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Dynamic light scattering experiments in acid-catalyzed silica sols are discussed. It is shown that in spite of limited parameter accuracy and limited absolute knowledge of the particle sizes, the scattering data from various experiments are comparable with one another and give information about structural differences. Measurements at various angles indicate changes between non-spherical and nearly spherical particles and allow the estimation of gelling times before gelation. 相似文献
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Luise Unger 《manuscripta mathematica》1986,57(1):1-31
Let
be the path algebra for some representation-infinite quiver
over some field k. There exists a bound
such that mI is faithful for all indecomposable injective
-modules I and all
, and such that there exists an indecomposable injective
-module J satisfying that
J is not faithful, denotes the Auslander-Reiten-translation. Let m() be the maximum of the
taken over all possible orientations of the underlying graph . In this article we determine the bounds m() for representation-infinite quivers
for which is a tree. 相似文献
6.
Organic compounds can be ionized by sputtering the solid sample. The resulting negative and positive secondary ions provide mass spectra which characterize both the molecular weights and the structures of the compounds. Ionization occurs either by direct ejection of charged species from the solid into vacuum or by electron or proton transfer. The sputtered secondary ions dissociate unimolecularly to give fragment ions. These reactions are identical to those which occur when the secondary ions are independently generated by chemical ionization, selected by mass and dissociated in a high energy gas phase collision. The negative ion SIMS spectra show molecular ions (M?.) or (M-H)? ions as the dominant high mass species together with fragments due to decarboxylation, dehydration and losses of other simple molecules. Stronger acids show larger (M-H)?/M?.abundance ratios. The positive ion spectra are complementary and also useful in characterizing molecular structures. Attachment of cations to organic molecules (cationization) occurs much more readily than anion attachment and this makes negative SIMS spectra simpler than these positive ion counterparts. 相似文献
7.
O. Böse E. Kemnitz A. Lippitz W. E. S. Unger 《Analytical and bioanalytical chemistry》1997,358(1-2):175-179
A number of partially catalytically active aluminium compounds characterised by powder XRD have been investigated by XPS and
XAES using a new method for static charge referencing [1, 2]. In detail, α-Al2O3, γ-Al2O3, boehmite γ-AlO(OH), bayerite α-Al(OH)3, hydrargillite γ-Al(OH)3, α-AlF3, β-AlF3, and AlF2.3(OH)0.7· H2O and a hexa-fluoropropylene oxide (HFPO) modified γ-Al2O3 are examined. Well defined and chemically inert 20 nm gold particles are deposited as a nearly statistical distribution on
the sample surface avoiding large coagulation effects. This procedure allows a determination of gold referenced XPS and XAES
data sets. Binding energies (BE) of Al 2p, Al 2s, O 1s and F 1s photoelectron peaks as well as kinetic energies (KE) of Al
KLL and F KLL Auger electron emission peaks are presented in relation to the Au 4f7/2 BE reference. XPS and XAES data found in literature are, in most cases, C 1s referenced and scatter in a broad range. BE
differences Δ between the C 1s charge reference BE and Au 4f7/2 charge reference BE obtained with our samples are monitored by using the Al 2p orbital. These BE differences Δ clearly suggest
that the chemical state of carbon observed in this study is not as uniform as required for reliable static charge referencing.
Received: 24 June 1996 / Revised: 12 December 1996 / Accepted: 14 December 1996 相似文献
8.
K. Unger 《Trends in analytical chemistry : TRAC》1983,2(12):271-274
High performance size exclusion chromatography (HPSEC), employing microparticulate, hydrophilic, surface-modified silicas or hydrophilic, cross-linked, organic polymers and buffered eluents, is an effective means of separating native and denatured proteins of molecular weights in the 10 000–500 000 range. HPSEC can be further used for molecular weight identification, and the fractionation and isolation of proteins. 相似文献
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