1,333 research outputs found
Reduction of tilt rotor download using circulation control
The effect of boundary layer control blowing on the download of a wing in the wake of a hovering rotor was measured in a small scale experiment. The objective was to evaluate the potential of boundary layer control blowing for reducing tilt rotor download. Variations were made in rotor thrust coefficient, blowing pressure ratio, and blowing slot height. The effect of these parameter variations on the wing download and wing surface pressures is presented. The boundary layer control blowing caused reductions in the wing download of 25 to 55 percent
Gravitational Lensing & Stellar Dynamics
Strong gravitational lensing and stellar dynamics provide two complementary
and orthogonal constraints on the density profiles of galaxies. Based on
spherically symmetric, scale-free, mass models, it is shown that the
combination of both techniques is powerful in breaking the mass-sheet and
mass-anisotropy degeneracies. Second, observational results are presented from
the Lenses Structure & Dynamics (LSD) Survey and the Sloan Lens ACS (SLACS)
Survey collaborations to illustrate this new methodology in constraining the
dark and stellar density profiles, and mass structure, of early-type galaxies
to redshifts of unity.Comment: 6 pages, 2 figures; Invited contribution in the Proceedings of XXIst
IAP Colloquium, "Mass Profiles & Shapes of Cosmological Structures" (Paris,
4-9 July 2005), eds G. A. Mamon, F. Combes, C. Deffayet, B. Fort (Paris: EDP
Sciences
Methods for heat transfer and temperature field analysis of the insulated diesel phase 2 progress report
This report describes work done during Phase 2 of a 3 year program aimed at developing a comprehensive heat transfer and thermal analysis methodology for design analysis of insulated diesel engines. The overall program addresses all the key heat transfer issues: (1) spatially and time-resolved convective and radiative in-cylinder heat transfer, (2) steady-state conduction in the overall structure, and (3) cyclical and load/speed temperature transients in the engine structure. During Phase 2, radiation heat transfer model was developed, which accounts for soot formation and burn up. A methodology was developed for carrying out the multi-dimensional finite-element heat conduction calculations within the framework of thermodynamic cycle codes. Studies were carried out using the integrated methodology to address key issues in low heat rejection engines. A wide ranging design analysis matrix was covered, including a variety of insulation strategies, recovery devices and base engine configurations. A single cylinder Cummins engine was installed at Purdue University, and it was brought to a full operational status. The development of instrumentation was continued, concentrating on radiation heat flux detector, total heat flux probe, and accurate pressure-crank angle data acquisition
Methods for heat transfer and temperature field analysis of the insulated diesel
Work done during phase 1 of a three-year program aimed at developing a comprehensive heat transfer and thermal analysis methodology oriented specifically to the design requirements of insulated diesel engines is reported. The technology developed in this program makes possible a quantitative analysis of the low heat rejection concept. The program is comprehensive in that it addresses all the heat transfer issues that are critical to the successful development of the low heat rejection diesel engine: (1) in-cylinder convective and radiative heat transfer; (2) cyclic transient heat transfer in thin solid layers at component surfaces adjacent to the combustion chamber; and (3) steady-state heat conduction in the overall engine structure. The Integral Technologies, Inc. (ITI) program is comprised of a set of integrated analytical and experimental tasks. A detailed review of the ITI program approach is provided, including the technical issues which underlie it and a summay of the methods that were developed
Determination of the Antiferroquadrupolar Order Parameters in UPd3
By combining accurate heat capacity and X-ray resonant scattering results we
have resolved the long standing question regarding the nature of the
quadrupolar ordered phases in UPd_3. The order parameter of the highest
temperature quadrupolar phase has been uniquely determined to be antiphase
Q_{zx} in contrast to the previous conjecture of Q_{x^2-y^2} . The azimuthal
dependence of the X-ray scattering intensity from the quadrupolar superlattice
reflections indicates that the lower temperature phases are described by a
superposition of order parameters. The heat capacity features associated with
each of the phase transitions characterize their order, which imposes
restrictions on the matrix elements of the quadrupolar operators.Comment: 4 pages, 5 figure
Optically-induced lensing effect on a Bose-Einstein condensate expanding in a moving lattice
We report the experimental observation of a lensing effect on a Bose-Einstein
condensate expanding in a moving 1D optical lattice. The effect of the periodic
potential can be described by an effective mass dependent on the condensate
quasi-momentum. By changing the velocity of the atoms in the frame of the
optical lattice we induce a focusing of the condensate along the lattice
direction. The experimental results are compared with the numerical predictions
of an effective 1D theoretical model. Besides, a precise band spectroscopy of
the system is carried out by looking at the real-space propagation of the
atomic wavepacket in the optical lattice.Comment: 5 pages, 4 figures; minor changes applied and typos corrected; a new
paragraph added; some references updated; journal reference adde
Detection of correlated galaxy ellipticities on CFHT data: first evidence for gravitational lensing by large-scale structures
We report the detection of a significant (5.5 sigma) excess of correlations
between galaxy ellipticities at scales ranging from 0.5 to 3.5 arc-minutes.
This detection of a gravitational lensing signal by large-scale structure was
made using a composite high quality imaging survey of 6300 arcmin^2 obtained at
the Canada France Hawaii Telescope (CFHT) with the UH8K and CFH12K panoramic
CCD cameras. The amplitude of the excess correlation is 2.2\pm 0.2 % at 1
arcmin scale, in agreement with theoretical predictions of the lensing effect
induced by large-scale structure.We provide a quantitative analysis of
systematics which could contribute to the signal and show that the net effect
is small and can be corrected for. We show that the measured ellipticity
correlations behave as expected for a gravitational shear signal. The
relatively small size of our survey precludes tight constraints on cosmological
models. However the data are in favor of cluster normalized cosmological
models, and marginally reject Cold Dark Matter models with (Omega=0.3,
sigma_8<0.6) or (Omega=1, sigma_8=1). The detection of cosmic shear
demonstrates the technical feasibility of using weak lensing surveys to measure
dark matter clustering and the potential for cosmological parameter
measurements, in particular with upcoming wide field CCD cameras.Comment: 19 pages. 19 Figures. Revised version accepted in A&
Quantum global vortex strings in a background field
We consider quantum global vortex string correlation functions, within the
Kalb-Ramond framework, in the presence of a background field-strength tensor
and investigate the conditions under which this yields a nontrivial
contribution to those correlation functions. We show that a background field
must be supplemented to the Kalb-Ramond theory, in order to correctly describe
the quantum properties of the vortex strings. The explicit form of this
background field and the associated quantum vortex string correlation function
are derived. The complete expression for the quantum vortex creation operator
is explicitly obtained. We discuss the potential applicability of our results
in the physics of superfluids and rotating Bose-Einstein condensates.Comment: To appear in Journal of Physics A: Mathematical and Genera
- …