The production ofLactobacillus brevis has been improved by changing the medium composition and the physiological conditions. The cellular concentration reaches 8.2 X 1010 cells/mL in 21 h with a fed-batch technique in MRS medium. Freeze-drying has been used as technology for drying the cells and survival rates have been improved with different additives such as glycerol, CaCO3, and skimmed-milk powder up to 70%. A model has been developed to predict the stability of freeze-dried cultures during long-term conservation. This model, based on Arrhenius equation, has been confirmed by experimental data.
相似文献Two kinds of measuring methods were described for the determination of Plutonium-241 in low level wastes in this study. Plutonium isotopes were separated and purified by highly selective UTEVA and TRU resin. LSC, alpha spectrometry, and ICP-MS were applied and compared for determination of Plutonium-241. There is a good agreement with the analytical results and also shows that the different analytical methods have high chemical recovery yields.
相似文献Magnetic isotope effects have been recently discovered in living nature. They were observed for the first time in experiments on cells enriched with various magnesium isotopes, magnetic 25Mg or non-magnetic ones. A catalytic effect of the magnetic isotope of magnesium was discovered in experiments with myosin, the most important biomolecular motor utilizing the energy of ATP to perform mechanical work. The rate of ATP hydrolysis with the magnetic 25Mg isotope is 2.0–2.5 times higher than that obtained with nonmagnetic 24Mg or 26Mg. A similar effect of the nuclear spin catalysis was experimentally observed for zinc isotopes. The rate of ATP hydrolysis in the case of magnetic 67Zn increased by 40–50% as compared to that observed experimentally for nonmagnetic isotopes (64Zn or 68Zn). Catalytic effects of the magnetic isotope of magnesium were also experimentally found for H+-ATPase isolated from yeast mitochondria and ATPase of the plasma membrane of the myometrium. The magnetic isotope effect indicates unambiguously that the chemomechanical processes involve a limiting step catalyzed by biomolecular motors, which depends on the electronic spin state, and that this step is accelerated in the presence of nuclear spin of the magnetic isotope.
相似文献A radiochemical analytical method, coupling different measurements techniques (alpha spectrometry, liquid scintillation counting and mass-spectrometry) for quantifying the content of the most significant plutonium and americium/curium isotopes in metal waste samples, is presented. The method based on the sequential determination of all the analytes of interest has the great advantage to perform the sample pre-treatment only once, resulting fast and cheap while maintaining sufficient selectivity and sensitivity. The mean values of radiochemical yields and the minimum detectable activities have been evaluated. Significant activity ratios between transuranic isotopes have been revealed and used to investigate the origin of the waste samples.
相似文献This study describes the facile synthesis of platinum nanoparticle-containing porous carbons (Pt/C) by carbonization of freeze-dried agarose gels containing potassium tetrachloroplatinate under a nitrogen atmosphere at 800 °C. By adjusting the ratio between agarose and platinate in the freeze-dried gels, the Pt content in the final Pt/C products could be systematically varied from 0–10 wt.%. Transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, X-ray photoelectron spectroscopy, Raman spectroscopy, and nitrogen physisorption measurements revealed that the Pt/C materials obtained by this method possess high surface areas (350–500 m2 g−1), narrow Pt nanoparticle size distributions (6 ± 3 nm) and nanocrystalline graphite –like carbon character. By immobilization of glucose oxidase on the surface of a 4 wt.% Pt/C electrocatalyst prepared by this route, a very sensitive amperometric glucose biosensor was obtained (response time <2 min, sensitivity 1.9 mA M−1; and a linear response with glucose concentration up to 10 mM). The simplicity and versatility of the described synthetic method suggests its application to the preparation of carbon supported noble metal catalysts including palladium/C and gold/C.
This study describes the facile synthesis of platinum nanoparticle-containing porous carbons (Pt/C) by carbonization of freeze-dried agarose gels containing potassium tetrachloroplatinate. The Pt/C materials exhibited excellent electrocatalytic activities, as demonstrated by their successful integration into amperometric glucose biosensor
The separation of zirconium and hafnium isotopes from the early actinides and rare earth elements (REE) with Eichrom’s Pb resin has been studied. Batch studies were performed to characterize the behavior of actinium, thorium, zirconium, hafnium, lutetium, and yttrium on Pb resin from HCl solutions (0.001 M to 11 M). The early actinides and REE had no affinity for the resin at any concentration of HCl, but zirconium and hafnium showed a moderate uptake at high concentrations of HCl with a maximum extraction at 11 M HCl. Several column separations were tested, including with only tracer isotopes and with mass. Rapid, simple separations of zirconium from actinium, thorium, protactinium, and the REE with high yields and low elution volumes are presented with applications for tracer isotope production and fission product separations. The resin is less suitable for hafnium separations as hafnium tends to bleed off the resin even at high concentrations of HCl.
相似文献Sargassum fusiforme, the common Chinese edible seaweeds, was investigated for total arsenic concentration by ICP-MS and for individual arsenic species by LC-ICP-MS. For this purpose, a microwave-assisted procedure was used for the extraction of arsenic species in freeze-dried seaweed and an analytical procedure for the sensitive and efficient speciation of the arsenic species As(III), dimethylarsinic acid, monomethyl arsonic acid, As(V), arsenobetaine and arsenocholine was optimized. Arsenic compounds were extracted from the seaweed with a methanol/water mixture; the extracts were evaporated to dryness, redissolved in water, and chromatographed on an anion exchange column. The arsenic species in Sargassum fusiforme are abundant. In some sample, the majority of arsenic compounds detected in the extracts were inorganic species, with a predominance of As (V). In addition, some significant amounts of unidentified arsenic compounds were also observed in the extracts.
相似文献The presented study reports on the purification of molybdenum oxide, which is one of the important tasks of the Advanced Mo based Rare process Experiment in searching for the neutrinoless double beta (0νββ) decay of 100Mo. Purified MoO3 powder is used as initial material for further growth of radiopure monocrystals. As purification technique, double sublimation, co-precipitation with calcium chloride carrier, and precipitation of polyammonium molybdate from acidic media were used. Concentrations of impurities like Sr, Ba, Pb, Th and U were measured by ICP-MS and radioactive isotopes were checked by a HPGe detector at the YangYang underground Laboratory in Korea.
相似文献The aim of this work is to present the method for sequential plutonium and americium activity determination in air filters using chromatographic radionuclide separation and alpha spectrometry measurement. The developed method may be employed for the purposes of workplace monitoring and as an indicator of the need of introducing the individual monitoring as well as a useful complementation of individual monitoring. Basic parameters describing the developed method such as values of chemical recoveries and minimum detectable activities for plutonium and americium isotopes have been determined. Applied counting efficiency was obtained using Monte Carlo calculation method.
相似文献Rapid radioanalytical methods are important in the case of a radiological emergency and for the defence against nuclear hazards, especially for pure alpha and beta emitters like 239/240Pu and 89Sr/90Sr. A new fast method was developed with an overall analysis time altogether around 11 h, for only strontium isotopes about 7 h. The method combines two extraction chromatography resins, DGA- and Sr-resin, to separate mainly strontium and plutonium. A broad variety of food samples with different fat, carbohydrate and protein contents were tested and successfully analysed. The yields obtained were typically around 95% and 70% for 90Sr and 242Pu.
相似文献Radionuclides for radiopharmaceuticals can be produced in cyclotrons or nuclear reactors. Each of these production modes has serious issues, such as high target costs, production of long-lived wastes and contaminants, expensive separation. For this reason, new methods are under consideration for the production of highly pure radionuclides. The ISOL (Isotope Separation On-Line) method is the major technique for the production of radioactive ion beams for nuclear physics applications. The SPES-ISOLPHARM project at INFN-LNL (Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Legnaro) is a feasibility study for the production of medical isotopes exploiting the ISOL method. The ongoing activities concerning a recent experiment focused on 111Ag, a study performed in collaboration with Padova and Trento Universities, is presented.
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