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1.
Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes 下载免费PDF全文
Manne Annapurna T. Parsharamulu P. Vishnuvardhan Reddy M. Suresh Pravin R. Likhar Mannepalli Lakshmi Kantam 《应用有机金属化学》2015,29(4):234-239
Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
2.
Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic
about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which
is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum)
energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density
of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are
constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure
and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third
of the combined value of radiation pressure and density. 相似文献
3.
Manne Annapurna P. Vishnuvardhan ReddySurya Prakash Singh Mannepalli Lakshmi Kantam 《Tetrahedron》2013
The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides and heteroaryl bromides is described using air and moisture stable N,N′,N″,O-tetrafunctional Pd catalyst under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were obtained in high to good yields. 相似文献
4.
Reenamoni Saikia Chaliha K. Annapurna Anal Tarafder V.S. Tiwari P.K. Gupta Basudeb Karmakar 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(1):243-250
Precursor glass of composition 25K2O–25Nb2O5–50SiO2 (mol%) doped with Er2O3 (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO3 nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO3 estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO3 phase. The measured visible photoluminescence spectra have exhibited green emission transitions of 2H11/2, 4S3/2 → 4I15/2 upon excitation at 377 nm (4I15/2 → 4G11/2) absorption band of Er3+ ions. The near infrared (NIR) emission transition 4I13/2 → 4I15/2 is detected around 1550 nm on excitation at 980 nm (4I15/2 → 4I11/2) of absorption bands of Er3+ ions. It is observed that photoluminescent intensity at 526 nm (2H11/2 → 4I15/2), 550 nm (4S3/2 → 4I15/2) and 1550 nm (4I13/2 → 4I15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (τf) of the 4I13/2 → 4I15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er3+ ions gradually enter into the KNbO3 nanocrystals. 相似文献
5.
This paper deals with the preparation and optical analysis of Er3+ (0.2 mol%) boro-fluoro-phosphate glasses in the following glass compositions:
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Series A: 69.8 B2O3–10 P2O5–10(ZnO/CdO/TeO2)–10 AlF3
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Series B: 69.8 B2O3–10 P2O5–10(ZnO/CdO/TeO2)–10 LiF
6.
The general dynamical equations for perfect fluid filled spheres with an outward flux of photons are derived. The vital role
played by the energy density of the free gravitational field in accelerating photon production has been emphasized. It is
pointed out that even when the material energy density is finite, the energy density of the free gravitational field can take
infinitely large values resulting in vanishing surface area of the star. A generalized Schwarzschild interior solution with
conformally flat geometry but with photon emission has been obtained. It is pointed out that the interior conformal coordinate
system bears a strong resemblance to the exterior Krushkal coordinates. It is shown that for spherical star the invariant
velocity of the fluid particles, falling towards the centre, is proportional to its radius suggesting that the outer envelopes
collapse at a faster rate than the core part. It is shown that the interior radiating solution can be matched with generalized
Schwarzchild exterior solution. 相似文献
7.
Nowduri Annapurna Adari Kalyan Kumar Parvataneni Vani Gollapalli Nageswara Rao 《Transition Metal Chemistry》2008,33(6):691-696
The kinetics of oxidation of l-cystine by MnIII have been studied in sulfuric acid medium at 30 °C. The reaction was followed spectrophotometrically at λmax = 500 nm. The
reaction shows first order dependence on both [MnIII] and [cystine]. It was found that the rate of the reaction decreases with increase of [H+] up to a certain point and then remains unchanged. The oxidation product of the reaction was found to be cysteic acid. A
plausible mechanism has been proposed to account for the experimental results. 相似文献
8.
Atul D. Sontakke Kaushik Biswas Ashis K. Mandal Kalyandurg Annapurna 《Journal of fluorescence》2010,20(1):425-434
This paper reports on the preparation and systematic analysis of energy transfer mechanisms in Nd3+–Yb3+–Er3+ co-doped new series of barium-alumino-metaphosphate glasses. The time resolved fluorescence of Nd3+ in triply doped Ba–Al-metaphosphate glasses have revealed that, Yb3+ ions could function as quite efficient bridge for an energy transfer between Nd3+ and Er3+ ions. As a result, a fourfold emission enhancement at 1.54 μm of Er3+ ions has been achieved through an excitation of 4F5/2 level of Nd3+ at 806 nm for the glass having 3 mol% Yb3+ with an energy transfer efficiency reaching up to 94%. Decay of donor (Nd3+) ion fluorescence has been analyzed based on theoretical models such as direct energy transfer model (Inokuti–Hirayama) and
migration assisted energy transfer models (Burshtein’s hopping and Yokota–Tanimoto’s diffusion). The corresponding energy
transfer parameters have been evaluated and discussed. Primarily, electrostatic dipole–dipole (s ~ 6) interactions are found
to be responsible for the occurrence of energy transfer process in theses glasses. 相似文献
9.
A. D. Sontakke K. Biswas A. K. Mandal K. Annapurna 《Applied physics. B, Lasers and optics》2010,101(1-2):235-244
This paper reports the dopant ion (Nd3+) concentration effects on its luminescence properties in a new glass system based on barium-alumino-metaphosphates. Amongst the studied concentrations range of 0.276–13.31×1020 ions/cm3, the glass with 2.879×1020 ions/cm3 (1 mol%) Nd3+ concentration shows intense NIR emission from 4F3/2 excited state, followed by a decrease in emission intensity for further increase in Nd3+ ion concentration. The observed luminescence quenching is ascribed to Nd3+ self-quenching through the donor-donor migration assisted cross-relaxation mechanism. The microscopic energy transfer parameters for donor-acceptor energy transfer, C DA, and donor-donor energy migration, C DD, have been obtained from the theoretical fittings to experimental decay curves and the spectral overlap model respectively. The C DD parameters (×10?39 cm6/sec) are found to be about three orders greater than that of C DA (×10?42 cm6/sec) for Nd3+ self-quenching in this host, demonstrating that the excitation energy migration among donors is due to the hopping mechanism. The energy transfer micoparameters obtained in the present study are comparable to the values reported for commercially available laser glasses LHG-8 and Q-98. 相似文献
10.
Himabindu M Ravichandra P Vishalakshi K Jetty A 《Applied biochemistry and biotechnology》2006,134(2):143-154
Optimization of the fermentation medium components for maximum gentamicin production by Micromonospora echinospora ATCC 15838 was carried out. Response surface methodology was applied to optimize the medium constituents. A 24full-factorial central composite design was chosen to explain the combined effects of the four medium constituents, viz. starch,
soyabean meal, K2HPO4, and CoCl2 and to design a minimum number of experiments. A second order model was developed and fitted using least square method. The
R
2 value of the model was 0.9723, which shows that model is best fit for the present studies. The results of analysis of variance
and regression of a second order model showed that the linear effects of starch (p<0.001697) and CoCl2(p<7.99E-13), and cross product effects of starch and soyabean meal (p<0.029876) and soyabean meal and CoCl2 (p<0.008909) were more significant, suggesting that these were critical variables having the greatest effect on the production
of gentamicin in the production medium. The optimized medium consisting of 9 g/L starch, 3 g/L soyabean meal, 0.9 g/L K2HPO4, and 0.01 g/L CoCL2 predicted 850 mg/L of gentamicin which was almost 110% higher than that of the unoptimized medium. The amounts of starch,
soyabean meal, and K2HPO4 required were also reduced with RSM. 相似文献