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Updated: 8 years 17 weeks ago

[This Week in Science] Extreme events under climate change

Thu, 09/24/2015 - 23:00
Author: Julia Fahrenkamp-Uppenbrink
Categories: Journal Articles

[This Week in Science] Flushing the deep ocean

Thu, 09/24/2015 - 23:00
Author: H. Jesse Smith
Categories: Journal Articles

[Editors' Choice] Successional specialism in forests

Thu, 09/24/2015 - 23:00
Author: Andrew M. Sugden
Categories: Journal Articles

[Editors' Choice] A wild hair day for mice

Thu, 09/24/2015 - 23:00
Author: Beverly A. Purnell
Categories: Journal Articles

[Editors' Choice] Traffic noise effects on birds

Thu, 09/24/2015 - 23:00
Author: Julia Fahrenkamp-Uppenbrink
Categories: Journal Articles

[Editors' Choice] Uncovering site selection bias

Thu, 09/24/2015 - 23:00
Author: Brad Wible
Categories: Journal Articles

[Editors' Choice] Giant virus varieties keep growing

Thu, 09/24/2015 - 23:00
Author: Barbara R. Jasny
Categories: Journal Articles

[Editors' Choice] Broadening the source for hot spots

Thu, 09/24/2015 - 23:00
Author: Brent Grocholski
Categories: Journal Articles

[Editors' Choice] Suspicious behavior by a harmless virus

Thu, 09/24/2015 - 23:00
Author: Paula A. Kiberstis
Categories: Journal Articles

[Research Article] The DNA damage response induces inflammation and senescence by inhibiting autophagy of GATA4

Thu, 09/24/2015 - 23:00
Cellular senescence is a terminal stress-activated program controlled by the p53 and p16INK4a tumor suppressor proteins. A striking feature of senescence is the senescence-associated secretory phenotype (SASP), a pro-inflammatory response linked to tumor promotion and aging. We have identified the transcription factor GATA4 as a senescence and SASP regulator. GATA4 is stabilized in cells undergoing senescence and is required for the SASP. Normally, GATA4 is degraded by p62-mediated selective autophagy, but this regulation is suppressed during senescence, thereby stabilizing GATA4. GATA4 in turn activates the transcription factor NF-κB to initiate the SASP and facilitate senescence. GATA4 activation depends on the DNA damage response regulators ATM and ATR, but not on p53 or p16INK4a. GATA4 accumulates in multiple tissues, including the aging brain, and could contribute to aging and its associated inflammation. Authors: Chanhee Kang, Qikai Xu, Timothy D. Martin, Mamie Z. Li, Marco Demaria, Liviu Aron, Tao Lu, Bruce A. Yankner, Judith Campisi, Stephen J. Elledge
Categories: Journal Articles

[Research Article] Structural origin of slow diffusion in protein folding

Thu, 09/24/2015 - 23:00
Experimental, theoretical, and computational studies of small proteins suggest that interresidue contacts not present in the folded structure play little or no role in the self-assembly mechanism. Non-native contacts can, however, influence folding kinetics by introducing additional local minima that slow diffusion over the global free-energy barrier between folded and unfolded states. Here, we combine single-molecule fluorescence with all-atom molecular dynamics simulations to discover the structural origin for the slow diffusion that markedly decreases the folding rate for a designed α-helical protein. Our experimental determination of transition path times and our analysis of the simulations point to non-native salt bridges between helices as the source, which provides a quantitative glimpse of how specific intramolecular interactions influence protein folding rates by altering dynamics and not activation free energies. Authors: Hoi Sung Chung, Stefano Piana-Agostinetti, David E. Shaw, William A. Eaton
Categories: Journal Articles

[Report] Observation of chiral edge states with neutral fermions in synthetic Hall ribbons

Thu, 09/24/2015 - 23:00
Chiral edge states are a hallmark of quantum Hall physics. In electronic systems, they appear as a macroscopic consequence of the cyclotron orbits induced by a magnetic field, which are naturally truncated at the physical boundary of the sample. Here we report on the experimental realization of chiral edge states in a ribbon geometry with an ultracold gas of neutral fermions subjected to an artificial gauge field. By imaging individual sites along a synthetic dimension, encoded in the nuclear spin of the atoms, we detect the existence of the edge states and observe the edge-cyclotron orbits induced during quench dynamics. The realization of fermionic chiral edge states opens the door for edge state interferometry and the study of non-Abelian anyons in atomic systems. Authors: M. Mancini, G. Pagano, G. Cappellini, L. Livi, M. Rider, J. Catani, C. Sias, P. Zoller, M. Inguscio, M. Dalmonte, L. Fallani
Categories: Journal Articles

[Report] Visualizing edge states with an atomic Bose gas in the quantum Hall regime

Thu, 09/24/2015 - 23:00
Bringing ultracold atomic gases into the quantum Hall regime is challenging. We engineered an effective magnetic field in a two-dimensional lattice with an elongated-strip geometry, consisting of the sites of an optical lattice in the long direction and of three internal atomic spin states in the short direction. We imaged the localized states of atomic Bose-Einstein condensates in this strip; via excitation dynamics, we further observed both the skipping orbits of excited atoms traveling down the system’s edges, analogous to edge magnetoplasmons in two-dimensional electron systems, and a dynamical Hall effect for bulk excitations. Our technique involves minimal heating, which will be important for spectroscopic measurements of the Hofstadter butterfly and realizations of Laughlin’s charge pump. Authors: B. K. Stuhl, H.-I. Lu, L. M. Aycock, D. Genkina, I. B. Spielman
Categories: Journal Articles

[Report] Atomically thin two-dimensional organic-inorganic hybrid perovskites

Thu, 09/24/2015 - 23:00
Organic-inorganic hybrid perovskites, which have proved to be promising semiconductor materials for photovoltaic applications, have been made into atomically thin two-dimensional (2D) sheets. We report the solution-phase growth of single- and few-unit-cell-thick single-crystalline 2D hybrid perovskites of (C4H9NH3)2PbBr4 with well-defined square shape and large size. In contrast to other 2D materials, the hybrid perovskite sheets exhibit an unusual structural relaxation, and this structural change leads to a band gap shift as compared to the bulk crystal. The high-quality 2D crystals exhibit efficient photoluminescence, and color tuning could be achieved by changing sheet thickness as well as composition via the synthesis of related materials. Authors: Letian Dou, Andrew B. Wong, Yi Yu, Minliang Lai, Nikolay Kornienko, Samuel W. Eaton, Anthony Fu, Connor G. Bischak, Jie Ma, Tina Ding, Naomi S. Ginsberg, Lin-Wang Wang, A. Paul Alivisatos, Peidong Yang
Categories: Journal Articles

[Report] Gravitational waves from binary supermassive black holes missing in pulsar observations

Thu, 09/24/2015 - 23:00
Gravitational waves are expected to be radiated by supermassive black hole binaries formed during galaxy mergers. A stochastic superposition of gravitational waves from all such binary systems would modulate the arrival times of pulses from radio pulsars. Using observations of millisecond pulsars obtained with the Parkes radio telescope, we constrained the characteristic amplitude of this background, Ac,yr, to be <1.0 × 10−15 with 95% confidence. This limit excludes predicted ranges for Ac,yr from current models with 91 to 99.7% probability. We conclude that binary evolution is either stalled or dramatically accelerated by galactic-center environments and that higher-cadence and shorter-wavelength observations would be more sensitive to gravitational waves. Authors: R. M. Shannon, V. Ravi, L. T. Lentati, P. D. Lasky, G. Hobbs, M. Kerr, R. N. Manchester, W. A. Coles, Y. Levin, M. Bailes, N. D. R. Bhat, S. Burke-Spolaor, S. Dai, M. J. Keith, S. Osłowski, D. J. Reardon, W. van Straten, L. Toomey, J.-B. Wang, L. Wen, J. S. B. Wyithe, X.-J. Zhu
Categories: Journal Articles

[Report] Conversion of alcohols to enantiopure amines through dual-enzyme hydrogen-borrowing cascades

Thu, 09/24/2015 - 23:00
α-Chiral amines are key intermediates for the synthesis of a plethora of chemical compounds at industrial scale. We present a biocatalytic hydrogen-borrowing amination of primary and secondary alcohols that allows for the efficient and environmentally benign production of enantiopure amines. The method relies on a combination of two enzymes: an alcohol dehydrogenase (from Aromatoleum sp., Lactobacillus sp., or Bacillus sp.) operating in tandem with an amine dehydrogenase (engineered from Bacillus sp.) to aminate a structurally diverse range of aromatic and aliphatic alcohols, yielding up to 96% conversion and 99% enantiomeric excess. Primary alcohols were aminated with high conversion (up to 99%). This redox self-sufficient cascade possesses high atom efficiency, sourcing nitrogen from ammonium and generating water as the sole by-product. Authors: Francesco G. Mutti, Tanja Knaus, Nigel S. Scrutton, Michael Breuer, Nicholas J. Turner
Categories: Journal Articles

[Report] Alkaline quinone flow battery

Thu, 09/24/2015 - 23:00
Storage of photovoltaic and wind electricity in batteries could solve the mismatch problem between the intermittent supply of these renewable resources and variable demand. Flow batteries permit more economical long-duration discharge than solid-electrode batteries by using liquid electrolytes stored outside of the battery. We report an alkaline flow battery based on redox-active organic molecules that are composed entirely of Earth-abundant elements and are nontoxic, nonflammable, and safe for use in residential and commercial environments. The battery operates efficiently with high power density near room temperature. These results demonstrate the stability and performance of redox-active organic molecules in alkaline flow batteries, potentially enabling cost-effective stationary storage of renewable energy. Authors: Kaixiang Lin, Qing Chen, Michael R. Gerhardt, Liuchuan Tong, Sang Bok Kim, Louise Eisenach, Alvaro W. Valle, David Hardee, Roy G. Gordon, Michael J. Aziz, Michael P. Marshak
Categories: Journal Articles

[Report] O–H hydrogen bonding promotes H-atom transfer from α C–H bonds for C-alkylation of alcohols

Thu, 09/24/2015 - 23:00
The efficiency and selectivity of hydrogen atom transfer from organic molecules are often difficult to control in the presence of multiple potential hydrogen atom donors and acceptors. Here, we describe the mechanistic evaluation of a mode of catalytic activation that accomplishes the highly selective photoredox α-alkylation/lactonization of alcohols with methyl acrylate via a hydrogen atom transfer mechanism. Our studies indicate a particular role of tetra-n-butylammonium phosphate in enhancing the selectivity for α C–H bonds in alcohols in the presence of allylic, benzylic, α-C=O, and α-ether C–H bonds. Authors: Jenna L. Jeffrey, Jack A. Terrett, David W. C. MacMillan
Categories: Journal Articles

[Report] Synchronous centennial abrupt events in the ocean and atmosphere during the last deglaciation

Thu, 09/24/2015 - 23:00
Antarctic ice-core data reveal that the atmosphere experienced abrupt centennial increases in CO2 concentration during the last deglaciation (~18 thousand to 11 thousand years ago). Establishing the role of ocean circulation in these changes requires high-resolution, accurately dated marine records. Here, we report radiocarbon data from uranium-thorium–dated deep-sea corals in the Equatorial Atlantic and Drake Passage over the past 25,000 years. Two major deglacial radiocarbon shifts occurred in phase with centennial atmospheric CO2 rises at 14.8 thousand and 11.7 thousand years ago. We interpret these radiocarbon-enriched signals to represent two short-lived (less than 500 years) “overshoot” events, with Atlantic meridional overturning stronger than that of the modern era. These results provide compelling evidence for a close coupling of ocean circulation and centennial climate events during the last deglaciation. Authors: Tianyu Chen, Laura F. Robinson, Andrea Burke, John Southon, Peter Spooner, Paul J. Morris, Hong Chin Ng
Categories: Journal Articles

[Report] Functional mismatch in a bumble bee pollination mutualism under climate change

Thu, 09/24/2015 - 23:00
Ecological partnerships, or mutualisms, are globally widespread, sustaining agriculture and biodiversity. Mutualisms evolve through the matching of functional traits between partners, such as tongue length of pollinators and flower tube depth of plants. Long-tongued pollinators specialize on flowers with deep corolla tubes, whereas shorter-tongued pollinators generalize across tube lengths. Losses of functional guilds because of shifts in global climate may disrupt mutualisms and threaten partner species. We found that in two alpine bumble bee species, decreases in tongue length have evolved over 40 years. Co-occurring flowers have not become shallower, nor are small-flowered plants more prolific. We argue that declining floral resources because of warmer summers have favored generalist foraging, leading to a mismatch between shorter-tongued bees and the longer-tubed plants they once pollinated. Authors: Nicole E. Miller-Struttmann, Jennifer C. Geib, James D. Franklin, Peter G. Kevan, Ricardo M. Holdo, Diane Ebert-May, Austin M. Lynn, Jessica A. Kettenbach, Elizabeth Hedrick, Candace Galen
Categories: Journal Articles