1,398 research outputs found
Thermodynamic and dynamic anomalies for a three dimensional isotropic core-softened potential
Using molecular dynamics simulations and integral equations (Rogers-Young,
Percus-Yevick and hypernetted chain closures) we investigate the thermodynamic
of particles interacting with continuous core-softened intermolecular
potential. Dynamic properties are also analyzed by the simulations. We show
that, for a chosen shape of the potential, the density, at constant pressure,
has a maximum for a certain temperature. The line of temperatures of maximum
density (TMD) was determined in the pressure-temperature phase diagram.
Similarly the diffusion constant at a constant temperature, , has a maximum
at a density and a minimum at a density .
In the pressure-temperature phase-diagram the line of extrema in diffusivity is
outside of TMD line. Although in this interparticle potential lacks
directionality, this is the same behavior observed in SPC/E water.Comment: 16 page
Obscuration and Origin of Nuclear X-ray emission in FR I Radio Galaxies
We present X-ray observations of the nuclear region of 25 Fanaroff-Riley I
radio galaxies from the 3CRR and B2 catalogs, using data from the Chandra and
XMM archives. We find the presence of a X-ray Central Compact Core (CCCX) in
13/25 sources, in 3/25 sources the detection of a CCCX is uncertain, while in
the remaining 9/25 sources no CCCX is found. All the sources are embedded in a
diffuse soft X-ray component, generally on kpc-scales, which is in agreement
with the halo of the host galaxy and/or with the intracluster medium. The X-ray
spectra of the cores are described by a power law with photon indices Gamma=1.1
- 2.6. In 8 sources excess absorption over the Galactic value is detected, with
rest-frame column densities N_H^z ~ 10^20 - 10^21 cm^-2; thus, we confirm the
previous claim based on optical data that most FRI radio galaxies lack a
standard optically-thick torus. We find significant correlations between the
X-ray core luminosity and the radio and optical luminosities, suggesting that
at least a fraction of the X-ray emission originates in a jet; however, the
origin of the X-rays remains ambiguous. If the X-ray emission is entirely
attributed to an isotropic, accretion-related component, we find very small
Eddington ratios, L_bol/L_Edd ~ 10^-3 - 10^-8, and we calculate the radiative
efficiency to be eta ~ 10^-2 - 10^-6, based on the Bondi accretion rates from
the spatial analysis. This suggests that radiatively inefficient accretion
flows are present in the cores of low-power radio galaxies.Comment: 20 pages, 7 figures, accepted for publication in The Astrophysical
Journa
X-ray-emitting Atmospheres of B2 Radio Galaxies
We report ROSAT PSPC spatial and spectral analysis of the eight B2 radio
galaxies NGC 315, NGC 326, 4C 35.03, B2 0326+39, NGC 2484, B2 1040+31, B2
1855+37, and 3C 449, expected to be representative of the class of low-power
radio galaxies. Multiple X-ray components are present in each, and the gas
components have a wide range of linear sizes and follow an extrapolation of the
cluster X-ray luminosity/temperature correlation, implying that there is no
relationship between the presence of a radio galaxy and the gas fraction of the
environment. No large-scale cooling flows are found. There is no correlation of
radio-galaxy size with the scale or density of the X-ray atmosphere. This
suggests that it is processes on scales less than those of the overall gaseous
environments which are the major influence on radio-source dynamics. The
intergalactic medium is usually sufficient to confine the outer parts of the
radio structures, in some cases even to within 5 kpc of the core. In the case
of NGC 315, an extrapolation suggests that the pressure of the atmosphere may
match the minimum pressure in the radio source over a factor of about 40 in
linear size (a factor of about 1600 in pressure).Comment: 34 pages, including 10 figures, using aasms4.sty To appear in the Ap
Soft Phonon Anomalies in the Relaxor Ferroelectric Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3
Neutron inelastic scattering measurements of the polar TO phonon mode
dispersion in the cubic relaxor Pb(Zn_1/3Nb_2/3)_0.92Ti_0.08O_3 at 500K reveal
anomalous behavior in which the optic branch appears to drop precipitously into
the acoustic branch at a finite value of the momentum transfer q=0.2 inverse
Angstroms, measured from the zone center. We speculate this behavior is the
result of nanometer-sized polar regions in the crystal.Comment: 4 pages, 4 figure
Future Research and Developments on Reuse and Recycling of Steelmaking By-Products
In the steel sector, sustainable management of by-products is a key challenge to preserve natural resources and achieve the zero waste goal. In this paper, the main trends of future research and development on reuse and recycling of by-products of the steel industry are presented in the form of a roadmap, which is the outcome of a dissemination project funded by the European Union based on the analysis of the most relevant and recent European projects concerning reuse and recycling of by-products from the steel production cycle. In particular, the developed roadmap highlights the
most important topics of future research activities and challenges related to reuse and recycling of by-products from the existing or alternative steelmaking routes. A time horizon of 10 years has been considered, taking into account the European Commission targets to achieve carbon neutrality in a circular economy context. In addition, current technological trends derived from past and ongoing research projects are analysed. Research needs are based on the main categories of by-products and residual materials. Due to the different pathways to reduce CO2 emissions, each category is divided into subcategories considering both current and novel process routes targeting decarbonization of steel production. This work identifies the most urgent and demanding research directions for the coming years based on a survey targeting the steel companies, services providers of the steel industry and research organizations active in the field
X-Ray Diffuse Scattering Study on Ionic-Pair Displacement Correlations in Relaxor Lead Magnesium Niobate
Ionic-pair equal-time displacement correlations in relaxor lead magnesium
niobate, , have been investigated at room
temperature in terms of an x-ray diffuse scattering technique. Functions of the
distinct correlations have been determined quantitatively. The results show the
significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O,
and O-O' pairs. Their spatial distribution forms an ellipse or a sphere with
the radii of 30-80. This observation of local structure in the system
proves precursory presence of the polar microregions in the paraelectric state
which leads to the dielectric dispersion.Comment: 11 pages, 3 figure
Dielectric nonlinearity of relaxor ferroelectric ceramics at low ac drives
Dielectric nonlinear response of
(PbMgNbO)(PbTiO) (0.9PMN-0.1PT) relaxor
ceramics was investigated under different ac drive voltages. It was observed
that: (i) the dielectric permittivity is independent on ac field amplitude at
high temperatures; (ii) with increasing ac drive, the permittivity maximum
increases, and the temperature of the maximum shifts to lower temperature;
(iii) the nonlinear effect is weakened when the measurement frequency
increases. The influences of increasing ac drive were found to be similar to
that of decreasing frequency. It is believed that the dielectric nonlinearities
of relaxors at low drives can be explained by the phase transition theory of
ergodic space shrinking in succession. A Monte Carlo simulation was performed
on the flips of micro polarizations at low ac drives to verify the theory.Comment: Submitted to J. Phys.: Cond. Matte
Anomalous transverse acoustic phonon broadening in the relaxor ferroelectric Pb(Mg_1/3Nb_2/3)O_3
The intrinsic linewidth of the transverse acoustic (TA) phonon
observed in the relaxor ferroelectric compound
Pb(MgNbTiO (PMN-20%PT) begins to broaden
with decreasing temperature around 650 K, nearly 300 K above the ferroelectric
transition temperature ( K). We speculate that this anomalous
behavior is directly related to the condensation of polarized, nanometer-sized,
regions at the Burns temperature . We also observe the ``waterfall''
anomaly previously seen in pure PMN, in which the transverse optic (TO) branch
appears to drop precipitously into the TA branch at a finite momentum transfer
\AA. The waterfall feature is seen even at
temperatures above . This latter result suggests that the PNR exist as
dynamic entities above .Comment: 6 pages, 4 figure
NA60 results on spectra and the spectral function in In-In collisions
The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158
AGeV In-In collisions. A strong excess of pairs is observed above the yield
expected from neutral meson decays. The unprecedented sample size of close to
400K events and the good mass resolution of about 2% have made it possible to
isolate the excess by subtraction of the decay sources (keeping the ).
The shape of the resulting mass spectrum exhibits considerable broadening, but
essentially no shift in mass. The acceptance-corrected transverse-momentum
spectra have a shape atypical for radial flow and show a significant mass
dependence, pointing to different sources in different mass regions.Comment: 4 pages, 4 figures, Quark Matter 2006 conference proceeding
Direct evidence of soft mode behavior near the Burns' temperature in PbMgNbO (PMN) relaxor ferroectric
Inelastic neutron scattering measurements of the relaxor ferroelectric
PbMgNbO (PMN) in the temperature range
490~KT880~K directly observe the soft mode (SM) associated with the
Curie-Weiss behavior of the dielectric constant (T). The results
are treated within the framework of the coupled SM and transverse optic (TO1)
mode and the temperature dependence of the SM frequency at q=0.075 a* is
determined. The parameters of the SM are consistent with the earlier estimates
and the frequency exhibits a minimum near the Burns temperature (
650K)Comment: 6 figure
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