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https://www.readbyqxmd.com/read/29326118/observation-of-bulk-fermi-arc-and-polarization-half-charge-from-paired-exceptional-points
#1
Hengyun Zhou, Chao Peng, Yoseob Yoon, Chia Wei Hsu, Keith A Nelson, Liang Fu, John D Joannopoulos, Marin Soljačić, Bo Zhen
The ideas of topology have found tremendous success in closed physical systems, but even richer properties exist in the more general open or dissipative framework. We theoretically propose and experimentally demonstrate a bulk Fermi arc that develops from non-Hermitian radiative losses in an open system of photonic crystal slabs. Moreover, we discover half-integer topological charges in the polarization of far-field radiation around the bulk Fermi arc. Both phenomena are shown to be direct consequences of the non-Hermitian topological properties of exceptional points, where resonances coincide in their frequencies and linewidths...
January 11, 2018: Science
https://www.readbyqxmd.com/read/29326117/ideal-weyl-points-and-helicoid-surface-states-in-artificial-photonic-crystal-structures
#2
Biao Yang, Qinghua Guo, Ben Tremain, Rongjuan Liu, Lauren E Barr, Qinghui Yan, Wenlong Gao, Hongchao Liu, Yuanjiang Xiang, Jing Chen, Chen Fang, Alastair Hibbins, Ling Lu, Shuang Zhang
Weyl points are the crossings of linearly dispersing energy bands of three-dimensional crystals, providing the opportunity to explore a variety of intriguing phenomena such as topologically protected surface states and chiral anomalies. However, the lack of an ideal Weyl system in which the Weyl points all exist at the same energy and are separated from any other bands, poses a serious limitation to the further development of Weyl physics and potential applications. By experimentally characterizing a microwave photonic crystal of saddle-shaped metallic coils, we observe ideal Weyl points that are related to each other through symmetry operations...
January 11, 2018: Science
https://www.readbyqxmd.com/read/29301962/structure-of-the-yeast-oligosaccharyltransferase-complex-gives-insight-into-eukaryotic-n-glycosylation
#3
Rebekka Wild, Julia Kowal, Jillianne Eyring, Elsy M Ngwa, Markus Aebi, Kaspar P Locher
Oligosaccharyltransferase (OST) is an essential membrane protein complex in the Endoplasmic Reticulum, where it transfers an oligosaccharide from a dolichol-pyrophosphate-activated donor to glycosylation sites of secretory proteins. We here describe the atomic structure of yeast OST determined by cryo-EM, revealing a conserved subunit arrangement. The active site of the catalytic STT3 subunit points away from the center of the complex, allowing unhindered access to substrates. The dolichol-pyrophosphate moiety binds to a lipid-exposed groove of STT3, while two non-catalytic subunits and an ordered N-glycan form a membrane-proximal pocket for the oligosaccharide...
January 4, 2018: Science
https://www.readbyqxmd.com/read/29301961/structure-of-a-human-catalytic-step-i-spliceosome
#4
Xiechao Zhan, Chuangye Yan, Xiaofeng Zhang, Jianlin Lei, Yigong Shi
Splicing by the spliceosome involves branching and exon ligation. The branching reaction leads to the formation of the catalytic step I spliceosome (C complex). Here we report the cryo-EM structure of the human C complex at an average resolution of 4.1 Å. Compared to the structure of the S. cerevisiae C complex, the human complex contains 11 additional proteins. The step I splicing factors CCDC49 and CCDC94 (Cwc25 and Yju2 in S. cerevisiae, respectively) closely interact with the DEAH-family ATPase/helicase Prp16 and bridge the gap between Prp16 and the active site RNA elements...
January 4, 2018: Science
https://www.readbyqxmd.com/read/29301960/genomic-correlates-of-response-to-immune-checkpoint-therapies-in-clear-cell-renal-cell-carcinoma
#5
Diana Miao, Claire A Margolis, Wenhua Gao, Martin H Voss, Wei Li, Dylan J Martini, Craig Norton, Dominick Bossé, Stephanie M Wankowicz, Dana Cullen, Christine Horak, Megan Wind-Rotolo, Adam Tracy, Marios Giannakis, Frank Stephen Hodi, Charles G Drake, Mark W Ball, Mohamad E Allaf, Alexandra Snyder, Matthew D Hellmann, Thai Ho, Robert J Motzer, Sabina Signoretti, William G Kaelin, Toni K Choueiri, Eliezer M Van Allen
Immune checkpoint inhibitors targeting the programmed cell death-1 receptor (PD-1) improve survival in a subset of patients with clear cell renal cell carcinoma (ccRCC). To identify genomic alterations in ccRCC that correlate with response to anti-PD-1 monotherapy, we performed whole exome sequencing of metastatic ccRCC from 35 patients. We found that clinical benefit was associated with loss-of-function mutations in the PBRM1 gene (p=0.012), which encodes a subunit of a SWI/SNF chromatin remodeling complex (the PBAF subtype)...
January 4, 2018: Science
https://www.readbyqxmd.com/read/29301959/multiplexed-gene-synthesis-in-emulsions-for-exploring-protein-functional-landscapes
#6
Calin Plesa, Angus M Sidore, Nathan B Lubock, Di Zhang, Sriram Kosuri
Improving our ability to construct and functionally characterize DNA sequences would broadly accelerate progress in biology. Here, we introduce DropSynth, a scalable, low-cost method to build thousands of defined gene-length constructs in a pooled (multiplexed) manner. DropSynth uses a library of barcoded beads that pull down the oligonucleotides necessary for a gene's assembly, which are then processed and assembled in water-in-oil emulsions. We use DropSynth to successfully build >7000 synthetic genes that encode phylogenetically-diverse homologs of two essential genes in E...
January 4, 2018: Science
https://www.readbyqxmd.com/read/29301958/a-major-chromatin-regulator-determines-resistance-of-tumor-cells-to-t-cell-mediated-killing
#7
Deng Pan, Aya Kobayashi, Peng Jiang, Lucas Ferrari de Andrade, Rong En Tay, Adrienne Luoma, Daphne Tsoucas, Xintao Qiu, Klothilda Lim, Prakash Rao, Henry W Long, Guo-Cheng Yuan, John Doench, Myles Brown, Shirley Liu, Kai W Wucherpfennig
Many human cancers are resistant to immunotherapy for reasons that are poorly understood. We used a genome-scale CRISPR/Cas9 screen to identify mechanisms of tumor cell resistance to killing by cytotoxic T cells, the central effectors of anti-tumor immunity. Inactivation of >100 genes sensitized mouse B16F10 melanoma cells to killing by T cells, including Pbrm1, Arid2 and Brd7, which encode components of the PBAF form of the SWI/SNF chromatin remodeling complex. Loss of PBAF function increased tumor cell sensitivity to interferon-γ, resulting in enhanced secretion of chemokines that recruit effector T cells...
January 4, 2018: Science
https://www.readbyqxmd.com/read/29301957/defective-cholesterol-clearance-limits-remyelination-in-the-aged-central-nervous-system
#8
Ludovico Cantuti-Castelvetri, Dirk Fitzner, Mar Bosch-Queralt, Marie-Theres Weil, Minhui Su, Paromita Sen, Torben Ruhwedel, Miso Mitkovski, George Trendelenburg, Dieter Lütjohann, Wiebke Möbius, Mikael Simons
Age-associated decline in regeneration capacity limits the restoration of nervous system functionality after injury. In a model for demyelination, we found that old mice fail to resolve the inflammatory response initiated after myelin damage. Aged phagocytes accumulated excessive amounts of myelin debris, which triggered cholesterol crystal formation, phagolysosomal membrane rupture, and stimulated inflammasomes. Myelin debris clearance required cholesterol transporters including apolipoprotein E. Remarkably, stimulation of reverse cholesterol transport was sufficient to restore the capacity of old mice to remyelinate lesioned tissue...
January 4, 2018: Science
https://www.readbyqxmd.com/read/29269423/coherent-single-atom-superradiance
#9
Junki Kim, Daeho Yang, Seung-Hoon Oh, Kyungwon An
Superradiance is a quantum phenomenon emerging in macroscopic systems whereby correlated single atoms cooperatively emit photons. Demonstration of controlled collective atom-field interactions has resulted from the ability to directly imprint correlations with an atomic ensemble. Here, we report cavity-mediated coherent single-atom superradiance: single atoms with predefined correlation traverse a high-Q cavity one by one, emitting photons cooperatively with the N atoms already gone through the cavity. Enhanced collective photoemission of N-squared dependence was observed even when the intracavity atom number was less than unity...
December 21, 2017: Science
https://www.readbyqxmd.com/read/29269422/dicer-uses-distinct-modules-for-recognizing-dsrna-termini
#10
Niladri K Sinha, Janet Iwasa, Peter S Shen, Brenda L Bass
Invertebrates rely on Dicer to cleave viral double-stranded RNA (dsRNA), and Drosophila Dicer-2 distinguishes dsRNA substrates by their termini. Blunt termini promote processive cleavage, while 3' overhanging termini are cleaved distributively. To understand this discrimination, we used cryo-electron microscopy to solve structures of Drosophila Dicer-2 alone and in complex with blunt dsRNA. While the Platform-PAZ domains have been considered the only Dicer domains that bind dsRNA termini, unexpectedly, we found that the helicase domain is required for binding blunt, but not 3' overhanging, termini...
December 21, 2017: Science
https://www.readbyqxmd.com/read/29269421/high-temperature-pairing-in-a-strongly-interacting-two-dimensional-fermi-gas
#11
Puneet A Murthy, Mathias Neidig, Ralf Klemt, Luca Bayha, Igor Boettcher, Tilman Enss, Marvin Holten, Gerhard Zürn, Philipp M Preiss, Selim Jochim
The nature of the normal phase of strongly correlated fermionic systems is an outstanding question in quantum many-body physics. We use spatially resolved radio-frequency spectroscopy to measure pairing energy of fermions across a wide range of temperatures and interaction strengths in a two-dimensional gas of ultracold fermionic atoms. We observe many-body pairing at temperatures far above the critical temperature for superfluidity. In the strongly interacting regime, the pairing energy in the normal phase significantly exceeds the intrinsic two-body binding energy of the system and shows a clear dependence on local density...
December 21, 2017: Science
https://www.readbyqxmd.com/read/29269420/structural-mechanisms-of-centromeric-nucleosome-recognition-by-the-kinetochore-protein-cenp-n
#12
Sagar Chittori, Jingjun Hong, Hayden Saunders, Hanqiao Feng, Rodolfo Ghirlando, Alexander E Kelly, Yawen Bai, Sriram Subramaniam
Accurate chromosome segregation requires the proper assembly of kinetochore proteins. A key step in this process is the recognition of the histone H3 variant CENP-A in the centromeric nucleosome by the kinetochore protein CENP-N. We report cryo-EM, biophysical, biochemical, and cell biological studies of the interaction between the CENP-A nucleosome and CENP-N. We show that human CENP-N confers binding specificity through interactions with the L1 loop of CENP-A, stabilized by electrostatic interactions with the nucleosomal DNA...
December 21, 2017: Science
https://www.readbyqxmd.com/read/29249696/superhuman-ai-for-heads-up-no-limit-poker-libratus-beats-top-professionals
#13
Noam Brown, Tuomas Sandholm
No-limit Texas hold'em is the most popular form of poker. Despite AI successes in perfect-information games, the private information and massive game tree have made no-limit poker difficult to tackle. We present Libratus, an AI that, in a 120,000-hand competition, defeated four top human specialist professionals in heads-up no-limit Texas hold'em, the leading benchmark and long-standing challenge problem in imperfect-information game solving. Our game-theoretic approach features application-independent techniques: an algorithm for computing a blueprint for the overall strategy, an algorithm that fleshes out the details of the strategy for subgames that are reached during play, and a self-improver algorithm that fixes potential weaknesses that opponents have identified in the blueprint strategy...
December 17, 2017: Science
https://www.readbyqxmd.com/read/29242235/mechanically-robust-readily-repairable-polymers-via-tailored-noncovalent-cross-linking
#14
Yu Yanagisawa, Yiling Nan, Kou Okuro, Takuzo Aida
Expanding the range of healable materials is an important challenge for sustainable societies. Noncrystalline, high molecular weight polymers generally form mechanically robust materials, which, however, are difficult to repair once they are fractured. This is because their polymer chains are heavily entangled and diffuse too sluggishly to unite fractured surfaces within reasonable timescales. Here, we report that low molecular weight polymers, when cross-linked by dense hydrogen bonds, give mechanically robust yet readily repairable materials, despite their extremely slow diffusion dynamics...
December 14, 2017: Science
https://www.readbyqxmd.com/read/29242233/quantum-liquid-droplets-in-a-mixture-of-bose-einstein-condensates
#15
C R Cabrera, L Tanzi, J Sanz, B Naylor, P Thomas, P Cheiney, L Tarruell
Quantum droplets are small clusters of atoms self-bound by the balance of attractive and repulsive forces. Here we report on the observation of droplets solely stabilized by contact interactions in a mixture of two Bose-Einstein condensates. We demonstrate that they are several orders of magnitude more dilute than liquid helium by directly measuring their size and density via in situ imaging. We show that the droplets are stablized against collapse by quantum fluctuations and that they require a minimum atom number to be stable...
December 14, 2017: Science
https://www.readbyqxmd.com/read/29242232/ralf4-19-peptides-interact-with-lrx-proteins-to-control-pollen-tube-growth-in-arabidopsis
#16
Martin A Mecchia, Gorka Santos-Fernandez, Nadine N Duss, Sofía C Somoza, Aurélien Boisson-Dernier, Valeria Gagliardini, Andrea Martínez-Bernardini, Tohnyui Ndinyanka Fabrice, Christoph Ringli, Jorge P Muschietti, Ueli Grossniklaus
The communication of changes in the extracellular matrix to the interior of the cell is crucial for a cell's function. The extracellular peptides of the RAPID ALKALINIZATION FACTOR (RALF) family have been identified as ligands of receptor-like kinases of the CrRLK1L subclass, but the exact mechanism of their perception is unclear. We found that Arabidopsis RALF4 and RALF19 redundantly regulate pollen tube integrity and growth, and that their function depends on pollen-expressed proteins of the LEUCINE-RICH REPEAT EXTENSIN (LRX) family, which play a role in cell wall development but whose mode of action is not understood...
December 14, 2017: Science
https://www.readbyqxmd.com/read/29242231/the-er-membrane-protein-complex-is-a-transmembrane-domain-insertase
#17
Alina Guna, Norbert Volkmar, John C Christianson, Ramanujan S Hegde
Insertion of proteins into membranes is an essential cellular process. The extensive biophysical and topological diversity of membrane proteins necessitates multiple insertion pathways that remain incompletely defined. Here, we found that known membrane insertion pathways fail to effectively engage tail-anchored membrane proteins with moderately hydrophobic transmembrane domains. These proteins are instead shielded in the cytosol by calmodulin. Dynamic release from calmodulin allowed sampling of the endoplasmic reticulum (ER), where the conserved ER membrane protein complex (EMC) was shown to be essential for efficient insertion in vitro and in cells...
December 14, 2017: Science
https://www.readbyqxmd.com/read/29229651/in-situ-measurements-of-saturn-s-ionosphere-show-that-it-is-dynamic-and-interacts-with-the-rings
#18
J-E Wahlund, M W Morooka, L Z Hadid, A M Persoon, W M Farrell, D A Gurnett, G Hospodarsky, W S Kurth, S-Y Ye, D J Andrews, N J T Edberg, A I Eriksson, E Vigren
The ionized upper layer of Saturn's atmosphere, its ionosphere, provides a closure of currents mediated by the magnetic field to other electrically charged regions (e.g., rings) and hosts ion - molecule chemistry. In 2017, the Cassini spacecraft passed inside the planet's rings, allowing in situ measurements of the ionosphere. The Radio and Plasma Wave Science (RPWS) instrument detected a cold, dense and dynamic ionosphere at Saturn that interacts with the rings. Plasma densities reached up to 1000 cm-3 and electron temperatures were below 1160 K near closest approach...
December 11, 2017: Science
https://www.readbyqxmd.com/read/29217588/tax-plans-and-science
#19
EDITORIAL
Jeremy Berg
No abstract text is available yet for this article.
December 7, 2017: Science
https://www.readbyqxmd.com/read/29217587/different-mutational-rates-and-mechanisms-in-human-cells-at-pregastrulation-and-neurogenesis
#20
Taejeong Bae, Livia Tomasini, Jessica Mariani, Bo Zhou, Tanmoy Roychowdhury, Daniel Franjic, Mihovil Pletikos, Reenal Pattni, Bo-Juen Chen, Elisa Venturini, Bridget Riley-Gillis, Nenad Sestan, Alexander E Urban, Alexej Abyzov, Flora M Vaccarino
Somatic mosaicism in the human brain may alter function of individual neurons. We analyzed genomes of single cells from the forebrains of three human fetuses (15 to 21 weeks post-conception) using clonal cell populations. We detected 200-400 single nucleotide variations (SNVs) per cell. SNV patterns resembled those found in cancer cell genomes, indicating a role of background mutagenesis in cancer. SNVs with a frequency of >2% in brain were shared with the spleen, revealing a pregastrulation origin. We reconstructed cell lineages for the first five post-zygotic cleavages and calculated a mutation rate of ~1...
December 7, 2017: Science
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