Gleichungen für die dynamische Viskosität und die Wärmeleitfähigkeit von reinem fluidem Wasser

Zusammenfassung Methoden zum Aufstellen von Gleichungen für die dynamische Viskosität und die Wärmeleitfähigkeit reiner fluider Stoffe werden angegeben und ihre Brauchbarkeit wird bei H₂O nachgewiesen. Es ergibt sich nur jeweils eine Gleichung für die Berechnung der Transportgrößen, die allerdings die Variablen Temperatur und Dichte anstelle von Temperatur und Druck enthält, dafür aber das ganze Gas- und Flüssigkeitsgebiet erfaßt. Es werden neue Erkenntnisse über die prinzipielle Abhängigkeit der Transportgrößen von Temperatur und Dichte gewonnen.

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Equations for the dynamic viscosity and the thermal conductivity of pure fluid water substance

Methods for formulating equations for the dynamic viscosity and the thermal conductivity of pure fluid substances are given; their applicability is proved for H₂O. It is found that only one equation is needed to calculate the transport properties, which has the variables temperature and density instead of temperature and pressure, but covers the whole gaseous and liquid region. New knowledge of the principal dependence of the transport properties on temperature and density is attained.

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Über dieses Thema wurde am 6. 10. 1969 auf dem Thermodynamik-Kolloquium des VDI in Zürich berichtet.     

Inelastic electron scattering from hydrogen at 50° and 60°

Inelastic electron scattering cross sections have been measured for four-momentum transfers between 4.1 GeV² and 30.5 GeV². At the large scattering angles of this experiment, the dominant contribution to the cross section comes from the W₁ structure function. In the conventional scaling variables, x and x′, this structure function does not exhibit scaling behavior, and at fixed x or x′ it is found to decrease with increasing four-momentum transfer.     

Two combinatorial covering theorems

A theorem in convex bodies (in fact, measure theory) and a theorem about translates of sets of integers are generalized to coverings by subsets of a finite set. These theorems are then related to quasigroups and (0, 1)-matrices.     

Light scattering from assemblies of spherulites

A general equation describing the small-angle H_v light-scattering intensity for a system of N undeformed spherulites located at random within the sample and taking into account the truncation and interference effects is given. Scattering contour plots or radial scans are reported for various arrangements of the N spherulites. The results show that the interference effect may explain the speckled appearance of the experimental patterns. Moreover, the interference and truncation effects (for the special cases where truncation is considered here) do not seem to shift the position of the maximum scattering angle of the cloverleaf pattern as calculated from the single spherulite theory. Finally, the calculations show that the truncation effect increases the relative intensity of the pattern at large and low scattering angles and at azimuthal angles 0 and 90°C, as compared with the intensity at the position of maximum scattering angle.     

Numerical studies on the anderson localization problem

The electron localization is studied for Anderson's tight-binding model with diagonal and off-diagonal disorder for a very large square lattice (10,000 sites) and diamond lattice (27,000 sites). The numerical investigations are based on the Lanczos recursion method. The convergence of the recursion coefficientsa _n ,b _n is discussed with regard to the electron localization.From Anderson's criterion and an exact real space renormalization method the energy of the localization edge is found as a function of the degree of disorder. Also the dependence of the spatial decay rate of localized wave functions on the energy and the degree of disorder is evaluated. Near the Anderson transition, where all states become localized, we get two critical exponentsv _E andv _W , which lead us to the tentative suggestion of multicritical scaling laws for this transition.     

Study of Anderson localization by a continued-fraction method

The electron localization is studied for Anderson's tight-binding model of a disordered two-dimensional square lattice. For a large system of 10⁴ sites the averaged squared modulus $\text{| G}{}_{00}\text{|}{}^2$ of the Green's function is evaluated by a continued-fraction method. From this quantity, following Anderson's criterion, the energy of the mobility edge is found as a function of the degree of disorder. Also the Anderson transition is recognized.     

Measurement of the analyzing power in p-->d-->(p p)n with a fast forward 1S0 proton pair

A measurement of the analyzing power A(y) of the p-->d--> (p p) + n reaction was carried out at the ANKE spectrometer at COSY at beam energies of 0.5 and 0.8 GeV by detection of a fast forward proton pair of small excitation energy E(pp) < 3 MeV. The S-wave dominance in the fast diproton is experimentally demonstrated in this reaction. While at T(p) = 0.8 GeV the measured analyzing power almost vanishes, it rises to nearly unity at T(p) = 0.5 GeV for neutrons emitted at theta(c.m.)(n) = 167 degrees. The results are compared with a model taking into account one-nucleon exchange, single scattering, and Delta(1232) excitation in the intermediate state. The model describes fairly well the unpolarized cross section obtained earlier and the analyzing power at 0.8 GeV; it fails to reproduce A(y) at 0.5 GeV.     

Surface-charge-governed ion transport in nanofluidic channels

A study of ion transport in aqueous-filled silica channels as thin as 70 nm reveals a remarkable degree of conduction at low salt concentrations that departs strongly from bulk behavior: In the dilute limit, the electrical conductances of channels saturate at a value that is independent of both the salt concentration and the channel height. Our data are well described by an electrokinetic model parametrized only by the surface-charge density. Using chemical surface modifications, we further demonstrate that at low salt concentrations, ion transport in nanochannels is governed by the surface charge.     

Steady shear rate rheology of suspensions, as described by the giant floc model

The break-down of a particle network by shear is described as the development of shear planes: a region able to withstand low shear stresses may break down under a larger stress; thus with increasing shear stress and shear rate, the mutual distance (A) between successive shear planes decreases until, at very high shear rates, A approaches the particle diameter. The shear planes are idealised as flat planes. Energy dissipation during shear is predominantly due to the energy dissipated through the movement of the particles; the energy dissipation due to breakage and renewed formation of bonds between particles is relatively small. A consideration of the energy dissipated during the encounters of particles during shear, including that dissipated by entrained particles, then leads to a relation between this energy dissipation and the average fraction L, over which a moving particle entrains a neighbour. L includes the effect of parts of the network which are rotating under the influence of the shear. In the limit of large shear rates, L is found to depend only to a small extent on whether the suspension is coagulated or not.     

The Electroviscous Behavior of Aqueous Dispersions of Amorphous Silica (Ludox)

The electroviscous effects in very dilute aqueous dispersions of amorphous silica (Ludox) were investigated at various levels of salt, pH, and volume fraction (<0.01) of solids. Viscosities were much higher than predicted from existing theories, which is ascribed to the formation of a thick, gel-like surface layer on the particle. The volume of a particle adjusts itself almost reversibly to the salt and pH levels of the liquid and can grow up to four times the dry volume. This explains the apparent discrepancy between published dry and wet particle sizes and also the reported anomalously large number of bound water layers around a particle. The existence of a gel layer leads to an abnormally large amount of surface conductance; this may explain the anomalities found in electrophoresis. The validity of the model is also supported by published results of the amount of nonbulk water as found with NMR. Copyright 2001 Academic Press.