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101.
We performed multifrequency electron spin resonance (ESR) on the antiferromagnetic (TN = 160 K) and charge-ordered (T co = 250 K) insulating manganite Nd0.5Ca0.5MnO3. Temperature (4–300 K) and frequency (9.4–285 GHz) dependence of the linewidth, intensity and position of the ESR line were studied. In the paramagnetic state we observe a single Lorentzian absorption line. For a given frequency, the ESR line position is temperature independent (close tog = 1.99). A strong linewidth broadening is observed below Tco. This indicates that there is no magnetic order in the temperature rangeT cos>T >T N but strong antiferromagnetic fluctuations are present. Below TN, due to high-frequency and high-field ESR (up to 12 T) measurements, we were able to observe unexpected lines within the antiferromagnetic gap revealing the presence of a phase separation. 相似文献
102.
103.
104.
Jeffrey M. Spraggins Julie A. Lloyd Murray V. Johnston Julia Laskin Douglas P. Ridge 《Journal of the American Society for Mass Spectrometry》2009,20(9):1579-1592
The gas-phase fragmentation reactions of singly charged angiotensin II (AngII, DR+VYIHPF) and the ozonolysis products AngII+O (DR+VY*IHPF), AngII+3O (DR+VYIH*PF), and AngII+4O (DR+VY*IH*PF) were studied using SID FT-ICR mass spectrometry, RRKM modeling, and molecular dynamics. Oxidation of Tyr (AngII+O)
leads to a low-energy charge-remote selective fragmentation channel resulting in the b
4
+O fragment ion. Modification of His (AngII+3O and AngII+4O) leads to a series of new selective dissociation channels. For
AngII+3O and AngII+4O, the formation of [MH+3O]
+
−45 and [MH+3O]
+
−71 are driven by charge-remote processes while it is suggested that b
5
and [MH+3O]
+
−88 fragments are a result of charge-directed reactions. Energy-resolved SID experiments and RRKM modeling provide threshold
energies and activation entropies for the lowest energy fragmentation channel for each of the parent ions. Fragmentation of
the ozonolysis products was found to be controlled by entropic effects. Mechanisms are proposed for each of the new dissociation
pathways based on the energies and entropies of activation and parent ion conformations sampled using molecular dynamics. 相似文献
105.
106.
Karyne M. Rogers Kerry Somerton Pamela Rogers Julie Cox 《Rapid communications in mass spectrometry : RCM》2010,24(16):2370-2374
Carbon isotope analyses (δ13C) of some New Zealand Manuka honeys show that they often fail the internationally recognised Association of Official Analytical Chemists sugar test (AOAC method 998.12) which detects added C4 sugar, although these honeys are from unadulterated sources. Failure of these high value products is detrimental to the New Zealand honey industry, not only in lost export revenue, but also in brand and market reputation damage. The standard AOAC test compares the carbon isotope value of the whole honey and corresponding protein isolated from the same honey. Differences between whole honey and protein δ13C values should not be greater than +1.0‰, as it indicates the possibility of adulteration with syrups or sugars from C4 plants such as high fructose corn syrup or cane sugar. We have determined that during the standard AOAC method, pollen and other insoluble components are isolated with the flocculated protein. These non‐protein components have isotope values which are considerably different from those of the pure protein, and can shift the apparent δ13C value of protein further away from the δ13C value of the whole honey, giving a false positive result for added C4 sugar. To eliminate a false positive C4 sugar test for Manuka honey, prior removal of pollen and other insoluble material from the honey is necessary to ensure that only the pure protein is isolated. This will enable a true comparison between whole honey and protein δ13C isotopes. Furthermore, we strongly suggest this modification to the AOAC method be universally adopted for all honey C4 sugar tests. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
107.
108.
109.
We study the steady-state three-dimensional flow which occurs in a horizontal crucible of molten metal under the action of a horizontal temperature gradient. The geometry and the boundary conditions are similar to those encountered in the Bridgman growth process of semiconductor crystals. We find that three-dimensional effects can have a dramatic influence upon the flow, which, before the onset of periodic disturbances, differs appreciably from its two-dimensional counterpart. We also investigate the sensitivity of the flow to non-symmetric disturbances. 相似文献
110.
Erwann Guénin Marc Lecouvey Julie Hardouin 《Rapid communications in mass spectrometry : RCM》2009,23(9):1395-1400
1‐Hydroxymethylene‐1,1‐bisphosphonic acids (or bisphosphonates) are compounds that have interesting pharmacological applications. However, few mass spectrometric investigations have been carried out to determine their fragmentation patterns. Herein, we evaluated different matrices for the study by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) of the formation and fragmentation of the protonated, the cationized (MNa+ and MK+) and the deprotonated bisphosphonates. Some in‐source fragmentations were observed both in positive and in negative ion modes. The fragmentation patterns obtained in post‐source decay mode are also discussed. In contrast to previous electrospray ionization/multi‐stage mass spectrometry (ESI‐MSn) studies, some new fragmentation pathways were deduced and the effects of alkali ions on the fragmentation patterns were shown. The results summarized here completed the data previously recorded by ESI‐MSn and could be used for the characterization of bisphosphonates as alkali complexes in biological mixtures. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献