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排序方式: 共有409条查询结果,搜索用时 31 毫秒
121.
A method for the preparation of novel oxaza and diaza polycyclic 9-oxa-4-azaphenanthrene, 5H-pyrido[2,3-a]pyrrolizine, 5H,6H-pyrido[3,2-g]indolizine, and 5H,6H-indeno[2,1-a]indole is described, based on tandem reactions: aza-Wittig reaction of N-vinylic phosphazenes with functionalized aldehydes and an intramolecular aza-Diels-Alder reaction. 相似文献
122.
Rafael Palacios Carlos E.S. Cesnik 《International Journal of Solids and Structures》2008,45(7-8):2097-2116
The paper presents a one-dimensional model for anisotropic active slender structures that captures arbitrary cross-sectional deformations. The 1-D geometrically-nonlinear static problem is derived by an asymptotic reduction process from the equations of 3-D electroelasticity. In addition to the conventional (bending–extension–shear–twist) beam strain measures, it includes a Ritz approximation to account for arbitrary deformation shapes of the finite-size cross-sections. As a particular case, closed-form analytical expressions are derived for the linear static equilibrium of a composite thin strip with surface-mounted piezoelectric actuators. This solution is based on a boundary-layer approximation to the static equilibrium equations in regions where Saint-Venant’s principle for elastic bodies cannot be applied and includes camber bending deformations to account for the local bimoments induced by the distributed actuation in a finite-width strip. 相似文献
123.
An alternative method to count and differentiate nuclear tracks in SSNTD is described. The method is based on the analysis of Fraunhofer diffraction pattern of coherent light produced by tracks of an etched SSNT detector. The diffraction pattern was also simulated by applying computational Fourier Optics. The comparison between results obtained by simulation and by the theoretical model gave satisfactory concordance. The proposed method is capable of differentiating tracks in CR-39 by their diameter and energies. The diameter resolution ranged between 8% and 25%, while the counting error was less than 15%. The discriminating ability to distinguish genuine etched tracks from defects and background anomalies is demonstrated. The incidence angle did not influence significantly the total count and the track parameter measuring capability. Errors due to track overlapping are only significant for track densities higher than 3×105 cm−2. 相似文献
124.
Pereyra P. López Herrera M. E. Palacios D. Viloria T. Vadillo E. Pérez B. Sajo-Bohus L. 《Journal of Radioanalytical and Nuclear Chemistry》2020,324(2):609-614
Journal of Radioanalytical and Nuclear Chemistry - Nuclear track methodology (NTM), is employed to analyze PADC detectors response to different energetic ion beams. Due to the passive device... 相似文献
125.
Dr. David Cantillo Prof. Martín Ávalos Prof. Reyes Babiano Prof. Pedro Cintas Prof. José L. Jiménez Prof. Juan C. Palacios 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(28):8795-8799
What accounts for a particular chiral selection in the case of a few sugars of prebiotic relevance, thereby mirroring the asymmetry observed in nature? By using first‐principles calculations, the generation of pentoses from glycolaldehyde (the initial product of the autocatalytic formose reaction), which has been detected in outer space), has been modeled by using L ‐Val‐L ‐Val as a primeval catalyst. Our theoretical study provides insight into the mechanism of this reaction and satisfactorily explains a few key molecular events. Our rationale agrees with the reported experimental data and shows that the D ‐configuration is only favored for ribose. L ‐pentoses are usually favored in the presence of L ‐configured dipeptides, as observed experimentally, although no chiral selection could be observed in the case of xylose. These results confirm that a prebiotic sugar soup could be fine‐tuned in the presence of shorter peptides as catalysts and that D ‐ribose would have also resulted in an advantageous imbalance for further amplification and chemical evolution. 相似文献
126.
The outstanding ability of nanosilica to stabilize dispersions of Nylon 6 droplets in a polypropylene matrix 下载免费PDF全文
Leire Sangroniz Marco Antonio Moncerrate Vladimir A. De Amicis Jordana K. Palacios Mercedes Fernández Antxon Santamaria Johan J. Sánchez Fouad Laoutid Philippe Dubois Alejandro J. Müller 《Journal of Polymer Science.Polymer Physics》2015,53(22):1567-1579
The effectiveness of hydrophobically modified nanosilica (NS) as interfacial modifying agent for immiscible polymer blends is evaluated. Blends of polypropylene (PP) with 20% of polyamide 6 (PA) and 5% hydrophobic NS were prepared by melt mixing. Compression molded sheets and extruded films were evaluated by scanning electron microscopy, transmission electron microscopy, tensile testing, and rheological measurements. Hydrophobic NS particles strongly reduce the polydispersity and droplet size of the dispersed phase, as a result of their preferential location at the interface. NS promotes outstanding stability of blend dispersion regardless of the processing or post‐processing technique employed. The viscoelastic terminal zone shows a plateau for PP/PA/NS, which corresponds to a suspension‐like behavior. Under large amplitude oscillatory shear, the increment in the non‐linearity parameter Q evidences the interactions between NS and blend components. Therefore, NS is an excellent morphological stabilizer that prevents coalescence, but cannot promote interfacial adhesion between immiscible PP and PA phases. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1567–1579 相似文献
127.
128.
Susan Berggren Antonio Palacios 《The European Physical Journal B - Condensed Matter and Complex Systems》2014,87(4):1-20
Coupled dynamical systems that operate near the onset of a bifurcation can lead, under certain conditions, to strong signal amplification effects. Over the past years we have studied this generic feature on a wide range of systems, including: magnetic and electric fields sensors, gyroscopic devices, and arrays of loops of superconducting quantum interference devices, also known as SQUIDs. In this work, we consider an array of SQUID loops connected in series as a case study to derive asymptotic analytical approximations to the exact solutions through perturbation analysis. Two approaches are considered. First, a straightforward expansion in which the non-linear parameter related to the inductance of the DC SQUID is treated as the small perturbation parameter. Second, a more accurate procedure that considers the SQUID phase dynamics as non-uniform motion on a circle. This second procedure is readily extended to the series array and it could serve as a mathematical framework to find approximate solutions to related complex systems with high-dimensionality. To the best of our knowledge, an approximate analytical solutions to an array of SQUIDs has not been reported yet in the literature. 相似文献
129.
Juan A. Alfonso Karla Pérez Daniel Palacios Helga Handt John J. LaBrecque Abrahan Mora Yaneth Vásquez 《Journal of Radioanalytical and Nuclear Chemistry》2014,300(1):219-224
The activity concentrations of 137Cs, 40K, 226Ra and 232Th in Bq/kg from 42 marine sediment samples collected at nine sampling sites were determined in order to establish a radiological baseline along the Venezuelan coast. The radioactivity levels were determined by means of a gamma-ray spectroscopy system using a hyper-pure germanium detector in a low-background configuration. Particle size distribution and total organic matter content were also determined. Activity concentrations of 137Cs were lower than the detection limit of the analytical technique (0.9 Bq/kg) in all studied sites. The results suggest that the variation of grain-size distribution is one of the most important factors influencing the spatial variations of 40K, 226Ra and 232Th in sediments along the Venezuelan coasts. In all sampling sites, average concentrations of 40K, 226Ra and 232Th were lower than the world average values. Activity concentrations of 226Ra, 232Th and 40K in coastal marine sediments along the Venezuelan coast could be considered to be low when compared with global average values, indicating that they are not apparently above of the range that might be considered normal or background. These results suggest that the studied sites do not pose any significant radiological threat to the population. The results attained in this study should be of considerable value as baseline data and background reference levels for Venezuelan coastlines. 相似文献
130.
Markowsky Greg Palacios José Luis 《Methodology and Computing in Applied Probability》2019,21(3):841-851
Methodology and Computing in Applied Probability - A symmetric relation in the probabilistic Green’s function for birth-death chains is explored. Two proofs are given, each of which makes use... 相似文献