357 research outputs found
Quantum Heisenberg Antiferromagnet: Improved Spin-Wave Theories Versus Exact-Diagonalization Data
We reconsider the results cocerning the extreme-quantum
square-lattice Heisenberg antiferromagnet with frustrating diagonal couplings
( model) drawn from a comparison with exact-diagonalization data. A
combined approach using also some intrinsic features of the self-consistent
spin-wave theory leads to the conclusion that the theory strongly overestimates
the stabilizing role of quantum flutcuations in respect to the N\'{e}el phase
in the extreme-quantum case . On the other hand, the analysis implies
that the N\'{e}el phase remains stable at least up to the limit which is pretty larger than some previous estimates. In addition, it is
argued that the spin-wave ansatz predicts the existence of a finite range
( in the linear spin-wave theory) where the Marshall-Peierls
sigh rule survives the frustrations.Comment: 13 pages, LaTex, 7 figures on reques
Pre-metamorphic melt infiltration in metasediments : geochemical, isotopic (Sr, Nd, and Pb), and field evidence from Serie dei Laghi (Southern Alps, Italy)
Gradual transitions from K-feldspar free gneisses to K-feldspar bearing augengneisses
are sometimes observed in metamorphic terranes. They have been explained with
metasomatic porphyroblastic growth connected with regional metamorphism, or with
pre-metamorphic presence of magmatic megacrysts. A transition of this kind can be
observed in the Serie dei Laghi (Southern Alps, Italy), where coarse-grained metaarenites
(Cenerigneiss) grade into Ceneri augengneisses with large K-feldspar porphyroclasts,
and banded amphibolites of the \u2018\u2018Strona Ceneri Border Zone\u2019\u2019 grade into Hbl
augengneisses rich in K-feldspar.
The Ceneri augengneisses are chemically indistinguishable from the Cenerigneiss, but
have higher 87Sr=86Sr (0.7256\u20130.7258 vs. 0.7215\u20130.7233), similar to those of the Ordovician
granites that were intruded, before the regional metamorphism, into the protoliths
of both Cenerigneiss and amphibolites. The Cenerigneiss contains two types of zircons:
(1) highly luminescent, rounded grains or fragments, yielding U\u2013Pb SHRIMP
ages from 0.43 to 1.0 Ga; (2) euhedral grains with oscillatory zoning (magmatic), with
U\u2013Pb SHRIMP concordant ages of 466 13 Ma. This age coincides with the Rb\u2013Sr
whole rock emplacement age of the Ordovician granitoids (466 5Ma).The Hbl augengneisses form three groups with distinct geochemical patterns,
whose distributions on inter-element diagrams trend towards the Ordovician metagranites
and meta-aplites. In addition, the Hbl augengneisses have higher 87Sr=86Sr
(0.7132\u20130.7147 vs. 0.7031\u20130.7046) and lower 143Nd=144Nd (0.51214\u20130.51219 vs.
0.51273\u20130.51297) than the amphibolites, suggesting the addition of an isotopically
evolved component.
The observed chemical and isotope patterns, as well as the vicinity of the augen
gneisses to the Ordovician intrusions, lead us to conclude that the Ceneri augengneisses
and Hbl augengneisses are the result of infiltration of residual hydrous
magmas into the protolith of both the Cenerigneiss and the amphibolites at the time
of Ordovician granite emplacement, long before the regional metamorphism in the Serie dei Laghi
Alignment and preliminary outcomes of an ELT-size instrument to a very large telescope: LINC-NIRVANA at LBT
LINC-NIRVANA (LN) is a high resolution, near infrared imager that uses a
multiple field-of-view, layer-oriented, multi-conjugate AO system, consisting
of four multi-pyramid wavefront sensors (two for each arm of the Large
Binocular Telescope, each conjugated to a different altitude). The system
employs up to 40 star probes, looking at up to 20 natural guide stars
simultaneously. Its final goal is to perform Fizeau interferometric imaging,
thereby achieving ELT-like spatial resolution (22.8 m baseline resolution). For
this reason, LN is also equipped with a fringe tracker, a beam combiner and a
NIR science camera, for a total of more than 250 optical components and an
overall size of approximately 6x4x4.5 meters. This paper describes the
tradeoffs evaluated in order to achieve the alignment of the system to the
telescope. We note that LN is comparable in size to planned ELT
instrumentation. The impact of such alignment strategies will be compared and
the selected procedure, where the LBT telescope is, in fact, aligned to the
instrument, will be described. Furthermore, results coming from early
night-time commissioning of the system will be presented.Comment: 8 pages, 6 pages, AO4ELT5 Proceedings, 201
Performance evaluation of a commercial protective coating through field-exposure tests on three stone substrates
In the last decades, there have been several studies on Cultural Heritage regarding the performance of protective and consolidating coatings for the prevention of decay. A coating must have several characteristics such as efficiency, breathability, and must be durable and reversible. In this research work, the performance of a commercial protective product (Fosbuild FBLE 200) was evaluated. This coating is composed of a TiO2 nanopowder dispersed in an aqueous solution of an acrylic polymer. The product, which exhibits depolluting, antimicrobial, water-repellent and self-cleaning properties, has been applied on three different lithotypes: Carrara marble, Noto stone, and Comiso stone. Field-exposure tests were carried out in two different outdoor environments (Catania and Palermo) in order to assess its suitability. Promising results were obtained for the Carrara marble after one year of exposure; however, a decrease in effectiveness was observed at the end of the second year
Italian multicenter study on infection hazards during dental practice: control of environmental microbial contamination in public dental surgeries.
BACKGROUND: The present study assessed microbial contamination in Italian dental surgeries. METHODS: An evaluation of water, air and surface microbial contamination in 102 dental units was carried out in eight Italian cities. RESULTS: The findings showed water microbial contamination in all the dental surgeries; the proportion of water samples with microbial levels above those recommended decreased during working. With regard to Legionella spp., the proportion of positive samples was 33.3%. During work activity, the index of microbial air contamination (IMA) increased. The level of microbial accumulation on examined surfaces did not change over time. CONCLUSION: These findings confirm that some Italian dental surgeries show high biocontamination, as in other European Countries, which highlights the risk of occupational exposure and the need to apply effective measures to reduce microbial loads
Persistent topology for natural data analysis - A survey
Natural data offer a hard challenge to data analysis. One set of tools is
being developed by several teams to face this difficult task: Persistent
topology. After a brief introduction to this theory, some applications to the
analysis and classification of cells, lesions, music pieces, gait, oil and gas
reservoirs, cyclones, galaxies, bones, brain connections, languages,
handwritten and gestured letters are shown
Magnetic susceptibility of EuTe/PbTe Heisenberg superlattices: experimental and theoretical studies
We report results on the temperature dependence of the susceptibilities of a
set of MBE-grown short-period EuTe/PbTe antiferromagnetic superlattices having
different EuTe layer thicknesses. In-plane and orthogonal susceptibilities have
been measured and display a strong anisotropy at low temperature, confirming
the occurrence of a magnetic phase transition in the thicker samples, as seen
also in neutron diffraction studies. We suggest that dipolar interactions
stabilize antiferromagnetic long-range order in an otherwise isotropic system
and we present numerical and analytical results for the low-temperature
orthogonal susceptibility.Comment: 30 pages, 8 ps figures, RevTe
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