Lower Critical Point Research Articles

Conditions inducing fertility alteration and ecological adaptation of photoperiod-sensitive genic male-sterile rice

The pollen fertility of photo-sensitive genic male-sterile (PGMS) lines is regulated interactively by photoperiod and temperature. There is a temperature range within which the pollen fertility alteration of PGMS is regulated by photoperiod, being sterile at long days and fertile at short days. The critical values of day length and temperature vary as the PGMS gene(s) is (are) transferred into different genic backgrounds. According to the temperature reactions in response to fertility alterations, the current sterile lines fall into four photothermal types. The climatic adaptation of these is different. Lines of the high-low (a high critical fertile temperature with a low critical sterile temperature point) group have both stable sterile and fertile periods in the low-altitude subtropical rice-growing areas, which are the major rice-production areas of the world. We could exploit them in hybrid rice production there by a two-line method, because there is no need for both male-sterile and maintainer lines. At high altitudes of the subtropical and tropical rice-growing areas, lines of this group are unstable in their sterility. The low-low group is stable in sterility in long-day conditions at all temperatures, and at high temperatures despite day length. They could be used for hybrid seed production from the tropical through to temperate rice-growing conditions. However, their pollen fertility, and hence, seed multiplication, is easily lost in short days if high temperatures occur. The high-high group of sterile lines can be conveniently multiplied in short days, but their sterility is not stable in long days if temperature decreases in the critical fertility alteration period. The low-high group is stable at higher temperature irrespective of photoperiod, and this could be used in the tropics, but their sterilities are not stable in long days if lower temperatures are encountered. Their multiplication in short-day conditions may also be affected by high temperature.

Low energy Skyrmion-Skyrmion scattering

We study the scattering of two Skyrmions at low energy and large separation. We use the method proposed by Manton for truncating the degrees of freedom of the system from infinite to a manageable finite number. This corresponds to identifying the manifold consisting of the union of the low energy critical points of the potential along with the gradient flow curves joining these together and by positing that the dynamics is restricted here. The kinetic energy provides an induced metric on this manifold while restricting the full potential energy to the manifold defines a potential. The low energy dynamics is now constrained to these finite number of degrees of freedom. For a large separation of the two Skyrmions the manifold is parametrized by the variables of the product ansatz. We find the interaction between two Skyrmions coming from the induced metric, which was independently found by Schroers. We find that the static potential is actually negligible in comparison to this interaction. Thus to lowest order, at large separation, the dynamics reduces to geodesic motion on the manifold. We consider the scattering to first order in the interaction using the perturbative method of Lagrange and find that the dynamics in the no spin or charge exchange sector reduces to the Kepler problem.

Changes of the oscillation frequency of a quartz resonator in contact with a binary liquid mixture of critical composition as function of temperature, revisited

AbstractNew results of measurements of the temperature dependence of changes of the oscillatory frequency Δf(T) of a quartz oscillator in contact with two binary liquid mixtures of critical composition are reported (systems: 2‐butoxyethanol/water; 2,6‐dimethyl pyridine/water, lower critical point). Both systems exhibit an unexpected Δf(T) behaviour approaching the critical temperature. The results lead to the conclusion that even near the critical temperature Δf(T) is determined only by the background viscosity of the systems. The influence of critical contributions to the viscosity can be neglected. It is assumed that this effect is caused by the large shear gradient produced by the quartz oscillator.

Viscosity of two non‐ionic amphiphile/water mixtures of critical composition: Study of the systems triethyleneglycolmonohexylether (C6E3)/water and tetraethyleneglycolmonooctylether (C8E4)/water

AbstractThe shear viscosity of a C6E3/water and a C8E4/water mixture of critical composition (lower critical point) is measured in a wide temperature range (C6E3/water: 2 mK≤(Tc‐T)≤43.913 K; C8E4/water: 5 mK≤(Tc‐T)≤ 39.517 K) using capillary viscometry. The viscosity η is dominated by singular contributions in a narrow temperature range only (C6E3/water: (Tc‐T)≤0.8K; C8E4/water: (Tc‐T)≤0.2K). This temperature range is much smaller than that found in “simple” binary mixtures of low molar mass components. The temperature dependence of η of the system C6E3/water at temperatures away from Tc, in the crossover regime and in the critical regime close to Tc is analyzed successfully by the same methods developed for the analysis of viscosity data of binary mixtures of low molar mass components. The method fails in the analysis of the viscosity data of the system C8E4/water. This is probably caused by the temperature‐dependent influence of micelles on the viscosity.

Ellipsometric measurement of a surface amplitude ratio near a critical end point

We present the experimental determination of a universal surface amplitude ratio near a critical end point. From ellipsometric measurements on five critical binary liquid mixtures, three with an upper critical point and two with a lower critical point, we obtain a value for the modified critical adsorption amplitude ratio of Rma=1.18±0.13, where the error represents three standard deviations. Reasonable agreement is obtained with the theoretical results of H. W. Diehl and M. Smock [Phys. Rev. B 47, 5841 (1993)], from which we obtain Rma=1.33.

Food and Energy Consumption in Rodents from Different Environments: The Role of Photoperiod in Seasonal Acclimatization

In several rodent species, changes in photoperiod are important signals for seasonal acclimatization of thermoregulatory mechanisms. Nocturnal rodents inhabiting extremely hot and arid areas like the Arava (Israeli Rift Valley), may be exposed to very low ambient temperatures, which may be far below their lower critical point. In contrast, nocturnal species from the mesic Mediterranean habitats are not exposed to such dramatic seasonal changes. In the present study, food consumption was measured as apparent digestible dry matter intake (DDMI), while energy was measured as digestible gross energy intake (DGEI), in four rodent species from different habitats. The studied mice were kept under two different photoperiod regimes 16L:8D long photophase, 8L:16D long scotophase at a constant ambient temperature (T =28°C). In Meriones crassus, which inhabits extremely arid habitats, apparent DDMI and DGEI were significantly higher in long scotophase acclimated individuals when compared with long photophase acclimated. However, in the mesic species Apodemus flavicollis these parameters were similar under acclimation to the two different photoperiod regimes. These results suggest that, in seasonal acclimatization, species from different habitats may have a different response to photoperiodic cues.

A search for the wetting transition in 2,6-dimethyl pyridine/water mixtures in contact with glass near the lower critical point

The pendant drop method and the capillary rise method are used to measure the interfacial tension σ of 2,6-dimethyl pyridine(2,6-lutidine)/water mixtures near the lower critical point. It is found that at temperatures 0.2 K≤(T−Tc)≤1.5 K the temperature dependence of σ is represented by a power law of the form σ=σ0 tμ (t=(T−Tc)/Tc) with μ=(1.25±0.01) and σ0=(32.4±0.6) mN m−1. The value of μ is consistent with the theoretically expected universal value of μ=1.26. At large temperature differences σ increases slower than expected by the power law. The values of the amplitude ratios Rσ,ξ+[=σ0(ξ0+)2/(kBTc)] and Rσ,A+[=(Av,0/kB)2/3(kBTc/σ0)] calculated from the experimental data [correlation length of local concentration fluctuations, ξ0+=(0.230±0.009) nm] and Av,0 (heat capacity per unit volume at constant pressure; Av,0=1.81 J cm−3 K−1) are consistent with accepted values. This indicates that the interfacial tension measurements are free from large systematic errors. The value of a2 (a, capillary constant) determined with the pendant drop method as well as with the capillary rise method agree with each other within the uncertainty of the measurements in a temperature range (T−Tc)≤7 K. The capillary rise data is analyzed by assuming that the contact angle θ of the lower water rich phase at the capillary wall is zero (θ=0). The data follows the same curve as that obtained with the pendant drop method in a temperature range (T−Tc)≤25 K. From these findings it is concluded that the water rich (lower) phase wets the wall of the glass capillary completely at least up to temperature differences (T−Tc)≤7 K. A wetting transition cannot be detected in that temperature range.

Temperature dependence of interfacial tension of 2‐butoxyethanol/water mixtures near the lower critical point

AbstractThe pendant drop method and the capillary rise method are used to measure the interfacial tension σ of 2‐butoxyethanol (2‐C4E1)/water mixtures near the lower critical point (critical composition, mass fraction of 2‐C4E1, yc = 0.2945; critical temperature Tc(visual) = 49.41°C) as function of temperature (0.6 K ≤ (T  Tc) ≤ 18.0 K). It is found that at temperatures 0.6 K ≤ (T  Tc) ≤ 7.0 K the temperature dependence of σ is represented by a power law of the form σ = σ0ϵμ (≤ = (T  Tc(visual))/Tc) with μ = (1.26 ± 0.02) and σ0 = (8.8 ± 0.2) mN m−1. The value of μ is consistent with the theoretically expected universal value of μ = 1.26. The amplitude ratio Rσ,ζ+ = σ0(ξ0ζ+)2/kBTc calculated from the system specific values of the critical amplitude σ0 and the critical amplitude ξ0 of the correlation length of local concentration fluctuations (ξ0ζ+ = (0.44 ± 0.04) nm) leads to a value of Rσ,ξ+ = (0.383 ± 0.070). It is close to the median value of Rσ,ξ+ calculated for several one‐ and two‐component fluids from experimental data taken from the literature (Moldover, Phys. Rev. A 31, 1022 (1985); median value Rσ,ξ+ = 0.386). – The ratio of [νT/R̄(∂T/∂z)] (νT, thermophoretic velocity (Marangoni convection); (∂T/∂z, temperature gradient) for droplets of radius R̄ of a 2‐C4E1) rich phase suspended in its coexisting H2O rich phase is calculated from the data.Values of [νT/R̄(∂T/∂z)] refering conditions along the liquid/liquid coexistence curve are given.

Static light scattering experiments with aqueous solutions of the nonionic tenside C12E5 with critical and non‐critical composition

AbstractConcentration fluctuations with long range correlations as well as non‐critical background contributions determine the light scattering properties of C12E5/H2O mixtures of critical composition near the lower critical point (critical mass fraction yc = 0.0123; critical temperature Tc = 31.8°C). If the influence of the non‐critical contributions is neglected, an evaluation of the light scattering data in terms of the power laws ξ = ξo · ϵ‐ν and χT = χT,o · ϵ−γ (ξ being the correlation length of local concentration fluctuations and χT the generalized susceptibility; ϵ = (Tc−T)/Tc is the reduced temperature) leads to values of the critical exponents ν and γ which are closer to the mean field values (ν = 0.5; γ = 1) than to the values theoretically expected for binary liquid mixtures from the Landau‐Ginzburg‐Wilson model (ν = 0.63, γ = 1.24). If the background contributions are taken into account empirically by adding temperature independent background terms ξb and χT,b respectively to the simple power laws, the analysis of the light scattering data leads to values of ν ≈︁ 0.65 and γ ≈︁ 1.2, which are close to the values given by the Landau‐Ginzburg‐Wilson model. The background term ξb has a value of about ξb ≈︁ 6 nm and the critical amplitude ξo a value of about ξo ≈︁ 1.2 nm. This value for ξo is one order of magnitude larger than that found for simple binary liquid mixtures (O(ξo) ≈︁ 0.1 nm). — In mixtures of non‐critical composition (−0.79 < (y−yc)/yc < 0.63) the scattered intensity shows an angular dependence which is also a function of temperature corresponding to correlation lengths 20 nm < ξ < 206 nm for 0.5 K < (TP−T) < 7.0 K. They are assumed to reflect contributions of micelles which also contribute to the scattering of the mixture of critical composition away from the critical temperature.

Percolation thresholds near lower critical points.

A lattice model of a two-component fluid that displays a closed-loop phase diagram is studied to determine the correlated site percolation threshold of one of the components. Both the phase diagram and the threshold of the three-dimensional system are determined within the Bethe approximation. A rapid variation of the threshold with temperature below the lower critical point is found, similar to that observed in a recent experiment. This variation is attributed to the tendency of the interactions to structure the fluid.

Determination of the Critical Points of Antiferromagnetic Ising Model with Next Nearest Neighbour Interactions on the Triangular Lattice

Positions of critical temperatures of antiferromagnetic Ising model with ferromagnetic next nearest neighbour interactions on the triangular lattice are investigated by making use of their properties of the Kosterlitz-Thouless type of phase transition. In particular, finite-size scaling method and Monte Carlo Renormalization Group methods (MCRG) with flow diagrams of the anomalous dimension η show the fixed line structure where the correlation length diverges. Another MCRG with flow diagram of the stiffness constant also shows a critical property clearly. The temperature dependence of the long range order is also discussed in order to locate the lower critical point.

Study of Non‐Equilibrium States of a Homogeneous 2‐Butoxyethanol/Water Mixture of Critical Composition in the Vicinity of Its Lower Critical Point Using Fast Pressure Jumps

AbstractThe pressure dependence of the critical temperature is used to bring a homogeneous 2‐butoxyethanol/ water mixture of critical composition (xc = 0.0598; mole fraction of 2‐butoxyethanol; critical temperature Tc (P = 1 bar) = 49.39°C) from a state away from its critical temperature to a state close to the critical temperature. This is accomplished by fast pressure jumps (expansions) with an amplitude in the range of −50 bar < ΔP < −5 bar (ΔP = (Pf‐Pi); Pf, hydrostatic pressure in the final state (Pf = 1 bar); Pi, hydrostatic pressure in the initial state) and a characteristic time constant of τp ≃ 0.3 ms. The coefficient characterizing the pressure dependence of the critical temperature has a value of (dTc/dP)c.l. = 43 mK bar−1. The delayed increase of the intensity of scattered light (“critical opalescence”) is measured as function of time at different scattering angles (10° ≤ θ ≤ 60°) and different temperature differences (Tc ‐ Tf) (Tc. critical temperature; Tf, final temperature after the pressure jump). The fast pressure jump leads to a small decrease of the temperature of the sample ((∂T/∂P)s = 6 mK bar−1). The measured relaxation curves are found to be single exponentials for times short compared with the relaxation time τT of the heat conduction process bringing the system back to its initial temperature Tf (τT is in the order of seconds). – For small values of the scaling variable (qζf) < 0.7 (q, absolute value of scattering wave vector; q = (4μñ/λ0) sin (0/2); 0, scattering angle; ñ, index of refraction; λ0, wavelength of incident light in vacuum; ζ, correlation length of local concentration fluctuations) the structure factor relaxes as expected on the basis of linear response (τhyd/τexp = 1; τhyd, hydrodynamic relaxation time calculated from independent dynamic and static light scattering experiments; τexp, experimental relaxation time). At larger values of (qζf) ((qζf) > 0.7) the structure factor relaxes more slowly than theoretically expected (i.e. τhyd/τexp < 1). This behaviour is similar to that of the systems 3‐methyl‐pentane/nitroethane and 2, 6‐dimethylpyridine/water.

Seasonal acclimatization and thermoregulation in the pouched mouse Saccostomus campestris

The pouched mouse Saccostomus compestris, a nocturnal, fossorial rodent, is widely distributed in the Southern-African subregion. Seasonal acclimatization of mechanisms of thermoregulation and body mass were studied in this species under the natural photoperiod conditions prevailing in Pretoria during January–February and July–August at room temperatures of 23.2–28.1 and 9.8–18.2°C, respectively. The following parameters were measured or calculated: body mass, oxygen consumption and body temperature at various ambient temperatures, minimal overall thermal conductance and capacity for non-shivering thermogenesis. In winter-acclimatized pouched mice, body mass, resting metabolic rates and non-shivering thermogenesis capacity are higher than in summer-acclimatized mice, while lower critical point and minimal thermal conductance are higher in summer-acclimatized mice than in winter-acclimatized. The seasonal changes of the studied parameters, may help explain the ability of this species to cope with its habitat in the two different seasons.

Symmetry Breaking and Nonlinear Susceptibility in a Complex Physical System, CoCl2-GIC

Nonlinear susceptibility X 2 is investigated in a quasi-two-dimensional complex magnet, CoCl 2 -GIC (graphite intercalation compound). A negative divergence and another different singularity that X 2 changes its sign from negative to positive, are concluded to occur at the upper and the lower critical points in the compound by observing nonlinear magnetic response to an AC excitation field. From the facts, it is shown that the symmetry of X 2 at the critical point reveals a breaking of spatial magnetic symmetry in the examined systems. On this basis, the dynamical structure of hierarchical spin ordering is discussed.

Kinetics of liquid–liquid phase separation in a binary mixture with miscibility gap: Study of noncritical mixtures of 2,6-dimethyl pyridine/water near the lower critical point

Temperature jump experiments with a characteristic heating time of 0.5 ms are used to study the kinetics of liquid/liquid phase separation in noncritical mixtures of 2,6-dimethyl pyridine and water (‖x-xc‖>0.02; x, mole fraction of 2,6-dimethyl pyridine; xc, critical composition) as functions of composition and supersaturation. The response of the system to a temperature jump is monitored by measuring the intensity of light scattered by the sample at different scattering angles Θ (30°<Θ<90°) as a function of time (up to several seconds). Starting from a level of constant intensity reached with a time constant in the range of milliseconds after a temperature jump the scattered intensity increases with time. For small supersaturations consecutive maxima and minima of scattered intensity develop. They reflect diffusion limited growth of droplets of the emerging second liquid phase (linear relationship between the square of the radius of growing droplets and time). The growth rate increases with increasing supersaturation. Practically no nucleation barrier is found for the onset of growth of droplets for small supersaturations and compositions (‖x−xc‖>0.03). The number density N of growing droplets is obtained from simultaneous measurements of scattered intensity and turbidity. For small supersaturations N is independent of time but changes with supersaturation in a characteristic way (classical nucleation model). There exists an upper limit of overheating δT* above which the number density N increases drastically. The ratio (δT*/ΔTc,p) is independent of the reduced temperature ε̃ of phase separation (ε̃=ΔTc,p/Tc; ΔTc,p=Tc−Tp; Tc, critical temperature, Tp, temperature of phase separation). This is expected for mixtures of noncritical composition. The theory proposed by Langer and Schwartz to treat nucleation and growth of droplets in metastable near critical fluids does not describe the phenomena observed in this study. The composition of the samples used (‖x−xc‖>0.02) appears to be too far away from the critical.

Microscopic model for microemulsions. II. Behavior at low temperatures and critical point

Low temperature properties and critical behavior for the more simple versions of the microemulsion model introduced in Ref. 1 are investigated. For the lattice case with nearest-neighbor interactions an analytic asymptotic expression for the surface tension at the oil–microemulsions–water coexistence is found for low T. For both lattice and continuum cases the critical point is determined, and we show how an oscillating phase (microemulsion) may be formed below the critical temperature.

Negative entropy, energy, and heat capacity in connection with surface tension: Artifact of a model or real?

It is only byneglecting self-adsorption (a treatment referred to as “pure-energy,” PE) that one gets textbook thermodynamics of a surface, based upon the tensionL as a function of temperatureT, and one finds negative specific heat for hot water. Any lower critical point and PE provides the other exciting negatives: nicotine-and-water is an example. In order toinclude adsorption,L must be known in terms ofT and chemical potentials asindependent variables; this forces measurement of the tension of curved menisci. Will the minus signs remain?

Study of a Binary Critical Mixture of 2,6‐Dimethyl Pyridine/Water: Measurements of Static and Dynamic Light Scattering and Specific Heat Near the Lower Critical Point

AbstractStatic and dynamic light scattering experiments are reported for the system 2,6‐dimethyl pyridine/water to determine the critical amplitude ζo of local concentration fluctuations and the critical amplitude Ωo of the characteristic frequency ΩD to scale ultrasound absorption data. It is found: ζo = (2.7 ± 0.2) · 10−8 cm and Ωo/π = 2.9 GHz. Measurements of the temperature dependence of specific heat capacity at constant pressure lead to a critical amplitude A = (0.183 ± 0.002) J g−1 K−1. The two scale factor universality is tested by combining the values of ζ0 and A as well as the values of ζ0 and τ*0 and B* (B*: critical amplitude of the coexistence curve, τ*0 critical amplitude of turbidity). The two ratios of the critical amplitudes calculated from the experimental data are higher by about 15% than the highest theoretical predicted value.

Reentrant phase transition of N-isopropylacrylamide gels in mixed solvents

Reentrant volume–phase transitions are observed in N-isopropyoacrylamide gels in the methanol–water mixtures. When the solvent composition is varied systematically, the gel undergoes two transitions: a discontinuous collapsing followed by a discontinuous swelling. The reentrant transition defines a closed-loop instability phase boundary having both upper and lower critical points. The closed-loop phase boundary depends on temperature and diminishes to a point at approximately 0 °C. A simple mean field theory is presented to describe the phenomenon, which reveals an alteration of free energy of alcohol–water interaction by presence of polymer network. In the case of ethanol–water mixtures, there appear two closed-loop phase boundaries, whose physico-chemical basis are not yet clear.

ポリスチレン‐シクロペンタン溶液の上限及び下限臨界共溶点近傍における光散乱

ポリスチレン‐シクロペンタン溶液の上限及び下限臨界共溶点近傍における光散乱