Visitors' Interpretive Strategies at Wolverhampton Art Gallery

Making Meaning in Art Museums is one of two research projects on the theme of art museums and interpretive communities. The first was published as Making Meaning 1:Visitors' Interpretive Strategies at Wolverhampton Art Gallery (RCMG 2001). Making Meaning in Art Museums 2 is the second of two research projects on the theme of art museums and interpretive communities. The Long Gallery at the Nottingham Castle Museum and Art Gallery was selected as the research site for this second study. Both studies have explored the ways in which visitors talked about their experience of a visit to the art museum-both what they said about the paintings and the whole of the visit.The research questions on which this project is based are: What interpretive strategies and repertories are deployed by art museum visitors? Can distinct interpretive communities be identified? What are the implications for the communication policies within art museums? This research is an ethnographic study, using qualitative methods.This research project was funded through a grant from the Arts and Humanities Research Boar

Asymptotic enumeration of dense 0-1 matrices with specified line sums

Let S=(s_1,s_2,..., s_m) and T = (t_1,t_2,..., t_n) be vectors of non-negative integers with sum_{i=1}^{m} s_i = sum_{j=1}^n t_j. Let B(S,T) be the number of m*n matrices over {0,1} with j-th row sum equal to s_j for 1 <= j <= m and k-th column sum equal to t_k for 1 <= k <= n. Equivalently, B(S,T) is the number of bipartite graphs with m vertices in one part with degrees given by S, and n vertices in the other part with degrees given by T. Most research on the asymptotics of B(S,T) has focused on the sparse case, where the best result is that of Greenhill, McKay and Wang (2006). In the case of dense matrices, the only precise result is for the case of equal row sums and equal column sums (Canfield and McKay, 2005). This paper extends the analytic methods used by the latter paper to the case where the row and column sums can vary within certain limits. Interestingly, the result can be expressed by the same formula which holds in the sparse case.Comment: Multiple minor adjustments. Accepted by JCT-

Toward a New Distance to the Active Galaxy NGC 4258: II. Centripetal Accelerations and Investigation of Spiral Structure

We report measurements of centripetal accelerations of maser spectral components of NGC 4258 for 51 epochs spanning 1994 to 2004. This is the second paper of a series, in which the goal is determination of a new geometric maser distance to NGC 4258 accurate to possibly ~3%. We measure accelerations using a formal analysis method that involves simultaneous decomposition of maser spectra for all epochs into multiple, Gaussian components. Components are coupled between epochs by linear drifts (accelerations) from their centroid velocities at a reference epoch. For high-velocity emission, accelerations lie in the range -0.7 to +0.7 km/s/yr indicating an origin within 13 degrees of the disk midline (the perpendicular to the line-of-sight to the black hole). Comparison of high-velocity emission projected positions in VLBI images, with those derived from acceleration data, provides evidence that masers trace real gas dynamics. High-velocity emission accelerations do not support a model of trailing shocks associated with spiral arms in the disk. However, we find strengthened evidence for spatial periodicity in high-velocity emission, of wavelength 0.75 mas. This supports suggestions of spiral structure due to density waves in the nuclear accretion disk of an active galaxy. Accelerations of low-velocity (systemic) emission lie in the range 7.7 to 8.9 km/s/yr, consistent with emission originating from a concavity where the thin, warped disk is tangent to the line-of-sight. A trend in accelerations of low-velocity emission as a function of Doppler velocity may be associated with disk geometry and orientation, or with the presence of spiral structure.Comment: Accepted to ApJ, 48 pages and 20 figure

The Discovery of Water Maser Emission from Eight Nearby Galaxies

Using the Green Bank Telescope, we conducted a ``snapshot'' survey for water maser emission toward the nuclei of 611 galaxies and detected eight new sources. The sample consisted of nearby (v < 5000 km/s) and luminous (M_B < -19.5) galaxies, some with known nuclear activity but most not previously known to host AGNs. Our detections include both megamasers associated with AGNs and relatively low luminosity masers probably associated with star formation. The detection in UGC 3789 is particularly intriguing because the spectrum shows both systemic and high-velocity lines indicative of emission from an AGN accretion disk seen edge-on. Based on six months of monitoring, we detected accelerations among the systemic features ranging from 2 to 8 km/s/yr, the larger values belonging to the most redshifted systemic components. High-velocity maser lines in UGC 3789 show no detectable drift over the same period. Although UGC 3789 was not known to be an AGN prior to this survey, the presence of a disk maser is strong evidence for nuclear activity, and an optical spectrum obtained later has confirmed it. With follow up observations, it may be possible to measure a geometric distance to UGC 3789.Comment: to appear in Astrophysical Journal, 1 May 200

Asymptotic enumeration of correlation-immune boolean functions

A boolean function of $n$ boolean variables is {correlation-immune} of order $k$ if the function value is uncorrelated with the values of any $k$ of the arguments. Such functions are of considerable interest due to their cryptographic properties, and are also related to the orthogonal arrays of statistics and the balanced hypercube colourings of combinatorics. The {weight} of a boolean function is the number of argument values that produce a function value of 1. If this is exactly half the argument values, that is, $2^{n-1}$ values, a correlation-immune function is called {resilient}. An asymptotic estimate of the number $N(n,k)$ of $n$-variable correlation-immune boolean functions of order $k$ was obtained in 1992 by Denisov for constant $k$. Denisov repudiated that estimate in 2000, but we will show that the repudiation was a mistake. The main contribution of this paper is an asymptotic estimate of $N(n,k)$ which holds if $k$ increases with $n$ within generous limits and specialises to functions with a given weight, including the resilient functions. In the case of $k=1$, our estimates are valid for all weights.Comment: 18 page

Unveiling Sources of Heating in the Vicinity of the Orion BN/KL Hot Core as Traced by Highly Excited Inversion Transitions of Ammonia

Using the Expanded Very Large Array, we have mapped the vicinity of the Orion BN/KL Hot Core with sub-arcsecond angular resolution in seven metastable inversion transitions of ammonia: (J,K)=(6,6) to (12,12). This emission comes from levels up to 1500 K above the ground state, enabling identification of source(s) responsible for heating the region. We used this multi-transition dataset to produce images of the rotational/kinetic temperature and the column density of ammonia for ortho and para species separately and on a position-by-position basis. We find rotational temperature and column density in the range 160-490 K and (1-4)x10^17 cm^-2, respectively. Our spatially-resolved images show that the highest (column) density and hottest gas is found in a northeast-southwest elongated ridge to the southeast of Source I. We have also measured the ortho-para ratio of ammonia, estimated to vary in the range 0.9-1.6. Enhancement of ortho with respect to para and the offset of hot ammonia emission peaks from known (proto)stellar sources provide evidence that the ammonia molecules have been released from dust grains into the gas-phase through the passage of shocks and not by stellar radiation. We propose that the combined effect of Source I's proper motion and its low-velocity outflow impinging on a pre-existing dense medium is responsible for the excitation of ammonia and the Orion Hot Core. Finally, we found for the first time evidence of a slow (5 km/s) and compact (1000 AU) outflow towards IRc7.Comment: To appear in Astrophysical Journal Letters Special Issue on the EVLA. 8 pages, 4 figure

Maser emission from SiO isotopologues traces the innermost 100 AU around Radio Source I in Orion BN/KL

We have used the Very Large Array (VLA) at 7 mm wavelength to image five rotational transitions (J=1-0) from three SiO isotopologues towards Orion BN/KL: 28SiO v=0,1,2; and 29SiO and 30SiO v=0. For the first time, we have mapped the 29SiO and 30SiO J=1-0 emission, established the maser nature of the emission, and confirmed association with the deeply embedded high-mass young stellar object commonly denoted radio Source I. The 28SiO v=0 maser emission shows a bipolar structure that extends over ~700 AU along a northeast-southwest axis, and we propose that it traces a bipolar outflow driven by Source I. The high-brightness isotopic SiO maser emission imaged with a ~0.2 arcsec resolution has a more compact distribution, generally similar to that of the 28SiO v=1,2 emission, and it probably traces bulk gas flows in a region of diameter <100 AU centered on Source I. On small scales of <10 AU, however, compact 29SiO/30SiO v=0 and 28SiO v=1,2 emission features may be offset from one another in position and line-of-sight velocity. From a radiative transfer analysis based on a large velocity gradient (LVG) pumping model, we derive similar temperatures and densities for the optimum excitation of both 29SiO/30SiO v=0 and 28SiO v=1,2 masers, significantly higher than required for 28SiO v=0 maser excitation. In order to account for the small-scale differences among the isotopologues (v=0) and the main species (v=1,2), follow-up radiative transfer modeling that incorporates non-local line overlap among transitions of all SiO isotopic species may be required.Comment: 10 pages, 3 figures, accepted for publication by Ap

21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies

The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation. Unfortunately, most of the gas in maser disks is currently not being probed; large maser gains favor paths that are characterized by a small velocity gradient and require rare edge-on orientations of the disk. Here we propose a method for mapping the atomic hydrogen distribution in nuclear disks through its 21cm absorption against the radio continuum glow around the central black hole. In NGC 4258, the 21cm optical depth may approach unity for high angular-resolution (VLBI) imaging of coherent clumps which are dominated by thermal broadening and have the column density inferred from X-ray absorption data, ~10^{23}/cm^2. Spreading the 21cm absorption over the full rotation velocity width of the material in front of the narrow radio jets gives a mean optical depth of ~0.1. Spectroscopic searches for the 21cm absorption feature in other galaxies can be used to identify the large population of inclined gaseous disks which are not masing in our direction. Follow-up imaging of 21cm silhouettes of accelerating clumps within these disks can in turn be used to measure cosmological distances.Comment: 4 page