Towards a laser neutron driver.

During the last few years, important experimental investigations have been made concerning the possibility of induced nuclear fission of high-Z elements by electromagnetic interaction (photofission, electron fission, neutron fission). Fast ions, neutrons and fission fragments from such interactions can be used to pump a laser medium, to produce energy from the (232)Th-(233)U nuclear fission cycle. The main aim of the present work is to study a three-step process, in a relatively new experimental scheme, in order to improve the number of both neutrons and fast ions. In the proposed scheme, high-energy particles and photons are produced by high-intensity laser beam interaction with a solid or gas target, which are utilized later on to trigger the nuclear reactions for the production of (photo) neutrons. These neutrons can give rise to fission of (232)Th that leads through a cascade of decays to (233)U --a highly fissionable material. Such a process will enhance, by an important factor, the final neutron flux and the energetic fission fragments. The use of a high intensity pulsed laser beam will control the turn-on and turn-off of the nuclear reactions and allow one to ensure the security of the whole operation. Finally, the produced neutrons are used to accomplish a major population inversion in an appropriate gas medium for the last stage of amplification of a high-contrast ultra-short laser seed pulse.

Arachidonic acid-induced calcium signalling in human airway smooth muscle cells.

The spatiotemporal distribution of Ca2+ signals evoked by arachidonic acid (AA) was investigated in human bronchial smooth muscle cells (SMC), using the single cell video imaging technique and Fura-2 as a fluorescent dye. Baseline Ca2+ levels were markedly heterogeneous in one and the same cell; the local Ca2 concentration laid between 90 +/- 11 and 215 +/- 18 nM (n = 15). AA (2 mM) induced propagating Ca2+ waves, travelling at a mean velocity of 18 +/- 3 microns/sec (n = 7). Ca2+ signals originated at discrete trigger zones, whose kinetic properties differed from those of neighbouring regions. Ca2+ in the trigger zones rose in two phases, with rates of 9.5 +/- 0.8 and 88 +/- 6 nM/sec (n = 17). A single cell frequently exhibited more than one trigger zones. In some cells, the wave did not reach all regions; such inert zones separated functionally the cell in independently active regions. Some regions presented Ca2+ signals that did not spread to the rest of the cell, forming isolated foci. The spatiotemporal variability of Ca2+ signals evoked by AA could result from the heterogeneity of Ca2+ homeostatic processes.

Insulin release by emiocytosis: demonstration with freeze-etching technique.

The technique of freeze-etching for electron microscopy applied to isolated islets of Langerhans has permitted a successful evaluation of emiocytotic events on the cell surface. The frequency of these events in stimulated cells suggests that emiocytosis represents a significant mechanism for insulin release.

Morphological and biochemical studies of B cells of fetal rat endocrine pancreas in organ culture. Evidence for (pro) insulin biosynthesis.

Fetal rat pancreases explanted on the 18th day of gestation and maintained in organ culture for 1-10 days were utilized for this series of studies. Ultrastructurally, at the time of explantation, the majority of fetal B cells was sparsely granulated and characterized by numerous free ribosomes and undeveloped rough endoplasmic reticulum (RER) and Golgi complexes. During the culture period, extensive development of the RER and Golgi complexes preceded an increasing accumulation of beta-granules. This later increase in the number of beta-granules and in the concentration of immunoreactive insulin was paralleled by a reduction of RER and Golgi complex activity. High resolution radioautographic studies of pulse-chase experiment over a 1 hr period demonstrated the shift of silver grains from the elements of the RER, through the Golgi region, and finally to the beta-granules. Incubation with (14)C-labeled leucine demonstrated the incorporation of radioactivity into molecules possessing the immunological and electrophoretic properties of insulin. These studies indicate that de novo synthesis of (pro)insulin occurs also during culture of fetal rat pancreas explanted relatively late in gestation.