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Alghamdi, Yusif A., Zhengbiao Peng, Caimao Luo, Zeyad Almutairi, Behdad Moghtaderi et Elham Doroodchi. « Systematic Study of Pressure Fluctuation in the Riser of a Dual Inter-Connected Circulating Fluidized Bed : Using Single and Binary Particle Species ». Processes 7, no 12 (1 décembre 2019) : 890. http://dx.doi.org/10.3390/pr7120890.
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This study systematically investigates the pressure fluctuation in the riser of a dual interconnected circulating fluidized bed (CFB) representing a 10 kWth cold-flow model (CFM) of a chemical-looping combustion (CLC) system. Specifically, a single-species system (SSS) and a binary-mixtures system (BMS) of particles with different sizes and densities were utilized. The pressure fluctuation was analyzed using the fast Fourier transform (FFT) method. The effect of introducing a second particle, changing the inventory, composition (i.e., 5, 10 to 20 wt.%), particle size ratio, and fluidization velocity were investigated. For typical SSS experiments, the results were similar to those scarcely reported in the literature, where the pressure fluctuation intensity was influenced by varying the initial operating conditions. The pressure fluctuations of BMS were investigated in detail and compared with those obtained from SSS experiments. BMS exhibited different behaviour; it had intense pressure fluctuation in the air reactor and in the riser when compared to SSS experiments. The standard deviation (SD) of the pressure fluctuation was found to be influenced by the fluidization regime and initial operating conditions, while the power spectrum density (PSD) values were more sensitive to the presence of the particles with the higher terminal velocity in the binary mixture.
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Prager, Michael, Da Zhang et Al Weiss. « Rotational Tunnelling in Binary Tetramethylmetal Mixtures ». Zeitschrift für Naturforschung A 50, no 4-5 (1 mai 1995) : 405–12. http://dx.doi.org/10.1515/zna-1995-4-513.
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Abstract Mixed PbcSn1-c(CH3)4 samples with c = 0.0, 0.1, 0.2,0.25, 0.48, 0.5, 0.75,0.85, and 1.0 and mixed [Pb(CH3)4](.[Sn(CD3)4]1-c. samples with c = 0.02 and 0.09 were investigated by high resolution inelastic neutron scattering. Rotational tunnelling transitions are observed for energy transfers hω<100 μeV. The global features are interpreted in a single particle model. A strong matrix effect of the Pb component is attributed to changes of potential symmetry. Effects beyond the expectation of the single particle description are found
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LEPTOUKH, GREGORY, BOWE STRICKLAND et CHRISTOPHER ROLAND. « PHASE SEPARATION OF TWO-DIMENSIONAL FLUID MIXTURES IN THE DISSIPATIVE REGIME ». Modern Physics Letters B 10, no 13 (10 juin 1996) : 577–98. http://dx.doi.org/10.1142/s021798499600064x.
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The phase separation of two-dimensional fluid mixtures was investigated with Molecular Dynamics simulations. The behavior of both single-component and binary mixtures as a function of temperature, volume fraction and average fluid density was studied. Binary systems with a size mismatch were also considered. In all cases, the diffusive coalescence of clusters is the primary mechanism of growth. In binary systems, the shape transformations of merging droplets induce important long-range flows at high volume fractions.
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Chen, Heng Zhi, et Zheng Kui Guo. « Characteristics of Mixing/Segregation in a Bubbling/Slugging Fluidized Bed with Binary Mixtures ». Advanced Materials Research 396-398 (novembre 2011) : 322–25. http://dx.doi.org/10.4028/www.scientific.net/amr.396-398.322.
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Fluidization behavior of binary mixtures with titanic slag particles and carbon particles had been investigated. Three solids states in the bed: fixed bed, transient fluidization and steady fluidization, emerges as increasing gas velocity. The extent of segregation of solids mixture in transient fluidization regime depended on the size difference between jetsam particles and flotsam particles. The effects of flotsam particle size, initial jetsam concentration and the superficial gas velocity on the segregation of binary solids had been measured.
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BERGEON, A., D. HENRY, H. BENHADID et L. S. TUCKERMAN. « Marangoni convection in binary mixtures with Soret effect ». Journal of Fluid Mechanics 375 (25 novembre 1998) : 143–77. http://dx.doi.org/10.1017/s0022112098002614.
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Marangoni convection in a differentially heated binary mixture is studied numerically by continuation. The fluid is subject to the Soret effect and is contained in a two-dimensional small-aspect-ratio rectangular cavity with one undeformable free surface. Either or both of the temperature and concentration gradients may be destabilizing; all three possibilities are considered. A spectral-element time-stepping code is adapted to calculate bifurcation points and solution branches via Newton's method. Linear thresholds are compared to those obtained for a pure fluid. It is found that for large enough Soret coefficient, convection is initiated predominantly by solutal effects and leads to a single large roll. Computed bifurcation diagrams show a marked transition from a weakly convective Soret regime to a strongly convective Marangoni regime when the threshold for pure fluid thermal convection is passed. The presence of many secondary bifurcations means that the mode of convection at the onset of instability is often observed only over a small range of Marangoni number. In particular, two-roll states with up-flow at the centre succeed one-roll states via a well-defined sequence of bifurcations. When convection is oscillatory at onset, the limit cycle is quickly destroyed by a global (infinite-period) bifurcation leading to subcritical steady convection.
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Perera, Aurélien, Martina Požar et Bernarda Lovrinčević. « Camel back shaped Kirkwood–Buff integrals ». Journal of Chemical Physics 156, no 12 (28 mars 2022) : 124503. http://dx.doi.org/10.1063/5.0084520.
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Some binary mixtures, such as specific alcohol–alkane mixtures or even water–tbutanol, exhibit two humps “camel back” shaped Kirkwood–Buff integrals (KBIs). This is in sharp contrast with the usual KBIs of binary mixtures having a single extremum. This extremum is interpreted as the region of maximum concentration fluctuations, usually occurs in binary mixtures presenting appreciable micro-segregation, and corresponds to where the mixture exhibits a percolation of the two species domains. In this paper, it is shown that two extrema occur in binary mixtures when one species forms “meta-particle” aggregates, the latter acts as a meta-species, and they have their own concentration fluctuations, hence their own KBI extremum. This “meta-extremum” occurs at a low concentration of the aggregate-forming species (such as alcohol in alkane) and is independent of the other usual extremum observed at mid-volume fraction occupancy. These systems are a good illustration of the concept of the duality between concentration fluctuations and micro-segregation.
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Shao, Yunqi, Aristeidis Voliotis, Mao Du, Yu Wang, Kelly Pereira, Jacqueline Hamilton, M. Rami Alfarra et Gordon McFiggans. « Chemical composition of secondary organic aerosol particles formed from mixtures of anthropogenic and biogenic precursors ». Atmospheric Chemistry and Physics 22, no 15 (2 août 2022) : 9799–826. http://dx.doi.org/10.5194/acp-22-9799-2022.
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Abstract. A series of experiments was designed and conducted in the Manchester Aerosol Chamber (MAC) to study the photo-oxidation of single and mixed biogenic (isoprene and α-pinene) and anthropogenic (o-cresol) precursors in the presence of NOx and ammonium sulfate seed particles. Several online techniques (HR-ToF-AMS, semi-continuous GC-MS, NOx and O3 analyser) were coupled to the MAC to monitor the gas and particle mass concentrations. Secondary organic aerosol (SOA) particles were collected onto a quartz-fibre filter at the end of each experiment and analysed using liquid chromatography–ultrahigh-resolution mass spectrometry (LC-Orbitrap MS). The SOA particle chemical composition in single and mixed precursor systems was investigated using non-targeted accurate mass analysis of measurements in both negative and positive ionization modes, significantly reducing data complexity and analysis time, thereby providing a more complete assessment of the chemical composition. This non-targeted analysis is not widely used in environmental science and has never been previously used in atmospheric simulation chamber studies. Products from α-pinene were found to dominate the binary mixed α-pinene–isoprene system in terms of signal contributed and the number of particle components detected. Isoprene photo-oxidation was found to generate negligible SOA particle mass under the investigated experimental conditions, and isoprene-derived products made a negligible contribution to particle composition in the α-pinene–isoprene system. No compounds uniquely found in this system sufficiently contributed to be reliably considered a tracer compound for the mixture. Methyl-nitrocatechol isomers (C7H7NO4) and methyl-nitrophenol (C7H7NO3) from o-cresol oxidation made dominant contributions to the SOA particle composition in both the o-cresol–isoprene and o-cresol–α-pinene binary systems in negative ionization mode. In contrast, interactions in the oxidation mechanisms led to the formation of compounds uniquely found in the mixed o-cresol-containing binary systems in positive ionization mode. C9H11NO and C8H8O10 made large signal contributions in the o-cresol–isoprene binary system. The SOA molecular composition in the o-cresol–α-pinene system in positive ionization mode is mainly driven by the high-molecular-weight compounds (e.g. C20H31NO4 and C20H30O3) uniquely found in the mixture. The SOA particle chemical composition formed in the ternary system is more complex. The molecular composition and signal abundance are both markedly similar to those in the single α-pinene system in positive ionization mode, with major contributions from o-cresol products in negative ionization mode.
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Strehle, F., et Th Dorfmüller. « Raman spectroscopic study of the single particle dynamics of CS2in liquid binary mixtures with CCl4 ». Molecular Physics 80, no 2 (10 octobre 1993) : 449–60. http://dx.doi.org/10.1080/00268979300102381.
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Semenov, I. L., A. G. Zagorodny et I. V. Krivtsun. « Numerical Study of Grain Charging Kinetics on the Basis of BGK Kinetic Equation ». Ukrainian Journal of Physics 56, no 2 (16 février 2022) : 138. http://dx.doi.org/10.15407/ujpe56.2.138.
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An investigation of charging a spherical particle in partially ionized nonisothermal plasma is carried out on the basis of the numerical solution of the BGK (Bhatnagar–Gross–Krook) model kinetic equation. Stationary values of the particle charge and the electron and ion currents are calculated for various collisional regimes. It is verified that, for the strongly collisional regime, the effective potential has a Coulomb form at large distance from the particle surface. A new BGK-type model for binary gas mixtures is proposed. It is shown that this model satisfies all the basic properties of Boltzmann collision integrals including the correct exchange coefficients. A high-order implicit numerical method for solving the kinetic equations is developed. The method is conservative with respect to the collision integrals for arbitrary values of the Knudsen number.
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Fang, Huang, Michael F. Hagan et W. Benjamin Rogers. « Two-step crystallization and solid–solid transitions in binary colloidal mixtures ». Proceedings of the National Academy of Sciences 117, no 45 (29 octobre 2020) : 27927–33. http://dx.doi.org/10.1073/pnas.2008561117.
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Crystallization is fundamental to materials science and is central to a variety of applications, ranging from the fabrication of silicon wafers for microelectronics to the determination of protein structures. The basic picture is that a crystal nucleates from a homogeneous fluid by a spontaneous fluctuation that kicks the system over a single free-energy barrier. However, it is becoming apparent that nucleation is often more complicated than this simple picture and, instead, can proceed via multiple transformations of metastable structures along the pathway to the thermodynamic minimum. In this article, we observe, characterize, and model crystallization pathways using DNA-coated colloids. We use optical microscopy to investigate the crystallization of a binary colloidal mixture with single-particle resolution. We observe classical one-step pathways and nonclassical two-step pathways that proceed via a solid–solid transformation of a crystal intermediate. We also use enhanced sampling to compute the free-energy landscapes corresponding to our experiments and show that both one- and two-step pathways are driven by thermodynamics alone. Specifically, the two-step solid–solid transition is governed by a competition between two different crystal phases with free energies that depend on the crystal size. These results extend our understanding of available pathways to crystallization, by showing that size-dependent thermodynamic forces can produce pathways with multiple crystal phases that interconvert without free-energy barriers and could provide approaches to controlling the self-assembly of materials made from colloids.
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Bykov, N. Y., et V. V. Zakharov. « Rarefied gas mixtures with large species mass ratio : Outflow into vacuum ». Physics of Fluids 34, no 5 (mai 2022) : 057106. http://dx.doi.org/10.1063/5.0089628.
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The theoretical study of the processes of the outflow of a binary gas mixture from a source into a vacuum through an orifice in an infinitely thin wall is presented. Two mixtures with a large species mass ratio K are considered: Au–Ne ( K = 9.76) and Au–He ( K = 49.21). The work continues the study of the flow of Ag–He mixture ( K = 26.95) started in Bykov and Zakharov [“Binary gas mixture outflow into vacuum through an orifice,” Phys. Fluids 32, 067109 (2020)]. The results of the direct simulation Monte Carlo made it possible to propose approximations of the mass flow rates of the species and the mixture depending on the species mass ratio, the flow rarefaction degree, and the mole fraction of light species in the source. It is shown that with an increase in the parameter K, an increase in the dimensionless mass flow rate of the mixture referred to the corresponding free molecular value is observed. The maximum dimensionless flow rate corresponds to the near-continuum regime and exceeds the value obtained using the hydrodynamic approximation and the equivalent single gas approach. A variation of K also leads to changes in the spatial distributions of the dimensionless density and velocity of the mixture and some axial focusing of the flow. An increase in the species mass ratio for the case of a small initial mole fraction of the heavy species in the source for a flow regime close to the hydrodynamic one leads to an increase in acceleration and axial focusing of the heavy species.
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Schöpf, Wolfgang, et Ingo Rehberg. « The influence of thermal noise on the onset of travelling-wave convection in binary fluid mixtures : an experimental investigation ». Journal of Fluid Mechanics 271 (25 juillet 1994) : 235–65. http://dx.doi.org/10.1017/s0022112094001758.
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When dealing with systems showing a Hopf bifurcation as the first instability from a conductive state leading to travelling waves, the distinction between convective and absolute instability becomes significant. The convectively unstable regime is characterized by the fact that a homogeneous disturbance may have a positive growth rate, while a single localized perturbation cannot trigger the onset of nonlinear convection. In this paper the convective instability occurring in binary fluid mixtures for a negative separation ratio is utilized for amplifying intrinsic thermal fluctuations, which in this way become accessible to quantitative measurements. The experiments are performed in a quasi-one-dimensional convection channel which, by means of subcritical ramps, effectively prevents the reflection of the travelling waves from the sidewalls. Thus, that range of the convective instability within which linear waves can be observed is strongly enhanced. The temperature variations involved in the observed travelling-wave states are quantified by using the shadowgraph method. By resonantly stimulating the system with its linear Hopf frequency, the reflection ability and some coefficients of the amplitude equation appropriate for describing the convection features near onset can be determined. Without stimulation, travelling-wave states of very small amplitudes showing an erratic spatio-temporal behaviour occur spontaneously inside the convectively unstable regime. The temporal correlation function calculated from the measured light intensity caused by these states is compared with a theoretical expression obtained from a Ginzburg—Landau equation containing a noise term. A very good agreement is found for the amplitude if thermal noise is assumed to be the reason for these fluctuating convection rolls, thus supporting the idea that the response of the system to thermal fluctuations is observed.
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Tripathi, Anurag, et D. V. Khakhar. « Density difference-driven segregation in a dense granular flow ». Journal of Fluid Mechanics 717 (1 février 2013) : 643–69. http://dx.doi.org/10.1017/jfm.2012.603.
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AbstractWe consider the segregation of spheres of equal size and different density flowing over an inclined plane, theoretically and computationally by means of distinct element method (DEM) simulations. In the first part of the work, we study the settling of a single higher-density particle in the flow of otherwise identical particles. We show that the motion of the high-density tracer particle can be understood in terms of the buoyancy and drag forces acting on it. The buoyancy force is given by Archimedes principle, with an effective volume associated with the particle, which depends upon the local packing fraction, $\phi $. The buoyancy arises primarily from normal forces acting on the particle, and tangential forces have a negligible contribution. The drag force on a sphere of diameter $d$ sinking with a velocity $v$ in a granular medium of apparent viscosity $\eta $ is given by a modified Stokes law, ${F}_{d} = c\pi \eta dv$. The coefficient ($c$) is found to decrease with packing fraction. In the second part of the work, we consider the case of binary granular mixtures of particles of the same size but differing in density. A continuum model for segregation is presented, based on the single-particle results. The number fraction profile for the heavy particles at equilibrium is obtained in terms of the effective temperature, defined by a fluctuation–dissipation relation. The model predicts the equilibrium number fraction profiles at different inclination angles and for different mass ratios of the particles, which match the DEM results very well. Finally, a complete model for the theoretical prediction of the flow and number fraction profiles for a mixture of particles of different density is presented, which combines the segregation model with a model for the rheology of mixtures. The model predictions agree quite well with the simulation results.
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Lee, Hansol D., Chathuri P. Kaluarachchi, Elias S. Hasenecz, Jonic Z. Zhu, Eduard Popa, Elizabeth A. Stone et Alexei V. Tivanski. « Effect of dry or wet substrate deposition on the organic volume fraction of core–shell aerosol particles ». Atmospheric Measurement Techniques 12, no 3 (2 avril 2019) : 2033–42. http://dx.doi.org/10.5194/amt-12-2033-2019.
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Abstract. Understanding the impact of sea spray aerosol (SSA) on the climate and atmosphere requires quantitative knowledge of their chemical composition and mixing states. Furthermore, single-particle measurements are needed to accurately represent large particle-to-particle variability. To quantify the mixing state, the organic volume fraction (OVF), defined as the relative organic volume with respect to the total particle volume, is measured after generating and collecting aerosol particles, often using deposition impactors. In this process, the aerosol streams are either dried or kept wet prior to impacting on solid substrates. However, the atmospheric community has yet to establish how dry versus wet aerosol deposition influences the impacted particle morphologies and mixing states. Here, we apply complementary offline single-particle atomic force microscopy (AFM) and bulk ensemble high-performance liquid chromatography (HPLC) techniques to assess the effects of dry and wet deposition modes on the substrate-deposited aerosol particles' mixing states. Glucose and NaCl binary mixtures that form core–shell particle morphologies were studied as model systems, and the mixing states were quantified by measuring the OVF of individual particles using AFM and compared to the ensemble measured by HPLC. Dry-deposited single-particle OVF data positively deviated from the bulk HPLC data by up to 60 %, which was attributed to significant spreading of the NaCl core upon impaction with the solid substrate. This led to underestimation of the core volume. This problem was circumvented by (a) performing wet deposition and thus bypassing the effects of the solid core spreading upon impaction and (b) performing a hydration–dehydration cycle on dry-deposited particles to restructure the deformed NaCl core. Both approaches produced single-particle OVF values that converge well with the bulk and expected OVF values, validating the methodology. These findings illustrate the importance of awareness in how conventional particle deposition methods may significantly alter the impacted particle morphologies and their mixing states.
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Voliotis, Aristeidis, Mao Du, Yu Wang, Yunqi Shao, M. Rami Alfarra, Thomas J. Bannan, Dawei Hu et al. « Chamber investigation of the formation and transformation of secondary organic aerosol in mixtures of biogenic and anthropogenic volatile organic compounds ». Atmospheric Chemistry and Physics 22, no 21 (4 novembre 2022) : 14147–75. http://dx.doi.org/10.5194/acp-22-14147-2022.
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Abstract. A comprehensive chamber investigation of photochemical secondary organic aerosol (SOA) formation and transformation in mixtures of anthropogenic (o-cresol) and biogenic (α-pinene and isoprene) volatile organic compound (VOC) precursors in the presence of NOx and inorganic seed particles was conducted. To enable direct comparison across systems, the initial concentration (hence reactivity) of the systems towards the dominant OH oxidant was adjusted. Comparing experiments conducted in single-precursor systems at various initial reactivity levels (referenced to a nominal base case VOC concentration, e.g. halving the initial concentration for a 1/2 initial reactivity experiment) as well as their binary and ternary mixtures, we show that the molecular interactions from the mixing of the precursors can be investigated and discuss challenges in their interpretation. The observed average SOA particle mass yields (the organic particle mass produced for a mass of VOC consumed) in descending order were found for the following systems: α-pinene (32 ± 7 %), α-pinene–o-cresol (28 ± 9 %), α-pinene at 1/2 initial reactivity (21 ± 5 %), α-pinene–isoprene (16 ± 1 %), α-pinene at 1/3 initial reactivity (15 ± 4 %), o-cresol (13 ± 3 %), α-pinene–o-cresol–isoprene (11 ± 4 %), o-cresol at 1/2 initial reactivity (11 ± 3 %), o-cresol–isoprene (6 ± 2 %), and isoprene (0 ± 0 %). We find a clear suppression of the SOA mass yield from α-pinene when it is mixed with isoprene, whilst no suppression or enhancement of SOA particle yield from o-cresol was found when it was similarly mixed with isoprene. The α-pinene–o-cresol system yield appeared to be increased compared to that calculated based on the additivity, whilst in the α-pinene–o-cresol–isoprene system the measured and predicted yields were comparable. However, in mixtures in which more than one precursor contributes to the SOA particle mass it is unclear whether changes in the SOA formation potential are attributable to physical or chemical interactions, since the reference basis for the comparison is complex. Online and offline chemical composition as well as SOA particle volatility, water uptake, and “phase” behaviour measurements that were used to interpret the SOA formation and behaviour are introduced and detailed elsewhere.
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Tafrishi, R., E. Taheri-Nassaj, A. Sadighzadeh et M. Jafari Eskandari. « Preparation and characterization of multilayer mesoporous γ-alumina membrane obtained via sol-gel using new precursors ». Materials Science-Poland 33, no 4 (1 décembre 2015) : 792–98. http://dx.doi.org/10.1515/msp-2015-0094.
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AbstractIn this paper, a mesoporous γ-alumina membrane coated on a macroporous α-alumina support via sol-gel method has been reported. A crack-free γ-alumina membrane was obtained by adding PVA to the alumina solution and optimum parameters of roughness, temperature and porosity were achieved. The support was dip-coated in different solutions using two new different solvents with different particle size distributions. Using these two solvents led to the uniform distribution of pore size in the final membrane. The alumina sols showed particle size distributions in the range of 20 to 55 nm which was measured by a DLS Zeta Sizer. X-ray diffraction technique, atomic force microscopy and scanning electron microscopy were used to characterize the membrane layer. XRD and DTA data for the γ-alumina membrane showed its thermal stability up to around 600 °C. The thickness of the mesoporous γ-alumina membrane was about 4 μm with 16 nm of surface roughness and 5 nm pore size. The resultant crack-free mesoporous membrane shows that the membrane preparation procedure was optimum. In this work, it has been investigated the performance of γ-alumina membranes for single gas permeation and separation of binary gas mixtures.
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Smith, Gregory N., Matthew J. Derry, James E. Hallett, Joseph R. Lovett, Oleksander O. Mykhaylyk, Thomas J. Neal, Sylvain Prévost et Steven P. Armes. « Refractive index matched, nearly hard polymer colloids ». Proceedings of the Royal Society A : Mathematical, Physical and Engineering Sciences 475, no 2226 (juin 2019) : 20180763. http://dx.doi.org/10.1098/rspa.2018.0763.
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Refractive index matched particles serve as essential model systems for colloid scientists, providing nearly hard spheres to explore structure and dynamics. The poly(methyl methacrylate) latexes typically used are often refractive index matched by dispersing them in binary solvent mixtures, but this can lead to undesirable changes, such as particle charging or swelling. To avoid these shortcomings, we have synthesized refractive index matched colloids using polymerization-induced self-assembly (PISA) rather than as polymer latexes. The crucial difference is that these diblock copolymer nanoparticles consist of a single core-forming polymer in a single non-ionizable solvent. The diblock copolymer chosen was poly(stearyl methacrylate)–poly(2,2,2-trifluoroethyl methacrylate) (PSMA–PTFEMA), which self-assembles to form PTFEMA core spheres in n -alkanes. By monitoring scattered light intensity, n -tetradecane was found to be the optimal solvent for matching the refractive index of such nanoparticles. As expected for PISA syntheses, the diameter of the colloids can be controlled by varying the PTFEMA degree of polymerization. Concentrated dispersions were prepared, and the diffusion of the PSMA–PTFEMA nanoparticles as a function of volume fraction was measured. These diblock copolymer nanoparticles are a promising new system of transparent spheres for future colloidal studies.
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Kanaan, Dima, Amine el Mahdi Safhi, Ahmed R. Suleiman et Ahmed M. Soliman. « Fresh, Hardened, and Microstructural Properties of Ambient Cured One-Part Alkali-Activated Self-Consolidating Concrete ». Sustainability 15, no 3 (30 janvier 2023) : 2451. http://dx.doi.org/10.3390/su15032451.
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Several studies have investigated the properties of alkali-activated materials (AAM), considering it as a substitute of cementitious concrete. However, the studies on alkali-activated self-consolidating concrete (AASCC) are extremely limited. This paper investigated the properties of AASCCs utilizing ground granulated blast furnace slag (GGBFS) as the main precursor. Single, binary, and ternary AASCCs were produced using fly ash Class-F (FA) and silica fumes (SF) as a replacement for GGBFS. The fresh properties including filing ability, passing ability and stability, as well as the hardened properties including unconfined compressive strength, ultrasonic pulse velocity, electrical resistivity, absorption, and sorptivity of the ambient cured one-part AASCC mixtures with different precursor blends were investigated. In addition, the microstructural properties of 90-day AASCC blends were studied by various microscale analysis methods. This paper demonstrated that the higher fraction of sodium carbonate/silicate activators, ranging from 20% to 25%, contributed to delayed reaction kinetics and satisfactory fresh and mechanical properties in all systems due to their nature. Slag replacement with variable SF or FA class-F ratios, instead, could indeed adjust the particle size distribution of the total binder material and improve the fresh concrete characteristics in binary and ternary systems. Finally, the formation of various reaction products and binding gels, i.e., C-(N)A-S-H, was found to have a significant impact on several transport mechanisms, including capillary sorptivity, permeable pores, and bulk electrical resistivity.
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GRAY, J. M. N. T., et C. ANCEY. « Multi-component particle-size segregation in shallow granular avalanches ». Journal of Fluid Mechanics 678 (1 juin 2011) : 535–88. http://dx.doi.org/10.1017/jfm.2011.138.
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A general continuum theory for particle-size segregation and diffusive remixing in polydisperse granular avalanches is formulated using mixture theory. Comparisons are drawn to existing segregation theories for bi-disperse mixtures and the case of a ternary mixture of large, medium and small particles is investigated. In this case, the general theory reduces to a system of two coupled parabolic segregation–remixing equations, which have a single diffusion coefficient and three parameters which control the segregation rates between each pair of constituents. Considerable insight into many problems where the effect of diffusive remixing is small is provided by the non-diffusive case. Here the equations reduce to a system of two first-order conservation laws, whose wave speeds are real for a very wide class of segregation parameters. In this regime, the system is guaranteed to be non-strictly hyperbolic for all admissible concentrations. If the segregation rates do not increase monotonically with the grain-size ratio, it is possible to enter another region of parameter space, where the equations may either be hyperbolic or elliptic, depending on the segregation rates and the local particle concentrations. Even if the solution is initially hyperbolic everywhere, regions of ellipticity may develop during the evolution of the problem. Such regions in a time-dependent problem necessarily lead to short wavelength Hadamard instability and ill-posedness. A linear stability analysis is used to show that the diffusive remixing terms are sufficient to regularize the theory and prevent unbounded growth rates at high wave numbers. Numerical solutions for the time-dependent segregation of an initially almost homogeneously mixed state are performed using a standard Galerkin finite element method. The diffuse solutions may be linearly stable or unstable, depending on the initial concentrations. In the linearly unstable region, ‘sawtooth’ concentration stripes form that trap and focus the medium-sized grains. The large and small particles still percolate through the avalanche and separate out at the surface and base of the flow due to the no-flux boundary conditions. As these regions grow, the unstable striped region is annihilated. The theory is used to investigate inverse distribution grading and reverse coarse-tail grading in multi-component mixtures. These terms are commonly used by geologists to describe particle-size distributions in which either the whole grain-size population coarsens upwards, or just the coarsest clasts are inversely graded and a fine-grained matrix is found everywhere. An exact solution is constructed for the steady segregation of a ternary mixture as it flows down an inclined slope from an initially homogeneously mixed inflow. It shows that for distribution grading, the particles segregate out into three inversely graded sharply segregated layers sufficiently far downstream, with the largest particles on top, the fines at the bottom and the medium-sized grains sandwiched in between. The heights of the layers are strongly influenced by the downstream velocity profile, with layers becoming thinner in the faster moving near-surface regions of the avalanche, and thicker in the slowly moving basal layers, for the same mass flux. Conditions for the existence of the solution are discussed and a simple and useful upper bound is derived for the distance at which all the particles completely segregate. When the effects of diffusive remixing are included, the sharp concentration discontinuities are smoothed out, but the simple shock solutions capture many features of the evolving size distribution for typical diffusive remixing rates. The theory is also used to construct a simple model for reverse coarse-tail grading, in which the fine-grained material does not segregate. The numerical method is used to calculate diffuse solutions for a ternary mixture and a sharply segregated shock solution is derived that looks similar to the segregation of a bi-disperse mixture of large and medium grains. The presence of the fine-grained material, however, prevents high concentrations of large or medium particles being achieved and there is a significant lengthening of the segregation distance.
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Jin, Lin, Curtis W. Jarand, Mark L. Brader et Wayne F. Reed. « Angle-dependent effects in DLS measurements of polydisperse particles ». Measurement Science and Technology 33, no 4 (10 janvier 2022) : 045202. http://dx.doi.org/10.1088/1361-6501/ac42b2.
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Abstract Dynamic light scattering (DLS) is widely used for analyzing biological polymers and colloids. Its application to nanoparticles in medicine is becoming increasingly important with the recent emergence of prominent lipid nanoparticle (LNP)-based products, such as the SARS-CoV-2 vaccines from Pfizer, Inc.-BioNTech (BNT162b2) and Moderna, Inc. (mRNA-1273). DLS plays an important role in the characterization and quality control of nanoparticle-based therapeutics and vaccines. However, most DLS instruments have a single detection angle θ, and the amplitude of the scattering vector, q, varies among them according to the relationship q = (4πn/λ 0) sin(θ/2), where λ 0 is the laser wavelength. Results for identical, polydisperse samples among instruments of varying q yield different hydrodynamic diameters, because, as particles become larger they scatter less light at higher q, so that higher-q instruments will under-sample large particles in polydisperse populations, and report higher z-average diffusion coefficients, and hence smaller effective hydrodynamic diameters than lower-q instruments. As particle size reaches the Mie regime the scattering envelope manifests angular maxima and minima, and the monotonic decrease of average size versus q is lost. The discrepancy among instruments of different q is hence fundamental, and not merely technical. This work examines results for different q-value instruments, using mixtures of monodisperse latex sphere standards, for which experimental measurements agree well with computations, and also polydisperse solutions of physically-degraded LNPs, for which results follow expected trends. Mie effects on broad unimodal populations are also considered. There is no way to predict results between two instruments with different q for samples of unknown particle size distributions. Initial analysis of the polydispersity index among different instruments shows a technical difference due to method of autocorrelation analysis, in addition to the fundamental q-effect.
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Partheniadis, Ioannis, Ioannis Nikolakakis, Constantinos K. Zacharis, Kyriakos Kachrimanis et Nizar Al-Zoubi. « Co-Spray Drying of Paracetamol and Propyphenazone with Polymeric Binders for Enabling Compaction and Stability Improvement in a Combination Tablet ». Pharmaceutics 13, no 8 (14 août 2021) : 1259. http://dx.doi.org/10.3390/pharmaceutics13081259.
Texte intégralRésumé :
Paracetamol (PCT) and propyphenazone (PRP) are analgesic drugs that are often combined in a single dosage form for enhanced pharmacological action. In this work, PCT and PRP were co-spray dried separately with hydroxypropyl methylcellulose (HPMC) and hydroxypropyl cellulose (HPC) using drug suspensions in polymer solutions as feed liquids. It was thought that because of polymer adherence to the surface of drug particles, the risk of PCT–PRP contact and interaction could be reduced. Such interaction may be caused by localized temperature gradients due to frictional forces during tableting, or during storage under harsh conditions. A worst-case scenario would be eutectic formation due to variations in powder mixture homogeneity since eutectic and therapeutic mass PCT/PRP ratios are close (65:35 and 60:40, respectively) and eutectic temperature is low (~56 °C). Uniform particle size, round shape, compaction improvement and faster release of the analgesics were important additional benefits of co-spray drying. Experimental design was first applied for each drug to optimize the polymer concentration on the yield of spray drying and melting point separation (Δmp) of heated binary mixtures of co-spray dried PCT/neat PRP, and vice versa, with the two drugs always included at their therapeutic 60:40 ratio. Optimal combinations with largest Δmp and production yield were: co-spray dried PCT (15% HPC) with neat PRP and co-spray dried PRP (10% HPMC) with neat PCT. Compression studies of these combinations showed tableting improvement due to the polymers, as reflected in greater work of compaction and solid fraction, greater fracture toughness and tablet strength, easier tablet detachment from the punch surface and ejectability. Faster release of both drugs was obtained from the tablet of co-spray dried PCT (15% HPC) with neat PRP. A one-month stability test (75% RH/40 °C) showed moisture-induced alteration tablet strength.
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Ganguli, Arijit, et Viraj Bhatt. « CFD simulations to study bed characteristics in gas–Solid fluidized beds with binary mixtures of Geldart-B particles : A qualitative analysis ». Frontiers in Energy Research 11 (20 février 2023). http://dx.doi.org/10.3389/fenrg.2023.1059503.
Texte intégralRésumé :
The bed dynamics of unary and binary fluidized beds play a key role in understanding the pressure drop and hence provides an opportunity for performance improvement of the beds. In the present work, characteristics of fluidized beds with binary mixtures of Geldart-B particles were investigated using CFD simulations. The phenomena of segregation and mixing using simulations were studied, both qualitatively and quantitatively, at a range of superficial gas velocities (0.3–0.6 m/s) and two different bed heights. The study was divided into two parts. In Part I, the current study, a qualitative analysis of flow patterns for seven different binary mixtures, is presented. The quantitative analysis, including particle and gas velocity profiles, particle volume fraction profiles, and correlations for minimum fluidization velocity and pressure drop, will be presented in Part II of this work. A mathematical model consisting of an Eulerian-Eulerian model with RNG k-ε model and KTGF model to capture the bubble dynamics was used. The standardized values of coefficients and plastic stresses have been used for all simulations. The CFD model was validated using experimental data from the literature. Qualitative predictions of volume fraction profiles of small-sized particles showed that, for mixtures within a range of 40%–60% Geldart-B type large particles, the bubble and solid particle dynamics were different from those of single particles of the superficial gas velocities considered. In contrast to the single particles in the given superficial gas velocity range that were in bubbling regime, the binary particles showed a transition from bubbling to slugging to turbulent regime, as demonstrated by qualitative analysis. A homogeneous regime was observed for lower superficial gas velocities for mixtures consisting of 0%–20% large particles.
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Busciglio, Antonio, Giuseppa Vella et Dr G. Micale. « Gas-Fluidization Characteristics of Binary Mixtures of Particles in 2D Geometry ». International Journal of Chemical Reactor Engineering 10, no 1 (16 mai 2012). http://dx.doi.org/10.1515/1542-6580.2994.
Texte intégralRésumé :
The bubbling behaviour of fluidized beds has been thoroughly investigated in the last decades by means of several techniques, e.g. X-ray, Inductance, Resistance and Impedance based techniques, PIV. In recent years, Digital Image Analysis Techniques have shown their potential for accurate and cost effectively measurements.Most of the work related to bubble behaviour analysis deals with single-sized particles, while almost all industrial equipment operates with multi-sized particles. Although considerable work has been done in the past with focus on the analysis of the mixing-segregation behaviour and predictions of fluid dynamics regime transitions, a lack of knowledge still exists in the analysis of bubbles properties measurements for the case of polydispersed systems.In this work, digital image analysis has been adopted to accurately measure fundamental global parameters such as bubble hold up and bed expansion as well as average bubble hold-up distribution maps or bubble size distributions in bubbling fluidized beds of binary mixtures of particles. The experiments have been carried out at steady state conditions with binary mixtures of corundum particles, at various inlet gas velocities. This preliminary study has been performed with the aim to collect valuable data for future development of predictive models and validation of CFD codes.
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Dhingra, Sandeep, Kang-Woo Kim et Mercouri G. Kanatzidis. « Polychalcogenide Complexes as Low Temperature Precursors for Quantum Size and Bulk Binary and Ternary Semiconductors ». MRS Proceedings 204 (1990). http://dx.doi.org/10.1557/proc-204-163.
Texte intégralRésumé :
ABSTRACTWe report the utility of \Cd(Se4)2]2-, \Cu4Se12]2- and \In3Se15]3- as convenient low temperature precursors to semiconducting CdSe and CuInSe2. DMF and DMSO solutions of these complexes react with Se-abstracting reagents such as CN- and n-(Bu3)P to yield the corresponding binary solids at 155 °C or less. Appropriate stoichiometric mixtures of \Cu4Se12]2- and \In3Se15]3- react to give CuInSe2. The semiconducting solids were characterized with UV/vis spectroscopic, X-ray crystallographic and electron (scanning and transmission) microscopic techniques. The particle size of these materials can range from the quantum-size regime to the bulk regime, depending on the reaction conditions, metal precursor complex and Se-abstracting reagent used.
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Kim, Kang-Woo, J. A. Cowen, Sandeep Dhingra et Mercouri G. Kanatzidis. « Nanocrystalline Binary, Ternary and Dilute Magnetic Semiconductors from Polychalcogenide Complexes ». MRS Proceedings 272 (1992). http://dx.doi.org/10.1557/proc-272-27.
Texte intégralRésumé :
ABSTRACTThe molecular polychalcogenide complexes [M(Se4)2]2−, (M=Mn, Zn, Cd, Hg), [Sn(Se4)3]2−, and [Cu4Se12]2− can be converted to the corresponding binary semiconducting solids. DMF and DMSO solutions of these complexes react with Se-abstracting reagents such as CN− and (n-Bu)3P to yield the corresponding binary solids at 155 °C or less. Appropriate stoichiometric mixtures of [Cu4Se12]2− and [In3Se15]3− react to give CulnSe2. Appropriate stoichiometric mixtures of [Cd(Se4)2]2− and [Mn(Se4)2]2− give solid solutions Cd1−xMnxSe where O<x<l. The Cd1−xMnxSe solid solutions were characterized by variable temperature magnetic measurements. Depending on the reaction conditions, metal precursor complex and Se-abstracting reagent used, the semiconductor particle size ranges from the quantum-size to the bulk regime. This method of synthesis produces the little known γ-MnSe in pure form.
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Duan, Yifei, Lu Jing, Paul B. Umbanhowar, Julio M. Ottino et Richard M. Lueptow. « Segregation forces in dense granular flows : closing the gap between single intruders and mixtures ». Journal of Fluid Mechanics 935 (3 février 2022). http://dx.doi.org/10.1017/jfm.2022.12.
Texte intégralRésumé :
Using simulations and a virtual-spring-based approach, we measure the segregation force, $F_{seg},$ in size-bidisperse sphere mixtures over a range of concentrations, particle-size ratios and shear rates to develop a semiempirical model for $F_{seg}$ that extends its applicability from the well-studied non-interacting intruders regime to finite-concentration mixtures where cooperative phenomena occur. The model predicts the concentration below which the single-intruder assumption applies and provides an accurate description of the pressure partitioning between species.
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Di Felice, Renzo, et Marco Rotondi. « Fluid-particle Drag Force in Binary-solid Suspensions ». International Journal of Chemical Reactor Engineering 10, no 1 (22 mai 2012). http://dx.doi.org/10.1515/1542-6580.3000.
Texte intégralRésumé :
The drag force on a particle in a multiparticle suspension is a function of the particle-fluid relative velocity and of the particle volume concentration. Its determination heavily relies on experimental observations, as theoretical support is still limited to viscous flow regime and dilute solid concentrations. When uniform particle suspensions are considered, there is a certain abundance of experimental data available which has permitted the proposition of simple and reliable relationships for the determination of the drag force: these relationships are normally expressed through the use of the so-called “voidage function”, i.e. a function by which the drag force on an isolated particle has to be multiplied in order to obtain the drag force on a particle in a multiparticle suspension. The extension of the approach mentioned above to suspensions made up of particles differing in size and density has been attempted here and new simple relationships are presented for the case of binary-solid systems. The basic idea draws an analogy between binary-solid suspension and single-particle suspensions thereby making possible the use of well established results. The simple relationships obtained for the estimation of the drag force on a particle in a binary-solid suspension have been tested, with satisfactory success, against experimental data available in literature.
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Anzivino, Carmine, Mathias Kasiulis, Tom Zhang, Amgad Moussa, Stefano Martiniani et Alessio Zaccone. « Estimating random close packing in polydisperse and bidisperse hard spheres via an equilibrium model of crowding ». Journal of Chemical Physics, 29 décembre 2022. http://dx.doi.org/10.1063/5.0137111.
Texte intégralRésumé :
We show that an analogy between crowding in fluid and jammed phases of hard spheres captures the density dependence of the kissing number for a family of numerically generated jammed states. We extend this analogy to jams of mixtures of hard spheres in $d=3$ dimensions, and thus obtain an estimate of the random close packing (RCP) volume fraction, $\phi_{\textrm{RCP}}$, as a function of size polydispersity. We first consider mixtures of particle sizes with discrete distributions. For binary systems, we show agreement between our predictions and simulations, using both our own and results reported in previous works, as well as agreement with recent experiments from the literature. We then apply our approach to systems with continuous polydispersity, using three different particle size distributions, namely the log-normal, Gamma, and truncated power-law distributions. In all cases, we observe agreement between our theoretical findings and numerical results up to rather large polydispersities for all particle size distributions, when using as reference our own simulations and results from the literature. In particular, we find $\phi_{\textrm{RCP}}$ to increase monotonically with the relative standard deviation, $s_{\sigma}$, of the distribution, and to saturate at a value that always remains below 1.A perturbative expansion yields a closed-form expression for $\phi_{\textrm{RCP}}$ that quantitatively captures a distribution-independent regime for $s_{\sigma} < 0.5$. Beyond that regime, we show that the gradual loss in agreement is tied to the growth of the skewness of size distributions.
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Wang, Da, Ernest B. van der Wee, Daniele Zanaga, Thomas Altantzis, Yaoting Wu, Tonnishtha Dasgupta, Marjolein Dijkstra, Christopher B. Murray, Sara Bals et Alfons van Blaaderen. « Quantitative 3D real-space analysis of Laves phase supraparticles ». Nature Communications 12, no 1 (25 juin 2021). http://dx.doi.org/10.1038/s41467-021-24227-0.
Texte intégralRésumé :
AbstractAssembling binary mixtures of nanoparticles into crystals, gives rise to collective properties depending on the crystal structure and the individual properties of both species. However, quantitative 3D real-space analysis of binary colloidal crystals with a thickness of more than 10 layers of particles has rarely been performed. Here we demonstrate that an excess of one species in the binary nanoparticle mixture suppresses the formation of icosahedral order in the self-assembly in droplets, allowing the study of bulk-like binary crystal structures with a spherical morphology also called supraparticles. As example of the approach, we show single-particle level analysis of over 50 layers of Laves phase binary crystals of hard-sphere-like nanoparticles using electron tomography. We observe a crystalline lattice composed of a random mixture of the Laves phases. The number ratio of the binary species in the crystal lattice matches that of a perfect Laves crystal. Our methodology can be applied to study the structure of a broad range of binary crystals, giving insights into the structure formation mechanisms and structure-property relations of nanomaterials.
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Kanholy, Santhip K., Jillian Chodak, Brian Y. Lattimer et Francine Battaglia. « Modeling and Predicting Gas-Solid Fluidized Bed Dynamics to Capture Nonuniform Inlet Conditions ». Journal of Fluids Engineering 134, no 11 (24 octobre 2012). http://dx.doi.org/10.1115/1.4007803.
Texte intégralRésumé :
The hydrodynamics of fluidized beds involving gas-solids interactions are very complex, and modeling such a system using computational fluid dynamics (CFD) modeling is even more challenging for mixtures composed of nonuniform particle characteristics such as diameter or density. Another issue is the presence of dead-zones, regions of particles that do not fluidize and accumulate at the bottom of the bed, affecting uniform fluidization of the material. The dead zones typically form between the gas jets and depend on the spacing of the distributor holes and gas velocity. Conventionally, in Eulerian–Eulerian modeling for gas-solid mixtures, the solid phase is assumed to behave like a fluid, and the presence of dead zones are not typically captured in a CFD simulation. Instead, the entire bed mass present in an experiment is usually modeled in the simulations assuming complete fluidization of the bed mass. A different modeling approach was presented that accounts for only the fluidizing mass by adjusting the initial mass present in the bed using the measured pressure drop and minimum fluidization velocity from the experiments. In order to demonstrate the fidelity of the new modeling approach, three different bed materials were examined that can be classified as Geldart B particles. Glass beads and ceramic beads of the same mean particle diameter were used, as well as larger-sized ceramic particles. Binary mixture models were also validated for two types of bed mixtures consisting of glass-ceramic and ceramic-ceramic compositions. It was found that adjusting the amount of fluidizing mass in the modeling of fluidized beds best predicted the fluidization dynamics of an experiment for both single phase and binary mixture fluidized beds.
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Sposini, Vittoria, Aleksei V. Chechkin, Igor M. Sokolov et Sándalo Roldán-Vargas. « Detecting temporal correlations in hopping dynamics in Lennard–Jones liquids ». Journal of Physics A : Mathematical and Theoretical, 4 juillet 2022. http://dx.doi.org/10.1088/1751-8121/ac7e0a.
Texte intégralRésumé :
Abstract Lennard--Jones mixtures represent one of the popular systems for the study of glass--forming liquids. Spatio/temporal heterogeneity and rare (activated) events are at the heart of the slow dynamics typical of these systems. Such slow dynamics is characterised by the development of a plateau in the mean--squared displacement (MSD) at intermediate times, accompanied by a non–Gaussianity in the displacement distribution identified by exponential tails. As pointed out by some recent works, the non--Gaussianity persists at times beyond the MSD plateau, leading to a Brownian yet non--Gaussian regime and thus highlighting once again the relevance of rare events in such systems. Single--particle motion of glass--forming liquids is usually interpreted as an alternation of rattling within the local cage and cage--escape motion and therefore can be described as a sequence of waiting times and jumps. In this work, by using a simple yet robust algorithm, we extract jumps and waiting times from single--particle trajectories obtained via Molecular Dynamics simulations. We investigate the presence of correlations between waiting times and find negative correlations, which becomes more and more pronounced when lowering the temperature.