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81.
Vasile Gutsanu Cristina Schitco Gabriela Lisa Constantin Turta 《Materials Chemistry and Physics》2011
The Mössbauer spectroscopy and SEM investigation shows that crosslinked ionic polymers containing strongly basic functional groups adsorb Fe(III)-containing cations from sulphate solution through the formation in the polymer phase of high dispersed particles of jarosite mineral type compounds. Using different procedures the particles sizes and morphology, their repartition on the surface and in the volume of the polymer granule, the composition of the “polymer-inorganic compound” structural units were modified that is important for sorbents and catalysts obtaining. On heating in water medium in a boiling water bath, a part of the jarosite type compounds in the polymer phase is converted into ultra fine β-FeOOH particles in superparamagnetic state and the rest, in relatively massive and magnetically ordered β-FeOOH particles. The higher is the content of the Fe(III) in the polymer phase, the shorter is the duration of heating in water for the appearance of relatively massive particles of β-FeOOH. The particles of the jarosite type compounds and of the β-FeOOH are formed both on the surface and in the volume of the polymer granule. Upon heating in water, a part of the Fe(III)-containing particles have migrated from the volume of the polymer granule to the surface. Thermogravimetric investigation (in an N2 atmosphere) shows that on heating of the Fe(III)-containing polymer sample up to 900 °C, complicated processes take place. 相似文献
82.
M. C. Bunescu G. Aldica F. Vasiliu P. Nita E. Vasile 《Journal of Materials Science》2000,35(16):4201-4205
The influence of the sintering time and pressing force on the pellets on the occurrence and morphology of the superconducting phases in BSCCO system were studied. Scanning electron microscopy, X-ray microanalysis and X-ray diffraction were used to identify the phases and their morphologies. The 2223 crystals had a plate-like morphology and 2212, a polyhedral-like one. The optimum parameters in order to obtain a majority of 2223 phase were identified: i.e. a longer sintering time and medium pressing force. 相似文献
83.
Natalia Candu Simona Coman Vasile I. Parvulescu Jamal El Haskouri Pedro Amoros Daniel Beltran 《Topics in Catalysis》2009,52(6-7):571-578
Strong Lewis acid SnTf-MCM-41 and SnTf-UVM-7 catalysts with unimodal and bimodal pore systems were prepared in a two-step synthesis in which the triflic acid (Tf) was incorporated into previously synthesized mesoporous tin-containing silicas. The Sn incorporation inside the pore walls was carried out through the Atrane method. The SnTf-UVM-7 catalysts were prepared by aggregating nanometric mesoporous particles defining a hierarchic textural-type additional pore system. Catalysts with different Si/Sn ratios in the range 21.8–50.8 for SnTf-MCM-41 and 18.4 for SnTf-UVM-7 were found to be efficient catalysts for the acylation of aromatics and heteroaromatics. Under microwave irradiation the reaction was possible even with acetic acid. The selectivity to the desired product (o-hydroxyacetophenone for phenol) or the unfavored three-substituted five ring heterocycles was dramatically increased under these conditions. The process is green, environmentally safe, and heterogeneous. 相似文献
84.
Marius Zimand 《Theory of Computing Systems》2010,46(4):707-722
The randomness rate of an infinite binary sequence is characterized by the sequence of ratios between the Kolmogorov complexity
and the length of the initial segments of the sequence. It is known that there is no effective procedure that transforms one
input sequence into another sequence with higher randomness rate. By contrast, we display such a uniform effective procedure
having as input two independent sequences with positive but arbitrarily small constant randomness rate. Moreover the transformation
is a truth-table reduction and the output has randomness rate arbitrarily close to 1. 相似文献
85.
Judit Molera Trinitat Pradell Nati Salvadó Marius Vendrell-Saz 《Journal of the American Ceramic Society》1999,82(10):2871-2875
Tin oxide (SnO2 ) particles that are a few hundred nanometers in size and are embedded in a lead glaze act as a white opacifier. The insolubility of SnO2 particles in a lead glaze is responsible for this microstructure. Although it is assumed that SnO2 particles do not react during the glaze formation, we demonstrate that the development of metastable phases prior to the fusion of the PbO-SiO2 -SnO2 mixture allows the SnO2 particles to react and then recrystallize subsequent to the fusion of the mixture. The recrystallization of SnO2 occurs during heating and/or cooling until the temperature is sufficiently low and/or the tin supply is exhausted. 相似文献
86.
Ana-Maria Lacr?m? Mihai V. Putz Vasile Ostafe 《International journal of molecular sciences》2007,8(8):842-863
Within the recently launched the spectral-structure activity relationship (S-SAR) analysis, the vectorial anionic-cationic model of a generic ionic liquid is proposed, along with the associated algebraic correlation factor in terms of the measured and predicted activity norms. The reliability of the present scheme is tested by assessing the Hansch factors, i.e. lipophylicity, polarizability and total energy, to predict the ecotoxicity endpoints of wide types of ionic liquids with ammonium, pyridinium, phosphonium, choline and imidazolium cations on the aquatic bacteria Vibrio fischeri. The results, while confirming the cationic dominant influence when only lipophylicity is considered, demonstrate that the anionic effect dominates all other more specific interactions. It was also proved that the S-SAR vectorial model predicts considerably higher activity for the ionic liquids than for its anionic and cationic subsystems separately, in all considered cases. Moreover, through applying the least norm-correlation path principle, the complete toxicological hierarchies are presented, unfolding the ecological rules of combined cationic and anionic influences in ionic liquid toxicity. 相似文献
87.
Marius Barat Dumitru-Bogdan Prelipcean Dragoş Teodor Gavriluţ 《Journal in Computer Virology》2013,9(4):171-178
With the exponential growth of malware in the last 5 years, the number of polymorphic malware increased as well. The aim of this paper is to describe the evolution throughout a year of four major malware families (FakeAlert, Sirefef, ZBot and Vundo). The analysis has been made in terms of polymorphic mechanisms with regards to the polymorphic mechanisms (such as changes in the packer module, changes in the geometry of file, variation of version information from the resource directory or different methods used to modify the icon of one file) which have been used in order to avoid their detection by anti-malware systems. The malware files were collected every week throughout one year’s time. For each family we have recorded the new variants and the updates that were added to the old ones in order to avoid detection. We have managed to examine more than 1,000 new versions of such files. The current article includes an additional study case. The latter focuses on the methods that have been used by the FakeAlert malware family in order to modify their icons. 相似文献
88.
Namrta Purwar Jason Tenboer Shailesh Tripathi Marius Schmidt 《International journal of molecular sciences》2013,14(9):18881-18898
Time-resolved spectroscopic experiments have been performed with protein in solution and in crystalline form using a newly designed microspectrophotometer. The time-resolution of these experiments can be as good as two nanoseconds (ns), which is the minimal response time of the image intensifier used. With the current setup, the effective time-resolution is about seven ns, determined mainly by the pulse duration of the nanosecond laser. The amount of protein required is small, on the order of 100 nanograms. Bleaching, which is an undesirable effect common to photoreceptor proteins, is minimized by using a millisecond shutter to avoid extensive exposure to the probing light. We investigate two model photoreceptors, photoactive yellow protein (PYP), and α-phycoerythrocyanin (α-PEC), on different time scales and at different temperatures. Relaxation times obtained from kinetic time-series of difference absorption spectra collected from PYP are consistent with previous results. The comparison with these results validates the capability of this spectrophotometer to deliver high quality time-resolved absorption spectra. 相似文献
89.
Anca Giorgiana Grigoras Marieta Constantin Vasile Cristian Grigoras Simona Isabela Dunca Lacramioara Ochiuz 《Reactive and Functional Polymers》2013,73(9):1249-1254
The physico-chemical properties of three grafted pullulans (P) having linked poly(3-acrylamidopropyl)trimethylammonium chloride (pAPTAC) as side chains (P-g-pAPTAC1, P-g-pAPTAC2 and P-g-pAPTAC3 with 22.53, 29.05, and 34.51 (wt.%) of pAPTAC content in polymer, respectively) and possessing polyelectrolyte character were determined by light scattering analysis. All grafted pullulan aqueous solutions were tested in the presence of 0.5 M NaCl, KCl, NaNO3 or KNO3. The biggest associations were recorded in 0.5 M NaCl aqueous solutions for P-g-pAPTAC1, P-g-pAPTAC2 and P-g-pAPTAC3 according to the maximum values for Rg extracted from MALLS (multiangle laser light scattering) measurements. Also, the dominant conformation in salted solution of these polyelectrolytes was random coil as Debye plot analysis revealed. Antibacterial activity was tested by Kirby–Bauer diffusion method and all grafted pullulans dissolved in aqueous solutions of 0.5 M NaCl have developed inhibition zone against Staphylococcus aureus (ATCC 25923). 相似文献
90.