Diffusion Mode Research Articles

A novel bidisperse diffusion model for coal particles considering micropores as the major sites of CH4 adsorption

Pores in coal have the characteristic of double peaks, and the bidisperse diffusion model is an effective method to describe the diffusion behavior in coal. At present, the traditional bidisperse diffusion models can be divided into “independent” mode and “dependent” mode, which have three main deficiencies as follows. Firstly, since the percentage of adsorbed CH4 in micropores or macropores cannot be accurately determined, the bidisperse diffusion model consists of two equations with three unknown parameters. It is impossible to get a unique solution only based on satisfying a high R2, which brings uncertainty to the solution of the model. Secondly, the ratio of macropore adsorption mass to the total adsorption mass β in some cases shows that CH4 is mainly stored in macropores, which is inconsistent with the physical phenomenon. Thirdly, the independent model is based on the assumption that the macropore diffusion and micropore diffusion are separate from each other, which is not consistent with the pore structure characteristics of coal. To solve the above problems, we put forward a novel two-stage diffusion mode via insightful analysis of the CH4 adsorption form, and the newly-established bidisperse diffusion model can better describe the CH4 diffusion behavior in coal. By using the novel model to analysis the CH4 diffusion behavior, we obtained the following results: (1) The CH4 adsorption form presents the characteristics of micropore filling and a monomolecular layer adsorption. Micropores are the main sites of CH4 adsorption. This adsorption form makes the desorption and diffusion resistance of CH4 vary in different pores, which leads to the CH4 source dynamic evolution during diffusion. (2) The novel model has been proved by experimental validation to have good applicability and can accurately describe the whole process of CH4 diffusion. Meanwhile, the obtained parameters by the new model not only with clear physical significance but also can explain the adsorption-diffusion mechanism of CH4 in multi-scale pores. (3) The traditional dependent model may degenerate into the unipore diffusion model under the condition of satisfying the CH4 occurrence characteristics and fitting accuracy, which results in losing the physical significance of the bidisperse diffusion model.

Guiding effect of runaway electrons in atmospheric pressure nanosecond pulsed discharge: mode transition from diffuse discharge to streamer

In this study, the role of runaway electrons (RAEs) during the pulsed breakdown in the atmosphere is investigated. Nanosecond pulsed discharge (NPD) is driven by high-voltage pulses between blade-to-plate electrodes (with the blade as the cathode). RAEs with an energy higher than 10 keV are selected by a titanium foil with a thickness of 1 μm and detected by a beam collector with a front of about 50 ps. The temporal-spatial evolution of the electric field over the NPD period is measured using electric field induced second harmonic method adopting a picosecond pulsed laser. It is verified that the current amplitude of RAEs decreases drastically with the voltage amplitude V p and the peak electric field at the front of the ionization wave formed during the breakdown of NPD plays a key role in maintaining the runaway state of electrons. With single-shot discharge imaging, it is observed that the discharge is initially in a diffuse mode near the cathode, while it branches and transits into streamers, which can be either synchronously propagating multi streamers (with a high V p) or certain dominant streamers (with a low V p). Using particle-in-cell Monte-Carlo collision simulation, a similar mode transition of diffuse to streamer is observed with RAEs emitted from the cathode and it is illustrated that the flux of RAEs controls the pre-ionization degree and further dictates branching and non-uniformity of discharge, which qualitatively explains the experimental observation. It is proposed that an enhanced RAEs emission would produce a large volume diffuse discharge at atmospheric pressure.

Permeation-diffusion characteristics and air-leakage blocking mechanism for the fire-extinguishing inorganic gel flows in loose broken coal particles

• Three various stages of gel slurry transports in loose coal particles were acquired experimentally and numerically. • Investigated the influence of grouting pressure and coal voids on permeation, diffusion, and filtration of gel. • Theoretically revealed the mechanisms for permeation-diffusion and wind-plugging of gel. Fire prevention with inorganic gel is the most efficient approach to the prevention and control for spontaneous fires of loose coal piles. This work explores the impact of grouting pressures on the seepage, diffusion, and filtration of fire-extinguishing inorganic gel in loose broken coal particles with different voids. Firstly, an experimental system for investigating the filtering effect, permeation behaviors, and diffusion modes for the permeation grouting of inorganic gel in loose coal particles was developed. A 2D discrete element numerical modeling was then performed to probe the intuitive features and underlying mechanisms in the experimental observation, with the numerical modeling matching fairly well with the experimental findings. Results showed that the entire permeation-diffusion process presents obvious stage characteristics with permeation-compaction, permeation-splitting flow, compacting-splitting flow-permeation, and the diffusion distance of gel slurry front increased exponentially while the diffusion velocity decreased initially and then retained stable gradually. Meanwhile, the permeability coefficient of gel slurry showed spatial–temporal properties affected by the filtration effect. Besides, the increasing grouting pressure would promote the filtration effect of gel slurry in loose coal particles, while the decreasing coal sample voids pose an opposite tendency. Under lower grouting pressures (P ≤ 0.3 MPa), the bubble radius increased slightly, and the variation in diffusion distance was faint with the increase in grouting pressure. Under higher grouting pressures (P ≥ 0.3 MPa), the bubble radius increased obviously, and the variation in diffusion distance increased obviously with the increase in grouting pressure, demonstrating that increasing grouting pressure would increase the diffusion distance and diffusion velocity significantly. In addition, increasing the gel grouting pressure and coal voids would result in a non-linear increase in the diffusion distance and diffusion velocity of the gel slurry front, which would also shorten the time required for coal particles to reach the saturation state. Moreover, the mechanisms of seepage-diffusion and wind-plugging of gel slurry in loose coal particles were discussed theoretically. This work would assist us in interpreting and illuminating the seepage-diffusion mechanism and macro–micro characteristics of inorganic gel for high-temperature loose broken coal particles.

Relativistic viscous hydrodynamics with angular momentum

Hydrodynamics is a general theoretical framework for describing the long-time large-distance behaviors of various macroscopic physical systems, with its equations based on conservation laws such as energy-momentum conservation and charge conservation. Recently there has been significant interest in understanding the implications of angular momentum conservation for a corresponding hydrodynamic theory. In this work, we examine the key conceptual issues for such a theory in the relativistic regime where the orbital and spin components get entangled. We derive the equations for relativistic viscous hydrodynamics with angular momentum through Navier-Stokes type of gradient expansion analysis and find five new transport coefficients for angular momentum diffusion modes.

Abnormal phase evolution and degradation behavior of Al-Si coating during 30,000 h aging

Degradation behavior of silicon-modified aluminide coating over 30,000 h aging at 650 ℃ was investigated. Significant microstructural evolutions, abnormal elemental distribution and newly-formed secondary internal oxides were observed after prolonged aging. As the aging time extended from 10,000 h to more than 20,000 h, interdiffusion induced the formation of α-Fe/AlNi/α-Fe structure, while the AlNi precipitates gradually replaced the Fe-rich matrix by acting as Al source for the formation of surface alumina scale. Based on the microstructural evolutions, a new regime of coating degradation involving both the transitions of diffusion mode and oxidation mechanism is proposed.

Genome-wide identification and functional analysis of silicon transporter family genes in moso bamboo (Phyllostachys edulis)

Silicon (Si) has crucial effects on plant development and stress resistance. Silicon transporters regulate Si absorption, transport, and distribution in plants. In this study, we identified and characterized the Si transporter gene family of moso bamboo (Phyllostachys edulis) and cloned seven putative Si transporter genes. Moso bamboo Si transporters contain conserved functional domains that mediate the accumulation of considerable amounts of Si. The analysis of gene duplication patterns and divergence times suggested that the expansion of the moso bamboo Si transporter family was mainly due to segmental duplications. The expression of moso bamboo Si transporter genes, which varied among organs, was significantly modulated by Si treatments. The subcellular localization analysis showed that Si transporters are plasma membrane proteins. The Si content increased in transgenic Arabidopsis overexpressing PeLsi1-1 or PeLsi1-2, which affected vegetative and reproductive growth. Our single-particle tracking analysis revealed the four diffusion modes of PeLsi1-1 on the plasma membrane. Moreover, the particle velocity, dwell time, and motion range of PeLsi1-1 decreased in response to Si treatments. The results of this study will further clarify the molecular mechanisms underlying Si absorption and accumulation in bamboo plants.

Neutron scattering studies on ionic diffusion behaviors of superionic α-Cu2−δ Se

We present studies on crystal structure and ionic diffusion behaviors of superionic Cu2−δ Se (δ = 0, 0.04, and 0.2) by utilizing neutron powder diffraction and quasi-elastic neutron scattering. In the superionic phase, the structural model with Cu ions occupying the Wyckoff sites of 8c and 32f provides the best description of the structure. As the content of Cu increasing in Cu2−δ Se, the Cu occupancy increases on the 32f site but decreases on the 8c site. Fitting to the quasi-elastic neutron scattering spectra reveals two diffusion modes: the localized diffusion between the 8c and 32f sites and the long-range diffusion between the adjacent 8c sites using the 32f site as a bypass. Between 430 and 650 K, we measured that the compound with more Cu content exhibits a larger long-range diffusion coefficient. Temperature in this range does not affect the long-range diffusion process obviously. Our results suggest the two diffusion modes cooperative and, thus, provide a microscopic understanding of the ionic diffusion of the Cu ions in superionic Cu2−δ Se.

A molecular dynamics study of evaporation mode transition of hydrocarbon fuels under supercritical conditions

The mode transition of evaporation for single- and multi-component hydrocarbon fuels is investigated at the molecular level. This study scrutinizes first the subcritical and supercritical evaporation of n-hexadecane droplets and liquid films by molecular dynamics (MD) simulations. The mode regime map of n-hexadecane droplets is obtained. Then the mode transition of evaporation of a three-component droplet and a six-component droplet is studied. A critical dimensionless number τ0.9P of 0.5 based on the average displacement increment (ADI) of fuel atoms is used to identify the evaporation mode transition of fuels with any type and number of components. It is found that in the diffusion mode of evaporation, the entropy becomes the dominant factor in the evaporation of fuels, and the disorder of the fuel molecules increases significantly compared with that in the classic evaporation mode. Compared with the case of the quiescent droplet, with increasing relative velocity between the droplet and the ambient gas, the mode transition becomes easier, although this is a non-linear process. Fuel droplets and liquid films with different initial sizes are investigated to understand the size effect. In addition, for the same ambient temperature and pressure, the smaller the normalized specific heat transfer surface area of the fuel is, the easier the mode transition of evaporation is. A correlation was proposed to compare the possibility of mode transition of evaporation for single- and multi-component fuels.

Cyclic cystine knot and its strong implication on the structure and dynamics of cyclotides.

The archetypal Viola odorata cyclotide cycloviolacin-O1 and its seven analogs, created by partial or total reduction of the three native S-S linkages belonging to the "cyclic cystine knot" (CCK) motif are studied for their structural and dynamical diversities using molecular dynamics simulations. The results indicate interesting interplay between the constraints imposed by the S-S bonds on the dynamical modes and the corresponding structure of the model peptide. Principal component analysis brings out the variation in the extent of dynamical freedom along the peptide backbone for each model. The motions are characterized by low amplitude diffusive modes in the peptides retaining most of the native S-S linkages in contrast to the large amplitude discrete jumps where at least two or all of the three S-S linkages are reduced. Simulation results further indicate that the disulfide bond between Cys1-18 is formed at a much faster pace compared with its two other peers Cys5-20 and Cys10-25 as found in the native peptide. This gives insight as to why the S-S linkages appear in the native peptide in a particular combination. Model therapeutics and drug delivery engines can potentially utilize this information to customize the engineered S-S bonds and gauge its impact on the dynamic flexibility of a model macrocyclic peptide.

Diffusion and memory effect in a stochastic process and the correspondence to an information propagation in a social system

A generalized Langevin equation is suggested to describe a diffusion particle system with memory. The equation can be transformed into the Fokker–Planck equation by using the Kramers–Moyal expansion. The solution of Fokker–Planck equation can describe not only the diffusion of particles but also that of opinion particles based on the similarities between the two. We find that the memory can restrain some non-equilibrium phenomena of velocity distribution in the system, without memory, induced by correlation between the noise and space (Wang et al., 2021). However, the memory can enhance the effective collision among particles as shown by the variation of diffusion coefficients, and changes the diffusion mode between the dissipative and pumping region by comparing with that in the aforementioned system without memory. As the discussions in this physical system is paralleled to a social system, the random diffusion of social ideology, such as the information propagation, can be suppressed by the correlation between the noise and space.

GhRabA4c coordinates cell elongation via regulating actin filament-dependent vesicle transport.

Plant cell expands via a tip growth or diffuse growth mode. In plants, RabA is the largest group of Rab GTPases that regulate vesicle trafficking. The functions of RabA protein in modulating polarized expansion in tip growth cells have been demonstrated. However, whether and how RabA protein functions in diffuse growth plant cells have never been explored. Here, we addressed this question by examining the role of GhRabA4c in cotton fibers. GhRabA4c was preferentially expressed in elongating fibers with its protein localized to endoplasmic reticulum and Golgi apparatus. Over- and down-expression of GhRabA4c in cotton lead to longer and shorter fibers, respectively. GhRabA4c interacted with GhACT4 to promote the assembly of actin filament to facilitate vesicle transport for cell wall synthesis. Consistently, GhRabA4c-overexpressed fibers exhibited increased content of wall components and the transcript levels of the genes responsible for the synthesis of cell wall materials. We further identified two MYB proteins that directly regulate the transcription of GhRabA4c Collectively, our data showed that GhRabA4c promotes diffused cell expansion by supporting vesicle trafficking and cell wall synthesis.

Investigation of Vacuum Arc and Erosion Characteristics of Spiral TMF Contacts With Different Materials

The transverse magnetic field (TMF) can drive the arc to rotate, to reduce the erosion of contact. In this article, TMF contacts of six commonly used materials (CuCr10, CuCr30, CuCr50, WCu10, WCu30, and CuW-WC) are investigated by experiments at the current of 5, 10, and 15 kA. Experimental results show that the contact material has a significant impact on the arc, the arc on CuCr materials rotates, and shows noisy voltage, while the arc on WCu hardly rotates and exhibits a stable arc voltage because of staying in the diffuse mode. Though the erosion of CuCr contacts is more severe than WCu contacts, the results of breaking operations also indicate that CuCr contacts outperform WCu contacts, where CuCr10 contact has a lower breaking capacity than CuCr30 and CuCr50. Moreover, the steel support disk of the interrupter contacts plays a role in the reignition of the arc after a half-cycle of current which is obvious from the erosion of the disk and from records of the arc appearance.

A comparison of benchtop and micro NIR spectrometers for infant milk formula powder storage time discrimination and particle size prediction using chemometrics and denoising methods

This study compared benchtop and micro NIR spectrometers in diffuse reflection mode (1158–2169 nm) to (i) discriminate infant milk formula (IMF) powder samples (n = 500) by storage time (0–12 months) and to (ii) predict IMF powder particle size parameters. Reference particle size parameters were determined using laser-light-scattering. Fast Fourier transform (FFT) and wavelet transform (WT) denoising methods were employed on micro NIR spectra to remove noise and enhance spectral features. Partial least square discriminant analysis (PLS-DA) and partial least squares regression (PLSR) modelling approaches were used to discriminate IMF by storage time and predict powder particle size, respectively. The models developed using the micro NIR denoised spectra had correct identifications (CI p ) of 89–100% for IMF storage time discrimination and RPDPs of 2.29–2.98 for particle size prediction, which were comparable to the model performances achieved using the benchtop NIR spectra (CI p values of 81.3–100% for IMF storage time discrimination and RPDPs of 2.08–3.07 for particle size prediction). This study demonstrated that the potential of micro NIR spectroscopy combined with chemometrics and denoising methods as a suitable process analytical technology (PAT) tool for IMF powder storage time discrimination and particle size prediction along the IMF distribution chain from production to consumer. • Benchtop and micro NIR models can assess IMF powder storage time and particle size. • IMF powder storage time was discriminated using PLS-DA modelling. • IMF powder particle size was predicted using PLSR modelling. • FFT and WT denoising methods are suitable to remove micro NIR spectral noise. • Micro NIR models had overall better performance than benchtop NIR models.

Real-time measuring energy characteristics of cane bagasse using NIR spectroscopy

Online measurement of moisture content (MC) and higher heating value (HHV) is desired for supporting the thermal conversion process in power plants. The main objective of this study was to develop a reliable and accurate method for online measuring of the HHV and MC of dried and as received sugarcane bagasse, respectively, using near-infrared (NIR) spectroscopy. Simulation of the conveyor belt in power plants and online energy quality analysis of bagasse for combustion process were designed. One hundred samples of bagasse were collected from different sugar mills at various locations of large piles of bagasse stored in both indoor and outdoor buildings. A long-wave spectrometer with a wavelength range of 860–1755 nm was used for scanning using diffuse reflection mode. The models were developed by partial least squares (PLS) regression using spectral sets obtained from the raw spectra, the preprocessed full spectra from the traditional approach, and the preprocessed spectra from the multi-block technique. The multi-blocks of the spectral pre-treatment technique provided effective models for both MC and HHV prediction. The best model for MC had a coefficient of determination of prediction (R2p) and the root mean square error of prediction (RMSEP) of 0.90 and 3.9% wb respectively. In the meantime, the best model for HHV had R2p and the RMSEP of 0.71 and 188.7 J g−1. This research demonstrated that NIR spectroscopy provides a feasible and reliable method for online analysis of MC and could be used for screening of HHV of bagasse.

Detailed analysis of particulate emissions of a multi-cylinder dual-mode dual-fuel engine operating with diesel and gasoline

Internal combustion engines are still within the future of highway transport. Low-temperature combustion modes are prone to substitute conventional diesel combustion engines, seeking better performance and improved emissions control. The dual-mode dual-fuel combustion approach has been confirmed as a feasible combustion mode for achieving ultra-low NOx and soot emissions simultaneously. The aim of this work is to experimentally measure the particle emissions of the dual-mode dual-fuel concept while maintaining good thermal efficiency and EURO VI engine-out NOx levels. A detailed analysis of the most relevant characteristics of the particle size distribution is carried out to depict the requirements of a potential filtering system considering the effects of an upstream diesel oxidation catalyst. The results show that total particle numbering is within the typical values of the current most popular technologies: around 2·1013 #/kWh for RCCI and around 1014 #/kWh for DMDF. RCCI combustion tends to produce more particles sized below 35 nm in diameter, while DMDF shows a clear dominance of sizes above 40 nm. In terms of total particulate matter, RCCI results in total mass concentrations around 4 mg/kWh thanks to the highly premixed combustion, but diffusive combustion mode results in total mass emissions over 50 mg/kWh.

Radium and Lead Radioisotopes Composition of Sediment and Its Biogeochemical Implication in Polymetallic Nodule Area of Clario-Clipperton Zone.

Radioactivity levels of 210Pb and 226Ra were detected in a sediment core obtained using a multi-corer from the polymetallic nodule area inside the Clarion-Clipperton Zone (CCZ), a contract area of the China Ocean Mineral Resources Association (COMR) in the eastern Pacific Ocean. The profile of excess 210Pb (210Pbex) shows that the specific activity of 210Pbex has three parts with different distributions at depths of 0–16 cm (I), 17–36 cm (II), and 37–48 cm (III). When the I section of nonlocal mixing was excluded, using a steady-state diffusion mode, the bioturbation coefficients of the core were estimated to be 24.2 cm2/a at 17–36 cm deep and 5.9 cm2/a at 37–48 cm deep, which were greater compared to previously published results. This is most likely owing to bioturbations caused by various organism species in the two sections.

Numerical and experimental study of diffusion law of foamed polymer grout in fracture considering viscosity variation of slurry

As a new type of chemical grouting material, polymers have been widely used in fractured rock masses, but the understanding of the diffusion characteristics of polymers still needs to be further improved. Due to the expansion of polymer slurry, the change of grouting pressure is not synchronized with the time change of diffusion radius, leading to the diffusion law of polymer slurry more complicated. Therefore, based on the rheological properties of the slurry and the theory of viscous hydrodynamics, a polymer fracture grouting diffusion model was established. Through the finite element level set method and adjusting the liquid level according to the fluid velocity, it can be obtained the diffusion interface of the fluid at the corresponding point in time and the change law of the pressure at the corresponding diffusion interface with time. Finally, the validity of the model is verified by the polymer slurry parallel plate grouting diffusion experiment. The research results indicated that: (1) The diffusion mode of the polymer fracture grouting diffusion model is basically consistent with the test results. (2) The grouting pressure gradually decreases along the direction of the diffusion radius, increases with the decrease of the crack width, and increases with the time, but the change of the grouting pressure lags behind the change of the diffusion radius. (3) The results are consistent with the pressure field curve measured by the experiment, indicating that the main factor causing the hysteresis effect of the pressure field change is the time-varying viscosity of the polymer slurry.

Diffuse reflectance mid infra-red spectroscopy combined with machine learning algorithms can differentiate spectral signatures in shallow and deeper soils for the prediction of pH and organic matter content

Precision and sustainable agriculture requires information about soil pH and organic matter (OM) content at higher spatial and temporal scales than current agronomic sampling and analytical methods allow. This study examined the accuracy of spectral models using high throughput screening (HTS) in diffuse reflectance mode in mid Infra-red (MIR)/DRIFT combined with machine learning algorithms to predict soil pH(CaCl2) and %OM in shallow and deeper topsoils compared to laboratory methods. Models were developed from an archive of samples taken on a 4 km2 grid from the northern half of Ireland (Terra Soil project), which includes 18,859 samples (9,396 shallow + 9,463 deeper). The application of Cubist models showed that for different depths there are minor different spectral group associations with pH and %OM values. These differences resulted in a loss of accuracy in the extrapolation of the topsoil model to predict values from deeper topsoils or vice versa. Therefore we recommend the use of samples from both depths to build a calibration model.The proposed methodology was able to determine %OM and pH using a unique multivariate regression model for both depths, with RMSEP values of 1.12 and 0.89 %; RPIQ values of 42.34 and 38.48; R2val of 0.9989 and 0.9993 for %OM determinations in shallow and deeper topsoils, respectively. For pH determinations the RMSEP values obtained were 0.25 and 0.34; RPIQ values of 6.04 and 4.94; R2val 0.9385 and 0.8954. Both regression models are classified as excellent predictions models, yielding RPIQ values >4.05 for shallow and deeper topsoils. The results demonstrated the high potential of HTS-DRIFT combined with machine learning algorithms as a rapid, accurate, and cost-effective method to build large soil spectral libraries, displaying predicted results similar to two separate soil laboratory methods (pH and LOI).

Hierarchy and diffusion of organizational forms.

In this paper we first of all summarize and rationalize current typologies of organizational forms, arranging available classifications in a hierarchy of increasing generality. The ensuing structure parallels the classification of living beings into classes of increasing generality such as species, genus, family, order, and so on. Subsequently, we analyze the structure of communications that favored the diffusion of each organizational form. We isolate a few stylized communication structures, pointing to the presence of several sources endowed with global connections as the most efficient diffusion mode. The empirical research that is being carried out on single organizations is close to observing their T-patterns, whereas nothing comparable is in sight for organizational forms as yet. However, at least in some cases, we dare to formulate tentative hypotheses on certain features that the ensuing T-patterns-of-patterns might exhibit.

A molecular dynamics study of evaporation of multicomponent stationary and moving fuel droplets in multicomponent ambient gases under supercritical conditions

The evaporation of a six-component fuel droplet under supercritical conditions is investigated using molecular dynamics (MD) simulations. The focus here is on effects of multicomponent ambient gases and the relative motion between the droplet and the ambient. The ambient pressure ranges from 8 MPa to 36 MPa and the ambient temperature ranges from 750 K to 3600 K. In the lower range of the temperature and pressure, the average displacement increment (ADI) per fuel atom gradually increases with time and the classic evaporation is observed. In the higher range of the temperature and pressure, the ADI profile has a unimodal distribution with time and the diffusive mixing between the droplet and the ambient gases dominates. Based on the ADI profile of fuel atoms, a criterion (τ0.9P) for mode transition from evaporation to diffusion is proposed. Among the ambient gases investigated, the mode transition is the most difficult in the nitrogen ambient but the easiest in combustion exhaust gases. For multicomponent fuel droplets close to or in diffusion mode, with higher relative velocities, the relative difference between evaporation rates for light/heavy fuel components is reduced. This study demonstrates that supercritical conditions alone are insufficient for mode transition of evaporation.