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251.
Machala Viktor Trávníček Zdeněk Šindelář Zdeněk Kvítek Libor Marek Jaromír 《Transition Metal Chemistry》2000,25(6):715-719
A series of NiII complexes with the O,O-di-isoamylester of dithiophosphoric acid and nitrogen-donor ligands of composition [Ni(i-Am2dtp)2(L)]; [dtp = O2PS2
–; L = 2,2-bipyridine (bpy); 1,10-phenanthroline (phen); 5-nitro-1,10-phenanthroline (nphen); 4,7-diphenyl-1,10-phenanthroline (baphen); 2,9-dimethyl-1,10-phenanthroline (neo), 2-aminomethylpyridine (amp), 2-(2-aminoethyl)pyridine (aep), 2,2-dipiridylamine (dpa), 1,2-diaminopropane (1,2-dap) or trans 1,2-diaminocyclohexane (dch)] have been prepared. The compounds have been characterized by elemental analyses (C,H,N,S), electronic and i.r. spectroscopy, magnetic and conductivity measurements and by cyclic voltammetry. The results show that all complexes behave as non-electrolytes in acetone. Electronic spectra and magnetic moments suggest a distorted cis-octahedral geometry around the NiII atom [eff/B <3.10, 3.40 >], except for [Ni(i-Am2dtp)2(aep)], where the measured temperature dependence of the magnetic susceptibility proved the tetrahedrally coordinated nickel [4.06 eff/B (298 K) – 3.20 eff/B (80 K)]. In the [Ni(i-Am2dtp)2(neo)] complex, the nickel atom is penta-coordinated. The X-ray crystal and molecular structure of [Ni(i-Am2dtp)2(1,2-dap)] has been determined. 相似文献
252.
We demonstrate that the temperature dependence of the electron spin polarization for the fractional states nu = 1/3 and nu = 2/3 displays activated behavior. This study enables the first measurement of the fractional quantum Hall spin-flip gaps. They are found to be systematically larger in comparison with the gaps simultaneously measured in transport. For nu = 1/3 and nu = 1/2, these spin-flip gaps allow the determination of the composite fermion interaction energy. This energy is investigated as a function of the finite width of the 2D channel. 相似文献
253.
Göres J Gamez G Smet JH Pfeiffer L West K Yacoby A Umansky V von Klitzing K 《Physical review letters》2007,99(24):246402
The correlated phases in a two-dimensional electron system with a high index partially filled Landau level are studied in transport under nonequilibrium conditions by imposing a dc-current drive. At filling 1/4 and 3/4 of these Landau levels, where the charge density wave picture predicts an isotropic bubble phase, the dc drive induces anisotropic transport behavior consistent with stripe order. The easy axis of the emerging anisotropic phase is perpendicular to the drive. At half filling the anisotropic stripe phase is stabilized by the dc drive provided drive and easy-axis directions coincide. 相似文献
254.
We demonstrate a novel class of trapping potentials, time-averaged adiabatic potentials (TAAP), which allows the generation of a large variety of traps for quantum gases and matter-wave guides for atom interferometers. Examples include stacks of pancakes, rows of cigars, and multiple rings or sickles. The traps can be coupled through controllable tunneling barriers or merged altogether. We present analytical expressions for pancake-, cigar-, and ring-shaped traps. The ring geometry is of particular interest for guided matter-wave interferometry as it provides a perfectly smooth waveguide of widely tunable diameter and thus adjustable sensitivity of the interferometer. The flexibility of the TAAP would make possible the use of Bose-Einstein condensates as coherent matter waves in large-area atom interferometers. 相似文献
255.
Neff PA Wunderlich BK Klitzing RV Bausch AR 《Langmuir : the ACS journal of surfaces and colloids》2007,23(7):4048-4052
The formation of polyelectrolyte multilayers (PEMs) is investigated using a silicon-on-insulator based thin film resistor which is sensitive to variations of the surface potential. The buildup of the PEMs at the silicon oxide surface of the device can be observed in real time as defined potential shifts. The influence of polymer charge density is studied using the strong polyanion poly(styrene sulfonate), PSS, combined with the statistical copolymer poly(diallyl-dimethyl-ammoniumchloride-stat-N-methyl-N-vinylacetamide), P(DADMAC-stat-NMVA), at various degrees of charge (DC). The multilayer formation stops after a few deposition steps for a DC below 75%. We show that the threshold of surface charge compensation corresponds to the threshold of multilayer formation. However, no reversion of the preceding surface charge was observed. Screening of polyelectrolyte charges by mobile ions within the polymer film leads to a decrease of the potential shifts with the number of layers deposited. This decrease is much slower for PEMs consisting of P(DADMAC-stat-NMVA) and PSS as compared to PEMs consisting of poly(allylamine-hydrochloride), PAH, and PSS. From this, significant differences in the dielectric constants of the polyelectrolyte films and in the concentration of mobile ions within the films can be derived. 相似文献
256.
Schollmeyer H Guenoun P Daillant J Novikov DV Klitzing RV 《The journal of physical chemistry. B》2007,111(16):4036-4042
Absolute ion concentration and its profile across polyelectrolyte multilayer films were studied. The films were prepared by alternating adsorption of polyanions and polycations from aqueous solution. Standing-wave X-ray fluorescence was used to map the ion profile. The well-studied multilayer system PSS/PAH was investigated, and bromide ions were used as probe entities. The results show that the sign of the charge of the outermost layer and the washing procedure after finishing the preparation have a decisive effect on the ion concentration and the ion profile. Multilayers with PSS as the outermost layer contain fewer bromide ions than the PAH-terminated multilayers. Exposure to water washes the ions out, but even after 6 h of washing, not all of the bromide ions had been removed. 相似文献
257.
Janečková L Kalíková K Vozka J Armstrong DW Bosáková Z Tesařová E 《Journal of separation science》2011,34(19):2639-2644
Cyclofructans (CFs), a new class of chiral selectors, have been recently introduced for application in liquid chromatography and capillary electrophoresis. So far, derivatized CFs have performed interesting separation possibilities for a variety of compounds. The current work is focused on characterization of three different CF-based chiral stationary phases (CF-based CSPs), i.e. isopropyl carbamate cyclofructan 6 (IP-CF6), R-naphthylethyl carbamate cyclofructan 6 (RN-CF6) and dimethylphenyl carbamate cyclofructan 7 (DMP-CF7). The linear free energy relationship (LFER) model was used to reveal the dominant interactions participating in the complex retention mechanism. A set of 44 different test solutes, with known solvation parameters, was used to determine the regression coefficients of the LFER equation under two mobile-phase compositions in normal separation mode. The LFER results showed that hydrogen bond acidity, hydrophobicity and dipolarity/polarizibility mostly affect the retention and separation process on the CF-based columns in the studied separation systems. 相似文献
258.
259.
Lee DS Riedl C Beringer T Castro Neto AH von Klitzing K Starke U Smet JH 《Physical review letters》2011,107(21):216602
We address the quantum Hall behavior in twisted bilayer graphene transferred from the C face of SiC. The measured Hall conductivity exhibits the same plateau values as for a commensurate Bernal bilayer. This implies that the eightfold degeneracy of the zero energy mode is topologically protected despite rotational disorder as recently predicted. In addition, an anomaly appears. The densities at which these plateaus occur show a magnetic field dependent offset. It suggests the existence of a pool of localized states at low energy, which do not count towards the degeneracy of the lowest band Landau levels. These states originate from an inhomogeneous spatial variation of the interlayer coupling. 相似文献
260.
Jan Schramla Eva Petráková Jan Pelnař Magdalena Kvíačlova Václav Chvalovský 《Journal of carbohydrate chemistry》2013,32(3):393-403
The 1H, 13C and 29Si NMR spectra of methyl β-D-xylopyranoside and three methyl β-D-xylopyranosyl-β-D-xylopyranosides have been measured and assigned by two-dimensional NMR spectroscopy. According to the determined proton-proton coupling constants, the ring conformer ratio is essential ly the same in the studied compounds. The assigned chemical shifts provide correct substituent chemical shifts for assignments in the spectra of higher trimethylsilylated xylooligosaccharides. Heteronuclear chemical shift correlated 2D NMR spectroscopy is proven to be a usable experimental method for 29Si NMR line assignment in carbohydrates. The assigned silicon shifts identify the site of glycosidation. 相似文献