Miguel A. Catalán

Learn More
Group theoretical methods are used to study some properties of the Riccati equation, which is the only differential equation admitting a nonlinear superposition principle. The Wei–Norman method is applied for obtaining the associated differential equation in the group SL(2,R). The superposition principle for first order differential equation systems and(More)
Higher dimensional Chern-Simons theories, even though constructed along the same topological pattern as in 2+1 dimensions, have been shown recently to have generically a non-vanishing number of degrees of freedom. In this paper, we carry out the complete Dirac Hamiltonian analysis (separation of first and second class constraints and calculation of the(More)
1550-7998=20 We present a set of boundary conditions for solving the elliptic equations in the initial data problem for space-times containing a black hole, together with a number of constraints to be satisfied by the otherwise freely specifiable standard parameters of the conformal thin sandwich formulation. These conditions altogether are sufficient for(More)
OBJECTIVE We compared conventional treatment with pumpless extracorporeal lung membrane (Interventional Lung Assist [iLA] Novalung; Novalung GmbH, Hechingen, Germany) support in a pig model of postpneumonectomy severe acute respiratory distress syndrome. METHODS Adult pigs underwent a left thoracotomy without (group I) or with a left extrapericardial(More)
A possible definition of strong/symmetric hyperbolicity for a second-order system of evolution equations is that it admits a reduction to first order which is strongly/symmetric hyperbolic. We investigate the general system that admits a reduction to first order and give necessary and sufficient criteria for strong/symmetric hyperbolicity of the reduction(More)
In attempting to solve the Einstein equations numerically as an initial or initial-boundary value problem, it is important to start with a well-posed continuum problem. For systems of first-order equations, there are two useful criteria for well-posedness: Strong hyperbolicity is a necessary and sufficient criterion for the initial value problem (without(More)
We prove that when the equations are restricted to the principal part the standard version of the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulation of the Einstein equations is equivalent to the Nagy-Ortiz-Reula (NOR) formulation for any gauge, and that the Kidder-Scheel-Teukolsky (KST) formulation is equivalent to NOR for a variety of gauges. We review(More)
OBJECTIVE Videothoracoscopic (VTC) resection of peripheral pulmonary nodules (PN) occasionally requires performing a mini-thoracotomy to locate them using palpation. The aim of this study is to evaluate the usefulness of inserting a CT-guided harpoon as a method for locating PN prior to surgery. MATERIAL AND METHODS A study was conducted on a total of 52(More)
The Ashtekar-Barbero formulation of general relativity admits a one-parameter family of canonical transformations that preserves the expressions of the Gauss and diffeomorphism constraints. The loop quantization of the connection formalism based on each of these canonical sets leads to different predictions. This phenomenon is called the Immirzi ambiguity.(More)
The Immirzi ambiguity arises in loop quantum gravity when geometric operators are represented in terms of different connections that are related by means of an extended Wick transform. We analyze the action of this transform in gravity coupled with matter fields and discuss its analogy with the Wick rotation on which the Thiemann transform between Euclidean(More)