360 research outputs found
Structure of the Draco Dwarf Spheroidal Galaxy
This article studies the structure of the Draco dwarf spheroidal galaxy with
an emphasis on the question of whether the spatial distribution of its stars
has been affected by the tidal interaction with the Milky Way, using R- and
V-band CCD photometry for eleven fields. The article reports coordinates for
the center, a position angle of the major axis, and the ellipticity. It also
reports the results of searches for asymmetries in the structure of Draco.
These results, and searches for a ``break'' in the radial profile and for the
presence of principal sequences of Draco in a color-magnitude diagram for
regions more than 50 arcmin from the center, yield no evidence that tidal
forces from the Milky Way have affected the structure of Draco.Comment: 25 pages, 11 figures, 3 tables. Accepted for publication in A
Classical conformal blocks, Coulomb gas integrals and Richardson-Gaudin models
Virasoro conformal blocks are universal ingredients of correlation functions
of two-dimensional conformal field theories (2d CFTs) with Virasoro symmetry.
It is acknowledged that in the (classical) limit of large central charge of the
Virasoro algebra and large external, and intermediate conformal weights with
fixed ratios of these parameters Virasoro blocks exponentiate to functions
known as Zamolodchikovs' classical blocks. The latter are special functions
which have awesome mathematical and physical applications. Uniformization,
monodromy problems, black holes physics, quantum gravity, entanglement, quantum
chaos, holography, N=2 gauge theory and quantum integrable systems (QIS) are
just some of contexts, where classical Virasoro blocks are in use. In this
paper, exploiting known connections between power series and integral
representations of (quantum) Virasoro blocks, we propose new finite closed
formulae for certain multi-point classical Virasoro blocks on the sphere.
Indeed, combining classical limit of Virasoro blocks expansions with a saddle
point asymptotics of Dotsenko-Fateev (DF) integrals one can relate classical
Virasoro blocks with a critical value of the "Dotsenko-Fateev matrix model
action". The latter is the "DF action" evaluated on a solution of saddle point
equations which take the form of Bethe equations for certain QIS (Gaudin spin
models). A link with integrable models is our main motivation for this research
line. ... .Comment: 49 pages, several diagrams and tables; conformal to version accepted
for publication in JHE
Hamiltonian anomalies of bound states in QED
The Bound State in QED is described in systematic way by means of nonlocal
irreducible representations of the nonhomogeneous Poincare group and Dirac's
method of quantization. As an example of application of this method we
calculate triangle diagram . We show that
the Hamiltonian approach to Bound State in QED leads to anomaly-type
contribution to creation of pair of parapositronium by two photon.Comment: 12 pages, 2 figures. Proceedings of the conference "Symmetry Methods
in Physics XV", July 12-16, 2011, Dubna, Russi
Core Formation by a Population of Massive Remnants
Core radii of globular clusters in the Large and Small Magellanic Clouds show
an increasing trend with age. We propose that this trend is a dynamical effect
resulting from the accumulation of massive stars and stellar-mass black holes
at the cluster centers. The black holes are remnants of stars with initial
masses exceeding 20-25 solar masses; as their orbits decay by dynamical
friction, they heat the stellar background and create a core. Using analytical
estimates and N-body experiments, we show that the sizes of the cores so
produced and their growth rates are consistent with what is observed. We
propose that this mechanism is responsible for the formation of cores in all
globular clusters and possibly in other systems as well.Comment: 5 page
Application of new methods of environment analysis and assessment in landscape audits : case studies of urban areas like Czestochowa, Poland
Following the 2000 European Landscape Convention, a new act strengthening landscape protection
instruments has been in force since 2015. It sets forth legal aspects of landscape shaping (Dziennik Ustaw 2015, poz.
774) and introduces landscape audits at the province level. A landscape audit consists in identification and
characterization of selected landscapes, assessment of their value, selection of so-called priority landscapes and
identification of threats for preservation of their value. An audit complies with GIS standards. Analyses use source
materials, i.e. digital maps of physical-geographical mesoregions, current topographic maps of digital resources of
cartographic databases, latest orthophotomaps and DTMs, maps of potential vegetation, geobotanic regionalization,
historic-cultural regionalization and natural landscape types, documentation of historical and cultural values and
related complementary resources. A special new methodology (Solon et al. 2014), developed for auditing, was tested
in 2015 in an urban area (Myga-Piatek et al. 2015). Landscapes are characterized by determining their analytic
(natural and cultural) and synthetic features, with particular focus on the stage of delimitation and identification of
landscape units in urban areas. Czestochowa was selected as a case study due to its large natural (karst landscapes of
the Czestochowa Upland, numerous forests, nature reserves) and cultural (Saint Mary’s Sanctuary, unique urban
architecture) potential. Czestochowa is also a city of former iron ore and mineral resources exploitation, still active
industry, dynamic urban sprawl within former farming areas, and dynamically growing tourism. Landscape
delimitation and identification distinguished 75 landscape units basing on uniform landscape background (uniform
cover and use of the land). Landscape assessment used a new assessment method for anthropogenic transformation of
landscape – the indicator describing the correlation between the mean shape index (MSI) and the Shannon diversity
index (SHDI) (Pukowiec-Kurda, Sobala 2016). Particular threats and planning suggestions, useful in development of
urban areas, were presented for selected priority landscapes
Clustering and Sharing Incentives in BitTorrent Systems
Peer-to-peer protocols play an increasingly instrumental role in Internet
content distribution. Consequently, it is important to gain a full
understanding of how these protocols behave in practice and how their
parameters impact overall performance. We present the first experimental
investigation of the peer selection strategy of the popular BitTorrent protocol
in an instrumented private torrent. By observing the decisions of more than 40
nodes, we validate three BitTorrent properties that, though widely believed to
hold, have not been demonstrated experimentally. These include the clustering
of similar-bandwidth peers, the effectiveness of BitTorrent's sharing
incentives, and the peers' high average upload utilization. In addition, our
results show that BitTorrent's new choking algorithm in seed state provides
uniform service to all peers, and that an underprovisioned initial seed leads
to the absence of peer clustering and less effective sharing incentives. Based
on our observations, we provide guidelines for seed provisioning by content
providers, and discuss a tracker protocol extension that addresses an
identified limitation of the protocol
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Life in the Atacama — Year 2: Geologic reconnaissance through long-range roving and implications on the search for life
The Life in the Atacama-2004 project, which included geological, morphological, and mineralogical mapping through combined satellite, field-based, and microscopic perspectives and long-range roving, led to the localization of potential habitats
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Spectroscopic results from the Life in the Atacama (LITA) project 2004 field season
Analysis of spectroscopy datasets from rover field tests in the Atacama Desert (Chile), focusing on the composition of the surface and identification of potential habitats for life
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Searching for life with rovers: exploration methods and science results from the 2004 field campaign of the “Life in the Atacama” project and applications to future Mars Missions
LITA develops and field tests a long-range automated rover and a science payload to search for microbial life in the Atacama. The Atacama's evolution provides a unique training ground for designing and testing exploration strategies and life detection methods for the search for life on Mars
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