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A tailless aerial robotic flapper reveals that flies use torque coupling in rapid banked turns

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Insects are among the most agile natural flyers. Hypotheses on their flight control cannot always be validated by experiments with animals or tethered robots. To this end, we developed a programmable and agile autonomous free-flying robot controlled through bio-inspired motion changes of its flapping wings. Despite being 55 times the size of a fruit fly, the robot can accurately mimic the rapid escape maneuvers of flies, including a correcting yaw rotation toward the escape heading. Because the robot’s yaw control was turned off, we showed that these yaw rotations result from passive, translation-induced aerodynamic coupling between the yaw torque and the roll and pitch torques produced throughout the maneuver. The robot enables new methods for studying animal flight, and its flight characteristics allow for real-world flight missions.

Organic and solution-processed tandem solar cells with 17.3% efficiency

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Although organic photovoltaic (OPV) cells have many advantages, their performance still lags far behind that of other photovoltaic platforms. A fundamental reason for their low performance is the low charge mobility of organic materials, leading to a limit on the active-layer thickness and efficient light absorption. In this work, guided by a semi-empirical model analysis and using the tandem cell strategy to overcome such issues, and taking advantage of the high diversity and easily tunable band structure of organic materials, a record and certified 17.29% power conversion efficiency for a two-terminal monolithic solution-processed tandem OPV is achieved.

A designed heme-[4Fe-4S] metalloenzyme catalyzes sulfite reduction like the native enzyme

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Multielectron redox reactions often require multicofactor metalloenzymes to facilitate coupled electron and proton movement, but it is challenging to design artificial enzymes to catalyze these important reactions, owing to their structural and functional complexity. We report a designed heteronuclear heme-[4Fe-4S] cofactor in cytochrome c peroxidase as a structural and functional model of the enzyme sulfite reductase. The initial model exhibits spectroscopic and ligand-binding properties of the native enzyme, and sulfite reduction activity was improved—through rational tuning of the secondary sphere interactions around the [4Fe-4S] and the substrate-binding sites—to be close to that of the native enzyme. By offering insight into the requirements for a demanding six-electron, seven-proton reaction that has so far eluded synthetic catalysts, this study provides strategies for designing highly functional multicofactor artificial enzymes.

Quantum entanglement of the spin and orbital angular momentum of photons using metamaterials

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Metamaterials constructed from deep subwavelength building blocks have been used to demonstrate phenomena ranging from negative refractive index and -near-zero to cloaking, emulations of general relativity, and superresolution imaging. More recently, metamaterials have been suggested as a new platform for quantum optics. We present the use of a dielectric metasurface to generate entanglement between the spin and orbital angular momentum of photons. We demonstrate the generation of the four Bell states on a single photon by using the geometric phase that arises from the photonic spin-orbit interaction and subsequently show nonlocal correlations between two photons that interacted with the metasurface. Our results show that metamaterials are suitable for the generation and manipulation of entangled photon states, introducing the area of quantum optics metamaterials.

Quantum metasurface for multiphoton interference and state reconstruction

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Metasurfaces based on resonant nanophotonic structures have enabled innovative types of flat-optics devices that often outperform the capabilities of bulk components, yet these advances remain largely unexplored for quantum applications. We show that nonclassical multiphoton interferences can be achieved at the subwavelength scale in all-dielectric metasurfaces. We simultaneously image multiple projections of quantum states with a single metasurface, enabling a robust reconstruction of amplitude, phase, coherence, and entanglement of multiphoton polarization-encoded states. One- and two-photon states are reconstructed through nonlocal photon correlation measurements with polarization-insensitive click detectors positioned after the metasurface, and the scalability to higher photon numbers is established theoretically. Our work illustrates the feasibility of ultrathin quantum metadevices for the manipulation and measurement of multiphoton quantum states, with applications in free-space quantum imaging and communications.

Classifying drivers of global forest loss

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Global maps of forest loss depict the scale and magnitude of forest disturbance, yet companies, governments, and nongovernmental organizations need to distinguish permanent conversion (i.e., deforestation) from temporary loss from forestry or wildfire. Using satellite imagery, we developed a forest loss classification model to determine a spatial attribution of forest disturbance to the dominant drivers of land cover and land use change over the period 2001 to 2015. Our results indicate that 27% of global forest loss can be attributed to deforestation through permanent land use change for commodity production. The remaining areas maintained the same land use over 15 years; in those areas, loss was attributed to forestry (26%), shifting agriculture (24%), and wildfire (23%). Despite corporate commitments, the rate of commodity-driven deforestation has not declined. To end deforestation, companies must eliminate 5 million hectares of conversion from supply chains each year.

Glutamate triggers long-distance, calcium-based plant defense signaling

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Animals require rapid, long-range molecular signaling networks to integrate sensing and response throughout their bodies. The amino acid glutamate acts as an excitatory neurotransmitter in the vertebrate central nervous system, facilitating long-range information exchange via activation of glutamate receptor channels. Similarly, plants sense local signals, such as herbivore attack, and transmit this information throughout the plant body to rapidly activate defense responses in undamaged parts. Here we show that glutamate is a wound signal in plants. Ion channels of the GLUTAMATE RECEPTOR–LIKE family act as sensors that convert this signal into an increase in intracellular calcium ion concentration that propagates to distant organs, where defense responses are then induced.

A continental system for forecasting bird migration

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Billions of animals cross the globe each year during seasonal migrations, but efforts to monitor them are hampered by the unpredictability of their movements. We developed a bird migration forecast system at a continental scale by leveraging 23 years of spring observations to identify associations between atmospheric conditions and bird migration intensity. Our models explained up to 81% of variation in migration intensity across the United States at altitudes of 0 to 3000 meters, and performance remained high in forecasting events 1 to 7 days in advance (62 to 76% of variation was explained). Avian migratory movements across the United States likely exceed 500 million individuals per night during peak passage. Bird migration forecasts will reduce collisions with buildings, airplanes, and wind turbines; inform a variety of monitoring efforts; and engage the public.

An ER surface retrieval pathway safeguards the import of mitochondrial membrane proteins in yeast

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

The majority of organellar proteins are translated on cytosolic ribosomes and must be sorted correctly to function. Targeting routes have been identified for organelles such as peroxisomes and the endoplasmic reticulum (ER). However, little is known about the initial steps of targeting of mitochondrial proteins. In this study, we used a genome-wide screen in yeast and identified factors critical for the intracellular sorting of the mitochondrial inner membrane protein Oxa1. The screen uncovered an unexpected path, termed ER-SURF, for targeting of mitochondrial membrane proteins. This pathway retrieves mitochondrial proteins from the ER surface and reroutes them to mitochondria with the aid of the ER-localized chaperone Djp1. Hence, cells use the expanse of the ER surfaces as a fail-safe to maximize productive mitochondrial protein targeting.

Semisynthetic sensor proteins enable metabolic assays at the point of care

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Monitoring metabolites at the point of care could improve the diagnosis and management of numerous diseases. Yet for most metabolites, such assays are not available. We introduce semisynthetic, light-emitting sensor proteins for use in paper-based metabolic assays. The metabolite is oxidized by nicotinamide adenine dinucleotide phosphate, and the sensor changes color in the presence of the reduced cofactor, enabling metabolite quantification with the use of a digital camera. The approach makes any metabolite that can be oxidized by the cofactor a candidate for quantitative point-of-care assays, as shown for phenylalanine, glucose, and glutamate. Phenylalanine blood levels of phenylketonuria patients were analyzed at the point of care within minutes with only 0.5 microliters of blood. Results were within 15% of those obtained with standard testing methods.

Ribonucleotide incorporation enables repair of chromosome breaks by nonhomologous end joining

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

The nonhomologous end–joining (NHEJ) pathway preserves genome stability by ligating the ends of broken chromosomes together. It employs end-processing enzymes, including polymerases, to prepare ends for ligation. We show that two such polymerases incorporate primarily ribonucleotides during NHEJ—an exception to the central dogma of molecular biology—both during repair of chromosome breaks made by Cas9 and during V(D)J recombination. Moreover, additions of ribonucleotides but not deoxynucleotides effectively promote ligation. Repair kinetics suggest that ribonucleotide-dependent first-strand ligation is followed by complementary strand repair with deoxynucleotides, then by replacement of ribonucleotides embedded in the first strand with deoxynucleotides. Our results indicate that as much as 65% of cellular NHEJ products have transiently embedded ribonucleotides, which promote flexibility in repair at the cost of more fragile intermediates.

New Products

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Learning to lead

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Differential IL-2 expression defines developmental fates of follicular versus nonfollicular helper T cells

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

In response to infection, naïve CD4+ T cells differentiate into two subpopulations: T follicular helper (TFH) cells, which support B cell antibody production, and non-TFH cells, which enhance innate immune cell functions. Interleukin-2 (IL-2), the major cytokine produced by naïve T cells, plays an important role in the developmental divergence of these populations. However, the relationship between IL-2 production and fate determination remains unclear. Using reporter mice, we found that differential production of IL-2 by naïve CD4+ T cells defined precursors fated for different immune functions. IL-2 producers, which were fated to become TFH cells, delivered IL-2 to nonproducers destined to become non-TFH cells. Because IL-2 production was limited to cells receiving the strongest T cell receptor (TCR) signals, a direct link between TCR-signal strength, IL-2 production, and T cell fate determination has been established.

Recurrent cortical circuits implement concentration-invariant odor coding

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Animals rely on olfaction to find food, attract mates, and avoid predators. To support these behaviors, they must be able to identify odors across different odorant concentrations. The neural circuit operations that implement this concentration invariance remain unclear. We found that despite concentration-dependence in the olfactory bulb (OB), representations of odor identity were preserved downstream, in the piriform cortex (PCx). The OB cells responding earliest after inhalation drove robust responses in sparse subsets of PCx neurons. Recurrent collateral connections broadcast their activation across the PCx, recruiting global feedback inhibition that rapidly truncated and suppressed cortical activity for the remainder of the sniff, discounting the impact of slower, concentration-dependent OB inputs. Eliminating recurrent collateral output amplified PCx odor responses rendered the cortex steeply concentration-dependent and abolished concentration-invariant identity decoding.

Asymmetric phosphoric acid-catalyzed four-component Ugi reaction

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

The Ugi reaction constructs α-acylaminoamide compounds by combining an aldehyde or ketone, an amine, a carboxylic acid, and an isocyanide in a single flask. Its appealing features include inherent atom and step economy together with the potential to generate products of broad structural diversity. However, control of the stereochemistry in this reaction has proven to be a formidable challenge. We describe an efficient enantioselective four-component Ugi reaction catalyzed by a chiral phosphoric acid derivative that delivers more than 80 α-acylaminoamides in good to excellent enantiomeric excess. Experimental and computational studies establish the reaction mechanism and origins of stereoselectivity.

Response to Comment on "Unexpected reversal of C3 versus C4 grass response to elevated CO2 during a 20-year field experiment"

ScienceNOW Daily News Feed - Jue, 09/13/2018 - 11:37

Nie and colleagues suggest a key role for interannual climate variation as an explanation for the temporal dynamics of an unexpected 20-year reversal of biomass responses of C3-C4 grasses to elevated CO2. However, we had already identified some climate-dependent differences in C3 and C4 responses to eCO2 and shown that these could not fully explain the temporal dynamics we observed.

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