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101.
The evolution of the filamentation of a femtosecond laser pulse in air is measured. The divergence of the filament core is almost constant over a long distance, encompassing a zone with efficient ionization followed by another where ionization is much weaker. At the end, the core diverges out linearly with a low divergence due to self-spatial filtering. 相似文献
102.
An experimental study was made of the normal force in a magnetorheological suspension under shear flow with the magnetic field
applied normally to the shear planes. Under no deformation, the normal force was found to increase with magnetic flux density,
and acted to push apart the rheometer plates. At the start-up of shearing under a constant shear rate, the normal force decreased
with strain and reached a plateau value which became smaller as shear rate was raised. This behaviour can be interpreted in
terms of the aggregate model of magnetorheological suspensions: the normal force arises from the elongated aggregates spanning
the gap between the plates, and these are broken up into smaller particle clusters under shearing. 相似文献
103.
Mohammad R. Kasaai Joseph Arul See L. Chin Grard Charlet 《Journal of photochemistry and photobiology. A, Chemistry》1999,120(3):3607-205
The use of ultrashort laser pulses for the fragmentation of chitosan was investigated. Femtosecond Ti-saphire laser pulses were focused into a flask containing 1.0% chitosan in 0.1 M acetic acid. The effects of the pulse energy (between 0.1 and 0.82 mJ) and the focal length on the laser-induced fragmentation were followed by viscometry and size exclusion chromatography. The chemical structure and degree of acetylation of chitosan and its fragments were studied using elemental analysis, IR and 1H NMR spectroscopy. The experimental results showed that (i) Ti-saphire laser irradiation induced chain scission in the chitosan macromolecules, (ii) the chemical structure, including the degree of acetylation, did not change significantly upon laser irradiation, (iii) the number of chain scission dependence on laser energy suggests that fragmentation was a two-photon process, and (iv) at constant pulse energy, the molecular weight dropped to a minimum as a function of the focal length (between 45 and 330 mm), indicating that the efficiency of fragmentation was very sensitive to the geometry of the laser beam. 相似文献
104.
B.A. See 《Optics & Laser Technology》1996,28(6):445-450
In a previous paper, the author presented an empirically derived mathematical model of a pulse pumped laser which allowed calculation of the output energy from the laser—from the mirrors-only resonator to the fully assembled Q-switched state. In this paper the model is developed further by deriving an expression for the peak output power. New coupling and loss time constant are stated. The validity of the model is demonstrated by the ability of calculate the laser parameters from a measured pulse shape, knowing the rod dimensions and the pump energy at which the pulse was measured. 相似文献
105.
Hua Nong Ting See Yan Chia Badrulzaman Abdul Hamid Siti Zamratol-Mai Sarah Mukari 《Journal of voice》2011,25(6):e305
The acoustic characteristics of sustained vowel have been widely investigated across various languages and ethnic groups. These acoustic measures, including fundamental frequency (F0), jitter (Jitt), relative average perturbation (RAP), five-point period perturbation quotient (PPQ5), shimmer (Shim), and 11-point amplitude perturbation quotient (APQ11) are not well established for Malaysian Malay young adults. This article studies the acoustic measures of Malaysian Malay adults using acoustical analysis. The study analyzed six sustained Malay vowels of 60 normal native Malaysian Malay adults with a mean of 21.19 years. The F0 values of Malaysian Malay males and females were reported as 134.85 ± 18.54 and 238.27 ± 24.06 Hz, respectively. Malaysian Malay females had significantly higher F0 than that of males for all the vowels. However, no significant differences were observed between the genders for the perturbation measures in all the vowels, except RAP in /e/. No significant F0 differences between the vowels were observed. Significant differences between the vowels were reported for all perturbation measures in Malaysian Malay males. As for Malaysian Malay females, significant differences between the vowels were reported for Shim and APQ11. Multiethnic comparisons indicate that F0 varies between Malaysian Malay and other ethnic groups. However, the perturbation measures cannot be directly compared, where the measures vary significantly across different speech analysis softwares. 相似文献
106.
See KC Spicer JB Brupbacher J Zhang D Vargo TG 《The journal of physical chemistry. B》2005,109(7):2693-2698
The interband transition contributions to the optical properties of silver nanoparticles in fluoropolymer matrices are investigated. For the materials in this study, nanoparticle synthesis within the existing polymer matrix is accomplished using an infusion process that consists of diffusing an organometallic precursor gas into the free volume of the fluoropolymer and decomposing the precursor followed by metal nanoparticle nucleation and growth. The resulting polymer matrix nanocomposite has optical properties that are dominated by the response of the nanoparticles owing to the broadbanded transparency of the fluoropolymer matrix. The optical properties of these composites are compared to Maxwell-Garnett and Mie theory with results indicating that interband transitions excited in the silver nanoparticles affect the optical absorption over a range of frequencies including the surface plasmon resonance. It is shown that calculations of the optical absorption spectrum using published data for the silver dielectric function do not accurately describe the measured material response and that a classical model for bound and free electron behavior can best be used to represent the dielectric function of silver. 相似文献
107.
Melvyn Rowen Churchill Ronald F. See Carol A. Bessel Kenneth J. Takeuchi 《Journal of chemical crystallography》1996,26(10):667-675
The complexcis-[Ru(bpy)2(PPr3)Cl+][ClO
4
–
] · 0.5 (toluene) crystallizes as a racemate in the monoclinic space group P21/n. Both the PPr3 ligand and the toluene of crystallization are subject to disorder. Ruthenium—ligand distances are: Ru–PPr3=2.348(2) Å, Ru–Cl=2.426(2) Å and Ru–N(bpy)=2.035(6)–2.112(5) Å. 相似文献
108.
M. Marsin Sanagi H. H. See Wan Aini Wan Ibrahim Ahmedy Abu Naim 《Chromatographia》2005,61(11-12):567-571
High temperature reversed-phase high performance liquid chromatography is evaluated as a new approach for the separation of vitamin E isomers (α-, γ-, δ-tocopherol, and α-, γ-, δ-tocotrienol) and α-tocopherol acetate. The separations of each analyte were examined by varying the eluent composition and column temperature. Using a polybutadiene-coated zirconia column at temperatures of 80 °C–140 °C, complete separations were achieved within 10–20 min using organic modifier (acetonitrile) in the range of 40–50%. Irregularity of the Van’t Hoff analysis was noted over the temperature studied. The plot tends to deviate from linearity at higher operating temperatures (140 °C and 150 °C) with linear deviation errors of 12.7% and 41.6%, respectively, for the mobile phase examined. 相似文献
109.
Paul Müller Corine Baud Doïna En Sharokh Motallebi Michael P. Doyle Bridget D. Brandes Alexey B. Dyatkin Marjorie M. See 《Helvetica chimica acta》1995,78(2):459-470
The Rh11-catalyzed carbenoid addition of diazoacetates to olefins was investigated with [Rh2{(4S)-phox}4] ( 1 ;phox = tetrakis[(4S)-tetrahydro-4-phenyloxazol-2-one]), [Rh2{(2S)-mepy}4] ( 2 ; mepy = tetrakis[methyl (2S)-tetrahydro-5-oxopyrrole-2-carboxylate]), and [Rh2(OAc)4] ( 3 ). While catalysis with 2 and 3 afford preferentially trans-cyclopropanecarboxylates, the cis-isomers are the major products with 1 . In general, the enantioselectivities achieved with 1 and 2 are comparable. Additions catalyzed by 1 are strongly sensitive to steric effects. Highly substituted olefins afford cyclopropanes in only poor yield. The preferential cis-selectivity observed in reactions catalyzed by 1 is attributed to dominant interactions between the ligand of the catalyst and the substituents of both olefin and diazoacetate, which overrule the steric interactions between olefin and diazoacetate in the transition state for carbene transfer. 相似文献
110.
The reaction of -LiM0(CO)2Cp with α-chloromethylnaphthalene gives a yellow, crystalline σ-benzyl type derivative of molybdenum (1). Irridation of (1) in n-hexane gives a red π-benzyl type derivative (2). Both complexes (1) and (2) are stable in air. 相似文献