8,220 research outputs found
The classification of LANDSAT data for the Orlando, Florida, urban fringe area
Procedures used to map residential land cover on the Orlando, Florida, Urban fringe zone are detailed. The NASA Bureau of the Census Applications Systems Verification and Transfer project and the test site are described as well as the LANDSAT data used as the land cover information sources. Both single-date LANDSAT data processing and multitemporal principal components LANDSAT data processing are described. A summary of significant findings is included
Active clearance control system for a turbomachine
An axial compressor is provided with a cooling air manifold surrounding a portion of the shroud, and means for bleeding air from the compressor to the manifold for selectively flowing it in a modulating manner axially along the outer side of the stator/shroud to cool and shrink it during steady state operating conditions so as to obtain minimum shroud/rotor clearance conditions. Provision is also made to selectively divert the flow of cooling air from the manifold during transient periods of operation so as to alter the thermal growth or shrink rate of the stator/shroud and result in adequate clearance with the compressor rotor
Coupled opto-electronic simulation of organic bulk-heterojunction solar cells: parameter extraction and sensitivity analysis
A general problem arising in computer simulations is the number of material
and device parameters, which have to be determined by dedicated experiments and
simulation-based parameter extraction. In this study we analyze measurements of
the short-circuit current dependence on the active layer thickness and
current-voltage curves in poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid
methyl ester (P3HT:PCBM) based solar cells. We have identified a set of
parameter values including dissociation parameters that describe the
experimental data. The overall agreement of our model with experiment is good,
however a discrepancy in the thickness dependence of the current-voltage curve
questions the influence of the electric field in the dissociation process. In
addition transient simulations are analyzed which show that a measurement of
the turn-off photocurrent can be useful for estimating charge carrier
mobilities.Comment: 10 pages, 12 figures, 2 tables, Accepted for publication in Journal
of Applied Physic
Extended Poincar\'e supersymmetry in three dimensions and supersymmetric anyons
We classify the unitary representations of the extended Poincar\'e
supergroups in three dimensions. Irreducible unitary representations of any
spin can appear, which correspond to supersymmetric anyons. Our results also
show that all irreducible unitary representations necessarily have physical
momenta. This is in sharp contrast to the ordinary Poincar\'e group in three
dimensions, that admits in addition irreducible unitary representations with
non-physical momenta, which are discarded on physical grounds.Comment: 7 pages; commentaries added in Sect. IV A and in Conclusion; added
reference
The hot and cold interstellar matter of early type galaxies and their radio emission
Over the last few years, the knowledge of the interstellar matter (ISM) of early type galaxies has increased dramatically. Many early type galaxies are now known to have ISM in three different phases: cold (neutral hydrogen (HI), dust and molecular material), warm (ionized) and hot (S-ray emitting) gas. Early type galaxies have smaller masses of cold ISM (10 to the 7th power - 10 to the 8th power solar mass; Jura et al. 1987) than later type spiral galaxies, while they have far more hot gas (10 to the 9th power - 10 to the tenth power solar mass; Forman et al. 1985, Canizares et al. 1987). In order to understand the relationship between the different phases of the ISM and the role of the ISM in fueling radio continuum sources and star formation, researchers compared observational data from a wide range of wavelengths
Identification of Bare-Airframe Dynamics from Closed-Loop Data Using Multisine Inputs and Frequency Responses
Amethod is presented for computing multiple-input multiple-output frequency responses of bare-airframe dynamics for systems excited using orthogonal phase-optimized multisines and including correlated data arising from control mixing or feedback control. The estimation was posed as the solution to an underdetermined system of linear equations, for which additional information was supplied using interpolation of the frequency responses. A simulation model of the NASA T-2 aircraft having two inputs and two outputs was used to investigate the method in the open-loop configuration and under closed-loop control. The method was also applied to flight test data from the X-56A aeroelastic demonstrator having five inputs and ten outputs and flying under closed-loop control with additional control allocation mixing. Results demonstrated that the proposed method accurately estimates the bare airframe frequency responses in the presence of correlated data from control mixing and feedback control. Results also agreed with estimates obtained using different methods that are less sensitive to correlated inputs
Calculations for Mirror Symmetry with D-branes
We study normal functions capturing D-brane superpotentials on several one-
and two-parameter Calabi-Yau hypersurfaces and complete intersections in
weighted projective space. We calculate in the B-model and interpret the
results using mirror symmetry in the large volume regime, albeit without
identifying the precise A-model geometry in all cases. We identify new classes
of extensions of Picard-Fuchs equations, as well as a novel type of topology
changing phase transition involving quantum D-branes. A 4-d domain wall which
is obtained in one region of closed string moduli space from wrapping a
four-chain interpolating between two Lagrangian submanifolds is, for other
values of the parameters, represented by a disk ending on a single Lagrangian.Comment: 42 page
The Cold and Hot Gas Content of Fine-Structure E and S0 Galaxies
We investigate trends of the cold and hot gas content of early-type galaxies
with the presence of optical morphological peculiarities, as measured by the
fine-structure index (Sigma). HI mapping observations from the literature are
used to track the cold-gas content, and archival ROSAT PSPC data are used to
quantify the hot-gas content. We find that E and S0 galaxies with a high
incidence of optical peculiarities are exclusively X-ray underluminous and,
therefore, deficient in hot gas. In contrast, more relaxed galaxies with little
or no signs of optical peculiarities span a wide range of X-ray luminosities.
That is, the X-ray excess anticorrelates with Sigma. There appears to be no
similar trend of cold-gas content with either fine-structure index or X-ray
content. The fact that only apparently relaxed E and S0 galaxies are strong
X-ray emitters is consistent with the hypothesis that after strong disturbances
such as a merger hot-gas halos build up over a time scale of several gigayears.
This is consistent with the expected mass loss from stars.Comment: 12 pages, latex, 5 figures. Accepted for publication in A
Electron dynamics in intentionally disordered semiconductor superlattices
We study the dynamical behavior of disordered quantum-well-based
semiconductor superlattices where the disorder is intentional and short-range
correlated. We show that, whereas the transmission time of a particle grows
exponentially with the number of wells in an usual disordered superlattice for
any value of the incident particle energy, for specific values of the incident
energy this time increases linearly when correlated disorder is included. As
expected, those values of the energy coincide with a narrow subband of extended
states predicted by the static calculations of Dom\'{\i}nguez-Adame {\em et
al.} [Phys. Rev. B {\bf 51}, 14 ,359 (1994)]; such states are seen in our
dynamical results to exhibit a ballistic regime, very close to the WKB
approximation of a perfect superlattice. Fourier transform of the output signal
for an incident Gaussian wave packet reveals a dramatic filtering of the
original signal, which makes us confident that devices based on this property
may be designed and used for nanotechnological applications. This is more so in
view of the possibility of controllingthe outp ut band using a dc electric
field, which we also discuss. In the conclusion we summarize our results and
present an outlook for future developments arising from this work.Comment: 10 pagex, RevTex, 13 Postscript figures. Physical Review B (in press
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