Jumpwise Change Research Articles

Morphology of a droplet deposited on a strip and triangular groove

The behavior of a droplet deposited on solid surfaces, one in the shape of a narrow strip and the other in the shape of a groove of triangular cross-section, was studied. Surface/interface energy of the droplet on the surfaces was calculated. In addition, Laplace pressure and linear size of the droplet were determined. Unexpected dependence of the shape of the droplet placed on the triangular groove on its volume, that is, the jumpwise change in the droplet shape taking place on increasing of its volume, was revealed. This change was found to show some features of a second-order phase transition.

Induced quadrupole effects near a crossover in a tetragonal TbLiF4 sheelite in a strong magnetic field up to 50 T

The anomalies of magnetic properties of TbLiF4 caused by the interaction of the energy levels of a rare-earth ion in a strong magnetic field up to 50 T directed along the [100] and [110] axes are studied experimentally and theoretically. The jumps in magnetization M(H) and the maxima of the differential magnetic susceptibility dM(H)/dH are found in critical fields H c = 28 and 31 T, where the lower component of the excited doublet approaches the ground-state singlet of a Tb3+ ion. Based on the crystal-field model with known interaction parameters, we calculated the Zeeman effect and the magnetization and magnetic susceptibility curves for the TbLiF4 crystal, which adequately describe magnetic anomalies and critical parameters of a crossover. It is shown that the jumpwise change in the α- and γ-symmetry quadrupole interactions in TbLiF4 caused by changes in the corresponding quadrupole moments during the crossing of energy levels leads, in accordance with experiments, to a decrease in the critical field H c by approximately 4 T and an increase in the maximum of the differential susceptibility dM(H)/dH near the crossover more than twofold. This behavior can be considered as an analog of the induced quadrupole transition caused by a change of the ground state of the rare-earth ion during crossover.

Oscillatory motion of coke in deactivated HZSM-5 zeolite

We have observed motion of coke in deactivated HZSM-5 with the displacement vector alternately directed toward the outer surface of the zeolite crystals and into the interior of the zeolite structure. The driving force for the oscillations is the higher chemical potential of massive carbon μm at 500 °C than for carbon clusters. The switching mechanism involves an alternating jumpwise change in the value of Δμ.

10.1007/s11451-008-3010-z

The main features of stepwise magnetization of dispersed ferromagnets caused by magnetic interparticle interactions are studied using a two-particle model. The ranges of values of the magnetic anisotropy constants of particles and of the dipole-dipole interaction between them are determined over which a reproducible jumpwise change in the magnetization of the system occurs in an external positive magnetic field. The proposed model is shown to explain the main specific features of the fine structure of the ferromagnetic resonance spectra.

Stepwise magnetization of dispersed ferromagnets due to magnetic interparticle interactions

The main features of stepwise magnetization of dispersed ferromagnets caused by magnetic interparticle interactions are studied using a two-particle model. The ranges of values of the magnetic anisotropy constants of particles and of the dipole-dipole interaction between them are determined over which a reproducible jumpwise change in the magnetization of the system occurs in an external positive magnetic field. The proposed model is shown to explain the main specific features of the fine structure of the ferromagnetic resonance spectra.

Giant fluctuations in the radiation intensity of two-dimensional electrons under quantum hall effect conditions

Giant fluctuations in the 2D-electron recombination radiation were studied in structures with a single or double GaAs quantum well under quantum Hall effect conditions. It is established that, if these conditions are exactly satisfied, the amplitude of the 2D-electron photoluminescence (PL) intensity is several orders of magnitude higher than the noise level, with the noise having a normal (Poisson) distribution. The fluctuations in the PL line intensity are accompanied by a jumpwise change in the line positions. Analogous jumps were also observed in the spectra of inelastic light scattering by 2D electrons in structures with a single GaAs quantum well. The fluctuation processes are correlated over macroscopic distances. The characteristic correlation length is 1–2 mm. The spectral density of giant fluctuations was found to exhibit narrow peaks. The ratios of the frequencies of these peaks are equal to those of Fibonacci numbers. The appearance of such frequencies in the fluctuation spectrum indicates that the fluctuations studied bear a resemblance to processes occurring in open dissipative dynamic systems. The methods developed in the theory of these systems can, in principle, be used to study giant fluctuations.

Pressure-induced phase transitions in crystalline l-serine studied by single-crystal and high-resolution powder X-ray diffraction

Pressure induces two isosymmetric reversible polymorphic transitions in l-serine related to a jumpwise change in the hydrogen bond networks and the conformation of the zwitter-ions. Single-crystal X-ray diffraction in situ allowed to find the structure of l-serine III at 8.0 GPa (the phase was previously reported based on Raman spectra [Kolesnik et al., Doklady Chem. 404 (2005) 169]). High-resolution X-ray powder diffraction data with a synchrotron radiation source suggest the formation of a superstructure with a and c parameters tripled as compared with the single-crystal model.

Microstructure and Conduction of Composites Bi2CuO4-Bi2O3 Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi2CuO4 + xBi2O3 (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi2CuO4, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi2O3 and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi2CuO4 crystallites.

Effect of hydrostatic pressure on the γ-polymorph of glycine. 1. A polymorphic transition into a new δ-form

Abstract The results of a high-resolution powder diffraction study of the effect of high hydrostatic pressure up to 8 GPa on the pure γ-polymorph of glycine (P31) are discussed. A phase transition with a jumpwise change of cell volume and cell parameters was observed. The transition starts at about 2.73 GPa and is still not complete even at 7.85 GPa. The crystal structure of the previously unknown high-pressure polymorph of glycine (δ-polymorph) could be solved and refined in the space group Pn. In this structure, glycine zwitter-ions are linked via NH…O hydrogen bonds into layers, which form double-layered bands via additional NH…O hydrogen bonds. The structure of the individual layers in the high-pressure polymorph is similar to that in the previously known α- (P21/n) and β- (P21) forms, but the packing of the layers is essentially different. The pressure-induced polymorphic transformation in the γ-glycine can be compared with a change in the secondary structure of a peptide, when a helix is transformed into a sheet.

Concerning the magnitude of the maximum heat flux and the mechanisms of superintensive bubble boiling

We have developed a stabilizer of the temperature of a thermoresistor wire electric heater based on a PID controller. Using this stabilizer, we investigated heat exchange of subcooled water in pool boiling. We found that on stabilization of the heater temperature up to that of the subcooled water, transition from convection to the regime of bubble boiling and vice versa occurs spontaneously and is accompanied by a jumpwise change in heat transfer. It is shown that in the regime of stable bubble boiling, the law of heat transfer is independent of the liquid temperature and the heater diameter and that the maximum heat loading may attain 50 MW/m 2, which is much above the values cited earlier in the literature. Based on the results obtained, a mechanism of implementation of bubble boiling for the regimes of a constant heat flux and a constant temperature is suggested. The assumption is made that the regime of heterogeneous vapour generation is possible only in the case of the heater constant temperature. In the regime of a stabilized heat flux on the heater, the spatially inhomogeneous regime of heat transfer is established. This regime represents a spatially distributed combination of three regimes: convective heat transfer, homogeneous boiling, manifesting itself in periodic boiling-up of overheated layers of the liquid near the surface and an unstable regime of heterogeneous vapour generation.

Effect of a magnetic field on the thermal and kinetic properties of the Sm0.55Sr0.45MnO3.02 manganite

The temperature and magnetic-field dependences of the heat capacity, thermal conductivity, thermopower, and electrical resistivity of the Sm0.55Sr0.45MnO3.02 ceramic material are studied in the temperature range 77–300 K and in magnetic fields up to 26 kOe. It is revealed that the quantities under investigation exhibit anomalous behavior due to a magnetic phase transition at the Curie temperature TC. An increase in the magnetic field strength H leads to an increase in the Curie temperature TC and a jump in the heat capacity ΔCp at TC. The temperature dependences of the measured quantities are characterized by hystereses that are considerably suppressed in a magnetic field of 26 kOe and depend neither on the thermocycling range nor on the rate of change in the temperature. The thermal conductivity K at temperatures above TC shows unusual behavior for crystalline solids (dK/dT>0) and, upon the transition to a ferromagnetic state, drastically increases as a result of a decrease in the phonon scattering by Jahn-Teller distortions. It is demonstrated that the hystereses of the studied properties of the Sm0.55Sr0.45MnO3.02 manganite are caused by a jumpwise change in the critical temperature due to variations in the lattice parameters upon the magnetic phase transition.

Neutron diffraction investigation of the structural transition in HgSe1−x Sx ternary mercury chalcogenide systems at high pressures

The structure of HgSe1−xSx ternary mercury chalcogenides at high pressures up to 35 kbar is investigated by neutron diffraction. It is found under pressure, that the HgSe1−xSx compounds undergo, a phase transition from the cubic sphalerite-type to the hexagonal cinnabar-type structure, which is accompanied by a jump-wise change in the unit cell volume and interatomic distances. The unit cell parameters and the positional parameters of Hg and Se (S) atoms in the high-pressure hexagonal phase are determined. A two-phase state is revealed in the phase transition region.

X-ray diffraction study of phase transitions in iron(II) trisnioximate hexadecylboronate clathrochelate complex

Crystals of the iron(II) nioximate hexadecylboronate clathrochelate complex—FeNx3(BHd)2 [tris(μ-1,2-cyclohexanedionedioximato-O:O′)di-n-hexadecyldiborato(2−)-N,N′, N″,N‴, N⁗,N″‴]iron(II)—are investigated by differential scanning calorimetry and X-ray diffraction. Two structural phase transitions are revealed at Tcr1 = 290(3) K and Tcr2 = 190(3) K. The crystal structures of phases I, II, and III are determined by X-ray diffraction analysis at 303, 243, and 153 K, respectively. It is demonstrated that the I ↔ II phase transition is due to a change in the system of translations, and the II ↔ III phase transition is accompanied only by a jumpwise change in the unit cell parameters. The possible mechanisms of phase transitions are discussed in terms of geometry and molecular packing of FeNx3(BHd)2 in all three phases.

Induced Jahn-Teller transition in DyPO4 caused by a change in ground state upon level crossing

The transition caused by a change in the ground state of a rare-earth ion upon level crossing, an analogue of the induced Jahn-Teller transition in rare-earth compounds, is observed. It is shown that a jumpwise change in the Jahn-Teller interactions of α and γ symmetries, caused by a change in the corresponding quadrupole moments in DyPO4 upon level crossing, diminishes the critical field by ∼20 kOe and leads to a sharper change in magnetization M and differential magnetic susceptibility dM/dH near the crossover point.

Investigation of superionic phase transition in the CuCr1−x VxS2 system by x-ray diffraction and magnetic methods

The unit cell parameters and the distribution of copper atoms over different crystallographic sites in the CuCr1−xVxS2 superionic conductors have been determined by x-ray diffraction. It is demonstrated that a jumpwise change in the copper occupancy of different crystallographic sites for the compositions with x=0, 0.05, 0.1, and 0.15 is associated with the transition to the superionic phase. The two-dimensional character of the ion transfer in the studied compounds is confirmed. No considerable anomalies in the temperature dependences of the paramagnetic susceptibility are revealed at temperatures of the superionic transition.

Study of High Frequency Relaxation Processes in Three Substances with the -CN Groups at the Lateral Positions

Abstract Three liquid crystalline (LC) substances with the cyano-groups attached at the lateral positions to the molecular cores were studied with the aid of dielectric spectroscopy methods. The high frequency relaxation process connected with the molecular reorientations around the long molecular axes was studied in the isotropic, nematic and several smectic phases. The dielectric spectra are rather complex, indicating a contribution from several molecular processes to the main relaxation process. The dielectric time changes smoothly at the phase transitions between "liquid-like" phases (isotropic -nematic -smectic A -smectic C), and becomes shorter at the transition to the "solid-like" smectic G phase with a low-ering of the activation barrier. This indicates that the molecules perform broad angle librational motions rather than overall rotational motions in this phase. In case of a substance having two cyano groups at-tached to the benzene ring, a pronounced jump-wise change of the relaxation time was observed at the isotropic -smectic A transition.

On possibility of a structural transition in the vicinity of the melting point in liquid copper

The temperature dependence of the kinematic viscosity of liquid copper has been studied by the method of torsional vibrations during heating and cooling within the temperature range 1080–1500°C. A reversible structural transition was discovered in the vicinity of 1170°C. This transition manifests itself in a jumpwise change of viscosity and the activation energy of viscous flow at this temperature.

Phase transition in swollen gels

Ionized networks of copolymers of N-vinylcaprolactam with charged comonomer, sodium itaconate (mole fraction of ionic comonomer X s = 0-0.1) and of a crosslinker, 3,3'-(ethane-1,1-diyl)bis(1-vinyl-2-pyrrolidone) were prepared by radiation polymerization in water/ethanol mixture (H 2 O/Et = 0.3/0.7 by vol.) and their swelling; mechanical behaviour in water was investigated as a function of temperature. On heating, a decrease in the swelling degree was observed. Increasing X s shifts the volume transition temperature T tr from the swollen to shrinked state to higher temperatures; in all cases, this transition is continuous. The observed decrease in swelling with temperature is accompanied by an increase in equilibrium modulus, so that mechanical behaviour is predominantly determined by swelling. The swelling of hydrogels can be in the first approximation described by the theory of polyelectrolyte networks in which repulsion of charges on the chain and finite chain extensibility were considered. In accord with this theory, as the Flory-Huggins interaction parameter X = 0.522 for the uncharged network swollen in water, no jumpwise change in volume with increasing temperature was observed.

Phase Transition in Swollen Gels XXIII. Effect of the Positive Charge Concentration on the Collapse and Mechanical Behavior of Poly(1-vinyl-2-pyrrolidone) Gels

The swelling and mechanical behavior of ionized networks of copolymers of 1-vinyl-2-pyrrolidone, ionic comonomer, N,N-dimethyl-N,N-diallylammonium chloride (molar fraction of salt xs=0–0.27) and crosslinker, 3,3′-ethylidenebis(1-vinyl-2-pyrrolidone) was investigated in water-acetone mixtures and aqueous NaCl solutions. The networks were prepared by a radiation copolymerization method. At xs≥0.038, the first-order phase transition (collapse) was observed. While the critical acetone concentration in the mixture at collapse, ac=76 vol%, is independent of xs the extent of the collapse (jumpwise change in the gel volume), Δ, increases with increasing salt concentration. The jumpwise change in the gel volume is accompanied by a similar change in equilibrium modulus. The swelling and mechanical behavior of ionized networks in aqueous NaCl solutions were also measured. The expected decrease in the swelling and the increase in the modulus with increasing electrolyte concentration cNaCl was found. The theory of swelling equilibria of polyelectrolyte networks, in which the effect of electrostatic interactions of the charges on the chain and a limited chain extensibility were included, semiquantitatively describes the swelling data provided an effective concentration of the charges (lower than xs) was introduced. Mechanical behavior of networks is predominantly determined by their degree of swelling.

Phase transition in swollen gels. 21. Effect of acrylamide quaternary salts with various alkyl lengths on the collapse, mechanical, and SAXS behavior of poly(acrylamide) networks

A series of ionic networks were prepared by copolymerization of acrylamide, methylenebis-(acrylamide), and N-[2-(alkyldimethylammonio)ethyl]acrylamide with Cl, C4, C6, C8, C12, and C16 straight-chain alkyls (mole fraction of the last comonomer x I = 0-0.15). Small-angle X-ray scattering, swelling, and mechanical behavior of the networks were investigated in water-ethanol mixtures. For the gels with C1-C8 alkyls collapse was found ; both the volume jump and the critical ethanol concentration at which the transition takes place, e c , increase with increasing content of the ionic component, x I . Increasing the alkyl length stabilizes the expanded state of the gel and increases the e c values, probably due to preferential sorption of ethanol by hydrophobic regions. Different swelling behavior was found for gels with C12 and C16 alkyls, where mostly a decrease in swelling in water at low ethanol concentrations was observed with increasing x I . This is caused by a distinct amphiphilic character of salts with the two longest alkyls ; in networks with the C16 alkyl formation of micelles was proved by SAXS. Mechanical behavior of the networks is predominantly determined by the degree of swelling ; a jumpwise change in the gel volume is accompanied by a similar change in the equilibrium modulus.