Lower Critical Point Research Articles

The salting out action of alkali metal nitrates on the water-diethylamine binary system

The results of a polythermal study of the salting out action of alkali metal (Na, K, and Cs) nitrates on the water-diethylamine binary system characterized by stratification with a lower critical solution point (LCSP) were comparatively analyzed. Alkali metal nitrates experiencing homoselective solvation in aqueousorganic solvents were found to decrease the LCSP of this binary system, that is, have a salting out action. A decrease in the radius of the cation in the series CsNO3-KNO3-NaNO3 decreased the temperature of critical tie line formation in the monotectic state of salt-water-diethylamine ternary systems (69.3, 48.1, and 22.9°C, respectively). In all ternary systems, first and foremost in the system with potassium nitrate, the effect of diethylamine salting out from aqueous solutions grew stronger as the temperature increased. The conclusion was drawn that, among the salts studied, sodium nitrate had the strongest salting out effect at 22.9–88.4°C, and potassium nitrate, at 88.4–150.0°C.

Nambu–Jona-Lasinio model of dense three-flavor matter with axial anomaly: The low temperature critical point and BEC-BCS diquark crossover

We study the QCD phase structure in the three-flavor Nambu-Jona-Lasinio model, incorporating the interplay between the chiral and diquark condensates induced by the axial anomaly. We demonstrate that for an appropriate range of parameters of the model, the interplay leads to the low temperature critical point in the phase structure predicted by a previous Ginzburg-Landau analysis. We also show that a Bose-Einstein condensate (BEC) of diquark molecules emerges in the intermediate density region, and as a result, a BEC-BCS crossover is realized with increasing quark chemical potential.

Self-focusing of acoustic beams in a guaiacol-glycerol solution: Concentration mechanism

The possibility of experimental observation of the self-focusing of ultrasonic beams as a result of temperature and concentration nonlinearities in a stratified guaiacol-glycerol solution with a closed stratification region has been analyzed. The estimation showed that the thermally induced ultrasound self-focusing can be observed in a frequency range from 1 to 10 MHz at ultrasonic pulse durations of 1 to 25 s and energies below 3 J. The concentration mechanism of self-focusing can be observed only in the immediate vicinity of the lower critical point of solution stratification at an average acoustic beam intensity of ∼1 Wm−2 and a pulse duration longer than 100 s. It is shown that a medium must be exposed to a pulsed periodic sound beam to experimentally implement these conditions.

A note on convergence of low energy critical points of nonlinear elasticity functionals, for thin shells of arbitrary geometry

We prove that the critical points of the 3d nonlinear elasticity functional on shells of small thickness h and around the mid-surface S of arbitrary geometry, converge as h → 0t o the critical points of the von Karman functional on S, recently proposed in (Lewicka et al., Ann. Scuola Norm. Sup. Pisa Cl. Sci. (to appear)). This result extends the statement in (Muller and Pakzad, Comm. Part. Differ. Equ. 33 (2008) 1018-1032), derived for the case of plates when S ⊂ R 2 . The convergence holds provided the elastic energies of the 3d deformations scale like h 4 and the external body forces scale like h 3 .

Phase behaviour of parallel hard rods in confinement: an Onsager theory study

The effect of confinement on the positional ordering is examined in a system of parallelhard cylinders using the second virial theory of Onsager. Hard cylinders are arranged in aslit-like pore (two parallel planar hard walls) in such a way that the long axes of theparticles are perpendicular to the surface of confining hard walls. We have incorporated thetheories of the bulk and the confined systems into a single formalism, where awij kernel function provides the link between the bulk and confined systems. It is shown thatthe presence of hard walls inhibits the second order nematic–smectic A phase transitionirrespective of the value of the wall-to-wall separation. Instead, due to accommodation problemsof the cylinders into the pore, an infinite number of first order layering phase transitionsappears. Coexisting curves, corresponding to the equilibrium between two phases havingn andn + 1 smectic-like periods, are bounded with lower critical points. The gap between theaverage densities of the coexisting phases shrinks with increasing pore width,while the properties of the critical points monotonically move towards those ofthe nematic–smectic A phase transition of the bulk system (). The effect of only one hard wall is related to the bulk nematic–smectic A phasetransition since a critical wetting transition of the wall induced layering takes place.

Density and refractive index measurements of critical mixture 1,4-dioxane + water + saturated KCl in homogenous phase region

The ternary critical mixture of 1,4-dioxane (1) + water (2) + saturated KCl (3) has a lower critical point. The density ρ and refractive index n of this system have been measured as function of temperature for nine critical mixtures along the coexistence curve below the temperature of phase-transition. The water mole fraction in free basis x 2 in the mixtures extends from (0.550 to 0.880) and the molality m of KCl from 0.47 to 2.039 mol kg −1. With increase of temperature, water mole fraction and KCl molality, the obtained density decreased, while the refractive index decreases with increase in temperature, water mole fraction and molality of salt. Both represented anomalies near the critical temperature T c. The molar fraction of critical mixture, increase less than 1%, with temperature and decrease by 10%, with water mass fraction and molality of salt. The critical density and the critical refractive index vary linearly with water mass fraction w 2 with molality m of KCl as a third degree polynomial. The temperature of separation of phase T t varies with critical composition in water and molality of KCl.

Liquid separation in the presence of vapor in synthetic fluid inclusions obtained from Na2CO3 solutions

Phase relations in the Na2CO3–H2O system are of special interest for geochemistry in the context of the problems of carbonatite genesis and particularly Old� onyo Lengai sodium carbonate lavas. The solubility of anhydrous Na2CO3 at 25°С is 8.13 wt % and decreases practically to zero with temperature growth up to the critical point of water. Consequently, the constitution diagram for this system belongs to the second (P–Q) type for which critical phenomena proceed both in undersaturated and saturated (in two points P and Q) solutions. The temperature of salt melting at normal pressure is 851°С and increases 17°С per 1 kbar. The peculiarities of sodium carbonate solutions at high temperatures and pressures were studied by M.I. Rav� ich (up to 550°С and 1900 bar) by the fixation of the trend of the curves of pressure dependence on temper� ature and volume during the phase transition [1] and Koster van Groos by differential thermal analysis up to 925°С and 400–3700 bar [2]. The coordinates of the lower critical point P are slightly above the critical point of water. The position of upper critical point Q was determined by M.I. Ravich [1] as 480°С, 1600 bar, and 30–40 wt % Na2CO3. Koster van Groos gives the following coordinates of Q point: 500 ± 10°С, 1505 ± 0.01 kbar, and 12 ± 2 wt % Na2CO3 [2]. Both publica� tions contain no data on liquid separation at tempera� tures below the Q point. However, according to [1], two liquids in equilibrium, but not liquid and vapor as was reported in [2], were registered in the upper two� phase area. This should provide evidence for the fact that the upper section of the critical curve connecting the critical Q point with the critical point of salt is not a continuation of the lower section passing from the critical point of water to point P. Consequently, both

Transport Properties in 1,4-Dioxane + Water + Saturated KCl Critical Mixture by Measuring Viscosity and Electrical Conductivity

The ternary critical mixture of 1,4-dioxane (1) + water (2) + saturated KCl (3) has a lower critical point. The viscosity η and electrical conductivity κ of this system have been measured as function of temperature for nine critical mixtures along the coexistence curve below the temperature of phase transition. The water mole fraction in free basis x′2 in the mixtures extends from (0.550 to 0.880) and the molality m of KCl from (0.47 to 2.039) mol·kg−1. The viscosity was found to decrease with an increase in temperature, water mole fraction, and the molality of KCl, while the electrical conductivity increases with an increase in temperature, with the water mole fraction and molality of salt. The viscosity and electrical conductivity represented anomalies near the critical temperature Tc. The critical electrical conductivity κc varies with water mass fraction w2 as a second degree polynomial and with the molality m of salt as a third degree polynomial. The variation of critical composition in water and in ...

How Solar Activity Influences Earth's Molecular Processes

The paper presents a solution to the two-century old problem of how solar activity influences biological objects on Earth. It gives a description of the modern state of the kT-problem, which for a long time has been the most difficult obstacle in the way of explaining solar activity effects. Based on recent advances in spin chemistry, magnetoplasticity physics, and physics of critical conditions, it is shown that a "molecular target" sensitive to weak electromagnetic fields and corresponding radio emissions of the Sun has spin dynamics in non-equilibrium and is near the lower critical point of dividing into layers. A way is proposed as to how solar activity can have an influence on Earth's molecular, including biological, processes through a "transparency window" of the Earth's atmosphere at the 80Mhz frequency.

The coupled dynamics of two cantilevered flexible plates in axial flow

This paper studies the coupled dynamics of two cantilevered flexible plates aligned parallel to each other in axial flow. The nonlinear governing equation of the two-dimensional plate is developed using the inextensibility condition; and an unsteady lumped vortex model, taking into account the interactions between the two plates, is used to calculate the pressure difference across each plate. The analysis of the system dynamics is carried out in the time-domain; both the instability and the post-critical behaviour are investigated. It is found that the system loses stability through flutter when the flow velocity is sufficiently high, and the flutter threshold is a function of the separation between the two plates. It is also found that the two plates may oscillate both in the out-of-phase and in-phase modes; the former always has a lower critical point than the latter. Moreover, flutter of the two-plate system in the in-phase mode is proved to be associated with an unstable branch of the solution, which can be obtained through numerical simulations with the aid of so-called virtual spring connections.

The heat capacity of the ethylene glycol-tetrahydrofuran system over the range of tetrahydrofuran concentrations 0–20 mol %

The heat capacity of the ethylene glycol (EG)-tetrahydrofuran (THF) system was measured over the range of THF concentrations 0–20 mol % and the temperature range 0–50°C using a DSC204FI differential scanning calorimeter. It was found that the heat capacity passed through a maximum at a THF concentration of 5 mol %; the maximum became more pronounced as the temperature increased. It was suggested that the maximum was caused by microphase separation at THF concentrations of 5–10 mol %. We were unable to observe phase separation with the lower critical point visually over this concentration range up to 95°C.

Thermally Stable Hf-silicate with Modification of Si Doping and Thermal Budget in MIM Capacitors

For the first time, modification of Si doping in Hf-silicates with respect to thermal budget is investigated. Tetragonal phase of HfO2 in Hf-silicate leads to higher dielectric constant after a critical point of thermal budget. Lower critical point (lower thermal budget) is needed for Hf-silicate with a lower Si doping. The tetragonal phase induced higher dielectric constant tends to remain constant even with longer annealing time while the leakage current tends to increase. The optimum condition is a trade-off between the pro of tetragonal phase and the con of the leakage current.

Effect of Solvent on the Phase Diagram of a Simple Anisotropic Model of Globular Proteins

Anisotropic protein interactions play a role in globular protein phase transitions, including the shape of fluid-fluid coexistence curves and the formation of hemoglobin polymer fibers in sickle cell disease. Also, the solvent has been shown to play an important role in the phase behavior of some aqueous protein solutions, through the release or trapping of water molecules upon crystallization. Both anisotropy and solvent effects have been treated separately in earlier theoretical studies. Here we propose and analyze a simple, composite model that treats both anisotropy and solvent effects. We find that this model qualitatively explains some phase behavior that has been observed in protein solutions, including normal and retrograde solubility curves and lower critical points.

Light Scattering and Phase Separation Studies on Cyclohexane Solutions of Six-Arm Star Polystyrene†

Light scattering and phase separation experiments were performed for four six-arm star polystyrene (6SPS) samples with weight-average molecular weights Mw of 9.62×104 to 1.16×106 in cyclohexane below the theta temperature (34.5 °C). From the former experiment, the apparent second virial coefficient J was obtained as functions of the polymer volume fraction φ and temperature T, along with the spinodals. In the latter experiment, the concentrations of coexisting two phases were determined as functions of T. The critical point Tc determined from the coexisting curve was lower than that for four-arm star polystyrene (4SPS) when compared at the same Mw. As was the case for 4SPS and linear polystyrene in cyclohexane, J for 6SPS at each T in a region of large φ was represented by a universal function of φ/P0.1 regardless of P (the volume of the polymer chain relative to that of the solvent molecule), although it differed from the common function previously found for the other two types of polystyrene. It was concluded that the solubility of 6SPS higher than that of 4SPS in cyclohexane as indicated by the lower critical point is attributable to the chain-end effect.

Improving the Efficiency of the Advanced Injection Low Pilot Ignited Natural Gas Engine Using Organic Rankine Cycles

Intense energy security debates amidst the ever increasing demand for energy in the US have provided sufficient impetus to investigate alternative and sustainable energy sources to the current fossil fuel economy. This paper presents the advanced (injection) low pilot ignition natural gas (ALPING) engine as a viable, efficient, and low emission alternative to conventional diesel engines, and discusses further efficiency improvements to the base ALPING engine using organic rankine cycles (ORC) as bottoming cycles. The ALPING engine uses advance injection (50–60deg BTDC) of very small diesel pilots in the compression stroke to compression ignite a premixed natural gas-air mixture. It is believed that the advanced injection of the higher cetane diesel fuel leads to longer in-cylinder residence times for the diesel droplets, thereby resulting in distributed ignition at multiple spatial locations, followed by lean combustion of the higher octane natural gas fuel via localized flame propagation. The multiple ignition centers result in faster combustion rates and higher fuel conversion efficiencies. The lean combustion of natural gas leads to reduction in local temperatures that result in reduced oxides of nitrogen (NOx) emissions, since NOx emissions scale with local temperatures. In addition, the lean premixed combustion of natural gas is expected to produce very little particulate matter emissions (not measured). Representative base line ALPING (60deg BTDC pilot injection timing) (without the ORC) half load (1700rpm, 21kW) operation efficiencies reported in this study are about 35% while the corresponding NOx emission is about 0.02g∕kWh, which is much lower than EPA 2007 Tier 4 Bin 5 heavy-duty diesel engine statutes of 0.2g∕kWh. Furthermore, the possibility of improving fuel conversion efficiency at half load operation with ORCs using “dry fluids” is discussed. Dry organic fluids, due to their lower critical points, make excellent choices for waste heat recovery Rankine cycles. Moreover, previous studies indicate that dry fluids are more preferable compared to wet fluids because the need to superheat the fluid to extract work from the turbine is eliminated. The calculations show that ORC—turbocompounding results in fuel conversion efficiency improvements of the order of 10% while maintaining the essential low NOx characteristics of ALPING combustion.

Detection of various phases in liquids from the hypersound velocity and damping near closed phase-separation regions of solutions

Theoretical analysis revealed that experimental results obtained in our studies on hypersound propagation in a guaiacol-glycerol solution in the vicinity of the closed phase-separation region, double critical point, and special point, as well as the origin of these regions, can be explained by the presence of two different phases (I and II) of the solution with phase-transition temperature T0. Temperature T0 coincides with the temperature at the center of closed phase-separation regions, as well as with the double critical point and with the special point. In (Frenkel) phase I, molecules are in potential wells whose depth exceeds the thermal energy of a molecule, while thermal energy in (gaslike) phase II is higher than the potential well depth. At the lower critical point, the thermodynamic potential of phase I is equal to the thermodynamic potential of the phase-separated solution. At the upper critical point, the thermodynamic potential of phase II is equal to the thermodynamic potential of the phase-separated solution. The observed broad dome of the hypersound absorption coefficient near T0 can be explained by the contribution associated with fluctuations of the order parameter corresponding to the transition from phase I to phase II. The difference in the temperature coefficients of hypersound velocity on different sides of T0 and some other effects are also explained.

VORTEX PHASE DIAGRAM OF UNDERDOPED YBa2Cu3Oy IN PARALLEL MAGNETIC FIELDS

In order to study the Josephson vortex phase diagram in high-Tc superconductors, we have prepared untwinned single crystals of underdoped YBa 2 Cu 3 O y and measured the c-axis resistivity ρc(T) in magnetic fields H parallel to the ab plane. In YBa 2 Cu 3 O y (Tc ~ 60 K ), the vortex liquid phase freezes into the Josephson vortex glass through two-stage processes with decreasing temperature in the high-H region above 5 T. Since the two phase transition lines consist of the first-order transition line T L (H) and the second-order transition line T g (H), the intermediated phase in the region of T g (H) < T < T L (H) is considered to be the vortex slush phase. We find that the oscillatory field dependence of T L (H) corresponds to the commensurability between the vortex spacing and the period of the CuO 2 planes. The lower critical point μ0H lcp ~ 5 T of T L (H) and the vortex slush phase result from the moderate disorder due to the oxygen vacancy in the CuO chain.

Vortex phase diagram in heavy ion irradiated untwinned YBa 2Cu 3O y single crystals

In order to study the effects of columnar disorder on the vortex phase diagram, we have measured the resistivity ρ( H, T) and magnetization M( H) in heavy ion irradiated untwinned YBa 2Cu 3O y single crystals. With increasing irradiation dose, the first-order vortex lattice melting transition H m( T) is suppressed near the upper and lower critical points. The first-order melting transition completely disappears when the irradiation dose has a value of 0.5 T < B Φ < 1.0 T and the transition becomes the second-order Bose glass transition when B Φ ⩾ 1.0 T. For B Φ = 0.5 T, the first-order melting transition exists in the very narrow field region between 4.5 T and 10 T without any characteristic features such as the order–disorder transition H ∗( T) line in the vortex solid phase.

Vortex phase diagram in untwinned YBa2Cu3Oy with columnar disorder

We have measured resistivity ρ(H, T) and magnetization M(H) up to 15T in heavy ion irradiated untwinned YBa2Cu3Oy single crystals in order to study effects of columnar disorder on the vortex phase diagram. With increasing irradiation dose B, the first-order vortex lattice melting transition Tm(H) is suppressed near the upper and lower critical points. For B = 0.5 T, the first-order transition exists in the very narrow field region between 4.5 T and 10 T without any characteristic features such as the field-driven order-disorder transition H*(T) line in the vortex solid phase. The first-order transition completely disappears and the transition becomes the second-order Bose glass transition when Bϕ ⩾ 1.0 T.

Ordering transition and demixing of a binary mixture of thick and thin rodlike molecules in the presence of an external field

The effect of an external field (electric/magnetic) on the phase behavior of the binary mixture of very long thick and thin rodlike particles is studied. Both the thick and thin particles possess positive but different susceptibility anisotropics (Delta alpha). The difference in the extent of interaction between the external field and the two species is varied by means of a coupling parameter (l = Delta alpha(thick)/Delta alpha(thin)). Isotropic-nematic phase transition and demixing phase transitions taking place both in the isotropic and nematic phases are examined as a function of field strength on the level of the second virial theory of Onsager in the range of 0 < l <1. The approximate sixth order Legendre polynomial expansion method is used to represent the excluded volume interaction between the rodlike particles. It is found that the isotropic phase becomes weakly nematic (paranematic) in the presence of external field and the field orients both components in the direction of the field even if the field does not have direct interaction with the thick component (l = 0). Analytical expressions are derived for the external field induced order parameters and birefringence. The increasing field destabilizes both types of demixing transitions (isotropic-isotropic and nematic-nematic) and the paranematic-nematic phase transition. Moreover it induces closed loop immiscibility, and upper and lower critical points terminating the paranematic-nematic phase coexistence may occur for low values of the coupling parameter. It is interesting that while the phase boundaries of the paranematic-paranematic demixing and the paranematic-nematic transitions are very sensitive to the value of the coupling parameter at low pressures, the paranematic-nematic and nematic-nematic phase boundaries are practically independent of the coupling parameter at high pressures.