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排序方式: 共有311条查询结果,搜索用时 11 毫秒
1.
We study the control of spontaneous emission in a five-level atomic system driven by four fields. We show that with the variation
of dynamical variables, namely, Rabi frequencies and carrier phases of driven fields, a wide variety of the spectral behavior
can be obtained, including extreme spectral narrowing. Our system can be found easily in real atoms. 相似文献
2.
Ahmad R Vikram DS Potter LC Kuppusamy P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,192(2):269-274
Electron paramagnetic resonance (EPR)-based oximetry is capable of quantifying oxygen content in samples. However, for a heterogeneous environment with multiple pO2 values, peak-to-peak linewidth of the composite EPR lineshape does not provide a reliable estimate of the overall pO2 in the sample. The estimate, depending on the heterogeneity, can be severely biased towards narrow components. To address this issue, we suggest a postprocessing method to recover the linewidth histogram which can be used in estimating meaningful parameters, such as the mean and median pO2 values. This information, although not as comprehensive as obtained by EPR spectral-spatial imaging, goes beyond what can be generally achieved with conventional EPR spectroscopy. Substantially shorter acquisition times, in comparison to EPR imaging, may prompt its use in clinically relevant models. For validation, simulation and EPR experiment data are presented. 相似文献
3.
Ahmad R Deng Y Vikram DS Clymer B Srinivasan P Zweier JL Kuppusamy P 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2007,184(2):236-245
In continuous wave (CW) electron paramagnetic resonance imaging (EPRI), high quality of reconstructed image along with fast and reliable data acquisition is highly desirable for many biological applications. An accurate representation of uniform distribution of projection data is necessary to ensure high reconstruction quality. The current techniques for data acquisition suffer from nonuniformities or local anisotropies in the distribution of projection data and present a poor approximation of a true uniform and isotropic distribution. In this work, we have implemented a technique based on Quasi-Monte Carlo method to acquire projections with more uniform and isotropic distribution of data over a 3D acquisition space. The proposed technique exhibits improvements in the reconstruction quality in terms of both mean-square-error and visual judgment. The effectiveness of the suggested technique is demonstrated using computer simulations and 3D EPRI experiments. The technique is robust and exhibits consistent performance for different object configurations and orientations. 相似文献
4.
Rizwan Wahab 《Applied Surface Science》2007,253(18):7622-7626
Single crystalline needle-shaped zinc oxide nanorods were synthesized via sonochemical methods using zinc acetate dihydrate and sodium hydroxide at room temperature. Morphological investigation revealed that the nanoneedles are of hexagonal surfaces along the length. The typical diameter and length vary from 120 to 160 nm and 3 to 5 μm, respectively. Sonication time appears to be a critical parameter for the shape determination. Detailed structural characterization confirmed that the nanorods are single crystalline with wurtzite hexagonal phase. A standard peak of zinc oxide was observed at 520 cm−1 from the Fourier transform infrared spectroscopy. The ultra-violet visible and room temperature photoluminescence (PL) spectroscopic results demonstrate that the synthesized material has good optical properties. 相似文献
5.
6.
Aboel‐Magd A. Abdel‐Wahab Omima S. Mohamed Saleh A. Ahmed Mostafa F. Mostafa 《Journal of Physical Organic Chemistry》2012,25(12):1418-1421
The superiority of silver‐doped titania for photocatalytic oxidation (PCO) of organic compounds inspired us to investigate PCO of 1,2‐cyclohexanediol. Ag/TiO2 was prepared, characterized (nanosize 19–24 nm) and used for oxidation of 1,2‐cyclohexanediol (1) in acetonitrile. The photolysate was analyzed using GC and GC/MS techniques. The PCO products are 2‐hydroxylcyclohexanone (2), 1,2‐cyclohexandione (3), 2‐cyclohexenone(4), cyclohexanone (5), and adipic acid (6).The formation of electron–hole pair at the surface of the catalyst followed by oxidation reactions was the suggested mechanism. Kinetic studies revealed first‐order mechanism for PCO of 1 and rate constant (k) = ?0.145 h–1. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
7.
Photopyroelectric spectroscopy of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> - ZnO ceramics
A. Zakaria Z. Rizwan M. Hashim A. Halim Shaari W. Mohmood Mat Yunus 《The European physical journal. Special topics》2008,153(1):33-35
Photopyroelectric spectroscopy is used to study the
band-gap energy of the ceramic (ZnO + xSb2O3), x = 0.1 - 1.5 mol%
and the ceramic (ZnO + 0.4 mol% Bi2O3 + xSb2O3), x = 0 - 1.5 mol% sintered at isothermal temperature, 1280 °C, for 1 and 2 hours. The wavelength of incident light, modulated
at 9 Hz, is kept in the visible range and the photopyroelectric spectrum with
reference to doping level is discussed. The band-gap energy is reduced from
3.2 eV, for pure ZnO, to 2.86, 2.83 eV for the samples without
Bi2O3at 0.1 mol% of Sb2O3 for 1 and 2 hours of
sintering time, respectively. It is reduced to 2.83, 2.80 eV for the samples
with Bi2O3 at 0 mol% of Sb2O3 for 1 and 2 hours of
sintering time, respectively. The steepness factor σA which
characterizes the slop of exponential optical absorption is discussed with
reference to the doping level. The phase constitution is determined by XRD
analysis; microstructure and compositional analysis of the selected areas
are analyzed using SEM and EDX. 相似文献
8.
Natural and anthropogenic radioactivity of sand and water samples collected from the four big rivers of Punjab province, Pakistan, was measured using a high-purity germanium detector coupled with a high resolution multichannel analyser. The average concentration of the naturally occurring radionuclides (226)Ra, (232)Th and (40)K in all the sand samples from the rivers Jhelum, Chenab, Ravi and Indus was found to be 22±0.6, 36±1 and 287±10 Bq kg (-1), respectively, while the concentration of the anthropogenic radionuclide (137)Cs was found to be below the minimum detectable activity, i.e. ~1.2 Bq?kg (-1). All the sand samples have Ra(eq) concentrations lower than the limit of 370 Bq kg (-1). Indoor (H (in)) and outdoor (H (out)) radiation hazard indices were calculated for the samples to assess the radiation hazards arising due to the use of this sand in construction, and were found to be less than unity in the study area. Calculated values of the absorbed dose rate were less than the typical world average value of 59 nGy h (-1), and the annual effective dose rate was also less than the typical world value of 70 μSv, except in the Indus river, in which it is slightly higher then the world average. Results show that the measured values are comparable with other global radioactivity measurements. None of the studied riverbeds was considered a radiological hazard, and their sand can be safely used in construction. 相似文献
9.
10.
Chitosan loaded with silver nanoparticles,CS‐AgNPs,using thymus syriacus,wild mint,and rosemary essential oil extracts as reducing and capping agents 下载免费PDF全文
Fadi AL‐Shnani Thanaa Al‐Haddad Francois Karabet Abdul Wahab Allaf 《Journal of Physical Organic Chemistry》2017,30(11)
The present study describes the green method for the preparation of chitosan loaded with silver nanoparticles (CS‐AgNPs) in the presence of 3 different extracted essential oils. The essential oils play dual roles as reductant and capping agents. The reducing power and DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) assay for the 3 essential oils—Thymus syriacus (T), wild mint (M), and rosemary (R)—have been reported. The preparation of CS‐AgNPs was performed by 2 steps. The 3 previously extracted essential oils have been used as reducing and capping agent in the first step, while in the second step, silver nanoparticles were integrated in chitosan. The integration of AgNPs in the structure of chitosan was confirmed by ultraviolet‐visible, Fourier transform infrared spectroscopy, scanning electron microscopy techniques, and energy dispersive X‐ray. Surface plasmon resonance confirmed the formation of CS‐AgNPs with maximum absorbance at λmax between 405 ‐ 410 and 410 ‐ 430 nm for colloidal and films of CS‐AgNPs, respectively. The intensity of bands at 3408 cm?1 in the fourier transform infrared spectroscopy measurements was decreased substantially and shifted slightly to lower frequency (?υ = 43 cm?1). Scanning electron microscopy shows a spherical morphology of AgNPs with size of 62 nm for both colloidal and film samples, and energy dispersive X‐ray analysis shows peaks confirming AgNPs formation. 相似文献