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11.
Georgy L Georgiev Barbara Trzebicka Bistra Kostova Petar D Petrov 《Polymer International》2017,66(9):1306-1311
Cryogenic treatment and UV irradiation were exploited for the preparation of super‐macroporous cryogels from non‐modified high‐molar‐mass dextran. The photo‐crosslinking process was initiated by (4‐benzoylbenzyl)trimethylammonium chloride and N,N′‐methylenebisacrylamide (BAAm) was used as a crosslinking agent. Gel fraction yield and degree of swelling of the dextran cryogels were determined gravimetrically. Cryogel morphology and mechanical properties were studied using environmental scanning electron microscopy and dynamic rheological measurements, respectively. The effects of dextran concentration in the initial polymer solution, polymer molar mass and BAAm content on the crosslinking efficacy, physico‐mechanical properties and morphology of the cryogels were evaluated. The dextran cryogels were assessed as carriers of the model water‐soluble drug metoprolol. © 2017 Society of Chemical Industry 相似文献
12.
N. G. Kostova A. A. Spojakina K. Jiratova O. Solcova L. D. Dimitrov L. A. Petrov 《Catalysis Today》2001,65(2-4):217-223
Hexagonal mesoporous materials (HMS) with and without zirconium were used as supports for preparation of HDS catalysts. The catalysts prepared by modification of the supports with 12-phosphomolybdic acid (HPMo) were characterised by nitrogen adsorption, IR spectroscopy, TPD of ammonia, TPR and catalytic activity in thiophene hydrodesulphurisation. Parent silicas showed mesoporous structure with BET surface area between 1200 and 800 m2 g−1, pore size diameter around 3.3 nm and acidity around 0.3 mmol NH3 g−1. Molybdenum catalysts possess stronger acidity than the supports used. The catalytic activities in hydrodesulphurisation of thiophene of the molybdenum containing catalysts prepared with HMS were higher than the activity of the catalyst prepared with amorphous silica. Higher acidity of Zr–HMS supports lead to lower stability in the thiophene conversion. 相似文献
13.
Ibell Tim Orr John Kostova Kaloyana Darby Antony Evernden Mark 《建筑结构》2014,(7):9-14,98
作为应用最广泛的建筑材料,混凝土是一种可以用来建造几乎所有几何形状的结构的流体。然而,伴随着大量的碳排放,混凝土流体被浇筑成刚性棱柱状模型来建造消耗大量材料的结构,而混凝土独特的流动性却很少被利用。文中论证了如何用低消耗的织物片材的柔性系统代替常规的正交模板,以便利用混凝土的流动性,为高度优化的、有建筑学趣味性的建筑形式提供特别的可能性。 相似文献
14.
Novel temperature sensitive cryogels of poly(ethoxytriethyleneglycol acrylate) (PETEGA), with in situ entrapped active substance, are synthesized employing the UV irradiation technique and tested as matrix for controlled release of the hydrophilic drug verapamil hydrochloride. PETEGA cryogels are non-toxic materials and, due to the macroporous structure, exhibit a reversible, ultra-rapid volume phase transition at temperature ca. 31 °C. Carriers based on PETEGA cryogels possess sustained release of verapamil hydrochloride over a period of more than 8 h, which is attributed to the hydrophobic state of the polymer network at physiological temperature and the method of drug immobilization. Drug release characteristics of PETEGA cryogels are compared with another cryogel systems, based on polyacrylamide (PAAm), poly(N-isopropylacrylamide) (PNIPAAm) and poly(2-hydroxyethyl methacrylate) (PHEMA), obtained via the same method. 相似文献
15.
The aim of the present investigation is to determine what is the place of cytological screening of the uterine cervix in sexually active teenagers. MATERIAL AND METHODS: The study was based on 83 girls aged between 14 and 19 (mean age 18.13 years) without childbirth in history, who visited our clinic with non-specific gynecological complaints. All patients were submitted to brush cytology applying the classical method and classifying the smears according to the Bethesda system (1991). RESULTS AND DISCUSSION: A high adequacy of the cytologic smears was found, reaching up to 98.8% and the following distribution of the findings according to the various criteria was observed: cells within normal limits in 34.1% of the patients, benign cellular changes due to reactive changes associated with inflammation in 34.1%, atypical epithelial cell abnormalities of undetermined significance in 18.4%, low grade SIL with HPV in 11.0%, without HPV in 1.2% and high grade SIL in 1.2% of thr patients. The role of cytological screening in sexually active adolescent girls is discussed in the context of the obtained results. 相似文献
16.
D. J. G. James S. P. Kostova V. G. Rumchev 《International journal of systems science》2013,44(12):1377-1388
Positive systems are defined as systems with trajectories entirely in the non-negative orthant whenever the initial state is non-negative. The cohort-type model represents the class of positive linear systems considered here. The method and procedure for pole-assignment of the corresponding closed-loop positive system is proposed. The method is based on inverse eigenspectrum conditions developed for the class of system under consideration and on monomial similarity of non-negative matrices. The relation between controllability and pole-assignment is also studied. Numerical examples illustrating the procedure are provided. 相似文献
17.
Lozan Todorov Maria Traykova Luciano Saso Irena Kostova 《International journal of molecular sciences》2020,21(22)
Increased levels of the superoxide radical are associated with oxidative damage to healthy tissues and with elimination of malignant cells in a living body. It is desirable that a chemotherapeutic combines pro-oxidant behavior around and inside tumors with antioxidant action near healthy cells. A complex consisting of a pro-oxidant cation and antioxidant ligands could be a potential anticancer agent. Ga(III) salts are known anticancer substances, and 5-aminoorotic acid (HAOA) is a ligand with antioxidant properties. The in vitro effects of HAOA and its complex with Ga(III) (gallium(III) 5-aminoorotate (GaAOA)) on the in vitro accumulation of superoxide and other free radicals were estimated. Model systems such as potassium superoxide (KO2), xanthine/xanthine oxidase (X/XO), and rat blood serum were utilized. Data suggested better antioxidant effect of GaAOA compared to HAOA. Evidently, all three ligands of GaAOA participated in the scavenging of superoxide. The effects in rat blood serum were more nuanced, considering the chemical and biochemical complexity of this model system. It was observed that the free-radical-scavenging action of both compounds investigated may be manifested via both hydrogen donation and electron transfer pathways. It was proposed that the radical-scavenging activities (RSAs) of HAOA and its complex with Ga(III) may be due to a complex process, depending on the concentration, and on the environment, nature, and size of the free radical. The electron transfer pathway was considered as more probable in comparison to hydrogen donation in the scavenging of superoxide by 5-aminoorotic acid and its gallium(III) complex. 相似文献
18.
Geoffrey M. Oxberry Tanya Kostova‐Vassilevska William Arrighi Kyle Chand 《International journal for numerical methods in engineering》2017,109(2):198-217
Reduced order models are useful for accelerating simulations in many‐query contexts, such as optimization, uncertainty quantification, and sensitivity analysis. However, offline training of reduced order models (ROMs) can have prohibitively expensive memory and floating‐point operation costs in high‐performance computing applications, where memory per core is limited. To overcome this limitation for proper orthogonal decomposition, we propose a novel adaptive selection method for snapshots in time that limits offline training costs by selecting snapshots according an error control mechanism similar to that found in adaptive time‐stepping ordinary differential equation solvers. The error estimator used in this work is related to theory bounding the approximation error in time of proper orthogonal decomposition‐based ROMs, and memory usage is minimized by computing the singular value decomposition using a single‐pass incremental algorithm. Results for a viscous Burgers' test problem demonstrate convergence in the limit as the algorithm error tolerances go to zero; in this limit, the full‐order model is recovered to within discretization error. A parallel version of the resulting method can be used on supercomputers to generate proper orthogonal decomposition‐based ROMs, or as a subroutine within hyperreduction algorithms that require taking snapshots in time, or within greedy algorithms for sampling parameter space. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
19.
Martin Fabian Maya Shopska Daniela Paneva Georgi Kadinov Nina Kostova Erika Turianicová Jaroslav Briančin Ivan Mitov Rolf A. Kleiv Peter Baláž 《Minerals Engineering》2010,23(8):616-620
Present work evaluates the structural changes in olivine (Mg,Fe)2SiO4 (deposit Åheim, Norway) generated by mechanical treatment as well as its adsorption properties for carbon dioxide. The high-energy attrition milling was applied for mechanical activation. Identification of the mechanically-induced changes in the mineral was carried out applying various techniques: scanning electron microscopy, Mössbauer spectroscopy, specific surface measurements, carbon dioxide adsorption and Fourier-transformed infrared spectroscopy. The observed changes in the physico-chemical properties illustrate the possibility of the applied activation to modify the surface and/or bulk properties of olivine. Sensitivity for atmospheric CO2 sequestration as well as sequestration of CO2 by chemisorption can be derived from the obtained results. 相似文献
20.
Maya B. Kostova Kalina I. Alipieva Simeon S. Popov Nedyalka V. Handjieva 《仪器科学与技术》2013,41(6):691-702
Abstract Five C10 iridoid glycosides (shanzhiside methyl ester, lamalbide, lamiide, sesamoside, and 5‐desoxysesamoside) were examined by electrospray ionization mass spectrometry (ESI‐MS). Considerable differences were observed in positive ion and negative ion mode. Only the positive ion spectra were useful for molecular mass determination on the basis of molecular alkali metal adducts, with the exception of two iridoids containing all 5β‐OH, 7β‐OH and 8β‐OH groups. Fragment characteristics for distinct functionalities were observed. Chelation studies of each iridoid with three different alkali metals were also conducted. 相似文献