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141.
The aggregation/deaggregation of chlorin p6 with the surfactants CTAB, SDS, and TX 100 have been studied by using absorption, fluorescence, and light scattering techniques. The ionic surfactants are found to cause aggregation of fluorophore at submicellar concentrations. The aggregates dissolve at higher surfactant concentrations to yield micellized monomers. This is rationalized by the interplay of electrostatic and hydrophobic effects. A prominent pH effect is observed in the ionic surfactant induced aggregation process as the charge on the fluorophore is controlled by the pH of the medium. Interestingly, the neutral TX-100 also induces aggregation of chlorin p6 at low concentrations, indicating that hydrophobic effects by themselves can cause aggregation unless there is a hindrance by repulsive electrostatic effects. 相似文献
142.
A.K.?Dharmadhikari A.S.?Sandhu J.A.?Dharmadhikari A.?Mishra G.R.?KumarEmail author 《Applied physics. B, Lasers and optics》2004,79(2):235-238
We report on the investigation of two-photon absorption (TPA) in 4-Diethylamino-N-Methyl-4-Stilbazolium Tosylate (DEST) with 40 picosecond, 1064 nm linear and circular polarization laser radiation. The TPA cross-section 2 measured is larger for linear polarized radiation (948 GM) than that for the circular polarized radiation (840 GM). The large TPA cross-section of DEST facilitates highly directional and efficient TPA induced upconverted emission in the range of 590–640 nm even though the fluorescence efficiency of DEST is very low (0.5%). The net single pass efficiency of upconversion is 7%. PACS 42.65.-k; 42.70.Jk 相似文献
143.
Bachhawat P Mishra S Bhatia Y Bisaria VS 《Applied biochemistry and biotechnology》2004,118(1-3):269-282
The biosynthetic activity of yeast Pichia etchellsii β-glucosidase II (BglII) expressed in recombinant Escherichia coli was utilized for synthesis of cellooligosaccharides, alkyl and terpene glucosides. Cellooligosaccharides with a degree of
polymerization of 3 and greater were resolved by thin-layer chromatography (TLC) using an ethyl acetate: 1-propanol:2-propanol:water
(8:5:1:1) solvent system followed by visualization with 0.2% naphthoresorcinol reagent. Using 2M cellobiose and 15 IU of partially purified BglII, 57 mmol/L of oligosaccharides (comprising mostly cellotriose and cellopentaose) was synthesized in 16 h. Similarly, alkyl
glucosides with chain lengths from 6 to 10 carbons were synthesized and products extracted to near purity by ethylacetate
extraction. The same extraction method was employed to separate, to near purity, various monoterpenyl (nerol, geraniol, citronellol)
glucosides. A reliable and simple method for separation of cellooligosaccharides using a combination of Bio-Gel P-2 gel filtration
and charcoal celite adsorption chromatography was developed. The cellooligosaccharides were separated to purity as confirmed
by TLC. The enzyme was among the very few that could synthesize a wide variety of glycoconjugates. 相似文献
144.
Yang UK Adams T Alton A Arroyo CG Avvakumov S de Barbaro L de Barbaro P Bazarko AO Bernstein RH Bodek A Bolton T Brau J Buchholz D Budd H Bugel L Conrad J Drucker RB Fleming BT Formaggio JA Frey R Goldman J Goncharov M Harris DA Johnson RA Kim JH King BJ Kinnel T Koutsoliotas S Lamm MJ Marsh W Mason D McFarland KS McNulty C Mishra SR Naples D Nienaber P Romosan A Sakumoto WK Schellman H Sciulli FJ Seligman WG Shaevitz MH Smith WH Spentzouris P Stern EG Suwonjandee N Vaitaitis A Vakili M Yu J 《Physical review letters》2001,86(13):2742-2745
We report on the extraction of the structure functions F2 and DeltaxF(3) = xF(nu)(3)-xF(nu;)(3) from CCFR nu(mu)-Fe and nu;(mu)-Fe differential cross sections. The extraction is performed in a physics model-independent (PMI) way. This first measurement of DeltaxF(3), which is useful in testing models of heavy charm production, is higher than current theoretical predictions. The ratio of the F2 (PMI) values measured in nu(mu) and mu scattering is in agreement (within 5%) with the predictions of next-to-leading-order parton distribution functions using massive charm production schemes, thus resolving the long-standing discrepancy between the two sets of data. 相似文献
145.
Sun Chi-Kuang Huang Yong-Liang Liang Jian-Chin Wang Jiun-Cheng Gan Kian-Giap Kao Fu-Jen Keller Stacia Mack Michael P. Mishra Umesh Denbaars Steven P. 《Optical and Quantum Electronics》2000,32(4-5):619-640
We have studied third order nonlinearities, including two-photon absorption coefficient and nonlinear refractive index n
2, of GaN in below bandgap ultraviolet (UV) wavelength regime by using UV femtosecond pulses. Two-photon absorption was investigated by demonstrating femtosecond UV pulsewidth autocorrelation in a GaN thin film while femtosecond Z-scan measurements revealed information for both n
2 and . The distribution of n
2 versus wavelength was found to be consistent with a model described by the quadratic Stark effect, which is the dominant factor contributed to the nonlinear refractive index near the bandgap. Large on the order of 10 cm/GW and large negative n
2 with a magnitude on the order of several 10–12 cm2/W were obtained. The at near mid-gap infrared (IR) wavelength was also found to be on the order of several cm/GW by using two-photon-type autocorrelations in a GaN thin film. Taking advantage of the large two-photon absorption at mid-gap wavelengths, we have demonstrated excellent image quality on two-photon confocal microscopy, including two-photon-scanning-photoluminescence imaging and two-photon optical-beam-induced current microscopy, on a GaN Hall measurement sample and an InGaN green light emitting diode. 相似文献
146.
With a view to obtain exact analytic solutions to the time-dependent Schrödinger equation for a few potentials of physical interest in three dimensions, transformation-group method is used. Interestingly, the integrals of motion in the new coordinates turn out to be the desired invariants of the systems. 相似文献
147.
In this paper we presented a method, which will allow multiple parameter control of the 3-dB bandwidth, center notch wavelength and attenuation level in a fiber-based acousto-optic tunable filter (AOTF). The method basically involves the variation of the interaction length, RF frequency and RF power on a single-fiber device to achieve multiple parameters tuning of the optical filter. The acousto-optic (AO) interaction inside a single-mode fiber (SMF) was studied theoretically and experimentally. 相似文献
148.
J. Rana G.L. Goswami S.K. Jha P.K. Mishra B.V.S.S.S. Prasad 《Optics & Laser Technology》2007,39(2):385-393
An experimental investigation with 5 kW CW CO2 laser system was carried out to study the effects of different laser and process parameters on the microstructure and hardness of carbon steel specimen with varying carbon percentage. The laser beam is allowed to scan on the surface of the work piece varying the power (1.1–2.5 kW) and traverse speed (6–15 mm/s) at two different spot sizes using TEM01* mode laser beam. The most hardenable microstructure achieved in case of three grades of carbon steel and the most influencing parameter on the value of hardness are reported. Besides the above study, some multipass operations are also carried out to recommend an appropriate gap between consecutive passes. 相似文献
149.