15,368 research outputs found
Closed timelike curves and chronology protection in quantum and classical simulators
In principe, General Relativity seems to allow the existence of closed
timelike curves (CTC). However, when quantum effects are considered, it is
likely that their existence is prevented by some kind of chronological
protection mechanism, as Hawking conjectured. Confirming or refuting the
conjecture would require a full quantum theory of gravity. Meanwhile, the use
of simulations could shed some light on this issue. We propose simulations of
CTCs in a quantum system as well as in a classical one. In the quantum
simulation, some restrictions appear that are not present in the classical
setup, which could be interpreted as an analogue of a chronology protection
mechanism.Comment: 6 pages, 4 figures. v2: published versio
Quantitative equidistribution for the solutions of systems of sparse polynomial equations
For a system of Laurent polynomials f_1,..., f_n \in C[x_1^{\pm1},...,
x_n^{\pm1}] whose coefficients are not too big with respect to its directional
resultants, we show that the solutions in the algebraic n-th dimensional
complex torus of the system of equations f_1=\dots=f_n=0, are approximately
equidistributed near the unit polycircle. This generalizes to the multivariate
case a classical result due to Erdos and Turan on the distribution of the
arguments of the roots of a univariate polynomial. We apply this result to
bound the number of real roots of a system of Laurent polynomials, and to study
the asymptotic distribution of the roots of systems of Laurent polynomials with
integer coefficients, and of random systems of Laurent polynomials with complex
coefficients.Comment: 29 pages, 2 figures. Revised version, accepted for publication in the
American Journal of Mathematic
Improving Knowledge Retrieval in Digital Libraries Applying Intelligent Techniques
Nowadays an enormous quantity of heterogeneous and distributed information is stored in the digital University. Exploring online collections to find knowledge relevant to a user’s interests is a challenging work. The artificial intelligence and Semantic Web provide a common framework that allows knowledge to
be shared and reused in an efficient way. In this work we propose a comprehensive approach for discovering E-learning objects in large digital collections based on analysis of recorded semantic metadata in those objects and the application of expert system technologies. We have used Case Based-Reasoning
methodology to develop a prototype for supporting efficient retrieval knowledge from online repositories.
We suggest a conceptual architecture for a semantic search engine. OntoUS is a collaborative effort that
proposes a new form of interaction between users and digital libraries, where the latter are adapted to users
and their surroundings
Effect of particle shape and fragmentation on the response of particle dampers
A particle damper (PD) is a device that can attenuate mechanical vibrations thanks to the dissipative collisions between grains contained in a cavity attached to the vibrating structure. It has been recently suggested that, under working conditions in which the damping is optimal, the PD has a universal response in the sense that the specific dissipative properties of the grains cease to be important for the design of the device. We present evidence from simulations of PDs containing grains of different sizes, shapes and restitution coefficients, that the universal response is also valid when fragmentation of the grains occurs (generally due to intensive operation of the PD). In contrast, the welding of grains (caused by operation under high temperatures) can take the PD out of the universal response and deteriorate the attenuation. Interestingly, we observed that even at working conditions off the optimal damping, the shape of the grains remains unimportant for the response of the PD.Fil: Sánchez, Martín. Universidad Tecnológica Nacional; ArgentinaFil: Carlevaro, Carlos Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física de Líquidos y Sistemas Biológicos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física de Líquidos y Sistemas Biológicos; ArgentinaFil: Pugnaloni, Luis Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; Argentin
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