Showing papers by "Paul Scherrer Institute published in 2017"

Particle-flow reconstruction and global event description with the CMS detector

Abstract: The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic τ decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8\TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions.

Dynamic surface self-reconstruction is the key of highly active perovskite nano-electrocatalysts for water splitting.

Abstract: The growing need to store increasing amounts of renewable energy has recently triggered substantial R&D efforts towards efficient and stable water electrolysis technologies. The oxygen evolution reaction (OER) occurring at the electrolyser anode is central to the development of a clean, reliable and emission-free hydrogen economy. The development of robust and highly active anode materials for OER is therefore a great challenge and has been the main focus of research. Among potential candidates, perovskites have emerged as promising OER electrocatalysts. In this study, by combining a scalable cutting-edge synthesis method with time-resolved X-ray absorption spectroscopy measurements, we were able to capture the dynamic local electronic and geometric structure during realistic operando conditions for highly active OER perovskite nanocatalysts. Ba0.5Sr0.5Co0.8Fe0.2O3-δ as nano-powder displays unique features that allow a dynamic self-reconstruction of the material's surface during OER, that is, the growth of a self-assembled metal oxy(hydroxide) active layer. Therefore, besides showing outstanding performance at both the laboratory and industrial scale, we provide a fundamental understanding of the operando OER mechanism for highly active perovskite catalysts. This understanding significantly differs from design principles based on ex situ characterization techniques.

Catalyst support effects on hydrogen spillover

Abstract: The mechanism of hydrogen spillover is described using a precisely nanofabricated model system, explaining why it is slower on an aluminum oxide catalyst support than on a titanium oxide catalyst support.

The CMS trigger system

Abstract: This paper describes the CMS trigger system and its performance during Run 1 of the LHC. The trigger system consists of two levels designed to select events of potential physics interest from a GHz (MHz) interaction rate of proton-proton (heavy ion) collisions. The first level of the trigger is implemented in hardware, and selects events containing detector signals consistent with an electron, photon, muon, tau lepton, jet, or missing transverse energy. A programmable menu of up to 128 object-based algorithms is used to select events for subsequent processing. The trigger thresholds are adjusted to the LHC instantaneous luminosity during data taking in order to restrict the output rate to 100 kHz, the upper limit imposed by the CMS readout electronics. The second level, implemented in software, further refines the purity of the output stream, selecting an average rate of 400 Hz for offline event storage. The objectives, strategy and performance of the trigger system during the LHC Run 1 are described.

Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV

Abstract: Improved jet energy scale corrections, based on a data sample corresponding to an integrated luminosity of 19.7 fb^(-1) collected by the CMS experiment in proton-proton collisions at a center-of-mass energy of 8 TeV, are presented. The corrections as a function of pseudorapidity η and transverse momentum p_T are extracted from data and simulated events combining several channels and methods. They account successively for the effects of pileup, uniformity of the detector response, and residual data-simulation jet energy scale differences. Further corrections, depending on the jet flavor and distance parameter (jet size) R, are also presented. The jet energy resolution is measured in data and simulated events and is studied as a function of pileup, jet size, and jet flavor. Typical jet energy resolutions at the central rapidities are 15–20% at 30 GeV, about 10% at 100 GeV, and 5% at 1 TeV. The studies exploit events with dijet topology, as well as photon+jet, Z+jet and multijet events. Several new techniques are used to account for the various sources of jet energy scale corrections, and a full set of uncertainties, and their correlations, are provided. The final uncertainties on the jet energy scale are below 3% across the phase space considered by most analyses (p_T > 30 GeV and 0|η| 30 GeV is reached, when excluding the jet flavor uncertainties, which are provided separately for different jet flavors. A new benchmark for jet energy scale determination at hadron colliders is achieved with 0.32% uncertainty for jets with p_T of the order of 165–330 GeV, and |η| < 0.8.

Selective anaerobic oxidation of methane enables direct synthesis of methanol

Abstract: Direct functionalization of methane in natural gas remains a key challenge. We present a direct stepwise method for converting methane into methanol with high selectivity (~97%) over a copper-containing zeolite, based on partial oxidation with water. The activation in helium at 673 kelvin (K), followed by consecutive catalyst exposures to 7 bars of methane and then water at 473 K, consistently produced 0.204 mole of CH3OH per mole of copper in zeolite. Isotopic labeling confirmed water as the source of oxygen to regenerate the zeolite active centers and renders methanol desorption energetically favorable. On the basis of in situ x-ray absorption spectroscopy, infrared spectroscopy, and density functional theory calculations, we propose a mechanism involving methane oxidation at CuII oxide active centers, followed by CuI reoxidation by water with concurrent formation of hydrogen.

The Direct Catalytic Oxidation of Methane to Methanol-A Critical Assessment.

Abstract: Despite the large number of disparate approaches for the direct selective partial oxidation of methane, none of them has translated into an industrial process. The oxidation of methane to methanol is a difficult, but intriguing and rewarding, task as it has the potential to eliminate the prevalent natural gas flaring by providing novel routes to its valorization. This Review considers the synthesis of methanol and methanol derivatives from methane by homogeneous and heterogeneous pathways. By establishing the severe limitations related to the direct catalytic synthesis of methanol from methane, we highlight the vastly superior performance of systems which produce methanol derivatives or incorporate specific measures, such as the use of multicomponent catalysts to stabilize methanol. We thereby identify methanol protection as being indispensable for future research on homogeneous and heterogeneous catalysis.

Observation of three-component fermions in the topological semimetal molybdenum phosphide

Abstract: In quantum field theory, Lorentz invariance leads to three types of fermion-Dirac, Weyl and Majorana. Although the existence of Weyl and Majorana fermions as elementary particles in high-energy physics is debated, all three types of fermion have been proposed to exist as low-energy, long-wavelength quasiparticle excitations in condensed-matter systems. The existence of Dirac and Weyl fermions in condensed-matter systems has been confirmed experimentally, and that of Majorana fermions is supported by various experiments. However, in condensed-matter systems, fermions in crystals are constrained by the symmetries of the 230 crystal space groups rather than by Lorentz invariance, giving rise to the possibility of finding other types of fermionic excitation that have no counterparts in high-energy physics. Here we use angle-resolved photoemission spectroscopy to demonstrate the existence of a triply degenerate point in the electronic structure of crystalline molybdenum phosphide. Quasiparticle excitations near a triply degenerate point are three-component fermions, beyond the conventional Dirac-Weyl-Majorana classification, which attributes Dirac and Weyl fermions to four- and two-fold degenerate points, respectively. We also observe pairs of Weyl points in the bulk electronic structure of the crystal that coexist with the three-component fermions. This material thus represents a platform for studying the interplay between different types of fermions. Our experimental discovery opens up a way of exploring the new physics of unconventional fermions in condensed-matter systems.

Diagnosis and treatment of brain metastases from solid tumors: guidelines from the European Association of Neuro-Oncology (EANO).

Abstract: The management of patients with brain metastases has become a major issue due to the increasing frequency and complexity of the diagnostic and therapeutic approaches. In 2014, the European Association of Neuro-Oncology (EANO) created a multidisciplinary Task Force to draw evidence-based guidelines for patients with brain metastases from solid tumors. Here, we present these guidelines, which provide a consensus review of evidence and recommendations for diagnosis by neuroimaging and neuropathology, staging, prognostic factors, and different treatment options. Specifically, we addressed options such as surgery, stereotactic radiosurgery/stereotactic fractionated radiotherapy, whole-brain radiotherapy, chemotherapy and targeted therapy (with particular attention to brain metastases from non-small cell lung cancer, melanoma and breast and renal cancer), and supportive care.

Review of Urban Secondary Organic Aerosol Formation from Gasoline and Diesel Motor Vehicle Emissions

Abstract: Secondary organic aerosol (SOA) is formed from the atmospheric oxidation of gas-phase organic compounds leading to the formation of particle mass. Gasoline- and diesel-powered motor vehicles, both on/off-road, are important sources of SOA precursors. They emit complex mixtures of gas-phase organic compounds that vary in volatility and molecular structure—factors that influence their contributions to urban SOA. However, the relative importance of each vehicle type with respect to SOA formation remains unclear due to conflicting evidence from recent laboratory, field, and modeling studies. Both are likely important, with evolving contributions that vary with location and over short time scales. This review summarizes evidence, research needs, and discrepancies between top-down and bottom-up approaches used to estimate SOA from motor vehicles, focusing on inconsistencies between molecular-level understanding and regional observations. The effect of emission controls (e.g., exhaust aftertreatment technologies...

Simultaneous explanation of R(D (∗)) and b→sμ + μ −: the last scalar leptoquarks standing

Abstract: Over the past years, experiments accumulated intriguing hints for new physics (NP) in flavor observables, namely in the anomalous magnetic moment of the muon (a μ ), in R(D (∗)) = Br(B → D (∗) τ ν)/Br(B → D (∗) lν) and in b → sμ + μ − transitions, which are all at the 3 − 4 σ level In this article we point out that one can explain the R(D (∗)) anomaly using two scalar leptoquarks (LQs) with the same mass and coupling to fermions related via a discrete symmetry: an SU(2) L singlet and an SU(2) L triplet, both with hypercharge Y = −2/3 In this way, potentially dangerous contributions to b → sνν are avoided and non-CKM suppressed effects in R(D (∗)) can be generated This allows for smaller overall couplings to fermions weakening the direct LHC bounds In our model, R(D (∗)) is directly correlated to b → sτ + τ − transitions where an enhancement by orders of magnitude compared to the standard model (SM) is predicted, such that these decay modes are in the reach of LHCb and BELLE II Furthermore, one can also naturally explain the b → sμ + μ − anomalies (including R(K)) by a C 9 = −C 10 like contribution without spoiling μ − e universality in charged current decays In this case sizable effects in b → sτ μ transitions are predicted which are again well within the experimental reach One can even address the longstanding anomaly in a μ , generating a sizable decay rate for τ → μγ However, we find that out of the three anomalies R(D (∗)), b → sμ + μ − and a μ only two (but any two) can be explained simultaneously We point out that a very similar phenomenology can be achieved using a vector leptoquark SU(2) L singlet with hypercharge 2/3 In this case, no tuning between couplings is necessary, but the model is non-renormalizable

High-resolution non-destructive three-dimensional imaging of integrated circuits

Abstract: A recently developed computational imaging technique, X-ray ptychographic tomography, is used to study integrated circuits, and a 3D image of a processor chip with a resolution of 14.6 nm is obtained. As computer chips have become increasingly crammed with nanometre-scale devices and circuitry, new microscopy techniques that can resolve the smallest features are required to enable chip design and inspection. X-ray imaging is uniquely suited for non-destructive, high-resolution imaging and Mirko Holler et al. make use of a recently developed computational imaging technique, X-ray ptychography, to generate high-resolution three-dimensional images of integrated circuits. They test X-ray ptychography on a circuit with known features, and then apply it to an Intel processor chip manufactured in the 22-nanometre technology, obtaining detailed three-dimensional maps of the devices with a resolution down to 14.6 nanometres. This technique could be used to assist quality control during chip production. Modern nanoelectronics1,2 has advanced to a point at which it is impossible to image entire devices and their interconnections non-destructively because of their small feature sizes and the complex three-dimensional structures resulting from their integration on a chip. This metrology gap implies a lack of direct feedback between design and manufacturing processes, and hampers quality control during production, shipment and use. Here we demonstrate that X-ray ptychography3,4—a high-resolution coherent diffractive imaging technique—can create three-dimensional images of integrated circuits of known and unknown designs with a lateral resolution in all directions down to 14.6 nanometres. We obtained detailed device geometries and corresponding elemental maps, and show how the devices are integrated with each other to form the chip. Our experiments represent a major advance in chip inspection and reverse engineering over the traditional destructive electron microscopy and ion milling techniques5,6,7. Foreseeable developments in X-ray sources8, optics9 and detectors10, as well as adoption of an instrument geometry11 optimized for planar rather than cylindrical samples, could lead to a thousand-fold increase in efficiency, with concomitant reductions in scan times and voxel sizes.

Critical Review—Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development

Abstract: Although polymer electrolyte water electrolyzers (PEWEs) have been used in small-scale (kW to tens of kW range) applications for several decades, PEWE technology for hydrogen production in energy applications (power-to-gas, power-to-fuel, etc.) requires significant improvements in the technology to address the challenges associated with cost, performance and durability. Systems with power of hundreds of kW or even MWs, corresponding to hydrogen production rates of around 10 to 20 kg/h, have started to appear in the past 5 years. The thin (∼0.2 mm) polymer electrolyte in the PEWE with low ohmic resistance, compared to the alkaline cell with liquid electrolyte, allows operation at high current densities of 1–3 A/cm2 and high differential pressure. This article, after an introductory overview of the operating principles of PEWE and state-of-the-art, discusses the state of understanding of key phenomena determining and limiting performance, durability, and commercial readiness, identifies important ‘gaps’ in understanding and essential development needs to bring PEWE science & engineering forward to prosper in the energy market as one of its future backbone technologies. For this to be successful, science, engineering, and process development as well as business and market development need to go hand in hand. © The Author(s) 2017. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.1441704jes] All rights reserved.

Charged-particle nuclear modification factors in PbPb and pPb collisions at √sNN=5.02 TeV

Abstract: we acknowledge the enduring support for the construction and operation of the LHC and the CMS detector provided by the following funding agencies: BMWFW and FWF (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China); COLCIENCIAS (Colombia); MSES and CSF (Croatia); RPF (Cyprus); SENESCYT (Ecuador); MoER, ERC IUT and ERDF (Estonia); Academy of Finland, MEC, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF (Germany); GSRT (Greece); OTKA and NIH (Hungary); DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); MSIP and NRF (Republic of Korea); LAS (Lithuania); MOE and UM (Malaysia); BUAP, CINVESTAV, CONACYT, LNS, SEP, and UASLP-FAI (Mexico); MBIE (New Zealand); PAEC (Pakistan); MSHE and NSC (Poland); FCT (Portugal); JINR (Dubna); MON, RosAtom, RAS and RFBR (Russia); MESTD (Serbia); SEIDI and CPAN (Spain); Swiss Funding Agencies (Switzerland); MST (Taipei); ThEPCenter, IPST, STAR and NSTDA (Thailand); TUBITAK and TAEK (Turkey); NASU and SFFR (Ukraine); STFC (United Kingdom); DOE and NSF (U.S.A.).

Measurements of properties of the Higgs boson decaying into the four-lepton final state in pp collisions at √s=13 TeV

Abstract: Properties of the Higgs boson are measured in the H → ZZ → 4l (l = e, μ) decay channel. A data sample of proton-proton collisions at $ \sqrt{s}=13 $ TeV, collected with the CMS detector at the LHC and corresponding to an integrated luminosity of 35.9 fb$^{−1}$ is used. The signal strength modifier μ, defined as the ratio of the observed Higgs boson rate in the H → ZZ → 4l decay channel to the standard model expectation, is measured to be μ = 1.05$_{− 0.17}^{+ 0.19}$ at m$_{H}$ = 125.09 GeV, the combined ATLAS and CMS measurement of the Higgs boson mass. The signal strength modifiers for the individual Higgs boson production modes are also measured. The cross section in the fiducial phase space defined by the requirements on lepton kinematics and event topology is measured to be 2. 92$_{− 0.44}^{+ 0.48}$ (stat)$_{− 0.24}^{+ 0.28}$ (syst)fb, which is compatible with the standard model prediction of 2.76 ± 0.14 fb. Differential cross sections are reported as a function of the transverse momentum of the Higgs boson, the number of associated jets, and the transverse momentum of the leading associated jet. The Higgs boson mass is measured to be m$_{H}$ = 125.26 ± 0.21 GeV and the width is constrained using the on-shell invariant mass distribution to be Γ$_{H}$ < 1.10 GeV, at 95% confidence level.

Direct Conversion of Methane to Methanol under Mild Conditions over Cu-Zeolites and beyond

Abstract: ConspectusIn the recent years methane has become increasingly abundant. However, transportation costs are high and methane recovered as side product is often flared rather than valorized. The chemical utilization of methane is highly challenging and currently mainly based on the cost-intensive production of synthesis gas and its conversion. Alternative routes have been discovered in academia, though high temperatures are mostly required. However, the direct conversion of methane to methanol is an exception. It can already be carried out at comparably low temperatures. It is challenging that methanol is more prone to oxidation than methane, which makes high selectivities at moderate conversions difficult to reach. Decades of research for the direct reaction of methane and oxygen did not yield a satisfactory solution for the direct partial oxidation toward methanol. When changing the oxidant from oxygen to hydrogen peroxide, high selectivities can be reached at rather low conversions, but the cost of hydrog...

Gapless Spin-Liquid Ground State in the S = 1 / 2 Kagome Antiferromagnet

Abstract: The defining problem in frustrated quantum magnetism, the ground state of the nearest-neighbor S=1/2 antiferromagnetic Heisenberg model on the kagome lattice, has defied all theoretical and numerical methods employed to date. We apply the formalism of tensor-network states, specifically the method of projected entangled simplex states, which combines infinite system size with a correct accounting for multipartite entanglement. By studying the ground-state energy, the finite magnetic order appearing at finite tensor bond dimensions, and the effects of a next-nearest-neighbor coupling, we demonstrate that the ground state is a gapless spin liquid. We discuss the comparison with other numerical studies and the physical interpretation of this result.

On-Surface Synthesis and Characterization of 9-Atom Wide Armchair Graphene Nanoribbons

Abstract: The bottom-up approach to synthesize graphene nanoribbons strives not only to introduce a band gap into the electronic structure of graphene but also to accurately tune its value by designing both the width and edge structure of the ribbons with atomic precision. We report the synthesis of an armchair graphene nanoribbon with a width of nine carbon atoms on Au(111) through surface-assisted aryl–aryl coupling and subsequent cyclodehydrogenation of a properly chosen molecular precursor. By combining high-resolution atomic force microscopy, scanning tunneling microscopy, and Raman spectroscopy, we demonstrate that the atomic structure of the fabricated ribbons is exactly as designed. Angle-resolved photoemission spectroscopy and Fourier-transformed scanning tunneling spectroscopy reveal an electronic band gap of 1.4 eV and effective masses of ≈0.1 me for both electrons and holes, constituting a substantial improvement over previous efforts toward the development of transistor applications. We use ab initio c...

A global multiproxy database for temperature reconstructions of the Common Era

Abstract: Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.

Spatially and time-resolved magnetization dynamics driven by spin-orbit torques.

Abstract: Time-resolved X-ray microscopy reveals the mechanism and speed of current-induced magnetization switching of Co/Pt dots under the combined effect of spin-orbit torques and Dzyaloshinskii–Moriya interaction.

Direct observation of lithium polysulfides in lithium–sulfur batteries using operando X-ray diffraction

Abstract: In the on going quest towards lithium-battery chemistries beyond the lithium-ion technology, the lithium–sulfur system is emerging as one of the most promising candidates. The major outstanding challenge on the route to commercialization is controlling the so-called polysulfide shuttle, which is responsible for the poor cycling efficiency of the current generation of lithium–sulfur batteries. However, the mechanistic understanding of the reactions underlying the polysulfide shuttle is still incomplete. Here we report the direct observation of lithium polysulfides in a lithium–sulfur cell during operation by means of operando X-ray diffraction. We identify signatures of polysulfides adsorbed on the surface of a glass-fibre separator and monitor their evolution during cycling. Furthermore, we demonstrate that the adsorption of the polysulfides onto SiO2 can be harnessed for buffering the polysulfide redox shuttle. The use of fumed silica as an electrolyte additive therefore significantly improves the specific charge and Coulombic efficiency of lithium–sulfur batteries. The presence of polysulfides in Li–S batteries is highly relevant to the battery performance, but their formation and evolution during battery operation are not well understood. Here the authors design an operando X-ray diffraction experiment to reveal their reaction mechanisms.

Coherent Nanotwins and Dynamic Disorder in Cesium Lead Halide Perovskite Nanocrystals

Abstract: Crystal defects in highy luminescent colloidal nanocrystals (NCs) of CsPbX3 perovskites (X = Cl, Br, I) are investigated. Here, using X-ray total scattering techniques and the Debye scattering equation (DSE), we provide evidence that the local structure of these NCs always exhibits orthorhombic tilting of PbX6 octahedra within locally ordered subdomains. These subdomains are hinged through a two-/three-dimensional (2D/3D) network of twin boundaries through which the coherent arrangement of the Pb ions throughout the whole NC is preserved. The density of these twin boundaries determines the size of the subdomains and results in an apparent higher-symmetry structure on average in the high-temperature modification. Dynamic cooperative rotations of PbX6 octahedra are likely at work at the twin boundaries, causing the rearrangement of the 2D or 3D network, particularly effective in the pseudocubic phases. An orthorhombic, 3D γ-phase, isostructural to that of CsPbBr3 is found here in as-synthesized CsPbI3 NCs.

Three-dimensional magnetization structures revealed with X-ray vector nanotomography

Abstract: Techniques exist for imaging the magnetization patterns of magnetic thin films and at the surfaces of magnets, but here hard-X-ray tomography is used to image the three-dimensional magnetic structure within a micrometre-sized magnet in the vicinity of Bloch points. Techniques have long existed for imaging the two-dimensional magnetization patterns of thin-film magnets, but the three-dimensional complexities of magnetization structure within the body of a magnet is not so amenable to direct investigation. Claire Donnelly et al. have made substantial progress in lifting this veil by harnessing hard-X-ray tomography to determine the inner magnetic structure of micrometre-sized magnets. The properties of current X-ray sources limit the spatial resolution to about 100 nanometres, but it is anticipated that future instrumental developments could greatly improve on this. In soft ferromagnetic materials, the smoothly varying magnetization leads to the formation of fundamental patterns such as domains, vortices and domain walls1. These have been studied extensively in thin films of thicknesses up to around 200 nanometres, in which the magnetization is accessible with current transmission imaging methods that make use of electrons or soft X-rays. In thicker samples, however, in which the magnetization structure varies throughout the thickness and is intrinsically three dimensional, determining the complex magnetic structure directly still represents a challenge1,3. We have developed hard-X-ray vector nanotomography with which to determine the three-dimensional magnetic configuration at the nanoscale within micrometre-sized samples. We imaged the structure of the magnetization within a soft magnetic pillar of diameter 5 micrometres with a spatial resolution of 100 nanometres and, within the bulk, observed a complex magnetic configuration that consists of vortices and antivortices that form cross-tie walls and vortex walls along intersecting planes. At the intersections of these structures, magnetic singularities—Bloch points—occur. These were predicted more than fifty years ago4 but have so far not been directly observed. Here we image the three-dimensional magnetic structure in the vicinity of the Bloch points, which until now has been accessible only through micromagnetic simulations, and identify two possible magnetization configurations: a circulating magnetization structure5 and a twisted state that appears to correspond to an ‘anti-Bloch point’. Our imaging method enables the nanoscale study of topological magnetic structures6 in systems with sizes of the order of tens of micrometres. Knowledge of internal nanomagnetic textures is critical for understanding macroscopic magnetic properties and for designing bulk magnets for technological applications7.

IrO2-TiO2: A High-Surface-Area, Active, and Stable Electrocatalyst for the Oxygen Evolution Reaction

Abstract: The utilization and development of efficient water electrolyzers for hydrogen production is currently limited due to the sluggish kinetics of the anodic process—the oxygen evolution reaction (OER). Moreover, state of the art OER catalysts contain high amounts of expensive and low-abundance noble metals such as Ru and Ir, limiting their large-scale industrial utilization. Therefore, the development of low-cost, highly active, and stable OER catalysts is a key requirement toward the implementation of a hydrogen-based economy. We have developed a synthetic approach to high-surface-area chlorine-free iridium oxide nanoparticles dispersed in titania (IrO2-TiO2), which is a highly active and stable OER catalyst in acidic media. IrO2-TiO2 was prepared in one step in molten NaNO3 (Adams fusion method) and consists of ca. 1–2 nm IrO2 particles distributed in a matrix of titania nanoparticles with an overall surface area of 245 m2 g–1. This material contains 40 molM % of iridium and demonstrates improved OER activi...

Gapless Spin Excitations in the Field-Induced Quantum Spin Liquid Phase of α − RuCl 3

Abstract: $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ is a leading candidate material for the observation of physics related to the Kitaev quantum spin liquid (QSL). By combined susceptibility, specific-heat, and nuclear-magnetic-resonance measurements, we demonstrate that $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ undergoes a quantum phase transition to a QSL in a magnetic field of 7.5 T applied in the $ab$ plane. We show further that this high-field QSL phase has gapless spin excitations over a field range up to 16 T. This highly unconventional result, unknown in either Heisenberg or Kitaev magnets, offers insight essential to establishing the physics of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$.

Current-driven dynamics and inhibition of the skyrmion Hall effect of ferrimagnetic skyrmions in GdFeCo films

Abstract: Magnetic skyrmions are swirling magnetic textures with novel characteristics suitable for future spintronic and topological applications. Recent studies confirmed the room-temperature stabilization of skyrmions in ultrathin ferromagnets. However, such ferromagnetic skyrmions show undesirable topological effect, the skyrmion Hall effect, which leads to their current-driven motion towards device edges, where skyrmions could easily be annihilated by topographic defects. Recent theoretical studies have predicted enhanced current-driven behaviour for antiferromagnetically exchange-coupled skyrmions. Here we present the stabilization of these skyrmions and their current-driven dynamics in ferrimagnetic GdFeCo films. By utilizing element-specific X-ray imaging, we find that the skyrmions in the Gd and FeCo sublayers are antiferromagnetically exchange-coupled. We further confirm that ferrimagnetic skyrmions can move at a velocity of ~50 m s-1 with reduced skyrmion Hall angle, {\theta}SkHE ~20°. Our findings open the door to ferrimagnetic and antiferromagnetic skyrmionics while providing key experimental evidences of recent theoretical studies.

Discovery of Lorentz-violating type II Weyl fermions in LaAlGe

Abstract: In quantum field theory, Weyl fermions are relativistic particles that travel at the speed of light and strictly obey the celebrated Lorentz symmetry. Their low-energy condensed matter analogs are Weyl semimetals, which are conductors whose electronic excitations mimic the Weyl fermion equation of motion. Although the traditional (type I) emergent Weyl fermions observed in TaAs still approximately respect Lorentz symmetry, recently, the so-called type II Weyl semimetal has been proposed, where the emergent Weyl quasiparticles break the Lorentz symmetry so strongly that they cannot be smoothly connected to Lorentz symmetric Weyl particles. Despite some evidence of nontrivial surface states, the direct observation of the type II bulk Weyl fermions remains elusive. We present the direct observation of the type II Weyl fermions in crystalline solid lanthanum aluminum germanide (LaAlGe) based on our photoemission data alone, without reliance on band structure calculations. Moreover, our systematic data agree with the theoretical calculations, providing further support on our experimental results.

Searches for invisible decays of the Higgs boson in pp collisions at √s = 7, 8, and 13 TeV

Abstract: Searches for invisible decays of the Higgs boson are presented. The data collected with the CMS detector at the LHC correspond to integrated luminosities of 5.1, 19.7, and 2.3 fb−1 at centre-of-mass energies of 7, 8, and 13 TeV, respectively. The search channels target Higgs boson production via gluon fusion, vector boson fusion, and in association with a vector boson. Upper limits are placed on the branching fraction of the Higgs boson decay to invisible particles, as a function of the assumed production cross sections. The combination of all channels, assuming standard model production, yields an observed (expected) upper limit on the invisible branching fraction of 0.24 (0.23) at the 95% confidence level. The results are also interpreted in the context of Higgs-portal dark matter models.

An interdisciplinary review of energy storage for communities: Challenges and perspectives

Abstract: Given the increasing penetration of renewable energy technologies as distributed generation embedded in the consumption centres, there is growing interest in energy storage systems located very close to consumers. These systems allow to increase the amount of renewable energy generation consumed locally, they provide opportunities for demand-side management and help to decarbonise the electricity, heating and transport sectors. In this paper, the authors present an interdisciplinary review of community energy storage (CES) with a focus on its potential role and challenges as a key element within the wider energy system. The discussion includes: the whole spectrum of applications and technologies with a strong emphasis on end user applications; techno-economic, environmental and social assessments of CES; and an outlook on CES from the customer, utility company and policy-maker perspectives. Currently, in general only traditional thermal storage with water tanks is economically viable. However, CES is expected to offer new opportunities for the energy transition since the community scale introduces several advantages for electrochemical technologies such as batteries. Technical and economic benefits over energy storage in single dwellings are driven by enhanced performance due to less spiky community demand profile and economies of scale respectively. In addition, CES brings new opportunities for citizen participation within communities and helps to increase awareness of energy consumption and environmental impacts.