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61.
Andrzej Bernasik Jakub Rysz Andrzej Budkowski Kazimierz Kowalski Jzef Camra Jerzy Jedliski 《Macromolecular rapid communications》2001,22(11):829-834
We describe the technique of dynamic secondary ion mass spectrometry developed to determine three‐dimensional phase domain structures of films of polymer blends. The polymers are composed of light elements or are labeled with deuterium or heavy elements. The applicability of this method to various polymer blends forming thin and ultrathin films with flat and undulated air/film interface is discussed. 相似文献
62.
A rotating shaft, rotary lip seal, and oil creating a film between the surfaces of a shaft and of a lip of the seal sets up a system, which is relatively simple geometrically, but complex physically and electrochemically. Such a system is characteristic of all machinery, engines, etc. where rotating parts and seals occur. In the experiments and tests performed to date different real commercial motor oils, original base oils, additives to base oils (antiwear and extreme pressure additives), lip seals, and shafts with different roughness have been used for a range of oil temperatures and shaft angular velocities. Tribocharging in the interfacial system: rotating shaft–oil–lip seal (the friction junction) is observed and analysed. Other experiments were performed to compensate for the electric field generated in the system applying an external DC electric field and to find its effect on friction and the braking torque of the shaft. The results show that tribocharging can exert influence on the braking torque of a rotating shaft. The reduction of the braking torque under the action of an external DC electric field is also observed. The similar experiments are repeated with the use of pure base oils and additives including zinc dialkyldithiophosphate (ZDDP). Tribocharging is evident in the case of pure base oils and when these are blended with ZDDP. The external DC electric field also reduces the braking torque while applying the DC voltage to the system. Here the authors try to interpret the former and last research results in their physical aspect and to answer some questions. 相似文献
63.
Robert Piech 《Electroanalysis》2009,21(16):1842-1847
A new adsorptive stripping voltammetric method for the determination of trace gallium(III) based on the adsorption of gallium(III)‐catechol complex on the cyclic renewable mercury film silver based electrode (Hg(Ag)FE) is presented. The effects of various factors such as: preconcentration potential and time, pulse height, step potential and supporting electrolyte composition are optimized. The calibration graph is linear from 2 nM (0.14 μg L?1) to 100 nM (6.97 μg L?1) for a preconcentration time of 30 s, with correlation coefficient of 0.9993. For a Hg(Ag)FE with a surface area of 9.7 mm2 the detection limit for a preconcentration time of 90 s is as low as 7 ng L?1. The repeatability of the method at a concentration level of the analyte as low as 0.05 μg L?1, expressed as RSD is 3.6% (n=5). The proposed method was successfully applied by studying the natural samples and simultaneous recovery of Ga(III) from spiked water and sediment samples. 相似文献
64.
Kazimierz Darowicki 《Journal of Solid State Electrochemistry》2009,13(11):1635-1635
65.
For set-valued dynamic systems in uniform spaces we introduce the concept of quasi-asymptotic contractions with respect to some generalized pseudodistances, describe a method which we use to establish general conditions guaranteeing the existence and uniqueness of endpoints (stationary points) of these contractions and exhibit conditions such that for each starting point each generalized sequence of iterations (in particular, each dynamic process) converges and the limit is an endpoint. The definition, result, ideas and techniques are new for set-valued dynamic systems in uniform, locally convex and metric spaces and even for single-valued maps. 相似文献
66.
Grota J Mattay J Piech K Bally T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(17):4559-4567
Three tricyclic vinylcyclobutanes (3-methylenetricyclo[5.3.0.0(2,6)]decanes 1-3) have been subjected to ionization by photoinduced electron transfer in solution and by X-irradiation in Ar matrices. All three compounds undergo oxidative cycloreversion; the cleavage of the four-membered ring, however, occurs in a different direction depending on the presence of a methyl group in position 6 of the tricyclic framework. In those derivatives, cycloreversion is found to lead to 1-methyl-8-methylene-1,6-cyclodecadiene radical cations (5.+ from 1, 8.+) from 2) which upon back electron transfer yield two different hydrocarbons (6 from 5.+, 9 from 8.+), depending on the configuration around the endocyclic double bonds of the respective cyclodecadiene derivative. In the absence of a methyl group on C6, the cycloreversion leads to a radical cation complex between 1-methylenecyclopent-2-ene and cyclopentene (12.+) which appears to revert to 3 on back electron transfer. The intermediate radical cations 5.+, 8.+, and 12.+ have been identified and characterized by UV/Vis and IR spectra in Ar matrices. The mechanism of their formation is elucidated by quantum chemical calculations. 相似文献
67.
68.
Gruszecki WI Trebacz K Iwaszko E 《Journal of photochemistry and photobiology. B, Biology》2002,66(2):141-147
A diaheliotropic response of sunflower, Helianthus annuus, following a short pulse of low intensity blue light to a small area of leaf surface was examined with the application of the very low-force-measurements technique (the order of magnitude of 10(-5) N). One leaf from a pair was illuminated with a low intensity blue-light-pulse and the force was recorded, generated by the stem of the plant tending to bend. A very low phototropic effect in response to blue light alone was observed which could be considerably enhanced by the application of background illumination with red light. Microelectrode measurements of the membrane potential of the mesophyll cells of the sunflower leaf showed hyperpolarization in response to a blue light pulse, observed very clearly under application of the red light background illumination. The hyperpolarization of the membrane potential was accompanied by acidification of extracellular compartments as monitored with a miniature pH-sensitive electrode, placed in the epidermis of the stem. The relatively short lag period between the hyperpolarization of the membrane potential and the decrease in pH suggests that the hyperpolarization is a direct effect of the blue light-induced proton extrusion. The acidification correlates with the light response, which suggests that acidification-induced stem wall loosening is responsible for the blue light-induced bending. The examined mechanisms are discussed in terms of sun tracking by a sunflower. 相似文献
69.
Coumarins are nowadays an important group of organic compounds from natural sources that are useful in a number of fields. Because they possess different pharmacological properties, finding the proper extraction conditions for their separation from plant matrices is a very important step. In this report Pressurized Liquid Extraction (PLE) under different temperature conditions and with different types of extraction solvents were tested. As a matrix, fruits of Heracleum leskowii have been used. A simple reverse phase high-performance liquid chromatographic method (RP-HPLC) coupled with a photodiode array detector (DAD) has been developed for separation and quantitative analysis of the main coumarins. Umbelliferone, xanthotoxin, angelicin, isopimpinellin, bergapten, imperatorin and isoimperatorin were investigated. Bergapten and imperatorin were dominant in almost all extracts in the range of 9.92 ± 0.02-20.93 ± 0.06 and 12.19 ± 0.98-19.07 ± 0.03 mg/100 g, respectively. Dichloromethane and methanol were chosen as the most proper suitable solvents for extraction of coumarins. By increasing the temperature the amount of extracted coumarins increases in petroleum ether and dichloromethane extracts. 相似文献
70.
A micro extraction – spectrophotometric procedure is developed for the determination of bismuth in pharmaceutical formulations.
The procedure is based on the extraction of tetraiodobismuthate(III) ion paired with benzyltributylammonium cation into chloroform.
The application of Nile Blue as internal standard (IS) enabled good analytical performance for micro-scale analysis. The ratio
between the absorbances measured at 491 nm (bismuth complex) and at 632 nm (IS) was taken as the analytical signal. The procedure
was carried out in Eppendorf tubes, lowering significantly the use of reagents and the volume of organic solvent. In the calibration
range up to 60 mgċl−1, the linear regression coefficient was 0.9999, the CV for 15 mgċl−1 and for 50 mgċl−1 Bi were 1.6% and 0.7% respectively. The results obtained in the analysis of pharmaceutical formulations were in good agreement
with the results of EDTA titration method.
Received November 25, 1999. Revision February 14, 2000. 相似文献