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81.
Dr. Richard Koch 《Monatshefte für Mathematik》1977,83(2):133-146
Let ={e(u)|uI} be a one-parameter family of straight lines forming a ruledC
r-2-surface E
n (n2,r1) without singular generatorse(u) (uI). As a synopsis, a generalization and an improvement of various results already known about the strictional properties of ruled surfaces E
n (especially in the casen=3) the author demonstrates a uniform geometrical way of defining and uniquely obtaining thestriction point S(u) and theparameter of distribution d(u) of a generatore(u) under the minimal assumptions thate(u)E
n
(n2) be noncylindrical andr1. Other methods of obtainingS(u) andd(u) are discussed in comparison, and special strictional properties ofskew ruled surfaces E
n are proved.
Herrn Prof. Dr. H. R. Müller zum 65. Geburtstag 相似文献
Herrn Prof. Dr. H. R. Müller zum 65. Geburtstag 相似文献
82.
Thomas Koch Franz R. Kogler Ulrich Schubert Sabine Seidler 《Monatshefte für Chemie / Chemical Monthly》2007,19(2):293-299
The mechanical properties of hybrid materials consisting of polystyrene (PS), which was cross-linked with different proportions of the multifunctional cluster Zr6O4(OH)4(methacrylate)12 (Zr6) were investigated. With the help of (micro)indentation and scratch testing, the influence of the Zr6 clusters on mechanical properties, such as hardness, stiffness, creep, craze initiation, and scratch resistance was shown.
There was only a slight increase in hardness and in indentation modulus with higher cluster loadings. While this observation
was in agreement with the compression behaviour of the materials, the tensile properties showed a much stronger dependence
on the Zr6 content. With increasing cluster loading, an increase of craze initiation stress, as determined by ball indentation experiments,
was found. Performing scratch testing with constant load, a reduction of pile-up and a stronger recovery were observed for
the hybrid materials compared to the neat PS. Scratch tests with a constant increase of load showed an increase of the critical load for crack opening during scratching. 相似文献
83.
Elemental I(2) and Br(2) cleanly react with the 3:3 Pt(ii) metallamacrocycle of 3,3,3',3'-tetra(n-butyl)-1,1'-terephthaloylbis(thiourea)(cis-[Pt(II)(3)(L(p)(1)-S,O)(3)]3), in chloroform at room temperature, to yield oxidative addition products; (195)Pt NMR studies reveal that a stepwise oxidative addition readily occurs to each of the Pt(ii) centres in the metallamacrocycle to yield the mixed valence species cis-[Pt(II)(2)Pt(IV)I(2)(L(p)(1)-S,O)(3)] and cis-[Pt(II)Pt(IV)(2)I(4)(L(p)(1)-S,O)(3)], and the fully oxidised cis-[Pt(IV)(3)I(6)(L(p)(1)-S,O)(3)] in solution, depending on the mole ratio I(2):3. Similar results are obtained on treatment of solutions of 3 with elemental Br(2). Treatment of the corresponding 2:2 Pt(ii) complex of 3,3,3',3'-tetraethyl-1,1'-isophthaloylbis(thiourea)(cis-[Pt(II)(2)(L(m)(1)-S,O)(2)]4) with iodine, results in facile oxidative addition to yield cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)I(4)], with a trans-Pt(iv)-iodo arrangement. Molecules in the crystal structure of 5 have their trans-Pt(iv)-iodo axes essentially aligned, with very close intermolecular iodide contacts (3.775(1)A), resulting in chains of weakly bound metallamacrocycles in the solid. An alternative electrolytic synthesis method, using a simple two-compartment glass cell containing 4 and a chosen halide salt in dichloromethane, led to the formation of cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)Br(4)] 6 and cis-[Pt(IV)(2)(L(m)(1)-S,O)(2)Cl(4)] 7, completing characterization of a series of first-reported trans-Pt(iv)-X (X=I, Br, Cl) metallamacrocyclic complexes. 相似文献
84.
Neuvonen H Neuvonen K Koch A Kleinpeter E 《The journal of physical chemistry. A》2005,109(28):6279-6289
Equilibria between the Z (tau1= 0 degrees) and E (tau1= 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, DeltaE(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mol(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between DeltaE of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (nO--> pi*C=O) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The nO --> pi*C=O electron donation has a minimum value with tau1= 90 degrees and a maximum value with tau1= 0 degrees (the Z conformer), the value with tau1= 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*C=O antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*C=O occupancies of the ester series 4 and 5. 相似文献
85.
Patrick Koch Carl Djerassi Vijai Lakshmi Francis J. Schmitz 《Helvetica chimica acta》1983,66(8):2431-2436
Thirty-two sterols are identified in the sponge Hyrtios sp. In addition to fourteen monohydroxylated compounds, the sterol fraction contains eight functionalized sidechain sterols, three of them new: 3 β-hydroxy-24-norchol-5-en-23-al (19) , (22-trans)-3 β-hydroxycholest-5, 22-dien-24-one (20) and (22R, 23R, 24S) or (22S, 23S, 24S)- 22,23-epoxy-24-methylchoest-5-en-3 β-ol (24). The probable biological origin, rather than artifact production, of these undescribed components is discussed. 相似文献
86.
Differential thermal analysis (DTA) is an effective means for studying chemical reactions, but its application to reaction kinetics is handicapped by the involvement of temperature feedback from the reaction heat and by the solvent dependence of the thermal conductivity.General, empirical relationships are derived from digital computer application which allow to transform half width and shape index of a DTA curve of any first-order process in a uniformly temperated sample to the values of the corresponding rate curve at linearly increased temperature.The expressions are complemented by some new relationships for an n-order reaction and are useful for the kinetic study of complex processes. 相似文献
87.
Matthias HeydenreichAndreas Koch László LázárIstván Szatmári Reijo SillanpääErich Kleinpeter Ferenc Fülöp 《Tetrahedron》2003,59(11):1951-1959
Starting from the 1′- or 2′-phenyl-substituted 1-(2′-hydroxyethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline diastereomers 3 and 6, 4-unsubstituted and 4-(p-nitrophenyl)- and 4-oxo-substituted 1-phenyl- and 2-phenyl-9,10-dimethoxy-2H,4H-1,6,7,11b-tetrahydro-1,3-oxazino[4,3-a]isoquinolines (7-12) were prepared. The relative configurations and the predominant conformations of the products were determined by NMR spectroscopy, by quantum chemical calculations and, for (2R∗,4S∗,11bR∗)-9,10-dimethoxy-4-(p-nitrophenyl)-2-phenyl-2H,4H-1,6,7,11b-tetrahydro-1,3-oxazino[4,3-a]isoquinoline (11), by X-ray diffraction. 相似文献
88.
K. H. Koch und K. Ohls 《Fresenius' Journal of Analytical Chemistry》1969,247(3-4):239-243
Zusammenfassung Ein neues lösungsspektrographisches Zerstäubungsverfahren wird beschrieben, bei dem die Lösung so zerstäubt wird, daß sie die Graphitelektroden nicht berührt. Mit diesem Verfahren könnten 10–3 bis 10–5 % Al, B, Cr, Cu, Mg, Mn, Mo, Ni, Si, Sn, Ti, V und Zr in Eisen und Stahl bestimmt werden.Zur Bestimmung von Verunreinigungen oder Einschlüssen in Stahl wird ein spektrographisches Verfahren mit Preßlingselektroden empfohlen, das nur 0,1–1 mg Rückstand benötigt. Oxide von Al, B, Ca, Co, Cu, Cr, Fe, Mg, Mn, Mo, Nb, Ni, Pb, Si, Sn, Sr, Ti, V, Zn und Zr konnten bis herab zu etwa 10–7 g erfaßt werden.
Methods for the determination of trace elements from metallic samples
The principles of a new spectrographical atomizing-method of solution are described. The solution has to be atomized into a gap without contacting the surface of the graphite electrodes. In this way the exact determination of 10–3 to 10–5 % of Al, B, Cr, Cu, Mg, Mn, Mo, Ni, Si, Sn, Ti, V and Zr in iron and steel is possible.The microanalytical determination of impurities or inclusions in steel has been achieved by a spectrographical method with briquette electrodes. The necessary amount of isolation residue is only 0.1–1 mg. The oxides of Al, B, Ca, Co, Cu, Cr, Fe, Mg, Mn, Mo, Nb, Ni, Pb, Si, Sn, Sr, Ti, V, Zn and Zr can be accurately determined by this procedure. The limit of determination is about 10–7 g.相似文献
89.
McCarthy TJ Plog MA Floy SA Jansen JA Soukup JK Soukup GA 《Chemistry & biology》2005,12(11):1221-1226
Natural RNA catalysts (ribozymes) perform essential reactions in biological RNA processing and protein synthesis, whereby catalysis is intrinsic to RNA structure alone or in combination with metal ion cofactors. The recently discovered glmS ribozyme is unique in that it functions as a glucosamine-6-phosphate (GlcN6P)-dependent catalyst believed to enable "riboswitch" regulation of amino-sugar biosynthesis in certain prokaryotes. However, it is unclear whether GlcN6P functions as an effector or coenzyme to promote ribozyme self-cleavage. Herein, we demonstrate that ligand is absolutely requisite for glmS ribozyme self-cleavage activity. Furthermore, catalysis both requires and is dependent upon the acid dissociation constant (pKa) of the amine functionality of GlcN6P and related compounds. The data demonstrate that ligand is integral to catalysis, consistent with a coenzyme role for GlcN6P and illustrating an expanded capacity for biological RNA catalysis. 相似文献
90.
O. G. Koch 《Fresenius' Journal of Analytical Chemistry》1977,286(1-2):14-19
Zusammenfassung Es wird eine automatisierte Apparatur zur schnellen, massenspektrometrischen Bestimmung von Sauerstoff und Stickstoff in Stahl beschrieben. Die Stahlprobe wird unter Argon im Gleichstrombogen geschmolzen und die extrahierten Gase Kohlenmonoxid und Stickstoff werden massenspektrometrisch bestimmt. Die relative Standardabweichung beträgt ±3–5% für Sauerstoff und ±3–8% für Stickstoff. Die Nachweisgrenzen liegen bei 10 pp106 O2 und 3 pp106 N2. Der Zeitbedarf für eine Analyse beträgt 85 s.Herrn H. Siffrin danke ich für die sorgfältige Durchführung der zahlreichen Versuche. 相似文献