6,826 research outputs found

    Non-collinearity in di-jet fragmentation in electron-positron scattering

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    We study fragmentation in electron-positron annihilation assuming a di-jet situation, using variables defined independent of any frame. In a collinear situation some of the variables are centered around zero with the small deviations attributed to intrinsic transverse momenta and large deviations attributed to additional hard subprocesses. Of course there is a gradual transition. Our modest goal is to show that covariantly defined variables are well suited to get a feeling for the magnitude of intrinsic transverse momenta.Comment: 10 pages, 12 figures, several minor correction

    Estimation of the jet energy scale corrections using top quark events

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    A least-square kinematic fit using Lagrange multipliers is applied to enforce the W boson and top quark mass constraints in the reconstructed pp→tt‾→qq‾bμνμb‾pp\rightarrow t\overline{t}\rightarrow q\overline{q}b\mu\nu_{\mu}\overline{b} events. Residual corrections are estimated on the energy scale of the jets arising from both the light quarks in the W boson decay and the heavier bottom quark in the top quark decay. Utilizing the first integrated luminosity of 100 pb−1^{-1} of proton collisions at 14 TeV detected by the CMS detector, an uncertainty smaller than 1\% can be obtained on the jet energy scale for both light and heavy jets

    Inclusive search for a fourth generation of quarks

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    We present a search for a fourth generation chiral quarks of the up- and down-type in 7 TeV proton collisions recorded by the CMS experiment at the LHC. Final state topologies with b and t quarks produced singly or in pairs are studied in the 2011 data corresponding to an integrated luminosity of 1.1 fb−1. Degenerate masses are assumed for the fourth generation quarks. The inclusive search is performed in the decay channel where one isolated muon with a high transverse momentum is identified and results in model dependent limits on the mass of the chiral quarks and the relevant CKM4 matrix elements. For minimal off-diagonal mixing between the third and the fourth generation, a limit mt > 490 GeV/c2 is obtained at 95% CL

    The top quark as a calibration tool at the LHC

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    Thanks to the large top quark pair production cross section and the relatively low background at the LHC, ttˉt\bar{t} events can be used for calibration at ATLAS and CMS. Assuming the Standard Model prediction BR(t→bW)BR(t\rightarrow bW)=1 to be true, the heavy flavour content of ttˉt\bar{t} events is well predicted, which allows to calibrate and measure the efficiency of bb-tagging algorithms directly from the data with a precision of about 5\%. The light (bb-) jet energy scale can also be extracted from ttˉt\bar{t} events at the 1\% level using WW (and top) hadronic decays

    Employees' Emotional, Cognitive, and Behavioral Responses to Increasing Statutory Retirement Ages

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    Increasing statutory retirement ages around the world are forcing employees to prolong their working lives. We study the different ways in which mid- and late-career workers respond to such changes. We distinguish between negative emotions about working longer, cognitive engagement with prolonged employment, and proactive behavior to facilitate longer working lives. We analyze data from 1,351 employees aged 40-66 from the Netherlands. We estimate a structural equation model to identify in which ways experiences of age discrimination, accessibility of accommodative HR facilities, and social norms in the workers' social networks are related to the three different types of responses. Results show that when employees do not experience age discrimination, when their employer offers easily accessible accommodative HR facilities, and the social norms support prolonged employment, employees have fewer negative emotional reactions and are more likely to behaviorally respond to facilitate longer working lives. When these contexts are misaligned, the reverse is generally found. We also find socioeconomic differences in the ways employees respond to the prospect of prolonged employment. This study shows the importance of supportive contexts at different levels—societally, in organizations, and in individuals' own lives—for policy changes such as increasing statutory retirement ages to be effective. Different responses between different socioeconomic groups may lead to growing long-term inequality

    On the Analysis and Synthesis of Wind Turbine Side-Side Tower Load Control via Demodulation

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    As wind turbine power capacities continue to rise, taller and more flexible tower designs are needed for support. These designs often have the tower's natural frequency in the turbine's operating regime, increasing the risk of resonance excitation and fatigue damage. Advanced load-reducing control methods are needed to enable flexible tower designs that consider the complex dynamics of flexible turbine towers during partial-load operation. This paper proposes a novel modulation-demodulation control (MDC) strategy for side-side tower load reduction driven by the varying speed of the turbine. The MDC method demodulates the periodic content at the once-per-revolution (1P) frequency in the tower motion measurements into two orthogonal channels. The proposed scheme extends the conventional tower controller by augmentation of the MDC contribution to the generator torque signal. A linear analysis framework into the multivariable system in the demodulated domain reveals varying degrees of coupling at different rotational speeds and a gain sign flip. As a solution, a decoupling strategy has been developed, which simplifies the controller design process and allows for a straightforward (but highly effective) diagonal linear time-invariant controller design. The high-fidelity OpenFAST wind turbine software evaluates the proposed controller scheme, demonstrating effective reduction of the 1P periodic loading and the tower's natural frequency excitation in the side-side tower motion.Comment: This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

    Gluon and Wilson loop TMDs for hadrons of spin ≤ 1

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    In this paper we consider the parametrizations of gluon transverse momentum dependent (TMD) correlators in terms of TMD parton distribution functions (PDFs). These functions, referred to as TMDs, are defined as the Fourier transforms of hadronic matrix elements of nonlocal combinations of gluon fields. The nonlocality is bridged by gauge links, which have characteristic paths (future or past pointing), giving rise to a process dependence that breaks universality. For gluons, the specific correlator with one future and one past pointing gauge link is, in the limit of small x, related to a correlator of a single Wilson loop. We present the parametrization of Wilson loop correlators in terms of Wilson loop TMDs and discuss the relation between these functions and the small-x ‘dipole’ gluon TMDs. This analysis shows which gluon TMDs are leading or suppressed in the small-x limit. We discuss hadronic targets that are unpolarized, vector polarized (relevant for spin-1/2 and spin-1 hadrons), and tensor polarized (relevant for spin-1 hadrons). The latter are of interest for studies with a future Electron-Ion Collider with polarized deuterons

    High-order Dy multipole motifs observed in DyB2C2 with resonant soft x-ray Bragg diffraction

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    Resonant soft x-ray Bragg diffraction at the Dy M4,5 edges has been exploited to study Dy multipole motifs in DyB2C2. Our results are explained introducing the intra-atomic quadrupolar interaction between the core 3d and valence 4f shell. This allows us to determine for the first time higher order multipole moments of dysprosium 4f4f electrons and to draw their precise charge density. The Dy hexadecapole and hexacontatetrapole moment have been estimated at -20% and +30% of the quadrupolar moment, respectively. No evidence for the lock-in of the orbitals at T_N has been observed, in contrast to earlier suggestions. The multipolar interaction and the structural transition cooperate along c but they compete in the basal plane explaining the canted structure along [110].Comment: 4 pages, 3 figure

    Multimodal multi-center analysis of electroconvulsive therapy effects in depression: Brainwide gray matter increase without functional changes

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    Background: Electroconvulsive therapy (ECT) is an effective treatment for severe depression and induces gray matter (GM) increases in the brain. Small-scale studies suggest that ECT also leads to changes in brain functioning, but findings are inconsistent. In this study, we investigated the influence of ECT on changes in both brain structure and function and their relation to clinical improvement using multicenter neuroimaging data from the Global ECT-MRI Research Collaboration (GEMRIC). Methods: We analyzed T1-weighted structural magnetic resonance imaging (MRI) and functional resting-state MRI data of 88 individuals (49 male) with depressive episodes before and within one week after ECT. We performed voxel-based morphometry on the structural data and calculated fractional amplitudes of low-frequency fluctuations, regional homogeneity, degree centrality, functional connectomics, and hippocampus connectivity for the functional data in both unimodal and multimodal analyses. Longitudinal effects in the ECT group were compared to repeated measures of healthy controls (n = 27). Results: Wide-spread increases in GM volume were found in patients following ECT. In contrast, no changes in any of the functional measures were observed, and there were no significant differences in structural or functional changes between ECT responders and non-responders. Multimodal analysis revealed that volume increases in the striatum, supplementary motor area and fusiform gyrus were associated with local changes in brain function. Conclusion: These results confirm wide-spread increases in GM volume, but suggest that this is not accompanied by functional changes or associated with clinical response. Instead, focal changes in brain function appear related to individual differences in brain volume increases.publishedVersio

    Warm gas at 50 AU in the disk around Herbig Be star HD 100546

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    The disk atmosphere is one of the fundamental elements of theoretical models of a protoplanetary disk. However, the direct observation of the warm gas (>> 100 K) at large radius of a disk (>> 10 AU) is challenging, because the line emission from warm gas in a disk is usually dominated by the emission from an inner disk. Our goal is to detect the warm gas in the disk atmosphere well beyond 10 AU from a central star in a nearby disk system of the Herbig Be star HD 100546. We measured the excitation temperature of the vibrational transition of CO at incremental radii of the disk from the central star up to 50 AU, using an adaptive optics system combined with the high-resolution infrared spectrograph CRIRES at the VLT. The observation successfully resolved the line emission with 0".1 angular resolution, which is 10 AU at the distance of HD 100546. Population diagrams were constructed at each location of the disk, and compared with the models calculated taking into account the optical depth effect in LTE condition. The excitation temperature of CO is 400-500 K or higher at 50 AU away from the star, where the blackbody temperature in equilibrium with the stellar radiation drops as low as 90 K. This is unambiguous evidence of a warm disk atmosphere far away from the central star.Comment: 7 pages, 5 figures, A&A in pres
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