13 research outputs found
Cytogenotoxicity potentials of cocoa pod and bean-mediated green synthesized silver nanoparticles on Allium cepa
MCM2-7 Form Double Hexamers at Licensed Origins in Xenopus Egg Extract
In late mitosis and G1, Mcm2-7 are assembled onto replication origins to license them for initiation in the upcoming S phase. After initiation, Mcm2-7 provide helicase activity to unwind DNA at the replication fork. Here we examine the structure of Mcm2-7 on chromatin in Xenopus egg extracts. We show that prior to replication initiation, Mcm2-7 is present at licensed replication origins in a complex with a molecular mass close to double that of the Mcm2-7 hexamer. This complex has approximately stoichiometric quantities of the 6 Mcm2-7 proteins and we conclude that it consists of a double heterohexamer. This provides a configuration potentially capable of initiating a pair of bidirectional replication forks in S phase. We also show that after initiation, Mcm2-7 associate with Cdc45 and GINS to form a relatively stable CMG (Cdc45-MCM-GINS) complex. The CMG proteins also associate less strongly with other replication proteins, consistent with the idea that a single CMG complex forms the core of the replisome
Shell effects in Fusion-Fission of heavy and superheavy nuclei
The process of fusion-fission of heavy and superheavy nuclei (SHE) with Z=82 12122 formed in the reactions with 48Ca and 58Fe ions at energies near and below the Coulomb barrier has been studied. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR) and at the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL) using the time-of-flight spectrometer of fission fragments CORSET and the neutron multi-detector DEMON. As a result of the experiments, mass and energy distributions (MED) of fission fragments, fission, quasi-fission and evaporation residues cross sections, multiplicities of neutrons and \u3b3 quanta and their dependence on the mechanism of formation and decay of compound systems have been studied
The peculiarities of the production and decay of superheavy nuclei
The interest in the study of the fission process of superheavy nuclei mainly deals with the opportunity to obtain information about the crossâsection of the compound nucleus (CN) formation at excitation energies Eââ15â30 MeV. It allows one to estimate the survival probability of the superheavy composite system after evaporation of 1â3 neutrons, i.e. in âcoldâ or âwarmâ fusion reactions. However, in order to solve this problem deeper understanding of the coalescence processes between colliding nuclei, the competition between fusionâfission and quasiâfission processes is needed. The characteristics of both processes, their manifestation in the experimental observables and the relative contribution to the capture crossâsection in dependence on the excitation energies, reaction entrance channel etc were investigated for a wide range of targetâprojectile combinations. Results of the experiments devoted to the study of the fusionâfission and quasiâfission processes in the reactions of the formation of the superheavy nuclei with Z = 102â122 are presented. The heavy ions 26Mg, 48Ca, 50Ti, 58Fe and 64Ni were used as projectiles. The choice of the reactions with 48Ca and actinideâtargets was inspired by the experiments on the production of the isotopes 283112, 289114 and 283116 in Dubna using the same reactions. The 50Ti, 58Fe and 64Ni projectiles were chosen since the corresponding projectileâtarget combinations lead to the synthesis of even heavier elements. The experiments were carried out at the Uâ400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia) and the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) using the timeâofâflight spectrometer of fission fragments CORSET. The role of the shell effects, the influence of the entrance channel asymmetry and the deformations of colliding nuclei on the mechanism of the fusionâfission and the competitive process of quasiâfission are discussed. The recent results on synthesis of superheavy nuclei and the perspectives of the âhotâ fusion reaction for the production of superheavy nuclei are considered
Shell effects in fission and quasi-fission of heavy and superheavy nuclei
Results of the experiments aimed at the study of fission and quasi-fission processes in the reactions 12C+204Pb,48Ca+144,154Sm,168Er,208Pb,244Pu,248Cm;58Fe+208Pb,244Pu,248Cm, and64Ni+186W,242Pu are presented in the work. The choice of the above-mentioned reactions was inspired by recent experiments on the production of the isotopes283112,289114 and283116 at Dubna [1],[2] using the same reactions. The58Fe and64Ni projectiles were chosen since the corresponding projectile-target combinations lead to the synthesis of even heavier elements. The experiments were carried out at the U-400 accelerator of the Flerov Laboratory of Nuclear Reactions (JINR, Russia), the XTU Tandem accelerator of the National Laboratory of Legnaro (LNL, Italy) and the Accelerator of the Laboratory of University of Jyvaskyla (JYFL, Finland) using the time-of-flight spectrometer of fission fragments CORSET[3] and the neutron multi-detector DEMON[4],[5]. The role of shell effects and the influence of the entrance channel on the mechanism of the compound nucleus fusion-fission and the competitive process of quasi-fission are discussed