loss tangent and reflection loss. The results showed that the spent automobile catalyst was a medium loss material. The average penetration depth was 1.11 m from room temperature to 800 °C. The optimum microwave heating thickness of the spent automobile catalyst was about 0.83 m or 0.75 times of the average penetration depth. Industrial application analysis indicated that the optimization of heating thickness could improve the uniform distribution of the temperature field and reduce energy consumption.

For a past few decades, metal matrix composite has a significant role in the various industrial and automobile applications. Production of metal matrix composite using stir casting technique is one of the most effective and economical technique. Achieving the uniform distribution of the reinforced particles was the major problem facing during the production of particle reinforced metal matrix composites and also achieving the effective fluid flow pattern was the greatest challenge to the research community. In this research, some of the major stir casting process parameters such as blade geometry, stirring speed and impeller position were optimized based on the vortex height of the fluid and settling time of the reinforced particles using visualization experiments and Grey relation analysis. Flow pattern of the fluid and the trace of the particles was analysed using a new technique called streak photography. Streak photography was one of the visualization experiments using glycerol water based model. Al8011/SiC metal matrix composites were manufactured based on the optimized stir casting process parameters. Finally, the fabricated composites were carried out for OM, SEM analysis and Brinell hardness testing for confirming the uniform distribution of the reinforced particles. Based on the confirmation results, 45ᴼ stirrer blade angle, impeller position 40 % from the base and 250 rpm stirring help to produce uniform distribution of the particles.

In the present study, the effects of equal channel angular pressing (ECAP) on the microstructure and mechanical property of the Mg-20Al alloy were systematically investigated. For the first time, the texture of Mg17Al12 phase and its evolution with ECAP conditions were reported. The results show that increasing the processing temperature and passes generates more uniform distribution and finer size of β-Mg17Al12 phases. The large pieces of β-Mg17Al12 phases are composed of many fine grains with different crystallographic orientations. For the β-Mg17Al12 phase, a preferred distribution of (001) appears at 523 K and 573 K, and hardly varies with temperature. Nevertheless, a random texture is observed at 623 K. The (0002) poles exhibit a preferred distribution at 473 K, but this preferred distribution varies with temperature. A random distribution of (0002) poles is observed when processed at 623 K. Many types of crystallographic planar relationship between β-Mg17Al12 phase and α-Mg matrix are observed and the relationships of {11 2 - 3}//{100} or {110} or {111} and {1 2 - 11}//{100} or //{110} or {111} have a relatively higher frequency than others. The texture of α-Mg matrix is much different from that of the ECAPed Mg alloys with a relative low Al content, in which a texture with basal poles inclining approximately 45° away from the extrusion direction often develops. The mechanical properties of Mg-20Al alloy are closely related to the temperature and passes of ECAP. A higher temperature often decreases the yield strength, but hardly alters the maximum strength. There is a low plasticity for all the samples and increasing processing temperature slightly enhances the plasticity. The corresponding mechanisms were deeply discussed.

The interaction between inlet concentration and inlet velocity is vitally important for the regulation of a hydrocyclone, but the interactive mechanism is still unclear. This study investigated the effect of inlet concentration on the hydrodyclone's separation performance within a wide range of inlet velocity via numerical analysis. Numerical results demonstrate that the number of the dislocated particles was enhanced at a too great or a too low inlet velocity, thereby leading to the decline in the separation performance. The results are appropriate for the prediction of the particle distribution. In addition, intense interaction existed between inlet concentration and inlet velocity. At a low inlet velocity, the cutting size and the separation precision exhibited no regular changes with the increasing inlet concentration. The cutting size and the separation precision changed alternately as the inlet concentration changed within 1% ~ 9%. This is mainly due to the fact that, despite of the enhanced interaction among particles, the turbulence intensity dropped gradually with the increasing inlet concentration. The combined actions led to the above alternate change. As the inlet concentration increased to over 20.25%, the interaction among particles far exceeded the effect induced by the decline in turbulence intensity, and therefore, the cutting size increased rapidly and the separation precision dropped. Certainly, the decline in the interaction among particles reduced both tangential velocity and axial velocity, which then destroyed the stability of the flow field and uniform distribution of particles in radial direction. As the inlet velocity increased, the cutting size increased with the increase of the inlet concentration, accompanied with the weakened cutting capability. High-quality hydrocyclone can be obtained at an inlet velocity of 5– 8 m/s and an inlet concentration of 1% ~ 9%. When the inlet concentration was fixed at around 20.25%, the separation performance reached the optimal at an inlet velocity of 15 m/s. conclusively, appropriately increasing the inlet velocity can lower the adverse effect induced by the fluctuation of the inlet concentration, which can contribute to achieving the expected cutting size and enhancing the separation precision

Friction hydro-pillar processing is a solid-state process to repair cracks in thick plates, pipes, and vessels. In this study, this process is modified to be used as a solid-state micro-alloying process to make in-depth alloys in steel plates. Alloying is carried out mostly in the liquid phase which results in problems such as dendritic microstructure. Also, there are some restrictions regarding mechanical alloying such as long sintering time. In the present study, The SiC powder was added to St37 steel. A cartridge was drilled in the center of the stud to place the alloying powder. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses were used to investigate the powder distribution. Although several agglomerated zones were detected, the results indicate a uniform distribution of the powder. The results also suggest that the SiC was dissolved during the process. Optical microscopic was also utilized to investigate the phase transformation during the process. Due to the high temperatures and strain rate experienced by the stud and the base material during the process, significant changes occur including the formation of Widmanstatten structure. The micro-hardness and tensile properties of the samples were also tested to evaluate their mechanical properties. The highest achieved average micro-hardness and ultimate tensile strength were 395.8 HV and 511.2 MPa, respectively.

We consider the problem of quantifying uncertainty for converging beam triple LIDAR when the input uncertainty follows a uniform distribution. We determine expressions for the range (i.e. set of reachable points) for the reconstructed velocity vector as a function of any particular setting of the nominal input parameters and determine an explicit lower (and upper) bound on the (averaged) volume (with respect to Lebesgue measure), in R 3 , of that range. We show that the size of any such bound is inversely proportional to the absolute value of the triple scalar product of the unit vectors characterizing the Doppler measurement directions (optimized over the uncertainty region) in R 6 associated with the nominal angle settings under consideration. This leads to the conclusion that the nominal LIDAR configurations that minimize output uncertainty ought to be those in which the value of the triple scalar product of the Doppler unit vectors is at its largest.

The models introduced in this paper describe a uniform distribution of plant stems competing for sunlight. The shape of each stem, and the density of leaves, are designed in order to maximize the captured sunlight, subject to a cost for transporting water and nutrients from the root to all the leaves. Given the intensity of light, depending on the height above ground, we first solve the optimization problem determining the best possible shape for a single stem. We then study a competitive equilibrium among a large number of similar plants, where the shape of each stem is optimal given the shade produced by all others. Uniqueness of equilibria is proved by analyzing the two-point boundary value problem for a system of ODEs derived from the necessary conditions for optimality., Comment: 36 pages, 6 figures

The study aims to investigate the effects of pore structure on the thermal shock resistance of porous refractory materials. Porous material is constituted by a solid frame and the pores filling with air. A direct thermo-mechanical coupling simulation and strain-life approach were employed to predict the number of thermal shock cycles of the materials; thus, influences of the porosity and distribution of pores on the thermal shock resistance were studied. The specimen was subjected to a mechanism of thermal shock damage in which alternating thermal stress under cyclic ‘hot’ and ‘cold’ shock. The simulation results show that the magnitude of thermal stress is large during the thermal shock process. And the residual thermal stresses generate at the solid/air interface since stress gradients occur inside the bulk. Furthermore, higher or lower porosity had no positive effect on the thermal shock resistance of the porous material; the highest thermal shock resistance was attained at a porosity of 20%. The uniform distribution of pores is favorable to improve the thermal shock resistance of materials of high porosity. The validation test results show that the number of thermal shock cycles of the two samples in the experiments were closer to the situations of chaotic pore distributions in the simulations.