72,245 research outputs found
Excitations of torelon
The excitations of gluonic flux tube in a periodic lattice are examined.
Monte Carlo simulations from an anisotropic lattice are presented and the
comparison with effective string models is discussed.Comment: Talk at Lattice 2003; 3 pages, 4 figure
Time-dependent ejection velocity model for the outflow of Hen 3--1475
We present 2D axisymmetric and 3D numerical simulations of the
proto-planetary nebula Hen 3-1475, which is characterized by a remarkably
highly collimated optical jet, formed by a string of shock-excited knots along
the axis of the nebula. It has recently been suggested that the kinematical and
morphological properties of the Hen 3-1475 jet could be the result of an
ejection variability of the central source (Riera et al. 2003). The
observations suggest a periodic variability of the ejection velocity
superimposed on a smoothly increasing ejection velocity ramp. From our
numerical simulations, we have obtained intensity maps (for different optical
emission lines) and position-velocity diagrams, in order to make a direct
comparison with the HST observations of this object. Our numerical study allows
us to conclude that a model of a precessing jet with a time-dependent ejection
velocity, which is propagating into an ISM previously perturbed by an AGB wind,
can succesfully explain both the morphological and the kinematical
characteristics of this proto-planetary nebula.Comment: Astronomy and Astrophysics (accepted) (8 figures
Lempel-Ziv Factorization May Be Harder Than Computing All Runs
The complexity of computing the Lempel-Ziv factorization and the set of all
runs (= maximal repetitions) is studied in the decision tree model of
computation over ordered alphabet. It is known that both these problems can be
solved by RAM algorithms in time, where is the length of
the input string and is the number of distinct letters in it. We prove
an lower bound on the number of comparisons required to
construct the Lempel-Ziv factorization and thereby conclude that a popular
technique of computation of runs using the Lempel-Ziv factorization cannot
achieve an time bound. In contrast with this, we exhibit an
decision tree algorithm finding all runs in a string. Therefore, in the
decision tree model the runs problem is easier than the Lempel-Ziv
factorization. Thus we support the conjecture that there is a linear RAM
algorithm finding all runs.Comment: 12 pages, 3 figures, submitte
Deconfinement transition and dimensional cross-over in the 3D gauge Ising model
We present a high precision Monte Carlo study of the finite temperature
gauge theory in 2+1 dimensions. The duality with the 3D Ising spin model allows
us to use powerful cluster algorithms for the simulations. For temporal
extensions up to we obtain the inverse critical temperature with a
statistical accuracy comparable with the most accurate results for the bulk
phase transition of the 3D Ising model. We discuss the predictions of T. W.
Capehart and M.E. Fisher for the dimensional crossover from 2 to 3 dimensions.
Our precise data for the critical exponents and critical amplitudes confirm the
Svetitsky-Yaffe conjecture. We find deviations from Olesen's prediction for the
critical temperature of about 20%.Comment: latex file of 21 pages plus 1 ps figure. Minor corrections in the
figure. Text unchange
High precision Monte Carlo simulations of interfaces in the three-dimensional Ising model: a comparison with the Nambu-Goto effective string model
Motivated by the recent progress in the effective string description of the
interquark potential in lattice gauge theory, we study interfaces with periodic
boundary conditions in the three-dimensional Ising model. Our Monte Carlo
results for the associated free energy are compared with the next-to-leading
order (NLO) approximation of the Nambu-Goto string model. We find clear
evidence for the validity of the effective string model at the level of the NLO
truncation.Comment: 20 pages, 1 figur
Inflating branes inside abelian strings
We study a 6-dimensional brane world model with an abelian string residing in
the two extra dimensions. We study both static as well as inflating branes and
find analytic solutions for the case of trivial matter fields in the bulk. Next
to singular space-times, we also find solutions which are regular including
cigar-like universes as well as solutions with periodic metric functions. These
latter solutions arise if in a singular space-time a static brane is replaced
by an inflating brane. We determine the pattern of generic solutions for
positive, negative and zero bulk cosmological constant.Comment: 14 Latex pages, 11 postscript figures; references added, discussion
extended; reference adde
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