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1.
Sajewicz Mieczysław Hauck Heinz-E. Drabik Gabriela Namysło Ewa Głód Bronisław Kowalska Teresa 《平面色谱法杂志一现代薄层色谱法》2006,19(4):278-281
JPC – Journal of Planar Chromatography – Modern TLC - We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of... 相似文献
2.
Ranasinghe MI Varnavski OP Pawlas J Hauck SI Louie J Hartwig JF Goodson T 《Journal of the American Chemical Society》2002,124(23):6520-6521
The search for a model that can be used to describe the optical excitation migration in dendrimers has attracted great attention. In most cases in a dendrimer the conjugation is disrupted at the branching point; however, the excitation is delocalized. The strength of interactions among neighboring chromophores plays a key role in determining the energy migration mechanism. Conversely, having many identical chromophores held tightly together in an ordered macromolecular architecture will allow for many dipoles to be accessible for optical excitation. Therefore, the relative orientation of dipoles will be important in determining the mechanism of energy migration. Here we report the synthesis and photo-physical investigation of triarylamine-based dendrimers. Two important synthetic steps were utilized in the synthesis. First, we employed diphenylmethyl protective groups on the amines to assist in deprotective hydrogenolysis of the larger structures. Second, highly active catalysts for formation of both di- and triarylamines that are based on a 1:1 ratio of P(t-Bu)3 and Pd(dba)2 improved reaction yields of the C-N bond formation and decreased reaction times The energy migration processes in the dendrimers were investigated utilizing ultrafast time-resolved fluorescence anisotropy measurements. The fluorescence anisotropy of all three dendrimers decayed to a residual value within approximately 100 fs. This fluorescence anisotropy decay showed a general trend in decreasing with increasing dendrimer generation. The residual anisotropy value also showed a gradual decrease with an increase in the dendrimer generation. This fast energy depolarization is discussed through a coherent excitonic mechanism among dipoles oriented in different directions. We believe that the formation of coherent domains leads to fast energy migration extending over a large part of the dendrimer. 相似文献
3.
J. Hauck 《Journal of solid state chemistry》1981,36(1):52-65
Subsolidus phase relations of ternary oxide systems containing divalent Fe, Mg, or Ni, trivalent Al, Cr, or Fe, and tetravalent Ti are characterized by solid solutions at metal/oxygen ratios , , and . At low temperatures only compounds with cubic or hexagonal close-packed oxygen and uniform oxygen coordination remain stable in the crystal structures NaCl, spinel, ilmenite-α-Al2O3, TiO2. The pseudobrookite phases FeTi2O5, MgTi2O5, Al2TiO5, Fe2TiO5, the V3O5 structure phase Cr2TiO5, and the Andersson phases Cr2Tin?2O2n?1 (n = 4,6,7,8,9) decompose. Additional phases with close-packed oxygen as predicted by a simple structure model for metal/oxygen ratios , , and do not form but presumably are important for nonstoichiometric solid solutions. Most differences between systems containing transition metals and the MgOAl2O3TiO2 system can be attributed to crystal field effects. 相似文献
4.
G. Hauck 《Fresenius' Journal of Analytical Chemistry》1973,267(5):337-341
Zusammenfassung Es wird über den Einsatz der flammenlosen AAS bei der Bestimmung von Blei, Zink und Thallium in Blut, Urin und Gewebe berichtet. Wegen der hohen Empfindlichkeit der Methode kann auf eine Abtrennung und Anreicherung der zu bestimmenden Elemente verzichtet werden. Durch die Verwendung eines Untergrundkompensators können Fehlbestimmungen, die durch das Auftreten von Rauch beim Atomisieren bedingt sind, vermieden werden. Wenn die Proben nur wenig verdünnt werden können, muß mit dem Einfluß dritter Partner aus dem biologischen Material gerechnet werden. Dieser Einfluß kann durch Zusatz von Salpetersäure zu den Proben im Graphitrohr vermindert, aber nicht völlig aufgehoben werden. Die Leistungsfähigkeit der flammenlosen AAS wird am Beispiel der Bleibestimmung in Eierschalen und Eiinhalt wild lebender Vögel gezeigt.Herrn Lühl vom Forstzoologischen Institut der Universität Freiburg sei auch hier für die Beschaffung der Proben und Frau Engel für die Durchführung der Untersuchungen gedankt. 相似文献
5.
Summary In a manner analogous to that for surface-active silica gel, HPTLC pre-coated plates for nano TLC have also been developed
from two inactive sorbents. The two materials are microcrystalline cellulose and a synthetically produced, porous silica (Silica
50000) with a very low specific surface area. The chromatographic properties of these inert sorbents and of the new HPTLC
pre-coated plates prepared therefrom are examined in relation to separations of amino acid mixtures and carbohydrate mixtures
and are related to the chromatographic properties of the inactive sorbents and TLC precoated plates used hitherto.
The figure 50000 characterizes the type of silica. The average pore diameter of this sorbent is about 5000 nm. 相似文献
6.
Mössbauer spectra of119Sn in Sn1–z
Eu
z
Mo6S8 (z=0, 1/3, 2/3) have been measured in the temperature range 4.9 KT293 K. The spectra consist of a quadrupole doublett with unequal intensities at all temperatures. The Debye-Waller factor, the isomeric shift and the asymmetry of the intensity of the quadrupole components show irregularities between 50 K and 110 K which are interpreted as arising from a structural phase transition. The temperature dependence of the Debye-Waller factor can be approximated by a simple phonon spectrum. No quantitative explanation can be given for the large values of the asymmetry. Evidence is presented that this behavior is connected with the properties of the librational modes of the Mo6S8-units in the crystal. 相似文献
7.
The three sheet-shaped palladium organyls 1a-c exhibit lyotropic nematic properties in apolar organic solvents. The occurrence of two nematic lyomesophases was verified by the investigation of the orientational properties of these liquid crystalline systems. In cells with obliquely deposited SiOx layers, the director of the high temperature phase N2 is aligned in a homogeneous, planar manner. In the low temperature phase N1, a different orientational pattern is observed. The specific pattern type depends on the deposition conditions of the SiOx layers. In samples homeotropically aligned in the N2 phase, the director is tilted away from the cell normal after the transition into the N1 phase. These changes of orientation are reversible. The experimental observations presented here support our proposed model for the structural change at the nematic-nematic phase transition. 相似文献
8.
Jürgen Hauck 《Mathematical Logic Quarterly》1976,22(1):265-282
9.
F D Doty G Entzminger C D Hauck 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,140(1):17-31
A new class of NMR RF volume coils is being developed that permits improved tuning range, B(1) homogeneity, tuning stability, and sensitivity compared to birdcages over a wide range of practical conditions, especially for microscopy and wraparound flexible applications. They are denoted litz coils, as their flux transparency and current distribution is obtained from woven foil patterns with insulated crossovers. Contrary to the design criteria of phased arrays, the parallel routes in litz coils use high coupling coefficients to achieve optimal current distribution, which is highly independent of tuning, balancing, and matching adjustments and is compatible with multiple capacitive segmentation. Magnetic filling factors, loaded Q, and inhomogeneity measurements and calculations are presented for a variety of litz coils with frequency-diameter products from 7 to 20 MHz-m and are compared to similar birdcages. 相似文献
10.