Time-dependent Particle Research Articles

In vitro measurement and dynamic modeling-based approaches for deposition risk assessment of inhaled aerosols in human respiratory system

Respiratory deposition dynamics of inhaled particle are developed rapidly in recent decades. Understandings of aerosol properties are useful for predicting respiratory deposition risk. This study conducted an aerosol exposure experiment to quantify the respiratory deposition dynamics of inhaled aerosols, and to infer the deposition risk probability. The experimental aerosols included reference oil droplets and road dust particles. This study developed an aerosol dynamic model to simulate time-dependent particle concentration in exposure chamber and respiratory system. The parameters of particle loss in exposure chamber and deposition in respiratory system can be estimated by experimental measurements. The deposition risks were estimated through particle size distributions and size-dependent deposition fractions. We showed that the experimental and predicted deposition fractions were consistent with the previous in vivo, in vitro and in silico studies. We found that the generated aerosols were polydisperse that followed a lognormal distribution with geometric mean diameters of 0.52 and 0.26 μm for resuspended oil droplet and road dust, respectively. The deposition rate estimates range from 0.015 to 0.362 and 0.013 to 0.157 s−1 in particle size ranging from 0.3 to 3.0 and 0.3 to 4.0 μm for oil droplet and road dust, respectively. Result also revealed that inhaled oil droplet had higher respiratory deposition risk than road dust aerosol. Our study has major implications for the respiratory tract burden of inhaled fine particles from long-term exposure in ambient air based on our developed probabilistic risk model.

Modeling trace element partitioning during coal combustion

A model to predict the partitioning of semi-volatile TEs such as arsenic, antimony and selenium, during coal combustion has been developed. Because the initial mode of occurrence of a trace element (TE) impacts its partitioning after coal combustion, the model uses computer controlled scanning electron microscopy data sets of the target coal's ash analysis to determine the mineral inclusion, mineral exclusion, and organically associated TE content, which are then modeled using a semi-random mineral placement approach. Previously developed mathematical approaches, in conjunction with pyritic mineral transformation mechanisms, exclusion fragmentation and recently determined experimental speciation details, were employed to predict TE partitioning during combustion and TE spatial evolution.Initial validation of the model was performed using a subbituminous coal. The residence time dependent particle temperature histories resulting from the combustion of this coal in a lab-scale down-fired combustor were generated using computational fluid dynamic simulations which were then used to predict the size-dependent TE evolution. A reasonable agreement with previously published measurements of the fractions of TEs vaporized was obtained. Of the original arsenic, antimony or selenium introduced in the simulated coal environment, 38%, 32% and 94% respectively were predicted to be released from pyritic family mineral inclusions. For excluded particles of similar size and temperature histories, a larger fraction (81%) of the initial selenium contained in pyritic family mineral exclusions was released than the fractions of either arsenic or antimony (33% and 26%, respectively). Fragmentation, which is associated with an increase in surface area, increased the TE release rates by 7–8%.

Asymmetrical flow field-flow fractionation for human serum albumin based nanoparticle characterisation and a deeper insight into particle formation processes

Nanoparticles used as drug delivery systems are of growing interest in the pharmaceutical field. Understanding the behaviour and effects of nanosystems in the human body is dependent on comprehensive characterisation of the systems especially with regard to size and size distribution. Asymmetrical flow field-flow fractionation (AF4) is a promising method for this challenge as this technique enables chromatographic separation of particles and solute molecules according to their respective size.Within this study AF4 was used for the characterisation of human serum albumin (HSA) based nanoparticles. In a first part, the most important aspects of method development like the choice of cross flow rate, focusing and the increase of sample concentration via outlet stream splitting on the sample separation were evaluated. Sample fractionation was controlled by inline-coupling of a dynamic light scattering detector (DLS, Zetasizer) and was confirmed by DLS batch mode measurements. In a second part the applicability of field-flow fractionation for characterisation of the HSA particle formation process by a desolvation method was evaluated. A time dependent particle formation was observed which was controlled by the amount of desolvating agent. Furthermore, field-flow fractionation in combination with in-line dynamic light scattering was used to monitor the increase of particle diameter during PEGylation of the resulting HSA nanoparticles. The separation of nanoparticles from dissolved polyethylene glycol (PEG) could successfully be used for determination of the particles’ PEGylation degree.

Formulation development and evaluation of the anti-malaria properties of sustained release artesunate-loaded solid lipid microparticles based on phytolipids

Contexts: Artemisinins and its derivatives are considered the basis in the treatment of Plasmodium falciparum malaria due to their high potency and rapid action. However, they have short half life, low solubility, and poor oral bioavailability, hence the need to formulate sustained release lipid particulate dosage form of these drugs.Objectives: To formulate and evaluate artesunate-loaded solid lipid microparticles (SLMs) based on structured lipid matrices consisting of soybean oil and dika wax.Materials and methods: The lipid matrices were characterized by differential scanning calorimetry (DSC), small-angle X-ray diffraction (SAXD), and wide-angle X-ray diffraction (WAXD). The SLMs were prepared by hot melt-homogenization. Time-dependent particle size analysis, time-dependent pH stability studies, encapsulation efficiency (EE%), and in vitro drug release were carried out on the SLMs. In vivo anti-malarial studies were performed using a modified Peter’s 4-day suppressive protocol using Plasmodium berghei infected mice.Results and discussion: Thermograms of the lipid matrices showed modifications in the microstructure of dika wax as a result of inclusion of soybean oil. SAXD and WAXD diffractograms showed that the lipid matrices were found to be non-lamellar. Particle size of SLM increased with time, while the pH was almost constant. The SLMs had maximum EE% of 80.6% and sustained the release of artesunate more than the reference tablet. In vivo pharmacodynamic studies showed that the SLMs had significant (p < 0.05) reduction in parasitaemia compared with reference tablet.Conclusion: Artesunate-loaded SLMs could be used once daily in the treatment of malaria.

State-space analysis of influencing factors on airborne particle concentration in aircraft cabins

Epidemiological studies have shown that exposure to airborne particles is strongly associated with human health. Air quality concerns in aircraft cabins increase as air travel is becoming more common. Analyzing factors that influence the concentrations of airborne particles and taking mitigating measures will protect human health during air travel. In this study, concentrations of particles larger than 0.3 μm were measured in aircrafts' supply air in 9 flights. Air change rates were evaluated by the concentration of CO2 in supply air and recirculation air. Human emission, deposition and resuspension of particles were analyzed with our previously published results. The state-space method was used to calculate time-dependent particle concentration in different particle diameter intervals. Afterwards, with variation ranges of the 5 factors above, deviation rates of particle concentration were defined to evaluate the importance of those factors. This study determined: 1) resuspension is not an important factor, especially as time elapses; 2) varied deposition rate slightly influences particles smaller than 5.0 μm; 3) air change rate and human emission rate strongly impact the concentration of particles smaller than 2.0 μm; 4) supply air concentration generally affects the concentration of larger particles.

Formulation of Novel Artesunate-Loaded Solid Lipid Microparticles (SLMs) Based on Dika Wax Matrices: In Vitro and in Vivo Evaluation

The aims of the work were to formulate artesunate-loaded solid lipid microparticles (SLMs) based on dika wax matrices and to study the in vitro and in vivo properties. Lipid matrices consisting of mixtures of Phospholipon 90G (P90G) and dika wax were formulated and characterized by differential scanning calorimetry (DSC), small angle X-ray diffraction (SAXD) and wide angle X-ray diffraction (WAXD). The SLMs were prepared by melt-homogenization. Time-dependent particle size analysis, pH studies, encapsulation efficiency (EE%), in vitro drug release and anti-malarial properties were studied. Results show that SAXD diffractograms showed strong reflection at 2θ = 2.48°, d = 3.56 A. Particle size of SLMs increased with time (from 1 to 90 days). The SLMs exhibited maximum EE% of 80.6 % and had good sustained release properties. In vivo studies showed that the SLMs had significant (p

Wavelength selection of ripples in a vertically vibrating dynamically thick granular layer due to density-wave refraction

A numerical study was made on the wavelength selection mechanism of the ripples observed on the surface of a granular layer that is oscillated vertically. Multiple collisions of the one-dimensional array of beads show a time-dependent particle distribution, which induces a density wave. The magnitude of the wave velocity is estimated by the theory of elasticity, which reveals the refraction of the density wave in a quasi-two-dimensional granular layer. Our theory explains how the vertical excitation of particles determines the horizontal characteristic scale on the surface, or the wavelength of the ripples, which is applicable even to the saturation regime of a dynamically thick granular layer, e.g., the one that is thick enough to allow an immobilized region in the lower part.

Evolution of quantum field, particle content, and classicality in the three stage universe

We study the evolution of a quantum scalar field in a toy universe which has three stages of evolution, viz., (i) an early (inflationary) de Sitter phase (ii) radiation dominated phase and (iii) late-time (cosmological constant dominated) de Sitter phase. Using Schr\"odinger picture, the scalar field equations are solved separately for the three stages and matched at the transition points. The boundary conditions are chosen so that field modes in the early de Sitter evolves from Bunch-Davies vacuum state. We determine the (time-dependent) particle content of this quantum state for the entire evolution of the universe and describe the various features both numerically and analytically. We also describe the quantum to classical transition in terms of a {\it classicality parameter} which tracks the particle creation and its effect on phase space correlation of the quantum field.

Bench-Scale and Modeling Study of Sulfur Capture by Limestone in Typical CO2 Concentrations and Temperatures of Fluidized-Bed Air and Oxy-fuel Combustion

In this study, the influence of CO2 on sulfur capture efficiency was studied during fluidized-bed desulfurization by experiments and modeling. During calcination–sulfation and direct sulfation, the effect was examined with one limestone type. A time-dependent multilayer particle model was used for analyzing the experimental results. The model determines the magnitude of the reactions and the diffusion as a function of the radius and time. In high temperatures (∼1200 K), CO2 increased the conversion degree during calcination–sulfation. In direct sulfation, the effect of CO2 was opposite; lower conversion was obtained when the CO2 concentration was increased. When the CO2 concentration was increased in low temperatures (∼1100 K) (close to the calcination curve), CO2 retarded the conversion strongly. The detected differences between the results are explained with the development of the Thiele number, conversion curve, and conversion profile during the reactions.

Improving the Quantitative Description of Reacting Porous Solids: Critical Analysis of the Shrinking Core Model by Comparison to the Generalized Grain Model

A numerical comparison between the shrinking core model and the grain model is carried out, in the case of a single noncatalytic gas–solid reaction within a spherical particle. The study is focused on the mathematical quantification of the divergence between the time dependent particle conversions predicted by the two models, taking into account the different relationships between kinetics and intraparticle diffusion. Sensitivity tests have been carried out, depending on the controlling regime (chemical, diffusive, intermediate). The comparison was extended to a generalized form of the grain model, in which the superficial area of the porous matrix can be described as nonspherical micrograins, with possible sintering phenomena occurring. The comparison between the two models is first made by trying to fit the shrinking core model kinetics to the more realistic continuous model. Finally, errors introduced by the shrinking core model extrapolated to particle sizes different from that used to identify its ap...

Nanosecond Pulses in a THz Gyrotron Oscillator Operating in a Mode-Locked Self-ConsistentQ-Switch Regime

An experimental study of a nanosecond pulsed regime in a THz gyrotron oscillator operating in a self-consistent Q-switch regime has been carried out. The gyrotron is operated in the TE(7,2) transverse mode radiating at a frequency of 260.5 GHz. The 5 W nanosecond pulses are obtained in a self-consistent Q-switch regime in which the cavity diffraction quality factor dynamically varies by nearly 2 orders of magnitude on a subnanosecond time scale via the nonlinear interaction of different mode-locked frequency-equidistant sidebands. The experimental results are in good agreement with numerical simulations performed with the TWANG code based on a slow time scale formulation of the self-consistent time-dependent nonlinear wave particle interaction equations.

Unsteady Euler/Lagrange simulation of a confined bluff-body gas–solid turbulent flow

An unsteady Euler–Lagrangian approach is adopted to predict the gaseous carrier and disperse phases flow dynamics. The turbulence is captured using two different methods, i.e. the unsteady Reynolds averaging based numerical simulation (URANS) and the large eddy simulation (LES). In the latter one, the dynamic Smagorinsky approach is used to model the sub-grid scale stresses. The time-dependent solid particle and gas phase flow properties of a confined bluff-body turbulent flow including two-way coupling effects are evaluated through comparisons with experimental data. The configuration under study features an important recirculation zone and has a mass loading of 22%. So, collision effects are not considered while tracking the disperse phase that consists of glass beads. A thermodynamically consistent turbulence modulation approach is applied for the determination of the source terms that account for the effect of particles on the turbulence level of the carrier phase. Within the URANS technique the dispersion of particles is captured by the Markov sequence approach; this model is modified by integrating a drift factor term while modeling the pressure gradient. A particular emphasis is put on the disperse phase feedback on the carrier phase and coupling procedure within each Eulerian time step along with an unsteady coupling of both codes, the (Eulerian) FASTEST3D and the (Lagrangian) LAG3D codes. Quantitative results of the disperse phase properties as well as those of the carrier phase are presented at different positions around the recirculation zone. The numerical results using both, the LES and/or the URANS delivered comparable results that agree reasonably with experimental data. However, a slight advantage of LES over URANS could be observed.

Photon-plasma: A modern high-order particle-in-cell code

We present the photon-plasma code, a modern high order charge conserving particle-in-cell code for simulating relativistic plasmas. The code is using a high order implicit field solver and a novel high order charge conserving interpolation scheme for particle-to-cell interpolation and charge deposition. It includes powerful diagnostics tools with on-the-fly particle tracking, synthetic spectra integration, 2D volume slicing, and a new method to correctly account for radiative cooling in the simulations. A robust technique for imposing (time-dependent) particle and field fluxes on the boundaries is also presented. Using a hybrid OpenMP and MPI approach, the code scales efficiently from 8 to more than 250.000 cores with almost linear weak scaling on a range of architectures. The code is tested with the classical benchmarks particle heating, cold beam instability, and two-stream instability. We also present particle-in-cell simulations of the Kelvin-Helmholtz instability, and new results on radiative collisionless shocks.

The Controlled Powders Morphology of Bismuth Niobium Titanate Depending upon the Isothermal Annealing

In order to investigate the effect of isothermal annealing on the powder morphology, Bi3NbTiO9 powders were first synthesized by molten salt method and then calcinated at different temperatures for different dwelling time. The microstructure observation revealed that the crystal morphology of Bi3NbTiO9 powder changed greatly with the prolonged dwelling time. The powders started to change from cube to sphere in shape with the dwelling time prolonged to 240min and then became cube again as the dwelling time was prolonged beyond 360min at 850oC. In addition to a time-dependent particle evolution study, we explored primarily the original drive force of morphology transform from the viewpoint of dynamics.

Analytical Solutions for Filtration Process Based on Constriction Size Concept

AbstractAn analytical model is proposed to describe the filtration process applicable to a base soil-filter system. The Navier-Stokes equations for porous media are used to capture the hydrodynamic behavior, whereas, numerically, a new algorithm is proposed to solve the Navier-Stokes equation in a nonlinear form. The various mixtures of base soil particles eroded and water flow within the system are computed using the work-energy principle incorporating the constriction size of the filter. The model can assess the filtration process through the flow rate and the accumulation and redistribution of fine particles within the filter. By discretizing the base soil and filter domains into discrete elements, the model can predict the time-dependent particle gradation of the filter for each element. Laboratory tests reported in other studies and those conducted by the authors validate the model in relation to other available models.

On the generalized canonical equations of Hamilton for a time-dependent mass particle

Fundamental principles of mechanics were primarily conceived for constant mass systems. Since the pioneering works of Meshcherskii (see historical review in Mikhailov (Mech. Solids 10(5):32–40, 1975), efforts have been made in order to elaborate an adequate mathematical formalism for variable mass systems. This is a current research field in theoretical mechanics. In this paper, attention is focused on the derivation of the so-called ‘generalized canonical equations of Hamilton’ for a variable mass particle. The applied technique consists in the consideration of the mass variation process as a dissipative phenomenon. Kozlov’s (Stek. Inst. Math 223:178–184, 1998) method, originally devoted to the derivation of the generalized canonical equations of Hamilton for dissipative systems, is accordingly extended to the scenario of variable mass systems. This is done by conveniently writing the flux of kinetic energy from or into the variable mass particle as a ‘Rayleigh-like dissipation function’. Cayley (Proc. R Soc. Lond. 8:506–511, 1857) was the first scholar to propose such an analogy. A deeper discussion on this particular subject will be left for a future paper.

Real-space, real-time calculation of dynamic hyperpolarizabilities

The finite-difference method to calculate hyperpolarizabilities is generalized for dynamical case. The calculation of the dynamical hyperpolarizabilities from non-perturbative, explicitly time-dependent single particle states obtained in the framework of the time-dependent density functional theory, is implemented in real space and real time. The optical response functions up to the third order are extracted in frequency domain. The present approach is free of deficiencies associated with atom centered basis sets and allows treatment of large molecules. The calculated results are in good agreement with experiments and with other theoretical calculations for various test cases.

A Novel Approach to Visualizing Dark Matter Simulations.

In the last decades cosmological N-body dark matter simulations have enabled ab initio studies of the formation of structure in the Universe. Gravity amplified small density fluctuations generated shortly after the Big Bang, leading to the formation of galaxies in the cosmic web. These calculations have led to a growing demand for methods to analyze time-dependent particle based simulations. Rendering methods for such N-body simulation data usually employ some kind of splatting approach via point based rendering primitives and approximate the spatial distributions of physical quantities using kernel interpolation techniques, common in SPH (Smoothed Particle Hydrodynamics)-codes. This paper proposes three GPU-assisted rendering approaches, based on a new, more accurate method to compute the physical densities of dark matter simulation data. It uses full phase-space information to generate a tetrahedral tessellation of the computational domain, with mesh vertices defined by the simulation's dark matter particle positions. Over time the mesh is deformed by gravitational forces, causing the tetrahedral cells to warp and overlap. The new methods are well suited to visualize the cosmic web. In particular they preserve caustics, regions of high density that emerge, when several streams of dark matter particles share the same location in space, indicating the formation of structures like sheets, filaments and halos. We demonstrate the superior image quality of the new approaches in a comparison with three standard rendering techniques for N-body simulation data.

Time-dependent particle acceleration in a Fermi reservoir

Context. A steady model was presented by Burn, in which energy conservation is used to constrain the parameters of stochastic Fermi acceleration. A steady model, however, is unlikely to be adequate for particle acceleration in impulsive solar flares. Aims. This paper describes a time-dependent model for particle acceleration in a Fermi reservoir Methods. The calculation is based on the original formulation of stochastic acceleration by Fermi, with additional physically motivated assumptions about the turbulent and particle energy densities within the reservoir, that are similar to those of the steady analysis. The problem is reduced to an integro-differential equation that possesses an analytical solution. Results. The model predicts the formation of a power-law differential energy spectrum N(E) ∼ E−2, that is observable outside the reservoir. The predicted spectral index is independent of the parameters of the model. The results may help in understanding particle acceleration in solar flares and other astrophysical applications.

From complex to simple: interdisciplinary stochastic models

We present two simple, one-dimensional, stochastic models that lead to a qualitative understanding of very complex systems from biology, nanoscience and social sciences. The first model explains the complicated dynamics of microtubules, stochastic cellular highways. Using the theory of random walks in one dimension, we find analytical expressions for certain physical quantities, such as the time dependence of the length of the microtubules, and diffusion coefficients. The second one is a stochastic adsorption model with applications in surface deposition, epidemics and voter systems. We introduce the ‘empty interval method’ and show sample calculations for the time-dependent particle density. These models can serve as an introduction to the field of non-equilibrium statistical physics, and can also be used as a pedagogical tool to exemplify standard statistical physics concepts, such as random walks or the kinetic approach of the master equation.