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41.
42.
Maria Bocheńska Robert Banach Anna Zielińska Victor CH. Kravtsov 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):219-228
Some di- and tetraamide tert-butylcalix[4]areneswere synthesized and described. Their ionophoric properties were studied in liquid membrane ion-selective electrodes. The correlation between thechemical structure (conformation in solution determined by 1H NMR) and potentiometric ion-selectivity and complex formation constant havebeen studied. The PVC membrane electrodes based on tetraamides 8–11 show high sodium selectivity, are stable and long lasting. Disubstituted amides 1–7 are selective for larger and more lipophilic ions, as for exampleguanidinium ion. The crystal structure of the diamide 4 was determined by single crystal X-ray analysis. Crystals of 4 are triclinic, spacegroup P-1, with: a = 16,669(8), b = 17.795(10), c = 20.984(8) Å, =91.08(4)°, = 91.60(3)°, = 90.73(4)° and Z = 4. Ionophore 4 posseses a distorted cone conformation and is substituted at the proximal phenol rings. 相似文献
43.
This paper is concerned with the asymptotic behaviour and the stability of a class of linear neutral delay difference equations with variable coefficients and constant delays. Via an appropriate solution of the so-called generalized characteristic equation, an asymptotic criterion and a stability result are established. 相似文献
44.
P. CH. Sahu N. V. Chandra Shekar N. Subramanian Mohammad Yousuf K. Govinda Rajan 《高压研究》2013,33(5):295-305
Abstract The UAI2, UAI2, AND UAI4 compounds have been studied by high pressure X-ray diffraction up to a maximum pressure of ~ 35 GPa. The compressibility behaviour of UAI2 has been found to be consistent with the itinerant 5f states, whereas that of UAI2 and UAI4, indicate a more localized nature. Further, UAI2 has been found to undergo a structural transition at ~ 11 GPa and the structure of the high pressure phase has been identified to be of MgNi2 type with space group P63/mmc. The structure of UAI2 at ambient pressure is of MgCu2 type with space group Fd3m. From the electronic considerations, for instance, free electrons per atom ratio e/a, it is anticipated that it may transform back to MgCu2 type structure at still higher pressures. On similar considerations, it is expected that most of the AB2 type Laves phase compounds of the ‘f’ electron systems may undergo the structural sequence: MgCu2 – MgZn2 (or MgNi2) – MgCu2 due to increased delocalization of their ‘f’ electron states. 相似文献
45.
Equilibrium between the ion exchange membrane and solutions of anions at various valences has been the subject of this investigation. Competitive ion exchange reactions were studied on a strong base anion exchange membrane AMX manufactured by Tokuyama, commercialized by Eurodia, involving Cl?, $ {\text NO}_3^{ - } $ and $ {\text SO}_4^{{2 - }} $ ions. Solution concentrations studied were 0.05 and 0.1 M for all the systems reported. Experiments were performed with sodium as the counter ion, and the temperature was kept constant (T?=?298 K). Ionic exchange isotherms for the binary systems— $ {{\text Cl}^{ - }}/{\text NO}_3^{ - } $ , $ {{\text Cl}^{ - }}/{\text SO}_4^{{2 - }} $ , and $ {\text NO}_3^{ - }/{\text SO}_4^{{2 - }} $ —were established. The obtained results show that the sulfate was the most strongly sorbed, and the selectivity order is $ {\text SO}_4^{{2 - }} > {\text NO}_3^{ - } > {{\text Cl}^{ - }} $ at 0.05 M and $ {\text NO}_3^{ - } > {\text SO}_4^{{2 - }} > {{\text Cl}^{ - }} $ at 0.1 M under the experimental conditions. Selectivity coefficients $ K_{{{{{\text Cl} }^{ - }}}}^{{{\text NO}_3^{ - }}} $ , $ K_{{2{{{\text Cl} }^{ - }}}}^{{{\text SO}_4^{{2 - }}}} $ , and $ K_{{2{\text NO}_3^{ - }}}^{{{\text SO}_4^{{2 - }}}} $ for the three binary systems were determined. All the results given by this membrane were compared with those obtained, in the same conditions, with the RPA membrane (produced by RHONE POULENC). Ternary equilibrium data were taken for $ {{\text Cl}^{ - }}/{\text NO}_3^{ - }/{\text SO}_4^{{2 - }} $ . The prediction of the ternary system based only on the binary data was consistent with the experimental data obtained for this system. The good agreement between the experimental and the predicted data showed that the proposed framework can be considered as an effective method to predict many ternary systems from binary systems. 相似文献
46.
47.
Mössbauer spectroscopy, X-ray diffractometry and chemical fractionation have been used to study the clay smaples in sediments of Charhan playa and Qinghai lake. The spectral components of the Mossbauer spectra of the samples are attributed to Fe2+ ions in chlorite and siderite, Fe3+ ions in clay minerals and hematite, and partly in amorphous ferric hydroxides. The essential difference in the mineral composition of the sediments of both lakes is the presence of siderite in the samples of Char han playa, whereas it is absent in the samples of Qinghai lake. The fraction of the amorphous ferric hydroxides is higher in the sediments of Qinghai lake. Total Fe2+/Fe3+ ratios increase with sediment depth of Charhan playa, whereas these ratios are altogether smaller and run through a maximum at a certain depth for Qinghai lake. 相似文献
48.
C.R. Ottermann CH. Schmitt G.G. Simon F. Borkowski V.H. Walther 《Nuclear Physics A》1982,379(3):396-406
Cross sections for elastic electron scattering from 40Ar have been measured for the momentum transfer range from 0.59 to 1.31 fm?1. We have analyzed with the Fourier-Bessel ansatz our data as well as the data of former experiments. The rms charge radius we have found is 3.423(14) fm. The results are in excellent agreement with latest muonic data. Furthermore, we have reanalyzed former 40Ca data and have discussed the 40Ca- 40Ar charge distribution. 相似文献
49.
H. Zarschizky CH. Gerndt M. Honsberg H. W. Schneider A. Stemmer 《Optical and Quantum Electronics》1994,26(5):S471-S481
Optical clock signal distribution has been widely discussed to be an attractive way to reduce the clock skew in high-speed digital systems. For short interconnect lengths, especially for chip level clock distribution, free space systems using diffractive optical elements (DOEs) have specific advantages. The optoelectronic pathway described in this paper consists of a GaAs laser diode, a microetched silicon mirror, a faceted diffractive element and four silicon photodiodes hybridized to a (dummy) silicon chip. The key element of the clock distribution demonstrator is the diffractive element which matches setup requirements like compactness, off-axis geometry and use of an unshaped laser beam. The whole setup meets the demands of alignment accuracy in an excellent way. This is achieved by the very good imaging characteristic of the DOE and by an alignment technique based on precision mounting of micromachined silicon components. The system was tested with clock rates up to 2.5 GHz, the cut-off frequency is 350 MHz. 相似文献
50.