Explicit asymptotic modelling of transient Love waves propagated along a thin coating

The official published version can be obtained from the link below.An explicit asymptotic model for transient Love waves is derived from the exact equations of anti-plane elasticity. The perturbation procedure relies upon the slow decay of low-frequency Love waves to approximate the displacement field in the substrate by a power series in the depth coordinate. When appropriate decay conditions are imposed on the series, one obtains a model equation governing the displacement at the interface between the coating and the substrate. Unusually, the model equation contains a term with a pseudo-differential operator. This result is confirmed and interpreted by analysing the exact solution obtained by integral transforms. The performance of the derived model is illustrated by numerical examples.This work is sponsored by the grant from Higher Education of Pakistan and by the Brunel University’s “BRIEF” research award

Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells

A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric fields into account. In addition, the many-body Coulomb ineraction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental conditions, our microscopic theory can be simplified and mapped onto a loaded string problem which can be easily solved.Comment: 20 pages, 17 figure

Whole-genome sequencing reveals host factors underlying critical COVID-19

Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2,3,4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes—including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)—in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease

Weed Control Economics : Applied Botany and Crop science

v, 169 hlm.; 23,5 cm

ELASTIC WAVE PROPAGATION IN THREE-DIMENSIONAL PERIODIC COMPOSITE MATERIALS

Nous avons effectué l'analyse d'ondes élastiques dans un solide à structure périodique.An elastodynamic theory, based on the concepts of Brillouin theory has been developed for elastic wave propagation in periodic composite materials

EXCITATION ET DÉTECTION PAR DES TRANSDUCTEURS INTERDIGITÉS DES ONDES TRANSVERSALES HORIZONTALES GUIDÉES DANS UNE PLAQUE DE QUARTZ

Les transducteurs à peignes interdigités, déposés sur un substrat piézoélectrique, peuvent exciter et détecter des ondes acoustiques de nature très différente (ondes de Rayleigh, ondes confinées sous la surface, ondes de volume, etc.). Dans le cas du quartz (coupe Y ± θ), si le transducteur est tourné de 90° par rapport à l'axe cristallin X, seules les ondes transversales horizontales sont excitées. Leurs directions, comme pour toutes les ondes de volume, sont déterminées par la fréquence du signal appliqué. Le transducteur d'excitation émet un faisceau acoustique qui, en se réfléchissant sur la surface inférieure, se dirige alors vers la surface supérieure, où il peut être détecté par un second transducteur. Le guidage des ondes est dû aux réflexions successives sur les faces parallèles de la plaque de quartz. Si elle est de faible épaisseur, l'interférence des ondes incidentes avec les ondes réfléchies, donne naissance à des modes de plaque se propageant à des fréquences discrètes. Les résultats de cette étude, à la fois théorique et expérimentale, sont présentés sous les deux aspects d'ondes guidées et de modes de plaque.The Interdigital Transducers (IDT) used in SAW devices are effective for launching various acoustic waves (Rayleigh Waves, Surface Skimming Bulk Waves and Bulk Acoustic Waves). In the Y-cut quartz, when the propagation is in the Y-Z plane, only the shear horizontal waves are generated. The direction of emission is scanned by the applied excitation frequency. The IDT is equivalent to an acoustic array antenna launching a collimated beam into the crystal bulk at such an angle that the beam reflected by the crystal plate bottom is redirected to the top surface where it can be intercepted by a receiving IDT. Guided waves are due to successive reflections on the parallel surfaces. If the plate thickness is weak, because of the interference between incident and reflected waves, plate modes are excited. In this paper, theoretical and experimental analysis of guided waves and plate modes are presented