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排序方式: 共有206条查询结果,搜索用时 15 毫秒
1.
M. H. El-Fouly A. F. Maged H. H. Amer M. A. Morsy 《Journal of Materials Science》1990,25(4):2264-2266
Temperature-induced transformations are considered to be interesting characteristic properties of amorphous materials including the Si
x
Te60–x
As30Ge10 system, withx=5, 10, 12 and 20. Density (), X-ray diffraction and differential thermal analysis (DTA) were used to characterize the compositions. DTA traces of each glass composition at different heating rates from 5 to 30° C min–1 were obtained and interpreted. Fast and slow cooling cycles were used to determine the rate of structure formation. Cycling studies of materials show no memory effect but only ovonic switching action. The compositional dependence of the crystallization activation energy (E) and the coefficient of glass-forming tendency (K
gl) have been calculated. The thermal transition temperatures and associated changes in specific heat have been examined as a function of the Te/Si ratio by differential scanning calorimetry. It was found that andE increase linearly with increasing tellurium content, while the heat capacity (c
p) andK
gl, decrease with increasing tellurium content.E=1.54 eV andc
p=0.246 J g–1 K–1 forx=20 whileE=2.74eV andc
p=0.22 J g–1 K–1 forx=5. 相似文献
2.
M. H. El-Fouly A. M. Morsy A. H. Ammar A. F. Maged H. H. Amer 《Journal of Materials Science》1989,24(7):2444-2448
The effect of composition on amorphous chalcogenide threshold switches of the system Si
x
Te60-x
As30Ge10, wherex = 5, 10, 12 and 20, has been studied. The compositionx = 5 shows the best switching characteristics, e.g. the smallest holding voltage (V
h = 0.4V), the highest ON state current (I
h = 45A) and smallest threshold voltage (V
s = 1.5V). Applying the three mechanisms of conductance of Mottet al. (Phil. Mag.
37 (1975) 961), it is found that for a particular composition
2 <
1 <
0 (the pre-exponential factors) andW
2 < (E
a –E
1 +W
1) < (E
c –E
f) (whereE
a,E
c andE
e = activation energies at band edge, fermi level and conduction band;W
1 andW
2 = activation energy for hopping). It was found that the density of states at the fermi levelN(E
f) increases with the decrease of silicon content. The results provided further evidence against thermal interpretations and thereby support electronic models of threshold switching for these glass systems. 相似文献
3.
Nabel?A.?NegmEmail author Salwa?M.?I.?Morsy 《Journal of surfactants and detergents》2005,8(3):283-287
A weight loss technique was used to determine the corrosion inhibition efficiency of synthesized alkyl mono-and dibenzoate
triethanolammonium bromide derivatives (TEAMB, TEADB) in an acidic medium (2 N HCl) at different doses (50, 100, and 200 ppm).
The results showed that monoderivatives had a higher corrosion inhibition efficiency than diderivatives. The results were
correlated with several factors, including the alkyl chain length of the hydrophobic chains, interfacial tension (IT), critical
micelle concentration (CMC), and adsorption free energy of these inhibitors. Increasing the geometric length of the alkyl
chains in the synthesized inhibitors had an increasing effect on their corrosion inhibition efficiency, whereas decreasing
the CMC and IT had an increasing effect on their tendency toward corrosion inhibition. The number of hydrophobic chains attached
to the inhibitor molecules had a vital influence on their efficiency as corrosion inhibitors. 相似文献
4.
A new mesoporous adsorbent for uranium removal from waste effluents was prepared, characterized, and impregnated with trioctylamine. The adsorption efficiency was investigated as a function of pH, contact time, initial uranium concentration, competing ions, solid/liquid ratio, and temperature using batch sorption techniques. The maximum adsorption capacity was 21.9 mg g–1 at pH 5. The equilibrium data fit well with the Langmuir adsorption isotherm. Kinetic study showed that the process was fast and reached equilibrium within 60 min. The kinetic data fit well with the pseudo-second-order law. Thermodynamic data show that the process is spontaneous and exothermic. 相似文献
5.
Solvent extraction of uranium ions with 4-methylpentan-2-one was examined. The diluent, extractant concentration, aqueous to organic phase ratio, and contact time were varied. Different stripping agents were examined to reach the optimum stripping conditions. The results obtained show that uranium can be quantitatively extracted from 5 M nitric acid with 7% 4-methylpentan-2-one dissolved in refined kerosene and stripped from the organic phase with 5% Na2CO3. The equilibrium is attained within 10 min. Uranium can be efficiently separated from a large number of elements by adding EDTA salt to the stripping solution before uranium precipitation. 相似文献
6.
7.
Correlation of In Vivo and In Vitro Assay Results for Assessment of Free Radical Scavenging Activity of Green Tea Nutraceuticals 下载免费PDF全文
Heba‐Alla H. Abd‐ElSalam Medhat A. Al‐Ghobashy Muhammad Al‐Shorbagy Noha Nassar Hala E. Zaazaa Mohamed A. Ibrahim 《Journal of food science》2016,81(7):C1707-C1715
Green tea (GT)‐derived catechins; epigallocatechin gallate (EGCG) in particular are commonly used nutraceuticals for their free‐radical scavenging activity (FRSA). The influence of photodegradation on the protective power of GT nutracenticals against oxidative stress was thoroughly explored. Photodegradation of GT extracts was carried out and monitored using orthogonal stability‐indicating testing protocol; in vitro and in vivo assays. Total polyphenol content (TPC) and FRSA were determined spectrophotometrically while EGCG was selectively monitored using SPE‐HPLC. In vivo assessment of photodegraded samples was investigated via measuring a number of biomarkers for hepatic oxidative stress and apoptosis (caspase‐3, inducible nitric oxide synthase, nitric oxide, mitogen‐activated protein kinase, glutathione, thiobarbituric acid reactive substances, nuclear factor kappa beta, and nuclear factor erythroid 2‐related factor) as well as liver damage (alanine transaminase and aspartate transaminase) in serum of rats previously subjected to oxidative stress. Results showed complete degradation of EGCG in photodegraded green tea samples with no correlation with either TPC or FRSA. On the other hand, in vivo assay results revealed not only loss of activity but formation of harmful pro‐oxidants. Photostability was found crucial for the protective effect of GT extract against lead acetate insult. Results confirmed that careful design of quality control protocols requires correlation of chemical assays to bioassays to verify efficacy, stability, and most importantly safety of nutraceuticals. 相似文献
8.
9.
Christophe Chlique Odile Merdrignac‐Conanec Noha Hakmeh Xianghua Zhang Jean‐Luc Adam 《Journal of the American Ceramic Society》2013,96(10):3070-3074
We report an efficient way of preparing transparent ZnS ceramics using the hot‐pressing technique. It has been found that the transparency is highly dependent on the purity and the grain size distribution of the starting ZnS powders. Highly pure and monodisperse ZnS powders have been obtained by posttreatment of the precipitated powders in a H2S/N2 flow for 2 h at 600°C. The obtained ZnS ceramics show fully dense and homogeneous microstructure with average grain size of ~1 μm and smooth grain boundaries, leading to an excellent transmission of around 70% in the mid‐ and far‐ IR regions. The preparation technique described in this study is highly reproducible. 相似文献
10.
Gamal ElMasry Noha Morsy Salim Al-Rejaie Charfedinne Ayed Robert Linforth Ian Fisk 《International Journal of Food Science & Technology》2019,54(11):2983-2997
The aim of this study was to use gas chromatography-mass spectrometry (GC-MS) and APCI-MS techniques to detect adulteration in honey. The key volatile compounds in the headspace of the adulterated honey were marked by GC-MS and their representative fragment ions were utilised in scanning honey samples using the real-time APCI-MS system. The PLS models validated using independent data sets resulted in coefficient of the determination () of 0.97 and 0.96 and root mean square error in prediction (RMSEP) of 2.62 and 2.45 for the GC-MS and APCI-MS data sets respectively. The most efficient volatiles from GC-MS analysis and their corresponding fragment ions m/z from APCI-MS data analysis were then identified and used to develop new PLS models to predict the level of adulteration. The best PLS model gave of 0.95 and RMEP of 2.60% in the independent validation set indicating that the model was very accurate in predicting the level of adulteration. 相似文献