Proceedings of the National Academy of Sciences of the United States of America

Journal: Proceedings of the National Academy of Sciences of the United States of America

Abbreviation

Proc Natl Acad Sci U S A

Publisher

National Academy of Sciences

ISSN

0027-8424
1091-6490

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Publications 1 - 10 of 1086

Efficient collective swimming by harnessing vortices through deep reinforcement learning
Verma, Siddhartha; Novati, Guido; Koumoutsakos, Petros (2018)
Proceedings of the National Academy of Sciences of the United States of America
Bistable metamaterial for switching and cascading elastic vibrations
Bilal, Osama R.; Foehr, André; Daraio, Chiara (2017)
Proceedings of the National Academy of Sciences of the United States of America
Molecular dynamics simulations of liquid silica crystallization
Niu, Haiyang; Piaggi, Pablo M.; Invernizzi, Michele; et al. (2018)
Proceedings of the National Academy of Sciences of the United States of America
Silica is one of the most abundant minerals on Earth and is widely used in many fields. Investigating the crystallization of liquid silica by atomic simulations is of great importance to understand the crystallization mechanism; however, the high crystallization barrier and the tendency of silica to form glasses make such simulations very challenging. Here we have studied liquid silica crystallization to β-cristobalite with metadynamics, using X-ray diffraction (XRD) peak intensities as collective variables. The frequent transitions between solid and liquid of the biased runs demonstrate the highly successful use of the XRD peak intensities as collective variables, which leads to the convergence of the free-energy surface. By calculating the difference in free energy, we have estimated the melting temperature of β-cristobalite, which is in good agreement with the literature. The nucleation mechanism during the crystallization of liquid silica can be described by classical nucleation theory.
Calculating the homology and intersection form of a 4-manifold from a trisection diagram
Feller, Peter; Klug, Michael; Schirmer, Trenton; et al. (2018)
Proceedings of the National Academy of Sciences of the United States of America
Functioning of a metabolic flux sensor in Escherichia coli
Kochanowski, Karl; Volkmer, Benjamin; Gerosa, Luca; et al. (2013)
Proceedings of the National Academy of Sciences of the United States of America
Arsenic pollution of groundwater in Vietnam exacerbated by deep aquifer exploitation for more than a century
Winkel, Lenny H.E.; Pham, Thi K.T.; Vi, Mai L.; et al. (2011)
Proceedings of the National Academy of Sciences of the United States of America
Interspecies interactions determine growth dynamics of biopolymer-degrading populations in microbial communities
D'Souza, Glen; Schwartzman, Julia; Keegstra, Johannes; et al. (2023)
Proceedings of the National Academy of Sciences of the United States of America
Microbial communities perform essential ecosystem functions such as the remineralization of organic carbon that exists as biopolymers. The first step in mineralization is performed by biopolymer degraders, which harbor enzymes that can break down polymers into constituent oligo- or monomeric forms. The released nutrients not only allow degraders to grow, but also promote growth of cells that either consume the degradation products, i.e., exploiters, or consume metabolites released by the degraders or exploiters, i.e., scavengers. It is currently not clear how such remineralizing communities assemble at the microscale—how interactions between the different guilds influence their growth and spatial distribution, and hence the development and dynamics of the community. Here, we address this knowledge gap by studying marine microbial communities that grow on the abundant marine biopolymer alginate. We used batch growth assays and microfluidics coupled to time-lapse microscopy to quantitatively investigate growth and spatial distribution of single cells. We found that the presence of exploiters or scavengers alters the spatial distribution of degrader cells. In general, exploiters and scavengers—which we collectively refer to as cross-feeder cells—slowed down the growth of degrader cells. In addition, coexistence with cross-feeders altered the production of the extracellular enzymes that break down polymers by degrader cells. Our findings reveal that ecological interactions by nondegrading community members have a profound impact on the functions of microbial communities that remineralize carbon biopolymers in nature.
Uncovering modern paint forgeries by radiocarbon dating
Hendriks, Laura; Hajdas, Irka; Ferreira, Ester S.B.; et al. (2019)
Proceedings of the National Academy of Sciences of the United States of America
Art forgeries have existed since antiquity, but with the recent rapidly expanding commercialization of art, the approach to art authentication has demanded increasingly sophisticated detection schemes. So far, the most conclusive criterion in the field of counterfeit detection is the scientific proof of material anachronisms. The establishment of the earliest possible date of realization of a painting, called the terminus post quem, is based on the comparison of materials present in an artwork with information on their earliest date of discovery or production. This approach provides relative age information only and thus may fail in proving a forgery. Radiocarbon (14C) dating is an attractive alternative, as it delivers absolute ages with a definite time frame for the materials used. The method, however, is invasive and in its early days required sampling tens of grams of material. With the advent of accelerator mass spectrometry (AMS) and further development of gas ion sources (GIS), a reduction of sample size down to microgram amounts of carbon became possible, opening the possibility to date individual paint layers in artworks. Here we discuss two microsamples taken from an artwork carrying the date of 1866: a canvas fiber and a paint chip (<200 µg), each delivering a different radiocarbon response. This discrepancy uncovers the specific strategy of the forger: Dating of the organic binder delivers clear evidence of a post-1950 creation on reused canvas. This microscale 14C analysis technique is a powerful method to reveal technically complex forgery cases with hard facts at a minimal sampling impact.
The Bering Strait was flooded 10,000 years before the Last Glacial Maximum
Farmer, Jesse R.; Pico, Tamara; Underwood, Ona M.; et al. (2023)
Proceedings of the National Academy of Sciences of the United States of America
The cyclic growth and decay of continental ice sheets can be reconstructed from the history of global sea level. Sea level is relatively well constrained for the Last Glacial Maximum (LGM, 26,500 to 19,000 y ago, 26.5 to 19 ka) and the ensuing deglaciation. However, sea-level estimates for the period of ice-sheet growth before the LGM vary by > 60 m, an uncertainty comparable to the sea-level equivalent of the contemporary Antarctic Ice Sheet. Here, we constrain sea level prior to the LGM by reconstructing the flooding history of the shallow Bering Strait since 46 ka. Using a geochemical proxy of Pacific nutrient input to the Arctic Ocean, we find that the Bering Strait was flooded from the beginning of our records at 46 ka until [Formula: see text] ka. To match this flooding history, our sea-level model requires an ice history in which over 50% of the LGM's global peak ice volume grew after 46 ka. This finding implies that global ice volume and climate were not linearly coupled during the last ice age, with implications for the controls on each. Moreover, our results shorten the time window between the opening of the Bering Land Bridge and the arrival of humans in the Americas.
A bimodular nuclear localization signal assembled via an extended double-stranded RNA-binding domain acts as an RNA-sensing signal for transportin 1
Barraud, Pierre; Banerjee, Silpi; Mohamed, Weaam I.; et al. (2014)
Proceedings of the National Academy of Sciences of the United States of America

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