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排序方式: 共有386条查询结果,搜索用时 15 毫秒
1.
International Journal of Theoretical Physics - A realizable delayed-choice quantum eraser, using a modified Mach-Zehnder (MZ) interferometer and polarization entangled photons, is theoretically... 相似文献
2.
In an erbium-doped fiber amplifier(EDFA), erbium ions act as a three-level system. Therefore, much higher pump energy is required to achieve the population inversion in an erbium-doped fiber(EDF). This higher pump energy requirement complicates the efficient design of an EDFA. However, efficient use of the pump power can improve the EDFA performance. The improved performance of an EDFA can be obtained by reducing the doping radius of the EDF. A smaller doping radius increases pump–dopant interactions and subsequently increases the pump–photon conversion efficiency. Decreasing the doping radius allows a larger proportion of dopant ions,which are concentrated near the core, to interact with the highest pump intensity. However, decreasing the doping radius beyond a certain limit will bring the dopant ions much closer and introduce detrimental ion–ion interaction effects. In this Letter, we show that an optimal doping radius in an EDF can provide the best gain performance. Moreover, we have simulated the well-known numerical aperture effects on EDFA gain performance to support our claim. 相似文献
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Suchinder K. Sharma Shreyas S. Pitale T.K. GunduRao M.S. Qureshi 《Journal of luminescence》2010,130(2):240-248
A simple solution combustion synthesis route for preparation of Cu-doped SrAl4O7 has been described. Average particle size of 33 nm and platelet-like morphology has been observed. ESR studies confirm the presence of Cu in polycrystalline SrAl4O7. Bright-green luminescence under near-UV irradiation arising due to transition between Cu+ levels with microsecond level decay time makes it suitable for application in phosphor converted light emitting diode (LED). TL measurements show broad glow peaks which when deconvoluted indicate activation energies in the range of 0.6-1.1 eV and elucidate the trapping dynamics. 相似文献
6.
Muhammad Nasimullah Qureshi Muhammad Siddique Inayat‐ur‐Rahman Kanwal Farina Kanwal 《中国化学会会志》2011,58(2):236-240
Methyl ester derivatives of fatty acids were analyzed for the determination of the constituents of Datura alba seed oil. Gas chromatography coupled to mass spectrometer was used for these analyses. Results delivered that there were saturated as well as unsaturated fatty acids in Datura alba seed oil. Total of 15 different fatty acid components were identified and quantified. Methyl linoleate was found in highest concentration (16.22%) among the identified analytes of interest. In addition methyl esters of Palmitic acid (6.59%), Oleic acid (5.41%) and Stearic acid (1.35%) were found. Concentrations of rest of the detected fatty acids were less than 1%. From the literature it appears that no such work has been performed for the determination of fatty acids in Datura alba seed oil. 相似文献
7.
Muhammad Nasimullah Qureshi Guenther Stecher Christian Huck Guenther K. Bonn 《Central European Journal of Chemistry》2011,9(2):206-212
This article discusses the preparation of different polymeric sorbents for solid phase extraction. Various monomers like acrylamide,
methacrylic acid and 4-vinylpyridine (VP), cross-linkers such as divinylbenzene (DVB) and ethyleneglycoldimethacrylate (EDMA),
porogens like tetrahydrofuran (THF) and dimethylsulphoxide (DMSO) / acetonitrile (ACN) with different ratios were investigated
in order to optimize recoveries. Resulting polymers were characterized through scanning electron microscope (SEM) and compared
with Oasis HLB (Waters, MA, USA) and Strata-X (Phenomenex, Torrance, USA) on the basis of extraction performance, recovery
efficiency and loading capacity. Sample applied was a mixture of flavonoid standards (rutin, myricetin, luteolin, quercetin,
apigenin and kaempferol). HPLC hyphenated with PDA was used for the analysis of samples. Results showed that among the prepared
SPE materials, 4-VP-co-EDMA produced best results. Comparison of the produced polymers with of Oasis HLB and Strata-X resulted
in comparable efficiencies; especially the polymer 4-VP-co-EDMA gave almost similar results for all analytes to those of commercially
available SPE materials. A general trend of decrease in retention efficiency with increase in polarity has been observed in
both synthesized and already available SPE materials. The newly synthesized polymeric materials can be employed as SPE sorbents
for efficient extraction of polyphenolic compounds especially for flavonoid aglycons. 相似文献
8.
Research on Chemical Intermediates - Palladium nanoparticles (~?1–3 nm, 0.4 wt% Pd) were uniformly distributed over the surface of fibrous silica nanospheres (KCC-1)... 相似文献
9.
Sequential Rhodium/Palladium Catalysis: Enantioselective Formation of Dihydroquinolinones in the Presence of Achiral and Chiral Ligands 下载免费PDF全文
Lei Zhang Zafar Qureshi Lorenzo Sonaglia Prof. Dr. Mark Lautens 《Angewandte Chemie (International ed. in English)》2014,53(50):13850-13853
Compatible combinations of achiral and chiral ligands can be used in rhodium/palladium catalysis to achieve highly enantioselective domino reactions. The difference in rates of catalysis and minimal effects of ligand interference confer control in the domino sequence. The “all‐in‐one” 1,4‐conjugate arylation and C? N cross‐coupling through sequential Rh/Pd catalysis provides access to enantioenriched dihydroquinolinone building blocks. 相似文献
10.
Theoretical investigations of atomic charges, conformers, frontier molecular orbitals, molecular geometries, thermodynamic
properties, hyperpolarizabilities and harmonic vibrational frequencies of 6-methyluracil (6MU) have been carried out using
ab initio Hartree-Fock (HF), density functional theory (DFT) and second order M?ller-Plesset (MP2) methods. All calculations were performed
using the GAMESS-US program package with the basis sets 6-31G(d,p) and 6-311G(d,p). FT-IR and Raman spectra of 6MU were recorded
in the regions 50–4000 cm−1 and 60–4000 cm−1 respectively. Optimized geometries were obtained using the global optimization procedure. The calculated structural parameters
for two conformers of 6MU have been compared with experimentally observed values. The energy barrier (ΔE=ELUMO-EHOMO) between
the HOMO and LUMO is predicted on the basis of theoretical calculations. The simulated TD-DFT spectrum has been compared with
experimental electronic spectrum for 6MU. The calculated potential energy distribution (PED) values have been utilized to
perform vibrational assignment of the infrared and Raman spectra. 相似文献