5,108 research outputs found
Biotechnology and the Creation of Ethics
Biotechnology promises to change the course of evolution. Rather than patiently waiting as natural selection channels the forces of biology into contouring the nature and character of the organisms that populate our world, biotechnology allows humans to directly manipulate the basis of life itself. By allowing the deliberate reorganization of the genetic programs of organisms, biotechnology affords the greatest revolution in scientific and cultural understanding in history. It also is beginning to severely strain our established concepts of right and wrong and to require us to rethink most of our basic moral assumptions.
Semiclassical approach to ground-state properties of hard-core bosons in two dimensions
Motivated by some inconsistencies in the way quantum fluctuations are
included beyond the classical treatment of hard-core bosons on a lattice in the
recent literature, we revisit the large-S semi-classical approach to hard-core
bosons on the square lattice at T=0. First of all, we show that, if one stays
at the purely harmonic level, the only correct way to get the 1/S correction to
the density is to extract it from the derivative of the ground state energy
with respect to the chemical potential, and that to extract it from a
calculation of the ground state expectation value of the particle number
operator, it is necessary to include 1/\sqrt{S} corrections to the harmonic
ground state. Building on this alternative approach to get 1/S corrections, we
provide the first semiclassical derivation of the momentum distribution, and we
revisit the calculation of the condensate density. The results of these as well
as other physically relevant quantities such as the superfluid density are
systematically compared to quantum Monte Carlo simulations. This comparison
shows that the logarithmic corrections in the dilute Bose gas limit are only
captured by the semi-classical approach if the 1/S corrections are properly
calculated, and that the semi-classical approach is able to reproduce the 1/k
divergence of the momentum distribution at k=0. Finally, the effect of 1/S^2
corrections is briefly discussed.Comment: 14 pages, 8 figure
Do fiscal councils impact fiscal performance?
In order to improve fiscal policy process and budget transparency, the European Union (EU) stated more stringent fiscal rules monitored by Independent Fiscal Bodies, that have the capacity to “tie the hands” of policymakers tempted by deviations from
socially optimal choices according to the academic circles.The present paper aims at empirically verifying if Fiscal Councils (FCs) in Europe (as a complement or substitute for the Fiscal Rules - FRs) have an impact on Governments’ fiscal decisions and if this impact exists and is positive which feature of their functioning is relevant for their effectiveness
Robustness of Synchrony in Complex Networks and Generalized Kirchhoff Indices
In network theory, a question of prime importance is how to assess network
vulnerability in a fast and reliable manner. With this issue in mind, we
investigate the response to parameter changes of coupled dynamical systems on
complex networks. We find that for specific, non-averaged perturbations, the
response of synchronous states critically depends on the overlap between the
perturbation vector and the eigenmodes of the stability matrix of the
unperturbed dynamics. Once averaged over properly defined ensembles of such
perturbations, the response is given by new graph topological indices, which we
introduce as generalized Kirchhoff indices. These findings allow for a fast and
reliable method for assessing the specific or average vulnerability of a
network against changing operational conditions, faults or external attacks.Comment: 5 pages + supplemental material Fina
Quantum stabilization of classically unstable plateau structures
Motivated by the intriguing report, in some frustrated quantum
antiferromagnets, of magnetization plateaus whose simple collinear structure is
{\it not} stabilized by an external magnetic field in the classical limit, we
develop a semiclassical method to estimate the zero-point energy of collinear
configurations even when they do not correspond to a local minimum of the
classical energy. For the spin-1/2 frustrated square-lattice antiferromagnet,
this approach leads to the stabilization of a large 1/2 plateau with
"up-up-up-down" structure for J_2/J_1>1/2, in agreement with exact
diagonalization results, while for the spin-1/2 anisotropic triangular
antiferromagnet, it predicts that the 1/3 plateau with "up-up-down" structure
is stable far from the isotropic point, in agreement with the properties of
Cs_2CuBr_4.Comment: 6 pages, 4 figure
Semiclassical theory of the magnetization process of the triangular lattice Heisenberg model
Motivated by the numerous examples of 1/3 magnetization plateaux in the
triangular lattice Heisenberg an- tiferromagnet with spins ranging from 1/2 to
5/2, we revisit the semiclassical calculation of the magnetization curve of
that model, with the aim of coming up with a simple method that allows one to
calculate the full mag- netization curve, and not just the critical fields of
the 1/3 plateau. We show that it is actually possible to calculate the
magnetization curve including the first quantum corrections and the appearance
of the 1/3 plateau entirely within linear spin-wave theory, with predictions
for the critical fields that agree to order 1/S with those derived a long-time
ago on the basis of arguments that required to go beyond linear spin-wave
theory. This calculation relies on the central observation that there is a kink
in the semiclassical energy at the field where the classical ground state is
the collinear up-up-down structure, and that this kink gives rise to a locally
linear behavior of the energy with the field when all semiclassical ground
states are compared to each other for all fields. The magnetization curves
calculated in this way for spin 1/2, 1 and 5/2 are shown to be in good
agreement with available experimental data.Comment: 11 pages - 7 figure
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