Onset of J/ψJ/\psi Melting in Quark-Gluon Fluid at RHIC

A strong $J/\psi$ suppression in central Au+Au collisions has been observed by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). We develop a hydro+$J/\psi$ model in which hot quark-gluon matter is described by the full (3+1)-dimensional relativistic hydrodynamics and $J/\psi$ is treated as an impurity traversing through the matter. The experimental $J/\psi$ suppression pattern in mid-rapidity is reproduced well by the sequential melting of $\chi_{\rm c}$, $\psi'$, and $J/\psi$ in dynamically expanding fluid. The melting temperature of directly produced $J/\psi$ is well constrained by the participant-number dependence of the $J/\psi$ suppression and is found to be about $2.T_{\rm c}$ with $T_{\rm c}$ being the pseudo-critical temperature.Comment: 5 pages, 5 figures, Submitted to Phys. Rev. C. (Rapid Communication

Analysis of one- and two-particle spectra at RHIC based on a hydrodynamical model

We calculate the one-particle hadronic spectra and correlation functions of pions based on a hydrodynamical model. Parameters in the model are so chosen that the one-particle spectra reproduce experimental results of $\sqrt{s}=130A$GeV Au+Au collisions at RHIC. Based on the numerical solution, we discuss the space-time evolution of the fluid. Two-pion correlation functions are also discussed. Our numerical solution suggests the formation of the quark-gluon plasma with large volume and low net baryon density.Comment: LaTeX, 4pages, 4 figures. To appear in the proceedings of Fourth International Conference on Physics and Astrophysics of Quark-Gluon Plasma (ICPAQGP-2001), Nov 26-30, 2001, Jaipur, Indi

Electromagnetic Spectrum from QGP Fluid

We calculate thermal photon and electron pair distribution from hot QCD matter produced in high energy heavy-ion collisions, based on a hydrodynamical model which is so tuned as to reproduce the recent experimental data at CERN SPS, and compare these electromagnetic spectra with experimental data given by CERN WA80 and CERES. We investigate mainly the effects of the off-shell properties of the source particles on the electromagnetic spectra.Comment: 5 pages, latex, 4 Postscript figures. A talk given at the International School on the Physics of Quark Gluon Plasma, June 3-6, 1997, Hiroshima, Japan. To be appeared in Prog. Theor. Phys. Supplemen

Can transport peak explain the low-mass enhancement of dileptons at RHIC?

We propose a novel relation between the low-mass enhancement of dielectrons observed at PHENIX and transport coefficients of QGP such as the charge diffusion constant $D$ and the relaxation time $\tau_{\rm J}$. We parameterize the transport peak in the spectral function using the second-order relativistic dissipative hydrodynamics by Israel and Stewart. Combining the spectral function and the full (3+1)-dimensional hydrodynamical evolution with the lattice EoS, theoretical dielectron spectra and the experimental data are compared. Detailed analysis suggests that the low-mass dilepton enhancement originates mainly from the high-temperature QGP phase where there is a large electric charge fluctuation as obtained from lattice QCD simulations.Comment: To appear in the conference proceedings for Quark Matter 2011, May 23 - May 28, Annecy, Franc

In vitro reactivation of spindle elongation in fission yeast nuc2 mutant cells.

To investigate the mechanisms of spindle elongation and chromosome separation in the fission yeast Schizosaccharomyces pombe, we have developed an in vitro assay using a temperature-sensitive mutant strain, nuc2. At the restrictive temperature, nuc2 cells are arrested at a metaphase-like stage with short spindles and condensed chromosomes. After permeabilization of spheroplasts of the arrested cells, spindle elongation was reactivated by addition of ATP and neurotubulin both at the restrictive and the permissive temperatures, but chromosome separation was not. This suggests that the nuc2 cells are impaired in function at a stage before sister chromatid disjunction. Spindle elongation required both ATP and exogenous tubulin and was inhibited by adenylyl imidodiphosphate (AMPPNP) or vanadate. The ends of yeast half-spindle microtubules pulse-labeled with biotinylated tubulin moved past each other during spindle elongation and a gap formed between the original half-spindles. These results suggest that the primary mechanochemical event responsible for spindle elongation is the sliding apart of antiparallel microtubules of the two half-spindles

Rapidity equilibration and longitudinal expansion at RHIC

The evolution of net-proton rapidity spectra with sqrt(s_NN) in heavy relativistic systems is proposed as an indicator for local equilibration and longitudinal expansion. In a Relativistic Diffusion Model, bell-shaped distributions in central collisions at AGS energies and double-humped nonequilibrium spectra at SPS show pronounced longitudinal collective expansion when compared to the available data. The broad midrapidity valley recently discovered at RHIC in central Au+Au collisions at sqrt(s_NN) = 200 GeV indicates rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion of the locally equilibrated subsystem. A prediction is made for Au+Au at sqrt(s_NN)= 62.4 GeV.Comment: 11 pages, 1 table, 2 figures; changes/additions in text, table, fig

The ABCs of SMC proteins: two-armed ATPases for chromosome condensation, cohesion and repair

The first draft of the human genome sequence was reported a year ago. It may be a good time to remind ourselves that the genetic information encoded in the ∼3000-Mb sequence is stored not only in the public or private databases but also in the tiny space of the cell nucleus. The total length of human genomic DNA, which resides in 23 chromosomes, reaches approximately one meter. It is by no means a simple task to fold up the long DNA molecules and package them within a cell nucleus whose diameter is only ∼10 μm. Even more striking is that the DNA molecules are faithfully duplicated and segregated into two daughter cells in an extremely limited space. Although more than 100 years have passed since Walther Flemming first described the dynamic behavior of chromosomes (or mitosis) during cell division, it remains highly mysterious how this remarkable process of chromosome segregation is achieved at a mechanistic level. From a cytological point of view, two dramatic events occur on chromosomes during mitosis. The first one is the conversion of an amorphous mass of interphase chromatin into a discrete set of rod-shaped chromosomes (chromosome condensation), which occurs from prophase to metaphase (Koshland and Strunnikov 1996; Hirano 2000). The second is the splitting of chromosomes into two halves, which takes place highly synchronously at the onset of anaphase (Dej and Orr-Weaver 2000; Nasmyth et al. 2000). As a crucial prerequisite for these events, duplicated chromosomes (sister chromatids) must be held together immediately after DNA replication in S phase and throughout G2 phase. The importance of this process (sister chromatid cohesion) has been fully appreciated only recently because the pairing of sister chromatids cannot be visualized by classical cytology before chromosomes condense in early mitosis. Recent genetic and biochemical studies have begun to shed light on the molecular mechanisms underlying cohesion, condensation, and separation of chromosomes during the mitotic cell cycle. One of the unexpected findings is that chromosome condensation and sister chromatid cohesion are regulated by distinct, yet structurally similar, protein complexes termed condensin and cohesin, respectively. At the heart of the two protein complexes lie members of a family of chromosomal ATPases, the structural maintenance of chromosomes (SMC) family. Equally intriguing, SMC proteins are found in most, if not all, bacterial and archaeal species, implicating that their fundamental contribution to chromosome dynamics started even before the acquisition of histones during evolution. The goal of this review article is to discuss the current understanding of higher-order chromosome dynamics with an emphasis on the role of SMC proteins. I start with the basic description and classification of SMC proteins and then summarize emerging information on the diverse chromosomal functions supported by SMC proteins. Finally, I discuss the mechanistic aspects of bacterial and eukaryotic SMC proteins and try to make an integrated picture of their seemingly different actions