321,925 research outputs found
The magnetic field structure in CTA 102 from high-resolution mm-VLBI observations during the flaring state in 2016-2017
CONTEXT: Investigating the magnetic field structure in the innermost regions of relativistic jets is fundamental to understanding the crucial physical processes giving rise to jet formation, as well as to their extraordinary radiation output up to γ-ray energies.
AIMS: We study the magnetic field structure of the quasar CTA 102 with 3 and 7 mm VLBI polarimetric observations, reaching an unprecedented resolution (∼50 μas). We also investigate the variability and physical processes occurring in the source during the observing period, which coincides with a very active state of the source over the entire electromagnetic spectrum.
METHODS: We perform the Faraday rotation analysis using 3 and 7 mm data and we compare the obtained rotation measure (RM) map with the polarization evolution in 7 mm VLBA images. We study the kinematics and variability at 7 mm and infer the physical parameters associated with variability. From the analysis of γ-ray and X-ray data, we compute a minimum Doppler factor value required to explain the observed high-energy emission.
RESULTS: Faraday rotation analysis shows a gradient in RM with a maximum value of ∼6 × 104⁴ rad m⁻² and intrinsic electric vector position angles (EVPAs) oriented around the centroid of the core, suggesting the presence of large-scale helical magnetic fields. Such a magnetic field structure is also visible in 7 mm images when a new superluminal component is crossing the core region. The 7 mm EVPA orientation is different when the component is exiting the core or crossing a stationary feature at ∼0.1 mas. The interaction between the superluminal component and a recollimation shock at ∼0.1 mas could have triggered the multi-wavelength flares. The variability Doppler factor associated with such an interaction is large enough to explain the high-energy emission and the remarkable optical flare occurred very close in time.Accepted manuscrip
The Bar--Halo Interaction--I. From Fundamental Dynamics to Revised N-body Requirements
Only through resonances can non-axisymmetric features such as spiral arms and
bars exert torques over large scales and change the overall structure of a
near-equilibrium galaxy. We describe the resonant interaction mechanism in
detail and derive explicit criteria for the particle number required to
simulate these dynamical processes accurately using N-body simulations and
illustrate them with numerical experiments. To do this, we perform direct
numerical solution of perturbation theory and make detailed comparisons with
N-body simulations. The criteria include: sufficient particle coverage in phase
space near the resonance and enough particles to minimize gravitational
potential fluctuations that will change the dynamics of the resonant encounter.
Some of our more surprising findings are as follows. First, the
Inner-Lindblad-like resonance (ILR), responsible for coupling the bar to the
central halo cusp, requires almost 10^9 equal mass particles within the virial
radius for a Milky-Way-like bar in an NFW profile. Second, orbits that linger
near the resonance receive more angular momentum than orbits that move through
the resonance quickly. Small-scale fluctuations present in state-of-the-art
particle-particle simulations can knock orbits out of resonance, preventing
them from lingering and, thereby, decrease the torque. The required particle
numbers are sufficiently high for scenarios of interest that apparent
convergence in particle number is misleading: the convergence is in the
noise-dominated regime. State-of-the-art simulations are not adequate to follow
all aspects of secular evolution driven by the bar-halo interaction. We present
a procedure to test the requirements for individual N-body codes for the actual
problem of interest. [abridged]Comment: 30 pages, 19 figures, submitted to Monthly Notices. For paper with
figures at full resolution:
http://www.astro.umass.edu/~weinberg/weinberg_katz_1.ps.g
Estimation of Scribble Placement for Painting Colorization
Image colorization has been a topic of interest since
the mid 70’s and several algorithms have been proposed that
given a grayscale image and color scribbles (hints) produce a colorized image. Recently, this approach has been introduced in the field of art conservation and cultural heritage, where B&W photographs of paintings at previous stages have been colorized. However, the questions of what is the minimum number of scribbles necessary and where they should be placed in an image remain unexplored. Here we address this limitation using an iterative algorithm that provides insights as to the relationship between locally vs. globally important scribbles. Given a color image we randomly select scribbles and we attempt to color the
grayscale version of the original.We define a scribble contribution measure based on the reconstruction error. We demonstrate our approach using a widely used colorization algorithm and images from a Picasso painting and the peppers test image. We show that areas isolated by thick brushstrokes or areas with high textural variation are locally important but contribute very little to the
overall representation accuracy. We also find that for the case of Picasso on average 10% of scribble coverage is enough and that flat areas can be presented by few scribbles. The proposed method can be used verbatim to test any colorization algorithm
Wage bargaining and the boundaries of the multinational firm
Do variations in labor market institutions across countries affect the cross-border organization of the firm? Using firm-level data on multinationals located in France, we show that firms are more likely to outsource the production of intermediate inputs to external suppliers when importing from countries with empowered unions. Moreover, this effect is stronger for firms operating in capital-intensive industries. We propose a theoretical mechanism that rationalizes these findings. The fragmentation of the value chain weakens the union's bargaining position, by limiting the amount of revenues that are subject to union extraction. The outsourcing strategy reduces the share of surplus that is appropriated by the union, which enhances the firm's incentives to invest. Since investment creates relatively more value in capital-intensive industries, increases in union power are more likely to be conducive to outsourcing in those industries. Overall, our findings suggest that multinational firms use their organizational structure strategically when sourcing intermediate inputs from unionized markets
Physics Potential of a Radio Surface Array at the South Pole (ARENA 2018)
A surface array of radio antennas will enhance the performance of the IceTop
array and enable new, complementary science goals. First, the accuracy for
cosmic-ray air showers will be increased since the radio array provides a
calorimetric measurement of the electromagnetic component and is sensitive to
the position of the shower maximum. This enhanced accuracy can be used to
better measure the mass composition, to search for possible mass-dependent
anisotropies in the arrival directions of cosmic rays, and for more thorough
tests of hadronic interaction models. Second, the sensitivity of the radio
array to inclined showers will increase the sky coverage for cosmic-ray
measurements. Third, the radio array can be used to search for PeV photons from
the Galactic Center. Since IceTop is planned to be enhanced by a scintillator
array in the near future, a radio extension sharing the same infrastructure can
be installed with minimal additional effort and excellent scientific prospects.
The combination of ice-Cherenkov, scintillation, and radio detectors at IceCube
will provide unprecedented accuracy for the study of highenergy Galactic cosmic
rays.Comment: Proceedings of 8th ARENA 2018, to appear in EPJ Wo
Link communities reveal multiscale complexity in networks
Networks have become a key approach to understanding systems of interacting
objects, unifying the study of diverse phenomena including biological organisms
and human society. One crucial step when studying the structure and dynamics of
networks is to identify communities: groups of related nodes that correspond to
functional subunits such as protein complexes or social spheres. Communities in
networks often overlap such that nodes simultaneously belong to several groups.
Meanwhile, many networks are known to possess hierarchical organization, where
communities are recursively grouped into a hierarchical structure. However, the
fact that many real networks have communities with pervasive overlap, where
each and every node belongs to more than one group, has the consequence that a
global hierarchy of nodes cannot capture the relationships between overlapping
groups. Here we reinvent communities as groups of links rather than nodes and
show that this unorthodox approach successfully reconciles the antagonistic
organizing principles of overlapping communities and hierarchy. In contrast to
the existing literature, which has entirely focused on grouping nodes, link
communities naturally incorporate overlap while revealing hierarchical
organization. We find relevant link communities in many networks, including
major biological networks such as protein-protein interaction and metabolic
networks, and show that a large social network contains hierarchically
organized community structures spanning inner-city to regional scales while
maintaining pervasive overlap. Our results imply that link communities are
fundamental building blocks that reveal overlap and hierarchical organization
in networks to be two aspects of the same phenomenon.Comment: Main text and supplementary informatio
Corporate Social and Financial Performance: Empirical Evidence from American Companies
The objective of this study is to address the issue of the relationship between
corporate social and financial performance by moderating company size and
financial leverage.with the use of type of industry as control variable. The
Corporate social performance (CSP/CSR) is measured using seven item
developed initially by Michael Jantzi Research Associate, Inc and used by
Mahoney and Robert (2007). To attaint main research objective, the measure
of CSP composite is used. Furthermore, company size, financial leverage,
and type ofindustry are measured by total asset, degree of intermal and
external source to finance the company’s assets, and dummy variable (0 for
non manufacture and 1 for manufacture), respectively. A moderated multiple
regression model is used in the present study. Four models are developed in
the study basedon the theory of slack resiurce and good management. The
result of the present study is that corporate social performance (CSP/CSR)
has no effect on corporate financial performance (CFP) under slack resource
and good management theory it is also shown that only financial leverage
could moderate the interaction between CSP/CSR and financial performance
(CSP). However, based on the overall analysis, it may be reasonable to
come to conclusion that the relationship between CSP and financial
performance is spurious as Orlitzki (2000) concluded.
Key Words: Corporate social performance, corporate social responsibility,
financial performance, good management theory, stakeholder, and slack
resource theory
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