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排序方式: 共有370条查询结果,搜索用时 15 毫秒
61.
This study examines the alkylation of diphenylamine (DPA) with nonene (NON) in a liquid phase catalyzed by acid-treated clay-based catalysts from commercial suppliers (Fulcat 22B, Nobelin MM, and Jeltar 300). Alkylations were conducted to achieve the highest possible selectivity of diisononyldiphenylamine (DNDPA), low selectivity of monoisononyldiphenylamine, and a maximum triisononyldiphenylamine yield of 4%. This study also examines the reaction conditions to selectively form dialkylated diphenylamine from DPA and NON in a batch reactor. Repeated use of the catalyst during the alkylation of DPA with NON was also investigated. Catalyst deactivation takes place during the alkylation of each batch and intensifies with repeated catalyst use, resulting in low DNDPA selectivity. The regenerated catalyst was sufficiently active only until the regeneration of the first and second batches. After the third batch, the catalyst’s selectivity for DNDPA was very low, and its reuse in the alkylation of DPA with NON was not efficient. Therefore, to achieve the maximum length of catalyst activity, the fresh catalyst was gradually added to the used catalyst from a previous batch, thus maintaining a high activity of eight batches. The reduction in catalyst activity was probably caused by the irreversible adsorption of substances on the surface, a loss of microporous structure, and a loss of surface acidity. DPA or alkylated products are adsorbed on the surface oxygen of the catalyst through nitrogen and form nitro formations. The fresh and regenerated catalysts were characterized by their surface area, surface acidity, pore size distribution, and pore volume. 相似文献
62.
63.
Pavol Farkašovský 《Zeitschrift für Physik B Condensed Matter》1997,104(1):147-151
The spin-1/2 Falicov-Kimball model for electronically driven valence and metal-insulator transitions is studied analytically using strong-coupling perturbation theory. It is shown that in the limit of the infinite interaction strength between localized and itinerant electrons the Falicov-Kimball model undergoes two types of discontinuous valence transitions: the insulator-metal transitions from an integer-valence ground state (n f = 1) into an inhomogeneous intermediate-valence ground state (0 < n f < 1) and the insulator-metal transitions from n f = 1 to n f = 0. In addition, we discuss the role of the electron-phonon interaction on the mechanism of valence transitions and we present possible extensions of the exact one dimensional results to higher dimensions. 相似文献
64.
Molecular characterization and first report of Cryptosporidium genotypes in human population in the Slovak Republic 下载免费PDF全文
Antónia Petrincová Alexandra Valenčáková Lenka Luptáková František Ondriska Jana Kalinová Monika Halánová Oľga Danišová Pavol Jarčuška 《Electrophoresis》2015,36(23):2925-2930
In our study, we examined 91 fecal samples from five different groups of people containing HIV patients, hemodialysis patients, kidney transplant recipients, immunocompetent humans without clinical signs, and humans with suspected cryptosporidiosis. The purpose of our study was to determine species and genotype composition of representatives of Cryptosporidium spp. using PCR analysis of small subunit ribosomal RNA gene and 60‐kDa glycoprotein gene and examine their phylogenetic relationship. In HIV‐positive/AIDS‐infected group of patients and in hemodialysis patients, no presence of Cryptosporidium species was detected. In two kidney transplant recipients, we detected species/genotypes Cryptosporidium parvum IIaA13G1T1R1 (KT355488) and Cryptosporidium hominis IaA11G2R8 (KT355489) and in two immunocompetent patients with clinical symptoms, we identified Cryptosporidium muris and C. hominis IbA10G2T1 (KT355490). In the group of healthy immunocompetent individuals without clinical signs, we identified species/genotype C. hominis IbA11G2 (KT355491) in one sample. 相似文献
65.
This study investigated the potential use of waste cooking oil (WCO) in the production of engine fuels and valuable chemicals via catalytic cracking. WCO was processed in its pure form and in a mixture with hydrotreated vacuum gas oil (HVGO). Catalytic cracking experiments were performed using a microactivity test (MAT) (simulation of the fluid catalytic cracking environment). In cracking over the standard fluid catalytic cracking equilibrium catalyst (FCC-ECAT), the oxygen contained in the feed was consumed in the formation of CO and CO2, water and into oxygenated organic compounds (phenolics, esters, carboxylic acids, etc.), which were found in the organic phase of the liquid product. In order to remove the unwanted organic oxygenates, the catalytic system based on pure FCC-ECAT was modified by addition of the ZSM-5-based FCC catalyst. By using the mixture containing FCC-ECAT and 10 mass % of FCC-ZSM-5, it was possible to reduce the amount of organic oxygenates to almost the feasible minimum when cracking pure WCO. The effect of the catalyst mixture on cracking the feed mixture of the vacuum gas oil with 10 vol. % of WCO was manifested in the practically zero formation of organic oxygenates and in a gasoline yield comparable with vacuum gas oil (VGO) cracking. 相似文献
66.
Pavol Brunovský Alexander Erdélyi Hans-Otto Walther 《Journal of Dynamics and Differential Equations》2004,16(2):393-432
A delay differential equation is presented which models how the behavior of traders influences the short time price movements of an asset. Sensitivity to price changes is measured by a parameter a. There is a single equilibrium solution, which is non-hyperbolic for all a>0. We prove that for a< 1 the equilibrium is asymptotically stable, and that for a>1 a 2-dimensional global center-unstable manifold connects the equilibrium to a periodic orbit. Its birth at a=1 is not of Hopf type and seems part of a Takens–Bogdanov scenario. 相似文献
67.
Effect of sol-gel preparation method on particle morphology in pure and nanocomposite PZT thin films
Double-scale composite lead zirconate titanate Pb(Zr0.52Ti0.48)O3 (PZT) thin films of 360 nm thickness were prepared by a modified composite sol-gel method. PZT films were deposited from
both the pure sol and the composite suspension on Pt/Al2O3 substrates by the spin-coating method and were sintered at 650°C. The composite suspension formed after ultrasonic mixing
of the PZT nanopowder and PZT sol at the powder/sol mass concentration 0.5 g mL−1. PZT nanopowder (≈ 40–70 nm) was prepared using the conventional sol-gel method and calcination at 500°C. Pure PZT sol was
prepared by a modified sol-gel method using a propan-1-ol/propane-1,2-diol mixture as a stabilizing solution. X-ray diffraction
(XRD) analysis indicated that the thin films possess a single perovskite phase after their sintering at 650°C. The results
of scanning electron microscope (SEM), energy-dispersive X-ray (EDX), atomic force microscopy (AFM), and transmission electron
microscopy (TEM) analyses confirmed that the roughness of double-scale composite PZT films (≈ 17 nm) was significantly lower
than that of PZT films prepared from pure sol (≈ 40 nm). The composite film consisted of nanosized PZT powder uniformly dispersed
in the PZT matrix. In the surface micrograph of the film derived from sol, large round perovskite particles (≈ 100 nm) composed
of small spherical individual nanoparticles (≈ 60 nm) were observed. The composite PZT film had a higher crystallinity degree
and smoother surface morphology with necklace clusters of nanopowder particles in the sol-gel matrix compared to the pure
PZT film. Microstructure of the composite PZT film can be characterized by a bimodal particle size distribution containing
spherical perovskite particles from added PZT nanopowder and round perovskite particles from the sol-matrix, (≈ 30–50 nm and
≈ 100–120 nm), respectively. Effect of the PZT film preparation method on the morphology of pure and composite PZT thin films
deposited on Pt/Al2O3 substrates was evaluated. 相似文献
68.
Imrich Gci Jn Imrich Pavol Kristian Henri Kivel Pauliina Valtamo Kalevi Pihlaja 《Journal of heterocyclic chemistry》2005,42(5):907-918
The synthesis of regioisomeric 3‐alkyl(aryl)‐2‐(acridin‐9′‐yl)imino‐1,3‐thiazolidin‐4‐ones ( 8b‐i ) and 2‐alkyl(aryl)imino‐3‐(acridin‐9′‐yl)‐1,3‐thiazolidin‐4‐ones ( 11a‐i ) was performed by the reaction of 3‐(acridin‐9‐yl)‐1‐alkyl(aryl)thioureas 5a‐i with methyl bromoacetate and bromoacetyl bromide, respectively, via the corresponding isothiourea hydrobromides with excellent regioselectivity. The structure, NMR spectra and mass spectrometric behavior of the resulting compounds are discussed. 相似文献
69.
Summary The homotopy method for solving systems of polynomial equations proposed by Chow, Mallet-Paret and Yorke is modified in two ways. The first modification allows to keep the homotopy solution curves bounded, the second one to work with real polynomials when solving a system of real equations. For the first method numerical results are presented. 相似文献
70.
Berkes D Jakubec P Winklerová D Povazanec F Daich A 《Organic & biomolecular chemistry》2007,5(1):121-124
Diastereoselective aza-Michael additions of phenylethylamine to 3-aroylbutenoic acids are reported. During these processes, efficient control over two new stereogenic centers on the Michael acceptor has been possible via crystallization-induced asymmetric transformation (CIAT). As an application, a convenient two-step synthesis of anti-beta-methylhomophenylalanines is also described. 相似文献