9,191 research outputs found
Using off-diagonal confinement as a cooling method
In a recent letter [Phys. Rev. Lett. 104, 167201 (2010)] we proposed a new
confining method for ultracold atoms on optical lattices, based on off-diagonal
confinement (ODC). This method was shown to have distinct advantages over the
conventional diagonal confinement (DC) that makes use of a trapping potential,
including the existence of pure Mott phases and highly populated condensates.
In this paper we show that the ODC method can also lead to temperatures that
are smaller than with the conventional DC method, depending on the control
parameters. We determine these parameters using exact diagonalizations for the
hard-core case, then we extend our results to the soft-core case by performing
quantum Monte Carlo (QMC) simulations for both DC and ODC systems at fixed
temperatures, and analysing the corresponding entropies. We also propose a
method for measuring the entropy in QMC simulations.Comment: 6 pages, 6 figure
Polaron relaxation in ferroelectric thin films
We report a dielectric relaxation in ferroelectric thin films of the ABO3
family. We have compared films of different compositions with several growth
modes: sputtering (with and without magnetron) and sol-gel. The relaxation was
observed at cryogenic temperature (T<100K) for frequencies from 100Hz up to
10MHz. This relaxation activation energy is always lower than 200meV. It is
very similar to the polaron relaxation that we reported in the parent bulk
perovskites. Being independent of the materials size, morphology and texture,
this relaxation can be a useful probe of defects in actual integrated
capacitors with no need for specific shapin
The population of deformed bands in Cr by emission of Be from the S + Mg reaction
Using particle- coincidences we have studied the population of final
states after the emission of 2 -particles and of Be in nuclei
formed in S+Mg reactions at an energy of . The data were obtained in a setup
consisting of the GASP -ray detection array and the multidetector array
ISIS. Particle identification is obtained from the E and E signals of
the ISIS silicon detector telescopes, the Be being identified by the
instantaneous pile up of the E and E pulses. -ray decays of the
Cr nucleus are identified with coincidences set on 2 -particles
and on Be. Some transitions of the side-band with show
stronger population for Be emission relative to that of 2
-particles (by a factor ). This observation is interpreted as
due to an enhanced emission of Be into a more deformed nucleus.
Calculations based on the extended Hauser-Feshbach compound decay formalism
confirm this observation quantitatively.Comment: 17 pages, 9 figures accepted for publication in J. Phys.
Cognitive distances between evaluators and evaluees in research evaluation : a comparison between three informetric methods at the journal and subject category aggregation level
This article compares six informetric approaches to determine cognitive distances between the publications of panel members (PMs) and those of research groups in discipline-specific research evaluation. We used data collected in the framework of six completed research evaluations from the period 2009–2014 at the University of Antwerp as a test case. We distinguish between two levels of aggregation—Web of Science Subject Categories and journals—and three methods: while the barycenter method (2-dimensional) is based on global maps of science, the similarity-adapted publication
vector (SAPV) method and weighted cosine similarity (WCS) method (both in higher dimensions) use a full similarity matrix. In total, this leads to six different approaches, all of which are based on the publication profile of research groups and PMs. We use Euclidean distances between barycenters and SAPVs, as well as values of WCS between PMs and research groups as indicators of cognitive distance. We systematically compare how these six approaches are related. The results show that the level of aggregation has minor influence on determining cognitive distances, but dimensionality (two versus a high number of dimensions) has a greater influence. The SAPV and WCS methods agree in most cases at both levels of aggregation on which PM has the closest cognitive distance to the group to be evaluated, whereas the barycenter approaches often differ. Comparing the results of the methods to the main assessor that was assigned to each research group, we find that the barycenter method usually scores better. However,the barycenter method is less discriminatory and suggests more potential evaluators, whereas SAPV and WCS are more precise
Hanbury Brown-Twiss Interferometry for Fractional and Integer Mott Phases
Hanbury-Brown-Twiss interferometry (HBTI) is used to study integer and
fractionally filled Mott Insulator (MI) phases in period-2 optical
superlattices. In contrast to the quasimomentum distribution, this second order
interferometry pattern exhibits high contrast fringes in the it insulating
phases. Our detailed study of HBTI suggests that this interference pattern
signals the various superfluid-insulator transitions and therefore can be used
as a practical method to determine the phase diagram of the system. We find
that in the presence of a confining potential the insulating phases become
robust as they exist for a finite range of atom numbers. Furthermore, we show
that in the trapped case the HBTI interferogram signals the formation of the MI
domains and probes the shell structure of the system.Comment: 13 pages, 15 figure
A MIP Model and Several Approaches to Schedule Maintenance in Wind Farms on a Short-term Horizon
Taking into account wind prediction when scheduling maintenance on wind turbines can lead to potential gains. Preemption, transfer times for resources, and outsourcing are considered in this problem. The objective is concerned with maximizing the difference between the profits of wind farms related to the estimated production and the costs associated with outsourcing and resources transfers. A MIP model, a benders decomposition technique and a constraint programming approach are proposed
A Benders-based branch-and-cut approach to solve a wind turbine maintenance scheduling problem
We deal with a maintenance scheduling problem rising in the onshore wind power industry. We address the problem on a short-term horizon considering an individual management of the technicians through a space-time tracking. The objective is to find a maintenance planning that maximizes the production of the turbines while taking into account wind predictions, multiple task execution modes, and task-technician assignment constraints. We introduce an exact method to solve this challenging problem. We first propose integer linear programming (ILP) formulations of this problem. Then, on this basis, we build up a Benders-based branch-and-cut approach making use of Benders cuts as well as problem-specific cuts. Our method solves to optimality most of the instances or delivers solutions with a small average gap with respect to upper bounds. The results suggest that our method significantly outperforms the direct resolution of ILP models
A branch-and-check approach to solve a short-term maintenance scheduling problem faced by the onshore wind industry
International audienc
Maintenance scheduling in the electricity industry: A literature review
The reliability of the power plants and transmission lines in the electricity industry is crucial for meeting demand. Consequently, timely maintenance plays a major role reducing breakdowns and avoiding expensive production shutdowns. By now, the literature contains a sound body of work focused on improving decision making in generating units and transmission lines maintenance scheduling. The purpose of this paper is to review that literature. We update previous surveys and provide a more global view of the problem: we study both regulated and deregulated power systems and explore some important features such as network considerations, fuel management, and data uncertainty
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