Equivalent Extinction Research Articles

Harnessing machine learning for accurate treatment of overlapping opacity species in general circulation models

To understand high precision observations of exoplanets and brown dwarfs, we need detailed and complex general circulation models (GCMs) that incorporate hydrodynamics, chemistry, and radiation. For this study, we specifically examined the coupling between chemistry and radiation in GCMs and compared different methods for the mixing of opacities of different chemical species in the correlated-k assumption, when equilibrium chemistry cannot be assumed. We propose a fast machine learning method based on DeepSets (DS), which effectively combines individual correlated-k opacities (k-tables). We evaluated the DS method alongside other published methods such as adaptive equivalent extinction (AEE) and random overlap with rebinning and resorting (RORR). We integrated these mixing methods into our GCM (expeRT/MITgcm) and assessed their accuracy and performance for the example of the hot Jupiter HD 209458 b. Our findings indicate that the DS method is both accurate and efficient for GCM usage, whereas RORR is too slow. Additionally, we observed that the accuracy of AEE depends on its specific implementation and may introduce numerical issues in achieving radiative transfer solution convergence. We then applied the DS mixing method in a simplified chemical disequilibrium situation, where we modeled the rainout of TiO and VO, and confirmed that the rainout of TiO and VO would hinder the formation of a stratosphere. To further expedite the development of consistent disequilibrium chemistry calculations in GCMs, we provide documentation and code for coupling the DS mixing method with correlated-k radiative transfer solvers. The DS method has been extensively tested to be accurate enough for GCMs; however, other methods might be needed for accelerating atmospheric retrievals.

A characterization of ASAS-SN core-collapse supernova environments with VLT+MUSE

Context. The analysis of core-collapse supernova (CCSN) environments can provide important information on the life cycle of massive stars and constrain the progenitor properties of these powerful explosions. The MUSE instrument at the Very Large Telescope (VLT) enables detailed local environment constraints of the progenitors of large samples of CCSNe. Using a homogeneous SN sample from the All-Sky Automated Survey for Supernovae (ASAS-SN) survey, an untargeted and spectroscopically complete transient survey, has enabled us to perform a minimally biased statistical analysis of CCSN environments. Aims. We analyze 111 galaxies observed by MUSE that hosted 112 CCSNe – 78 II, nine IIn, seven IIb, four Ic, seven Ib, three Ibn, two Ic-BL, one ambiguous Ibc, and one superluminous SN – detected or discovered by the ASAS-SN survey between 2014 and 2018. The majority of the galaxies were observed by the All-weather MUse Supernova Integral field Nearby Galaxies (AMUSING) survey. Here we analyze the immediate environment around the SN locations and compare the properties between the different CCSN types and their light curves. Methods. We used stellar population synthesis and spectral fitting techniques to derive physical parameters for all H II regions detected within each galaxy, including the star formation rate (SFR), Hα equivalent width (EW), oxygen abundance, and extinction. Results. We found that stripped-envelope supernovae (SESNe) occur in environments with a higher median SFR, Hα EW, and oxygen abundances than SNe II and SNe IIn/Ibn. Most of the distributions have no statistically significant differences, except between oxygen abundance distributions of SESNe and SNe II, and between Hα EW distributions of SESNe and SNe II. The distributions of SNe II and IIn are very similar, indicating that these events explode in similar environments. For the SESNe, SNe Ic have higher median SFRs, Hα EWs, and oxygen abundances than SNe Ib. SNe IIb have environments with similar SFRs and Hα EWs to SNe Ib, and similar oxygen abundances to SNe Ic. We also show that the postmaximum decline rate, s, of SNe II correlates with the Hα EW, and that the luminosity and the Δm15 parameter of SESNe correlate with the oxygen abundance, Hα EW, and SFR at their environments. This suggests a connection between the explosion mechanisms of these events to their environment properties.

Numerical investigation on the accuracy of size information of fractal soot aerosols retrieved by lidar: Optical property, morphology effect, and parameterization scheme

Lidar is effective in retrieving size distribution of atmospheric particles such as soot aerosols in real-time based on Mie scattering theory. However, the fundamental spherical shape assumption of Mie theory is obviously discrepant with the actual situations of atmospheric soot particles which are fractal and mixed with coating materials. In this study, the effects of fractal shapes and morphological parameters such as fractal dimension (Df), volume fraction (Vf), and particle radius (r) of soot aerosols on the size information retrieved by lidar based on Mie theory were investigated from the numerical aspect, closed-cell and coated-aggregate models were employed to represent soot aerosols thinly and heavily coated by non-absorbing materials, respectively. Optical properties of fractal soot particles were calculated at first, then backscattering and extinction properties were employed to retrieve backscattering equivalent radius (rbk) and extinction equivalent radius (rext) based on Mie theory, just like the lidar retrieval. Results revealed that optical properties of spherical and fractal models differ significantly with the variation of volume equivalent radius (rvol). Radius retrieval errors based on extinction cross-section are much smaller than that based on backscattering cross-section. The retrieval accuracy of coated-aggregate is higher than bare fractal aggregate and closed-cell models. Retrieved size distribution parameters mean radius are generally underestimated while standard deviation are overestimated for both models. Furthermore, parameterization schemes connecting rext and rvol of soot were constructed, retrieval errors are effectively reduced from about 25% to 10%, which is meaningful for the improvement of size retrieval accuracy of soot using lidar observations.

Analysis on influences of micro-scale ligament morphology and pore-level structure parameter on spectral properties of alumina foam

The radiative behaviors occurring inside ceramic alumina foams are influenced by the multi-scale structures ranging from micro-scale to pore-level, which determine the equivalent radiative properties. In this work, the microscopic morphologies of ligament and pore-level porous structure of alumina foam are introduced, while the spectral apparent and volumetric radiative parameters are predicted by performing a trans-scale simulation coupling the FDTD method with the Monte Carlo ray tracing method. By applying different simplified models at different scales and reconstructed realistic structure models respectively, the corresponding spectral radiative parameters of alumina foam sheets are compared and discussed, with different microscopic morphology characteristics and pore-level structure parameters considered. By comprehensive analysis, it can be observed that the spectral radiative properties of alumina foam are affected by complex multi-scale structural characteristics. The pore-level parameters have great influences on the apparent spectral radiative properties and equivalent extinction coefficient, while the micro-scale ligament structures change the spectral selectivity and scattering asymmetry factor obviously. For the scattering albedo, the effects produced by various micro-scale and pore-level structural parameters are close.

Male and Female Sprague Dawley Rats Exhibit Equivalent Natural Reward, Nicotine Self-Administration, Extinction, and Reinstatement During Adolescent-Initiated Behaviors.

The initiation of nicotine and tobacco use peaks during adolescence. How adolescent males and females differ based on the acquisition of nicotine use and nicotine-seeking behavior is less understood. Our current studies develop a preclinical intravenous self-administration and reinstatement paradigm in male and female Sprague Dawley rats to evaluate how sex impacts the acquisition of nicotine self-administration and nicotine-seeking, when behavior is initiated during adolescence. Male and female adolescent rats were food trained under a fixed-ratio one (FR1) schedule of reinforcement and progressively increased to FR5. Animals were implanted with catheters and began nicotine self-administration (0.015 mg/kg/infusion) at FR5 during adolescence on postnatal day 34. Upon reaching stable reinforced responding, animals were tested for progressive ratio (PR) schedules of reinforcement followed by extinction via the removal of drug and associated cues for a minimum of 5 days or until responding was reduced to ≤25% of baseline. Reinstatement testing began for cue only, nicotine only, and a combination of nicotine plus cues using a Latin square design. Animals returned to extinction conditions for 2 days minimum between testing. No sex differences were observed for natural rewards, acquisition, and PR schedules of nicotine self-administration, days to extinction, and reinstatement condition. Our findings provide evidence that sex does not impact natural rewards, nicotine reinforcement, reward, and reinstatement, when behavior is initiated during adolescence. Our study offers a feasible approach for assessing nicotine-seeking in male and female Sprague Dawley rats during the unique developmental window of adolescence. This study demonstrates the impact of nicotine and associated cues in the reinstatement of nicotine-seeking in male and female rats when behavior is initiated during adolescence. Findings support the equivalent impact of nicotine and the nonpharmacological stimuli of cues between male and female adolescent rats that began nicotine self-administration during adolescence.

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

Engineering of inorganic nanostructures with hierarchy of chiral geometries at multiple scales

GALACTICNUCLEUS: A high-angular-resolution JHKs imaging survey of the Galactic centre

Context. The extreme extinction (AV ~ 30 mag) and its variation on arc-second scales towards the Galactic centre hamper the study of its stars. Analysis of them is restricted to the near infrared (NIR) regime, where the extinction curve can be approximated by a broken power law for the JHKs bands. Therefore, it is fundamental to correct for extinction at these wavelengths in order to analyse the structure and stellar population of the central regions of our Galaxy. Aims. We aim to, (1) discuss different strategies to de-redden the photometry and check the usefulness of extinction maps to deal with variable stars; (2) build extinction maps for the NIR bands JHKs and make them publicly available; (3) create a de-reddened catalogue of the GALACTICNUCLEUS (GNS) survey, identifying foreground stars; and (4) perform a preliminary analysis of the de-reddened Ks luminosity functions (KLFs). Methods. We used photometry from the GNS survey to create extinction maps for the whole catalogue. We took red clump (RC) and red giant stars of similar brightnesses as a reference to build the maps and we de-reddened the GNS photometry. We also discussed the limitations of the process and analysed non-linear effects of the de-reddening. Results. We obtained high resolution (~3″) extinction maps with low statistical and systematics uncertainties (≲5%) and computed average extinctions for each of the regions covered by the GNS. We checked that our maps effectively correct the differential extinction reducing the spread of the RC features by a factor of ~2. We assessed the validity of the broken power law approach computing two equivalent extinction maps AH using either JH and HKs photometry for the same reference stars and obtained compatible average extinctions within the uncertainties. Finally, we analysed de-reddened KLFs for different lines of sight and found that the regions belonging to the NSD contain a homogeneous stellar population that is significantly different from that in the innermost bulge regions.

Optimal power of laser beams propagating from the ground through the atmosphere to space orbits

It is shown that, when a high-power laser beam propagates from the ground through the atmosphere to space orbits, there is an optimal beam power that maximizes the target intensity due to self-focusing effect in the atmosphere, even if the atmospheric extinction exists. The B integral is an important parameter to describe self-focusing effect quantitatively. It is found that the value of B integral corresponding to optimal beam power is a constant. Based on this characteristic of the optimal B integral and the concept of the equivalent atmospheric extinction coefficient proposed in this paper, we derive the analytical formula of the optimal beam power, which presents an effective design rule to optimize the target intensity. In addition, it is shown that the optimal beam power increases as the initial beam radius, the wavelength, the atmospheric extinction coefficient, and the aerosol scale height increase.

Experimental characterization of the coupled conductive and radiative heat transfer in ceramic foams with a flash method at high temperature

During recent decades, numerous studies on ceramic foams improved their efficiency and made their use possible in a myriad of engineering applications. Some studies showed that a good understanding of the link between structural parameters (porosity, pore diameter, or tortuosity) and thermal properties could lead to a better system performance. Ceramic foams are often used at high temperatures, where radiation plays an important role. This paper explores, both conductive and radiative heat transfers in such media, using a flash method experiment. The direct model developed is based on the resolution of the Energy Balance Equation (EBE), solved by a Finite Volume Method and the Radiative Transfer Equation (RTE), computed with an Optimized Emission Reciprocity Method (OERM). An inversion procedure made it possible to simultaneously characterize both equivalent conductivity for conduction and equivalent optical thickness for radiation of structured and random foams with different pore size distributions at 800 ∘C. Results showed that the influence of each heat transfer mode can be characterized separately with single experiment and a good agreement was found between the developed model and the experimental measurements. Radiative transfers can be described by a single equivalent, Beerian and gray extinction coefficient dependings strongly on the size of the cells and the organization of the solid matrix. The equivalent conductivity depends on the porosity, the ceramic constituting the solid matrix, the organization of the porous medium and the internal porosity. We estimated the associated equivalent total and radiative conductivities, allowing the quantification of the conduction/radiation ratio, for a wide variety of structures.

Influence of Scattering Phase Function on Estimated Thermal Properties of Al2O3 Ceramic Foams

Open ceramic foams are usually constituted of three-dimensional networks with randomly interconnected solid struts and fluid within pores. The heat transport within this material can be understood as the coupling of conduction, convection as well as radiation. The cooperative control of different heat transfer mechanisms is critical to successful design and optimization of components working at high temperatures. An answer to this problem usually requires good knowledge and understanding of the corresponding thermal properties in a wide range of temperatures. In the present paper, an inverse identification method was developed to determine coupled thermal properties from transient thermal measurements at temperatures up to 900 K for full description of conduction/radiation heat transports of foam media with absorbing, emitting, and anisotropic scattering effects. The influence of postulated phase function on the identified equivalent extinction coefficient, scattering albedo, anisotropic scattering factor, and two-phase thermal conductivity was discussed for better understanding of thermal behavior within ceramic foams. The estimated thermal properties under each postulated phase function of the sample at transient temperature profiles were used to calculate equivalent thermal conductivities, which were then compared with the measured results at more than 1000 K. The accordance between them indicated that linear anisotropic scattering phase function demonstrates superiority in description of radiation behavior within Al2O3 ceramic foam.

Design and deposition of a metal-like and admittance-matching metamaterial as an ultra-thin perfect absorber

A stratiform metamaterial, comprising metal and dielectric thin films, exhibits both near-perfect antireflection and strong light extinction to function as a perfect and ultra-thin light absorber. The equivalent admittance and extinction coefficient of the metamaterial are tailored using a visual method that is based on an admittance diagram. A five-layered metamaterial was designed and deposited with a total thickness of 260 nm on a mirror to exhibit strong and wide angle absorption over wavelengths from 400 nm to 2000 nm. A seven-layered metamaterial with a total thickness of less than 200 nm was designed and deposited to have equivalent admittance around unity and an extinction coefficient that is comparable to that of metal. Such a metal-like metamaterial exhibits low reflectivity so couples most visible light energy into the films and dissipates energy with an equivalent skin depth of less than 55 nm over visible wavelengths.

Postretrieval Extinction Attenuates Alcohol Cue Reactivity in Rats.

Conditioned responses to alcohol-associated cues can hinder recovery from alcohol use disorder (AUD). Cue exposure (extinction) therapy (CET) can reduce reactivity to alcohol cues, but its efficacy is limited by phenomena such as spontaneous recovery and reinstatement that can cause a return of conditioned responding after extinction. Using a preclinical model of alcohol cue reactivity in rats, we evaluated whether the efficacy of alcohol CET could be improved by conducting CET during the memory reconsolidation window after retrieval of cue-alcohol associations. Rats were provided with intermittent access to unsweetened alcohol. Rats were then trained to predict alcohol access based on a visual cue. Next, rats were treated with either standard extinction (n=14) or postretrieval extinction (n=13). Rats were then tested for long-term memory of extinction and susceptibility to spontaneous recovery and reinstatement. Despite equivalent extinction, rats treated with postretrieval extinction exhibited reduced spontaneous recovery and reinstatement relative to rats treated with standard extinction. Postretrieval CET shows promise for persistently attenuating the risk to relapse posed by alcohol cues in individuals with AUD.

Treatment of overlapping gaseous absorption with the correlated-kmethod in hot Jupiter and brown dwarf atmosphere models

The correlated-k method is frequently used to speed up radiation calculations in both one-dimensional and three-dimensional atmosphere models. An inherent difficulty with this method is how to treat overlapping absorption, i.e. absorption by more than one gas in a given spectral region. We have evaluated the applicability of three different methods in hot Jupiter and brown dwarf atmosphere models, all of which have been previously applied within models in the literature: (i) Random overlap, both with and without resorting and rebinning, (ii) equivalent extinction and (iii) pre-mixing of opacities, where (i) and (ii) combine k-coefficients for different gases to obtain k-coefficients for a mixture of gases, while (iii) calculates k-coefficients for a given mixture from the corresponding mixed line-by-line opacities. We find that the random overlap method is the most accurate and flexible of these treatments, and is fast enough to be used in one-dimensional models with resorting and rebinning. In three-dimensional models such as GCMs it is too slow, however, and equivalent extinction can provide a speed-up of at least a factor of three with only a minor loss of accuracy while at the same time retaining the flexibility gained by combining k-coefficients computed for each gas individually. Pre-mixed opacities are significantly less flexible, and we also find that particular care must be taken when using this method in order to to adequately resolve steep variations in composition at important chemical equilibrium boundaries. We use the random overlap method with resorting and rebinning in our one-dimensional atmosphere model and equivalent extinction in our GCM, which allows us to e.g. consistently treat the feedback of non-equilibrium chemistry on the total opacity and therefore the calculated P-T profiles in our models.

MAPPING THE INTERSTELLAR MEDIUM WITH NEAR-INFRARED DIFFUSE INTERSTELLAR BANDS

We map the distribution and properties of the Milky Way's interstellar medium as traced by diffuse interstellar bands (DIBs) detected in near-infrared stellar spectra from the SDSS-III/APOGEE survey. Focusing exclusively on the strongest DIB in the H-band, at ~1.527 microns, we present a projected map of the DIB absorption field in the Galactic plane, using a set of about 60,000 sightlines that reach up to 15 kpc from the Sun and probe up to 30 magnitudes of visual extinction. The strength of this DIB is linearly correlated with dust reddening over three orders of magnitude in both DIB equivalent width (W_DIB) and extinction, with a power law index of 1.01 +/- 0.01, a mean relationship of W_DIB/A_V = 0.1 Angstrom mag^-1, and a dispersion of ~0.05 Angstrom mag^-1 at extinctions characteristic of the Galactic midplane. These properties establish this DIB as a powerful, independent probe of dust extinction over a wide range of A_V values. The subset of about 14,000 robustly detected DIB features have an exponential W_DIB distribution. We empirically determine the intrinsic rest wavelength of this transition to be lambda_0 = 15,272.42 Angstrom, and then calculate absolute radial velocities of the carrier, which display the kinematical signature of the rotating Galactic disk. We probe the DIB carrier distribution in three dimensions and show that it can be characterized by an exponential disk model with a scaleheight of about 100 pc and a scalelength of about 5 kpc. Finally, we show that the DIB distribution also traces large-scale Galactic structures, including the central long bar and the warp of the outer disk.

Phenomenology of Ground Scattering in a Tropical Forest Through Polarimetric Synthetic Aperture Radar Tomography

This paper aims at characterizing the scattering mechanisms occurring at the ground level in a tropical forest illuminated by a P-band synthetic aperture radar (SAR). The analysis is carried out based on the multibaseline, fully polarimetric, data set collected by ONERA over Paracou, French Guyana, in the frame of the European space agency campaign TropiSAR. The favorable baseline distribution of this data set results in the possibility of removing most contributions from the vegetation layer by tomographic techniques, thus allowing the generation of a new fully polarimetric single look complex SAR image relative to scattering contributions from the ground level only. Such a ground layer image is then analyzed by considering the variation of its polarimetric signature with respect to terrain local slope and Radar look angle. Two major conclusions are drawn: 1) double bounce scattering from trunk-ground interactions is observed to be the dominant scattering mechanism at the ground level on flat terrains, whereas it rapidly tends to vanish as the topographic slope increases, and 2) the characteristic parameter that rules trunk-ground scattering is not the tree height, but rather the available free path facing the tree, as a result of the presence of nearby trees, undulating topography, or understory preventing double bounce scattering from taking place whenever the ground bounce occurs too far away from the considered tree. The mean free path length resulting from the analysis of this data-set is found to be L ≅ 7 m. Finally, we discuss how the concept of free path length can be accounted for in simple terms by assuming an equivalent extinction model characterized by a variation along the horizontal dimension.

Identification of radiative properties of reticulated ceramic porous inert media using ray tracing technique

The radiative properties of reticulated porous inert media are computationally identified using the real three-dimensional structural data of porous media. The computational grids data are reconstructed from three-dimensional computer tomography scans and magnetic resonance image scans of different reticulated porous media. A ray tracing algorithm is used to track the rays inside the grid structure. Statistically large numbers of rays are traced for their path length and incident angle, which are used to find the probability based equivalent extinction coefficient and scattering phase function. The equivalent extinction coefficients are found for porous media with different porosities and pore densities. The dependency of specular and diffuse scattering phase functions on the porous structure and surface reflectance are also studied.

Two ways to deepen extinction and the difference between them.

A series of experiments used rats to compare and contrast the effects of subjecting an already extinguished target conditioned stimulus (CS) to additional extinction in compound with either another extinguished or a nonextinguished CS. Exposure to either compound restored responding and their extinction deepened the loss of fear responses (freezing) to the target relative to a CS given equivalent extinction in isolation. This deepening was greater to the target extinguished in compound with the nonextinguished than with the extinguished CS. Summation tests showed that the target suppressed responding to an excitor or an excitatory context when it had been extinguished in compound with a nonextinguished but not with an extinguished CS. The results were interpreted to mean that additional extinction in compound with another extinguished CS resulted in the target acquiring the additional inhibition required to more fully oppose its original excitation. In contrast, additional extinction in compound with a nonextinguished CS resulted in the target acquiring not only the additional inhibition required to oppose its original excitation but also that of the nonextinguished CS, thereby converting the target into a net inhibitor.

Modeling Approach for Determining Equivalent Optical Constants of Plastic Shading Nets under Solar Radiation Conditions

The radiative properties of several plastic shading nets were measured under natural solar radiation conditions. We found that the plastic nets behave as homogeneous translucent materials (e.g., plastic film, plastic sheets, and glass). Based on this behavior, we suggest that it is possible to treat plastic nets as translucent materials and to characterize them with equivalent optical constants (i.e., equivalent refractive indexes,neq, and equivalent extinction coefficients,σeq). Here a physical model to determineneqandσeqof plastic nets was described in analogy to homogeneous translucent materials. We examined three groups of nets based on their color (black, black-green, and beige). Each group consisted of nets with four or five different porosities. Nets of each group had almost the same texture structure. For each group, we derived an equation forneqas a function of the net porosity and determined an average value forσeq. Once values ofneqandσeqwere determined, the solar radiative properties of a net could then be calculated fromneqandσeqfor any incident angle of solar beam radiation without the need of measurements. The present model was validated by comparing the calculated with the measured radiative properties of three nets at different incident angle of solar beam radiation. The calculated radiative properties reasonably agreed with measured values.

Structural and optical characterization of undoped, doped, and clustered ZnO thin films obtained by PLD for gas sensing applications

The synthesis by pulsed laser deposition technique of zinc oxide thin films suitable for gas sensing applications is herein reported. The ZnO targets were irradiated by an UV KrF * ( λ = 248 nm, τ FWHM ∼7 ns) excimer laser source, operated at 2.8 J/cm 2 incident fluence value, whilst the substrates consisted of SiO 2(0 0 1) wafers heated at 150 °C during the thin films growth process. The experiments were performed in an oxygen dynamic pressure of 10 Pa. Structural and optical properties of the thin films were investigated. The obtained results have demonstrated that the films are c-axis oriented. Their average transmission in the visible-infrared spectral region was found to be about 85%. The equivalent refractive indexes and extinction coefficients were very close to those of the tabulated reference values. Doping with 0.5% Au and coating with 100 pulses of Au clusters caused but a very slight decrease (with a few percent) of both transmission and refractive index values. The coatings with the most appropriate optical properties as waveguides have been selected and their behavior was tested for butane sensing.

Radiative Properties of MoO3 and Al Nanopowders From Light-Scattering Measurements

The combustion behavior of nanometer-scale energetic materials is much different than micron size or larger materials. Burning rates up to 950 m∕s have been reported for a thermite composition of nanosized aluminum and molybdenum trioxide. The energy transport mechanisms in the reactive wave are still uncertain. The relative contribution of radiation has not yet been quantified. To do so analytically requires dependent scattering theory, which has not yet been fully developed. Radiative properties for nanoaluminum and nanomolybdenum-trioxide were obtained experimentally by comparing light scattering measurements on a one-dimensional slab of powder with multiple-scattering simulations using Monte Carlo and discrete ordinate methods. The equivalent isotropic-scattering extinction coefficient for close-packed molybdenum trioxide (MoO3) nanopowder was found to be 5900±450cm−1; the equivalent isotropic-scattering albedo was 0.97±0.035. Aluminum (Al), which proved to be more difficult to work with, had an albedo of 0.35 and 0.38 from two tests. The radiative conductivity based on the MoO3 results is two orders of magnitude less than the diffusive thermal conductivity, indicating that radiation is not a dominant heat transfer mode for the reactive wave propagation of nanothermites under optically thick conditions.