17,013 research outputs found

### A Solenoidal Finite Element Approach for Prediction of Radar Cross Sections

This report considers the solution of problems that involve the scattering of plane electromagnetic waves by perfectly conducting obstacles. Such problems are governed by the Maxwell equations. An interesting facet of the solution of Faraday's law and Ampere's law, which on their own form a complete equation set for the determination of the field intensity components, is that there are the additional conservation statements of Coulomb's law and Gauss's law, which appear to be in excess of requirements. Often, these additional constraints are neglected due to an inability to incorporate them into the solution scheme. With the successful development of a solenoidal finite element for the solution of viscous incompressible flows, such a device now offers a practical means for the solution of the full Maxwell equations. To demonstrate the validity of this assertion, a suitable solution scheme is presented, accompanied by sample results for various test problems

### Simulation capability for dynamics of two-body flexible satellites

An analysis and computer program were prepared to realistically simulate the dynamic behavior of a class of satellites consisting of two end bodies separated by a connecting structure. The shape and mass distribution of the flexible end bodies are arbitrary; the connecting structure is flexible but massless and is capable of deployment and retraction. Fluid flowing in a piping system and rigid moving masses, representing a cargo elevator or crew members, have been modeled. Connecting structure characteristics, control systems, and externally applied loads are modeled in easily replaced subroutines. Subroutines currently available include a telescopic beam-type connecting structure as well as attitude, deployment, spin and wobble control. In addition, a unique mass balance control system was developed to sense and balance mass shifts due to the motion of a cargo elevator. The mass of the cargo may vary through a large range. Numerical results are discussed for various types of runs

### Water separator

An apparatus for separating liquids from gases or gaseous fluids is described. Features of the apparatus include: (1) the collection and removal of the moisture in the fluid is not dependent upon, or affected by gravity; (2) all the collected water is cyclically drained from the apparatus irrespective of the attitude of the separator; and (3) a fluid actuator is utilized to remove the collected water from the separator

### Direct QR factorizations for tall-and-skinny matrices in MapReduce architectures

The QR factorization and the SVD are two fundamental matrix decompositions
with applications throughout scientific computing and data analysis. For
matrices with many more rows than columns, so-called "tall-and-skinny
matrices," there is a numerically stable, efficient, communication-avoiding
algorithm for computing the QR factorization. It has been used in traditional
high performance computing and grid computing environments. For MapReduce
environments, existing methods to compute the QR decomposition use a
numerically unstable approach that relies on indirectly computing the Q factor.
In the best case, these methods require only two passes over the data. In this
paper, we describe how to compute a stable tall-and-skinny QR factorization on
a MapReduce architecture in only slightly more than 2 passes over the data. We
can compute the SVD with only a small change and no difference in performance.
We present a performance comparison between our new direct TSQR method, a
standard unstable implementation for MapReduce (Cholesky QR), and the classic
stable algorithm implemented for MapReduce (Householder QR). We find that our
new stable method has a large performance advantage over the Householder QR
method. This holds both in a theoretical performance model as well as in an
actual implementation

### Perturbing forces in the lunar gravitational potential, part 3 Final report

Spherical harmonics for evaluating perturbing forces on lunar satellite due to nonsymmetric mass distribution of moo

### Contamination cannot explain the lack of large-scale power in the cosmic microwave background radiation

Several anomalies appear to be present in the large-angle cosmic microwave
background (CMB) anisotropy maps of WMAP. One of these is a lack of large-scale
power. Because the data otherwise match standard models extremely well, it is
natural to consider perturbations of the standard model as possible
explanations. We show that, as long as the source of the perturbation is
statistically independent of the source of the primary CMB anisotropy, no such
model can explain this large-scale power deficit. On the contrary, any such
perturbation always reduces the probability of obtaining any given low value of
large-scale power. We rigorously prove this result when the lack of large-scale
power is quantified with a quadratic statistic, such as the quadrupole moment.
When a statistic based on the integrated square of the correlation function is
used instead, we present strong numerical evidence in support of the result.
The result applies to models in which the geometry of spacetime is perturbed
(e.g., an ellipsoidal Universe) as well as explanations involving local
contaminants, undiagnosed foregrounds, or systematic errors. Because the
large-scale power deficit is arguably the most significant of the observed
anomalies, explanations that worsen this discrepancy should be regarded with
great skepticism, even if they help in explaining other anomalies such as
multipole alignments.Comment: 9 pages. Submitted to Phys. Rev.

### Tensor Spectral Clustering for Partitioning Higher-order Network Structures

Spectral graph theory-based methods represent an important class of tools for
studying the structure of networks. Spectral methods are based on a first-order
Markov chain derived from a random walk on the graph and thus they cannot take
advantage of important higher-order network substructures such as triangles,
cycles, and feed-forward loops. Here we propose a Tensor Spectral Clustering
(TSC) algorithm that allows for modeling higher-order network structures in a
graph partitioning framework. Our TSC algorithm allows the user to specify
which higher-order network structures (cycles, feed-forward loops, etc.) should
be preserved by the network clustering. Higher-order network structures of
interest are represented using a tensor, which we then partition by developing
a multilinear spectral method. Our framework can be applied to discovering
layered flows in networks as well as graph anomaly detection, which we
illustrate on synthetic networks. In directed networks, a higher-order
structure of particular interest is the directed 3-cycle, which captures
feedback loops in networks. We demonstrate that our TSC algorithm produces
large partitions that cut fewer directed 3-cycles than standard spectral
clustering algorithms.Comment: SDM 201

### RTCC requirements for mission G - Landing site determination using onboard observations, part 2 Final report

Computer programs for evaluation of telemetered rendezvous radar tracking data of orbiting command module and lunar module landing site determinatio

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