Numerical modeling and observations of seismo-acoustic waves propagating as modes in a fluid-solid waveguide.

This paper discusses the nature of the low-frequency seismo-acoustic waves generated by submarine earthquakes in the ocean. In a finite-depth homogeneous ocean over a semi-infinite solid crust, the derivation of the acoustic equations shows that waves propagate as modes. The waves propagating with the speed of sound in water (T waves) are preceded by waves with frequencies below the Airy phase.

Three-dimensional modeling of earthquake generated acoustic waves in the ocean in simplified configurations.

The low-frequency (4-40 Hz) acoustic waves generated by undersea earthquakes are of great importance to monitor the low-level seismic activity associated with seafloor spreading ridges. To better understand the near-source interaction of seismic waves with the seafloor and the resulting generation of low-frequency acoustic waves, the wave propagation in a solid medium (the Earth's crust) and in the overlaying fluid medium (the ocean) were jointly simulated using a three-dimensional (3D) spectral finite-element code (SPECFEM3D). Due to numerical limitations of 3D simulations, the focus was on simple model configurations with a 1 Hz source located below a Gaussian seamount or ridge.

T-wave generation and propagation: a comparison between data and spectral element modeling.

T-waves are underwater acoustic waves generated by earthquakes. Modeling of their generation and propagation is a challenging problem. Using a spectral element code-SPECFEM2D, this paper presents the first realistic simulations of T-waves taking into account major aspects of this phenomenon: The radiation pattern of the source, the propagation of seismic waves in the crust, the seismic to acoustic conversion on a non-planar seafloor, and the propagation of acoustic waves in the water column.

Differential effects of several retinoid receptor-selective ligands on squamous differentiation and apoptosis in airway epithelial cells.

The roles of the different retinoid receptors on the differentiation of rabbit tracheal epithelial (RbTE) cells in primary culture were analysed using selective agonists for the retinoid acid receptor subtypes RARalpha (CD336), RARbeta (CD2019), RARgamma (CD437), an RAR panagonist (CD367), a retinoid X receptor RXR panagonist (CD2624) and an antagonist for RARbeta/gamma (CD2665). Squamous differentiation was assessed via expression of cytokeratins CK13/CK4 and transglutaminase I (TGI), specific markers of metaplasia. Treatment with RARalpha and beta agonists or RAR panagonist, but not the RARgamma agonist or RXR agonist, is required for the inhibition of squamous metaplasia, evidenced by inhibition of CK13/CK4 and TGI expression.

Responses of the rabbit tracheal epithelium in vitro to H(2)O(2)-induced oxidative stress.

A model of rabbit tracheal epithelial (RTE) cells in primary culture was used to characterize specific and repair responses of airway epithelial cells to oxidative stress. Two well-known reactive oxygen species (ROS) generating systems were used: H(2)O(2) alone or in combination with Fe(2+) to produce the hydroxyl radical. RTE cells exhibited lipid peroxidation when exposed to H(2)O(2) + Fe(2+).

Differential expression and cellular distribution of centrin isoforms during human ciliated cell differentiation in vitro.

Centrin protein is an ubiquitously expressed cytoskeletal component and is a member of the EF-hand superfamily of calcium-binding proteins. It was first discovered in the flagellar apparatus of unicellular green algae where it is involved in contraction of Ca(2+)-sensitive structures. Centrin protein is associated with centrosome-related structures such as spindle pole body in yeast, and centriole/basal bodies in flagellar and ciliated cells.

Ciliated differentiation of rabbit tracheal epithelial cells in vitro.

Primary cultures of rabbit tracheal epithelial (RbTE) cells have been performed in two different ways. Quantitative analysis of both proliferative capacities and ciliated differentiation process were carried out using epithelial cell cultures from tracheal explants and from dissociated tracheal epithelial cells in air-liquid interface conditions. We show that both alpha- and beta-tubulins from RbTE cells are polyglutamylated and that this posttranslational modification is restricted to cilia axonemes and centrioles of non-ciliated cells.

In vitro exposure of rabbit tracheal epithelium to SO(2): Effects on morphology and ciliary beating.

The aim of this in vitro study was to characterize the direct effects of short-term exposure to low concentrations of sulfur dioxide (SO(2)) on both the morphology and the physiology of rabbit tracheal primary cultures. Scanning electron microscopy (SEM) studies revealed that ciliated cells exposed for 1 hr to 10 ppm or 30 ppm SO(2) exhibited aggregated cilia. Transmission electron microscopy revealed numerous swollen mitochondria in cells exposed to 30 ppm SO(2) for 1 hr.

Toxic effects of mechlorethamine on mammalian respiratory mucociliary epithelium in primary culture.

Mechlorethamine (HN2) is an alkylating agent usually used in cancer chemotherapy. Nevertheless, HN2 is extremely toxic and its use is accompanied by severe side-effects that may cause lung complications. Many studies report the morphological and biochemical modifications induced by sulfur mustard (SM) but no report has been published concerning the toxic effects of HN2 on the ultrastructural and functional activity of surface respiratory epithelial cells.

Extracellular matrix-dependent differentiation of rabbit tracheal epithelial cells in primary culture.

The differentiation of tracheal epithelial cells in primary culture was investigated according to the nature of the extracellular matrix used. Cultures obtained by the explant technique were realized on a type I collagen substratum either as a thin, dried coating or as a thick, hydrated gel supplemented with culture medium and serum. These two types of substratum induced distinct cell morphology and cytokeratin expression in the explant derived cells.

Effect of mineral particles containing iron on primary cultures of rabbit tracheal epithelial cells: possible implication of oxidative stress.

Environmental mineral particles such as asbestos are responsible for numerous respiratory diseases. In addition to effects related to their geometry, particles are now assumed to act by triggering an oxidative stress process. Iron-containing particles, in particular, can produce oxygen-activated species by oxidizing their iron.

Measurement of the epithelial barrier integrity in tracheal cell cultures exposed to irritant compounds.

A simple method has been developed to measure epithelial barrier alteration, in order to evaluate the irritant effect of inhaled compounds on the respiratory tract. In vitro primary cell cultures from rabbit tracheal epithelium were grown on permeable filters and used to study the effect of two pollutants-acrolein and parathion-on epithelial barrier integrity. The transepithelial potential difference and [(14)C]mannitol permeability were measured.

Primary cultures of tracheal epithelial cells for the evaluation of respiratory toxicity.

Cytotoxic assays have been carried out to evaluate toxic effects of acrolein, mechlorethamin, parathion and paraoxon, using primary cultures of rabbit tracheal epithelium obtained by the explant outgrowth technique. The effect of drug exposure was first evaluated by the tetrazolium salt assay, neutral red uptake and release of cellular lactate dehydrogenase. These assays, previously developed for cell line cultures, were adapted to our model.