Control of ultralow pressures: an absolute thermodynamic manometer

A method of accurately manipulating the pressure of helium gas in the range P=10^–1 to 10^–20 Torr, T<5 K is presented. The method requires only a very modest apparatus and makes use of thermodynamic measurements on the 4He–Grafoil system. A calibration curve and a pressure scale for the manometer are developed which will allow convenient application in other laboratories. An experiment which utilizes the technique is briefly disscussed

„Wer hat, hat.“ Über den sog. Freien Relativsatz als Realisierung des Sprechaktes Generalisieren im deutsch-polnischen Vergleich

„Wer hat, hat.“ Über den sog. Freien Relativsatz als Realisierung des Sprechaktes Generalisieren im deutsch-polnischen Vergleic

From nonwetting to prewetting: the asymptotic behavior of 4He drops on alkali substrates

We investigate the spreading of 4He droplets on alkali surfaces at zero temperature, within the frame of Finite Range Density Functional theory. The equilibrium configurations of several 4He_N clusters and their asymptotic trend with increasing particle number N, which can be traced to the wetting behavior of the quantum fluid, are examined for nanoscopic droplets. We discuss the size effects, inferring that the asymptotic properties of large droplets correspond to those of the prewetting film

Order-disorder criticality, wetting, and morphological phase transitions in the irreversible growth of far-from-equilibrium magnetic films

An exhaustive numerical investigation of the growth of magnetic films in confined $(d+1)$-dimensional stripped geometries ($d=1,2$) is carried out by means of extensive Monte Carlo simulations. Thin films in contact with a thermal bath are grown by adding spins with two possible orientations and considering ferromagnetic (nearest-neighbor) interactions. At low temperatures, it is observed that the films exhibit ``spontaneous magnetization reversals'' during the growth process. Furthermore, it is found that for $d=1$ the system is non-critical, while a continuous order-disorder phase transition at finite temperature takes place in the $d=2$ case. Using standard finite-size scaling procedures, the critical temperature and some relevant critical exponents are determined. Finally, the growth of magnetic films in $(2+1)$ dimensions with competing short-range magnetic fields acting along the confinement walls is studied. Due to the antisymmetric condition considered, an interface between domains with spins having opposite orientation develops along the growing direction. Such an interface undergoes a localization-delocalization transition that is the precursor of a wetting transition in the thermodynamic limit. Furthermore, the growing interface also undergoes morphological transitions in the growth mode. A comparison between the well-studied equilibrium Ising model and the studied irreversible magnetic growth model is performed throughout. Although valuable analogies are encountered, it is found that the nonequilibrium nature of the latter introduces new and rich physical features of interest.Comment: 23 pages, 10 figure

Metastability, Mode Coupling and the Glass Transition

Mode coupling theory (MCT) has been successful in explaining the observed sequence of time relaxations in dense fluids. Previous expositions of this theory showing this sequence have required the existence of an ideal glass transition temperature $T_0$. Recent experiments show no evidence of $T_0$. We show here how the theory can be reformulated, in a fundamental way, such that one retains this sequence of relaxation behaviors but with a smooth temperature dependence and without any indication of $T_0$. The key ingredient in the reformulation is the inclusion of the metastable nature of the glass transition problem through a coupling of the mass density to the defect density. A main result of our theory is that the exponents governing the sequence of time relaxations are weak functions of the temperature in contrast to the results from conventional MCT.Comment: 14 pages (2 figures upon request), REVTEX

Simulations of Coulombic Fission of Charged Inviscid Drops

We present boundary-integral simulations of the evolution of critically charged droplets. For such droplets, small ellipsoidal perturbations are unstable and eventually lead to the formation of a "lemon"-shaped drop with very sharp tips. For perfectly conducting drops, the tip forms a self-similar cone shape with a subtended angle identical to that of a Taylor cone. At the tip, quantities such and pressure and fluid velocity diverge in time with power-law scaling. In contrast, when charge transport is described by a finite conductivity, we find that small progeny drops are formed at the tips whose size decreases as the conductivity is increased. These small progeny drops are of nearly critical charge, and are precursors to the emission of a sustained flow of liquid from the tips as observed in experiments of isolated charged drops.Comment: 4 pages, 3 figure

Onset of Superfluidity in 4He Films Adsorbed on Disordered Substrates

We have studied 4He films adsorbed in two porous glasses, aerogel and Vycor, using high precision torsional oscillator and DC calorimetry techniques. Our investigation focused on the onset of superfluidity at low temperatures as the 4He coverage is increased. Torsional oscillator measurements of the 4He-aerogel system were used to determine the superfluid density of films with transition temperatures as low as 20 mK. Heat capacity measurements of the 4He-Vycor system probed the excitation spectrum of both non-superfluid and superfluid films for temperatures down to 10 mK. Both sets of measurements suggest that the critical coverage for the onset of superfluidity corresponds to a mobility edge in the chemical potential, so that the onset transition is the bosonic analog of a superconductor-insulator transition. The superfluid density measurements, however, are not in agreement with the scaling theory of an onset transition from a gapless, Bose glass phase to a superfluid. The heat capacity measurements show that the non-superfluid phase is better characterized as an insulator with a gap.Comment: 15 pages (RevTex), 21 figures (postscript