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921.
Merlín Rosales Otto Soto Beatriz González Inés Pacheco Pablo J. Baricelli 《Transition Metal Chemistry》2018,43(5):451-461
Limonene hydroformylation was studied in the presence of Rh-based catalytic systems, which were prepared in situ by addition of three equivalents of PPh3, one of 1,2-bis(diphenylphosphino)ethane (dppe), or one of 1,1,1-tris(diphenylphosphino)ethane (triphos) to Rh(CO)2(acac) (1). These systems were efficient precatalysts for the target reaction, generating limonenal regio-specifically under mild reaction conditions (80 °C and 20 atm of syngas). The found activity order was: (1)/3 PPh3?>?(1)/triphos?>?(1)/dppe. The active catalytic species are proposed to be square planar hydrido-carbonyl complexes containing two phosphorus atoms coordinated at the rhodium centre. A kinetic study of this reaction catalysed by (1)/3 PPh3, the most active catalytic system, allowed us to propose that the mechanism of hydroformylation of limonene is similar to those reported for other olefins using RhH(CO)(PPh3)3 or Rh systems containing either dppe or triphos as precatalysts. 相似文献
922.
Segundo Moran Irazu Gallardo-Wong Gustavo Rodriguez-Leal Paulina Mccollough Jorge Mendez Beatriz Castañeda 《Isotopes in environmental and health studies》2013,49(3):192-197
The aim of this study was to compare the oxidation of l-[1-13C]phenylalanine (13C-PheOx) in patients with chronic liver failure due to different etiologies using l-[1-13C]phenylalanine breath test. Breath samples were collected before the administration of 100 mg l-[1-13C]phenylalanine, and every 10 min thereafter until completion of 1 h. Control subjects (n=9) presented a larger cumulative percentage of 13C dose recovery (CPDR) than patients (n=124) with chronic liver disease, regardless of the etiology (7.5±0.7 vs. 4.2±0.2, p=0.001). No differences in CPDR were found considering the Child-Pugh (CP) class or etiology: alcoholic (CP A=7.7±0.7, CP B=4.1±0.5, CP C=2.0±0.3), hepatitis C virus (CP A=5.4±0.5, CP B=4.0±0.2, CP C=2.2±0.3), hepatocellular carcinoma (CP A=5.5±1.6, CP B=3.6±1.8, CP C=2.2±1.0); or cryptogenic cirrhotic patients (CP A=7.4±1.5, CP B=4.4±0.4, CP C=2.1±0.7). Results confirm that 13C-PheOx decreases in patients with cirrhosis with respect to controls, notwithstanding the etiology. 相似文献
923.
Francisco D. Avila Orozco Antonio C. Sousa Claudia E. Domini Mario Cesar Ugulino Araujo Beatriz S. Fernández Band 《Ultrasonics sonochemistry》2013,20(3):820-825
Biodiesel is considered an alternative energy because it is produced from fats and vegetable oils by means of transesterification. Furthermore, it consists of fatty acid alkyl esters (FAAS) which have a great influence on biodiesel fuel properties and in the storage lifetime of biodiesel itself. The biodiesel storage stability is directly related to the oxidative stability parameter (Induction Time – IT) which is determined by means of the Rancimat® method. This method uses condutimetric monitoring and induces the degradation of FAAS by heating the sample at a constant temperature. The European Committee for Standardization established a standard (EN 14214) to determine the oxidative stability of biodiesel, which requires it to reach a minimum induction period of 6 h as tested by Rancimat® method at 110 °C. In this research, we aimed at developing a fast and simple alternative method to determine the induction time (IT) based on the FAAS ultrasonic-accelerated oxidation. The sonodegradation of biodiesel samples was induced by means of an ultrasonic homogenizer fitted with an immersible horn at 480 Watts of power and 20 duty cycles. The UV–Vis spectrometry was used to monitor the FAAS sonodegradation by measuring the absorbance at 270 nm every 2. Biodiesel samples from different feedstock were studied in this work. In all cases, IT was established as the inflection point of the absorbance versus time curve. The induction time values of all biodiesel samples determined using the proposed method was in accordance with those measured through the Rancimat® reference method by showing a R2 = 0.998. 相似文献
924.
A time-domain approach for damage detection in beam structures using vibration data with a moving oscillator as an excitation source 总被引:1,自引:0,他引:1
Luna Majumder 《Journal of sound and vibration》2003,268(4):699-716
The problem of detecting local/distributed change of stiffness in bridge structures using ambient vibration data is considered. The vibration induced by a vehicle moving on the bridge is taken to be the excitation source. A validated finite element model for the bridge structure in its undamaged state is assumed to be available. Alterations to be made to this initial model, to reflect the changes in bridge behaviour due to occurrence of damage, are determined using a time-domain approach. The study takes into account complicating features arising out of dynamic interactions between vehicle and the bridge, bridge deck unevenness, spatial incompleteness of measured data and presence of measurement noise. The inclusion of vehicle inertia, stiffness and damping characteristics into the analysis makes the system time variant, which, in turn, necessitates treatment of the damage detection problem in time domain. The efficacy of the procedures developed is demonstrated by considering detection of localized/distributed damages in a beam-moving oscillator model using synthetically generated vibration data. 相似文献
925.
Maria De Ftima V. Marques Ana Beatriz A. S. Marinha 《Journal of polymer science. Part A, Polymer chemistry》2004,42(12):3038-3048
Commercial zeolite acid mordenite was thermally treated for use as a support for bis(n‐butyl‐cyclopentadienyl)zirconium dichloride [(n‐BuCp)2ZrCl2] for the further evaluation of ethylene/1‐hexene copolymerization. The polymerization time, temperature, and solvent, as well as the addition of tri(isobutyl)aluminum in the hexane medium, were evaluated. The catalytic activity and 1‐hexene content in the copolymer synthesized with the supported system were very near those obtained with the homogeneous precursor. A comonomer effect was observed for both systems. The polymerization rate profiles were obtained for ethylene polymerization, and the activation energy and monomer reactivity were calculated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3038–3048, 2004 相似文献
926.
María José Castro-Castro Beatriz Candás-Estébanez Gemma Solé-Enrech Xavier Fuentes-Arderiu 《Accreditation and quality assurance》2009,14(10):525-528
In the clinical laboratory, one of the most objective ways to perform the final review of measurement results is the use of
the so-called plausibility control (i.e., set of procedures used to decide if a measurement result is valid or not according to established clinical and biological
criteria). The present study is focused on the estimation of several prediction equations derived from pairs of biological
quantities having a pathophysiological relationship and statistically correlated to detect objectively doubtful results in
the context of plausibility control. These prediction intervals, that may be used alone or combined with other procedures
involved in the plausibility control, are a very useful tool for the improvement of the final review of the laboratory results. 相似文献
927.
Fernando J. Luna 《Foundations of Chemistry》2002,4(2):173-177
928.
The correlation between recent PAS results and the outcomes from mechanical testing of RPV model alloys are presented, here significant changes due to different chemical composition and different irradiation levels are observed. The influence of alloying elements to the microstructure degradation process following irradiation was identified by analysis of the mean-lifetime parameter, since an interesting interdependency of this parameter with hardness was observed. 相似文献
929.
Joana S Amaral Susana Casal Duarte Torres Rosa M Seabra Beatriz P P Oliveira 《Analytical sciences》2005,21(12):1545-1548
A normal-phase high-performance liquid chromatography (NP-HPLC) method for the determination of tocopherols and tocotrienols in hazelnuts is reported. Three extraction procedures (with and without saponification) were assayed; the best results were obtained with a simple solid-liquid extraction procedure. Chromatographic separation was achieved using an Inertsil 5 SI column using isocratic elution with hexane/1,4-dioxane (95.5:4.5, v/v) at a flow rate of 0.7 mL/min. The effluent was monitored by a series arrangement of a diode-array followed by a fluorescence detector. All compounds were separated in a short period of time (17 min). The method proved to be rapid, sensitive, reproducible and accurate, allowing the simultaneous determination of all vitamin E homologues. 相似文献
930.
Michael Sekita Beatriz Ballesteros Franois Diederich Dirk M. Guldi Giovanni Bottari Toms Torres 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2016,128(18):5650-5654
A cycloaddition–retroelectrocyclization reaction between tetracyanoethylene and two zinc phthalocyanines (ZnIIPcs) bearing one or four anilino‐substituted alkynes has been used to install a strong, electron‐accepting tetracyanobuta‐1,3‐diene (TCBD) between the electron‐rich ZnIIPc and aniline moieties. A combination of photophysical, electrochemical, and spectroelectrochemical investigations with the ZnIIPc‐TCBD‐aniline conjugates, which present panchromatic absorptions in the visible region extending all the way to the near infrared, show that the formal replacement of the triple bond by TCBD has a dramatic effect on their ground‐ and excited‐state features. In particular, the formation of extremely intense, ground‐state charge‐transfer interactions between ZnIIPc and the electron‐accepting TCBD were observed, something unprecedented not only in Pc chemistry but also in TCBD‐based porphyrinoid systems. 相似文献