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121.
M. Clarembeau A. Cravador W. Dumont L. Hevesi A. Krief J. Lucchetti D. Van Ende 《Tetrahedron》1985,41(21):4793-4812
This paper reports our results concerning the syntheses of various bis(alkylseleno)alkanes and some of their arylseleno analogues by different methods. The scope and limitation of each of them are presented. 相似文献
122.
Erik L. Demeulemeester Willy S. Herroelen Salah E. Elmaghraby 《European Journal of Operational Research》1996
We describe two algorithms, based on dynamic programming logic, for optimally solving the discrete time/cost trade-off problem (DTCTP) in deterministic activity-on-arc networks of the CPM type, where the duration of each activity is a discrete, nonincreasing function of the amount of a single nonrenewable resource committed to it. The first algorithm is based on a procedure proposed by Bein, Kamburowski and Stallmann for finding the minimal number of reductions necessary to transform a general network to a series-parallel network. The second algorithm minimizes the estimated number of possibilities that need to be considered during the solution procedure. Both procedures have been programmed in C and tested on a large set of representative networks to give a good indication of their performance, and indicate the circumstances in which either algorithm performs best. 相似文献
123.
T. Dumont S. Lazare T. Lippert A. Wokaun 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1271-1274
The ablation rates of a polyimide and a triazene polymer were studied gravimetrically by a quartz micro balance for 248-nm and 308-nm irradiation. Special care was taken to examine the dependence of the ablation rate at constant fluences for single pulses and the influence of consecutive pulses at the same position. A clear trend was observed in these measurements, i.e., that the mass loss after the first pulse is always different from values for the following pulses. This implies that it is very difficult to determine true ablation rates, which are the foundation of most ablation models. The differences of the mass loss between the first pulse and the following pulses is most probably due to carbonization of the material, resulting in varying ablation rates for the following pulses. The ablation rates are thus not a real material property but a superposition of the material ablation rates with the ablation rates of carbon and carbonized material. PACS 52.38.Mf; 71.20.Rv; 07.10.Lw 相似文献
124.
Caitriona Mc Hugh-Munier Klaus R. Scherer Willy Lehmann Ursula Scherer 《Journal of voice》1997,11(4):452-461
Emotional state affects the physiological mechanism involved inphonation. Differences in acoustical parameters of the voice under stress have been attributed to the coping mechanism used, which is based on the individual's perception of the situation. This study examines the relationship between coping strategies, personality, and voice in female subjects, ranging in age from 19.3–55.7 years, diagnosed with vocal nodules or polyps. The differences between coping strategies and personality are examined and compared with another group with no history of voice pathology. The relationship of personality and coping strategies to voice quality variables is reported. Results show that patients use emotional coping strategies more and cognitive coping strategies less than the comparison group. Type of voice pathology was found to be related to dominance, and a number of coping and personality variables were found to correlate significantly with voice quality. 相似文献
125.
The reversible cis-trans photoisomerization of disperse red 1 (DR1) in PMMA thin films has been demonstrated to be strongly polarization sensitive [1]. In this communication two mechanisms are identified: the angular hole burning and the angular redistribution of molecules. It is shown that, in the presence of a DC electric field, the redistribution is not centrosymmetric and produces a poling of the film. The evolution of the second-order nonlinear susceptibility, (2), is monitored by measuring the electro-optic effect by attenuated total reflection and by second-harmonic generation. 相似文献
126.
p-Azidophenylalanine13-α-melantropin ([Pap13]-α-MSH) was synthesized in homogeneous solution by the fragment condensation method, and its biological activity was determined in three different assay systems. The pigment-dispersing activity relative to α-MSH was 65%, measured with melanophores of Rana pipiens or of Xenopus laevis tadpoles. The tyrosinase-stimulating activity was 50%, determined with cultured mouse melanoma cells. UV. irradiation of solutions containing ≤10?4M[Pap13]-α-MSH at 338 nm (intensity: 10?3 W · cm?2) led to complete photolysis of the photolabel within <20 min. Under these conditions [Pap13]-α-MSH was covalently inserted into MSH-receptors which produced a longlasting pigment dispersion in Xenopus melanphores (see [3]). The extent of this prolonged stimulation depended on the hormone concentration used during photolysis. 1.8·10?9M [Pap13]-α-MSH which produced a full initial response failed to prolong the effect, whereas 1.2·10?8M hormone caused irreversible stimulation. It appears that only about 10% of the initially occupied receptors were covalently labelled because the log dose response curve was shifted to ~ 10x higher concentration after a 200 min wash period: EC50 immediately after photolysis was 6 · 10?10M; after 200 min EC50 increased to ~8·10?9M. 相似文献
127.
Otto Bekers Jantina J. Van Den Bosch Kettenes Steven P. Van Helden Don Seijkens Jos H. Beijnen Auke Bulti Willy J. M. Underberg 《Journal of inclusion phenomena and macrocyclic chemistry》1991,11(2):185-193
The inclusion complexation of the anthracyline antibiotics doxorubicin and daunorubicin with cyclodextrins has been studied by proton NMR and molecular modelling. The anthracyclines were found to complex with -cyclodextriny-cyclodextrin, whereby the aglyconic part of the molecule is included in the cyclodextrin cavity. Job ratio plots based on NMR data indicate that the complex has a stoichiometry of 1 : 1. Complex constant values of 345 M–1 and 323 M–1 (at pH 3) were found for doxorubicin and daunorubicin, respectively. 相似文献
128.
Willy Friedrichsen Winfried Seidel Tony Debaerdemaeker 《Journal of heterocyclic chemistry》1983,20(6):1621-1628
6,6-Diphenylfulvene (6) reacts with 2,4,6-triphenylpyrylium-3-olate (7) to give three [π2 + π-4] cyclo-adducts 8, 9, 10. Reduction of 8 with sodium borohydride yields a cage-like compound 12 whereas the action of the same reagent on 9 results in the formation of three carbinols 13, 14, 15 . Treatment of 9 with acetic acid/hydrogen chloride yields an isomer 18 . The structures of both 12 and 18 have been established by X-ray crystallography. 相似文献
129.
Enhanced method performance due to a shorter chromatographic run-time in a liquid chromatography-tandem mass spectrometry assay for paclitaxel 总被引:1,自引:0,他引:1
Liquid chromatography-tandem mass spectrometry (LC-MS-MS) is often performed in a high-throughput environment. Unfortunately, with atmospheric pressure ionization (API) techniques, shorter run-times or reduced sample clean-up often result in ion or matrix suppression, which can lead to erroneous results. The present work on the analysis of paclitaxel compares ion suppression, sensitivity and linearity of a high-throughput LC-MS-MS method (0.8 min run-time, method B) to a method with increased separation (2.0 min run-time, method A). An atmospheric pressure chemical ionization (APCI) interface was used for both methods. The high-sample-throughput method uses an increased amount of organic solvent in the mobile phase (isocratic, 85% versus 70% of methanol) and a higher flow-rate (600 microl/min versus 400 micro/min). As a result, internal standard (docetaxel) and target analyte (paclitaxel) co-elute, close to, although separated from the solvent front. Ion suppression of both methods was evaluated by comparing pure standard to plasma and plasma containing a vehicle. Sensitivity and linearity were compared by injecting matrix matched calibration samples with both methods. Ion suppression by the vehicle Cremophor EL led to poor data quality for the standard method (A), while for the short method (B), ion suppression was compensated for by the co-eluting internal standard. The short method showed similar linearity but increased sensitivity by at least a factor five. This work provides a strategy to compensate for ion suppression without the use of labeled internal standards. In addition, a better sensitivity and a shorter run-time are noted. 相似文献
130.
By condensation of the chlorides of the three 9-oxo-fluorene-2-, -3-, and -4-carboxylic acids with 4-bromo-1,2-xylene on one side, and of the chlorides of o-bromobenzoic acid, 2-bromo-4-methyl-benzoic acid and 2-bromo-4,5-dimethyl-benzoic acid with fluorene, 2-methylfluorene and 3-methylfluorene on the other side, followed by direct or indirect cyclisation and by final reduction, several new methyl derivatives of the indenofluorenes I, II and IV are synthesized. 相似文献