Search results for "Velocity"
showing 10 items of 881 documents
An algorithm for computing geometric relative velocities through Fermi and observational coordinates
2013
We present a numerical method for computing the \textit{Fermi} and \textit{observational coordinates} of a distant test particle with respect to an observer. We apply this method for computing some previously introduced concepts of relative velocity: \textit{kinematic}, \textit{Fermi}, \textit{spectroscopic} and \textit{astrometric} relative velocities. We also extend these concepts to non-convex normal neighborhoods and we make some convergence tests, studying some fundamental examples in Schwarzschild and Kerr spacetimes. Finally, we show an alternative method for computing the Fermi and astrometric relative velocities.
Eulerian models of the rotating flexible wheelset for high frequency railway dynamics
2019
Abstract In this paper three formulations based on an Eulerian approach are presented to obtain the dynamic response of an elastic solid of revolution, which rotates around its main axis at constant angular velocity. The formulations are especially suitable for the study of the interaction of a solid with a non-rotating structure, such as occurs in the coupled dynamics of a railway wheelset with the track. With respect to previous publications that may adopt similar hypotheses, this paper proposes more compact formulations and eliminates certain numerical problems associated with the presence of second-order derivatives with respect to the spatial coordinates. Three different models are dev…
Effect of angular velocity on soleus and medial gastrocnemius H-reflex during maximal concentric and eccentric muscle contraction.
2009
At rest, the H-reflex is lower during lengthening than shortening actions. During passive lengthening, both soleus (SOL) and medial gastrocnemius (MG) H-reflex amplitudes decrease with increasing angular velocity. This study was designed to investigate whether H-reflex amplitude is affected by angular velocity during concentric and eccentric maximal voluntary contraction (MVC). Experiments were performed on nine healthy men. At a constant angular velocity of 60 degrees /s and 20 degrees /s, maximal H-reflex and M-wave potentials were evoked at rest (i.e., H(max) and M(max), respectively) and during concentric and eccentric MVC (i.e., H(sup) and M(sup), respectively). Regardless of the muscl…
Spectroscopy of red giants in the open clusters NGC 1545 and Tr2
2011
The results of local thermodynamic equilibrium (LTE) abundance analysis are presented for four red giants in the fields of open clusters NGC 1545 and Tr2. The membership of HD 27276, HD 27292 and HD 16068 was confirmed and the age of NGC 1545 was updated: log age(yr) = 7.95. A mild deficiency of iron-group elements was found on average for NGC 1545 and Tr2, [Fe/H]=−0.13 and −0.07 with an uncertainty of about 0.08 dex. Oxygen and carbon are moderately depleted in all cluster giants, [O/Fe]=−0.23 ± 0.05 dex and [C/Fe]=−0.56 ± 0.07 dex on average. Nitrogen is enhanced, [N/Fe] values in range +0.4 to +1.2 dex, and lithium depleted. Sodium is slightly enhanced, [Na/Fe]=+0.26 ± 0.04 dex on avera…
The Mechanics of Rigid Bodies
1990
The theory of rigid bodies is a particularly important part of general mechanics. Firstly, next to the spherically symmetric mass distributions that we studied in Sect. 1.30, the top is the simplest example of a body with finite extension. Secondly, its dynamics is a particularly beautiful model case to which one can apply the general principles of canonical mechanics and where one can study the consequences of the various space symmetries in an especially transparent manner.
Hβ photometry for UVBY standard stars
1988
From 1984 to 1986 the authors made several observational campaigns at Calar Alto and La Palma Observatories using the uvby and β photometric systems to monitor a selected sample of late-type variable stars. In this paper they present the β values for 38 uvby standard stars to contribute to the uvby-β calibration works on late-type stars. In the final discussion, the β computed values are plotted against the Stroemgren b-y, m_(1), and c_(1) indices.
DYNAMICAL PHENOMENA IN THE ATMOSPHERE OF THE PROTO-PLANETARY NEBULA IRAS 22272+5435
2009
Radial velocity monitoring of the star HD 235858 confirmed regular variations with a peak-to-peak amplitude of about 10 km s–1 and a period of about 131.2 days. The light, color, and velocity variations are typical for RV Tauri stars. Splitting of low-excitation atomic lines was detected. The components are both blue- and redshifted relative to the systemic velocity. Significant variations are observed in the intensity of C2 and CN lines. Variable emission in the Hα profile, splitting of low-excitation atomic absorption lines, appearance of CN emission lines, blue wings of strong lines, and recent reddening give evidence of shocks and mass outflow obviously induced by atmospheric pulsations.
The Alignment of Galaxy Structures
2015
We analyzed the orientation of the sample of ACO galaxy clusters. We examined the alignment in a subsample of 1056 galaxy structures taken from the Panko–Flin (2006) Catalog with known BM morphological types. We were looking for a correlation between the orientation of the cluster and the positions of neighboring clusters. The Binggeli effect (the excess of small values of the Δθ angles between the direction toward neighboring clusters and the cluster position angle) is observed, having a range up to about 45 h−1 Mpc. The strongest effect was found for elongated BM type I clusters. This is probably connected with the origins of the supergiant galaxy and with cluster formation along a long f…
Large‐Scale Vector Modes and the First CMB Temperature Multipoles
2008
Recent observations have pointed out various anomalies in some multipoles (small $\ell $) of the cosmic microwave background (CMB). In this paper, it is proved that some of these anomalies could be explained in the framework of a modified concordance model, in which, there is an appropriate distribution of vector perturbations with very large spatial scales. Vector modes are associated with divergenceless (vortical) velocity fields. Here, the generation of these modes is not studied in detail (it can be done "a posteriori"); on the contrary, we directly look for the distributions of these vector modes which lead to both alignments of the second and third multipoles and a planar octopole. A …
VLT/Flames observations of the star forming region NGC 6530
2006
Mechanisms regulating the evolution of pre-main sequence stars can be understood by studying stellar properties such as rotation, disk accretion, internal mixing and binarity. To investigate such properties, we studied a sample of 332 candidate members of the massive and populous star forming region NGC 6530. We want to select cluster members by using different membership criteria,to study the properties of pre-main sequence stars with or without circumstellar disks. We use intermediate resolution spectra including the Li I 6707.8 Angstroms line to derive radial and rotational velocities, binarity and to measure the Equivalent Width of the lithium line; these results are combined with X-ray…