Rough Interfaces Beyond the Gaussian Approximation

We compare predictions of the Capillary Wave Model with Monte Carlo results for the energy gap and the interface energy of the 3D Ising model in the scaling region. Our study reveals that the finite size effects of these quantities are well described by the Capillary Wave Model, expanded to two-loop order (one order beyond the Gaussian approximation).Comment: Contribution to LATTICE 94. 3 pages, PostScript fil

Finite Size Effects in Fluid Interfaces

It is shown that finite size effects in the free energy of a rough interface of the 3D Ising and three--state Potts models are well described by the capillary wave model at {\em two--loop} order. The agreement between theoretical predictions and Monte Carlo simulations strongly supports the idea of the universality of this description of order--order interfaces in 3D statistical systems above the roughening temperature.Comment: 3 pages, uuencoded .ps file, figures included. (Proceeding of Lattice '93

Finite-Size Effects in the Interface of 3D Ising Model

The interface between domains of opposite magnetization in the 3D Ising model near the critical temperature displays universal finite-size effects which can be described in terms of a gaussian model of capillary waves. It turns out that these finite-size corrections depend rather strongly on the shape of the lattice. This prediction, which has no adjustable parameters, is tested and accurately verified for various lattice shapes by means of numerical simulations with a cluster algorithm. This supports also a long-standing conjecture on the finite-size effects in Wilson loops of Lattice Gauge Theories.Comment: 13 pages, plain latex, two figures not included, sorry DFTT 68/9

Interface Tension of the Electroweak Phase Transition

In our nonperturbative lattice investigation we study the interface tension of the finite-temperature electroweak phase transition. In this analysis the Higgs mass has been chosen to be about $35$ GeV. At the transition point of a finite volume system, tunnelling between the symmetric and the Higgs phase takes place. This phenomenon leads to a splitting of the ground state, which can be used to determine the interface tension. The result obtained this way agrees with the result of the two-coupling method and with the prediction of the perturbative approach.Comment: 10 pages, five figures in uuencoded PS format, Latex + epsf.st

Ein neues, unkompliziert auszuführendes Verfahren zur Bestimmung kleiner Konzentrationen an Wasser in organischen Lösungsmitteln

A new procedure for the determination of water (even in trace amounts) in organic solvents is described. The solvatochromism of the pyridiniumphenol betaine, E T30, determined by a simple UV-absorption measurement, together with a two-parameter equation, permits an exact determination. The procedure is rapid and is, therefore, an alternative to the Karl-Fischer titration

Bestimmung der Zusammensetzung binärer Flüssigkeitsgemische mit Hilfe von Fluorescenzmessungen

A simple procedure for the determination of water in organic solvents and more generally of the composition of binary liquid mixtures by use of solvatochromic fluorescent dyes is described even for samples with low transparency. The procedure can be carried out without any spectrometer using only an array of optical filters

Numerical Investigation of the Interface Tension in the three-dimensional Ising Model

The interface tension in the three-dimensional Ising model in the low temperature phase is investigated by means of the Monte Carlo method. Together with other physically relevant quantities it is obtained from a calculation of time-slice correlation functions in a cylindrical geometry. The results at three different values of the temperature are compared with the predictions from a semiclassical approximation in the framework of renormalized $\phi^4$ theory in three dimensions, and are in good agreement with them.Comment: 17 pages, MS-TPI-92-13 (replaced due to correction of minor numerical errors

Comparison of Monte Carlo Results for the 3D Ising Interface Tension and Interface Energy with (Extrapolated) Series Expansions

We compare Monte Carlo results for the interface tension and interface energy of the 3-dimensional Ising model with Pad\'e and inhomogeneous differential approximants of the low temperature series that was recently extended by Arisue to $17^{\rm th}$ order in $u=\exp(-4\beta)$. The series is expected to suffer from the roughening singularity at $u\approx 0.196$. The comparison with the Monte Carlo data shows that the Pad\'e and inhomogeneous differential approximants fail to improve the truncated series result of the interface tension and the interface energy in the region around the roughening transition. The Monte Carlo data show that the specific heat displays a peak in the smooth phase. Neither the truncated series nor the Pad\'e approximants find this peak. We also compare Monte Carlo data for the energy of the ASOS model with the corresponding low temperature series that we extended to order $u^{12}$.Comment: 22 pages, 9 figures appended as 3 PS-files, preprints CERN-TH.7029/93, MS-TPI-93-0

Fragment Molecular Orbitals for Molecules and Interacting Systems

Different approaches to describe the structure and properties of molecules as well as reactions between molecules in terms of localized fragment orbitals and their interactions are briefly reviewed and the method of fragments-in-molecules (FIM) is delineated: The FIM method is formulated entirely in terms of strictly transfera< ble fragment orbitals (FO\u27s) which makes it possible to reduce the basis set in order to simplify the calculations, to save computer time and to make the results even more visual. Calculations within the CND0/2 approximation on CH3-S molecules with S = CH3, NH2, OH, F, CN, CH=CH2 and CH=O are used to demonstrate the effect of limiting the number of virtual orbitals taken into account and to an<l\u27lyse inductive and mesomeric interactions. It appears that the same orbital interactions between occupied and virtual FO\u27s of different fragments which are responsible for the rotational barrier also have the largest effect on the total energies of the systems under consideration. A partitioning of the energy of interaction between molecular fragments based on the formulation of the FIM approach yields definitions of inductive and mesomeric effects which are in good accord with chemical experience and is closely connected with other energy partitioning schemes