429 research outputs found
The Levi-Civita spacetime
We consider two exact solutions of Einstein's field equations corresponding
to a cylinder of dust with net zero angular momentum. In one of the cases, the
dust distribution is homogeneous, whereas in the other, the angular velocity of
dust particles is constant [1]. For both solutions we studied the junction
conditions to the exterior static vacuum Levi-Civita spacetime. From this study
we find an upper limit for the energy density per unit length of the
source equal for the first case and for the second
one. Thus the homogeneous cluster provides another example [2] where the range
of is extended beyond the limit value previously found in
the literature [3,4]. Using the Cartan Scalars technics we show that the
Levi-Civita spacetime gets an extra symmetry for or
. We also find that the cluster of homogeneous dust has a superior
limit for its radius, depending on the constant volumetric energy density
Multiple Photonic Shells Around a Line Singularity
Line singularities including cosmic strings may be screened by photonic
shells until they appear as a planar wall.Comment: 6 page
Quasi-BiHamiltonian Systems and Separability
Two quasi--biHamiltonian systems with three and four degrees of freedom are
presented. These systems are shown to be separable in terms of Nijenhuis
coordinates. Moreover the most general Pfaffian quasi-biHamiltonian system with
an arbitrary number of degrees of freedom is constructed (in terms of Nijenhuis
coordinates) and its separability is proved.Comment: 10 pages, AMS-LaTeX 1.1, to appear in J. Phys. A: Math. Gen. (May
1997
Levi-Civita cylinders with fractional angular deficit
The angular deficit factor in the Levi-Civita vacuum metric has been
parametrized using a Riemann-Liouville fractional integral. This introduces a
new parameter into the general relativistic cylinder description, the
fractional index {\alpha}. When the fractional index is continued into the
negative {\alpha} region, new behavior is found in the Gott-Hiscock cylinder
and in an Israel shell.Comment: 5 figure
Evaluation of a sampling method for Xylella fastidiosa detection in olive trees
To assess the presence of the xylem-limited bacterium Xylella
fastidiosa subsp. pauca strain CoDiRO in olive trees, a specific
sampling method was evaluated. Symptomatic and symptomless
plants were randomly selected in four olive orchards located in the
province of Lecce (Southern Italy). The crown of each plant was
subdivided into a lower and an upper portion; four samples were
collected from each layer in the main four cardinal directions. A
total of eight samples per plant, composed of one- or two-year-old
asymptomatic twigs, were collected next to branches showing leafscorch
symptoms. In this preliminary study, the null hypothesis was
tested. i.e. there is no difference between the lower and the upper
portions of the tree canopy and across the four cardinal directions. Samples (472), collected from 60 plants belonging to 11 different
olive cultivars, were tested by qPCR. Out of 236 samples taken
from the upper and lower parts of the canopy only 38.1% of lower
samples, in contrast to 56.8% taken from the upper crown layer,
were positive to the bacterium,. The McNemar test determined that
there is a statistically significant difference in the proportion of
positive samples between the upper and lower crown (p < 0.001).
The Cochranâs Q test was performed to evaluate differences in the
four cardinal directions. The null hypothesis suggesting there is
no difference across cardinal directions was confirmed (p = 0.097).
Based on these preliminary results, it appears that sampling should
be directed to the upper part of the canopy. However, further studies
are needed to improve the efficiency of the sampling technique
The Geometry of Integrable and Superintegrable Systems
The group of automorphisms of the geometry of an integrable system is
considered. The geometrical structure used to obtain it is provided by a normal
form representation of integrable systems that do not depend on any additional
geometrical structure like symplectic, Poisson, etc. Such geometrical structure
provides a generalized toroidal bundle on the carrier space of the system.
Non--canonical diffeomorphisms of such structure generate alternative
Hamiltonian structures for complete integrable Hamiltonian systems. The
energy-period theorem provides the first non--trivial obstruction for the
equivalence of integrable systems
Gyroscope precession in cylindrically symmetric spacetimes
We present calculations of gyroscope precession in spacetimes described by
Levi-Civita and Lewis metrics, under different circumstances. By doing so we
are able to establish a link between the parameters of the metrics and
observable quantities, providing thereby a physical interpretation for those
parameters, without specifying the source of the field.Comment: 13 pages, Latex. To appear in Class.Q.Gra
Experimental test for extra dimensions in Kaluza-Klein gravity
5D Kaluza-Klein gravity has several nonasymptotically flat solutions which
generally, possessed both electric and magnetic charges. In this paper we
suggest that these solutions can act as quantum virtual handles (wormholes) in
spacetime foam models. By applying a sufficently large, external electric
and/or magnetic field it may be possible to ``inflate'' these solutions from a
quantum to a classical state. This effect would lead to a possible experimental
signal for higher dimensions in multidimensional gravity.Comment: 11 pages, 3 PS.figures, REVTEX, the quality of the figures are
improve
On the physical meaning of Fermi coordinates
(Some Latex problems should be removed in this version) Fermi coordinates
(FC) are supposed to be the natural extension of Cartesian coordinates for an
arbitrary moving observer in curved space-time. Since their construction cannot
be done on the whole space and even not in the whole past of the observer we
examine which construction principles are responsible for this effect and how
they may be modified. One proposal for a modification is made and applied to
the observer with constant acceleration in the two and four dimensional
Minkowski space. The two dimensional case has some surprising similarities to
Kruskal space which generalize those found by Rindler for the outer region of
Kruskal space and the Rindler wedge. In perturbational approaches the
modification leads also to different predictions for certain physical systems.
As an example we consider atomic interferometry and derive the deviation of the
acceleration-induced phase shift from the standard result in Fermi coordinates.Comment: 11 pages, KONS-RGKU-94/02 (Latex
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