Jerry James - Academia.edu (original) (raw)

Papers by Jerry James

Research paper thumbnail of Na-O anticorrelation and horizontal branches

Astronomy & Astrophysics, 2007

We are studying the Na-O anticorrelation in several globular clusters of different Horizontal Bra... more We are studying the Na-O anticorrelation in several globular clusters of different Horizontal Branch (HB) morphology in order to derive a possible relation between (primordial) chemical inhomogeneities and morphological parameters of the cluster population. We used the multifiber spectrograph FLAMES on the ESO Very Large Telescope UT2 and derived atmospheric parameters and elemental abundances of Fe, O and Na for about 150 red giant stars in the Galactic globular cluster NGC 6752. The average metallicity we derive is [Fe/H] = −1.56, in agreement with other results from red giants, but lower than obtained for dwarfs or early subgiants. In NGC 6752 there is not much space for an intrinsic spread in metallicity: on average, the rms scatter in [Fe/H] is 0.037 ± 0.003 dex, while the scatter expected on the basis of the major error sources is 0.039 ± 0.003 dex. The distribution of stars along the Na-O anticorrelation is different to what was found in the first paper of this series for the globular cluster NGC 2808: in NGC 6752 it is skewed toward more Na-poor stars, and it resembles more the one in M 13. Detailed modeling is required to clarify whether this difference may explain the very different distributions of stars along the HB.

Research paper thumbnail of Design of the Kan distributed object system

Concurrency: Practice and Experience, 2000

Research paper thumbnail of Surface and borehole electromagnetic imaging of conducting contaminant plumes

Electromagnetic induction tomography is a promising new tool for imaging electrical conductivity ... more Electromagnetic induction tomography is a promising new tool for imaging electrical conductivity variations in the earth. The EM source field is produced by induction coil (magnetic dipole) transmitters deployed at the surface or in boreholes. Vertical and horizontal component magnetic field detectors are deployed in other boreholes or on the surface. Sources and receivers are typically deployed in a configuration surrounding the region of interest. The goal of this procedure is to image electrical conductivity variations in the earth, much as x-ray tomography is used to image density variations through cross-sections of the body. Although such EM field techniques have been developed and applied, the algorithms for inverting the magnetic data to produce the desired images of electrical conductivity have not kept pace. One of the main reasons for the lag in the algorithm development has been the fact that the magnetic induction problem is inherently three dimensional: other imaging methods such as x-ray and seismic can make use of two-dimensional approximations that are not too far from reality, but we do not have this luxury in EM induction tomography. In addition, previous field experiments were conducted at controlled test sites that typically do not have much external noise or extensive surface clutter problems often associated with environmental sites. To use the same field techniques in environments more typical of cleanup sites requires a new set of data processing tools to remove the effects of both noise and clutter. The goal of this project is to join theory and experiment to produce enhanced images of electrically conducting fluids underground, allowing better localization of contaminants and improved planning strategies for the subsequent remediation efforts. After explaining the physical context in more detail, this report will summarize the progress made in the first year of this project: (1) on code development and (2) on field tests of these methods. We conclude with a brief statement of the research directions for the second year of the project.

Research paper thumbnail of Analysis of approximate inverses in tomography II. Iterative inverses

This paper continues the analysis of approximate inverses from Part I by concentrating on iterati... more This paper continues the analysis of approximate inverses from Part I by concentrating on iterative inverses in linear tomographic applications. The importance of differentiating between the ideal resolution of the operator/matrix to be inverted and the actual or effective resolution obtained by the approximate inverse during an iterative procedure is stressed. Means of obtaining the effective resolution operator for standard iterative procedures such as conjugate gradients, Lanczos, and LSQR are provided, while circumventing the usual need to produce a singular-value decomposition of the operator being inverted. The methods discussed produce very simple results in calculations with infinite precision, but require reorthogonalization of the Krylov vectors/operators produced by the iterative procedures in finite precision. Although this need for reorthogonalization increases the expense of the procedure somewhat, it still produces the desired results much more efficiently than what could be obtained using a full singular-value decomposition of the operator.

Research paper thumbnail of Compositional verification of a multi-agent system for one-to-many negotiation

Applied Intelligence, Mar 1, 2004

Verification of multi-agent systems hardly occurs in design practice. One of the difficulties is ... more Verification of multi-agent systems hardly occurs in design practice. One of the difficulties is that required properties for a multi-agent system usually refer to multi-agent behaviour which has nontrivial dynamics. To constrain these multi-agent behavioural dynamics, often a form of organisational structure is used, for example, for negotiating agents, by following strict protocols. The claim is that these negotiation protocols entail a structured process that is manageable with respect to analysis, design and execution of such a multi-agent system. ...

Research paper thumbnail of Na-O anticorrelation and horizontal branches

Astronomy & Astrophysics, 2007

We are studying the Na-O anticorrelation in several globular clusters of different Horizontal Bra... more We are studying the Na-O anticorrelation in several globular clusters of different Horizontal Branch (HB) morphology in order to derive a possible relation between (primordial) chemical inhomogeneities and morphological parameters of the cluster population. We used the multifiber spectrograph FLAMES on the ESO Very Large Telescope UT2 and derived atmospheric parameters and elemental abundances of Fe, O and Na for about 150 red giant stars in the Galactic globular cluster NGC 6752. The average metallicity we derive is [Fe/H] = −1.56, in agreement with other results from red giants, but lower than obtained for dwarfs or early subgiants. In NGC 6752 there is not much space for an intrinsic spread in metallicity: on average, the rms scatter in [Fe/H] is 0.037 ± 0.003 dex, while the scatter expected on the basis of the major error sources is 0.039 ± 0.003 dex. The distribution of stars along the Na-O anticorrelation is different to what was found in the first paper of this series for the globular cluster NGC 2808: in NGC 6752 it is skewed toward more Na-poor stars, and it resembles more the one in M 13. Detailed modeling is required to clarify whether this difference may explain the very different distributions of stars along the HB.

Research paper thumbnail of Design of the Kan distributed object system

Concurrency: Practice and Experience, 2000

Research paper thumbnail of Surface and borehole electromagnetic imaging of conducting contaminant plumes

Electromagnetic induction tomography is a promising new tool for imaging electrical conductivity ... more Electromagnetic induction tomography is a promising new tool for imaging electrical conductivity variations in the earth. The EM source field is produced by induction coil (magnetic dipole) transmitters deployed at the surface or in boreholes. Vertical and horizontal component magnetic field detectors are deployed in other boreholes or on the surface. Sources and receivers are typically deployed in a configuration surrounding the region of interest. The goal of this procedure is to image electrical conductivity variations in the earth, much as x-ray tomography is used to image density variations through cross-sections of the body. Although such EM field techniques have been developed and applied, the algorithms for inverting the magnetic data to produce the desired images of electrical conductivity have not kept pace. One of the main reasons for the lag in the algorithm development has been the fact that the magnetic induction problem is inherently three dimensional: other imaging methods such as x-ray and seismic can make use of two-dimensional approximations that are not too far from reality, but we do not have this luxury in EM induction tomography. In addition, previous field experiments were conducted at controlled test sites that typically do not have much external noise or extensive surface clutter problems often associated with environmental sites. To use the same field techniques in environments more typical of cleanup sites requires a new set of data processing tools to remove the effects of both noise and clutter. The goal of this project is to join theory and experiment to produce enhanced images of electrically conducting fluids underground, allowing better localization of contaminants and improved planning strategies for the subsequent remediation efforts. After explaining the physical context in more detail, this report will summarize the progress made in the first year of this project: (1) on code development and (2) on field tests of these methods. We conclude with a brief statement of the research directions for the second year of the project.

Research paper thumbnail of Analysis of approximate inverses in tomography II. Iterative inverses

This paper continues the analysis of approximate inverses from Part I by concentrating on iterati... more This paper continues the analysis of approximate inverses from Part I by concentrating on iterative inverses in linear tomographic applications. The importance of differentiating between the ideal resolution of the operator/matrix to be inverted and the actual or effective resolution obtained by the approximate inverse during an iterative procedure is stressed. Means of obtaining the effective resolution operator for standard iterative procedures such as conjugate gradients, Lanczos, and LSQR are provided, while circumventing the usual need to produce a singular-value decomposition of the operator being inverted. The methods discussed produce very simple results in calculations with infinite precision, but require reorthogonalization of the Krylov vectors/operators produced by the iterative procedures in finite precision. Although this need for reorthogonalization increases the expense of the procedure somewhat, it still produces the desired results much more efficiently than what could be obtained using a full singular-value decomposition of the operator.

Research paper thumbnail of Compositional verification of a multi-agent system for one-to-many negotiation

Applied Intelligence, Mar 1, 2004

Verification of multi-agent systems hardly occurs in design practice. One of the difficulties is ... more Verification of multi-agent systems hardly occurs in design practice. One of the difficulties is that required properties for a multi-agent system usually refer to multi-agent behaviour which has nontrivial dynamics. To constrain these multi-agent behavioural dynamics, often a form of organisational structure is used, for example, for negotiating agents, by following strict protocols. The claim is that these negotiation protocols entail a structured process that is manageable with respect to analysis, design and execution of such a multi-agent system. ...