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31.
32.
We present new results for the time reversal of weakly nonlinear pulses traveling in a random dissipative environment. Also we describe a new theory for calculating the eddy viscosity for weakly nonlinear waves propagating over a random surface. The turbulent viscosity is calculated from first principles, namely, without imposing any stress-strain hypothesis. A viscous shallow water model is considered and its effective viscosity characterized. We also show that weakly nonlinear waves can still be time reversed under weak dissipation. Incoherently scattered signals are recompressed, both for time reversal in transmission as well as in reflection. Under the weakly nonlinear, weakly dissipative regime, dissipation only affects the refocused pulse profile regarding its amplitude, but its shape is not corrupted. Numerical experiments are presented. 相似文献
33.
We have performed a series of measurements to study the low temperature dynamics of an interacting magnetic nanoparticle system. The results obtained demonstrate striking memory effects in the dc magnetization and magnetic relaxation that support the existence of a spin-glass-like phase in interacting magnetic nanoparticles. Moreover, we observe an asymmetric response with respect to temperature change that supports a hierarchical picture, rather than the droplet model discussed in other works on nanoparticle systems. 相似文献
34.
35.
Gamblin DP Garnier P Ward SJ Oldham NJ Fairbanks AJ Davis BG 《Organic & biomolecular chemistry》2003,1(21):3642-3644
Controlled site-selective glycosylation can be achieved by combining site-directed cysteine mutagenesis with chemical modification of the introduced thiol; a new class of more efficient chemoselective reagents, glycosyl phenylthiosulfonates, allow rapid glycosylations of representative simple thiols, peptides and proteins. 相似文献
36.
Piarulli U Claverie C Daubos P Gennari C Minnaard AJ Feringa BL 《Organic letters》2003,5(23):4493-4496
[reaction: see text] A highly regio-, diastereo-, and enantioselective desymmetrization of five-, six-, and seven-membered meso-cyclic allylic bis-diethyl phosphates (2a, 2b, and 2c, respectively) was obtained with diethylzinc, using catalytic amounts of [Cu(OTf)](2).C(6)H(6) and phosphoramidite ligands 5. Enantiomeric excesses of up to 87, 94, and >98% were obtained for the addition of diethylzinc to cyclopentene, cyclohexene, and cycloheptene bis-diethyl phosphates, respectively. 相似文献
37.
Synthesis of chiral ortho-thio-substituted phenyl phosphonodiamidates via a P-S to P-C rearrangement
Christelle Mauger 《Tetrahedron letters》2004,45(20):3855-3859
The ortho-lithiation of a phenyl phosphorodiamidothioate derived from an enantiopure C2-symmetric diamine is studied. It is shown that the migration of the diaminophosphoryl group from sulfur to carbon, leading to an ortho-sulfanylated phenyl phosphonodiamidate, only occurs in the presence of an alkylating agent or a Lewis acid as BF3·Et2O. The influence of the chiral diaminophosphoryl group on the stereoselectivity of the oxidation of the ortho-sulfanyl or alkylsulfanyl group is also examined. 相似文献
38.
R.J. Panlener R.N. Blumenthal J.E. Garnier 《Journal of Physics and Chemistry of Solids》1975,36(11):1213-1222
Thermogravimetric measurements were performed on nonstoichiometric CeO2?x in the temperature range 750–1500°C and from oxygen pressures of 10?2 to 10?26 atm. From this data the deviation from stoichiometry x = x(T, Po2) was determined. The thermodynamic quantities Δo2 and Δo2 were calculated in the region 0.001? x ? 0.3 and found to be independent of temperature.In the composition region 0.001< x < 0.006, the variation of Δo2 with x is consistent with a defect model involving randomly distributed doubly ionized oxygen vacancies. The experimental dependence of x and σ (electrical conductivity) is shown to be consistent with this model as Δo2 (≈ -10 eV) exhibits a slight dependence on x. It is postulated that the variation in Δo2 may result from lattice parameter increases with x, while the defects remain essentially randomly distributed.In the composition region 0.006 < x < 0.1, x ∝ with 1 < n < 5, and in the region 0.1 < x < 0.3, x ∝ with n increasing rapidly with x to n? 30. This behavior is believed to result from increasing defect interaction with increasing departures from stoichiometry. It is interesting to note that the ordered phase observed by Bevan and Kordis between CeO1·72 and CeO1·70 was not observed in this study at temperatures between 1300° and 1500°C. 相似文献
39.
Christelle Vangenot Christophe Claramunt 《International Journal of Infrared and Millimeter Waves》1994,15(8):1361
First announcement the 20th annual international conference on infrared and millimeter waves 相似文献
40.
Martínez-Viviente E Pregosin PS Vial L Herse C Lacour J 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(12):2912-2918
1H, (19)F and (31)P pulsed field gradient spin-echo (PGSE) diffusion studies on chiral organic salts that contain hexacoordinate phosphate anions, namely tris(tetrachlorobenzenediolato)phosphate(V) (TRISPHAT) and bis(tetrachlorobenzenediolato)mono([1,1']binaphthalenyl-2,2'diolato)-phosphate(V) (BINPHAT), are reported. The first example of the dependence of a diffusion value on diastereomeric structure is presented. Marked solvent and concentration effects on the diffusion constants (D) of these salts are noted and the question of ion pairing is discussed. 相似文献