Paul Scherrer Institute

About: Paul Scherrer Institute is a facility organization based out in Villigen, Switzerland. It is known for research contribution in the topics: Neutron & Large Hadron Collider. The organization has 9248 authors who have published 23984 publications receiving 890129 citations. The organization is also known as: PSI.

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.

X-ray emission from T Tauri stars and the role of accretion: inferences from the XMM-Newton extended survey of the Taurus molecular cloud

Abstract: Context. T Tau stars display di erent X-ray properties depending on whether they are accreting (classical T Tau stars; CTTS) or not (weak-line T Tau stars; WTTS). X-ray properties may provide insight into the accretion process between disk and stellar surface. Aims. We use data from the XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST) to study di erences in X-ray properties between CTTS and WTTS. Methods. XEST data are used to perform correlation and regression analysis between X-ray parameters and stellar properties. Results. We confirm the existence of a X-ray luminosity (LX) vs. mass (M) relation, LX/ M 1:69 0:11 , but this relation is a consequence of X-ray saturation and a mass vs. bolometric luminosity (L ) relation for the TTS with an average age of 2.4 Myr. X-ray saturation indicates LX= constL , although the constant is di erent for the two subsamples: const= 10 3:73 0:05 for CTTS and const= 10 3:39 0:06 for WTTS. Given a similar L distribution of both samples, the X-ray luminosity function also reflects a real X-ray deficiency in CTTS, by a factor of 2 compared to WTTS. The average electron temperatures Tav are correlated with LX in WTTS but not in CTTS; CTTS sources are on average hotter than WTTS sources. At best marginal dependencies are found between X-ray properties and mass accretion rates or age. Conclusions. The most fundamental properties are the two saturation laws, indicating suppressed LX for CTTS. We speculate that some of the accreting material in CTTS is cooling active regions to temperatures that may not significantly emit in the X-ray band, and if they do, high-resolution spectroscopy may be required to identify lines formed in such plasma, while CCD cameras do not detect these components. The similarity of the LX vs. Tav dependencies in WTTS and main-sequence stars as well as their similar X-ray saturation laws suggests similar physical processes for the hot plasma, i.e., heating and radiation of a magnetic corona.

Characterization of Layered Lithium Nickel Manganese Oxides Synthesized by a Novel Oxidative Coprecipitation Method and Their Electrochemical Performance as Lithium Insertion Electrode Materials

Abstract: Lithium nickel manganese oxides, LiNi 1-y Mn y O 2+δ , (0 ≤ y ≤ 05) were prepared via a new solution technique The corresponding mixed nickel manganese hydroxide precursors were synthesized in an oxidative coprecipitation method Subsequent calcination in the presence of LiOH leads to crystalline products with a partially disordered layered-type α-NaFeO 2 structure X-ray photoelectron spectroscopic analysis has indicated a strong enrichment of lithium at the surface The electrochemical performance of these materials as positive electrodes in lithium-ion batteries was evaluated as a function of the calcination temperature and manganese content A calcination temperature of 700°C leads to the best cycling stability At this temperature, a sufficiently high degree of crystallinity was achieved, having a strong influence on the cycling stability of these 4 V materials The specific charge and cycling stability obtained for the solution-prepared pure lithium nickel oxide, LiNiO 2 , was low, but was significantly enhanced by replacing some nickel with manganese With increasing manganese content, the specific charge increased to about 170 mAh g -1 for materials with a Ni:Mn ratio of about 1:1 Ex situ magnetic susceptibility measurements proved that during lithium deinsertion, the trivalent manganese is preferentially oxidized, and seems to be the more reactive redox center in these oxides

Dimples on nanocrystalline fracture surfaces as evidence for shear plane formation.

Abstract: Tensile experiments of fully dense nanocrystalline structures with a mean grain size of less than 100 nanometers demonstrate a considerable increase in hardness but a remarkable drop in elongation-to-failure, indicating brittle behavior. However, dimple structures are often observed at the fracture surface, indicating some type of ductile fracture mechanism. Guided by large-scale atomistic simulations, we propose that these dimple structures result from local shear planes formed around clustered grains that, because of their particular misorientation, cannot participate in the grain boundary accommodation processes necessary to sustain plastic deformation. This raises the expectation that general high-angle grain boundaries are necessary for good ductility.

Review: Photochemical and Thermochemical Production of Solar Fuels from H2O and CO2 Using Metal Oxide Catalysts

Abstract: Metal oxides are reviewed as catalysts to convert H2O and CO2 to fuels using solar energy. For photochemical conversion, TiO2 has been found to be the most stable and useful oxide material, but it is currently limited by its large bandgap and a mismatch between its conduction band and the redox couples for water splitting and CO2 reduction. A theoretical framework has been utilized to understand the basic thermodynamics and energetics in photochemical energy conversion systems. This is applied to model systems comprised of Ag2O and AgCl to examine why the former reacts thermochemically in air, while the latter reacts photochemically. For thermochemical conversion, zinc-, ceria-, and ferrite-based redox cycles are examined and examples of high-temperature solar reactors driven by concentrated solar radiation are presented. For CO2 splitting, theoretical solar-to-fuel energy conversion efficiencies can be up to 26.8% for photochemical systems, and can exceed 30% for thermochemical systems, provided that sen...