15,013 research outputs found
Peculiar Velocities and the Mean Density Parameter
We study the peculiar velocity field inferred from the Mark III spirals using
a new method of analysis. We estimate optimal values of Tully-Fisher scatter
and zero-point offset, and we derive the 3-dimensional rms peculiar velocity
() of the galaxies in the samples analysed. We check our statistical
analysis using mock catalogs derived from numerical simulations of CDM models
considering measurement uncertainties and sampling variations. Our best
determination for the observations is . We use the
linear theory relation between , the density parameter , and
the galaxy correlation function to infer the quantity where is the linear bias parameter
of optical galaxies and the uncertainties correspond to bootstrap resampling
and an estimated cosmic variance added in quadrature. Our findings are
consistent with the results of cluster abundances and redshift space distortion
of the two-point correlation function. These statistical measurements suggest a
low value of the density parameter if optical galaxies are
not strongly biased tracers of mass.Comment: Accepted for publication in MNRAS. 8 pages latex (mn.sty), including
7 figure
Change in the Magnetic Domain Alignment Process at the Onset of a Frustrated Magnetic State in Ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 Double Perovskite
We have performed a combined study of magnetization hysteresis loops and time
dependence of the magnetization in a broad temperature range for the
ferrimagnetic La2Ni(Ni1/3Sb2/3)O6 double perovskite. This material has a
ferrimagnetic order transition at ~100 K and at lower temperatures (~ 20 K)
shows the signature of a frustrated state due to the presence of two competing
magnetic exchange interactions. The temperature dependence of the coercive
field shows an important upturn below the point where the frustrated state sets
in. The use of the magnetization vs. applied magnetic field hysteresis data,
together with the magnetization vs. time data provides a unique opportunity to
distinguish between different scenarios for the low temperature regime. From
our analysis, a strong domain wall pinning results the best scenario for the
low temperature regime. For temperatures larger than 20K the adequate scenario
seems to correspond to a weak domain wall pinning.Comment: 4 pages, 5 figures included. Manuscript submitted to IEEE
Transactions on Magnetics, proceedings of the LAW3M 2013 conferenc
Agglomeration in a global Economy: A Survey
This review of recent contributions reveals common conclusions about the effects of integration on location. For high trade costs, the need to supply markets locally encourages firms to spread across different regions. Integration weakens the incentives for self-sufficiency and for intermediate values of trade costs pecuniary externalities induce firms and workers to cluster together, turning location into a self-reinforcing process. However, agglomeration raises the price of immobile local factors and goods, so far low transport costs firms may spread to regions where those prices are lower.
Properties of galaxies in SDSS Quasar environments at z < 0.2
We analyse the environment of low redshift, z < 0.2, SDSS quasars using the
spectral and photometric information of galaxies from the Sloan Digital Sky
Survey Third Data Release (SDSS-DR3). We compare quasar neighbourhoods with
field and high density environments through an analysis on samples of typical
galaxies and groups. We compute the surrounding surface number density of
galaxies finding that quasar environments systematically avoid high density
regions. Their mean environments correspond to galaxy density enhancements
similar to those of typical galaxies. We have also explored several galaxy
properties in these environments, such as spectral types, specific star
formation rates, concentration indexes, colours and active nuclei activity. We
conclude that low redshift quasar neighbourhoods (r_p < 1 Mpc h^-1, Delta V <
500 km/s) are populated by bluer and more intense star forming galaxies of
disk-type morphology than galaxies in groups and in the field. Although star
formation activity is thought to be significantly triggered by interactions, we
find that quasar fueling may not require the presence of a close companion
galaxy (r_p < 100 kpc h^-1, Delta V< 350 km/s). As a test of the unified AGN
model, we have performed a similar analysis to the neighbours of a sample of
active galaxies. The results indicate that these neighbourhoods are comparable
to those of quasars giving further support to this unified scenario.Comment: 7 pages, 8 figures, submitted to MNRA
Boundary Conformal Anomalies on Hyperbolic Spaces and Euclidean Balls
We compute conformal anomalies for conformal field theories with free
conformal scalars and massless spin fields in hyperbolic space
and in the ball , for . These
spaces are related by a conformal transformation. In even dimensional spaces,
the conformal anomalies on and are shown to
be identical. In odd dimensional spaces, the conformal anomaly on
comes from a boundary contribution, which exactly coincides
with that of provided one identifies the UV short-distance
cutoff on with the inverse large distance IR cutoff on
, just as prescribed by the conformal map. As an
application, we determine, for the first time, the conformal anomaly
coefficients multiplying the Euler characteristic of the boundary for scalars
and half-spin fields with various boundary conditions in and .Comment: 16 pages. V3: small correction
Operator Mixing in Large Superconformal Field Theories on and Correlators with Wilson loops
We find a general formula for the operator mixing on the of
chiral primary operators (CPO) for the theory at large in
terms of Chebyshev polynomials. As an application, we compute the correlator of
a CPO and a Wilson loop, reproducing an earlier result by Giombi and Pestun
obtained from a two-matrix model proposal. Finally, we discuss a simple method
to obtain correlators in general superconformal field theories in
perturbation theory in terms of correlators of the theory.Comment: 15 pages, no figure
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