States in 65Cu from the 65Cu(p,p′γ) reaction

Previous measurements by two authors of K-capture to positon emission ratios in the high-Z region are inconsistent. The nuclide ¹⁴⁰Pr was remeasured for the following reasons. Firstly, to remove the ambiguity in the above data and secondly, to reduce the uncertainty in the result by a careful choice of source material and detector system. An important advantage in the choice of ¹⁴⁰Pr is that the theoretical ratio is known with great accuracy (≈ 1 %). The result obtained agrees with one of the authors and shows that the experimental and theoretical ratios differ by ≈ 15 %.     

The ratio of K-capture to positon emission in the decay of P

The ratio of K-capture to positon emission in the 2.5 min decay of ³⁰P has been measured by a proportional counter-flow technique. The experimental value of the K/β⁺ was found to be (1.24 ± 0.04) × 10⁻³ in agreement with the conventional theoretical ratio i.e. apparently supporting the view that exchange and overlap effects are small.     

Studies onSaccharomyces cerevisiae arrying the plasmid pCYG4 related with ammonia assimilation

Batch culture experiments of three different strains ofSaccharomyces cerevisiae have been carried out. The first strain was transformed by a plasmid pCYG4, which carries the glutamate dehydrogenase (NADP-GDH, E.C. 1.4.14) gene conferring an 11-fold increase in activity. The second was transformed by the same plasmid, but without NADP-GDH, and the third was the wild type. The specific growth rates of the two recombinant DNA strains were below that of the wild type, which can be related to extra plasmid protein production.     

Uptake of ammonia by saccharomyces cerevisiae carrying the plasmid pCYG4 related with ammonia assimilation

Batch culture experiments involving ammonia uptake in Saccharomyces cerevisiae BC55 pCYG4 have been carried out. This strain carries the plasmid pCYG4 that directs substantial overproduction of NADP-GDH, conferring an 11-fold increase in activity. The wild type cells had a specific growth rate greater than BC55 pCYG4. The ammonia uptake was practically the same until 15 h of growth. However, the amount of ammonia hydroxide added during growth (60 h) was two and half times greater in the BC55 pCYG4 than wild type cells. The results suggest that the presence of the plasmid pCYG4 can increase the amount of ammonia taken by the cells, but not the amount of biomass.     

Lipase from a Brazilian strain ofPenicillium citrinum

A lipases (glycerol ester hydrolases E. C. 3.1.1.3) from a brazilian strain ofPenicillium citrinum has been investigated. When the microorganism was cultured in the simple medium (1.0% olive oil and 0.5% yeast extract), using olive oil in as carbon source in the inocula, the enzyme extracted showed maximum activity (409 IU/mL). In addition, decrease of yeast extract concentration also reduces the lipase activity. Nevertheless, when yeast extract was replaced by ammonium sulfate, no activity was detected. Purification by precipitation with ammonium sulfate showed best activity in the 40–60% fraction. The optimum temperature for enzyme activity was found in the range of 34–37°C. However, after 30 min at 60°C, the enzyme was completely inactivated. The enzyme showed optimum at pH 8.0. The dried concentrated fraction (after dialysis and lyophilization) maintained its lipase activity at room temperature (28°C) for 8 mo. This result in lipase stability suggests an application of lipases fromP. citrinum in detergents and other products that require a high stability at room temperature.     

Ammonia assimilation inS. cerevisiae under chemostatic growth

Glutamate, glutamine, and ammonia pool size have been determined in twoS. cerevisiae strains (GOGAT⁺ and GOGAT^-) growing under ammonia excess and limitation at a dilution rate of 0.10/h. The biomass levels and glutamate dehydrogenase NADPH-dependent (NADPH-GDH) activities were also measured for both strains. The strain that lacks GOGAT activity showed lower levels of metabolites under both media and lower levels of biomass under carbon limitation (ammonia excess) compared to the GOGAT⁺ strain. Under nitrogen limitation, the biomass level was the same for both strains, but GOGAT^- changed from rounded to ellipsoidal cells.     

Photonuclear physics when a multiterawatt laser pulse interacts with solid targets

When a laser pulse of intensity 10(19) W cm(-2) interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional gamma-ray beam that can be used to carry out photonuclear reactions. The isotopes 11C, 38K, (62,64)Cu, 63Zn, 106Ag, 140Pr, and 180Ta have been produced by (gamma,n) reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in 238U has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the 11C and the 62Cu beta(+) activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of approximately 10(19) W cm(-2).     

Observations and analysis of resonant laser ablation of GaAs

Laser ablation of solid GaAs samples has been studied using one tunable pulsed dye laser. At relatively low laser power, enhancements of up to several hundred times have been observed in the yield of resonantly ionised Ga using laser wavelengths corresponding to the atomic transition 4² P _1/2-4² D _3/2. The influences of laser power and target geometry, on the ion yield and spectral profile, are discussed. It is argued that the resonant excitation and ionisation processes occur in the gas phase of the atoms ablated from the sample surface, and the observed asymmetric spectral profile results from laser-induced collisional processes, e.g., optical collisions, under conditions of relatively high atomic density in the interaction region. Potential applications are foreseen for resonant laser ablation in trace analysis.     

High-intensity-laser-driven Z pinches

Experiments were performed in which ultrahigh intensity laser pulses (I>5 x 10(19) W cm(-2)) were used to irradiate thin wire targets. It was observed that such interactions generate a large number of relativistic electrons which escape the target and induce multimega ampere return currents within the wire. MHD instabilities can subsequently be observed in the pinching plasma along with field emission of electrons from nearby objects. Coherent optical transition radiation from adjacent objects was also observed.