4,600 research outputs found
Planification hospitalière, visions et actions : essai de modélisation pour la Suisse
Constatant que la Suisse n'a pas encore su trouver une démarche systématique pour maîtriser les coûts du secteur de la santé, l'auteur propose une approche globale de la planification hospitalière. D'abord, partant d'une enquête réalisée par la CDS (Conférence des directeurs sanitaires) et des comparaisons internationales. Il démontre la faisabilité d'une importante diminution du nombre de lits hospitaliers. Ensuite, à l'aide d'un modèle mathématique d'optimisation, croisant des données démographiques et routières (modèle GEOSTAT de l'Office fédéral des statistiques), il montre que ces lits pouvaient être distribués dans environ 40 hôpitaux dont aucun ne serait à plus de 60 minutes de temps d'accès. Il termine par une estimation approximative et très sommaire du potentiel d'économie de cette rationalisation. L'auteur reconnaît les difficultés pratiques d'une refonte si fondamentale du système hospitalier, mais conclut qu'une approche stratégique basée sur des techniques de modélisation a un potentiel majeur, encore peu utilisé en Suisse, comme aide à la décision dans la planification hospitalière. [Editeur]
Notes: Fig 11, p. 25: Taux de lits hospitaliers en Suisse à l'horizon 2005/2010: moyenne suisse: 3,17 arrondi à 3,2 lits/1000 habitants. Fig. 12, p. 29: Nombre de lits de soins aigus par 1000 habitants, OCDE, 1993-1999
Ordering monomial factors of polynomials in the product representation
The numerical construction of polynomials in the product representation (as
used for instance in variants of the multiboson technique) can become
problematic if rounding errors induce an imprecise or even unstable evaluation
of the polynomial. We give criteria to quantify the effects of these rounding
errors on the computation of polynomials approximating the function . We
consider polynomials both in a real variable and in a Hermitian matrix. By
investigating several ordering schemes for the monomials of these polynomials,
we finally demonstrate that there exist orderings of the monomials that keep
rounding errors at a tolerable level.Comment: Latex2e file, 7 figures, 32 page
New Dependencies of Hierarchies in Polynomial Optimization
We compare four key hierarchies for solving Constrained Polynomial
Optimization Problems (CPOP): Sum of Squares (SOS), Sum of Diagonally Dominant
Polynomials (SDSOS), Sum of Nonnegative Circuits (SONC), and the Sherali Adams
(SA) hierarchies. We prove a collection of dependencies among these hierarchies
both for general CPOPs and for optimization problems on the Boolean hypercube.
Key results include for the general case that the SONC and SOS hierarchy are
polynomially incomparable, while SDSOS is contained in SONC. A direct
consequence is the non-existence of a Putinar-like Positivstellensatz for
SDSOS. On the Boolean hypercube, we show as a main result that Schm\"udgen-like
versions of the hierarchies SDSOS*, SONC*, and SA* are polynomially equivalent.
Moreover, we show that SA* is contained in any Schm\"udgen-like hierarchy that
provides a O(n) degree bound.Comment: 26 pages, 4 figure
Combination of improved multibondic method and the Wang-Landau method
We propose a method for Monte Carlo simulation of statistical physical models
with discretized energy. The method is based on several ideas including the
cluster algorithm, the multicanonical Monte Carlo method and its acceleration
proposed recently by Wang and Landau. As in the multibondic ensemble method
proposed by Janke and Kappler, the present algorithm performs a random walk in
the space of the bond population to yield the state density as a function of
the bond number. A test on the Ising model shows that the number of Monte Carlo
sweeps required of the present method for obtaining the density of state with a
given accuracy is proportional to the system size, whereas it is proportional
to the system size squared for other conventional methods. In addition, the new
method shows a better performance than the original Wang-Landau method in
measurement of physical quantities.Comment: 12 pages, 3 figure
Contribution of a time-dependent metric on the dynamics of an interface between two immiscible electro-magnetically controllable Fluids
We consider the case of a deformable material interface between two
immiscible moving media, both of them being magnetiable. The time dependence of
the metric at the interface introduces a non linear term, proportional to the
mean curvature, in the surface dynamical equations of mass momentum and angular
momentum. We take into account the effects of that term also in the singular
magnetic and electric fields inside the interface which lead to the existence
of currents and charges densities through the interface, from the derivation of
the Maxwell equations inside both bulks and the interface. Also, we give the
expression for the entropy production and of the different thermo-dynamical
fluxes. Our results enlarge previous results from other theories where the
specific role of the time dependent surface metric was insufficiently stressed.Comment: 25 page
Quantum Monte Carlo Loop Algorithm for the t-J Model
We propose a generalization of the Quantum Monte Carlo loop algorithm to the
t-J model by a mapping to three coupled six-vertex models. The autocorrelation
times are reduced by orders of magnitude compared to the conventional local
algorithms. The method is completely ergodic and can be formulated directly in
continuous time. We introduce improved estimators for simulations with a local
sign problem. Some first results of finite temperature simulations are
presented for a t-J chain, a frustrated Heisenberg chain, and t-J ladder
models.Comment: 22 pages, including 12 figures. RevTex v3.0, uses psf.te
Transition Matrix Monte Carlo Reweighting and Dynamics
We study an induced dynamics in the space of energy of single-spin-flip Monte
Carlo algorithm. The method gives an efficient reweighting technique. This
dynamics is shown to have relaxation times proportional to the specific heat.
Thus, it is plausible for a logarithmic factor in the correlation time of the
standard 2D Ising local dynamics.Comment: RevTeX, 5 pages, 3 figure
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