27,721 research outputs found
Revised estimation of 550-km times 550-km mean gravity anomalies
The calculation of 550-km x 550-km mean gravity anomalies from 1 degree x 1 degree mean free-air gravimetry data is discussed. The block estimate procedure developed by Kaula is used to obtain 1,504 of the 1,654 possible mean block anomalies. The estimated block anomalies calculated from 1 deg x 1 deg mean anomalies referred to the reference ellipsoid and from 1 degree x 1 degree mean anomalies referred to a 24th-degree-and-order field are compared
Geophysical data base
A general data-management system that provides a random-access capability for large amounts of data is described. The system operates on a CDC 6400 computer using a combination of magnetic tape and disk storage. A FORTRAN subroutine package is provided to simplify the maintenance and use of the data
Revision of geodetic parameters
Laser data from nine satellites and 12 stations are combined with surface-gravity data to obtain spherical harmonics representing the geopotential complete through degree and order 18. This laser-data-only solution provides a reasonable improvement to the gravity field
Robot docking using mixtures of Gaussians
This paper applies the Mixture of Gaussians probabilistic model, combined with Expectation Maximization optimization to the task of summarizing three dimensionals range data for the mobile robot. This provides a flexible way of dealing with uncertainties in sensor information, and allows the introduction of prior knowledge into low-level perception modules. Problems with the basic approach were solved in several ways: the mixture of Gaussians was reparameterized to reflect the types of objects expected in the scene, and priors on model parameters were included in the optimization process. Both approaches force the optimization to find 'interesting' objects, given the sensor and object characteristics. A higher level classifier was used to interpret the results provided by the model, and to reject spurious solutions
Anomalous enhancement of a penguin hadronic matrix element in B->K eta'
We estimate the density matrix element for the pi^0, eta and eta' production
from the vacuum in the large-N_c limit. As a consequence, we find that the QCD
axial anomaly leads to highly non-trivial corrections to the usual flavour
SU(3) relations between B^0-> K^0 pi^0, B^0-> K^0 eta and B^0-> K^0 eta' decay
amplitudes. These corrections may explain why the B-> K eta' branching ratio is
about six times larger than the B-> K pi one.Comment: 5 pages, 1 figur
Spinodal fractionation in a polydisperse square well fluid
Using Kinetic Monte Carlo simulation, we model gas-liquid spinodal
decomposition in a size-polydisperse square well fluid, representing a
'near-monodisperse' colloidal dispersion. We find that fractionation (demixing)
of particle sizes between the phases begins asserting itself shortly after the
onset of phase ordering. Strikingly, the direction of size fractionation can be
reversed by a seemingly trivial choice between two inter-particle potentials
which, in the monodisperse case, are identical -- we rationalise this in terms
of a perturbative, equilibrium theory of polydispersity. Furthermore, our
quantitative results show that Kinetic Monte Carlo simulation can provide
detailed insight into the role of fractionation in real colloidal systems.Comment: 7 pages, 7 figures, to be published in Phys. Rev.
Radio-wave propagation in the non-Gaussian interstellar medium
Radio waves propagating from distant pulsars in the interstellar medium
(ISM), are refracted by electron density inhomogeneities, so that the intensity
of observed pulses fluctuates with time. The theory relating the observed pulse
time-shapes to the electron-density correlation function has developed for 30
years, however, two puzzles have remained. First, observational scaling of
pulse broadening with the pulsar distance is anomalously strong; it is
consistent with the standard model only when non-uniform statistics of electron
fluctuations along the line of sight are assumed. Second, the observed pulse
shapes are consistent with the standard model only when the scattering material
is concentrated in a narrow slab between the pulsar and the Earth.
We propose that both paradoxes are resolved at once if one assumes stationary
and uniform, but non-Gaussian statistics of the electron-density distribution.
Such statistics must be of Levy type, and the propagating ray should exhibit a
Levy flight. We propose that a natural realization of such statistics may be
provided by the interstellar medium with random electron-density
discontinuities. We develop a theory of wave propagation in such a non-Gaussian
random medium, and demonstrate its good agreement with observations. The
qualitative introduction of the approach and the resolution of the
anomalous-scaling paradox was presented earlier in [PRL 91, 131101 (2003); ApJ
584, 791 (2003)].Comment: 27 pages, changes to match published versio
Interface design in the process industries
Every operator runs his plant in accord with his own mental model of the process. In this sense, one characteristic of an ideal man-machine interface is that it be in harmony with that model. With this theme in mind, the paper first reviews the functions of the process operator and compares them with human operators involved in control situations previously studied outside the industrial environment (pilots, air traffic controllers, helmsmen, etc.). A brief history of the operator interface in the process industry and the traditional methodology employed in its design is then presented. Finally, a much more fundamental approach utilizing a model definition of the human operator's behavior is presented
A guide for performing system safety analysis
A general guide is presented for performing system safety analyses of hardware, software, operations and human elements of an aerospace program. The guide describes a progression of activities that can be effectively applied to identify hazards to personnel and equipment during all periods of system development. The general process of performing safety analyses is described; setting forth in a logical order the information and data requirements, the analytical steps, and the results. These analyses are the technical basis of a system safety program. Although the guidance established by this document cannot replace human experience and judgement, it does provide a methodical approach to the identification of hazards and evaluation of risks to the system
- …