Showing papers on "Center of mass published in 1997"

Nonlinear Dynamics of a Rigid Unbalanced Rotor in Journal Bearings. Part I: Theoretical Analysis

Abstract: The dynamic behaviour of a rigid rotor supported on plain journal bearings was studied, focusing particular attention on its nonlinear aspects Under the hypothesis that the motion of the rotor mass center is plane, the rotor has five Lagrangian co-ordinates which are represented by the co-ordinates of the mass center and the three angular co-ordinates needed to express the rotor's rotation with respect to its center of mass In such conditions, the system is characterised not only by the nonlinearity of the bearings but also by the nonlinearity due to the trigonometric functions of the three assigned angular co-ordinates However, if two angular co-ordinates have values that are generally quite small because of the small radial clearances in the bearings, the system is de facto linear in these angular co-ordinates Moreover, if the third angular co-ordinate is assumed to be cyclic [18], the number of degrees of freedom in the system is reduced to four and nonlinearity depends solely on the presence of the journal bearings, whose reactions were predicted with the π-film, short bearing model After writing the equations of motion in this way and determining a numerical routine for a Runge–Kutta integration the most significant aspects of the dynamics of a symmetrical rotor were studied, in the presence of either pure static or pure couple unbalance and also when both types of unbalance were present Two categories of rotors, whose motion is prevailingly a cylindrical whirl or a conical whirl, were put under investigation

Distant Companions and Planets around Millisecond Pulsars

Abstract: We present a general method for determining the masses and orbital parameters of binary millisecond pulsars with long orbital periods (Porb 1 yr), using timing data in the form of pulse frequency derivatives. Our method can be used even when the available timing data cover only a small fraction of an orbit, but it requires high-precision measurements of up to five successive derivatives of the pulse frequency. With five derivatives a complete determination of the mass and orbital parameters is in principle possible (up to the usual inclination factor sin i). With less than five derivatives, only partial information can be obtained, but significant constraints can sometimes be placed on, e.g., the mass of the companion. We apply our method to analyze the properties of the second companion in the PSR B1620-26 triple system. We use the latest timing data for this system, including a recent detection of the fourth time derivative of the pulse frequency, to constrain the mass and orbital parameters of the second companion. We find that all possible solutions have a mass m2 in the range 2.4 × 10-4 M☉ ≤ m2 sin i2 ≤ 1.2 × 10-2 M☉, i.e., almost certainly excluding a second companion of stellar mass and suggesting instead that the system contains a planet or brown dwarf. To further constrain this system, we have used preliminary measurements of the secular perturbations of the inner binary. Using Monte Carlo realizations of the triple configuration in three dimensions, we find the most probable value of m2 to be 0.01 ± 0.005 M☉, corresponding to a distance of 38 ± 6 AU from the center of mass of the inner binary (the errors indicate 80% confidence intervals). We also apply our method to analyze the planetary system around PSR B1257+12, where a distant, giant planet may be present in addition to the three well-established Earth-mass planets. We find that the simplest interpretation of the frequency derivatives implies the presence of a fourth planet with a mass of ~100 M⊕ in a circular orbit of radius ~40 AU.

Interactive identi?cation of the center of mass reachable space for an articulated manipulator

Abstract: We propose an efficient kinematic position control for the center of mass of an articulated arm. The algorithm integrates the context of multiple joints reaching their limit value together with a singular configuration on the remaining joint space. We demonstrate the resulting fine control by interactively outlining the reachable area borders of the center of mass (in a 2D context for clarity). Moreover, the identification is also possible under any position or orientation constraint of an end effector. This tool can easily be integrated in the early conception stage of mobile articulated structures combining strong requirements on reachability and balance.

Mass Transport by Brownian Flows

Abstract: We consider the motion of a mass distribution in a random velocity field which is “δ-correlated” in time but which has arbitrary spatial correlations. We discuss the rigorous formulation of this problem in terms of Brownian flows and stochastic calculus. We use numerical simulations to illustrate the effect of the flow on the mass. We present results concerning the evolution of the mass distribution and, in particular, the long-time asymptotics of the center of mass and relative dispersion.

Motion of a Rigid Body in a Tidal Field

Abstract: We investigate the motion, near the equilibrium configurations, of an initially spinless rigid body subject to an external tidal field. Two cases are considered: when the center of mass of the body is at rest at the equilibrium point of the field generated by a generic mass distribution, and when it is placed on a circular orbit subject to a spherically symmetric potential. A complete analysis of the equilibrium configurations is carried out for both cases. First, we derive the conditions for the stable equilibria, and then we analyze the frequencies of oscillations around the equilibrium positions. In view of these results, we consider the problem of alignment of galaxies in clusters. After estimating the period of the oscillations induced on the galaxies by the tidal field of the cluster, we discuss the possible effect of resonances between stellar orbits inside the galaxy and the oscillations of the galaxy as a whole; this may be a mechanism responsible for producing an intracluster stellar population.

Photoproduction of K^0 and Lambda at HERA and a Comparison with Deep Inelastic Scattering

Abstract: Inclusive $K^0$ and $\Lambda$ photoproduction has been investigated at HERA with the H1 detector at an average photon-proton center of mass energy of 200 GeV in the transverse momentum range 0.5

The Phase in Three-Pion Correlations

Abstract: We discuss the complex phase generated in three pion correlation functions. The lowest order contribution to the phase is of order $q^2 R/K$, where $q$ is a typical relative momentum, $K$ is a typical center of mass momentum and $R$ is a typical radius parameter. This contribution is of purely kinematic origin. At next order we find a generic contribution of order $(qR)^3$ which is a result of odd modifications to the source emission function. We argue, that the scale for typical HBT correlations in ultrarelativistic heavy ion collisions is $q/K \ll qR \sim 1$, so that the third order correction actually dominates the phase in the experimentally relevant momentum range. We study in detail such contributions which arise from source asymmetries generated by flow, the source geometry and resonance decays.

Making a pitch for the center of mass and the moment of inertia

Abstract: We propose some simple experiments to measure moments of inertia of certain physical pendula having high and low symmetry. Periods of oscillation, mass, and distance of the pivot from the center of mass are used to measure ICM for: (a) the “floating eagle,” an intriguing toy, and (b) a rectangular plate. Values of ICM obtained from measurements about different parallel axes may be checked for consistency.

Two interacting charged particles in strong static fields: A variety of two-body phenomena

Abstract: In the presence of a homogeneous magnetic field the center of mass and internal motion of a neutral or charged two-body system cannot be separated. We review the effects and phenomena which occur due to the inherent two-body character of these systems. The most prominent effects that occur for neutral species are the chaotic classical diffusion of the center of mass, the intermittent near-threshold behavior and the appearance of weakly bound states with an extraordinarily large electric dipole moment in crossed electric and magnetic fields. For ionic two-body systems the regions of strong mixing of the center of mass and internal motion are identified and investigated. As major effects we observe the classical self-stabilization as well as selfionization processes of the ion.

Compton scattering on blackbody photons

Abstract: We examine Compton scattering of electrons on blackbody photons in the case where the electrons are highly relativistic, but the center of mass energy is small in comparison with the electron mass. We derive the partial lifetime of electrons in the large electron positron (LEP) accelerator due to this form of scattering in the vacuum beam pipe and compare it with previous results.

Measurement of quasi-elastic 12C(p,2p) scattering at high momentum transfer

Abstract: We measured the high-momentum quasi-elastic 12C(p,2p) reaction (at center of mass angle near 90 degrees) for 6 and 7.5 GeV/c incident protons. The three-momentum components of both final state protons were measured and the missing energy and momentum of the target proton in the nucleus were determined. The validity of the quasi-elastic picture was verified up to Fermi momenta of about 450 MeV/c, where it might be questionable. Transverse and longitudinal Fermi momentum distributions of the target proton were measured and compared to independent particle models which do not reproduce the large momentum tails. We also observed that the transverse Fermi distribution gets wider as the longitudinal component increases in the beam direction, in contrast to a simple Fermi gas model.

Quantum Decoherence Induced by Gravitational Fluctuations in the Measurement Apparatus

Abstract: From the interaction of a quantum system with its own gravity, we derive bound states for the center of mass of a body with a mass greater than a critical value, which we obtain too. Also, in a more general, different approach, we obtain a master equation for the density matrix of that center of mass (with a non-unitary term responsible for decoherence). Both results are in agreement.