57,147 research outputs found
Is nonrelativistic gravity possible?
We study nonrelativistic gravity using the Hamiltonian formalism. For the
dynamics of general relativity (relativistic gravity) the formalism is well
known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the
lapse function is constrained correctly, then nonrelativistic gravity is
described by a consistent Hamiltonian system. Surprisingly, nonrelativistic
gravity can have solutions identical to relativistic gravity ones. In
particular, (anti-)de Sitter black holes of Einstein gravity and IR limit of
Horava gravity are locally identical.Comment: 4 pages, v2, typos corrected, published in Physical Review
An Introduction to Conformal Ricci Flow
We introduce a variation of the classical Ricci flow equation that modifies
the unit volume constraint of that equation to a scalar curvature constraint.
The resulting equations are named the Conformal Ricci Flow Equations because of
the role that conformal geometry plays in constraining the scalar curvature.
These equations are analogous to the incompressible Navier-Stokes equations of
fluid mechanics inasmuch as a conformal pressure arises as a Lagrange
multiplier to conformally deform the metric flow so as to maintain the scalar
curvature constraint. The equilibrium points are Einstein metrics with a
negative Einstein constant and the conformal pressue is shown to be zero at an
equilibrium point and strictly positive otherwise. The geometry of the
conformal Ricci flow is discussed as well as the remarkable analytic fact that
the constraint force does not lose derivatives and thus analytically the
conformal Ricci equation is a bounded perturbation of the classical
unnormalized Ricci equation. That the constraint force does not lose
derivatives is exactly analogous to the fact that the real physical pressure
force that occurs in the Navier-Stokes equations is a bounded function of the
velocity. Using a nonlinear Trotter product formula, existence and uniqueness
of solutions to the conformal Ricci flow equations is proven. Lastly, we
discuss potential applications to Perelman's proposed implementation of
Hamilton's program to prove Thurston's 3-manifold geometrization conjectures.Comment: 52 pages, 1 figur
Testing of pear trees on their own roots in comparison with important used rootstocks under organic farming conditions with special regard to fire blight (E. amylovora)
Pear trees on their own roots are tested in comparison to grafted trees in growth and yield
characteristics and with special regard to the tolerance to diseases, above all fire blight
(Erwinia amylovora). In spring 2004 15 randomized trees of the cultivar 'Williams' from
three variants (self rooted in vitro, self rooted long cuttings, grafted on Quince A) were
planted in a pear orchard, which was heavily infected with fire blight (Erwinia amylovora)
the previous years. The trees were left untreated. Growth and yield characteristics, plant
diseases and tree losses were observed. After four years the in vitro self rooted trees were
significantly more vigorous in growth than those grafted on quince A. The self rooted long
cuttings were comparable in growth with grafts on quince, but showed high tree losses
probably due to frost damages in the first winter one year after planting. However no
infections with Erwinia amylovora could be observed so far. In a field trial with more
cultivars and rootstock variants planted in 2006 at two organically managed sites more
significant effects are expected in the next years
Microscopic model for Bose-Einstein condensation and quasiparticle decay
Sufficiently dimerized quantum antiferromagnets display elementary S=1
excitations, triplon quasiparticles, protected by a gap at low energies. At
higher energies, the triplons may decay into two or more triplons. A strong
enough magnetic field induces Bose-Einstein condensation of triplons. For both
phenomena the compound IPA-CuCl3 is an excellent model system. Nevertheless no
quantitative model was determined so far despite numerous studies. Recent
theoretical progress allows us to analyse data of inelastic neutron scattering
(INS) and of magnetic susceptibility to determine the four magnetic couplings
J1=-2.3meV, J2=1.2meV, J3=2.9meV and J4=-0.3meV. These couplings determine
IPA-CuCl3 as system of coupled asymmetric S=1/2 Heisenberg ladders
quantitatively. The magnetic field dependence of the lowest modes in the
condensed phase as well as the temperature dependence of the gap without
magnetic field corroborate this microscopic model.Comment: 6 pages, 5 figure
Predicting the frequencies of diverse exo-planetary systems
Extrasolar planetary systems range from hot Jupiters out to icy comet belts
more distant than Pluto. We explain this diversity in a model where the mass of
solids in the primordial circumstellar disk dictates the outcome. The star
retains measures of the initial heavy-element (metal) abundance that can be
used to map solid masses onto outcomes, and the frequencies of all classes are
correctly predicted. The differing dependences on metallicity for forming
massive planets and low-mass cometary bodies are also explained. By
extrapolation, around two-thirds of stars have enough solids to form Earth-like
planets, and a high rate is supported by the first detections of low-mass
exo-planets.Comment: 5 pages, 2 figures; accepted by MNRA
The Spectator Electromagnetic Effect on Charged Pion Spectra in Peripheral Ultrarelativistic Heavy-Ion Collisions
We estimate the electromagnetic effect of the spectator charge on the
momentum spectra of and produced in peripheral Pb+Pb collisions
at SPS energies. We find that the effect is large and results in strongly
varying structures in the dependence of the ratio,
especially at low transverse momenta where a deep valley in the above ratio is
predicted at 0.15 -- 0.20.
It appears that the effect depends on initial conditions. Thus, it provides
new information on the space and time evolution of the non-perturbative pion
creation process.Comment: 20 pages and 8 figure
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