Symmetry properties and renormalization group in the stable superfluid phase of bosons at zero temperature

The appearence of divergences in perturbation theory for a system in a stable phase requires the existence of an underlying symmetry and related Ward identities to remove exactly these singularities in the physical response functions. In this paper we consider explicitly the Ward identities associated with the (gauge) symmetry of the interacting neutral Bose gas at zero temperature to solve the old-standing problem of infrared divergencies due to Bose- Einstein condensation. The exact infrared behavior of the system is achieved for any dimension d > 1. For 1 < d ? 3 the system is controlled by a non trivial line of fixed point distant from the Bogoliubov solution, while above d = 3 the Bogoliubov fixed point is found to be stable.     

On Bose-Einstein condensation in any dimension

A general property of an ideal Bose gas as temperature tends to zero and when conditions of degeneracy are satisfied is to have an arbitrarily large population in the groud state (or in its neighborhood); thus, condensation occurs in any dimension D but for D ≤ 2 there is no critical temperature. Some astrophysical consequences, as well as the temperature-dependent mass case, are discussed.     

Schichten aus amorphem Eisen

Thin films of iron are condensed onto a substrate at 20 ?K. After condensation and during annealing the electrical resistance is measured and Debye-Scherrer-diagramms are taken. The structure of the films depends on the evaporation rate and the vacuum conditions during condensation. In a good vacuum (10^?6 Torr) and for a high evaporation rate (100 å/sec) the films grow crystalline. Greater residual gas pressures and a slow evaporation rate (5 å/sec) lead to amorphous films. The amorphous structure is supposed to be induced by residual oxygen. A method is described to produce amorphous films of iron also in a high vacuum by condensing simultaneously small additions of Fe-oxide, Fe-selenide, Fe-sulfide, Si or Ge on a substrate at 20 ?K. During annealing the amorphous films change into the body-centered cubic structure of α-iron within a narrow range of temperature. Si is found to be the most effective substance to prevent crystallisation. Admixtures of Cu, Ag, Pb or SiO only lead to a state of high disorder, they do not prevent crystallisation of the Fe-films at any temperature of condensation.     

Exciton gas compression and metallic condensation in a single semiconductor quantum wire

We study the metal-insulator transition in individual self-assembled quantum wires and report optical evidence of metallic liquid condensation at low temperatures. First, we observe that the temperature and power dependence of the single nanowire photoluminescence follow the evolution expected for an electron-hole liquid in one dimension. Second, we find novel spectral features that suggest that in this situation the expanding liquid condensate compresses the exciton gas in real space. Finally, we estimate the critical density and critical temperature of the phase transition diagram at n{c} approximately 1 x 10;{5} cm;{-1} and T{c} approximately 35 K, respectively.     

Bose-Einstein Condensation of Photons and Photon Pairs

We investigate the Bose-Einstein condensation of photons and photon pairs in a two-dimension optical microcavity. We find that in the paraxial approximation, the mixed gas of photons and photon pairs is formally equivalent to a two dimension system of massive bosons with non-vanishing chemical potential, which implies the existence of two possible condensate phase. We also discuss the quantum phase transition of the system and obtain the critical point analytically. Moreover, we find that the quantum phase transition of the system can be interpreted as second harmonic generation.     

Condensation Characteristics of Flue Gas/Steam Mixtures with Fine Lignite and Ash Particles along Horizontal Finned Tube Bundles

The condensation behavior for a gas/steam mixture with fine lignite particles and lignite ash particles is experimentally investigated as the particles flow over horizontal finned tube bundles. The effects of the gas velocity, inlet temperature of cooling water, excess air coefficient, and particle dimension are discussed. The total mass flow rate of the condensate and the condensation heat transfer coefficient for flue gas including particles are higher than those of flue gas excluding particles when Reynolds number is higher than 2,300. The area covered by ash depositions tends to grow from the leeward toward the windward side with increasing particle diameter.     

Bose-Einstein Condensation of Photons and Photon Pairs

We investigate the Bose-Einstein condensation of photons and photon pairs in a two-dimension optical microcavity. We find that in the paraxial approximation, the mixed gas of photons and photon pairs is formally equivalent to a two dimension system of massive bosons with non-vanishing chemical potential, which implies the existence of two possible condensate phase. We also discuss the quantum phase transition of the system and obtain the critical point analytically. Moreover, we find that the quantum phase transition of the system can be interpreted as second harmonic generation.     

The influence of temperature gradients on the kinetic boundary layer problem for a condensing droplet

We extend an earlier method for solving kinetic boundary layer problems to the case of particles moving in aspatially inhomogeneous background. The method is developed for a gas mixture containing a supersaturated vapor and a light carrier gas from which a small droplet condenses. The release of heat of condensation causes a temperature difference between droplet and gas in the quasistationary state; the kinetic equation describing the vapor is the stationary Klein-Kramers equation for Brownian particles diffusing in a temperature gradient. By means of an expansion in Burnett functions, this equation is transformed into a set of coupled algebrodifferential equations. By numerical integration we construct fundamental solutions of this equation that are subsequently combined linearly to fulfill appropriate mesoscopic boundary conditions for particles leaving the droplet surface. In view of the intrinsic numerical instability of the system of equations, a novel procedure is developed to remove the admixture of fast growing solutions to the solutions of interest. The procedure is tested for a few model problems and then applied to a slightly simplified condensation problem with parameters corresponding to the condensation of mercury in a background of neon. The effects of thermal gradients and thermodiffusion on the growth rate of the droplet are small (of the order of 1%), but well outside of the margin of error of the method.     

Heat transfer performance of a toluene loaded two-phase thermosyphon

Large dimension thermosyphons are efficient heat transfer components in heat recovery systems. Their performance limits depend on the following parameters: geometrical (length, diameter, inclination angle), physical (fluid, fill charge), thermal (temperature, heat flux).An experimental investigation was carried out with a large dimension, closed, two-phase thermosyphon which correspond to a device used in industrial recuperators. A vertical or inclinded steel thermosyphon, 3 m long and 27 mm inner diameter, was tested at temperatures varying from 100°C to 300°C with toluene as the working fluid. The lower part of the pipe was electrically heated along a variable length and the upper zone was cooled with an air stream whose flow rate and temperature were controlled. The maximum heat flux was measured as a function of temperature for different liquid fill charges and inclination angles. From these experimental data, boiling and condensation heat transfer coefficients were deduced. It was observed that the critical heat flux depends little on the fill ratio unless the charge is less than 20% for which a local dry-out occurs. The optimal fill charge was found to be between 20% and 50%. Experimental data have been compared with existing theories. The inclination effects have been taken into account with an empirical formula.     

Bose-Einstein condensation of the magnetized ideal Bose gas

We study the charged non-relativistic Bose gas interacting with a constant magnetic field but which is otherwise free. The notion of Bose-Einstein condensation for the three-dimensional case is clarified, and we show that although there is no condensation in the sense of a phase transition, there is still a maximum in the specific heat which can be used to define a critical temperature. Although the absence of a phase transition persists for all values of the magnetic field, we show how as the magnetic field is reduced the curves for the specific heat approach the free field curve. For large values of the magnetic field we show that the gas undergoes a “dimensional reduction” and behaves effectively as a one-dimensional gas except at very high temperatures. These general features persist for other spatial dimensions D and we show results for D = 5. Finally we examine the magnetization and the Meissner-Ochsenfeld effect.     

On the Bose-Einstein condensation of an ideal gas

A mathematically precise treatment is given of the well-known Bose-Einstein condensation of an ideal gas in the grand canonical ensemble at fixed density. The method works equally well for any of the standard boundary conditions and it is shown that the finite volume activity converges and that in three dimensions condensation occurs for Dirichlet, Neumann, periodic, and repulsive walls.     

Surface bubble nucleation stability

Recent research has revealed several different techniques for nanoscopic gas nucleation on submerged surfaces, with findings seemingly in contradiction with each other. In response to this, we have systematically investigated the occurrence of surface nanobubbles on a hydrophobized silicon substrate for various different liquid temperatures and gas concentrations, which we controlled independently. We found that nanobubbles occupy a distinct region of this parameter space, occurring for gas concentrations of approximately 100%-110%. Below the nanobubble region we did not detect any gaseous formations on the substrate, whereas micropancakes (micron wide, nanometer high gaseous domains) were found at higher temperatures and gas concentrations. We moreover find that supersaturation of dissolved gases is not a requirement for nucleation of bubbles.     

Island formation and condensation of a chemisorbed overlayer

The condensation of a chemisorbed overlayer from a lattice gas into a particular ordered structure in discussed in terms of the lattice-gas theory of Lee and Yang. The formation of islands of ordered structure is identified with the condensation phenomenon predicted by the theory. The phase diagram (transition temperature versus coverage) based on the theory of a two-dimensional Ising ferromagnet in zero magnetic field is constructed for the condensation of a lattice gas system with net attractive interactions between the particles. It is demonstrated that critical points at coverages other than θ = 0.5 are achieved for overlayer systems with unit meshes larger than (1 × 1). Low-energy electron diffraction results of the thermal disordering (island dissolution) for oxygen chemisorbed on W(110) are compared with the theory, and the effect of substrate surface heterogeneity on the phase diagram is discussed.     

Time-resolved PLIF imaging of Cu in a laser-ablated copper plasmaplume

Planar laser-induced fluorescence (PLIF) has been used to determine the relative number density of ground state copper atoms in laser-ablated plasma plumes. An ablation laser power flux of ~1.5 GW/cm ² is applied to a solid copper target in a background gas, producing a plasma plume suitable for studying homogeneous copper vapor condensation. Density is measured at postablation time delays ranging from 5 μs to 10 ms with 1-100 torr of either argon or helium as the background gas. Planar laser-induced fluorescence images are used to spatially resolve the relative density within the plume, The decrease in density is due to the homogeneous condensation of copper vapor to form particulate     

Two-dimensional gas phases of Ar,Kr, AND Xe on Ag(111)

Observations and calculations are reported for the 2D gas phase of Ar, Kr, and Xe adsorbed on the (111) face of Ag. The measurement of the coverage of 2D gas is sensitive to the gas adsorbed on the coherently diffracting regions of the Ag; appreciable contributions to the measured coverage from gas adsorbed at extrinsic sites can be excluded. The gas density at the condensation of the solid monolayer is remarkably high, of the order of 15% of the 2D solid density. Statistical mechanical calculations, using Monte Carlo simulations, show that the unusually dense 2D gas is stabilized against condensation because substrate-mediated interactions raise the energy of the 2D solid relative to the value which would be calculated using the bare 3D pair potentials. The simulations show that the gas is very nonideal, with large specific heat and large density fluctuations. The only comparable states of a 3D gas occur near the gas-liquid critical point.     

Proof of Bose-Einstein condensation for dilute trapped gases

The ground state of bosonic atoms in a trap has been shown experimentally to display Bose-Einstein condensation (BEC). We prove this fact theoretically for bosons with two-body repulsive interaction potentials in the dilute limit, starting from the basic Schr?dinger equation; the condensation is 100% into the state that minimizes the Gross-Pitaevskii energy functional. This is the first rigorous proof of BEC in a physically realistic, continuum model.     

Quantitative and Qualitative Analysis of Bose-Einstein Condensation in Harmonic Traps

A simple and direct approach to handle summation is presented. With this approach, we analytically investigate Bose-Einstein condensation of ideal Bose gas trapped in an isotropic harmonic oscillator potential. We get the accurate expression of Tc which is very close to (0.43% larger than) the experimental data. We find the curve of internal energy of the system vs. temperature has a turning point which marks the beginning of a condensation. We also find that there exists specific heat jump at the transition temperature, no matter whether the system is macroscopic or finite. This phenomenon could be a manifestation of a phase transition in finite systems.     

Diamond anvil cell for measurements in high magnetic fields

Abstract

We constructed a diamond anvil cell for pressures up to 100 GPa in magnetic fields up to 12 T. The cell can be operated at any temperature between 10 and 350 K. Loading by condensation of gases is possible.