Survey for Galaxies Associated with z~3 Damped Lyman alpha Systems I: Spectroscopic Calibration of u'BVRI Photometric Selection

We present a survey for z~3 Lyman break galaxies (LBGs) associated with damped Lyman alpha systems (DLAs) with the primary purpose of determining the DLA-LBG cross-correlation. This paper describes the acquisition and analysis of imaging and spectroscopic data of 9 quasar fields having 11 known z~3 DLAs covering an area of 465 arcmin^2. Using deep u'BVRI images, 796 LBG candidates to an apparent R_AB magnitude of 25.5 were photometrically selected from 17,343 sources detected in the field. Spectroscopic observations of 529 LBG candidates using Keck LRIS yielded 339 redshifts. We have conservatively identified 211 z>2 objects with =3.02+/-0.32. We discuss our method of z~3 LBG identification and present a model of the u'BVRI photometric selection function. We use the 339 spectra to evaluate our u'BVRI z~3 Lyman break photometric selection technique.Comment: 26 pages, 6 tables, 11 figures, accepted for publication in Ap

Refining Finite-Time Lyapunov Exponent Ridges and the Challenges of Classifying Them

While more rigorous and sophisticated methods for identifying Lagrangian based coherent structures exist, the finite-time Lyapunov exponent (FTLE) field remains a straightforward and popular method for gaining some insight into transport by complex, time-dependent two-dimensional flows. In light of its enduring appeal, and in support of good practice, we begin by investigating the effects of discretization and noise on two numerical approaches for calculating the FTLE field. A practical method to extract and refine FTLE ridges in two-dimensional flows, which builds on previous methods, is then presented. Seeking to better ascertain the role of a FTLE ridge in flow transport, we adapt an existing classification scheme and provide a thorough treatment of the challenges of classifying the types of deformation represented by a FTLE ridge. As a practical demonstration, the methods are applied to an ocean surface velocity field data set generated by a numerical model. (C) 2015 AIP Publishing LLC.ONR N000141210665Center for Nonlinear Dynamic

Closed form solution for a double quantum well using Gr\"obner basis

Analytical expressions for spectrum, eigenfunctions and dipole matrix elements of a square double quantum well (DQW) are presented for a general case when the potential in different regions of the DQW has different heights and effective masses are different. This was achieved by Gr\"obner basis algorithm which allows to disentangle the resulting coupled polynomials without explicitly solving the transcendental eigenvalue equation.Comment: 4 figures, Mathematica full calculation noteboo

Designing a mobile augmented memory system for people with traumatic brain injuries

Augmented memory systems help people remember events in their lives. Individuals with Traumatic Brain Injury (TBI) often have memory impairments. We conducted a user study to learn about strategies individuals with TBI use to remember events in their lives. We explored what characteristics individuals with TBI expect of an augmented memory system. We then investigated these aspects in an initial mobile app design, and propose here a concept for a rehearsal application that addresses the issues found in our studies

Old high-redshift galaxies and primordial density fluctuation spectra

We have discovered a population of extremely red galaxies at $z\simeq 1.5$ which have apparent stellar ages of \gs 3 Gyr, based on detailed spectroscopy in the rest-frame ultraviolet. In order for galaxies to have existed at the high collapse redshifts indicated by these ages, there must be a minimum level of power in the density fluctuation spectrum on galaxy scales. This paper compares the required power with that inferred from other high-redshift populations. If the collapse redshifts for the old red galaxies are in the range $z_c\simeq 6$ -- 8, there is general agreement between the various tracers on the required inhomogeneity on 1-Mpc scales. This level of small-scale power requires the Lyman-limit galaxies to be approximately $\nu\simeq 3.0$ fluctuations, implying a very large bias parameter $b\simeq 6$. The high collapse redshifts of the red galaxies as deduced from gravitational collapse provides independent support for the ages estimated from their stellar populations. Such early-forming galaxies are rare, and their contribution to the cosmological stellar density is consistent with an extrapolation to higher redshifts of the star-formation rate measured at $z<5$; there is no evidence for a general era of spheroid formation at extreme redshifts.Comment: 9 Pages MNRAS in press. Uses MNRAS Plain TeX macro

The Evolution of Radio Galaxies at Intermediate Redshift

We describe a new estimate of the radio galaxy 1.4 GHz luminosity function and its evolution at intermediate redshifts (z~0.4). Photometric redshifts and color selection have been used to select Bj<23.5 early-type galaxies from the Panoramic Deep Fields, a multicolor survey of two 25 sq deg fields. Approximately 230 radio galaxies have then been selected by matching early-type galaxies with NVSS radio sources brighter than 5 mJy. Estimates of the 1.4 GHz luminosity function of radio galaxies measure significant evolution over the observed redshift range. For an Omega_M=1 cosmology the evolution of the radio power is consistent with luminosity evolution where P(z)=P(0)(1+z)^{k_L} and 3<k_L<5. The observed evolution is similar to that observed for UVX and X-ray selected AGN and is consistent with the same physical process being responsible for the optical and radio luminosity evolution of AGN.Comment: 26 pages, 9 Figures, Accepted for Publication in A

The LBDS Hercules sample of mJy radio sources at 1.4 GHz - II. Redshift distribution, radio luminosity function, and the high-redshift cut-off

{Abridged} A combination of spectroscopy and broadband photometric redshifts has been used to find the complete redshift distribution of the Hercules sample of millijansky radio sources. These data have been used to examine the evolution of the radio luminosity function (RLF) and its high-redshift cut-off. New redshifts have been measured for eleven sources, and a further ten upper limits are given. The total number of sources with known redshifts in the sample is now 47 (65%). We calculated broadband photometric redshifts for the remaining one-third of the sample. For the luminosity range probed by the present study (P_1.4 > 10^24.5 W/Hz/sr), we use the V/V_max test to show conclusively that there is a deficit of high-redshift (z > 2-2.5) objects. Comparison with the model RLFs of Dunlop & Peacock (1990) shows that our data can now exclude pure luminosity evolution. Two of the models of DP90, and the RLF deduced by direct binning of the data, both favour a luminosity dependence for the high-redshift cut-off, with lower-luminosity sources (P_1.4 \simeq 10^24 W/Hz/sr) in decline by z \simeq 1-1.5 while higher-luminosity sources (P_1.4 \simeq 10^{25-26} W/Hz/sr) decline in comoving number density beyond z \simeq 2-2.5.Comment: Revised version submitted to MNRAS. 16 pages, 12 figure

Timing attack detection on BACnet via a machine learning approach

Building Automation Systems (BAS), alternatively known as Building Management Systems (BMS), which centralise the management of building services, are often connected to corporate networks and are routinely accessed remotely for operational management and emergency purposes. The protocols used in BAS, in particular BACnet, were not designed with security as a primary requirement, thus the majority of systems operate with sub-standard or non-existent security implementations. As intrusion is thus likely easy to achieve, intrusion detection systems should be put in place to ensure they can be detected and mitigated. Existing intrusion detection systems typically deal only with known threats (signature-based approaches) or suffer from a high false positive rate (anomaly-based approaches). In this paper we present an overview of the problem space with respect to BAS, and suggest that state aware machine learning techniques could be used to discover threats that comprise a collection of legitimate commands. We provide a first step showing that the concept can be used to detect an attack where legitimate write commands being sent in rapid succession may cause system failure. We capture the state as a ‘time since last write’ event and use a basic artificial neural network classifier to detect attacks

Hyperextended Cosmological Perturbation Theory: Predicting Non-linear Clustering Amplitudes

We consider the long-standing problem of predicting the hierarchical clustering amplitudes $S_p$ in the strongly non-linear regime of gravitational evolution. N-body results for the non-linear evolution of the bispectrum (the Fourier transform of the three-point density correlation function) suggest a physically motivated ansatz that yields the strongly non-linear behavior of the skewness, $S_3$, starting from leading-order perturbation theory. When generalized to higher-order ($p>3$) polyspectra or correlation functions, this ansatz leads to a good description of non-linear amplitudes in the strongly non-linear regime for both scale-free and cold dark matter models. Furthermore, these results allow us to provide a general fitting formula for the non-linear evolution of the bispectrum that interpolates between the weakly and strongly non-linear regimes, analogous to previous expressions for the power spectrum.Comment: 20 pages, 6 figures. Final version accepted by ApJ. Includes new paragraphs on factorizable hierarchical models and agreement of HEPT with the excursion set model for white-noise Gaussian fluctuation