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Search Results: 1 - 10 of 191414 matches for " D. Crampton "
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Companions of Qsos at Redshift 1.1
J. B. Hutchings,D. Crampton,Andrea Johnson
Physics , 1994, DOI: 10.1086/117257
Abstract: We discuss broad- and narrow-band imaging of 7 arcmin fields of 14 QSOs with redshift ~1.1. The narrow-band filters were chosen to detect redshifted [O II] 3727A, and the broad bands are R and I, which correspond to rest wavelengths {}~3300A and ~3800A. In 100 arcsec subfields surrounding the QSOs, we detect an excess of typically 15 detected objects over the background of 25. Several of the QSO subfields also contain an excess of blue (R-I < 1.0) galaxies compared with the other subfields. Finally, several of the QSO subfields contain an excess of galaxies with significant narrow-band flux compared with the other subfields, and many of these are also blue. Most of the QSOs are radio-quiet in a region of sky overpopulated with z=1.1 QSOs, and 3 others are radio-loud from other parts of the sky. We suggest that most of these z=1.1 QSOs are in compact groups of starbursting galaxies. In our data, there is no significant difference between radio-loud and radio-quiet QSOs. We discuss cosmic evolutionary implications.
Radio Galaxies at z = 1.1 to 3.8: Adaptive-Optics Imaging and Archival Hubble Space Telescope Data
E. Steinbring,D. Crampton,J. B. Hutchings
Physics , 2001, DOI: 10.1086/339241
Abstract: We have undertaken a program of high-resolution imaging of high-redshift radio galaxies (HzRGs) using adaptive optics on the Canada-France-Hawaii Telescope. We report on deep imaging in J, H,and K bands of 6 HzRGs in the redshift range 1.1 to 3.8. At these redshifts, near-infrared bandpasses sample the rest-frame visible galaxian light. The radio galaxy is resolved in all the fields and is generally elongated along the axis of the radio lobes. These images are compared to archival Hubble Space Telescope Wide-Field Planetary Camera 2 optical observations of the same fields and show the HzRG morphology in rest-frame ultraviolet and visible light is generally very similar: a string of bright compact knots. Furthermore, this sample - although very small - suggests the colors of the knots are consistent with light from young stellar populations. If true, a plausible explanation is that these objects are being assembled by mergers at high redshift.
Clustering around the radio-galaxy MRC0316-257 at z=3.14
O. Le Fevre,J. M. Deltorn,D. Crampton,M. Dickinson
Physics , 1996, DOI: 10.1086/310319
Abstract: We report here the spectroscopic identification of galaxies in the neighborhood of the radio-galaxy MRC0316-257, at a redshift $z\sim3.14$. Candidate cluster galaxies were selected from deep V and I images combined with narrow band imaging at the wavelength of redshifted Ly$\alpha$. Follow-up multi-slit spectroscopy has allowed confirmation of the redshift of the radio-galaxy, $z=3.1420\pm0.0020$, and identification of two associated galaxies at redshifts $z=3.1378\pm0.0028$ and $z=3.1351\pm0.0028$ respectively. The first galaxy is 0.3 $h_{50}^{-1}$ Mpc from the radio-galaxy, is resolved with an intrinsic size $11.6\pm h_{50}^{-1}$ kpc, and shows $Ly\alpha$ in emission with rest $W_{Ly\alpha}=55\pm14$\AA. In addition, its extremely blue $V-I$ color might possibly indicate a proto-galaxy forming a first generation of stars in a low dust medium. The second galaxy is 1.3 $h_{50}^{-1}$ Mpc away from the radio-galaxy, is marginally resolved and, in addition to Ly$\alpha$ in emission, shows CIV in emission with a broad component indicating the contribution from an AGN. The comoving density of galaxies with $V<23.8$ and a $Ly\alpha$ flux $>10^{-16}$ ergcm$^{-2}$sec$^{-1}$ in the vicinity of MRC0316-257 is $\sim2.5\times10^{-3}h^3_{50}Mpc^{-3}$, significantly higher than the expected background density of field galaxies with similar properties, and might indicate a rich cluster or proto-cluster environment.
Emission line imaging of QSOs with high resolution
J. B. Hutchings,S. L. Morris,D. Crampton
Physics , 2000, DOI: 10.1086/318013
Abstract: We report the first detection of emission line gas within the host galaxies of high redshift QSOs. This was done using narrow-band imaging at the redshifted wavelengths of [O III] and H alpha, using the PUEO adaptive optics camera of the CFHT. The QSOs are all radio-quiet or very compact radio sources. In all five observed QSOs, which have redshifts 0.9 to 2.4, we find extended line emission that lies within 0.5" (a few Kpc) of the nucleus. The emission (redshifted) equivalent widths range from 35 to 300A. Where there is radio structure, the line emission is aligned with it. We also report on continuum fluxes and possible companions. Two of the QSOs are very red, and have high resolved continuum flux.
Algorithms for the workflow satisfiability problem engineered for counting constraints
D. Cohen,J. Crampton,A. Gagarin,G. Gutin,M. Jones
Computer Science , 2015, DOI: 10.1007/s10878-015-9877-7
Abstract: The workflow satisfiability problem (WSP) asks whether there exists an assignment of authorized users to the steps in a workflow specification that satisfies the constraints in the specification. The problem is NP-hard in general, but several subclasses of the problem are known to be fixed-parameter tractable (FPT) when parameterized by the number of steps in the specification. In this paper, we consider the WSP with user-independent counting constraints, a large class of constraints for which the WSP is known to be FPT. We describe an efficient implementation of an FPT algorithm for solving this subclass of the WSP and an experimental evaluation of this algorithm. The algorithm iteratively generates all equivalence classes of possible partial solutions until, whenever possible, it finds a complete solution to the problem. We also provide a reduction from a WSP instance to a pseudo-Boolean SAT instance. We apply this reduction to the instances used in our experiments and solve the resulting PB SAT problems using SAT4J, a PB SAT solver. We compare the performance of our algorithm with that of SAT4J and discuss which of the two approaches would be more effective in practice.
Cartography and the calculation of territory
Jeremy Crampton
lo Squaderno , 2010,
Abstract: In this short essay I would like to consider the calculative relationships of cartography and territory. By this, I mean something more specific than the idea of maps producing territory – the “power of maps” – but of how and with what effects specifically calculative cartographic rationalities operate. We can begin by clarifying some of these terms.
The High Redshift Universe with Adaptive Optics: Recent results from CFHT
David Crampton
Physics , 1998,
Abstract: The CFHT Adaptive Optics Bonnette (AOB) has been used to obtain high spatial resolution (0.1") observations of several extragalactic targets including the nuclei of nearby galaxies, high redshift galaxies, AGN, radiogalaxies, the host galaxies of quasars and gravitational lenses. Examples of these are discussed and the role of adaptive optics in exploring the high redshift universe is critically assessed in light of these results.
Practical Constructions for the Efficient Cryptographic Enforcement of Interval-Based Access Control Policies
Jason Crampton
Computer Science , 2010,
Abstract: The enforcement of access control policies using cryptography has received considerable attention in recent years and the security of such enforcement schemes is increasingly well understood. Recent work in the area has considered the efficient enforcement of temporal and geo-spatial access control policies, and asymptotic results for the time and space complexity of efficient enforcement schemes have been obtained. However, for practical purposes, it is useful to have explicit bounds for the complexity of enforcement schemes. In this paper, we consider interval-based access control policies, of which temporal and geo-spatial access control policies are special cases. We define enforcement schemes for interval-based access control policies for which it is possible, in almost all cases, to obtain exact values for the schemes' complexity, thereby subsuming a substantial body of work in the literature. Moreover, our enforcement schemes are more practical than existing schemes, in the sense that they operate in the same way as standard cryptographic enforcement schemes, unlike other efficient schemes in the literature. The main difference between our approach and earlier work is that we develop techniques that are specific to the cryptographic enforcement of interval-based access control policies, rather than applying generic techniques that give rise to complex constructions and asymptotic bounds.
Near-IR Images of the Torus and Micro-Spiral Structure in NGC 1068 using Adaptive Optics
D. Rouan,F. Rigaut,D. Alloin,R. Doyon,O. Lai,D. Crampton,E. Gendron,R. Arsenault
Physics , 1998,
Abstract: We present diffraction-limited near-IR images in J, H and K of the nucleus of NGC 1068, obtained with the Adaptive Optics system {Pueo} at CFHT. The achieved resolution (0.12") reveals several components, particularly prominent on the [J-K] image: a) an unresolved, conspicuous core (size < 9 pc); b) an elongated structure at P.A. ~102 deg, beginning to show up at radius ~ 15 pc; c) a S-shaped structure with radial extent ~ 20 pc, including a bar-like central elongation at P.A. ~ 15 deg and two short spiral arms. The K core is at the location of the putative central engine (radio source S1) : the core is likely the emission from the hot inner walls of the dust/molecular torus. The extremely red colors of the central 0.2", [J-K]=7.0, [H-K]=3.8, lead to an extinction Av > 25. The elongated structure at P.A.~ 102 deg may trace the presence of cooler dust within and around the torus. This interpretation is supported by two facts : a) the elongated structure is perpendicular to the local radio jet originating at S1; b) its direction follows exactly that of the disk of ionized gas recently found with the VLBA. The S-shaped feature suggests an extremely compact barred spiral structure, that would be the innermost of a series of nested spiral structures, as predicted by simulations. This is supported by the inner stellar distribution - deduced from the J image - which clearly follows an exponential disk with a 19 pc scale-length, precisely that expected from the rotation of a bar.
The Canada France Redshift Survey VIII: Evolution of the clustering of galaxies from z~1
O. Le Fevre,D. Hudon,S. J. Lilly,D. Crampton,F. Hammer,L. Tresse
Physics , 1995, DOI: 10.1086/177080
Abstract: We have used the projected two-point correlation function, $w(r_p)$, to investigate the spatial distribution of the 591 galaxies with secure redshifts between $0 \leq z \leq 1.3$ in the five CFRS fields. The slope of the two-point correlation function for the sample as a whole is $\gamma=1.64\pm0.05$, very similar to the local slope, and $\gamma$ is therefore not strongly evolving with redshift. However, the amplitude of the correlation function decreases strongly with increasing redshift, so that at $z\approx0.6$ it is a factor of 10 lower (for $q_0=0.5$) than for a similarly-selected local galaxy population, on scales $0.1
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