4,550 research outputs found
Black hole formation in bidimensional dilaton gravity coupled to scalar matter systems
This work deals with the formation of black hole in bidimensional dilaton
gravity coupled to scalar matter fields. We investigate two scalar matter
systems, one described by a sixth power potential and the other defined with
two scalar fields containing up to the fourth power in the fields. The
topological solutions that appear in these cases allow the formation of black
holes in the corresponding dilaton gravity models.Comment: Latex, 9 pages. Published in Mod. Phys. Lett. A14 (1999) 268
Influence of Lorentz- and CPT-violating terms on the Dirac equation
The influence of Lorentz- and CPT-violating terms (in "vector" and "axial
vector" couplings) on the Dirac equation is explicitly analyzed: plane wave
solutions, dispersion relations and eigenenergies are explicitly obtained. The
non-relativistic limit is worked out and the Lorentz-violating Hamiltonian
identified in both cases, in full agreement with the results already
established in the literature. Finally, the physical implications of this
Hamiltonian on the spectrum of hydrogen are evaluated both in the absence and
presence of a magnetic external field. It is observed that the fixed
background, when considered in a vector coupling, yields no qualitative
modification in the hydrogen spectrum, whereas it does provide an effective
Zeeman-like splitting of the spectral lines whenever coupled in the axial
vector form. It is also argued that the presence of an external fixed field
does not imply new modifications on the spectrum.Comment: 13 pages, no figures, revtex4 styl
Patient centred diagnosis: sharing diagnostic decisions with patients in clinical practice.
Patient centred diagnosis is best practised through shared decision making; an iterative dialogue between doctor and patient, whichrespects a patient’s needs, values, preferences, and circumstances.
Shared decision making for diagnostic situations differs fundamentally from that for treatment decisions. This has important implications when considering its practical application.
The nature of dialogue should be tailored to the specific diagnostic decision; scenarios with higher stakes or uncertainty usually require more detailed conversation
Study of the effect of thermal processing on passion fruit juice by means of 1H NMR spectroscopy and chemometrics.
Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions
Using non-equilibrium Green functions we calculate the spin-polarized current
and shot noise in a ferromagnet--quantum-dot--ferromagnet (FM-QD-FM) system.
Both parallel (P) and antiparallel (AP) magnetic configurations are considered.
Coulomb interaction and coherent spin-flip (similar to a transverse magnetic
field) are taken into account within the dot. We find that the interplay
between Coulomb interaction and spin accumulation in the dot can result in a
bias-dependent current polarization . In particular, can be
suppressed in the P alignment and enhanced in the AP case depending on the bias
voltage. The coherent spin-flip can also result in a switch of the current
polarization from the emitter to the collector lead. Interestingly, for a
particular set of parameters it is possible to have a polarized current in the
collector and an unpolarized current in the emitter lead. We also found a
suppression of the Fano factor to values well below 0.5.Comment: Published version. 13 pages, 7 figure
Velocity Tails for Inelastic Maxwell Models
We study the velocity distribution function for inelastic Maxwell models,
characterized by a Boltzmann equation with constant collision rate, independent
of the energy of the colliding particles. By means of a nonlinear analysis of
the Boltzmann equation, we find that the velocity distribution function decays
algebraically for large velocities, with exponents that are analytically
calculated.Comment: 4 pages, 2 figure
Inoculação com Rhizobium tropici e adubação nitrogenada em linhagens de feijoeiro do grupo preto.
Evaluation of the carioca and black beans group lines inoculed with Rhizobium Tropici strains.
Chemical abundances for 11 bulge stars from high-resolution, near-IR spectra
It is debated whether the Milky Way bulge has the characteristics of a
classical bulge sooner than those of a pseudobulge. Detailed abundance studies
of bulge stars is a key to investigate the origin, history, and classification
of the bulge. The aim is to add to the discussion on the origin of the bulge
and to study detailed abundances determined from near-IR spectra for bulge
giants already investigated with optical spectra, the latter also providing the
stellar parameters which are very significant for the results of the present
study. Especially, the important CNO elements are better determined in the
near-IR. High-resolution, near-infrared spectra in the H band are recorded
using the CRIRES spectrometer on the Very Large Telescope. The CNO abundances
can all be determined from the numerous molecular lines in the wavelength range
observed. Abundances of the alpha elements are also determined from the near-IR
spectra. [O/Fe], [Si/Fe] and [S/Fe] are enhanced up to metallicities of at
least [Fe/H]=-0.3, after which they decline. This suggests that the Milky Way
bulge experienced a rapid and early star-formation history like that of a
classical bulge. However, a similarity between the bulge trend and the trend of
the local thick disk seems present. Such a similarity could suggest that the
bulge has a pseudobulge origin. Our [C/Fe] trend does not show any increase
with [Fe/H] which could have been expected if W-R stars have contributed
substantially to the C abundances. No "cosmic scatter" can be traced around our
observed abundance trends; the scatter found is expected, given the
observational uncertainties.Comment: Accepted for publication in A&
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