Properties Of Medium Research Articles

Thermal performance of a novel composite phase change material for solar-assisted air source heat pump packed bed thermal energy storage application

The thermal properties of the heat storage medium in the solar-assisted air source heat pump (SAASHP) systems must be aligned with the system’s heat generation temperature while satisfying the heat demand. In this study, a novel composite phase change material (CPCM) for efficient heat storage in SAASHP systems was developed. Our investigation revealed that the incorporation of 8 wt% KNO3, 1.5 wt% thickener, and 1.0 wt% Al2O3 nanoparticles into sodium acetate trihydrate resulted in the manifestation of desirable properties suitable for SAASHP systems. The compound exhibited a suitable melting point of 48.66 °C, high latent heat of 235.97 kJ/kg, low supercooling degree of 2.25 °C, and good thermal conductivity of 0.905 W/(m·K). Furthermore, the novel CPCM demonstrated exceptional thermal stability, with only an 8.64 % loss of latent heat after undergoing 200 cycles, while maintaining a supercooling degree within a range of 6 °C for each cycle. Moreover, molecular dynamics simulation results further indicated that the presence of KNO3 weakened the interaction between CH3COONa molecules and water molecules, leading to a reduction of the melting point. Additionally, numerical analysis revealed that the total heat storage capacity and exergy storage capacity of the packed bed thermal energy storage (PBTES) system filled with the novel CPCM are 358.8 MJ and 25.1 MJ, respectively. With an increase in the heating power of the SAASHP system from 10 kW to 30 kW, the cycle heat storage time of the PBTES system can decrease by 38.8 %, while an increase in the flow rate from 2 m3/h to 6 m3/h can reduce the time by 26.3 %. These findings have significant implications for the selection and composition design of thermal storage materials in SAASHP systems.

Utilizing numerical techniques for modeling radiating Casson nanofluid flow with thermophoretic phenomenon on a heated stretching surface

This work aims to use mathematical modeling to investigate the mechanics of heat and mass transport in dissipative Casson nanofluid flows over a linear rough sheet. This study considers various elements such as thermal radiation, magnetic fields, heat generation, the varied properties of porous media, and the thermophoretic impact. Besides that, it looks into the variations in viscosity, diffusivity, and thermal conductivity, as well as the energy dissipation from viscous internal friction and fluid temperature modifications. The method involves coming up with and changing the boundary layer equations into a group of linked nonlinear ordinary differential equations that use variables that do not have any dimensions. The foundation of the solution strategy for these equations is the Hermite collocation method (HCM), which is renowned for its precision and adaptability. It offers an organized approach to solving the complex differential equations, allowing for accurate numerical solutions. The use of graphical representations ensures thorough data analysis and clarity, while also providing insightful information about the computed outcomes. The code validation method uses numerical comparisons with recent research to confirm the algorithm’s accuracy and dependability, as well as its resilience in comparison to the existing literature. Important conclusions from the study show that thermal boundary layers and nanofluid velocity decrease with increases in the porosity parameter, slip parameter, and magnetic field parameter.

The SDSS-V Local Volume Mapper (LVM): Scientific Motivation and Project Overview

We present the Sloan Digital Sky Survey V Local Volume Mapper (LVM). The LVM is an integral-field spectroscopic survey of the Milky Way, Magellanic Clouds, and a sample of local volume galaxies, connecting resolved parsec-scale individual sources of feedback to kiloparsec-scale ionized interstellar medium (ISM) properties. The 4 yr survey covers the southern Milky Way disk at spatial resolutions of 0.05–1 pc, the Magellanic Clouds at 10 pc resolution, and nearby large galaxies at larger scales totaling >4300 deg2 of sky and more than 55M spectra. It utilizes a new facility of alt–alt mounted siderostats feeding 16 cm refractive telescopes, lenslet-coupled fiber optics, and spectrographs covering 3600–9800 Å at R ∼ 4000. The ultra-wide-field integral-field unit has a diameter of 0.°5 with 1801 hexagonally packed fibers of 35.″3 apertures. The siderostats allow for a completely stationary fiber system, avoiding instability of the line-spread function seen in traditional fiber feeds. Scientifically, LVM resolves the regions where energy, momentum, and chemical elements are injected into the ISM at the scale of gas clouds, while simultaneously charting where energy is being dissipated (via cooling, shocks, turbulence, bulk flows, etc.) to global scales. This combined local and global view enables us to constrain physical processes regulating how stellar feedback operates and couples to galactic kinematics and disk-scale structures, such as the bar and spiral arms, as well as gas in- and outflows.

Transverse-momentum dependent model for hadronization in deep-inelastic lepton-nucleus scattering off heavy nuclei

Semi-inclusive deep inelastic scattering off nuclei is a unique process to study the parton propagation mechanism and its modification induced by the presence of the nuclear medium. It allows us to probe the medium properties, particularly the cold nuclear matter transport coefficient, which can be directly linked to the nuclear gluon density. We present here a model for hadron production in deep inelastic lepton-nucleus scattering, which takes into account the hadronic transverse momentum of final state particles via transverse-momentum dependent parton distributions and fragmentation functions. We implement parton energy loss and hadronic absorption with a geometrical model of the nucleus. The model is compared with the nuclear semi-inclusive deep-inelastic scattering multiplicity ratios and transverse-momentum broadening data from the CLAS, HERMES, and EMC collaborations, aiming for a simultaneous description of these data sets. We obtain a good agreement over the various nuclear targets and the wide kinematical range of those experiments. We best describe the data with a transport coefficient q̂=0.3GeV/fm2, and we highlight the importance and the role of correlations in extracting this quantity. Published by the American Physical Society 2024

Ground-penetrating radar subsurface attenuation analysis based on a sparsity-promoting time-frequency transform

The attenuation characteristics of a medium involve the absorption of electromagnetic wave energy during its propagation and represent a crucial parameter for describing the properties of subsurface media. Due to the complex nature of signal attenuation, demanding consideration of numerous parameters, quantitative analysis is challenging. Time-frequency (TF) analysis is a promising technique that simultaneously analyzes nonstationary signals in the time and frequency domains. Although the quantitative characterization of attenuation factors using TF tools can be challenging, TF analysis retains substantial potential for qualitatively estimating attenuation from ground-penetrating radar (GPR) data. The sparsity-promoting TF (SPTF) transform method with [Formula: see text] and [Formula: see text] norms joint constraints has a significantly higher TF resolution than the linear TF transform in the time and frequency domains. We develop a method for high-resolution qualitative estimation of GPR attenuation based on the SPTF method. Synthetic experiments indicate that SPTF surpasses other methods regarding TF resolution, noise robustness, and fidelity to dominant frequencies. Subsequent qualitative attenuation results using synthetic and field data agree with synthetic model outcomes and actual leakage ranges. This alignment substantiates the superior resolution and accuracy of our approach compared with alternative methods, affirming its efficacy and superiority in GPR attenuation depiction.

Blocking of Gas–Liquid Coalescing Filters with Accumulated Oil during the On–Off Operation of a Filtration System

The study aims to eliminate the effect of coalescing filter blocking due to on–off operation by changing the wetting properties of the non-woven fiberglass filter media through their chemical modification with the use of a polydimethylsiloxane (PDMS) solution in hexane and a few commercial products that give the surface oleophobic properties. The best results—high separation efficiency, no redispersion of droplets at the outlet, and low flow resistance—were obtained for materials coated by immersion in a 0.2% PDMS solution, for which a reduction in oleophilicity was found, but the material was not oleophobic and still moderately wetted with the test liquid. The corresponding static contact angle with the VG-46 rotary compressor oil measured on the flat borosilicate glass wafer made of the same material as the fiberglass media was equal to 54° for the PDMS dip-coated surface. Moreover, the good stability of the applied polymer on the material surface was confirmed by the SEM imaging, the FTIR analysis, and maintaining a high performance in multiple tests run for a single coalescing element.

Tuneable vibration control of beams using granular multilayer composite

We explore a passive control solution of bending waves in beams, which takes advantage of the dissipative properties of granular media. It consists in a layer of particles confined between two beams and interacting with each other through their contacts. The inter-particles contacts are intrinsically dissipative due to friction, which efficiently works under shear. In practice, the mechanical response of such a multilayer inherit Hertz contact mechanics, thus conferring confining pressure dependent elasticity and dissipation. Previous work have shown that the hysteretic shear behaviour of a granular medium confined in a box can be reasonably captured by a single DOF model using Dahl model fed by an effective medium theory of granular media. Using this reduced model together with finite element method, we simulate the dynamic response of a three-layer composite beam whose core is made of confined frictional particles. This model makes it possible to characterize its elastic and damping properties, revealing in particular a high and tuneable loss factor with respect to shear strain amplitude and confining pressure, suitable for vibro-acoustics applications.

Sound absorbers from walnut shell waste: measurement and models

Waste walnut shells have been cleaned, dried, chopped, glued, pressed, and molded to form porous cylinders for measurement of normal incidence sound absorption coefficient spectra in an impedance tube. Porosities and flow resistivities have been measured non-acoustically. Field Emission Scanning Electron Microscopy images, used to obtain fragment size for determining shell density, reveal that the fragment surfaces are rough, which may influence acoustical performance. Measured absorption spectra have been compared with predictions of two analytical models for acoustical properties of rigid porous media, which assume microstructures of identical uniform parallel slanted slits (SS) and non-uniform cylindrical pores with a log normal radius distribution (NUPSD) respectively. Measured values of flow resistivity and porosity are used in the models but tortuosity is adjusted to give best agreement with the quarter wavelength resonance in the measured absorption coefficient spectra. Predictions agree best with data for samples made from the smallest shell fragments. These samples have the highest values of tortuosity, flow resistivity and offer good absorption at speech frequencies which suggests that recyclable and sustainable sound absorbers made from walnut shell wastes could be useful for controlling indoor reverberation..

Towards estimating acoustic surface impedances at low frequencies in a reverberation chamber

To accurately simulate interior acoustical fields, reliable descriptions of the physical properties of the acoustical space are required. While geometry, propagation medium properties, and source characteristics are, in general, easily accessible, the absorption characteristics of the bounding surfaces of a space can be difficult to obtain. For commonly used materials, databases of absorption coefficients could be used. However, absorption coefficient databases are of limited use at low frequencies, especially below 100 Hz. Furthermore, measurement-based estimations tend to be more reliable. Thus, there is incentive to perform measurement-based estimations of the absorption characteristics of a room's bounding surfaces at low frequencies. This work considers the estimation of sound absorption, given in terms of locally-reacting surface impedance, at modal frequencies. This is made feasible by solving an inverse eigenvalue problem. The spatially-uniform, frequency-dependent impedance of the bounding surfaces of a reverberation chamber is estimated. The method is validated by comparing measured transfer functions to simulated transfer functions, which are generated using the estimated impedance. It is shown that the proposed method can be used to estimate locally-reacting surface impedance from measured room impulse responses at low frequencies.

Hydrodynamics of molten media bubble columns for hydrogen production through methane pyrolysis

Methane pyrolysis using a molten media bubble column reactor is a promising technique for hydrogen production with low carbon dioxide emissions at a feasible price. Understanding the bubble dynamics in molten media is essential to elucidate the reaction mechanisms and establish design requirements for efficient reactors. Computational fluid dynamics provides an effective means to understand the hydrodynamics in opaque molten media. This research used the volume of fluid method to study the effects of gas injection rate as well as variations in gas and molten media (iron, aluminum, and a salt mixture of sodium bromide and potassium bromide in a 48.7:51.3 molar ratio) properties on bubble dynamics. The computational model was first validated using existing experimental and empirical observations. This study makes fundamental contributions to the understanding of bubble dynamics in molten media. First, it was confirmed that gas properties had a small effect on bubble dynamics. The difference in bubble diameters between argon at ambient temperature and 1600 °C was less than 10%. Second, it was found that the volumetric gas injection rate and molten media properties significantly impacted the bubble dynamics, including the bubble diameter and flow regime. Future work will build on these findings to recommend appropriate operating conditions and molten media for specific pyrolysis reactor designs.

Utilizing polydispersity in three-dimensional random fibrous based sound absorbing materials

The distribution of fiber diameters plays a crucial role in the transport and sound absorbing properties of a three-dimensional random fibrous (3D-RF) medium. Conventionally, volume-weighted averaging of fiber diameters has been utilized as an appropriate microstructural descriptor to predict the static viscous permeability of 3D-RF media. However, the long wavelength acoustical properties of a 3D-RF medium are also sensitive to the smallest fibers, this is particularly true in the high-frequency regime. In our recent research, we demonstrated that an inverse volume-weighted averaging of fiber diameters can effectively serve as a complementary microstructural descriptor to capture the high-frequency behavior of polydisperse fibrous media. In the present work, we reexamine the identification of two representative volume elements (RVEs) which relies on the reconstruction of 3D-RF microstructures having volume-weighted and inverse-volume weighted averaged fiber diameters, respectively in the low-frequency and high frequency regimes. We investigate the implication of such a weighting procedure on the transport and sound absorbing properties of polydisperse fibrous media, highlighting their potential advantages. Furthermore, we discuss the challenges associated with this research field. Finally, we provide a brief perspective of the future directions and opportunities for advancing this area of study.

Complexes of polymeric acids and short polyamines as binary stimulus-sensitive systems

Stimulus-sensitive polymers are of great interest due to their unusual properties in solution and diverse applications. Copolymers with different groups (hydrophilic, hydrophobic and ionizable) are typical stimulus-sensitive polymers, and varying the copolymer composition allows the pH and thermal sensitivity to be adjusted for a particular application. We found that complexes of polymeric acids with short methylated polyamines having trimethylene insertions between amine groups exhibit stimulus-sensitive properties in aqueous media at moderate pH and temperature. The position of the lower critical temperature of the solution depends on the ratio of polyacid to polyamine and on the pH. The complex of poly(acrylic acid) and pentaamine was found to be electrosensitive: exposure to an electric field with reversible polarity (8 Hz) led to precipitation of the polymer. These binary stimulus-sensitive compositions consist of two simple substances and are a promising alternative to copolymer-based systems, since the adjustment of properties does not require the synthesis of new substances and expensive toxicological studies in the case of biomedical applications.

FOS: A fully integrated open-source program for Fast Optical Spectrum calculations of nanoparticle media

FOS, which means light in Greek, is an open-source program for Fast Optical Spectrum calculations of nanoparticle media. This program takes the material properties and a description of the system as input, and outputs the spectral response including the reflectance, absorptance, and transmittance. Previous open-source codes often include only one portion of what is needed to calculate the spectral response of a nanoparticulate medium, such as Mie theory or a Monte Carlo method. FOS is designed to provide a convenient fully integrated format to remove the barrier as well as providing a significantly accelerated implementation with compiled Python code, parallel processing, and pre-trained machine learning predictions. This program can accelerate optimization and high throughput design of optical properties of nanoparticle or nanocomposite media, such as radiative cooling paint and solar heating liquids, allowing for the discovery of new materials and designs. FOS also enables convenient modeling of lunar dust coatings, combustion particulates, and many other particulate systems. In this paper we discuss the methodology used in FOS, features of the program, and provide four case studies.

Theoretical investigation of the optical and plasmonic properties of the nanocomposite media composed of silver nanoparticles embedded in rubidium

This theoretical study investigates, the optical response of a metal-dielectric nanocomposite of silver and rubidium (Ag/Rb) is theoretically studied via Maxwell-Garnett Model by varying the size, shape and volume ratio of the silver nanoparticles (AgNPs) in the coherently driven four levels rubidium dielectric atomic media. The rubidium being an alkali metal behaves as dielectric under quantum coherence effect. It was found that the optical response of this nanocomposite media strongly depends on the coherent driving fields applied in the atomic ensemble, the volume fraction of the AgNPs as well as their size and the applied frequencies. It was found that the dielectric function decreases with the increase in AgNPs’ size, while increase in Rabi frequency increases the refractive index. Similarly, the dispersion and absorption decrease with decrease in volume fraction of the AgNPs. Our results suggest important applications of this nanocomposite in various fields such as energy harvesting, photovoltaics and quantum plasmonics. The modeling approach developed in this study provides great freedom for tuning optical properties of the metal-dielectric nanocomposites.

The Local Group L-band Survey: The First Measurements of Localized Cold Neutral Medium Properties in the Low-metallicity Dwarf Galaxy NGC 6822

Abstract Measuring the properties of the cold neutral medium (CNM) in low-metallicity galaxies provides insights into heating and cooling mechanisms in early Universe-like environments. We report detections of two localized atomic neutral hydrogen (H i) absorption features in NGC 6822, a low-metallicity (0.2 Z ⊙) dwarf galaxy in the Local Group. These are the first unambiguous CNM detections in a low-metallicity dwarf galaxy outside the Magellanic Clouds. The Local Group L-band Survey (LGLBS) enabled these detections, due to its high spatial (15 pc for H i emission) and spectral (0.4 km s−1) resolution. We introduce LGLBS and describe a custom pipeline for searching for H i absorption at high angular resolution and extracting associated H i emission. A detailed Gaussian decomposition and radiative transfer analysis of the NGC 6822 detections reveals five CNM components, with key properties: a mean spin temperature of 32 ± 6 K, a mean CNM column density of 3.1 × 1020 cm−2, and CNM mass fractions of 0.33 and 0.12 for the two sightlines. Stacking nondetections does not reveal low-level signals below our median optical depth sensitivity of 0.05. One detection intercepts a star-forming region, with the H i absorption profile encompassing the CO (2−1) emission, indicating coincident molecular gas and a depression in high-resolution H i emission. We also analyze a nearby sightline with deep, narrow H i self-absorption dips, where the background warm neutral medium is attenuated by intervening CNM. The association of CNM, CO, and Hα emissions suggests a close link between the colder, denser H i phase and star formation in NGC 6822.

Constraining the Properties of the Multicomponent Local Interstellar Medium: MHD-kinetic Modeling Validated by Voyager and New Horizons Data

We introduce the first solar-cycle simulations from our 3D, global MHD-plasma/kinetic-neutrals model, where both hydrogen and helium atoms are treated kinetically, while electrons and helium ions are described as individual fluids. Using Voyager/PWS observations of electron density up to 160 au from the Sun for validation of several different global models, we conclude that the current estimates for the proton density in the local interstellar medium (LISM) need a revision. Our findings indicate that the commonly accepted value of 0.054 cm−3 may need to be increased to values exceeding 0.07 cm−3. We also show how different assumptions regarding the proton velocity distribution function in the outer heliosheath may affect the global solution. A new feature revealed by our simulations is that the helium ion flow may be significantly compressed and heated in the heliotail at heliocentric distances exceeding ∼400 au. Additionally, we identify a Kelvin–Helmholtz instability at the boundary of the slow and fast solar wind in the inner heliosheath, which acts as a driver of turbulence in the heliotail. These results are crucial for inferring the properties of the LISM and of the global heliosphere structure.

Understanding the role of flux chamber configuration in the measurement of VOC emissions from porous media

The accurate quantification of volatile organic compound (VOC) emission rates from porous media to the air is a challenging problem, as measurements are affected by the chemical and physical characteristics of the porous media, and the operating parameters of the sampling device itself. The main objective of this study is to investigate how flux chamber (the most commonly used sampling device) configurations influence emission rate measurement from three selected porous media. Various parameters were studied, including sweep air flow rate, presence of a mixing fan, headspace volume and thickness of media. Controlled experiments focused on the behaviour of two VOCs commonly found in area sources: acetic acid and 1-butanol. Sweep gas flow rate emerged as the most influential factor, inducing turbulence and dilution over porous media surfaces and impacting emission rate measurements more significantly than headspace volume and fan installation. Variations in porous media properties also affected mass transfer, with emissions from coco coir showing higher mass transfer as its porosity and particle size facilitated gas transportation. While behaviour of acetic acid emission through the media supported the diffusion theory, emission of 1-butanol was affected by a combination of factors, highlighting the role of both diffusive and advective transport mechanisms. Understanding how flux chamber setups and porous media properties influence emission rates is crucial for accurately interpreting data. This knowledge also guides the design of studies, especially when investigating complex sources like biosolids and organic-amended soil.

A new census of dust and polycyclic aromatic hydrocarbons at z = 0.7–2 with JWST MIRI

Aims. This paper utilises the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) to extend the observational studies of dust and polycyclic aromatic hydrocarbon (PAH) emission to a new mass and star formation rate (SFR) parameter space beyond our local Universe. The combination of fully sampled spectral energy distributions (SEDs) with multiple mid-infrared (mid-IR) bands and the unprecedented sensitivity of MIRI allows us to investigate dust obscuration and PAH behaviour from z = 0.7 up to z = 2 in typical main-sequence galaxies. Our focus is on constraining the evolution of PAH strength and the dust-obscured luminosity fraction before and during cosmic noon, the epoch of peak star formation activity in the Universe. Methods. In this study, we utilise MIRI multi-band imaging data from the SMILES survey (5 to 25 μm), complemented with NIRCam photometry from the JADES survey (1 to 5 μm), available HST photometry (0.4 to 0.9 μm), and spectroscopic redshifts from the FRESCO and JADES surveys in GOODS-S for 443 star-forming (without dominant active galactic nucleus (AGN)) galaxies at z = 0.7 − 2.0. This redshift range was chosen to ensure that the MIRI data cover mid-IR dust emission. Our methodology involved employing ultraviolet (UV) to IR energy balance SED fitting to robustly constrain the fraction of dust mass in PAHs and dust-obscured luminosity. Additionally, we inferred dust sizes from MIRI 15 μm imaging data, enhancing our understanding of the physical characteristics of dust within these galaxies. Results. We find a strong correlation between the fraction of dust in PAHs (PAH fraction, qPAH) with stellar mass. Moreover, the sub-sample with robust qPAH measurements (N = 216) shows a similar behaviour between qPAH and gas-phase metallicity to that at z ∼ 0, suggesting a universal relation: qPAH is constant (∼3.4%) above a metallicity of Z ∼ 0.5 Z⊙ and decreases to < 1% at metallicities ≲0.3 Z⊙. This indicates that metallicity is a good indicator of the interstellar medium properties that affect the balance between the formation and destruction of PAHs. The lack of a redshift evolution from z ∼ 0 − 2 also implies that above Z ∼ 0.5 Z⊙ the PAH emission effectively traces obscured luminosity and the previous locally calibrated PAH-SFR calibrations remain applicable in this metallicity regime. We observe a strong correlation between the obscured UV luminosity fraction (ratio of obscured to total luminosity) and stellar mass. Above the stellar mass of M* > 5 × 109 M⊙, on average, more than half of the emitted luminosity is obscured, while there exists a non-negligible population of lower-mass galaxies with > 50% obscured fractions. At a fixed mass, the obscured fraction correlates with SFR surface density. This is a result of higher dust covering fractions in galaxies with more compact star-forming regions. Similarly, galaxies with high IRX (IR to UV luminosity) at a given mass or UV continuum slope (β) tend to have higher ΣSFR and shallower attenuation curves, owing to their higher effective dust optical depths and more compact star-forming regions.

Mathematical modeling of sound propagation through the respiratory tract in a modified gas environment

The aim of the work was to develop a mathematical model of sound propagation through the human respiratory tract when breathing certain respiratory gas mixtures. We based the model on an assembler model of branching of the respiratory tract. For calculations, we presented the human tracheobronchial tree in the form of an equivalent T-shaped cut section diagram, which includes parameters of the walls of the respiratory tract. We carried the simulation out in two main stages. At the first stage, we calculated the impedance of the flow from the small airways to the larger airways. At the second stage, we calculated the sound pressure caused by breathing. As a result, we obtained the curves of the impedance dependence on the frequency spectrum, as well as the sound power from the respiratory flow. We noted that when breathing air, the impedance value remains constant with increasing frequency. Moreover, we also noted that when exposed to a heavier gas than air, the impedance value constantly increases, and when exposed to lighter gases, after reaching a maximum, the impedance value decreases. We found that the highest sound pressure is typical for the oxygen-krypton mixture, and the lowest for the oxygen–helium mixture. We also found that in the case of modeling the laminar flow regime (with a critical Reynolds number equal to 1800), sound affects how many generations of bronchi more than in the case of modeling the transient flow regime (with a critical Reynolds number equal to 2700). Thus, we drew conclusions about the influence of the physical properties of gaseous media on the amount of sound pressure and the propagation of sound through the human respiratory tract.

Protein Medium Facilitates Electron Transfer in Photosynthetic Heliobacterial Reaction Center.

This computational study addresses the question of how large membrane-bound proteins of electron transport chains facilitate fast vector-based charge transport. We study electron transfer reactions following ultrafast initial charge separation induced by absorption of light by P800 primary pair and leading to the electron localization at the A0 cofactor. Two subsequent, much slower reactions, electron transfer to the iron-sulfur cluster Fx and reduction of the menaquinone (MQ) cofactor, are studied by combining molecular dynamics simulations, electronic structure calculations, and theoretical modeling. The low value of the electronic coupling between A0 and Fx brings this reaction to the microsecond time scale even at the zero activation barrier. In contrast, A0-MQ electron transfer occurs on a subnanosecond time scale and might become the preferred route for charge transport. We elucidate mechanistic properties of the protein medium allowing fast, vectorial charge transfer. The electric field is high and inhomogeneous inside the protein and is coupled to high polarizabilities of cofactors to significantly lower the reaction barrier. The A0-MQ separation puts this reaction at the edge between the plateau characterizing the reaction dynamical control and exponential falloff due to electronic tunneling. A strong separation in relaxation times of the medium dynamics for the forward and backward reactions promotes vectorial charge transfer.