2,805 research outputs found
New analytic solutions of the collective Bohr hamiltonian for a beta-soft, gamma-soft axial rotor
New analytic solutions of the quadrupole collective Bohr hamiltonian are
proposed, exploiting an approximate separation of the beta and gamma variables
to describe gamma-soft prolate axial rotors. The model potential is a sum of
two terms: a beta-dependent term taken either with a Coulomb-like or a
Kratzer-like form, and a gamma-dependent term taken as an harmonic oscillator.
In particular it is possible to give a one parameter paradigm for a beta-soft,
gamma-soft axial rotor that can be applied, with a considerable agreement, to
the spectrum of 234U.Comment: (Dipartimento di Fisica ``G.Galilei'' and INFN, via Marzolo 8,
I-35131 Padova, Italy) 10 pages, 3 figure
The Krause-Hegselmann Consensus Model with Discrete Opinions
The consensus model of Krause and Hegselmann can be naturally extended to the
case in which opinions are integer instead of real numbers. Our algorithm is
much faster than the original version and thus more suitable for applications.
For the case of a society in which everybody can talk to everybody else, we
find that the chance to reach consensus is much higher as compared to other
models; if the number of possible opinions Q<=7, in fact, consensus is always
reached, which might explain the stability of political coalitions with more
than three or four parties. For Q>7 the number S of surviving opinions is
approximately the same independently of the size N of the population, as long
as Q<N. We considered as well the more realistic case of a society structured
like a Barabasi-Albert network; here the consensus threshold depends on the
outdegree of the nodes and we find a simple scaling law for S, as observed for
the discretized Deffuant model.Comment: 12 pages, 6 figure
Number of spanning clusters at the high-dimensional percolation thresholds
A scaling theory is used to derive the dependence of the average number
of spanning clusters at threshold on the lattice size L. This number should
become independent of L for dimensions d<6, and vary as log L at d=6. The
predictions for d>6 depend on the boundary conditions, and the results there
may vary between L^{d-6} and L^0. While simulations in six dimensions are
consistent with this prediction (after including corrections of order loglog
L), in five dimensions the average number of spanning clusters still increases
as log L even up to L = 201. However, the histogram P(k) of the spanning
cluster multiplicity does scale as a function of kX(L), with X(L)=1+const/L,
indicating that for sufficiently large L the average will approach a finite
value: a fit of the 5D multiplicity data with a constant plus a simple linear
correction to scaling reproduces the data very well. Numerical simulations for
d>6 and for d=4 are also presented.Comment: 8 pages, 11 figures. Final version to appear on Physical Review
Universality of the Threshold for Complete Consensus for the Opinion Dynamics of Deffuant et al
In the compromise model of Deffuant et al., opinions are real numbers between
0 and 1 and two agents are compatible if the difference of their opinions is
smaller than the confidence bound parameter \epsilon. The opinions of a
randomly chosen pair of compatible agents get closer to each other. We provide
strong numerical evidence that the threshold value of \epsilon above which all
agents share the same opinion in the final configuration is 1/2, independently
of the underlying social topology.Comment: 8 pages, 4 figures, to appear in Int. J. Mod. Phys. C 15, issue
Distributed Graph Clustering using Modularity and Map Equation
We study large-scale, distributed graph clustering. Given an undirected
graph, our objective is to partition the nodes into disjoint sets called
clusters. A cluster should contain many internal edges while being sparsely
connected to other clusters. In the context of a social network, a cluster
could be a group of friends. Modularity and map equation are established
formalizations of this internally-dense-externally-sparse principle. We present
two versions of a simple distributed algorithm to optimize both measures. They
are based on Thrill, a distributed big data processing framework that
implements an extended MapReduce model. The algorithms for the two measures,
DSLM-Mod and DSLM-Map, differ only slightly. Adapting them for similar quality
measures is straight-forward. We conduct an extensive experimental study on
real-world graphs and on synthetic benchmark graphs with up to 68 billion
edges. Our algorithms are fast while detecting clusterings similar to those
detected by other sequential, parallel and distributed clustering algorithms.
Compared to the distributed GossipMap algorithm, DSLM-Map needs less memory, is
up to an order of magnitude faster and achieves better quality.Comment: 14 pages, 3 figures; v3: Camera ready for Euro-Par 2018, more
details, more results; v2: extended experiments to include comparison with
competing algorithms, shortened for submission to Euro-Par 201
Study of Giant Pairing Vibrations with neutron-rich nuclei
We investigate the possible signature of the presence of giant pairing states
at excitation energy of about 10 MeV via two-particle transfer reactions
induced by neutron-rich weakly-bound projectiles. Performing particle-particle
RPA calculations on Pb and BCS+RPA calculations on Sn, we
obtain the pairing strength distribution for two particles addition and removal
modes. Estimates of two-particle transfer cross sections can be obtained in the
framework of the 'macroscopic model'. The weak-binding nature of the projectile
kinematically favours transitions to high-lying states. In the case of (~^6He,
\~^4He) reaction we predict a population of the Giant Pairing Vibration with
cross sections of the order of a millibarn, dominating over the mismatched
transition to the ground state.Comment: Talk presented in occasion of the VII School-Semina r on Heavy Ion
Physics hosted by the Flerov Laboratory (FLNR/JINR) Dubna, Russia from May 27
to June 2, 200
Soft triaxial roto-vibrational motion in the vicinity of
A solution of the Bohr collective hamiltonian for the soft,
soft triaxial rotor with is presented making use
of a harmonic potential in and Coulomb-like and Kratzer-like
potentials in . It is shown that, while the angular part in the
present case gives rise to a straightforward extension of the rigid triaxial
rotor energy in which an additive harmonic term appears, the inclusion of the
part results instead in a non-trivial expression for the spectrum. The
negative anharmonicities of the energy levels with respect to a simple rigid
model are in qualitative agreement with general trends in the experimental
data.Comment: 4 pages, 2 figures, accepted in Phys.Rev.
Percolation in high dimensions is not understood
The number of spanning clusters in four to nine dimensions does not fully
follow the expected size dependence for random percolation.Comment: 9-dimensional data and more points for large lattices added;
statistics improved, text expanded, table of exponents inserte
Implementation of the Quantum Fourier Transform
The quantum Fourier transform (QFT) has been implemented on a three bit
nuclear magnetic resonance (NMR) quantum computer, providing a first step
towards the realization of Shor's factoring and other quantum algorithms.
Implementation of the QFT is presented with fidelity measures, and state
tomography. Experimentally realizing the QFT is a clear demonstration of NMR's
ability to control quantum systems.Comment: 6 pages, 2 figure
An NMR Analog of the Quantum Disentanglement Eraser
We report the implementation of a three-spin quantum disentanglement eraser
on a liquid-state NMR quantum information processor. A key feature of this
experiment was its use of pulsed magnetic field gradients to mimic projective
measurements. This ability is an important step towards the development of an
experimentally controllable system which can simulate any quantum dynamics,
both coherent and decoherent.Comment: Four pages, one figure (RevTeX 2.1), to appear in Physics Review
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