1,229 research outputs found
Magnetic field measurements at milliarcsecond resolution around massive young stellar objects
Magnetic fields have only recently been included in theoretical simulations
of high-mass star formation. The simulations show that magnetic fields can play
a crucial role not only in the formation and dynamics of molecular outflows,
but also in the evolution of circumstellar disks. Therefore, new measurements
of magnetic fields at milliarcsecond resolution close to massive young stellar
objects (YSOs) are fundamental for providing new input for numerical
simulations and for understanding the formation process of massive stars. The
polarized emission of 6.7 GHz CH3OH masers allows us to investigate the
magnetic field close to the massive YSO where the outflows and disks are
formed. Recently, we have detected with the EVN CH3OH maser polarized emission
towards 10 massive YSOs. From a first statistical analysis we have found
evidence that magnetic fields are primarily oriented along the molecular
outflows. To improve our statistics we are carrying on a large observational
EVN campaign for a total of 19 sources, the preliminary results of the first
seven sources are presented in this contribution. Furthermore, we also describe
our efforts to estimate the Lande' g-factors of the CH3OH maser transition to
determine the magnetic field strength from our Zeeman-splitting measurements.Comment: Accepted for publication in the proceeding of the "12th European VLBI
Network Symposium and Users Meeting", eds Tarchi et al. PoS(EVN 2014)04
Tomonaga-Luttinger features in the resonant Raman spectra of quantum wires
The differential cross section for resonant Raman scattering from the
collective modes in a one dimensional system of interacting electrons is
calculated non-perturbatively using the bosonization method. The results
indicate that resonant Raman spectroscopy is a powerful tool for studying
Tomonaga-Luttinger liquid behaviour in quasi-one dimensional electron systems.Comment: 4 pages, no figur
On Renyi entropies characterizing the shape and the extension of the phase space representation of quantum wave functions in disordered systems
We discuss some properties of the generalized entropies, called Renyi
entropies and their application to the case of continuous distributions. In
particular it is shown that these measures of complexity can be divergent,
however, their differences are free from these divergences thus enabling them
to be good candidates for the description of the extension and the shape of
continuous distributions. We apply this formalism to the projection of wave
functions onto the coherent state basis, i.e. to the Husimi representation. We
also show how the localization properties of the Husimi distribution on average
can be reconstructed from its marginal distributions that are calculated in
position and momentum space in the case when the phase space has no structure,
i.e. no classical limit can be defined. Numerical simulations on a one
dimensional disordered system corroborate our expectations.Comment: 8 pages with 2 embedded eps figures, RevTex4, AmsMath included,
submitted to PR
On the Singularity Structure and Stability of Plane Waves
We describe various aspects of plane wave backgrounds. In particular, we make
explicit a simple criterion for singularity by establishing a relation between
Brinkmann metric entries and diffeomorphism-invariant curvature information. We
also address the stability of plane wave backgrounds by analyzing the
fluctuations of generic scalar modes. We focus our attention on cases where
after fixing the light-cone gauge the resulting world sheet fields appear to
have negative "mass terms". We nevertheless argue that these backgrounds may be
stable.Comment: 21 pages, 1 figur
Investigating the topology of interacting networks - Theory and application to coupled climate subnetworks
Network theory provides various tools for investigating the structural or
functional topology of many complex systems found in nature, technology and
society. Nevertheless, it has recently been realised that a considerable number
of systems of interest should be treated, more appropriately, as interacting
networks or networks of networks. Here we introduce a novel graph-theoretical
framework for studying the interaction structure between subnetworks embedded
within a complex network of networks. This framework allows us to quantify the
structural role of single vertices or whole subnetworks with respect to the
interaction of a pair of subnetworks on local, mesoscopic and global
topological scales.
Climate networks have recently been shown to be a powerful tool for the
analysis of climatological data. Applying the general framework for studying
interacting networks, we introduce coupled climate subnetworks to represent and
investigate the topology of statistical relationships between the fields of
distinct climatological variables. Using coupled climate subnetworks to
investigate the terrestrial atmosphere's three-dimensional geopotential height
field uncovers known as well as interesting novel features of the atmosphere's
vertical stratification and general circulation. Specifically, the new measure
"cross-betweenness" identifies regions which are particularly important for
mediating vertical wind field interactions. The promising results obtained by
following the coupled climate subnetwork approach present a first step towards
an improved understanding of the Earth system and its complex interacting
components from a network perspective
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