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111.
The paper deals with the assignment of a single server to two retrial queues. Each customer reapplies for service after an
exponentially distributed amount of time. The server operates at customer dependent exponential rates. There are holding costs
and costs during service per customer and per unit of time. We provide conditions on which it is optimal to allocate the server
to queue 1 or 2 in order to minimize the expected total costs until the system is cleared. 相似文献
112.
Ethyl 4-methyl-2-oxo-7-phenylthio-2,3,6,7-tetrahydro-1H-1,3-diazepine-5-carboxylate and/or ethyl 6-methyl-2-oxo-4-(phenylthiomethyl)-1,2,3,4-tetrahydropyrimidine-5-carboxylate were obtained in the reaction of ethyl 4-chloromethyl-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate with PhSNa or PhSK with or without PhSH, depending on the reagent ratio, reaction time, or temperature, as a result of ring expansion and/or nucleophilic substitution. The reaction pathway was affected strongly by the basicity-nucleophilicity of the reaction media. The results obtained were confirmed by reactions of 4-mesyloxymethyl-6-methyl-5-tosyltetrahydropyrimidin-2-one with PhSNa/PhSH and ethyl 4-chloromethyl-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate with NaCN/HCN or NaCH(COOEt)2/CH2(COOEt)2. 相似文献
113.
Anastasia A. Fesenko 《Tetrahedron》2010,66(35):7219-462
A four-step method for the synthesis of 5-arylsulfonyl-substituted 1,2-dihydropyrimidin-2-ones has been developed. The reaction of readily available N-[(1-acetoxy-2,2,2-trichloro)ethyl]ureas with sodium enolates of α-arylsulfonylketones followed by heterocyclization-dehydration of the oxoalkylureas formed gave 5-arylsulfonyl-4-trichloromethyl-1,2,3,4-tetrahydropyrimidin-2-ones. The latter, in the presence of strong bases, eliminate CHCl3 to give the target compounds. 相似文献
114.
115.
A sensitive high-performance liquid chromatographic method for the simultaneous determination of 11 biogenic amines has been developed. The method involves addition of an internal standard (1,7-diaminoheptane), pre-column dansylation of the amines and subsequent solid-phase extraction of the derivatives through C18 cartridges. The dansylamides were separated on an Inertsil ODS-3 column (250 x 4 mm I.D., 5 microm) using a 35-min gradient elution with a binary system of acetonitrile-water, a flow-rate of 1 ml min(-1) and fluorescence detection at excitation and emission wavelengths of 320 and 523 nm, respectively. The identity of the dansyl derivatives was confirmed by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. Linearity of derivatization was obtained for concentrations ranging from 0.008 to 40.0 mg l(-1). The within- and between-day relative standard deviations ranged from 0.2 to 7.6% and 0.3 to 8.6%, respectively. The overall process was successfully applied to identify and quantify biogenic amines in white-, red- and Retsina Greek wines and Greek beers, after treatment with polyvinylpyrrolidone. 相似文献
116.
John Alfred Stone Dena Ellen Splinter Joanne McLaurin Anastasia C. M. Wojtyniak 《Journal of mass spectrometry : JMS》1984,19(8):375-378
Compounds C6H5X(X ? F, Cl, Br, NO2, CN, OCH3) have been studied under chemical ionization conditions with ammonia as reagent gas. A pulsed electron beam and time resolved ion collection has allowed the determination of the reaction leading to the formation of [C6H5NH3]+ (m/z 94). [NH4]+ reacts with C6H5X(X ? F, Cl, Br) to yield m/z 94 but C6H5X (X ? CN, NO2) forms this ion only by reactions involving either [NH3]+ or [C6H5X]+. C6H5OCH3 does not form m/z 94. 相似文献
117.
Dr. Sebastian Mai Sarah Klingler Dr. Ivan Trentin Julian Kund Marcus Holzer Anastasia Andreeva Dr. Robert Stach Prof. Christine Kranz Prof. Carsten Streb Prof. Boris Mizaikoff Prof. Leticia González 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):17078-17086
We report IR and UV/Vis spectroscopic signatures that allow discriminating between the oxidation states of the manganese-based water oxidation catalyst [(Mn4O4)(V4O13)(OAc)3]3−. Simulated IR spectra show that V=O stretching vibrations in the 900–1000 cm−1 region shift consistently by about 20 cm−1 per oxidation equivalent. Multiple bands in the 1450–1550 cm−1 region also change systematically upon oxidation/reduction. The computed UV/Vis spectra predict that the spectral range above 350 nm is characteristic of the managanese-oxo cubane oxidation state, whereas transitions at higher energy are due to the vanadate ligand. The presence of absorption signals above 680 nm is indicative of the presence of MnIII atoms. Spectroelectrochemical measurements of the oxidation from [Mn Mn ] to [Mn ] showed that the change in oxidation state can indeed be tracked by both IR and UV/Vis spectroscopy. 相似文献
118.
James D. Grayson Matthew P. Baumgartner Cleide Dos Santos Souza Samuel J. Dawes Imane Ghafir El Idrissi Jennifer C. Louth Sasha Stimpson Emma Mead Charlotte Dunbar Joanna Wolak Gary Sharman David Evans Anastasia Zhuravleva Margarita Segovia Roldan Nicola Antonio Colabufo Ke Ning Claire Garwood James A. Thomas Benjamin M. Partridge Antonio de la Vega de Leon Valerie J. Gillet Amlia P. Rauter Beining Chen 《Chemical science》2021,12(10):3768
Amyloid β oligomers (Aβo) are the main toxic species in Alzheimer''s disease, which have been targeted for single drug treatment with very little success. In this work we report a new approach for identifying functional Aβo binding compounds. A tailored library of 971 fluorine containing compounds was selected by a computational method, developed to generate molecular diversity. These compounds were screened for Aβo binding by a combined 19F and STD NMR technique. Six hits were evaluated in three parallel biochemical and functional assays. Two compounds disrupted Aβo binding to its receptor PrPC in HEK293 cells. They reduced the pFyn levels triggered by Aβo treatment in neuroprogenitor cells derived from human induced pluripotent stem cells (hiPSC). Inhibitory effects on pTau production in cortical neurons derived from hiPSC were also observed. These drug-like compounds connect three of the pillars in Alzheimer''s disease pathology, i.e. prion, Aβ and Tau, affecting three different pathways through specific binding to Aβo and are, indeed, promising candidates for further development.A new approach combining virtual screening, 19F and STD NMR, and biochemical assays using hiPSC and targetting multiple pathways involving Aβ, PrPC and Tau provides a more effective strategy for Alzheimer''s disease drug discovery than Aβ only approach. 相似文献
119.
Fannie S. Varveri Anastasia E. Mantaka-Marketou George Vassilopoulos John Nikokavouras 《Monatshefte für Chemie / Chemical Monthly》1988,119(6-7):703-710
The quantum yields of the lucigenin light reaction in didodecyldimethylammonium bromide (DDAB) are affected by the presence of Mg(OH)2; a 35% increase is observed in lamellar and a 65% increase in vesicular aggregates. The system is insensitive to benzyl alcohol. The quantum yields inDDAB versus those in water, as a function of temperature show a slope change in the region of the phase transition in lamelar aggregates. This effect is far less pronounced in vesicular aggregates. In contrast to theDDAB aggregates, anionic sodium dimethyldidodecylphosphate (SDDP) sonicated aggregates are associated with lower quantum yields and no apparent slope change in the region of the phase transition.
Chemilumineszenz in Modell-Membranstrukturen. Die Chemilumineszenz von Lucigenin in der Gegenwart von Mg(OH)2 und Benzylalkohol. Temperatureffekte
Zusammenfassung Die Quantenausbeuten der Lichtreaktion von Lucigenin in Didodecyldimethylammoniumbromid (DDAB) werden durch die Gegenwart von Mg(OH)2 beeinflußt. Es wird 35% Verstärkung in lamellaren und 65% Verstärkung in vesicularen Aggregaten beobachtet. Das System ist Benzylalkohol gegenüber unempflindlich. Eine Gegenüberstellung der Quantenausbeuten inDDAB bzw. in Wasser als eine Funktion der Temperatur zeigt eine Änderung des Anstiegs im Bereich des Phasenüberganges bei lamellaren Aggregaten. Dieser Effekt ist in vesicularen Aggregaten nicht so ausgeprägt. Im Gegensatz zu denDDAB-Aggregaten sind die beschallten anionischen Natriumdimethyldodecylphosphat (SDDP)-Aggregate durch geringere Quantenausbeuten und keine offensichtlichen Anstiegsänderungen im Bereich des Phasenüberganges gekennzeichnet.相似文献
120.
Synthesis of (Z)-4-hydroxytamoxifen and (Z)-2-[4-[1-(p-hydroxyphenyl)-2-phenyl]-1butenyl]phenoxyacetic acid 总被引:1,自引:0,他引:1
The synthesis of (Z)-4-hydroxytamoxifen and (Z)-2-[4-[1-(p-hydroxyphenyl)-2-phenyl]-1-butenyl]phenoxyacetic acid was accomplished using a McMurry reaction as the key step. The perfluorotolyl derivatives of the McMurry products enabled the separation of the minor undesirable geometrical isomer. The methodology proceeds without E,Z isomerization, employs a very mild final debenzylation step compatible with a large array of functional groups, and can be applied to the generation of a variety of 4-hydroxytamoxifen analogues. 相似文献