Carmen L. Sigüenza

Unified dark energy thermodynamics: varying w and the −1-crossing

We investigate, in a unified and general way, the thermodynamic properties of dark energy with an arbitrary, varying equation-of-state parameter w(a). We find that all quantities are well defined and regular for every w(a), including the −1-crossing, with the temperature being negative in the phantom regime (w(a) −1). The density and entropy are always positive while the chemical potential can be arbitrary. At the −1-crossing, both temperature and chemical potential are zero. The temperature negativity can only be interpreted in the quantum framework. The regular behavior of all quantities at the −1-crossing leads to the conclusion that such a crossing does not correspond to a phase transition, but rather to a smooth crossover.

Vibrational study of some alkylamine hydrochlorides

Abstract The i.r. spectra of some solid amine hydrochlorides are studied. The bands originating from strong hydrogen bonds between the physically adsorbed molecules and either the bromide of the polycrystalline KBr, the chloride, or other hydrochloride molecules are tentatively assigned and discussed.

Infrared study of some solid chlorophenols: Part 1. Symmetric derivatives

Abstract The IR spectra of some halogenated symmetric derivatives of phenol in solid state are reported. The CNDO/2 method has been applied to calculate the V 2 torsional barrier; this method gives larger values than those obtained from other conventional methods. The origin of the tilt angle in phenols is discussed.

Closed timelike curves in superfluid 3He

Abstract It is shown that the curved spacetime induced in a thin film of superfluid 3 He-A by the presence of symmetric vortices with the unbroken symmetry phase, admits the existence of closed timelike curves through which only superfluid clusters formed by anti- 3 He atoms can travel and violate causality.

Laser Raman spectroscopy of some local anesthetics

Abstract The Raman spectra of benzocaine and procaine hydrochlorides in solid phase are reported. From the assigned inversion and torsion modes we have also estimated the corresponding barriers by using the harmonic approximation.

THE FUTURE OF A Λ-UNIVERSE

It is argued that the accretion of phantom energy onto a wormhole in a universe with a positive cosmological constant leads also to a gradual increase of the wormhole throat radius, which eventually overtakes the super-accelerated expansion of the universe and becomes infinite at a time in the future before the big rip. Thus, the universe as a whole can time travel toward the past or the future.

Monochromatic two beam multiphoton dissociation of CF2HCl

Abstract Infrared multiphoton dissociation induced by monochromatic two-beam excitation has been carried out by controlling the time delay between the two laser beams. The maximum dissociation yield is found to occur at time delays around 5 μs, when the absorbed energy becomes largely stochastized and an equilibrium among the distinct processes of energy relaxation is manifested. It is shown that this behaviour essentially differs from that which occurs in dichromatic multiphoton dissociation.

Vibrational study of intermolecular hydrogen bonds in dichloroanilines

Abstract The stretching infrared bands of the amine groups associated by intermolecular hydrogen bonding in solid polyethylene solution have been identified at 140 cm −1 in 3,4 dichloaniline and at 176 and 215 cm −1 in 2,6 dichloroaniline. That assignment has been carried out using medium- and far-infrared spectroscopy and some theoretical considerations.