We investigate in this paper the cosmological evolution of a dark energy model with two scalar fields where one of the scalar has canonical kinetic energy and another scalar has negative kinetic energy term. For such a system with exponential potentials we find that during the evolution of the universe the equation of state w changes from w > −1 to w < −1, which is consistent with the recent observations. A phase-plane analysis shows that the "phantom"-dominated scaling solution is the stable late-time attractor of this type of models. PACS number(s): 98

We have established a novel cell line, designated as TF-1, from a patient with erythroleukemia, which showed complete growth dependency on granulocyte-macrophage colony-stimulating factor (GM-CSF) or on interleukin-3 (IL-3) and carried a homogeneous chromosomal abnormality (54X). Erythropoietin (EPO) also sustained the short-term growth of TF-1, but did not induce erythroid differentiation. These three hematopoietic growth factors acted on TF-1 synergistically. Transforming growth factor-beta and interferons inhibited the factor-dependent growth of TF-1 cells in a dose-dependent fashion, and monocyte-colony stimulating factor and interkeukin-1 enhanced the GM-CSF-dependent growth of TF-1. Ultrastructural studies revealed some very immature features in this cell line. Although TF-1 cells do not express glycophorin A or carbonyl anhydrase I, the morphological and cytochemical features, and the constitutive expression of globin genes, indicate the commitment of TF-1 to erythroid lineage. When induced to differentiate, TF-1 entered two different pathways. Specifically, hemin and delta-aminolevulinic acid induced hemoglobin synthesis, whereas TPA induced dramatic differentiation of TF-1 into macrophage-like cells. In summary, TF-1 is a cell line of immature erythroid origin that requires GM-CSF, IL-3, or EPO for its growth and that has the ability to undergo differentiation into either more mature erythroid cells or into macrophage-like cells. TF-1 is a useful tool for analyzing the human receptors for IL-3, GM-CSF, and EPO or the signal transduction of these hemopoietic growth factors.

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. *

Recent released WMAP data show a low value of quadrupole in the CMB temperature fluctuations, which confirms the early observations by COBE. In this paper, a scenario, in which a contracting phase is followed by an inflationary phase, is constructed. We calculate the perturbation spectrum and show that this scenario can provide a reasonable explanation for lower CMB anisotropies on large angular scales.PACS numbers: 98.80. Cq, 98.70.Vc Recently the high resolution full sky Wilkinson Microwave Anisotropy Probe (WMAP) data [1,2,3,4,5] have been released and it is shown that the data is consistent with the predictions of the standard concordance ΛCDM model. However, there remain two intriguing discrepancies between WMAP observations and the concordance model. The data predict a high reionization optical depth [6][7] and a running of the spectral index [4], as claimed by WMAP team. The need of a running has been studied widely [8,9,10,11] and many inflation models with large running of a spectral index have been built [12,13]. Another surprising discrepancy comes from the low temperature-temperature(TT) correlation quadrupole, which has previously been observed by COBE [14]. It is pointed out by Ref.[9] that there might be some connection between the need for running of the spectral index and the suppressed CMB quadrupole, and the significance of the low multipoles has been discussed widely in the literature [15].Several possibilities to alleviate the low-multipoles problem have been discussed in the literature [16,17,18,19]. One straightforward way is to build suppressed primordial spectrum on the largest scales [9]. This can also lead to other observable consequences [20,21]. In the framework of inflation, changing the inflaton potential and the initial conditions at the onset of inflation have been proposed [17]. For the latter case, the inflaton has to be assumed in the kinetic dominated regime initially. Since there are no primordial perturbations exiting the horizon in such a phase, the inflation [19] or contracting phase before kinetic domination should be required.In this paper we consider a scenario where a contracting is followed by an inflationary phase and study its implications in suppressing CMB quadrupole. For a contracting phase with a kinetic domination, the primordial perturbations exiting the horizon can be obtained similar to that of Pre Big Bang (PBB) scenario [22](for a review see [23] tive to the inflation scenario, but its spectrum is strongly blue and does not provide the nearly scale-invariant perturbation spectrum implied by the observations by the evolution of background field. In the literature there are some proposals of alternatives for seeding the nearly scale-invariant spectrum in the contracting phase. In addition to the ekpyrotic/cyclic scenario [24], there is a possibility to seed a scale-invariant spectrum [25] in which the pressureless matter is used. For the expanding phase, in addition to the usual inflation scenario, a slowly expanding phase may also be feasible [26]. In g...