10,064 research outputs found
Internal Migration and Regional Population Dynamics in Europe: Estonia Case Study
Estonia has experienced a long-lasting and strong influence of international migration on regional population growth. Post-war immigrants account for about 36 per cent of the total population, and are concentrated in larger cities of Northern Estonia. Regionally, the relative proportions of the native-born and immigrant origin sub-populations are important for the understanding of population change and internal migration flows in the 1980-1990s.
In Estonia, the quality of migration data requires careful assessment. The preservation of Soviet-type record-keeping has reduced data quality in the 1990s, already low, and use of the data should keep data quality problems in mind. Otherwise, false conclusions can be reached.
To describe internal migration patterns, it has proved technically feasible and very useful to disaggregate the county population into rural and urban components, and correspondingly, the migration flows into four directions (urban-urban, urban-rural, rural-urban and rural-rural).
During the 1980s the pattern of population growth and internal migration has changed in Estonia. Reflecting the turnaround in long-term population processes, migration development reached the advanced stage with more or less regionally balanced in- and out-migration flows and decreasing importance of net migration. Accordingly, to understand current trends and patterns, explanations must be sought from the 1980s which has served a starting point for the present trends rather than from the period of economic transition in the 1990s.
As a part of the turnaround, the century-long persistent rural depopulation has come to an end and the moderate growth has started reflecting natural population increase as well as deurbanization. In the 1980s two developments have occurred in parallel: migratory increase of rural population led by a deurbanizing native-born population, and continued urban population growth as a result of the population momentum of pre-transition immigrants. In future decades, the urban deconcentration will probably be the underlying trend in Estonia. In Estonia, noticeable proportion of territory and population is located in islands. However, the island population does not show any systematic difference in the type of internal migration. Particularly, the depopulation of island populations, observed in several comparable European cases, is not occurring.
Each life-course stage was found to have its specific migration pattern, more stable than the pattern for the total population. In many cases the changes of internal migration are determined by the change in the proportion of population in different life-course stages. Additionally, the life-course approach has been useful in demonstrating the features of the present Estonian internal migration pattern which appear closer to the countries of comparable in demographic development, more or less regardless of the significant differences in the level of economic development. Among life-course groups, in Estonia the older working age population was characterized by the strongest deurbanization intensities in 1995. The same group has also undergone the largest modification of migration pattern during the economic transition (1987-1995)
X-ray Polarization Signatures of Compton Scattering in Magnetic Cataclysmic Variables
Compton scattering within the accretion column of magnetic cataclysmic
variables (mCVs) can induce a net polarization in the X-ray emission. We
investigate this process using Monte Carlo simulations and find that
significant polarization can arise as a result of the stratified flow structure
in the shock-ionized column. We find that the degree of linear polarization can
reach levels up to ~8% for systems with high accretion rates and low
white-dwarf masses, when viewed at large inclination angles with respect to the
accretion column axis. These levels are substantially higher than previously
predicted estimates using an accretion column model with uniform density and
temperature. We also find that for systems with a relatively low-mass white
dwarf accreting at a high accretion rate, the polarization properties may be
insensitive to the magnetic field, since most of the scattering occurs at the
base of the accretion column where the density structure is determined mainly
by bremsstrahlung cooling instead of cyclotron cooling.Comment: 7 pages, 8 figures, accepted by MNRA
Gamma Ray Bursts: recent results and connections to very high energy Cosmic Rays and Neutrinos
Gamma-ray bursts are the most concentrated explosions in the Universe. They
have been detected electromagnetically at energies up to tens of GeV, and it is
suspected that they could be active at least up to TeV energies. It is also
speculated that they could emit cosmic rays and neutrinos at energies reaching
up to the eV range. Here we review the recent developments in
the photon phenomenology in the light of \swift and \fermi satellite
observations, as well as recent IceCube upper limits on their neutrino
luminosity. We discuss some of the theoretical models developed to explain
these observations and their possible contribution to a very high energy cosmic
ray and neutrino background.Comment: 12 pages, 7 figures. Text of a plenary lecture at the PASCOS 12
conference, Merida, Yucatan, Mexico, June 2012; to appear in J.Phys. (Conf.
Series
Scattering in the vicinity of relativistic jets: a method for constraining jet parameters
Relativistic jets of radio loud active galactic nuclei (AGN) produce highly
directed, intense beams of radiation. A fraction of this beamed radiation
scatters on the thermal plasma generally surrounding an AGN. The morphology of
the scattered emission can thus provide constraints on the physical properties
of the jet. We present a model to study the feasibility of constraining the
parameters of a jet, especially its inclination angle and bulk Lorentz factor
in this way. We apply our model to the well studied jet of M87 and the
surrounding diffuse gas and find that the observational limits of the surface
brightness measured in the region of the putative counterjet provide the
tightest constraints on the jet parameters consistent with constraints derived
by other methods. We briefly discuss the applicability of our model to other
sources exhibiting relativistic motionsComment: 17 pages, 15 figures, to appear in A&A, 420, 33 (2004
Thinking territory historically.
BACKGROUND:
While the randomised controlled trial (RCT) is generally regarded as the design of
choice for assessing the effects of health care, within the social sciences there is
considerable debate about the relative suitability of RCTs and non-randomised
studies (NRSs) for evaluating public policy interventions.
// OBJECTIVES:
To determine whether RCTs lead to the same effect size and variance as NRSs of
similar policy interventions; and whether these findings can be explained by other
factors associated with the interventions or their evaluation.
// METHODS:
Analyses of methodological studies, empirical reviews, and individual health and
social services studies investigated the relationship between randomisation and
effect size of policy interventions by:
1) Comparing controlled trials that are identical in all respects other than the use of
randomisation by 'breaking' the randomisation in a trial to create non-randomised
trials (re-sampling studies).
2) Comparing randomised and non-randomised arms of controlled trials mounted
simultaneously in the field (replication studies).
3) Comparing similar controlled trials drawn from systematic reviews that include
both randomised and non-randomised studies (structured narrative reviews and
sensitivity analyses within meta-analyses).
4) Investigating associations between randomisation and effect size using a pool of
more diverse RCTs and NRSs within broadly similar areas (meta-epidemiology).
// RESULTS:
Prior methodological reviews and meta-analyses of existing reviews comparing
effects from RCTs and nRCTs suggested that effect sizes from RCTs and nRCTs
may indeed differ in some circumstances and that these differences may well be
associated with factors confounded with design.
Re-sampling studies offer no evidence that the absence of randomisation directly
influences the effect size of policy interventions in a systematic way. No consistent
explanations were found for randomisation being associated with changes in effect
sizes of policy interventions in field trials
TeV Gamma Rays from Geminga and the Origin of the GeV Positron Excess
The Geminga pulsar has long been one of the most intriguing MeV-GeV gamma-ray
point sources. We examine the implications of the recent Milagro detection of
extended, multi-TeV gamma-ray emission from Geminga, finding that this reveals
the existence of an ancient, powerful cosmic-ray accelerator that can plausibly
account for the multi-GeV positron excess that has evaded explanation. We
explore a number of testable predictions for gamma-ray and electron/positron
experiments (up to ~100 TeV) that can confirm the first "direct" detection of a
cosmic-ray source.Comment: 4 pages and 3 figures; Minor revisions, accepted for publication in
Physical Review Letter
- …