Diffuse Component Research Articles

Association of sleep quality and diffusion MRI derived interstitial fluid content – insights in cerebral waste clearance

AbstractBackgroundDisruptions in sleep are associated with Alzheimer’s disease (AD) progression. As cerebral waste clearance is most active during sleep, these reductions in sleep quality could induce impaired clearance function. Waste products are washed through the parenchyma in the interstitial fluid (ISF), its volume being regulated by the sleep‐wake cycle. A smaller ISF‐volume is found in awake states and after sleep deprivation. IntraVoxel Incoherent Motion (IVIM) MRI can detect the diffusion of cerebral ISF (Dint) and its volume fraction (fint).Using IVIM, the current exploratory study investigates whether alterations in a proxy of ISF‐volume (fint) are related to hours of sleep or self‐reported sleep quality.MethodTwenty neurotypical elderly subjects (Table 1) underwent ultra‐high field MRI (7T research system, Siemens Healthcare GmbH, Erlangen, Germany) (Table 2).The intermediate diffusion components (Dint) in the range 1.5*10‐3<Diffusivity<4.0*10‐3 mm2/s were calculated using spectral analysis (Figure 1). The relative signal contribution of Dint was quantified by the ISF‐fraction (fint). Median fint values were extracted from the white matter (WM) and gray matter (GM).Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). In addition to the clinically used total PSQI (sum of all 7 components), the PSQI1 (Subjective sleep quality) and PSQI3 (Sleep duration) components were considered.Pearson correlations were computed between the PSQI scores and fint for WM and GM. To check for potential confounding influences, partial correlations were performed adjusting for age and time of MRI‐acquisition.ResultThe sample characteristics and descriptive statistics are summarized in Table 1. Worse reported sleep quality (PSQI1) significantly relates to lower WM fint (Table 3 and Figure 2). After adjusting for potential confounding influences, a trend towards significance remained (R=‐0.437, p=0.061).ConclusionThe current explorative study identified a lower diffusion MRI‐derived proxy of ISF‐volume in the WM of subjects who reported a subjective feeling of long‐term sleep deprivation. A reduction in ISF‐volume may leave less space for waste products, such as soluble Amyloid‐beta, to be cleared from in‐between the cells. Thereby, this study puts forward a potential method for future studies to investigate impaired clearance function in relation to sleep in patients with AD pathology.

On the origin of a potential clearance marker: The contribution of enlarged perivascular fluid diffusion to an MRI derived proxy of interstitial fluid

AbstractBackgroundIntraVoxel Incoherent Motion (IVIM) MRI can detect the diffusion of cerebral interstitial fluid (ISF) (Dint) and its volume fraction (fint), which has the potential as a proxy of cerebral waste clearance. fint has been suggested to both be driven by fluid diffusivity within enlarged perivascular spaces (ePVS) ‐ transporting fluid from the subarachnoid space into the parenchyma ‐ and the ISF between the parenchymal cells. Both factors play a crucial role in soluble protein clearance, e.g., Amyloid‐Beta (Aβ).This study simultaneously aims to verify the contribution of ePVS fluid diffusivity to fint and highlights the ability to specifically assess ePVS fluid diffusion in the cerebrum using a non‐invasive MR method.MethodTwenty neurotypical elderly subjects (Table 1) underwent ultra‐high field MRI (7T research system, Siemens Healthcare GmbH, Erlangen, Germany) (Table 2).The intermediate diffusion components (Dint) in the range 1.5*10‐3<Diffusivity<4.0*10‐3 mm2/s were calculated using spectral analysis (Fig.1). The relative signal contribution of Dint was quantified by fint.ePVS were segmented from the enhanced perivascular contrast images (Fig.2). Median fint values were extracted from ePVS and non‐ePVS voxels within the basal ganglia (BG).fint and Dint values from within the ePVS mask were compared with values from surrounding non‐ePVS voxels in the BG using Wilcoxon Signed Ranks Tests.ResultFigure 3 contains a graphic summary of the statistical comparison of Dint and fint values from the ePVS and non‐ePVS voxels in the BG. Higher Dint and fint values are observed in the ePVS compared to the non‐ePVS tissue.ConclusionThe current study identified a higher IVIM‐derived proxy of ISF within the ePVS compared to surrounding non‐ePVS tissue, confirming that ePVS indeed contribute to the waste clearance markerfint.ePVS are fluid‐filled spaces surrounding cerebral blood vessels, in which ISF diffusivity is less restricted. This explains the higher Dint values in ePVS compared to non‐ePVS.Furthermore, this study suggests a potential method to investigate diffusivity within the microscopic ePVS, independent of the ISF diffusivity between parenchymal cells. In patients with Alzheimer’s disease, this method could be applied to investigate alterations in ISF diffusivity which could be representative of potential Aβ blockages in ePVS.

On the origin of a potential clearance marker: The contribution of enlarged perivascular fluid diffusion to an MRI derived proxy of interstitial fluid

AbstractBackgroundIntraVoxel Incoherent Motion (IVIM) MRI can detect the diffusion of cerebral interstitial fluid (ISF) (D int) and its volume fraction (f int), which has the potential as a proxy of cerebral waste clearance. fint has been suggested to both be driven by fluid diffusivity within enlarged perivascular spaces (ePVS) ‐ transporting fluid from the subarachnoid space into the parenchyma ‐ and the ISF between the parenchymal cells. Both factors play a crucial role in soluble protein clearance, e.g., Amyloid‐Beta (Aβ).This study simultaneously aims to verify the contribution of ePVS fluid diffusivity to fint and highlights the ability to specifically assess ePVS fluid diffusion in the cerebrum using a non‐invasive MR method.MethodTwenty neurotypical elderly subjects (Table 1) underwent ultra‐high field MRI (7T research system, Siemens Healthcare GmbH, Erlangen, Germany) (Table 2).The intermediate diffusion components (Dint) in the range 1.5*10‐3< Diffusivity<4.0*10‐3 mm2/s were calculated using spectral analysis (Fig.1). The relative signal contribution of Dint was quantified by fint.ePVS were segmented from the enhanced perivascular contrast images (Fig.2). Median fint values were extracted from ePVS and non‐ePVS voxels within the basal ganglia (BG).fint and Dint values from within the ePVS mask were compared with values from surrounding non‐ePVS voxels in the BG using Wilcoxon Signed Ranks Tests.ResultFigure 3 contains a graphic summary of the statistical comparison of Dint and fint values from the ePVS and non‐ePVS voxels in the BG. Higher Dint and fint values are observed in the ePVS compared to the non‐ePVS tissue.ConclusionThe current study identified a higher IVIM‐derived proxy of ISF within the ePVS compared to surrounding non‐ePVS tissue, confirming that ePVS indeed contribute to the waste clearance marker fint.ePVS are fluid‐filled spaces surrounding cerebral blood vessels, in which ISF diffusivity is less restricted. This explains the higher Dint values in ePVS compared to non‐ePVS.Furthermore, this study suggests a potential method to investigate diffusivity within the microscopic ePVS, independent of the ISF diffusivity between parenchymal cells. In patients with Alzheimer’s disease, this method could be applied to investigate alterations in ISF diffusivity which could be representative of potential Aβ blockages in ePVS.

Association of sleep quality and diffusion MRI derived interstitial fluid content – insights in cerebral waste clearance

AbstractBackgroundDisruptions in sleep are associated with Alzheimer’s disease (AD) progression. As cerebral waste clearance is most active during sleep, these reductions in sleep quality could induce impaired clearance function. Waste products are washed through the parenchyma in the interstitial fluid (ISF), its volume being regulated by the sleep‐wake cycle. A smaller ISF‐volume is found in awake states and after sleep deprivation. IntraVoxel Incoherent Motion (IVIM) MRI can detect the diffusion of cerebral ISF (Dint) and its volume fraction (fint).Using IVIM, the current exploratory study investigates whether alterations in a proxy of ISF‐volume (fint) are related to hours of sleep or self‐reported sleep quality.MethodTwenty neurotypical elderly subjects (Table 1) underwent ultra‐high field MRI (7T research system, Siemens Healthcare GmbH, Erlangen, Germany) (Table 2).The intermediate diffusion components (Dint) in the range 1.5*10‐3<Diffusivity<4.0*10‐3 mm2/s were calculated using spectral analysis (Figure 1). The relative signal contribution of Dint was quantified by the ISF‐fraction (fint). Median fint values were extracted from the white matter (WM) and gray matter (GM).Sleep quality was assessed with the Pittsburgh Sleep Quality Index (PSQI). In addition to the clinically used total PSQI (sum of all 7 components), the PSQI1 (Subjective sleep quality) and PSQI3 (Sleep duration) components were considered.Pearson correlations were computed between the PSQI scores and fint for WM and GM. To check for potential confounding influences, partial correlations were performed adjusting for age and time of MRI‐acquisition.ResultThe sample characteristics and descriptive statistics are summarized in Table 1. Worse reported sleep quality (PSQI1) significantly relates to lower WM fint (Table 3 and Figure 2). After adjusting for potential confounding influences, a trend towards significance remained (R=‐0.437, p=0.061).ConclusionThe current explorative study identified a lower diffusion MRI‐derived proxy of ISF‐volume in the WM of subjects who reported a subjective feeling of long‐term sleep deprivation. A reduction in ISF‐volume may leave less space for waste products, such as soluble Amyloid‐beta, to be cleared from in‐between the cells. Thereby, this study puts forward a potential method for future studies to investigate impaired clearance function in relation to sleep in patients with AD pathology.

Regularity of transition densities and ergodicity for affine jump‐diffusions

AbstractThis paper studies the transition density and exponential ergodicity for affine processes on the canonical state space . Under a Hörmander‐type condition for diffusion components as well as a boundary nonattainment condition, we derive the existence and regularity of the transition densities and then prove the strong Feller property of the associated semigroup. Moreover, we also show that, under an additional subcriticality condition on the drift, the corresponding affine process is exponentially ergodic in the total variation distance.

Peering into the Milky Way by FAST: II. Ionized gas in the inner Galactic disk revealed by the piggyback line observations of the FAST GPPS survey

As one of the major components of the interstellar medium, the ionized gas in our Milky Way, especially the low-density diffuse component, has not been extensively observed in the radio band. The Galactic Plane Pulsar Snapshot (GPPS) survey covers the sky area within the Galactic latitude of $\pm10^\circ$ around the Galactic plane visible by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and the spectral line data are simultaneously recorded during the pulsar survey observations. With an integration time of 5 minutes for each beam, the GPPS survey project provides the most sensitive piggyback spectra for tens of radio recombination lines (RRLs) in the band of 1000$-$1500 MHz for H$n\alpha$, He$n\alpha$, C$n\alpha$, as well as H$n\beta$ and H$n\gamma$. We processed the spectral data of RRLs, and obtained a sensitive averaged H$n\alpha$ RRL map of a sky area of 88 square degrees in the inner Galaxy of 33$^\circ$ $\leqslant l \leqslant$ 55$^\circ$ and $|b| \leqslant$ 2.0$^\circ$. The final spectral data of the H$n\alpha$ RRLs have a spatial resolution of $\sim$3$^\prime$, a spectral resolution of 2.2 km s$^{-1}$, and a typical spectral rms noise of 0.25 mJy beam$^{-1}$ or 6.3 mK in main-beam brightness temperature. The new H$n\alpha$ RRL map shows complex structural features dominated by a number of HII regions and large extended diffuse ionized gas regions. We detect about 94% of the known HII regions and confirm 43 WISE HII regions in the observed sky area. Several large HII regions or star-forming complexes in the distant outer Galaxy are resolved in the map of H$n\alpha$ RRLs. Extended RRL features of the diffuse ionized gas are detected. The RRL data products of the GPPS survey will be published and updated at http://zmtt.bao.ac.cn/MilkyWayFAST/

Quasi-3-dimensional simulations and experimental validation of surface leakage currents in high operating temperature type-II superlattice infrared detectors

The surface leakage in InAs/GaSb type-II superlattice (T2SL) is studied experimentally and theoretically for photodiodes with small sizes down to 10 × 10 μm2. The dependence of dark current density on mesa size is studied at 110 and 200 K, and surface leakage is shown to impact both generation–recombination (GR) and diffusion dark current mechanisms. A quasi-3-dimensional model to simulate the fabrication process using surface traps on the pixel's sidewall is presented and is used to accurately represent the dark current of large and small pixels with surface leakage in the different temperature regimes. The simulations confirmed that the surface leakage current has a GR and diffusion component at low and high temperature, respectively. Finally, the surface leakage current has been correlated with the change in minority carrier concentration at the surface due to the presence of donor traps.

Exploring the effect of pavement reflection and photometric properties on road lighting performance

The reflection properties of pavement have an impact on the lit environment and thus upon drivers’ vision and comfort and the energy consumption of the lighting installation. The reflection properties combine diffuse and specular components. The specular reflection component changes with different materials: it also changes when the surface is wet, although this is sometimes ignored in lighting design. This study used simulation (DIALux 4.13) to investigate the effect on lighting parameters (luminance, overall uniformity, longitudinal uniformity and threshold increment (TI)) of changes in pavement reflection properties using different pavement materials and under dry and wet conditions. Furthermore, comparison of lighting parameters was made with different road lighting arrangements. The results show that an increase in the specular reflection component leads to an increase in luminance and a decrease in uniformity. Of the surfaces investigated, the porous pavement had the lower luminance but better uniformity. Arranging the lighting installation based on the extreme wettest condition could make luminance and uniformity rise but with an increase of 2–2.5 kWh/m2 annual energy consumption. When trying to control glare problems during design process, it is suggested that uniformity cannot be neglected except the TI.

Quality control procedure for 1-minute pyranometric measurements of global and shadowband-based diffuse solar irradiance

A novel automatic filtering methodology is proposed for 1-min GHI and DIF data using surface measurements obtained at five sites located in various climate zones of Argentina. The methodology contemplates DIF information obtained through the use of a shadowband or shading ring instead of the shading ball that requires a solar tracker. Three different flags are presented for suspicious or erroneous data identified by the filters of the methodology, which respond to the weight or strictness of the corresponding filter. The methodology uses filters established in the literature and proposes new filters capable of identifying slight misalignments of the shadowband as well as measurements below a minimum threshold empirically established for heavily overcast or thunderstorm conditions. A statistical analysis based on data obtained at a high-quality reference station and the modification of a pre-existing methodology is also presented. In general terms and at all sites, it is observed that the total amount of suspicious data increases significantly as the solar zenith angle increases. Overall, the methodology is able to identify and flag 15.0–44.6% erroneous or suspicious values, depending on site. The proposed methodology is applicable at any world station where the global and diffuse irradiance components are both measured.

Numerical solution of compartment-based reaction/diffusion models with DABOSS algorithm

The intracellular diffusive movement of molecular substances that are buffered by diffusing chelators is often modeled as movement between compartments with constant concentrations within which the buffering occurs. Here, an algorithm to solve such a system of time-dependent differential equations is presented. This Dynamic and Balanced Operator Splitting Scheme (DABOSS) combines dynamic time stepping and operator splitting techniques. The time stepping minimizes the number of time steps while bounding local errors. The balanced operator splitting separates the diffusion and reaction components (each of which is solved efficiently) in a way that preserves the correct steady-state behavior. Analysis shows that DABOSS scales almost linearly in the number of compartments and remains accurate over very long simulations. Moreover, DABOSS works efficiently for nanometer-sized compartments with sources of flux, showing that it is applicable to situations where more spatial resolution is desired.

A three-component multi-b-value diffusion-weighted imaging might be a useful biomarker for detecting microstructural features in gliomas with differences in malignancy and IDH-1 mutation status.

The purpose of the study was to explore the performance of a three-component diffusion model in evaluating the degree of malignancy and isocitrate dehydrogenase 1 (IDH-1) gene type of gliomas. Overall, 60 patients with gliomas were enrolled. The intermediate and perfusion-related diffusion coefficients (Dint and Dp) and fractions of strictly limited, intermediate, and perfusion-related diffusion (Fvery-slow, Fint, and Fp) were obtained with a three-component diffusion model. Parameters were also obtained from a diffusion kurtosis model and mono- and biexponential models. All parameters were compared between different tumor grades and IDH-1 gene types. Diagnostic performance and logistic regression analyses were performed. High-grade gliomas (HGGs) had significantly higher Fint, Fvery-slow, and Dp values but significantly lower Fp and Dint values than low-grade gliomas (LGGs), and Fint and Fp differed significantly among grade II, III, and IV gliomas (p < 0.05 for all). Fint achieved the highest AUC of 0.872 in differentiating between LGGs and HGGs. Logistic regression analysis revealed that in each model, Fint, diffusion coefficient (D), apparent diffusion coefficient (ADC), mean diffusivity (MD), and mean kurtosis (MK) were associated with glioma grading. After multiple regression analysis, Fint remained the only differentiator. Additionally, Fint and Fp showed significant differences between IDH-1 mutated and IDH-1 wild-type gliomas (p = 0.007 and 0.01, respectively). The three-component DWI model served as a useful biomarker for detecting microstructural features in gliomas with different grades and IDH-1 mutation statuses. • The three-component model enables the estimation of an intermediate diffusion component. • The three-component model performed better than the other models in glioma grading and genotyping. • Fint was useful in evaluating the grade and genotype of gliomas.

Bird’s eye view of molecular clouds in the Milky Way

Context. The kinematics of molecular gas are crucial for setting the stage for star formation. One key question related to the kinematic properties of gas is how they depend on the spatial scale. Aims. We aim to describe the CO spectra, velocity dispersions, and especially the linewidth-size relation of molecular gas from cloud (parsec) scales to kiloparsec scales in a complete region within the Milky Way disk. Methods. We used the census of molecular clouds within 2 kpc from our earlier work, together with CO emission data for them from the literature. We studied the kinematics and the Larson relations for the sample of individual clouds. We also mimicked a face-on view of the Milky Way and analysed the kinematics of the clouds within apertures of 0.25–2 kpc in size. In this way, we describe the scale-dependence of the CO gas kinematics and Larson’s relations. Results. We describe the spectra of CO gas at cloud scales and in apertures between 0.25 and 2 kpc in our survey area. The spectra within the apertures are relatively symmetric, but show non-Gaussian high-velocity wings. At cloud scales, our sample shows a linewidth-size relation σv = 1.5 · R0.3±0.1 with a large scatter. The mass-size relation in the sample of clouds is MCO = 794 · R1.5±0.5. The relations are also present for the apertures at kiloparsec-scales. The best-fit linewidth-size relation for the apertures is σv = 0.5 · R0.35±0.01, and the best-fit mass-size relation is MCO = 229 · R1.4±0.1. A suggestive dependence on Galactic environment is seen. Apertures closer to the Galactic centre and the Sagittarius spiral arm have slightly higher velocity dispersions. We explore the possible effect of a diffuse component in the survey area and find that such a component would widen the CO spectra and could flatten the linewidth-size relation. Understanding the nature of the possible diffuse CO component and its effects on observations is crucial for connecting Galactic and extragalactic data.

Enhancing cross correlations of ocean ambient noise in the time domain based on random matrix theory.

Cross correlations of diffuse noise can be utilized to recover the time domain Green's function (TDGF) between two points. This principle allows for a variety of practical applications, such as seismic tomography, ocean thermometry, passive localization, etc. However, in the real ocean environment, loud interference noise sources usually bias the travel time estimates of the TDGF or result in poor recovery quality. To deal with this issue, a diffuse noise reconstruction approach is proposed to eliminate the influence of the strong interference noise by utilizing the time domain statistical property of ocean ambient noise recorded on single hydrophones with the help of random matrix theory. Simulation and experimental data analysis indicate that this algorithm can effectively extract the diffuse noise component from the ocean ambient noise field and retrieve the TDGF with a higher signal-to-noise ratio when coherent accumulation of cross correlations of the reconstructed diffuse noise is performed.

Dust extinction map of the Galactic plane based on the VVV survey data

ABSTRACT Dust extinction is one of the most reliable tracers of the gas distribution in the Milky Way. The near-infrared (NIR) Vista Variables in the Vía Láctea (VVV) survey enables extinction mapping based on stellar photometry over a large area in the Galactic plane. We devise a novel extinction mapping approach, XPNICER, by bringing together VVV photometric catalogues, stellar parameter data from StarHorse catalogues, and previously published X percentile and PNICER extinction mapping techniques. We apply the approach to the VVV survey area, resulting in an extinction map that covers the Galactic disc between 295° ≲ l ≲ 350° and −2° ≲ b ≲ 2°, and the Galactic bulge between −10° ≲ b ≲ 5°. The map has 30 arcsec spatial resolution and it traces extinctions typically up to AV ∼ 10–20 mag and maximally up to AV ∼ 30 mag. We compare our map to previous dust-based maps, concluding that it provides a high-fidelity extinction-based map, especially in its ability to recover both the diffuse dust component of the Galaxy and moderately extincted giant molecular cloud regions. The map is especially useful as independent, extinction-based data on the Galactic dust distribution and applicable for a wide range of studies from individual molecular clouds to the studies of the Galactic stellar populations.

Effects of inter-reflections on the correlated colour temperature and colour rendition of the light field

In everyday scenes, the effective light (the actual light in a space) can be defined as a complex light field, resulting from a mixture of emissive light sources and indirect mutual surface (inter-)reflections. Hence, the light field typically consists of diffuse and directional illumination and varies in spectral irradiance as a function of location and direction. The spatially varying differences between the diffuse and directional illumination spectra induce correlated colour temperature (CCT) and colour rendition variations over the light fields. Here, we aim to investigate the colourimetric properties of the actual light, termed the effective CCT and colour rendition, for spaces of one reflectance (uni-chromatic spaces). The spectra of the diffuse light-field component (light density) and the directional light-field component (light vector) were measured in both physical and simulated uni-chromatic spaces illuminated by ordinary white light sources. We empirically tested the effective CCT and colour rendition for the light density and the light vector, separately. There were significant differences between the lamp-specified CCT and colour rendition and the actual light-based effective CCT and effective colour rendition. Inter-reflections predominantly affected the CCT and colour rendition of the light density relative to the light vector. Treating the diffuse and directional light-field components in a linear model reveals the separate influences of the light source and scene. These effects show the importance of a 3D version of colour checkers for lighting designers, architects or in general computer graphics applications, for which we propose simple Lambertian spheres.

Clinical characteristics and prognosis of patients with co-existing follicular lymphoma and diffuse large B-cell lymphoma components in rituximab era.

This single-centre study aimed to determine the clinicopathological characteristics and prognosis for patients with co-existing FL and DLBCL components (FL/DLBCL). We retrospectively analysed the clinical characteristics and prognosis of patients diagnosed with FL/DLBCL (n = 56) and with pure FL (n = 260) or de novo DLBCL (n = 812) (controls) between January 2013 and December 2021. The median age of patients with FL/DLBCL was 52years. The amount of the DLBCL component ranged from 5 to 95%. Among the 56 FL/DLBCL cases analysed, 67.9% were of germinal centre B-cell (GCB) origin, 26.8% non-GCB origin, and 5.3% were unclassified. The clinical features of patients with FL/DLBCL were intermediate, falling between those of FL and DLBCL. Propensity-score matching was performed for patients with similar baseline characteristics who were receiving the rituximab plus cyclophosphamide, doxorubicin or epirubicin, vindesine, and prednisone (R-CHOP) regimen. Patients with FL/DLBCL showed inferior outcomes compared to those with FL, with a lower complete remission (CR) rate, progression-free survival (PFS), and overall survival (OS). Bone marrow involvement and B symptoms were identified as independent adverse prognostic factors for PFS among patients with FL/DLBCL. Patients with FL/DLBCL presented a lower CR rate and PFS but similar OS to those with DLBCL when receiving the R-CHOP regimen. Patients with FL/DLBCL showed inferior treatment response and survival than those with pure FL and had a lower CR rate and PFS, but similar OS to those with DLBCL in the rituximab era.

Robust extension of the simple sea-surface irradiance model to handle cloudy conditions for the global ocean using satellite remote sensing data

Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em−2day−1; and a mean net bias of 2.917 Em−2day−1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions.

Valuing basket-spread options with default risk under Hawkes jump-diffusion processes

In this paper, we investigate the pricing of basket-spread options with default risk under Hawkes jump-diffusion processes. A self-exciting Hawkes process is employed to describe jump clustering, and jump amplitudes of different assets in baskets are all correlated. In addition, the diffusive components of assets are also assumed to be correlated with each other. We obtain option prices by approximating the arithmetic average of the underlying assets in the basket with their second moment-matched geometric average values, and numerical experiments show that our approximated prices are quite accurate, spanning different underlying asset numbers and alternative strike prices. Finally, we illustrate the effects of default risk and clustered jump risk on the prices of basket-spread options.

Structural measurement of electron-phonon coupling and electronic thermal transport across a metal-semiconductor interface

Scattering of energetic charge carriers and their coupling to lattice vibrations (phonons) in dielectric materials and semiconductors are crucial processes that determine the functional limits of optoelectronics, photovoltaics, and photocatalysts. The strength of these energy exchanges is often described by the electron-phonon coupling coefficient, which is difficult to measure due to the microscopic time- and length-scales involved. In the present study, we propose an alternate means to quantify the coupling parameter along with thermal boundary resistance and electron conductivity by performing a high angular-resolution time-resolved X-ray diffraction measurement of propagating lattice deformation following laser excitation of a nanoscale, polycrystalline metal film on a semiconductor substrate. Our data present direct experimental evidence for identifying the ballistic and diffusive transport components occurring at the interface, where only the latter participates in thermal diffusion. This approach provides a robust measurement that can be applied to investigate microscopic energy transport in various solid-state materials.

Surface scattering model for dual-polarization planetary radars

This work presents a surface scattering model to interpret radar polarimetry derived from dual-polarization planetary radar systems, such as Arecibo Observatory and the Goldstone Solar System Radar. This model divides surface scattering contributions within a radar echo into quasi-specular and diffuse components, and further divides the quasi-specular component into single- and double-bounce scattering. In particular, the increase in the degree of linear polarization resulting from dihedral double-bounce scattering is emphasized, in addition to the increase in the circular polarization ratio. This mechanism is illustrated in radar observations of young craters on the Moon by the Mini-RF radar on board the Lunar Reconnaissance Orbiter. Arecibo radar observations of 8 near-Earth asteroids are compared to this model and the implications for the physical properties of these objects are discussed. This work provides new insight in interpreting radar polarimetry from dual-polarization planetary radar systems and is broadly applicable to all solar system targets.