Large plasma velocities along the magnetic field line in the auroral zone

In the auroral zone, ionospheric plasma often moves horizontally at more than 1 km s−1, driven by magnetospheric electric fields, but it has usually been assumed that vertical velocities are much smaller. On occasions, however, plasma has been seen to move upwards along the magnetic field line at several hundred m s−1. These upward velocities are associated with electric fields strong enough to heat the ion population and drive it into a non-thermal state1,2. Here we report observations of substantial upwards acceleration of plasma, to velocities as high as 500 m s−1. An initial upthrust was provided by a combined upwelling of the neutral atmosphere and ionosphere but the continued acceleration at greater heights is explained by a combination of enhanced plasma pressure and the 'hydrodynamic mirror force'3. This acceleration marks an important stage in the transport of plasma from the ionosphere into the magnetosphere.

Measurement of the epicycle frequency in the Galactic disc and initial velocities of open clusters

A new method to measure the epicycle frequency kappa in the Galactic disc is presented. We make use of the large data base on open clusters completed by our group to derive the observed velocity vector (amplitude and direction) of the clusters in the Galactic plane. In the epicycle approximation, this velocity is equal to the circular velocity given by the rotation curve, plus a residual or perturbation velocity, of which the direction rotates as a function of time with the frequency kappa. Due to the non-random direction of the perturbation velocity at the birth time of the clusters, a plot of the present-day direction angle of this velocity as a function of the age of the clusters reveals systematic trends from which the epicycle frequency can be obtained. Our analysis considers that the Galactic potential is mainly axis-symmetric, or in other words, that the effect of the spiral arms on the Galactic orbits is small; in this sense, our results do not depend on any specific model of the spiral structure. The values of kappa that we obtain provide constraints on the rotation velocity of the in particular, V(0) is found to be 230 +/- 15 km s(-1) even if the scale (R(0) = 7.5 kpc) of the Galaxy is adopted. The measured kappa at the solar radius is 43 +/- 5 km s(-1) kpc(-1). The distribution of initial velocities of open clusters is discussed.

Effects of a single habituation session on neuromuscular isokinetic profile at different movement velocities

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Debris perturbed by radiation pressure: relative velocities across circular orbits

In the present work we consider a dynamical system of mum size particles around the Earth subject to the effects of radiation pressure. Our main goal is to study the evolution of its relative velocity with respect to the co-planar circular orbits that it crosses. The particles were initially in a circular geostationary orbit, and the particles size were in the range between 1 and 100 mum. The radiation pressure produces variations in its eccentricity, resulting in a change in its orbital velocity. The results indicated the maximum linear momentum and kinetic energy increases as the particle size increases. For a particle of 1 mum the kinetic energy is approximately 1.56 x 10(-7) J and the momentum is 6.27 x 10(-11) kg m/s and for 100 mum the energy is approximately 1.82 x 10(-4) J and the momentum is 2.14 x 10(-6) kg m/s. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

A study of the relative velocities of small particles that are orbiting the earth

The evolution of the velocity of the particles with respect to the circular orbits of satellites that are around the Earth that the particles will cross, suggests a range of possible velocities of impact as a function of the altitude of the satellite. A study made from those results show that the maximum relative velocities occur at the semi-latus rectum, independent of the initial semi-major axis of the particle. Considering both the solar radiation pressure and the oblateness of the Earth, it is visible that a precession in the orbit occurs and there is also a variation in the eccentricity of the particle as a function of its orbital region and its size. This is important information, because the damage caused in a spacecraft depends on the impact velocity.

On the prediction of pickup and saltation velocities in pneumatic conveying

This paper presents a comparative study of the critical pickup and saltation velocities of particles in horizontal pipelines for pneumatic conveying design. A comparative study is performed using different existing correlations in the literature for the determination of the minimum velocity of transport as a function of the particle and pipe diameter, particle density, solid mass flow rate and particle sphericity. Their limitations and difficulties in predicting those critical velocities are analyzed. For the pickup velocity, an experimental study was also carried out in order to support the analysis. Recommendations are presented on the use of such correlations.

A study of low velocities regions near the Roche lobe during the gas giant planets formation

In this paper were studied regions close to the Roche lobe of a planet like Jupiter, in order to find regions with low velocities. We simulated a two dimensional and non-self-gravitating disk, where tidal and viscous torques are considered, using the hydrodynamic numerical integrator FARGO 2D. As stated earlier we are interested in find low velocities regions for in future works study the possibility of satellites formation in these regions.

Homogeneous metallicities and radial velocities for Galactic globular clusters

Well determined radial velocities and abundances are essential for analyzing the properties of the globular cluster system of the Milky Way. However more than 50% of these clusters have no spectroscopic measure of their metallicity. In this context, this work provides new radial velocities and abundances for twenty Milky Way globular clusters which lack or have poorly known values for these quantities. The radial velocities and abundances are derived from spectra obtained at the Ca II triplet using the FORS2 imager and spectrograph at the VLT, calibrated with spectra of red giants in a number of clusters with well determined abundances. For about half of the clusters in our sample we present significant revisions of the existing velocities or abundances, or both. We also confirm the existence of a sizable abundance spread in the globular cluster M 54, which lies at the center of the Sagittarius dwarf galaxy. In addition evidence is provided for the existence of a small intrinsic internal abundance spread (sigma[Fe/H](int) approximate to 0.11-0.14 dex, similar to that of M 54) in the luminous distant globular cluster NGC 5824. This cluster thus joins the small number of Galactic globular clusters known to possess internal metallicity ([Fe/H]) spreads.

Referencing geostrophic velocities using ADCP data at 24.5 ºN

Diploma de Estudios Avanzados

Referencing geostrophic velocities using ADCP data at 24.5°N (North Atlantic)

[EN] Acoustic Doppler Current Profilers (ADCPs) have proven to be a useful oceanographic tool in the study of ocean dynamics. Data from D279, a transatlantic hydrographic cruise carried out in spring 2004 along 24.5°N, were processed, and lowered ADCP (LADCP) bottom track data were used to assess the choice of reference velocity for geostrophic calculations. The reference velocities from different combinations of ADCP data were compared to one another and a reference velocity was chosen based on the LADCP data. The barotropic tidal component was subtracted to provide a final reference velocity estimated by LADCP data. The results of the velocity fields are also shown. Further studies involving inverse solutions will include the reference velocity calculated here.

High precision radial velocities with giano spectra

Radial velocities measured from near-infrared (NIR) spectra are a potential tool to search for extrasolar planets around cool stars. High resolution infrared spectrographs now available reach the high precision of visible instruments, with a constant improvement over time. GIANO is an infrared echelle spectrograph and it is a powerful tool to provide high resolution spectra for accurate radial velocity measurements of exo-planets and for chemical and dynamical studies of stellar or extragalactic objects. No other IR instruments have the GIANO's capability to cover the entire NIR wavelength range. In this work we develop an ensemble of IDL procedures to measure high precision radial velocities on a few GIANO spectra acquired during the commissioning run, using the telluric lines as wevelength reference. In Section 1.1 various exoplanet search methods are described. They exploit different properties of the planetary system. In Section 1.2 we describe the exoplanet population discovered trough the different methods. In Section 1.3 we explain motivations for NIR radial velocities and the challenges related the main issue that has limited the pursuit of high-precision NIR radial velocity, that is, the lack of a suitable calibration method. We briefly describe calibration methods in the visible and the solutions for IR calibration, for instance, the use of telluric lines. The latter has advantages and problems, described in detail. In this work we use telluric lines as wavelength reference. In Section 1.4 the Cross Correlation Function (CCF) method is described. This method is widely used to measure the radial velocities.In Section 1.5 we describe GIANO and its main science targets. In Chapter 2 observational data obtained with GIANO spectrograph are presented and the choice criteria are reported. In Chapter 3 we describe the detail of the analysis and examine in depth the flow chart reported in Section 3.1. In Chapter 4 we give the radial velocities measured with our IDL procedure for all available targets. We obtain an rms scatter in radial velocities of about 7 m/s. Finally, we conclude that GIANO can be used to measure radial velocities of late type stars with an accuracy close to or better than 10 m/s, using telluric lines as wevelength reference. In 2014 September GIANO is being operative at TNG for Science Verification and more observational data will allow to further refine this analysis.

Comparison of Doppler-derived aortic velocities obtained from various transducer sites in healthy dogs and cats

In normal dogs and dogs with subaortic stenosis, it is known that the subcostal transducer site provides higher left ventricular ejection velocities than does the left apical site. We hypothesized that aortic flow velocities could also be obtained from the right parasternal long-axis view, optimized for the placement of the Doppler cursor as parallel as possible into the aortic root. In 15 healthy dogs and 13 healthy cats, high-pulsed repetition frequency Doppler flow velocity measurements in the proximal aorta were performed using two-dimensional echocardiographic guidance. The mean [ +/- standard error of the mean (SEM)] peak aortic flow velocities in healthy dogs were as follows: subcostal site 1.46 +/- 0.05 m/s; apical site 1.12 +/- 0.06 m/s; right parasternal long-axis site 1.09 +/- 0.05 m/s. In healthy cats, the following peak aortic flow velocities were observed: apical site 0.87 +/- 0.03m/s; right parasternal long-axis site 0.87 +/- 0.03 m/s. Aortic flow velocities obtained from the subcostal site were significantly higher in healthy dogs than those obtained from the left apical and right parasternal long-axis site (P< 0.001). There was no statistical difference between the peak aortic flow velocities obtained from right parasternal long-axis and left apical transducer position in all groups. We conclude therefore that right parasternal long-axis and left apical-derived aortic flow velocities are similar and may be used interchangeably in healthy dogs and cats.