37,492 research outputs found
Flight and wind-tunnel correlation of boundary-layer transition on the AEDC transition cone
Transition and fluctuating surface pressure data were acquired on a 10 deg included angle cone, using the same instrumentation and technique over a wide range of Mach and Reynolds numbers in 23 wind tunnels and in flight. Transition was detected with a traversing pitot-pressure probe in contact with the surface. The surface pressure fluctuations were measured with microphones set flush in the cone surface. Good correlation of end of transition Reynolds number RE(T) was obtained between data from the lower disturbance wind tunnels and flight up to a boundary layer edge Mach number, M(e) = 1.2. Above M(e) = 1.2, however, this correlation deteriorates, with the flight Re(T) being 25 to 30% higher than the wind tunnel Re(T) at M(e) = 1.6. The end of transition Reynolds number correlated within + or - 20% with the surface pressure fluctuations, according to the equation used. Broad peaks in the power spectral density distributions indicated that Tollmien-Schlichting waves were the probable cause of transition in flight and in some of the wind tunnels
In-flight transition measurement on a 10 deg cone at Mach numbers from 0.5 to 2.0
Boundary layer transition measurements were made in flight on a 10 deg transition cone tested previously in 23 wind tunnels. The cone was mounted on the nose of an F-15 aircraft and flown at Mach numbers room 0.5 to 2.0 and altitudes from 1500 meters (5000 feet) to 15,000 meters (50,000 feet), overlapping the Mach number/Reynolds number envelope of the wind tunnel tests. Transition was detected using a traversing pitot probe in contact with the surface. Data were obtained near zero cone incidence and adiabatic wall temperature. Transition Reynolds number was found to be a function of Mach number and of the ratio of wall temperature to adiabatic all temperature. Microphones mounted flush with the cone surface measured free-stream disturbances imposed on the laminar boundary layer and identified Tollmien-Schlichting waves as the probable cause of transition. Transition Reynolds number also correlated with the disturbance levels as measured by the cone surface microphones under a laminar boundary layer as well as the free-stream impact
A near zero velocity dispersion stellar component in the Canes Venatici dwarf spheroidal galaxy
We present a spectroscopic survey of the newly-discovered Canes Venatici
dwarf galaxy using the Keck/DEIMOS spectrograph. Two stellar populations of
distinct kinematics are found to be present in this galaxy: an extended,
metal-poor component, of half-light radius 7'.8(+2.4/-2.1), which has a
velocity dispersion of 13.9(+3.2/-2.5) km/s, and a more concentrated
(half-light radius 3'.6(+1.1/-0.8) metal-rich component of extremely low
velocity dispersion. At 99% confidence, the upper limit to the central velocity
dispersion of the metal-rich population is 1.9 km/s. This is the lowest
velocity dispersion ever measured in a galaxy. We perform a Jeans analysis on
the two components, and find that the dynamics of the structures can only be
consistent if we adopt extreme (and unlikely) values for the scale length and
velocity dispersion of the metal-poor population. With a larger radial velocity
sample and improved measurements of the density profile of the two populations,
we anticipate that it will be possible to place strong constraints on the
central distribution of the dark matter in this galaxy.Comment: 5 pages, 7 figures, accepted by MNRA
Anti-de Sitter massless scalar field spacetimes in arbitrary dimensions
We consider -dimensional static spacetimes in Einstein gravity with a
cosmological constant in the presence of a minimally coupled massless scalar
field. The spacetimes have a -dimensional base manifold given by an
Einstein space and the massless scalar field depends only on the radial
coordinate. The field equations are decoupled in the general case, and can be
solved exactly for the cases when either the cosmological constant vanishes or
the base manifold is Ricci flat. We focus on the case of a negative
cosmological constant and a Ricci-flat base manifold. The solution has a
curvature singularity located at the origin, where also the scalar field
diverges. Since there is no event horizon surrounding this singularity, the
solution describes a naked singularity dressed with a nontrivial scalar field.
This spacetime is an asymptotically locally anti-de Sitter one when the
Ricci-flat base manifold is locally flat. The asymptotic solution for an
arbitrary Einstein base manifold is found and the corresponding mass,
calculated through the canonical generator of the time-translation invariance,
is shown to be finite. The contribution to the mass from the scalar field at
infinity is also discussed.Comment: 14 pages, 1 figure. Typos correcte
Recovery of the Shape of the Mass Power Spectrum from the Lyman-alpha Forest
We propose a method for recovering the shape of the mass power spectrum on
large scales from the transmission fluctuations of the Lyman-alpha forest,
which takes into account directly redshift-space distortions. The procedure, in
discretized form, involves the inversion of a triangular matrix which projects
the mass power spectrum in 3-D real-space to the transmission power spectrum in
1-D redshift-space. We illustrate the method by performing a linear calculation
relating the two. A method that does not take into account redshift-space
anisotropy tends to underestimate the steepness of the mass power spectrum, in
the case of linear distortions. The issue of the effective bias-factor for the
linear distortion kernel is discussed.Comment: 18 pages, 4 figures; minor revision
Southern Sky Redshift Survey: Clustering of Local Galaxies
We use the two-point correlation function to calculate the clustering
properties of the recently completed SSRS2 survey. The redshift space
correlation function for the magnitude-limited SSRS2 is given by xi(s)=(s/5.85
h-1 Mpc)^{-1.60} for separations between 2 < s < 11 h-1 Mpc, while our best
estimate for the real space correlation function is xi(r) = (r/5.36 h-1
Mpc)^{-1.86}. Both are comparable to previous measurements using surveys of
optical galaxies over much larger and independent volumes. By comparing the
correlation function calculated in redshift and real space we find that the
redshift distortion on intermediate scales is small. This result implies that
the observed redshift-space distribution of galaxies is close to that in real
space, and that beta = Omega^{0.6}/b < 1, where Omega is the cosmological
density parameter and b is the linear biasing factor for optical galaxies. We
also use the SSRS2 to study the dependence of xi on the internal properties of
galaxies. We confirm earlier results that luminous galaxies (L>L*) are more
clustered than sub-L* galaxies and that the luminosity segregation is
scale-independent. We find that early types are more clustered than late types,
but that in the absence of rich clusters, the relative bias between early and
late types in real space, is not as strong as previously estimated.
Furthermore, both morphologies present a luminosity-dependent bias, with the
early types showing a slightly stronger dependence on luminosity. We also find
that red galaxies are significantly more clustered than blue ones, with a mean
relative bias stronger than that seen for morphology. Finally, we find that the
relative bias between optical and iras galaxies in real space is b_o/b_I
1.4.Comment: 43 pages, uses AASTeX 4.0 macros. Includes 8 tables and 16 Postscript
figures, updated reference
Density Matrix Renormalization Group Method for the Random Quantum One-Dimensional Systems - Application to the Random Spin-1/2 Antiferromagnetic Heisenberg Chain -
The density matrix renormalization group method is generalized to one
dimensional random systems. Using this method, the energy gap distribution of
the spin-1/2 random antiferromagnetic Heisenberg chain is calculated. The
results are consistent with the predictions of the renormalization group theory
demonstrating the effectiveness of the present method in random systems. The
possible application of the present method to other random systems is
discussed.Comment: 13 pages, 3 figures upon reques
On the finite-size behavior of systems with asymptotically large critical shift
Exact results of the finite-size behavior of the susceptibility in
three-dimensional mean spherical model films under Dirichlet-Dirichlet,
Dirichlet-Neumann and Neumann-Neumann boundary conditions are presented. The
corresponding scaling functions are explicitly derived and their asymptotics
close to, above and below the bulk critical temperature are obtained. The
results can be incorporated in the framework of the finite-size scaling theory
where the exponent characterizing the shift of the finite-size
critical temperature with respect to is smaller than , with
being the critical exponent of the bulk correlation length.Comment: 24 pages, late
An Inversion Method for Measuring Beta in Large Redshift Surveys
A precision method for determining the value of Beta= Omega_m^{0.6}/b, where
b is the galaxy bias parameter, is presented. In contrast to other existing
techniques that focus on estimating this quantity by measuring distortions in
the redshift space galaxy-galaxy correlation function or power spectrum, this
method removes the distortions by reconstructing the real space density field
and determining the value of Beta that results in a symmetric signal. To remove
the distortions, the method modifies the amplitudes of a Fourier plane-wave
expansion of the survey data parameterized by Beta. This technique is not
dependent on the small-angle/plane-parallel approximation and can make full use
of large redshift survey data. It has been tested using simulations with four
different cosmologies and returns the value of Beta to +/- 0.031, over a factor
of two improvement over existing techniques.Comment: 16 pages including 6 figures Submitted to The Astrophysical Journa
Radial Redshift Space Distortions
The radial component of the peculiar velocities of galaxies cause
displacements in their positions in redshift space. We study the effect of the
peculiar velocities on the linear redshift space two point correlation
function. Our analysis takes into account the radial nature of the redshift
space distortions and it highlights the limitations of the plane parallel
approximation. We consider the problem of determining the value of \beta and
the real space two point correlation function from the linear redshift space
two point correlation function. The inversion method proposed here takes into
account the radial nature of the redshift space distortions and can be applied
to magnitude limited redshift surveys that have only partial sky coverage.Comment: 26 pages including 11 figures, to appear in Ap
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