6,282 research outputs found
Structure-acidity-IR spectra correlations for p-substituted N-phenylsulfonylbenzamides
The wavenumbers of the IR absorption bands of the C=O, S=O and N-H stretching vibrations for a series of p-substituted N-phenylsulfonylbenzamides were measured in trichloromethane. The bond orders, Mulliken charges, charge densities and heats of formation were calculated using the PM3 method. Fifty significant mutual mono parameter (MP) and six dual parameter (DP) correlations were found for the IR spectral, theoretical structural data, substituent constants and previously reported dissociation constants in five polar organic solvents. The transmission of the substituent effects has been discussed and the solvent effect on the slopes of some linear correlations was evaluated using different solvent parameters. The results showed that the factors describing the electronic structure and controlling the dissociation equilibrium and the IR spectra properties of p-substituted N-phenylsulfonylbenzamides must be the same
Automatic structures, rational growth and geometrically finite hyperbolic groups
We show that the set of equivalence classes of synchronously
automatic structures on a geometrically finite hyperbolic group is dense in
the product of the sets over all maximal parabolic subgroups . The
set of equivalence classes of biautomatic structures on is
isomorphic to the product of the sets over the cusps (conjugacy
classes of maximal parabolic subgroups) of . Each maximal parabolic is a
virtually abelian group, so and were computed in ``Equivalent
automatic structures and their boundaries'' by M.Shapiro and W.Neumann, Intern.
J. of Alg. Comp. 2 (1992) We show that any geometrically finite hyperbolic
group has a generating set for which the full language of geodesics for is
regular. Moreover, the growth function of with respect to this generating
set is rational. We also determine which automatic structures on such a group
are equivalent to geodesic ones. Not all are, though all biautomatic structures
are.Comment: Plain Tex, 26 pages, no figure
Origin of the large phonon band-gap in SrTiO3 and the vibrational signatures of ferroelectricity in ATiO3 perovskite: First principles lattice dynamics and inelastic neutron scattering of PbTiO3, BaTiO3 and SrTiO3
We report first principles density functional perturbation theory
calculations and inelastic neutron scattering measurements of the phonon
density of states, dispersion relations and electromechanical response of
PbTiO3, BaTiO3 and SrTiO3. The phonon density-of-states of the quantum
paraelectric SrTiO3 is found to be fundamentally distinct from that of
ferroelectric PbTiO3 and BaTiO3 with a large 70-90 meV phonon band-gap. The
phonon dispersion and electromechanical response of PbTiO3 reveal giant
anisotropies. The interplay of covalent bonding and ferroelectricity, strongly
modulates the electromechanical response and give rise to spectacular
signatures in the phonon spectra. The computed charge densities have been used
to study the bonding in these perovskites. Distinct bonding characteristics in
the ferroelectric and paraelectric phases give rise to spectacular vibrational
signatures. While a large phonon band-gap in ATiO3 perovskites seems a
characteristic of quantum paraelectrics, anisotropy of the phonon spectra
correlates well with ferroelectric strength. These correlations between the
phonon spectra and ferroelectricity, can guide future efforts at custom
designing still more effective piezoelectrics for applications. These results
suggest that vibrational spectroscopy can help design novel materials.Comment: 11 pages, 4 color figures and 2 Table
Synaptobrevin N-terminally bound to syntaxin–SNAP-25 defines the primed vesicle state in regulated exocytosis
Time-resolved measurements of exocytosis identify a domain of the SNARE complex required to keep vesicles readily releasable
Moduli of smoothness and rate of a.e. convergence for some convolution operators
Vegeu el resum a l'inici del document del fitxer adjunt
Black hole growth and stellar assembly at high-z
Context. Observations indicate a strong link between star formation and black
hole (BH) growth, but some questions remain unanswered: whether both activities
are coeval or whether one precedes the other, what their characteristic
timescales are, and what kinds of physical processes are responsible for this
interplay.
Aims. We examine stellar and BH masses (M_star and M_BH) in z~2 active
systems at the peak of their AGN or star formation activity to investigate how
they are linked and whether AGN radiative or else radio power provides a
feedback mechanism that regulates the stellar growth in these systems.
Methods. We analyze the infrared (IR) spectral energy distributions of radio,
sub-millimeter and mid-IR selected AGNs at z~1-3 and constrain their stellar
and AGN luminosities using AGN and host-galaxy templates.
Results. We find evidence of increasing stellar light, thereby decreasing the
AGN mid-IR power going from mid-IR selected AGNs, to radio galaxies, and to
sub-millimeter AGNs. This trend can be explained by either decreasing Eddington
ratios or increasing offsets from the local M_BH-M_star relation. All systems
are characterized by high star formation rates regardless of their different
AGN powers, thus neither AGN radiative power nor AGN-driven radio activity
seems to influence the star formation rate in the selected AGNs. We discuss two
possible evolutionary scenarios that might link these three AGN classes.Comment: A&A Letters accepte
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