11,221 research outputs found
Review and synthesis of problems and directions for large scale geographic information system development
Problems and directions for large scale geographic information system development were reviewed and the general problems associated with automated geographic information systems and spatial data handling were addressed
Computations on Sofic S-gap Shifts
Let be an increasing finite or infinite subset of and the -gap shift associated to . Let
be the entropy function which will be
vanished at where is the entropy of the system. Suppose
is sofic with adjacency matrix and the characteristic polynomial
. Then for some rational function ,
. This will be explicitly determined.
We will show that or
when or
respectively. Here is the zeta function of . We will also compute
the Bowen-Franks groups of a sofic -gap shift.Comment: This paper has been withdrawn due to extending results about SFT
shifts to sofic shifts (Theorem 2.3). This forces to apply some minor changes
in the organization of the paper. This paper has been withdrawn due to a flaw
in the description of the adjacency matrix (2.3
Registration of retinal images from Public Health by minimising an error between vessels using an affine model with radial distortions
In order to estimate a registration model of eye fundus images made of an
affinity and two radial distortions, we introduce an estimation criterion based
on an error between the vessels. In [1], we estimated this model by minimising
the error between characteristics points. In this paper, the detected vessels
are selected using the circle and ellipse equations of the overlap area
boundaries deduced from our model. Our method successfully registers 96 % of
the 271 pairs in a Public Health dataset acquired mostly with different
cameras. This is better than our previous method [1] and better than three
other state-of-the-art methods. On a publicly available dataset, ours still
better register the images than the reference method
Evaluation of the Effect of Myocardial Localisation Errors on Myocardial Blood Flow Estimates from Myocardial Perfusion MRI
Hardware and software status of QCDOC
QCDOC is a massively parallel supercomputer whose processing nodes are based
on an application-specific integrated circuit (ASIC). This ASIC was
custom-designed so that crucial lattice QCD kernels achieve an overall
sustained performance of 50% on machines with several 10,000 nodes. This strong
scalability, together with low power consumption and a price/performance ratio
of $1 per sustained MFlops, enable QCDOC to attack the most demanding lattice
QCD problems. The first ASICs became available in June of 2003, and the testing
performed so far has shown all systems functioning according to specification.
We review the hardware and software status of QCDOC and present performance
figures obtained in real hardware as well as in simulation.Comment: Lattice2003(machine), 6 pages, 5 figure
QSO clustering and the AAT 2dF redshift survey
We review previous results on the clustering and environments of QSOs. We
show that the correlation length for QSOs derived from existing surveys is
r~5/h Mpc, similar to the observed correlation length for field galaxies at the
present epoch. The galaxy environment for z<1 radio-quiet QSOs is also
consistent with field galaxies. The evolution of the QSO correlation length
with redshift is currently uncertain, largely due to the small numbers of QSOs
(~2000) in surveys suitable for clustering analysis. We report on intial
progress with the AAT 2dF QSO redshift survey, which, once completed will
comprise almost 30000 QSOs. With over 1000 QSOs already observed, it is already
the largest single homogeneous QSO survey. We discuss prospects for deriving
limits on cosmological parameters from this survey, and on the evolution of
large-scale structure in the Universe.Comment: Invited talk at RS meeting on 'Large Scale Structure in the Universe'
held at the Royal Society on 25-26 March 1998 14 pages, 11 figre
Discovery of a Clustered Quasar Pair at z ~ 5: Biased Peaks in Early Structure Formation
We report a discovery of a quasar at z = 4.96 +- 0.03 within a few Mpc of the
quasar SDSS 0338+0021 at z = 5.02 +- 0.02. The newly found quasar has the SDSS
i and z magnitudes of ~ 21.2, and an estimated absolute magnitude M_B ~ -25.2.
The projected separation on the sky is 196 arcsec, and the redshift difference
Delta z = 0.063 +- 0.008. The probability of finding this quasar pair by chance
in the absence of clustering in this particular volume is ~ 10^-4 to 10^-3. We
conclude that the two objects probably mark a large-scale structure, possibly a
protocluster, at z ~ 5. This is the most distant such structure currently
known. Our search in the field of 13 other QSOs at z >~ 4.8 so far has not
resulted in any detections of comparable luminous QSO pairs, and it is thus not
yet clear how representative is this structure at z ~ 5. However, along with
the other evidence for clustering of quasars and young galaxies at somewhat
lower redshifts, the observations are at least qualitatively consistent with a
strong biasing of the first luminous and massive objects, in agreement with
general predictions of theoretical models. More extensive searches for
clustered quasars and luminous galaxies at these redshifts will provide
valuable empirical constraints for our understanding of early galaxy and
structure formation.Comment: Latex file, 8 pages, 3 eps figures, sty files included. To appear in
the Ap
- …