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991.
A new strategy for deprotonative functionalization of aromatics using t-Bu-P4 base has been developed, and highly chemoselective transformations have been achieved with unique regioselectivities. 相似文献
992.
A micro-macro approach of multiaxial fatigue in unlimited endurance is proposed. It allows one to take into account plasticity and damage mechanisms which occur at the scale of Persistent Slip Bands (PSB). The proposed macroscopic fatigue criterion, which corresponds to microcracks nucleation at the PSB-matrix interface, is derived for different homogenization schemes (Sachs, Lin-Taylor and Kröner). The role of a mean stress and of the hydrostatic pressure in high cycle fatigue is shown; in particular, in the case of Lin-Taylor scheme and linear isotropic hardening rule at microscale, one recovers the linear dependance in pressure postulated by K. Dang Van for the macroscopic fatigue criterion. This dependence is related here to the damage micro-mechanism. Finally, the particular case of affine loading is presented as an illustration. To cite this article: V. Monchiet et al., C. R. Mecanique 334 (2006). 相似文献
993.
The ultrasonic velocity profile measurement of flow structure in the near field of a square free jet
Coherent structures in the near field of a three-dimensional jet have been investigated. Experiments were carried out for
a free jet issuing from a square nozzle using a water channel. Instantaneous velocity profiles were obtained in the axial
and radial directions by using an ultrasonic velocity profile (UVP) monitor. Axial variations of dominant time-scales of vortex
structures were examined from one-dimensional wavelet spectra. Wavenumber-frequency spectra were calculated by two-dimensional
Fourier transform along the axial direction in a mixing layer, and it was found that a convective velocity of flow structures
was nearly constant independently of their scales in space and time. Coherent structures in the axial direction were investigated
in terms of proper orthogonal decomposition (POD). Eigenfunctions are similar to a sinusoidal wave, and reconstructed velocity
fields by the lower-order and higher-order POD modes demonstrate large-scale and smaller-scale coherent structures, respectively.
Received: 8 May 2000/Accepted: 23 January 2001 Published online: 29 November 2001 相似文献
994.
Because of the inherent small size of optical fiberscopes, they provide access and relative handling ease in given closed vessels, which are hardly equipped with extra windows for conventional flow visualization. The use of an optical fiberscope in conjunction with a conventional particle image velocimetry/particle tracking velocimetry (PIV/PTV) system without optimization can lead to degraded transmission of images. The present study proposes a processing technique to filter background noise contained within the coarse bundle image by subtracting the original image of the bundle as reference image. Additionally, efforts were made to increase the reliability of vector processing using particle streak images via judicious pulse interval and duration adjustments. As an applications test we measured classic jet flow using the developed system and using established conventional measurement techniques. Our tests confirmed that our fiberscope PTV system provides vector fields with sufficient accuracy. 相似文献
995.
Jiro Kondo Yoshinari Tada Takenori Dairaku Hisao Saneyoshi Itaru Okamoto Yoshiyuki Tanaka Akira Ono 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(45):13521-13524
Metallo‐base pairs have been extensively studied for applications in nucleic acid‐based nanodevices and genetic code expansion. Metallo‐base pairs composed of natural nucleobases are attractive because nanodevices containing natural metallo‐base pairs can be easily prepared from commercially available sources. Previously, we have reported a crystal structure of a DNA duplex containing T HgII T base pairs. Herein, we have determined a high‐resolution crystal structure of the second natural metallo‐base pair between pyrimidine bases C AgI C formed in an RNA duplex. One AgI occupies the center between two cytosines and forms a C AgI C base pair through N3 AgI N3 linear coordination. The C AgI C base pair formation does not disturb the standard A‐form conformation of RNA. Since the C AgI C base pair is structurally similar to the canonical Watson–Crick base pairs, it can be a useful building block for structure‐based design and fabrication of nucleic acid‐based nanodevices. 相似文献
996.
The peak top frequency of the stretching vibration of hydroxyl (OH) groups on amorphous silica reversibly changes accompanied by the change of the sample in temperature under the constant concentration. Using this phenomenon, the estimation of the real temperatures of samples in infrared (IR) cell can be achieved. The temperatures measured from outside the cell are first calibrated to real ones. The OH frequency of silica can be correlated to the real temperature of the sample inside the cell via the calibration of the measured and the real temperatures of samples in each IR cell. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
997.
The aqueous counter collision (ACC) method can provide single bacterial nanocellulose ribbons (ACC-BNC) in a desired width, from a pellicle produced by Gluconacetobacter xylinus. Kose et al. (Biomacromolecules, 12:716–720, 2011) reported that the ACC process transformed the major Iα crystalline phase of the native fiber to a stable Iβ phase, without decreasing the overall crystallinity. The current study investigated the variation of the crystalline phases of ACC-BNC, upon interaction with poly(vinyl alcohol) (PVA). ACC-BNC of desired width was mixed with PVA, without any chemical reaction occurring. This resulted in a homogeneous suspension. The equilibrium melting point of PVA in cast nanocomposite films was investigated, as a probe for evaluating the crystalline surface properties of the ACC-BNC. A decrease in the equilibrium melting point of PVA would have indicated attractive interactions between the PVA and ACC-BNC. However, the nature of the ACC-BNC surface in the presence of PVA depended on the ACC-BNC width. Thicker ACC-BNC acted as a nucleating agent for PVA. Thinner ACC-BNC acted as a diluent of PVA. This tendency was opposite to the case for Iβ-dominant ACC-wood nanocellulose. ACC-BNC acting as a nucleating agent was more efficient than ACC-wood nanocellulose. The results suggested that ACC-BNC surfaces, which probably contained I α phases, had different characteristics to those of Iβ-dominant ACC-wood nanocellulose surfaces. 相似文献
998.
Synthesis of 8-aryl-3,5,7,3′,4′-penta-O-methylcyanidins from the corresponding quercetin derivatives by reduction with LiAlH4 is reported. Regioselective iodination at the 8-position of penta-O-methylquercetin followed by a Suzuki-Miyaura reaction gave the 8-arylated quercetin derivatives. By the reduction of 8-arylated quercetins using 4 equiv. of LiAlH4 at room temperature for 30 min, the corresponding anthocyanidins were obtained with a good yield. 相似文献
999.
1000.
Spherical molecular assemblies with diameters of ∼2 nm were quantitatively formed in water from new amphiphilic meta-terphenyls with two hydrophilic pendants at the central benzene ring. Whereas intermolecular interactions between small aromatic rings are typically weak, the obtained nanoassemblies are stable enough at wide-ranging concentrations and mostly remain intact even in the presence of similar nanoassemblies with polyaromatic frameworks. The nanoassembly with pentamethyl-substituted terminal benzene rings provides superior host capability for fluorescent dyes in water. 相似文献