20 research outputs found
Chemical composition and antigenotoxic properties of Lippia alba essential oils
The present work evaluated the chemical composition and the DNA protective effect of the essential oils (EOs) from Lippia alba against bleomycin-induced genotoxicity. EO constituents were determined by Gas Chromatography/Mass Spectrometric (GC-MS) analysis. The major compounds encountered being citral (33% geranial and 25% neral), geraniol (7%) and trans-β-caryophyllene (7%) for L. alba specimen COL512077, and carvone (38%), limonene (33%) and bicyclosesquiphellandrene (8%) for the other, COL512078. The genotoxicity and antigenotoxicity of EO and the compounds citral, carvone and limonene, were assayed using the SOS Chromotest in Escherichia coli. The EOs were not genotoxic in the SOS chromotest, but one of the major compound (limonene) showed genotoxicity at doses between 97 and 1549 mM. Both EOs protected bacterial cells against bleomycin-induced genotoxicity. Antigenotoxicity in the two L. alba chemotypes was related to the major compounds, citral and carvone, respectively. The results were discussed in relation to the chemopreventive potential of L. alba EOs and its major compounds
High-frequency variability in neutron-star low-mass X-ray binaries
Binary systems with a neutron-star primary accreting from a companion star
display variability in the X-ray band on time scales ranging from years to
milliseconds. With frequencies of up to ~1300 Hz, the kilohertz quasi-periodic
oscillations (kHz QPOs) represent the fastest variability observed from any
astronomical object. The sub-millisecond time scale of this variability implies
that the kHz QPOs are produced in the accretion flow very close to the surface
of the neutron star, providing a unique view of the dynamics of matter under
the influence of some of the strongest gravitational fields in the Universe.
This offers the possibility to probe some of the most extreme predictions of
General Relativity, such as dragging of inertial frames and periastron
precession at rates that are sixteen orders of magnitude faster than those
observed in the solar system and, ultimately, the existence of a minimum
distance at which a stable orbit around a compact object is possible. Here we
review the last twenty years of research on kHz QPOs, and we discuss the
prospects for future developments in this field.Comment: 66 pages, 37 figures, 190 references. Review to appear in T. Belloni,
M. Mendez, C. Zhang, editors, "Timing Neutron Stars: Pulsations, Oscillations
and Explosions", ASSL, Springe