Concentration Decay Research Articles

Application of Hausdorff fractal derivative to the determination of the vertical sediment concentration distribution

The Rouse formula and its variants have been widely used to calculate the steady-state vertical concentration distribution for suspended sediment in steady sediment-laden flows, where the diffusive flux is assumed to be Fickian. Turbulent flow, however, exhibits fractal properties, leading to non-Fickian diffusive flux for sediment particles. To characterize non-Fickian dynamics of suspended sediment, the current study proposes a Hausdorff fractal derivative based advection-dispersion equation (HADE) model, where the Fickian diffusive flux in the Rouse model is replaced by a fractal derivative re-scaled using a constant diffusivity. The order of the Hausdorff fractal derivative is designed to characterize the influence of the multi-fractal turbulence structure on sediment diffusion. Applications show that the HADE model, with the analytical solution expressed using a stretched exponential function, can accurately describe the observed vertical concentration profiles for suspended sediment with different sizes. This improvement well captures the non-exponential decay of the vertical sediment concentration in turbulent flow. Further analyses of measured sediment concentration profiles reveal that the Hausdorff fractal order decreases with the Rouse parameter, which describes the stronger impact of turbulent flow and a more uniform sediment concentration profile for smaller particles. Model comparisons also show that the HADE model provides better performance in describing the sediment concentration profiles than the improved Rouse formula and the standard fractional derivative advection-dispersion equation (FADE), which either under- or over-estimates vertical displacement of sediment particles, likely due to coherent turbulent structures.

Relationship of carbon concentration and slow decays of photoluminescence in homoepitaxial n-type GaN layers

In this study, we analyzed the slow decay in time-resolved photoluminescence (TR-PL) of n-type GaN homoepitaxial layers with carbon concentrations of (0.26–4.0) × 1016 cm−3. The relative signal intensities of the slow decays to the TR-PL signals at t = 0 s increased almost linearly with increased carbon concentration, suggesting that the carrier recombination process is subjected to the deep level formed by the carbon atoms in GaN. Slow decay curves were calculated based on the rate equations for trapping and emission at the deep level. The experimental carbon concentration dependence of the time constants and the relative signal intensities was reproduced by calculation. TR-PL is a technique used to estimate carbon concentrations in GaN homoepitaxial layers.

Experimental study of flow and mass transport in the near-wake region of a rigid planar metal net panel

Aquaculture cages constructed from rigid material have become increasingly popular in recent years due in part to the continuous expansion of the aquaculture industry offshore, where cages need to withstand much harsher ocean conditions. Most previous studies of hydrodynamic interactions with aquaculture cages have explored the impacts of more traditional flexible cage net panels on wake flow fields and mass transport properties. In the current experimental study, Particle Image Velocimetry and Planar Laser Induced Fluorescence techniques were used to measure flow and concentration fields in the near wake region of a steady current through a rigid metal net panel to analyze both the flow patterns and mass transport processes. The results indicated that, similar to a flexible polyethylene net panel, the time-average velocities and turbulence characteristics in the near wake region were highly inhomogeneous and anisotropic, with the turbulent intensity following a short-range, power-law decay downstream of the panel. In direct comparison with a flexible net panel of similar net solidity, the rigid net panel was found to slightly enhance the lateral spreading of the plume, with cross-sectional profiles of the mean concentration and concentration fluctuation shown to exhibit self-similar Gaussian distributions. The rigid net panel also resulted in a lower flow blockage, as measured by a velocity reduction coefficient, with the corresponding turbulent intensity also reduced compared to the flexible panel due to an overall reduction in the drag force. In addition, the rigid panel tended to create larger wake eddies than the flexible panel, leading to enhanced scalar mixing and, hence, faster rates of concentration decay in the near-wake region. These experimental findings have potential implications for cage-based aquaculture operations, where rigid fish cages are comparatively more likely to generate favorable environments for fish growth, as well as helping to reduce negative impacts on the surrounding aquatic environment.

Numerical study of particle spatial distribution under column attachment ventilation

Column attachment ventilation mode (CAV) is a new form of air distribution based on pillars widely distributed in buildings and uses the column-based Coanda effect to efficiently transport the supply air from the top of the room to the lower occupied zone. Since CAV is essentially a down-supply ventilation mode, it may lead to the resuspension of particulate matter (PM). In this study, considering the pollutant particle size, air supply velocity (u0), and air supply temperature difference (ΔT) (including cooling and heating conditions), a numerical simulation method was used to study the PM movement and diffusion characteristics. The results indicated that the particles (<20 μm) could be suspended and carried by the airflow and have good airflow followability. The particles of 50–100 μm were mainly deposited in the airflow intersection zone. 21% of the particles can be blown up by the airflow and finally discharged through the air exhaust outlets. The concentration decay of PM 2.5 in the vertical direction decreased linearly with u0. The air supply temperature difference (ΔT) did not affect the indoor PM distribution in cooling conditions but significantly affected the heating conditions. In this study, the indoor PM concentration exceeded the Chinese standard threshold of 35 μg/m3, when the air supply temperature difference was 10 K. In the CAV mode, the airflow intersection zone between the two columns showed a larger PM mass concentration. The results of this study proved that the CAV mode can provide suitable IAQ under reasonable design parameters.

Experimental investigation of hydrogen dispersion characteristics with liquid helium spills in moist air

As green energy, Liquid hydrogen promises to be widely used in the future. However, its security issue has become a great concern because liquid hydrogen will quickly form a low-temperature, flammable, and explosive vapor cloud when leaking or spilling occurs. In this work, liquid helium spilling experiments were designed and performed to predict the dispersion characteristics of liquid hydrogen in confined space with controlled and comparable boundary conditions. The concentration cloud and the infrared cloud images near the liquid helium pool were obtained at the same time. Results show that the air humidity has an impact on the vapor cloud temperature change, i.e., every 10% increase in air humidity will lead to a 5 ℃-temperature increase. The presence of high air humidity increases the vapor cloud buoyancy and promotes the cloud's dispersion in the vertical direction. The visible range of the helium vapor cloud is much smaller than the measured combustible concentration range with air humidity of 50–70%. The helium vapor concentration range at different vertical heights and horizontal distances also increases with the air humidity. The experimental data fits the cloud concentration decay curve under different ambient humidity satisfying the exponential function. The work is expected to provide a technical basis for safety studies of liquid hydrogen and liquid helium spilling.

Impaired Pharmacokinetics of Amiodarone under Veno-Venous Extracorporeal Membrane Oxygenation: From Bench to Bedside.

Background: Adjusting drug therapy under veno-venous extracorporeal membrane oxygenation (VV ECMO) is challenging. Although impaired pharmacokinetics (PK) under VV ECMO have been reported for sedative drugs and antibiotics, data about amiodarone are lacking. We evaluated the pharmacokinetics of amiodarone under VV ECMO both in vitro and in vivo. Methods: In vitro: Amiodarone concentration decays were compared between closed-loop ECMO and control stirring containers over a 24 h period. In vivo: Potassium-induced cardiac arrest in 10 pigs with ARDS, assigned to either control or VV ECMO groups, was treated with 300 mg amiodarone injection under continuous cardiopulmonary resuscitation. Pharmacokinetic parameters Cmax, Tmax AUC and F were determined from both direct amiodarone plasma concentrations observation and non-linear mixed effects modeling estimation. Results: An in vitro study revealed a rapid and significant decrease in amiodarone concentrations in the closed-loop ECMO circuitry whereas it remained stable in control experiment. In vivo study revealed a 32% decrease in the AUC and a significant 42% drop of Cmax in the VV ECMO group as compared to controls. No difference in Tmax was observed. VV ECMO significantly modified both central distribution volume and amiodarone clearance. Monte Carlo simulations predicted that a 600 mg bolus of amiodarone under VV ECMO would achieve the amiodarone bioavailability observed in the control group. Conclusions: This is the first study to report decreased amiodarone bioavailability under VV ECMO. Higher doses of amiodarone should be considered for effective amiodarone exposure under VV ECMO.

Elucidating the low-frequency ultrasound effect on mass transfer resistances during phenol adsorption over microporous materials

To improve the adsorption rate of pollutants on microporous materials, a comparative study of the adsorption of phenol on activated carbon pellets (ACP) in the presence of conventional agitation and low-frequency ultrasound (US) was accomplished. Additionally, the effect of chemical and textural properties over the equilibrium and adsorption rate was evaluated by modifying the ACP with a physical reactivation process at different times. The textural properties of the adsorbents were obtained by physisorption of N2 at −196 °C and CO2 at 0 °C, while the functional groups were identified using XPS spectroscopy. The phenol adsorption equilibrium was studied at 25 and 45 °C, while the adsorption rate was conducted by varying the initial phenol concentration, stirring speed, and ultrasound amplitude. The results showed that the reactivation process improves the average micropore width and mesopore volume, which allows better diffusion of phenol towards the microporosity of the material, increasing the adsorption capacity from 164 to 217 mg/g at pH ≈ 7 and 25 °C. The concentration decay curves of phenol were predicted using a 3D-diffusional model. The results evidenced that in absence or presence of US, the overall adsorption rate is controlled by intraparticle diffusion. Moreover, the surface diffusion mechanism proved to be more important than the pore volume diffusion for both scenarios. Finally, it was demonstrated that US decreases the equilibrium times by enhancing the intraparticle diffusion causing a 2.36-fold increase in the value of the surface diffusion coefficients. Finally, the external mass transport was enhanced exclusively for ultramicroporous materials.

Mixing in the confined vortical flow in non-aligned T-jets reactors

In this work, flow dynamics and mixing performances in a non-aligned T-jets reactor are experimentally studied within a Reynolds number (Re) range of 50–160. Plane Laser-Induced Fluorescence (PLIF) is used to measure concentration fields and explore underlying vortical flow structures. Two vortex rings are identified in the mixing channel of the reactor at Re≥90, and the fluid pulsation induced by the vortex ring is demonstrated. The mixing in the reactor is qualified by an area-based distribution of mixing intensity, and the scale and intensity of segregation. Results show that the scale and intensity of segregation are reduced as the vortex ring appears, and the overall mixing is closely associated with vortex rings and the fluid pulsation, of which the former dominates. Further insight into the mixing is obtained by analyzing the decay time of the fluid. It is found that long decay time of the fluid in vortex rings causes the formation of well-mixed regions, and the concentration decay time in the second vortex ring is more than twice that in the first vortex ring despite the smaller size of the second vortex ring.

A comprehensive investigation of external mass transfer and intraparticle diffusion for batch and continuous adsorption of heavy metals using pore volume and surface diffusion model

Separation of heavy metals from water bodies is a need of hour, to protect human kind, marine life, and the environment. In this context, adsorptive separation of heavy metal over cheap and environmental friendly biosorbent remains promising. Numerous studies have been carried out to characterize the adsorption of heavy metal ions through isotherms, kinetics, and simple mathematical models. However, such studies lacked in detailed mass transfer models evaluating heavy metal adsorption in batch and continuous modes. This work reports the application of pore volume and surface diffusion (PVSD) model investigating mass transfer processes of Cu (II), Cd (II), and Pb (II) adsorptions over alkali-treated Caryotaurens seeds, chemically modified Albizia lebbeck pods, and Schleichera oleosa bark, respectively, in batch and continuous modes. Heavy metal-biosorbent systems are represented by Freundlich, Temkin, and Langmuir isotherms, respectively. PVSD model equations (algebraic, ordinary, and partial differential equations) for batch and continuous modes are solved in gPROMS (General Process Modelling System). For validation, concentration decay and breakthrough curves concerning batch and continuous modes, respectively, are predicted and matched excellently with in-house experimental data and justified with R2 and RMSE values. In batch mode, external mass transfer coefficient suggested no constraint for heavy metal external transport, whereas, surface and pore volume diffusion coefficients were found to control the adsorption process. For continuous mode, breakthrough curves are predicted concerning metal solution flowrate, initial metal concentration, and bed height, and parameters viz. breakthrough time, exhaustion time, adsorption column capacity, and mass transfer zone are calculated. Axial dispersion and mass transfer coefficients signify negligible resistance for metal ions' bulk transport within the column. Surface and pore volume diffusions affected continuous adsorption process, with surface diffusion being dominant. The current PVSD model may represent other metal-biosorbent systems to estimate transport parameters suitable for continuous adsorber operation.

Charging and dynamics of polystyrene latex aerosols under bipolar and unipolar ion field–ELPI measurements and comparison with charging theories

The nuclear reactor research community is interested in charged aerosol dynamics in a confined environment. Various aerosol charging theories described for bipolar and unipolar ion field exposures are reviewed using experimental measurements with PSL aerosols and ELPI. The (n+/n-) ratio of bipolar ions marginally increases as more negative ions get attached to aerosols. The charge level obtained from generation reduces under bipolar ion field but increases enormously under unipolar ion field. The charged aerosol concentration decay is not changed significantly under bipolar ion field when compared to the baseline condition but enhanced by more than one order under unipolar ion field.

Long-Term Clearance and Biodistribution of Magnetic Nanoparticles Assessed by AC Biosusceptometry.

Once administered in an organism, the physiological parameters of magnetic nanoparticles (MNPs) must be addressed, as well as their possible interactions and retention and elimination profiles. Alternating current biosusceptometry (ACB) is a biomagnetic detection system used to detect and quantify MNPs. The aims of this study were to evaluate the biodistribution and clearance of MNPs profiles through long-time in vivo analysis and determine the elimination time carried out by the association between the ACB system and MnFe2O4 nanoparticles. The liver, lung, spleen, kidneys, and heart and a blood sample were collected for biodistribution analysis and, for elimination analysis, and over 60 days. During the period analyzed, the animal’s feces were also collectedd. It was possible to notice a higher uptake by the liver and the spleen due to their characteristics of retention and uptake. In 60 days, we observed an absence of MNPs in the spleen and a significant decay in the liver. We also determined the MNPs’ half-life through the liver and the spleen elimination. The data indicated a concentration decay profile over the 60 days, which suggests that, in addition to elimination via feces, there is an endogenous mechanism of metabolization or possible agglomeration of MNPs, resulting in loss of ACB signal intensity.

Investigation of Hydrogen Dispersion Characteristics with Liquid Helium Spills

Liquid hydrogen is an important way for hydrogen energy storage and transportation in the future. However, the safety issue should be a concern because it will quickly form a low- temperature, flammable and explosive vapor cloud when liquid hydrogen leaks. A new liquid helium spill experiment method was used to predict the dispersion characteristics of liquid hydrogen in confined space at this work. The concentration cloud and the infrared cloud images near the liquid helium pool were obtained at the same time. Results show it is a safe and reliable way to study the leakage and diffusion characteristics of liquid hydrogen instead of liquid helium. After the liquid helium leaks and diffuses, a white cloud cluster will quickly form, and the vapor cloud cluster has a clear temperature boundary observed by infrared thermal imaging equipment. The concentration decay rate of the helium concentration near the leakage port along the vertical height is less than the concentration decay rate of the horizontal distance, which are 0.098%/mm and 0.118%/mm, respectively. The research results have certain technical guidance for the application and safety protection of liquid hydrogen.

Decay rates of two tracer gases compared to DNA-tagged liquid aerosol tracer particles: Impact of varying dilution rate and filtration

Current gas-and aerosol-based tracers do not adequately simulate the emission and transport of liquid aerosols containing a pathogen indoors. To evaluate a liquid aerosol tracer containing synthetic DNA, the tracer was emitted in a chamber to measure changes in decay rates as outdoor air dilution rate and filter rating varied. DNA tracer concentration decay rates were compared to decay rates of size distributions of liquid tracer aerosols and two tracer gases (CO2 and SF6) to characterize the evolution of the particle size distribution simulated by the aerosols containing DNA tracer compared to common air change rate measurements. The effect of dilution ventilation on tracer decay rates was assessed at four air change rates using HEPA-filtered outdoor air (0, 1.3, 2.5, and 4.2 ACH), and the simultaneous impact of filtration of recirculated air (0, 1.3, 2.5, and 4.2 ACH) was tested using MERV8 and MERV13 filters. DNA tracer concentrations decayed at a rate comparable to liquid aerosols of 5–25 μm in diameter. Filter type did not consistently impact the rate of coarse particle or DNA tracer removal, though differences were observed for fine aerosols. Results indicate DNA-tagged tracer aerosols can simulate liquid aerosol emission and transport in a room, and the effectiveness of aerosol control strategies can be evaluated by observing the decay rate of DNA tracer concentrations.

3D mathematical modeling of external mass transfer effect in high-rate adsorption process

The effect of external mass transfer on the high-rate adsorption system was evaluated in the present study. In the experimental section, the removal of methyl orange (MO) was carried out by using surfactant modified chitosan-clinoptilolite at specific conditions such as the optimum adsorbent dosage of 11 g L−1, solution pH of 3.5, contact time of about 3 min and constant temperature of 30 °C. The characterization of adsorbent showed the porosity value of 0.064 and the BET surface area of 10.5 m2 g−1. These features of adsorbent established the high-rate adsorption process in which the shape of decay curves is not smooth and the concentration of adsorbate falls quickly. In high-rate adsorption processes, the external mass transfer mechanism has a significant effect on total mass transfer at early time of adsorption. The pore volume and surface diffusion model (PVSDM) were applied for predicting MO concentration decay curves. This model and its parameters could not estimate properly the concentration of MO at the early time of the adsorption process. To overcome this problem, in addition to optimization of surface diffusion coefficient (Ds), the external mass transfer coefficient (ke) was optimized and the effect of those parameters was studied in three dimensions. The optimization provided a better agreement between the model and experimental data in such a way to reduce the error rate. To show better the effect of external mass transfer, Biot number (between (2.15 and 24.05) × 10−3) was applied and it revealed that the adsorption mechanism was controlled by external mass transport. The high external surface area illustrated that in all values of ke and initial concentration of MO, surface diffusion is the dominant mechanism in intraparticle diffusion and the low porosity of adsorbent limited the penetration of adsorbate species into the adsorbent cavities, whereby the pore volume diffusion could be considered negligible.

Numerical simulation of the Marangoni flow on mass transfer from single droplet with different Reynolds numbers

The interfacial flow and mass transfer of multicomponent droplets remain an unsolved basic problem, although multicomponent droplets are widely used in droplet microfluidics, fine chemicals. In this paper, Level-set method is used to capture the phase interface, and the evolution of Marangoni convection under different Reynolds numbers is investigated by CFD simulation. The influence of Marangoni effect on the macroscopic characteristics such as droplet velocity and concentration decay rate under different motion states are reported, and the divergence of velocity at the interface is statistically analyzed at microscopic level. The results reveal that the droplet Reynolds number has a great influence on the development of Marangoni convection in life and space; The local divergence can clearly reflect the influence of flow structure and flow velocity on interphase material transport; The Marangoni vortices are multi-scale, and the interphase mass transfer containing the Marangoni effect is non-Gaussian and oscillating, which similar to turbulence. Compared to previous research, this work complements a lot of micro information of the interface Marangoni flow, and deeply discusses the competition between Marangoni and internal circulation flow in droplets under different Reynolds numbers.

Coupling 1D blood circulation model and substance absorption model to study drug metabolization

The introduction of substances into the bloodstream initiates a complex series of chemical reactions. The study of drug absorption, metabolization and excretion processes is relevant for a better understanding of current treatments, by providing a better understanding, which helps improve them or propose new methods. In this project we propose a novel model for drug absorption, which is obtained by coupling a ID full-body blood flow model with the Wagner-Nelson absorption equation for a single compartment model through two established elimination rates Ket. For our experiments, we take the constant values from previous studies on the intravenous administration of ibuprofen and epinephrine, having Ket = 0.32 per hour, and Ket = 0.2 per minute respectively, and one large Ket = 3200 per hour to test absorption in a detailed full-body model. Our result plots show a decay in the concentration of drug over the time, which reflects the correct coupling of our models with the subtraction of drug amounts and the update of the current drug concentration by the absorption model over our ID blood flow model. To overcome resources limitations, we run our simulations for short periods of time, with an increased Ket value in the same order to generate an accelerated decay of the drug concentration in a more detailed model.

Optical stress concentration and stress gradient monitoring during elasto-plastic fatigue tests with Digital Image Correlation

Predictions of fatigue failure at stress concentrations rely on prediction by empirical formulae or experimental test data. However, there remains a level of uncertainty in the life estimation, which can be reduced when monitoring the behavior around the stress concentration. In this contribution, the stress field, calculated for an isotropic material from optical strain measurement, is monitored over specimen fatigue life. Changes in the maximum relative stress gradient χmax, describing the decay of a stress concentration, and the distance of the maximum gradient from the hole are evaluated. Experimental data on three specimens with different load levels in the high-cycle fatigue range show that both parameters change significantly shortly before fatigue failure. These encouraging results indicate that failure can be predicted by monitoring either, the value of χmax, or the distance of χmax from the hole edge.

Determination and analysis of time series of CFC-11 (CCl3F) from FTIR solar spectra, in situ observations, and model data in the past 20 years above Jungfraujoch (46°N), Lauder (45°S), and Cape Grim (40°S) stations

Analysis of the last 20 years ground-based FTIR time series of CFC-11 from NDACC stations in the northern and southern hemispheres confirm the slowdown in the CFC-11 atmospheric concentration decay, related to emissions from non-reported production.

The dynamics of an axisymmetric turbulent jet in ambient turbulence interpreted from the passive scalar field statistics

The effect of approximately homogeneous isotropic turbulence on the dynamics of an axisymmetric turbulent jet (Re = 10 600 and 5800) in an ambient with a negligible mean flow is interpreted from the statistics of the passive scalar field. The ambient turbulence is generated by a random jet array and scalar concentrations are measured in orthogonal cross sections of the jet using planar laser-induced fluorescence. Statistics of the scalar field of the jet in a turbulent ambient are compared to those in a quiescent ambient, using classical Eulerian averages and those conditioned on the jet centroid. A two-region model for the jet structure in ambient turbulence is proposed based on the centroidal statistics. Following the developing region of the jet, the ambient turbulence disrupts the jet structure, due to modulation of the jet interface, meandering of the jet by large eddies, and entrainment of the turbulent ambient fluid, resulting in a faster concentration decay and reduced entrainment compared to the quiescent ambient. Further downstream, once the ambient turbulence has destroyed the jet, only molecular and turbulent diffusion modify the scalar concentrations. The regions' relative lengths depend primarily on the relative turbulence intensity (ξ) between the ambient and the jet, as assessed using centroidal analysis, which removes the effect of the relative length scale (l) on the jet behavior in the turbulent ambient. The centroidal scalar statistics reveal self-similarity and self-preservation in mean scalar properties before jet breakup, which occurs abruptly once ξ&amp;gt; 0.5. The smaller scales of ambient turbulence modulate the jet boundary and, when entrained, lead to a wider range of centerline concentrations and root mean square concentrations, which are hypothesized to increase local concentration gradients within the jet and reduce jet mixing.

Investigation of Airflow Distribution and Contamination Control with Different Schemes in an Operating Room

Controlling contamination via proper airflow distribution in an operating room becomes vital to ensure the reliable surgery process. The heating, ventilation, and air conditioning (HVAC) systems significantly influence the operating room environment, including temperature, relative humidity, pressurization, particle counts, filtration, and ventilation rate. A full-scale operating room has been investigated extensively through field measurements and numerical analyses. Computational fluid dynamics (CFD) simulation was conducted and verified with the field measurement data. The simulation was analyzed with three different operating room schemes, including at-rest conditions (case 1), normal operational conditions with personnel (case 2), and actual conditions with personnel inside and some medical equipment blocking the return air (case 3). The concentration decay method was used to evaluate this study. The results revealed that the contamination concentration in case 1 could be diluted quickly with the average value of 404 ppm, whereas the concentration in case 2 slightly increased while performing a surgery with the average value of 420 ppm. The return air grilles in case 3, blocked by obstacles from some medical equipment, resulted in the average concentration value of 474 ppm. Other than that, the contaminant dilution could be obstructed dramatically, which revealed that proper and smooth airflow distribution is essential for contamination control. The ventilation efficiency of case 2 and case 3 dropped around 6% and 17.91% compared to case 1 in the unoccupied and ideal condition. Ventilation efficiency also decreased along with decreasing the air change rate per hour (ACH), while with increasing ACH, the ventilation efficiency in case 3 actually increased, approaching case 2 in the ideal condition.