Experimental and numerical investigation of effects of particle shape and size distribution on particles’ dispersion in a coaxial jet flow

In this study, an experimental and a numerical investigations are performed to investigate the effect of particle’s shape and size distribution on its dispersion behavior. Firstly, particle dispersion of pulverized coal and spherical polymer particles is observed by Particle Image Velocimetry (PIV) technique in the experiment. Secondly, a simulation is performed to analyze the particle dispersion in detail. Spherical and spheroidal motion models are applied to particle’s movement to investigate the shape effect. Furthermore, monodisperse and polydisperse for particles are applied to investigate the size distribution effect on the dispersion. Experimental results show that in the jet turbulence flow, pulverized coal particles, which have complex shapes and various sizes, have quite different dispersion behavior compared to spherical particles. In terms of the results of the simulation, this difference is mainly caused by the size distribution effect. Although particle’s shape affects the dispersity, it is weakened by the size distribution effect.     

Comment on ‘Operator formalism for the Wigner phase distribution’

Abstract

The operator associated with the radially integrated Wigner function is found to lack justification as a phase operator.     

Experimental investigation on punching resistance of R-UHPFRC–RC composite slabs

An effective method to strengthen existing reinforced concrete (RC) structures is to add a thin layer of ultra-high performance fiber reinforced cement-based composite (UHPFRC), with or without steel rebars, over the concrete slab to create a composite element. It was demonstrated by previous test series that this method increases rigidity, bending and shear strength of one-way RC members. This paper presents the results of punching tests on six composite slabs without transverse reinforcement. The parameters of the tests included the thickness of the UHPFRC layer and the amount of reinforcement in it. All slabs failed in punching mode with a drop in resistance after the maximum resistance was measured. For a layer of 50 mm of UHPFRC, the normalised resistance was at least 1.69 times greater than the normalised resistance of the RC reference slab. The layer of UHPFRC increased the rigidity of the slab and provided added shear resistance to the cracked RC section by out of plane bending. By doing so, it allowed more deformation to take place in the RC section before punching failure. This results in rotations and deflections at maximum resistance similar to what was observed for the reference RC slab.     

Experimental investigation on low-frequency vibration-assisted µ-ED milling of Inconel 718

The microelectric discharge (µ-ED) milling is a competent process for the fabrication of complex 3-D shapes, but longer machining time limits the wide applications of the process. Therefore, in this work, a novel approach of low-frequency workpiece vibration-assisted µ-ED milling has used intending to improve the process performance. The experimental investigation has been performed using Taguchi L-16 orthogonal array to examine the effects of low-frequency workpiece vibration assistance in the µ-ED milling while fabricating microchannels on Inconel 718. The gap voltage, capacitance, and vibration frequency were selected as input parameters while material removal rate (MRR) and frontal electrode wear (FEW) were chosen as response variables. It has been observed that the MRR increases and FEW decreases with an increase in vibrational frequency up to an optimal value and then decreases for further increase in vibration frequency. The results disclose a positive influence of the low-frequency workpiece vibration of both MRR and FEW during µ-ED milling of Inconel 718. Finally, the effects of vibration and discharge energy on surface quality of fabricated microchannels were analyzed using field emission scanning electron microscopic images.     

Correlation between ultrasonic shear wave velocity and Poisson’s ratio for isotropic porous materials

A new correlation between ultrasonic shear wave velocity and Poisson’s ratio has been established for isotropic porous material based on physical acoustic theory. Poisson’s ratio may decrease, increase or remain unchanged with decrease in shear wave velocity depending on pore-shape and Poisson’s ratio of the bulk solid. In case of decreasing Poisson’s ratio with decreasing shear wave velocity, it passes through a minimum and then increases again to reach a limiting value of 0.5. It has been further demonstrated that the Poisson’s ratio versus porosity relation deduced from the proposed correlation agrees with the experimental data extremely well.

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Experimental and numerical investigation on bolted joint in glass–fiber reinforced composites

In this paper, vacuum assisted resin injection technique was employed to prepare the composite laminates with different plies ways. The macro-mechanical performances of the bolted joint of the composite laminates were investigated by experimental and finite element simulation. The influence mechanism of different parameters on the joint performance and failure models of the composite laminates were analyzed. A VUMAT subroutine was developed, according to the failure criteria and corresponding stiffness degradation criteria, to describe the progressive damage process of bolted joint composite laminates through finite element analysis method. The results indicated that the failure strength of composite laminates would be improved with the increasing of tightening torque, and the strength of three-ply-way hybrid composite laminates is higher than that of two-way hybrid laminates. The comparisons between numerical simulation results and experimental results showed that the developed subroutine can effectively predict the macroscopic response of bolted joint glass–fiber reinforced composite laminates.     

Progressive combustion in SI-Engines—Experimental investigation on influence of combustion related parameters

The fuel heat release rate which virtually controls the combustion process is dependent on the ‘Mass-Fraction-Burnt (MFB)’. In the present research work, a ‘logistic model with conditional variability in MFB’, has been developed for precise simulation of combustion in SI engines as the model has built in routines to take into account such factors as location of spark plug, single/dual spark plugs, intake generated swirl, combustion chamber geometry (associated with Bore/Stroke ratio), etc. A major contribution of this paper is that new and improved models for the ‘overall combustion duration’, and ‘ignition delay/flame development angle’, taking into account primarily the influence of compression ratio on the overall combustion process in SI engine have been developed. Taylor’s original equation for estimating the overall combustion duration has been modified by including a logistic equation for the error term and incorporating it in the original equation. Ignition delay as proposed by Keck et al has been modified by incorporating a polynomial of 3^rd order into the original equation. The empirical correlations that have been proposed in this paper may serve to be the starting point for simulation of ‘photodetonation concept’ to simulate HCCI combustion which is presently the hot research work in the area of pre-mixed combustion. A program in Turbo-C++ has been developed for the complete simulation of SI engine combustion, taking into account the conditional variability effect, variable specific heats of burnt gases, dissociation of gases at high temperatures, progressive combustion phenomena, heat transfer (based onWoschni’s equation), gas exchange process based on 1D-steady gas flow equation employing Taylor’s mach index of 0.6 for valve design.     

Simulation and Experimental Validation of Spacer Fabrics Based on their Structure and Yarn’s Properties

Warp-knitted spacer fabrics are considered, which are plates or shells composed of two knitted plane layers connected by vertical beams. Our aim is to compute the effective stiffness and permeability of such spacer fabrics on the basis of their structure and properties of yarns and the monofil. In order to reduce the computational effort and simplify the computational model, homogenization and dimension reduction techniques are applied. They replace the fabric by an equivalent two-dimensional plate or shell with effective elastic properties. To compute the effective permeability, the fluid simulation is done on the fully resolved micro-structure. The paper demonstrates the algorithm on application examples. We compute the elastic properties of a spacer fabric and its effective permeability for different outer-plane compression stages. Numerical examples were performed by applying the multi-scale simulation tools, developed at Fraunhofer ITWM and by comparing with the corresponding experimental results, based on measurements performed at the TU Dresden. The developed algorithms and simulation tools enable a full virtualisation of the material design adapted to exposure scenarios in various technical application cases, i.e. infiltration processes with polymers in the field of fiber reinforced composites, which enables new discoveries for the designing and manufacturing process of 3D warp-knitted spacer fabrics.     

A Fully Discrete Spectral Method for Fisher’s Equation on the Whole Line

A generalised Hermite spectral method for Fisher’s equation in genetics with different asymptotic solution behaviour at infinities is proposed, involving a fully discrete scheme using a second order finite difference approximation in the time. The convergence and stability of the scheme are analysed, and some numerical results demonstrate its efficiency and substantiate our theoretical analysis.     

Frequency shift attack on ‘plug-and-play’ quantum key distribution systems

Many imperfections in a practical quantum key distribution (QKD) system have been exploited by an eavesdropper (Eve) to attack the system. However, most of these attacks will introduce perturbations to the system while collecting information about the key. For example, the phase-remapping attack [Phys. Rev. A2007,75, 032314], in which Eve performs time shift on the signal pulse from the constant acting range of the phase modulation voltage to its rising edge to introduce an imperfection, results in an quantum bit error rate (QBER) of 14.6%, which is too high and will be discovered by careful users. In this paper, a frequency shift (FS) attack on ‘plug-and-play’ QKD systems with phase-coding BB84 protocol is proposed, in which Eve introduces an imperfection by the same method as she used in the phase-remapping attack. The most novel advantage of our FS attack is that Eve can get full information without introducing detectable QBER, which is more deceptive than the phase-remapping attack.     

Some Notes on Maxwell’s Colour Photograph

An investigation of Maxwell’s famous demonstration of three-colour photography in 1861 reveals that the picture he projected was in fact based on three-colour separation negatives in spite of the fact that the photographic material was not sensitive to either green or red. The filters used gave colour separation In the blue and ultra-violet. The reoson he obtained red separation correctly seems to be due to the fact that the red cloth he used had a secondary reflectance band in the ultra-violet as do most red cloths available today     

Experimental investigation on the influence of high temperature on viscosity,thermal conductivity and absorbance of ammonia–water nanofluids

To select the optimal ammonia–water nanofluids and apply to ammonia–water absorption refrigeration systems (AARS), this paper investigated the influence of heating on viscosity, thermal conductivity and absorbance of binary nanofluids. The hysteresis phenomenon was observed after heating at high temperature which is rarely reported in the literature. Experimental results show that most of nanofluids' thermal conductivity increased by about 3–12% after heating. However, their viscosities increased by as much as 15% to 25% except the γ-TiO₂ ammonia–water nanofluid, which was reduced by 2% to 7%. This study also shows that the trend of viscosity is consistent with the absorbance. Due to fact that the thermal conductivity of γ-TiO₂/NH₃–H₂O mixture increased after heating, while the viscosity decreased, even if the concentration of the base liquid is 12.5% or 25%, therefore it is the optimal choice for practical research in AARS at present.     

Literature-related discovery: common factors for Parkinson’s Disease and Crohn’s Disease

Literature-related discovery (LRD) is the linking of two or more literature concepts that have heretofore not been linked (i.e., disjoint), in order to produce novel, interesting, and intelligible knowledge (i.e., potential discovery). The mainstream software for assisting LRD is Arrowsmith. It uses text-based linkage to connect two disjoint literatures, and it generates intermediate linking literatures by matching Title phrases from two disjoint literatures (literatures that do not share common records). Arrowsmith then prioritizes these linking phrases through a series of text-based filters. The present study examines citation-based linkage in addition to text-based linkage to link disjoint literatures through a process called bibliographic coupling. Two disjoint literatures were selected for the demonstration: Parkinson’s Disease (PD) (neurodegeneration) and Crohn’s Disease (CD) (autoimmune). Three cases were examined: (1) matching phrases in records with no shared references (text-based linkage only); (2) shared references in records with no matching phrases (citation-based linkage only); (3) matching phrases in records with shared references (text-based and citation-based linkages). In addition, the main themes in the body of shared references were examined through grouping techniques to identify the common themes between the two literatures. All the high-level concepts in the Case 1) records could be found in Case 3) records Some new concepts (at the sub-set level of the main themes) not found in the Case 3) records were identified in the Case 2) records. The synergy of matching phrases and shared references provides a strong prioritization to the selection of promising matching phrases as discovery mechanisms. There were three major themes that unified the PD and CD literatures: Genetics; Neuroimmunology; Cell Death. However, these themes are not completely independent. For example, there are genetic determinants of the inflammatory response. Naturally occurring genetic variants in important inflammatory mediators such as TNF-alpha appear to alter inflammatory responses in numerous experimental and a few clinical models of inflammation. Additionally, there is a strong link between neuroimmunology and cell death. In PD, for example, neuroinflammatory processes that are mediated by activated glial and peripheral immune cells might eventually lead to dopaminergic cell death and subsequent disease progression.     

Theoretical investigation of a semiconductor ring laser driven by Chua’s oscillator

The modeling and numerical investigation of the dynamical behavior of a semiconductor ring laser (SRL) driven by Chua’s oscillator are reported. By increasing the coupling strength between the SRL and Chua’s oscillator at a fixed bias current, the SRL exhibits an intermittency route to anti-phase chaos. However, for a fixed value of the coupling strength, we report a period-doubling route to out-of-phase and anti-phase chaos when varying one of the parameters of the Chua’s oscillator are reported. We also demonstrate that a SRL driven by the chaotic output of Chua’s oscillator generates a more complex chaos compared to the one found in a SRL subject to a sinusoidally modulated current. This new way of modulation of semiconductor lasers would not only bring a general benefit in the physical equipment and reduce their cost but could have an impact for some relevant engineering applications.     

Experimental analysis on particle fluctuation velocity in a horizontal air–solid two-phase pipe flow having a dune model

To further elucidate the mechanism of energy-conserving conveying in horizontal pneumatic conveying with the dune model, the high-speed particle image velocimetry is applied to measure particle fluctuation velocity near the minimum conveying velocity of the conventional pneumatic conveying. This study focuses on the effect of mounting dune models on the horizontal pneumatic conveying in terms of power spectrum, autocorrelation coefficients, two-point correlation coefficients, fluctuation intensity of particle velocity, skewness factor, and probability density function. It is found that the power spectrum peaks with the dune model are larger than those of the nondune system, suggesting the acceleration and suspending efficiency of the dune model, especially dune models mounted at the bottom of the pipe. Meanwhile, the profiles of particle fluctuation velocity intensity indicate that the large particle fluctuating energy is generated due to mounting the dune model so that the particles are more easily accelerated and suspended. This is one of the important reasons why the mounted dune model results in a low pressure drop and low minimum conveying velocity. Based on the distribution of skewness factor and probability density function, it is found that the particle fluctuation velocities of all cases follow the Gaussian distribution in the lower and middle parts of the pipe. The particle fluctuation velocities in the case of the dune models mounted at the bottom of the pipe obey the Gaussian-type fluctuation more.     

Dynamic Green’s functions for a poroelastic half-space

The dynamic responses of a poroelastic half-space to an internal point load and fluid source are investigated in the frequency domain in this paper. By virtue of a method of displacement potentials, the 3D general solutions of homogeneous wave equations and fundamental singular solutions of inhomogeneous wave equations are derived, respectively, in the frequency domain. The mirror-image technique is then applied to construct the dynamic Green’s functions for a poroelastic half-space. Explicit analytical solutions for displacement fields and pore pressure are obtained in terms of semi-infinite Hankel-type integrals with respect to the horizontal wavenumber. In two limiting cases, the solutions presented in this study are shown to reduce to known counterparts of elastodynamics and those of Lamb’s problem, thus ensuring the validity of our result.     

Spectral converters for photovoltaics – What’s ahead

The effective incorporation of photovoltaic (PV) elements into the urban environment, specifically in buildings, is a challenging process. Apart from the aesthetic limitations of having black and opaque PV cells when installed in building façades, they are not optimally positioned for high-efficiency electric energy generation because of shadowing effects due to neighboring trees and buildings. Emphasis is given to luminescent solar concentrators (LSCs) that have emerged as an appealing solution for concentrating a large area of sunlight into a small beam of high field intensity. The coupling of PV cells to the edges of LSCs also presents an exciting strategy to PV urban integration. Here, we outline the mechanistic framework for LSCs, review the current experimental state of the art involving optically active centers in various geometrical device configurations, and discuss the performance quantification of LSCs currently in development. For the sake of completeness, a brief discussion of the other spectral converters suitable for PV applications is also reported.