1,380 research outputs found
Near-infrared Circular Polarization Images of NGC 6334-V
We present results from deep imaging linear and circular polarimetry of the massive star-forming region NGC 6334-V. These observations show high degrees of circular polarization (CP), as much as 22% in the Ks band, in the infrared nebula associated with the outflow. The CP has an asymmetric positive/negative pattern and is very extended (~80'' or 0.65 pc). Both the high CP and its extended size are larger than those seen in the Orion CP region. Three-dimensional Monte Carlo light-scattering models are used to show that the high CP may be produced by scattering from the infrared nebula followed by dichroic extinction by an optically thick foreground cloud containing aligned dust grains. Our results show not only the magnetic field orientation of around young stellar objects, but also the structure of circumstellar matter such as outflow regions and their parent molecular cloud along the line of sight. The detection of the large and extended CP in this source and the Orion nebula may imply the CP origin of the biological homochirality on EarthPeer reviewe
Infrared Dark Cloud Cores in the SCUBA Legacy Catalogue
We present an investigation of candidate Infrared Dark Cloud cores as
identified by Simon et al. (2006) located within the SCUBA Legacy Catalogue.
After applying a uniform noise cut to the Catalogue data we identify 154
Infrared Dark Cloud cores that were detected at 850um and 51 cores that were
not. We derive column densities for each core from their 8um extinction and
find that the IRDCs detected at 850um have higher column densities (a mean of
1.7x10^22 cm-2) compared to those cores not detected at 850um (a mean of
1.0x10^22 cm-2). Combined with sensitivity estimates, we suggest that the cores
not detected at 850um are low mass, low column density and low temperature
cores that are below the sensitivity limit of SCUBA at 850um. For a subsample
of the cores detected at 850um those contained within the MIPSGAL area) we find
that two thirds are associated with 24um sources. Cores not associated with
24um emission are either ``starless'' IRDC cores that perhaps have yet to form
stars, or contain low mass YSOs below the MIPSGAL detection limit. We see that
those ``starless'' IRDC cores and the IRDC cores associated with 24um emission
are drawn from the same column density population and are of similar mass. If
we then assume the cores without 24um embedded sources are at an earlier
evolutionary stage to cores with embedded objects we derive a statistical
lifetime for the quiescent phase of a few 10^3-10^4 years. Finally, we make
conservative predictions for the number of observed IRDCs that will be observed
by the Apex Telescope Galactic Plane Survey (ATLASGAL), the Herschel Infrared
Galactic Plane Survey (Hi-GAL), the JCMT Galactic Plane Survey (JPS) and the
SCUBA-2 ``All Sky'' Survey (SASSy).Comment: 18 pages, 3 tables, 10 figure
A Novel Asymptotic Solution to the Sommerfeld Radiation Problem: Analytic field expressions and the emergence of the Surface Waves
The well-known "Sommerfeld radiation problem" of a small -Hertzian- vertical
dipole above flat lossy ground is reconsidered. The problem is examined in the
spectral domain, through which it is proved to yield relatively simple integral
expressions for the received Electromagnetic (EM) field. Then, using the Saddle
Point method, novel analytical expressions for the scattered EM field are
obtained, including sliding observation angles. As a result, a closed form
solution for the subject matter is provided. Also, the necessary conditions for
the emergence of the so-called Surface Wave are discussed as well. A complete
mathematical formulation is presented, with detailed derivations where
necessary.Comment: 14 pages, 3 figures, Submitted for publication to "Progress in
Electromagnetics Research" (PIER) at 21/09/201
The critical temperature of the 2D-Ising model through Deep Learning Autoencoders
We investigate deep learning autoencoders for the unsupervised recognition of
phase transitions in physical systems formulated on a lattice. We focus our
investigation on the 2-dimensional ferromagnetic Ising model and then test the
application of the autoencoder on the anti-ferromagnetic Ising model. We use
spin configurations produced for the 2-dimensional ferromagnetic and
anti-ferromagnetic Ising model in zero external magnetic field. For the
ferromagnetic Ising model, we study numerically the relation between one latent
variable extracted from the autoencoder to the critical temperature . The
proposed autoencoder reveals the two phases, one for which the spins are
ordered and the other for which spins are disordered, reflecting the
restoration of the symmetry as the temperature increases. We
provide a finite volume analysis for a sequence of increasing lattice sizes.
For the largest volume studied, the transition between the two phases occurs
very close to the theoretically extracted critical temperature. We define as a
quasi-order parameter the absolute average latent variable , which
enables us to predict the critical temperature. One can define a latent
susceptibility and use it to quantify the value of the critical temperature
at different lattice sizes and that these values suffer from only
small finite scaling effects. We demonstrate that extrapolates to the
known theoretical value as suggesting that the autoencoder can
also be used to extract the critical temperature of the phase transition to an
adequate precision. Subsequently, we test the application of the autoencoder on
the anti-ferromagnetic Ising model, demonstrating that the proposed network can
detect the phase transition successfully in a similar way.Comment: 17 pages, 14 figures, accepted for publication in Eur. Phys. J.
When the State Fails: The Rise of Informal Civil Society Organizations in Greece
This thesis by using quantitative and qualitative data investigates the new forms of social and political collective action that rose after the financial crisis of 2009 in Greece. It attempts to study the rise of Informal Civil Society Organizations (ICSO) through the use of the research question, how can we understand the rise of informal civil society organizations in Greece after the onset of the crisis in 2009? With survey data from individuals involved in ICSOs, I analyze the motivations of these individuals, answering the question, what motivates people to voluntarily engage in informal civil society organizations? Through the use of interviews, I investigate the question, why did people establish informal civil society organizations? The quantitative results show that people are motivated to volunteer mostly because of altruistic reasons. The qualitative results show that ICSOs were created to promote social solidarity, as well as to protest against societal change. This thesis concludes that the rise of ICSOs can be interpreted as a new form of social movements
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