TY - JOUR AB - Context. Observations of massive stars in open clusters younger than ∼8 Myr have shown that a majority of them are in binary systems, most of which will interact during their life. While these can be used as a proxy of the initial multiplicity properties, studying populations of massive stars older than ∼20 Myr allows us to probe the outcome of these interactions after a significant number of systems have experienced mass and angular momentum transfer and may even have merged. Aims. Using multi-epoch integral-field spectroscopy, we aim to investigate the multiplicity properties of the massive-star population in the dense core of the ∼40 Myr old cluster NGC 330 in the Small Magellanic Cloud in order to search for possible imprints of stellar evolution on the multiplicity properties. Methods. We obtained six epochs of VLT/MUSE observations operated in wide-field mode with the extended wavelength setup and supported by adaptive optics. We extracted spectra and measured radial velocities for stars brighter than mF814W = 19. We identified single-lined spectroscopic binaries through significant RV variability with a peak-to-peak amplitude larger than 20 km s−1. We also identified double-lined spectroscopic binaries, and quantified the observational biases for binary detection. In particular, we took into account that binary systems with similar line strengths are difficult to detect in our data set. Results. The observed spectroscopic binary fraction among stars brighter than mF814W = 19 (approximately 5.5 M⊙ on the main sequence) is fSBobs = 13.2 ± 2.0%. Considering period and mass ratio ranges from log(P) = 0.15−3.5 (about 1.4 to 3160 d), q = 0.1−1.0, and a representative set of orbital parameter distributions, we find a bias-corrected close binary fraction of fcl = 34−7+8%. This fraction seems to decline for the fainter stars, which indicates either that the close binary fraction drops in the B-type domain, or that the period distribution becomes more heavily weighted toward longer orbital periods. We further find that both fractions vary strongly in different regions of the color-magnitude diagram, which corresponds to different evolutionary stages. This probably reveals the imprint of the binary history of different groups of stars. In particular, we find that the observed spectroscopic binary fraction of Be stars (fSBobs = 2 ± 2%) is significantly lower than that of B-type stars (fSBobs = 9 ± 2%). Conclusions. We provide the first homogeneous radial velocity study of a large sample of B-type stars at a low metallicity ([Fe/H] ≲ −1.0). The overall bias-corrected close binary fraction (log(P) < 3.5 d) of the B-star population in NGC 330 is lower than the fraction reported for younger Galactic and Large Magellanic Cloud clusters in previous works. More data are needed, however, to establish whether the observed differences are caused by an age or a metallicity effect. AU - Bodensteiner, J. AU - Sana, H. AU - Wang, C. AU - Langer, N. AU - Mahy, L. AU - Banyard, G. AU - de Koter, A. AU - de Mink, S. E. AU - Evans, C. J. AU - Götberg, Ylva Louise Linsdotter AU - Patrick, L. R. AU - Schneider, F. R. N. AU - Tramper, F. ID - 13457 JF - Astronomy & Astrophysics KW - Space and Planetary Science KW - Astronomy and Astrophysics SN - 0004-6361 TI - The young massive SMC cluster NGC 330 seen by MUSE. II. Multiplicity properties of the massive-star population VL - 652 ER - TY - JOUR AB - The majority of massive stars live in binary or multiple systems and will interact with a companion during their lifetimes, which helps to explain the observed diversity of core-collapse supernovae. Donor stars in binary systems can lose most of their hydrogen-rich envelopes through mass transfer. As a result, not only are the surface properties affected, but so is the core structure. However, most calculations of the core-collapse properties of massive stars rely on single-star models. We present a systematic study of the difference between the pre-supernova structures of single stars and stars of the same initial mass (11–21 M⊙) that have been stripped due to stable post-main-sequence mass transfer at solar metallicity. We present the pre-supernova core composition with novel diagrams that give an intuitive representation of the isotope distribution. As shown in previous studies, at the edge of the carbon-oxygen core, the binary-stripped star models contain an extended gradient of carbon, oxygen, and neon. This layer remains until core collapse and is more extended in mass for higher initial stellar masses. It originates from the receding of the convective helium core during core helium burning in binary-stripped stars, which does not occur in single-star models. We find that this same evolutionary phase leads to systematic differences in the final density and nuclear energy generation profiles. Binary-stripped star models have systematically higher total masses of carbon at the moment of core collapse compared to single-star models, which likely results in systematically different supernova yields. In about half of our models, the silicon-burning and oxygen-rich layers merge after core silicon burning. We discuss the implications of our findings for the “explodability”, supernova observations, and nucleosynthesis of these stars. Our models are publicly available and can be readily used as input for detailed supernova simulations. AU - Laplace, E. AU - Justham, S. AU - Renzo, M. AU - Götberg, Ylva Louise Linsdotter AU - Farmer, R. AU - Vartanyan, D. AU - de Mink, S. E. ID - 13455 JF - Astronomy & Astrophysics KW - Space and Planetary Science KW - Astronomy and Astrophysics SN - 0004-6361 TI - Different to the core: The pre-supernova structures of massive single and binary-stripped stars VL - 656 ER - TY - JOUR AB - Helium star–carbon-oxygen white dwarf (CO WD) binaries are potential single-degenerate progenitor systems of thermonuclear supernovae. Revisiting a set of binary evolution calculations using the stellar evolution code MESA, we refine our previous predictions about which systems can lead to a thermonuclear supernova and then characterize the properties of the helium star donor at the time of explosion. We convert these model properties to near-UV/optical magnitudes assuming a blackbody spectrum and support this approach using a matched stellar atmosphere model. These models will be valuable to compare with pre-explosion imaging for future supernovae, though we emphasize the observational difficulty of detecting extremely blue companions. The pre-explosion source detected in association with SN 2012Z has been interpreted as a helium star binary containing an initially ultra-massive WD in a multiday orbit. However, extending our binary models to initial CO WD masses of up to 1.2 M⊙, we find that these systems undergo off-center carbon ignitions and thus are not expected to produce thermonuclear supernovae. This tension suggests that, if SN 2012Z is associated with a helium star–WD binary, then the pre-explosion optical light from the system must be significantly modified by the binary environment and/or the WD does not have a carbon-rich interior composition. AU - Wong, Tin Long Sunny AU - Schwab, Josiah AU - Götberg, Ylva Louise Linsdotter ID - 13454 IS - 2 JF - The Astrophysical Journal KW - Space and Planetary Science KW - Astronomy and Astrophysics SN - 0004-637X TI - Pre-explosion properties of Helium star donors to thermonuclear supernovae VL - 922 ER - TY - JOUR AB - Most massive stars are born in binaries close enough for mass transfer episodes. These modify the appearance, structure, and future evolution of both stars. We compute the evolution of a 100-day-period binary, consisting initially of a 25 M⊙ star and a 17 M⊙ star, which experiences stable mass transfer. We focus on the impact of mass accretion on the surface composition, internal rotation, and structure of the accretor. To anchor our models, we show that our accretor broadly reproduces the properties of ζ Ophiuchi, which has long been proposed to have accreted mass before being ejected as a runaway star when the companion exploded. We compare our accretor to models of single rotating stars and find that the later and stronger spin-up provided by mass accretion produces significant differences. Specifically, the core of the accretor retains higher spin at the end of the main sequence, and a convective layer develops that changes its density profile. Moreover, the surface of the accretor star is polluted by CNO-processed material donated by the companion. Our models show effects of mass accretion in binaries that are not captured in single rotating stellar models. This possibly impacts the further evolution (either in a binary or as single stars), the final collapse, and the resulting spin of the compact object. AU - Renzo, M. AU - Götberg, Ylva Louise Linsdotter ID - 13453 IS - 2 JF - The Astrophysical Journal KW - Space and Planetary Science KW - Astronomy and Astrophysics SN - 0004-637X TI - Evolution of accretor stars in massive binaries: Broader implications from modeling ζ Ophiuchi VL - 923 ER - TY - JOUR AB - We report the observation of an anomalous nonlinear optical response of the prototypical three-dimensional topological insulator bismuth selenide through the process of high-order harmonic generation. We find that the generation efficiency increases as the laser polarization is changed from linear to elliptical, and it becomes maximum for circular polarization. With the aid of a microscopic theory and a detailed analysis of the measured spectra, we reveal that such anomalous enhancement encodes the characteristic topology of the band structure that originates from the interplay of strong spin–orbit coupling and time-reversal symmetry protection. The implications are in ultrafast probing of topological phase transitions, light-field driven dissipationless electronics, and quantum computation. AU - Baykusheva, Denitsa Rangelova AU - Chacón, Alexis AU - Lu, Jian AU - Bailey, Trevor P. AU - Sobota, Jonathan A. AU - Soifer, Hadas AU - Kirchmann, Patrick S. AU - Rotundu, Costel AU - Uher, Ctirad AU - Heinz, Tony F. AU - Reis, David A. AU - Ghimire, Shambhu ID - 13996 IS - 21 JF - Nano Letters KW - Mechanical Engineering KW - Condensed Matter Physics KW - General Materials Science KW - General Chemistry KW - Bioengineering SN - 1530-6984 TI - All-optical probe of three-dimensional topological insulators based on high-harmonic generation by circularly polarized laser fields VL - 21 ER - TY - JOUR AB - We investigate theoretically the strong-field regime of light-matter interactions in the topological-insulator class of quantum materials. In particular, we focus on the process of nonperturbative high-order harmonic generation from the paradigmatic three-dimensional topological insulator bismuth selenide (Bi2Se3) subjected to intense midinfrared laser fields. We analyze the contributions from the spin-orbit-coupled bulk states and the topological surface bands separately and reveal a major difference in how their harmonic yields depend on the ellipticity of the laser field. Bulk harmonics show a monotonic decrease in their yield as the ellipticity increases, in a manner reminiscent of high harmonic generation in gaseous media. However, the surface contribution exhibits a highly nontrivial dependence, culminating with a maximum for circularly polarized fields. We attribute the observed anomalous behavior to (i) the enhanced amplitude and the circular pattern of the interband dipole and the Berry connections in the vicinity of the Dirac point and (ii) the influence of the higher-order, hexagonal warping terms in the Hamiltonian, which are responsible for the hexagonal deformation of the energy surface at higher momenta. The latter are associated directly with spin-orbit-coupling parameters. Our results thus establish the sensitivity of strong-field-driven high harmonic emission to the topology of the band structure as well as to the manifestations of spin-orbit interaction. AU - Baykusheva, Denitsa Rangelova AU - Chacón, Alexis AU - Kim, Dasol AU - Kim, Dong Eon AU - Reis, David A. AU - Ghimire, Shambhu ID - 13997 IS - 2 JF - Physical Review A SN - 2469-9926 TI - Strong-field physics in three-dimensional topological insulators VL - 103 ER - TY - JOUR AB - Shape resonances play a central role in many areas of science, but the real-time measurement of the associated many-body dynamics remains challenging. Here, we present measurements of recoil frame angle-resolved photoionization delays in the vicinity of shape resonances of CF4. This technique provides insights into the spatiotemporal photoionization dynamics of molecular shape resonances. We find delays of up to ∼600 as in the ionization out of the highest occupied molecular orbital (HOMO) with a strong dependence on the emission direction and a pronounced asymmetry along the dissociation axis. Comparison with quantum-scattering calculations traces the asymmetries to the interference of a small subset of partial waves at low kinetic energies and, additionally, to the interference of two overlapping shape resonances in the HOMO-1 channel. Our experimental and theoretical results establish a broadly applicable approach to space- and time-resolved photoionization dynamics in the molecular frame. AU - Heck, Saijoscha AU - Baykusheva, Denitsa Rangelova AU - Han, Meng AU - Ji, Jia-Bao AU - Perry, Conaill AU - Gong, Xiaochun AU - Wörner, Hans Jakob ID - 13995 IS - 49 JF - Science Advances KW - Multidisciplinary TI - Attosecond interferometry of shape resonances in the recoil frame of CF4 VL - 7 ER - TY - GEN AB - UVEX is a proposed medium class Explorer mission designed to provide crucial missing capabilities that will address objectives central to a broad range of modern astrophysics. The UVEX design has two co-aligned wide-field imagers operating in the FUV and NUV and a powerful broadband medium resolution spectrometer. In its two-year baseline mission, UVEX will perform a multi-cadence synoptic all-sky survey 50/100 times deeper than GALEX in the NUV/FUV, cadenced surveys of the Large and Small Magellanic Clouds, rapid target of opportunity followup, as well as spectroscopic followup of samples of stars and galaxies. The science program is built around three pillars. First, UVEX will explore the low-mass, low-metallicity galaxy frontier through imaging and spectroscopic surveys that will probe key aspects of the evolution of galaxies by understanding how star formation and stellar evolution at low metallicities affect the growth and evolution of low-metallicity, low-mass galaxies in the local universe. Such galaxies contain half the mass in the local universe, and are analogs for the first galaxies, but observed at distances that make them accessible to detailed study. Second, UVEX will explore the dynamic universe through time-domain surveys and prompt spectroscopic followup capability will probe the environments, energetics, and emission processes in the early aftermaths of gravitational wave-discovered compact object mergers, discover hot, fast UV transients, and diagnose the early stages of stellar explosions. Finally, UVEX will become a key community resource by leaving a large all-sky legacy data set, enabling a wide range of scientific studies and filling a gap in the new generation of wide-field, sensitive optical and infrared surveys provided by the Rubin, Euclid, and Roman observatories. This paper discusses the scientific potential of UVEX, and the broad scientific program. AU - Kulkarni, S. R. AU - Harrison, Fiona A. AU - Grefenstette, Brian W. AU - Earnshaw, Hannah P. AU - Andreoni, Igor AU - Berg, Danielle A. AU - Bloom, Joshua S. AU - Cenko, S. Bradley AU - Chornock, Ryan AU - Christiansen, Jessie L. AU - Coughlin, Michael W. AU - Criswell, Alexander Wuollet AU - Darvish, Behnam AU - Das, Kaustav K. AU - De, Kishalay AU - Dessart, Luc AU - Dixon, Don AU - Dorsman, Bas AU - Kareem El-Badry, Kareem El-Badry AU - Evans, Christopher AU - Ford, K. E. Saavik AU - Fremling, Christoffer AU - Gansicke, Boris T. AU - Gezari, Suvi AU - Götberg, Ylva Louise Linsdotter AU - Green, Gregory M. AU - Graham, Matthew J. AU - Heida, Marianne AU - Ho, Anna Y. Q. AU - Jaodand, Amruta D. AU - Christopher M. Johns-Krull, Christopher M. Johns-Krull AU - Kasliwal, Mansi M. AU - Lazzarini, Margaret AU - Lu, Wenbin AU - Margutti, Raffaella AU - Martin, D. Christopher AU - Masters, Daniel Charles AU - McKernan, Barry AU - Naze, Yael AU - Nissanke, Samaya M. AU - Parazin, B. AU - Perley, Daniel A. AU - Phinney, E. Sterl AU - Piro, Anthony L. AU - Raaijmakers, G. AU - Rauw, Gregor AU - Rodriguez, Antonio C. AU - Sana, Hugues AU - Senchyna, Peter AU - Singer, Leo P. AU - Spake, Jessica J. AU - Stassun, Keivan G. AU - Stern, Daniel AU - Teplitz, Harry I. AU - Weisz, Daniel R. AU - Yao, Yuhan ID - 14097 T2 - arXiv TI - Science with the ultraviolet explorer (UVEX) ER - TY - JOUR AB - We study systems of nonlinear partial differential equations of parabolic type, in which the elliptic operator is replaced by the first-order divergence operator acting on a flux function, which is related to the spatial gradient of the unknown through an additional implicit equation. This setting, broad enough in terms of applications, significantly expands the paradigm of nonlinear parabolic problems. Formulating four conditions concerning the form of the implicit equation, we first show that these conditions describe a maximal monotone p-coercive graph. We then establish the global-in-time and large-data existence of a (weak) solution and its uniqueness. To this end, we adopt and significantly generalize Minty’s method of monotone mappings. A unified theory, containing several novel tools, is developed in a way to be tractable from the point of view of numerical approximations. AU - Bulíček, Miroslav AU - Maringová, Erika AU - Málek, Josef ID - 10005 IS - 09 JF - Mathematical Models and Methods in Applied Sciences KW - Nonlinear parabolic systems KW - implicit constitutive theory KW - weak solutions KW - existence KW - uniqueness SN - 0218-2025 TI - On nonlinear problems of parabolic type with implicit constitutive equations involving flux VL - 31 ER - TY - CONF AB - The popularity of permissioned blockchain systems demands BFT SMR protocols that are efficient under good network conditions (synchrony) and robust under bad network conditions (asynchrony). The state-of-the-art partially synchronous BFT SMR protocols provide optimal linear communication cost per decision under synchrony and good leaders, but lose liveness under asynchrony. On the other hand, the state-of-the-art asynchronous BFT SMR protocols are live even under asynchrony, but always pay quadratic cost even under synchrony. In this paper, we propose a BFT SMR protocol that achieves the best of both worlds -- optimal linear cost per decision under good networks and leaders, optimal quadratic cost per decision under bad networks, and remains always live. AU - Gelashvili, Rati AU - Kokoris Kogias, Eleftherios AU - Spiegelman, Alexander AU - Xiang, Zhuolun ID - 10553 KW - optimal KW - state machine replication KW - fallback KW - asynchrony KW - byzantine faults SN - 9-781-4503-8548-0 T2 - Proceedings of the 2021 ACM Symposium on Principles of Distributed Computing TI - Brief announcement: Be prepared when network goes bad: An asynchronous view-change protocol ER - TY - JOUR AB - The analogy between an equilibrium partition function and the return probability in many-body unitary dynamics has led to the concept of dynamical quantum phase transition (DQPT). DQPTs are defined by nonanalyticities in the return amplitude and are present in many models. In some cases, DQPTs can be related to equilibrium concepts, such as order parameters, yet their universal description is an open question. In this Letter, we provide first steps toward a classification of DQPTs by using a matrix product state description of unitary dynamics in the thermodynamic limit. This allows us to distinguish the two limiting cases of “precession” and “entanglement” DQPTs, which are illustrated using an analytical description in the quantum Ising model. While precession DQPTs are characterized by a large entanglement gap and are semiclassical in their nature, entanglement DQPTs occur near avoided crossings in the entanglement spectrum and can be distinguished by a complex pattern of nonlocal correlations. We demonstrate the existence of precession and entanglement DQPTs beyond Ising models, discuss observables that can distinguish them, and relate their interplay to complex DQPT phenomenology. AU - De Nicola, Stefano AU - Michailidis, Alexios AU - Serbyn, Maksym ID - 9048 IS - 4 JF - Physical Review Letters KW - General Physics and Astronomy SN - 0031-9007 TI - Entanglement view of dynamical quantum phase transitions VL - 126 ER - TY - JOUR AB - The quality control system for messenger RNA (mRNA) is fundamental for cellular activities in eukaryotes. To elucidate the molecular mechanism of 3'-Phosphoinositide-Dependent Protein Kinase1 (PDK1), a master regulator that is essential throughout eukaryotic growth and development, we employed a forward genetic approach to screen for suppressors of the loss-of-function T-DNA insertion double mutant pdk1.1 pdk1.2 in Arabidopsis thaliana. Notably, the severe growth attenuation of pdk1.1 pdk1.2 was rescued by sop21 (suppressor of pdk1.1 pdk1.2), which harbours a loss-of-function mutation in PELOTA1 (PEL1). PEL1 is a homologue of mammalian PELOTA and yeast (Saccharomyces cerevisiae) DOM34p, which each form a heterodimeric complex with the GTPase HBS1 (HSP70 SUBFAMILY B SUPPRESSOR1, also called SUPERKILLER PROTEIN7, SKI7), a protein that is responsible for ribosomal rescue and thereby assures the quality and fidelity of mRNA molecules during translation. Genetic analysis further revealed that a dysfunctional PEL1-HBS1 complex failed to degrade the T-DNA-disrupted PDK1 transcripts, which were truncated but functional, and thus rescued the growth and developmental defects of pdk1.1 pdk1.2. Our studies demonstrated the functionality of a homologous PELOTA-HBS1 complex and identified its essential regulatory role in plants, providing insights into the mechanism of mRNA quality control. AU - Kong, W AU - Tan, Shutang AU - Zhao, Q AU - Lin, DL AU - Xu, ZH AU - Friml, Jiří AU - Xue, HW ID - 9368 IS - 4 JF - Plant Physiology SN - 0032-0889 TI - mRNA surveillance complex PELOTA-HBS1 eegulates phosphoinositide-sependent protein kinase1 and plant growth VL - 186 ER - TY - JOUR AB - A tight frame is the orthogonal projection of some orthonormal basis of Rn onto Rk. We show that a set of vectors is a tight frame if and only if the set of all cross products of these vectors is a tight frame. We reformulate a range of problems on the volume of projections (or sections) of regular polytopes in terms of tight frames and write a first-order necessary condition for local extrema of these problems. As applications, we prove new results for the problem of maximization of the volume of zonotopes. AU - Ivanov, Grigory ID - 10860 IS - 4 JF - Canadian Mathematical Bulletin KW - General Mathematics KW - Tight frame KW - Grassmannian KW - zonotope SN - 0008-4395 TI - Tight frames and related geometric problems VL - 64 ER - TY - JOUR AB - Polar subcellular localization of the PIN exporters of the phytohormone auxin is a key determinant of directional, intercellular auxin transport and thus a central topic of both plant cell and developmental biology. Arabidopsis mutants lacking PID, a kinase that phosphorylates PINs, or the MAB4/MEL proteins of unknown molecular function display PIN polarity defects and phenocopy pin mutants, but mechanistic insights into how these factors convey PIN polarity are missing. Here, by combining protein biochemistry with quantitative live-cell imaging, we demonstrate that PINs, MAB4/MELs, and AGC kinases interact in the same complex at the plasma membrane. MAB4/MELs are recruited to the plasma membrane by the PINs and in concert with the AGC kinases maintain PIN polarity through limiting lateral diffusion-based escape of PINs from the polar domain. The PIN-MAB4/MEL-PID protein complex has self-reinforcing properties thanks to positive feedback between AGC kinase-mediated PIN phosphorylation and MAB4/MEL recruitment. We thus uncover the molecular mechanism by which AGC kinases and MAB4/MEL proteins regulate PIN localization and plant development. AU - Glanc, Matous AU - Van Gelderen, K AU - Hörmayer, Lukas AU - Tan, Shutang AU - Naramoto, S AU - Zhang, Xixi AU - Domjan, David AU - Vcelarova, L AU - Hauschild, Robert AU - Johnson, Alexander J AU - de Koning, E AU - van Dop, M AU - Rademacher, E AU - Janson, S AU - Wei, X AU - Molnar, Gergely AU - Fendrych, Matyas AU - De Rybel, B AU - Offringa, R AU - Friml, Jiří ID - 9290 IS - 9 JF - Current Biology SN - 0960-9822 TI - AGC kinases and MAB4/MEL proteins maintain PIN polarity by limiting lateral diffusion in plant cells VL - 31 ER - TY - JOUR AB - Plants are able to orient their growth according to gravity, which ultimately controls both shoot and root architecture.1 Gravitropism is a dynamic process whereby gravistimulation induces the asymmetric distribution of the plant hormone auxin, leading to asymmetric growth, organ bending, and subsequent reset of auxin distribution back to the original pre-gravistimulation situation.1, 2, 3 Differential auxin accumulation during the gravitropic response depends on the activity of polarly localized PIN-FORMED (PIN) auxin-efflux carriers.1, 2, 3, 4 In particular, the timing of this dynamic response is regulated by PIN2,5,6 but the underlying molecular mechanisms are poorly understood. Here, we show that MEMBRANE ASSOCIATED KINASE REGULATOR2 (MAKR2) controls the pace of the root gravitropic response. We found that MAKR2 is required for the PIN2 asymmetry during gravitropism by acting as a negative regulator of the cell-surface signaling mediated by the receptor-like kinase TRANSMEMBRANE KINASE1 (TMK1).2,7, 8, 9, 10 Furthermore, we show that the MAKR2 inhibitory effect on TMK1 signaling is antagonized by auxin itself, which triggers rapid MAKR2 membrane dissociation in a TMK1-dependent manner. Our findings suggest that the timing of the root gravitropic response is orchestrated by the reversible inhibition of the TMK1 signaling pathway at the cell surface. AU - Marquès-Bueno, MM AU - Armengot, L AU - Noack, LC AU - Bareille, J AU - Rodriguez Solovey, Lesia AU - Platre, MP AU - Bayle, V AU - Liu, M AU - Opdenacker, D AU - Vanneste, S AU - Möller, BK AU - Nimchuk, ZL AU - Beeckman, T AU - Caño-Delgado, AI AU - Friml, Jiří AU - Jaillais, Y ID - 8824 IS - 1 JF - Current Biology SN - 0960-9822 TI - Auxin-regulated reversible inhibition of TMK1 signaling by MAKR2 modulates the dynamics of root gravitropism VL - 31 ER - TY - JOUR AB - Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li–O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li–O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li–O2 reaction mechanism ought to be reconsidered. AU - Prehal, Christian AU - Samojlov, Aleksej AU - Nachtnebel, Manfred AU - Lovicar, Ludek AU - Kriechbaum, Manfred AU - Amenitsch, Heinz AU - Freunberger, Stefan Alexander ID - 9301 IS - 14 JF - Proceedings of the National Academy of Sciences KW - small-angle X-ray scattering KW - oxygen reduction KW - disproportionation KW - Li-air battery SN - 0027-8424 TI - In situ small-angle X-ray scattering reveals solution phase discharge of Li–O2 batteries with weakly solvating electrolytes VL - 118 ER - TY - JOUR AB - Dendritic cells (DCs) are crucial for the priming of naive T cells and the initiation of adaptive immunity. Priming is initiated at a heterologous cell–cell contact, the immunological synapse (IS). While it is established that F-actin dynamics regulates signaling at the T cell side of the contact, little is known about the cytoskeletal contribution on the DC side. Here, we show that the DC actin cytoskeleton is decisive for the formation of a multifocal synaptic structure, which correlates with T cell priming efficiency. DC actin at the IS appears in transient foci that are dynamized by the WAVE regulatory complex (WRC). The absence of the WRC in DCs leads to stabilized contacts with T cells, caused by an increase in ICAM1-integrin–mediated cell–cell adhesion. This results in lower numbers of activated and proliferating T cells, demonstrating an important role for DC actin in the regulation of immune synapse functionality. AU - Leithner, Alexander F AU - Altenburger, LM AU - Hauschild, R AU - Assen, Frank P AU - Rottner, K AU - TEB, Stradal AU - Diz-Muñoz, A AU - Stein, JV AU - Sixt, Michael K ID - 9094 IS - 4 JF - Journal of Cell Biology SN - 0021-9525 TI - Dendritic cell actin dynamics control contact duration and priming efficiency at the immunological synapse VL - 220 ER - TY - JOUR AB - The sensory and cognitive abilities of the mammalian neocortex are underpinned by intricate columnar and laminar circuits formed from an array of diverse neuronal populations. One approach to determining how interactions between these circuit components give rise to complex behavior is to investigate the rules by which cortical circuits are formed and acquire functionality during development. This review summarizes recent research on the development of the neocortex, from genetic determination in neural stem cells through to the dynamic role that specific neuronal populations play in the earliest circuits of neocortex, and how they contribute to emergent function and cognition. While many of these endeavors take advantage of model systems, consideration will also be given to advances in our understanding of activity in nascent human circuits. Such cross-species perspective is imperative when investigating the mechanisms underlying the dysfunction of early neocortical circuits in neurodevelopmental disorders, so that one can identify targets amenable to therapeutic intervention. AU - Hanganu-Opatz, Ileana L. AU - Butt, Simon J. B. AU - Hippenmeyer, Simon AU - De Marco García, Natalia V. AU - Cardin, Jessica A. AU - Voytek, Bradley AU - Muotri, Alysson R. ID - 9073 IS - 5 JF - The Journal of Neuroscience KW - General Neuroscience SN - 0270-6474 TI - The logic of developing neocortical circuits in health and disease VL - 41 ER - TY - JOUR AB - We study the problem of recovering an unknown signal 𝑥𝑥 given measurements obtained from a generalized linear model with a Gaussian sensing matrix. Two popular solutions are based on a linear estimator 𝑥𝑥^L and a spectral estimator 𝑥𝑥^s. The former is a data-dependent linear combination of the columns of the measurement matrix, and its analysis is quite simple. The latter is the principal eigenvector of a data-dependent matrix, and a recent line of work has studied its performance. In this paper, we show how to optimally combine 𝑥𝑥^L and 𝑥𝑥^s. At the heart of our analysis is the exact characterization of the empirical joint distribution of (𝑥𝑥,𝑥𝑥^L,𝑥𝑥^s) in the high-dimensional limit. This allows us to compute the Bayes-optimal combination of 𝑥𝑥^L and 𝑥𝑥^s, given the limiting distribution of the signal 𝑥𝑥. When the distribution of the signal is Gaussian, then the Bayes-optimal combination has the form 𝜃𝑥𝑥^L+𝑥𝑥^s and we derive the optimal combination coefficient. In order to establish the limiting distribution of (𝑥𝑥,𝑥𝑥^L,𝑥𝑥^s), we design and analyze an approximate message passing algorithm whose iterates give 𝑥𝑥^L and approach 𝑥𝑥^s. Numerical simulations demonstrate the improvement of the proposed combination with respect to the two methods considered separately. AU - Mondelli, Marco AU - Thrampoulidis, Christos AU - Venkataramanan, Ramji ID - 10211 JF - Foundations of Computational Mathematics KW - Applied Mathematics KW - Computational Theory and Mathematics KW - Computational Mathematics KW - Analysis SN - 1615-3375 TI - Optimal combination of linear and spectral estimators for generalized linear models ER - TY - JOUR AB - We quantise Whitney’s construction to prove the existence of a triangulation for any C^2 manifold, so that we get an algorithm with explicit bounds. We also give a new elementary proof, which is completely geometric. AU - Boissonnat, Jean-Daniel AU - Kachanovich, Siargey AU - Wintraecken, Mathijs ID - 8940 IS - 1 JF - Discrete & Computational Geometry KW - Theoretical Computer Science KW - Computational Theory and Mathematics KW - Geometry and Topology KW - Discrete Mathematics and Combinatorics SN - 0179-5376 TI - Triangulating submanifolds: An elementary and quantified version of Whitney’s method VL - 66 ER -