Home  About us  Contact
 

Linear Size (linear + size)

Distribution by Scientific Domains
Physics and Astronomy85%

Selected Abstracts

Concepts of scale held by students with visual impairment

JOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 5 2009
M. Gail Jones
Abstract This study investigated students' with visual impairment concepts about linear size and scale. Specifically the study examined the accuracy of students' concepts over many orders of magnitude as well as experiences students have had in and out-of-school learning about size and scale. The results of assessments of 17 students with visual impairment were compared to those of students with normal sight. The study showed that students with visual impairment were most accurate for measurements in the human scale and were least accurate with very large and very small scales that cannot be directly experienced. However, when compared to students with normal sight, students with visual impairment were more accurate at large and small scales than their normally sighted peers. © 2009 Wiley Periodicals, Inc. J Res Sci Teach 46: 506,519, 2009 [source]

Evolutionary models for radio sources from compact sources to classical doubles

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000
P. Alexander
An analytical model is presented for the evolution of powerful double radio sources on small physical scales less than about 100 kpc when radiative losses can be neglected. The self-similar model of Kaiser & Alexander is extended to allow for expansion in an atmosphere with a King profile. Distribution functions for the number of sources in a logarithmic interval of linear size within a flux-limited sample are calculated and compared with observation. The observational data can be reproduced if it is assumed that there exists a population of sources that evolve and survive to sizes greater than the core radius, together with a population that suffer disruption of their jets before escaping the core radius. The latter population, while they may be regarded as frustrated sources, are not old sources, but just short-lived. [source]

Two-step mean-field renormalization group results for the large square Ising clusters

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
G. Kamieniarz
Abstract A transfer matrix approach has been worked out to test the predictions of the improved three-step mean-field renormalization group approach to square Ising clusters with linear size up to L = 11. Performing the asymptotic analysis, the convergence of the finite-size critical couplings and the critical exponents towards the exact values is shown. [source]

From observations to physics: Cosmological evolution of radio galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
A.D. Kapi
Abstract Recent theoretical progress has allowed us to determine the influence of the intrinsic properties of radio galaxies and their environments on their luminosity and size evolution. There are still, however, considerable uncertainties regarding our understanding of radio source evolution, in particular the relationship between CSS and GPS sources and larger radio galaxies. Here, we present our preliminary results on the cosmological evolution of the entire radio galaxy population. We use recent analytical models for the dynamical and luminosity evolution of FR II radio galaxies to convert observational data into distributions of source properties such as pressure of the source lobes. As input parameters we use the observed P - D (radio power,linear size) diagrams built up from flux-limited radio samples with complete redshift information. This allows us to examine the environments of evolving radio sources, and to shed more light on the (early) evolutionary tracks of radio galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Fate of baby radio galaxies: Dead or alive?

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
N. Kawakatu
Abstract In order to reveal the long-term evolution of relativistic jets in active galactic nuclei (AGNs), we examine the dynamical evolution of variously-sized radio galaxies [i.e., compact symmetric objects (CSOs), medium-size symmetric objects (MSOs), Fanaroff-Riley type II radio galaxies (FRIIs)]. By comparing the observed relation between the hot spot size and the linear size of radio source with a coevolution model of hot spot and cocoon, we find that the advance speed of hot spots and lobes inevitably show the deceleration phase (CSO-MSO phase) and the acceleration phase (MSO-FRII phase). The deceleration is caused by the growth of the cross-sectional area of the cocoon head. Moreover, by comparing the hot spot speed with the sound speed of the ambient medium, we predict that only CSOs whose initial advance speed is higher than 0.3,0.5 c can evolve into FRIIs (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ionization, shocks and evolution of the emission-line gas of distant 3CR radio galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000
P. N. Best
An analysis of the kinematics and ionization state of the emission-line gas of a sample of 14 3CR radio galaxies with redshifts z,1 is carried out. The data used for these studies, deep long-slit spectroscopic exposures from the William Herschel Telescope, are presented in an accompanying paper. It is found that radio sources with small linear sizes (,150 kpc) have lower ionization states, higher emission-line fluxes and broader line widths than larger radio sources. An analysis of the low-redshift sample of Baum et al. demonstrates that radio galaxies at low redshift show similar evolution in their velocity structures and emission-line ratios from small to large radio sources. The emission-line ratios of small radio sources are in agreement with theoretical shock ionization predictions, and their velocity profiles are distorted. Together with the other emission-line properties, this indicates that shocks associated with the radio source dominate the kinematics and ionization of the emission-line gas during the period that the radio source is expanding through the interstellar medium. Gas clouds are accelerated by the shocks, giving rise to the irregular velocity structures observed, whilst shock compression of emission-line gas clouds and the presence of the ionizing photons associated with the shocks combine to lower the ionization state of the emission-line gas. By contrast, in larger sources the shock fronts have passed well beyond the emission-line regions; the emission-line gas of these larger radio sources has much more settled kinematical properties, indicative of rotation, and emission-line ratios consistent with the dominant source of ionizing photons being the active galactic nucleus. This strong evolution with radio size of the emission-line gas properties of powerful radio galaxies mirrors the radio size evolution seen in the nature of the optical,ultraviolet continuum emission of these sources, implying that the continuum alignment effect is likely to be related to the same radio source shocks. [source]

Are radio-loud Broad Absorption Line Quasars young sources?

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
F.M. Montenegro-Montes
Abstract Studying Broad Absorption Line Quasars (BAL QSOs) is interesting because they probe the physics of the AGN environment, and because AGN outflows are important ingredients in many recent astrophysical puzzles. In the last decade, a substantial population of radio BAL QSOs was discovered and we have started a characterisation of the radio-loud BAL QSO population studying their radio spectra, radio morphology and polarisation properties. Our high-resolution radio maps show that BAL QSOs are compact radio sources with projected linear sizes below 1 kpc. Most BAL QSOs in our sample are unpolarised or weakly polarised at 8.4 GHz. They display convex radio spectra which typically flatten at low frequencies and become steeper at high frequencies, i.e. above 20 GHz. Many of these characteristics are common to the population of young radio sources, like Compact Steep Spectrum (CSS) or Gigahertz-Peaked Spectrum (GPS) sources. The above supports the hypothesis that BAL QSOs might be related to the initial stages in the AGN evolution (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]