The 4-dimensional Langevin approach to low energy nuclear fission

We applied the four-dimensional Langevin approach to the description of fission of 235U by neutrons and calculated the dependence of the excitation energy of fission fragments on their mass number. For this we have fitted the compact just-before-scission configuration obtained by the Langevin calculations by the two separated fragments and calculated the intrinsic excitation and the deformation energy of each fragment accurately taking into account the shell and pairing effects and their dependence on the temperature and mass of the fragments. For the sharing of energy between the fission fragments we have used the simplest and most reliable assumption - the temperature of each fragment immediately after the neck rupture is the same as the temperature of mother nucleus just before scission. The calculated excitation energy of fission fragments clearly demonstrates the saw-tooth structure in the dependence on fragment mass number.

Fermi-motion effect on the intermediate energy nucleus–nucleus collision

The Glauber model is modified with the Fermi-motion effect in the calculation of elastic differential cross-sections and momentum distributions of a fragment from mother nucleus. Different reaction systems at low energies are calculated with the modified Glauber model. It is found that calculations including the Fermi-motion provide a better prescription relating the model to a proper nuclear density distribution by comparing with the experimental data. On the basis of the studies, the influence of the correction on the extracted nuclear radius is quantified. The results further confirm the importance of the Fermi-motion in the nucleus–nucleus collision reactions at low energies.

Inheritance of yeast nuclear pore complexes requires the Nsp1p subcomplex

In the yeast Saccharomyces cerevisiae, organelles and macromolecular complexes are delivered from the mother to the emerging daughter during cell division, thereby ensuring progeny viability. Here, we have shown that during mitosis nuclear pore complexes (NPCs) in the mother nucleus are actively delivered through the bud neck and into the daughter cell concomitantly with the nuclear envelope. Furthermore, we show that NPC movement into the daughter cell requires members of an NPC subcomplex containing Nsp1p and its interacting partners. NPCs lacking these nucleoporins (Nups) were blocked from entry into the daughter by a putative barrier at the bud neck. This selection process could be observed within individual cells such that NPCs containing Nup82p (an Nsp1p-interacting Nup) were transferred to the daughter cells while functionally compromised NPCs lacking Nup82p were retained in the mother. This mechanism is proposed to facilitate the inheritance of functional NPCs by daughter cells.

ANGULAR MOMENTA OF NEAR-SPHERICAL FISSION FRAGMENTS

Angular momenta of fission fragments are sometimes exceeding 10 ℏ for thermal neutron induced and spontaneous fission. This is surprising since in the latter case the mother nucleus may have zero spin (e.g. 252Cf). In theory fragment spins are explained as a quantum mechanical effect. It is argued that they are due to zero-point oscillations of fragments being deformed at scission. In contrast to current theory it is shown that, for the specific case of near-magic 132Te, a large spin is generated by thermal excitation of single-particle states.

Copy number and partition of the Saccharomyces cerevisiae 2 micron plasmid controlled by transcription regulators.

The 2 micron plasmid of Saccharomyces cerevisiae is maintained by the action of plasmid-encoded gene products that control copy number and promote equipartition of plasmid copies at cell division. We show that the REP1 and REP2 plasmid-encoded gene products are master regulators that act in concert to autoregulate the level of their own transcripts and to regulate transcript levels of the FLP gene that promotes plasmid copy amplification. REP1 and REP2 are also shown to repress transcription at REP3, the cis-acting site essential for plasmid equipartitioning. We propose a model in which REP3 acts by dislodging transcription apparatuses that otherwise cause plasmid molecules to adhere to the mother nucleus and segregate asymmetrically. On the basis of their ability to generate specific chromatin structures, we also propose that the REP1 and REP2 gene products interact with different specific sequences found iterated in the 2 micron plasmid.

Copy number and partition of the Saccharomyces cerevisiae 2 micron plasmid controlled by transcription regulators

The 2 micron plasmid of Saccharomyces cerevisiae is maintained by the action of plasmid-encoded gene products that control copy number and promote equipartition of plasmid copies at cell division. We show that the REP1 and REP2 plasmid-encoded gene products are master regulators that act in concert to autoregulate the level of their own transcripts and to regulate transcript levels of the FLP gene that promotes plasmid copy amplification. REP1 and REP2 are also shown to repress transcription at REP3, the cis-acting site essential for plasmid equipartitioning. We propose a model in which REP3 acts by dislodging transcription apparatuses that otherwise cause plasmid molecules to adhere to the mother nucleus and segregate asymmetrically. On the basis of their ability to generate specific chromatin structures, we also propose that the REP1 and REP2 gene products interact with different specific sequences found iterated in the 2 micron plasmid.

VESSEL MEMBERS IN THE STEM OF DIOSCOREA ALATA L.

The internodal and nodal vessel elements and certain aspects of their ontogeny in the stem of Dioscorea alata L., the common cultivated yam of Gujarat State, India, are described. The internodal vessel elements are unusually long with foraminate, scalariform, reticulate, or rarely simple perforation plates. The nodal vessel elements are comparatively short with two to five perforation plates. They generally differ from internodal vessel elements in characters such as (i) size and shape and (ii) nature, number, inclination, and distribution of perforation plates. The ontogenetic study of the vessel element revealed that the coenocytic condition is a result of frequent mitotic divisions of the mother nucleus. The formation of the perforation plate occurs after the vessel element has reached final length. The protoplast persists after the formation of the perforation plate. In D. alata the cell wall in the region of the perforation shows primordial pits.