17,380 research outputs found
Dynamic stall modeling and correlation with experimental data on airfoils and rotors
Two methods for modeling dynamic stall have been developed. The alpha, A, B method generates lift and pitching moments as functions of angle of attack and its first two time derivatives. The coefficients are derived from experimental data for oscillating airfoils. The Time Delay Method generates the coefficients from steady state airfoil characteristics and an associated time delay in stall beyond the steady state stall angle. Correlation with three types of test data shows that the alpha, A, B method is somewhat better for use in predicting helicopter rotor response in forward flight. Correlation with lift and moment hysteresis loops generated for oscillating airfoils was good for both models
Remote sensing in Iowa agriculture: Identification and classification of Iowa's crops, soils and forestry resources using ERTS-1 and complimentary underflight imagery
The author has identified the following significant results. Springtime ERTS-1 imagery covering pre-selected test sites in Iowa showed considerable detail with respect to broad soil and land use patterns. Additional imagery has been incorporated into a state mosaic. The mosaic was used as a base for soil association lines transferred from an existing map. The regions of greatest contrast are between the Clarion-Nicollet-Webster soil association area and adjacent areas. Landscape characteristics in this area result in land use patterns with a high percentage of pasture, hay, and timber. The soil association areas of the state that have patterns interpreted to be associated with intensive row crop production are: Moody, Galva-Primghar-Sac, Clarion-Nicollet-Webter, Tama-Muscatine, Dinsdale-Tama, Cresco-Lourdes, Clyde, Kenyon-Floyd-Clyde, and the Luton-Onawa-Salix area on the Missouri River floodplain. Forestland estimates have been attained for an area in central Iowa using wintertime ERTS-1 imagery. Visual analysis of multispectral, temporal imagery indicates that temporal analysis for cropland identification and acreage analyses procedures may be a very useful tool. Combinations of wintertime, springtime, and summertime ERTS-1 imagery separate most vegetation types. Timing can be critical depending upon crop development and harvesting times because of the dynamic nature of agricultural production
Effective Widths and Effective Number of Phonons of Multiphonon Giant Resonances
We discuss the origin of the difference between the harmonic value of the
width of the multiphonon giant resonances and the smaller observed value.
Analytical expressions are derived for both the effective width and the average
cross-section. The contribution of the Brink-Axel mechanism in resolving the
discrepancy is pointed out.Comment: 9 pages, 4 figure
Scaling and Duality in Semi-exclusive Processes
We discuss extending scaling and duality studies to semi-exclusive processes.
We show that semi-exclusive hard pion photoproduction should exhibit scaling
behavior in kinematic regions where the photon and pion both interact directly
with the same quark. We show that such kinematic regions exist. We also show
that the constancy with changing momentum transfer of the resonance
peak/scaling curve ratio, familiar for many resonances in deep inelastic
scattering, is also expected in the semi-exclusive case.Comment: 8 pages, 4 figures, submitted to Phys.Rev.
Leading-Log Effects in the Resonance Electroweak Form Factors
We study log corrections to inelastic scattering at high Bjorken x for Q^2
from 1 to 21 GeV^2. At issue is the presence of log corrections, which can be
absent if high x scattering has damped gluon radiation. We find logarithmic
correction of the scaling curve extrapolated to low Q^2 improves the duality
between it and the resonance plus background data in the Delta region,
indicating log corrections exist in the data. However, at W > 2 GeV and high x,
the data shows a (1-x)^3 form. Log corrections in one situation but not in
another can be reconciled by a W- or Q^2- dependent higher twist correction.Comment: 13 pages, report nos. RPI-94-N90 and WM-94-106, revtex, two figures
(available by fax or post
The Breakdown of Kinetic Theory in Granular Shear Flows
We examine two basic assumptions of kinetic theory-- binary collisions and
molecular chaos-- using numerical simulations of sheared granular materials. We
investigate a wide range of densities and restitution coefficients and
demonstrate that kinetic theory breaks down at large density and small
restitution coefficients. In the regimes where kinetic theory fails, there is
an associated emergence of clusters of spatially correlated grains
Predictability of Self-Organizing Systems
We study the predictability of large events in self-organizing systems. We
focus on a set of models which have been studied as analogs of earthquake
faults and fault systems, and apply methods based on techniques which are of
current interest in seismology. In all cases we find detectable correlations
between precursory smaller events and the large events we aim to forecast. We
compare predictions based on different patterns of precursory events and find
that for all of the models a new precursor based on the spatial distribution of
activity outperforms more traditional measures based on temporal variations in
the local activity.Comment: 15 pages, plain.tex with special macros included, 4 figure
Remote sensing in Iowa agriculture: Identification and classification of Iowa's crops, soils and forestry resources using ERTS-1 and complimentary underflight imagery
There are no author-identified significant results in this report
On the Nucleon Distribution Amplitude: The Heterotic Solution
We present a new nucleon distribution amplitude which amalgamates features of
the Chernyak-Ogloblin-Zhitnitsky model with those of the Gari-Stefanis model.
This "heterotic" solution provides the possibility to have asymptotically a
small ratio \hbox{}, while fulfilling
most of the sum-rule requirements up to the third order. Using this nucleon
distribution amplitude we calculate the electromagnetic and weak nucleon form
factors, the transition form factor and the decay widths
of the charmonium levels , , and into .
The agreement with the available data is remarkable in all cases.Comment: 15 pages, RUB-TPII-21/92 Preprin
Anomaly freedom in Seiberg-Witten noncommutative gauge theories
We show that noncommutative gauge theories with arbitrary compact gauge group
defined by means of the Seiberg-Witten map have the same one-loop anomalies as
their commutative counterparts. This is done in two steps. By explicitly
calculating the \epsilon^{\m_1\m_2\m_3\m_4} part of the renormalized
effective action, we first find the would-be one-loop anomaly of the theory to
all orders in the noncommutativity parameter \theta^{\m\n}. And secondly we
isolate in the would-be anomaly radiative corrections which are not BRS
trivial. This gives as the only true anomaly occurring in the theory the
standard Bardeen anomaly of commutative spacetime, which is set to zero by the
usual anomaly cancellation condition.Comment: LaTeX 2e, no macros, no figures, 32 A4 page
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