419 research outputs found
Differential Flatness of Quadrotor Dynamics Subject to Rotor Drag for Accurate Tracking of High-Speed Trajectories
No full textIn this letter, we prove that the dynamical model of a quadrotor subject to linear rotor drag effects is differentially flat in its position and heading. We use this property to compute feedforward control terms directly from a reference trajectory to be tracked. The obtained feedforward terms are then used in a cascaded, nonlinear feedback control law that enables accurate agile flight with quadrotors. Compared to the state-of-the-art control methods, which treat the rotor drag as an unknown disturbance, our method reduces the trajectory tracking error significantly. Finally, we present a method based on a gradient-free optimization to identify the rotor drag coefficients, which are required to compute the feedforward control terms. The new theoretical results are thoroughly validated trough extensive comparative experiments
Transverse spin structure of hadrons from lattice QCD
No full textThis paper presents recent lattice QCD calculations of transverse spin densities of quarks in hadrons.22This contribution is based on Refs. [M. Göckeler, et al., Phys. Rev. Lett. 98 (2007) 222001; D. Brömmel, et al., [QCDSF Collaboration]. arXiv:hep-lat/0708.2249]. Based on our simulation results for the tensor generalized form factors, we find substantial correlations between spin and coordinate degrees of freedom in the nucleon and the pion. They lead to strongly distorted transverse spin densities of quarks in the nucleon and a surprisingly non-trivial transverse spin structure of the pion. Following recent arguments by Burkardt [M. Burkardt, Phys. Rev. D 72 (2005) 094020], our results imply that the Boer-Mulders function h1⊥, describing correlations of the transverse spin and intrinsic transverse momentum of quarks, is large and negative for up-quarks in the proton and the π+. This supports the recent hypothesis that all Boer-Mulders functions are alike [arXiv:0705.1573], and also provides additional motivation for future studies of azimuthal asymmetries in π p Drell-Yan production at, e.g., COMPASS. © 2008 Elsevier B.V. All rights reserved.D. Brömmel, M. Diehl, M. Göckeler, Ph. Hägler, R. Horsley, Y. Nakamura, D. Pleiter, P.E.L. Rakow, A. Schäfer, G. Schierholz, H. Stüben, J.M. Zanotti (QCDSF/UKQCD Collaborations
D* and D Meson Production in Muon Nucleon Interactions at 160 GeV/c
No full textAdolph C, Alekseev MG, Alexakhin VY, et al. D* and D Meson Production in Muon Nucleon Interactions at 160 GeV/c. Eur.Phys.J. C. 2012;72(12): 2253.The production of D* and D mesons in inelastic scattering of 160 GeV/c muonsoff a ^6LiD target has been investigated with the COMPASS spectrometer at CERNfor 0.003 (GeV/c)^2 0.6
Spin asymmetry A(1)(d) and the spin-dependent structure function g(1)(d) of the deuteron at low values of x and Q(2)
No full textAlexakhin VY, Amoroso A, Badelek B, et al. Spin asymmetry A(1)(d) and the spin-dependent structure function g(1)(d) of the deuteron at low values of x and Q(2). Phys.Lett. B. 2007;647(5-6):330-340.We present a precise measurement of the deuteron longitudinal spin asymmetry A(1)(d) and of the deuteron spin-dependent structure function g(1)(d) at Q(2) < 1 (GeV/c)(2) and 4 x 10(-5) < x < 2.5 x 10(-2) based on the data collected by the COMPASS experiment at CERN during the years 2002 and 2003. The statistical precision is tenfold better than that of the previous measurement in this region. The measured A(1)(d) and g(1)(d) are found to be consistent with zero in the whole range of x. (c) 2007 Elsevier B.V. All rights reserved
The deuteron spin-dependent structure function g(1)(d) and its first moment
No full textAlexakhin VY, Alexandrov Y, Alexeev GD, et al. The deuteron spin-dependent structure function g(1)(d) and its first moment. Phys.Lett. B. 2007;647(1):8-17.We present a measurement of the deuteron spin-dependent structure function g(1)(d) based on the data collected by the COMPASS experiment at CERN during the years 2002-2004. The data provide an accurate evaluation for Gamma(d)(1), the first moment of g(1)(d) (x), and for the matrix element of the singlet axial current, a(0). The results of QCD fits in the next to leading order (NLO) on all g(1) deep inelastic scattering data are also presented. They provide two solutions with the gluon spin distribution function Delta G positive or negative, which describe the data equally well. In both cases, at Q(2) = 3 (GeV/c)(2) the first moment of Delta G(x) is found to be of the order of 0.2-0.3 in absolute value. (c) 2007 Elsevier B.V. All rights reserved
Vitamin D Deficiency Strongly Predicts Adverse Medical Outcome Across Different Medical Inpatient Populations: Results From a Prospective Study
No full textVitamin D deficiency has been associated with several adverse outcomes mainly in the outpatient setting. The objective of this study was to examine the prevalence of vitamin D deficiency and its association with risk of adverse clinical outcomes in a large prospective cohort of medical inpatients.We collected clinical data and measured 25(OH)D levels in adult medical patients upon hospital admission and followed them for 30 days. Regression analyses adjusted for age, gender, comorbidities, and main medical diagnosis were performed to study the effect of vitamin D deficiency on several hospital outcomes.Of 4257 included patients, 1510 (35.47%) had 25(OH)D levels of 25 to 50 nmol/L (vitamin D insufficiency) and 797 (18.72%) had levels of 0.05).In this comprehensive and large medical inpatient cohort, vitamin D deficiency was highly prevalent and strongly associated with adverse clinical outcome. Interventional research is urgently needed to prove the effect of vitamin D supplementation on these outcomes
Extracellular Matrix as a Structural Mediator of Morphological and Homeostatic Information
No full textSéminaire FSER organisé par Dan Rifkin (University Medical Center, New-York) du 4 au 9 octobre 2010 Participants Clair Baldock, Rik Derynck, Harry C. Dietz, Reinhard Faessler, Daniel S. Greenspan, Matthias Hammerschmidt, Penny Handford, Boris Hinz, Thomas D. Mueller, Tomoyuki Nakamura, Edgar M. Pera, Francesco Ramirez, Daniel Rifkin, Lynn Y. Sakai, Dean Sheppard, Pascal Thérond, Ellen Van Obberghen-Schilling, Harlad Von Melchner. -- Compte-rendu From October 4th to October 9th a meeting was h..
Leading and Next-to-Leading Order Gluon Polarisation in the Nucleon and Longitudinal Double Spin Asymmetries from Open Charm Muoproduction
No full textAdolph C, Alekseev MG, Alexakhin VY, et al. Leading and Next-to-Leading Order Gluon Polarisation in the Nucleon and Longitudinal Double Spin Asymmetries from Open Charm Muoproduction. Physical Review D. 2013;87(5): 52018.The gluon polarisation in the nucleon was measured using open charmproduction by scattering 160 GeV/c polarised muons off longitudinally polarisedprotons or deuterons. The data were taken by the COMPASS collaboration between2002 and 2007. A detailed account is given of the analysis method that includesthe application of neural networks. Several decay channels of D^0 mesons areinvestigated. Longitudinal spin asymmetries of the D meson productioncross-sections are extracted in bins of D^0 transverse momentum and energy. Atleading order QCD accuracy the average gluon polarisation is determined as(Delta g/G)^LO=-0.06 +/- 0.21 (stat.) +/- 0.08 (syst.) at the scale ~13(GeV/c)^2 and an average gluon momentum fraction ~ 0.11. For the first time,the average gluon polarisation is also obtained at next-to-leading order QCDaccuracy as (Delta g/G)^NLO = -0.13 +/- 0.15 (stat.) +/- 0.15 (syst.) at thescale ~ 13 (\GeV/c)^2 and ~ 0.20
Exotic meson π1 (1600) with JPC=1-+ and its decay into ρ (770)π
No full textWe study the spin-exotic JPC=1-+ amplitude in single-diffractive dissociation of 190 GeV/c pions into π-π-π+ using a hydrogen target and confirm the π1(1600)→ρ(770)π amplitude, which interferes with a nonresonant 1-+ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile these experimental findings. We study the nonresonant contributions to the π-π-π+ final state using pseudodata generated on the basis of a Deck model. Subjecting pseudodata and real data to the same partial-wave analysis, we find good agreement concerning the spectral shape and its dependence on the squared four-momentum transfer for the JPC=1-+ amplitude and also for amplitudes with other JPC quantum numbers. We investigate for the first time the amplitude of the π-π+ subsystem with JPC=1 - in the 3π amplitude with JPC=1-+ employing the novel freed-isobar analysis scheme. We reveal this π-π+ amplitude to be dominated by the ρ(770) for both the π1(1600) and the nonresonant contribution. These findings largely confirm the underlying assumptions for the isobar model used in all previous partial-wave analyses addressing the JPC=1-+ amplitude
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