225 research outputs found
Coverage-dependent electronic and optical properties of H- or F-passivated Si/Ag(111) from first principles
Chemical functionalization of silicene can be devised to tune the intrinsic properties for optoelectronic applications of this material, as well as for optimizing the interface formed by ultrathin Si and a substrate. This work is focused on the (2 1a3
72 1a3)R30 18 phase of silicene grown on Ag(111), and the adsorption of H or F atoms, at half and full coverage, is simulated within density functional theory. The optical response is constructed through the independent particle\u2013random-phase approximation and analyzed thoroughly. The connection between the electronic structure and the features in the optical absorption and reflection is therefore investigated in order to highlight either the role of the adatoms or the effect of the metallic surface. As the coverage is increased, the silicene phases are effectively decoupled from Ag by H or F adatoms and the freestanding properties of the corresponding systems are recovered, for which a coverage-dependent band gap is opened in the states of the overlayer. However, despite being effectively decoupled from the substrate, the properties of functionalized silicene do not show the peculiar characteristics expected from the ideal freestanding Si layer
Adsorption of water and organic solvents on the calcite [101ÂŻ4] surface: Implications for marble conservation treatments
When exposed outdoors, marble artefacts are subject to degradation caused by dissolution in rain. To improve acid-resistance of marble, surface treatments involving the in situ formation of a passivating calcium phosphate (CaP) layer have been developed. Adding alcohol to the treatment improves CaP coverage but the reason is still unclear. Here, we use computational and experimental studies to ascertain whether the interaction of the organic additives with the marble surface plays a role in determining the treatment outcome. Density functional theory calculations are employed to determine the binding energy of additives on the calcite [101ÂŻ4] surface and identify acetone as a promising new additive due to its weak adsorption. Molecular dynamics calculations show that ethanol and isopropanol displace water from the calcite [101ÂŻ4] surface forming an immobile, ordered, and hydrophobic layer, while acetone and water form a mixed, dynamic environment. In experimental trials, a continuous (yet cracked) layer of carbonate hydroxyapatite is formed after 24 h, with all organic additives improving the final coating. This result suggests that the interaction of the additive with the marble surface does not play a major role in determining treatment outcomes and other factors should be investigated for the design of improved treatments
Choosing the consolidant for carbonate substrates: Technical performance and environmental sustainability of selected inorganic and organic products
This study aims at providing a dataset for selecting the most suitable consolidant for marble, limestone and lime
mortar. Diammonium hydrogen phosphate (DAP), nanolimes (NL), ethyl silicate (ES) and acrylic resin (B72)
were compared. Application was performed by brushing in different amounts to investigate the influence of the
product consumption. Effectiveness, compatibility, durability and sustainability were evaluated. DAP showed
several advantages over the alternative consolidants, in terms of both technical performance and sustainability.
ES exhibited high efficacy but also risks of poor compatibility and durability, together with a high global
warming potential. NL and B72 provided the least promising results
Erythromycin resistance in Streptococcus pyogenes in Italy.
In a prospective study of acute pharyngitis in Italian children, 69 (38.3%) of 180 isolates of Streptococcus pyogenes were resistant to macrolides. S. pyogenes was eradicated in 12 (63.1%) of 19 patients with erythromycin-resistant S. pyogenes treated with clarithromycin and in 22 (88%) of 25 patients with erythromycin-susceptible strains. The constitutive-resistant phenotype was correlated with failure of macrolide treatment
Activating Killer Immunoglobulin Receptors and HLA-C: A successful combination providing HIV-1 control
Several studies demonstrated a relevant role of polymorphisms located within the HLA-B and -C loci and the Killer Immunoglobulin Receptors (KIRs) 3DL1 and 3DS1 in controlling HIV-1 replication. KIRs are regulatory receptors expressed at the surface of NK and CD8+ T-cells that specifically bind HLA-A and -B alleles belonging to the Bw4 supratype and all the -C alleles expressing the C1 or C2 supratype. We here disclose a novel signature associated with the Elite Controller but not with the long-term nonprogressor status concerning 2DS activating KIRs and HLA-C2 alleles insensitive to miRNA148a regulation. Overall, our findings support a crucial role of NK cells in the control of HIV-1 viremia
Observation of the Shadowing of Cosmic Rays by the Moon using a Deep Underground Detector
Using data collected by the MACRO experiment during the years 1989-1996, we
show evidence for the shadow of the moon in the underground cosmic ray flux
with a significance of 3.6 sigma. This detection of the shadowing effect is the
first by an underground detector. A maximum-likelihood analysis is used to
determine that the angular resolution of the apparatus is 0.9+/-0.3 degrees.
These results demonstrate MACRO's capabilities as a muon telescope by
confirming its absolute pointing ability and quantifying its angular
resolution.Comment: 14 pages, 8 figures Submitted to Phys. Rev.
Atmospheric neutrino induced muons in the MACRO detector
A measurement of the flux of neutrino-induced muons using the MACRO detector
is presented. Different event topologies, corresponding to different neutrino
parent energies can be detected. The upward throughgoing muon sample is the
larger event sample. The observed upward-throughgoing muons are 26% fewer than
expected and the zenith angle distribution does not fit with the expected one.
Assuming neutrino oscillations, both measurements suggest maximum mixing and
Dm2 of a few times 10-3 eV2. The other samples are due to the internally
produced events and to upward-going stopping muons. These data show a regular
deficit of observed events in each angular bin, as expected assuming neutrino
oscillations with maximum mixing, in agreement with the analysis of the
upward-throughgoing muon sample.Comment: 7 pages 6 figures to appear in the proceedings of XVIII International
Conference on Neutrino Physics and Astrophysics (Neutrino'98), Takayama,
Japan 4-9 June, 199
Nuclearite search with the MACRO detector at Gran Sasso
In this paper we present the results of a search for nuclearites in the
penetrating cosmic radiation using the scintillator and track-etch subdetectors
of the MACRO apparatus. The analyses cover the beta =v/c range at the detector
depth (3700 hg/cm^2) 10^-5 < beta < 1; for beta = 2 x 10^-3 the flux limit is
2.7 x 10^-16 cm^-2 s^-1 sr^-1 for an isotropic flux of nuclearites, and twice
this value for a flux of downgoing nuclearites.Comment: 16 pages, 4 Encapsulated Postscript figures, uses article.sty.
Submitted to The European Physical Journal
Measurement of the atmospheric neutrino-induced upgoing muon flux using MACRO
We present a measurement of the flux of neutrino-induced upgoing muons
(~100 GeV) using the MACRO detector. The ratio of the number of observed
to expected events integrated over all zenith angles is 0.74 +/- 0.036 (stat)
+/- 0.046(systematic) +/- 0.13 (theoretical). The observed zenith distribution
for -1.0 < cos(theta) < -0.1 does not fit well with the no oscillation
expectation, giving a maximum probability for chi^2 of 0.1%. The acceptance of
the detector has been extensively studied using downgoing muons, independent
analyses and Monte-Carlo simulations. The other systematic uncertainties cannot
be the source of the discrepancies between the data and expectations. We have
investigated whether the observed number of events and the shape of the zenith
distribution can be explained by a neutrino oscillation hypothesis. Fitting
either the flux or zenith distribution independently yields mixing parameters
of sin^2 (2theta)=1.0 and delta m^2 of a few times 10^-3 eV^2. However, the
observed zenith distribution does not fit well with any expectations giving a
maximum probability for chi^2 of 5% for the best oscillation hypothesis, and
the combined probability for the shape and number of events is 17%. We conclude
that these data favor a neutrino oscillation hypothesis, but with unexplained
structure in the zenith distribution not easily explained by either the
statistics or systematics of the experiment.Comment: 7 pages (two-column) with 4 figure
Limits on dark matter WIMPs using upward-going muons in the MACRO detector
We perform an indirect search for Weakly Interacting Massive Particles
(WIMPs) using the MACRO detector to look for neutrino-induced upward-going
muons resulting from the annihilation of WIMPs trapped in the Sun and Earth.
The search is conducted in various angular cones centered on the Sun and Earth
to accommodate a range of WIMP masses. No significant excess over the
background from atmospheric neutrinos is seen and limits are placed on the
upward-going muon fluxes from Sun and Earth. These limits are used to constrain
neutralino particle parameters from supersymmetric theory, including those
suggested by recent results from DAMA/NaI.Comment: 14 pages, 7 figures, submitted to Phys. Rev.
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