Source experiment

Most Mossbauer experiments are currently performed with commercially available radioactive sources. For some applications, however, a so-called source experiment may be useful, in which the sample is labeled with the radioactive parent-isotope of the Mossbauer nucleus such as Co. The y-radiation of the radioactive sample is then analyzed by moving a single-line absorber for Doppler modulation in front of the detector. 

Salomon and Shirley [296] have performed Mossbauer-source experiments on Fe( Os) alloys with less than 0.1 at% osmium against a metallic Ir absorber. Their spectra were well-resolved magnetic eight-line patterns, which the authors could satisfactorily analyze using the Hamiltonian... 

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

Figure 1.3. Phagocytosis of Staphylococcus aureus by a human neutrophil. Neutrophils were incubated with opsonised S. aureus and fixed after 15 min incubation. The bacterium in the centre has been lysed, and only the cell wall remains. Source Experiment of Bernard Davies and John Humphreys, reproduced with permission from Colour Atlas of Paediatric Infectious Diseases, by Hart and Broadhead (Mosby Year Book Europe).

Figure 6.20. Role of phospholipase D in NADPH oxidase activation. In (a) neimophils were preincubated with [3H]-alkyl-lyso-PAF (5 /iCi/ml) for 60 nun at 37 C. The cells were then washed twice with RPMI 1640 medium and finally resuspended at 2 x 10 cells/ ml in the presence ( ) and absence ( ) of 100 mM ethanol. The cells were then stimulated with 1 pM fMet-Leu-Phe and, at time intervals,aliquots were removed for analysis ofphos-phatidic acid ( ) and phosphatidylethanol ( ) by thin layer chromatography (TLC). In (b), neutrophils were incubated in the presence and absence of 10 mM butanol, and luminol chemiluminescence (10 jUM, final concentration of luminol) was measured after stimulation by 1 jUM fMet-Leu-Phe. Source Experiment of Gordon Lowe and Fiona Watson.

Figure 6.21. Role of phospholipase D in receptor up-regulation. Neutrophils were incubated in the presence or absence of fMet-Leu-Phe and butanol for 15 min prior to analysis of expression of CDllb by FACS analysis. In (a), neutrophils were not stimulated and suspensions did not contain butanol. In (b), suspensions did not contain butanol, but were stimulated with fMet-Leu-Phe. The hatched lines show the receptor expression of suspensions incubated with 10, 20 and 30 mM butanol for 5 min prior to stimulation by fMet-Leu-Phe. Source Experiment of Fiona Watson.

Figure 7.1. Effect of GM-CSF on neutrophil protein biosynthesis. Human neutrophils were incubated in RPMI1640 medium supplemented with 2.5% foetal calf serum and 60 jtCi/ml [35S]-methionine, in the presence and absence of 50 U/ml GM-CSF. After 4 h incubation at 37 °C, the cells were pelleted by low-speed centrifugation. The proteins in the cell pellets were precipitated by 10% trichloracetic acid and then analysed by two-dimensional polyacrylamide gel electrophoresis, using iso-electrofocussing in the first dimension. Electrophoresis in the second dimension was performed in the presence of SDS and used a 12% acrylamide gel. Source Experiment of Becky Stringer.

Figure 7.10. IL-l/J expression by GM-CSF-stimulated neutrophils. Human neutrophils were incubated in the absence (-) and presence (+) of 50 U/ml GM-CSF, and at time intervals total RNA was extracted. After electrophoresis on formamide-containing gels, IL-1/3 mRNA levels were probed. Source Experiment of Julie Quayle.

Obviously, the various electronically excited states of an atomic or molecular ion vary in their respective radiative lifetime, t. The probability distribution applicable to formation of such states is thus a function of the time that elapses following ionization. Ions in metastable states, which have no allowed transitions to the ground state, are most likely to contribute to ion-neutral interactions observed under any experimental conditions since these states have the longest lifetimes. In addition, the experimental time scale of a particular experiment may favor some states over others. In single-source experiments, short-lived excited states may be of greater relative importance than in ion-beam experiments, in which there is typically a time interval of a few microseconds between ion formation and the collision of that ion with a neutral species, so that most of the short-lived states will have decayed before collision. There are several recent compilations of lifetimes of excited ionic states.lh,20 ,2,... 

Due to effects caused by the nuclear decay in the sample, these so-called source experiments may be difficult to perform and interpret. Several papers dealing with these effects can be found (23). In principle, however, the applicability of Mossbauer spectroscopy to catalytic studies can be extended to include both the Mossbauer isotopes and the corresponding parent nuclides. We therefore list below the Mossbauer isotopes and corresponding parent nuclides that may be of greatest use in catalytic studies, as deduced from their nuclear properties. 

Ultrasounds can be applied to chemical systems by using ultrasonic baths or probes. Although baths are more widely used, probes are more efficient as a result of (a) the lack of uniformity in the transmission of ultrasounds (in baths, only a small fraction of the total liquid volume in the immediate vicinity of the ultrasound source experiences the effects of cavitation) and (b) the decline in power with time, which leads to exhaustion of the energy applied to baths. Both phenomena result in substantially decreased experimental repeatability and reproducibility. For this reason, the use of baths should be restricted to cleaning operations and removal of dissolved gases, their intended applications. A wide variety of commercially available ultrasonic baths exists ranging from laboratory to industrial-scale models. 

Materials selection for corrosion resistance is as reliable as the information upon which it is based. Corrosion information derives from two sources— experience or test results. 

The reactor source experiment is extremely wasteful as most of the neutrons are discarded at the monochromation stage. Spallation sources use all the neutrons produced after the moderation stage, but the neutrons are first produced in a slightly different way. 

Potential therapeutic uses for (- )-swainsonine have led to several studies aimed at optimizing the yield of the alkaloid from natural sources. Experiments with root cultures of Swainsona galegifolia transformed with Agrobacterium rhizogenes produced higher levels of the alkaloid than untransfoimed cultures and responded favorably to various stimuli (pH, addition of copper sulfate, supplementation with malonic and pipecolic acids), but still did not produce the... 

Mahlman, J.D., and W.J. Moxim, Tracer simulation using a global general circulation model Results from a mid-latitude instantaneous source experiment. J Atmos Sci ... 

Fiber source Experiment 1 y moles/50 mg Experiment 2 y moles/lOO mg... 

We believe that our CPS differs advantageously from the thermoelectric CPS available in Russian and world markets with the electrical output of 12-160 W (for example, of the GT-G-10-12 / 30-12 / 160-12 and other types fabricated in Russia by the company Pravdinsky current sources experiment plant - POZIT) and of 15 to 550 W (for example, like 5015 / 5030 / 5060 / 5120 / 5220 / and 8550-24 models fabricated in Canada by the company Global Thermoelectric ). 

Although single-source experiments are not satisfactory for determining rate constants as a function of time, it is quite obvious from the above-mentioned study that the reaction rate constant will vary with the energy of collision in the source and that, as a consequence, the only meaningful statement that can be made about a rate constant determined with continuous ion extraction must include a statement of the terminal energy. Many investigators now do express reaction rate constants in this form. 

In other studies of reaction (29), Curran reported that charge transfer occurred in an ion source experiment with Cl formed by dissociative attachment in CCI4 and concluded that A(N02) EA(C ) = 3.613 eV. However, Ferguson et a/. - were unable to observe reaction (29) in the flowing afterglow with A" = Cl and F. 

The N2O ion was first observed in an ion source experiment and ascribed to charge transfer between O and N2O. More recent work has shown that the N2O is instead produced by collisions of NO with... 

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