Redistribution Of Particles Research Articles

Possibilities of using rheological parameters as physical indicators of soil structural changes

The rheological parameters of structured soddy-podzolic soils (Albic Glossic Retisols (Lomic, Cutanic)) and chernozems (Haplic Chernozems (Loamic, Pachic)) in their natural state and involved in agricultural use were studied by the oscillation amplitude sweep test. Shear resistance parameters of the studied soils (shear stress at the end of the linear viscoelasticity range – LVE-range t L , shear stress t F at the Crossover point and maximum shear stress t max ) were more informative and indicated pronounced differences between soil genetic horizons in contrast to viscoelasticity parameters (deformation γ L at the end of the LVE-range and the integral zone Z) when comparing natural and arable soils. The agricultural land use resulted in decreased organic carbon content and, as a consequence, reduced viscoelasticity and shear resistance of the soils. At the same time, the higher bulk density of arable horizons and the redistribution of fine soil particles (physical clay) could explain maximal values of the rheological parameters in the upper arable horizons and their slight differentiation with depth. Further development in the application of the proposed and studied rheological parameters can give insight into the nature and strength evaluation of interparticle bonds, the soil processes under the impact of agricultural machinery, and can also be integrated into the system of physical indicators of soil structural changes.

Adaptive Method for Tuning Dynamic Properties of Beams by Means of Particles Redistribution

Adaptive Method for Tuning Dynamic Properties of Beams by Means of Particles Redistribution

3D hotspots of marine litter in the Mediterranean: A modeling study

The 3D dispersion of marine litter (ML) over the Mediterranean basin has been simulated using the velocity fields from a high resolution circulation model as base to run a 3D Lagrangian model. Three simulations have been performed to mimic the evolution of ML with density lower, similar, or higher than seawater. In all cases a realistic distribution of ML sources was used. Our results show that the accumulation/dispersion areas of the floating and buoyancy neutral particles are practically the same, although the latter are distributed in the water column, 80% of them found in the photic layer (average depth of 35m). Regarding to the densest particles, they rapidly sink and reach the seafloor close to their source. The regions of higher temporal variability mostly coincide with the ML accumulation regions. Weak seasonal variability occurs at a sub-basin scale as a result of the particles redistribution induced by the seasonal variability of the current field.

Mechanical and tribological characterization of industrial wastes reinforced aluminum alloy composites fabricated via friction stir processing

Abstract The fabrication of particulate reinforced metal matrix composites via melt based processes poses issues like aggregation, wettability and formation of detrimental phases which may severely affect their performance. Recently developed solid-state process i.e., friction stir processing (FSP), is an efficient fabrication technique to counter the limitations of melt based processes. However, the incorporation of industrial waste in the metal matrix by using friction stir processing is rarely reported. Thus, the present investigation was carried out to reinforce the particulate type industrial waste in cast A356 alloy by friction stir processing. The performance of the fabricated composites as well as the as-cast A356 alloy was assessed through mechanical and tribological characterization. It was observed that FSP resulted in the eradication of porosity, fragmentation of α-Al dendrites, breakage and redistribution of Si particles, and grain refinement. A fair homogeneous distribution of reinforcement was observed in stir zone (SZ) with negligible aggregation of particulate reinforcement. The particle/matrix interface was free from any detrimental phase. The improvement in strength, ductility, and wear resistance was observed as compared to as-cast A356 alloy which was attributed to the microstructural changes that occurred during FSP, and the efficient reinforcement of particles via FSP.

Coastal Lakes as a Buffer Zone for the Accumulation and Redistribution of Plastic Particles from Continental to Marine Environment: A Case Study of the Dishui Lake in Shanghai, China

Microplastics, as an emerging environmental contaminant, have attracted increasing attention worldwide. Previous studies have addressed this environmental problem in either the marine or continental environment, but ignored the water bodies in between. Coastal lakes are transitional aquatic systems and may play an important role in transport, reworking and redistribution of plastics across catchment scale. Here, we report results of our investigation of plastic pollution in sediment of a coastal lake, the Dishui Lake, in Shanghai, China. The lake is located in coastal Shanghai and connected to the East China Sea via a 7-km long canal. Sediment samples were collected from around the lake and the canal. Plastic particles were detected in the sediment with various shapes, colors and compositions. The total particle count in the canal sediment was orders of magnitude higher than in the lake sediment. Polypropylene was the dominant polymer in the sediment. Our results suggest that coastal lakes can serve as a reworking zone for accumulation and reworkings of plastic particles, and a buffer zone contributing to plastic pollution in the marine environment. This study addresses the most understudied area of plastic pollution, i.e., reworking and redistribution of plastic debris at catchment scale across the marine and continental environment.

The dependence of the strain path on the microstructure, texture and mechanical properties of cryogenic rolled Al-Cu alloy

An investigation was conducted on Al-4%Cu alloy sheets to study the role of deformation path on the strength properties, evolution of microstructure and crystallographic texture during cryogenic rolling. Samples were rolled to two distinct thickness strains (50% and 75%) by unidirectional and cross rolling (bidirectional) routes. The strength and hardness properties were found to be more efficient in the cross rolled samples at 50% reduction than their counterparts rolled unidirectionally. Dynamic recovery was observed at higher rolling reductions on cross rolling. Microscopic features observed by EBSD revealed the occurrence of significant grain refinement on the samples rolled with a change of strain path. Also, the alteration of the rolling route resulted in distinct deformation textures and microstructures. TEM studies pointed out the scattered diffusion of the disintegrated dislocation cores and the redistribution of the second phase particles on higher rolling reductions with the change of strain path. Furthermore, the texture results showed a threefold increase on the Goss/Brass ratio which indicated the good fracture toughness behaviour of the cross rolled samples at lower reductions.

Эффективный способ моделирования системы Leksell Gamma Knife Perfexion методом поворота в файле фазового пространства

Purpose: To develop an effective method of Monte Carlo simulation of the GammaKnife Perfexion system by rotating particles in the phase space file (PSF). This method does not require simulating of all 192 sources that are distributed in the conical form of the Perfexion collimator. The simulation was performed only for 5 out of 192 sources for each collimator size.
 Material and methods: Monte Carlo simulation of dose distribution for previous models of GammaKnife system requires phase space file for only one source, since this phase space is identical for all the 201 sources. The Perfexion model is more complex due to the non-coaxial positions of the sources and the complexity of the collimator system itself.
 In this work, we present an effective method to simulate the Perfexion model using a phase space file. Penelope Monte Carlo code was used to perform this simulation. In this method, the PSF was obtained for one source in each ring, resulting in five files for each collimator size. PSF for other sources were created by azimuthal redistribution of particles, in the obtained PSF, by rotation around the Z-axis. The phase space files of the same ring were then stored together in a single file.
 Results: The paper presented MC simulation using the azimuthal redistribution of particles in the phase space file by rotation around the Z-axis. The simulation has been validated comparing the dose profiles and output factors with the data of the algorithm TMR10 planning system Leksell Gamma Plan (LGP) in a homogeneous environment. The acceptance criterion between TMR10 and Monte Carlo calculations for the profiles was based on the gamma index (GI). Index values more than one were not detected in all cases, which indicates a good agreement of results. The differences between the output factors obtained in this work and the TMR10 data for collimators 8 mm and 4 mm are 0.74 and 0.73 %, respectively.
 Conclusion: In this work successfully implemented an effective method of simulating the Leksell Gamma knife Perfexion system. The presented method does not require modeling for all 192 sources distributed in the conical form of the Perfexion collimator. The simulation was performed for only five sources for each collimator and their files PSF were obtained. These files were used to create the PSF files for other sources by azimuthal redistribution of particles, in these files, by rotation around the Z-axis providing correct calculations of dose distributions in a homogeneous medium for 16, 8 and 4 mm collimators.

Zinc leachability in contaminated soil stabilized/solidified by cement-soda residue under freeze-thaw cycles

The effectiveness of stabilization/solidification (S/S) method for the remediation of heavy metal contaminated soil is challenged by suffering freeze-thaw (F-T) cycles under long-term conditions. On this basis, the current paper performed semi-dynamic leaching test to assess the long-term stability of zinc contaminated soil treated with cement-soda residue under F-T cycles. Sequential F-T cycles increased the cumulative fraction of leached (CFL) Zn2+ by 4.4% and 9.4% for sample Zn0.05 and Zn1.0, respectively, but had minimal impact on the pH value of leached solution. After experiencing 10 F-T cycles, the effective diffusion coefficient (De) of Zn2+ increased from 1.6 × 10−11 to 1.37 × 10−9 cm2/s for sample Zn0.05, and 1.5 × 10−9 to 1.1 × 10−8 cm2/s for sample Zn1.0. The environmental risk of the treated soils after subjecting to F-T cycles would also be enhanced, which was predicted by the variations of the leachability index (LX). Zn2+ leachability in the specimen with high initial Zn2+ concentration was initially controlled by diffusion, and that with low concentration was dissolution. Over the long period of leaching, surface wash-off became dominant. Microstructural analysis based on X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests highlighted the absence of chemical changes in the mineral compositions, as well as the redistribution of the soil particles and pore sizes in the specimen.

Coagulation behavior of spherical particles embedded in laminar shear flow in presence of DLVO-and non-DLVO forces

HypothesisComplex and coupled interaction between coagulation mechanisms results in a nonlinear variation of coagulation rate with shear rate. CalculationsCoagulation behavior of colloidal dispersions is investigated in a laminar shear flow by solving the Fokker-Plank equation for pair probability density function, simultaneously incorporating the effect of (i) Brownian diffusion, (ii) fluid flow, (iii) van der Waals attraction and (iv) double layer repulsion force. Furthermore, analysis foremost studies the effect of non-DLVO solvation force. FindingsTheoretical analysis with experimental validation reveals that, coagulation rate varies non-linearly with the shear rate in presence of double-layer repulsion force, due to the strong coupling of coagulation mechanisms. This is observed by an occurrence of coagulation minima at intermediate shear rate. Increase in double layer repulsion force either facilitates or hinders the occurrence of redistribution of particles, as observed by early or late fall of coagulation rate. Systems with different ionic strengths show a crossover of coagulation rates, whereas those with different solvation forces do not show similar trend. Analysis also shows that, ad hoc additivity assumption of individual Brownian and shear coagulation rates does not hold in case of laminar shear flow, against to that observed in extensional flow [Melis et al. (AIChE J., 999, 1383)].

Модель біогенних потоків і депо 90Sr у забруднених соснових насадженнях

Лісові екосистеми вважають найбільш постраждалими внаслідок радіаційного забруднення після аварій на Чорнобильській і Фукусімській АЕС. Потрапивши у довкілля 137Cs і 90Sr, швидко включилися у біогеокругообіг речовини деревних фітоценозів. Останнього із перелічених радіонуклідів стосується значно менша кількість наукових публікацій за цим напрямом досліджень, тому подано розроблену модель біогенних потоків та депо 90Sr типового соснового насадження Чорнобильської зони відчуження. Спираючись на вихідні дані спостережень упродовж 2016–2019 рр. за сосновою ділянкою: концентрації і запаси радіонукліда у вивчених депо та потоках органічної речовини та інші показники, здійснено оптимізацію параметрів системи рівнянь потоків 90Sr між його депо імітаційної математичної моделі біокругообігу досліджуваного радіоізотопу методом стохастичного градієнтного спуску шляхом мінімізації суми квадратів відхилень цільової функції. Оцінено динаміку перерозподілу активностей 90Sr у компонентах біогеоценозу. Встановлено можливість депонування компонентами біомаси більшої половини активності 90Sr від наявної у сосновому біогеоценозі. Прогнозовано часові ряди коефіцієнтів переходу радіонукліда від ґрунту до елементів стовбура. Виявлено "стабілізацію" значень коефіцієнтів переходу 90Sr розрахованих, використовуючи щільність забруднення метрового шару ґрунту, що в разі підтвердження на більшому масиві спостережень за лісовими ділянками з контрастними ґрунтами та іншим деревним складом можна використовувати як простий спосіб прогнозування вмісту радіонукліда в компонентах біомаси.

Temperature assisted reorganization of silver nanoparticles in free-standing, flexible chitosan functionalized reduced graphene oxide thick films: A potential SERS probe for folic acid sensing

Chitosan and silver functionalized free standing reduced graphene oxide (rGO) films were prepared using simple soak and dry strategy. Redistribution of silver aggregates on chitosan functionalized rGO films were observed by thermally annealing these films at 450 °C, in an inert atmosphere. The re-organization / redistribution of silver aggregates in the rGO films were studied using in-situ Raman scattering signals. The redistribution of silver particles occurs through melting of micron sized silver aggregates during annealing. The rearrangement of the micro-sized silver aggregates to spherical silver nanoparticle on chitosan functionalized rGO film, as a result of temperature was assisted through factors such as graphene surface ripple rearrangement and the denaturation of rGO surface interacting chitosan chains. These free-standing films with redistributed silver nanoparticles showed excellent surface enhanced Raman scattering (SERS) effect with enhanced Raman signals for folic acid sensing, showcasing its potentiality to be utilized as flexible SERS based sensors.

Tribo-performance of Thixoformed A356-5TiB2 in-situ Composites

In the current work, thixoformedA356-5wt%TiB2in-situ composites were subjected to dry sliding wear. Further, the wear surface topography and wear debris was analyzed. The results show that wear rate is significantly influenced by redistribution of TiB2 particles in the matrix, refinement of fine globular α-Al grains and modification of eutectic Si. As expected, the thixoformed composites show better wear resistance than the alloy. Moreover TiB2 particles lower the coefficient of friction when reinforced in A356 alloy, in both gravity cast and thixoformed conditions. Also, it is interesting to note that there exist a linear relationship between wear rate and hardness of composites, irrespective of the processing history. The wear rate in the thixoformed composite is reduced by 48% as compared to gravity cast alloy. The improvement in wear resistance in the present thixoformed composite is not only due to the presence of fine TiB2 particles but also due to refinement of α-Al and eutectic Si caused due to the plastic deformation during thixoforming. In addition, high hardness and strength of thixoformed specimens compared with gravity cast parts has resulted in lower coefficient of friction in thixoformed A356-5TiB2 in-situ composite.

Coexistence of giant Cooper pairs with a bosonic condensate and anomalous behavior of energy gaps in the BCS-BEC crossover of a two-band superfluid Fermi gas

We investigate Bardeen-Cooper-Schrieffer (BCS)- Bose-Einstein condensation (BEC) crossover in a two-band superfluid Fermi gas with an energy shift between the bands. When the intraband coupling in the cold (first) band is fixed as weak, we find that in the case of vanishing interband interaction and in the strong-coupling limit of the hot (second) band the system undergoes a transition to a single-component configuration with the full suppression of the first energy gap and with the full redistribution of particles between bands. For non-vanishing interband interaction we reveal the non-monotonic dependence of the energy gap in the first band vs intraband coupling in the second band with the presence of a hump. In the case of weak interband coupling the system shows a significant amplification of the intrapair correlation length of the condensate in the first band in the strong-coupling regime of the second band, which clearly indicates the coexistence of giant Cooper pairs and a bosonic condensate even for nonzero temperatures. This can lead to a non-monotonic temperature dependence of the second energy gap with a peak. Here predicted coexistence of the giant Cooper pairs and bosonic molecules can be verified by means of the visualization of vortex cores in the two-component atomic condensates as well as in some iron-based superconductors.

Effect of tool rotational speed on the particle distribution in friction stir welding of AA6092/17.5 SiCp-T6 composite plates and its consequences on the mechanical property of the joint

This study investigates the effect of tool rotational speed (TRS) on particle distribution in nugget zone (NZ) through quantitative approach and its consequences on the mechanical property of friction stir welded joints of AA6092/17.5 SiCp-T6 composite. 6 mm thick plates are welded at a constant tool tilt angle of 2° and tool traverse speed of 1 mm/s by varying the TRS at 1000 rpm, 1500 rpm and 2000 rpm with a taper pin profiled tool. Microstructure analysis shows large quantity of uniformly shaped smaller size SiC particle with lower average particle area which are homogeneously distributed in the NZ. The fragmentation of bigger size particles has been observed because of abrading action of the hard tool and resulting shearing effect and severe stress generation due to the rotation of tool. The particles occupy maximum area in the matrix compared to that of the base material (BM) due to the redistribution of broken particles as an effect of TRS. The migration of particles towards the TMAZ-NZ transition zone has been also encountered at higher TRS (2000 rpm). The microhardness analysis depicts variation in average hardness from top to bottom of the NZ, minimum for 1500 rpm and maximum for 2000 rpm. The impact strength at 1000 rpm and 1500 rpm remains close to that of BM (21.6 J) while 2000 rpm shows the accountable reduction. The maximum joint efficiency has been achieved at 1500 rpm (84%) and minimum at 1000 rpm (68%) under tensile loading. Fractographic analysis shows mixed mode of failure for BM, 1000 rpm and 1500 rpm, whereas 2000 rpm shows the brittle mode of failure.

Study of filler microstructure in magnetic soft composites

Electron and atomic force microscopy were used for the study of magnetoactive filler surface microstructure in a magnetorheological composite. The particles redistribution phenomena of filler aggregates on the surface of elastomers under the action of a small external applied constant magnetic field are visualized. A model is proposed for the interaction of a magnetoactive filler with an elastomeric matrix of the composite, which explains the observed experimental results.

Investigation of fast particle redistribution induced by sawtooth instability in NSTX-U

The effects of sawtooth on fast ion transport have been studied in reproducible, 2 s long sawtoothing L-mode discharges during the 2016 experimental campaign on National Spherical Torus Experiment Upgrade (NSTX-U) (Menard et al 2012 Nucl. Fusion 52 083015). Analysis of the discharges demonstrated that standard sawtooth models (full/partial reconnection models) in the TRANSP code were not capable to fully reproduce the fast ion redistribution induced by sawtooth crashes. Some global parameters such as neutron rate can be recovered while detailed features, e.g. distribution functions, estimated using the models were different from the experimental observation. The standard sawtooth models in TRANSP do not take into account the different effect of sawtooth crashes depending on fast ion energy and orbit type and that may cause the disagreement between experiments and simulations. In this work, the newly developed kick model has been applied to replace the standard sawtooth models for the fast ion transport. TRANSP simulation results using the kick model, taking into account the characteristics of fast ion such as energy and pitch angle, can reproduce experimental neutron rates within 10% difference. The qualitative comparison of the measurements and synthetic diagnostics of fast ion D-alpha (FIDA) and solid state neutral particle analyser (SSNPA) using the TRANSP simulation results with kick model shows good agreements.

Kinetic theory of nonthermal fixed points in a Bose gas

We outline a kinetic theory of non-thermal fixed points for the example of a dilute Bose gas, partially reviewing results obtained earlier, thereby extending, complementing, generalizing and straightening them out. We study universal dynamics after a cooling quench, focusing on situations where the time evolution represents a pure rescaling of spatial correlations, with time defining the scale parameter. The non-equilibrium initial condition set by the quench induces a redistribution of particles in momentum space. Depending on conservation laws, this can take the form of a wave-turbulent flux or of a more general self-similar evolution, signaling the critically slowed approach to a non-thermal fixed point. We identify such fixed points using a non-perturbative kinetic theory of collective scattering between highly occupied long-wavelength modes. In contrast, a wave-turbulent flux, possible in the perturbative Boltzmann regime, builds up in a critically accelerated self-similar manner. A key result is the simple analytical universal scaling form of the non-perturbative many-body scattering matrix, for which we lay out the concrete conditions under which it applies. We derive the scaling exponents for the time evolution as well as for the power-law tail of the momentum distribution function, for a general dynamical critical exponent $z$ and an anomalous scaling dimension $\eta$. The approach of the non-thermal fixed point is, in particular, found to involve a rescaling of momenta in time $t$ by $t^{\beta}$, with $\beta=1/z$, within our kinetic approach independent of $\eta$. We confirm our analytical predictions by numerically evaluating the kinetic scattering integral as well as the non-perturbative many-body coupling function. As a side result we obtain a possible finite-size interpretation of wave-turbulent scaling recently measured by Navon et al.

Particle distribution and velocity in electrokinetically induced banding

Colloidal particles may be repelled from/attracted to the walls of glass micro-channels when an electro-osmotic flow is combined with a Poiseuille flow. Under certain conditions, the particles assemble into bands after accumulating near the walls (Cevheri and Yoda in Lab Chip 14(8):1391–1394, 2014). The fundamental physical mechanisms behind these phenomena remain unclear and up to now only measurements within $$1\,\upmu \hbox {m}$$ of the walls have been available. In this work, we applied a 3D particle-tracking technique, astigmatism particle tracking velocimetry, to measure the concentration and velocity distribution of particles across the depth of the entire micro-channel. The experiments show that the particles are depleted in the bulk as they become concentrated near the bottom and top walls and this particle redistribution depends strongly upon the bulk particle concentration. The results suggest that bands form in a region where particles are practically immobile and their volume fraction increases at least an order of magnitude with respect to the original volume fraction. Our results suggest that particle accumulation and band formation near the walls may be triggered by forces generated in the bulk since the banding and particle accumulation extends at least a few $$\upmu \hbox {m}$$ into the channel, or at length scales beyond the range of surface forces due to wall interactions.

Sediment microbial assemblage structure is modified by marine polychaete gut passage.

Invertebrate activities in sediments, predominantly the redistribution of particles and porewater, are well-known to regulate the structure of associated microbial assemblages; however, relatively little attention has been given to the effects of sediment ingestion, gut passage and excretion by deposit-feeding invertebrates. Here, we use high-throughput sequencing and quantitative PCR to examine how passage through the gut of the marine polychaete Hediste diversicolor affects the structure of bacterial and archaeal assemblages and the abundance of nitrogen cycling taxa. We show that the digestive tract of H. diversicolor contains unique transitory microbial assemblages that, during gut passage, become more like the surrounding sediment assemblages. Enrichment of similar microbial taxa in both the hindgut and the burrow wall suggest that these transitory gut assemblages may influence the composition of the local sediment community. The hindgut of H. diversicolor also forms a reservoir for unique ammonia-oxidising archaeal taxa. Furthermore, distinct microbial assemblages on external polychaete surfaces suggest that deposit-feeding invertebrates act as vectors that transport microbes between sediment patches. Collectively, these findings suggest that the passage of sediment and associated microbial assemblages through the gut of deposit feeding invertebrates is likely to play a significant role in regulating sediment microbial assemblages and biogeochemical functioning.

Effect of compressive stresses on permeability of coal with fracture filled with lightweight proppant

The paper presents laboratory testing results on effect of hydraulic fracturing on permeability of coal with and without wedging of created fractures by proppant. The tests were carried out with hollow aluminosilicate microspheres ASPM-500 without and with additional polymeric thermoreactive coating, specimens of dense long flame (grade D) coal with permeability of less than 3·10−3 μm2 and fractured fat coking coal (grade ZH) with permeability over 60·10−3 μm2. It is found that creation of fractures with and without propping considerably improves gas permeability of dense coal with weakly developed natural jointing. Created fractures are less effective in highly jointed highly permeable coal. It is experimentally proved that filling of created fractures with small opening of 0.4 mm with lightweight proppant under uniform compression of 1–5 MPa improves permeability of dense coal by 7–19.5 times. In jointed coal, application of lightweight proppant under the same conditions improves permeability less considerably—by 1.2–2.6 times. It is revealed that efficiency gas drainage in coal by hydraulic fractures without propping lowers as compressive stresses decrease. Reduction in permeability of coal with propped fracture under growing compression is probably connected with redistribution and compaction of proppant particles in the fracture. The obtained results show that application of lightweight propping materials is a promising way of advance in the technology of hydraulic fracturing for stimulation of coalbed methane drainage. The long-range research, in the authors’ opinion, should be focused on the development of lightweight proppants with improved strength characteristics.