160,302 research outputs found

### The First Moments of Nucleon Generalized Parton Distributions

We extrapolate the first moments of the generalized parton distributions
using heavy baryon chiral perturbation theory. The calculation is based on the
one loop level with the finite range regularization. The description of the
lattice data is satisfactory and the extrapolated moments at physical pion mass
are consistent with the results obtained with dimensional regularization,
although the extrapolation in the momentum transfer to $t=0$ does show
sensitivity to form factor effects which lie outside the realm of chiral
perturbation theory. We discuss the significance of the results in the light of
modern experiments as well as QCD inspired models.Comment: 14 pages, 9 figure

### Coefficient of restitution for viscoelastic disks

The dissipative collision of two identical viscoelastic disks is studied. By
using a known law for the elastic part of the interaction force and the
viscoelastic damping model an analytical solution for the coefficient of
restitution shall be given. The coefficient of restitution depends
significantly on the impact velocity. It approaches one for small velocities
and decreases for increasing velocities.Comment: 11 pages, 3 figure

### Quark structure and nuclear effective forces

We formulate the quark meson coupling model as a many-body effective
Hamiltonian. This leads naturally to the appearance of many-body forces. We
investigate the zero range limit of the model and compare its Hartree-Fock
Hamiltonian to that corresponding to the Skyrme effective force. By fixing the
three parameters of the model to reproduce the binding and symmetry energy of
nuclear matter, we find that it allows a very satisfactory interpretation of
the Skyrme force.Comment: 4 pages, 1tabl

### Phase transition from hadronic matter to quark matter

We study the phase transition from nuclear matter to quark matter within the
SU(3) quark mean field model and NJL model. The SU(3) quark mean field model is
used to give the equation of state for nuclear matter, while the equation of
state for color superconducting quark matter is calculated within the NJL
model. It is found that at low temperature, the phase transition from nuclear
to color superconducting quark matter will take place when the density is of
order 2.5$\rho_0$ - 5$\rho_0$. At zero density, the quark phase will appear
when the temperature is larger than about 148 MeV. The phase transition from
nuclear matter to quark matter is always first order, whereas the transition
between color superconducting quark matter and normal quark matter is second
order.Comment: 18 pages, 11 figure

### The Alignment of Clusters using Large Scale Simulations

The alignment of clusters of galaxies with their nearest neighbours and
between clusters within a supercluster is investigated using simulations of
512^{3} dark matter particles for \LambdaCDM and \tauCDM cosmological models.
Strongly significant alignments are found for separations of up to 15h^{-1}Mpc
in both cosmologies, but for the \LambdaCDM model the alignments extend up to
separations of 30h^{-1}Mpc. The effect is strongest for nearest neighbours, but
is not significant enough to be useful as an observational discriminant between
cosmologies. As a check of whether this difference in alignments is present in
other cosmologies, smaller simulations with 256^{3} particles are investigated
for 4 different cosmological models. Because of poor number statistics, only
the standard CDM model shows indications of having different alignments from
the other models.Comment: 6 pages, 5 figures Submitted to MNRA

### Combining Semi-Analytic Models of Galaxy Formation with Simulations of Galaxy Clusters: the Need for AGN Heating

We present hydrodynamical N-body simulations of clusters of galaxies with
feedback taken from semi-analytic models of galaxy formation. The advantage of
this technique is that the source of feedback in our simulations is a
population of galaxies that closely resembles that found in the real universe.
We demonstrate that, to achieve the high entropy levels found in clusters,
active galactic nuclei must inject a large fraction of their energy into the
intergalactic/intracluster media throughout the growth period of the central
black hole. These simulations reinforce the argument of Bower et al. (2008),
who arrived at the same conclusion on the basis of purely semi-analytic
reasoning.Comment: 4 pages, 1 figure. To appear in the proceedings of "The Monster's
Fiery Breath", Eds. Sebastian Heinz and Eric Wilcots (AIP conference series

### Memristive switching of MgO based magnetic tunnel junctions

Here we demonstrate that both, tunnel magneto resistance (TMR) and resistive
switching (RS), can be observed simultaneously in nano-scale magnetic tunnel
junctions. The devices show bipolar RS of 6 % and TMR ratios of about 100 %.
For each magnetic state, multiple resistive sates are created depending on the
bias history which provides a method for multi-bit data storage and logic. The
electronic transport measurements are discussed in the framework of a
memristive system. Differently prepared MgO barriers are compared to gain
insight into the switching mechanism

### Multipole moments as a tool to infer from gravitational waves the geometry around an axisymmetric body

A binary system, composed of a compact object orbiting around a massive
central body, will emit gravitational waves which will depend on the central
body's spacetime geometry. We expect that the gravitational wave observables
will somehow ``encode'' the information about the spacetime structure. On the
other hand, it has been known for some time that the geometry around an
axisymmetric body can be described by its (Geroch-Hansen) multipole moments.
Therefore one can speculate that using the multipole moments can prove to be a
helpful tool for extracting this information. We will try to demonstrate this
in this talk, following the procedure described by [F. D. Ryan, Phys. Rev. D
{\bf 52} 5707 (1995)] and [T. P. Sotiriou and T. A. Apostolatos, Phys. Rev. D
{\bf 71} 044005 (2005)].Comment: Talk given by T. P. S. at Albert Einstein's Century International
Conference, Paris, France, 18-22 Jul 200

### Measuring mass moments and electromagnetic moments of a massive, axisymmetric body, through gravitational waves

The electrovacuum around a rotating massive body with electric charge density
is described by its multipole moments (mass moments, mass-current moments,
electric moments, and magnetic moments). A small uncharged test particle
orbiting around such a body moves on geodesics if gravitational radiation is
ignored. The waves emitted by the small body carry information about the
geometry of the central object, and hence, in principle, we can infer all its
multipole moments. Due to its axisymmetry the source is characterized now by
four families of scalar multipole moments: its mass moments $M_l$, its
mass-current moments $S_l$, its electrical moments $E_l$ and its magnetic
moments $H_l$, where $l=0,1,2,...$. Four measurable quantities, the energy
emitted by gravitational waves per logarithmic interval of frequency, the
precession of the periastron (assuming almost circular orbits), the precession
of the orbital plane (assuming almost equatorial orbits), and the number of
cycles emitted per logarithmic interval of frequency, are presented as power
series of the newtonian orbital velocity of the test body. The power series
coefficients are simple polynomials of the various moments.Comment: Talk given by T. A. A. at Recent Advances in Astronomy and
Astrophysics, Lixourion, Kefallinia island, Greece, 8-11 Sep 200

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