101,540 research outputs found
Determinants and consequences of internal and international migration
This paper analyzes the current migration in rural population in the south of Veracruz state (Mexico). We identify three different spaces of migration, traditional markets, the northern border and the United States. Applying a multinomial logistic model and taking into account individual, family, and local characteristics of the migrants, we find different determinants in each space. These determinants are related to the objectives, needs and means of the migrants and their families. Otherwise, each space involves different consequences to the family in terms of the relationships between migrants and the rest of their relatives.consequences, determinants, family, intergenerational relations, internal migration, international migration, Mexico, migration, reproduction, rural population
Linking gravitational waves and X-ray phenomena with joint LISA and Athena observations
The evolution of cosmic structures, the formation and growth of the first
black holes and the connection to their baryonic environment are key unsolved
problems in astrophysics. The X-ray Athena mission and the gravitational-wave
Laser Interferometer Space Antenna (LISA) offer independent and complementary
angles on these problems. We show that up to 10 black hole binaries in the mass
range 10^5 - 10^8 Msun discovered by LISA at redshift <~ 3.5 could be detected
by Athena in an exposure time up to 100 ks, if prompt X-ray emission of ~ 1% -
10% of the Eddington luminosity is present. Likewise, if any LISA-detected
extreme mass ratio inspirals occur in accretion disks, Athena can detect
associated electromagnetic emission out to redshift ~ 1. Finally, warned by
LISA, Athena can point in advance and stare at stellar-mass binary black hole
mergers at redshift <~ 0.1. These science opportunities emphasise the vast
discovery space of simultaneous observations from the two observatories, which
would be missed if they were operated in different epochs.Comment: Published in Nature Astronom
Measuring the parameters of massive black hole binary systems with Pulsar Timing Array observations of gravitational waves
The observation of massive black hole binaries (MBHBs) with Pulsar Timing
Arrays (PTAs) is one of the goals of gravitational wave astronomy in the coming
years. Massive (>10^8 solar masses) and low-redshift (< 1.5) sources are
expected to be individually resolved by up-coming PTAs, and our ability to use
them as astrophysical probes will depend on the accuracy with which their
parameters can be measured. In this paper we estimate the precision of such
measurements using the Fisher-information-matrix formalism. We restrict to
"monochromatic" sources. In this approximation, the system is described by
seven parameters and we determine their expected statistical errors as a
function of the number of pulsars in the array, the array sky coverage, and the
signal-to-noise ratio (SNR) of the signal. At fixed SNR, the gravitational wave
astronomy capability of a PTA is achieved with ~20 pulsars; adding more pulsars
(up to 1000) to the array reduces the source error-box in the sky \Delta\Omega
by a factor ~5 and has negligible consequences on the statistical errors on the
other parameters. \Delta\Omega improves as 1/SNR^2 and the other parameters as
1/SNR. For a fiducial PTA of 100 pulsars uniformly distributed in the sky and a
coherent SNR = 10, we find \Delta\Omega~40 deg^2, a fractional error on the
signal amplitude of ~30% (which constraints only very poorly the chirp mass -
luminosity distance combination M_c^{5/3}/D_L), and the source inclination and
polarization angles are recovered at the ~0.3 rad level. The ongoing Parkes PTA
is particularly sensitive to systems located in the southern hemisphere, where
at SNR = 10 the source position can be determined with \Delta\Omega ~10 deg^2,
but has poorer performance for sources in the northern hemisphere. (Abridged)Comment: 20 pages, 12 figures, 2 color figures, submitted to Phys. Rev.
The stochastic gravitational-wave background from massive black hole binary systems: implications for observations with Pulsar Timing Arrays
Massive black hole binary systems, with masses in the range ~10^4-10^10
\msun, are among the primary sources of gravitational waves in the frequency
window ~10^-9 Hz - 0.1 Hz. Pulsar Timing Arrays (PTAs) and the Laser
Interferometer Space Antenna (LISA) are the observational means by which we
will be able to observe gravitational radiation from these systems. We carry
out a systematic study of the generation of the stochastic gravitational-wave
background from the cosmic population of massive black hole binaries. We
consider a wide variety of assembly scenarios and we estimate the range of
signal strength in the frequency band accessible to PTAs. We show that, taking
into account the uncertainties surrounding the actual key model parameters, the
amplitude lies in the interval h_c(f = 10^-8 Hz)~5x10^-16 - 8x10^-15. The most
optimistic predictions place the signal level at a factor of ~3 below the
current sensitivity of Pulsar Timing Arrays, but within the detection range of
the complete Parkes PTA for a wide variety of models, and of the future
Square-Kilometer-Array PTA for all the models considered here. We also show
that at frequencies >10^-8 Hz the frequency dependency of the generated
background follows a power-law significantly steeper than f^-2/3, that has been
considered so far. Finally we show that LISA observations of individual
resolvable massive black hole binaries are complementary and orthogonal to PTA
observations of a stochastic background from the whole population in the
Universe. In fact, the detection of gravitational radiation in both frequency
windows will enable us to fully characterise the cosmic history of massive
black holes.Comment: 21 pages, 14 figures, minor revisions, accepted for publication in
MNRA
Twin deficits in CEEC economies: evidence from panel unit root tests
This paper analyses the relation between the external and government deficits in a panel of CEEC economies. We first assess by panel unit root tests whether the fiscal and external intertemporal budget constraints hold, and then examine the role of public and private expenditure in the dynamics of external indebtedness by panel regression. The results show that government deficit is a significant but relatively minor source of external imbalances, and that the external indebtedness of CEEC economies is sustainable.current account, budget deficit, panel data, twin deficits, sustainability
The Kac Jordan superalgebra: automorphisms and maximal subalgebras
The group of automorphisms of the Kac Jordan superalgebra is described, and
used to classify the maximal subalgebras.Comment: 10 page
Edge states in a two-dimensional quantum walk with disorder
We investigate the effect of spatial disorder on the edge states localized at
the interface between two topologically different regions. Rotation disorder
can localize the quantum walk if it is strong enough to change the topology,
otherwise the edge state is protected. Nonlinear spatial disorder, dependent on
the walker's state, attracts the walk to the interface even for very large
coupling, preserving the ballistic transport characteristic of the clean
regime.Comment: extended new version; 10 pages, 10 figure
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