1,073 research outputs found

    Choreographic Three Bodies on the Lemniscate

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    We show that choreographic three bodies {x(t), x(t+T/3), x(t-T/3)} of period T on the lemniscate, x(t) = (x-hat+y-hat cn(t))sn(t)/(1+cn^2(t)) parameterized by the Jacobi's elliptic functions sn and cn with modulus k^2 = (2+sqrt{3})/4, conserve the center of mass and the angular momentum, where x-hat and y-hat are the orthogonal unit vectors defining the plane of the motion. They also conserve the moment of inertia, the kinetic energy, the sum of square of the curvature, the product of distance and the sum of square of distance between bodies. We find that they satisfy the equation of motion under the potential energy sum_{i<j}(1/2 ln r_{ij} -sqrt{3}/24 r_{ij}^2) or sum_{i<j}1/2 ln r_{ij} -sum_{i}sqrt{3}/8 r_{i}^2, where r_{ij} the distance between the body i and j, and r_{i} the distance from the origin. The first term of the potential energies is the Newton's gravity in two dimensions but the second term is the mutual repulsive force or a repulsive force from the origin, respectively. Then, geometric construction methods for the positions of the choreographic three bodies are given

    Study of the derivative expansions for the nuclear structure functions

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    We study the convergence of the series expansions sometimes used in the analysis of the nuclear effects in Deep Inelastic Scattering (DIS) proccesses induced by leptons. The recent advances in statistics and quality of the data, in particular for neutrinos calls for a good control of the theoretical uncertainties of the models used in the analysis. Using realistic nuclear spectral functions which include nucleon correlations, we find that the convergence of the derivative expansions to the full results is poor except at very low values of xx

    Mission design for LISA Pathfinder

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    Here we describe the mission design for SMART-2/LISA Pathfinder. The best trade-off between the requirements of a low-disturbance environment and communications distance is found to be a free-insertion Lissajous orbit around the first co-linear Lagrange point of the Sun-Earth system L1, 1.5x 10^6 km from Earth. In order to transfer SMART-2/LISA Pathfinder from a low Earth orbit, where it will be placed by a small launcher, the spacecraft carries out a number of apogee-raise manoeuvres, which ultimatively place it to a parabolic escape trajectory towards L1. The challenges of the design of a small mission are met, fulfilling the very demanding technology demonstration requirements without creating excessive requirements on the launch system or the ground segment.Comment: 7 pages, 6 figures, 5th International LISA Symposium, see http://www.landisoft.de/Markus-Landgra

    Generic Twistless Bifurcations

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    We show that in the neighborhood of the tripling bifurcation of a periodic orbit of a Hamiltonian flow or of a fixed point of an area preserving map, there is generically a bifurcation that creates a ``twistless'' torus. At this bifurcation, the twist, which is the derivative of the rotation number with respect to the action, vanishes. The twistless torus moves outward after it is created, and eventually collides with the saddle-center bifurcation that creates the period three orbits. The existence of the twistless bifurcation is responsible for the breakdown of the nondegeneracy condition required in the proof of the KAM theorem for flows or the Moser twist theorem for maps. When the twistless torus has a rational rotation number, there are typically reconnection bifurcations of periodic orbits with that rotation number.Comment: 29 pages, 9 figure

    Weak production of strange Ξ baryons off the nucleon

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    The authors would like to thank Luis Alvarez-Ruso and Manuel Jose Vicente Vacas for useful discussions. One of the authors (MRA) would like to thank the pleasant hospitality at University of Granada where part of the work has been done.The charged current Cabibbo-suppressed associated KΞ production off the nucleon induced by antineutrinos is studied at low and intermediate energies. The nonresonant terms are obtained using a microscopical model based on the SU(3) chiral Lagrangian. The basic parameters of the model are fπ, the pion decay constant, Cabibbo’s angle, the proton and neutron magnetic moments, and the axial vector coupling constants for the baryons octet, D and F, that are obtained from the analysis of the semileptonic decays of neutron and hyperons. In addition, we also consider Σ∗(1385) resonance, which can decay in KΞ final state when this channel is open. The studied mechanism is the prime source of Ξ production at antineutrino energies around 2 GeV and the calculated cross sections at these energies can be measured at the current and future neutrino experiments.This research has been supported by MINECO (Spain) and the ERDF (European Commission) Grants No. FIS2017-84038-C2-1-P, No. FIS2017-85053-C2-1-P, No. SEV-2014-0398, and by Junta de Andalucia (Grant No. FQM-225)

    Efectividad de las técnicas de relajación en oncología antes de realizar pruebas diagnósticas en neuroimagen

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    Psychophysiological arousal was observed in cancer patients during the application of relaxation techniques prior to a diagnostic scan (PET-CT). The aim of the study is twofold: firstly, it is sought to establish whether such techniques can minimize patient arousal before diagnostic screening begins, and secondly to measure which of them are most effective. The dependent variable is electrodermal activity, recording the attentional level and emotional response, and the independent variable comprises the relaxation techniques used, namely Jacobson, breathing and visualization. The 39 patients were split into experimental groups to whom the relaxation techniques (Jacobson, breathing exercises, and visualization) were applied before they went for the PET-CT. An activity-module procedure was applied to track electrodermal activity during the relaxation sessions, consisting of instructions, timeout; wait, task; relaxation and end of the recording session. The control group received no relaxation techniques before the PET-CT. Session-end results show that patients who perform relaxation techniques achieve greater attentional focus using Jacobson''s technique (M = .212) and enhanced emotional containment using visualization (M = .206). It is concluded that relaxation techniques minimize the state of activation during the waiting period before a diagnostic scan

    Usefulness of Ultrasound in Assessing the Impact of Bariatric Surgery on Body Composition : a Pilot Study

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    Bariatric surgery (BS) has a significant impact on body composition. The purpose of the study is to evaluate the usefulness of musculoskeletal ultrasound (MUS) to bioelectrical impedance (BIA) in the follow-up of patients undergoing BS in terms of body composition and quality of life (QoL). This is a prospective pilot study including 32 subjects (75% female, mean age: 49.15 ± 1.9 years) who underwent BS. Fat mass (FM), lean mass (LM), and skeletal muscle index (SMI) were calculated by BIA. MUS measured subcutaneous fat (SF) and thigh muscle thickness (TMT) of the quadriceps. QoL was assessed by the Moorehead-Ardelt questionnaire. All these measurements were performed 1 month prior to BS and at 12-month follow-up. The mean BMI decreased by 6.63 ± 1.25 kg/m 2 (p =0.001). We observed significant reductions in FM (p =0.001) and SF (p =0.007) and in LM (p =0.001) but not in SMI and TMT. We found a correlation between the FM and SF (pre-surgical, r =0.42, p =0.01; post-surgical, r =0.52, p =0.003) and between SMI and TMT (pre-surgical, r =0.35, p =0.04; post-surgical, r =0.38, p =0.03). QoL test showed significant improvement (p =0.001). In addition, a correlation between the QoL questionnaire and TMT post-surgery (r =0.91, p =0.019) was observed. However, we did not find any statistically significant correlation between QoL assessment and SMI or LM. Our results suggest that MUS can be complementary to BIA for the evaluation and the follow-up of body composition after BS. TMT of quadriceps can provide relevant information about regional sarcopenia and has a significant correlation with QoL
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