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1.
We consider the vector space of globally differentiable piecewise polynomial functions defined on a three-dimensional polyhedral domain partitioned into tetrahedra. We prove new lower and upper bounds on the dimension of this space by applying homological techniques. We give an insight of different ways of approaching this problem by exploring its connections with the Hilbert series of ideals generated by powers of linear forms, fat points, the so-called Fröberg–Iarrobino conjecture, and the weak Lefschetz property. 相似文献
2.
Vianey Villamizar 《Wave Motion》1991,14(4):299-320
An elastic membrane backed by a fluid-filled cavity in an elastic body is set into an infinite plane baffle. A time harmonic wave propagating in the acoustic fluid in the upper half-space is incident on the plane. It is assumed that the densities of this fluid and the fluid inside the cavity are small compared with the densities of the membrane and of the elastic walls of the cavity, thus defining a small parameter . Asymptotic expansions of the solution of this scattering problem as →0, that are uniform in the wave number k of the incident wave, are obtained using the method of matched asymptotic expansions. When the frequency of the incident wave is bounded away from the resonant frequencies of the membrane, the cavity fluid, and the elastic body, the resultant wave is a small perturbation (the “outer expansion”) of the specularly reflected wave from a completely rigid plane. However, when the incident wave frequency is near a resonant frequency (the “inner expansion”) then the scattered wave results from the interaction of the acoustic fluid with the membrane, the membrane with the cavity fluid, and finally the cavity fluid with the elastic body, and the resulting scattered field may be “large”. The cavity backed membrane (CBM) was previously analyzed for a rigid cavity wall. In this paper, we study the effects of the elastic cavity walls on modifying the response of the CBM. For incident frequencies near the membrane resonant frequencies, the elasticity of the cavity gives only a higher order (in ) correction to the scattered field. However, near a cavity fluid resonant frequency, and, of course, near an elastic body resonant frequency the elasticity contributes to the scattered field. The method is applied to the two dimensional problem of an infinite strip membrane backed by an infinitely long rectangular cavity. The cavity is formed by two infinitely long rectangular elastic solids. We speculate on the possible significance of the results with respect to viscoelastic membranes and viscoelastic instead of elastic cavity walls for surface sound absorbers. 相似文献
3.
Pedro Zaragoza‐Gasca Omar J. Villamizar‐Gálvez Roeb García‐Arrazola Miquel Gimeno Eduardo Bárzana 《先进技术聚合物》2010,21(6):454-456
Ionic liquid and buffer mixture media are first reported in the peroxidase‐catalyzed polymerization of phenol. Yield of 100% with molecular weights of 7000 KDa, as assessed by size‐exclusion chromatography (SEC), were attained using 1‐butyl‐3‐methylimidazolium tetrafluoroborate–buffer mixtures with added hydrogen peroxide. The simplicity of the process and the low vapor pressure of the solvent media allow an eco‐friendly alternative to the general synthesis of polyphenolic‐type biopolymers. Evidence for the consequent polyphenol (PPO) was obtained from solid‐state 13C cross‐polarization magic angle spinning (CP‐MAS) NMR spectroscopy and FT‐IR. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
4.
Carlos Banquet Lucas C. F. Ferreira Élder J. Villamizar‐Roa 《Mathematical Methods in the Applied Sciences》2017,40(15):5613-5618
We consider a semilinear wave equation with nonlinear damping in the whole space . Local‐in‐time existence and uniqueness results are obtained in the class of Bessel‐potential spaces . Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
5.
Popularity of new psychoactive substances, known as legal highs or herbal highs, is continuously growing. These products are
typically sold via internet and in so-called head shops. The aim of this study was to identify active ingredients of herbal
highs and to compare their chemical composition. Twenty-nine various products seized by the police in one of the “head shops”
were analysed. Herbal mixtures (0.2 g) were prepared by ultrasonic-assisted extraction with 2.0 ml of ethanol for 2 h. The
extracts were analysed by gas chromatography coupled to mass spectrometry (GC/MS). The main active compounds of the herbal
mixtures were synthetic cannabinoids: JWH-018, JWH-073 and cannabicyclohexanol (CP-47,497-C8-homolog). Their content differed
between the products; some contained only one cannabinoid whereas the others contained two or more. Cluster analysis and principal
component analysis revealed that chemical composition of many products was very similar. The similarity was connected with
their flavour and not the common name. This statement was true for the synthetic cannabinoids, other potential agonists of
cannabinoid receptors (amides of fatty acids) and ingredients of natural origin and confirms that herbal highs are a threat
to human health because the purchaser has no information on their real composition. 相似文献
6.
Vianey Vasquez-Ruiz M. Ángeles Ramírez-Cisneros Maria Yolanda Rios 《Magnetic resonance in chemistry : MRC》2022,60(3):275-358
Cedrela genus, a member of the Meliaceae family, presents both chemical characteristics associated with and those that distinguish it from the rest of its members. The presence of triterpenes and limonoids is the characteristic of the Meliaceae family, but the class and type of these chemical constituents are distinctive for each genus. Cedrela includes cycloartane, ursane, oleanane, tirucallane, butyrospermane, and apotirucallane triterpenes, and its limonoids belongs to six class and nine types, known as class Ia-type havanensines, class Ib-type delevoyin, class II-type gedunin, class IIIb-type andirobin, class IIIg-type mexicanolide, class IVa-type evoludone, class Va-type obacunol, class V-type limonin, and class VIII. Each of these structural arrangements includes specific traits, defined by their biosynthetic origin, which can be established by means of structural elucidation techniques, particularly 1H and 13C NMR, which assisted by 2D NMR techniques, allowing to deduce their structures unequivocally. The constant presence of these skeletal arrangements in Cedrela ensures that they are its chemophenetic markers and their recurrence is an important criterion for their identity. This review is a compilation of the occurrence of triterpenes and limonoids in Cedrela genus, detailing their biosynthetic association and collecting and organizing their NMR data, with the purpose of facilitating its location, analysis, and use in the phytochemical study of species from this genus. 相似文献
7.
Marlyn C. Ortiz Villamizar Carlos E. Puerto Galvis Silvia A. Pedraza Rodríguez Fedor I. Zubkov Vladimir V. Kouznetsov 《Molecules (Basel, Switzerland)》2022,27(23)
A rapid, efficient, and original synthesis of novel pyrido[3,2,1-de]phenanthridin-6-ones is reported. First, the key cinnamamide intermediates 8a–f were easily prepared from commercial substituted anilines, cinnamic acid, and 2-bromobenzylbromide in a tandem amidation and N-alkylation protocol. Then, these N-aryl-N-(2-bromobenzyl) cinnamamides 8a–f were subjected to a TFA-mediated intramolecular Friedel-Crafts alkylation followed by a Pd-catalyzed direct C–H arylation to obtain a series of potentially bioactive 4-phenyl-4,5-dihydro-6H,8H-pyrido[3,2,1-de]phenanthridin-6-one derivatives 4a–f in good yields. Finally, the toxicological profile of the prepared final compounds, including their corresponding intermediates, was explored through in silico computational methods, while the acute toxicity toward zebrafish embryos (96 hpf-LC50, 50% lethal concentration) was also determined in the present study. 相似文献
8.
W. Villamizar M. Casales J. G. Gonzalez-Rodriguez L. Martinez 《Journal of Solid State Electrochemistry》2007,11(5):619-629
The corrosion behavior of hydroxyethyl, amino ethyl and amid ethyl imidazolines corrosion inhibitors was evaluated by using
potenthiodynamic polarization curves, linear polarization resistance, and electrochemical impedance spectroscopy techniques.
Solutions included deaerated 3% NaCl, 3% NaCl+diesel saturated with CO2 at 50 °C with and without inhibitors. Regardless of the presence of diesel, the corrosion rate was decreased with the addition
of the inhibitors, but the time to reach a steady state was longer than when the oily part, i.e., diesel, was present. In
the absence of the oily part, the impedance results showed that the film formed was porous, allowing the electrolyte to diffuse
through it and corrode the metal. When the oily part was present, the film formed was much more stable, not porous, and did
not allow the electrolyte to corrode the sample. The most efficient inhibitor was the amid ethyl imidazoline, whereas the
least efficient was the hydroxyethyl imidazoline, because the film formed by the former was much more stable from the beginning
of the test. 相似文献
9.
10.
David Duarte-Correa Alberto Pastrana-Palma Carlos A. Olvera-Olvera Sergio R. Ramírez-Rodríguez Daniel Alaniz-Lumbreras Domingo Gómez-Meléndez Ismael de la Rosa Salvador Noriega Vianey Torres Victor M. Castaño 《Optik》2013
The computational efficiency of 14 optical detectors over six types of transformations, namely: blur, illumination, rotation, viewpoint, zoom, and zoom-rotation changes, was analyzed. Images with the same resolution (750 × 500 pixels) were studied, in terms of correspondences, repeatability and computing time, and the correspondence was measured by using homographies i.e. projective transformations, to obtain the best efficiency for imaging applications. Results show that the multi-scale Harris Hessian detector is the most efficient for blur, illumination, and zoom-rotation changes. Meanwhile, multi-scale Hessian and Hessian Laplace are the best methods for rotation, viewpoint, and zoom changes. 相似文献