Measurement of isolated-photon pair production in pp collisions at sqrts=7 TeV with the ATLAS detector

The ATLAS experiment at the LHC has measured the production cross section of events with two isolated photons in the final state, in proton-proton collisions at root s = 7 TeV. The full data set collected in 2011, corresponding to an integrated luminosity of 4.9 fb(-1), is used. The amount of background, from hadronic jets and isolated electrons, is estimated with data-driven techniques and subtracted. The total cross section, for two isolated photons with transverse energies above 25 GeV and 22 GeV respectively, in the acceptance of the electromagnetic calorimeter (vertical bar eta vertical bar < 1.37 and 1.52 < vertical bar eta vertical bar 2.37) and with an angular separation Delta R > 0.4, is 44.0(-4.2)(+3.2) pb. The differential cross sections as a function of the di-photon invariant mass, transverse momentum, azimuthal separation, and cosine of the polar angle of the largest transverse energy photon in the Collins-Soper di-photon rest frame are also measured. The results are compared to the prediction of leading-order parton-shower and next-to-leading-order and next-to-next-to-leading-order parton-level generators.

Limits on Spin-Dependent WIMP-Nucleon Cross Sections from 225 Live Days of XENON100 Data

We present new experimental constraints on the elastic, spin-dependent WIMP-nucleon cross section using recent data from the XENON100 experiment, operated in the Laboratori Nazionali del Gran Sasso in Italy. An analysis of 224.6 live days x 34 kg of exposure acquired during 2011 and 2012 revealed no excess signal due to axial-vector WIMP interactions with Xe-129 and Xe-131 nuclei. This leads to the most stringent upper limits on WIMP-neutron cross sections for WIMP masses above 6 GeV/c(2), with a minimum cross section of 3.5 x 10(-40) cm(2) at a WIMP mass of 45 GeV/c(2), at 90% confidence level.

Measurements of jet vetoes and azimuthal decorrelations in dijet events produced in pp collisions at √s = 7 TeV using the ATLAS detector

Additional jet activity in dijet events is measured using pp collisions at ATLAS at a centre-of-mass energy of 7 TeV, for jets reconstructed using the anti-kt algorithm with radius parameter R=0.6. This is done using variables such as the fraction of dijet events without an additional jet in the rapidity interval bounded by the dijet subsystem and correlations between the azimuthal angles of the dijets. They are presented, both with and without a veto on additional jet activity in the rapidity interval, as a function of the mean transverse momentum of the dijets and of the rapidity interval size. The double differential dijet cross section is also measured as a function of the interval size and the azimuthal angle between the dijets. These variables probe differences in the approach to resummation of large logarithms when performing QCD calculations. The data are compared to POWHEG, interfaced to the PYTHIA 8 and HERWIG parton shower generators, as well as to HEJ with and without interfacing it to the ARIADNE parton shower generator. None of the theoretical predictions agree with the data across the full phase-space considered; however, POWHEG+PYTHIA 8 and HEJ+ARIADNE are found to provide the best agreement with the data.These measurements use the full data sample collected with the ATLAS detector in 7 TeV pp collisions at the LHC and correspond to integrated luminosities of 36.1 pb−1 and 4.5 fb−1 for data collected during 2010 and 2011 respectively.

Measurement of the production of a W boson in association with a charm quark in pp collisions at sqrts = 7 TeV with the ATLAS detector

The production of a W boson in association with a single charm quark is studied using 4.6 fb−1 of pp collision data at ps = 7TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96+0.26−0.30 at Q2 = 1.9 GeV2, which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio ơ(W++c)/ơ(W−+c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s–s quark asymmetry.

Physiological responses of the marine diatom Thalassiosira pseudonana to increased pCO2 and seawater acidity

We studied the effects of elevated CO2 concentration and seawater acidity on inorganic carbon acquisition, photoinhibition and photoprotection as well as growth and respiration in the marine diatom Thalassiosira pseudonana. After having grown under the elevated CO2 level (1000 µatm, pH 7.83) at sub-saturating photosynthetically active radiation (PAR, 75 µmol photons/m**2/s) for 20 generations, photosynthesis and dark respiration of the alga increased by 25% (14.69 ± 2.55 fmol C/cell/h) and by 35% (4.42 ± 0.98 fmol O2/cell/h), respectively, compared to that grown under the ambient CO2 level (390 µatm, pH 8.16), leading to insignificant effects on growth (1.09 ± 0.08 (1/d))v 1.04 ± 0.07 (1/d)). The photosynthetic affinity for CO2 was lowered in the high-CO2 grown cells, reflecting a down-regulation of the CO2 concentrating mechanism (CCM). When exposed to an excessively high level of PAR, photochemical and non-photochemical quenching responded similarly in the low- and high-CO2 grown cells, reflecting that photoinhibition was not influenced by the enriched level of CO2. In T. pseudonana, it appeared that the energy saved due to the down-regulated CCM did not contribute to any additional light stress as previously found in another diatom Phaeodactylum tricornutum, indicating differential physiological responses to ocean acidification between these two diatom species.

Simplified longitudinal seismic analysis of buried tunnels

In this paper an analytical static approach to analyse buried tunnels under seismic surface waves (Rayleigh and Love waves), propagating parallel to the tunnels axis, is provided. In the proposed method, the tunnel is considered as a beam on elastic foundation by using a Winkler model to represent the subgrade reaction and the soil-structure interaction. The seismic load is imposed by giving at the base of the soil springs a determined configuration corresponding to the free-field motion. From the solution of the differential governing equations of the problem, results are obtained in form of relative displacements between points of tunnel, and therefore the seismic bending moments and shearing forces, acting on the tunnel cross section, can be computed.

Influencia del viento transversal en sistemas ferroviarios = Cross-wind effects on railway infrastructure

El viento, como factor medio-ambiental, ha sido objeto de numerosos estudios por los efectos que induce tanto en vehículos como en estructuras. Dentro del ámbito ferroviario, las cargas aerodinámicas debidas a la acción del viento transversal pueden poner en compromiso la seguridad de los vehículos en circulación, pudiendo llegar a ocasionar el vuelco del mismo. Incluso el sistema de cables encargado de realizar el suministro eléctrico necesario para la tracción del tren, conocido como catenaria, es sensible a la acción del viento. De hecho, al igual que ocurre en ciertas estructuras de cables, la interacción entre las fuerzas aerodinámicas no estacionarias y la catenaria puede ocasionar la aparición de oscilaciones de gran amplitud debido al fenómeno de galope. Una forma sencilla de reducir los efectos no deseados de la acción del viento, es la instalación de barreras cortavientos aguas arriba de la zona que se desea proteger. La instalación de estos dispositivos, reduce la velocidad en la estela generada, pero también modifica las propiedades del flujo dentro de la misma. Esta alteración de las condiciones del flujo puede contribuir a la aparición del fenómeno de galope en estructuras caracterizadas por su gran flexibilidad, como la catenaria ferroviaria. Estos dos efectos contrapuestos hacen evidente la importancia de mantener cierta visión global del efecto introducido por la instalación de barreras cortavientos en la plataforma ferroviaria. A lo largo de este documento, se evalúa desde un enfoque multidisciplinar el efecto inducido por las barreras cortavientos en varios subsistemas ferroviarios. Por un lado se analizan las mejoras en la estabilidad lateral del vehículo mediante una serie de ensayos en túnel de viento. La medición de la distribución de presiones en la superficie de un modelo bidimensional de vehículo ferroviario proporciona una buena estimación del nivel de protección que se consigue en función de la altura de una barrera cortavientos. Por otra parte, se analiza la influencia del mismo juego de barreras cortavientos en las características del flujo situado sobre la plataforma ferroviaria, mediante la utilización de anemometría de hilo caliente (HWA) y velocimetría de imágenes de párticulas (PIV). En particular se centra la atención en las características en la posición correspondiente a los hilos conductores de la catenaria. En la última parte del documento, se realiza un análisis simplificado de la aparición oscilaciones en la catenaria, por el efecto de la inestabilidad de galope. La información obtenida sobre las características del flujo se combinan con las propiedades aerodinámicas del hilo de contacto, obtenidas en mediante una serie de ensayos en túnel de viento. De esta manera se realiza una evaluación del riesgo a la aparición de este tipo de inestabilidad aeroeslástica aplicada a una catenaria ferroviaria situada sobre un viaducto tipo. ABSTRACT Wind as an environmental factor may induce undesirable effects on vehicles and structures. The analysis of those effects has caught the attention of several researchers. Concerning the railway system, cross-wind induces aerodynamic loads on rolling stock that may increase the overturning risk of the vehicle, threatening its safe operation. Even the cable system responsible to provide the electric current required for the train traction, known as the railway overhead or catenary, is sensitive to the wind action. In fact, the interaction between the unsteady aerodynamic forces and the railway overhead may trigger the development of undamped oscillations due to galloping phenomena. The inclusion of windbreaks upstream the area that needs wind protection is a simple mean to palliate the undesirable effects caused by the wind action. Although the presence of this wind protection devices reduces the wind speed downstream, they also modify the flow properties inside their wake. This modification on the flow characteristics may ease the apparition of the galloping phenomena on flexible structures, such as the railway overhead. This two opposite effects require to maintain a global perspective on the analysis of the influence of the windbreak presence. In the present document, a multidisciplinary analysis on the effect induced by windbreaks on several railways subsystems is conducted. On the one hand, a set of wind tunnel tests is conducted to assess the improvement on the rolling stock lateral stability. The qualitative estimation of the shelter effect, as function of the windbreak height, is established through the pressure distribution measured on the surface of a two-dimensional train model. On the other hand, the flow properties above the railway platform are assessed using the same set of windbreaks. Two experimental techniques are used to measure the flow properties, hot-wire anemometry (HWA) and particle image velocimetry (PIV). In particular, the attention is focused on the flow characteristics on the contact wire location. A simplified analysis on the catenary oscillations due to galloping phenomena is conducted in the last part of the document. Both, the flow characterization performed via PIV and the aerodynamic properties of the contact wire cross-section are combined. In this manner, the risk of the aeroelastic instabilities on a railway overhead placed on a railway bridge is assessed through a practical application.

Effects of cross sections tables generation and optimization on rod ejection transient analyses

Best estimate analysis of rod ejection transients requires 3D kinetics core simulators. If they use cross sections libraries compiled in multidimensional tables,interpolation errors – originated when the core simulator computes the cross sections from the table values – are a source of uncertainty in k-effective calculations that should be accounted for. Those errors depend on the grid covering the domain of state variables and can be easily reduced, in contrast with other sources of uncertainties such as the ones due to nuclear data, by choosing an optimized grid distribution. The present paper assesses the impact of the grid structure on a PWR rod ejection transient analysis using the coupled neutron-kinetics/thermal-hydraulicsCOBAYA3/COBRA-TF system. Forthispurpose, the OECD/NEA PWR MOX/UO2 core transient benchmark has been chosen, as material compositions and geometries are available, allowing the use of lattice codes to generate libraries with different grid structures. Since a complete nodal cross-section library is also provided as part of the benchmark specifications, the effects of the library generation on transient behavior are also analyzed.Results showed large discrepancies when using the benchmark library and own-generated libraries when compared with benchmark participants’ solutions. The origin of the discrepancies was found to lie in the nodal cross sections provided in the benchmark.

Application of the Boundary Method to the determination of the properties of the beam cross-sections

Using the 3-D equations of linear elasticity and the asylllptotic expansion methods in terms of powers of the beam cross-section area as small parameter different beam theories can be obtained, according to the last term kept in the expansion. If it is used only the first two terms of the asymptotic expansion the classical beam theories can be recovered without resort to any "a priori" additional hypotheses. Moreover, some small corrections and extensions of the classical beam theories can be found and also there exists the possibility to use the asymptotic general beam theory as a basis procedure for a straightforward derivation of the stiffness matrix and the equivalent nodal forces of the beam. In order to obtain the above results a set of functions and constants only dependent on the cross-section of the beam it has to be computed them as solutions of different 2-D laplacian boundary value problems over the beam cross section domain. In this paper two main numerical procedures to solve these boundary value pf'oblems have been discussed, namely the Boundary Element Method (BEM) and the Finite Element Method (FEM). Results for some regular and geometrically simple cross-sections are presented and compared with ones computed analytically. Extensions to other arbitrary cross-sections are illustrated.

Shear stress distribution on beam cross-sections under shear loading

In this work, some results obtained by Trabucho and Viaño for the shear stress distribution in beam cross sections using asymptotic expansions of the three-dimensional elasticity equations are compared with those calculated by the classical formulae of the Strength of Materials. We use beams with rectangular and circular cross section to compare the degree of accuracy reached by each method.

Experimental and theoretical cross sections for positron scattering from the pentane isomers.

Isomerism is ubiquitous in chemistry, physics, and biology. In atomic and molecular physics, in particular, isomer effects are well known in electron-impact phenomena; however, very little is known for positron collisions. Here we report on a set of experimental and theoretical cross sections for low-energy positron scattering from the three structural isomers of pentane: normal-pentane, isopentane, and neopentane. Total cross sections for positron scattering from normal-pentane and isopentane were measured at the University of Trento at incident energies between 0.1 and 50 eV. Calculations of the total cross sections, integral cross sections for elastic scattering, positronium formation, and electronic excitations plus direct ionization, as well as elastic differential cross sections were computed for all three isomers between 1 and 1000 eV using the independent atom model with screening corrected additivity rule. No definitive evidence of a significant isomer effect in positron scattering from the pentane isomers appears to be present. (C) 2016 AIP Publishing LLC.

Integral elastic, electronic-state, ionization, and total cross sections for electron scattering with furfural

We report absolute experimental integral cross sections (ICSs) for electron impact excitation of bands of electronic-states in furfural, for incident electron energies in the range 20-250 eV. Wherever possible, those results are compared to corresponding excitation cross sections in the structurally similar species furan, as previously reported by da Costa et al. [Phys. Rev. A 85, 062706 (2012)] and Regeta and Allan [Phys. Rev. A 91, 012707 (2015)]. Generally, very good agreement is found. In addition, ICSs calculated with our independent atom model (IAM) with screening corrected additivity rule (SCAR) formalism, extended to account for interference (I) terms that arise due to the multi-centre nature of the scattering problem, are also reported. The sum of those ICSs gives the IAM-SCAR+I total cross section for electron-furfural scattering. Where possible, those calculated IAM-SCAR+I ICS results are compared against corresponding results from the present measurements with an acceptable level of accord being obtained. Similarly, but only for the band I and band II excited electronic states, we also present results from our Schwinger multichannel method with pseudopotentials calculations. Those results are found to be in good qualitative accord with the present experimental ICSs. Finally, with a view to assembling a complete cross section data base for furfural, some binary-encounter-Bethe-level total ionization cross sections for this collision system are presented. (C) 2016 AIP Publishing LLC.

Absorption cross-sections of hole polarons in glassy and β-phase polyfluorene

Absorption induced by electrochemically injected holes is studied in poly-9,9-dioctylfluorene (PFO) films. Injected charges form positive polarons which are delocalised over four fluorene units in the glassy phase and about seven fluorene units in its β-phase. Polaron absorption cross-sections at the 640 nm peak are similar to the published values of chemically reduced oligofluorenes in solution. The absorption cross-section of polaron in the β-phase at 470 nm is about eight times smaller than the stimulated emission cross-section derived from published data. This indicates that β-phase-rich PFO is an attractive candidate for a light-emitting layer in double-heterostructure organic laser diodes.

Cross sections for transuranium element production /

"Reactor technology- - TID-4500."