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31.
L.?Basit S.?A.?Nepijko I.?Shukoor V.?Ksenofontov M.?Klimenkov G.?H.?Fecher G.?Sch?nhense W.?Tremel C.?Felser 《Applied Physics A: Materials Science & Processing》2009,94(3):619-625
Nanoparticles of solid solution Fe x Pt1?x , where 0.25≥x≥0 (?fcc lattice) with γ-Fe2O3 shell (lattice of the spinel type) were synthesised and characterised by high-resolution transmission electron microscopy, energy dispersive X-ray analysis, electron energy loss spectroscopy, Mössbauer spectroscopy and magnetometry. From the point of view of magnetic properties, such two-phase particles are interesting because their core is antiferromagnetic or paramagnetic (at very small values of x) whereas the shell is ferrimagnetic. The size of the particles was in the range of several nanometers. The Mössbauer measurements revealed a blocking temperature of about 100 K above which the particles are superparamagnetic. Towards lower temperatures, the magnetic characteristics of an ensemble of such particles show an increase of magnetic rigidity. 相似文献
32.
Methyl-methine linkages of Novolac, a commercially available t-butylphenol acetylene condensed (TBPA) resin, have been identified by recognition of pyrolysis pathways using pyrolysis-gas chromatography/mass spectrometry (Py-GC/mS) in vulcanized rubber. The diagnostic mass spectrum of t-butylphenol with methyl-methine linkages between phenolic rings was observed at m/z 192, corresponding to 4-t-butyl-2-ethyl-6-methylphenol. Other molecular ions were observed at m/z 178, 164, and 150 in the characteristic pyrolyzates. The ion at m/z 192 in the TBPA resin was observed to be characteristic for methyl-methine linkages between the phenolic groups, and the analytical pyrolysis-GC/mS method was thus able to identify the resin at low levels in vulcanized rubber. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
33.
Common white sugar was ashed in a muffle furnace under controlled heating at 450 degrees C. Together with these samples, sugar with added amounts of Pb and Cd (20, 50 micro g) was mineralized in the same furnace. Depending on the absolute amount of Pb and Cd present in the furnace, an increase in the 'blank' values of the unspiked sugar samples was found. The same effect was observed when reference material containing natural amounts of Pb and Cd (TORT-1, Lobster) was present in the furnace. Although the results strongly depend on the blank levels of the muffle furnace, cross contamination effects could be demonstrated for both elements. The investigations demonstrate, that at a temperature of 450 degrees C, both Cd and Pb are lost during ashing of samples. The type of matrix in a sample with high contents of Pb and Cd has no significant effect on the volatility of these elements. The vapor lost from a sample containing high amounts of Pb and Cd will falsify the concentration in low level samples present in the furnace. 相似文献
34.
Strizhak PE Demjanchyk Fecher F Schneider FW Münster AF 《Angewandte Chemie (International ed. in English)》2000,39(24):4391
The cover picture shows the catalysis of a Diels-Alder reaction by an artificial ribozyme. A series of anthracene and maleimide derivatives are converted with high efficiency, and with suitable substituents enantioselectivites greater than 95 % ee can be achieved. Shown in the mirror is a picture of a synthetic ribozyme built from unnatural L-ribonucleotides, which, as expected, catalyzes the formation of the other enantiomer of the product. The threadlike molecules in the background symbolize the combinatorial RNA pool from which the ribozymes were originally isolated. More about the fascinating properties of these ribozymes is reported by J?schke and co-workers on page 4576 ff. (The 3D model of a folded RNA molecule was generated with the program MOLMOL from the data set 1EHT.pdb.) 相似文献
35.
36.
Seven algae samples, five purchased from food stores and two reference algae (BCR 279 Sea Lettuce) were distributed as blind
samples to 13 laboratories from which five labs attempted a full characterisation of the water-soluble fraction with respect
to their arsenic species. The extraction efficiency is largely dependant on the algae and varied from 3% to 96%. Besides inorganic
arsenic (mainly as As(V)) DMA(V) and, in particular, several arsenosugars were identified in all samples. From the five labs, three labs gave agreeable results
in respect of the arsenic species identification and its quantification, although different chromatographic methods were used.
Different Hijiki samples seem to contain largely different arsenic concentration (67–113 mg As/kg) which may also have an
influence on the distribution of inorganic arsenic and arsenosugars. 相似文献
37.
38.
Pb particles on a Si(111) substrate were investigated using a photoemission electron microscope (PEEM). The electrons have been excited by a linearly polarised femtosecond laser beam with a wavelength of λ = 400 nm. The PEEM images exhibit an unusually high contrast. They arise due to photoemission being of a nontrivial nature because the photon energy is lower than the work function of the sample. It may be caused by the following processes: two‐ or multi‐photon absorption, tunnel‐photoeffect induced by a strong lowering of the potential barrier owing to enhancement of the electrical field of the powerful incident light wave on a rough surface, generation of second harmonic with its following absorption, or electron gas heating. Images obtained with orthogonal directions of the photon polarisation were compared to estimate the shape of different Pb particles. The size of the islands was determined by two methods, either from the shape of the spatial brightness distribution or from the area under the curve of this distribution. 相似文献
39.
G. H. Fecher J. Braun N. A. Cherepkov L. V. Chernysheva Th. Jentzsch J. Morais A. Oelsner Ch. Ostertag J. Paul H. Ufer G. Schönhense 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(1):161-175
We present investigations of the electronic and magnetic structure of the Rare Earth valence states. In particular, we have
examined ultra thin films of the rare earth metals gadolinium and neodymium epitaxially grown on tungsten (110). Various experiments on dichroism in
angular resolved photoemission have been performed using circularly as well as linearly polarised light in the VUV-range with
photon energies below 40 eV. A special emphasis was placed on the investigation of the surface state, which was observed for both Gd and Nd. A
very small magnetic splitting of about 25 meV was observed for the surface state of ferromagnetic Gd. A magnetic ordering
of a Nd-monolayer on a remanently magnetised Fe-film is observed. Large dichroism effects are found for the surface state
as well as the valence bands of paramagnetic Nd. In the latter case, these are used to determine the dispersion of the valence
bands. Different numerical approaches are presented, one based on atomic photoionisation theory, another is based on a one-step
model of solid state photoemission. Atomic photoionisation theory is used together with three-step calculations to explain
the non-magnetic circular dichroism observed in the Gd 4f emission. The capability of dichroism experiments for resolving details of the electronic structure and for sensitive tests
of photoemission calculations is demonstrated.
Received 21 September 1998 相似文献
40.