471 research outputs found
No Evidence for a Aystematic FEII Emission Line Redshift in Type 1 AGN
We test the recent claim by Hu et al. (2008) that FeII emission in Type 1 AGN
shows a systematic redshift relative to the local source rest frame and
broad-line Hbeta. We compile high s/n median composites using SDSS spectra from
both the Hu et al. sample and our own sample of the 469 brightest DR5 spectra.
Our composites are generated in bins of FWHM Hbeta and FeII strength as defined
in our 4D Eigenvector 1 (4DE1) formalism. We find no evidence for a systematic
FeII redshift and consistency with previous assumptions that FeII shift and
width (FWHM) follow Hbeta shift and FWHM in virtually all sources. This result
is consistent with the hypothesis that FeII emission (quasi-ubiquitous in type
1 sources) arises from a broad-line region with geometry and kinematics the
same as that producing the Balmer lines.Comment: 12 pages, 1 table, 1 figure - accepted for publication in ApJ Letter
Balmer line shifts in quasars
We offer a broad review of Balmer line phenomenology in type 1 active
galactic nuclei, briefly sum- marising luminosity and radio loudness effects,
and discussing interpretation in terms of nebular physics along the 4D
eigenvector 1 sequence of quasars. We stress that relatively rare, peculiar
Balmer line profiles (i.e., with large shifts with respect to the rest frame or
double and multiple peaked) that start attracted attentions since the 1970s are
still passable of multiple dynamical interpretation. More mainstream objects
are still not fully understood as well, since competing dynamical models and
geometries are possible. Further progress may come from inter-line comparison
across the 4D Eigenvector 1 sequence.Comment: Accepted for publication in Astrophysics and Space Science, Special
Issue on Line Shifts in Astrophysics and Laboratory Plasm
Systematics of 2+ states in semi-magic nuclei
We propose a simple systematics of low lying 2+ energy levels and
electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and
isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus
quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase
Approximation (QRPA). We derive a simple relation connecting the 2+ energy with
the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns
out that the systematics of energy levels and B(E2) values predicted by this
simple model is fulfilled with a reasonable accuracy by all available
experimental data. Both systematics suggest that not only active nucleons but
also those filling closed shells play an important role
High-Pressure InfiltrationâExpulsion of Aqueous NaCl in Planar Hydrophobic Nanopores
Pressure-driven permeation of water in a poorly wettable material results in a conversion of mechanical work into surface free energy representing a new form of energy storage, or absorption. When water is replaced by a concentrated electrolyte solution, the storage capacity of a nanoporous medium becomes comparable to high-end supercapacitors. The addition of salt can also reduce the hysteresis of the infiltration/expulsion cycle. Our molecular simulations provide a theoretical perspective into the mechanisms involved in the process, and underlying structures and interactions in compressed nanoconfined solutions. Specifically, we consider aqueous NaCl in planar confinements of widths of 1.0 nm and 1.64 nm and pressures of up to 3 kbar. Open ensemble Monte Carlo simulations utilizing fractional exchanges of molecules for efficient additions/removal of ions have been utilized in conjunction with pressure-dependent chemical potentials to model bulk phases under pressure. Confinements open to these pressurized bulk, aqueous electrolyte phases show reversibility at narrow pore sizes, consistent with experiment, as well as strong hysteresis at both pore size. The addition of salt results in significant increases in the solid/liquid interfacial tension in narrower pores and associated infiltration and expulsion pressures. These changes are consistent with strong desalination effects at the lower pore size observed irrespective of external pressure and initial concentration
Molecular Polarizability in Open Ensemble Simulations of Aqueous Nanoconfinements under Electric Field
Molecular polarization at aqueous interfaces involves fast degrees of freedom that are often averaged-out in atomistic-modeling approaches. The resulting effective interactions depend on a specific environment, making explicit account of molecular polarizability particularly important in solutions with pronounced anisotropic perturbations, including solid/liquid interfaces and external fields. Our work concerns polarizability effects in nanoscale confinements under electric field, open to an unperturbed bulk environment. We model aqueous molecules and ions in hydrophobic pores using the Gaussian-charge-on-spring BK3-AH representation. This involves nontrivial methodology devel- opments in expanded ensemble Monte Carlo simulations for open systems with long-ranged multibody interactions and necessitates further improvements for efficient modeling of polarizable ions. Structural differences between fixed-charge and polarizable models were captured in molecular dynamics simulations for a set of closed systems. Our open ensemble results with the BK3 model in neat-aqueous systems capture the âŒ10% reduction of molecular dipoles within the surface layer near the hydrophobic pore walls in analogy to reported quantum mechanical calculations at water/vapor interfaces. The polarizability affects the interfacial dielectric behavior and weakens the electric-field dependence of water absorption at pragmatically relevant porosities. We observe moderate changes in thermodynamic properties and atom and charged-site spatial distributions; the Gaussian distribution of mobile charges on water and ions in the polarizable model shifts the density amplitudes and blurs the charge-layering effects associated with increased ion absorption. The use of polarizable force field indicates an enhanced response of interfacial ion distributions to applied electric field, a feature potentially important for in silico modeling of electric double layer capacitors
Transition from the Seniority to the Anharmonic Vibrator Regime in Nuclei
A recent analysis of experimental energy systematics suggests that all
collective nuclei fall into one of three classes -- seniority, anharmonic
vibrational, or rotational -- with sharp phase transitions between them. We
investigate the transition from the seniority to the anharmonic vibrator regime
within a shell model framework involving a single large j-orbit. The
calculations qualitatively reproduce the observed transitional behavior, both
for U(5) like and O(6) like nuclei. They also confirm the preeminent role
played by the neutron-proton interaction in producing the phase transition.Comment: 9 pages with 2 tables, submitted to Physical Review C, November 199
Possible experimental signature of octupole correlations in the 0 states of the actinides
= 0 states have been investigated in the actinide nucleus
Pu up to an excitation energy of 3 MeV with a high-resolution (p,t)
experiment at = 24 MeV. To test the recently proposed = 0
double-octupole structure, the phenomenological approach of the
spdf-interacting boson model has been chosen. In addition, the total 0
strength distribution and the strength fragmentation have been compared
to the model predictions as well as to the previously studied (p,t) reactions
in the actinides. The results suggest that the structure of the 0 states
in the actinides might be more complex than the usually discussed pairing
isomers. Instead, the octupole degree of freedom might contribute
significantly. The signature of two close-lying 0 states below the
2-quasiparticle energy is presented as a possible manifestation of strong
octupole correlations in the structure of the 0 states in the actinides.Comment: 6 pages, 5 figures, published in Phys. Rev. C 88, 041303(R) (2013
Long-term urbanization dynamics and the evolution of green/blue areas in eastern europe: Insights from Romania
Urbanization is a dynamic process performed at the expense of natural and/or semi-natural areas, with direct impacts on the ecosystem services provided to human society. The increasing population density in urban areas and the associated demand for housing and public services have led to progressive changes in the structure, architecture, and design of urban areas. The present study analyzes long-term urban development in Western Romania, focusing on green/blue areasâ strategies in Timisoara over centuries. The empirical results of a literature review carried out with a historical perspective have delineated the time periods that favored âurban green developmentâ (1716â1918 and 1918â1940) and those restricting their development (1940â2000), as well as the factors that influenced long-term urbanization dynamics and the evolution of green/blue areas. These factors can be generalized to other socioeconomic contexts in Eastern Europe. Characteristic issues of this geographical area impacting the evolution of urban green/blue areas include (i) common historical aspects (e.g., the influence of geo-political and strategic dimensions, the dominations of former great empires such as the Turkish empire and the communist period) and (ii) population migration after 1990
On the origin of X-shaped radio-sources: new insights from the properties of their host galaxies
A significant fraction of extended radio sources presents a peculiar X-shaped
radio morphology: in addition to the classical double lobed structure, radio
emission is also observed along a second axis of symmetry in the form of
diffuse wings or tails. We re-examine the origin of these extensions relating
the radio morphology to the properties of their host galaxies. The orientation
of the wings shows a striking connection with the structure of the host galaxy
as they are preferentially aligned with its minor axis. Furthermore, wings are
only observed in galaxies of high projected ellipticity. Hydrodynamical
simulations of the radio-source evolution show that X-shaped radio-sources
naturally form in this geometrical situation: as a jet propagates in a
non-spherical gas distribution, the cocoon surrounding the radio-jets expands
laterally at a high rate producing wings of radio emission, in a way that is
reminiscent of the twin-exhaust model for radio-sources.Comment: 7 pages, 6 figures, 1 table, accepted for publication in A&
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