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101.
E. Eugster L. Jörissen H. Kunz 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1969,20(4):596-598
Ohne Zusammenfassung 相似文献
102.
103.
A method to enhance sampling of rare events is presented. It makes use of distance or dihedral-angle restraints to overcome an energy barrier separating two metastable states or to stabilize a transition state between the two metastable states. In order not to perturb these metastable end states themselves, a prefactor is introduced into the restraining energy function, which smoothly increases the weight of this function from zero to one at the transition state or on top of the separating energy barrier and then decreases the weight again to zero at the final state. The method is combined with multi-configurational thermodynamic integration and applied to two biomolecular systems, which were difficult to treat using standard thermodynamic integration. As first example the free energy difference of a cyclic alpha-aminoxy-hexapeptide-ion complex upon changing the ion from Cl- to Na+ was calculated. A large conformational rearrangement of the peptide was necessary to accommodate this change. Stabilizing the transition state by (hidden) restraints facilitates that. As a second example, the free energy difference between the 4C1 and the 1C4 conformation of beta-D-glucopyranoside was calculated. In unrestrained simulations the change from the 4C1 into the 1C4 conformation was never observed because of the high energy barrier separating the two states. Using (hidden) restraints, the transition from the 4C1 into the 1C4 state and back could be enforced without perturbing the end states. As comparison, for the same transitions the potential of mean force as obtained by using dihedral-angle constraints is provided. 相似文献
104.
Minofar B Vacha R Wahab A Mahiuddin S Kunz W Jungwirth P 《The journal of physical chemistry. B》2006,110(32):15939-15944
Molecular dynamics simulations in slab geometry and surface tension measurements were performed for aqueous solutions of magnesium acetate and magnesium nitrate at various concentrations. The simulations reveal a strong affinity of acetate anions for the surface, while nitrate exhibits only a very weak surface propensity, and magnesium is per se strongly repelled from the air/water interface. CH3COO- also exhibits a much stronger tendency than NO3- for ion pairing with Mg2+ in the bulk and particularly in the interfacial layer. The different interfacial behavior of the two anions is reflected by the opposite concentration dependence (beyond 0.5 M) of surface tension of the corresponding magnesium salts. Measurements, supported by simulations, show that the surface tension of Mg(NO3)2(aq) increases with concentration as for other inorganic salts. However, in the case of Mg(OAc)2(aq) the surface tension isotherm exhibits a turnover around 0.5 M, after which it starts to decrease, indicating a positive net solute excess in the interfacial layer at higher concentrations. 相似文献
105.
Valeria Kagramanova Jutta Kunz Claus Lämmerzahl 《General Relativity and Gravitation》2008,40(6):1249-1278
Orbits of test particles and light rays are an important tool to study the properties of space-time metrics. Here we systematically
study the properties of the gravitational field of a globally regular magnetic monopole in terms of the geodesics of test
particles and light. The gravitational field depends on two dimensionless parameters, defined as ratios of the characteristic
mass scales present. For critical values of these parameters the resulting metric coefficients develop a singular behavior,
which has profound influence on the properties of the resulting space-time and which is clearly reflected in the orbits of
the test particles and light rays. 相似文献
106.
Burkhard Kleihaus Jutta Kunz Francisco Navarro-Lérida Ulrike Neemann 《General Relativity and Gravitation》2008,40(6):1279-1310
We consider globally regular and black hole solutions in SU(2) Einstein–Yang–Mills–Higgs theory, coupled to a dilaton field.
The basic solutions represent magnetic monopoles, monopole–antimonopole systems or black holes with monopole or dipole hair.
When the globally regular solutions carry additionally electric charge, an angular momentum density results, except in the
simplest spherically symmetric case. We evaluate the global charges of the solutions and their effective action, and analyze
their dependence on the gravitational coupling strength. We show, that in the presence of a dilaton field, the black hole
solutions satisfy a generalized Smarr type mass formula.
B. Kleihaus gratefully acknowledges support by the German Aerospace Center.
F. Navarro-Lérida gratefully acknowledges support by the Ministerio de Educación y Ciencia under grant EX2005-0078. 相似文献
107.
Daniel Loof Oliver Thüringer Dr. Marco Schowalter Dr. Christoph Mahr Anmona Shabnam Pranti Prof. Dr. Walter Lang Prof. Dr. Andreas Rosenauer Dr. Volkmar Zielasek Dr. Sebastian Kunz Prof. Dr. Marcus Bäumer 《ChemistryOpen》2021,10(7):697-712
Porous networks of Pt nanoparticles interlinked by bifunctional organic ligands have shown high potential as catalysts in micro-machined hydrogen gas sensors. By varying the ligand among p-phenylenediamine, benzidine, 4,4‘‘-diamino-p-terphenyl, 1,5-diaminonaphthalene, and trans-1,4-diaminocyclohexane, new variants of such networks were synthesized. Inter-particle distances within the networks, determined via transmission electron microscopy tomography, varied from 0.8 to 1.4 nm in accordance with the nominal length of the respective ligand. While stable structures with intact and coordinatively bonded diamines were formed with all ligands, aromatic diamines showed superior thermal stability. The networks exhibited mesoporous structures depending on ligand and synthesis strategy and performed well as catalysts in hydrogen gas microsensors. They demonstrate the possibility of deliberately tuning micro- and mesoporosity and thereby transport properties and steric demands by choice of the right ligand also for other applications in heterogeneous catalysis. 相似文献
108.
Vapor pressure osmometry was applied to the systems calcium l-aspartate ((S)-aminobutanedioic acid calcium salt)?+?water for varying molalities of Ca–l-Asp (mCa–l-Asp?=?0.01–1.02 mol·kg?1) and guanidinium hydrochloride (methanamidine hydrochloride)?+?sodium L–aspartate ((S)–aminobutanedioic acid sodium salt)?+?water, varying the molalities of GndmCl and Na–l-Asp (mNa–l-Asp?=?0.1, 0.25, 0.4, 0.57 mol·kg?1 and mGndmCl?=?0.1–1.1 mol·kg?1) at T?=?298.15 K and 310.15 K. From vapor pressure osmometry, activities of water, and the corresponding osmotic coefficients of the mixtures Ca–l-Asp?+?water and Na–l-Asp?+?GndmCl?+?water have been calculated, both being directly related to the chemical potentials of the different species and therefore to their Gibbs energy. Mean molal ion activity coefficients were obtained from experimental data fits with the Pitzer equations and the corresponding dual and triple interaction parameters were derived for the Ca–l-Asp?+?water binary system. β(2) Pitzer parameters different from zero are required for Ca–l-Asp in water to reproduce the osmotic coefficient decrease with increasing concentration. Mean Spherical Approximation parameters accounting for Coulomb and short range interactions that describe the calcium and magnesium aspartates and glutamates are given. The decrease in the chemical potential of the aspartates corresponds to the Hofmeister series: NaAsp?>?Mg(Asp)2?>?CaAsp. A strong interaction between amino acid and salt due to specific dispersion interactions in amino acid salt systems containing guanidinium based salt has been revealed that is in agreement with MD and half-empirical quantum-chemical calculations. 相似文献
109.
110.