Radiative Transfer Properties Research Articles

Toward a robust physical and chemical characterization of heterogeneous lines of sight: The case of the Horsehead nebula

Dense and cold molecular cores and filaments are surrounded by an envelope of translucent gas. Some of the low- J emission lines of and isotopologues are more sensitive to the conditions either in the translucent environment or in the dense and cold one because their intensities result from a complex interplay of radiative transfer and chemical properties of these heterogeneous lines of sight (LoSs). We extend our previous single-zone modeling with a more realistic approach that introduces multiple layers to take account of possibly varying conditions along the LoS. We used the IRAM-30m data from the ORION-B large program toward the Horsehead nebula in order to demonstrate our method's capability and effectiveness. We propose a cloud model composed of three homogeneous slabs of gas along each LoS, representing an outer envelope and a more shielded inner layer. We used the non-LTE radiative transfer code RADEX to model the line profiles from the kinetic temperature ( the volume density ( kinematics, and chemical properties of the different layers. We then used a fast and robust maximum likelihood estimator to simultaneously fit the observed lines of the and isotopologues. To limit the variance on the estimates, we propose a simple chemical model by constraining the column densities. A single-layer model cannot reproduce the spectral line asymmetries that result from a combination of different radial velocities and absorption effects among layers. A minimal heterogeneous model (three layers only) is sufficient for the Horsehead application, as it provides good fits of the seven fitted lines over a large part of the studied field of view. The decomposition of the intensity into three layers allowed us to discuss the distribution of the estimated physical or chemical properties along the LoS. About 80<!PCT!> of the integrated intensity comes from the outer envelope, while $ of the integrated intensity of the and lines of comes from the inner layer. For the lines of the and the isotopologues, integrated intensities are more equally distributed over the cloud layers. The estimated column density ratio NCeiO in the envelope increases with decreasing visual extinction, and it reaches $25$ in the pillar outskirts. While the inferred of the envelope varies from $25$ to K$ that of the inner layer drops to K$ in the western dense core. The estimated in the inner layer is pccm$ toward the filament, and it increases by a factor of ten toward dense cores. Our proposed method correctly retrieves the physical and chemical properties of the Horsehead nebula. It also offers promising prospects for less supervised model fits of wider-field datasets.

Elevating high-temperature insulation performance of silica aerogels enabled by innovative surface-structured opacifiers

Silica aerogel, recognized as an exceptional material for thermal insulation, has gained considerable attention in thermal protection. However, its inherent infrared transparency compromises its insulating performance at high temperatures. To address this limitation, incorporating micron-sized opacifier particles has emerged as a crucial strategy. This study introduces a novel opacifier particle, distinguished by surface protrusions inspired by the ’structural absorption’ mechanism, and assesses its extinction capabilities. Then, a thorough analysis was conducted to understand how the shape, volume, and numbers of these surface protrusions influence the radiative heat transfer properties of silica aerogels. The findings reveal that the presence of protrusions on the opacifier surface significantly enhances its extinction capacity, consequently reducing the radiative thermal conductivity of silica aerogels. Notably, cylindrical protrusions demonstrate the most effective extinction properties compared to spherical protrusions and rectangular protrusions. Additionally, for opacifier particles with cylindrical protrusions, there exists an optimal number of 12 protrusions that minimize the radiative thermal conductivity of the aerogel. At 1300 K, the radiative thermal conductivity of the silica aerogel doped with opacifiers featuring 12 protrusions is 22.6 % lower than that of the silica aerogel doped with opacifiers lacking protrusions. Moreover, it was observed that maintaining a constant diameter of cylindrical protrusions while increasing their height diminishes the radiative thermal conductivity of silica aerogel. However, the effect on the radiative thermal conductivity becomes less significant beyond a certain protrusion height. The outcomes of this study provide significant insights into the innovation of opacifiers.

Thermal analysis on a novel natural convection flat plate collector with perforated tilted transparent insulation material parallel slats (TIM-PS) in Mediterranean climate

The purpose of this research is the evaluation of heat transfer by natural convection in an innovative flat plate solar collector operating in natural convection mode. The design consists of inclined, perforated slats of transparent insulation material installed between the absorber and the glass cover. Hourly climatic data on the four specific days of solstices and equinoxes was used to investigate the behavior of the novel collector design in the city of Monastir; Tunisia. A comprehensive process, ANSYS FLUENT, was implemented to properly evaluate the thermal performance of the collector. In order to obtain accurate thermal properties of the smart collector façade unit containing the TIM-PS to exploit in the simulation, a validated three-dimensional finite volume model developed using the CFD software was used to solve the conductive, convective and radiative heat transfer properties of the system. We have explored in depth the effect of optical characteristics of the TIM-PS on the collector performance. Present research focuses on the analysis of thermal efficiency profile of flat plate collector with innovative façade in comparison with conventional collector for different climatic conditions. The analysis indicated that innovative façade collector’s efficiency is highly influenced by solar intensity. It was found that TIM-PS façade can effectively reduce the convective heat losses through the front of collector. The simulation results show that perforated tilted TIM-PS offer better performance than conventional façade of collector during all the seasons of the year. Simulations performed for one year predict that with careful selection of the parallel slats properties, the new façade system can generate an efficiency up to 83% in June, 76% in September, 53% in March and 42% in December. The results of the thermal evaluation of this research will help guide the future development of this system, as we have demonstrated that the innovative façade collector can be used all year round. In conclusion, the TIM-PS have great potential and a very wide range of applications in the field of flat plate solar collector.

Polarized radiative transfer in seawater-in-oil emulsions floated on seawater considering the impact of oil absorption on seawater droplet scattering.

Among various remote sensing approaches, optical polarization remote sensing shows great advantages in identifying oil-water emulsions in seawater and has become one of the most promising detection technologies. Herein, we focus on exploring the sensitivity of polarized radiative transfer properties for oil emulsion polarization detection to the influence factors of viewing angle, droplet volume fraction and radius, incident wavelength, and emulsion thickness. The radiative properties of seawater droplets dispersed in crude oil are calculated using the improved Lorenz-Mie theory considering the absorption of crude oil as the host medium, after which the reflected Stokes vector and the degree of linear polarization (DOLP) of seawater-in-oil emulsions floating on seawater are obtained using the spectral element method. By analyzing the calculation results of a 0° viewing azimuth angle, the detection wavelength and viewing zenith angles corresponding to the highest sensitivity of the DOLP to the above factors are significantly different; thus, quantitative remote sensing detection of the droplet volume fraction, droplet diameter, and emulsion thickness is possible. Exploring the sensitivity of polarized remote sensing signals for oil emulsion polarization detection to the above factors is a prerequisite for quantitative polarization detection of oil emulsions.

Properties of radiative charge transfer in heterogeneous noble-gas clusters

Radiative charge transfer (RCT) from cationic to neutral atoms is a fundamental and frequently occurring process in ion-neutral collisions and in van der Waals clusters. In contrast to collisions with only two collision partners, RCT in clusters is more involved as it may depend on the cluster size, the cluster stoichiometry, and the local arrangement of atoms in the cluster. Here, we present a systematic investigation of an RCT photon spectrum as a function of cluster size, stoichometry, and local atom arrangement. For this purpose, we utilize RCT in heterogeneous NeKr and NeXe clusters after Ne $2p$ photoionization. Our results confirm that Ne dimer ions form prior to RCT if enough Ne is available and we observe that different features dominate the photon spectrum depending on the cluster production parameters. Additionally, we find that the lifetime of the radiative decay is sensitive to the cluster stoichiometry, which we explain and interpret by theoretical calculations on the RCT decay width for different local geometric structures of the involved atoms. We conclude that RCT properties such as photon spectrum and lifetime in turn exhibit information on the mean size and stoichiometry of a cluster jet and the arrangement of the involved atoms.

Long-Term Observations of Microwave Brightness Temperatures over a Metropolitan Area: Comparison of Radiometric Data and Spectra Simulated with the Use of Radiosonde Measurements

Ground-based microwave radiometers are increasingly used in operational meteorology and nowcasting. These instruments continuously measure the spectra of downwelling atmospheric radiation in the range 20–60 GHz used for the retrieval of tropospheric temperature and water vapor profiles. Spectroscopic uncertainty is an important part of the retrieval error budget, as it leads to systematic bias. In this study, we analyze the difference between observed and simulated microwave spectra obtained from more than four years of microwave and radiosonde observations over Nizhny Novgorod (56.2° N, 44° E). We focus on zenith-measured and elevation-scanning data in clear-sky conditions. The simulated spectra are calculated by a radiative transfer model with the use of radiosonde profiles and different absorption models, corresponding to the latest spectroscopy research. In the case of zenith-measurements, we found a systematic bias (up to ~2 K) of simulated spectra at 51–54 GHz. The sign of bias depends on the absorption model. A thorough investigation of the error budget points to a spectroscopic nature of the observed differences. The dependence of the results on the elevation angle and absorption model can be explained by the basic properties of radiative transfer and by cloud contamination at elevation angles.

A weighted-sum-of-gray soot-fractal-aggregates model for nongray heat radiation in the high temperature gas-soot mixture

Soot, a product of insufficient combustion, is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties, which is rarely considered in predicting the radiative heat transfer in combustion flame. In the present study, based on the Rayleigh-Debey-Gans-Fractal-Aggregate (RDG-FA) theory, a model, named Weighted Sum of Gray Soot fractal Aggregates (WSGSA), used to calculate the radiative properties of nongray soot fractal aggregates in gas-soot mixture is developed by combining the features of full-spectrum k-distribution (FSK) model and Weighted-Sum-of-Gray-Gases (WSGG) model. Four gray soot fractal aggregates obtained from reordering in the form of the k-distribution at Gauss-Legendre integral points are selected to represent the nongray soot fractal aggregate, while corresponding weighting factors are obtained by fitting the radiation data obtained by the line-by-line (LBL) model with soot radiation data. Then, the WSGSA model is systematically validated by studying the radiative heat transfer properties in a one-dimensional plane-parallel slab system only with soot aggregates. The maximum relative discrepancies of emittance under different temperatures and different path lengths are less than 12%, while the maximum relative discrepancies of radiative heat source term and radiative heat flux are both less than 11% with path length less than 3 m. Moreover, combined with the WSGG model, the performance of the WSGSA model is further validated by predicting the radiative heat transfer properties in the mixture consisted of gases and soot aggregates, and acceptable results are also obtained. All the results reveal that the developed model can be applied to predict the radiative heat transfer in the mixture containing gases and soot aggregates, even in the case of significant changes in temperature and species concentration.

Applications of radiative transfer models to greenhouse vegetation

In greenhouse horticulture, efficiency of climate control and plant protection can be improved by having an accurate impression of plant status, such as photosynthesis or chemical composition. Recent advances in remote sensing technologies have brought about a range of innovations in precision agriculture, with the potential for adaptation to greenhouses. Simple, traditionally used indices employ only one or two spectral bands, in which the contributions of various pigments and leaf or canopy structure can highly overlap. Consequently, such indices may be insufficient for applications. State-of-the-art models have been developed that can better interpret hyper- and multispectral leaf and canopy imagery by employing the biochemical and radiative transfer properties of vegetation. An example is the soil-canopy observation of photosynthesis and energy balance (SCOPE) model, which was developed specifically for crop canopies. Here we present one of the pillars of SCOPE, the leaf radiative transfer (RT) model Fluspect. Fluspect simulates leaf chlorophyll fluorescence, reflectance and transmittance spectra. The model can be inverted to obtain estimates of leaf chlorophylls, carotenoids, anthocyanins, xanthophyll epoxidation, water and dry matter content. Moreover, it can be linked to a model for leaf photosynthesis and when inverted, provide a method to estimate photosynthesis directly from leaf spectral information. We test the model against a tomato data set, with measured hyperspectral images, chlorophyll, sugar, acid, starch, dry matter content and nutrients. The first study of the data set, using partial least square regression, showed that hyperspectral images have a high correlation with important fruit and leaf compounds. We compared these results to Fluspect retrievals and conventional vegetation indices. In the paper, we discuss the potential added value of using RT models in greenhouse horticulture.

Radiative transfer, absorption, and reflection by metal powder beds in laser powder-bed processing

Laser powder-bed processing is widely employed in 3D printing. The technological processes strongly depend on such effective radiative-transfer properties of powder beds as the absorptance and the radiation penetration depth. However, it is still not completely clear what are the principal factors influencing these properties and what are the possible ranges of their variation. For theoretical investigation of the radiative transfer, a ray-tracing method is developed where the effective properties of powder beds are expanded in series of the reflectance of the solid-phase surface. Once the coefficients of the power series are calculated, they can be used for any combination wavelength/material thus facilitating parametric analysis. Powder beds are modeled by equal spheres packed in regular cubic-symmetry structures of various density. The calculated radiation penetration depth can vary from few particle diameters for close-packed structures with moderate solid-phase absorptance to few tens of particle diameters for less dense power beds of a highly reflecting material. The effective absorptance of the powder bed is revealed to decrease significantly with the packing density. The calculated dependence of the powder-bed absorptance versus the solid-phase absorptance and the density is validated by the known experimental data. The calculated angular distribution of the radiation reflected by a powder bed slightly deviates from the cosine-like distribution corresponding to the diffuse reflection law. It is validated by the known experimental data. A modified model of equivalent medium is proposed to approximate the obtained ray tracing results by analytic expressions.

Development in the Heat Transfer Properties of Nanofluid Due to the Interaction of Inclined Magnetic Field and Non-Uniform Heat Source

In the current scenario a new mathematical model is designed and examined for the unsteady course of nanofluid through permeable vertical surface due to the interaction of inclined magnetic field. Radiative heat transfer properties is included assuming the Cogley radiation, dissipative heat energy due to the conjunction o magnetic field i.e., Joule dissipation and the space and time-dependent heat source/sink amplifies the study as well. Depending upon todays need in various industries the implementation of nanofluid is vital. Therefore, present study involves the behavior of both metal and oxide nanoparticles in the base fluid kerosene. Involvement of transformation rules the problem is converted into nonlinear set of ODEs and further these are solved employing approximate analytical technique such as Variational Iteration Method (VIM). The characteristics of various flow parameters are analyzed via graphs and the numerical simulation along with the validation of the result is obtained through tables. The comparative study brings out the convergence criterion of the methodology adopted herein. However, the favorable results are; the fluid temperature augments with increasing nanoparticle volume fraction and suction enriches both the fluid velocity and temperature whereas injection retards it significantly.

Moist Processes in the Atmosphere

Processes related to water in the atmosphere lead to severe uncertainties in weather forecasting and climate research. Atmospheric water vapor and cloud water strongly influence the Earth’s energy budget through, e.g., energy conversions associated with phase changes, fluid dynamical effects associated with buoyancy, and through their influence on radiative transfer properties of the atmosphere. Given the critical green-house effect of water vapor, it seems astounding that climate modellers cannot with certainty state whether the Earth’s cloud system has a positive or negative influence on the global mean temperature. The formation of clouds involves small-scale processes currently unresolved by climate models, and thus cloud cover is one of the main sources of uncertainty. This large uncertainty has its roots in the extremely wide range of length and time scales associated with moist processes, which pose an equally wide range of challenges to mathematical and computational modelling. New and innovative methods, modeling frameworks, efficient computational techniques, and complex statistical data analysis procedures as well as their mathematical analysis are urgently needed in order to make progress in this new field – from the mathematicians point of view. One of the main goals of this workshop is to show the path forward for current and future applied mathematical scientists, to work hand in hand across the disciplines of mathematics, physics, and atmospheric science, in order to tackle the complex problem of dynamical and thermodynamical processes associated with clouds and moisture, both from the theoretical and the applied view points.

New Constraints on Thermal and Dielectric Properties of Lunar Regolith from LRO Diviner and CE‐2 Microwave Radiometer

AbstractWe derive a new constraint on the thermal and dielectric properties of the lunar regolith layer by reconciling data from the Lunar Reconnaissance Orbiter (LRO) Diviner infrared radiometer and Chang'E‐2 (CE‐2) microwave radiometer (MRM). The bolometric Bond albedo of the lunar surface, which characterizes the ability of the lunar surface to reflect visible radiation, is a function of incidence angle. We determined the Bond albedo by using the Lunar Orbiter Laser Altimeter 1,064‐nm normal albedo and the surface temperature at noon as a function of latitude. The results suggest a modification to existing regolith thermal conductivity models based on a fit to the diurnal variation of Diviner data. Based on the thermal model, a 1‐D radiative transfer and dielectric properties model is developed to fit MRM data for the global Moon. With a new dielectric loss tangent equation for highland regolith applied, our model matches MRM data well at 19.35 and 37 GHz, which are generally accepted to be well calibrated. A global map of loss tangent of the Moon at these frequencies is also obtained by fitting the diurnal amplitude of microwave brightness temperature (TB) of each location on the Moon. We find that the loss tangent of highlands regolith has a slight frequency dependence and is larger than previous studies. We also identify a large discrepancy between our theoretical model and TB obtained by CE‐2 MRM at low frequencies, which is attributed to issues caused by contamination on calibration horn.

THz wave background radiation at upper troposphere

THz wave has advantages in targets detecting and imaging, however, the severe atmospheric attenuation limits its application range. To perform a higher transmittance through clouds and higher resolution, upper troposphere should be considered to be the application senario of THz wave. Therefore, it is necessary to study on the atmospheric radiative transfer properties at different altitudes. Atmospheric Radiative Transfer Simulator (ARTS) was used to calculate path attenuation in 6 window frequencies selected, as well as 6 peak frequencies to analyze the difference. The brightness temperature and path attenuation at different frequencies and altitudes in different directions are calculated and analyzed. Results show that the brightness temperature in up-looking directions at 0.34 THz is smaller than 50 K for all altitudes which indicates small background noise, therefore, this frequency has great potential in targets detecting at all altitudes. At altitudes higher than 15 km, the brightness temperatures at all selected window frequencies are smaller than 50 K, which means that these frequencies also have potential in the targets detecting or imaging and the path attenuation is small, too. All 6 selected window frequencies have the potential for targets detecting in up-looking directions due to low attenuation and small background radiation. The calculations are all under the assumption of clear sky, the clouds will be considered in the further work.

Ab-Initio Calculation of Spectral Absorption Coefficients in Molten Fluoride Salts with Metal Impurities

Molten salts have been proposed as coolants for numerous advanced reactor designs. It is envisioned that these reactors, both fluoride-salt–cooled high-temperature reactors and molten-salt–fueled reactors will operate at high temperatures, where the radiative heat transfer properties of the salts may be required for accurate heat transfer analysis. Experimental challenges have prevented the measurement of absorption coefficients in most salts. In an attempt to fill this gap in data, the Vienna Ab-Initio Simulation Package is used in the present research to calculate the absorption coefficient resulting from photoelectric interactions in numerous molten salts. Ab-initio molecular dynamics is used to generate the amorphous structures of a variety of salts. The pure halide salts LiF, FLiNaK, and FLiBe, are shown to be optically clear through a wide portion of the electromagnetic spectrum. Conversely, the transition metal fluoride salt KF-ZrF4 is shown to be substantially opaque. As chromium is a known impurity of concern from the corrosion of steels in reactor environments, the effect on absorption of low levels of chromium in an otherwise transparent salt is investigated and found to significantly increase absorption at relevant wavelengths.

Light Scattering by Fractal Dust Aggregates. II. Opacity and Asymmetry Parameter

Abstract Optical properties of dust aggregates are important at various astrophysical environments. To find a reliable approximation method for optical properties of dust aggregates, we calculate the opacity and the asymmetry parameter of dust aggregates by using a rigorous numerical method, the T-Matrix Method, and then the results are compared to those obtained by approximate methods: the Rayleigh–Gans–Debye (RGD) theory, the effective medium theory (EMT), and the distribution of hollow spheres method (DHS). First of all, we confirm that the RGD theory breaks down when multiple scattering is important. In addition, we find that both EMT and DHS fail to reproduce the optical properties of dust aggregates with fractal dimensions of 2 when the incident wavelength is shorter than the aggregate radius. In order to solve these problems, we test the mean field theory (MFT), where multiple scattering can be taken into account. We show that the extinction opacity of dust aggregates can be well reproduced by MFT. However, it is also shown that MFT is not able to reproduce the scattering and absorption opacities when multiple scattering is important. We successfully resolve this weak point of MFT, by newly developing a modified mean field theory (MMF). Hence, we conclude that MMF can be a useful tool to investigate radiative transfer properties of various astrophysical environments. We also point out an enhancement of the absorption opacity of dust aggregates in the Rayleigh domain, which would be important to explain the large millimeter-wave opacity inferred from observations of protoplanetary disks.

Linear Parameter-varying Approach for Modeling and Control of Rapid Thermal Processes

In the present paper, a new approach is presented to model and control single wafer rapid thermal processing (RTP) systems. In the past decade, RTP has achieved acceptance as the mainstream technology for semiconductor manufacturing. Thermal processing is one of the most efficient ways to control the phase-structure properties. Moreover, the time duration of RTP systems reduces the so-called thermal budget significantly compared to the traditional methods. RTP implementation is based on the use of light from heating lamps to provide a heat flux. This process is highly nonlinear due to the radiative heat transfer and material properties. By invoking the first principles-based models, we develop in this paper a linear parameter-varying (LPV) model to directly account for the nonlinearities within the system. The model is then discretized into a high-order LPV model; thereafter, principal component analysis (PCA) method is utilized to reduce the number of LPV model’s scheduling variables, followed by the use of proper orthogonal decomposition (POD) for model order reduction. Using the reduced order model, we then design a gain-scheduled controller to satisfy an induced L2 gain performance for tracking of a temperature profile and show improvement over other controller design methods suggested in the literature.

Spectral tuning of near-field radiative heat transfer by graphene-covered metasurfaces

When two gratings are respectively covered by a layer of graphene sheet, the near-field radiative heat transfer between two parallel gratings made of silica (SiO2) could be greatly improved. As the material properties of doped silicon (n-type doping concentration is 1020 cm−3, marked as Si-20) and SiO2 differ greatly, we theoretically investigate the near-field radiative heat transfer between two parallel graphene-covered gratings made of Si-20 to explore some different phenomena, especially for modulating the spectral properties. The radiative heat flux between two parallel bulks made of Si-20 can be enhanced by using gratings instead of bulks. When the two gratings are respectively covered by a layer of graphene sheet, the radiative heat flux between two gratings made of Si-20 can be further enhanced. By tuning graphene chemical potential μ and grating filling factor f, due to the interaction between surface plasmon polaritons (SPPs) of graphene sheets and grating structures, the spectral properties of the radiative heat flux between two parallel graphene-covered gratings can be effectively regulated. This work will develop and supplement the effects of materials on the near-field radiative heat transfer for this kind of system configuration, paving a way to modulate the spectral properties of near-field radiative heat transfer.

Near-field radiative heat transfer in graphene plasmonic nanodisk dimers

Near-field thermal radiation mediated by surface plasmons in parallel graphene nanodisk dimers is studied using a semianalytical model under the electrostatic approximation. The radiative heat transfer between two disks as a function of the distance between them in coaxial and coplanar configurations is first considered. Three regimes are identified and their extents determined using nondimensional analysis. When the edge-to-edge separation is smaller than the disk diameter, near-field coupling and surface plasmon hybridization lead to an enhancement of the radiative heat transfer by up to four orders of magnitude compared to the Planck blackbody limit. A mismatch in the disk diameters affects the plasmonic mode hybridization and can either diminish or enhance the near-field radiation. Destructive interference between eigenmodes that emerge when the relative orientation between disks is varied can induce a twofold reduction in the radiative heat transfer. In all configurations, the radiative heat transfer properties can be controlled by tuning the disk size/orientation, the substrate optical properties, and graphene's doping concentration and electron mobility.

Characteristics of L-band transmissivity and effective scattering albedo of boreal forests: a case study in northeast China

ABSTRACTModeling of forest transmissivity (tF), or nadir optical depth (nF), and effective scattering albedo (ωF) of L-band radiometer, helps to reduce the uncertainty in retrieved forest soil parameters. To address this issue, the L-band downward brightness temperatures of boreal forests in Northeast China were observed. Forest tF (or nF) and ωF were derived from in-situ soil parameters and observed forest brightness temperature by combining the advanced integral equation model (AIEM), the zero-order radiative transfer model (τ-ω), and a genetic algorithm (GA). Some conclusions about forest radiative transfer properties are revealed here: 1) tF is nearly 0.3 higher in summer than in winter, and this seasonal difference in tF is bigger than was previously thought. Next to the difference in the amount of leaves present, air temperature might be an important factor influencing this seasonal variation in tF. 2) A moderate dependence of nF on polarization exists. 3) Dependence of nF on the incidence angle was only observed in winter. 4) Forest ωF is independent of polarization, incidence angle, woody volume and forest type, but the ωF value derived in this study is significantly higher than the default values of the SMOS and SMAP algorithms.

Dispersive Properties of Mesoporous Gold: van der Waals and Near-Field Radiative Heat Interactions

We present a theoretical calculation of the dispersive interaction of mesoporous Au sponges. The ability to manipulate the dielectric function of the sponge by varying its porosity is applied to the calculation of the Hamaker constant using Lifshitz theory and the near radiative heat transfer properties. By using an effective medium approximation the dielectric function of the mesoporous sponge is calculated. As the porosity increases, our calculations show that the Hamaker constant decreases significantly. This is also used to calculate the van der Waals force between a gold nanoparticle and a gold mesoporous sponge as a function of the porosity. Also, using the fluctuating electrodynamics formalism, the change in the local electromagnetic density of states in the near field is calculated. As an application, the near field radiative heat absorbed by a SiC nanoparticle at a fixed distance from a Au sponge is calculated for different values of the porosity. The maximum heat transfer is achieved for high porosities near a metal–insulator percolation transition.