Numerous specimens of a linear low density polyethylene sample were uniaxially deformed up to different elongations to study the double yield phenomenon. Extruded samples were analyzed to calculate the crystallinity and to estimate the mean crystal size, under stressed state and released state (after removal of the stress), using the wide angle X-ray scattering technique. The crystallinity degree and the mean crystal dimension associated to the (110) orthorhombic reflection of the specimen without deformation were of 55% and 16 nm. These parameters in the stressed state, as functions of the elongation, presented a multi-step behavior. A decrement after the first yield point (48%, 13 nm), then another decrement, and an abrupt increment followed by a decrement at higher strain values around the second yield point (28, 40, and 30%; 12, 14.5, and 11 nm). The behavior was more notorious in the stressed state than in the released state. The latter results were interpreted in terms of a partial melting followed by a recrystallization process. These experimental findings show that the second yield is not only associated with the deformation of the crystalline region. This partial meltingrecrystallization process is one of the main mechanisms of the double yield phenomenon.

In the present work, we analyze the corrections caused by an anomalous dispersion relation, suggested in several quantum gravity models, upon the speed of sound in a weakly interacting Bose-Einstein Condensate, trapped in a potential of the form V (r) ∼ r 2 . We show that the corresponding ground state energy and consequently, the associated speed of sound, present corrections respect to the usual case, which may be used to explore the sensitivity to Planck-scale effects on these relevant properties associated with the condensate. Indeed, we stress that this type of macroscopic bodies may be more sensitive, under certain conditions, to Planck-scale manifestations than its constituents. In addition, we prove that the inclusion of a trapping potential, together with manybody contributions, improves the sensitivity to Planck-scale signals, compared to the homogeneous system.

We analyze the possible effects arising from Planck scale regime upon the interference pattern of two non-interacting Bose-Einstein condensates. We start with the analysis of the free expansion of a condensate, taken into account the effects produced by a deformed dispersion relation, suggested in several quantum-gravity models. The analysis of the condensate free expansion, in particular, the modified free velocity expansion, suggests in a natural way, a modified uncertainty principle that could leads to new phenomenological implications related to the quantum structure of space time. Finally, we analyze the corresponding separation between the interference fringes after the two condensates overlap, in order to explore the sensitivity of the system to possible signals caused by the Planck scale regime.

We consider the consequences of the presence of metric fluctuations upon the properties of a hydrogen atom. Particularly, we introduce these metric fluctuations in the corresponding effective Schrödinger equation and deduce the modifications that they entail upon the hyperfine structure related to a hydrogen atom. We will find the change that these effects imply for the ground state energy of the system and obtain a bound for its size comparing our theoretical predictions against the experimental uncertainty reported in the literature. In addition, we analyze the corresponding Lamb shift effect emerging from these fluctuations of spacetime. Once again, we will set a bound to these oscillations resorting to the current experimental outcomes.

In the present work we consider the role that metric fluctuations could have upon the properties of a Bose-Einstein condensate. In particular we consider the Bogoliubov space associated to it and show that there are, at least, two independent ways in which the average size of these metric fluctuations could be, experimentally, determined. Indeed, we prove that the pressure and the speed of sound of the ground state define an expression allowing us to determine the average size of these fluctuations. Afterwards, an interferometric experiment involving Bogoliubov excitations of the condensate and the pressure (or the speed of sound of the ground state) provides a second and independent way in which this average size could be determined, experimentally.