New Constructions for Mechanisms with Verification

A social choice function A is implementable with verification if there exists a payment scheme P such that (A,P) is a truthful mechanism for verifiable agents [Nisan and Ronen, STOC 99]. We give a simple sufficient condition for a social choice function to be implementable with verification for comparable types. Comparable types are a generalization of the well-studied one-parameter agents. Based on this characterization, we show that a large class of objective functions μ admit social choice functions that are implementable with verification and minimize (or maximize) μ.We then focus on the well-studied case of oneparameter agents.We give a general technique for constructing efficiently computable social choice functions that minimize or approximately minimize objective functions that are non-increasing and neutral (these are functions that do not depend on the valuations of agents that have no work assigned to them). As a corollary we obtain efficient online and offline mechanisms with verification for some hard scheduling problems on related machines

Revisiting the Paxos algorithm

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1997.Includes bibliographical references (p. 138-142).by Roberto de Prisco.M.S

Radiating Shear-Free Gravitational Collapse with Charge

We present a new shear free model for the gravitational collapse of a spherically symmetric charged body. We propose a dissipative contraction with radiation emitted outwards. The Einstein field equations, using the junction conditions and an ansatz, are integrated numerically. A check of the energy conditions is also performed. We obtain that the charge delays the black hole formation and it can even halt the collapse.Comment: 22 pages, 9 figures. It has been corrected several typos and included several references. Accepted for publication in GR

Space-time inhomogeneity, anisotropy and gravitational collapse

We investigate the evolution of non-adiabatic collapse of a shear-free spherically symmetric stellar configuration with anisotropic stresses accompanied with radial heat flux. The collapse begins from a curvature singularity with infinite mass and size on an inhomogeneous space-time background. The collapse is found to proceed without formation of an even horizon to singularity when the collapsing configuration radiates all its mass energy. The impact of inhomogeneity on various parameters of the collapsing stellar configuration is examined in some specific space-time backgrounds.Comment: To appear in Gen. Relativ. Gra

Nonadiabatic charged spherical gravitational collapse

We present a complete set of the equations and matching conditions required for the description of physically meaningful charged, dissipative, spherically symmetric gravitational collapse with shear. Dissipation is described with both free-streaming and diffusion approximations. The effects of viscosity are also taken into account. The roles of different terms in the dynamical equation are analyzed in detail. The dynamical equation is coupled to a causal transport equation in the context of Israel-Stewart theory. The decrease of the inertial mass density of the fluid, by a factor which depends on its internal thermodynamic state, is reobtained, with the viscosity terms included. In accordance with the equivalence principle, the same decrease factor is obtained for the gravitational force term. The effect of the electric charge on the relation between the Weyl tensor and the inhomogeneity of energy density is discussed.Comment: 23 pages, Latex. To appear in Phys. Rev. D. Some references correcte

Mortality risk according to different clinical characteristics of first episode of liver decompensation in cirrhotic patients: a nationwide, prospective, 3-year follow-up study in Italy.

OBJECTIVES: The occurrence of decompensation marks a crucial turning point in the course of cirrhosis. The purpose of this study was to assess the risk of mortality according to the clinical characteristics of first decompensation, considering also the impact of acute-on-chronic liver failure (AoCLF). METHODS: We conducted a prospective nationwide inception cohort study in Italy. Decompensation was defined by the presence of ascites, either overt or detected by ultrasonography (UD), gastroesophageal variceal bleeding (GEVB), and hepatic encephalopathy (HE). AoCLF was defined according to the Asian Pacific Association for the Study of the Liver criteria. Multivariable Cox proportional hazards regression was used to analyze the risk of failure (death or orthotopic liver transplantation (OLT)). RESULTS: A total of 490 consecutive cirrhotic patients (314 males, mean age 60.9±12.6 years) fulfilled the study criteria. AoCLF was identified in 59 patients (12.0%). Among the remaining 431 patients, ascites were found in 330 patients (76.6%): in 257 (77.8%) as overt ascites and in 73 (22.2%) as UD ascites. GEVB was observed in 77 patients (17.9%) and HE in 30 patients (7.0%). After a median follow-up of 33 months, 24 patients underwent OLT and 125 died. The cumulative incidence of failure (death or OLT) after 1, 2, and 3 years was, respectively, 28, 53, and 62% in patients with AoCLF; 10, 18, and 25% in patients with UD ascites; 17, 31, and 41% in patients with overt ascites; and 8, 12, and 24% in patients with GEVB (P<0.0001). CONCLUSIONS: AoCLF is responsible for a relevant proportion of first decompensation in cirrhotic patients and is associated with the poorest outcome. Patients with UD ascites do not have a negligible mortality rate and require clinical monitoring similar to that of patients with overt ascites