2,060 research outputs found
Research on an expert system for database operation of simulation-emulation math models. Volume 2, Phase 1: Results
A reference manual is provided for NESS, a simulation expert system. This manual gives user information regarding starting and operating NASA expert simulation system (NESS). This expert system provides an intelligent interface to a generic simulation program for spacecraft attitude control problems. A menu of the functions the system can perform is provided. Control repeated returns to this menu after executing each user request
Research on an expert system for database operation of simulation-emulation math models. Volume 1, Phase 1: Results
The results of the first phase of Research on an Expert System for Database Operation of Simulation/Emulation Math Models, is described. Techniques from artificial intelligence (AI) were to bear on task domains of interest to NASA Marshall Space Flight Center. One such domain is simulation of spacecraft attitude control systems. Two related software systems were developed to and delivered to NASA. One was a generic simulation model for spacecraft attitude control, written in FORTRAN. The second was an expert system which understands the usage of a class of spacecraft attitude control simulation software and can assist the user in running the software. This NASA Expert Simulation System (NESS), written in LISP, contains general knowledge about digital simulation, specific knowledge about the simulation software, and self knowledge
Development of a coupled expert system for the spacecraft attitude control problem
A majority of the current expert systems focus on the symbolic-oriented logic and inference mechanisms of artificial intelligence (AI). Common rule-based systems employ empirical associations and are not well suited to deal with problems often arising in engineering. Described is a prototype expert system which combines both symbolic and numeric computing. The expert system's configuration is presented and its application to a spacecraft attitude control problem is discussed
A Randomized Controlled Trial of Extended Brief Intervention for Alcohol-Dependent Patients in an Acute Hospital Setting
To determine whether alcohol-dependent patients in a hospital setting benefit from extended brief interventions (EBI) delivered by an Alcohol Specialist Nurse. Methods Alcohol-dependent patients recruited via screening at the emergency department (ED) (n = 267), whether or not admitted to hospital, were randomized to EBI (up to six counselling sessions offered) or control. At 6 months, 84.2% of patients were assessed by a researcher blinded to the intervention. The primary outcome was a fall in Severity of Alcohol Dependence Questionnaire. Results There was no difference between groups in the primary outcome [odds ratio (OR) 1.02; 95% confidence interval (CI): 0.38, 2.75, P = 0.97]. Secondary outcomes including alcohol consumption and readiness to change did not show a significant difference between groups. However, all secondary outcome measures improved, on average, in both arms. Conclusions Although EBI can be delivered in an ED or inpatient setting, it was not shown to be an advantage over screening and usual management (which included advice on alternative services), with patients in both groups showing an average improvement
Vorticity alignment results for the three-dimensional Euler and Navier-Stokes equations
We address the problem in Navier-Stokes isotropic turbulence of why the
vorticity accumulates on thin sets such as quasi-one-dimensional tubes and
quasi-two-dimensional sheets. Taking our motivation from the work of Ashurst,
Kerstein, Kerr and Gibson, who observed that the vorticity vector
{\boldmath\omega} aligns with the intermediate eigenvector of the strain
matrix , we study this problem in the context of both the three-dimensional
Euler and Navier-Stokes equations using the variables \alpha =
\hat{{\boldmath\xi}}\cdot S\hat{{\boldmath\xi}} and {\boldmath\chi} =
\hat{{\boldmath\xi}}\times S\hat{{\boldmath\xi}} where
\hat{{\boldmath\xi}} = {\boldmath\omega}/\omega. This introduces the
dynamic angle , which lies between
{\boldmath\omega} and S{\boldmath\omega}. For the Euler equations a
closed set of differential equations for and {\boldmath\chi} is
derived in terms of the Hessian matrix of the pressure . For
the Navier-Stokes equations, the Burgers vortex and shear layer solutions turn
out to be the Lagrangian fixed point solutions of the equivalent
(\alpha,{\boldmath\chi}) equations with a corresponding angle .
Under certain assumptions for more general flows it is shown that there is an
attracting fixed point of the (\alpha,\bchi) equations which corresponds to
positive vortex stretching and for which the cosine of the corresponding angle
is close to unity. This indicates that near alignment is an attracting state of
the system and is consistent with the formation of Burgers-like structures.Comment: To appear in Nonlinearity Nov. 199
Surface critical exponents at a uniaxial Lifshitz point
Using Monte Carlo techniques, the surface critical behaviour of
three-dimensional semi-infinite ANNNI models with different surface
orientations with respect to the axis of competing interactions is
investigated. Special attention is thereby paid to the surface criticality at
the bulk uniaxial Lifshitz point encountered in this model. The presented Monte
Carlo results show that the mean-field description of semi-infinite ANNNI
models is qualitatively correct. Lifshitz point surface critical exponents at
the ordinary transition are found to depend on the surface orientation. At the
special transition point, however, no clear dependency of the critical
exponents on the surface orientation is revealed. The values of the surface
critical exponents presented in this study are the first estimates available
beyond mean-field theory.Comment: 10 pages, 7 figures include
Greenhouse Gas Measurements Over a 144 km Open Path in the Canary Islands
A new technique for the satellite remote sensing of greenhouse gases in the atmosphere via the absorption of short-wave infrared laser signals transmitted between counter-rotating satellites in low Earth orbit has recently been proposed; this would enable the acquisition of a long-term, stable, global set of altitude-resolved concentration measurements. We present the first ground-based experimental demonstration of this new infrared-laser occultation method, in which the atmospheric absorption of CO2 near 2.1µm was measured over a ∼144km path length between two peaks in the Canary Islands (at an altitude of ∼2.4 km), using relatively low power diode lasers (∼4 to 10mW). The retrieved CO2 volume mixing ratio of 400 ppm (±15 ppm) is consistent within experimental uncertainty with simultaneously recorded in situ validation measurements. We conclude that the new method has a sound basis for monitoring CO2 in the free atmosphere; other greenhouse gases such as methane, nitrous oxide and water vapour can be monitored in the same way
Transition Matrix Monte Carlo Reweighting and Dynamics
We study an induced dynamics in the space of energy of single-spin-flip Monte
Carlo algorithm. The method gives an efficient reweighting technique. This
dynamics is shown to have relaxation times proportional to the specific heat.
Thus, it is plausible for a logarithmic factor in the correlation time of the
standard 2D Ising local dynamics.Comment: RevTeX, 5 pages, 3 figure
Evidence for a singularity in ideal magnetohydrodynamics: implications for fast reconnection
Numerical evidence for a finite-time singularity in ideal 3D
magnetohydrodynamics (MHD) is presented. The simulations start from two
interlocking magnetic flux rings with no initial velocity. The magnetic
curvature force causes the flux rings to shrink until they come into contact.
This produces a current sheet between them. In the ideal compressible
calculations, the evidence for a singularity in a finite time is that the
peak current density behaves like for a range of
sound speeds (or plasma betas). For the incompressible calculations consistency
with the compressible calculations is noted and evidence is presented that
there is convergence to a self-similar state. In the resistive reconnection
calculations the magnetic helicity is nearly conserved and energy is
dissipated.Comment: 4 pages, 4 figure
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