5,099 research outputs found
Solving Optimal Control Problems for Delayed Control-Affine Systems with Quadratic Cost by Numerical Continuation
- In this paper we introduce a new method to solve fixed-delay optimal
control problems which exploits numerical homotopy procedures. It is known that
solving this kind of problems via indirect methods is complex and
computationally demanding because their implementation is faced with two
difficulties: the extremal equations are of mixed type, and besides, the
shooting method has to be carefully initialized. Here, starting from the
solution of the non-delayed version of the optimal control problem, the delay
is introduced by numerical homotopy methods. Convergence results, which ensure
the effectiveness of the whole procedure, are provided. The numerical
efficiency is illustrated on an example
Thermally-activated non-local amplification in quantum energy transport
We study energy-transport efficiency in light-harvesting planar and 3D
complexes of two-level atomic quantum systems, embedded in a common thermal
blackbody radiation. We show that the collective non-local dissipation induced
by the thermal bath plays a fundamental role in energy transport. It gives rise
to a dramatic enhancement of the energy-transport efficiency, which may largely
overcome . This effect, which improves the understanding of transport
phenomena in experimentally relevant complexes, suggests a particularly
promising mechanism for quantum energy management.Comment: 7 pages, 4 figures. New version in which the RP line of Figure 1 has
been amended with the correct parameter
Labor Market Policies, Institutions and Employment Rates in the EU-27
We compare labor market policies, institutions and outcomes for the EU member states, for the period 2000-2005. We document the main differences in Labor Market Policies across EU members, including new member states after 2004. We focus on indicators of policy generosity (expenditures relative to GDP) and relate these and other policy indicators to indicators of labor market outcomes and performance. Our results show that, on a cross-country basis, higher rates of employment are in general associated with: (i) higher expenditures on labor market policies, especially on active policies for countries with a high pro-work attitude; (ii) a lower degree of rigidity in labor market institutions and in product market regulation.labor market policies, labor market outcomes, European social models
Science Software on Demand
Presentation of the Science Software on Demand service at the EGI 2020 Conference. A complete description of the involved components and the summary of almost three years of activities have been presented
Distributed thermal tasks on many-body systems through a single quantum machine
We propose a configuration of a single three-level quantum emitter embedded
in a non-equilibrium steady electromagnetic environment, able to stabilize and
control the local temperatures of a target system it interacts with, consisting
of a collection of coupled two-level systems. The temperatures are induced by
dissipative processes only, without the need of further external couplings for
each qubit. Moreover, by acting on a set of easily tunable geometric
parameters, we demonstrate the possibility to manipulate and tune each qubit
temperature independently over a remarkably broad range of values. These
findings address one standard problem in quantum-scale thermodynamics,
providing a way to induce a desired distribution of temperature among
interacting qubits and to protect it from external noise sources.Comment: 6 pages, 5 figure
First 100 ms of a long-lived magnetized neutron star formed in a binary neutron star merger
The recent multimessenger observation of the short gamma-ray burst (SGRB) GRB
170817A together with the gravitational wave (GW) event GW170817 provides
evidence for the long-standing hypothesis associating SGRBs with binary neutron
star (BNS) mergers. The nature of the remnant object powering the SGRB, which
could have been either an accreting black hole (BH) or a long-lived magnetized
neutron star (NS), is, however, still uncertain. General relativistic
magnetohydrodynamic (GRMHD) simulations of the merger process represent a
powerful tool to unravel the jet launching mechanism, but so far most
simulations focused the attention on a BH as the central engine, while the
long-lived NS scenario remains poorly investigated. Here, we explore the latter
by performing a GRMHD BNS merger simulation extending up to ~100 ms after
merger, much longer than any previous simulation of this kind. This allows us
to (i) study the emerging structure and amplification of the magnetic field and
observe a clear saturation at magnetic energy
erg, (ii) follow the magnetically supported expansion of the outer layers of
the remnant NS and its evolution into an ellipsoidal shape without any
surrounding torus, and (iii) monitor density, magnetization, and velocity along
the axis, observing no signs of jet formation. We also argue that the
conditions at the end of the simulation disfavor later jet formation on
subsecond timescales if no BH is formed. Furthermore, we examine the rotation
profile of the remnant, the conversion of rotational energy associated with
differential rotation, the overall energy budget of the system, and the
evolution of the GW frequency spectrum. Finally, we perform an additional
simulation where we induce the collapse to a BH ~70 ms after merger, in order
to gain insights on the prospects for massive accretion tori in case of a late
collapse. We find that...Comment: 14 pages, 16 figures, matches published version in PR
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