914 research outputs found
Crowd-sourcing with uncertain quality - an auction approach
This article addresses two important issues in crowd-sourcing: ex ante uncertainty about the quality and cost of different workers and strategic behaviour. We present a novel multi-dimensional auction that incentivises the workers to make partial enquiry into the task and to honestly report quality-cost estimates based on which the crowd-sourcer can choose the worker that offers the best value for money. The mechanism extends second score auction design to settings where the quality is uncertain and it provides incentives to both collect information and deliver desired qualities
The One-Body and Two-Body Density Matrices of Finite Nuclei and Center-of-Mass Correlations
A method is presented for the calculation of the one-body and two-body
density matrices and their Fourier transforms in momentum space, that is
consistent with the requirement for translational invariance, in the case of a
nucleus (a finite self-bound system). We restore translational invariance by
using the so-called fixed center-of-mass approximation for constructing an
intrinsic nuclear ground state wavefunction by starting from a
non-translationally invariant wavefunction and applying a projection
prescription. We discuss results for the one-body and two-body momentum
distributions of the 4He nucleus calculated with the Slater determinant of the
harmonic oscillator orbitals, as the initial non-translationally invariant
wavefunction. Effects of such an inclusion of CM correlations are found to be
quite important in the momentum distributions.Comment: 5 pages, incl. 2 figures; Proc. Int. Conf. on Frontiers in Nuclear
Structure, Astrophysics and Reactions (FINUSTAR), Kos, Greece, Sept.200
Giant Resonances based on Unitarily Transformed Two-Nucleon plus Phenomenological Three-Nucleon Interactions
We investigate giant resonances of spherical nuclei on the basis of the
Argonne V18 potential after unitary transformation within the Similarity
Renormalization Group or the Unitary Correlation Operator Method supplemented
by a phenomenological three-body contact interaction. Such Hamiltonians can
provide a good description of ground-state energies and radii within
Hartree-Fock plus low-order many-body perturbation theory. The standard Random
Phase Approximation is applied here to calculate the isoscalar monopole,
isovector dipole, and isoscalar quadrupole excitation modes of the 40Ca, 90Zr,
and 208Pb nuclei. Thanks to the inclusion of the three-nucleon interaction and
despite the minimal optimization effort, a reasonable agreement with
experimental centroid energies of all three modes has been achieved. The role
and scope of the Hartree-Fock reference state in RPA methods are discussed.Comment: v2: 11 pages, incl. 3 figures; extended discussion and outlook; to
appear in J.Phys.
Universality aspects of the d=3 random-bond Blume-Capel model
The effects of bond randomness on the universality aspects of the simple
cubic lattice ferromagnetic Blume-Capel model are discussed. The system is
studied numerically in both its first- and second-order phase transition
regimes by a comprehensive finite-size scaling analysis. We find that our data
for the second-order phase transition, emerging under random bonds from the
second-order regime of the pure model, are compatible with the universality
class of the 3d random Ising model. Furthermore, we find evidence that, the
second-order transition emerging under bond randomness from the first-order
regime of the pure model, belongs to a new and distinctive universality class.
The first finding reinforces the scenario of a single universality class for
the 3d Ising model with the three well-known types of quenched uncorrelated
disorder (bond randomness, site- and bond-dilution). The second, amounts to a
strong violation of universality principle of critical phenomena. For this case
of the ex-first-order 3d Blume-Capel model, we find sharp differences from the
critical behaviors, emerging under randomness, in the cases of the
ex-first-order transitions of the corresponding weak and strong first-order
transitions in the 3d three-state and four-state Potts models.Comment: 12 pages, 12 figure
Learning morphological phenomena of Modern Greek an exploratory approach
This paper presents a computational model for the description of concatenative morphological phenomena of modern Greek (such as inflection, derivation and compounding) to allow learners, trainers and developers to explore linguistic processes through their own constructions in an interactive openâended multimedia environment. The proposed model introduces a new language metaphor, the âpuzzleâmetaphorâ (similar to the existing âturtleâmetaphorâ for concepts from mathematics and physics), based on a visualized unificationâlike mechanism for pattern matching. The computational implementation of the model can be used for creating environments for learning through design and learning by teaching
Uncovering the secrets of the 2d random-bond Blume-Capel model
The effects of bond randomness on the ground-state structure, phase diagram
and critical behavior of the square lattice ferromagnetic Blume-Capel (BC)
model are discussed. The calculation of ground states at strong disorder and
large values of the crystal field is carried out by mapping the system onto a
network and we search for a minimum cut by a maximum flow method. In finite
temperatures the system is studied by an efficient two-stage Wang-Landau (WL)
method for several values of the crystal field, including both the first- and
second-order phase transition regimes of the pure model. We attempt to explain
the enhancement of ferromagnetic order and we discuss the critical behavior of
the random-bond model. Our results provide evidence for a strong violation of
universality along the second-order phase transition line of the random-bond
version.Comment: 6 LATEX pages, 3 EPS figures, Presented by AM at the symposium
"Trajectories and Friends" in honor of Nihat Berker, MIT, October 200
A robust optimisation approach using CVaR for unit commitment in a market with probabilistic offers
The large scale integration of renewable energy sources (RES) challenges power system planners and operators alike as it can potentially introduce the need for costly investments in infrastructure. Furthermore, traditional market clearing mechanisms are no longer optimal due to the stochastic nature of RES. This paper presents a risk-aware market clearing strategy for a network with significant shares of RES.We propose an electricity market that embeds the uncertainty brought by wind power and other stochastic renewable sources by accepting probabilistic offers and use a risk measure defined by conditional value-at-risk (CVaR) to evaluate the risk of high re-dispatching cost due to the mis-estimation of renewable energy. The proposed model is simulated on a 39-bus network, whereby it is shown that significant reductions can be achieved by properly managing the risks of mis-estimation of stochastic generation
The one-body and two-body density matrices of finite nuclei with an appropriate treatment of the center-of-mass motion
The one-body and two-body density matrices in coordinate space and their
Fourier transforms in momentum space are studied for a nucleus (a
nonrelativistic, self-bound finite system). Unlike the usual procedure,
suitable for infinite or externally bound systems, they are determined as
expectation values of appropriate intrinsic operators, dependent on the
relative coordinates and momenta (Jacobi variables) and acting on intrinsic
wavefunctions of nuclear states. Thus, translational invariance (TI) is
respected. When handling such intrinsic quantities, we use an algebraic
technique based upon the Cartesian representation, in which the coordinate and
momentum operators are linear combinations of the creation and annihilation
operators a^+ and a for oscillator quanta. Each of the relevant multiplicative
operators can then be reduced to the form: one exponential of the set {a^+}
times other exponential of the set {a}. In the course of such a normal-ordering
procedure we offer a fresh look at the appearance of "Tassie-Barker" factors,
and point out other model-independent results. The intrinsic wavefunction of
the nucleus in its ground state is constructed from a
nontranslationally-invariant (nTI) one via existing projection techniques. As
an illustration, the one-body and two-body momentum distributions (MDs) for the
4He nucleus are calculated with the Slater determinant of the
harmonic-oscillator model as the trial, nTI wavefunction. We find that the TI
introduces important effects in the MDs.Comment: 13 pages, incl. 3 figures - to appear in Eur. Phys. J.
The Effect of the Short-Range Correlations on the Generalized Momentum Distribution in Finite Nuclei
The effect of dynamical short-range correlations on the generalized momentum
distribution in the case of , -closed shell
nuclei is investigated by introducing Jastrow-type correlations in the
harmonic-oscillator model. First, a low order approximation is considered and
applied to the nucleus He. Compact analytical expressions are derived and
numerical results are presented and the effect of center-of-mass corrections is
estimated. Next, an approximation is proposed for of
heavier nuclei, that uses the above correlated of He.
Results are presented for the nucleus O. It is found that the effect of
short-range correlations is significant for rather large values of the momenta
and/or and should be included, along with center of mass corrections
for light nuclei, in a reliable evaluation of in the whole
domain of and .Comment: 29 pages, 8 figures. Further results, figures and discussion for the
CM corrections are added. Accepted by Journal of Physics
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