Phase Function Research Articles

Experimental Scattering Matrices of Martian Dust Aerosols with Narrow Particle-size Distributions

We present experimental scattering matrices of the JSC Mars-1, MMS-2, and MGS-1 simulants at 488 and 640 nm. The analogs were processed so that narrow size distributions representative of Martian dust aerosols during different dust cycles were obtained. We find that the forward peak of the phase function depends on particle size as it becomes narrower with increasing size, whereas the side- and backscattering directions depend on both composition and size so that increasing size and decreasing absorption produce a flatter curve. The position and maximum of the degree of linear polarization varies based on particle size and composition, and the negative polarization branch is more prominent for wavelength-scale particles diminishing with increasing size. The linear depolarization is strongly affected by size and composition. Finally, we compare sky-brightness curves measured by the Navcam and Hazcam engineering cameras on board the Mars Science Laboratory rover to the measured phase functions. The observations show a narrower peak at the forward direction and a flatter curve toward the side- and backscattering directions with an increasing dust load in the atmosphere, similar to what can be seen for the measured phase functions of the analogs with increasing particle size. In the case of the analogs, the flattening of the curve can be caused by an increase in multiple scattering within a particle by wavelength-scale surface roughness and/or internal inclusions. For the observed sky brightnesses, particle aggregation and multiple scattering among particles in denser dust conditions play a major role.

The model and characteristics of polarized light transmission applicable to polydispersity particle underwater environment

The information about the polarization of underwater objects can be affected by the absorption and scattering of water particles, making it challenging to detect underwater targets accurately. Therefore, it is essential to analyze the characteristics of polarization transmission in water. Traditional Monte Carlo simulations have yet to effectively treat particle size in water, which is unsuitable for the underwater environment of polydispersity particles with significant particle size differences. In this paper, a new simulation model using a Monte Carlo method with random sampling fitting phase functions is proposed, which makes the transmission characteristics of water particles more in line with the actual probability model of complex water bodies. The experimental results demonstrate that the proposed Monte Carlo method produces polarization closer to experimental results. The larger the particle size of water suspensions, the greater change of the polarization degree of polarized light. The polarization-maintaining characteristics of circularly polarized light are better than those of linearly polarized light, providing data support for the transmission and detection of underwater light.

Bridge Sampling for Connections via Multiple Scattering Events

AbstractExplicit sampling of and connecting to light sources is often essential for reducing variance in Monte Carlo rendering. In dense, forward‐scattering participating media, its benefit declines, as significant transport happens over longer multiple‐scattering paths around the straight connection to the light. Sampling these paths is challenging, as their contribution is shaped by the product of reciprocal squared distance terms and the phase functions. Previous work demonstrates that sampling several of these terms jointly is crucial. However, these methods are tied to low‐order scattering or struggle with highly‐peaked phase functions.We present a method for sampling a bridge: a subpath of arbitrary vertex count connecting two vertices. Its probability density is proportional to all phase functions at inner vertices and reciprocal squared distance terms. To achieve this, we importance sample the phase functions first, and subsequently all distances at once. For the latter, we sample an independent, preliminary distance for each edge of the bridge, and afterwards scale the bridge such that it matches the connection distance. The scale factor can be marginalized out analytically to obtain the probability density of the bridge. This approach leads to a simple algorithm and can construct bridges of any vertex count. For the case of one or two inserted vertices, we also show an alternative without scaling or marginalization.For practical path sampling, we present a method to sample the number of bridge vertices whose distribution depends on the connection distance, the phase function, and the collision coefficient. While our importance sampling treats media as homogeneous we demonstrate its effectiveness on heterogeneous media.

Growth phase-dependent changes in conformational and physicochemical properties of bacterial surface biopolymers lead to changes in bacterial adhesion strength at nanoscale and macroscale

This study presents a detailed investigation into conformational, physicochemical and adhesive characteristics of biopolymers on the surfaces of Escherichia coli and potential probiotic Bacillus subtilis harvested from middle-exponential phase (mid-EP), late-exponential phase (late-EP) and early-stationary phase (early-SP) of growth. The lengths to which bacterial surface biopolymers extend (biopolymer brush lengths), densities of grafted bacterial surface biopolymers indicating the amounts of molecules covering the bacterial surfaces (biopolymer grafting densities), adhesion forces of bacterial surface biopolymers to the model inert surfaces of silicon nitride (Si3N4), and the pull-off distances of biopolymers from Si3N4 were measured in water by atomic force microscopy (AFM). The Weibull analysis of AFM adhesion data showed that as the culture aged, the adhesive bonds between Si3N4 AFM tips and surface molecules of E. coli harvested from the culture were broken with a higher applied force. However, the highest applied force to break the bonds was required for B. subtilis in late-EP, followed by those required for cells in early-SP and mid-EP, respectively. The results of a steric model fitting to AFM approach force-distance (FD) curves and analysis of the pull-off distances in the AFM retraction FD curves showed higher biopolymer grafting density for E. coli in early-SP and longer biopolymer brush layer for B. subtilis in late-EP, which were associated with stronger adhesion to Si3N4 in water. The results of thermodynamic adhesion energy calculations based on the Wu model showed that polar interaction energy dominated the bacterial adhesion at the macroscale, the strength of which varied as a function of the growth phase for both E. coli and B. subtilis. The growth phase-dependent variation in polar components of thermodynamic adhesion energies between the bacteria and Si3N4 in water was consistent with the growth phase-dependent variation in the bond strengths between the bacteria and Si3N4 in water as revealed by the Weibull analysis of AFM adhesion data. Therefore, information obtained by Weibull analysis of nanoscale AFM bacterial adhesion data can be used to predict macroscale bacterial adhesion to the model inert Si3N4 surface in water.

Polarization characterization of a nonspherical sea salt aerosol model

The T-matrix method was utilized to study the polarization characteristics of nonspherical sea salt aerosol models within the wavelength range of 0.48–2.5 µm. Analysis was conducted on the polarization characteristics of nonspherical sea salt aerosols across different wavelengths as a function of scattering angle. This included scrutinizing linear depolarization ratios under typical visible and near-infrared wavelengths for various aspect ratios. The impact of particle nonsphericity on the linear depolarization ratios of monodisperse and polydisperse sea salt aerosol particles was examined. The results indicate: (1) In the analysis of the polarization characteristics of sea salt aerosols, the trends of polarization properties are similar between monodisperse and polydisperse systems. The scattering phase function P11(θ) is predominantly more significant in the forward-scattering direction. P11(θ) is insensitive to wavelength changes in the backward-scattering direction. P33(θ)/P11(θ) varies across different bands; in the visible light spectrum, there are significant fluctuating changes, while in the infrared spectrum, it trends towards nearly linear changes. The variation trends of −P12(θ)/P11(θ) and P34(θ)/P11(θ) with scattering angle are similar, and both are significantly affected by changes in wavelength. (2) Regarding the depolarization ratio of sea salt aerosols, the value for polydisperse systems is more than twice that of monodisperse systems, and the greater the nonsphericity, the higher the linear depolarization ratio. In monodisperse systems, at a wavelength of 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 118.82, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum depolarization ratio is near 97.52; under polydisperse conditions, at 0.633 µm for visible light and an aspect ratio of 0.4, the maximum depolarization ratio is around 117.18, while at 1.65 µm in the near-infrared, with an aspect ratio of 0.2, the maximum linear depolarization ratio is near 215.66. Investigating the polarization characteristics and linear depolarization ratios of nonspherical spheroid sea salt aerosol particle models at all scattering angles is important for remote-sensing detection, high-precision calibration, and other optoelectronic applications.

Modeling the Doppler spectrum of waves backscattered from an expanding cloud for anisotropic phase functions

Modeling the Doppler spectrum of waves backscattered from an expanding cloud for anisotropic phase functions

The scandium effect in Gd-rich BMGs: How and why does this ingredient work better than others?

Scandium is commonly known as a superior modifier for most alloys and compounds, substantially improving their phase stability and physical properties, as well as glass-forming ability. A special case is rare-earth based magnetic metallic glasses, which are an unique platform for intra-elemental substitution due to the chemical affinity of the lanthanides, yttrium and scandium. The latter, used as an alloying additive and being the smallest atom among the entire family, can drastically affect structure formation and magnetism in these metallic glasses. The main issue is that its modifying role is not well understood due to scarce information on the scandium effects in such rare-earth systems. This study is focused on thermal and magnetic analysis of some popular Gd-based BMGs redesigned with minor Sc additives. Here, we consider temperature behavior of specific heat capacity and entropy functions for both amorphous and crystalline phases to estimate the scandium effect on GFA and thermal stability of the glasses. As well, we inspect magnetic and magnetocaloric properties of these BMGs to understand whether this very expensive metal can radically improve the alloy magnetism and make these materials suitable for potential applications.

Compression and self-compression of frequency modulated spherical photon density waves in anisotropic scattering media

We report on the results of a simulation of the photon density waves with pulse amplitude modulation by a complex frequency modulated signal. The problem is considered for the optical properties typical for sea water with anisotropy factor values varying from 0.75 to 0.93 at source-detector distances up to 120 m. It is shown that multiple scattering in a medium does not prevent effective compression of a signal registered using matched detection. Two competing phenomena affecting the detected pulse duration and depending on the central frequency of the modulation signal are discussed. The effect of faster attenuation of high harmonics in a complexly modulated signal leads to the detected signal duration increase as a consequence of multiple scattering. On the other hand, anomalous dispersion of photon density waves in media with scattering anisotropy leads to the pulse self-compression. The simulation results presented in the paper demonstrate the prevalence of different phenomena depending on the central frequency of the modulation signal resulting in a pulse duration decrease or increase in different frequency ranges covering the band from 107 to 2⋅109 Hz. The effect of the phase function shape on the observed effect is also discussed.

Structural details of helix-mediated TDP-43 C-terminal domain multimerization.

The primarily disordered C-terminal domain (CTD) of TAR DNA binding protein-43 (TDP-43), a key nuclear protein in RNA metabolism, forms neuronal inclusions in several neurodegenerative diseases. A conserved region (CR, spanning residues 319-341) in CTD forms transient helix-helix contacts important for its higher-order oligomerization and function that are disrupted by ALS-associated mutations. However, the structural details of CR assembly and the explanation for several ALS-associated variants' impact on phase separation and function remain unclear due to challenges in analyzing the dynamic association of TDP-43 CTD using traditional structural biology approaches. By employing an integrative approach, combining biophysical experiments, biochemical assays, AlphaFold2-Multimer (AF2-Multimer), and atomistic simulations, we generated structural models of helical oligomerization of TDP-43 CR. Using NMR, we first established that the native state of TDP-43 CR under physiological conditions is α-helical. Next, alanine scanning mutagenesis revealed that while hydrophobic residues in the CR are important for CR assembly, phase separation and TDP-43 nuclear retention function, polar residues down regulate these processes. Finally, pairing AF2-Multimer modeling with AAMD simulations indicated that dynamic, oligomeric assemblies of TDP-43 that are stabilized by a methionine-rich core with specific contributions from a tryptophan/leucine pair. In conclusion, our results advance the structural understanding of the mechanisms driving TDP-43 function and provide a window into the initial stages of its conversion into pathogenic aggregates.

Predictions for Sparse Photometry of Jupiter-family Comet Nuclei in the LSST Era

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory will deliver high-quality, temporally sparse observations of millions of solar system objects on an unprecedented scale. Such data sets will likely enable the precise estimation of small-body properties on a population-wide basis. In this work, we consider the possible applications of photometric data points from LSST to the characterization of Jupiter-family comet (JFC) nuclei. We simulate sparse-in-time lightcurve points with an LSST-like cadence for the orbit of a JFC between 2024 and 2033. Convex lightcurve inversion is used to assess whether the simulation input parameters can be accurately reproduced for a sample of nucleus rotation periods, pole orientations, activity onsets, shapes, and sizes. We find that the rotation period and pole direction can be reliably constrained across all nucleus variants tested, and that the convex shape models, while limited in their ability to describe complex or bilobed nuclei, are effective for correcting sparse photometry for rotational modulation to improve estimates of nucleus phase functions. Based on this analysis, we anticipate that LSST photometry will significantly enhance our present understanding of the spin state and phase function distributions of JFC nuclei.

A method for calculating two-phase equilibrium: Constrained gray prediction evolutionary algorithm with a surrogate model based on quadratic interpolation

Traditional methods, including direct solution methods based on Newton's method and indirect solution methods based on thermodynamic principles, are the mainstream methods used to solve the volume-temperature flash calculation (called NVT-flash), even though they suffer from drawbacks such as sensitivity to initial value and complexity of derivative calculations. A constrained backtracking search algorithm (CBSA), proposed in 2024, was the first and only metaheuristic algorithm to successfully tackle the NVT-flash problem, which overcomes shortcomings of traditional methods. Considering the advantages of metaheuristic algorithms, a constrained gray prediction evolutionary algorithm with a surrogate model based on quadratic interpolation (CGPE-QI) is proposed in this paper to deal with the NVT-flash problem. CGPE-QI considers total Helmholtz free energy as the objective function, moles vector, and volume of a single phase as variables. Constraints to solve the NVT-flash problem are addressed by using a direct search method and an exterior point method. Numerical experiments on two-phase equilibrium of pure substance and mixtures are carried out employing CGPE-QI. Experimental results are the same as those obtained by traditional methods, which confirms that CGPE-QI can effectively tackle the NVT-flash problem and possesses energy decay property. In particular, the results demonstrate that CGPE-QI is more competitive than CBSA in terms of convergence speed, stability, and calculation cost. CGPE-QI proposed in this paper is the second metaheuristic algorithm to successfully solve the NVT-flash problem, illustrating that metaheuristic algorithms have great potential in solving phase equilibrium calculation problems.

Phase and amplitude responses for delay equationsusing harmonic balance.

Robust delay induced oscillations, common in nature, are often modeled by delay-differential equations(DDEs). Motivated by the success of phase-amplitude reductions for ordinary differential equationswith limit cycle oscillations, there is now a growing interest in the development of analogous approaches for DDEs to understand their response to external forcing. When combined with Floquet theory, the fundamental quantities for this reduction are phase and amplitude response functions. Here, we develop a framework for their construction that utilizes the method of harmonic balance.

The radiative properties in the near-infrared band of crude oil emulsion dispersed in the seawater

The complex refractive index and radiative properties of crude oils are essential parameters for remote sensing, which is paramount for accurately and quantitatively detecting marine oil spills. In this study, the complex refractive index in the near-infrared band of crude oil from Daqing Oilfield is measured by the combined transmission - KK transformation method, and the absorption spectral features are analyzed. A modified-Mie method is employed to calculate the radiative properties of crude oil droplets immersed in an absorbing medium, and the impact of medium absorption is examined. Furthermore, the spectral absorption/scattering coefficient and scattering phase function of the oil-in-water (OW) emulsion dispersed in seawater are calculated, and the corresponding correlations between the radiative properties and chemical compositions of the crude oil are analyzed. The research reveals that the differences in the components of crude oil and seawater result in variations in the absorption peaks/troughs in their absorption spectra curve, which subsequently cause a gradual increase/decrease in absorption and scattering coefficients as the volume fraction of emulsion increases. The quantitative correlations of the absorption/scattering coefficient with the volume fraction of OW emulsion are presented, which are significant for improving the quantification monitoring of emulsified oil spills and identifying different types of pollutants.

Combined spin orientation and phase function of asteroids

Context. Large sky surveys provide numerous non-targeted observations of small bodies of the Solar System. The upcoming LSST of the Vera C. Rubin Observatory will be the largest source of small body photometry in the next decade. With non-coordinated epochs of observation, colors – and therefore taxonomy and composition – can only be computed by comparing absolute magnitudes obtained in each filter by solving the phase function (evolution of brightness of the small body against the solar phase angle). Current models in use in the community (HG, HG12*, and HG1G2), however, fail to reproduce the long-term photometry of many targets due to the change in the aspect angle between apparitions. Aims. We aim to derive a generic yet simple phase function model accounting for the variable geometry of the small bodies over multiple apparitions. Methods. As a spinoff of the HG1 G2 model, we propose the sHG1G2 phase function model in which we introduce a term describing the brightness changes due to spin orientation and polar oblateness. We applied this new model to 13 245 908 observations of 122 675 Solar System objects (SSOs). These observations were acquired in the g and r filters with the Zwicky Transient Facility between November 1, 2019 and December 1, 2023. We retrieved them and implemented the new sHG1G2 model in FINK, a broker of alerts designed for the LSST. Results. The sHG1G2 model leads to smaller residuals than other phase function models, providing a better description of the photometry of asteroids. We determined the absolute magnitude, H, and phase function coefficients (G1, G2) in each filter, the spin orientation (α0, δ0), and the polar-to-equatorial oblateness, R, for 95 593 SSOs, which constitutes about a tenfold increase in the number of characterized objects compared to the current census. Conclusions. The application of the sHG1 G2 model to ZTF alert data using the FINK broker shows that the model is appropriate for extracting physical properties of asteroids from multi-band and sparse photometry, such as the forthcoming LSST survey.

TESS Light Curves of Cataclysmic Variables. IV. A Synoptic View of Eclipsing Old Novae and Novalike Variables

Based mainly on the months-long 2 minutes time-resolution light curves observed by the Transiting Exoplanet Survey Telescope (TESS) space mission of 48 eclipsing old novae and novalike variables (commonly referred to as NLs) selected from the Ritter & Kolb catalog, a synoptic view of some basic properties of these systems is provided. The supraorbital variations exhibit a large diversity of behavior. Data taken from the literature and many additional eclipse epochs measured in the TESS and in AAVSO light curves are used to update the orbital ephemerides of 21 targets. The large majority of these suffer period variations which defy current theoretical understanding. Orbital waveforms are constructed and, if possible, their variation over time is studied, revealing some common characteristics but also substantial differences between individual systems. The dependence of the eclipse depth on the out-of-eclipse flux reveals that in all systems a fraction of the light source responsible for the out-of-eclipse variations escapes eclipse and is probably located in the outer disk regions. In systems exhibiting superhumps, both eclipse width and epoch are modulated with the accretion disk precession period. This suggests an expansion and contraction of the eclipsed light source, as well as a periodic shift of its light center as a function of the accretion disk precession phase. The dependence of the orbital and superhump waveforms on the disk precession phase is also examined but does not lead to a consistent picture. Two cataclysmic variables are newly identified as eclipsing. Attention is drawn to specific peculiarities in some of the target stars.

Timed topical dexamethasone eye drops improve mitochondrial function to prevent severe retinopathy of prematurity.

Pathological neovascularization in retinopathy of prematurity (ROP) can cause visual impairment in preterm infants. Current ROP treatments which are not preventative and only address late neovascular ROP, are costly and can lead to severe complications. We showed that topical 0.1% dexamethasone eye drops administered prior to peak neovessel formation prevented neovascularization in five extremely preterm infants at high risk for ROP and suppressed neovascularization by 30% in mouse oxygen-induced retinopathy (OIR) modeling ROP. In contrast, in OIR, topical dexamethasone treatment before any neovessel formation had limited efficacy in preventing later neovascularization, while treatment after peak neovessel formation had a non-statistically significant trend to exacerbating disease. Optimally timed topical dexamethasone suppression of neovascularization in OIR was associated with increased retinal mitochondrial gene expression and decreased inflammatory marker expression, predominantly found in immune cells. Blocking mitochondrial ATP synthetase reversed the inhibitory effect of dexamethasone on neovascularization in OIR. This study provides new insights into topical steroid effects in retinal neovascularization and into mitochondrial function in phase II ROP, and suggests a simple clinical approach to prevent severe ROP.

Exploring VAE-driven implicit parametric unit cells for multiscale topology optimization

The simulation and optimization of metamaterial, known for their engineered properties in various applications, encounter intricate challenges due to complex microstructure interactions, extensive design spaces, and substantial computational requirements. To address these challenges, our research introduces a novel data-driven framework utilizing deep generative modeling to enhance the design process of metamaterials.Focusing on composite metamaterial with double negative coefficients of thermal expansion and Poisson's ratio, we apply an Alternative Active Phase and Objective functions (AAPO) method for deciding the initial metamaterial dataset. To enhance dataset diversity, a distortion filter is applied, broadening the range of design possibilities. Subsequently, we utilize a Variational Autoencoder (VAE), integrated with a regressor, to train on this diversified database. This training effectively maps complex unit cell geometries to a coherent latent space, simultaneously correlating them with continuous material properties.Our approach demonstrates robustness in multi-phase and multi-physics optimization as well as efficiency in generating specialized databases of unit cells. This framework is pivotal in systematically designing unit cells and multiscale systems, specifically aiming for distinct thermo-mechanical behavior targets.To mitigate the computational demands encountered during multiple design meta-materials via gradient-based topology optimization, we have integrated high-performance methods and automatic differentiation. This integration marks a significant advancement in the data-driven design of metamaterials, offering substantial practical and theoretical benefits in the field.

Polarization images of the Moon as a function of the lunar phase.

Moonlight has a partial polarization state that varies with the lunar phase angle. This needs to be characterized for the Moon to be used as a calibration source for polarization-sensitive instruments or as the illumination source in nighttime passive remote sensing. To contribute to this characterization, a pixelated polarization imager was calibrated with a telescope and with a telephoto lens and used to record images of the Moon at 40 phase angles from -138° to 125°. High-resolution images of relative intensity, degree of linear polarization (DoLP), and angle of polarization (AoP) were recorded in a spectral band from 400-1000 nm and were used to calculate disk-averaged DoLP values. These images are made available to readers. Results showed higher DoLP in regions of lower reflectivity (the Umov effect), higher DoLP for waning phases (maximum DoLP of 8.3%) than for waxing (maximum DoLP of 6.8%), and consistent DoLP to disk-averaged values published previously for wavelengths contained within our broader band.

Elastic scattering study of $$\alpha$$- $$^3$$H and $$\alpha$$- $$^3$$He modeled by Malfliet–Tjon potential using phase function method

Elastic scattering study of $$\alpha$$- $$^3$$H and $$\alpha$$- $$^3$$He modeled by Malfliet–Tjon potential using phase function method

Low phase angle is associated with swallowing outcomes in patients with acute stroke

Background and purposeStroke-induced dysphagia is a critical complication that can lead to severe secondary worldwide health issues. This retrospective cohort study investigated the association between phase angle (PhA) and swallowing function in the acute phase of stroke. We aim to establish whether nutritional and muscular interventions associated with PhA could enhance swallowing recovery and reduce related risks post-stroke. MethodsStroke patients requiring rehabilitation were assessed for the association between low PhA—with cutoff values for low PhA defined as less than 5.28 for men and 4.32 for women—and swallowing function using a functional oral intake scale (FOIS) on Day 7 after admission and after the completion of acute stroke treatment. ResultsIn this study of 140 acute stroke patients (median age 74[69–81], and 85 men and 55 women), 76 patients with low PhA significantly exhibited older age, lower body mass index, more decline in skeletal muscle mass index, and lower premorbid modified Rankin Scale scores compared to 64 patients with high PhA. Multivariate linear regression revealed that low PhA was independently associated with FOIS scores on Day 7 after admission (β=-0.143 and p=0.036) and after the completion of acute stroke treatment (β=-0.513 and p=0.024), even when adjusting for confounding factors. ConclusionsLow PhA is associated with swallowing function in patients with acute stroke. Nutritional and physical interventions improving PhA may lead to a reduction of the risk associated with stroke sequelae.