排序方式: 共有53条查询结果,搜索用时 62 毫秒
51.
Victor Pupkevich Vassili Glibin Dimitre Karamanev 《Journal of Solid State Electrochemistry》2007,11(10):1429-1434
Recently, rejuvenated interest to fuel cells has posed a number of problems regarding the polymer electrolyte membrane properties
and their behaviour in different electrolyte solutions. This work was dedicated to study the conductivity of H+-, Fe3+- and mixed H+/Fe3+-forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117 and Selemion HSF under conditions similar to these
in the Fe3+/Fe2+–H2/H+ fuel cell in the range of current densities 0–90 mA/cm2. It was found that the conductivities of these membranes in 1.09 M H2SO4 solution decrease in the following order: Selemion HSF › Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS › Nafion 112. Conductivities
of perfluorinated membranes were discussed in terms of Hsu and Gierke percolation theory [20]. The Fe3+-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation
of gradual conversion of the Fe3+-form into H+-form of these membranes. Unlike the Nafion membranes, the Fe3+-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities
(more than 70 mA/cm2) that is most probably a result of concentration polarization. 相似文献
52.
A battery-operated, atmospheric pressure, self-igniting, planar geometry Ar–H2 microplasma for elemental analysis of liquid microsamples is described. The inexpensive microplasma device (MPD) fabricated
for this work was a hybrid plastic–quartz structure that was formed on chips with an area (roughly) equal to that of a small-sized
postage stamp (MPD footprint, 12.5-mm width by 38-mm length). Plastic substrates were chosen due to their low cost, for rapid
prototyping purposes, and for a speedy microplasma device evaluation. To enhance portability, the microplasma was operated
from an 18-V rechargeable battery. To facilitate portability even further, it was demonstrated that the battery can be recharged
by a portable solar panel. The battery-supplied dc voltage was converted to a high-voltage ac. The ∼750-μm (diameter) and
12-mm (long) Ar–H2 (3% H2) microplasma was formed by applying the high-voltage ac between two needle electrodes. Spectral interference from the electrode
materials or from the plastic substrate was not observed. Operating conditions were found to be key to igniting and sustaining
a microplasma that was simply “warm” to the touch (thus alleviating the need for cooling or other thermal management) and
that had a stable background emission. A small-sized (900 μL internal volume) electrothermal vaporization system (40-W max
power) was used for microsample introduction. Microplasma background emission in the spectral region between 200 and 850 nm
obtained using a portable fiber-optic spectrometer is reported and the effect of the operating conditions is described. Analyte
emission from microliter volumes of dilute single-element standard solutions of Cd, Cu, K, Li, Mg, Mn, Na, Pb, and Zn is documented.
The majority of spectral lines observed for the elements tested were from neutral atoms. The relative lack of emission from
ion lines simplified the spectra, thus facilitating the use of a portable spectrometer. Despite the relative spectral simplicity,
some spectral interference effects were noted when running a multi-element solution. An example of how interference in the
spectral domain can be resolved in the time domain using selective thermal vaporization is provided. Analytical utility and
performance characteristics are reported; for example, K concentrations in diluted (∼30 times) bottled water were determined
to be 4.1 ± 1.0 μg/mL (4 μg/mL was the stated concentration), precision was about 25%, and the estimated detection limits
were in the picogram range (or in nanograms per milliliter in relative units). 相似文献
53.
Danylo I. Kravchuk Ganna V. Sotkis Mykola M. Shcherbatiuk Ruslan M. Kravchuk Vassili G. Nazarenko Petro P. Gorbyk Yaroslav M. Shuba 《Photochemistry and photobiology》2023,99(1):78-82
Caged compounds comprise the group of artificially synthesized, light-sensitive molecules that enable in situ derivation of biologically active constituents capable of affecting cells, tissues and/or biological processes upon exposure to light. Ruthenium-bispyridine (RuBi) complexes are photolyzed by biologically harmless visible light. In the present study, we show that RuBi-caged nicotine can be used as a source of free nicotine to induce proliferation of A549 nonsmall-cell lung cancer (NSCLC) cells by acting on nicotinic acetylcholine receptors expressed in these cells. RuBi-nicotine was photolyzed using LED light source with the spectrum matching RuBi-absorption. Photorelease of free nicotine ([Nic]p/r) was quantified by high-performance liquid chromatography (HPLC). 5-s-long light exposure of 10 μm of RuBi-nicotine generated 2 μm [Nic]p/r which enhanced A549 cell proliferation similarly to the 2 μm of plain nicotine during 72 h of cell culturing. Both RuBi-nicotine per se and its photolysis byproduct exerted no effect on A549 cells. We conclude that RuBi-nicotine can be a good source of free nicotine for inducing short- and long-term biological effects. Photolysis of RuBi-nicotine is quite effective, and can produce biologically relevant concentrations of nicotine at acceptable concentrations of the source material with the use of simple, inexpensive, and easily accessible light sources. 相似文献