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1.
A number of practical issues must be addressed when using thin carbon films as quarter-wave plates for Zernike phase-contrast electron microscopy. We describe, for example, how we meet the more stringent requirements that must be satisfied for beam alignment in this imaging mode. In addition we address the concern that one might have regarding the loss of some of the scattered electrons as they pass through such a phase plate. We show that two easily measured parameters, (1) the low-resolution image contrast produced in cryo-EM images of tobacco mosaic virus particles and (2) the fall-off of the envelope function at high resolution, can be used to quantitatively compare the data quality for Zernike phase-contrast images and for defocused bright-field images. We describe how we prepare carbon-film phase plates that are initially free of charging or other effects that degrade image quality. We emphasize, however, that even though the buildup of hydrocarbon contamination can be avoided by heating the phase plates during use, their performance nevertheless deteriorates over the time scale of days to weeks, thus requiring their frequent replacement in order to maintain optimal performance. 相似文献
2.
A two sorbents was to synthesize for heavy metals removal: silica gel modified with 5-amino-1,3,4-thiadiazole-2-thiol (S5A)
and pure silica gel. Modification of silica gel is achieved by tetraethyl orthosilicate (TEOS) preliminary hydrolyzed at room
temperature. 5-Amino-1,3,4-thiadiazole-2-thiol is added, with continuous stirring with a magnetic stirrer, to the hydrolyzed
TEOS. Pure silica gel (sample SG) is obtained by the classical sol–gel method using the same conditions and initial component
ratios. The sorbents have been characterized as to their surface area, pore volumes, content of the functional groups, IR
spectra, sulfur and nitrogen content. Their sorption properties to heavy (Cu(II), Co(II), Ni(II), Cd(II), Pb(II) and Hg(II)
metals are investigated. The investigations indicate that modified silica gel is characterized by a relatively higher sorption
capacity than is the unmodified one. The highest sorption capacity belongs to Hg(II) in presence of unmodified silica gel
due to which this sorbent can be used for selective extraction of mercury ions from aqueous solutions. 相似文献
3.
Daniela Stoyanova Radostin Nickolov Mariana Khristova Daniela Paneva Dimitar Mehandjiev 《Journal of Porous Materials》2009,16(1):1-7
The influence of the nature of the impregnating solutions media (aqueous or non-aqueous) on the forming of active phases is investigated in case of preparing iron catalysts, supported on activated carbon with respect to their catalytic activity in the reaction of NO reduction by CO. The catalysts are characterized by chemical analysis (AAS), BET surface area, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), magnetic susceptibility, and Mössbauer spectroscopy (MS). The catalytic investigations and TPD are carried out in a flow apparatus. Three peculiarities are observed with respect to this influence—the ratio between the separate iron species in different oxidation state of Fe species, which build up the catalytic active complexes (CAC), common participation of superficial groups of the carbon support and Fe components of the impregnating solutions as well as different dispersion of the active phase on the surface of the samples. As a result the highest catalytic activity was observed with the sample, obtained by impregnation with an aqueous solution, while with the other samples, obtained from organic solutions, the catalytic activity decreases in the order of: Methanol > Ethyl Ether > Acetone. It was assumed that the different catalytic activities are connected most probably with the process of forming of CAC during the process of preparation of the samples. 相似文献
4.
V. Mavrodinova M. Popova Ch. Minchev R. Nickolov M. Linden 《Journal of Porous Materials》2007,14(2):213-218
The structure characteristics of Ni-modified (7 wt% Ni) mesoporous materials with cubic (Ia3d and Fm3m space groups) structure
have been compared to that of the hexagonal MCM-41 material with uni- dimentional channel arrangement by X-ray diffraction
and N2 adsorption–desorption measurements. Thermal gravimetric analysis and toluene hydrogenation have been used for characterization
of the reducibility of the supported Ni phase and its catalytic activity in this test reaction, respectively. The results
from N2 physisorption suggest that substantially higher pore blockage with Ni occurs when it is deposited on the 1D channel structure
of MCM-41 compared to the cage-like pores of Fm3m and the interconnected pores of Ia3d material. It is proposed that the pore
architecture determines the distribution of the oxide metal phase and its reducibility and strongly influences the hydrogenation
activity of the catalysts. 相似文献
5.
Radostin Stefanov Pavlov Juan B. Carda Castelló Vicente Blasco Marzá J. M. Hohembergerger 《Journal of the American Ceramic Society》2002,85(5):1197-1202
New high-stability red-shade ceramic pigments based on pyrochlore solid solutions Y2 Sn2− x Cr x O7−δ ( x = 0–1, 0 < δ= 0–1/2 x ) were developed employing conventional solid-state reaction synthesis. The relationship between their optical properties and microstructure was analyzed by X-ray diffractometry and ultraviolet–visible-light spectroscopy. Decomposition of the structure with formation of the perovskite YCrO3 observed for chromium substitutions x ≥ 5 was attributed mainly to high concentration of defects. The structural and optical parameters of the materials were found to correlate with the concentration of a species with higher oxidation state than Cr(III), such as Cr(IV) or Cr(V). 相似文献
6.
Alexandre Loukanov Naomi Kamasawa Radostin Danev Ryuichi Shigemoto Kuniaki Nagayama 《Ultramicroscopy》2010
We present a method for immunolabeling of multiple species of membrane proteins with high spatial resolution. It allows differentiation of equally sized very small markers with different chemical compositions, which leads to high labeling efficiency and reduces steric hindrance of closely spaced immunolabeled biomolecules. Markers such as CdSe/ZnS semiconductor quantum dots and colloidal gold particles are distinguished by differential contrast in high-angle annular detector dark-field STEM mode or by EDX microanalysis of their elemental contents. This method was tested by observation of labeled AMPA- and NMDA-type glutamate receptors on sodium-dodecyl-sulfate-digested replica prepared from rat hippocampus. To improve particle visibility and detectability, the replica films were made exclusively with carbon to avoid the high background of conventional platinum/carbon replica. Extension of the method is suggested by detection of 1.4 nm nanogold particles and its potential application in the biological imaging research. 相似文献
7.
Removal of ammonium ions from aqueous solutions with coal-based activated carbons modified by oxidation 总被引:3,自引:0,他引:3
The main purpose of this work is to study the possibilities for removal of ammonium ions from aqueous solutions by the two coal-based activated carbons (one obtained from Bulgarian lignite from the Chukurovo deposit, and the second, available as commercial product) and their oxidized modifications. The porous texture and surface chemistry of the adsorbents were characterized. Adsorption of ions was investigated using solutions with different concentrations in the range 35-280 mg l−1 in a static mode. Equilibrium modeling data were fitted to linear Langmuir’s and Freundlich’s equations and maximum adsorption capacities were calculated. 相似文献
8.
Ana Da Silva Costa Peter Mortensen Maria P. Hortigon-Vinagre Marcel A. G. van der Heyden Francis L. Burton Hao Gao Radostin D. Simitev Godfrey L. Smith 《International journal of molecular sciences》2021,22(12)
The immature electrophysiology of human-induced pluripotent stem cell-derived cardiomyocytes (hiCMs) complicates their use for therapeutic and pharmacological purposes. An insufficient inward rectifying current (IK1) and the presence of a funny current (if) cause spontaneous electrical activity. This study tests the hypothesis that the co-culturing of hiCMs with a human embryonic kidney (HEK) cell-line expressing the Kir2.1 channel (HEK-IK1) can generate an electrical syncytium with an adult-like cardiac electrophysiology. The mechanical activity of co-cultures using different HEK-IK1:hiCM ratios was compared with co-cultures using wildtype (HEK–WT:hiCM) or hiCM alone on days 3–8 after plating. Only ratios of 1:3 and 1:1 showed a significant reduction in spontaneous rate at days 4 and 6, suggesting that IK1 was influencing the electrophysiology. Detailed analysis at day 4 revealed an increased incidence of quiescent wells or sub-areas. Electrical activity showed a decreased action potential duration (APD) at 20% and 50%, but not at 90%, alongside a reduced amplitude of the aggregate AP signal. A computational model of the 1:1 co-culture replicates the electrophysiological effects of HEK–WT. The addition of the IK1 conductance reduced the spontaneous rate and APD20, 50 and 90, and minor variation in the intercellular conductance caused quiescence. In conclusion, a 1:1 co-culture HEK-IK1:hiCM caused changes in electrophysiology and spontaneous activity consistent with the integration of IK1 into the electrical syncytium. However, the additional electrical effects of the HEK cell at 1:1 increased the possibility of electrical quiescence before sufficient IK1 was integrated into the syncytium. 相似文献
9.
A. A. Kalinina S. Yu. Radostin S. Yu. Chloponin T. N. Sokolova A. N. Moskvichev E. N. Razov V. R. Kartashov 《Protection of Metals and Physical Chemistry of Surfaces》2016,52(7):1193-1196
The effect of reactive oxygen intermediates, such as superoxide radical and hydrogen peroxide, on the initiation of biological zinc corrosion is demonstrated. A correlation between the amounts of formed hydrogen peroxide and the corrosive activity of the studied bacteria is revealed. 相似文献
10.