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排序方式: 共有268条查询结果,搜索用时 31 毫秒
111.
Hadeer Jasem Angham G. Hadi Gamal A. El-Hiti Mohammed A. Baashen Hassan Hashim Ahmed A. Ahmed Dina S. Ahmed Emad Yousif 《Molecules (Basel, Switzerland)》2021,26(12)
Poly(vinyl chloride) degrades when exposed to ultraviolet light for long durations; therefore, the photostability of polymeric materials should be enhanced through the application of additives. New organotin complexes containing 4-aminonaphthalene-1-sulfonic acid were synthesized and their role as poly(vinyl chloride) photostabilizers were evaluated. The reaction of 4-amino-3-hydroxynaphthalene-1-sulfonic acid and appropriate di- or trisubstituted tin chloride (triphenyltin chloride, tributyltin chloride, dibutyltin dichloride, and dimethyltin dichloride) in methanol under reflux gave the corresponding tin-naphthalene complexes with yields of 75%–95%. Elemental analyses and spectroscopic techniques including infrared and nuclear magnetic resonance (proton and tin) were used to confirm their structures. The tin complexes were added to poly(vinyl chloride) to produce thin films that irradiated with ultraviolet light. Various parameters were assessed, such as the weight loss, formation of specific functional groups, changes in the surface due to photoirradiation, and rate constant of photodegradation, to test the role played by the organotin complexes to reduce photodegradation in polymeric films. The results proved that organotin complexes acted as photostabilizers in these circumstances. The weight loss, formation of fragments containing specific functional groups, and undesirable changes in the surface of polymeric films were limited in the presence of organotin complexes. Organotin complexes containing three phenyl groups showed the most desirable stabilization effect. These act as efficient primary and secondary photostabilizers, and as decomposers for peroxides. In addition, such an additive inhibits the dehydrochlorination process, which is the main cause of poly(vinyl chloride) photodegradation. 相似文献
112.
The application of low energy ion scattering spectroscopy (LEIS) in sub 28‐nm CMOS technology 下载免费PDF全文
Kornelia Dittmar Dina H. Triyoso Elke Erben Joachim Metzger Robert Binder Hidde H. Brongersma Martin Weisheit Hans‐Jürgen Engelmann 《Surface and interface analysis : SIA》2017,49(12):1175-1186
With the transition to ≤28‐nm CMOS technology nodes, the surface analytical challenges with regard to steadily decreasing dimensions and still growing materials options raise the demand of high performing surface analysis techniques. Characterization of ultrathin films and multilayer stacks, especially in high‐k metal gate stacks, by means of low energy ion scattering spectroscopy (LEIS) with its monolayer sensitivity has been established as a very useful analysis technique next to Auger electron spectroscopy, X‐ray photoelectron spectroscopy , and time‐of‐flight secondary ion mass spectrometry. Questions regarding film nucleation, growth, coverage, and diffusion can be answered, thereby enabling those processes to be controlled appropriately. In this work, growth studies of ALD HfO2 and TiN are shown, as well as film thickness determination based on surface spectra. PVD aluminum and lanthanum, acting as work function metals on the gate oxide, were deposited, and their film formation and closure were investigated. Further application fields of LEIS have emerged from the characterization of in‐die features on patterned wafers. As presented on test arrays, it is possible to detect material deep in trenches. This is an advantage if residues need to be identified after etch or clean processes. 相似文献
113.
Valvular heart diseases (VHDs) are a major health problem increasing morbidity and mortality worldwide. Currently, treatment of VHDs relies on valve replacement with mechanical or biological valves, which have major drawbacks in terms of durability and the ability to grow, repair and remodel. To this end, tissue-engineered heart valves (TEHVs) have emerged as ideal substitutes. TEHVs are composed of biodegradable, biocompatible and mechanically stable scaffolds that resemble the native valves. These scaffolds are seeded with autologous cells and conditioned in a bioreactor prior to implantation. Scaffolds that have been utilized so far for such application are (i) biological, (ii) synthetic and (iii) cell entrapment in polymerized extra-cellular matrix based scaffolds. Synthetic scaffolds are considered superior over the other two types in terms of controlled mechanical properties and degradation rate. They can be subdivided into porous, hydrogel and fibrous scaffolds. Among the three subcategories, fibrous scaffolds are preferred because they resemble the natural extra-cellular matrix for the native valve. Such scaffolds can be fabricated using phase separation, self-assembly and electrospinning. Electrospinning is a versatile technique for fabricating scaffolds for tissue engineering applications that possess many advantages. Electrospun scaffolds processed using a wide range of synthetic and natural polymers were proven to be promising in terms of mechanical properties comparable to the native valves, fiber diameter within the range of the natural extracellular matrix and good cellular response. However, further investigation in fabricating fibrous scaffolds for tissue-engineered heart valves is still needed. In this review, we discussed electrospun scaffolds as TEHVs matrices, how far they succeeded in meeting the criteria of ideal scaffolds for such application and what the shortage aspects and possible solutions are. 相似文献
114.
Dina Orazbayeva Bulat Kenessov Jacek A. Koziel Dayana Nassyrova Nadezhda V. Lyabukhova 《Chromatographia》2017,80(8):1249-1256
There is a great demand for simple, fast and accurate methods for quantification of volatile organic contaminants in soil samples. Solid-phase microextraction (SPME) has a huge potential for this purpose, but its application is limited by insufficient accuracy caused by a matrix effect. The aim of this research was to develop the method for BTEX quantification in soil using combined standard addition (SA) and internal standard (IS) calibration. Deuterated benzene (benzene-d6) was used as the internal standard for all analytes. The optimized method includes spiking replicate samples with different concentrations of BTEX standards and the same concentration of benzene-d6, equilibration of soil samples at 40 °C during 2 h, and SPME–GC–MS analysis. Precision and accuracy of IS and SA methods were compared on different soil matrices. Combined SA + IS method provided more precise calibration plots compared to the conventional SA calibration. The SA + IS calibration provided more precise and accurate results compared with a reference method based on solvent extraction followed by GC–MS when applied to BTEX quantification in real soil samples (spiked with diesel fuel and aged). Recoveries of BTEX from soil samples spiked with known concentrations of analytes using the developed method were in the range of 73–130% with RSD values less than 15% for all BTEX. The proposed simultaneous standard addition and internal standard approach can be advantageous and adopted for improved quantification of other toxic VOCs in soil. 相似文献
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116.
Three supramolecular coordination polymers (SCPs) [(AgSCN)2L] {L = 4,4′-bipyridine (bpy) (1), trans-1,2-bis(4-pyridyl)ethylene (tbpe) (2) and phenazine (phenz) (3)} have been synthesized and structurally characterized by single-crystal X-ray diffraction. Synthesis was affected in H2O/acetonitrile/NH3 media at room temperature. The bpy, tbpe and phenz bipodal ligands adopt different conformations which would affect the skeleton of the (AgSCN)n building blocks that allow the interconnection of the (AgSCN)n fragments and propagation of the network structure in three dimensions. Supramolecular interactions such as hydrogen-bonding, argentophilic interaction and π–π stacking play an important role in the assembly of these coordination polymers. 相似文献
117.
El-Kady Dina S. Abd Rabou Ahmed A. Tantawy Mohamed A. Abdel-Rahman Adel A.-H. Abdel-Megeed Amira A.-S. AbdElhalim Mervat M. Elmegeed Gamal A. 《Applied biochemistry and biotechnology》2019,188(3):635-662
Applied Biochemistry and Biotechnology - Modification of steroid molecules by introducing heterocyclic ring into the core structure of steroids has been utilized as an attractive approach for... 相似文献
118.
Vladislav V. Fomenko Dina V. Korchagina Nariman F. Salakhutdinov Vladimir A. Barkhash 《Helvetica chimica acta》2001,84(11):3477-3487
The reactions of the natural sesquiterpene caryophyllene with phenols on various solid acid catalysts gave the corresponding terpenylphenols and phenyl terpenyl ethers with essentially caryolane structures. The selectivity of the process and yield of product can be raised by varying the catalyst and solvent. 相似文献
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120.