Feasibility study of ionospheric perturbations triggered by monochromatic infrasonic waves emitted with a ground-based experiment

International audienceIn the framework of an active experiment preparation with a powerful ground-based monochromatic emitter, the modification of ionospheric plasma by infrasonic waves is examined. In this paper, theoretical models and numerical calculations take into account realistic altitude temperature dependence. A modulation of the electron density for an altitude equal to similar to100 km was determined under the assumption that the plasma is a small passive admixture. To study the expected ionospheric effects we intend to use data from an ionospheric sounder and from the low-altitude Demeter satellite, which can register representative electromagnetic signals scattered by artificial ionospheric inhomogeneities. The comparison between the obtained results and the expected ones is important for the analysis of possible acoustic-gravity wave contribution to the formation of an electromagnetic earthquake precursor. The calculations developed in this paper indicate that the power of an emitter of infrasonic waves with frequencies below than 20 Hz must be equal to or larger than 10 kW to be able to trigger ionospheric perturbations

VLF electromagnetic field structures in ionosphere disturbed by Sura RF heating facility

International audience[1] Observation of spatial VLF field structures in an artificially disturbed ionosphere is reported. The disturbed area with horizontal sizes ∼50 km in a quiet middle‐latitude ionosphere was produced by the powerful RF Sura heating facility (56°1′N, 46°1′E). Measurements were carried out onboard the DEMETER satellite while passing the disturbed area at height ∼700 km. Spectra broadening (Df < ±1 kHz) and considerable (up to 30 dB) increase of signal intensity of VLF transmitters' signals were observed. The VLF field and electron density irregularities have similar spatial structure. The characteristics of the VLF field in disturbed by RF heating area are analyzed. Parrot, and J.‐L. Rauch (2010), VLF electromagnetic field structures in ionosphere disturbed by Sura RF heating facility

Posted: The Campaign Sign Landscape, Race, and Political Participation in Mississippi

Cultural landscapes offer potential insights into cultural processes. As a cultural/political landscape element, the domestic campaign sign is linked to a variety of socio-cultural and political processes. Examination of the geographical distribution of 2004 presidential election campaign signs posted throughout the town of Hattiesburg, Mississippi, illustrates that race is a factor in understanding who chooses to post signs. Historically, limitations on political participation in the South would have included use of landscape for communication, imposing a sort of metacommunicative landscape hegemony. Further, patterns of sign postings and voter turnout indicate that both activities are forms of political participation that are embraced differently by different social groups

Static Clathrin Assemblies at the Peripheral Vacuole—Plasma Membrane Interface of the Parasitic Protozoan Giardia lamblia

Giardia lamblia is a parasitic protozoan that infects a wide range of vertebrate hosts including humans. Trophozoites are non-invasive but associate tightly with the enterocyte surface of the small intestine. This narrow ecological specialization entailed extensive morphological and functional adaptations during host-parasite co-evolution, including a distinctly polarized array of endocytic organelles termed peripheral vacuoles (PVs), which are confined to the dorsal cortical region exposed to the gut lumen and are in close proximity to the plasma membrane (PM). Here, we investigated the molecular consequences of these adaptations on the Giardia endocytic machinery and membrane coat complexes. Despite the absence of canonical clathrin coated vesicles in electron microscopy, Giardia possesses conserved PV-associated clathrin heavy chain (GlCHC), dynamin-related protein (GlDRP), and assembly polypeptide complex 2 (AP2) subunits, suggesting a novel function for GlCHC and its adaptors. We found that, in contrast to GFP-tagged AP2 subunits and DRP, CHC::GFP reporters have no detectable turnover in living cells, indicating fundamental differences in recruitment to the membrane and disassembly compared to previously characterized clathrin coats. Histochemical localization in electron tomography showed that these long-lived GlCHC assemblies localized at distinctive approximations between the plasma and PV membrane. A detailed protein interactome of GlCHC revealed all of the conserved factors in addition to novel or highly diverged proteins, including a putative clathrin light chain and lipid-binding proteins. Taken together, our data provide strong evidence for giardial CHC as a component of highly stable assemblies at PV-PM junctions that likely have a central role in organizing continuities between the PM and PV membranes for controlled sampling of the fluid environment. This suggests a novel function for CHC in Giardia and the extent of molecular remodeling of endocytosis in this species