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排序方式: 共有192条查询结果,搜索用时 15 毫秒
1.
A critical survey of approximate scattering wave theories from random rough surfaces 总被引:4,自引:0,他引:4
Tanos Mikhael Elfouhaily Charles-Antoine Gu rin 《Waves in Random and Complex Media》2004,14(4):R1-R40
This review is intended to provide a critical and up-to-date survey of the analytical approximate methods that are encountered in scattering from random rough surfaces. The underlying principles of the different methods are evidenced and the functional form of the corresponding scattering amplitude or cross-section is given. The reader is referred to the original papers in order to obtain the explicit expressions of the coefficients and kernels. We have tried to identify the main strengths and weaknesses of the various theories. We provide synthetic tables of their respective performances, according to a dozen important requirements a valuable method should meet. Both scalar acoustic and vector electromagnetic theories are equally addressed. 相似文献
2.
Below a critical thickness, of about 60 nm, the glass transition temperature of polystyrene (PS) films decreases with film thickness, as demonstrated using free‐standing films. A geometrical model is developed here describing this phenomenon in the case of ideal (Gaussian) chains. This model, which can be considered as an application of the free volume model, assumes that the decrease of the glass transition temperature from thick to ultrathin films is due to the modification of the interpenetration between neighboring chains. The theoretical curve deduced from the model is in excellent agreement with the PS experimental results, without using any adjustable parameters. From these results, it can be concluded that new chain motions, usually buried in bulk samples, are expressed by the presence of the surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 10–17, 2007 相似文献
3.
Kickham JE Guérin F Stewart JC Stephan DW 《Angewandte Chemie (International ed. in English)》2000,39(18):3263-3266
4.
The ternary rare-earth nickel arsenides R3Ni7As5 (R=La, Ce, Pr, Nd, Sm) were prepared by arc melting the elemental components and subsequent annealing at T=1070 K. The crystal structure of Ce3Ni7As5 was determined from single-crystal X-ray data: space group Pmmn, Z=2; a=1.24210(6), b=0.40797(2), c=0.96436(5) nm, RF=0.037 (Rw=0.044); 596 independent reflections; 53 variable parameters. It is a new structure type, which belongs to the family of BaAl4-related structures. The magnetic properties are as follows: La3Ni7As5 is a Pauli-type paramagnet above 4.2 K, Pr3Ni7As5 remains paramagnetic in the temperature range investigated and Nd3Ni7As5 undergoes a ferromagnetic ordering at TC=24 K. Sm3Ni7As5 orders antiferromagnetically at a Néel temperature of TN=18 K followed by a spin flip towards parallel spin-alignment below TC=6 K. Ce3Ni7As5 reveals a strong deflection of the linear temperature dependence of the inverse susceptibility due to an intermediate valence behavior. The temperature dependence of the electrical resistivities for the La, Pr, Nd, Sm containing samples corroborates with the metallic state of the non-magnetic (La) and the magnetically ordered compounds, whereas in case of Ce3Ni7As5 the resistivity seems to be determined by an interplay of Kondo scattering and crystalline field effects. LIII X-ray absorption spectra confirm the demagnetization effects owing from valence fluctuations, the actual valence thereby changes from ν=3.10-3.14 at room temperature and 10 K, respectively. 相似文献
5.
[reaction: see text] Reported herein is a strategy employing a Mukaiyama reaction in tandem with a hydrogen transfer reaction for the elaboration of 2,3-anti-3,4-anti and 2,3-anti-3,4-syn propionate motifs. The mode of complexation is controlled through monodentate or chelate pathways for the Mukaiyama reaction to give access to either syn or anti aldol products, precursors of the free-radical reduction reaction. Boron Lewis acid is used to control the free-radical reaction through the exocyclic pathway. 相似文献
6.
J T Arnason B Guèrin M M Kraml B Mehta R W Redmond J C Scaiano 《Photochemistry and photobiology》1992,55(1):35-38
Sanguinarine, a commercial drug exhibiting antimicrobial and antitumor properties, was studied with respect to its basic photochemical characteristics and also with regard to its phototoxicity to mosquito larvae (Aedes atropalpus). Sanguinarine proved to be clearly phototoxic to larvae, with an LD50 of 0.096 mg/mL with near UV exposure as compared with 23.3 mg/mL without. Flash photolysis experiments enabled the study of the triplet state of sanguinarine to be undertaken. Quenching by oxygen occurs with a rate constant of 6 x 10(9) M-1s-1 and time-resolved emission studies indicate that sanguinarine produces a significant amount of singlet oxygen (phi delta = 0.16) as does the isoquinoline alkaloid, berberine (phi delta = 0.25). These values represent the first direct quantitative measurements of photosensitization parameters of these compounds. Additionally, sanguinarine exhibits efficient electron donation properties, undergoing reaction with methyl viologen with a rate constant greater than 10(10) M-1s-1, but is a poor electron acceptor. Phototoxicity of sanguinarine can thus be explained in terms of its photosensitization properties. 相似文献
7.
Dr. Matthieu Autillo Md. Ashraful Islam Julie Héron Laetitia Guérin Dr. Eleonor Acher Dr. Christelle Tamain Dr. Marie-Claire Illy Dr. Philippe Moisy Dr. Eric Colineau Dr. Jean-Christophe Griveau Dr. Claude Berthon Dr. Hélène Bolvin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(24):7138-7153
Actinide +VI complexes ( = , and ) with dipicolinic acid derivatives were synthesized and characterized by powder XRD, SQUID magnetometry and NMR spectroscopy. In addition, and complexes were described by first principles CAS based and two-component spin-restricted DFT methods. The analysis of the 1H paramagnetic NMR chemical shifts for all protons of the ligands according to the X-rays structures shows that the Fermi contact contribution is negligible in agreement with spin density determined by unrestricted DFT. The magnetic susceptibility tensor is determined by combining SQUID, pNMR shifts and Evans’ method. The SO-RASPT2 results fit well the experimental magnetic susceptibility and pNMR chemical shifts. The role of the counterions in the solid phase is pointed out; their presence impacts the magnetic properties of the complex. The temperature dependence of the pNMR chemical shifts has a strong contribution, contrarily to Bleaney's theory for lanthanide complexes. The fitting of the temperature dependence of the pNMR chemical shifts and SQUID magnetic susceptibility by a two-Kramers-doublet model for the complex and a non-Kramers-doublet model for the complex allows for the experimental evaluation of energy gaps and magnetic moments of the paramagnetic center. 相似文献
8.
Guillaume Erbland Dr. Seifallah Abid Yohan Gisbert Nathalie Saffon-Merceron Yuichiro Hashimoto Leonardo Andreoni Théo Guérin Dr. Claire Kammerer Prof. Dr. Gwénaël Rapenne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(71):16328-16339
The design and synthesis of two families of molecular-gear prototypes is reported, with the aim of assembling them into trains of gears on a surface and ultimately achieving controlled intermolecular gearing motion. These piano-stool ruthenium complexes incorporate a hydrotris(indazolyl)borate moiety as tripodal rotation axle and a pentaarylcyclopentadienyl ligand as star-shaped cogwheel, equipped with five teeth ranging from pseudo-1D aryl groups to large planar 2D paddles. A divergent synthetic approach was followed, starting from a pentakis(p-bromophenyl)cyclopentadienyl ruthenium(II) complex as key precursor or from its iodinated counterpart, obtained by copper-catalyzed aromatic Br/I exchange. Subsequent fivefold cross-coupling reactions with various partners allowed high structural diversity to be reached and yielded molecular-gear prototypes with aryl-, carbazole-, BODIPY- and porphyrin-derived teeth of increasing size and length. 相似文献
9.
10.
Jean-Cyrille Hierso Matthieu Beaupérin Samer Saleh André Job Jacques Andrieu Michel Picquet 《Comptes Rendus Chimie》2013,16(6):580-596
Conjugated alkynes are recurring building blocks in natural products and in a wide range of important compounds, such as pharmaceuticals, agrochemicals, or molecular materials. The palladium-catalysed cross-coupling reaction between the sp2-hybridized carbon atoms of aryl, heteroaryl, and vinyl halides with the sp-hybridized carbon atoms of terminal alkynes is one of the most important developments in the field of alkyne chemistry over the past 50 years. Room for improvement still exists in these important reactions of direct arylation of terminal alkynes. In this prospect, the present authors have developed several strategies aiming at improving the reactivity, the selectivity, and several aspects of processes involving the palladium-catalysed alkyne arylation and heteroarylation reactions, in relation with sustainable chemistry. Various original approaches have thus been adopted: (i) the development of catalytic systems efficient at low metal loading below 1 mol% of palladium and copper (to reduce metal contamination) from polydentate ligands chemistry, (ii) the limitation of diyne formation by undesired side-reaction, this from a better mechanistic understanding and the innovating use of copper adducts, (iii) and the development of cost-efficient catalytic reactions in ionic liquid solvents. These topics have been developed with the general outlook of a large scope in organic synthesis. In addition, the investigation of recycling opportunities and the unprecedented production of extendedly conjugated bis(aryl)diynes has been also achieved. The present account reviews all this work, as it has been presented by the corresponding author at GECOM–CONCOORD 2012 as recipient of the 2012 European journal of Inorganic Chemistry Young Investigator Award. 相似文献