Jump-like Transition Research Articles

Glass Polymorphism in Hyperquenched Aqueous LiCl Solutions

We investigate the glass polymorphism of dilute LiCl-H2O in the composition range of 0-5.8 mol % LiCl. The solutions are vitrified at ambient pressure (requires hyperquenching with ∼106 K s-1) and transformed to their high-density state using a special high-pressure annealing protocol. Ex situ characterization was performed via isobaric heating experiments using X-ray diffraction and differential scanning calorimetry. We observe signatures from a distinct high-density and a distinct low-density glass for all solutions with a mole fraction xLiCl of ≤ 4.3 mol %, where the most notable are (i) the jumplike polyamorphic transition from high-density to low-density glass and (ii) two well-separated glass-to-liquid transitions Tg,1 and Tg,2, each pertaining to one glass polymorph. These features are absent for solutions with xLiCl ≥ 5.8 mol %, which show only continuous densification and relaxation behavior. That is, a switch from water-dominated to solute-dominated region occurs between 4.3 mol % LiCl and 5.8 mol % LiCl. For the water-dominated region, we find that LiCl has a huge impact only on the low-density form. This is manifested as a shift in halo peak position to denser local structures, a lowering of Tg,1, and a significant change in relaxation dynamics. These effects of LiCl are observed both for hyperquenched samples and low-density samples obtained via heating of the high-density glasses, suggesting path independence. Such behavior further necessitates that LiCl is distributed homogeneously in the low-density glass. This contrasts earlier studies in which structural heterogeneity is claimed: ions were believed to be surrounded by only high-density states, thereby enforcing a phase separation into ion-rich high-density and ion-poor low-density glasses. We speculate the difference arises from the difference in cooling rates, which are higher by at least 1 order of magnitude in our case.

Observation of a Jump-Like Transition from Fast to Normal Kinetics of Facets for Free-Growing Helium Crystals

The growth kinetics is studied of free-growing helium crystals within the temperature range 0.5-0.83 K and supersaturations to 10 mbar. For the pressure supersaturations above 0.5 mbar, numerous drastic changes are observed in the growth kinetics for all crystalline facets from the normal and slow kinetics to the anomalously high or burst-like one. It is found for the first time that the anomalous to normal transition in the facet growth kinetics occurs in a jump like manner within a time 80 {\mu}s interval of the measurement record.

Features of the thermal stabilization theory of composite superconductors: The nonlinear description of the dissipative states

The features of the Joule's energy dissipation in a composite high-temperature superconductor with a power equation of the voltage-current characteristic cooled by liquid helium or hydrogen are discussed. It is shown that the non-standard thermal stabilization conditions of composite superconductors can exist if the nonlinear temperature dependences of the electrical resistivity of the stabilizing matrix and heat flux to liquid refrigerant are considered. First, there may be no minimum currents of the existence and propagation of a normal zone. Second, the intensive cooling of a composite superconductor by liquid refrigerant significantly increases the range of the stable currents, which leads to the existence of the supercritical applied currents. Third, an increase in the temperature of a composite superconductor may occur under the conditions close to adiabatic during irreversible propagation of the thermal instability despite its intensive cooling by liquid refrigerant. This effect must be considered when determining the burnout conditions of a composite superconductor. The performed numerical experiments are compared with the results obtained from the existing thermal stabilization theory of the composite superconductors, which is based on the linear temperature dependence of the critical current density of superconductor and jump-like transition from the superconducting state to the normal.

Nonlinear mechanisms of the thermal instability propagation in composite superconductors during magnetic flux creep

The features of the irreversible propagation of thermal instabilities in composite superconductors are investigated under different cooling conditions (intensive and non-intensive) during magnetic flux creep. The analysis was performed with two models of the voltage-current characteristic of a superconductor: an ideal model having a jump-like transition from a superconducting state to a normal, and an actual model described by a power equation. The non-stationary and quasi-stationary (autowave) propagation velocities of the thermal instabilities along the composite are calculated taking into account the nonlinear properties of the composite and the refrigerant. The calculations of the propagation velocities of thermal instability are performed for both subcritical and supercritical currents. It is shown that the autowave velocities of the irreversible propagation of the thermal instability in the intensively cooled composite may only be positive since the conditions of the equal-area theorem may not be fulfilled. It is proved that the propagation of thermal instabilities in the composite superconductors is similar to the diffusion phenomena occurring in chain reactions of the exploding type.

Long-Range Order in the Dislocation Structure of Martensite Crystals

Optimal estimation of the diffraction observations over the object reliably detects periodicity in the dislocation structure of martensitic transformation as an exhibition of its wave nature. The period along normal to the slip planes is comparable with the radius of dislocation loops in crystals. The measured degree of one-dimensional long-range order in the arrangement of the loops is close to the upper limit equal to unity. Subject to the theory of metals, the observed structure could be generated by quantum lattice vibrations, which actuate a jump-like phase transition. A simple explanation exists: after a sharp fall in temperature, the excess energy of conduction electrons causes the crystal to expand instantly with the transformation of translational symmetry. Internal shifts of the crystal lattice caused by electron-phonon interactions concurrently trigger the wave process of formation of thin martensitic plates in the surrounding matrix, which are observed in metallography. Based on an in-depth analysis of the dislocation structure of martensite crystals, a physically founded concept is advanced in which the martensitic transformation is a macroscopic quantum phenomenon connected with the symmetry properties of a crystal system in metals.

Design of the conceptual implementation of an apparatus with the induced heat and mass transfer for vaporization and rectification

The need to find solutions to problems on the efficient use of energy resources has been substantiated, under conditions for meeting the requirements to the environmental sustainability of production in the process of executing such technological operations as vaporization and rectification. We have identified the prospects of searching for and applying the induced processes, which are characterized by high energy efficiency and are environmentally friendly. The kinetics of temperature have been investigated under the effect from the induced heat transfer of the components of the internal thermostat volume, under condition of using different liquids in its internal environment. Our study has established the impossibility for the liquid in the inner volume thermostat to achieve the boiling temperature under condition of the effect of the induced heat and mass transfer, proven by the visual observations and by the value of its temperature. In the experiment under atmospheric pressure, the thermostat temperature was equal to 115...116 °C, while the temperature of the volumetric water did not exceed 97 °C. It was established that at the thermostat temperature of 105...106 °C and under atmospheric pressure, the ethyl alcohol temperature did not exceed 72...73 °C, and for water ‒ 83...85 °C, under the condition of the effect of the induced heat-and-mass transfer. It was found that ethyl alcohol and water are transferred to the gas state under the effect of the induced heat-and-mass transfer separately. It is possible to register the removal of the liquid phase of the mixture components based on the jump-like transition in the kinetics of the fluid temperature. It was established that the liquid phase did not boil for a mixture of ethyl alcohol with water under the effect of the induced heat-and-mass transfer at the thermostat temperature of 105 °C and under atmospheric pressure. We have proposed a conceptual solution to the technical implementation of the universal device that employs the effect of the induced heat-and-mass transfer in order to execute technological operations of vaporization and rectification excluding the boiling phase. Based on a given conceptual solution, we have built a laboratory prototype of the installation, in which vaporization is carried out under atmospheric pressure at the liquid phase temperature of 83...85 °C. The economic effect from the installation is achieved through the simplified equipment and reduction in energy consumption per product unit by larger than 1.3 times compared to the vacuum-evaporator apparatus

Metamagnetic texture in a polar antiferromagnet

The notion of a simple ordered state implies homogeneity. If the order is established by a broken symmetry, elementary Landau theory of phase transitions shows that only one symmetry mode describes this state. Precisely at points of phase coexistence domain states formed of large regions of different phases can be stabilized by long range interactions. In uniaxial antiferromagnets the so-called metamagnetism is an example of such a behavior, when an antiferromagnetic and field-induced spin-polarized paramagnetic/ferromagnetic state co-exist at a jump-like transition in the magnetic phase diagram. Here, combining experiment with theoretical analysis, we show that a different type of mixed state between antiferromagnetism and ferromagnetism can be created in certain acentric materials. In the small-angle neutron scattering experiments we observe a field-driven spin-state in the layered antiferromagnet Ca3Ru2O7, which is modulated on a scale between 8 and 20 nm and has both antiferromagnetic and ferromagnetic parts. We call this state a metamagnetic texture and explain its appearance by the chiral twisting effects of the asymmetric Dzyaloshinskii-Moriya (DM) exchange. The observation can be understood as an extraordinary coexistence, in one thermodynamic state, of spin orders belonging to different symmetries. Experimentally, the complex nature of this metamagnetic state is demonstrated by measurements of anomalies in electronic transport which reflect the spin-polarization in the metamagnetic texture, determination of the magnetic orbital moments, which supports the existence of strong spin-orbit effects, a pre-requisite for the mechanism of twisted magnetic states in this material.

Vibration effect on double-diffusive instability in an inhomogeneous porous layer underlying a binary fluid layer

A linear stability problem for mechanical equilibrium in an inhomogeneous fluid-saturated porous layer underlying a horizontal binary fluid layer is numerically simulated. The layers are subjected to high-frequency vertical vibration in a gravity field. Different values of temperature and concentration are fixed at the outer impermeable boundaries of the two-layer system. Porosity of a porous layer linearly depends on a transverse z-coordinate. Permeability is given by the Carman-Kozeny formula. To describe a fluid flow in layers, we use the vibrational convection equations written in the Boussinesq approximation and obtained by the averaging method. It is shown that when the fluid is heated from below, vibration effectively increases the equilibrium stability threshold and wavelength of its most dangerous perturbations. If a temperature gradient coincides with the direction of a concentration gradient for the heavier component of binary fluid, average convection is excited in an oscillatory manner. In the opposite case, there is a monotonic instability of equilibrium. Effects of the dimensionless porosity gradient mz and vibrational parameter pv on the instability threshold are studied. For pv<0.0134 and a fixed solutal Rayleigh number (-5⩽Rmc⩽15) an abrupt jump-like transition from the long-wave to short-wave most dangerous perturbations occurs as mz grows in the range of 0.030–0.162. Long-wave perturbations penetrate both layers. Short-wave perturbations mainly locate in the fluid layer. The transition is smoothed for pv>0.0134. When the fluid is heated from above, wavelength of critical perturbations smoothly varies with a change in pv and mz. A convective fluid flow arises monotonously and mostly in the form of long wavelength rolls (a wave number is of k<3.3). Vibration weakly lowers the equilibrium stability threshold in layers. The effect is most pronounced at high enough Rayleigh numbers (Rm=-40) for a porous medium with the porosity increasing with depth at mz=-0.2.

Experimental and theoretical study of the radial density distribution of metastable atoms in a dc glow discharge in neon

Radial distributions of the number density of metastable atoms in the positive column of a dc glow discharge in neon were studied both experimentally and theoretically in a wide range of gas pressures (0.1–50 Torr) and discharge currents (10–40 mA, for gas pressures of 0.1–10 Torr, and 20–100 mA, for the gas pressure of 50 Torr). Measurements were performed in a glass discharge tube 4 cm in diameter using the optical absorption technique. It was found that, at pressures of 0.1–1 Torr, the radial profiles of the number density of metastable atoms are almost independent of a discharge current value. At higher pressures, noticeable narrowing of the profiles with discharge current was observed; at a pressure of 50 Torr, measurements were performed up to the jump-like transition of the positive column from the diffuse form to the constricted one. Theoretical studies of the discharge plasma parameters under experimental conditions were carried out in the framework of a one-dimensional (along the tube radius) discharge model. For the case of the diffuse form of the discharge, the results of simulations appeared to be in a reasonable agreement with the experimental data.

Nonlinear acoustic spectroscopy of carbonate rocks

The paper presents the results of experimental research into the nonlinear acoustic properties of carbonate rocks depending on saturation. The linear acoustic properties of the same sample depending on saturation were presented earlier in Physical Acoustics. The previously obtained data point to the isotropy of the material, which makes it possible to restrict analysis to only two vibration modes. Responses for finite deformations were measured for the longitudinal and shear modes of an isotropic sample, which made it possible to analyze the nonlinear properties of macroscopic deformations with a change in volume and pure displacement. A heretofore unknown feature of the response was revealed for finite deformation values; it is related to the occurrence of a jumplike transition from classical nonlinearity to a hysteresis type of nonlinearity. As well, the deformation amplitude corresponding to the transition depends on fluid saturation. We studied the slow relaxation that occurs after long-term excitation of a sample with a deformation amplitude on the order of 10−6. Data are presented on relaxation for deformation from pure displacement and deformation with a change in volume, which made it possible to isolate features related to the type of deformation and to compare the obtained data with the earlier published theoretical model. These data are compared with the results of other research groups.

Complex coacervates formed across liquid interfaces: A self-consistent field analysis

The Scheutjens–Fleer self-consistent field (SF-SCF) theory is used to study complexation between two oppositely charged polyelectrolytes across an interface formed by two solvents, here called oil and water. The focus is on the composition and the lateral stability of such interfacial coacervate. One polyelectrolyte is chosen to be oil soluble and the other one prefers water, whereas the counter and salt ions are taken to distribute ideally over all phases. There exists an electrostatic associative driving force for the formation of the coacervate phase which increases with decreasing ionic strength and may be assisted by some specific affinity between the associating units and an effective poor solvency for the coacervate. As with respect to the lateral stability an unusual wetting scenario, called pseudo-partial wetting, presents itself, which results from interactions on two different length scales. On the segmental length the screening of oil–water contacts promotes the wetting by the coacervate: a pre-wetting jump-like transition takes place off-coexistence from a microscopically thin to a mesoscopically thin film. Usually this implies complete wetting. However, the mesoscopically thin film is exposed to long-ranged attractive electrostatic interactions and therefore cannot grow to macroscopic dimensions upon approach towards coexistence. Hence the system remains partial wet. The bulk correlation length controls the thickness of the mesoscopically thin film and as a result the wetting transition occurs extremely close to the bulk critical point. We therefore expect that a thick coacervate film typically is laterally inhomogeneous: there are drops on top of a mesoscopically thin coacervate film. This conclusion qualitatively explains the experimental observation that such a coacervate film scatters visible light.

Canted spin structure and the first order magnetic transition in CoFe2O4 nanoparticles coated by amorphous silica

The functional polymer (PMA-co-MAA) latex microspheres were used as a core template to prepare magnetic hollow spheres consisting of CoFe2O4/SiO2 composites. The spinel type crystal structure of CoFe2O4 ferrite is formed under annealing, whereas the polymer cores are completely removed after annealing at 450°C. Magnetic and Mössbauer spectroscopy measurements reveal very interesting magnetic properties of the CoFe2O4/SiO2 hollow spheres strongly dependent on the particle size which can be tuned by the annealing temperature. In the ground state of low temperatures, the CoFe2O4 nanoparticles are in antiferromagnetic state due to the canted magnetic structure. Under heating in the applied field, the magnetic structure gradually transforms from canted to collinear, which increases the magnetization. The Mössbauer data revealed that the small size CoFe2O4/SiO2 particles (2.2–4.3nm) do not show superparamagnetic behavior but transit from the magnetic to the paramagnetic state by a jump-like magnetic transition of the first order This effect is a specific property of the magnetic nanoparticles isolated by inert material, and can be initiated by internal pressure creating at the particle surface. The suggested method of synthesis can be modified with various bio-ligands on the silane surface, and such materials can find many applications in diagnostics and bio-separation.

Three-dimensional divergent waves on a model viscoelastic coating in a potential incompressible fluid flow

Generation of three-dimensional nonlinear waves on a model viscoelastic coating in a potential flow of an incompressible fluid is studied. Periodic nonlinear waves enhanced by the development of quasi-static instability (wave divergence) are considered. The coating is modeled by a flexible flat plate supported by a distributed nonlinearly-elastic spring foundation. Plate flexure is described on the basis of the Karman equations of the theory of thin plates. Perturbations of surface pressure in the potential flow are found in the small slope approximation to an accuracy to terms of the second order of smallness. Numerical simulation reveals a jump-like transition from two-dimensional nonlinear waves to three-dimensional wave structures, which are also observed in experiments.

Diblock copolymer–selective nanoparticle mixtures in the lamellar phase confined between two parallel walls: a mean field model

We present a mean field model for a mixture of AB diblock-copolymers and A-block selective nanoparticles confined between two identical non-selective walls. A horizontally symmetric lamellar structure of the nanocomposite is considered where nanoparticles are allowed to segregate between the polymer–wall interfaces. For a fixed value of wall separation, we study changes in the free energy as a function of the number of lamellar layers and the amount of nanoparticle uptake in the A-phase denoted by y = ϕx with 0 ≤ x ≤ 1 for a given value of ϕ, where ϕ is the overall nanoparticle volume fraction. The absorption isotherm for nanoparticle uptake in the A-phase as a function of ϕ shows saturation beyond a threshold value ϕs, and the optimal value of uptake y increases with increasing strength of monomer–nanoparticle attractive interaction. Increasing ϕ above ϕs produces a decrease in the optimal number of lamellar layers which is related to a jump-like transition of the chain extension. The effect of varying film thickness is also studied. By considering A-block selective walls we also investigated a wetting transition of the copolymer film and found the transition to be discontinuous. A corresponding phase diagram is constructed.

Effect of electron–lattice interaction on the phase separation in strongly correlated electronsystems with two types of charge carriers

The effect of electron–lattice interaction is studied for a strongly correlated electron systemdescribed by the two-band Hubbard model. A two-fold effect of electron–lattice interactionis taken into account: in non-diagonal terms, it changes the effective bandwidth, whereas indiagonal terms, it shifts the positions of the bands and the chemical potential. It is shownthat this interaction significantly affects the doping range corresponding to the electronicphase separation and can even lead to a jump-like transition between states with differentvalues of strains.

Metamagnetism, giant negative magnetoresistance and spin glass state in the Sm1−xSrxMnO3 (x=0.33, 0.45) and RE0.55Sr0.45MnO3 (RE0.55=Eu0.397Nd0.153, Tb0.25Nd0.30) manganites as well as in the CuCr2X4 (X=S, Se) spinels doped with Sb

Abstract The experimental evidence of metamagnetism, giant negative magnetoresistance and spin glass state is presented for the compounds under study. An attempt is made to explain the jump-like phase transition of the colossal negative magnetoresistance of −4433% at 153.2 K into the colossal positive magnetoresistance of +980% at 154.2 K for the spinel sample with selenium. It was emphasized that in all the phenomena described in this paper the double exchange magnetic interaction plays the main role.

Spin glass state and its correlations with the magnetic and electrical properties as well as with the defectiveness in the spinels CuCr 2X 4 (X = S, Se) doped with Sb

High degree of defectiveness both in the stoichiometric CuCr 2− x Sb x S 4 ( x = 0.3, 0.4, 0.5) and nonstoichiometric Cu 1 + x Cr 1.5 + y Sb 0.5 + z Se 4 + t (where: −0.02 ≤ x ≤ 0.01, 0.03 ≤ y ≤ 0.35, −0.2 ≤ z ≤ −0.02, 0.01 ≤ t ≤ 0.08) spinels doped with Sb has been determined with the aid of the vacancy model. From the analysis carried out of the effective magnetic moments and the exchange integrals, it follows that in the spinels with sulphur mainly the cation subarrays are defected whereas in the spinels with selenium the defectiveness appears mainly in the anion subarrays. It turned out that in the spinels with sulphur the ferromagnetic cluster spin glass states appear accompanied by the large negative magnetoresistance, whereas in the spinels with selenium the corresponding clusters are antiferromagnetic and the giant magnetoresistance has been observed both positive and negative. A jump-like phase transition was here observed changing both the sign and the measured value of the magnetoresistance from −4433% at 153.2 K up to +980% at 154.24 K. Moreover, in the spinels with selenium both semiconductor–metal and metal–semiconductor phase transitions have been observed from the temperature dependence of the resistance.

Criteria for thermal stability of parabolically oxidable heterogeneous systems

A system of equations that interaction of an isolated particle or a dense ensemble of particles with an oxidizing agent in the case of parabolic growth of the product layer is analytically treated in the one-temperature approximation. It is shown that a jumplike transition from the lower reacting mode (regime with a temperature maximum) to the upper reacting mode (regime with a monotonically increasing temperature) occurs with a continuously changing ignition parameter. The critical ignition parameter obtained differs from its numerically predicted value by 7%.

EPR studies of phase transitions in perchlorates [M 2+(ClO4)2 · 6H2O] at high pressures

The EPR spectra of the Mn2+ ion in crystals of the perchlorate hexahydrates Zn(ClO4)2 · 6H2O, Mg(ClO4)2 · 6H2O, and Cd(ClO4)2 · 6H2O were studied in the temperature range 77–320 K under hydrostatic pressure. It is shown that the octahedron of six molecules H2O surrounding this paramagnetic ion is contracted along the c axis and that pressure decreases this distortion. The second-order phase transition that occurs near 200 K in the perchlorates and in other crystal hydrates is shown to be associated with changes in the bonds in the nearest ligand environment. As the pressure is increased, the phase-transition temperatures shift and the perchlorate crystals tend to a single-phase state. The low-temperature phase is assumed to disappear as the pressure increases, and this phase exists in a closed T-P region in the phase diagram. As the pressure increases, the character of the high-temperature transition in the Cd(ClO4)2 · 6H2O changes: the jumplike transition at T 1 with a 1-K hysteresis changes into a smooth transition and then disappears as the pressure increases further.

Steady evaporating flow in rectangular microchannels

Analytical and numerical solutions are presented for steady evaporating flow in open microchannels having a rectangular cross section and a uniform depth. The flow, driven by the axial gradient of capillary pressure, generally consists of an entry region where the meniscus is attached to the top corners of the channel followed by a jump-like transition to a corner-flow region in which the meniscus progressively recedes into the bottom corners of the channel. Illustrative numerical solutions are used to guide the derivation of an easily applied analytical approximation for the maximum sustainable heat flux or capillary limit.