99 research outputs found
Massive scalar states localized on a de Sitter brane
We consider a brane scenario with a massive scalar field in the
five-dimensional bulk. We study the scalar states that are localized on the
brane, which is assumed to be de Sitter. These localized scalar modes are
massive in general, their effective four-dimensional mass depending on the mass
of the five-dimensional scalar field, on the Hubble parameter in the brane and
on the coupling between the brane tension and the bulk scalar field. We then
introduce a purely four-dimensional approach based on an effective potential
for the projection of the scalar field in the brane, and discuss its regime of
validity. Finally, we explore the quasi-localized scalar states, which have a
non-zero width that quantifies their probability of tunneling from the brane
into the bulk.Comment: 14 pages; 5 figure
Reciprocating excitation of a flexible beam: Benchmark study
A long and slender flexible beam is set in oscillatory motion to observe its deflection. A novel application of digital image processing is employed to obtain contactless discrete measurements of the beam tip deflection. We compare the measured data to those predicted by a flexible multibody dynamics simulation (flxdyn). This study is intended as a benchmark. Moreover, the system is described in sufficient detail to enable other investigators to repeat, and build upon results herein presented for the first time
Dynamics and vibration analysis of the interface between a non-rigid sphere and omnidirectional wheel actuators
This paper presents analysis of the dynamics and vibration of an orientation motion platform utilizing a sphere actuated by omnidirectional wheels. The purpose of the analysis is to serve as a design tool for the construction of a six-degree-of-freedom motion platform with unlimited rotational motion. The equations of motion are presented taking flexibility of the system into account. The behaviour of the system is illustrated by sample configurations with a range of omnidirectional wheel types and geometries. Vibration analysis follows, and
Atlas motion platform generalized kinematic model: Atlas motion platform
Conventional training simulators commonly use a hexapod configuration to provide motion cues. While widely used, studies have shown that hexapods are incapable of producing the range of motion required to achieve high fidelity simulation required in many applications. A novel alternative is the Atlas motion platform. This paper presents a new generalized kinematic model of the platform which can be applied to any spherical platform actuated by three omnidirectional wheels. In addition, conditions for slip-free and singularity-free motions are identified. Two illustrative examples are given for different omnidirectional wheel configurations
Bulk gravitational field and dark radiation on the brane in dilatonic brane world
We discuss the connection between the dark radiation on the brane and the
bulk gravitational field in a dilatonic brane world model proposed by Koyama
and Takahashi where the exact solutions for the five dimensional cosmological
perturbations can be obtained analytically. It is shown that the dark radiation
perturbation is related to the non-normalizable Kaluza-Klein (KK) mode of the
bulk perturbations. For the de Sitter brane in the anti-de Sitter bulk, the
squared mass of this KK mode is where is the Hubble parameter on
the brane. This mode is shown to be connected to the excitation of small black
hole in the bulk in the long wavelength limit. The exact solution for an
anisotropic stress on the brane induced by this KK mode is found, which plays
an important role in the calculation of cosmic microwave background radiation
anisotropies in the brane world.Comment: 11 page
Fluctuating brane in a dilatonic bulk
We consider a cosmological brane moving in a static five-dimensional bulk
spacetime endowed with a scalar field whose potential is exponential. After
studying various cosmological behaviours for the homogeneous background, we
investigate the fluctuations of the brane that leave spacetime unaffected. A
single mode embodies these fluctuations and obeys a wave equation which we
study for bouncing and ever-expanding branes.Comment: 17 pages, 7 figures, revte
A discrete dynamic programming approximation to the multiobjective deterministic finite horizon optimal control problem
This paper addresses the problem of finding an approximation to the minimal element set of the objective space for the class of multiobjective deterministic finite horizon optimal control problems. The objective space is assumed to be partially ordered by a pointed convex cone containing the origin. The approximation procedure consists of a two-step discretization in time and state space. Following the first-order time discretization, the dynamic programming principle is used to find the multiobjective discrete dynamic programming equation equivalent to the resulting discrete multiobjective optimal control problem. The multiobjective discrete dynamic programming equation is finally discretized in the state space. The convergence of the approximation for both discretization steps is discussed
Disk Evolution Study Through Imaging of Nearby Young Stars (DESTINYS):Scattered light detection of a possible disk wind in RY Tau
HD 142527: quantitative disk polarimetry with SPHERE
We present high-precision photometry and polarimetry for the protoplanetary
disk around HD142527, with a focus on determining the light scattering
parameters of the dust. We re-reduced polarimetric differential imaging data of
HD142527 in the VBB (735 nm) and H-band (1625 nm) from the ZIMPOL and IRDIS
subinstruments of SPHERE/VLT. With polarimetry and photometry based on
reference star differential imaging, we were able to measure the linearly
polarized intensity and the total intensity of the light scattered by the
circumstellar disk with high precision. We used simple Monte Carlo simulations
of multiple light scattering by the disk surface to derive constraints for
three scattering parameters of the dust: the maximum polarization of , the asymmetry parameter , and the single-scattering albedo .
We measure a reflected total intensity of mJy and mJy
and a polarized intensity of mJy and mJy in the VBB
and H-band, respectively. We also find in the visual range a degree of
polarization that varies between on the far side of the disk and
on the near side. The disk shows a red color for the scattered light intensity
and the polarized intensity, which are about twice as high in the near-infrared
when compared to the visual. We determine with model calculations the
scattering properties of the dust particles and find evidence for strong
forward scattering (), relatively low single-scattering
albedo (), and high maximum polarization () at the surface on the far side of the disk for both observed
wavelengths. The optical parameters indicate the presence of large aggregate
dust particles, which are necessary to explain the high maximum polarization,
the strong forward-scattering nature of the dust, and the observed red disk
color.Comment: 20 pages, 14 figure
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