3,837 research outputs found
Human behavior in Prisoner's Dilemma experiments suppresses network reciprocity
During the last few years, much research has been devoted to strategic
interactions on complex networks. In this context, the Prisoner's Dilemma has
become a paradigmatic model, and it has been established that imitative
evolutionary dynamics lead to very different outcomes depending on the details
of the network. We here report that when one takes into account the real
behavior of people observed in the experiments, both at the mean-field level
and on utterly different networks the observed level of cooperation is the
same. We thus show that when human subjects interact in an heterogeneous mix
including cooperators, defectors and moody conditional cooperators, the
structure of the population does not promote or inhibit cooperation with
respect to a well mixed population.Comment: 5 Pages including 4 figures. Submitted for publicatio
IGR J19294+1816: a new Be-X ray binary revealed through infrared spectroscopy
The aim of this work is to characterize the counterpart to the INTEGRAL High
Mass X-ray Binary candidate IGR J19294+1816 so as to establish its true nature.
We obtained H band spectra of the selected counterpart acquired with the NICS
instrument mounted on the Telescopio Nazionale Galileo (TNG) 3.5-m telescope
which represents the first infrared spectrum ever taken of this source. We
complement the spectral analysis with infrared photometry from UKIDSS, 2MASS,
WISE and NEOWISE databases. We classify the mass donor as a Be star.
Subsequently, we compute its distance by properly taking into account the
contamination produced by the circumstellar envelope. The findings indicate
that IGR J19294+1816 is a transient source with a B1Ve donor at a distance of
kpc, and luminosities of the order of erg s,
displaying the typical behaviour of a Be X-ray binary.Comment: 8 pages, 6 figures, accepted to be published in MNRA
How different Fermi surface maps emerge in photoemission from Bi2212
We report angle-resolved photoemission spectra (ARPES) from the Fermi energy
() over a large area of the () plane using 21.2 eV and 32 eV
photons in two distinct polarizations from an optimally doped single crystal of
BiSrCaCuO (Bi2212), together with extensive
first-principles simulations of the ARPES intensities. The results display a
wide-ranging level of accord between theory and experiment and clarify how
myriad Fermi surface (FS) maps emerge in ARPES under various experimental
conditions. The energy and polarization dependences of the ARPES matrix element
help disentangle primary contributions to the spectrum due to the pristine
lattice from those arising from modulations of the underlying tetragonal
symmetry and provide a route for separating closely placed FS sheets in low
dimensional materials.Comment: submitted to PR
Interactions between sub-10 nm iron and cerium oxide nanoparticles and 3T3 fibroblasts : the role of the coating and aggregation state
Recent nanotoxicity studies revealed that the physico-chemical
characteristics of engineered nanomaterials play an important role in the
interactions with living cells. Here, we report on the toxicity and uptake of
the cerium and iron oxide sub-10 nm nanoparticles by NIH/3T3 mouse fibroblasts.
Coating strategies include low-molecular weight ligands (citric acid) and
polymers (poly(acrylic acid), MW = 2000 g mol-1). Electrostatically adsorbed on
the surfaces, the organic moieties provide a negatively charged coating in
physiological conditions. We find that most particles were biocompatible, as
exposed cells remained 100% viable relative to controls. Only the bare and the
citrate-coated nanoceria exhibit a slight decrease of the mitochondrial
activity for cerium concentrations above 5 mM (equivalent to 0.8 g L-1). We
also observe that the citrate-coated particles are internalized by the cells in
large amounts, typically 250 pg per cell after a 24 h incubation for iron
oxide. In contrast, the polymer-coated particles are taken up at much lower
rates (< 30 pg per cell). The strong uptake shown by the citrate-coated
particles is related to the destabilization of the dispersions in the cell
culture medium and their sedimentation down to the cell membranes. In
conclusion, we show that the uptake of nanomaterials by living cells depends on
the coating of the particles and on its ability to preserve the colloidal
nature of the dispersions.Comment: 9 figures, 2 table
An XMM-Newton view of FeK{\alpha} in HMXBs
We present a comprehensive analysis of the whole sample of available
XMM-Newton observations of High Mass X-ray Binaries (HMXBs) until August, 2013,
focusing on the FeK{\alpha} emission line. This line is a key tool to better
understand the physical properties of the material surrounding the X-ray source
within a few stellar radii (the circumstellar medium). We have collected
observations from 46 HMXBs, detecting FeK{\alpha} in 21 of them. We have used
the standard classification of HMXBs to divide the sample in different groups.
We find that: (1) FeK{\alpha} is centred at a mean value of 6.42 keV.
Considering the instrumental and fits uncertainties, this value is compatible
with ionization states lower than FeXVIII. (2) The flux of the continuum is
well correlated with the flux of the line, as expected. Eclipse observations
show that the Fe fluorescence emission comes from an extended region
surrounding the X-ray source. (3) FeK{\alpha} is narrow (width lower than
0.15keV), reflecting that the reprocessing material does not move at high
speeds. We attempt to explain the broadness of the line in terms of three
possible broadening phenomena: line blending, Compton scattering and Doppler
shifts (with velocities of the reprocessing material V=1000-2000 km/s). (4) The
equivalent hydrogen column (NH) directly correlates with the EW of FeK{\alpha},
displaying clear similarities to numerical simulations. It highlights the
strong link between the absorbing and the fluorescent matter. The obtained
results clearly point to a very important contribution of the donors wind in
the FeK{\alpha} emission and the absorption when the donor is a supergiant
massive star.Comment: Accepted for publication in A&A. 13 pages, 16 figures + Appendice
Magnetic properties and energy absorption of CoFe2O4 nanoparticles for magnetic hyperthermia
We have studied the magnetic and power absorption properties of three samples
of CoFe2O4 nanoparticles with sizes from 5 to 12 nm prepared by thermal
decomposition of Fe (acac)3 and Co(acac)2 at high temperatures. The blocking
temperatures TB estimated from magnetization M(T) curves spanned the range 180
< TB < 320 K, reflecting the large magnetocrystalline anisotropy of these
nanoparticles. Accordingly, high coercive fields HC \approx 1.4 - 1.7 T were
observed at low temperatures. Specific Power Absorption (SPA) experiments
carried out in ac magnetic fields indicated that, besides particle volume, the
effective magnetic anisotropy is a key parameter determining the absorption
efficiency. SPA values as high as 98 W/g were obtained for nanoparticles with
average size of \approx12 nm.Comment: 4 pages, 3 figure
Measurement of 1323 and 1487 keV resonances in 15N({\alpha}, {\gamma})19F with the recoil separator ERNA
The origin of fluorine is a widely debated issue. Nevertheless, the
^{15}N({\alpha},{\gamma})^{19}F reaction is a common feature among the various
production channels so far proposed. Its reaction rate at relevant temperatures
is determined by a number of narrow resonances together with the DC component
and the tails of the two broad resonances at E_{c.m.} = 1323 and 1487 keV.
Measurement through the direct detection of the 19F recoil ions with the
European Recoil separator for Nuclear Astrophysics (ERNA) were performed. The
reaction was initiated by a 15N beam impinging onto a 4He windowless gas
target. The observed yield of the resonances at Ec.m. = 1323 and 1487 keV is
used to determine their widths in the {\alpha} and {\gamma} channels. We show
that a direct measurement of the cross section of the
^{15}N({\alpha},{\gamma})^{19}F reaction can be successfully obtained with the
Recoil Separator ERNA, and the widths {\Gamma}_{\gamma} and {\Gamma}_{\alpha}
of the two broad resonances have been determined. While a fair agreement is
found with earlier determination of the widths of the 1487 keV resonance, a
significant difference is found for the 1323 keV resonance {\Gamma}_{\alpha} .
The revision of the widths of the two more relevant broad resonances in the
15N({\alpha},{\gamma})19F reaction presented in this work is the first step
toward a more firm determination of the reaction rate. At present, the residual
uncertainty at the temperatures of the ^{19}F stellar nucleosynthesis is
dominated by the uncertainties affecting the Direct Capture component and the
364 keV narrow resonance, both so far investigated only through indirect
experiments.Comment: 8 pages, 11 figures. Accepted for publication in PR
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