排序方式: 共有37条查询结果,搜索用时 265 毫秒
21.
The BICO0.20–xNIxVOX solid electrolyte was synthesized by the standard solid-state reaction. The effect of Ni(II) substitution for Co(III) on phase stabilization and oxide-ion performance has been investigated in the compositional range 0?≤?x?≤?0.20 using X-ray powder diffraction, differential thermal analysis and AC impedance spectroscopy. The highly conductive γ′-phase was effectively stabilized at room temperature for compositions with x?≥?0.13 whose thermal stability increases with Ni content. The complex plane plots of impedance were typically represented at temperatures below 380?°C, suggesting a major contribution of polycrystalline grains to the overall electrical conductivity. The dielectric permittivity measurements revealed the fact that suppression of the ferroelectric transition is compositionally dependent. Interestingly, the maximum ionic conductivity at lower temperatures (~2.56?×?10?4?S?cm?1 at 300?°C) was observed for the composition with x?=?0.13. The variation of low-temperature conductivity with Ni content was accompanied with a general drop in the corresponding values of ΔELT. However, the local minimum high-temperature conductivity, σ600?°C?~?2.26?×?10?2?S?cm?1 for x?=?0.10, coupled with a local maximum value of ΔEHT?~?0.48?eV was attributed to an increased defect trapping effect correlated with the V(V)?→?V(IV) reduction at elevated temperatures. 相似文献
22.
Ghaleb A. Husseini Natalya Y. Rapoport Douglas A. Christensen John D. Pruitt William G. Pitt 《Colloids and surfaces. B, Biointerfaces》2002,24(3-4):253-264
The aim of this research was to measure and model the kinetics of acoustic release and subsequent re-encapsulation of Doxorubicin (DOX) from Pluronic P105 micelles. A fluorescence detection ultrasound exposure chamber was used. Experimental data showed that no significant release was observed when DOX loaded in Pluronic P105 micelles was exposed to ultrasound for less than 0.1 s at a power density of 58 mW/cm2 and a frequency of 20 kHz. Above this threshold, the amount of release was shown to increase as the pulse length increased up to 0.6 s. The same experiments showed that it requires at least 0.1 s of no ultrasound for measurable re-encapsulation to occur. Release and re-encapsulation are completed within about 0.6 s of the beginning of the ON and OFF phases of pulsed ultrasound. Several physical models and their corresponding mathematical solutions were analyzed to see which most closely fit the data. The model of zero-order release with first-order re-encapsulation appears to represent data from this polymeric system better than other models. This technique has possible applications in site-specific chemotherapy. 相似文献
23.
24.
Two series of Sm-, Gd-codoped aluminoborosilicate glasses with different total rare earth content have been studied in order to examine the codoping effect on the structural modifications of β-irradiated glasses. The data obtained by electron paramagnetic resonance (EPR) spectroscopy indicated that the relative amount of Gd3+ ions located in network former positions reveals a non-linear dependence on the Sm/Gd ratio. Besides, codoping leads to the evolution of the EPR signal attributed to defects created by irradiation. The superhyperfine structure of boron oxygen hole centres EPR line becomes less noticeable and less resolved with the increase of Gd. This fact manifests that Gd3+ ions are mainly diluted in the vicinity of the boron network. By Raman spectroscopy, we showed that the structural changes induced by the irradiation also reveal non-linear behavior with the Sm/Gd ratio. In fact, the shift of the Si-O-Si bending vibration modes has a clear minimum for the samples containing equal amount of Sm and Gd (50:50) in both series of the investigated glasses. In contrast, for single-doped glass there is no influence of dopant’s content on Si-O-Si shift (in the case of Gd) or its diminution (in the case of Sm) occurs, which is explained by the reduction process influence. At the same time, no noticeable effect of codoping on Sm3+ intensity as well as on Sm2+ emission or on Sm reduction process was observed. 相似文献
25.
In order to study the effect of substitution of Fe3+ by Al3+ and Cr3+ in Li0.5Fe2.5O4 on its structural and magnetic properties, the spinel system Li0.5Al x Cr x Fe2.5?2x O4 (x=0.0, 0.2, 0.4, 0.5, 0.6 and 0.8) has been characterized by X-ray diffraction, high field magnetization, low field ac susceptibility and 57Fe Mossbauer spectroscopy. Contrary to the earlier reports, about 50% of Al3+ is found to occupy the tetrahedral sites. The system exhibits canted spin structure and a central paramagnetic doublet was found superimposed on magnetic sextet in the Mössbauer spectra (x>0.5). 相似文献
26.
Using Born–Mayer–Huggins potentials, a molecular dynamics model of a series of 5-oxide (SiO2, B2O3, Na2O, Al2O3, and ZrO2) glasses of various compositions was developed. The evolution of the glass structure according to the composition provides an overview of the behavior of each species. Some experimental observations were correctly reproduced, e.g., the gradual incorporation of the boron in the silicate network, the attraction of sodium atoms by four-coordinate boron, and the shorter distances between network formers and non-bridging oxygen atoms. Moreover, direct visualization of the structures reveals boron-enriched segregation zones in a composition containing no aluminum, as well as smaller regions comprising only aluminum atoms. 相似文献
27.
A. Ghaleb A. Aouidate A. Sbai M. Bouachrine T. Lakhlifi 《Journal of Structural Chemistry》2018,59(7):1544-1554
The 3D QSAR analysis using the comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) techniques is performed on novel nalidixic acid based 1,2,4-triazole derivatives suggested earlier as antibacterial agents. The CoMFA and CoMSIA models employed for a training set of 28 compounds gives reliable values of Q2 (0.53 and 0.52, respectively) and R2 (0.79 and 0.85, respectively). The contour maps produced by the CoMFA and CoMSIA models are used to determine a three-dimensional quantitative structure-activity relationship. Based on the 3D QSAR contours new molecules with high predicted activities are designed. In addition, surflex-docking is performed to confirm the stability of predicted molecules in the receptor. 相似文献
28.
Photothermal spectrometry for detection in miniaturized systems: relevant features, strategies and recent applications 总被引:1,自引:0,他引:1
Ghaleb KA Georges J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2004,60(12):2793-2801
There is a growing interest in using miniaturized analytical devices because they allow to execute the different steps of an analytical process within very short times and with drastic reduction in the amounts of solvents, reagents and samples. As for capillary electrophoresis, these systems require detectors which are sensitive, versatile and adaptable to very small detection volumes. In this respect, photothermal spectrometry which is complementary to fluorescence seems to be a promising detection method. This review describes the basic principle of photothermal spectrometry along with the related methods based on colinear-beam or crossed-beam configuration of the pump and probe lasers. Two experimental set ups especially designed for microfluidic systems as well as for capillary electrophoresis are described. Their characteristics and key features are discussed and the main applications are outlined. 相似文献
29.
Rajashri R. Naik Ashok K. Shakya Benedetta Ferri Ghaleb A. Oriquat Luisa Pistelli Nawfal A. M. Numan 《Molecules (Basel, Switzerland)》2021,26(18)
The present paper reports the GC-HS-SPME analysis of volatile emission and GC-MS analysis of chemical composition of essential oil of R. coriaria fruits of eight different samples of R. coriaria L. fruits (“sumac” folk name), collected from Jordanian agricultural field and the local market. The analyses show an important variability among the Sumac samples probably due to the origin, cultivation, harvesting period, drying, and conservation of the plant material. The main class of component present in all samples was monoterpenes (43.1 to 72.9%), except for one sample which evidenced a high percentage of sesquiterpene hydrocarbons (38.5%). The oxygenated monoterpenes provided a contribution to total class of monoterpenes ranging from 10.1 to 24.3%. A few samples were rich in monoterpene hydrocarbons. Regarding the single components present in all the volatile emissions, β-caryophyllene was the main compound in most of the analyzed samples, varying from 34.6% to 7.9%. Only two samples were characterized by α-pinene as the main constituent (42.2 and 40.8% respectively). Essential oils were collected using hydro-distillation method. Furfural was the main constituent in almost all the analyzed EOs (4.9 to 48.1%), except in one of them, where β-caryophyllene was the most abundant one. β-caryophyllene ranged from 1.2 to 10.6%. Oxygenated monoterpenes like carvone and carvacrol ranged from 3.2–9.1% and 1.0–7.7% respectively. Cembrene was present in good amount in EO samples EO-2 to EO-8. The antioxidant capacities of the fruit essential oils from R. coriaria were assessed using spectrophotometry to measure free radical scavenger 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and inhibition of β-carotene bleaching (BCB). The essential oils from the fruits of the different samples of R. coriaria exhibited the MIC value ranging from 32.8 to 131.25 µg/mL against S. aureus ATCC 6538 and 131.25 to 262.5 µg/mL against E. coli ATCC 8739. The MIC values of ciprofloxacin were 0.59 and 2.34 µg/mL against S. aureus ATCC 6538 and E. coli ATCC 8739, respectively. 相似文献
30.
A. R. El-Dhaba A. F. Ghaleb M. S. Abou-Dina 《Archive of Applied Mechanics (Ingenieur Archiv)》2014,84(9-11):1393-1407
The static, plane uncoupled problem of thermo-magnetoelasticity for a long elastic cylinder of square cross-section carrying a steady, axial electric current is investigated numerically by a boundary integral method. The lateral surface of the cylinder may be subjected, additionally, to an external distribution of pressures. The deformation is induced by the combined action of Joule heat, the magnetic forces due to the current and the external pressure. Following a smoothing process of the boundary, the applied numerical method yields the values of all quantities of practical interest at the boundary. The corresponding values in the bulk and the magnetic field in the space surrounding the conductor may be easily determined by quadrature. The results are represented graphically and discussed. 相似文献