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81.
Divalent dipeptides have been introduced as counter ions in aqueous CZE. The dipeptides form ion pairs with amino alcohols in the BGE and facilitate the separation of amino alcohols. High concentrations of dipeptide caused reversed effective mobility for the analytes. The net charge of the dipeptide can be controlled using a buffer or a strong base, and regulates the interaction between the dipeptide and the amino alcohol. A stronger interaction and higher selectivity of amino alcohols was observed when the dipeptides were used as divalent counter ions, than in monovalent or uncharged form. Association constants for ion pairs between divalent dipeptides and amino alcohols can be used to enhance selectivity for amino alcohols in CZE. No chiral separation of amino alcohols was observed when using the dipeptides as ion‐pairing chiral selectors in aqueous BGE, but addition of methanol to the BGE promoted enantioselectivity. 相似文献
82.
Philipp Wachter Christian Schreiner Hans-Georg Schweiger Heiner Jakob Gores 《The Journal of chemical thermodynamics》2010,42(7):900-903
The determination of phase transition points of nine different ionic liquids (ILs) was performed by thermal analysis with simultaneous recording of conductivity. Conductivity of electrolyte solutions and ILs drastically changes during phase transitions and thus is an additional and very sensitive indicator for measuring phase transition points. Evaluation of temperature–time functions and conductivity–time functions with our computer-coupled automated equipment enabled the determination of melting temperatures with high accuracy and reliability. This claim is based on large samples, low temperature change rates and by regularly repeated measurements, i.e. at least seven measurements per IL. The melting temperatures of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium tris(penta-fluoroethyl)trifluorophosphate, and 1-methyl-3-propylimidazolium iodide were, to our knowledge, determined for the first time. The melting temperatures of the other 1-butyl-1-methylpyrrolidinium-, 1-ethyl-3-methylimidazolium-, 1-hexyl-3-methylimidazolium-, and trimethylsulfonium-based ILs showed either a very good accordance with values published in literature or were distinctly higher. 相似文献
83.
We provide two sharp sufficient conditions for immersed Willmore surfaces in $\mathbb{R }^3$ to be already minimal surfaces, i.e. to have vanishing mean curvature on their entire domains. These results turn out to be particularly suitable for applications to Willmore graphs. We can therefore show that Willmore graphs on bounded $C^4$ -domains $\overline{\varOmega }$ with vanishing mean curvature on the boundary $\partial \varOmega $ must already be minimal graphs, which in particular yields some Bernstein-type result for Willmore graphs on $\mathbb{R }^2$ . Our methods also prove the non-existence of Willmore graphs on bounded $C^4$ -domains $\overline{\varOmega }$ with mean curvature $H$ satisfying $H \ge c_0>0 \,{\text{ on }}\, \partial \varOmega $ if $\varOmega $ contains some closed disc of radius $\frac{1}{c_0} \in (0,\infty )$ , and they yield that any closed Willmore surface in $\mathbb{R }^3$ which can be represented as a smooth graph over $\mathbb{S }^2$ has to be a round sphere. Finally, we demonstrate that our results are sharp by means of an examination of some certain part of the Clifford torus in $\mathbb{R }^3$ . 相似文献
84.
85.
86.
Ch. Schwan F. Martin G. Jakob J.C. Martinez H. Adrian 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):477-481
We have investigated the crystal structure and the ferroelectric properties of BaTiO3 thin films with YBa2Cu3O as the bottom and Au as the top electrode. Epitaxial heterostructures of YBa2Cu3O and BaTiO3 were prepared by dc and rf sputtering, respectively. The crystal structure of the films was characterised by X-ray diffraction.
The ferroelectric behaviour of the BaTiO3 films was confirmed by hysteresis loop measurements using a Sawyer Tower circuit. We obtain a coercive field of 30 kV/cm
and a remanent polarisation of 1.25 μC/cm2. At sub-switching fields the capacitance of the films obeys a relation analogous to the Rayleigh law. This behaviour indicates
an interaction of domain walls with randomly distributed pinning centres. At a field of 5 MV/m we calculate a 3% contribution
of the irreversible domain wall motion to the total dielectric constant.
Received 24 June 1999 and Received in final form 27 August 1999 相似文献
87.
88.
Ohne Zusammenfassung
Vorliegende Untersuchung war bereits vor l?ngerer Zeit (1921) abgeschlossen und kommt lediglich aus ?u?eren Gründen erst jetzt
zur Ver?ffentlichung. 相似文献
89.
Mónica C. Gonzalez Tarek M. Hashem Laurent Jakob André M. Braum 《Fresenius' Journal of Analytical Chemistry》1995,351(1):92-97
The oxidative degradation of 3-amino 5-methyl isoxazole initiated by the VUV photolysis of water at 172 nm has been studied. Mineralization of CO2, H2O, NO
3
–
and NH
4
+
is more efficient when reductive conditions (argon saturated solutions) are favoured. Formation of compounds which cannot be completely oxidised to CO2 is observed. Experiments performed under strictly oxidative conditions show higher yields of these inert compounds and, hence, incomplete mineralization. Cyanide was formed in concentrations lower than 5×10–5 mol/l. In alkaline aqueous solutions, cyanide is completely transformed into CO
3
2–
, NH
4
+
and NO
3
–
during the irradiation time needed to mineralize the isoxazole. Therefore, cyanide does not present a potential risk for the use of the VUV photolysis for isoxazole degradation. Similarly, organic nitrogen is converted into both, NO
3
–
and NH
4
+
. The relative concentrations of the two ions depend on total irradiation time, oxygen saturation and reactor geometry. A sequence of reactions is proposed and discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday 相似文献
90.
The ground state energy of an atom of nuclear charge Ze in a magnetic field B is evaluated exactly to leading order as Z → ∞. In this and a companion work (see [28]) we show that there are five regions as Z → ∞: B < Z4/3, B ~ Z4/3, Z4/3 < B < Z3, B ~ Z3, B > Z3. Regions 1, 2, 3, and 4 (and conceivably 5) are relevant for neutron stars. Different regions have different physics and different asymptotic theories. Regions 1, 2, and 3 are described by a simple density functional theory of the semiclassical Thomas-Fermi form. Here we concentrate mainly on regions 4 and 5 which cannot be so described, although 3, 4, and 5 have the common feature (as shown here) that essentially all electrons are in the lowest Landau band. Region 5 does have, however, a simple non-classical density functional theory (which can be solved exactly). Region 4 does not, but, surprisingly, it can be described by a novel density matrix functional theory. © 1994 John Wiley & Sons, Inc. 相似文献