arXiv subjects

B. Carvalho

Publications and source records attributed to B. Carvalho.

2 recordsLinked to original sources

arXiv2022

Unfocused laser ignition of high-pressure He-H2-O2 combustible mixtures

We report consistent ignition of high-pressure (p > 20-30 bar) hydrogen-oxygen mixtures diluted with helium, using an unfocused Nd:YAG laser. This corresponds to laser irradiances several orders of magnitude below the minimum ignition energies reported in the literature. By placing a mirror inside a cylindrical vessel and filling it up to 100 bar with H2-He or O2-He non-combustible mixtures, we obtain the pressure-dependent absorptivity of the combustible He-H2-O2 mixture. We find no measurable absorption of the laser signal by the medium, for the overall pressure range, to the experimental apparatus sensitivity (about 1% of the laser irradiance). This leads credence to the theory that ignition stems from seed electrons created by autofocusing ionization of dust/impurities in the gas.

physics.chem-ph↗

arXiv2019

Beyond topological hyperbolicity: the L-shadowing property

In this paper we further explore the L-shadowing property defined in [17] for dynamical systems on compact spaces. We prove that structurally stable diffeomorphisms and some pseudo-Anosov diffeomorphisms of the two-dimensional sphere satisfy this property. Homeomorphisms satisfying the L-shadowing property have a spectral decomposition where the basic sets are either expansive or contain arbitrarily small topological semi-horseshoes (periodic sets where the restriction is semiconjugate to a shift). To this end, we characterize the L-shadowing property using local stable and unstable sets and the classical shadowing property. We exhibit homeomorphisms with the L-shadowing property and arbitrarily small topological semi-horseshoes without periodic points. At the end, we show that positive finite-expansivity jointly with the shadowing property imply that the space is finite.

math.DS↗