Diffusion Phenomena Research Articles

Regression rate model assessed by ballistic reconstruction technique in hybrid rocket engines burning liquefying fuels

This work presents a novel approach for the modelling of the regression rate in hybrid rocket engines loaded with paraffin-fuel. Two different motor thrust classes have been considered in this work to extend the validity of the numerical model on two motor geometries (200 N and 1 kN). The work consists of two parts. Firstly, a unique and general empirical law of the regression rate was found for both the motor configurations, which are governed by different consumption mechanisms due to the injection system. Ballistic reconstruction techniques have been introduced to reproduce the temporal trend of the regression rate during the burning time and to increase the number of experimental tests used for the development of accurate and reliable regression laws. Experimental observations in the larger motor suggest that the entrainment is dominated by mass diffusive transport phenomena, which is modelled here by a Fick-like relation. This model, coupled with a sophisticated gas-surface interaction treatment, allowed the evaluation of the regression rate in each point of the grain surface by computational fluid dynamic simulations. Then, the overall model has been validated on experimental and reconstructed data. Finally, the effect of the motor configuration on the fuel consumption is shown, thus revealing the crucial influence of the separation zone delivered by the axial injection.

Simultaneous determination of different class of parameters for a diffusion equation from a single measurement

This article is devoted to the simultaneous resolution of several inverse problems, among the most important formulation of inverse problems for partial differential equations, stated for some class of diffusion equations from a single boundary measurement. Namely, we consider the simultaneous unique determination of several class of coefficients, some internal sources (a source term and an initial condition) and the fractional order in a diffusion equation from a single boundary measurement. Our problem can be formulated as the simultaneous determination of information about a diffusion process (velocity field, density of the medium) and of the source of diffusion. We consider this problems in the context of a classical diffusion process described by a convection–diffusion equation as well as an anomalous diffusion phenomena described by a time fractional diffusion equation.

Voices change my name

IntroductionWe present the clinical case of a patient where the psychotic clinic coexists with gender dysphoria. This scenario can be the result of a change in gender identity derived from the psychotic process or appear independently of it.ObjectivesWe want to explain the importance of knowing how to act with a patient in whom these two processes coexist.Methods20-year-old woman, with no history of mental health. She comes to the emergency department for behavioral alteration. The family observes strange behaviors, unmotivated laughter, soliloquies and aggressive episodes. Abandonment of studies, hobbies and radical physical change. Delusions of prejudice and self-referential delusions. Possible phenomena of echo and diffusion of the thought. Auditory hallucinations talking to her in male gender, since then she presents doubts about her sexual identity and manifests her desire to change sex. Altered judgment of reality.Results During admission, we started treatment with an antipsychotic with good tolerance and she was referred to mental health team, where psychopharmacological treatment was adjusted with good response. In the following medical appointments the psychotic clinic disappeared at the same time that sexual identification was completely restored and made a critique of the behavior and experiences.ConclusionsThis case highlights the importance of assessing the chronology of symptoms, the patient’s criticality, the response to antipsychotic treatment and the need to exclude the psychotic background of the desire for gender reassignment before making a therapeutic decision.DisclosureNo significant relationships.

Drug Carriers: A Review on the Most Used Mathematical Models for Drug Release

Carriers are protective transporters of drugs to target cells, facilitating therapy under each points of view, such as fast healing, reducing infective phenomena, and curing illnesses while avoiding side effects. Over the last 60 years, several scientists have studied drug carrier properties, trying to adapt them to the release environment. Drug/Carrier interaction phenomena have been deeply studied, and the release kinetics have been modeled according to the occurring phenomena involved in the system. It is not easy to define models’ advantages and disadvantages, since each of them may fit in a specific situation, considering material interactions, diffusion and erosion phenomena, and, no less important, the behavior of receiving medium. This work represents a critical review on main mathematical models concerning their dependency on physical, chemical, empirical, or semi-empirical variables. A quantitative representation of release profiles has been shown for the most representative models. A final critical comment on the applicability of these models has been presented at the end. A mathematical approach to this topic may help students and researchers approach the wide panorama of models that exist in literature and have been optimized over time. This models list could be of practical inspiration for the development of researchers’ own new models or for the application of proper modifications, with the introduction of new variable dependency.

Diffusion in large networks

We investigate the phenomenon of diffusion in a countably infinite society of individuals interacting with their neighbors in a network. At a given time, each individual is either active or inactive. The diffusion is driven by two characteristics: the network structure and the diffusion mechanism represented by an aggregation function. We distinguish between two diffusion mechanisms (probabilistic, deterministic) and focus on two types of aggregation functions (strict, Boolean). Under strict aggregation functions, polarization of the society cannot happen, and its state evolves towards a mixture of infinitely many active and infinitely many inactive agents, or towards a homogeneous society. Under Boolean aggregation functions, the diffusion process becomes deterministic and the contagion model of Morris (2000) becomes a particular case of our framework. Polarization can then happen. Our dynamics also allows for cycles in both cases. The network structure is not relevant for these questions, but is important for establishing irreducibility, at the price of a richness assumption: the network should contain at least one complex star and have enough space for storing local configurations. Our model can be given a game-theoretic interpretation via a local coordination game, where each player would apply a best-response strategy in a random neighborhood.

From characteristic response to target edge diffusion: An approach to small infrared target detection

Small Infrared (IR) target detection plays an important role in flight guidance and target early warning. Most existing solutions we call local contrast (LC) based methods utilize the local contrast between the targets and the background to detect small infrared targets. This paper designs a characteristic response curve (CRC) to demonstrate characteristics of LC-based methods and proposes a multi-scale target edge diffusion model (M-TED) for small infrared target detection. First, considering the edge diffusion phenomenon on small infrared targets, the transition region is integrated with the target and the background regions to measure local contrast. In addition, global information can be used to suppress the background. Next, a customized multi-scale strategy based on the CRC is applied to generate an appropriate response map. Finally, small targets are detected via segmentation of the response map. Experiments show that the CRC-customized multi-scale strategy can significantly improve LC-based methods’ performance and our M-TED performs best on various evaluations.

Proses difusi relativistik melalui persamaan langevin dan fokker-planck

Brownian motion theory is always challenging how to describe diffusion phenomena with the main issue is how to extend the classical theory of Brownian motion to the special relativity framework. In this study, we formulated dynamics and distribution of a Brownian particle in relativistic framework by using Langevin and Fokker-Planck equation. By representing Brownian particle dynamics by Langevin equation, the velocity curves were dependent on the presence of viscous friction coefficient (heat bath), and were used generalized in special relativity theory, A relativistic Langevin equation reduces to the classical theory at low velocities. Likewise, the distribution of Brownian particles is represented as a stationary solution of the relativistic Fokker-Planck equation. From numerical results, we found that the probability density in the relativistic Fokker-Planck equation for was reduced to the standard Fokker-Planck equation in Netownian classical theory. For the calculation result showed that the Hanggi-Klimontovich approach has a consistent result to the relativistic Maxwell distribution. This work could open a promising interpretation to formulate the diffusion phenomena into general relativity theory.

On the thermal stability and oxidation resistance of Zr/X(Cr, Ni, Si) multilayer structure

The application of multilayer coatings in the field of nuclear-grade zirconium alloy protection has attracted much attention. However, the phenomenon of element diffusion between layers at high temperature has not been systematically studied. In this work, by selecting specific elements X (Cr, Ni, Si), the stability and oxygen barrier properties of the multilayer film coupled with Zr layer were investigated. The key characteristic indicators were clarified, including grain boundary effect, oxygen diffusion coefficient and Zr/X inter-diffusion ability. Zr/Si multilayer system outstripped others with excellent oxidation resistance, and only the surface Zr layer was completely oxidized at both 400 °C and 700 °C in air. At hot steam environment of 400 °C/10.3 MPa, the formation of a thin amorphous Zr-Si-O layer and an amorphous silicon oxide layer guarantee good oxygen barrier effect and greatly reduce the oxygen partial pressure at oxidation front.

Coherent Hole Transport in Selective Area Grown Ge Nanowire Networks.

Holes in germanium nanowires have emerged as a realistic platform for quantum computing based on spin qubit logic. On top of the large spin–orbit coupling that allows fast qubit operation, nanowire geometry and orientation can be tuned to cancel out charge noise and hyperfine interaction. Here, we demonstrate a scalable approach to synthesize and organize Ge nanowires on silicon (100)-oriented substrates. Germanium nanowire networks are obtained by selectively growing on nanopatterned slits in a metalorganic vapor phase epitaxy system. Low-temperature electronic transport measurements are performed on nanowire Hall bar devices revealing high hole doping of ∼1018 cm–3 and mean free path of ∼10 nm. Quantum diffusive transport phenomena, universal conductance fluctuations, and weak antilocalization are revealed through magneto transport measurements yielding a coherence and a spin–orbit length of the order of 100 and 10 nm, respectively.

Experimental study of turbulent thermal diffusion of particles in inhomogeneous and anisotropic turbulence

We experimentally studied the turbulent thermal diffusion of small particles in inhomogeneous and anisotropic stably stratified turbulence produced by one oscillating grid in the air flow. The velocity fields have been measured using Particle Image Velocimetry (PIV). We have determined various turbulence characteristics: the mean and turbulent velocities, two-point correlation functions of the velocity field, and an integral scale of turbulence from the measured velocity fields. The temperature field has been measured with a temperature probe equipped with 12 E thermocouples. Spatial distributions of micrometer-sized particles have been determined by a PIV system using the effect of the Mie light scattering by particles in the flow. The experiments have demonstrated that particles are accumulated at the minimum of mean fluid temperature due to the phenomenon of turbulent thermal diffusion. Using measured spatial distributions of particles and temperature fields, we have determined the effective turbulent thermal diffusion coefficient of particles in inhomogeneous temperature-stratified turbulence. This experimental study has clearly detected the phenomenon of turbulent thermal diffusion in inhomogeneous turbulence.

Systematic Analysis and Characterization of Extreme Failure for IGCT in MMC-HVdc System—Part II: Failure Mechanism and Short Circuit Characteristics

Short circuit failure mode (SCFM) of integrated gate commutated thyristor (IGCT) under extreme failure is of vital importance in high voltage direct current power transmission based on modular multilevel converter technology. Due to the sealing housing package of IGCT, the short circuit mechanism is hard to be clarified. Considering this limitation, the current density changes in IGCT with different failure modes are studied under different current levels in a built integrated test system with the placed magnetic sensor array and thermal couple array. Then, the short circuit mechanism of failed IGCT is proposed based on the experimental results. IGCT with turn-<small>off</small> failure performs self-triggering effect due to the focused short current and increased temperature in the initial destruction area, which is usually located in a single position of the outer cathode rings. While IGCT with surge current failure shares the short current among multiple initial destruction areas, which are usually distributed evenly in the wafer area. Scanning electron microscope picture and energy dispersive X-Ray spectroscopy (EDX) analysis show that the formed conducting alloy has spread into the molybdenum plate deeply and the phenomenon of atom diffusion (molybdenum, silicon and aluminum) near the interface is observed. Finally, long term short circuit tests of more than 12&#x00A0;h with both turn-<small>off</small> failure and surge current failure under 3000&#x00A0;A prove the stable SCFM of IGCT.

Modeling particulate pollutants dispersed in the atmosphere using fractional turbulent diffusion

Dispersion of particulate matter from natural or anthropogenic sources into the atmosphere, such as that produced by volcanoes, fires, or industries, often causes severe damages. In particular, fine-sized particles are a serious threat to human health. Therefore, it is important to identify them and evaluate their concentration. This paper aims to quantify the finest-grained ash concentration of a volcanic eruption using a turbulent diffusion model. A stationary regime at some distance from the eruption is considered and axial symmetry is assumed, with the axis in the direction of the wind, neglecting gravitational effects. To account for anomalous diffusion phenomena due to heterogeneities and/or turbulence in the medium where fine particles are dispersed, one of the derivatives in the radial direction is replaced by a fractional derivative of Caputo type. We find approximate analytical solutions in cylindrical coordinates by the Adomian Decomposition Method and compare them with solutions obtained using a numerical scheme. The analytical concentration profiles obtained are successfully compared with satellite images of a real plume originating in an explosive volcanic eruption. We have found that the concentration components depend on a parameter that seems to be directly related to particle size.

A Multi-Scale Entropy Approach to Study Collapse and Anomalous Diffusion in Shared Mobility Systems.

In this paper, we study the phenomena of collapse and anomalous diffusion in shared mobility systems. In particular, we focus on a fleet of vehicles moving through a stations network and analyse the effect of self-journeys in system stability, using a mathematical simplex under stochastic flows. With a birth-death process approach, we find analytical upper bounds for random walk and we monitor how the system collapses by super diffusing under different randomization conditions. Using the multi-scale entropy metric, we show that real data from a bike-sharing fleet in the city of Salamanca (Spain) present a complex behaviour with more of a signal than a disorganized system with a white noise signal.

Review of calculating models of unsteady natural ventilation rate due to wind fluctuations

Natural ventilation is an important form of sustainable building technique that can be used to adjust the indoor environment to ensure indoor thermal comfort and maintain acceptable indoor air quality. Correct estimation of the ventilation rate is a necessary step in natural ventilation design. Natural wind fluctuation and interaction between the wind and buildings determine models of mean flow rate inaccuracy in predicting actual ventilation. In this paper, a summary of calculation models for unsteady natural ventilation is given. Unsteady natural ventilation mechanisms are classified into continuous airflow, pulsating flow, eddy penetration and diffusion phenomena. The theories of different ventilation mechanisms and the differences between various research reports are expounded and discussed. Additionally, an in-situ measurement of the eddy penetration caused by wind turbulence at the opening was conducted to verify the proposed model. The actual application condition of different eddy penetration models is proposed via the comparison between previous models. With respect to the ‘pumping’ mechanism, this is regarded as a special type of eddy penetration for the first time. Research on ‘pumping’ airflow has just started, the mechanism and influencing factors of which will need to be further explored.

Computational Methods for Parameter Identification in 2D Fractional System with Riemann-Liouville Derivative.

In recent times, many different types of systems have been based on fractional derivatives. Thanks to this type of derivatives, it is possible to model certain phenomena in a more precise and desirable way. This article presents a system consisting of a two-dimensional fractional differential equation with the Riemann–Liouville derivative with a numerical algorithm for its solution. The presented algorithm uses the alternating direction implicit method (ADIM). Further, the algorithm for solving the inverse problem consisting of the determination of unknown parameters of the model is also described. For this purpose, the objective function was minimized using the ant algorithm and the Hooke–Jeeves method. Inverse problems with fractional derivatives are important in many engineering applications, such as modeling the phenomenon of anomalous diffusion, designing electrical circuits with a supercapacitor, and application of fractional-order control theory. This paper presents a numerical example illustrating the effectiveness and accuracy of the described methods. The introduction of the example made possible a comparison of the methods of searching for the minimum of the objective function. The presented algorithms can be used as a tool for parameter training in artificial neural networks.

Mathematical modeling of concentration/ time-activity profiles of radiotracers in positron emission tomography

ABSTRACT As an advancement in medical sciences, radioactive tracers are used in nuclear medicine, not only to understand the flow process and to make optimal diagnosis but also for staging, monitoring and evaluation of response to therapy. To this outlook, four mathematical models are devised to study the diffusion phenomena and kinetics of radiotracers injected intravenously into the bloodstream of the human body. The models are developed with the aim of studying and estimating the flow and concentration profiles of the radiotracer in biological tissues and studying the kinetics of reversible and irreversible tracers (i.e. 18F-Fludeoxyglucose), respectively. These profiles are helpful to determine the appropriate dose of the radiotracer to be administered, in positron emission tomography for the diagnostics, anticipation and treatment of various diseases. Finally, the results are simulated graphically and are also compared with the published/experimental work to check the feasibility and validity of the formulated models.

Modeling and Calibration of Active Thermal-Infrared Visual System for Industrial HMI

In the industrial application of the human-machine interface (HMI), thermal-infrared cameras can detect objects that are limited by visible-spectrum cameras. It can receive the energy radiated by a target through an infrared detector and obtain the thermal image corresponding to the heat distribution field on the target surface. Because of its special imaging principle, a thermal-infrared camera is not affected by the light source when imaging. Compared to visible-spectrum cameras, thermal imaging cameras can better detect defects with poor contrast but temperature differences or internal defects in products. Therefore, it can be used in many specific industrial inspection applications. However, thermal-infrared imaging has the phenomenon of thermal diffusion, which leads to noisy thermal infrared images and limits its applications in high precision industrial environments. In this paper, we proposed a high precision measurement system for industrial HMI based on thermal-infrared vision. The accurate measurement model of the system was established to deal with the problems caused by imaging noise. The experiments conducted suggest that the proposed model and calibration method is valid for the active thermal-infrared visual system and achieves high precision measurements.

Radical Diffusion Crossover Phenomenon in Glass-Forming Liquids.

We studied the diffusivities of a nitroxide radical at various temperatures in six glass-forming molecular liquids by electron spin resonance. By comparing the radical diffusivities and solvent self-diffusivities, we found that the radical diffusivities are lower than the self-diffusivities at high temperatures and approach them at low temperatures in all liquids. This crossover behavior was considered as evidence that a single-molecule diffusion process transforms into a collective process with temperature lowering. The crossover phenomenon was analyzed by a novel, simple diffusion model, combining collective and single-molecule diffusion processes, and it was compared to the Arrhenius crossover phenomenon. The obtained results suggest that future studies of tracer diffusion could contribute to a better understanding of diffusion mechanisms in glass-forming liquids. The proposed diffusion model could be used to study the crossover phenomena of tracer diffusion measured by other techniques, and it could serve as a base for developing more advanced models.

Ceramic-glass pellet thickness and Li diffusion in NASICON-type LAGP (Li1.5Al0.5Ge1.5(PO4)3) studied by pulsed field gradient NMR spectroscopy

LAGP (Li1.5Al0.5Ge1.5(PO4)3) is one of inorganic solid electrolytes (ISEs) and is relatively stable against atmospheric CO2 and H2O. Five LAGP pellet samples with thicknesses ranging from 0.5 to 4 mm (10−3 m) were investigated by pulsed field gradient (PFG) 7Li NMR spectroscopy. PFG was applied in the thickness direction and the Li diffusion in the same direction was observed. The apparent diffusion coefficients (Dapparent) of Li were determined over the observation time (Δ) ranging from 5 to 100 × 10−3 s and the distances from 0.1 to 1 × 10−6 m. The Dapparent of LAGP samples was 10−11 to 10−13 m2s−1 at 28 °C. The results showed that the Li diffusion phenomenon was thickness dependent. When Δ was short, diffusion of Li was slower for thinner samples, suggesting that the Li pathway was made to avoid surface boundaries. The Li ions were found to diffuse through preferential and longer paths of the pellet samples. As Δ became longer, the diffusion process of Li averaged out and the diffusion coefficient converged to a constant value regardless of the thickness. The PFG-NMR observes a diffusion coefficient of 7Li species which are marked by the first PFG and detected by the second PFG after Δ. Impedance spectroscopy, on the other hand, measures the ionic conductivity for continuous charge transfer between electrodes under electric field, and higher ionic conductivities have been reported for thinner samples.

A Comparative Evaluation of Sustained Release of Chlorphenamine Based on a Nanocomposite of Chitosan, Pectin and Montmorillonite

AbstractThe scenario of the current investigation is to prepare an inclusion complex (IC) of chlorphenamine (CPM) and montmorillonite (MONT) by microwave method for sustained drug delivery system and to analyze the comparison of inclusion complex with direct loading of free drug. A nanocomposite was synthesized from chitosan (CH), pectin (PC) by incorporating montmorillonite (MONT). The confirmation of inclusion complex formation and nanocomposite was characterized by FTIR, XRD, and FESEM‐EDS. Drug release study from chitosan, pectin nanocomposite containing free CPM and inclusion complex of CPM: MONT were investigated under different pH 2, 7 and 7.4 at 37 °C. The concentration of drug release from inclusion complex loaded nanocomposite was found to be 97.4 % in 22 hours. Four different kinetic models were studied to check the real mechanism involved in drug release. In all cases, the best fitted kinetic model for CPM release from the inclusion complex loaded nanocomposite was Peppas‐Sahlin and Korsmeyer Peppas, implying that diffusion and relaxation phenomena were responsible for the drug release. Diffusion phenomena have more contribution than relaxation is confirmed by the Peppas‐Sahlin equation. Montmorillonite is responsible for the sustained drug release because of host‐guest interactions. Montmorillonite has a layered structure that allows it to intercalate the drug molecule into its cavity, resulting in sustained chlorphenamine release.