Higher Critical Pressure Research Articles

Two modes of phase inversion in a drying emulsion

We report two different modes of phase inversion in surfactant-stabilized oil-in-water emulsions subjected to a unidirectional drying stress. Coalescence occurs either through a nucleation-and-growth mechanism, where coalesced pockets form and grow randomly throughout the sample, or through a coalescence front that propagates into the sample from the drying end. This drying-induced coalescence results from the development of a pressure gradient from the drying front into the bulk of the sample, established by limited water transport through the Plateau borders. Depending on the steepness of this pressure profile, coalescence occurs throughout the sample or only at the drying front. Moreover, we find that surfactant concentration plays a significant role through its effect on the critical disjoining pressure at which coalescence occurs. Very stable emulsions, characterized by a high critical pressure, tend to develop steep pressure profiles, which favours front-dominated coalescence, while unstable emulsions with low critical pressures develop shallow pressure gradients, favouring nucleation-and-growth dominated coalescence. These results offer new insights into the microscopic mechanisms governing the complex and poorly understood macroscopic phenomena during phase inversion of drying emulsions.

Thermodynamic Properties of Liquids from Speed of Sound Measurements

A strategy for deriving thermodynamic properties of liquids ( r , c p , c v ) from speed of sound is presented. It is based on numerical integration of differential equations connecting speed of sound with other thermodynamic properties. Two different procedures are recommended: One for liquids with lower and moderate critical pressures (LMCP), and another for liquids with higher critical pressures (HCP). The set of differential equations is solved as the initial value problem in both cases. However, for LMCP liquids initial conditions (several accurate values of r and c p ) are specified along isobar near the critical pressure, and for HCP liquids along the liquid-vapor saturation curve. The procedures are tested on ethane, carbon dioxide, and water.

Thermodynamic analysis of double-stage biomass fired Organic Rankine Cycle for micro-cogeneration

A biomass fired double-stage Organic Rankine Cycle (ORC) for micro-cogeneration is studied. Focus is laid on optimizing thermal efficiency in summer mode by appropriate working fluid and pressure level selection. Simulation and thermodynamic analysis show that in double-stage ORC, the working fluid in the low-temperature circuit (LTC) effects total efficiency more than the working fluid in the high-temperature circuit (HTC). Within the chosen boundary conditions, isopentane gives best thermal efficiency, whereas R227ea is the least efficient in the LTC. Among the working fluids for the HTC, maximum total efficiency is similar for several working fluids. Simulations demonstrate that a prediction of thermal efficiencies with respect to physico-chemical characteristics of different working fluids is only feasible within certain chemical classes. In the HTC, low critical temperature, low molar mass, and high critical pressure increase the efficiency, whereas in the LTC, condensation pressure is most crucial for high efficiency. Constructional analysis indicate that in the majority of cases, an increase in thermal efficiency is connected with high-volume flow rates at the outlet of the turbine, which leads to voluminous expansion units and high investment costs, respectively. Appropriate working fluid combinations within a double-stage ORC reach total efficiencies of up to 35% at flue gas temperatures from 950 to 150 °C. Copyright © 2012 John Wiley & Sons, Ltd.

Effects of elastin degradation and surrounding matrix support on artery stability

Tortuous arteries are often associated with aging, hypertension, atherosclerosis, and degenerative vascular diseases, but the mechanisms are poorly understood. Our recent theoretical analysis suggested that mechanical instability (buckling) may lead to tortuous blood vessels. The objectives of this study were to determine the critical pressure of artery buckling and the effects of elastin degradation and surrounding matrix support on the mechanical stability of arteries. The mechanical properties and critical buckling pressures, at which arteries become unstable and deform into tortuous shapes, were determined for a group of five normal arteries using pressurized inflation and buckling tests. Another group of nine porcine arteries were treated with elastase (8 U/ml), and the mechanical stiffness and critical pressure were obtained before and after treatment. The effect of surrounding tissue support was simulated using a gelatin gel. The critical pressures of the five normal arteries were 9.52 kPa (SD 1.53) and 17.10 kPa (SD 5.11) at axial stretch ratios of 1.3 and 1.5, respectively, while model predicted critical pressures were 10.11 kPa (SD 3.12) and 17.86 kPa (SD 5.21), respectively. Elastase treatment significantly reduced the critical buckling pressure (P < 0.01). Arteries with surrounding matrix support buckled into multiple waves at a higher critical pressure. We concluded that artery buckling under luminal pressure can be predicted by a buckling equation. Elastin degradation weakens the arterial wall and reduces the critical pressure, which thus leads to tortuous vessels. These results shed light on the mechanisms of the development of tortuous vessels due to elastin deficiency.

Size-driven ferroelectric effects in TGS induced by high hydrostatic pressure

The parameters P S , E c , ε and T C of TGS monocrystals were investigated under high hydrostatic pressure of up to 2.5 GPa. It has been found that above a critical pressure p c of about ≈ 1.8 GPa the derivative d T C d p starts to be negative and ferroelectricity disappears at about 2.5 GPa. The analysis of the reciprocal permittivity ε − 1 reveals that after the avalanche-type structure destruction the TGS samples show a relaxor-like behavior. It is suggested that polar nano-regions formed under high critical pressure mutually interact, in contrast to the case of a superparamagnetic. It is concluded that the TGS phase above 2.5 GPa may be referred to as a superparaelectric limit.

Thermodynamic Properties of Gases from Speed-of-Sound Measurements

A strategy for deriving thermodynamic properties of liquids (, cp, cv) from speed of sound is presented. It is based on numerical integration of differential equations connecting speed of sound with other thermodynamic properties. Two different procedures are recommended: One for liquids with lower and moderate critical pressures (LMCP), and another for liquids with higher critical pressures (HCP). The set of differential equations is solved as the initial value problem in both cases. However, for LMCP liquids initial conditions (several accurate values of  and cp) are specified along isobar near the critical pressure, and for HCP liquids along the liquid-vapor saturation curve. The procedures are tested on ethane, carbon dioxide, and water. The average absolute deviation of derived thermodynamic properties of ethane (, cp, cv), with respect to corresponding reference values, is 0.0014%, 0.0741%, and 0.1124%, respectively. Corresponding deviations for carbon dioxide are 0.0008%, 0.0363%, 0.0601%, and for water 0.0001%, 0.0206%, 0.0289%.

Viscosity Measurements of Water at High Temperatures and Pressures Using Dynamic Light Scattering

The application of dynamic light scattering to measure viscosity of water at high temperatures and pressures is demonstrated. Viscosity was obtained from the translational diffusion coefficient of probe particles dispersed in the medium by the Einstein-Stokes relationship. Measurements were carried out with polystyrene latex, colloidal silica, and colloidal gold. Under a constant pressure of 25 MPa, good agreement was found between the measured and calculated viscosities up to 275 degrees C with the polystyrene latex, 200 degrees C with the colloidal silica, and 297 degrees C with the colloidal gold. It was found that failure of the measurements at high temperatures is ascribed to change in either the dispersion stability or chemical stability of the probe particles. The present results indicate that the technique could also be used for other supercritical fluids having high critical temperature and pressure, such as methanol (T(c) = 239.4 degrees C, P(c) = 8.1 MPa) and ethanol (T(c) = 243.1 degrees C, P(c) = 6.4 MPa).

More on shear modulus collapse of lattices at high pressure

In his recent paper, Shear modulus collapse of lattices at high pressure, J. Phys. Cond. Matt. 16 (2004) L125, V.V. Kechin claims that the zero temperature shear modulus of a metallic solid vanishes at a high critical pressure, and the critical pressures for this shear modulus collapse lie in the range 0–250 Mbar for elemental metals. Here we demonstrate that Kechin's arguments contain an erroneous assumption, and therefore, do not prove that all metals become mechanically unstable at high pressures. Ab initio calculations and experimental results on a number of solids are analyzed to confirm our conclusion.

Evidence for triggering of the Vogtland swarms 2000 by pore pressure diffusion

Seismicity triggered by fluid injection in boreholes usually has certain typical spatiotemporal characteristics. These characteristics can be partly recognized as signatures, when pore pressure diffusion is the dominant triggering mechanism. Starting from these diffusion‐typical signatures of man‐made earthquakes, we seek analogous patterns for the earthquakes in Vogtland/NW Bohemia (VB) at the German/Czech border region in central Europe. VB is characterized by recurring intraplate earthquake swarms with magnitudes up to ML 4.5. There is strong geophysical evidence that the seismic events are correlated to fluid‐related processes in the crust. This study aims to investigate the possible role of fluids in VB. We test the hypothesis that ascending magmatic fluids trigger earthquakes by the mechanism of pore pressure diffusion (i.e., relaxation). This triggering process is mainly controlled by two physical fields, the hydraulic diffusivity and the seismic criticality (i.e., critical pore pressure value leading to failure; stable locations are characterized by higher critical pressures), both heterogeneously distributed in rocks. The results of the analysis of the year 2000 VB earthquake swarm data support this concept. We were able to recognize diffusive signatures and to obtain scalar estimates of hydraulic diffusivities with values between 0.3 and 10 m2/s for the seismically active region. Using a numerical model, where spatially correlated diffusivity and criticality patches (where patches with higher diffusivity are assumed to be less stable) are considered, we successfully simulate a general seismicity pattern of the swarms 2000, including the spatiotemporal clustering of events and the migration of seismic activity.

Collapse of the antiferromagnetic ground state in the alkali-metal electrosodalites

(Received 24 September 2002; published 26 February 2003) We have studied the collapse under pressure of the antiferromagnetic ground state in F centers contained in alkali-metal-doped sodalites. In agreement with experiment we find that the spin-polarized F-center bands in the sodium-doped sodalite initially narrow with applied pressure. Consequently a high critical pressure for the phase transition from a magnetic insulator to a nonmagnetic metal is predicted (127 GPa). Surprisingly the critical pressures of the potassium- and rubidium-doped sodalites are found to be an order of magnitude lower (20 GPa and 13 GPa, respectively). The collapse of magnetism is found to occur when the unoccupied p states of the alkali-metal atoms hybridize with the F-center bands. The low critical pressure for the potassium and rubidium compounds can therefore be explained by the smaller energy difference between the unoccupied p states and the occupied states compared to sodium. Furthermore we find the sodalite lattice to be softer than previously reported, which is explained by a simple structural model.

Phase equilibria of (methane-long chain ester cuts) systems in drilling conditions

During the drilling operation, the drilling fluid interacts with the formation at the well bore leading to the dissolution of hydrocarbons in the mud. Berthezene et al. [J. Petroleum Sci. Eng. 23 (1999) 71] studied the methane solubility in different fluids representing the drilling mud. They concluded that the ester remains immiscible with methane up to very high pressures. Additional experimental work at pressures up to 100 MPa has been performed on different esters. The effect of chain length and the presence of the ester group onto the chain on the phase equilibrium with methane is investigated. The conclusions of this work are identical to that of Berthezene et al. for critical points: the high molecular weight esters yield very high critical pressures, but the lower the molar mass, the lower the critical pressure. The position of the ester group in the chain has been found to have a negligible influence on the phase envelope. Several cubic equations of state have been used to model the bubble pressure data. The Peng–Robinson (PR) and the Elliott–Suresh–Donohue (ESD) equations of state have been combined with the classical mixing rule using binary interaction parameters equal to zero ( k ij =0) and the Soave–Redlich–Kwong (SRK) equation-of-state has been used with the MHV2 and UNIFAC mixing rule. In all cases, group contribution methods have been used for predicting the critical properties of the pure components since we are looking for a completely predictive method. We have found that the SRK/MHV2/UNIFAC gives very poor results. The PR/ k ij =0 model gives the best results for the low pressures but the predictions are poor for high pressures. The ESD/ k ij =0 model appears to provide much better predictions, especially for high pressures, which is interesting for us.

Miscibility Critical Pressures in Monolayers of Ternary Lipid Mixtures

When phospholipids are mixed with cholesterol in a monolayer at an air–water interface, coexisting 2-dimensional liquid phases can be observed if the surface pressure, π, is lower than the miscibility critical pressure, π c. Ternary mixtures of two phospholipid species with dihydrocholesterol have been reported to have critical pressures that are linearly proportional to the relative composition of the phospholipids. However, we report here that, if the acyl chains of the two phospholipids differ significantly in length or unsaturation, the behavior is markedly different. In this case, the critical pressure of the ternary mixture can be remarkably high, exceeding the critical pressures of the corresponding binary mixtures. High critical pressures are also seen in binary mixtures of phospholipid and dihydrocholesterol when the two acyl chains of the phospholipid differ sufficiently in length. Using regular solution theory, we interpret the elevated critical pressures of these mixtures as an attractive interaction between the phospholipid components.

Nitrogenated carbon films deposited using filtered cathodic arc

Abstract Nitrogenated carbon films were deposited on various substrates using filtered cathodic arc. Non-uniformity of the film thickness was less than 5% over a 15 cm diameter area. Mechanical, optical (refraction index, extinction coefficient versus wavelength) and electrical properties were investigated as a function of nitrogen flow rate. Deposited coatings demonstrated high hardness of 40–65 GPa, Young's modulus 200–285 GPa, excellent elastic recovery, high critical pressure for scratch formation, and surface smoothness. While the hardness showed a relatively small decrease with nitrogen flow increase, the stress decrease was more significant (8–3.8 GPa). Extremely low wear rates were observed, even at high contact pressures, and no substantial debris was detected indicating that carbon is oxidized during wear. Clear correlation was found between transparency, electrical resistivity and stress of the films. Transparency and resistivity showed a significant rise with an increase of stress. An explanation of the film properties is based on the assumption that the basic characteristics of the deposited films were determined by the relative proportion of two three dimensional complementary type of bonds; the tetrahedral sp 3 bonds leading to stiff networks, and the trigonal sp 2 arrangments close to fullerene-like, or nanotube-like, structures.

The diversity of gas vesicle genes in Planktothrix rubescens from Lake Zürich.

Part of the gas vesicle gene cluster was amplified by PCR from three strains of Planktothrix rubescens isolated from Lake Zürich, Switzerland. Each contains multiple alternating copies of gvpA and gvpC. All of the gvpA sequences in the different strains are identical. There are two types of gvpC: gvpC20, of length 516 bp, encodes a 20 kDa protein of 172 amino acid residues (whose N-terminal amino acid sequence is homologous with the sequence of GvpC in Planktothrix [Oscillatoria] agardhii); gvpC16, of length 417 bp, encodes a 16 kDa protein of 139 amino acid residues that differs in lacking an internal 33-residue section. An untranslated 72 bp fragment from the 3' end of gvpC, designated omegaC, is also present in some strains. The two types of gvpC and presence of omegaC could be distinguished by the different lengths of PCR amplification products obtained using pairs of oligonucleotide primers homologous to internal sequences in gvpC and gvpA. Three genotype classes were found: GV1, containing only gvpC20; GV2, containing gvpC20 and omegaC; and GV3, containing gvpC16, gvpC20 and omegaC. Subclasses of GV2 and GV3 contained either one or two copies of omegaC. The accompanying paper by D. I. Bright & A. E. Walsby (Microbiology 145, 2769-2775) shows that strains of the GV3 genotype produce gas vesicles with a higher critical pressure than those of GV1 and GV2. A PCR survey of 185 clonal cultures of P. rubescens isolated from Lake Zürich revealed that 3 isolates were of genotype GV1, 73 were of GV2 and 109 were of GV3. The PCR technique was used to distinguish the gas vesicle genotype, and thence the associated critical-pressure phenotype, of single filaments selected from lakewater samples. Sequence analysis of the 16S rDNA and of regions within the operons encoding phycoerythrin, phycocyanin and Rubisco confirmed that these strains of Planktothrix form a tight phylogenetic group.

Pressure-induced delocalization of negative- U centres in semiconducting glasses

Delocalization of the negative- U centres and/or their excitations, strongly localized at ambient pressure, is predicted to occur in semiconducting glasses at the accessible high critical pressure p c ≈ 10 5 bar. The phenomenon is shown to exist because of the increase of the centres overlap with growing pressure, which increases the centres concentration. Then, non-localized charge carriers, related to the negative- U centres, become essential at sufficiently high p > p c, giving rise to dramatic changes in electron (e.g., transport) processes in semiconducting glasses.

高性能ＢＷＲ燃料集合体の開発 サイクロンスペーサの熱水力性能

The purpose of this study is to develop a new BWR fuel with high critical power and low pressure drop performance. In this report, the spacer which has a significant effect on thermal hydraulic performance, has been improved and the performance has been measured. The improved high performance spacer is a ferrule type spacer with twisted tape and improved flow tab. This spacer is called CYCLONE spacer. The test bundle consists of electrically heated rods in a 4×4 array configuration. The axial power shape is cosine. Two test assemblies with different radial power distribution have been used. One test assembly has the maximum power rods at the center of the test assembly and the other has the maximum power rods near the channel wall. The results show that the critical power performance of the bundle with CYCLONE spacers is 10 to 22% higher than that of the current bundle with ferrule spacers at BWR rated flow rate, while the pressure drop is about 3% higher at BWR rated conditions (quality 15%).

Crystal structure and physical properties of molecular metal (DI-DCNQI)2Cu (DI-DCNQI=2,5-Diiodo-N,N′-Dicyanoquinonediimine)

Abstract (DI-DCNQI) 2 Cu belongs to a new category in a series of exotic mixed-valence copper complexes (R1, R2-DCNQI) 2 Cu. This salt is metallic down to 4.2 K. Anisotropy of the resistivity is small ( ϱ // c : ϱ ⊥ c = 1:3). In the DCNQI-Cu system, pressure induces the metal-insulator transition and the distortion of the coordination tetrahedron around Cu (∠ NCuN angle; α) is correlated to the stability of the metallic state. (DI-DCNQI) 2 Cu has the smallest α value (122.3 • ) and the highest critical pressure ( ca 15 kbar). It is remarkable that the pressure induced metal-insulator transition is suppressed above ca 20 kbar. Enhanced and temperature-dependent magnetic susceptibility and T 2 -dependence of the resistivity suggest an existence of the strong electron-electron interaction.

Gas vesicles

The gas vesicle is a hollow structure made of protein. It usually has the form of a cylindrical tube closed by conical end caps. Gas vesicles occur in five phyla of the Bacteria and two groups of the Archaea, but they are mostly restricted to planktonic microorganisms, in which they provide buoyancy. By regulating their relative gas vesicle content aquatic microbes are able to perform vertical migrations. In slowly growing organisms such movements are made more efficiently than by swimming with flagella. The gas vesicle is impermeable to liquid water, but it is highly permeable to gases and is normally filled with air. It is a rigid structure of low compressibility, but it collapses flat under a certain critical pressure and buoyancy is then lost. Gas vesicles in different organisms vary in width, from 45 to &gt; 200 nm; in accordance with engineering principles the narrower ones are stronger (have higher critical pressures) than wide ones, but they contain less gas space per wall volume and are therefore less efficient at providing buoyancy. A survey of gas-vacuolate cyanobacteria reveals that there has been natural selection for gas vesicles of the maximum width permitted by the pressure encountered in the natural environment, which is mainly determined by cell turgor pressure and water depth. Gas vesicle width is genetically determined, perhaps through the amino acid sequence of one of the constituent proteins. Up to 14 genes have been implicated in gas vesicle production, but so far the products of only two have been shown to be present in the gas vesicle: GvpA makes the ribs that form the structure, and GvpC binds to the outside of the ribs and stiffens the structure against collapse. The evolution of the gas vesicle is discussed in relation to the homologies of these proteins.

Postoperative Atelectasis Reexpansion by Selective Insufflation Through a Balloon-Tipped Catheter

Although treatment of refractory atelectasis has been improved by pulmonary insufflation through FOB with balloon cuff, low pulmonary compliance and high critical opening pressure of alveoli in the atelectatic areas require a more selective approach to prevent pressure dispersion to highly compliant zones. To achieve the highest insufflation selectivity and reduce patient discomfort, we have devised a small caliber balloon-tipped catheter to easily reach even the minor branches of the bronchial tree. This result was obtained by utilizing the performed curve of the catheter distal end after withdrawing the internal stylet. The catheter was introduced through the nostrils (16 patients) or through an endotracheal tube (two patients) and advanced under fluoroscopic guidance. Reexpansion of atelectatic areas was accomplished by repeated air injections through a 60-ml syringe. No complications were observed. Complete disappearance of x-ray film evidence of atelectasis was obtained in 15 patients and partial reexpansion in 3 patients.

The mechanical properties of the Microcystis gas vesicle

Gas vesicles isolated from the cyanobacterium Microcystis sp. retained their high stability and critical pressure on storage and could be held under a sustained pressure of 0·5 MPa without collapse. Application and release of pressures up to 0·5 MPa gave reversible changes in volume that indicated an elastic compressibility of 0·0087 MPa−1, which was linear with pressure. The elastic bulk modulus of the Microcystis gas vesicle was 115 MPa. The average yield pressure of the gas vesicles, 4·3 MPa, was determined by infiltrating them with gas at high pressure and then releasing the pressure so that they exploded. From these two measurements the proteinaceous wall of the gas vesicle was calculated to have a Young’s modulus of 3·8 GPa and a yield stress of 78 MPa. These values correspond closely to those of nylon, which has a similar secondary structure to that of the gas vesicle protein. The critical collapse pressure of the Microcystis gas vesicle, 0·8 MPa, is substantially higher than the theoretical buckling pressure, 0·2 MPa, for an unstiffened homogeneous cylinder of similar relative dimensions. The stiffening of the gas vesicle may be provided by its outer layer of GVPc, since the removal of this protein decreases the critical pressure to 0·23 MPa. The volumetric compressibility of the gas vesicle generates a small reversible change in turbidity (0·008 MPa−1). Spectrophotometric measurements showed that a gas vesicle suspension containing 1 μl ml−1 of gas gives a pressure-sensitive optical density of 2·03 cm−1 at a wavelength of 500 nm.