Dominant Transport Research Articles

A semi-probabilistic Bayesian method to identify the number and location of potential sources in 3D unconfined aquifer using limited observed concentration

Source identification of a contaminant has always been challenging for accurately modeling groundwater transport. Source identification problems are classified into several parts, such as identifying the location of contamination, the strength of contamination, the time the contaminant is introduced into the groundwater, and the duration of its activity. Identifying the sources considering all the parts as variables increases the computational complexity. Reducing the number of variables in source identification problems is necessary for a swift solution through optimization approaches. The most challenging variable in source identification modeling is the location of contamination, as it is a discrete variable for almost all the numerical solutions of groundwater models. In this research study, we have created a methodology to narrow the location of contamination from a random distribution throughout the aquifer to a reasonable number of probable locations. Although methods to identify the location of contamination were devised earlier, we have attempted an approach of combining a particle tracking approach with Bayesian method of updating the probabilities as a novel approach, where the observation data is limited. We have considered the aquifer parameters and observation well data and devised a method with a Lagrangian approach to particle movement to identify the potential source locations. We have refined the source locations to a narrower probability distribution using the Bayesian method of updating the probability through new information of refined grid space. We have tested the models to identify the potential sources with different hypothetical problems and identified the sources in advective dominant transport with an average probability of 0.53, diffusion dominant transport with an average probability of 0.62, heterogenous soils with an average probability of 0.99, anisotropic aquifer with an average probability of 0.91, and aquifer with irregular boundary with an average probability of 0.96 to identify the location nearest to the actual contaminant source. The results are satisfactory in identifying the number of potential sources with an accuracy of 88 % (15 identified out of 17 sources with a probability greater than 0.4) and their locations in the aquifer with a probability of 0.223 for exact location identification. The probability of finding a source nearest to the actual location is 0.745 at an average distance of 11.6 m from the actual source location.

Prediction Method for the Distribution of the Effective Dominant Path of Sand Bodies Transporting Oil and Gas and Its Application

To study the oil and gas distribution law in the slope area of a hydrocarbon-bearing basin, one must first define the dominant hydrocarbon transport paths of sand bodies as the superimposed area of the contiguously distributed area of the sand bodies and the paleotectonic ridges at the top interface of the formation. Then, the oil and gas supply area of the oil source faults must be defined, as the overlapped area of the favorable transport paths of oil source faults and the width of their associated fracture zones. Stacking the two areas, we can delineate the distribution of the effective dominant paths of sand bodies transporting oil and gas. The results from our case study of the Qinan area show that the effective dominant paths of sand bodies transporting oil and gas in the lower sub-member within the first member of the Shahejie Formation (Es1L) in the Qinan area are distributed throughout the region, with better development in the west than in the east. And, the effective dominant paths in the eastern part extend from north to south, while those in the western part extend from northeast to southwest. These are favorable for the convergence of oil and gas generated from source rocks in the third member of the Shahejie Formation (Es3) in the main depression of Qikou Sag in the Es1L in the Qinan area. The results are consistent with the fact that oil and gas discovered in the Es1L in the Qinan area are mainly distributed in the central and western regions, with a small amount in the southeast. Therefore, the suggested method is feasible for predicting the effective dominant paths of sand bodies transporting oil and gas.

"V"-Shaped Changing Electronic Performance of Iodinene-Based Nanoflakes as a Function of Width.

Special structures and prominent performance make 2D iodinene more appealing and valuable at the molecular level. Here, new-type electronic devices have been constructed with iodinene-based nanoflakes in different sizes and are theoretically studied for electronic transport properties. Our findings reveal that iodinene-based nanoflakes possess great electron transport suppression, achieving the same function as SiO2 on single molecule scale. Such transport suppression shows surprisingly nonlinear "V"-shaped trend with the width of the iodinene-based nanoflake. The medium-width iodinene-based nanoflake exhibits the strongest electron transport suppression, while the narrowest and widest ones display the largest electron transmission coefficients due to delocalized transmission eigenstates. Essentially, the weakest electron transport originates from an extremely small DOS and wide HOMO-LUMO gap. Specifically, increasing the width would diminish the extension of electronic states for the dominant transport orbitals, resulting in more butterfly-like electronic states. In non-equilibrium, negative differential resistance effect can be observed in iodinene-based devices, caused by the weakening and staying away from the Fermi level of transmission peaks influenced by the bias. Our findings provide insights into the relationship between the width of iodinene-based nanoflake and electronic transport properties, and lay a foundation in the device design and applications in molecular insulators and controllable-functional devices.

Sewer transport conditions and their role in the decay of endogenous SARS-CoV-2 and pepper mild mottle virus from source to collection

This study presents a comprehensive analysis of the decay patterns of endogenous SARS-CoV-2 and Pepper mild mottle virus (PMMoV) within wastewaters spiked with stool from infected patients expressing COVID-19 symptoms, and hence explores the decay of endogenous SARS-CoV-2 and PMMoV targets in wastewaters from source to collection of the sample. Stool samples from infected patients were used as endogenous viral material to more accurately mirror real-world decay processes compared to more traditionally used lab-propagated spike-ins. As such, this study includes data on early decay stages of endogenous viral targets in wastewaters that are typically overlooked when performing decay studies on wastewaters harvested from wastewater treatment plants that contain already-degraded endogenous material. The two distinct sewer transport conditions of dynamic suspended sewer transport and bed and near-bed sewer transport were simulated in this study at temperatures of 4 °C, 12 °C and 20 °C to elucidate decay under these two dominant transport conditions within wastewater infrastructure. The dynamic suspended sewer transport was simulated over 35 h, representing typical flow conditions, whereas bed and near-bed transport extended to 60 days to reflect the prolonged settling of solids in sewer systems during reduced flow periods. In dynamic suspended sewer transport, no decay was observed for SARS-CoV-2, PMMoV, or total RNA over the 35-h period, and temperature ranging from 4 °C to 20 °C had no noticeable effect. Conversely, experiments simulating bed and near-bed transport conditions revealed significant decreases in SARS-CoV-2 and total RNA concentrations by day 2, and PMMoV concentrations by day 3. Only PMMoV exhibited a clear trend of increasing decay constant with higher temperatures, suggesting that while temperature influences decay dynamics, its impact may be less significant than previously assumed, particularly for endogenous RNA that is bound to dissolved organic matter in wastewater. First order decay models were inadequate for accurately fitting decay curves of SARS-CoV-2, PMMoV, and total RNA in bed and near-bed transport conditions. F-tests confirmed the superior fit of the two-phase decay model compared to first order decay models across temperatures of 4 °C–20 °C. Finally, and most importantly, total RNA normalization emerged as an appropriate approach for correcting the time decay of SARS-CoV-2 exposed to bed and near-bed transport conditions. These findings highlight the importance of considering decay from the point of entry in the sewers, sewer transport conditions, and normalization strategies when assessing and modelling the impact of viral decay rates in wastewater systems. This study also emphasizes the need for ongoing research into the diverse and multifaceted factors that influence these decay rates, which is crucial for accurate public health monitoring and response strategies.

Investigating sediment dynamics on a continental shelf mud patch under the influence of a macrotidal estuary: A numerical modeling analysis

Shelf mud patches represent major sinks for fine-grained particles on continental shelves, as well as for carbon and contaminants of continental origin. The West Gironde Mud Patch (WGMP) is an interesting example of such offshore marine systems as it is an active mud deposition area located offshore the Gironde estuarine mouth (France) at depths between 30 and 70 m. It is known to be the trap of fine particles coming from the estuary, but the contribution of this material to the total mass of the depocenter is poorly quantified. In addition, despite the economic and ecological issues at stake, the response of such subtidal sedimentary structure to the combination of tidal currents, waves, and river supply remain poorly understood. Thus, using a realistic 3-D hydrodynamic and mixed (mud/sand) sediment transport model, this study aims at investigating the sediment dynamics of the WGMP under different hydrometeorological conditions. The analysis of the residual fluxes at the estuarine mouth exhibited large discrepancies between the different sediment classes as well as for contrasted hydro-and meteorological conditions induced by different dominant transport mechanisms. During winter, the reinforced density gradients drive strong up-estuary baroclinic circulation at the bottom that dominates the sediment dynamics over the barotropic export of mud particles. The model also reproduced the signature of a subtidal mud accumulation area over the continental shelf around 30–40 m water depth, on the proximal side of the observed WGMP. On average over two years, 26% of the mud mass accumulating on the simulated subtidal mudflat comes from the estuary. The trapping efficiency of this mud patch is negatively correlated with the significant wave height. Moreover, due to the estuarine turbid plume being more concentrated and developed at the surface during high river discharge, the trapping efficiency of the mud body is enhanced compared to lower discharge. This study highlights the sensitivity of mud and sand fluxes to vertical and horizontal residual circulation, and points out the uncertainties associated with the simulation of short-term (i.e., years) fine particle deposits compared to long-term (i.e., centuries) sediment accumulation trends. In addition, these results show the primordial effects of both wave action and riverine sediment supply on the dynamics of such subtidal muddy structures, which raises concern about their fate facing climate change and human activities in the future.

Toxicity of extracellular cGAMP and its analogs to T cells is due to SLC7A1-mediated import.

STING agonists are promising innate immune therapies and can synergize with adaptive immune checkpoint blockade therapies for cancer treatment, but their effectiveness is limited by the toxicity to activated T cells. An important class of STING agonists are analogs of the endogenous STING agonist, cGAMP, and while transporters for these small molecules are known in some cell types, how they enter and kill T cells remains unknown. Here, we identify the cationic amino acid transporter SLC7A1 as the dominant transporter of cGAMP and its analogs in activated primary mouse and human T cells. T cells upregulate this transporter upon activation and rapid proliferation to meet their high metabolic demand, but this comes at the cost of enabling increased transport and toxicity of cGAMP. To circumvent the essentiality of SLC7A1 to proliferating T cells, we found that the residues responsible for cGAMP transport are separate from the arginine binding pocket allowing us to perturb cGAMP transport and STING-activation mediated killing without impacting arginine transport. These results suggest that SLC7A1 is a potential target for alleviating T cell toxicity associated with cGAMP and its analogs.

Unraveling the properties of [TPA]2Cu2Br6: A holistic investigation into structure, optics, magnetism and dielectric characteristics

The recent technological advances require an aligned innovation in the materials used for the construction of electronic devices. Hybrid materials play a important role in the optoelectronic applications because they combine both the organic and inorganic components To this end, the [TPA]2Cu2Br6 compound was successfully synthesized using the slow evaporation solution growth approach at room temperature. The [TPA]2Cu2Br6 compound crystallizes in the triclinic system with P1‾space group. The atomic arrangement can be described by an alternation of organic and inorganic layers stacked along the c direction and made up of [N(C3H7)4]+ and [CuBr3]− groups, respectively. The examination of SEM analysis allows us to raise the morphology and the good quality of the crystals. The EDX analysis was performed to ensure that all chemical elements were discovered and located in the relevant locations.For the compound under study, the UV–visible spectroscopy spectrum shows the direct band-gap value of ∼3.52 eV, indicating that it is a semiconductor material. Magnetic measurements revealed the superparamagnetic behavior. Studies of the dielectric constant permittivity ε*(ω) confirmed that the relaxation process was thermally activated. The dominant transport mechanism is the s the non-overlapping small polaron tunneling (NSPT) model.

Functional Characterization of Reduced Folate Carrier and Protein-Coupled Folate Transporter for Antifolates Accumulation in Non-Small Cell Lung Cancer Cells.

Antifolates are important for chemotherapy in non-small cell lung cancer (NSCLC). They mainly rely on reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) to enter cells. PCFT is supposed to be the dominant transporter of the two in tumors, as it operates optimally at acidic pH and has limited transport activity at physiological pH, whereas RFC operates optimally at neutral pH. In this study, we found RFC showed a slightly pH-dependent uptake of antifolates, with similar affinity values at pH 7.4 and 6.5. PCFT showed a highly pH-dependent uptake of antifolates, with an optimum pH of 6.0 for pemetrexed and 5.5 for methotrexate. The Michaelis-Menten constant (Km ) value of PCFT for pemetrexed at pH 7.4 was more than 10 times higher than that at pH 6.5. Interestingly, we found that antifolate accumulations mediated by PCFT at acidic pH were significantly affected by the efflux transporter, breast cancer resistance protein (BCRP). The highest pemetrexed concentration was observed at pH 7.0-7.4 after a 60-minute accumulation in PCFT-expressing cells, which was further evidenced by the cytotoxicity of pemetrexed, with the IC50 value of pemetrexed at pH 7.4 being one-third of that at pH 6.5. In addition, the in vivo study indicated that increasing PCFT and RFC expression significantly enhanced the antitumor efficacy of pemetrexed despite the high expression of BCRP. These results suggest that both RFC and PCFT are important for antifolates accumulation in NSCLC, although there is an acidic microenvironment and high BCRP expression in tumors. SIGNIFICANCE STATEMENT: Evaluating the role of reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) on antifolates accumulation in non-small cell lung cancer (NSCLC) is necessary for new drug designs. By using cell models, we found both RFC and PCFT were important for antifolates accumulation in NSCLC. Breast cancer resistance protein (BCRP) significantly affected PCFT-mediated antifolates accumulation at acidic pH but not RFC-mediated pemetrexed accumulation at physiological pH. High expression of PCFT or RFC enhanced the cytotoxicity and antitumor effect of pemetrexed.

Non‐Monotonic Variation of the Low Lattice Thermal Conductivity with Temperature in Penta‐HgO2 Sheet

AbstractInspired by the experimental synthesis of bulk HgO2 with the potential of exfoliation to form a penta‐HgO2 sheet composed entirely of pentagonal motifs, a detailed theoretical study on the lattice thermal conductivity by using first‐principles calculations combined with the unified theory of thermal transport is performed. It is found that the penta‐HgO2 sheet is semiconducting with an indirect bandgap of 1.18 eV and possesses a low lattice thermal conductivity of 2.07 W m−1 K−1 (3.28 W m−1 K−1) along the x (y)‐direction at 300 K. More interestingly, the variation of its thermal conductivity with temperature is non‐monotonic, different from most cases. The phonon dispersion, phonon scattering, and phonon coherence is further systematically investigated to understand the underlying physics. This results suggest that the strong intrinsic anharmonicity resulting from its unique atomic configuration with the buckled structure and the heavy element of Hg leads to a high scattering rate, resulting in the ultralow particle‐like thermal transport of 0.20 W m−1 K−1 (0.01 W m−1 K−1) in the x (y)‐direction, while the narrow average frequency interval and strong phonon linewidth are responsible for the dominant coherent thermal transport and non‐monotonic variation of the low lattice thermal conductivity of the penta‐HgO2 sheet.

Towards Stable Helical Structures with Enhanced Molecular Conductance by Strengthening Through-Space Conjugation.

Developing long-chain molecules with stable helical structures is of significant importance for understanding and modulating the properties and functions of helical biological macromolecules, but challenging. In this work, an effective and facile approach to stabilize folded helical structures by strengthening through-space conjugation is proposed, using new ortho-hexaphenylene (o-HP) derivatives as models. The structure-activity relationship between the through-space conjugation and charge transport behavior of the prepared folded helical o-HP derivatives is experimentally and theoretically investigated. It is demonstrated that the through-space conjugation within o-HP derivatives can be strengthened by introducing electron-withdrawing pyridine and pyrazine, which can effectively stabilize the helical structures of o-HP derivatives. Moreover, scanning tunneling microscopy-break junction measurements reveal that the stable regular helical structures of o-HP derivatives open up dominant through-space charge transport pathways, and the single-molecule conductance is enhanced by more than 70% by strengthening through-space conjugation with pyridine and pyrazine. But the through-bond charge transport pathways contribute much less to the conductance of o-HP derivatives. These results not only provide a new method for exploring stable helical molecules, but also pave a stepping stone for deciphering and modulating the charge transport behavior of helical systems at the single-molecule level.

Exploring Kp,uu,BBB values smaller than unity in remoxipride: A physiologically-based CNS model approach highlighting brain metabolism in drugs with passive blood-brain barrier transport

(Aim)Kp,uu,BBB values are crucial indicators of drug distribution into the brain, representing the steady-state relationship between unbound concentrations in plasma and in brain extracellular fluid (brainECF). Kp,uu,BBB values < 1 are often interpreted as indicators of dominant active efflux transport processes at the blood-brain barrier (BBB). However, the potential impact of brain metabolism on this value is typically not addressed. In this study, we investigated the brain distribution of remoxipride, as a paradigm compound for passive BBB transport with yet unexplained brain elimination that was hypothesized to represent brain metabolism. (Methods)The physiologically-based LeiCNS pharmacokinetic predictor (LeiCNS-PK model) was used to compare brain distribution of remoxipride with and without Michaelis-Menten kinetics at the BBB and/or brain cell organelle levels. To that end, multiple in-house (IV 0.7, 3.5, 4, 5.2, 7, 8, 14 and 16 mg kg-1) and external (IV 4 and 8 mg kg-1) rat microdialysis studies plasma and brainECF data were analysed. (Results)The incorporation of active elimination through presumed brain metabolism of remoxipride in the LeiCNS-PK model significantly improved the prediction accuracy of experimentally observed brainECF profiles of this drug. The model integrated with brain metabolism in both barriers and organelles levels is named LeiCNS-PK3.5. (Conclusion)For drugs with Kp,uu,BBB values < 1, not only the current interpretation of dominant BBB efflux transport, but also potential brain metabolism needs to be considered, especially because these may be concentration dependent. This will improve the mechanistic understanding of the processes that determine brain PK profiles.

Image-based quantitative probing of 3D heterogeneous pore structure in CBM reservoir and permeability estimation with pore network modeling

Coalbed methane (CBM) recovery is attracting global attention due to its huge reserve and low carbon burning benefits for the environment. Fully understanding the complex structure of coal and its transport properties is crucial for CBM development. This study describes the implementation of mercury intrusion and μ-CT techniques for quantitative analysis of 3D pore structure in two anthracite coals. It shows that the porosity is 7.04%–8.47% and 10.88%–12.11%, and the pore connectivity is 0.5422–0.6852 and 0.7948–0.9186 for coal samples 1 and 2, respectively. The fractal dimension and pore geometric tortuosity were calculated based on the data obtained from 3D pore structure. The results show that the pore structure of sample 2 is more complex and developed, with lower tortuosity, indicating the higher fluid deliverability of pore system in sample 2. The tortuosity in three-direction is significantly different, indicating that the pore structure of the studied coals has significant anisotropy. The equivalent pore network model (PNM) was extracted, and the anisotropic permeability was estimated by PNM gas flow simulation. The results show that the anisotropy of permeability is consistent with the slice surface porosity distribution in 3D pore structure. The permeability in the horizontal direction is much greater than that in the vertical direction, indicating that the dominant transportation channel is along the horizontal direction of the studied coals. The research results achieve the visualization of the 3D complex structure of coal and fully capture and quantify pore size, connectivity, curvature, permeability, and its anisotropic characteristics at micron-scale resolution. This provides a prerequisite for the study of mass transfer behaviors and associated transport mechanisms in real pore structures.

Xenolith Petrochronology (San Luis Potosi, Mexico) Constrains Heat Sources for Cenozoic Ultrahigh‐Temperature Metamorphism in the Lower Crust

AbstractUltrahigh‐temperature (UHT; &gt;900°C) metamorphism drives crustal differentiation and is widely recognized in the rock record, but its geodynamic causes are debated. Previous work on granulite‐facies metapelite xenoliths from San Luis Potosí, Mexico suggests the lower crust experienced a protracted UHT metamorphic event that coincided with the onset of regional extension. To determine the duration, conditions, and heat sources of UHT metamorphism recorded by these xenoliths, this study characterizes the major‐element, trace‐element, and U‐Pb isotopic systematics of quartz, rutile, feldspar, garnet, and zircon by in situ electron microprobe (EPMA) and laser‐ablation inductively coupled‐plasma mass spectrometry (LA‐ICP‐MS), and augments these data with detailed petrography, thermobarometry, phase equilibria modeling, and diffusion modeling. Thermobarometry and phase equilibria modeling suggest peak metamorphic conditions exceeded 0.7 GPa and 900°C. Zircon petrochronology confirms &gt;15 Myr of UHT conditions since its onset at ∼30 Ma. A small population of zircon record elevated temperatures following transition from backarc compression to extension during the waning stages of orogenesis (60–37 Ma). Garnet preserves trace‐element zoning and mineral inclusions consistent with suprasolidus garnet growth and subsequent compositional modification by intracrystalline rare‐earth element diffusion during protracted heating, with diffusion chronometry timescales in agreement with zircon data, followed by fluid‐driven remobilization of trace elements along now‐healed fractures within ∼1 Myr of eruption. In sum, these data are most compatible with lithospheric mantle attenuation or removal as the dominant heat transport mechanism driving synextensional UHT metamorphism and crustal melting, which has bearing on models for crustal differentiation and formation of modern and ancient granulite terranes globally.

Turbulence-reduced high-performance scenarios in Wendelstein 7-X

In the Wendelstein 7-X (W7-X) stellarator, turbulence is the dominant transport mechanism in most discharges. This leads to a ‘clamping’ of ion temperature over a wide range of heating power, predominantly flat density profiles where hollow profiles driven by neoclassical thermo-diffusion would be expected and by rapid impurity transport in injection experiments. Significantly reduced turbulent transport is observed in the presence of strong core density gradients found transiently after core pellet injection and irregularly after boronisation or boron pellet injection. Density peaking is also achieved in a controlled manner in purely neutral beam heated discharges where particle transport analysis reveals an abrupt reduction in the main-ion particle flux leading to significant density profile peaking not explained by the NBI particle source alone. The plasmas exhibit a heat diffusivity of around χ=0.25±0.1m2 s−1 at mid radius, a factor of around 4 lower than ECRH dominated discharges. Despite the improved confinement, the achieved ion temperature is limited by broader heat deposition and the lower power-per-particle given the higher density. This is overcome with limited reintroduction of ECRH power, where the low heat diffusivity diffusivity is maintained, the density rise supressed and ion temperatures above the clamping limit are achieved. The applicability of these plasmas for a high performance scenario on transport relevant time scales is assessed, including initial predictions for planned heating upgrades of W7-X, based on a range of assumptions about particle transport.

Evaluating the Effect of Morphologic Units on Fractional Sediment Mobility and Bedload Transport in a Small Pool‐Riffle Reach

AbstractThis study examines the spatial pattern of fractional sediment mobility and assesses the influence of morphologic units on bedload transport in a small pool‐riffle reach with limited supply. Using a 2D hydraulic model and a subsurface‐based sediment transport model, shear stresses, fractional sediment mobility, and bedload transport were examined for flow events ranging in magnitude between 0.2Qbf and 1.5Qbf. Results reveal that while spatial variations in shear stress decrease as discharge increases, only a small proportion of the bed experiences high transport rates. At the reach scale, riffles are the primary morphological unit contributing to fully mobile sediment for all size fractions. However, at a subunit scale, there is evidence of sediment transport reversal for grains &gt;32 mm at flows near or exceeding bankfull discharge in association with shear stress reversal. These transport reversals are important for maintaining pools despite their infrequent occurrence in the study reach. Sediment transport maps indicate that bed morphology considerably influences sediment transport at low to moderate flows. During these events, the shear stress is sensitive to local bed topography and partial mobility is the dominant transport process. In contrast, variations in bedload transport rates decrease during high flows when the flow is less sensitive to variations in bed topography and the bed becomes fully mobile.

Electrical transport and dielectric relaxation mechanism in Zn0.5Cd0.5Fe2O4 spinel ferrite: A temperature- and frequency-dependent complex impedance study

In the present study, the frequency-dependent dielectric relaxation and electrical conduction mechanisms in sol-gel-derived Zn0.5Cd0.5Fe2O4 (ZCFO) spinel ferrite were studied in the temperature range of 343–438 K. The formation of the ZCFO spinel ferrite phase with space group Fd3m was confirmed by X-ray diffraction analysis. The dielectric relaxation and electrical conduction mechanisms were studied using complex impedance spectroscopy (CIS). In the Nyquist plots, depressed semicircles were fitted with an equivalent circuit model with configuration (RGBQGB) (RGQG), signifying the contributions from grain boundaries and grains to the charge transport mechanism in the sample. The frequency-dependent AC conductivity was found to follow Jonscher's power law, and the frequency exponent term depicted the overlapping large polaron hopping (OLPH) model as the dominant transport mechanism. The activation energies for conductivity, electric modulus and impedance were calculated to identify the nature of the charge carriers governing the relaxation and conduction mechanisms in the prepared sample. Complex modulus studies confirmed the non-Debye type of dielectric relaxation, whereas tangent loss and dielectric constant analyses confirmed the thermally activated hopping mechanism of charge carriers in Zn0.5Cd0.5Fe2O4 spinel ferrite.

Electrical field enhanced CO2 permeation through a carbon molecular sieve membrane: A combined density functional based tight binding and computational fluid dynamics study

An important challenge in membrane technology for gas separation is to simultaneously improve their permeability and selectivity. Often, the increase in one performance leads to the decline of the other. This study presents a solution to that problem by utilizing electrical field coupling to improve CO2 permeation through a nitrile-containing poly (arylene-ether-ketone) (PEK-C(CN)) carbon molecular sieve membrane. Density functional based tight binding simulations of CO2, CH4, and N2 adsorption on PEK-C(CN) monolayer were conducted without and with electric field. The findings revealed that the electric field strength and orientation affected the molecules bond lengths, atomic charges, and bond angles. Investigation of their adsorption energy dominantly favored CO2 adsorption. Analysis of the partial density of states confirmed that adsorption interactions with the membrane were due to CO2 responses to the applied electric field. It additionally proved the electrical stability of PEK-C(CN) membrane. Computational fluid dynamics simulations of gas permeation through PEK-C(CN) membrane were performed without and with electric field. Results indicated an average pore distribution around 0.5 nm. The velocity flow distribution aided locate the interconnected pores, bringing to the fore the dominant transportation paths of gas molecules. It was uncovered that although the application of an electric field significantly improved the membrane gas permeability, it was not necessarily beneficial to its selectivity. −5 V was determined to be the optimum potential for an improvement of CO2 permeability from 57.32 Barrer (no field) to 15924.91 Barrer, while also enhancing the selectivity. This work demonstrates the benefits of the electric field and its promising application in gas separation processes.

Minority-carrier transport through an isotype amorphous-crystalline Ge2Sb2Te5 heterojunction under forward bias

To predict possible minority-carrier effects in multi-level phase change memory devices, minority-carrier transport through an isotype amorphous-crystalline Ge2Sb2Te5 heterojunction under forward bias is studied for the first time. Electron thermionic emission, thermal generation, drift, diffusion, radiative recombination, Auger recombination, Schockley–Read–Hall recombination via conduction band tails, valence band tails, acceptor-type mid-gap, donor-type mid-gap and multivalent defect distributions, as well as surface recombination are considered in the construction of the steady-state Continuity Equation relevant to the representative amorphous-crystalline Ge2Sb2Te5 heterojunction, which is then numerically solved at 0.15 V and 0.40 V using solar cell capacitance simulations. Provided that radiative recombination is negligible and defect distributions within the band gap of either layer are energetically localised, the simulated electron concentration, electron current density and electron quasi-Fermi level distributions across the heterojunction reveal that transport through the amorphous layer limits electron flow through the device. At low applied bias, net recombination and diffusion within the quasi-neutral region (QNR) of the amorphous layer dominate, whereas at larger applied bias, drift across the QNR, due to the electric field induced by the significant majority-carrier current density, as well as surface recombination at the amorphous layer contact contribute significantly. Within the crystalline layer, net generation of electrons supplies the amorphous layer at all biases, assuming that the crystalline layer contact does not limit electron transport. Thus, the effect of forward bias on the dominant transport mechanisms through the amorphous-crystalline Ge2Sb2Te5 heterojunction demonstrated herein represents the key contribution of this paper.

Tunnel oxide thickness-dependent dominant carrier transport in crystalline silicon solar cells

Silver consumption reduction is a current development in commercial tunnel passivated contact (TOPCon) crystalline silicon solar cell devices aimed at lowering the entire production cost of photovoltaic energy sources. It depends on the number of fingers and/or finger spacing (SP) on a cell area. In this paper, we analyze the possibility of minimizing silver use with respect to the dominant carrier transport mechanism. The carrier transporting mechanism, such as “pinhole” and/or “tunnel” models, is identified by examining temperature-dependent I–V characteristics of polysilicon passivating contact as a function of tunnel oxide (TO) thickness from 0.6 to 2.2 nm. Thermal oxidation was used to produce ultrathin TO films (0.6–2.2 nm) with temperature and gas ratio controlled. We find that the “pinholes” transport mechanism prevails when the TO thickness exceeds 1.6 nm, whereas the “tunnel” mode dominates when the TO thickness is less than 1.4 nm. The pinhole density is critical in pinhole mode for increasing SP. It is found that low pinhole densities and thick TO thickness (more than 1.6 nm) are two of the primary causes of narrow SP in TOPCon devices, which need a considerable quantity of silver. The experimental TOPCon devices as a function of TO thickness show a considerable trade-off between open circuit voltage (Voc) and fill factor (FF). While Voc rises, FF drops as TO thickness increases. The mechanism is described.

Lead‐Free halide perovskites for optoelectronic application: Investigation of structural, optical, electric and dielectric behaviors

Lead-free all-inorganic perovskite single crystals (SCs) are currently the subject of a lot of research because of their enhanced material stability and lower biological toxicity. These advancements are essential for removing major obstacles to the real-world implementation of device applications. The lead-free hybrid organic-inorganic compound (CH3NH3)2MnCl4 was synthesized in this work at room temperature employing the slow evaporation solution growth approach. Investigating its structural, optical, and electric characteristics was the key objective of the study. The (CH3NH3)2MnCl4 compound crystallises in the orthorhombic system (Pccn space group). For the compound under study, the UV–visible spectroscopy spectrum shows the direct band-gap value of ∼3.6 eV, indicating that it is a semiconductor material. The electric studies were conducted in a wide frequency range from 10−1 Hz–106 Hz and a temperature range from 348 to 388 K. Nyquist plots revealed only a semicircle in the whole impedance spectra due to the effect of interior grains. The obtained results were analyzed by fitting the experimental data to an equivalent circuit model R//C//CPE. The Alternating current conductivity (σAC) follows Jonscher's power law. The fitting of σAC curves reveals that the activation energy is equal to 0.706 eV. The dominant transport mechanism is the CBH model in the temperature range from 348 to 388 K. Studies of the dielectric constant permittivity ε*(ω) confirmed that the relaxation process was thermally activated.