The bouncing universe provides a possible solution to the Big Bang singularity problem. In this paper we study the bouncing solution in the universe dominated by the Quintom matter with an equation of state (EoS) crossing the cosmological constant boundary. We will show explicitly the analytical and numerical bouncing solutions in three types of models for the Quintom matter with an phenomenological EoS, the two scalar fields and a scalar field with a modified Born-Infeld action. *

Ethylene is a gaseous phytohormone that plays vital roles in plant growth and development. Previous studies uncovered EIN2 as an essential signal transducer linking ethylene perception on ER to transcriptional regulation in the nucleus through a "cleave and shuttle" model. In this study, we report another mechanism of EIN2-mediated ethylene signaling, whereby EIN2 imposes the translational repression of EBF1 and EBF2 mRNA. We find that the EBF1/2 3' UTRs mediate EIN2-directed translational repression and identify multiple poly-uridylates (PolyU) motifs as functional cis elements of 3' UTRs. Furthermore, we demonstrate that ethylene induces EIN2 to associate with 3' UTRs and target EBF1/2 mRNA to cytoplasmic processing-body (P-body) through interacting with multiple P-body factors, including EIN5 and PABs. Our study illustrates translational regulation as a key step in ethylene signaling and presents mRNA 3' UTR functioning as a "signal transducer" to sense and relay cellular signaling in plants. VIDEO ABSTRACT.

We study in this paper the perturbations of the quintom dark energy model and the effects of quintom perturbations on the current observations. Quintom describes a scenario of dark energy where the equation of state gets across the cosmological constant boundary w = −1 during evolution. We present a new method to show that the conventional dark energy models based on single k-essence field and perfect fluid cannot act as quintom due to the singularities and classical instabilities of perturbations around w = −1. One needs to add extra degrees of freedom for successful quintom model buildings. There are no singularities or classical instabilities in perturbations of realistic quintom models and they are potentially distinguishable from the cosmological constant. Basing on the realistic quintom models in this paper we provide one way to include the perturbations for dark energy models with parametrized equation of state across −1. Compare with those assuming no dark energy perturbations, we find that the parameter space which allows the equation of state to get across −1 will be enlarged in general when including the perturbations.

Current observations seem to mildly favor an evolving dark energy with the equation of state getting across -1. This form of dark energy, dubbed Quintom, is studied phenomenologically in this paper with an oscillating equation of state. We find oscillating Quintom can unify the early inflation and current acceleration of the universe, leading to the oscillations of the Hubble constant and a recurring universe. Our oscillating Quintom would not lead to a big crunch nor big rip. The scale factor keeps increasing from one period to another and leads naturally to a highly flat universe. The universe in this model recurs itself and we are only staying among one of the epochs, in which sense the coincidence problem is reconciled. PACS numbers: 98.80.Cq In 1998, two groups [1, 2] independently showed the accelerating expansion of our universe, which established the existence of dark energy where the equation of state is less than −1/3 today. The simplest form of dark energy is the cosmological constant. A cosmological constant which leads to current acceleration would encounter many theoretical problems, such as the fine-tuning problem and the coincidence problem [3]. A light scalar field of quintessence [4,5,6] which evolves with time is to some extent likely to resolve the coincidence problem. The model of phantom [7] has also been put forward which leads to an equation of state w ≤ −1. Normally quintessence with a canonic kinetic term can only have w ≥ −1, meanwhile k-essence[8] can have both w ≥ −1 and w < −1. For the cosmological constant and many quintessence models the event horizon would lead to a potential incompatibility with the string theory, meanwhile for models where w < −1 one would get the Big Rip[9] of the universe.The accumulation of the current observational data has opened a robust window for probing the recent behavior of dark energy. Measurements from type Ia Supernova (SNe Ia), the Cosmic Microwave Background (CMB) Radiation, Large Scale Structure (LSS), weak lensing, clusters and galaxies all contain the imprints of dark energy. Specifically the recently released first year Wilkinson Microwave Anisotropy Probe (WMAP) measurement[10], the Sloan Digital Sky Survey (SDSS) measurement of the three-dimensional power spectrum [11] and most importantly, the recent discovery of 16 SNe Ia [12] with the Hubble Space Telescope during the GOODS ACS Treasury survey, together with former SNe Ia data have provided the most precise up-to-date measurements of dark energy. Many other sources have also been studied to make crosschecks and reveal new physics on the dark energy and the concordance cosmological model. Recently many authors in the literature have fitted the behavior of dark energy using various parameterizations. The best fit value of the equation of state is found to be less than −1 when using SNe Ia [12,13,14,15,16,17] or the X-ray mass fraction data[18] with a cosmological constant still well within the central regions 1 . It has also been pointed out by many authors that an evolving dark energy ...