34,529 research outputs found
Some statistics on permutations avoiding generalized patterns
In the last decade a huge amount of articles has been published studying
pattern avoidance on permutations. From the point of view of enumeration,
typically one tries to count permutations avoiding certain patterns according
to their lengths. Here we tackle the problem of refining this enumeration by
considering the statistics "first/last entry". We give complete results for
every generalized patterns of type or as well as for some cases
of permutations avoiding a pair of generalized patterns of the above types.Comment: 5 figure
Detection of spatial pattern through independence of thinned processes
Let N, N' and N'' be point processes such that N' is obtained from N by
homogeneous independent thinning and N''= N- N'. We give a new elementary proof
that N' and N'' are independent if and only if N is a Poisson point process. We
present some applications of this result to test if a homogeneous point process
is a Poisson point process.Comment: 11 pages, one figur
Modelling the Kinked Jet of the Crab Nebula
We investigate the dynamical propagation of the South-East jet from the Crab
pulsar interacting with supernova ejecta by means of three-dimensional
relativistic MHD numerical simulations with the PLUTO code.
The initial jet structure is set up from the inner regions of the Crab
Nebula.
We study the evolution of hot, relativistic hollow outflows initially
carrying a purely azimuthal magnetic field.
Our jet models are characterized by different choices of the outflow
magnetization ( parameter) and the bulk Lorentz factor ().
We show that the jet is heavily affected by the growth of current-driven kink
instabilities causing considerable deflection throughout its propagation
length.
This behavior is partially stabilized by the combined action of larger flow
velocities and/or reduced magnetic field strengths.
We find that our best jet models are characterized by relatively large values
of () and small values of .
Our results are in good agreement with the recent X-ray (\textit{Chandra})
data of the Crab Nebula South-East jet indicating that the jet changes
direction of propagation on a time scale of the order of few years.
The 3D models presented here may have important implications in the
investigation of particle acceleration in relativistic outflows.Comment: 15 pages, 20 figure
Anisotropic KPZ growth in 2+1 dimensions: fluctuations and covariance structure
In [arXiv:0804.3035] we studied an interacting particle system which can be
also interpreted as a stochastic growth model. This model belongs to the
anisotropic KPZ class in 2+1 dimensions. In this paper we present the results
that are relevant from the perspective of stochastic growth models, in
particular: (a) the surface fluctuations are asymptotically Gaussian on a
sqrt(ln(t)) scale and (b) the correlation structure of the surface is
asymptotically given by the massless field.Comment: 13 pages, 4 figure
Complete electroweak one loop contributions to the pair production cross section of MSSM charged and neutral Higgs bosons in e+e- collisions
In this paper, we review the production cross section for charged and neutral
Higgs bosons pairs in collisions beyond the tree level, in the
framework of the Minimal Supersymmetric Standard Model (MSSM). A complete list
of formulas for all electroweak contributions at the one loop level is given. A
numerical code has been developed in order to compute them accurately and, in
turn, to compare the MSSM Higgs bosons pair production cross sections at tree
level and at the one loop level.Comment: 58 pages, 3 eps figure
Empirical orbit determination using Apollo 14 data
An empirical orbit determination method is shown to yield highly accurate navigation results when applied to lunar orbit tracking data. Regressions and predictions of free flight Apollo 14 tracking data exhibit minimal residual growth, and the solution orbital elements behave in a very consistent manner. Solutions from data acquired during propulsive maneuvers result in degraded predictions. The residual patterns from free flight processing are shown to be consistent from pass to pass and are correlated with lunar topographic features
A model for multifragmentation in heavy-ion reactions
From an experimental point of view, clear signatures of multifragmentation
have been detected by different experiments. On the other hand, from a
theoretical point of view, many different models, built on the basis of totally
different and often even contrasting assumptions, have been provided to explain
them. In this contribution we show the capabilities and the shortcomings of one
of this models, a QMD code developed by us and coupled to the nuclear
de-excitation module taken from the multipurpose transport and interaction code
FLUKA, in reproducing the multifragmentation observations recently reported by
the INDRA collaboration for the reaction Nb + Mg at a 30 MeV/A projectile
bombarding energy. As far as fragment production is concerned, we also briefly
discuss the isoscaling technique by considering reactions characterized by a
different isospin asymmetry, and we explain how the QMD + FLUKA model can be
applied to obtain information on the slope of isotopic yield ratios, which is
crucially related to the symmetry energy of asymmetric nuclear matter.Comment: 8 pages, 2 figures, Proc. 12th International Conference on Nuclear
Reaction Mechanisms, Varenna, Italy, June 15 - 19 200
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