321 research outputs found
Non-equilibrium hysteresis and spin relaxation in the mixed-anisotropy dipolar coupled spin-glass LiHoErF
We present a study of the model spin-glass LiHoErF using
simultaneous AC susceptibility, magnetization and magnetocaloric effect
measurements along with small angle neutron scattering (SANS) at sub-Kelvin
temperatures. All measured bulk quantities reveal hysteretic behavior when the
field is applied along the crystallographic c axis. Furthermore avalanche-like
relaxation is observed in a static field after ramping from the
zero-field-cooled state up to Oe. SANS measurements are employed to
track the microscopic spin reconfiguration throughout both the hysteresis loop
and the related relaxation. Comparing the SANS data to inhomogeneous mean-field
calculations performed on a box of one million unit cells provides a real-space
picture of the spin configuration. We discover that the avalanche is being
driven by released Zeeman energy, which heats the sample and creates positive
feedback, continuing the avalanche. The combination of SANS and mean-field
simulations reveal that the conventional distribution of cluster sizes is
replaced by one with a depletion of intermediate cluster sizes for much of the
hysteresis loop.Comment: 6 pages, 4 figure
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 Maryâs 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 â 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
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
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 â 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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Searching for life with rovers: exploration methods and science results from the 2004 field campaign of the âLife in the Atacamaâ 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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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
On the isolated dwarf galaxies: from cuspy to flat dark matter density profiles and metallicity gradients
The chemodynamical evolution of spherical multi-component self-gravitating
models for isolated dwarf galaxies is studied. We compare their evolution with
and without feedback effects from star formation processes. We find that
initially cuspy dark matter profiles flatten with time as a result of star
formation, without any special tuning conditions. Thus the seemingly flattened
profiles found in many dwarfs do not contradict the cuspy profiles predicted by
cosmological models. We also calculate the chemical evolution of stars and gas,
to permit comparisons with observational data.Comment: Accepted the 28/01/1
Probing strongly hybridized nuclear-electronic states in a model quantum ferromagnet
We present direct local-probe evidence for strongly hybridized nuclear-electronic spin states of an Ising ferromagnet LiHoF4 in a transverse magnetic field. The nuclear-electronic states are addressed via a magnetic resonance in the GHz frequency range using coplanar resonators and a vector network analyzer. The magnetic resonance spectrum is successfully traced over the entire field-temperature phase diagram, which is remarkably well reproduced by mean-field calculations. Our method can be directly applied to a broad class of materials containing rare-earth ions for probing the substantially mixed nature of the nuclear and electronic moments
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