Discovery of a hypersaline subglacial lake complex beneath Devon Ice Cap, Canadian Arctic.

Subglacial lakes are unique environments that, despite the extreme dark and cold conditions, have been shown to host microbial life. Many subglacial lakes have been discovered beneath the ice sheets of Antarctica and Greenland, but no spatially isolated water body has been documented as hypersaline. We use radio-echo sounding measurements to identify two subglacial lakes situated in bedrock troughs near the ice divide of Devon Ice Cap, Canadian Arctic. Modeled basal ice temperatures in the lake area are no higher than -10.5°C, suggesting that these lakes consist of hypersaline water. This implication of hypersalinity is in agreement with the surrounding geology, which indicates that the subglacial lakes are situated within an evaporite-rich sediment unit containing a bedded salt sequence, which likely act as the solute source for the brine. Our results reveal the first evidence for subglacial lakes in the Canadian Arctic and the first hypersaline subglacial lakes reported to date. We conclude that these previously unknown hypersaline subglacial lakes may represent significant and largely isolated microbial habitats, and are compelling analogs for potential ice-covered brine lakes and lenses on planetary bodies across the solar system

Comparative expression of cell wall related genes in four maize RILs and one parental line of variable lignin content and cell wall degradability

A comparison of gene expression in maize between the parental line F271 and four RILs derived from the cross F288 x F271 was investigated based on hybridization on the 17,555 probes Affymetrix micro-array, targeting nearly one third of the genes present in maize genomes. The parental line had unfavorable alleles for cell wall degradability traits at the major QTL position in bin 6.06, while the set of RILs had both the favorable allele and high cell wall degradability. 360 genes were differentially expressed in the four RIL in comparison to F271, including nine genes underlying the major QTL position and 36 underlying two other QTL positions. However, their proposed function (whenever is described) do not allow us to firmly consider their involvement in the observed variation of cell wall related traits. Only a few genes involved in monolignol biosynthesis or polymerization located elsewhere in the genome were differentially expressed between the four RILs and F271, corroborating with the fact that these genes are probably not involved in major determinants of cell wall degradability in the studied set of lines. Among the investigated regulation factors, three ZmMYB, one NAC and one C3HC4 zinc finger were differentially expressed between the four RILs and F271, but they were not located in bin 6.06. Notwithstanding, the obtained results especially strengthened the probable involvement of these genes in maize secondary wall assembly and/ or lignification

Comparative expression of cell wall related genes in four maize RILs and one parental line of variable lignin content and cell wall degradability

A comparison of gene expression in maize between the parental line F271 and four RILs derived from the cross F288 x F271 was investigated based on hybridization on the 17,555 probes Affymetrix micro-array, targeting nearly one third of the genes present in maize genomes. The parental line had unfavorable alleles for cell wall degradability traits at the major QTL position in bin 6.06, while the set of RILs had both the favorable allele and high cell wall degradability. 360 genes were differentially expressed in the four RIL in comparison to F271, including nine genes underlying the major QTL position and 36 underlying two other QTL positions. However, their proposed function (whenever is described) do not allow us to firmly consider their involvement in the observed variation of cell wall related traits. Only a few genes involved in monolignol biosynthesis or polymerization located elsewhere in the genome were differentially expressed between the four RILs and F271, corroborating with the fact that these genes are probably not involved in major determinants of cell wall degradability in the studied set of lines. Among the investigated regulation factors, three ZmMYB, one NAC and one C3HC4 zinc finger were differentially expressed between the four RILs and F271, but they were not located in bin 6.06. Notwithstanding, the obtained results especially strengthened the probable involvement of these genes in maize secondary wall assembly and/ or lignification

Etude de la surface et de la subsurface de Mars par sondage radar. Analyse des données MRO/Sharad

This thesis presents several geophysical studies using the Sharad radar sounder dataset(NASA/ASI). Sharad is exploring the surface and subsurface of Mars with a frequency of 20 5 MHzfrom a low polar orbit. The mission goals are to constrain the soil composition and to detect someburied structures in order to interpret the Martian geological context at a regional scale.First, the radar signal has been analyzed over the North polar deposits to retrieve the dielectricproperties of the bulk ice. We deduce a purity rate of the ice > 95%. This study required thereconstruction of the bedrock by interpolating the surrounding topography. From this, we provide amap of the deposits thickness that agreed with a volume of ice of 1.14 106 km3.In a second study, we compare the Sharad cross-sections to surface topography and opticalimages in order to develop a complete morphologic and stratigraphic description of polar scarps in theregion of Ultimi Lobe, Planum Boreum. This description is similar to listric faults associated with rolloveranticlines. It leads us to propose a new formation process hypothesis implying a macromechanicalfailure of the ice under stress and a subsequent basal sliding.Then we studied the surface radar reflectivity whose magnitude depends on the roughness andpermittivity of the soil. We develop a method to build up a global map of the reflectivity. To separatethe physical parameters contributing to the signal, we propose a simple statistical method associated tosurface backscattering models at normal incidence. We show that the vertical roughness can bederived without prior calibration for surfaces whose correlation length is > 500 m. In this case,permittivity can be estimate only if a reference area is known to calibrate the signal. Finally, we detecta seasonal variation of the reflectivity at poles that we attribute to the seasonal CO2 frost. Ourstatistical approach for the reflectivity, associated with a three layers backscattering model, allowsderiving the thickness variation of the frost. We report a late recession in the cryptic region.Le radar sondeur Sharad (NASA/ASI) prospecte actuellement la surface et le sous-sol de Mars àune fréquence de 20 ±5 MHz depuis une orbite polaire basse (Mars Reconnaissance Orbiter).L'instrument a pour but de contraindre la composition du sol et de détecter, puis d'interpréter, desinterfaces enfouies afin de restituer le contexte géologique martien à l'échelle régionale. Ce travail dethèse se propose de contribuer à ces objectifs en se focalisant principalement sur l'étude de terrainsglaciaires et péri-glaciaires Martien.Dans un premier temps, par une méthode d'inversion impliquant la reconstruction d'un sousbassementrocheux par interpolation, nous obtenons les paramètres diélectriques représentatifs duvolume de glace d'eau constituant la calotte polaire Nord, Planum Boreum. Nous en déduisons un tauxde pureté du matériel glaciaire > 95 %. Nous fournissons une carte de l'épaisseur des dépôts qui vérifieun volume de glace de 1,14106 km3.Dans une deuxième étude, en confrontant les transects Sharad à des données topographiques etd'imagerie visible, nous élaborons un profil morphologique et stratigraphique complet d'escarpementsglaciaires présents dans la région d'Ultimi Lobe, Planum Australe. Nous appelons ces escarpements"Laps" (large and assymetric polar scarps). La similarité avec des failles listriques associées à desanticlinaux de roll-over nous amène à proposer l'hypothèse de macro-ruptures mécaniques d'une glacesous contrainte extensive et d'un mouvement subséquent par glissement basal.Puis, nous nous intéressons à la réflectivité radar de la surface dont l'amplitude dépend de larugosité et de la permittivité du sol. Nous élaborons une méthode nous permettant de construire unecarte globale de la réflectivité. Afin de séparer les paramètres physiques qui constituent ce signal, nousproposons des méthodes statistiques simples, inspirés du SAR (radar à synthèse d'ouverture) terrestre,complétées par l'élaboration de modèles de rétrodiffusion de surface à incidence normale. Nousmontrons des résultats de cette approche et leur adéquation avec les modèles théoriques. Enfin, nousmettons en évidence une variation temporelle de la réflectivité aux pôles que nous attribuons à laprésence des condensats saisonniers de CO2. Notre méthode d'analyse statistique de la réflectivité,associée à un modèle de rétrodiffusion à trois couches, nous permet d'évaluer la variation d'épaisseurdes condensats dans des régions à très hautes latitudes (80°-85°)

Study of the Surface and Subsurface of Mars by radar sounding (SHARAD/MARSIS)

Le radar sondeur Sharad (NASA/ASI) prospecte actuellement la surface et le sous-sol de Mars àune fréquence de 20 ±5 MHz depuis une orbite polaire basse (Mars Reconnaissance Orbiter).L'instrument a pour but de contraindre la composition du sol et de détecter, puis d'interpréter, desinterfaces enfouies afin de restituer le contexte géologique martien à l'échelle régionale. Ce travail dethèse se propose de contribuer à ces objectifs en se focalisant principalement sur l'étude de terrainsglaciaires et péri-glaciaires Martien.Dans un premier temps, par une méthode d'inversion impliquant la reconstruction d'un sousbassementrocheux par interpolation, nous obtenons les paramètres diélectriques représentatifs duvolume de glace d'eau constituant la calotte polaire Nord, Planum Boreum. Nous en déduisons un tauxde pureté du matériel glaciaire > 95 %. Nous fournissons une carte de l'épaisseur des dépôts qui vérifieun volume de glace de 1,14106 km3.Dans une deuxième étude, en confrontant les transects Sharad à des données topographiques etd'imagerie visible, nous élaborons un profil morphologique et stratigraphique complet d'escarpementsglaciaires présents dans la région d'Ultimi Lobe, Planum Australe. Nous appelons ces escarpements"Laps" (large and assymetric polar scarps). La similarité avec des failles listriques associées à desanticlinaux de roll-over nous amène à proposer l'hypothèse de macro-ruptures mécaniques d'une glacesous contrainte extensive et d'un mouvement subséquent par glissement basal.Puis, nous nous intéressons à la réflectivité radar de la surface dont l'amplitude dépend de larugosité et de la permittivité du sol. Nous élaborons une méthode nous permettant de construire unecarte globale de la réflectivité. Afin de séparer les paramètres physiques qui constituent ce signal, nousproposons des méthodes statistiques simples, inspirés du SAR (radar à synthèse d'ouverture) terrestre,complétées par l'élaboration de modèles de rétrodiffusion de surface à incidence normale. Nousmontrons des résultats de cette approche et leur adéquation avec les modèles théoriques. Enfin, nousmettons en évidence une variation temporelle de la réflectivité aux pôles que nous attribuons à laprésence des condensats saisonniers de CO2. Notre méthode d'analyse statistique de la réflectivité,associée à un modèle de rétrodiffusion à trois couches, nous permet d'évaluer la variation d'épaisseurdes condensats dans des régions à très hautes latitudes (80°-85°).This thesis presents several geophysical studies using the Sharad radar sounder dataset(NASA/ASI). Sharad is exploring the surface and subsurface of Mars with a frequency of 20 5 MHzfrom a low polar orbit. The mission goals are to constrain the soil composition and to detect someburied structures in order to interpret the Martian geological context at a regional scale.First, the radar signal has been analyzed over the North polar deposits to retrieve the dielectricproperties of the bulk ice. We deduce a purity rate of the ice > 95%. This study required thereconstruction of the bedrock by interpolating the surrounding topography. From this, we provide amap of the deposits thickness that agreed with a volume of ice of 1.14 106 km3.In a second study, we compare the Sharad cross-sections to surface topography and opticalimages in order to develop a complete morphologic and stratigraphic description of polar scarps in theregion of Ultimi Lobe, Planum Boreum. This description is similar to listric faults associated with rolloveranticlines. It leads us to propose a new formation process hypothesis implying a macromechanicalfailure of the ice under stress and a subsequent basal sliding.Then we studied the surface radar reflectivity whose magnitude depends on the roughness andpermittivity of the soil. We develop a method to build up a global map of the reflectivity. To separatethe physical parameters contributing to the signal, we propose a simple statistical method associated tosurface backscattering models at normal incidence. We show that the vertical roughness can bederived without prior calibration for surfaces whose correlation length is > 500 m. In this case,permittivity can be estimate only if a reference area is known to calibrate the signal. Finally, we detecta seasonal variation of the reflectivity at poles that we attribute to the seasonal CO2 frost. Ourstatistical approach for the reflectivity, associated with a three layers backscattering model, allowsderiving the thickness variation of the frost. We report a late recession in the cryptic region

Etude de la surface et de la subsurface de Mars par sondage radar. Analyse des données MRO/Sharad

Le radar sondeur Sharad (NASA/ASI) prospecte actuellement la surface et le sous-sol de Mars àune fréquence de 20 +-5 MHz depuis une orbite polaire basse (Mars Reconnaissance Orbiter).L'instrument a pour but de contraindre la composition du sol et de détecter, puis d'interpréter, desinterfaces enfouies afin de restituer le contexte géologique martien à l'échelle régionale. Ce travail dethèse se propose de contribuer à ces objectifs en se focalisant principalement sur l'étude de terrainsglaciaires et péri-glaciaires Martien.Dans un premier temps, par une méthode d'inversion impliquant la reconstruction d'un sousbassementrocheux par interpolation, nous obtenons les paramètres diélectriques représentatifs duvolume de glace d'eau constituant la calotte polaire Nord, Planum Boreum. Nous en déduisons un tauxde pureté du matériel glaciaire > 95 %. Nous fournissons une carte de l'épaisseur des dépôts qui vérifieun volume de glace de 1,14 106 km3.Dans une deuxième étude, en confrontant les transects Sharad à des données topographiques etd'imagerie visible, nous élaborons un profil morphologique et stratigraphique complet d'escarpementsglaciaires présents dans la région d'Ultimi Lobe, Planum Australe. Nous appelons ces escarpements"Laps" (large and assymetric polar scarps). La similarité avec des failles listriques associées à desanticlinaux de roll-over nous amène à proposer l'hypothèse de macro-ruptures mécaniques d'une glacesous contrainte extensive et d'un mouvement subséquent par glissement basal.Puis, nous nous intéressons à la réflectivité radar de la surface dont l'amplitude dépend de larugosité et de la permittivité du sol. Nous élaborons une méthode nous permettant de construire unecarte globale de la réflectivité. Afin de séparer les paramètres physiques qui constituent ce signal, nousproposons des méthodes statistiques simples, inspirés du SAR (radar à synthèse d'ouverture) terrestre,complétées par l'élaboration de modèles de rétrodiffusion de surface à incidence normale. Nousmontrons des résultats de cette approche et leur adéquation avec les modèles théoriques. Enfin, nousmettons en évidence une variation temporelle de la réflectivité aux pôles que nous attribuons à laprésence des condensats saisonniers de CO2. Notre méthode d'analyse statistique de la réflectivité,associée à un modèle de rétrodiffusion à trois couches, nous permet d'évaluer la variation d'épaisseurdes condensats dans des régions à très hautes latitudes (80-85).This thesis presents several geophysical studies using the Sharad radar sounder dataset(NASA/ASI). Sharad is exploring the surface and subsurface of Mars with a frequency of 20 5 MHzfrom a low polar orbit. The mission goals are to constrain the soil composition and to detect someburied structures in order to interpret the Martian geological context at a regional scale.First, the radar signal has been analyzed over the North polar deposits to retrieve the dielectricproperties of the bulk ice. We deduce a purity rate of the ice > 95%. This study required thereconstruction of the bedrock by interpolating the surrounding topography. From this, we provide amap of the deposits thickness that agreed with a volume of ice of 1.14 106 km3.In a second study, we compare the Sharad cross-sections to surface topography and opticalimages in order to develop a complete morphologic and stratigraphic description of polar scarps in theregion of Ultimi Lobe, Planum Boreum. This description is similar to listric faults associated with rolloveranticlines. It leads us to propose a new formation process hypothesis implying a macromechanicalfailure of the ice under stress and a subsequent basal sliding.Then we studied the surface radar reflectivity whose magnitude depends on the roughness andpermittivity of the soil. We develop a method to build up a global map of the reflectivity. To separatethe physical parameters contributing to the signal, we propose a simple statistical method associated tosurface backscattering models at normal incidence. We show that the vertical roughness can bederived without prior calibration for surfaces whose correlation length is > 500 m. In this case,permittivity can be estimate only if a reference area is known to calibrate the signal. Finally, we detecta seasonal variation of the reflectivity at poles that we attribute to the seasonal CO2 frost. Ourstatistical approach for the reflectivity, associated with a three layers backscattering model, allowsderiving the thickness variation of the frost. We report a late recession in the cryptic region.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

The Possibility of Systematic Research Fraud Targeting Under-Studied Human Genes: Causes, Consequences, and Potential Solutions

International audienc

Quantitative analysis of Mars surface radar reflectivity at 20 MHz

The radar surface echoes taken from SHARAD observations are extracted to obtain a reflectivity map covering almost half of the martian surface, and then compared to available roughness maps. Then, we used a 2-step method, based on a stochastic description of reflectivity, in order to (i) separate the coherent/incoherent components of the signal by means of a probability density function fitting of amplitude distributions, and (ii) express these components with respect to roughness/permittivity values by adapting common backscattering models to the nadir case. Scattering is found to be the most important process dominating reflectivity over the martian terrains. Reflectivity is best correlated with roughness maps derived from the slope parameter. The stochastic behavior of reflectivity is confirmed by the excellent agreement of our models and demonstrates the low probability of retrieving permittivity from scattering surfaces. The non-stationary nature of most martian terrains is consolidated by a very good fit to K-distributions, justifying the use of the fractal theory for describing surface roughness on Mars. A few slightly-rough regions exhibit both a coherent and incoherent component. When surface correlation length is non-significant within the resolution cell, we show that the RMS roughness at a decameters baseline can be derived with sub-decimeter sensitivity without prior signal calibration, improving the capabilities of SHARAD in determining surface roughness with a view to landing site selection. Sets of derived dielectric constants are obtained and analyzed with regard to the reference signal used for calibration. Given the very different implications of each set to the composition of martian terrains, we emphasize the importance of good signal calibration as a major issue for SHARAD and the next interplanetary radar missions. (C) 2012 Elsevier Inc. All rights reserved

Martian Surface Reflectivity seen by MARSIS

Abstract P33B-1465Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a low frequency radar. The MARSIS wavelength is about 50-100 m. These radar waves penetrate deeply in the Martian ground and the first radar echo is due to few tens meters of the surface. The amplitude of this surface echo provides useful information on the shallow subsurface. Using MARSIS radar data, we extract the reflectivity of the Martian surface from the radargrams and then we build a global radar reflectivity map. We will describe our method for the extraction and the calibration of the reflectivity. In this calibration, we correct the absorption due to the two-way of radar waves through the Martian ionosphere and compensate the surface roughness effect. The surface roughness effect is estimated by simulating the radar surface returns for each MARSIS orbit. Finally, we will present a reflectivity map without roughness effect and discuss the reflectivity variations due to change in the dielectric constant

Semi-automated fact-checking of nucleotide sequence reagents in biomedical research publications: The Seek & Blastn tool

International audienceNucleotide sequence reagents are verifiable experimental reagents in biomedical publications , because their sequence identities can be independently verified and compared with associated text descriptors. We have previously reported that incorrectly identified nucleotide sequence reagents are characteristic of highly similar human gene knockdown studies, some of which have been retracted from the literature on account of possible research fraud. Because of the throughput limitations of manual verification of nucleotide sequences, we developed a semi-automated fact checking tool, Seek & Blastn, to verify the targeting or non-targeting status of published nucleotide sequence reagents. From previously described and unknown corpora of 48 and 155 publications, respectively, Seek & Blastn correctly extracted 304/342 (88.9%) and 1066/1522 (70.0%) nucleotide sequences and a predicted targeting/ non-targeting status. Seek & Blastn correctly predicted the targeting/ non-targeting status of 293/304 (96.4%) and 988/1066 (92.7%) of the correctly extracted nucleotide sequences. A total of 38/39 (97.4%) or 31/79 (39.2%) Seek & Blastn predictions of incorrect nucleotide sequence reagent use were correct in the two literature corpora. Combined Seek & Blastn and manual analyses identified a list of 91 misidentified nucleotide sequence reagents, which could be built upon through future studies. In summary, incorrect nucleotide sequence reagents represent an under-recognized source of error within the biomedical literature , and fact checking tools such as Seek & Blastn may help to identify papers and manuscripts affected by these errors