4,736 research outputs found
Gust penetration loads and elastic vehicle response for Saturn 5 launch vehicles
Analysis of gust penetration loads and associated elastic vehicle response of Saturn 5 launch vehicles AS-505 through AS-508 penetrating sinusoidal gust
An evaluation of aft-end ignition for solid propellant rocket motors
Performance evaluation of solid propellant rocket motor ignition to determine igniter design and parameters to avoid overpressurizatio
Experience with fluorine and its safe use as a propellant
The industrial and the propulsion experience with fluorine and its derivatives is surveyed. The hazardous qualities of fluorine and safe handling procedures for the substance are emphasized. Procedures which fulfill the safety requirements during ground operations for handling fluorinated propulsion systems are discussed. Procedures to be implemented for use onboard the Space Transportation System are included
Thermodynamics of viscous dark energy in an RSII braneworld
We show that for an RSII braneworld filled with interacting viscous dark
energy and dark matter, one can always rewrite the Friedmann equation in the
form of the first law of thermodynamics, , at apparent horizon.
In addition, the generalized second law of thermodynamics can fulfilled in a
region enclosed by the apparent horizon on the brane for both constant and time
variable 5-dynamical Newton's constant . These results hold regardless of
the specific form of the dark energy. Our study further support that in an
accelerating universe with spatial curvature, the apparent horizon is a
physical boundary from the thermodynamical point of view.Comment: 11 page
A search for flares and mass ejections on young late-type stars in the open cluster Blanco-1
We present a search for stellar activity (flares and mass ejections) in a
sample of 28 stars in the young open cluster Blanco-1. We use optical spectra
obtained with ESO's VIMOS multi-object spectrograph installed on the VLT. From
the total observing time of 5 hours, we find four H flares but
no distinct indication of coronal mass ejections (CMEs) on the investigated
dK-dM stars. Two flares show "dips" in their light-curves right before their
impulsive phases which are similar to previous discoveries in photometric
light-curves of active dMe stars. We estimate an upper limit of 4 CMEs per
day per star and discuss this result with respect to a semi- empirical
estimation of the CME rate of main-sequence stars. We find that we should have
detected at least one CME per star with a mass of 1-15 g
depending on the star's X-ray luminosity, but the estimated H fluxes
associated with these masses are below the detection limit of our observations.
We conclude that the parameter which mainly influences the detection of stellar
CMEs using the method of Doppler-shifted emission caused by moving plasma is
not the spectral resolution or velocity but the flux or mass of the CME.Comment: Accepted for publication in MNRAS, accepted 2014 June 10, received
2014 June 5, in original form 2014 March 24, 14 pages, 5 figure
A multiwavelength radial velocity search for planets around the brown dwarf LP 944-20
The nearby brown dwarf LP 944-20 has been monitored for radial velocity
variability at optical and near-infrared wavelengths using the VLT/UVES and the
Keck/NIRSPEC spectrographs, respectively. The UVES radial velocity data
obtained over 14 nights spanning a baseline of 841 days shows significant
variability with an amplitude of 3.5 km s. The periodogram analysis of
the UVES data indicates a possible period between 2.5 hours and 3.7 hours,
which is likely due to the rotation of the brown dwarf. However, the NIRSPEC
data obtained over 6 nights shows an rms dispersion of only 0.36 km s
and do not follow the periodic trend. These results indicate that the
variability seen with UVES is likely to be due to rotationally modulated
inhomogeneous surface features. We suggest that future planet searches around
very low-mass stars and brown dwarfs using radial velocities will be better
conducted in the near-infrared than in the optical.Comment: accepted by ApJ Letter
Generalized Paraxial Ray Trace Procedure Derived from Geodesic Deviation
Paraxial ray tracing procedures have become widely accepted techniques for
acoustic models in seismology and underwater acoustics. To date a generic form
of these procedures including fluid motion and time dependence has not appeared
in the literature. A detailed investigation of the characteristic curves of the
equations of hydrodynamics allows for an immediate generalization of the
procedure to be extracted from the equation form geodesic deviation. The
general paraxial ray trace equations serve as an ideal supplement to ordinary
ray tracing in predicting the deformation of acoustic beams in random
environments. The general procedure is derived in terms of affine
parameterization and in a coordinate time parameterization ideal for
application to physical acoustic ray propagation. The formalism is applied to
layered media, where the deviation equation reduces to a second order
differential equation for a single field with a general solution in terms of a
depth integral along the ray path. Some features are illustrated through
special cases which lead to exact solutions in terms of either ordinary or
special functions.Comment: Original; 40 pages (double spaced), 1 figure Replaced version; 36
pages single spaced, 7 figures. Expanded content; Complete derivation of the
equations from the equations of hydrodynamics, introduction of an auxiliary
basis for three dimensional wave-front modeling. Typos in text and equations
correcte
A Physical Limit to the Magnetic Fields of T Tauri Stars
Recent estimates of magnetic field strengths in T Tauri stars yield values
--. In this paper, I present an upper limit to the
photospheric values of by computing the equipartition values for different
surface gravities and effective temperatures. The values of derived from
the observations exceed this limit, and I examine the possible causes for this
discrepancy
Effects of shock-induced separation Technical summary report
Supersonic and subsonic shock wave boundary layer separation studies on aeroelasticity of Saturn launch vehicle
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