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121.
We have investigated both theoretically and experimentally the spectral behavior and the transmission and reflection performance of a photonic-crystal (PhC) mode converter upon an InP substrate. This taper exhibits 70% transmission efficiency on an 80-nm bandwidth when it couples a ridge access guide to a strongly confined single-missing-row PhC guide. Such a taper design included in a PhC bend contributes a large benefit to the overall transmission budget of the PhC-based link. 相似文献
122.
Duquesne E Degée P Habimana J Dubois P 《Chemical communications (Cambridge, England)》2004,(6):640-641
A new supported catalytic system, i.e. nickel bromide catalyst ligated by triphenylphosphine (TPP) ligands immobilized onto crosslinked polystyrene resins (PS-TPP) is reported. Per se, this catalyst does not allow any control over the polymerization of methyl methacrylate (MMA) initiated by ethyl 2-bromoisobutyrate but, in the presence of a given amount of purposely added free TPP, it promotes controlled ATRP of MMA. Indeed colorless PMMA chains of low polydispersity indices are readily recovered, the molecular weight of which linearly increases with monomer conversion and agrees with the expected values. Recycling of the supported catalyst is evidenced and does not prevent the polymerization from being controlled. 相似文献
123.
The liquid-gas phase transition is analyzed from the topologic properties of the event distribution in the observables space. A multicanonical formalism allows one to directly relate the standard phase transition with neutral particles to the case where the nonsaturating Coulomb interaction is present, and to interpret the Coulomb effect as a deformation of the probability distributions and a rotation of the order parameter. This formalism is applied to a statistical multifragmentation model and consequences for the nuclear multifragmentation phase transitions are drawn. 相似文献
124.
Dinu LC Muller HG Kazamias S Mullot G Augé F Balcou P Paul PM Kovacev M Breger P Agostini P 《Physical review letters》2003,91(6):063901
The absolute timing of the high-harmonic attosecond pulse train with respect to the generating IR pump cycle has been measured for the first time. The attosecond pulses occur 190+/-20 as after each pump field maxima (twice per optical cycle), in agreement with the "short" quantum path of the quasiclassical model of harmonic generation. 相似文献
125.
Kazamias S Douillet D Weihe F Valentin C Rousse A Sebban S Grillon G Augé F Hulin D Balcou P 《Physical review letters》2003,90(19):193901
We investigate the relevance of the absorption limit concept in the optimization of high harmonic generation. Thanks to the first direct observation of the coherence length of the process from high-contrast Maker fringes, we unravel experimental conditions for which the harmonic dipole response is enhanced when phase matching is realized within the absorption limit, leading to record conversion efficiencies in argon. Moreover, we show that harmonic generation in guided or freely propagating geometries are equivalent in the loose focusing regime. This analysis is generalized to other advanced phase-matching schemes, thereby predicting the possibility to boost the conversion efficiencies using light noble gases. 相似文献
126.
New very effective results on the liquid-phase oxidation of cyclohexene to cyclohexanone by nitrous oxide are analyzed using the B3LYP/6-31G* approximation to predict a two-step reaction mechanism correlated with the experimental data. 相似文献
127.
128.
Chen Cs Ran S Liu W Yang Ph Peng Dk Bouwmeester HJ 《Angewandte Chemie (International ed. in English)》2001,40(4):784-786
129.
The kinetics of metal beta-diketonates sonolysis was studied in hexadecane solutions using a UV/VIS spectrophotometric technique. The following complexes were prepared and studied: Cu(HFAA)(2), Cu(DPM)(2), Fe(ACAC)(3), Ni(DPM)(2), Er(DPM)(3), Nd(DPM)(3), Th(DPM)(4), UO(2)(BTFA)(2).TOPO, and Np(HFAA)(4), where HHFAA is hexafluoroacetylacetone, HDPM is dipivaloylmethane, HACAC is acetylacetone, HBTFA is benzoyltrifluoroacetone, and TOPO is trioctylphosphine oxide. Sonolysis was performed under the following conditions: ultrasonic frequency 22 kHz, intensity of ultrasound 3-5 Wcm(-2), temperature 70-92 degrees C, Ar atmosphere. The kinetic behavior of the studied complexes are interpreted using a two-site model of the sonochemical processes. In the case of metal beta-diketonates with high vapor pressure the sonochemical reactions tend to occur in the gaseous phase of the cavitating bubbles. The sonolysis of less volatile complexes first occur in the liquid reaction zone surrounding the bubbles. Sonication of the studied complexes results in the formation of X-ray amorphous products consisted of a mixture of metal beta-diketonates partial degradation products. Heating of as-prepared sonication products in air yields nanocrystalline oxides of corresponding metals. 相似文献
130.
Fehr C Dieudonné P Primera J Woignier T Sauvajol JL Anglaret E 《The European physical journal. E, Soft matter》2003,12(Z1):S13-S16
Solid polymorphism of 4-alkyl-4'-cyanobiphenyl (nCB) was studied so far as a function of thermal history. In this paper we show that metastable solid phases of 4-octyl-4'-cyanobiphenyl (8CB) are also formed when the mesogens are confined in porous silica matrices and we study their structure by neutron diffraction and by Raman spectroscopy. Three metastable solid states are identified: one crystalline phase K', two frozen-in smectic-like phases K(s) and K'(s). We discuss the relation between the structure of the metastable solid phases and that of the mesomorph phases. 相似文献