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排序方式: 共有818条查询结果,搜索用时 218 毫秒
71.
Aleksandra Mitrović Nenad Mitrović Vesna Miletić Gordana Bakić Miloš Milošević 《Journal of Adhesion Science and Technology》2013,27(24):2684-2695
The study showed an application of the 3?D Digital Image Correlation Method (3?D-DIC) for detection of von Mises strain in samples of the self-etch, self-adhesive resin based cement (RBC). The aim was to determine and compare strain in the self-cured and light-cured Maxcem Elite, furthermore to investigate the hardness of these two cement-types. The experiment was carried out using two groups of Maxcem Elite (Kerr, Orange, CA, USA) samples; each tested group includes five (ø5?×?2?mm sized) samples, for both self-curing and light-curing mode. All samples were prepared by filling teflon ring-type molds. In addition, Vickers micro-hardness was measured for all samples. Maxcem Elite showed similar maximum strain values from 10% to 12% for both groups. Besides the maximum strain value, the 3?D-DIC method also enabled monitoring the change of strain field even after the recommended polymerization time. This method has shown that the polymerization shrinkage continues even after 10?min which disagreed with manufacturer’s suggestion. Group II showed maximum strain values of 12% in the peripheral zone after 10?min, in the last Stage (Stage 60). Statistically significant difference was not found in the overall strain between self- and light-cured Maxcem Elite neither peripherally (p?=?0.118) nor centrally (p?=?0.879). However, statistical significance was found in strain regarding central and peripheral zone in both, self-cured (p?=?0.020) and light-cured (p?=?0.002) Maxcem Elite. The mean von Mises strain values in the periphery of the samples (Section 0) were significantly higher compared to strain values in the center of the samples (for Section 1 and 2). The last stage (Stage 60) of the light-cured Maxcem Elite polymerization showed significantly higher values of von Mises strain compared to initial stage (Stage 0). Higher values of micro-hardness were noticed on the surfaces directly exposed to LED lamp after performing measurements of micro-hardness on light-cured samples. 相似文献
72.
The role of MCM-41 composition in the creation of basicity by alkali metal impregnation 总被引:3,自引:0,他引:3
Aleksandra Michalska Marco Daturi Jacques Saussey Izabela Nowak Maria Ziolek 《Microporous and mesoporous materials》2006,90(1-3):362-369
Three types of mesoporous molecular sieves (silicate MCM-41, niobosilicate NbMCM-41, and aluminosilicate AlMCM-41) were impregnated with alkali metal acetates. The textural stability of the samples was estimated on the basis of XRD measurements and nitrogen adsorption/desorption methods. The acidic–basic properties of the obtained materials were tested in the cyclization of acetonylacetone and studied by FTIR spectroscopy after adsorption of methylacetylene (propyne) and pyridine. Two types of chemical reactions between mesoporous matrix and alkali metal salt/oxide were observed: the reaction between alkali metal salt and silica/silicate and the reaction between basic oxide and silanol groups or Na+ cations. In the first one the alkali metal silicate formation decreases from Li to Cs species and leads to the destruction of the material. The second reaction places alkali metal cations in extra framework positions, which increases from Li to Cs species and is only observed in the case of AlMCM-41 and NbMCM-41 materials. As a result of the second reaction Lewis acidity is generated. The average effect of these two interactions leads to the volcanic curve for basicity of M/AlMCM-41 and M/NbMCM-41 with the maximum for K-samples. In contrast, basicity of M/MCM-41 systematically increases from Li to Cs form since the second type of interaction does not occur for these samples. 相似文献
73.
Predrag Osmokrovic Boris Loncar Srboljub Stankovic Aleksandra Vasic 《Microelectronics Reliability》2002,42(12):1959-1966
The aim of this work is examining the influence of the number of the activation––over-voltage pulses to the aging of over-voltage protection elements. Both non-linear (gas-filled surge arresters (GFSA), varistors, over-voltage diodes) and linear (capacitors––constituents of filters) over-voltage protection elements were tested. The instruments employed allow reliable measurements, 1000 consecutive activation were tested. The double-exponential current pulse (amplitude I1max=13 A, I2max=16 A, rise time T1=8 μs, fall time T2=20 μs) for non-linear elements and a double-exponential over-voltage pulse (rise time T1=1.2 μs, fall time T2=50 μs) of the amplitude U1max=320 V, U2max=480 V and U3max=640 V for capacitors were used. The experimental results show that the over-voltage diodes are the most reliable elements in view of characteristic modifications that are consequence of aging. However, it was observed that varistors, GFSA and capacitors undergo noticeable changes in characteristics. 相似文献
74.
Zhukovsky M Onishchenko A Varaksin A Vasilyev A 《Radiation protection dosimetry》2011,145(2-3):243-247
To analyse the influence of the parameters of case and control groups and uncertainties of radon concentration assessments on the dose-effect dependence, a special computer program was designed. The influence of measurement errors on the uncertainties of radon case-control analysis is demonstrated on examples of hypothetical case and control groups with sizes from 250-500 to 7000-14,000 members. The modelling was conducted using a Monte Carlo technique for different values of measurement uncertainties. The random errors of radon assessment affect both the numerical value of the slope coefficient β of the linear dependence of relative risk of lung cancer incidence on indoor radon concentration and the accuracy of this value. The extrapolation of the dependence of the slope coefficient β on the total (initial plus additional) random error of radon concentration assessment is suggested for the assessment of an unbiased value of the slope coefficient β. 相似文献
75.
Paulina Kosikowska-Adamus Emilia Sikorska Dariusz Wyrzykowski Aleksandra Walewska Anna Golda Milena Deptua Micha Obuchowski Adam Prahl Micha Pikua Adam Lesner 《International journal of molecular sciences》2021,22(13)
The alarming raise of multi-drug resistance among human microbial pathogens makes the development of novel therapeutics a priority task. In contrast to conventional antibiotics, antimicrobial peptides (AMPs), besides evoking a broad spectrum of activity against microorganisms, could offer additional benefits, such as the ability to neutralize toxins, modulate inflammatory response, eradicate bacterial and fungal biofilms or prevent their development. The latter properties are of special interest, as most antibiotics available on the market have limited ability to diffuse through rigid structures of biofilms. Lipidation of AMPs is considered as an effective approach for enhancement of their antimicrobial potential and in vivo stability; however, it could also have undesired impact on selectivity, solubility or the aggregation state of the modified peptides. In the present work, we describe the results of structural modifications of compounds designed based on cationic antimicrobial peptides DK5 and CAR-PEG-DK5, derivatized at their N-terminal part with fatty acids with different lengths of carbon chain. The proposed modifications substantially improved antimicrobial properties of the final compounds and their effectiveness in inhibition of biofilm development as well as eradication of pre-formed 24 h old biofilms of Candida albicans and Staphylococcus aureus. The most active compounds (C5-DK5, C12-DK5 and C12-CAR-PEG-DK5) were also potent against multi-drug resistant Staphylococcus aureus USA300 strain and clinical isolates of Pseudomonas aeruginosa. Both experimental and in silico methods revealed strong correlation between the length of fatty acid attached to the peptides and their final membranolytic properties, tendency to self-assemble and cytotoxicity. 相似文献
76.
Aleksandra Sowa 《Datenschutz und Datensicherheit - DuD》2007,31(6):441-445
Mit steigender Durchdringung der Kreditinstitute mit der IT und immer st?rker werdender Abh?ngigkeit des Bankgesch?fts von
dem Netz steigen auch die mit der Verletzbarkeit und Ausfall der IT-Systeme verbundenen Risiken. Für die IT-Revision bedeutet
dies ein wachsendes Engagement im Rahmen von Sicherheitsprüfungen und- Beratungen, um diesen Risiken in angemessener Weise
zu begegnen. Durch Einsatz geeigneter Prüfungsmethodik und hoher fachlichen Qualifikationen der Revisoren k?nnen die Sicherheitsprüfungen
zu einer wichtigen Erfolgsdeterminante eines Instituts werden. 相似文献
77.
Nowadays many leading companies understand that creating outstanding customer value is necessary to achieving sustainable market success. The main problem discussed in this article is the examination of factors affecting perceived value, emphasizing the relationship between perceived price and perceived value. Based on literature and their own findings, the authors designed a model of relationships between researched factors. This model was tested using structural equation modeling. The results reflected that statistically significant relationships exists and that perceived price has direct as well as indirect efects on perceived product value. 相似文献
78.
Aleksandra Turkovi Bojan Orel Magdy Lu
i-Lav
evi Pavo Dub
ek Zorica Crnjak Orel Sigrid Bernstorff 《Solar Energy Materials & Solar Cells》2007,91(14):1299-1304
Cerium vanadate films on glass substrate were obtained by sol–gel process. The morphology of these nanostructured and porous films was studied by grazing-incidence small-angle X-ray scattering (GISAXS) at synchrotron ELETTRA, Trieste, Italy. The aim of the GISAXS study was to investigate the changes in grain sizes due to the temperature evolution with three different time intervals (5, 15 and 30 min) of annealing at 673 K. We found that the effects of the different times of annealing are different for surface and bulk properties of this V/Ce oxide. 相似文献
79.
Stefan Goszczyski Jan Szymanowski Aleksandra Borowiak-Resterna 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1981,31(1):333-340
The study of copper extraction shows that the position of the chain (5 or 4′) does not influence the statics of copper extraction from ammonia solutions by alkyl derivatives of 2-hydroxybenzophenone oxime. Acid solutions of 2-hydroxy-4′-n-nonylbenzo-phenone oxime can extract more copper than 2-hydroxy-5-n-nonylbenzophenone oxime, but less than 2-hydroxy-5-n-alkylbenzaldehyde oxime. 相似文献
80.
Aleksandra Lazarenko Lyudmila Vovchenko Lyudmila Matzui Victor Kozachenko Yuriy Prylutskyy Peter Scharff Uwe Ritter 《Polymer Composites》2011,32(1):14-17
This study was performed to measure the thermal diffusivity of different types of nanocarbon composites. Thermoexfoliated graphite (TEG), ultrasonically dispersed TEG, and multiwalled carbon nanotubes were used as fillers in epoxy polymer matrixes. The nanocarbon filler content was 1–10 wt%. The temperature dependence of the thermal conductivity and the heat capacity were extensively characterized in the temperature range between 150 and 425 K. For this purpose, the thermal diffusivity of the composites was investigated by two experimental methods: dynamic λ‐calorimeter and photoacoustic. The comparative analysis of thermal diffusivity of compacted TEG samples with different densities and of nanocarbon‐epoxy with different filler content was carried out. It was found that for the composites with a low distribution of the nanocarbon filler, the thermal diffusivity increases and that the value is determined by the structural and morphological properties of the filler. The orientation function for the TEG‐epoxy composites and the compact TEG samples differs due to the epoxy matrix that reduced anisotropy of the composite. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers 相似文献