The Holographic Life of the eta'

In the string holographic dual of large-N_c QCD with N_f flavours of Kruczenski et al, the eta' meson is massless at infinite N_c and dual to a collective fluctuation of N_f D6-brane probes in a supergravity background. Here we identify the string diagrams responsible for the generation of a mass of order N_f/N_c, consistent with the Witten-Veneziano formula, and show that the supregravity limit of these diagrams corresponds to mixings with pseudoscalar glueballs. We argue that the dependence on the theta-angle in the supergravity description occurs only through the combination theta + 2 \sqrt{N_f} eta' / f_pi, as dictated by the U(1) anomaly. We provide a quantitative test by computing the linear term in the eta' potential in two independent ways, with perfect agreement.Comment: 1+26 pages, 8 figures; V4: Appendix added, version published in JHE

Guam's Small-Boat-based Fisheries

Recent trends in Guam's small-boat fisheries and current knowledge of their biology, management, and economics are summarized. Annual estimates of participation, effort, and harvest are given for the pelagic and bottomfish fisheries for 1980-91 and for the spearfishing and atulai fisheries for 1985. The pelagic fishery is the largest, with annual landings ranging from 168 to 364 metric tons (t), followed by the bottomfish fishery (14-43 t), spearfishingf ishery (517 t), and bigeye scad fishery (3-20 t). All of the pelagic species are highly migratory and require regional management. They are heavily exploited by Guam-based domestic purse-seine and foreign longline fisheries, but region-wide catch and effort as well as the status of the stocks are largely unknown. Bottomfish and reef-fish stocks are shared to an unknown extent with those of the northern Marianas and are locally manageable. Certain vulnerable species of bottomfishes and reeffishes are overfished. Bottomfish and spearedfish landings are dominated by small species with high turnover rates

Dissecting the Gaseous Halos of z~2 Damped Lyα\alpha Systems with Close Quasar Pairs

We use spectroscopy of close pairs of quasars to study diffuse gas in the circumgalactic medium (CGM) surrounding a sample of 40 Damped Lya systems (DLAs). The primary sightline in each quasar pair probes an intervening DLA in the redshift range 1.6 < z_DLA < 3.6, such that the second quasar sightline then probes Lya, CII, SiII, and CIV absorption in the CGM transverse to the DLA to projected distances $R_{\perp} < 300$ kpc. Analysis of the Lya profiles in these CGM sightlines constrains the covering fraction (f_C) of optically thick HI (having column density N_HI > 10^17.2 cm^-2) to be greater than ~30% within $R_{\perp} < 200$ kpc of DLAs. Strong SiII 1526 absorption with equivalent width W_1526 > 0.2 Ang occurs with an incidence f_C (W_1526 > 0.2 Ang) = 20(+12/-8)% within $R_{\perp}<100$ kpc, indicating that low-ionization metal absorption associated with DLAs probes material at a physical distance R_3D < 30 kpc. However, we find that strong CIV 1548 absorption is ubiquitous in these environments (f_C (W_1548 > 0.2 Ang) = 57(+12/-13)% within $R_{\perp} < 100$ kpc), and in addition exhibits a high degree of kinematic coherence on scales up to ~175 kpc. We infer that this high-ionization material arises predominantly in large, quiescent structures extending beyond the scale of the DLA host dark matter halos rather than in ongoing galactic winds. The Lya equivalent width in the DLA-CGM is anticorrelated with $R_{\perp}$ at >98% confidence, suggesting that DLAs arise close to the centers of their host halos rather than on their outskirts. Finally, the average Lya, CII and CIV equivalent widths are consistent with those measured around z~2 Lyman Break Galaxies. Assuming that DLAs trace a galaxy population with lower masses and luminosities, this finding implies that the absorption strength of cool circumgalactic material has a weak dependence on dark matter halo mass for M_h < 10^12 M_sun.Comment: Submitted to ApJ. 30 pages, 13 figures, 3 tables, 1 appendix. Uses emulateapj forma

Higher-Order Angular Galaxy Correlations in the SDSS: Redshift and Color Dependence of non-Linear Bias

We present estimates of the N-point galaxy, area-averaged, angular correlation functions $\bar{\omega}_{N}$($\theta$) for $N$ = 2,...,7 for galaxies from the fifth data release of the Sloan Digital Sky Survey. Our parent sample is selected from galaxies with $18 \leq r < 21$, and is the largest ever used to study higher-order correlations. We subdivide this parent sample into two volume limited samples using photometric redshifts, and these two samples are further subdivided by magnitude, redshift, and color (producing early- and late-type galaxy samples) to determine the dependence of $\bar{\omega}_{N}$($\theta$) on luminosity, redshift, and galaxy-type. We measure $\bar{\omega}_{N}$($\theta$) using oversampling techniques and use them to calculate the projected, $s_{N}$. Using models derived from theoretical power-spectra and perturbation theory, we measure the bias parameters $b_1$ and $c_2$, finding that the large differences in both bias parameters ($b_1$ and $c_2$) between early- and late-type galaxies are robust against changes in redshift, luminosity, and $\sigma_8$, and that both terms are consistently smaller for late-type galaxies. By directly comparing their higher-order correlation measurements, we find large differences in the clustering of late-type galaxies at redshifts lower than 0.3 and those at redshifts higher than 0.3, both at large scales ($c_2$ is larger by $\sim0.5$ at $z > 0.3$) and small scales (large amplitudes are measured at small scales only for $z > 0.3$, suggesting much more merger driven star formation at $z > 0.3$). Finally, our measurements of $c_2$ suggest both that $\sigma_8 < 0.8$ and $c_2$ is negative.Comment: 46 pages, 19 figures, Accepted to Ap

Design and Analysis of a Dynamically Configured Log-based Distributed Security Event Detection Methodology

Military and defense organizations rely upon the security of data stored in, and communicated through, their cyber infrastructure to fulfill their mission objectives. It is essential to identify threats to the cyber infrastructure in a timely manner, so that mission risks can be recognized and mitigated. Centralized event logging and correlation is a proven method for identifying threats to cyber resources. However, centralized event logging is inflexible and does not scale well, because it consumes excessive network bandwidth and imposes significant storage and processing requirements on the central event log server. In this paper, we present a flexible, distributed event correlation system designed to overcome these limitations by distributing the event correlation workload across the network of event-producing systems. To demonstrate the utility of the methodology, we model and simulate centralized, decentralized, and hybrid log analysis environments over three accountability levels and compare their performance in terms of detection capability, network bandwidth utilization, database query efficiency, and configurability. The results show that when compared to centralized event correlation, dynamically configured distributed event correlation provides increased flexibility, a significant reduction in network traffic in low and medium accountability environments, and a decrease in database query execution time in the high-accountability case

A new wrinkle on the enhancon

We generalize the basic enhancon solution of Johnson, Peet and Polchinski by constructing solutions without spherical symmetry. A careful consideration of boundary conditions at the enhancon surface indicates that the interior of the supergravity solution is still flat space in the general case. We provide some explicit analytic solutions where the enhancon locus is a prolate or oblate sphere.Comment: 19 pages, no figure

Spitzer, Near-Infrared, and Submillimeter Imaging of the Relatively Sparse Young Cluster, Lynds 988e

We present {\it Spitzer} images of the relatively sparse, low luminosity young cluster L988e, as well as complementary near-infrared (NIR) and submillimeter images of the region. The cluster is asymmetric, with the western region of the cluster embedded within the molecular cloud, and the slightly less dense eastern region to the east of, and on the edge of, the molecular cloud. With these data, as well as with extant H$\alpha$ data of stars primarily found in the eastern region of the cluster, and a molecular $^{13}$CO gas emission map of the entire region, we investigate the distribution of forming young stars with respect to the cloud material, concentrating particularly on the differences and similarities between the exposed and embedded regions of the cluster. We also compare star formation in this region to that in denser, more luminous and more massive clusters already investigated in our comprehensive multi-wavelength study of young clusters within 1 kpc of the Sun.Comment: 21 pages, 6 tables, 13 figures. Full resolution figures at: http://astro.pas.rochester.edu/~tom/Preprints/L988e.pd

An automated pattern recognition system for the quantification of inflammatory cells in hepatitis-C-infected liver biopsies

This paper presents an automated system for the quantification of inflammatory cells in hepatitis-C-infected liver biopsies. Initially, features are extracted from colour-corrected biopsy images at positions of interest identified by adaptive thresholding and clump decomposition. A sequential floating search method and principal component analysis are used to reduce dimensionality. Manually annotated training images allow supervised training. The performance of Gaussian parametric and mixture models is compared when used to classify regions as either inflammatory or healthy. The system is optimized using a response surface method that maximises the area under the receiver operating characteristic curve. This system is then tested on images previously ranked by a number of observers with varying levels of expertise. These results are compared to the automated system using Spearman rank correlation. Results show that this system can rank 15 test images, with varying degrees of inflammation, in strong agreement with five expert pathologists

Cosmic Censorship: As Strong As Ever

Spacetimes which have been considered counter-examples to strong cosmic censorship are revisited. We demonstrate the classical instability of the Cauchy horizon inside charged black holes embedded in de Sitter spacetime for all values of the physical parameters. The relevant modes which maintain the instability, in the regime which was previously considered stable, originate as outgoing modes near to the black hole event horizon. This same mechanism is also relevant for the instability of Cauchy horizons in other proposed counter-examples of strong cosmic censorship.Comment: 4 pages RevTeX style, 1 figure included using epsfi