@unpublished{14327, abstract = {A common assumption in causal modeling posits that the data is generated by a set of independent mechanisms, and algorithms should aim to recover this structure. Standard unsupervised learning, however, is often concerned with training a single model to capture the overall distribution or aspects thereof. Inspired by clustering approaches, we consider mixtures of implicit generative models that ``disentangle'' the independent generative mechanisms underlying the data. Relying on an additional set of discriminators, we propose a competitive training procedure in which the models only need to capture the portion of the data distribution from which they can produce realistic samples. As a by-product, each model is simpler and faster to train. We empirically show that our approach splits the training distribution in a sensible way and increases the quality of the generated samples.}, author = {Locatello, Francesco and Vincent, Damien and Tolstikhin, Ilya and Rätsch, Gunnar and Gelly, Sylvain and Schölkopf, Bernhard}, booktitle = {arXiv}, title = {{Competitive training of mixtures of independent deep generative models}}, doi = {10.48550/arXiv.1804.11130}, year = {2018}, } @article{145, abstract = {Aged proteins can become hazardous to cellular function, by accumulating molecular damage. This implies that cells should preferentially rely on newly produced ones. We tested this hypothesis in cultured hippocampal neurons, focusing on synaptic transmission. We found that newly synthesized vesicle proteins were incorporated in the actively recycling pool of vesicles responsible for all neurotransmitter release during physiological activity. We observed this for the calcium sensor Synaptotagmin 1, for the neurotransmitter transporter VGAT, and for the fusion protein VAMP2 (Synaptobrevin 2). Metabolic labeling of proteins and visualization by secondary ion mass spectrometry enabled us to query the entire protein makeup of the actively recycling vesicles, which we found to be younger than that of non-recycling vesicles. The young vesicle proteins remained in use for up to ~ 24 h, during which they participated in recycling a few hundred times. They were afterward reluctant to release and were degraded after an additional ~ 24–48 h. We suggest that the recycling pool of synaptic vesicles relies on newly synthesized proteins, while the inactive reserve pool contains older proteins.}, author = {Truckenbrodt, Sven M and Viplav, Abhiyan and Jähne, Sebsatian and Vogts, Angela and Denker, Annette and Wildhagen, Hanna and Fornasiero, Eugenio and Rizzoli, Silvio}, issn = {0261-4189}, journal = {The EMBO Journal}, number = {15}, publisher = {Wiley}, title = {{Newly produced synaptic vesicle proteins are preferentially used in synaptic transmission}}, doi = {10.15252/embj.201798044}, volume = {37}, year = {2018}, } @article{146, abstract = {The root cap protects the stem cell niche of angiosperm roots from damage. In Arabidopsis, lateral root cap (LRC) cells covering the meristematic zone are regularly lost through programmed cell death, while the outermost layer of the root cap covering the tip is repeatedly sloughed. Efficient coordination with stem cells producing new layers is needed to maintain a constant size of the cap. We present a signalling pair, the peptide IDA-LIKE1 (IDL1) and its receptor HAESA-LIKE2 (HSL2), mediating such communication. Live imaging over several days characterized this process from initial fractures in LRC cell files to full separation of a layer. Enhanced expression of IDL1 in the separating root cap layers resulted in increased frequency of sloughing, balanced with generation of new layers in a HSL2-dependent manner. Transcriptome analyses linked IDL1-HSL2 signalling to the transcription factors BEARSKIN1/2 and genes associated with programmed cell death. Mutations in either IDL1 or HSL2 slowed down cell division, maturation and separation. Thus, IDL1-HSL2 signalling potentiates dynamic regulation of the homeostatic balance between stem cell division and sloughing activity.}, author = {Shi, Chun Lin and Von Wangenheim, Daniel and Herrmann, Ullrich and Wildhagen, Mari and Kulik, Ivan and Kopf, Andreas and Ishida, Takashi and Olsson, Vilde and Anker, Mari Kristine and Albert, Markus and Butenko, Melinka A and Felix, Georg and Sawa, Shinichiro and Claassen, Manfred and Friml, Jirí and Aalen, Reidunn B}, journal = {Nature Plants}, number = {8}, pages = {596 -- 604}, publisher = {Nature Publishing Group}, title = {{The dynamics of root cap sloughing in Arabidopsis is regulated by peptide signalling}}, doi = {10.1038/s41477-018-0212-z}, volume = {4}, year = {2018}, } @article{147, abstract = {The trafficking of subcellular cargos in eukaryotic cells crucially depends on vesicle budding, a process mediated by ARF-GEFs (ADP-ribosylation factor guanine nucleotide exchange factors). In plants, ARF-GEFs play essential roles in endocytosis, vacuolar trafficking, recycling, secretion, and polar trafficking. Moreover, they are important for plant development, mainly through controlling the polar subcellular localization of PIN-FORMED (PIN) transporters of the plant hormone auxin. Here, using a chemical genetics screen in Arabidopsis thaliana, we identified Endosidin 4 (ES4), an inhibitor of eukaryotic ARF-GEFs. ES4 acts similarly to and synergistically with the established ARF-GEF inhibitor Brefeldin A and has broad effects on intracellular trafficking, including endocytosis, exocytosis, and vacuolar targeting. Additionally, Arabidopsis and yeast (Sacharomyces cerevisiae) mutants defective in ARF-GEF show altered sensitivity to ES4. ES4 interferes with the activation-based membrane association of the ARF1 GTPases, but not of their mutant variants that are activated independently of ARF-GEF activity. Biochemical approaches and docking simulations confirmed that ES4 specifically targets the SEC7 domain-containing ARF-GEFs. These observations collectively identify ES4 as a chemical tool enabling the study of ARF-GEF-mediated processes, including ARF-GEF-mediated plant development.}, author = {Kania, Urszula and Nodzyński, Tomasz and Lu, Qing and Hicks, Glenn R and Nerinckx, Wim and Mishev, Kiril and Peurois, Francois and Cherfils, Jacqueline and De, Rycke Riet Maria and Grones, Peter and Robert, Stéphanie and Russinova, Eugenia and Friml, Jirí}, issn = {1040-4651}, journal = {The Plant Cell}, number = {10}, pages = {2553 -- 2572}, publisher = {Oxford University Press}, title = {{The inhibitor Endosidin 4 targets SEC7 domain-type ARF GTPase exchange factors and interferes with sub cellular trafficking in eukaryotes}}, doi = {10.1105/tpc.18.00127}, volume = {30}, year = {2018}, } @article{148, abstract = {Land plants evolved from charophytic algae, among which Charophyceae possess the most complex body plans. We present the genome of Chara braunii; comparison of the genome to those of land plants identified evolutionary novelties for plant terrestrialization and land plant heritage genes. C. braunii employs unique xylan synthases for cell wall biosynthesis, a phragmoplast (cell separation) mechanism similar to that of land plants, and many phytohormones. C. braunii plastids are controlled via land-plant-like retrograde signaling, and transcriptional regulation is more elaborate than in other algae. The morphological complexity of this organism may result from expanded gene families, with three cases of particular note: genes effecting tolerance to reactive oxygen species (ROS), LysM receptor-like kinases, and transcription factors (TFs). Transcriptomic analysis of sexual reproductive structures reveals intricate control by TFs, activity of the ROS gene network, and the ancestral use of plant-like storage and stress protection proteins in the zygote.}, author = {Nishiyama, Tomoaki and Sakayama, Hidetoshi and De Vries, Jan and Buschmann, Henrik and Saint Marcoux, Denis and Ullrich, Kristian and Haas, Fabian and Vanderstraeten, Lisa and Becker, Dirk and Lang, Daniel and Vosolsobě, Stanislav and Rombauts, Stephane and Wilhelmsson, Per and Janitza, Philipp and Kern, Ramona and Heyl, Alexander and Rümpler, Florian and Calderón Villalobos, Luz and Clay, John and Skokan, Roman and Toyoda, Atsushi and Suzuki, Yutaka and Kagoshima, Hiroshi and Schijlen, Elio and Tajeshwar, Navindra and Catarino, Bruno and Hetherington, Alexander and Saltykova, Assia and Bonnot, Clemence and Breuninger, Holger and Symeonidi, Aikaterini and Radhakrishnan, Guru and Van Nieuwerburgh, Filip and Deforce, Dieter and Chang, Caren and Karol, Kenneth and Hedrich, Rainer and Ulvskov, Peter and Glöckner, Gernot and Delwiche, Charles and Petrášek, Jan and Van De Peer, Yves and Friml, Jirí and Beilby, Mary and Dolan, Liam and Kohara, Yuji and Sugano, Sumio and Fujiyama, Asao and Delaux, Pierre Marc and Quint, Marcel and Theissen, Gunter and Hagemann, Martin and Harholt, Jesper and Dunand, Christophe and Zachgo, Sabine and Langdale, Jane and Maumus, Florian and Van Der Straeten, Dominique and Gould, Sven B and Rensing, Stefan}, journal = {Cell}, number = {2}, pages = {448 -- 464.e24}, publisher = {Cell Press}, title = {{The Chara genome: Secondary complexity and implications for plant terrestrialization}}, doi = {10.1016/j.cell.2018.06.033}, volume = {174}, year = {2018}, } @phdthesis{149, abstract = {The eigenvalue density of many large random matrices is well approximated by a deterministic measure, the self-consistent density of states. In the present work, we show this behaviour for several classes of random matrices. In fact, we establish that, in each of these classes, the self-consistent density of states approximates the eigenvalue density of the random matrix on all scales slightly above the typical eigenvalue spacing. For large classes of random matrices, the self-consistent density of states exhibits several universal features. We prove that, under suitable assumptions, random Gram matrices and Hermitian random matrices with decaying correlations have a 1/3-Hölder continuous self-consistent density of states ρ on R, which is analytic, where it is positive, and has either a square root edge or a cubic root cusp, where it vanishes. We, thus, extend the validity of the corresponding result for Wigner-type matrices from [4, 5, 7]. We show that ρ is determined as the inverse Stieltjes transform of the normalized trace of the unique solution m(z) to the Dyson equation −m(z) −1 = z − a + S[m(z)] on C N×N with the constraint Im m(z) ≥ 0. Here, z lies in the complex upper half-plane, a is a self-adjoint element of C N×N and S is a positivity-preserving operator on C N×N encoding the first two moments of the random matrix. In order to analyze a possible limit of ρ for N → ∞ and address some applications in free probability theory, we also consider the Dyson equation on infinite dimensional von Neumann algebras. We present two applications to random matrices. We first establish that, under certain assumptions, large random matrices with independent entries have a rotationally symmetric self-consistent density of states which is supported on a centered disk in C. Moreover, it is infinitely often differentiable apart from a jump on the boundary of this disk. Second, we show edge universality at all regular (not necessarily extreme) spectral edges for Hermitian random matrices with decaying correlations.}, author = {Alt, Johannes}, issn = {2663-337X}, pages = {456}, publisher = {Institute of Science and Technology Austria}, title = {{Dyson equation and eigenvalue statistics of random matrices}}, doi = {10.15479/AT:ISTA:TH_1040}, year = {2018}, } @article{150, abstract = {A short, 14-amino-acid segment called SP1, located in the Gag structural protein1, has a critical role during the formation of the HIV-1 virus particle. During virus assembly, the SP1 peptide and seven preceding residues fold into a six-helix bundle, which holds together the Gag hexamer and facilitates the formation of a curved immature hexagonal lattice underneath the viral membrane2,3. Upon completion of assembly and budding, proteolytic cleavage of Gag leads to virus maturation, in which the immature lattice is broken down; the liberated CA domain of Gag then re-assembles into the mature conical capsid that encloses the viral genome and associated enzymes. Folding and proteolysis of the six-helix bundle are crucial rate-limiting steps of both Gag assembly and disassembly, and the six-helix bundle is an established target of HIV-1 inhibitors4,5. Here, using a combination of structural and functional analyses, we show that inositol hexakisphosphate (InsP6, also known as IP6) facilitates the formation of the six-helix bundle and assembly of the immature HIV-1 Gag lattice. IP6 makes ionic contacts with two rings of lysine residues at the centre of the Gag hexamer. Proteolytic cleavage then unmasks an alternative binding site, where IP6 interaction promotes the assembly of the mature capsid lattice. These studies identify IP6 as a naturally occurring small molecule that promotes both assembly and maturation of HIV-1.}, author = {Dick, Robert and Zadrozny, Kaneil K and Xu, Chaoyi and Schur, Florian and Lyddon, Terri D and Ricana, Clifton L and Wagner, Jonathan M and Perilla, Juan R and Ganser, Pornillos Barbie K and Johnson, Marc C and Pornillos, Owen and Vogt, Volker}, issn = {1476-4687}, journal = {Nature}, number = {7719}, pages = {509–512}, publisher = {Nature Publishing Group}, title = {{Inositol phosphates are assembly co-factors for HIV-1}}, doi = {10.1038/s41586-018-0396-4}, volume = {560}, year = {2018}, } @article{15143, abstract = {To maintain genome integrity, segmented double-stranded RNA viruses of the Reoviridae family must accurately select and package a complete set of up to a dozen distinct genomic RNAs. It is thought that the high fidelity segmented genome assembly involves multiple sequence-specific RNA–RNA interactions between single-stranded RNA segment precursors. These are mediated by virus-encoded non-structural proteins with RNA chaperone-like activities, such as rotavirus (RV) NSP2 and avian reovirus σNS. Here, we compared the abilities of NSP2 and σNS to mediate sequence-specific interactions between RV genomic segment precursors. Despite their similar activities, NSP2 successfully promotes inter-segment association, while σNS fails to do so. To understand the mechanisms underlying such selectivity in promoting inter-molecular duplex formation, we compared RNA-binding and helix-unwinding activities of both proteins. We demonstrate that octameric NSP2 binds structured RNAs with high affinity, resulting in efficient intramolecular RNA helix disruption. Hexameric σNS oligomerizes into an octamer that binds two RNAs, yet it exhibits only limited RNA-unwinding activity compared to NSP2. Thus, the formation of intersegment RNA–RNA interactions is governed by both helix-unwinding capacity of the chaperones and stability of RNA structure. We propose that this protein-mediated RNA selection mechanism may underpin the high fidelity assembly of multi-segmented RNA genomes in Reoviridae.}, author = {Bravo, Jack Peter Kelly and Borodavka, Alexander and Barth, Anders and Calabrese, Antonio N and Mojzes, Peter and Cockburn, Joseph J B and Lamb, Don C and Tuma, Roman}, issn = {1362-4962}, journal = {Nucleic Acids Research}, keywords = {Genetics}, number = {15}, pages = {7924--7937}, publisher = {Oxford University Press}, title = {{Stability of local secondary structure determines selectivity of viral RNA chaperones}}, doi = {10.1093/nar/gky394}, volume = {46}, year = {2018}, } @article{152, abstract = {Complex I has an essential role in ATP production by coupling electron transfer from NADH to quinone with translocation of protons across the inner mitochondrial membrane. Isolated complex I deficiency is a frequent cause of mitochondrial inherited diseases. Complex I has also been implicated in cancer, ageing, and neurodegenerative conditions. Until recently, the understanding of complex I deficiency on the molecular level was limited due to the lack of high-resolution structures of the enzyme. However, due to developments in single particle cryo-electron microscopy (cryo-EM), recent studies have reported nearly atomic resolution maps and models of mitochondrial complex I. These structures significantly add to our understanding of complex I mechanism and assembly. The disease-causing mutations are discussed here in their structural context.}, author = {Fiedorczuk, Karol and Sazanov, Leonid A}, journal = {Trends in Cell Biology}, number = {10}, pages = {835 -- 867}, publisher = {Elsevier}, title = {{Mammalian mitochondrial complex I structure and disease causing mutations}}, doi = {10.1016/j.tcb.2018.06.006}, volume = {28}, year = {2018}, } @article{15232, abstract = {In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced “spectral-timing-polarimetry” techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process. }, author = {Rosa, Alessandra De and Uttley, Phil and Gou, LiJun and Liu, Yuan and Bambi, Cosimo and Barret, Didier and Belloni, Tomaso and Berti, Emanuele and Bianchi, Stefano and Caiazzo, Ilaria and Casella, Piergiorgio and Feroci, Marco and Ferrari, Valeria and Gualtieri, Leonardo and Heyl, Jeremy and Ingram, Adam and Karas, Vladimir and Lu, FangJun and Luo, Bin and Matt, Giorgio and Motta, Sara and Neilsen, Joseph and Pani, Paolo and Santangelo, Andrea and Shu, XinWen and Wang, JunFeng and Wang, Jian-Min and Xue, YongQuan and Xu, YuPeng and Yuan, WeiMin and Yuan, YeFei and Zhang, Shuang-Nan and Zhang, Shu and Agudo, Ivan and Amati, Lorenzo and Andersson, Nils and Baglio, Cristina and Bakala, Pavel and Baykal, Altan and Bhattacharyya, Sudip and Bombaci, Ignazio and Bucciantini, Niccoló and Capitanio, Fiamma and Ciolfi, Riccardo and Cui, Wei K. and D’Ammando, Filippo and Dauser, Thomas and Del Santo, Melania and De Marco, Barbara and Di Salvo, Tiziana and Done, Chris and Dovčiak, Michal and Fabian, Andrew C. and Falanga, Maurizio and Gambino, Angelo Francesco and Gendre, Bruce and Grinberg, Victoria and Heger, Alexander and Homan, Jeroen and Iaria, Rosario and Jiang, JiaChen and Jin, ChiChuan and Koerding, Elmar and Linares, Manu and Liu, Zhu and Maccarone, Thomas J. and Malzac, Julien and Manousakis, Antonios and Marin, Frédéric and Marinucci, Andrea and Mehdipour, Missagh and Méndez, Mariano and Migliari, Simone and Miller, Cole and Miniutti, Giovanni and Nardini, Emanuele and O’Brien, Paul T. and Osborne, Julian P. and Petrucci, Pierre Olivier and Possenti, Andrea and Riggio, Alessandro and Rodriguez, Jerome and Sanna, Andrea and Shao, LiJing and Sobolewska, Malgosia and Sramkova, Eva and Stevens, Abigail L. and Stiele, Holger and Stratta, Giulia and Stuchlik, Zdenek and Svoboda, Jiri and Tamburini, Fabrizio and Tauris, Thomas M. and Tombesi, Francesco and Torok, Gabriel and Urbanec, Martin and Vincent, Frederic and Wu, QingWen and Yuan, Feng and in’ t Zand, Jean J. M. and Zdziarski, Andrzej A. and Zhou, XinLin}, issn = {1869-1927}, journal = {Science China Physics, Mechanics & Astronomy}, keywords = {General Physics and Astronomy}, number = {2}, publisher = {Springer Nature}, title = {{Accretion in strong field gravity with eXTP}}, doi = {10.1007/s11433-018-9297-0}, volume = {62}, year = {2018}, } @article{15233, abstract = {In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission for studies of strongly magnetized objects. We will focus on the physics and astrophysics of strongly magnetized objects, namely magnetars, accreting X-ray pulsars, and rotation powered pulsars. We also discuss the science potential of eXTP for QED studies. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to be launched in the mid 2020s.}, author = {Santangelo, Andrea and Zane, Silvia and Feng, Hua and Xu, RenXin and Doroshenko, Victor and Bozzo, Enrico and Caiazzo, Ilaria and Zelati, Francesco Coti and Esposito, Paolo and González-Caniulef, Denis and Heyl, Jeremy and Huppenkothen, Daniela and Israel, Gianluca and Li, ZhaoSheng and Lin, Lin and Mignani, Roberto and Rea, Nanda and Orlandini, Mauro and Taverna, Roberto and Tong, Hao and Turolla, Roberto and Baglio, Cristina and Bernardini, Federico and Bucciantini, Niccolo’ and Feroci, Marco and Fürst, Felix and Göğüş, Ersin and Güngör, Can and Ji, Long and Lu, FangJun and Manousakis, Antonios and Mereghetti, Sandro and Mikusincova, Romana and Paul, Biswajit and Prescod-Weinstein, Chanda and Younes, George and Tiengo, Andrea and Xu, YuPeng and Watts, Anna and Zhang, Shu and Zhan, Shuang-Nan}, issn = {1869-1927}, journal = {Science China Physics, Mechanics & Astronomy}, keywords = {General Physics and Astronomy}, number = {2}, publisher = {Springer Nature}, title = {{Physics and astrophysics of strong magnetic field systems with eXTP}}, doi = {10.1007/s11433-018-9234-3}, volume = {62}, year = {2018}, } @article{15234, abstract = {Using parallaxes from Gaia Data Release 2 (Gaia DR2), we estimate the distance to the globular clusters 47 Tuc and NGC 362, taking advantage of the background stars in the Small Magellanic Cloud and quasars to account for various parallax systematics. We found the parallax to be dependent on the Gaia DR2 G-band apparent magnitude for stars with 13 < G < 18, where brighter stars have a lower parallax zero point than fainter stars. The distance to 47 Tuc was found to be 4.45 ± 0.01 ± 0.12 kpc, and for NGC 362 8.54 ± 0.20 ± 0.44 kpc, with random and systematic errors listed, respectively. This is the first time a precise distance measurement directly using parallaxes has been determined for either of these two globular clusters.}, author = {Chen, Seery and Richer, Harvey and Caiazzo, Ilaria and Heyl, Jeremy}, issn = {1538-4357}, journal = {The Astrophysical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {2}, publisher = {American Astronomical Society}, title = {{Distances to the globular clusters 47 Tucanae and NGC 362 using Gaia DR2 parallaxes}}, doi = {10.3847/1538-4357/aae089}, volume = {867}, year = {2018}, } @article{15235, abstract = {Radiative corrections of quantum electrodynamics cause a vacuum threaded by a magnetic field to be birefringent. This means that radiation of different polarizations travels at different speeds. Even in the strong magnetic fields of astrophysical sources, the difference in speed is small. However, it has profound consequences for the extent of polarization expected from strongly magnetized sources. We demonstrate how the birefringence arises from first principles, show how birefringence affects the polarization state of radiation and present recent calculations for the expected polarization from magnetars and X-ray pulsars.}, author = {Heyl, Jeremy and Caiazzo, Ilaria}, issn = {2075-4434}, journal = {Galaxies}, keywords = {Astronomy and Astrophysics}, number = {3}, publisher = {MDPI}, title = {{Strongly magnetized sources: QED and X-ray polarization}}, doi = {10.3390/galaxies6030076}, volume = {6}, year = {2018}, } @article{15236, abstract = {Radio pulsars found in binary systems with short orbital periods are usually fast spinning as a consequence of recycling via mass transfer from their companion stars; this process is also thought to decrease the magnetic field of the neutron star being recycled. Here, we report on timing observations of the recently discovered binary PSR J1755−2550 and find that this pulsar is an exception: with a characteristic age of 2.1 Myr, it is relatively young; furthermore, with a spin period of 315 ms and a surface magnetic field strength at its poles of 0.88 × 1012 G, the pulsar shows no sign of having been recycled. Based on its timing and orbital characteristics, the pulsar either has a massive white dwarf (WD) or a neutron star (NS) companion. To distinguish between these two cases, we searched radio observations for a potential recycled pulsar companion and analysed archival optical data for a potential WD companion. Neither work returned conclusive detections. We apply population synthesis modelling and find that both solutions are roughly equally probable. Our population synthesis also predicts a minimum mass of 0.90 M⊙ for the companion star to PSR J1755−2550 and we simulate the systemic runaway velocities for the resulting WDNS systems which may merge and possibly produce Ca-rich supernovae. Whether PSR J1755−2550 hosts a WD or a NS companion star, it is certainly a member of a rare subpopulation of binary radio pulsars.}, author = {Ng, C and Kruckow, M U and Tauris, T M and Lyne, A G and Freire, P C C and Ridolfi, A and Caiazzo, Ilaria and Heyl, J and Kramer, M and Cameron, A D and Champion, D J and Stappers, B}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {4}, pages = {4315--4326}, publisher = {Oxford University Press}, title = {{PSR J1755−2550: A young radio pulsar with a massive, compact companion}}, doi = {10.1093/mnras/sty482}, volume = {476}, year = {2018}, } @article{15237, abstract = {The effect of vacuum birefringence is one of the first predictions of quantum electrodynamics (QED): the presence of a charged Dirac field makes the vacuum birefringent when threaded by magnetic fields. This effect, extremely weak for terrestrial magnetic fields, becomes important for highly magnetized astrophysical objects, such as accreting black holes. In the X-ray regime, the polarization of photons traveling in the magnetosphere of a black hole is not frozen at emission but is changed by the local magnetic field. We show that, for photons traveling along the plane of the disk, where the field is expected to be partially organized, this results in a depolarization of the X-ray radiation. Because the amount of depolarization depends on the strength of the magnetic field, this effect can provide a way to probe the magnetic field in black-hole accretion disks and to study the role of magnetic fields in astrophysical accretion in general.}, author = {Caiazzo, Ilaria and Heyl, Jeremy}, issn = {2075-4434}, journal = {Galaxies}, keywords = {Astronomy and Astrophysics}, number = {2}, publisher = {MDPI}, title = {{Probing black hole magnetic fields with QED}}, doi = {10.3390/galaxies6020057}, volume = {6}, year = {2018}, } @article{15238, abstract = {In the next decade, x-ray polarimetry will open a new window on the high-energy Universe, as several missions that include an x-ray polarimeter are currently under development. Observations of the polarization of x rays coming from the accretion disks of stellar-mass and supermassive black holes are among the new polarimeters’ major objectives. In this paper, we show that these observations can be affected by the quantum electrodynamic (QED) effect of vacuum birefringence: after an x-ray photon is emitted from the accretion disk, its polarization changes as the photon travels through the accretion disk’s magnetosphere, as a result of the vacuum becoming birefringent in the presence of a magnetic field. We show that this effect can be important for black holes in the energy band of the upcoming polarimeters and has to be taken into account in a complete model of the x-ray polarization that we expect to detect from black-hole accretion disks, both for stellar mass and for supermassive black holes. We find that, for a chaotic magnetic field in the disk, QED can significantly decrease the linear polarization fraction of edge-on photons, depending on the spin of the hole and on the strength of the magnetic field. This effect can provide, for the first time, a direct way to probe the magnetic field strength close to the innermost stable orbit of black-hole accretion disks and to study the role of magnetic fields in astrophysical accretion in general.}, author = {Caiazzo, Ilaria and Heyl, Jeremy}, issn = {2470-0029}, journal = {Physical Review D}, number = {8}, publisher = {American Physical Society}, title = {{Vacuum birefringence and the x-ray polarization from black-hole accretion disks}}, doi = {10.1103/physrevd.97.083001}, volume = {97}, year = {2018}, } @article{154, abstract = {We give a lower bound on the ground state energy of a system of two fermions of one species interacting with two fermions of another species via point interactions. We show that there is a critical mass ratio m2 ≈ 0.58 such that the system is stable, i.e., the energy is bounded from below, for m∈[m2,m2−1]. So far it was not known whether this 2 + 2 system exhibits a stable region at all or whether the formation of four-body bound states causes an unbounded spectrum for all mass ratios, similar to the Thomas effect. Our result gives further evidence for the stability of the more general N + M system.}, author = {Moser, Thomas and Seiringer, Robert}, issn = {1572-9656}, journal = {Mathematical Physics Analysis and Geometry}, number = {3}, publisher = {Springer}, title = {{Stability of the 2+2 fermionic system with point interactions}}, doi = {10.1007/s11040-018-9275-3}, volume = {21}, year = {2018}, } @inproceedings{155, abstract = {There is currently significant interest in operating devices in the quantum regime, where their behaviour cannot be explained through classical mechanics. Quantum states, including entangled states, are fragile and easily disturbed by excessive thermal noise. Here we address the question of whether it is possible to create non-reciprocal devices that encourage the flow of thermal noise towards or away from a particular quantum device in a network. Our work makes use of the cascaded systems formalism to answer this question in the affirmative, showing how a three-port device can be used as an effective thermal transistor, and illustrates how this formalism maps onto an experimentally-realisable optomechanical system. Our results pave the way to more resilient quantum devices and to the use of thermal noise as a resource.}, author = {Xuereb, André and Aquilina, Matteo and Barzanjeh, Shabir}, editor = {Andrews, D L and Ostendorf, A and Bain, A J and Nunzi, J M}, location = {Strasbourg, France}, publisher = {SPIE}, title = {{Routing thermal noise through quantum networks}}, doi = {10.1117/12.2309928}, volume = {10672}, year = {2018}, } @inproceedings{156, abstract = {Imprecision in timing can sometimes be beneficial: Metric interval temporal logic (MITL), disabling the expression of punctuality constraints, was shown to translate to timed automata, yielding an elementary decision procedure. We show how this principle extends to other forms of dense-time specification using regular expressions. By providing a clean, automaton-based formal framework for non-punctual languages, we are able to recover and extend several results in timed systems. Metric interval regular expressions (MIRE) are introduced, providing regular expressions with non-singular duration constraints. We obtain that MIRE are expressively complete relative to a class of one-clock timed automata, which can be determinized using additional clocks. Metric interval dynamic logic (MIDL) is then defined using MIRE as temporal modalities. We show that MIDL generalizes known extensions of MITL, while translating to timed automata at comparable cost.}, author = {Ferrere, Thomas}, location = {Oxford, UK}, pages = {147 -- 164}, publisher = {Springer}, title = {{The compound interest in relaxing punctuality}}, doi = {10.1007/978-3-319-95582-7_9}, volume = {10951}, year = {2018}, } @article{157, abstract = {Social dilemmas occur when incentives for individuals are misaligned with group interests 1-7 . According to the 'tragedy of the commons', these misalignments can lead to overexploitation and collapse of public resources. The resulting behaviours can be analysed with the tools of game theory 8 . The theory of direct reciprocity 9-15 suggests that repeated interactions can alleviate such dilemmas, but previous work has assumed that the public resource remains constant over time. Here we introduce the idea that the public resource is instead changeable and depends on the strategic choices of individuals. An intuitive scenario is that cooperation increases the public resource, whereas defection decreases it. Thus, cooperation allows the possibility of playing a more valuable game with higher payoffs, whereas defection leads to a less valuable game. We analyse this idea using the theory of stochastic games 16-19 and evolutionary game theory. We find that the dependence of the public resource on previous interactions can greatly enhance the propensity for cooperation. For these results, the interaction between reciprocity and payoff feedback is crucial: neither repeated interactions in a constant environment nor single interactions in a changing environment yield similar cooperation rates. Our framework shows which feedbacks between exploitation and environment - either naturally occurring or designed - help to overcome social dilemmas.}, author = {Hilbe, Christian and Šimsa, Štepán and Chatterjee, Krishnendu and Nowak, Martin}, journal = {Nature}, number = {7713}, pages = {246 -- 249}, publisher = {Nature Publishing Group}, title = {{Evolution of cooperation in stochastic games}}, doi = {10.1038/s41586-018-0277-x}, volume = {559}, year = {2018}, }