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201.
In the present paper an improved approximation for the Rayleigh wave velocity in isotropic elastic solids is obtained using the method of least squares. It is of Bergmann’s form, i.e. the form of the ratio of two binomials. It is shown that this approximation is the best one of the Rayleigh wave velocity, in the sense of least squares, with respect to the class of functions whose elements are the ratio of two binomials. This approximation is much more accurate than Bergmann’s one. Its maximum percentage error is 10 times smaller than that of Bergmann’s. It is 7.6 times better than the one obtained recently by Royer and Clorennec [D. Royer, D. Clorennec, An improved approximation for the Rayleigh wave equation, Ultrasonics 46 (2007) 23–24]. An approximation of Bergmann’s form for the squared Rayleigh wave velocity is also derived and its maximum percentage error is 5 times smaller than that of Royer and Clorennec’s approximation. Some polynomial approximations with very high accuracy are also obtained. 相似文献
202.
Several recurrent problems have always hindered mono-dimensional liquid chromatography-mass spectrometry proteomic analyses. Polymer contamination is a major problem because polymers could co-elute with compounds of interest (peptides). In this case spectral suppression degrades dynamic range and sensitivity. Polyethylene glycol derivatives count among the major contaminants. They are targeted in this work. They are eluted at 35-40% acetonitrile from C18 phase in every single reversed-phase run. Moreover, they are also observed in two-dimensional liquid chromatography in every salt fraction. A simple and robust method is presented here for rapid and efficient on-line removal of these impurities using self-regenerating purification microdevices. 相似文献
203.
204.
To extend modal analysis to nonlinear structures, and adopting the Volterra series as a mathematical framework, we present some new routes together with progress on signal processing. The closed form expressions of higher-order transfer function on the other hand would permit one to obtain eigenvalues of various orders and eigenvectors. Existing signal processing analyzers are initially devoted to linear systems. Programs treating input and output signals of systems are tailored for one-time (or frequency) variable functions. Nonlinear systems can indeed be analyzed by one-dimensional (direct or inverse) Fourier transforms. However, the experimenter rapidly discovers their limitation when dealing with coupling phenomena that require functions with many time (or frequency) variables. In this framework, multidimensional Fourier transforms are necessary. 相似文献
205.
Volumetric-correlation particle image velocimetry (VPIV) is a new technique that provides a 3-dimensional 2-component velocity
field from a single image plane. This single camera technique is simpler and cheaper to implement than multi-camera systems
and has the capacity to measure time-varying flows. Additionally, this technique has significant advantages over other 3D
PIV velocity measurement techniques, most notably in the capacity to measure highly seeded flows. Highly seeded flows, often
unavoidable in industrial and biological flows, offer considerable advantages due to higher information density and better
overall signal-to-noise ratio allowing for optimal spatial and temporal resolution. Here, we further develop VPIV adding the
capability to measure concentration and increasing the robustness and accuracy of the technique. Particle concentrations are
calculated using volumetric auto-correlations, and subsequently the velocities are calculated using volumetric cross-correlation
corrected for variations in particle concentration. Along with the ability to calculate the particle concentration profile,
our enhanced VPIV produces significant improvement in the accuracy of velocity measurements. Furthermore, this technique has
been demonstrated to be insensitive to out-of-plane flows. The velocity measurement accuracy of the enhanced VPIV exceeds
that of standard micro-PIV measurements, especially in near-wall regions. The 3D velocity and particle-concentration measurement
capability of VPIV are demonstrated using both synthetic and experimental results. 相似文献
206.
Hien Luong T. Nguyen I. Elishakoff Vinh T. Nguyen 《International Journal of Solids and Structures》2009,46(24):4163-4168
This study focuses on the buckling of cylindrical shells with small thickness variations under external pressure. Asymptotic formulas in terms of the thickness non-uniformity parameter are derived by the combined perturbation and Bubnov–Galerkin methods. In addition to the analytic investigation based on the thin shell theory, a numerical analysis is also performed. Results from these formulas are discussed and compared with those obtained by other authors. 相似文献
207.
Lynn Ferres Luca Evangelisti Assimo Maris Sonia Melandri Walther Caminati Wolfgang Stahl Ha Vinh Lam Nguyen 《Molecules (Basel, Switzerland)》2022,27(9)
The rotational spectrum of phenyl acetate, CH3COOC6H5, is measured using a free jet absorption millimeter-wave spectrometer in the range from 60 to 78 GHz and two pulsed jet Fourier transform microwave spectrometers covering a total frequency range from 2 to 26.5 GHz. The features of two large amplitude motions, the methyl group internal rotation and the skeletal torsion of the CH3COO group with respect to the phenyl ring C6H5 (tilted at about 70°), characterize the spectrum. The vibrational ground state is split into four widely spaced sublevels, labeled as A0, E0, A1, and E1, each of them with its set of rotational transitions and with additional interstate transitions. A global fit of the line frequencies of the four sublevels leads to the determination of 51 spectroscopic parameters, including the ΔEA0/A1 and ΔEE0/E1 vibrational splittings of ~36.4 and ~33.5 GHz, respectively. The V3 barrier to methyl internal rotation (~136 cm−1) and the skeletal torsion B2 barrier to the orthogonality of the two planes (~68 cm−1) are deduced. 相似文献
208.
A technique for the growth of single crystals of Lanthanum Sulphate Enneahydrate from saturated aqueous solution by slow program-heating under different growing conditions has been developed. Polarized Raman spectrum and vibrational assignments of an oriented single crystal are reported. 相似文献
209.
Dr. Qiaoqiao Teng Ping Siang Ng Jia Nuo Leung Prof. Han Vinh Huynh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(61):13956-13963
The suitability and accuracy of the Huynh electronic parameter (HEP) was further tested to reveal remote substituent effects in pyridines, which are located five or six bonds away from the reporter probe. These values show an excellent correlation to Hammett σ-constants of the respective substituents with coefficients of R2=0.9856 (σm) and R2=0.9857 (σp). Based on this observation, a methodology for the re-evaluation of certain Hammett constants with larger uncertainties has been proposed and demonstrated. Moreover, the scope of HEP was extended to various neutral pnictogen and chalcogen donors during which “transphobia effects” were revealed for mixed NHC complexes containing phosphites, arsine and stibine for the first time. 相似文献
210.
Prof. Dr. Ming Li Prof. Dr. Andrew P. Dove Dr. Vinh X. Truong 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(6):2304-2308
Photochemical ligation is important in biomaterials engineering for spatiotemporal control of biochemical processes. Such reactions however generally require activation by high energy UV or short wavelength blue light, which can limit their use as a consequence of the potential of these high energy light sources to damage living cells. Herein, we present an additive-free, biocompatible, chemical ligation triggered by mild visible light. BODIPY dyes with a pendant thioether attached at the meso-position undergo photolysis of the [C−S] bond under green light (λ=530 nm) excitation, producing an ion pair intermediate that can react specifically with a propiolate group. The utility of this photochemical ligation in materials science is demonstrated by the fabrication of hydrogels with specific architectures, photo-immobilization of biomacromolecules, and live cell encapsulation within a hydrogel scaffold. 相似文献