How do galaxies acquire their mass?

We introduce a toy model that describes (in a single equation) the mass in stars as a function of halo mass and redshift. Our model includes the suppression of gas accretion from gravitational shock heating and AGN jets mainly for M_halo > M_shock ~ 10^12 M_Sun and from a too hot IGM onto haloes with v_circ < 40 km/s, as well as stellar feedback that drives gas out of haloes mainly with v_circ < 120 km/s. We run our model on the merger trees of the haloes and subhaloes of a high-resolution dark matter cosmological simulation. The galaxy mass is taken as the maximum between the mass given by the model and the sum of the masses of its progenitors (reduced by tidal stripping). Designed to reproduce the present-day stellar mass function of galaxies, our model matches fairly well the evolution of the cosmic stellar density. It leads to the same z=0 relation between central galaxy stellar and halo mass as the one found by abundance matching and also as that previously measured at high mass on SDSS centrals. Our model also predicts a bimodal distribution (centrals and satellites) of stellar masses for given halo mass, in good agreement with SDSS observations. The relative importance of mergers depends much more on stellar than halo mass. Galaxies with m_stars > 10^11 M_Sun/h acquire most of their mass through mergers (mostly major and gas-poor), as expected from our model's shutdown of gas accretion at high M_halo. However, mergers are rare for m_stars < 10^11 M_Sun/h (greater than our mass resolution), a consequence of the curvature of the stellar vs. halo mass relation. So gas accretion must be the dominant growth mechanism for intermediate and low mass galaxies, e.g. dwarf ellipticals in clusters, except that gas-rich galaxy mergers account for the bulk of the growth of ellipticals with m_stars ~ 10^10.5 M_Sun/h, which we predict must be the typical mass of ULIRGs.Comment: 18 pages, 12 figures, A&A in press (major re-write and updated figures from version 1

Universal properties of the near-horizon optical geometry

We make use of the fact that the optical geometry near a static non-degenerate Killing horizon is asymptotically hyperbolic to investigate universal features of black hole physics. We show how the Gauss-Bonnet theorem allows certain lensing scenarios to be ruled in or out. We find rates for the loss of scalar, vector and fermionic `hair' as objects fall quasi- statically towards the horizon. In the process we find the Lienard-Wiechert potential for hyperbolic space and calculate the force between electrons mediated by neutrinos, extending the flat space result of Feinberg and Sucher. We use the enhanced conformal symmetry of the Schwarzschild and Reissner-Nordstrom backgrounds to re-derive the electrostatic field due to a point charge in a simple fashion

Preparing Students for Adulthood: Comparing the Experiences of Degree and Non-Degree Seeking Graduates

The role of secondary education is critical to preparing graduates for adulthood. This study explored the transition experiences of high school graduates and factors that impacted their preparation for adulthood. This descriptive study focused on the experiences of degree and non-degree-seeking graduates. Surveys were distributed to students enrolled in a general education course at a state university and marketing research participants not enrolled in post-secondary programs. The survey sought to identify overall preparedness, responsibilities deemed necessary to teach in high school, and influence factors that prepared them for adulthood. The overall findings displayed that graduates seeking degrees felt more prepared for adulthood. While both groups agreed that many adulthood-responsibility topics should be taught, degree-seekers found less value in teaching parenting skills in a high school class despite identifying that parents have a more significant impact on preparing them for adulthood. Researchers recommend that in addition to college and career-ready curricula, instruction should include preparation topics that align with 21st-century markers that better support non-degree-seeking graduates toward successful transitions into adulthood

Effects of Integrating Mathematical Concepts into a Nutrition Unit in the Animal Science Curriculum

Achievement test scores in mathematics have been a concern among educators for many years. Teaching contextualized mathematics has been found to be effective and includes providing a direct application to real-life scenarios rather than teaching linear equations and algebraic principles in isolation. This study measured the effects of integrating mathematical skills in one instructional unit in an animal science curriculum. Students from eight schools participated in the research study. Students completed a pretest measuring their existing mathematical skills and self-efficacy in math. All students were taught a unit of instruction about animal nutrition and feeding. The control group received a typical nutrition unit and the treatment group received the same unit of instruction with the addition of mathematical skill integration. Following the unit of instruction, students completed a posttest survey, which included a mathematics attitudinal scale, posttreatment self-efficacy scale, and posttreatment mathematics skills questions. No statistically significant difference was found in mathematics self-efficacy or mathematics skills between the control group and treatment. However, results indicated a strong positive relationship between students’ mathematics self-efficacy and their mathematics skills. Further, highest level of mathematics courses completed and overall grade point average were statistically significant factors in predicting mathematics self-efficacy

Performance of polarimetric beamformers for phased array radio telescopes

The results of four recently introduced beamforming schemes for phased array systems are discussed, each of which is capable to provide high sensitivity and accurate polarimetric performance of array-based radio telescopes. Ideally, a radio polarimeter should recover the actual polarization state of the celestial source, and thus compensate for unwanted polarization degradation effects which are intrinsic to the instrument. In this paper, we compare the proposed beamforming schemes through an example of a practical phased array system (APERTIF prototype) and demonstrate that the optimal beamformer, the max-SLNR beamformer, the eigenvector beamformer, and the bi-scalar beamformer are sensitivity equivalent but lead to different polarization state solutions, some of which are sub-optimal

Efficient Prediction of Array Element Patterns Using Physics-Based Expansions and a Single Far-Field Measurement

A method is proposed to predict the antenna array beam through employing a relatively small set of physics-based basis functions-called characteristic basis function patterns (CBFPs)-for modeling the embedded element patterns. The primary CBFP can be measured or extracted from numerical simulations, while additional (secondary) CBFPs are derived from the primary one. Furthermore, each numerically generated CBFP, which is typically simulated/measured for discrete directions only, can in turn be approximated by analytical basis functions with fixed expansion coefficients to evaluate the resulting array pattern at any angle through interpolation. This hierarchical basis reduces the number of unknown expansion coefficients significantly. Accordingly, the CBFP expansion coefficients can be determined through a single far-field measurement of only a few reference sources in the field of view. This is particularly important for multibeam array applications where only a limited number of reference sources are available for predicting the beam shape. Furthermore, this instantaneous beam calibration is fast, i.e., potentially capable to speed up the array calibration by one or two orders of magnitude, which is particularly important if the antenna radiation characteristics are subject to drifts

Polarimetry With Phased Array Antennas: Sensitivity and Polarimetric Performance Using Unpolarized Sources for Calibration

Polarimetric phased arrays require a calibration method that allows the system to measure the polarization state of the received signals. In this paper, we assess the polarimetric performance of two commonly used calibration methods that exploit unpolarized calibration sources. The first method obtains a polarimetrically calibrated beamforming solution from the two dominant eigenvectors of the measured signal covariance matrix. We demonstrate that this method is sensitivity equivalent to the theoretical optimal method, but suffers from an ambiguity that has to be resolved by additional measurements on (partially) polarized sources or by exploiting the intrinsic polarimetric quality of the antenna system. The easy-to-implement bi-scalar approach assumes that the feed system consists of two sets of orthogonally oriented antenna elements, each associated with one polarization. We assess its sensitivity and polarimetric performance over a wide field-of-view (FoV) using simulations of a phased array feed system for the Westerbork Synthesis Radio Telescope. Our results indicate that the sensitivity loss can be limited to 4.5% and that the polarimetric performance over the FoV is close to the best achievable performance. The latter implies that the intrinsic polarimetric quality of the antennas remains a crucial factor despite the development of novel polarimetric calibration methods

Polarimetry With Phased Array Antennas: Theoretical Framework and Definitions

For phased array receivers, the accuracy with which the polarization state of a received signal can be measured depends on the antenna configuration, array calibration process, and beamforming algorithms. A signal and noise model for a dual-polarized array is developed and related to standard polarimetric antenna figures of merit, and the ideal polarimetrically calibrated, maximum-sensitivity beamforming solution for a dual-polarized phased array feed is derived. A practical polarimetric beamformer solution that does not require exact knowledge of the array polarimetric response is shown to be equivalent to the optimal solution in the sense that when the practical beamformers are calibrated, the optimal solution is obtained. To provide a rough initial polarimetric calibration for the practical beamformer solution, an approximate single-source polarimetric calibration method is developed. The modeled instrumental polarization error for a dipole phased array feed with the practical beamformer solution and single-source polarimetric calibration was -10 dB or lower over the array field of view for elements with alignments perturbed by random rotations with 5 degree standard deviation

Simple generalizations of Anti-de Sitter space-time

We consider new cosmological solutions which generalize the cosmological patch of the Anti-de Sitter (AdS) space-time, allowing for fluids with equations of state such that $w\neq -1$. We use them to derive the associated full manifolds. We find that these solutions can all be embedded in flat five-dimensional space-time with $--+++$ signature, revealing deformed hyperboloids. The topology and causal-structure of these spaces is therefore unchanged, and closed time-like curves are identified, before a covering space is considered. However the structure of Killing vector fields is entirely different and so we may expect a different structure of Killing horizons in these solutions.Comment: 6 Pages, 5 Figures, Corrections and additions made for publication in Journal of Classical and Quantum Gravit