Radiative Transfer Research Articles

Abstract The density limit is investigated in the DIII-D negative triangularity (NT) plasmas which lack a standard H-mode edge. We find the limit may not be a singular disruptive boundary but a multifaceted density saturation phenomenon governed by distinct core and edge transport mechanisms. Sustained, non-disruptive operation is achieved at densities up to 1.8 times the Greenwald limit ($n_\mathrm{G}$) until the termination of auxiliary heating. Systematic power scans reveal distinct power scalings for the core ($n_e \propto P_\mathrm{SOL}^{0.27\pm0.03}$) and edge ($n_e \propto P_\mathrm{SOL}^{0.42\pm0.04}$) density limits. The edge density saturation is triggered abruptly by the onset of a non-disruptive, high-field side radiative instability that clamps the edge density below $n_\mathrm{G}$. In contrast, the core density continues to rise until it saturates, a state characterized by substantially enhanced core turbulence. Core transport evolves from a diffusive to an intermittent, avalanche-like state, as indicated by heavy-tailed probability density functions (kurtosis $\approx 6$), elevated Hurst exponents, and a $1/f$-type power spectrum. These findings suggest that the density limit in the low-confinement regime is determined by a combination of edge radiative instabilities and core turbulent transport. This distinction provides separate targets for control strategies aimed at extending the operational space of future fusion devices.

Abstract We utilize James Webb Space Telescope (JWST) Mid Infrared Instrument (MIRI) integral field unit observations to investigate the behavior and excitation of H 2 in the nearby Seyfert galaxies NGC 3081 and NGC 5506, both part of the Galactic Activity, Torus, and Outflow Survey (or GATOS). We compare population levels of the S(1) to S(8) rotational H 2 emission lines visible to JWST/MIRI spectroscopy to models assuming local thermodynamic equilibrium (LTE), in order to estimate the column density and thermal scaling of the molecular gas. For the nuclear regions, we incorporate Very Large Telescope Spectrograph for INtegral Field Observations in the Near Infrared (or VLT/SINFONI) K -band observations to estimate population levels for available rovibrational H 2 emission lines, and compare the resultant population curves to non-LTE radiative transfer models and shock modeling. We report a differing set of prominent active galactic nuclei (AGN)-driven excitation mechanisms between the two galaxies. For NGC 3081, we find that a non-LTE radiative transfer environment is adequate to explain observations of the nuclear region, indicating that the primary mode in which the AGN transfers excitation energy is likely irradiation. We estimate the extent of AGN photoionization along the ionization bicone to be ≈330 pc. In contrast, for NGC 5506, we find a shock scenario to be a more plausible excitation mechanism, a conclusion bolstered by an observed spatial correlation between higher-energy rotational H 2 and [Fe II ] 5.34 μ m emission. In addition, we identify potential nuclear H 2 outflows resulting from an interaction between the ionization bicone and the rotational disk. By isolating the outflowing component of the H 2 emission, we estimate the warm molecular mass outflow rate to be 0.07 M ⊙ yr −1 .

The interpretation of infrared (IR) measurements of photon-dominated regions (PDRs) relies on understanding the properties of dust. Additionally, the dependence of dust properties on the environment provides key insights into dust composition, evolution, as well as formation and destruction processes. This work is conducted as part of the Physics and Chemistry of PDR Fronts program dedicated to the study of dust and gas in PDRs with the James Webb Space Telescope (JWST). A significant component of interstellar dust consists of carbonaceous nano-grains which often dominate the mid-IR output of PDRs. In this paper, we study the evolution of the nano-grains across the illuminated edge of the Horsehead nebula and especially their abundance and size properties. We used NIRCam (3.0, 3.35, and 4.3,μm) and MIRI (5.6, 7.7, 10.0, 11.3, 12.8, 15.0, 18.0, 21.0, and 25.5,μm) photometric bands, along with NIRSpec and MRS spectroscopic observations to map the illuminated edge of the Horsehead. We modeled dust emission, including the aromatic and aliphatic IR bands, using the THEMIS interstellar dust model together with the 3D radiative transfer code SOC, in order to fit the photometric bands. A detailed modeling of high angular resolution JWST data (∼ 6 times higher than that of former observations) allowed us to obtain quantitative constraints on the size distribution of nano-grains. In addition, original constraints on the optical properties of these nano-grains were derived from the JWST NIRSpec spectroscopic data. We find that the diffuse interstellar medium (DISM) dust cannot account for the observed data, and it is necessary to use evolved grains. A sharp increase in density is observed at the illuminated edge, consistent with recent ALMA observations, which reveal a very sharp transition between molecular and ionized gas. Although the PDR length along the line of sight (łpdr) could not be directly determined from this study, we estimate an upper limit of ∼ 0.015 pc based on geometric considerations and low extinction measured in the IR. This constraint implies a lower limit on the abundance of small grains ( > 0.003), showing that small grains are not depleted at the external edge of the Horsehead nebula, unlike in other PDRs such as the Orion Bar. Our findings indicate a high-density environment and a less steep size distribution for nano-grains at the illuminated edge, in contrast with the DISM. This implies that nano-grain destruction mechanisms, such as UV-induced destruction, might be less efficient in the Horsehead's moderate-UV field than in PDRs with more intense radiation, such as the Orion Bar. These results support a model where nano-grain population recovery, potentially through grain reformation due to the fragmentation of larger grains, is slower in moderate-ultraviolet (UV) environments, leading to a unique dust size distribution at the edge of the Horsehead nebula.

Climate change is causing major sea ice losses, leading to increased light availability across polar marine ecosystems, however the consequences are largely unknown. We quantify how future conditions for sea ice and snow, storm-driven waves, clouds, ozone, air and ocean temperature, and chlorophyll-a will affect seasonal absorption and reflection of light in Arctic seas, alongside growth and survival of fish. Using four CMIP6 model inputs and a spectral radiative transfer model, we predict a 75-160% increase in visible light by 2100 in the Northern Bering, Chukchi, and Barents Seas. We predict increased sunlight and warmer summer waters, with reduced phytoplankton levels, will negatively impact cold-water fish species growth and survival during summer, demonstrated here for polar cod. Asynchrony in prey and light availability, with prolonged periods of warmer waters, will reduce polar cod survival in the fall and restrict habitats in these regions after 2060. Warmer-water species like walleye pollock and Atlantic cod will be less impacted but may struggle at high latitudes during the polar night. Ocean warming coupled with increased light availability will accelerate changes in Arctic ecosystems, compromising the growth and survival of Arctic species in transitional zones and facilitating the northward expansion of boreal species.

Recently, the International Commission on Radiological Protection (ICRP) has released adult and pediatric mesh-type reference computational phantoms (MRCPs) through its Publications 145 and 156, which incorporate anatomically refined respiratory tract structures that overcome the limitations of earlier voxel and stylized models. In this study, a comprehensive dataset of specific absorbed fractions (SAFs) and radionuclideSvalues was generated for the respiratory tract across the entire age- and sex-specific series of ICRP MRCPs. The phantoms were implemented in the Geant4 Monte Carlo radiation transport code (version 11.3) to compute SAFs for photons, electrons, and alpha particles over the energy ranges of 0.001-10 MeV for photons and electrons and 1-12 MeV for alpha particles, with certain low-energy values supplemented by a limiting SAF interpolation approach. The calculated SAFs were subsequently combined with nuclear decay data from ICRP Publication 107 to derive S values for all relevant source regions following inhalation exposures to radionuclides. Photon and electron SAFs were obtained for 36 source-target combinations, and alpha SAFs for 18 combinations, whileSvalues were produced for 1,252 radionuclides. The calculated SAFs exhibited clear age-dependent trends, with larger values in younger phantoms. Furthermore, the calculated SAFs andSvalues were generally greater than previously reported ICRP values. The complete dataset is available through an open-access repository, representing the first effort to provide SAFs andSvalues for the respiratory tract using the ICRP MRCPs. The calculations explicitly accounted for micrometre-scale source and target regions within anatomically realistic respiratory tract structures, while also incorporating inter-tissue irradiation cases, which had not been possible with previous models.

Abstract Modeling of pyrolytic carbon (PyC) coating on spheronized graphite particles was performed with the goal of developing a high-performance anode material for lithium-ion batteries. The model takes into account convective and radiative heat transfer, particle movement in a fluidized bed, benzene pyrolysis kinetics and carbon deposition in view of the adhesion coefficient. It has been shown that efficient benzene decomposition for PyC coating formation occurs at temperature of 1000–1100℃. A nitrogen pulse feed rate of 10 pulses min-1 maximizes particle concentration in the benzene active decomposition zone. A semi-empirical model predicting PyC coating thickness as a function of temperature and particle diameter was presented. The calculated layer thickness varies from 20 to 45 nm and is in good agreement with the experiment. The obtained anode material exhibits ≤ 5% loss in specific discharge capacity at 2C and recovers up to 99% capacity at 0.1C.

Abstract This paper presents the first part of a two‐part study to develop a new algorithm to retrieve the aerosol vertical extinction profile using the hyperspectral measurements at ultraviolet bands, O 2 A‐band and B‐band, from the Tropospheric Monitoring Instrument (TROPOMI). We represent the aerosol vertical profile by the weighted sum of 3–5 most important EOFs (empirical orthogonal function, i.e., eigenvectors) from the principal component analysis (PCA) of the 15‐year record of aerosol extinction profiles from spaceborne lidar Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP). Hence, the retrieval is simplified to derive 3–5 coefficients or weights of corresponding EOFs to capture the variation of aerosol vertical profiles. A new PCA module was developed in the Unified Linearized Vector Radiative Transfer Model (UNL‐VRTM) for calculating the Jacobians of top‐of‐atmosphere (TOA) reflectance with respect to the weights of EOFs, which is used to facilitate the optimal inversion of the EOF weights. The analytical Jacobian calculations are validated against the Jacobians computed from a finite difference method. The averaging kernel analysis for directly retrieving the aerosol extinction profiles from measurements of TROPOMI and high‐resolution metagrating spectropolarimeter for aerosol profiling was provided. Finally, the retrieval experiments with synthetic TROPOMI measurements generated by UNL‐VRTM were conducted to verify the self‐consistency and feasibility of the inversion algorithm on a theoretical basis.

Abstract Optical and infrared surveys have detected increasing numbers of disc accretion outbursts in young stars. Some models of these FU Ori-type events predict that the outburst should start at near- to mid-infrared wavelengths before an optical rise is detected, and this lag between infrared and optical bursts has been observed in at least two systems. Detecting and characterizing infrared precursors can constrain the outburst trigger region, and thus help identify the mechanism producing the outburst. However, because FU Ori objects are generally young and usually embedded in dusty protostellar envelopes, it is not clear whether or how well such infrared precursors can be detected in the presence of strong envelope extinction. To explore this question, we combine time-dependent outburst models of the inner disc with an outer dusty disc and protostellar envelope, and calculate the resulting spectral energy distributions (SEDs) using the radiative transfer code RADMC3D. We find that, for envelope mass infall rates ≳ 10−5M⊙ yr−1 (rc/30 au)−1/2, where rc is a characteristic inner radius for the infalling envelope, the infrared precursor is only apparent in the SED when viewed along an outflow cavity. At other inclinations, the precursor is most easily distinguished with limited envelope extinction at infall rates ≲ 10−6M⊙ yr−1 (rc/30 au)−1/2. We also show that far-infrared and submm/mm monitoring can enable the indirect detection of precursor evolution long before the optical outburst, emphasizing the potential of long-wavelength monitoring for studying the earliest stages of protostar formation.

Soil moisture simulations in semi-arid inland river basins remain highly uncertain due to complex land–atmosphere interactions and multiple parameterization schemes in land surface models. This study evaluated the ability of the Noah-Multiparameterization Land Surface Model (Noah-MP) to simulate soil moisture at meteorological sites representing the upstream, midstream and downstream regions of a semi-arid inland river basin with contrasting climates. A large physics-ensemble experiment (17,280 simulations per site) combining different parameterization schemes for 10 main physical processes was conducted. Natural selection, Tukey’s test and uncertainty contribution analysis were applied to identify sensitive processes and quantify their contributions to simulation uncertainty. Results indicate that Noah-MP captures soil moisture variability across the basin but with notable biases. Three physical processes—frozen soil permeability, supercooled liquid water in frozen soil and ground resistance to sublimation—were sensitive at all sites, whereas radiation transfer and surface albedo were consistently insensitive. At the upstream and midstream sites, supercooled liquid water contributed about half of the ensemble uncertainty, and at the downstream site ground resistance to sublimation contributed roughly 51%. These findings reveal which physical processes most strongly affect Noah-MP soil moisture simulations in semi-arid basins and provide guidance for improving parameterization schemes to reduce uncertainty.

Emulation of radiation transport in 3D stochastic media using 1D planar Monte Carlo stochastic media radiation transport algorithms

External radiative heat transfer corrections for film-cooled turbine blades in hot environments

Emulating non-gray gas radiative heat transfer in combustion scenarios by machine learning method

Enhanced radiative heat transfer between graphene and Weyl semimetals based on surface plasmon coupling

Experimental study on the radiative heat transfer characteristics of individual droplets in space liquid droplet radiators

Monolayer group-IV monochalcogenides: A promising platform for near-field radiative heat transfer

Aerosol optical depth retrieval from Geostationary Environment Monitoring Spectrometer (GEMS): Advancing the first hyperspectral geostationary air quality mission using deep learning.

Implementation of low stream interpolation technique to accelerate scattering calculations in the 4A/OP radiative transfer model

Context. The new generation of optical spectrographs, including WEAVE, 4MOST, DESI, and WST, offers huge multiplexing capabilities and excellent spectral resolution. This is an unprecedented opportunity to statistically unveil the details of the star formation histories (SFHs) of galaxies. However, these observations are not easily comparable with the predictions of cosmological simulations. Aims. Our goal is to build a reference framework for comparing spectroscopic observations with cosmological simulations and to test the currently available tools for deriving the stellar population properties of mock galaxies as well as their SFHs. We focus on the observational strategy of the Stellar Population at intermediate redshift Survey (StePS) carried out with the WEAVE instrument. Methods. We created mock datasets of ∼750 galaxies at redshifts of z = 0.3, 0.5, and 0.7 from the TNG50 cosmological simulation. We performed radiative transfer calculations using SKIRT and analyzed the spectra with the pPXF algorithm, treating them as if they were real observations. Results. This work presents the methodology used to generate the mock datasets, providing an initial exploration of stellar population properties (i.e. mass-weighted ages and metallicities) and SFHs of a test sample of three galaxies at z = 0.7 and their descendants at z = 0.5 and 0.3. We show that there is very good agreement between mock WEAVE-like spectra compared to the intrinsic values in TNG50 (average difference of 0.2 ± 0.3 Gyr). We also report that an overall agreement is seen when retrieving the SFHs of galaxies, especially if they form the bulk of their stars on short timescales and at early epochs. While we did identify a tendency to overestimate the weight of old stellar populations in galaxies with complex SFHs, we were able to properly recover the timescales on which galaxies build up 90% of their mass, with almost no difference in the measured and intrinsic cumulative SFHs over the last 4 Gyr. Conclusions. We have released the datasets concurrently with this publication of this paper, which consist of multi-wavelength imaging and spectroscopic data of ∼750 galaxies at redshift z = 0.3, 0.5, and 0.7. This work provides a fundamental bench-test for forthcoming WEAVE observations, providing the community with realistic mock spectra of galaxies that can be used to test currently available tools for deriving first-order stellar populations parameters (i.e. ages and metallicities) as well as more complex diagnostics, such as mass and SFHs.

Radiative transfer modeling of the low-mass proto-binary system, IRAS 4A1 and 4A2

Abstract Field et al. (2018, https://doi.org/10.1029/2018ef000820 ) had proposed spreading hollow glass microspheres (HGMs) over Arctic sea ice to increase its albedo. Webster and Warren (2022, https://doi.org/10.1029/2022ef002815 ) assessed that proposal with a radiative transfer model that used (a) HGMs with optical properties published by Field et al., indicating 10% absorption by a thin layer, and (b) hypothetical non‐absorbing HGMs. Strawa et al. (2025, https://doi.org/10.1029/2024ef004749 ) have now obtained updated optical properties indicating that HGMs are less absorptive than previously thought. However, field experiments produce less albedo‐enhancement than predicted by radiative transfer models, by 0.1 or more, regardless of which value of HGM absorptance is used in the model.