Maxwell-Garnett mixing rule in the presence of multiple scattering: Derivation and accuracy

We give a rigorous and original derivation of the Maxwell-Garnett mixing rule in the dynamical regime for a composite dielectric random medium with small spherical inclusions. For certain configurations of scatterers, we show that contrarily to the common belief, the Maxwell-Garnett formula can remain very accurate at a high concentration of scatterers and incorporate multiple-scattering effects as well as attenuation of the mean field. We provide a realistic numerical example for which this is the case

Effective-medium theory for finite-size aggregates

We propose an effective-medium theory for random aggregates of small spherical particles that accounts for the finite size of the embedding volume. The technique is based on the identification of the first two orders of the Born series within a finite volume for the coherent field and the effective field. Although the convergence of the Born series requires a finite volume, the effective constants that are derived through this identification are shown to admit of a large-scale limit. With this approach we recover successively, and in a simple manner, some classical homogenization formulas: the Maxwell Garnett mixing rule, the effective-field approximation, and a finite-size correction to the quasi-crystalline approximation (QCA). The last formula is shown to coincide with the usual low-frequency QCA in the limit of large volumes, while bringing substantial improvements when the dimension of the embedding medium is of the order of the probing wavelength. An application to composite spheres is discussed

Correlation dimension of self-similar surfaces and application to Kirchhoff integrals

Abstract For surfaces generated by a class of asymptotically self-similar processes we define a probability measure, supported by the surface. We show that the correlation dimension of that surface measure is linked to the self-similarity exponent almost surely. This result is applied to the Kirchhoff integral well known in scattering from rough surfaces. We show that a certain average of the scattered intensity exhibits almost surely a scaling that allows us to recover the self-similarity index of the surface in an experiment involving only one sample of the surface

On the use of rigorous microwave interaction models to support remote sensing of natural surfaces

A study has been undertaken which objective is to contribute to the investigation of the validity of microwave surface scattering models used in remote sensing applications, particularly when applied to realistic representations of natural surfaces. These investigations are based on recent implementations of rigorous methods (MoM and FDTD) and cover a wide range of configurations of observation (mono- and bi-static). Both land (bare soils) and sea surfaces are being investigated

L’EROP : 10 ans pour le rétablissement des oiseaux de proie au Québec

L’Équipe de rétablissement des oiseaux de proie du Québec (EROP) a été fondée en 2004, à la suite de la fusion des équipes de rétablissement du faucon pèlerin (Falco peregrinus), du pygargue à tête blanche (Haliaeetus leucocephalus) et de l’aigle royal (Aquila chrysaetos). À ces espèces d’intérêt pour l’EROP s’est ajouté récemment le hibou des marais (Asio flammeus). À l’aide des plans de rétablissement de chacune des espèces, l’EROP veille à la mise en oeuvre de mesures de conservation (p. ex. acquisition de connaissances, sensibilisation, protection) visant à redresser la situation des populations d’oiseaux de proie en situation précaire au Québec. Cet article présente le mandat, le mode de fonctionnement et les principales réalisations de l’EROP au cours de la dernière décennie. The Québec raptor recovery team (EROP) was established in 2004 following the merger of the peregrine falcon (Falcoperegrinus), bald eagle (Haliaeetus leucocephalus) and golden eagle (Aquilachrysaetos) recovery teams. Recently, the short-eared owl (Asioflammeus) has also been added to the list of species covered by EROP. The team aims to foster conservation measures (e.g., data collection, public awareness and protection) to improve the population status of endangered birds of prey, and achieves this through the publication of species recovery plans. This article outlines the mission, and the working and main achievements of EROP over the past decade

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

A note on the generalized fractal dimensions of a probability measure

We prove the following result on the generalized fractal dimensions $D^{±}_q$ of a probability measure $\mu$ on $R^n$. Let $g$ be a complex-valued measurable function on $R^n$ satisfying the following conditions: (1) $g$ is rapidly decreasing at infinity, (2) $g$ is continuous and nonvanishing at (at least) one point, (3) $\int g≠0$. Define the partition function $\Lambda_a(μ,q)=a^{n(q−1)}‖g_a * μ‖\lim_q q$, where $g_a(x)=a^{−n}g(a^{−1}x)$ and  $*$  is the convolution in $R^n$. Then for all $q>1$ we have $D^{±}_q=1/(q−1)\lim_{r→0} {}^{sup}_{inf}[\log \Lambda_a \mu(r,q) / \log r]$

On estimating the Hurst exponent of a fractional Brownian surface from scattering data surfaces

ISBN: 9782912328168International audienc

Separation of surface and volume effects in scattering from heterogeneous rough surfaces : derivation of a splitting rule

International audienc