Éditeur(s) : HAL CCSD
Résumé : 38 pages
Rapport
The Chicxulub impact crater, México, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic peak ring. Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on the Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic.During International Ocean Discovery Program (IODP) Expedition 364, Paleogene sediments and lithologies that make up the Chicxulub peak ring were cored to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of post-impact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Other key targets included sampling the transition through a rare midlatitude section that might include Eocene and Paleocene hyperthermals and/or the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of the impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Paleocene–Eocene Chicxulub impact basin infill; the chronology of the peak-ring rocks; and any observations from the core that may help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs acquired during Expedition 364 will be used to calibrate geophysical models, including seismic reflection and potential field data, and the integration of all the data will calibrate impact crater models for crater formation and environmental effects. The proposed drilling directly contributes to IODP Science Plan goals:Climate and Ocean Change: How resilient is the ocean to chemical perturbations? The Chicxulub impact represents an external forcing event that caused a 75% level mass extinction. The impact basin may also record key hyperthermals within the Paleogene.Biosphere Frontiers: What are the origin, composition, and global significance of subseafloor communities? What are the limits of life in the subseafloor? How sensitive are ecosystems and biodiversity to environmental change? Impact craters can create habitats for subsurface life, and Chicxulub may provide information on potential habitats for life, including extremophiles, on the early Earth and other planetary bodies. Paleontological and geochemical studies at ground zero will document how large impacts affect ecosystems and effects on biodiversity.Earth Connections/Earth in Motion: What are the composition, structure and dynamics of Earth’s upper mantle? What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami? Mantle uplift in response to impacts provides insight into dynamics that differ between Earth and other rocky planets. Impacts generate earthquakes, landslides, and tsunami, and scales that generally exceed plate tectonic processes yield insight into effects, the geologic record, and potential hazards.IODP Expedition 364 was a Mission Specific Platform expedition to obtain subseabed samples and downhole logging measurements from the sedimentary cover sequence and peak ring of the Chicxulub impact crater. A single borehole was drilled into the Chicxulub impact crater on the Yucatán continental shelf, recovering core from 505.7 to 1334.73 m below seafloor with ~99% core recovery and acquiring downhole logs for the entire depth.
International Ocean Discovery Program

hal-01639520
https://hal.archives-ouvertes.fr/hal-01639520
DOI : 10.14379/iodp.pr.364.2017

Éditeur(s) : HAL CCSD Human Kinetics
Résumé : International audience
In order to study the acclimatization process over 14 days of exposure to tropical climate, 9 triathletes performed 4 outdoor indirect continuous multistage tests in both thermoneutral and tropical conditions. The thermoneutral test (TN, 14 C, 45% rh) was performed before traveling to the tropical area (Martinique, FWI). The tropical tests were performed 2, 8, and 14 days after arrival (32.9 C, 78% rh). During each trial, we measured tympanic temperature, sweat rate, body mass loss, heart rate (HR), and performance. The results showed that 1) the mean tympanic temperature was greater in T2 (P < .001), T8 (P < .01) and T14 (P < .01) than in TN and significantly lower in T14 than in T2 (P < .05); 2) the mean sweat rate was significantly greater (P < .001) in T2, T8 and T14 than in TN and significantly greater (P < .05) in T8 and T14 than in T2; 3) the body mass loss after trials was significantly greater (P < .001) in T2, T8 and T14 than in TN and significantly greater (P < .05) in T8 and T14 than in T2; 4) the mean HR and HR at rest were significantly higher (P < .005) in T2 than in TN, T8, T14 and the mean HR was significantly lower (P < .05) in T14 than in the other trials; and 5) the performance time was significantly lower in T2 (P < 0.02), T8 (P < 0.03) and T14 (P < 0.05) than in TN. We concluded that 14 days of exposure.
ISSN: 1066-7814

hal-00720075
https://hal.univ-antilles.fr/hal-00720075
https://hal.univ-antilles.fr/hal-00720075/document
https://hal.univ-antilles.fr/hal-00720075/file/02.Voltaire_551_.pdf

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
This study demonstrates that 20-100 GHz range can be used for spatially-accurate focusing of heating inside the skin achieved by varying frequency and exposure beam size, as well as by enforcing air convection. The latter is also used to reduce overheating of skin surface. Heating at different skin depths depending on these parameters is investigated in detail using the hybrid bio-heat equation. In particular, it is shown that decreasing frequency and/or increasing exposure beam size at forced airflow result in elevation of heating of deeper layers of tissue and decrease of skin surface temperature. Changes of water content within 15%, which exceed those due to aging and presence of tumors, only slightly affect heating. Exposure intensity necessary to reach a target temperature significantly increases in different areas of body with elevated blood flow. Dependence on exposure intensity and hyperthermia treatment duration is also investigated and discussed. Results of this study suggest that the lower part of the millimeter-wave range is an attractive alternative for non-invasive thermal treatment of skin cancer with a high spatial resolution. Bioelectromagnetics. 36:464-475, 2015. © 2015 Wiley Periodicals, Inc
ISSN: 0197-8462

hal-01187403
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01187403
DOI : 10.1002/bem.21929
PUBMED : 26179286

Éditeur(s) : HAL CCSD Public Library of Science
Résumé : International audience
Radiofrequency radiations constitute a new form of environmental pollution. Among them, millimeter waves (MMW) will be widely used in the near future for high speed communication systems. This study aimed therefore to evaluate the biocompatibility of MMW at 60 GHz. For this purpose, we used a whole gene expression approach to assess the effect of acute 60 GHz exposure on primary cultures of human keratinocytes. Controls were performed to dissociate the electromagnetic from the thermal effect of MMW. Microarray data were validated by RT-PCR, in order to ensure the reproducibility of the results. MMW exposure at 20 mW/cm2, corresponding to the maximum incident power density authorized for public use (local exposure averaged over 1 cm2), led to an increase of temperature and to a strong modification of keratinocyte gene expression (665 genes differentially expressed). Nevertheless, when temperature is artificially maintained constant, no modification in gene expression was observed after MMW exposure. However, a heat shock control did not mimic exactly the MMW effect, suggesting a slight but specific electromagnetic effect under hyperthermia conditions (34 genes differentially expressed). By RT-PCR, we analyzed the time course of the transcriptomic response and 7 genes have been validated as differentially expressed: ADAMTS6, NOG, IL7R, FADD, JUNB, SNAI2 and HIST1H1A. Our data evidenced a specific electromagnetic effect of MMW, which is associated to the cellular response to hyperthermia. This study raises the question of co-exposures associating radiofrequencies and other environmental sources of cellular stress.
ISSN: 1932-6203

hal-01118066
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01118066
PUBMED : 25302706
DOI : 10.1371/journal.pone.0109435
PUBMEDCENTRAL : PMC4193780

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Cnidarian-dinoflagellate symbiosis mainly relies on nutrient recycling, thus providing both partners with a competitive advantage in nutrient-poor waters. Essential processes related to lipid metabolism can be influenced by various factors, including hyperthermal stress. This can affect the lipid content and distribution in both partners, while contributing to symbiosis disruption and bleaching. In order to gain further insight into the role and distribution of lipids in the cnidarian metabolism, we investigated the lipid composition of the sea anemone Anemonia viridis and its photosynthetic dinoflagellate endosymbionts (Symbiodinium). We compared the lipid content and fatty acid profiles of the host cellular layers, non-symbiotic epidermal and symbiont-containing gastrodermal cells, and those of Symbiodinium, in a mass spectrometry-based assessment. Lipids were more concentrated in Symbiodinium cells, and the lipid class distribution was dominated by polar lipids in all tissues. The fatty acid distribution between host cell layers and Symbiodinium cells suggested potential lipid transfers between the partners. The lipid composition and distribution was modified during short-term hyperthermal stress, mainly in Symbiodinium cells and gastrodermis. Exposure to elevated temperature rapidly caused a decrease in polar lipid C18 unsaturated fatty acids and a strong and rapid decrease in the abundance of polar lipid fatty acids relative to sterols. These lipid indicators could therefore be used as sensitive biomarkers to assess the physiology of symbiotic cnidarians, especially the effect of thermal stress at the onset of cnidarian bleaching. Overall, the findings of this study provide some insight on key lipids that may regulate maintenance of the symbiotic interaction.
ISSN: 1095-6433

hal-01546160
https://hal.archives-ouvertes.fr/hal-01546160
DOI : 10.1016/j.cbpa.2015.10.017

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
Due to shallow penetration of millimeter waves (MMW) and convection in liquid medium surrounding cells, the problem of accurate assessment of local MMW heating in in vitro experiments remains unsolved. Conventional dosimetric MMW techniques, such as infrared imaging or fiber optic (FO) sensors, face several inherent limits. Here we propose a methodology for accurate local temperature measurement and subsequent specific absorption rate (SAR) retrieval using microscale thermocouples (TC). SAR was retrieved by fitting the measured initial temperature rise to the numerical solution of an equivalent thermal model. It was found that the accuracy of temperature measurement depends on thermosensor size, that is, the smaller TC, the more accurate the temperature measurement. SAR determined using TC with lead diameters of 25 and 75m demonstrated 98.5% and 80.4% match with computed SAR, respectively. However, both TC provided the same temperature rises in long run (>10min). FO probe failed to measure adequately local heating both for short and long exposures due to the relatively large size of the probe sensor (400m) and time constant (0.6s). Calculated SAR in the cell monolayer was almost two times lower than that in the surrounding liquid. It was shown that the impact of the cell monolayer on heating due to its small thickness (5 to 10m) can be considered as negligible. Moreover, we demonstrated the possibility of accurate measurement of MMW-induced thermal pulses (up to 10 degrees C) using 25m TC. Bioelectromagnetics. 38:11-21, 2017. (c) 2016 Wiley Periodicals, Inc.
ISSN: 0197-8462

hal-01436768
https://hal-univ-rennes1.archives-ouvertes.fr/hal-01436768
DOI : 10.1002/bem.21999
PUBMED : 27571392

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Cnidarian-dinoflagellate symbiosis disruption and subsequent bleaching are major concerns, especially regarding their ecological consequences on coral reefs and temperate coralligenous communities. Cnidarian bleaching is caused by a variety of environmental stressors, such as elevated seawater temperature associated with global climate change, and by pollutants, such as herbicides and metals. Several cellular events have been described to explain symbiosis dysfunction and bleaching. Excess or damaged Symbiodinium symbionts are removed through a variety of mechanisms, including exocytosis, apoptosis, necrosis and autophagy. However, few studies have compared in the same species the relative involvement of these mechanisms, according to the stress inducing the bleaching. In this study, we used two different treatments —temperature and menthol— to induce bleaching in the sea anemone Anemonia viridis. By monitoring the ultrastructural tissue modifications, in control specimens we observed a basal rate of in situ symbiont digestion —or symbiophagy— induced by starvation. Symbiophagy was strongly induced in menthol-treated specimens and was the main cellular process of bleaching, whereas apoptosis and necrosis predominated in hyperthermal-induced bleaching. These results suggested a host effect through autophagy in menthol-treated specimens. These observations also suggested that symbiont removal may result from reengagement of the phagosomal maturation process in the host. These overall data demonstrate that several Symbiodinium cell removal mechanisms coexist and that stressors can activate one or more of these pathways, depending on the stress type, intensity or duration.
ISSN: 0334-5114

hal-01546908
http://hal.upmc.fr/hal-01546908
DOI : 10.1007/s13199-016-0406-y