8,398 research outputs found
Guidance, flight mechanics and trajectory optimization. Volume 12 - Relative motion, guidance equations for terminal rendezvous
Equations of relative motion and guidance for orbital transfer and docking maneuvers in spacecraft rendezvou
Scalar Quantum Field Theory with Cubic Interaction
In this paper it is shown that an i phi^3 field theory is a physically
acceptable field theory model (the spectrum is positive and the theory is
unitary). The demonstration rests on the perturbative construction of a linear
operator C, which is needed to define the Hilbert space inner product. The C
operator is a new, time-independent observable in PT-symmetric quantum field
theory.Comment: Corrected expressions in equations (20) and (21
Harmonic oscillator well with a screened Coulombic core is quasi-exactly solvable
In the quantization scheme which weakens the hermiticity of a Hamiltonian to
its mere PT invariance the superposition V(x) = x^2+ Ze^2/x of the harmonic and
Coulomb potentials is defined at the purely imaginary effective charges
(Ze^2=if) and regularized by a purely imaginary shift of x. This model is
quasi-exactly solvable: We show that at each excited, (N+1)-st
harmonic-oscillator energy E=2N+3 there exists not only the well known harmonic
oscillator bound state (at the vanishing charge f=0) but also a normalizable
(N+1)-plet of the further elementary Sturmian eigenstates \psi_n(x) at
eigencharges f=f_n > 0, n = 0, 1, ..., N. Beyond the first few smallest
multiplicities N we recommend their perturbative construction.Comment: 13 pages, Latex file, to appear in J. Phys. A: Math. Ge
A photometric and kinematic study of the stars and interstellar medium in the central two kpc of NGC 3379
HST images of NGC 3379 show that the V and I luminosity profiles in the inner
13 arcsec of this E1 galaxy are represented by two different components: a
stellar bulge following a Sersic Law with exponent n = 2.36, and a central core
(r < 0.7 arcsec) with a characteristic "cuspy" profile. Subtraction of the
underlying stellar component represented by the fitted Sersic profile revealed
the presence of a small (r ~ 105 pc) dust disk of about 150 solar masses,
oriented at PA = 125 degrees and inclined ~ 77 degrees with respect to the line
of sight. The same absorption structure is detected in the color-index (V-I)
image. The stellar rotation in the inner 20 arcsec is well represented by a
parametric planar disk model, inclined ~ 26 degrees relative to the plane of
the sky, and apparent major axis along PA ~ 67 degrees. The gas velocity curves
in the inner 5 arcsec show a steep gradient, indicating that the gas rotates
much faster than the stars, although in the same direction. The velocity field
of the gaseous system, however, is not consistent with the simple model of
Keplerian rotation sustained by the large (7 x 10E9 solar masses within a
radius of ~ 90 pc) central mass implied by the maximum velocity observed, but
the available data precludes a more detailed analysis.Comment: 23 pages, LaTeX(aaspp4.sty), 9 figures included. Figs. 1 and 5 are
colour plates. Accepted for publication in The Astrophysical Journal (part 1
Deconfined quantum criticality and generalised exclusion statistics in a non-hermitian BCS model
We present a pairing Hamiltonian of the Bardeen-Cooper-Schrieffer form which
exhibits two quantum critical lines of deconfined excitations. This conclusion
is drawn using the exact Bethe ansatz equations of the model which admit a
class of simple, analytic solutions. The deconfined excitations obey
generalised exclusion statistics. A notable property of the Hamiltonian is that
it is non-hermitian. Although it does not have a real spectrum for all choices
of coupling parameters, we provide a rigorous argument to establish that real
spectra occur on the critical lines. The critical lines are found to be
invariant under a renormalisation group map.Comment: 7 pages, 1 figure. Stylistic changes, results unchange
Global study of quadrupole correlation effects
We discuss the systematics of ground-state quadrupole correlations of binding
energies and mean-square charge radii for all even-even nuclei, from O16 up to
the superheavies, for which data are available. To that aim we calculate their
correlated J=0 ground state by means of the angular-momentum and
particle-number projected generator coordinate method, using the axial mass
quadrupole moment as the generator coordinate and self-consistent mean-field
states only restricted by axial, parity, and time-reversal symmetries. The
calculation is performed within the framework of a non-relativistic
self-consistent mean-field model using the same non-relativistic Skyrme
interaction SLy4 and a density-dependent pairing force to generate the
mean-field configurations and mix them. (See the paper for the rest of the
abstract).Comment: 28 pages revtex, 29 eps figures (2 of which in color), 10 tables.
submitted to Phys. Rev.
Correlation energies by the generator coordinate method: computational aspects for quadrupolar deformations
We investigate truncation schemes to reduce the computational cost of
calculating correlations by the generator coordinate method based on mean-field
wave functions. As our test nuclei, we take examples for which accurate
calculations are available. These include a strongly deformed nucleus, 156Sm, a
nucleus with strong pairing, 120Sn, the krypton isotope chain which contains
examples of soft deformations, and the lead isotope chain which includes the
doubly magic 208Pb. We find that the Gaussian overlap approximation for angular
momentum projection is effective and reduces the computational cost by an order
of magnitude. Cost savings in the deformation degrees of freedom are harder to
realize. A straightforward Gaussian overlap approximation can be applied rather
reliably to angular-momentum projected states based on configuration sets
having the same sign deformation (prolate or oblate), but matrix elements
between prolate and oblate deformations must be treated with more care. We
propose a two-dimensional GOA using a triangulation procedure to treat the
general case with both kinds of deformation. With the computational gains from
these approximations, it should be feasible to carry out a systematic
calculation of correlation energies for the nuclear mass table.Comment: 11 pages revtex, 9 eps figure
Contact line motion for partially wetting fluids
We study the flow close to an advancing contact line in the limit of small
capillary number. To take into account wetting effects, both long and
short-ranged contributions to the disjoining pressure are taken into account.
In front of the contact line, there is a microscopic film corresponding to a
minimum of the interaction potential. We compute the parameters of the contact
line solution relevant to the matching to a macroscopic problem, for example a
spreading droplet. The result closely resembles previous results obtained with
a slip model
The Isophotal Structure of Early-Type Galaxies in the SDSS: Dependence on AGN Activity and Environment
We study the dependence of the isophotal shape of early-type galaxies on
their absolute B-band magnitude, their dynamical mass, and their nuclear
activity and environment, using an unprecedented large sample of 847 early-type
galaxies identified in the SDSS by Hao et al (2006). We find that the fraction
of disky galaxies smoothly decreases with increasing luminosity. The large
sample allows us to describe these trends accurately with tight linear
relations that are statistically robust against the uncertainty in the
isophotal shape measurements. There is also a host of significant correlations
between the disky fraction and indicators of nuclear activity (both in the
optical and in the radio) and environment (soft X-rays, group mass, group
hierarchy). Our analysis shows however that these correlations can be
accurately matched by assuming that the disky fraction depends only on galaxy
luminosity or mass. We therefore conclude that neither the level of activity,
nor group mass or group hierarchy help in better predicting the isophotal shape
of early-type galaxies.Comment: 31 pages, 10 figures, accepted for publication in Ap
VLT and NTT Observations of Two EIS Cluster Candidates. Detection of the Early-Type Galaxies Sequence at z~1
Optical data from the ESO VLT-UT1 Science Verification observations are
combined with near-infrared data from SOFI at the NTT to obtain
optical-infrared color-magnitude diagrams for the objects in the fields of two
EIS cluster candidates. In both cases, evidence is found for a well-defined
sequence of red galaxies that appear to be significantly more clustered than
the background population. These results suggest that the two systems are real
physical associations. The (R-Ks), (I-Ks) and (J-Ks) colors of the red
sequences are used, in conjunction with similar data for spectroscopically
confirmed clusters, to obtain redshift estimates of z ~ 0.9 and z ~ 1.0 for
these two systems. These results make these EIS cluster candidates prime
targets for follow-up spectroscopic observations to confirm their reality and
to measure more accurately their redshift.Comment: 6 pages, 5 figures, to appear in Astronomy & Astrophysics (Special
Letters Edition on "First Science with the VLT"
- …