Properties of Interfaces in the two and three dimensional Ising Model

To investigate order-order interfaces, we perform multimagnetical Monte Carlo simulations of the $2D$ and $3D$ Ising model. Following Binder we extract the interfacial free energy from the infinite volume limit of the magnetic probability density. Stringent tests of the numerical methods are performed by reproducing with high precision exact $2D$ results. In the physically more interesting $3D$ case we estimate the amplitude $F^s_0$ of the critical interfacial tension $F^s = F^s_0 t^\mu$ to be $F^s_0 = 1.52 \pm 0.05$. This result is in good agreement with a previous MC calculation by Mon, as well as with experimental results for related amplitude ratios. In addition, we study in some details the shape of the magnetic probability density for temperatures below the Curie point.Comment: 25 pages; sorry no figures include

Specific Heat of Liquid Helium in Zero Gravity very near the Lambda Point

We report the details and revised analysis of an experiment to measure the specific heat of helium with subnanokelvin temperature resolution near the lambda point. The measurements were made at the vapor pressure spanning the region from 22 mK below the superfluid transition to 4 uK above. The experiment was performed in earth orbit to reduce the rounding of the transition caused by gravitationally induced pressure gradients on earth. Specific heat measurements were made deep in the asymptotic region to within 2 nK of the transition. No evidence of rounding was found to this resolution. The optimum value of the critical exponent describing the specific heat singularity was found to be a = -0.0127+ - 0.0003. This is bracketed by two recent estimates based on renormalization group techniques, but is slightly outside the range of the error of the most recent result. The ratio of the coefficients of the leading order singularity on the two sides of the transition is A+/A- =1.053+ - 0.002, which agrees well with a recent estimate. By combining the specific heat and superfluid density exponents a test of the Josephson scaling relation can be made. Excellent agreement is found based on high precision measurements of the superfluid density made elsewhere. These results represent the most precise tests of theoretical predictions for critical phenomena to date.Comment: 27 Pages, 20 Figure

ELLIPSOMETRY OF THIN FILMS ON VAPOR-LIQUID INTERFACES

Dans certaines solutions binaires, la phase inférieure des deux phases liquides peut former une couche qui s'immisce entre la phase liquide supérieure et la vapeur. Nous trouvons qu'une telle couche se forme au dessus des solutions composées par un fluorocarbone (C7F14) et par un alcool (i-C3H7OH). Lorsque la température augmente, la couche apparaît brutalement à une température de mouillage TW=311K. Cette température est bien en-dessous de la température de solubilisation (TC=363K). Au dessous de Tw, l'épaisseur de la couche (mesurée par ellipsométrie) peut être nulle et n'est pas plus grande que 2 nm. Au dessus de TW l'épaisseur de la couche est de plusieurs centaines d'Angstroems et sa variation avec la température est extrêmement faible. Lorsque la température d'un échantillon particulier a été augmentée jusqu'à un certain niveau vers TC, la phase inférieure s'est dissoute dans la phase supérieure. A 328K la phase inférieure a disparu. Au voisinage (±0,05K) de cette température l'épaisseur du film s'est annulée brutalement. Ces données expérimentales montrent clairement que les deux transitions sont du premier ordre.In certain binary solutions the lower of the two liquid phases can form a layer which intrudes between the upper liquid phase and the vapor. We find that such a layer does form above binary solutions of a fluorocarbon (C7F14) and an alcohol (i-C3H7OH). As the temperature is increased, the intruding layer abruptly appears at a characteristic wetting temperature TW=311K. This temperature is well below the consolute temperature (TC=363K). Below TW, the layer's thickness (measured by ellipsometry) may be zero and is no greater than 2 nm. Above TW the intruding layer's thickness is several hundred Angstroms and its variation with temperature is extremely weak. As the temperature of a particular sample was raised still further towards TC the lower phase dissolved into the upper liquid phase. At 328K the lower phase disappeared. Within ±0.05 K of this temperature the film thickness abruptly returned to zero. These data provide strong experimental evidence that both transitions are first order

Measurement of the universal gas-constant R using a spherical acoustic resonator

We report a new determination of the Universal Gas Constant R: (8.314 471 ±0.000 014) J·mol−1K−1. The uncertainty in the new value is 1.7 ppm (standard error), a factor of 5 smaller than the uncertainty in the best previous value. The gas constant was determined from measurements of the speed of sound in argon as a function of pressure at the temperature of the triple point of water. The speed of sound was measured with a spherical resonator whose volume was determined by weighing the mercury required to fill it at the temperature of the triple point. The molar mass of the argon was determined by comparing the speed of sound in it to the speed of sound in a standard sample of argon of accurately known chemical and isotoptic composition

Correlations among acoustic measurements of the Boltzmann constant

We review correlated uncertainties among the accurate determinations of the Boltzmann constant kB that used the techniques of primary acoustic gas thermometry (AGT). We find correlated uncertainty contributions from four sources: (1) the uncertain chemical and isotopic compositions of the test gases that lead to an uncertain average molar mass, (2) measurements of the temperature, (3) measurements of the shape and dimensions of the cavity resonators, and (4) fitting acoustic resonance frequencies as a function of the pressure. Molar-massdependent uncertainties are correlated among those measurements that used argon with isotopic abundances determined using an isotopic standard prepared at the Korea Research Institute of Standards and Science in 2006. Correlated, cavity-dependent uncertainties result from using the same cavity for more than one measurement. Small, correlated uncertainties propagate into all the AGT determinations of kB when acoustic resonance frequencies are fit for kB using uncertain literature data for the Avogadro constant and for the thermal conductivity and the higher acoustic virial coefficients of helium or argon

Relative permittivity and refractive index

A review on the measurements of the relative elec. permittivity (dielec. const. or relative permittivity) and refractive index of fluids as a function of pressure and temp

Towards an electromagnetic pressure standard: dielectric permittivity of helium and argon measured with quasi-spherical microwave resonators and cross capacitors

To develop electrically based pressure standards, we measured the dielectric permittivity of helium εHe(p,T) and argon εAr(p,T) using two independent techniques (quasispherical microwave cavities and cross capacitors). At 7 MPa, the microwave results for helium differ from NIST’s pressure standards by (18±37)×10−6

Acoustic Gas Thermometry

We review the principles, techniques and results from primary acoustic gas thermometry (AGT). Since the establishment of ITS-90, the International Temperature Scale of 1990, spherical and quasi-spherical cavity resonators have been used to realize primary AGT in the temperature range 7K to 552 K. Throughout the sub-range 90K < T < 384 K, at least two laboratories measured (T − T90). (Here T is the thermodynamic temperature and T90 is the temperature on ITS-90.) With a minor exception, the resulting values of (T −T90) are mutually consistent within 3 × 10−6 T . These consistent measurements were obtained using helium and argon as thermometric gases inside cavities that had radii ranging from 40mm to 90mm and that had walls made of copper or aluminium or stainless steel. The AGT values of (T − T90) fall on a smooth curve that is outside ±u(T90), the estimated uncertainty of T90. Thus, the AGT results imply that ITS-90 has errors that could be reduced in a future temperature scale. Recently developed techniques imply that low-uncertainty AGT can be realized at temperatures up to 1350K or higher and also at temperatures in the liquid-helium range