293 research outputs found
Out of the swampland with multifield quintessence?
Multifield models with a curved field space have already been shown to be able to provide viable quintessence models for steep potentials that satisfy swampland bounds. The simplest dynamical systems of this type are obtained by coupling Einstein gravity to two scalar fields with a curved field space. In this paper we study the stability properties of the non-trivial fixed points of this dynamical system for a general functional dependence of the kinetic coupling function and the scalar potential. We find the existence of non-geodesic trajectories with a sharp turning rate in field space which can give rise to late-time cosmic acceleration with no need for flat potentials. In particular, we discuss the properties of the phase diagram of the system and the corresponding time evolution when varying the functional dependence of the kinetic coupling. Interestingly, upon properly tuning the initial conditions of the field values, we find trajectories that can describe the current state of the universe. This could represent a promising avenue to build viable quintessence models out of the swampland if they could be consistently embedded in explicit string constructions
ROFRAQ: A statistics-based empirical method for assessing accident risk from rockfalls in quarries. International Journal of Rock Mechanics and Mining Sciences.
This paper describes an empirical method, called Rockfall Risk Assessment for Quarries (ROFRAQ), which assesses the risk associated with rock falls in quarries. The method is based on aprobabilistic approach that assumes that an accident occurs as a consequence of as equence of events. This method has been applied to slopes in a number of quarries, and has proved useful indetecting trouble some slopes on the basis of empirical evidence. Thus far, it has been applied to around 100 slopes from various quarries of different rocks. These results show satisfactory agreement with results for empirical methods applied in the civil engineering field to highways and roads. The authors describe a case study of a granite aggregate quarry that highlights a number of issues in relation to practical application of the method
Fluorinated surfactants in solution: Diffusion coefficients of fluorinated alcohols in water
Intra-diffusion coefficients of three
fluorinated alcohols, 2,2,3,3,3-pentafluoropropan-1-ol (PFP),
2,2,3,3,4,4,4-heptafluorobutan-1-ol (HFB) and 2,2,3,3,4,4,5,5,5-nonafluoropentan-1-ol (NFP) in water
have been measured by the PFG–NMR spin-echo technique as a function of temperature and
composition, focusing on the alcohol dilute region. For comparison, intra-diffusion coefficients of 2,2,2-
trifluoroethanol (TFE) and HFB have also been measured in heavy water using the same method and
conditions. As far as we know, these are the
first experimental measurements of this property for these
binary systems. Intra-diffusion coefficients for NFP in water and for TFE and HFB in heavy water have also
been obtained by molecular dynamics simulation, complementing those for TFE, PFP and HFB reported in
a previous work. The agreement between experimental and simulated results for PFP, HFB and NFP in
water is reasonable, although presenting higher deviations than for the TFE/water system. From the
dependence of the intra-diffusion coefficients on temperature, diffusion activation energies were
estimated for all the solutes in water and heavy water
Pre - Inflationary Clues from String Theory ?
"Brane supersymmetry breaking" occurs in String Theory when the only
available combinations of D-branes and orientifolds are not mutually BPS and
yet do not introduce tree-level tachyon instabilities. It is characterized by
the emergence of a steep exponential potential, and thus by the absence of
maximally symmetric vacua. The corresponding low-energy supergravity admits
intriguing spatially-flat cosmological solutions where a scalar field is forced
to climb up toward the steep potential after an initial singularity, and
additional milder terms can inject an inflationary phase during the ensuing
descent. We show that, in the resulting power spectra of scalar perturbations,
an infrared suppression is typically followed by a pre-inflationary peak that
reflects the end of the climbing phase and can lie well apart from the
approximately scale invariant profile. A first look at WMAP9 raw data shows
that, while the chi^2 fits for the low-l CMB angular power spectrum are clearly
compatible with an almost scale invariant behavior, they display nonetheless an
eye-catching preference for this type of setting within a perturbative string
regime.Comment: 34 pages, LaTeX, 16 eps figures. Relative displacement in fig. 14 and
some typos corrected, references and acknowledgments updated. To appear in
JCA
Large-Scale Production of LGR5-Positive Bipotential Human Liver Stem Cells
Background and Aims: The gap between patients on transplant waiting lists and available donor organs is steadily increasing. H
Viscosity of liquid systems involving hydrogenated and fluorinated substances: Liquid mixtures of (hexane+perfluorohexane)
Envolvimento dos receptores 5-HT2 da amígdala nos níveis de ansiedade induzidos pela exposição de ratos ao labirinto em cruz elevado
Human toxocariasis: contribution by Brazilian researchers
In the present paper the main aspects of the natural history of human infection by Toxocara larvae that occasionally result in the occurrence of visceral and/or ocular larva migrans syndrome were reviewed. The contribution by Brazilian researchers was emphasized, especially the staff of the Tropical Medicine Institute of São Paulo (IMT)
Atividade quimioprofilática na esquistossomose mansoni de sabonetes contendo óleo essencial de frutos de Pterodon pubescens
- …