1,082 research outputs found
Cartographic Modeling: Computer-assisted Analysis of Spatially Defined Neighborhoods
Cartographic models addressing a wide variety of applications are composed of fundamental map processing operations. These primitive operations are neither data base nor application-specific. By organizing the set of operations into a mathematical-like structure, the basis for a generalized cartographic modeling framework can be developed. Among the major classes of primitive operations are those associated with reclassifying map categories, overlaying maps, determining distance and connectivity, and characterizing cartographic neighborhoods. The conceptual framework of cartographic modeling is established and techniques for characterizing neighborhoods are used as a means of demonstrating some of the more sophisticated procedures of computer-assisted map analysis. A cartographic model for assessing effective roundwood supply is briefly described as an example of a computer analysis. Most of the techniques described have been implemented as part of the map analysis package developed at the Yale School of Forestry and Environmental Studies
Identification of nonlinear sparse networks using sparse Bayesian learning
© 2017 IEEE. This paper considers a parametric approach to infer sparse networks described by nonlinear ARX models, with linear ARX treated as a special case. The proposed method infers both the Boolean structure and the internal dynamics of the network. It considers classes of nonlinear systems that can be written as weighted (unknown) sums of nonlinear functions chosen from a fixed basis dictionary. Due to the sparse topology, coefficients of most groups are zero. Besides, only a few nonlinear terms in nonzero groups contribute to the internal dynamics. Therefore, the identification problem should estimate both group-and element-sparse parameter vectors. The proposed method combines Sparse Bayesian Learning (SBL) and Group Sparse Bayesian Learning (GSBL) to impose both kinds of sparsity. Simulations indicate that our method outperforms SBL and GSBL when these are applied alone. A linear ring structure network also illustrates that the proposed method has improved performance to the kernel approach
A New Simulation Metric to Determine Safe Environments and Controllers for Systems with Unknown Dynamics
We consider the problem of extracting safe environments and controllers for
reach-avoid objectives for systems with known state and control spaces, but
unknown dynamics. In a given environment, a common approach is to synthesize a
controller from an abstraction or a model of the system (potentially learned
from data). However, in many situations, the relationship between the dynamics
of the model and the \textit{actual system} is not known; and hence it is
difficult to provide safety guarantees for the system. In such cases, the
Standard Simulation Metric (SSM), defined as the worst-case norm distance
between the model and the system output trajectories, can be used to modify a
reach-avoid specification for the system into a more stringent specification
for the abstraction. Nevertheless, the obtained distance, and hence the
modified specification, can be quite conservative. This limits the set of
environments for which a safe controller can be obtained. We propose SPEC, a
specification-centric simulation metric, which overcomes these limitations by
computing the distance using only the trajectories that violate the
specification for the system. We show that modifying a reach-avoid
specification with SPEC allows us to synthesize a safe controller for a larger
set of environments compared to SSM. We also propose a probabilistic method to
compute SPEC for a general class of systems. Case studies using simulators for
quadrotors and autonomous cars illustrate the advantages of the proposed metric
for determining safe environment sets and controllers.Comment: 22nd ACM International Conference on Hybrid Systems: Computation and
Control (2019
Probing shell structure and shape changes in neutron-rich sulfur isotopes through transient-field g factor measurements on fast radioactive beams of 38S and 40S
The shell structure underlying shape changes in neutron-rich nuclei near N=28
has been investigated by a novel application of the transient field technique
to measure the first-excited state g factors in 38S and 40S produced as fast
radioactive beams. There is a fine balance between proton and neutron
contributions to the magnetic moments in both nuclei. The g factor of deformed
40S does not resemble that of a conventional collective nucleus because spin
contributions are more important than usual.Comment: 10 pages, 6 figures, accepted in PR
C-5A/orbiter wind tunnel testing and analysis: Piggyback ferry
Wind tunnel testing and analytical studies of the feasibility of ferrying the NASA Shuttle Orbiter on the C-5A in a piggyback mode have been accomplished. Testing was conducted in the 8x12 foot low speed wind tunnel using an existing 0.0399 scale C-5A model in conjunction with a NASA 0.0405 scale Orbiter model. Six component force and moment data were measured over a range of pitch and yaw angles to determine lift and drag characteristics, lateral/directional stability characteristics and longitudinal and directional control powers. A description of the wind tunnel test program with a run schedule and the complete plotted data for all the test runs are presented. Initial emphasis was given to determining the effects of the Orbiter above the C-5A and the optimum location for minimum interference on C-5A characteristics. A comprehensive series of cruise configurations were tested including a range of Orbiter longitudinal and vertical locations, incidences, and afterbody fairings. Subsequently, a series of configurations were devised during the test program to determine means of recovering directional stability degradation due to Orbiter interference
Shell structure underlying the evolution of quadrupole collectivity in S-38 and S-40 probed by transient-field g-factor measurements on fast radioactive beams
The shell structure underlying shape changes in neutron-rich nuclei between
N=20 and N=28 has been investigated by a novel application of the transient
field technique to measure the first-excited state g factors in S-38 and S-40
produced as fast radioactive beams. Details of the new methodology are
presented. In both S-38 and S-40 there is a fine balance between the proton and
neutron contributions to the magnetic moments. Shell model calculations which
describe the level schemes and quadrupole properties of these nuclei also give
a satisfactory explanation of the g factors. In S-38 the g factor is extremely
sensitive to the occupation of the neutron p3/2 orbit above the N=28 shell gap
as occupation of this orbit strongly affects the proton configuration. The g
factor of deformed S-40 does not resemble that of a conventional collective
nucleus because spin contributions are more important than usual.Comment: 10 pages, 36 figures, accepted for publication in Physical Review
Turkdean Roman Villa, Gloucestershire: archaeological investigations 1997-1998
Before the transmission of the first ‘live’ Time Team television programme on 23 August 1997, the existence of a Roman villa near Chalkhill Barn in the parish of Turkdean, 12 miles north-east of Cirencester and 2 miles from the Fosse Way, was hardly known to the archaeological community (FIG. 1). That a Roman building did exist in this location had, however, been suspected for a number of years by the landowner, the late Mr Wilf Mustoe. Distinctive linear parchmarks suggestive of buildings had been clearly visible at ground level in the grass pasture each dry summer, and in 1976 Mr Mustoe made a measured sketch plan of them on the back of an envelope. Subsequently the sketch was drawn up into a scale plan entitled ‘Roman villa’ by Simon Goddard, a relation. There was little knowledge of the site outside of Mr Mustoe's family until it was independently ‘discovered’ by local archaeologist Roger Box in August 1996 whilst fortuitously flying over the site in a helicopter. In the evening light Mr Box instantly recognised the parchmarks of an unmistakable Roman villa and took a series of photographs (FIG. 2). Mr Box showed his photographs to Mr Mustoe, and with his agreement wrote to Time Team suggesting that this would be an excellent site for a television programme. Arrangements were duly set in place and the evidence of the cropmarks was confirmed by a trial geophysical survey in March 199
A no-singularity scenario in loop quantum gravity
Canonical methods allow the derivation of effective gravitational actions
from the behavior of space-time deformations reflecting general covariance.
With quantum effects, the deformations and correspondingly the effective
actions change, revealing dynamical implications of quantum corrections. A new
systematic way of expanding these actions is introduced showing as a first
result that inverse-triad corrections of loop quantum gravity simplify the
asymptotic dynamics near a spacelike collapse singularity. By generic quantum
effects, the singularity is removed.Comment: 10 page
- …