7,158 research outputs found
Development and application of an analysis of axisymmetric body effects on helicopter rotor aerodynamics using modified slender body theory
A computationally efficient body analysis designed to couple with a comprehensive helicopter analysis is developed in order to calculate the body-induced aerodynamic effects on rotor performance and loads. A modified slender body theory is used as the body model. With the objective of demonstrating the accuracy, efficiency, and application of the method, the analysis at this stage is restricted to axisymmetric bodies at zero angle of attack. By comparing with results from an exact analysis for simple body shapes, it is found that the modified slender body theory provides an accurate potential flow solution for moderately thick bodies, with only a 10%-20% increase in computational effort over that of an isolated rotor analysis. The computational ease of this method provides a means for routine assessment of body-induced effects on a rotor. Results are given for several configurations that typify those being used in the Ames 40- by 80-Foot Wind Tunnel and in the rotor-body aerodynamic interference tests being conducted at Ames. A rotor-hybrid airship configuration is also analyzed
Trends of Reynolds number effects on two-dimensional airfoil characteristics for helicopter rotor analyses
The primary effects of Reynolds number on two dimensional airfoil characteristics are discussed. Results from an extensive literature search reveal the manner in which the minimum drag and maximum lift are affected by the Reynolds number. C sub d sub min and C sub l sub max are plotted versus Reynolds number for airfoils of various thickness and camber. From the trends observed in the airfoil data, universal scaling laws and easily implemented methods are developed to account for Reynolds number effects in helicopter rotor analyses
Enhanced thermoelectric properties of NaxCoO2 whisker crystals
Single-crystalline whiskers of thermoelectric cobalt oxide, NaxCoO2, have
been grown by an unconventional method from potassium-containing compositions,
and their transport properties, and chemical compositions were determined. The
growth mechanism was analyzed and interpreted by means of thermogravimetric
analysis. At 300 K, electrical resistivity r and thermoelectric power S of the
whisker are 102 u ohm cm and 83 uV/K, respectively. The power-factor, S2/r,
thus is enhanced up to ~ 68 uW/K2 cm.Comment: 8 pages, 4 figures, to appear in Appl. Phys. Let
Development of 2MASS Catalog Server Kit
We develop a software kit called "2MASS Catalog Server Kit" to easily
construct a high-performance database server for the 2MASS Point Source Catalog
(includes 470,992,970 objects) and several all-sky catalogs. Users can perform
fast radial search and rectangular search using provided stored functions in
SQL similar to SDSS SkyServer. Our software kit utilizes open-source RDBMS, and
therefore any astronomers and developers can install our kit on their personal
computers for research, observation, etc. Out kit is tuned for optimal
coordinate search performance. We implement an effective radial search using an
orthogonal coordinate system, which does not need any techniques that depend on
HTM or HEALpix. Applying the xyz coordinate system to the database index, we
can easily implement a system of fast radial search for relatively small (less
than several million rows) catalogs. To enable high-speed search of huge
catalogs on RDBMS, we apply three additional techniques: table partitioning,
composite expression index, and optimization in stored functions. As a result,
we obtain satisfactory performance of radial search for the 2MASS catalog. Our
system can also perform fast rectangular search. It is implemented using
techniques similar to those applied for radial search. Our way of
implementation enables a compact system and will give important hints for a
low-cost development of other huge catalog databases.Comment: 2011 PASP accepte
Hub loads analysis of the SA349/2 helicopter
The forces and moments at the rotor hub of an Aerospatiale SA349/2 helicopter were investigated. The study included three main topics. First, measured hub forces and moments for a range of level flight conditions (mu = 0.14 to 0.37) were compared with predictions from a comprehensive rotorcraft analysis to examine the influence of the wake model on the correlations. Second, the effect of changing the blade mass distribution and blade chordwise center of gravity location on the 3/rev nonrotating frame hub loads was studied for a high-speed flight condition (mu = 0.37). Third, the use of higher harmonic control to reduce nonrotating frame 3/rev hub shear forces was investigated. The last two topics were theoretical studies only
Positions of Point-Nodes in Borocarbide Superconductor YNi2B2C
To determine the superconducting gap function of YNi2B2C, we calculate the
local density of states (LDOS) around a single vortex core with the use of
Eilenberger theory and the band structure calculated by local density
approximation assuming various gap structures with point-nodes at different
positions. We also calculate the angular-dependent heat capacity in the vortex
state on the basis of the Doppler-Shift method. Comparing our results with the
STM/STS experiment, the angular-dependent heat capacity and thermal
conductivity, we propose the gap-structure of YNi2B2C, which has the
point-nodes and gap minima along . Our gap-structure is consistent with
all results of angular-resolved experiments.Comment: 7 pages, 5 figure
Chandra deep X-ray observation on the Galactic plane
Using the Chandra ACIS-I instruments, we have carried out the deepest X-ray
observation on a typical Galactic plane region at l 28.5 deg, where no discrete
X-ray sources have been known previously. We have detected, as well as strong
diffuse emission, 275 new point X-ray sources (4 sigma confidence) within two
partially overlapping fields (~250 arcmin^2 in total) down to ~3 x 10^{-15} erg
s^{-1} cm^{-2} (2 -- 10 keV) or ~ 7 x 10^{-16} erg s^{-1} cm^{-2} (0.5 -- 2
keV). We have studied spectral distribution of these point sources, and found
that very soft sources detected only below ~ 3 keV are more numerous than hard
sources detected only above ~ 3 keV. Only small number of sources are detected
both in the soft and hard bands. Surface density of the hard sources is almost
consistent with that at high Galactic regions, thus most of the hard sources
are considered to be Active Galactic Nuclei seen through the milky way. On the
other hand, some of the bright hard X-ray sources which show extremely flat
spectra and iron line or edge features are considered to be Galactic,
presumably quiescent dwarf novae. The soft sources show thermal spectra and
small interstellar hydrogen column densities, and some of them exhibit X-ray
flares. Therefore, most of the soft sources are probably X-ray active nearby
late type stars.Comment: Contribution to the proceedings of the "New Visions of the X-Ray
Universe in the XMM-Newton and Chandra Era" symposium at ESTEC, The
Netherlands. 26-30 Nov. 200
Recreational fishing: its impact on state and local economies
Bibliographical footnotes.Mode of access: Internet
Charge Ordering and Ferroelectricity in Half-doped Manganites
By means of density-functional simulations for half-doped manganites, such as
pseudocubic Pr0.5Ca0.5MnO3 and bilayer PrCa2Mn2O7, we discuss the occurrence of
ferroelectricity and we explore its crucial relation to the crystal structure
and to peculiar charge/spin/orbital ordering effects. In pseudocubic
Pr0.5Ca0.5MnO3, ferroelectricity is induced in the Zener polaron type
structure, where Mn ions are dimerized. In marked contrast, in bilayer
PrCa2Mn2O7, it is the displacements of apical oxygens bonded to either Mn3+ or
Mn4+ ions that play a key role in the rising of ferroelectricity. Importantly,
local dipoles due to apical oxygens are also intimately linked to charge and
orbital ordering patterns in MnO2 planes, which in turn contribute to
polarization. Finally, an important outcome of our work consists in proposing
Born effective charges as a valid mean to quantify charge disproportionation
effects, in terms of anisotropy and size of electronic clouds around Mn ions.Comment: 5 pages, 2 figures, submitted for publicatio
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