Relativistic electron generation in interactions of a 30 TW laser pulse with a thin foil target.

Energy and angular distributions of the fast outgoing electron beam induced by the interaction of a 1 J, 30 fs, 2 x 10(19) W/cm(2), 10 Hz laser with a thin foil target are characterized by electron energy spectroscopy and photonuclear reactions. We have investigated the effect of the target thickness and the intensity contrast ratio level on the electron production. Using a 6-microm polyethylene target, up to 4 x 10(8) electrons with energies between 5 and 60 MeV were produced per laser pulse and converted to gamma rays by bremsstrahlung in a Ta secondary target. The rates of photofission of U as well as photonuclear reactions in Cu, Au, and C samples have been measured. In optimal focusing conditions, about 0.06% of the laser energy has been converted to outgoing electrons with energies above 5 MeV. Such electrons leave the target in the laser direction with an opening angle of 2.5 degrees.

White adipose tissue fatty acids of Alpine marmots during their yearly cycle.

Alpine marmots (Marmota marmota) were maintained on a laboratory diet, and the fatty acid composition of gonadal and subcutaneous white adipose tissues (WAT) was studied during a yearly cycle. Fatty acids (FA) released from isolated adipocytes were also identified after stimulation of in vitro lipolysis. Analysis of the FA composition of WAT depots showed that marmot WAT mainly contained monounsaturated FA (65%, mostly oleic acid, 18:1n-9) although laboratory food contained 45% of linoleic acid (18:2n-6) and only 21% of 18:1n-9. During stimulated lipolysis, saturated FA were preferentially released from isolated adipocytes whereas unsaturated FAs were retained. Despite this selective release of FA from isolated WAT cells in vitro, and despite the FA composition of the food, marmots maintained a constant FA composition in both WAT depots throughout the year. Six months of hibernation and fasting as well as an intense feeding period did not affect this composition. The potential adaptive benefit of such regulation of WAT composition, based on a high level of monounsaturated FA, might be to maintain fat with appropriate physical properties allowing animals to accommodate to and survive the wide range of body temperatures experienced during hibernation.

Regional variation of white adipocyte lipolysis during the annual cycle of the alpine marmot.

During winter, hibernating animals rely on their lipid stores for survival. In vitro lipolytic activity of isolated adipocytes from gonadal and subcutaneous white adipose tissue (WAT) was studied in captive alpine marmots (Marmota marmota) at two different times of their yearly cycle. During the summer, when marmots were eating, adipocyte responsiveness and sensitivity to isoprenaline and noradrenaline were higher in gonadal than in subcutaneous WAT. During hibernation, when marmots were spontaneously fasting. both the response and sensitivity to catecholamines decreased in gonadal WAT to the level of subcutaneous WAT. A similar pattern of response was also observed when lipolysis was stimulated with glucagon but the lipolytic rate was three times lower than with catecholamines. Adenosine deaminase (ADA) had a marked stimulatory effect on lipolysis, especially during the 'feeding' period, suggesting that adenosine may be a potent lipolytic modulator in marmot adipocytes. It is concluded that in marmots, lipolysis could be differentially regulated between fat depots during the annual cycle possibly to optimize either the building-up or the use of fat reserves.

Environmental impact of diuron transformation: a review.

Diuron is a biologically active pollutant present in soil, water and sediments. A synthesis of literature data on its physicochemical properties, partitioning behaviour, abiotic and biotic transformations, toxicological and ecotoxicological impacts has been here performed. Data have shown that diuron is generally persistent in soil, water and groundwater. It is also slightly toxic to mammals and birds as well as moderately toxic to aquatic invertebrates. However, its principal product of biodegradation, 3,4-dichloroaniline exhibits a higher toxicity and is also persistent in soil, water and groundwater. Thus, diuron indirectly possesses a significant amount of toxicity and could be a potential poisoning pesticide contaminant of groundwater. Unfortunately, groundwater contamination will still persist despite the progressive suppression of diuron (Directive 200/60/CE). Therefore, determining the main factors influencing its degradation and its ecotoxicological effects on the environment and health could provide a basis for further development of bioremediation processes.

Ice crystallization by Pseudomonas syringae.

Several bacterial species can serve as biological ice nuclei. The best characterized of these is Pseudomonas syringae, a widely distributed bacterial epiphyte of plants. These biological ice nuclei find various applications in different fields, but an optimized production method was required in order to obtain the highly active cells which may be exploited as ice nucleators. The results presented here show that P. syringae cells reduce supercooling of liquid or solid media and enhance ice crystal formation at sub-zero temperatures, thus leading to a remarkable control of the crystallization phenomenon and a potential for energy savings. Our discussion focuses on recent and future applications of these ice nucleators in freezing operations, spray-ice technology and biotechnological processes.

Effect of water activity on production of beta-lactam antibiotics by Streptomyces clavuligerus in submerged culture.

The amount of available water in the environment of micro-organisms, defined as water activity (aw), has been shown to affect growth, respiration, enzyme synthesis, sporulation and other physiological functions. The aim of this study was to examine the impact of aw on production/excretion of a secondary metabolite. For this purpose, the production of beta-lactam antibiotics and biomass of Streptomyces clavuligerus was studied in relation to the aw-depressing agents glucose, sorbitol and NaCl. These were chosen because NaCl and sorbitol are often used to depress aw and glucose was not thought to be taken up by S. clavuligerus. The filamentous bacterium S. clavuligerus NRRL 3585 (ATCC 27064) is a prokaryotic producer of penicillin N, cephalosporins including cephamycin C and clavulanic acid. Under water stress conditions, a greater effect upon antibiotic biosynthesis than upon growth was consistently observed. When aw was decreased to below 0.997, antibiotic production began to decrease. For growth, inhibition was much more gradual and did not become intensive until an aw of 0.990 was reached.