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81.
Optical bistability for two-level atomic system in a ring cavity is investigated outside the rotating wave approximation (RWA) using non-autonomous Maxwell-Bloch equations with Fourier decomposition up to first harmonic. The first harmonic output field component exhibits reversed or closed loop bistability simultaneously with the usual (anti-clockwise) bistability in the fundamental field component. 相似文献
82.
Yasser M.Z. Ahmed Mohamed I. Riad Ahmed I. Zaky Mohammed Abdel-Aziz Mohamed M.H. Shalabi 《中国颗粒学报》2007,5(6):391-394
In line with recent attention on porous metals having low and medium porosities in the range of 20-50%, this paper studies the effect of porosity on the mechanical properties of sintered copper compacts. Experiments were designed to investigate the effect of porosity, applied stress and sliding velocity on the wear rate of copper compacts, leading to the finding that the effects of both porosity and applied stress of the wear test on the wear rate are approximately similar and higher than that of sliding velocity. The investigation concerning the effect of porosity on compressive strength indicated that the stress-strain curve of high-porosity compact exhibited identifiable ultimate strength points, though low-porosity compact showed distinct stages of elastic plastic behavior. 相似文献
83.
Yasser A. El-Ossaily Saoud A. Metwally Nayef S. Al-Muailkel Ahmed Fawzy Hazim M. Ali Yousra A. Naffea 《Journal of heterocyclic chemistry》2020,57(4):1729-1736
A green, rapid, and efficient methodology is developed for the synthesis of 1-phenyl-3,5-pyrazolidinedione ( 3 ) by the reaction of malonic acid with phenyl hydrazine in the presence of phosphorous oxychloride under solvent-free conditions. The later compound 3 was used as a versatile precursor for green synthesis of chalcone derivatives ( 4a-h ) and spiroheterocyclic compounds ( 5a-h ) with good to excellent isolated yields. The chemical structures of the synthesized compounds were elucidated on the basis of elemental and spectral analyses. 相似文献
84.
Fawzy A. Attaby Hussein M. Mostafa Ahmed H. H. Elghandour Yasser M. Ibrahem 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2753-2772
Cyanothioacetamide ( 1 ) reacted with acrylonitrile ( 2 ) to afford the corresponding 6-oxo-2-sulfanylpiperidine-3-carbonitrile ( 6 ), which oxidized to give compounds 7 and 8 under different conditions. Moreover, compound 6 was used as a starting material to synthesize 12a-c , 16a-d , 26a-c , 27a-c , and 30a-c via reactions with aromatic aldehydes 9a-c , diazonium chlorides 13a-d , and 3-arylpropennitrile derivatives 18a-i respectively. Considering the data of IR, 1 H NMR, mass spectra, elemental analyses, and theoretical calculations, all the structures of the newly synthesized heterocyclic compounds were elucidated. 相似文献
85.
Mohsen S. Al-Omar Hamdoon A. Mohammed Salman A. A. Mohammed Essam Abd-Elmoniem Yasser I. Kandil Hussein M. Eldeeb Sridevi Chigurupati Ghassan M. Sulaiman Hadeel K. Al-Khurayyif Basma S. Almansour Prarthana M. Suryavamshi Riaz A. Khan 《Molecules (Basel, Switzerland)》2020,25(22)
Halophytes are the category of plants growing under harsh conditions of super-salinity, and are wide-spread in the coastal Mediterranean climatic conditions and desert oasis. They are adept at surviving through maintaining excessive production of enzymatic, and non-enzymatic secondary metabolites, especially phenolics and flavonoids that primarily work as anti-oxidants and phytoalexins. Five major halophyte species growing in the kingdom’s Qassim’s high-salted desert regions were investigated for confirming their traditionally used biological activity of sugar-control and anti-infectious properties. In this context, the comparative presence of phenolics, and flavonoids together with anti-microbial, anti-oxidants, and the anti-diabetic potentials of the plants’ extracts were investigated through the α-amylase inhibition method. The highest concentrations of phenolics and flavonoids were detected in Salsola imbricata (360 mg/g of the extract as Gallic-Acid-Equivalents/GAE, and 70.5 mg/g of the extract as Rutin-Equivalents/RE). In contrast, the lowest concentrations of phenolics and flavonoids were detected in Salsola cyclophylla (126.6 mg/g GAE, and 20.5 mg/g RE). The halophytes were found rich in trace elements, a factor for water-retention in high-salinity plants, wherein iron and zinc elements were found comparatively in higher concentrations in Aeluropus lagopoides (4113 µg/kg, and 40.1 µg/kg, respectively), while the copper was detected in higher concentration (11.1 µg/kg) in S. imbricata, analyzed through Inductively Coupled Plasma Optical Emission Spectrometric (ICP-OES) analysis. The anti-oxidant potentials and α-amylase enzyme inhibition-based anti-diabetic activity of S. imbricata was significantly higher than the other halophytes under study, wherein S. cyclophylla exhibited the lowest level of α-amylase inhibition. The maximum DPPH radicals’ (52.47 mg/mL), and α-amylase inhibitions (IC50 22.98 µg/mL) were detected in A. lagopoides. The anti-microbial activity against the Methicillin-Resistant Staphylococcus aureus was strongly exhibited by Zygophyllum simplex (33 mm Inhibition Zone-Diameter, 50 µg/mL Minimum-Inhibitory-Concentration), while Escherichia coli, Enterococcus faecalis, and Candida albicans growths were moderately inhibited by Tamarix aphylla. The current findings exhibited significant differences among the locally distributed halophytic plants species with regards to their bioactivity levels, anti-oxidant potentials, and the presence of trace elements. The ongoing data corroborated the plants’ traditional uses in infections and diabetic conditions. The enhanced local distribution of the plants’ diaspora and higher density of occurrence of these plants species in this region, in comparison to their normal climatic condition’s counterparts, seemed to be affected by humans’ use of the species as part of the traditional and alternative medicine over a period of long time. 相似文献
86.
The integration of microactuators within a silicon photonic chip gave rise to the field of optical micro‐electro‐mechanical systems (MEMS) that was originally driven by the telecommunication market. Following the latter's bubble collapse in the beginning of the third millennium, new directions of research with considerable momentum appeared focusing on the realization and applications of miniaturized instrumentation in biology, chemistry, physics and materials science. At the heart of these applications light interferometry is a key optical phenomenon, in which miniaturized scanning interferometers are the manipulating optical devices. Monolithic free‐space optical interferometers realized on a silicon chip take advantage of the recent progress in the microfabrication technology that is enabling accurate control of the etching depth, the aspect ratio, the verticality and the curvature of the etched surfaces. The fabrication technology, the library of micro‐optical and mechanical components, the realized architectures and their characterization are described in detail in this review, followed by a discussion of the foreseen challenges.
87.
Maged El-Kemary Yasser Abdel-Moneam Ibrahim El-Mehasseb 《Journal of luminescence》2011,131(4):570-576
Nanostructure titanium dioxide (TiO2) has been synthesized by hydrolysis of titanium tetrachloride in aqueous solution and Ag-TiO2 nanoparticles were synthesized by photoreduction method. The resulting materials were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier-transform infrared (FT-IR) and UV-vis absorption spectroscopy. The experimental results showed that the sizes of the synthesized TiO2 and Ag-TiO2 particles are in the range of 1.9-3.2 nm and 2-10 nm, respectively. Moreover, Ag-TiO2 nanoparticles exhibit enhanced photocatalytic activity on photodegradation of Safranin-O (SO) dye as compared to pure TiO2. The positive effect of silver on the photocatalytic activity of TiO2 may be explained by its ability to trap electrons. This process reduces the recombination of light generated electron-hole pairs at TiO2 surface and therefore enhances the photocatalytic activity of the synthesized TiO2 nanoparticles. The effects of initial dye and nanoparticle concentrations on the photocatalytic activity have been studied and the results demonstrate that the dye photodegradation follows pseudo-first-order kinetics. The observed maximum degradation efficiency of SO is about 60% for TiO2 and 96% for Ag-TiO2. 相似文献
88.
Nathalie?Favre Yasser?Ahmad Alain?C.?PierreEmail author 《Journal of Sol-Gel Science and Technology》2011,58(2):442-451
As part of an effort to develop biomaterials for the capture of CO2 catalyzed by a carbonic anhydrase enzyme, the effects of an aqueous CO2 saturated solution and a carbonic anhydrase on the gelation and texture of SiO2 gels derived from tetramethoxysilane (TMOS), were studied. Both aqueous CO2 and the enzyme were found to accelerate the gelation of silica, with a stronger effect when both the enzyme and CO2 saturated aqueous water, were used. According to the gel texture data, aqueous CO2 acted as an acid type catalyst, while the carbonic anhydrase acted as a weak base type catalyst. Moreover, a gel with a more
granular visual aspect was obtained when both the enzyme and CO2 saturated water were used. The latter characteristic was consistent with a double action of the enzyme, first as a gelation
catalyst on the silica precursor, secondly as a reverse protonation catalyst which accelerated the back nucleation of CO2 gas bubbles from aqueous HCO3
− anions. 相似文献
89.
In this paper, we introduce and study the dual notion of simple-direct-injective modules. Namely, a right R-module M is called simple-direct-projective if, whenever A and B are submodules of M with B simple and M/A ? B ?⊕M, then A ?⊕M. Several characterizations of simple-direct-projective modules are provided and used to describe some well-known classes of rings. For example, it is shown that a ring R is artinian and serial with J2(R) = 0 if and only if every simple-direct-projective right R-module is quasi-projective if and only if every simple-direct-projective right R -module is a D3-module. It is also shown that a ring R is uniserial with J2(R) = 0 if and only if every simple-direct-projective right R-module is a C3-module if and only if every simple-direct-injective right R -module is a D3-module. 相似文献
90.
A right R-module M is called a D3-module, if M 1 and M 2 are direct summands of M with M = M 1 + M 2, then M 1 ∩ M 2 is a direct summand of M. Following the work of Bass on projective covers, we introduce the notion of D3-covers and provide new characterizations of several well-known classes of rings in terms of D3-modules and D3-covers. 相似文献