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1.
Poly(ether amide)s were prepared by polycondensation of 1,13‐diamino‐4,7,11‐trioxatridecane (DTT) with the bisimidazolide or with the bis N‐hydroxysuccinimide ester of sebacic acid. Four different solvents and three different temperatures were compared. The highest molecular weights were obtained with the bisimidazolide in dimethylsulfoxide (DMSO) at 60°C. MALDI‐TOF mass spectra revealed the existence of cyclic oligoamides and polyamides in all samples. The molar fraction of cycles considerably increased with higher molecular weights of the entire sample. The polycondensations were repeated under optimum conditions in the presence of α‐cyclodextrin to prepare polydisperse catenanes consisting of α‐cyclodextrin threaded on cyclic polyamides. Yet, despite broad variation of the reaction conditions, only cylic polyamides free of cyclodextrin were isolated. Furthermore, a pseudorotaxane was prepared from DTT and α‐cyclodetrin and polycondensed with bis‐(4‐chlorophenyl)sebacate. Again, only cyclic polyamides free of cyclodextrin were detectable. 相似文献
2.
3.
Ch. Rösel P. David H. Folger H. Hänscheid J. Konijn C. T. A. M. de Laat C. Petitjean H. W. Reist F. Rissel L. A. Schaller L. Schellenberg W. Schrieder L. M. Simons A. K. Sinha A. Taal 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(2):199-208
The probabilities for non-radiative (n.r.) excitationsP n.r. in the muonic nuclides208Pb,232Th, and238U have been determined from (μ?,γγ)-measurements by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The value ofP n.r. (3p→1s), measured for the first time, is about 90% for the actinides232Th and238U, but only about 8% for208Pb. The value ofP n.r. (3d→1s) is found to be 10 % for233Th, 13% for238U, and about 4% for208Pb. For208Pb a vanishing strength of the n.r. decay of the 2p-level is found, while for232Th and for238U n.r. strengths of about 20% and 26%, respectively, are observed. By regarding two subcomplexes of the 2p→1s transitions leading to different mean excitation energies the n.r. transition probabilities were found to be different for238U only, 21.6% and 31.1.%, respectively. 相似文献
4.
Frequency modulation (FM) spectroscopy is demonstrated to be an attractive tool for gain analysis. It offers the three major features: a) potential high sensitivity in absolute gain measurement, b) high spectral resolution allowing the determination of the spectral gain profile, c) high temporal resolution capable of monitoring gain in short-pulsed systems. As an example, results of a gain analysis of the 6328 å line in a He-Ne discharge are presented. 相似文献
5.
An equidistant permutation array (EPA) which we denote by A(r, λ; ν) is a ν × r array such that every row is a permutation of the integers 1, 2,…, r and such that every pair of distinct rows has precisely λ columns in common. R(r, λ) is the maximum ν such that there exists an A(r, λ; ν). In this paper we show that R(n2 + n + 2, 1) ? 2n2 + n where n is a prime power. 相似文献
6.
Jung K Richter J Kabrodt K Lücke IM Schellenberg I Herrling T 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(4):846-850
In the last decade, naturally occurring antioxidants continue to play an important role in the food-supplement industry. The content of antioxidants in a plant depends on the species, temperature, humidity, period of growth, harvest month, part of the plant used and many other variables. Herein, we present a new method able to determine the all over antioxidative power (AP) of plant extracts or lyophilised plant parts based on the reducing activity against a stable test radical. The method is performed by ESR spectroscopy and is based on the well-known 1,1-diphenyl-2-picryl-hydrazil (DPPH) method with the major difference that both the antioxidative capacity and the antioxidative activity are used to characterise an antioxidant. The resulting antioxidative power is expressed in antioxidative units (AU), where 1AU corresponds to the activity of a 1 ppm solution of Vitamin C as a benchmark. This method allows a rapid, unexpensive and general applicable technique for the measurement of the antioxidative power of very different kinds of substances. The inclusion of the kinetic behaviour of the reducing process of the antioxidant for the determination of the AP allows the identification of the main antioxidant present in a sample. Herein, we present the application example of seeds, sprouts and adult parts of dandelion, amaranth, quinoa, fenugreek, broccoli, red clover and mugwort, where the AP method permits to characterise the plants with the highest antioxidant capacity and reaction velocity. The method permits to select active plant extracts for the food and nutrition industry. 相似文献
7.
Bjorn Schellenberg 《International Journal of Mathematical Education in Science & Technology》2013,44(3):311-321
A set of axioms for classical absolute geometry is proposed that is accessible to students new to axioms. The metric axioms adopted are the ruler axiom, triangle inequality and the bisector axiom. Angle measure is derived from distance, and all properties needed to establish a consistent system are derived. In particular, the SAS congruence theorem is proved. The proofs are broken into many small steps suitable for the target audience. Some explorations with geometry drawing programmes are shown. 相似文献
8.
A. Werthmüller A. Adamczak R. Jacot‐Guillarmod F. Mulhauser L.A. Schaller L. Schellenberg H. Schneuwly Y.‐A. Thalmann S. Tresch 《Hyperfine Interactions》1998,116(1-4):1-16
The charge exchange reaction of negative muons from the
atom to oxygen has been measured in gaseous mixtures of H2 + O2. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of
, describing the transfer from the ground state of thermalized
atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the
thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate
=3.9
1011 s-1 in the energy interval 0.12–0.22 eV. The analysis with the model of Two components shows that all measured time spectra can be reproduced with the same set of parameters. 相似文献
9.
B. Gartner P. Ackerbauer M. Augsburger W.H. Breunlich M. Cargnelli D. Chatellard J.-P. Egger T. von Egidy F.J. Hartmann R. Jacot-Guillarmod E. Jeannet P. Kammel R.C. King A. Kosak B. Lauss J. Marton M. Mühlbauer F. Mulhauser C. Petitjean C. Piller W. Prymas L.A. Schaller L. Schellenberg H. Schneuwly W. Schott Y.A. Thalmann S. Tresch A. Werthmüller J. Zmeskal 《Hyperfine Interactions》1999,119(1-4):103-108
The energy and time distributions of the decay X-rays of excited, metastable, molecular (dμHe)*-resonances were measured. The comparison of the observed energy spectra with calculated ones suggests that decay from
the rotational state J = 1 dominates at the investigated conditions. The muon transfer rates from ground state deuterium to the helium isotopes
3He and 4He at low temperatures were determined from the time distributions of these spectra. Additionally, the temperature dependence
of the muon transfer rate was clearly established in deuterium / 4He mixtures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
Jürgen Schellenberg 《Journal of polymer science. Part A, Polymer chemistry》2000,38(13):2428-2439
The syndiospecific polymerization of styrene was investigated with the fluorine‐containing half‐sandwich complexes η5‐pentamethylcyclopentadienyl titanium bis(trifluoroacetate) dimer, η5‐octahydrofluorenyl titanium tristrifluoro‐acetate, η5‐octahydrofluorenyl titanium dimethoxymonotrifluoroacetate, and η5‐octahydrofluorenyl titanium tris(pentafluorobenzoate) in comparison to known chloride and methoxide complexes in the presence of relatively low amounts of methylalumoxane and triisobutylaluminum. After the selection of effective reaction conditions for a solvent‐free polymerization, the following orders of decreasing polymerization activity of the titanium complexes can be observed: for pentamethylcyclopentadienyl compounds, Cp*Ti(OMe)3 > [Cp*Ti(OCOCF3)2]2O ≈ Cp*TiCl3, and for octahydrofluorenyl compounds, [656]Ti(OMe)3 > [656]Ti(OCOC6F5)3 > [656]Ti(OCH3)2(OCOCF3) > [656]Ti (OCOCF3)3. The [656]Ti complexes, showing the highest polymerization conversions at 70 °C and in comparison with the Cp* Ti compounds, turned out to be highly efficient catalysts for the syndiospecific styrene polymerization. The fluorine‐containing Cp* and [656]Ti complexes lead to much higher molecular weights than the chloride and methoxide compounds because of a reduction in chain‐limiting transfer reactions. The introduction of only one fluorine‐containing ligand into the coordination sphere of the metal compound is obviously sufficient for a significant increase in molecular weight. The active polymerization sites of the [656]Ti complexes with methylalumoxane and triisobutylaluminum are extremely stable during storage at room temperature in regard to their polymerization activity. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2428–2439, 2000 相似文献