254 research outputs found
Some aspects on the observation of the gravitomagnetic clock effect
http://arxiv.org/abs/gr-qc/0101089As a consequence of gravitomagnetism, which is a fundamental weak-field prediction of general relativity and ubiquitous in gravitational phenomena, clocks show a difference in their proper periods when moving along identical orbits in opposite directions about a spinning mass. This time shift is induced by the rotation of the source and may be used to verify the existence of the terrestrial gravitomagnetic field by means of orbiting clocks. A possible mission scenario is outlined with emphasis given to some of the major difficulties which inevitably arise in connection with such a venture
The inheritance of the hypersensitivity resistance of European plum (Prunus domestica L.) against the Plum pox virus
In between 2003 and 2009 more than 500 seedlings have been tested for hypersensitivity resistance against the Plum pox virus (PPV), which causes Sharka disease. The seedlings had at least one hypersensitive parent genotype. They were tested for hypersensitivity resistance by double grafting onto PPV infected interstem in the green house. In crossing combinations with two hypersensitive parents the percentage of hypersensitive seedlings was highest. There is also no equal distribution of the genotypes over the individual hypersensitivity classes (HC) in all crossing combinations. The percentage of hypersensitive seedlings strongly depends on the parentage. Furthermore investigations regarding the origin of the hypersensitivity resistance of the cultivar ‘Jojo’, which is a descendant of a crossing combination from ‘Ortenauer’ × ‘Stanley’, were done. It was shown that the cultivar ‘Ortenauer’ is the donor of the hypersensitivity trait.Keywords: Plum pox virus, hypersensitivity, inheritance, Prunus domestica L., resistanc
Detection of the gravitomagnetic clock effect
The essence of the gravitomagnetic clock effect is properly defined showing
that its origin is in the topology of world lines with closed space
projections. It is shown that, in weak field approximation and for a
spherically symmetric central body, the loss of synchrony between two clocks
counter-rotating along a circular geodesic is proportional to the angular
momentum of the source of the gravitational field. Numerical estimates are
presented for objects within the solar system. The less unfavorable situation
is found around Jupiter.Comment: 14 pages; Latex. To be published on Classical and Quantum Gravit
Gravitomagnetism, clocks and geometry
New techniques to evaluate the clock effect using light are described. These
are based on the flatness of the cylindrical surface containing the world lines
of the rays constrained to move on circular trajectories about a spinning mass.
The effect of the angular momentum of the source is manifested in the fact that
inertial observers must be replaced by local non rotating observers. Starting
from this an exact formula for circular trajectories is found. Numerical
estimates for the Earth environment show that light would be a better probe
than actual clocks to evidence the angular momentum influence. The advantages
of light in connection with some principle experiments are shortly reviewed.Comment: TCI Latex, 12 pages, 2 figures. To appear in European Journal of
Physic
On the Possibility of Measuring the Gravitomagnetic Clock Effect in an Earth Space-Based Experiment
In this paper the effect of the post-Newtonian gravitomagnetic force on the
mean longitudes of a pair of counter-rotating Earth artificial satellites
following almost identical circular equatorial orbits is investigated. The
possibility of measuring it is examined. The observable is the difference of
the times required to in passing from 0 to 2 for both senses of
motion. Such gravitomagnetic time shift, which is independent of the orbital
parameters of the satellites, amounts to 5 s for Earth; it is
cumulative and should be measured after a sufficiently high number of
revolutions. The major limiting factors are the unavoidable imperfect
cancellation of the Keplerian periods, which yields a constraint of 10
cm in knowing the difference between the semimajor axes of the satellites,
and the difference of the inclinations of the orbital planes which, for
, should be less than . A pair of spacecrafts
endowed with a sophisticated intersatellite tracking apparatus and drag-free
control down to 10 cm s Hz level might allow to meet
the stringent requirements posed by such a mission.Comment: LaTex2e, 22 pages, no tables, 1 figure, 38 references. Final version
accepted for publication in Classical and Quantum Gravit
Spinning test particles and clock effect in Schwarzschild spacetime
We study the behaviour of spinning test particles in the Schwarzschild
spacetime. Using Mathisson-Papapetrou equations of motion we confine our
attention to spatially circular orbits and search for observable effects which
could eventually discriminate among the standard supplementary conditions
namely the Corinaldesi-Papapetrou, Pirani and Tulczyjew. We find that if the
world line chosen for the multipole reduction and whose unit tangent we denote
as is a circular orbit then also the generalized momentum of the
spinning test particle is tangent to a circular orbit even though and
are not parallel four-vectors. These orbits are shown to exist because the spin
induced tidal forces provide the required acceleration no matter what
supplementary condition we select. Of course, in the limit of a small spin the
particle's orbit is close of being a circular geodesic and the (small)
deviation of the angular velocities from the geodesic values can be of an
arbitrary sign, corresponding to the possible spin-up and spin-down alignment
to the z-axis. When two spinning particles orbit around a gravitating source in
opposite directions, they make one loop with respect to a given static observer
with different arrival times. This difference is termed clock effect. We find
that a nonzero gravitomagnetic clock effect appears for oppositely orbiting
both spin-up or spin-down particles even in the Schwarzschild spacetime. This
allows us to establish a formal analogy with the case of (spin-less) geodesics
on the equatorial plane of the Kerr spacetime. This result can be verified
experimentally.Comment: IOP macros, eps figures n. 2, to appear on Classical and Quantum
gravity, 200
The twin paradox and Mach's principle
The problem of absolute motion in the context of the twin paradox is
discussed. It is shown that the various versions of the clock paradox feature
some aspects which Mach might have been appreciated. However, the ultimate
cause of the behavior of the clocks must be attributed to the autonomous status
of spacetime, thereby proving the relational program advocated by Mach as
impracticable.Comment: Latex2e, 11 pages, 6 figures, 33 references, no tables. Accepted for
publication in The European Physical Journal PLUS (EPJ PLUS
Solar cycle variability of Mars dayside exospheric temperatures: Model evaluation of underlying thermal balances
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95086/1/grl25450.pd
- …