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Two families of exocomets in the β Pictoris system

Nature - Wed, 10/22/2014 - 00:00

Two families of exocomets in the β Pictoris system

Nature 514, 7523 (2014). doi:10.1038/nature13849

Authors: F. Kiefer, A. Lecavelier des Etangs, J. Boissier, A. Vidal-Madjar, H. Beust, A.-M. Lagrange, G. Hébrard & R. Ferlet

The young planetary system surrounding the star β Pictoris harbours active minor bodies. These asteroids and comets produce a large amount of dust and gas through collisions and evaporation, as happened early in the history of our Solar System. Spectroscopic observations of β Pictoris reveal a high rate of transits of small evaporating bodies, that is, exocomets. Here we report an analysis of more than 1,000 archival spectra gathered between 2003 and 2011, which provides a sample of about 6,000 variable absorption signatures arising from exocomets transiting the disk of the parent star. Statistical analysis of the observed properties of these exocomets allows us to identify two populations with different physical properties. One family consists of exocomets producing shallow absorption lines, which can be attributed to old exhausted (that is, strongly depleted in volatiles) comets trapped in a mean motion resonance with a massive planet. Another family consists of exocomets producing deep absorption lines, which may be related to the recent fragmentation of one or a few parent bodies. Our results show that the evaporating bodies observed for decades in the β Pictoris system are analogous to the comets in our own Solar System.

Categories: Literature

Characterizing and predicting the magnetic environment leading to solar eruptions

Nature - Wed, 10/22/2014 - 00:00

Characterizing and predicting the magnetic environment leading to solar eruptions

Nature 514, 7523 (2014). doi:10.1038/nature13815

Authors: Tahar Amari, Aurélien Canou & Jean-Jacques Aly

The physical mechanism responsible for coronal mass ejections has been uncertain for many years, in large part because of the difficulty of knowing the three-dimensional magnetic field in the low corona. Two possible models have emerged. In the first, a twisted flux rope moves out of equilibrium or becomes unstable, and the subsequent reconnection then powers the ejection. In the second, a new flux rope forms as a result of the reconnection of the magnetic lines of an arcade (a group of arches of field lines) during the eruption itself. Observational support for both mechanisms has been claimed. Here we report modelling which demonstrates that twisted flux ropes lead to the ejection, in support of the first model. After seeing a coronal mass ejection, we use the observed photospheric magnetic field in that region from four days earlier as a boundary condition to determine the magnetic field configuration. The field evolves slowly before the eruption, such that it can be treated effectively as a static solution. We find that on the fourth day a flux rope forms and grows (increasing its free energy). This solution then becomes the initial condition as we let the model evolve dynamically under conditions driven by photospheric changes (such as flux cancellation). When the magnetic energy stored in the configuration is too high, no equilibrium is possible and the flux rope is ‘squeezed’ upwards. The subsequent reconnection drives a mass ejection.

Categories: Literature

Identification of an iridium-containing compound with a formal oxidation state of IX

Nature - Wed, 10/22/2014 - 00:00

Identification of an iridium-containing compound with a formal oxidation state of IX

Nature 514, 7523 (2014). doi:10.1038/nature13795

Authors: Guanjun Wang, Mingfei Zhou, James T. Goettel, Gary J. Schrobilgen, Jing Su, Jun Li, Tobias Schlöder & Sebastian Riedel

One of the most important classifications in chemistry and within the periodic table is the concept of formal oxidation states. The preparation and characterization of compounds containing elements with unusual oxidation states is of great interest to chemists. The highest experimentally known formal oxidation state of any chemical element is at present VIII, although higher oxidation states have been postulated. Compounds with oxidation state VIII include several xenon compounds (for example XeO4 and XeO3F2) and the well-characterized species RuO4 and OsO4 (refs 2, 3, 4). Iridium, which has nine valence electrons, is predicted to have the greatest chance of being oxidized beyond the VIII oxidation state. In recent matrix-isolation experiments, the IrO4 molecule was characterized as an isolated molecule in rare-gas matrices. The valence electron configuration of iridium in IrO4 is 5d1, with a formal oxidation state of VIII. Removal of the remaining d electron from IrO4 would lead to the iridium tetroxide cation ([IrO4]+), which was recently predicted to be stable and in which iridium is in a formal oxidation state of IX. There has been some speculation about the formation of [IrO4]+ species, but these experimental observations have not been structurally confirmed. Here we report the formation of [IrO4]+ and its identification by infrared photodissociation spectroscopy. Quantum-chemical calculations were carried out at the highest level of theory that is available today, and predict that the iridium tetroxide cation, with a Td-symmetrical structure and a d0 electron configuration, is the most stable of all possible [IrO4]+ isomers.

Categories: Literature

Methane dynamics regulated by microbial community response to permafrost thaw

Nature - Wed, 10/22/2014 - 00:00

Methane dynamics regulated by microbial community response to permafrost thaw

Nature 514, 7523 (2014). doi:10.1038/nature13798

Authors: Carmody K. McCalley, Ben J. Woodcroft, Suzanne B. Hodgkins, Richard A. Wehr, Eun-Hae Kim, Rhiannon Mondav, Patrick M. Crill, Jeffrey P. Chanton, Virginia I. Rich, Gene W. Tyson & Scott R. Saleska

Permafrost contains about 50% of the global soil carbon. It is thought that the thawing of permafrost can lead to a loss of soil carbon in the form of methane and carbon dioxide emissions. The magnitude of the resulting positive climate feedback of such greenhouse gas emissions is still unknown and may to a large extent depend on the poorly understood role of microbial community composition in regulating the metabolic processes that drive such ecosystem-scale greenhouse gas fluxes. Here we show that changes in vegetation and increasing methane emissions with permafrost thaw are associated with a switch from hydrogenotrophic to partly acetoclastic methanogenesis, resulting in a large shift in the δ13C signature (10–15‰) of emitted methane. We used a natural landscape gradient of permafrost thaw in northern Sweden as a model to investigate the role of microbial communities in regulating methane cycling, and to test whether a knowledge of community dynamics could improve predictions of carbon emissions under loss of permafrost. Abundance of the methanogen Candidatus ‘Methanoflorens stordalenmirensis’ is a key predictor of the shifts in methane isotopes, which in turn predicts the proportions of carbon emitted as methane and as carbon dioxide, an important factor for simulating the climate feedback associated with permafrost thaw in global models. By showing that the abundance of key microbial lineages can be used to predict atmospherically relevant patterns in methane isotopes and the proportion of carbon metabolized to methane during permafrost thaw, we establish a basis for scaling changing microbial communities to ecosystem isotope dynamics. Our findings indicate that microbial ecology may be important in ecosystem-scale responses to global change.

Categories: Literature

Dendritic cells control fibroblastic reticular network tension and lymph node expansion

Nature - Wed, 10/22/2014 - 00:00

Dendritic cells control fibroblastic reticular network tension and lymph node expansion

Nature 514, 7523 (2014). doi:10.1038/nature13814

Authors: Sophie E. Acton, Aaron J. Farrugia, Jillian L. Astarita, Diego Mourão-Sá, Robert P. Jenkins, Emma Nye, Steven Hooper, Janneke van Blijswijk, Neil C. Rogers, Kathryn J. Snelgrove, Ian Rosewell, Luis F. Moita, Gordon Stamp, Shannon J. Turley, Erik Sahai & Caetano Reis e Sousa

After immunogenic challenge, infiltrating and dividing lymphocytes markedly increase lymph node cellularity, leading to organ expansion. Here we report that the physical elasticity of lymph nodes is maintained in part by podoplanin (PDPN) signalling in stromal fibroblastic reticular cells (FRCs) and its modulation by CLEC-2 expressed on dendritic cells. We show in mouse cells that PDPN induces actomyosin contractility in FRCs via activation of RhoA/C and downstream Rho-associated protein kinase (ROCK). Engagement by CLEC-2 causes PDPN clustering and rapidly uncouples PDPN from RhoA/C activation, relaxing the actomyosin cytoskeleton and permitting FRC stretching. Notably, administration of CLEC-2 protein to immunized mice augments lymph node expansion. In contrast, lymph node expansion is significantly constrained in mice selectively lacking CLEC-2 expression in dendritic cells. Thus, the same dendritic cells that initiate immunity by presenting antigens to T lymphocytes also initiate remodelling of lymph nodes by delivering CLEC-2 to FRCs. CLEC-2 modulation of PDPN signalling permits FRC network stretching and allows for the rapid lymph node expansion—driven by lymphocyte influx and proliferation—that is the critical hallmark of adaptive immunity.

Categories: Literature

Arid and Mediterranean Ecosystems Seem More Resistant to Drought than Expected

Yale Environment 360 - Tue, 10/21/2014 - 11:35

Desert and Mediterranean ecosystems may be more resistant to climate change, particularly long-term Plants in a Mediterranean ecosystem in Chile. drought, than previously thought, a new study published in Nature Communications shows. Over the course of a nine-year experiment, researchers subjected plants in four different climatic zones to rainfall conditions predicted under future climate change scenarios. The ecosystems typically received 3.5 to 30.7 inches of precipitation annually, and researchers cut that total by roughly 30-percent to simulate drought conditions. Surprisingly, the researchers found no measurable changes in plant biomass, density, or species composition and richness in any of the four ecosystems over the course of nine generations of plants. The ecosystems already receive highly variable amounts of rainfall and the 30-percent drop likely falls within the plants’ natural "comfort zone," the researchers say, which could explain the unexpected resilience to drought.

Categories: Environmental News

Toxic influence

Nature - Tue, 10/21/2014 - 00:00

Toxic influence

Nature 514, 7523 (2014). doi:10.1038/514404a

Europe must act to stop livestock drugs from wiping out its vulture populations.

Categories: Literature

Stormy outlook for long-term ecology studies

Nature - Tue, 10/21/2014 - 00:00

Stormy outlook for long-term ecology studies

Nature 514, 7523 (2014). http://www.nature.com/doifinder/10.1038/514405a

Author: Tim Birkhead

The closure of a 40-year project to understand and protect seabirds shows the false priorities of funders, warns Tim Birkhead.

Categories: Literature

US midterm elections offer little hope for science

Nature - Tue, 10/21/2014 - 00:00

US midterm elections offer little hope for science

Nature 514, 7523 (2014). http://www.nature.com/doifinder/10.1038/514412a

Author: Lauren Morello

November vote is unlikely to break a political stalemate that has squeezed research funding.

Categories: Literature

Sun’s stroke keeps Kepler online

Nature - Tue, 10/21/2014 - 00:00

Sun’s stroke keeps Kepler online

Nature 514, 7523 (2014). http://www.nature.com/doifinder/10.1038/514414a

Author: Mark Zastrow

Space telescope beats mechanical failures to begin a second mission that will trace new celestial targets.

Categories: Literature

Human-subjects research: The ethics squad

Nature - Tue, 10/21/2014 - 00:00

Human-subjects research: The ethics squad

Nature 514, 7523 (2014). http://www.nature.com/doifinder/10.1038/514418a

Author: Elie Dolgin

Bioethicists are setting up consultancies for research — but some scientists question whether they are needed.

Categories: Literature

Anaerobic oxidation of long-chain n-alkanes by the hyperthermophilic sulfate-reducing archaeon, Archaeoglobus fulgidus

ISME - Tue, 10/21/2014 - 00:00

Anaerobic oxidation of long-chain n-alkanes by the hyperthermophilic sulfate-reducing archaeon, Archaeoglobus fulgidus

The ISME Journal 8, 2153 (November 2014). doi:10.1038/ismej.2014.58

Authors: Nadia Khelifi, Oulfat Amin Ali, Philippe Roche, Vincent Grossi, Céline Brochier-Armanet, Odile Valette, Bernard Ollivier, Alain Dolla & Agnès Hirschler-Réa

Categories: Literature

Composition and enzymatic function of particle-associated and free-living bacteria: a coastal/offshore comparison

ISME - Tue, 10/21/2014 - 00:00

Composition and enzymatic function of particle-associated and free-living bacteria: a coastal/offshore comparison

The ISME Journal 8, 2167 (November 2014). doi:10.1038/ismej.2014.67

Authors: Lindsay D'Ambrosio, Kai Ziervogel, Barbara MacGregor, Andreas Teske & Carol Arnosti

Categories: Literature

Facets of diazotrophy in the oxygen minimum zone waters off Peru

ISME - Tue, 10/21/2014 - 00:00

Facets of diazotrophy in the oxygen minimum zone waters off Peru

The ISME Journal 8, 2180 (November 2014). doi:10.1038/ismej.2014.71

Authors: Carolin R Loescher, Tobias Großkopf, Falguni D Desai, Diana Gill, Harald Schunck, Peter L Croot, Christian Schlosser, Sven C Neulinger, Nicole Pinnow, Gaute Lavik, Marcel M M Kuypers, Julie LaRoche & Ruth A Schmitz

Categories: Literature

Reprograming of gut microbiome energy metabolism by the FUT2 Crohn’s disease risk polymorphism

ISME - Tue, 10/21/2014 - 00:00

Reprograming of gut microbiome energy metabolism by the FUT2 Crohn’s disease risk polymorphism

The ISME Journal 8, 2193 (November 2014). doi:10.1038/ismej.2014.64

Authors: Maomeng Tong, Ian McHardy, Paul Ruegger, Maryam Goudarzi, Purna C Kashyap, Talin Haritunians, Xiaoxiao Li, Thomas G Graeber, Emma Schwager, Curtis Huttenhower, Albert J Fornace, Justin L Sonnenburg, Dermot PB McGovern, James Borneman & Jonathan Braun

Categories: Literature

Amphibian skin may select for rare environmental microbes

ISME - Tue, 10/21/2014 - 00:00

Amphibian skin may select for rare environmental microbes

The ISME Journal 8, 2207 (November 2014). doi:10.1038/ismej.2014.77

Authors: Jenifer B Walke, Matthew H Becker, Stephen C Loftus, Leanna L House, Guy Cormier, Roderick V Jensen & Lisa K Belden

Categories: Literature

Impact of diet and individual variation on intestinal microbiota composition and fermentation products in obese men

ISME - Tue, 10/21/2014 - 00:00

Impact of diet and individual variation on intestinal microbiota composition and fermentation products in obese men

The ISME Journal 8, 2218 (November 2014). doi:10.1038/ismej.2014.63

Authors: Anne Salonen, Leo Lahti, Jarkko Salojärvi, Grietje Holtrop, Katri Korpela, Sylvia H Duncan, Priya Date, Freda Farquharson, Alexandra M Johnstone, Gerald E Lobley, Petra Louis, Harry J Flint & Willem M de Vos

Categories: Literature

Arbuscular mycorrhizal fungal communities are phylogenetically clustered at small scales

ISME - Tue, 10/21/2014 - 00:00

Arbuscular mycorrhizal fungal communities are phylogenetically clustered at small scales

The ISME Journal 8, 2231 (November 2014). doi:10.1038/ismej.2014.72

Authors: Sebastian Horn, Tancredi Caruso, Erik Verbruggen, Matthias C Rillig & Stefan Hempel

Categories: Literature

Inference of interactions in cyanobacterial–heterotrophic co-cultures via transcriptome sequencing

ISME - Tue, 10/21/2014 - 00:00

Inference of interactions in cyanobacterial–heterotrophic co-cultures via transcriptome sequencing

The ISME Journal 8, 2243 (November 2014). doi:10.1038/ismej.2014.69

Authors: Alexander S Beliaev, Margie F Romine, Margrethe Serres, Hans C Bernstein, Bryan E Linggi, Lye M Markillie, Nancy G Isern, William B Chrisler, Leo A Kucek, Eric A Hill, Grigoriy E Pinchuk, Donald A Bryant, H Steven Wiley, Jim K Fredrickson & Allan Konopka

Categories: Literature

Cross-feeding and interkingdom communication in dual-species biofilms of Streptococcus mutans and Candida albicans

ISME - Tue, 10/21/2014 - 00:00

Cross-feeding and interkingdom communication in dual-species biofilms of Streptococcus mutans and Candida albicans

The ISME Journal 8, 2256 (November 2014). doi:10.1038/ismej.2014.73

Authors: Helena Sztajer, Szymon P Szafranski, Jürgen Tomasch, Michael Reck, Manfred Nimtz, Manfred Rohde & Irene Wagner-Döbler

Categories: Literature

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